Principles of

Geochemical

Prospecting

GEOLOGICAL SURVEY BULLETIN 1000-F

CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING 

FOR MINERALS

PRINCIPLES OF GEOCHEMICAL PROSPECTING

By H. E. HAWKES

ABSTRACT

Geochemical prospecting for minerals includes any method of mineral 

exploration based on systematic measurement of the chemical properties of 

a naturally occurring material. The purpose of the measurements is the 

location of geochemical anomalies or of areas where the chemical pattern 

indicates the presence of ore in the vicinity. Anomalies may be formed 

either at depth by igneous and metamorphic processes or at the earth's 

surface by agents of weathering, erosion, and surficial transportation.

Geochemical anomalies of deep-seated origin primary anomalies may 

result from (1) apparent local variation in the original composition of the 

earth's crust, defining a distinctive "geochemical province" especially favorable for the occurrence of ore, (2) impregnation of rocks by mineralizing 

fluids related to ore formation, and (3) dispersion of volatile elements 

transported in gaseous form.

Anomalies of surficial origin-^secondary anomalies take the form 

either of residual materials from weathering of rocks and ores in place or of 

material dispersed from the ore deposit by gravity, moving water, or glacial 

ice. The mobility of an element, or tendency for it to migrate in the.surficial 

environment, determines the characteristics of the geochemical anomalies it 

can form. Water is the principal transporting agency for the products of 

weathering. Mobility is, therefore, closely related to the tendency of an 

element to be stable in water-soluble form. The chemical factors affecting 

the mobility of elements include hydrogen-ion concentration, solubility of 

salts, coprecipitation, sorption, oxidation potential, and the formation of 

complexes and colloidal solutions. The mobility of the elements may be 

further modified by biological factors.

Secondary anomalies may occur in residual materials or in materials 

transported by ice, frost, underground water, animals, soil-forming processes, 

plant activity, and surface water. Each one of these transporting agencies 

gives a characteristic distribution pattern to the weathering products of ore 

deposits.

Geochemical methods have been applied most extensively in the Soviet 

Union, Scandinavia, the United States, Canada, Africa, and Japan. The 

most uniformly successful geochemical prospecting work has been based on 

sampling and analysis of residual soil and vegetation; anomalies caused by

225
226

movement of metals in ground and surface water show promise as an ' 

effective means of locating buried ore deposits. Some suggestions for the 

execution of geochemical surveys and the interpretation of geochemical dataV«"*

in terms of possible ore are presented.

h

INTRODUCTION

Geochemical prospecting for minerals, as denned by common V 

usage, includes any method of mineral exploration based on systematic measurement of one or more chemical properties of a *" 

naturally occurring material. The chemical property measured is 

most commonly the trace content of some element or group of 

elements; the naturally occurring material may be rock, soil, gossan, glacial debris, vegetation, stream sediment, or water. The 

purpose of the measurements is the discovery of a geochemical 

"anomaly" or area where the chemical pattern indicates the presence of ore in the vicinity. *

The broader science of geochemistry, as originally defined by f 

Goldschmidt and summarized by Mason (1952, p. 2), is concerned 

with:

1. The determination of the relative and absolute abundance of the elements * * * in the earth.

2. The study of the distribution and migration of the individual elements «. 

in the various parts of the earth * * * with the object of discovering 

the principles governing this distribution and migration. * 

The application of the principles of .geochemistry to practical > 

problems in mineral exploration requires the same basic approach.

It is built upon the investigation of the average abundance of 

certain elements in earth materials and of the laws that govern A 

the distribution of elements and the formation of geochemical 

anomalies. A thorough understanding of geochemical anomalies, * 

how they form, how to find them, and how to appraise them when

they are found that is, an understanding of some of the funda- (

mental laws of geochemistry is essential in effective geochemical 

prospecting.

This report is intended primarily as a review of the most important geochemical principles involved in the evolution of geo- * 

chemical anomalies. A section has also been included on the historical development and application of .geocnemical methods Of 

prOSpeCting. The data Of geochemical prospecting surveys will be 

reviewed only insofar as they illustrate the principles of geo- (_

chemical dispersion; detailed information on the results of geochemical prospecting surveys may be found in the reviews cited ^ 

in Harbaugh (1953) or the literature reviewed. The methods of 

chemical analysis used in geochemical prospecting are covered in
PRINCIPLES OF GEOCHEMICAL PROSPECTING 227

other publications. In this report only incidental reference is made 

to geochemical methods of exploration for petroleum. A glossary 

of terms and conversion tables for units of measurement are included at the end of the report.

This report summarizes the results and conclusions of many 

workers over a period of 20 years. The intent has been to give 

full acknowledgment by reference to the literature or other notation for all ideas and data that have gone into the preparation of 

this summary. Many of the concepts, however, have grown out of 

personal conversations and contacts where the writer may have 

adopted the ideas of others without realizing the source. In this 

regard, special mention should be made of the intangible contributions of W. H. Newhouse, T. S. Lovering, L. C. Huff, Helen 

Cannon, H. W. Lakin, V. P. Sokoloff, F. C. Oanney, V. C. Kennedy, 

J. S. Webb, and J. E. Riddell. The literature used in assembling 

the data for this report includes only that published before March 

1954.

ABUNDANCE OF ELEMENTS IN EARTH MATERIALS

Geochemical anomalies, indicative of commercially important 

concentrations of elements, can be recognized only by their contrast with unmineralized areas. The normal abundance of an element in any material where the equilibrium has not been upset 

by the presence of a mineral deposit is commonly referred to as 

"background." Background values can vary widely owing to 

natural chemical and physical processes whereby certain elements 

are enriched and others correspondingly impoverished. For a 

general guide to the range of background values that may be expected, it is helpful to refer to data that have been compiled on 

the composition of average igneous rocks, fresh water, and 

terrestrial plants (table 1). The data on igneous rocks and 

terrestrial plants have been obtained from published estimates.

The data in table 1 on the major element composition of fresh 

river water have been taken from estimates by Con way (1942) 

and Polynov (1937). Estimates for the minor constituents of fresh 

water have been newly computed from individual published analyses of representative river waters, as summarized in table 2. So 

far as the writer is competent to judge, only the most reliable data 

were selected. Because of the wide range in the reported content 

of many elements in surface waters, the median value as well as the 

average was computed. As Ahrens (1954) has pointed out, the 

median of a series of widely scattered values may give a more significant indication of the normal value than the arithmetic mean,
.228 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

-Abundance of some dements in igneous rocks, fresh water, 

and terrestrial plants

Element

Aluminum __ .

Antimony. _ _ _

Beryllium. _ ____

Bismuth. ________

Boron. _______ .

Cadmium. __ _ .

Calcium _ _ ...

Cobalt...........

Copper _ _. ...

Fluorine

Gallium _ ......

Germanium .....

Gold.. __._......

Iron.. ______ ...

Lead. _______ .

Magnesium _ ....

Manganese.

Nickel.... _______

Niobium __

Platinum.

Rhenium _ ______

ftjlvpT

Sulfur.. .........

Tantalum __ ...

Tellurium........

Thallium _ .....

Tin..... ....... ._

Titanium ...

Tungsten.. ______

Zinc. . ---._

Igneous rocks ' 

(ppm)

81,300 

1 

5 

250

6 

.2 

3 

.15 

36,300 

200 

23 

70 

600-900 

15 

7 

.005 

.1 

50,000 

16 

65 

20,900 

1,000 

0.077-0.5 

2.5-15 

80 

24 

.005 

25,900 

120 

.001 

310 

.09 

277,200 

.1 

28,300 

300 

520 

2.1

.0018 

5 1.3 

40 

4,400 

1.5-69 

150 

132

220

Fresh water 2

Water (micrograins per liter)

700

1 

160

110

29,600 

5.3 

4.9 

20-70 

250

.0033

510 

3.4

4,400 

52 

.05

15

2,900

8 

8,000 

.0071 

3,800

5,500

25

~I6

Residue 

(ppm)

4,800

7 

1,100

750

202,700 

36 

33 

140-480 

1,700

.023

3, £00 

23

30,300 

360 

.34

ioo

20,200

55 

54,500 

.048 

26,300

37,900

170

~70

Terrestrial plants (ppm) 3

Dry 

weight

20

30

5

5,000

4 5

.1 

700

.5

3,000 

.4

2

1,500

200 

20 

500

~2

.2 4 32

Ash

800

1,200

200

200,000

4 200

4 

28,000

20

120,000 

16

80

60,000

8,000 

800 

20,000

80

8 

4 1,300

1 Rankama and Sahama (1950, p. 39-40), except as noted.

a For sources, see table 2.

'Hutchinson (1943) except as noted; ash computed on basis of 2.5 percent average ash content ot

errestrial plants.

« Shaw (1952).
TABLE 2. Source data for abundance of elements in fr

Element

Aluminum

Arsenic -

Barium. _

Boron. . .

Calcium ... _

Chromium.

Cobalt. -------

Copper 4 _,--_

Copper 5 ,.

Gold----.-----

Manganese.

NickeL ------

Silver-. -------

Sulfur.--. -,._-

Zinc-____ ---

Number 

of 

samples

37 

27 

51

24 

16 

61

67 

404 

23 

172 

38

74

3

44

69

23

3

Fresh water

Water (micrograms per liter)

Average 

(1)

700 

1 

160 

110

29 , 600 

5.3 

4.9 

70

21 

250 

.0033 

510 

3.4

4,400

52

.05 

15 

2,900 

8 

8,000 

.0071 

3,800 

5,500 

25

Median 2 

(2)

<3 

120 

80

2 

2.3 

30

5 

200 

.0014 

220 

2

10

.05 

4

1

.0034

~20 

~10

Range * 

(3)

50-300 

20-lcO

1-10 

.82-10 

20-200

<2-33 

< 100-400 

.0001-. 0073 

40-1 , 500 

<l-9

2-50

.Ol-.l 

1-13

<1-20

<.0001-.01

Residue (ppm) '

Average 

(4)

4,800 

7 

1,100 

750

202 , 700 

36 

33

480

140 

1,700 

.023 

3 , 500 

23

30,300 

360

.34 

100 

20,200 

55 

54,500 

.048 

26,300 

37 , 900 

170

Median 

(5)

820 

550

14 

16 . 

200

34 

1,400 

.00

1,£00 

14

70

.34

27

7

.02

~140 

~70

1 Figures for composition of mineral residue of river water are computed from data in columns 1 and 2 on the 

1942).

1 The median (or mode) is statistically .the most common value; if all the values quoted are listed in ascendin

* The figures listed represent the range after the highest and lowest 16 percent of the reported values have been 

4 Determinations by spectrographic analysis.

5 Determinations by wet chemical analysis.
230 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

inasmuch as the distorting effect of the few excessively high values 

is eliminated. A measure of the scatter is indicated in column 3 

of table 2 by the range of values after the highest and lowest 16 

percent have been omitted.

For most elements, the composition of residual and glacial material will not differ greatly from the composition of the rocks from 

which it was derived, so that the data on average igneous rocks 

will be a first approximation of the composition of average soils.

DISTRIBUTION AND MIGRATION OF ELEMENTS

The second, and for the purposes of this report the most significant, phase of the science of geochemistry is the study of the 

laws of equilibrium governing the distribution and migration of 

elements in the earth. As Clarke (1924a, p. 10) has stated:

Each rock may be regarded, for present purposes, as a chemical system, 

in which, by various agencies, chemical changes can be brought about. 

Every such change implies a disturbance of equilibrium, with the ultimate 

formation of a new system, which, under the new conditions, is itself stable 

in turn.

Although Clarke is considering only petrogenesis, his comments 

apply equally well to processes of weathering, transportation, and 

sedimentation at the earth's surface.

THE GEOCHEMICAL CYCLE

The disturbance of equilibrium necessary in Clarke's concept

of changing chemical systems can be caused by a static change in 

the temperature and pressure within a closed system or by a dynamic movement of material into new chemical and physical environments. In nature, closed systems are rarely if ever found;

virtually all geologic processes involve a certain amount of movement of material.

The movement of earth materials from one environment to another can be conveniently visualized in terms of a partly closed 

cycle, as illustrated in figure 32. Starting on the right-hand side

of the dkgram ano! moving clockwise, sedimentary rocks are progressively metamorphosed as they are subjected to increasing temperature, pressure, and availability of juvenile increments from

depths, They may eventually attain a state of fluidity such that on

recrystallization they can differentiate into several kinds of igneous 

rocks and hydrothernial extracts. When erosion brings the resulting suite or rocKs into me surnclal environment again, the component elements are re-sorted by weathering agencies in accordance 

with their relative solubility in water. A new series of sedimentary 

rocks is then deposited and the cycle is closed. The diagram pre-
PRINCIPLES OF GEOCHEMICAL PROSPECTING 281

sented as figure 32 is, of course, highly simplified, as in reality 

large parts of the cycle may be missing in any given case. It is 

quite normal, for example, for sedimentary sandstone and shale 

to be exposed to weathering and erosion without remelting or 

even significant metamorphism.

WEATHERING SEDIMENTATION

FIGURE 32. The geochemical cycle.

The geochemical cycle consists of two major parts, one embracing the deep-seated processes of metamorphism and igneous differentiation, and the other the surficial processes of weathering, 

transportation, and sedimentation at the surface of the earth. The 

horizontal division in figure 32 indicates the 'boundary between 

these two sectors of the geochemical cycle. Petrologists (Holmes, 

1928) and some economic geologists (Light, 1953) have referred
232 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

to deep-seated processes as "endogenetic," and surficial processes 

as "exogenetic." These terms, although accurately derived and 

defined, have not been generally adopted outside specialized 

branches of geology. Economic geologists may refer to ores deposited from upward-moving fluids as "hypogene" and those 

formed principally by solution and redeposition by surficial solutions as "supergene." These terms also have been accepted only 

ir, a specialized sense.

* In the previous literature of geochemical prospecting, the two 

phases have been classified as "primary" and "secondary," respectively. However, the use of these terms leads to some awkward 

ambiguities. Sedimentary ores can with good reason be called primary, yet they are not of deep-seated origin; also, dispersion of 

material by hydrothermal solutions from previously formed ore 

deposits forms a true secondary dispersion pattern that is unrelated to the earth's surface. In this -report the Somewhat Unsatisfactory terms "primary" and "secondary" are used inasmuch as 

they are perhaps too deeply rooted in the literature to be changed. 

The chemical environment of the primary and secondary sectors 

of the geochemical cycle are entirely different. In the deep-seated 

environment, temperatures and pressures are high, increasing with 

depth, and free oxygen is absent; in the surficial environment, 

temperatures are low, pressures are low and constant, and oxygen 

is abundant. TO tills may be added the powerful catalytic effect 

of organic activity at the surface of the earth, which 18 foment in 

the deep-seated environment. Pairs of elements that behave similarly in metamorphic and igneous processes may behave entirely 

differently when they enter the SUlflCial environment-^and vice

versa.

DISPERSION PATTERNS

As a result of the movement of earth materials from one chemical environment to another, each element is distributed in patterns 

that reflect both the abundance of the element in the moving 

material and the chemical equilibria characteristic of the local 

environment. In the literature of geOChemiCal prospecting these 

patterns Of distribution have come to be known as dispersion patterns, a term that emphasizes the dynamic processes involved in

their formation,

Dispersion patterns may be classified aS VViWlSilJ OY

depending, respectively, On Whether tfiey were for^ea 

by igneous and metamorphic processes or at the earth's 

by agents of weathering, erosion, and surficial transportation. Secondary patterns have been further classified as halos, fans, and
PRINCIPLES OF GEOCHEMICAL PROSPECTING 233

trains, according to the characteristic shape of the pattern and 

its geometrical relationship to the ore deposit or other locus of 

enrichment. A halo is a nearly equidimensional dispersion pattern, 

enclosing or overlying the source of material. A fan is a pattern 

spreading outward in one direction from a well-defined source. 

A train is a linear dispersion pattern formed by movement along 

drainage channels.

GEOCHEMICAL ANOMALIES

Dispersion patterns in geochemical survey data appear as areas 

where the abundance of an element is higher than in the surrounding areas. They can be the effect of special features of the environment that cause local enrichments of the element from source 

material of background composition, or of a source of material 

containing a higher-than-average amount of the element. If the 

enriched source is an ore deposit or is related in some way to oreforming processes, the resulting dispersion pattern may be of 

material help in mineral exploration, and thus by definition is a 

geochemical anomaly. One of the principal problems in interpreting the data of geochemical surveys is distinguishing geochemical 

anomalies from dispersion patterns of no economic significance.

Certain empirical parameters can be worked out that are helpful 

in identifying and interpreting geochemical anomalies. These involve a consideration of (1) the range of nonsignificant variations 

in background, (2) the threshold between nonsignificant and 

anomalous values, (3) the contrast between anomalous and background values, and (4) the homogeneity of the anomalous pattern.

Background range. Normally, the geochemical data obtained 

in areas where the equilibrium has not been upset by the presence 

of a mineral deposit lie statistically within a well-defined range. 

An example of a background range is presented in column 3 of 

table 2 for the composition of river water. Geometrical patterns 

of nonsignificant variations all of which fall within the background 

range will appear in geochemical survey data and can readily be 

misinterpreted as geochemical anomalies if their true significance 

is not recognized. Background variations are somewhat analogous 

to static in a radio signal or to the "noise" of an electronic amplifier.

Threshold. If background variations may be compared with 

noise in an amplifying circuit, the geochemical anomaly is the 

analogue of the "signal." In interpreting the geochemical pattern 

of an area containing anomalies, it is usually possible to select a 

certain limiting cutoff, or "threshold" value below which the variations represent only normal background effects and above which 

they have significance in terms of possible ore. For example, War-
234 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

ren, Delavault, and Irish (1952b) have reported that in interpreting the copper content of conifer twigs in British Columbia, a 

value of twice the average background value may be considered 

"probably anomalous," that is, probably indicative of a mineralized 

zone lying within reach of the root system of the tree. In their work, 

the value of twice the average background is the threshold. Similarly, Cannon (1957) has found in the Colorado Plateau area that 

trees containing more than 1 ppm uranium on an ash basis indicate 

areas that are probably mineralized. No hard-and-fast rules can 

be established as to what the threshold value is likely to be in any 

given area because it will depend on local geochemical factors which 

are different for different areas. However, it is usually possible 

to select a threshold contour suitable for the area in question by 

careful appraisal of the geochemical data from that area.

Threshold, as used in this sense, is not to be confused with the 

same term sometimes used in analytical chemistry, where it means 

the limit of detection, or sensitivity, of an analytical method.

Contrast. Some qualitative measure of the probable significance of an anomalous area is helpful in interpreting geochemical 

data in terms of probable mineralization. One criterion for significance of an anomaly is the geochemical relief or contrast between anomalous values and background values. This contrast may 

be expressed as a ratio either of maximum to threshold, maximum 

to background, or threshold to background, depending on which 

figure appears to be the most significant. Because of its characteristic response to factors causing enrichment or impoverishment,

each element will normally show a different and characteristic degree of contrast with its background; A qualitative idea of the kind

of contrast resulting from ore-forming processes can be gained toy

considering the relative enrichment of elements in ores (table 3) . 

II is reasonable to expect that elements showing a high factor of

enrichment in ores will also show a strong contrast in the associated primary anomalies. In secondary anomalies, the contrast for

each element will be a complex effect of the enrichment factor in

the ore and the factors affecting the mobility of the element in the

surncial environment. 

A practical example of the importance of contrast in geochemical

prospecting was encountered in the BlacKbird colrait district of

central Idaho1 . Here .the regional anomalies associated with cobaltite ore show a maximum arsenic and cobalt content of about 1,000

3OO ppm, respectively, as compared to thresholds of 10 and

1 Canney, F. C., and others, 1053, A preliminary report of geochemical investigations in 

the Blackbird district: U.S. Geol. Survey open-nl* rept.
235

30 ppm. The maximum-to-threshold ratiQ. or contrast, is thus 100 

for arsenic and 10 for cobalt, and the anomaly as expressed by the 

arsenic pattern is statistically more significant than that expressed 

by cobalt.

TABLK 3. Enrichment by ore-forming processes

Metal*

Principal metals:

Cobalt________. _______

Gold.................

Iron... ..._-_-_____---

Lead ... . ...

Mercury _____ _____._.

Molybdenum. _____ ...

Nickel. ------..-.. ..

Tin. ___.-. -_ ___.__.

Tungsten.... __ .__ .

Vanadium. ___- _ . ...

Zinc

Igneous rocks 

(ppm)

(1)

200

23

70

0.005

50.000

10

1,000

0.077-0.5

2.5-15

80

O.J

40

1 . 5-69

150

132

Workable ore ' 

(ppm) 

(:0

250,000

5,000

10,000

10

300,000

50,000

250,000

3,000

5,000

15.000

500

10,000

5,000

25,000

SO, 000

Enrichment factor: 

nitio (-2) to (1) 

(»)

1 , 2CO

200

140

2.000

(i

3,000

250

10,000

TOO

190

5,000

2.;o

200

160

620

Maximum content in ore (ppm)

Byproduct metals: 

Antimony. __.. . ...

Arsenic- .____ . _

Cadmium.... . _

Selonium. .._._.__ ....

Tellurium _ __ .

1

0.2

.1.1

.09

.0018

ro.ooo

1 5 , 000

3 . 500

1.000

200

2-1.000

50,000

5,000

17.500

7,000

2.000

1 3 , 000 , 000

-Ks for Or, Cu, An, Fc, I'b, Mn, Ni, AB, Sn, ami Zn from Floisclier

Homogeneity. The homogeneity of a geocheinical anomaly is a 

measure of the smoothness, or absence of strong local variations, in 

the distribution of the indicator element. Anomalous areas where 

smooth geochemical profile curves or contours can be drawn arc 

relatively homogeneous. Anomalies within which values vary erratically through a wide range within short distances may be considered relatively inhomogtmeous. The homogeneity of a geochemi-
236 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

cal anomaly is a prime consideration in establishing the optimum 

spacing of samples for a geoehemical survey.

PRIMARY DISPERSION

Although the same basic principles of physical chemistry apply 

under all conditions, the processes that dominate the migration 

of elements in the depths of the earth are very different from the 

principal processes that are operative under surficial conditions. 

In a deep-seated environment, geoehemical processes are controlled 

by the relative stability of minerals under any given set of conditions of pressure, temperature, and availability of material. Elements that can enter into the crystal lattice of a stable mineral are 

immobilized; those that cannot remain in a mobile state until they 

reach an environment where they can be accommodated in a stable 

mineral. In a general way, this rule holds true regardless of whether 

the rock-forming process is regarded as primarily metamorphism, 

metasomatism, or crystallization from a magma.

The effect of availability of material is such that most minerals 

are stable only in the presence of an abundant supply of the component elements. The common rock-forming minerals, therefore, 

are those containing only the nine most common elements as major 

constituents. These elements are, in order of decreasing abundance, 

oxygen, silicon, aluminum, iron, calcium, sodium, potassium, magnesium, and titanium. In terms of atomic abundance, hydrogen is 

also a major constituent of rocks, although its relative abundance

is difficult to estimate in quantitative terms. Rare elements occur 

as major constituents only in a few accessory minerals of igneous 

and metamorphic rocks, principally zircon (zirconium), and monazite (rare earths, phosphorus). Thus out of the 88 naturally occurring elements, only 12 plus the rare earths occur as major constituents in common rock-forming minerals.

. Many of thQ remaining elements m to p1^ incorporated into

One Or more Of the common minerals iby occupying a position in the 

orystai lattice that is ordinarily filled by OYiQ Of the mSJOF COM- ponent dements, Tiiie can take place omy wnen ^e Puy»u*a ^OPerties of the substituting ion are within certain limits 01 mOSG 01 

the ion for which it is proxying. For example, the ionic radius and 

ionization potential of lead are close to those of potassium, and 

therefore lead can substitute for potassium in potash feldspai'S.

similarly, zinc, copper, and cobalt can proxy for iron and magnesium in amphiboly M flWOffi, aflfl Mourn m jiw *~ T

droxyl in micas. It is generally assumed that the abundance of 

rare elements in minerals of this kind is proportional to their
PRINCIPLES OF GEOGHEMICAL. PROSPECTING 237

relative abundance in the material from which the crystals were 

formed. Other factors being constant, therefore, a tin-rich mica 

from a pegmatite dike implies a tin-rich pegmatitic fluid. 

. The constituents that cannot be accommodated in the lattice 

structures of rock-forming minerals remain behind and are concentrated in the mobile residual fluid. A very small part may be 

mechanically trapped either within the lattice or as minute films 

between the crystal interfaces. The bulk of it, however, goes out 

of the system. The progressive enrichment of rare elements in 

the residual fluid makes possible the formation of minerals containing rare elements as major constituents and accounts for the 

assemblage of unusual minerals found in pegmatite and greisen. 

Water, which cannot be entirely accommodated in the high-temperature minerals, is continuously enriched in the residual fluids. 

With decreasing temperature, the water-rich residual fluids begin 

to assume the familiar properties of aqueous solutions. The hydrothermal vein deposits that comprise most of our base-metal sulfide 

deposits are .generally believed to be precipitated at this stage in 

the primary geochemical cycle. Eventually the residual fluids reach 

the surface of the earth where they may either blend with the 

ground water or come to the surface as springs.

Primary dispersion patterns, properly speaking, include the end 

products of all the processes of metamorphism, metasomatism, and 

magmatic differentiation outlined above. All phases of the process 

are closely interrelated, and the chemical equilibria at one stage 

will predetermine to a great extent the course of the process at 

later stages. When the predetermining conditions are favorable, 

ore bodies will be formed. At the same time, the formation of ore 

bodies predetermines the processes and products of later fractionation. These equilibria may be reflected in easily measured chemical 

characteristics of primary dispersion patterns that are formed 

before, during, or after ore deposition.

Three kinds of primary dispersion patterns, or primary anomalies, are of particular importance in ore finding: the geochemical 

province, within which the chemical composition of rocks can be 

correlated with the occurrence of certain kinds of ore; dispersion 

patterns formed by the movement of aqueous fluids at the time of 

ore deposition; and dispersion patterns produced by movement of 

gases at low temperatures.

GEOCHEMICAL PROVINCES

A geochemical province, for these purposes, may be defined as 

a segment of the earth's crust in which the chemical composition 

is significantly different from the average. Evidence for the exist-
238

enoe of a geochemical province is commonly sought by studying 

comparisons in the composition of igneous rocks.

In working with the major-element content of igneous rocks, 

normal processes of petrogenesis may cause variations that mask 

the pattern due to fundamental differences in the composition of 

the parent magmas or other deep-seated fluids. A variation in the 

minor-element composition of igneous rocks that are otherwise 

similar, however, may provide reliable criteria for distinguishing 

a true geochemical province. Here it may be presumed that igneous 

rocks of similar major-element composition are the results of similar processes of petrogenesis but that the contrasts in minorelement composition reflect an original difference in the composition of the primary materials out of which the igneous rock was 

formed. Thus, if an area is found where all diabase intrusions contain four times as much titanium as similar intrusions outside the 

area, it is probable that the diabase magma was enriched in titanium. The area may then be considered a titanium-rich province, 

at least as far as the composition of diabase is concerned.

Metallogenic provinces, or areas characterized by an unusual 

abundance of ores of a particular metal, have long been recognized 

by economic geologists. Examples are cited of the copper-producing 

areas of the southwestern United States, and of the gold fields of 

the South African Witwatersrand (Bateman, 1950, p. 319-325). 

These classic examples of metallogenic provinces are defined largely 

or entirely on the basis of production figures. As more data are 

gathered it is becoming apparent that at least some metallogenic 

provinces coincide with areas where the igneous l*oCkg 316 fliSO 

enriched in the same metals; that is, an abundance of ores of a 

certain kind is Simply one manifestation of a geochemical province.

Tin is an element that enters into the crystal lattice of the common igfIl OUS minerals only to a very limited extent, with the result 

that if abnormally large amounts of tin WQ available in the fluids 

that form the igneous rocks it will be enriched in the residual juices

from which it may be precipitated late in the igneous cycle as hydrothermal cassiterite. At th« sa*ne time the abundance of tin 

available in the primary igneous environment will be renectea by 

a higher-than-normal tin content Of certain minerals of igneous 

rocks.

A relationship of this kind has been reported by Ahrens and

Liefoenberg (1950) from south-West Africa, where the mica of 

pegmatite dikes near till V6JnS COntainS from 10 to 100 times as 

much tin as mica from similar dikes in areas where no tin mineralization is known. A somewhat similar relationship has been
PRINCIPLES OF GBOCHEMICAL PROSPECTING 289

reported from the tin fields of Malaya and Indochina, where 

Goloubinoff (1937) has reported from 100 to 2,500 ppm tin in late 

igneous differentiates from this area as compared with 40 ppm 

for average igneous rocks.

The same writer also reports that a suite of igneous rocks, including pegmatite, norite, and diabase, collected from gold-bearing 

districts contain from 8 to 25 times as much gold as equivalent 

rocks from barren areas. A similar correlation between the nickel 

content of ferromagnesian minerals in basic igneous rocks and 

the tenor of nickel in associated pyrrhotite ores has been pointed 

out by J. H. L. Vogt (1923).

Igneous rocks and hydrothermal extracts that are associated 

in space but formed at widely separated times may be enriched in 

the same suite of elements. For example, in northern Nigeria where 

a niobium-thorium province has been described not only igneous 

rocks of the post-Cretaceous alkaline complex but also pegmatite 

dikes of probable Precambrian age all contain niobium and thorium 

minerals in noteworthy quantities (Davidson, 1951). Similarly, a 

boron province in southern California is indicated by the coincidence of tourmaline-rich pegmatites, recent saline deposits, and 

modern borate-rich thermal waters.

To the prospector, geochemical provinces may be useful as preliminary guides in his selection of areas for more detailed search. 

It has long been a maxim in the exploration business that "if you 

are looking for elephants, go to elephant country." This could be 

paraphrased in geochemical language to read: "If you are looking 

for deposits of a certain element, go to a geochemical or metallogenic province that is enriched in that element." The traditional 

prospector identifies his province on the basis of previous mineral 

discoveries. This is effective, of course, only where earlier prospecting activity has uncovered enough mineral occurrences to attract attention. Many areas of the earth, however, are either so 

remote or so heavily covered by overburden that no preliminary 

prospecting of any kind has been possible. In such areas it would 

be most helpful to have some simple means of selecting promising 

areas. The evidence to date indicates that under favorable conditions it may be possible to select favorable areas by trace analysis 

of relatively few samples of igneous rocks or minerals and by interpretation of the data in terms of metallogenic provinces.

DISPERSION IN AQUEOUS FLUIDS

Most mineral deposits are the result of deposition of material 

from an aqueous fluid of some kind moving through a system of 

channels in the rock. The exact nature of the fluid from which the
240 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

ore is .precipitated may be very different for different kinds of 

mineralization. Under some conditions it may be an aqueous solution at relatively low temperatures; under others a water-rich 

gaseous or supercritical fluid or even an aqueous magma. The 

nature of the ore-forming fluid is a subject of very active investigation and debate at the present time.

As the aqueous fluid passes along its system of channels, its 

physical and chemical environment is constantly changing; chemical reactions take place within the fluid and between the fluid 

and the wall rock of the channel in an effort to maintain equilibrium 

with the environment. The most conspicuous of these reactions, 

or at least the most important economically, is the creation of ore 

minerals and their deposition as an ore deposit.

Alteration patterns, where the effect of the mineralizing solution is primarily the modification of the original mineral assemblage, have been the subject of active investigation by economic 

geologists for many years, and their importance in ore finding 

is well established. Alteration studies are based on mapping the 

distribution of diagnostic secondary minerals that can be identified directly either in hand specimen or under the microscope. 

Patterns of hydrothermally dispersed metals, however, normally 

cannot be mapped without chemical analyses of the altered material. With the recent application of rapid analytical techniques 

to the study of hydrothermally modified rock, the importance of 

hydrothermal dispersion patterns of metals is being recognized

as an aid both in explaining the genesis of ore deposits and in 

prospecting for them.

In considering the characteristics of the dispersion patterns and 

particularly the geochemical anomalies that are formed by hydrothermal and pneumatolytic transportation of material, the character of the fluid is perhaps not as important as the geometry of 

the channels through which it flows, or the "plumbing" of the

mineralizing system. On a geometrical basis, dispersion patterns 

in channels can be conveniently classified as (1) areal patterns, 

resulting from widespread impregnation of a large mass of rock

by hydrothermal solutions or other fluids emanating from depth,

(2) "leakage" patterns within a well-defined system of solution

channels and (3) wall-rock patterns, where the minor-element 

composition of the rock adjoining the solution channels has been

modified by hydrothermal activity.

Areal 'patterns. Areal patterns of dispersed metal may enclose 

groups of deposits and thereby serve to define the boundary of 

the area in which ore is likely to occur.
PRINCIPLES OF GEOCHEMICAL PROSPECTING 241

Gross (1950, 1952) in studying the relation of gold mineralization to .granitic stocks in western Ontario found increasing radioactivity of granite in the direction of the mineralized area. Chemical studies showed that with the increasing radioactivity there was 

an increasing content of uranium, thorium, zirconium, silicon, and 

heavy metals in the granite. He postulates that these elements were 

all concentrated by movement of igneous extracts in the direction 

of easiest release of pressure. The same pressure factor may have 

controlled the localization of the gold ore.

An areal pattern of perhaps somewhat different origin was observed in the Blackbird cobalt district of central Idaho.2 Analysis 

of soil samples collected at 100-foot intervals along traverses covering a total area of about 8 square miles outlined an area at least 

3 miles long and as much as 1 mile wide where the average cobalt 

content is about 100 ppm as compared with a background of about 

10 ppm. The threshold for the cobalt-rich area is 35 ppm. Within 

the cobalt-rich area, the principal cobalt mineral in all the known 

sulfide deposits is cobaltite, whereas outside the area the principal 

cobalt mineral in all but one deposit is cobaltiferous arsenopyrite, 

which is of no commercial value. Thus, the only likely place to look 

for cobaltite deposits is within the area of cobalt-rich soils. Although the mode of occurrence of the cobalt in the parent rock 

from which the cobalt-rich residual soil was derived is not known, 

a dissemination of hydrothermally deposited cobalt minerals in an 

intricate lacework of mineralized fractures would not be inconsistent with the evidence.

Kimura, Fujiwara, and Yasudo (1950) describe altered volcanic rocks near the Sado gold mine in Japan in which the copper 

and silver content apparently is an indication of gold-copper mineralization. Particularly, they report a high silver-copper ratio 

in the rocks near some of the mines.

Leakage. Patterns of metal dispersed in the rocks and in 

fracture zones over blind ore deposits have been mapped in a 

number of areas. Dispersion patterns of this kind have been called 

"leakage halos," following the concept that some of the metal has 

"leaked" upward from the ore deposit. It is presumed, but by no 

means proved, that leakage halos represent the spoor of nearly 

spent mineralizing fluids moving upward after the major part of 

their metallic load has been left behind. The evidence could be 

applied equally well to downward-moving solutions that have not 

yet reached the site of deposition.

- See footnote 1 on p. 234.
242 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

Perhaps the best example of a leakage halo over blind ore is 

that reported by Levering, Sokoloff, and Morris (1948) in the Tintic district of Utah. In that area complex lead-zinc-silver ore occurs in limestone of Paleozoic age overlain by preore, but barren, 

rhyolite. Surface studies of the rhyolite over known ore have disclosed areas of argillic and pyritic alteration that include the uprake projections of the underlying ore. The alteration halos, 

however, cover so large an area as compared with the ore bodies 

that they are of limited use in guiding diamond-drill exploration. 

Sampling and chemical analysis of the altered rhyolite, however, 

disclosed a heavy-metal anomaly that coincides closely with the 

up-rake projections of one of the principal ore shoots. The writers 

suggest that this anomaly corresponds to the surface trace of the 

channels through which the nearly spent mineralizing solutions 

escaped. Even though the rhyolite was not a favorable host for 

ore deposition, enough metal was deposited along the solution channels to be detectable by trace analysis.

Another example of a leakage halo was reported by Kennedy3 in 

his studies of the rocks overlying zinc ore in the Shullsburg district 

of southwestern Wisconsin. Analysis of cores from four drill holes, 

penetrating ore contained in a sequence of flat-lying sedimentary 

rocks, showed high zinc values extending 58, 108,128-J-, and 138+ 

feet, respectively, into the rocks overlying the ore. In the same 

holes, high iron values extended upwards for 103, 108, 128+, and 

138+ feet. The somewhat erratic variations observed in the anomalous values over ore are interpreted as evidence that the halo was 

accounted for more by small veinlets than by a homogeneous diffusion of metals. Kennedy concluded that weathering of the zincrich rocks comprising the leakage halo might produce zinc-rich 

soils and that prospecting for ore buried 50 to 100 feet below the 

surface might be possible by soil analysis.

At Johnson Camp near Willcox, Ariz., Cooper and Huff (1951) 

have described a leakage halo in the fractured rock 600 feet above

the concealed Moore ore body. The ore is localized in 0116 bed Of a 

moderately dipping sequence of partly silicated calcareous rocks.

Oh.ip samples of rock collected at close intervals aCrOSS OU'tcrOP

SlirfeCeS Were COmpOSited 111 Sections Of 50 feet or more. The heavymetal content of samples collected in this manner along & SGF16S

of profile lines showed an anomalous area similar in shape to the

hOriZOIlt&l prOleCtlOn Of tlie Ore deposit, tout displaced about 200

feet 'to one side.

 Kennedy, V. C., 1949, Mineralization surrounding ore in the southwestern Wisconsin 

lead-zinc district: Pa. State CoNege, unpublished thesis.
PRINCIPLES OP GEOCHEMICAL PROSPECTING 243

At the Amulet deposit near Noranda, Quebec, RiddeH (1950) 

analyzed rock samples for heavy metal that could be extracted in 

cold acid. He outlined an area of high-metal content in the rock 

directly overlying two flat-dipping ore bodies. His threshold was 

9 ppm of extractable metal, compared with a background of about 

2 ppm. An alteration halo is also associated with the ore, but is 

not related in any simple way to the geochemical anomaly and is 

thought to be preore.

The above examples of leakage halos are taken from studies of 

the essentially unweathered rock. In each example, the traces of 

metal were presumably distributed throughout fairly large masses 

of rock in intricate fracture systems, some of which were visible, 

as at Johnson Camp, but most of which were either so fine or had 

been resealed so tightly that they were not obvious on casual inspection. Also, each of these examples of leakage halos shows a 

pattern crosscutting the depositional structure of the overlying 

rocks.

Another variety of leakage halo is in barren veins and fissure 

zones over ore shoots, where presumably the ore-forming fluids 

moved upward along the vein or fissure system. Here the leakage 

halo occurs only within the limits of a well-defined planar structure, rather than being dispersed throughout a large volume of 

rock. For example, in the Parral district of Mexico, Schmitt (1939) 

reports that the distribution of silver in noncommercial veins can 

be used as an indication of an ore shoot at depth. In the Santa Rita 

district of New Mexico, Graf and Kerr (1950) found lead anomalies in Tertiary fault zones that could be correlated with ore 

bodies in the underlying pre-Tertiary rocks.

Leakage halos have also been mapped by analyzing soil or vegetation over the geochemical anomaly in the immediately underlying 

bedrock. Kennedy (1956) and Cooper and Huff (1951) mapped 

soil anomalies that corresponded with observed leakage halos in 

the bedrock. White and Alien (1954) found a copper anomaly in 

glacial soil 75 feet above the top of a blind ore body in the Boundary 

district of British Columbia. In the Austinville zinc district of 

Virginia, Fulton (1950) mapped zinc anomalies in soils along the 

trace of preore faults that intersect the zinc ore at depth.

Wall-rock dispersion. Several examples have been described 

where traces of the ore metals are dispersed into the wall rock of 

the ore body. Most of these dispersion patterns were undoubtedly 

formed at the time the ore bodies were being deposited, when 

juvenile mineralizing fluids provided a ready source of metals. A 

few, however, may be the effect of later hydrothermal solutions
:244 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

entering a preexisting ore deposit and remobilizing the constituent 

: elements.

.... In the East Tintic district of Utah, Morris (1952) describes a 

wall-rock halo where the copper, lead, and zinc content of the limestone .country rock decays logarithmically from a maximum value 

next to the ore, to background within a distance of 5 to 20 feet. 

The logarithmic shape of the decay curve and the fact that the 

curves for each of the three metals are different are interpreted 

as evidence that the metals moved by a process of ionic diffusion 

through a static solvent contained in the pore spaces of the rock.

Graf and Kerr (1950), working at Santa Rita, N. M., found 

wall-rock halos of lead and zinc in fractured limestone adjoining 

lead-zinc deposits, with the maximum zinc content close to the 

ore and the maximum lead content farther away. They conclude 

that the metal was introduced through systems of small fractures, 

inasmuch as they found only negligible dispersion into unfractured 

wall rock.

H. D. B. Wilson (1944) at Goldfield, Nev., reports a complex 

pattern of leaching and enrichment of many of the common elements in the wall rock of gold veins, but no well-defined pattern 

of dispersion of the minor elements.

Stoll (1945), in studying the minor-element content of the wall 

rocks of New England pegmatite deposits, found increased concentrations of beryllium. He postulates that the beryllium was 

added to the wall rock by solutions emanating laterally from the 

main channels through which the pegmatitic liquids were flowing.

Mitcham (1952) describes envelopes of "indicator" minerals, 

particularly arsenopyrite and hydrothermal chlorite around ore 

shoots in the Coeur d'Alene district of Idaho.

Applications. Each of the various kinds of primary anomalies 

formed t>y the movement of aqueous fluids has its particular sphere

Of Usefulness in prospecting. Areal patterns will probably be most

useful in reconnaissance exploration for mineralized districts. 

Leakage halos are outstanding in that they are one of the few

available indicators of deep ore 'bodies that do not come to the

surface of bedrock. Wall-rock halos are likely to be most useful 

in underground exploration, where it would be helpful to kllOW 

whether or not the end of a crosscut or drill hole is within a short 

distance of ore. Morris (1952), in fact, describes an example of a

crosscut ending: in limestone wOaere tiie KJ<?1tfVl Wltf/Ont WfllS WCll

afeve Mclcgrouno1^; later extension of the crosscut broke into a new 

ore body within 10 feet.
PRINCIPLES OF GEOCHEMICAL PROSPECTING 245

GASEOUS DISPERSION

A few of the components of the earth's crust move at low temperatures as gases through the pore spaces of rocks and soils from 

which they escape directly into the atmosphere. Movement of this 

kind depends on the existence of continuous open channels through 

which the gas can move without hindrance. Near the surface the 

flow of gas may be modified by changes in barometric pressure, 

causing alternating inward and outward movement or "breathing."

Gaseous dispersion patterns may be detected either by direct 

analysis of the gas itself, or under some conditions by analyzing 

the material through which the gas has passed for products of 

condensation.

It is claimed that volatile hydrocarbons may escape from oil 

reservoirs through the overlying rocks and pass by way of the 

soil into the air. This possibility is the basis for many of the 

geochemical methods of exploration for petroleum, where soil or 

soil air is systematically sampled and analyzed for traces of certain 

diagnostic hydrocarbon compounds. Hydrocarbon anomalies may 

be thought of as very weak oil seeps, so weak that the deposition of 

material at the surface cannot be recognized without chemical 

analysis. Although geochemical methods of locating petroleum are 

the subject of a very extensive literature, their general effectiveness is a matter of considerable difference of opinion among oil 

men. A full discussion of these problems is beyond the scope of 

this report.

The nuclear decay of certain radioactive elements results in the 

generation of noble gases. Radon and helium are produced from the 

disintegration of uranium, and thoron and helium from thorium. 

Similarly, argon is produced by the decay of the K40 isotope of 

potassium. Under favorable conditions these may travel substantial distances from the source to form patterns that are helpful in 

prospecting for the parent elements. Arndt and Kuroda (1953) 

found a significant radon content of stream waters draining the 

uraniferous black shale beds of Arkansas. They also report a high 

radon content of spring water emanating from a uranium-bearing 

syenite. Inasmuch as the noble gases are chemically unreactive, 

they cannot have any chemical effect on the matrix through which 

they travel and tend to escape into the atmosphere by the shortest 

possible route. It has been estimated that radioactive spring water 

loses 41 percent of its radon to the atmosphere in the first 4 feet 

of surface flow. Radon and thoron, however, decay through a series 

of intermediate radioactive products including isotopes of polonium, lead, and bismuth. Conceivably dispersion patterns formed
246 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

by the radioactive daughter products of radon and thoron could 

be detected and measured by systematic studies of soils and waters.

Of the nonradioactive ore metals, mercury is the only one whose 

gaseous dispersion patterns have been given any serious thought 

as an aid in prospecting. At the Khpek mercury mine in Russia, 

Saukov (1946) describes a zone of mercury-rich shale and sandstone 2,000 meters wide embracing all the known occurrences of 

mercury in that vicinity. From a consideration of the vapor pressure of mercury occurring in mercury minerals, he interprets the 

pattern as the effect of gaseous dispersion of mercury from the 

primary deposits into the porous country rock.

Like leakage halos, the patterns formed by gaseous dispersion 

can provide an indication of buried ore that does not come to the 

surface of bedrock. Its usefulness in prospecting, however, is limited to the very few materials that are either volatile or that 

give off a volatile product, particularly petroleum, mercury, and 

uranium.

MOBILITY OF ELEMENTS IN THE SURFICIAL 

ENVIRONMENT

The physical and chemical environment of the earth's surface 

differs in almost every respect from that prevailing at depth where 

igneous and metamorphic rocks with their associated mineral deposits are formed. Minerals that are stable under deep-seated conditions are decomposed in the new environment, and a new suite 

of stable materials is formed. A complex series of new physical,

Chemical, and biological equilibria arises, beginning with the initial 

disintegration of the primary rocks and ending ultimately with the

deposition of a fresh sequence of sedimentary rocks.

A radical change in the habits of movement of the elements results from this Change in the physical and Chemical environment.

The factors affecting the relative mobility of elements Under deepSeated Conditions are no longer operative, and the scene is dominated by a completely new set of influences. A few elements, SUcK

as cobalt, that were originally immobilized by incorporation into

high-temperature minerals, Ibecome relatively imolbile under sur-ficial conditions; for a few others, such as silicon, the reverse relationship holds, In general, there is no immediately obvious correia

tion between the mobility of elements in the primary and in the

secondary geochemical cycles.

The mobility Of element in the surficial environment and the 

factor* governing it are of particular importance in geochemical 

prospecting. The characteristic behavior of elements released by
247

the weathering of mineral deposits determines the nature of the 

resulting dispersion patterns and geochemical anomalies. An understanding of the principles controlling mobility is necessary if the 

geochemical surveys are to be planned intelligently and the resulting anomalies interpreted accurately.

Mobility, or the ease and speed with which material moves, is the 

resultant of a vast complex of physical, chemical, and biological 

factors. The most important of these factors will be reviewed. 

Inasmuch as the net effect of all these factors acting at once cannot be computed on a quantitative basis, some empirical estimates 

of the relative mobility of the important elements in the surficial 

environment will be given.

PHYSICAL FACTORS AFFECTING MOBILITY

Gravity is the dominant force causing nongaseous material to 

move on the surface of the earth. Gravity, however, is opposed by 

the forces of friction, which must be overcome before movement 

can take place. In solid dry aggregates, the frictional force is high, 

but with the addition of moisture the system may become lubricated to a point where movement can begin. Depending on the 

composition and structure of the solid aggregate, movement takes 

the form of landslides, slumping, mudflows, or other commonly 

observed phenomena. Where the material moving under the influence of gravity is largely aqueous, the frictional force arises out 

of surface attraction and drag against the solid sides of the channel. In a rock where the moisture is held in minute fractures, the 

effect of gravity may be negligible compared with the forces tending to hold the water molecules in place. In a moderately permeable 

soil, the gravity movement is slow but measurable. In the open 

channels of streams and rivers gravity flow is relatively free, and 

movement for great distances can take place in a relatively short 

time.

These elementary considerations lead to a conclusion of prime 

importance in evaluating the mobility of elements in the surficial 

environment: inasmuch as water can move more freely than any 

other material on the earth's surface, an equivalent mobility is 

imparted to anything carried by the water. Materials that travel 

in solution or colloidal suspension in the water have the highest 

mobility. Material occurring as fragments swept along or lubricated by water have a lower mobility. Materials that are moved 

by water only rarely have the lowest mobility. Mobility, therefore, 

is almost synonymous with the tendency of a material to be stable 

in aqueous solutions or suspensions.
In addition to gravity and the forces impeding its action, some 

other physical forces play an important role in the movement of 

material under some conditions. Capillarity can move solutions 

through the fine pore spaces of soils against the force of gravity. 

If moisture is removed from the upper part of the capillary fringe 

by evaporation or plant growth, a substantial volume of water 

can be moved by capillary forces.

Diffusion through a static aqueous system can move ions in the 

direction of decreasing ion concentration. In a fine-grained crystalline matrix, ions can also move along the surface of mineral particles and migrate from one particle to another even when the pore 

spaces between particles are empty.

The action of ice and frost as a transporting agent will be reviewed in later sections. The action of wind is of little economic 

importance in the dispersion of the weathering products of ore 

bodies.

CHEMICAL FACTORS AFFECTING MOBILITY

It has been shown how water responding to the force of gravity 

is the dominant agent of physical transport on the earth's surface. 

Anything that can be carried by water is mobile, and material that 

cannot is relatively immobile. Water also dominates all chemical 

reactions in the surficial environment. It is the solvent within which 

virtually all the chemical reactions on the surface of the earth take 

place, Without water the effect of oxygen and carbon dioxide would 

be negligible, and biological processes would be impossible.

The unique catalytic effect that water has on chemical reactions 

stems from its capacity to dissociate soluble inorganic compounds 

into their component ions; that is, to break some of the bonds holding the compounds together. All chemical changes involve the

breaking Of bonds. At elevated temperatures, bonds are broken by

thermal agitation Of the atoms within the molecule, and chemical

reactions Can then proceed quickly to equilibrium. At atmospKeHC 

temperatures, however, broken bonds can exist and reactlOnS PfOCCed Only Under the influence Of a powerful catalytic agent such

as water.

Because of the dominant importance of water as a catalyst m

all Chemical reactions «,t «xe surf ae<a of tKe earth, some of the properties of aqueous solutions should be reviewed, The properties ox

ionic Solutions Of mOSt Importance in understanding the formation 

Of Secondary geochemical -anomalies are hydrogen-ion concentration, solubility of salts, coprecipitation, sorptkffl, OXldatiOll potential, and the formation of complex ions and organic compounds.
PRINCIPLES OF GEOCHEMICAL PROSPECTING 249

Hydrogen-ion concentration. The relative acidity or alkalinity 

of an aqueous solution may be quantitatively expressed in terms 

of the concentration of hydrogen or hydroxyl ions in solution. Pure 

water under standard conditions is neutral; that is, it has an equal 

concentration (10-7 moles per liter) of both hydrogen and hydroxyl 

ions. A 1 N acid contains approximately 1 mole per liter of hydrogen ions, and by virtue of the dissociation constant of water 

contains at the same time KH4 moles of hydroxyl ions; the reverse 

holds for a 1 N solution of a base. It is customary to express acidity 

in terms of the negative logarithm of the hydrogen-ion concentration; a value known as the pH. Thus under idealized conditions a 

neutral solution has a pH of 7.0, a 1 AT" acid has a pH of 0, and a 

1 N base, 14.

The pH of a solution may be measured quantitatively by determining the electrical potential developed between a special electrically conducting glass electrode and a reference electrode when 

both are immersed in the same solution. Portable pH meters employing this principle are best suited for the measurement of the 

pH of natural waters. The pH may also be measured by means of 

colored indicator reagents, marketed either as solutions or as impregnated papers. Colorimetric pH determinations, however, apparently cannot be depended upon for weakly buffered natural 

waters.

The pH of a soil is denned as the pH of an aqueous mud prepared 

by adding distilled water to the soil (Lepper, 1950, p. 44). A similar measurement can be made for pure minerals by pulverizing the 

mineral grains in pure water -and testing the pH of the resulting 

suspension (Stevens and Carron, 1948).

The normal pH of surface waters ranges, from about 4.5 to 8.5, 

and most of the chemical reactions in the weathering cycle take 

place within this range. The outstanding exception to this rule is 

the oxidation of pyrite and marcasite, where the free sulfuric acid 

formed creates local conditions of extreme acidity. The normal 

range of pH for soils lies between 4.0 and 9.0.

The solubility of most elements and the stability of their compounds is extremely sensitive to the pH of the aqueous environment. Only a few elements, among which are the alkali metals 

(such as sodium and potassium), and some of the elements forming 

acid radicals (such as nitrate and chloride), are normally soluble 

as dissociated ions throughout the pH range. Most metallic. elements are soluble as cations in acid solutions but tend to be precipitated as hydroxides or basic salts with increasing pH. Table 4 

gives the general order in which ions of some of the important
260 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

metals begin to be precipitated from aqueous solutions as the pH 

is increased. As the pH is further increased some of these again 

become soluble as complex anions, such as the zincate, aluminate, 

and chromate radicals. Some other elements, notably silicon, are 

soluble in water only as complex anions in alkaline solutions. The 

simple relationships described above apply only in the absence of 

ions that form insoluble precipitates or soluble complex ions with 

any of the other components of the system. The figures given in 

table 4, therefore, indicate only trends and tendencies; in natural 

solutions of a wide diversity of composition, marked deviations 

from these rules may be noted on occasion.

TABLE 4. pH of hydrolysis of inelals from aqueous solutions an 

hydroxide or basic salt

[From Britton (1942, v. 2, p. 79); the concentration of metal salts in the solutions used falls 

within the range from 0.025 M to 0.0025 M]

Element

Magnesium __ __

Silver...........

Manganous..._._

Lanthanum _

Cerous.. . ...

Mercuric (Cl)___

Praseodymium ..

Neodymium

Zinc.... ..

pH

10.5

7.5-8.0

8.5-8.8

8.4

7.4

7.3

7.1

7.0

7.0

6.8

fc3* 

Element

Cobalt.........

Cadmium. ....

Nickel .....___.

Beryllium.. ...

Ferrous . _ ...

Cupric ... .

> H-$fc.

'.'. PH

6.8

6.8

6.7

6.7

6.0

5.7

5.5

5.3

5.3

4.2

Element

IVFprm i rni i Q

Thorium

Mercuric (N03 ).

Zirconium------

Ferric___ ..--

pH

4.1

0

3.5

Q A

9 7

0

2

2

2

The strong acids evolved by the oxidation of pyrite or marcasite 

not only have a strong corrosive effect on other ore minerals and

on the waii rocks but also can stabilize most of the ore metals as 

simple soluble cations. As the acidity of these solutions is reduced

by Chemical reactions and by dilution, the metals tend to precipitate in the order of increasing pH Of hydrolysis, as shown in table 4. 

In normal soils, the pH of the soil has a profound effect on the 

rate at which the components are either leached or accumulated.

This r^tio^Hip has been the subject of intensive study by agricultural Scientists, Who are concerned with the availability Of mineral nutrients to crops. Availability of an element is a function of 

its solubility, which in turn is rented to FH. m some experiments 

it has been found that optimum availability of a nutrient element 

occurs in a soil where the pH is near the pH of hydrolysis. In the 

acid range where the element is readily soluble, leaching may have 

reduced the content of the element below a healthy nutrient status;
PRINCIPLES OF GEOCHEMICAL PROSPECTING 251

in the range where the element has been rendered insoluble by 

hydrolysis, the available fraction may also be too low.

A few of the experimental results of agricultural research might 

profitably be compared with the idealized data of table 4. Trenel 

(1946) reports that a soil pH below 5 causes the solubility of toxic 

aluminum. Knowles (1945) finds that adding lime to a soil increases the pH from 6.2 to 7.3 and reduces the content of exchangeable (soluble) zinc by a factor of 30. Lott (1938) reports that the 

upper pH limit of zinc toxicity in his soils is 6.0. Peech (1941) 

observed that only a very small fraction of the exchangeable copper in soils could be removed by leaching with solutions of pH 6 

and above; the same effect for zinc was observed at pH 7.5, and 

for manganese at pH 7. Lucas (1948) conducted experiments that 

indicated a precipitation of copper hydroxide in soils where the 

pH is greater than 4.7.

Throughout these experiments with soils, the limiting pH of 

solubility of the metals in natural solutions obviously departs somewhat from the values quoted in table 4, which are based on experimental solutions of known composition. The values illustrate the 

intimate relationship existing in nature between solubility and the 

pH of the solution, however.

Solubility of salts. The ability of an ion to remain in an aqueous solution is limited by the solubility of the salts it forms with 

ions of opposite charge present in the same solution. The precipitating effect of the hydroxyl ion has already been discussed in 

considering the pH of solutions. Other anions commonly present 

in natural solutions are carbonate, chloride, and sulfate. The metal 

content of saturated aqueous solutions of some salts that occur 

in nature as secondary minerals is given in table 5.

In dealing with laboratory solutions of known composition it 

is helpful to visualize the solubility of an inorganic precipitate in 

terms of a function known as the solubility product. At a specified 

temperature and pressure, the solubility product is equal to 

[M~]x [N^\ y where [M] and [AT] are the ion concentrations in moles 

per liter in a saturated solution of the solid MXNV. For example, 

the solubility product of CaF2 (fluorite) is [Ca++ ] [F~2 ] and is numerically equal to 3.9 X 10"11 . The solubility product rule tells us 

that a salt may be precipitated from a saturated solution by increasing the concentration of any of the participating ions. Conversely, a salt can dissolve in any solution where the product of 

the concentrations of the common ions is numerically less than 

tht solubility product constant.
252 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

" Except as noted, the data of table 5 are for solubility in water 

at a pH of 7, The solubilities of the salts of weak acids, such as 

fluorides, carbonates, and phosphates, commonly increase with decreasing pH. Also, the amount of carbon dioxide dissolved in the* 

water will modify the solubility of carbonates. Because of the; 

wide variations in the pH and carbon dioxide content of natural 

waters, absolute values for solubility cannot be assigned. The data 

of table 5 are intended only to give a qualitative idea of the general 

order of magnitude of mineral solubilities.

TABLE 5. Solubility of salts occurring in nature as secondary minerals

Salt

AgCL .............. .

BaS04 --- --- -.

CaF»..-.. ....-... _...-.-

CaSO4 -2H2O.. _________

CuCOs Cu(OH),.....-..

2CuCO,-Cu(OH)'j . ....

FbCO,__ ____-.____-._

PbSO«._... ......

FhCKPOOi- -- 

ZnCO, --____-____--

Equivalent mineral

Cerargyrite

Fluorite. _ _. . --

Gypsum _

Malachite _ _ _

Smithsonite

Composition of 

saturated aqueous 

solution ' (ppm)

Ag+ 1.46

Ba+2 1.3

F- 8

sor2 ii4o

Cu+2 2 12

Gu+2 s 7

Pb+2 1 . 3

Pb+2 27

Pb+2 -4 .03

Zn +2 107

Temperature

(°C)

25

25

18

18

20

20

18

18

37.5

18

1 Unless otherwise specified, figures are for solubility in pure neutral water taken from data assembled 

by SeideU (1940).

2 In presence of 0.29 g COz per liter. 

»In presence of 0.34 g COz per liter.

«Computed from solubility product value of IQ-"' 115 determined by Jowett and Price (Iyo2). ^ 

pH 5.0, solubility of pyromorphite is O.G ppm.

In nature, the formation of moat 0£ the minerals listed in table 

5 appears to be limited to very Special environmental conditions 

where Kigh concentrations of the reacting ions are being introduced into the syste«x from a local enriched source. Outstanding 

among these special conditions is t,w environment of an oxidizing 

sulfide deposit. The local abundance of both le^a. ^ gujfate ions 

produced by the oxidation of galena and other SUlfide mm^^ 

very commonly exceeds the solubility product Of lead sulfate, Wlwl 

the ensuing formation of anglesite. Cerargyrite forms by the reaction of abundant silver ions with the chloride naturally present 

in ground waters; gypsum precipitates where abundant sulfate 

reacts with the lime dissolved in normal waters. Similarly, smithsonite, witherite, copper carbonates, wulfenite, and many other'
: PRINCIPLES OF GEOCHEMICAL PROSPECTING-- '.-. 253

minerals are precipitated from aqueous solutions near the/site 

of oxidizing sulfide minerals, where the concentrations of the component ions is relatively high. Minerals of this kind will not .be 

formed, of course, if the precipitates take the form of colloidal 

dispersions that are removed with the circulating ground water, 

as is commonly observed with the precipitation of iron oxide and 

silica (Moore and Maynard, 1929). . ;

The breakdown of simple compounds in the surficial environment 

is also governed by the abundance of component ions in the solvent 

solution. Many secondary minerals that are stable in the presence 

of the acid, metal-rich, and sulfate-rich solutions characteristic.of 

the environment of an oxidizing sulfide deposit redissolve when 

they come in contact with normal solutions. Secondary zinc minerals can survive only when they are fairly close to an active source 

of zinc; they will begin to redissolve as soon as the protective effect 

of zinc-rich solutions is removed.

In general, computed or experimentally determined solubilities 

of common secondary minerals containing the ore metals are very 

greatly in excess of observed concentrations of those metals in 

natural waters from unmineralized areas: It is possible that the 

identity of the most stable (least soluble) mineral of a given element in an unmineralized environment may not be known. Pyromorphite, for example, is not generally regarded as a common 

secondary mineral. The very low solubility of pyromorphite as compared with the more familiar oxidized lead minerals (table 5) indicates that it may be the mineral responsible for the immobilization 

of lead in soils and sediments. Perhaps other highly insoluble 

minerals, as yet unrecognized, are the hosts for traces of many 

other metals in soils.

Coprecipitation. It is common to find that minerals precipitated from natural solutions will contain traces of many other 

elements in addition to the major components. Limonite may contain substantial amounts of arsenic, copper, and cobalt. Manganese 

oxides may carry barium, cobalt, and a long list of other minor 

elements. Barite precipitated from thermal spring water may contain significant concentrations of radium. The precipitating mineral iii each case "scavenges" traces of certain elements from the 

solution in which it forms and incorporates them into its crystal 

lattice. For this to take place it is necessary that the physical properties of the scavenged ion the ionic radius and ionic potential 

lie within limits where it can readily substitute for ions of the 

major constituents in the lattice of the newly formed mineral; The 

ionic'properties of radium are so nearly identical with ^those of
254 CONTRIBUTIONS TO QBOCHEMICAL PROSPECTING FOR MINERALS

barium, for example, that radium ions are quantitatively removed 

from solution by coprecipitation with barium sulfate, even though 

the concentration of radium ions is well below the limits of solubility set by the solubility product of radium sulfate.

Exotic ions may also be mechanically trapped, or occluded, within 

the body of the host crystal without necessarily occupying a systematic position in the crystal lattice. Simple occlusion, however, 

does not normally result in a quantitative removal of the foreign 

ions from the solution.

Adsorption. Wherever ionic solutions are in contact with solid 

particles, forces of attraction are active that tend to bind the 

ions to the surface of the particle. The attractive force is the effect 

of the unsatisfied electrical charges or broken bonds on the ruptured surface of the mineral. The strength of the bond will depend 

on the magnitude of the surface charge and on the properties of 

the ion species and will be different for different ions. Also, the 

number of available bonds and hence the "exchange capacity," 

or the total number of ions that can be held by adsorption, varies 

with the grain size and crystal lattice of the mineral. Clay minerals 

and organic matter have the greatest exchange capacity, so that 

adsorption becomes of greatest importance in dealing with soils 

and fine-grained sediments that are especially rich in these materials. A measurable amount of adsorption takes place on the

surfaces of all minerals, even the rock-forming silicate minerals 

(Sullivan, 1907). The surfaces of the root tips of plants have a

particularly high exchange capacity, which assists materially in 

the uptake of mineral nutrients (Williams and Coleman, 1950). 

Ions held by surface forces are in a state of active equilibrium 

with the solutions in which they are immersed. A change in the 

ionic content of the solutions will be reflected in a change in the 

ratio of adsorbed ions. In a very real sense, therefore, the adsorbed

ions are still part of the aqueous system, even though they may be 

temporarily restricted in their movement. Adsorbed ions, by virtue of their mobility, can move through the adsorbing matrix by

traveling along the surface of a particle and then jumping the

DarrOW gap tO an adjoining particle Without necessarily freeing 

themselves of the attractive forces at the surface of the particles 

(Jenny and Overstreet, 1939).

The Strength Of <the t»0nd holding the ion to the surface of a.

particle is different for different ion species. The common cations 

kave been arranged in a series Of decreasing exchangeability, as

follows:

Li> Na> K NH4 > Rb> Cs> Mg> Ca> Ba> H
PRINCIPLES OF GEOCHEMICAL PROSPECTING 255

In this series, lithium has the weakest bond and hydrogen tlie 

strongest. Thus, ions to the left in the series will tend to give up 

their exchange positions to ions on the right. The pH of a soil is 

effectively a measure of the abundance of exchangeable hydrogen 

ions. Inasmuch as exchange reactions obey the law of mass action, 

increasing the concentration of an ion in the solution can effect 

replacement of substantial amounts of more tightly held ions. As 

Grim (1953, p. 144) has pointed out, there is "no single universal 

replaceability series. The series vary depending on the experimental conditions, on the cations involved, and on the kind of clay material."

Most field studies of adsorption and exchange capacity have 

been carried out by agricultural scientists, who were interested 

primarily in the nutrient status of soils. Ions held by adsorptive 

forces are as available for plant nutrition as ions in solution, and 

hence the exchange capacity of a soil becomes an extremely important factor in fertility. Exchange capacity is commonly expressed in terms of milliequivalents per 100 cc of oven-dry soil, 

and commonly ranges from 1 or less for sandy soils to 150 for 

some clay soils. Cation exchange capacity is generally determined 

by saturating the soil with ammonium or barium ions and determining the amount held at pH 7 (Grim, 1953, p. 155; Lepper, 1950, 

P. 41).

Absorption. Under certain conditions, ions can enter the open 

lattice structure of some minerals and either occupy a void of the 

appropriate size or replace an ion already present. This phenomenon is observed most frequently with clay minerals of the 

montmorillonite group. These minerals are characterized by a 

relatively open lattice structure that contains passageways 

through wnich ions can enter both the spaces between the lattice 

layers and the layered structures themselves. The slow modification 

of montmorillonite to "illite" under surficial conditions is visualized 

as the absorption of potassium, magnesium, calcium, iron, and 

other cations into the relatively open spaces between the layers 

where they take up stable positions. In one laboratory experiment, montmorillonite and kaolinite were dried with K2Si03 . 

X-ray studies of the product showed "illite" crystal structures had 

been formed in the montmorillonite sample, whereas the kaolinite was unaltered (Mortland and Gieseking, 1951). Experiments in which montmorillonite is treated with aqueous zinc 

chloride solution show that a substantial part of the zinc ions is 

absorbed in a nonexchangeable form. This is interpreted as the 

absorption of Zn+2 ions into voids within the oxygen tetrahedra
256 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

of the aluminosilicate lattice (Elgabaly, 1950). It is probable 

that many other minerals in addition to montmorillonite have 

the property of absorbing ions to a greater or less extent.

Absorption is most commonly shown by an increase of nonexchangeable ions in a mineral at the expense of exchangeable 

ions. It is, therefore, to a certain extent an empirical concept, 

as the content of exchangeable ions varies with the leaching 

reagents used in effecting their removal. Probably no clear-cut 

distinction is possible between absorbed and adsorbed ions, inasmuch as the exchangeability depends on the strength of the 

bonds that hold the ions to any given position on or within the 

lattice. For this reason, many workers prefer to consider the two 

phenomena under the general concept of "sorption."

Oxidation potential. One of the outstanding characteristics of 

the environment of weathering is the abundance of free oxygen, 

as compared with the relative deficiency of oxygen in the environment where igneous and metamorphic rocks are formed. 

Many minerals that are stable under deep-seated conditions become unstable and break down under the influence of atmospheric 

oxygen.

The reason for the potency of oxygen to stimulate chemical 

reactions is its capacity to increase the positive valence state of 

many ions. Sulfides will tend to react with oxygen-rich waters to 

form sulfates, and ferrous iron will change to ferric iron. Similar reactions can take place in nature with manganese, copper, 

vanadium, uranium, and a host of other minor elements (Shcherbina, 1950).

The opposite of oxidation is reduction, in which the positive 

valence of certain component ions in the system is decreased. Reducing conditions can arise as a result of organic activity, where 

the oxygen has been consumed and an abundance of carbonaceous matter has accumulated. Reactions here are the reverse of

those where oxidizing waters come into contact with unweathered 

rocks; sulfates are again reduced to sulfides, and Fe+3 is transformed to Fe+2.

Oxidation, or the increase of r>*^ -«ience or an ion, is a

vro*^^ r^ovmg electrons from an ion. The oxidation of Fe+2 

to Fe+3 is basically the removal of one electron from the shell of an

ion, and the oxidation of S~* to S+e is the removal of eight electrons. Not only oxygen but ^y substance, such as chlorine or

fluorine, that has the Capacity to remove electrons from other 

ions is an oxidizing agent. From a consideration of the electronic 

nature of oxidation, it is seen that in a relatively oxidized sys-
PRINCIPLES OF GEOCHEMICAL. PROSPECTING 257

.tern, the "electron escaping tendency" is greater than in a lessoxidized system. The relative freedom of the electrons can be 

measured by bringing a nonreactive conducting metal, such as 

platinum, into contact with the solution and measuring the electrical potential between the metallic electrode and a hydrogen 

electrode. This measurement is called Eh, and has been found 

to be a useful indication of the degree of oxidation of a solution 

(ZoBell, 1946; Castano and Garrels, 1950; Krumbein and Garrels, 1952; Garrels, 1954). . . : . When the Eh of an aqueous solution is raised above a certain 

limiting value, the water decomposes with the evolution of elemental oxygen. If it is lowered below another limiting value, a 

decomposition to elemental hydrogen results. These two limits 

restrict the range of oxidation potentials that are stable in natural aqueous solutions, and all oxidation and reductions at the 

earth's surface occur within this range.

The Eh at which most oxidation or reduction reactions take 

place varies with the pH of the solution. Except for a few reactions that are essentially independent of pH, increasing the pH 

of the system decreases the Eh at which the oxidation reaction 

can occur (Mason, 1952, p. 144). That is, making a solution more 

alkaline can cause the oxidation of many ions. Thus ferrous iron 

may be stable in relatively acid water even in the presence.of 

abundant oxygen; if this water enters a basin where conditions 

are relatively alkaline, the Fe+2 may be oxidized to Fe+3 and be 

precipitated as ferric hydroxide. The Mn+2 ion is similarly stable 

in acid water, but with increasing pH is oxidized to Mn+4 which 

immediately hydrolyses to Mn02 , pyrolusite. In acid solutions, 

Mn02 lies outside the stability limits set by. the Eh>of decomposition of water. Thus the presence of pyrolusite indicates that the 

pH of the aqueous environment in which it is formed may have 

been relatively alkaline.

Oxidation or reduction completely changes the species of ions 

.involved in the reactions. In this respect, oxidation potential is 

different from the properties of ionic solutions already considered, where the ions retain their inherent properties, throughout the various reactions and equilibria. In simple chemical jr,eactions, the Fe+3 ion has no more similarity to, the F!e+2 ion than 

it does to ions of magnesium or copper. Ions of- each oxidation 

state form their characteristic dispersion patterns in the surficial environment and have their own retinue of associated elements. Under the same set of conditions, an ion .of one oxidation state may be readily soluble, whereas in another oxidation
258 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

state it may form extremely insoluble compounds. Oxidation or 

reduction, therefore, can cause almost quantitative precipitation of the reacting element. Evidence of this can be seen in 

the precipitation of bog manganese ores and of metallic sulfides 

in organic muds and shales.

An intimate association of organic activity with many oxidation and reduction reactions has been noted. Biological proCCSSes have received particular attention in considering the mode 

of precipitation of sedimentary iron and manganese oxides, and 

in the reduction of sulfates to elemental sulfur. There is no question that living processes can have -a strong catalytic effect on 

speeding oxidation or reduction; however, they can influence 

only the rate of reaction. The reactions that are possible and 

the compounds that can be formed are restricted to those consistent with the Eh of the environment.

Inorganic complexes. Any ion which contains several atoms, 

such as the sulf ate ion, is a complex ion. Complex ions are more 

commonly thought of as combinations of simple ions, either 

with a neutral compound or with another ion. Examples are the 

formation of Cu(NH3 ) 2+ and Cu(CN) 2- from Cu+ . The new ionized compounds can have completely different properties than the 

original ions from which they were formed. The formation of inorganic complex ions, therefore, like oxidation and reduction reactions, effectively changes the species of ion and thus may 

modify the dispersion patterns that are formed in the surficial 

environment. An example of a complexing agent familiar to 

every mining man is cyanide, which is used to dissolve native 

gold from gold ore. The gold cyanide complex has chemical 

properties that bear no resemblance to those of the simple gold

ion.

In the laboratory, extensive work has been done with the

complexing effects of water, ammonia, flttd lOnS Of CyEnlde, ChlOI*-

ide, hydroxide, and sulfide. Very little is known, however, about

the part played by complexing .agents in nature, other than

that they are probably extremely important factors in keeping Certain elements in soluble form when by all the simple rules 

tl)?y^?^vll<i be ^soluble. Some evidence for the existence Of

(CllOH) f, (ZHOHr, ailti (ZnClJr ions has been obtained m t**e

course of studies on exchange equilibria in Soils (BrOWn, 1950!

Bower and Truog, 1940). It is probable -that chloride also forms 

soluble complexes with copper and 5J]yer and that under S0me

conditions sulfide forms similar soluble complexes with many 

metals.
259

Organic compounds. Simple ions can also combine with some 

naturally occurring organic compounds to form so-called 

"metallo-organic complexes." Two principal kinds of compounds of 

this kind have received particular attention: the porphyrins, and 

soluble salts of organic acids.

Familiar examples of porphyrins in living organisms are the 

chlorophyll of plants with its magnesium and the hemoglobin of 

red-blooded animals with its iron. Porphyrin complexes with 

vanadium, nickel, copper, and many other metals have been 

identified in petroleum (Scott, Collins, and Hodgson, 1954). 

Similar compounds are probably present in all carbonaceous rocks 

containing enrichments of germanium, arsenic, vanadium, cobalt, beryllium, silver, gold, and nickel (Haberlandt, 1944). The 

latter writer found a gallium-porphyrin in calcite, which was 

proved to be spectroscopically identical with the synthetic material.

Many metals form soluble but undissociated compounds with 

organic acids. A common effect of the formation of organic salts, 

therefore, is to sequester the metallic ion so that although it 

remains in the solution it is not available for chemical reaction. 

An organic sequestering agent commonly used in the analytical 

laboratory is a solution containing citrate, which forms a nonionizing complex with iron under conditions where iron would 

ordinarily precipitate as ferric hydroxide. Organic acids have 

been reported as effective solvents for rock-forming minerals 

(Fetzer, 1946), possibly by the formation of soluble salts with 

the organic acid radicals. In soils, laboratory studies have 

shown that a great number of organic acids are capable either 

of "solubilizing" the otherwise insoluble mineral constituents or 

of preventing their precipitation from solution (Mandl, Grauer, 

and Neuberg, 1953). The organic acids used in this experiment 

are all thought to be present in natural soils.

Undoubtedly, therefore, porphyrins, salts of organic acids, and 

possibly other organic compounds containing metals as part of 

their molecular structure play a significant role in the movement of metals in the surficial environment. Some of these compounds may be soluble, and some are probably insoluble. It has 

been observed, for example, that organic matter is effective in 

decreasing the availability of zinc for plant nutrition, possibly 

by the formation of insoluble organic zinc compounds. The formation of metallo-organic compounds is considered responsible 

for the mobilization of lead in the zone of secondary enrichment in the Breckenridge district, Colorado (Lovering, 1934).
260 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

Beyond a number, of- empirical observations of this kind, how- 

'ever, the nature of the compounds actually formed under natural 

conditions is largely conjectural.

1 Colloidal solutions. A colloidal solution, or sol, consists of a 

liquid medium containing dispersed solid particles larger than 

simple molecules, but too small to be resolved by the ordinary 

microscope. As so denned, the size range of colloids lies between SOOm/i and lm/i (Im/x, or 1 millimicron, is 0.000001 mm). 

Because of the extremely small size of colloidal particles, their 

movement in the liquid medium is governed more by their electrical surface charges than by gravity. As a result, suspended 

material of colloidal dimensions will not settle out of the liquid 

medium by the simple action of gravity, but will remain in suspension and move with the liquid in the same manner as true 

solutions.

Water is the common dispersion medium in nature. Colloidal 

solutions can form in the zone of weathering where material 

is : chemically precipitated from true aqueous solutions, but for 

one reason or another cannot grow into large aggregates or crystals. Hydrated silica, alumina, and iron oxide precipitated during 

weathering may, under proper conditions, be dispersed as submicroscopic particles in a colloidal solution. Very finely divided 

.clay minerals may also be held in colloidal suspensions. In this 

state, these constituents can be carried out of the system with 

the, circulating water and do not remain behind with the other 

insoluble products of weathering.

Colloidal particles may be aggregated and precipitated by

changing, the concentration of electrolytes in the dispersion medium, This effect, however, may be offset by the presence of 

certain stabilizing agents, particularly organic matter, that apparently can inhibit the aggregation of colloidal particles (Moore 

and Maynard, 1929). 

About all that is positively known of the part played by colloids in the surfioial . environment is that substantial quantities

of colloidal material are moved in ground and surface waters,

and that they are precipitated on coming into COntact with tuG

salt water of the ocean.

FACTORS AFFECTINO MOBILITY

. The metabolic processes of living micro-organisms Kave an important part to play in the dispersion of elements in the sur- Mal environment, Micro-orpniomDj ftr pwp^ °f this «-

port, may be taken to include bacteria, algae, fungi, and any 

others of the relatively small forms of plant and animal life that
PRINCIPLES OF GEOCHEMICAL PROSPECTING ' 261

inhabit soils and natural waters. Micro-organisms may modify; 

their chemical environment either by assimilating and concentrating elements from their nutrient solutions or by catalyzing oxidation-reduction reactions. 

Assimilation of elements. Many micro-organisms have the 

capacity to remove large quantities of certain elements from the 

nutrient solution and incorporate them into their body structures.

Water organisms have perhaps the greatest effect on the mo-' 

bility of elements. Riley (1939) found that a very large part of 

the total copper contained in the water of glacial lakes in Connecticut was tied up in the body structures of organisms in the 

plankton. Analysis of the fresh-water alga, Spirogyra, growing 

in mine-drainage water containing 16 ppm total heavy metals 

showed a concentration of 2,900 ppm zinc, 6,600 ppm lead, and 

920 ppm copper in the dried algal material (Cannon, 1955). 

Micro-organisms have, in fact, been found to be effective agents 

in removing traces of radioactive contaminants from waters 

used to cool nuclear reactors (Ruchhoft and Setter, 1953). The 

enrichment of trace elements by marine organisms has long been 

the subject of active research and is well known (Vinogradov, 

1953).

Soil micro-organisms, in addition to their effect in maintaining a physical texture that can support plant growth, can also 

have profound chemical effects. The most spectacular is the fixation by Azotobacter of atmospheric nitrogen in the form of nitrogen compounds that can be used by plants for the synthesis of 

proteins. The cycle of nitrogen on the earth's surface is largely due to the efforts of this micro-organism. Experiments with 

another species of soil bacterium, Aspergillus niger, show that 

mineral nutrients can be removed from the minerals of unweattiered rocks. Bacteria grown in cultures in contact with 15 different rocks and 65 minerals extracted iron and molybendum in 

the largest quantities, followed in order by manganese, copper, 

and zinc. Igneous rocks were found to be better sources of nutrients than the metamorphic or sedimentary rocks (Swaby and 

Passey, 1953). Under some conditions, soil micro-organisms may 

immobilize the nutrient elements to such an extent that they 

are not available in adequate amounts for plants. An example 

of zinc deficiency caused in this manner is described by Hoagland, Chandler, and Stout (1937).

Oxidation-reduction reactions. In considering the effect: of 

micro-organisms on oxidation-reduction reactions, it should be
f

262 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS ) 

remembered that their influence is simply catalytic, speeding the 

formation of products already stable at the pH and Eh of the 

environment in which the reaction occurs.

One important oxidation reaction is the decay of vegetable 

litter, whereby the mineral content originally held in the struc- ' 

ture of the plants is released in soluble form. A tenfold increase 

in the copper content of stream water in the autumn has been 

attributed to the release of copper from rotting leaves (Riley, ( 

1939). Variations in the potassium and nitrate content of stream ^ 

waters are probably due in part to the variations in the rate of 

decay of dead organic matter.

The effect of bacteria in the precipitation of manganese dioxide 

has long been known. Mann and Quastel (1946) have found that 

this process takes place in two steps. First the soluble Mn+2 ion 

is oxidized to Mn+3 . The Mn+3 ion is unstable and undergoes spon- <t 

taneous "dismutation" to Mn+2 and Mn+4 which immediately 

hydrolyzes to Mn02 . In another experiment (Thiel, 1925), man- > 

ganese was precipitated by fungi from a solution of MnS04 , 

probably as MnC03 , with concomitant reduction of sulfate to 

sulfide.

The precipitation of iron hydroxide to form sedimentary iron 

formations has been attributed to bacterial oxidation of soluble 

Fe+2 to Fe+3 which immediately hydrolyzes and precipitates (Harder, 1919). Sulfur and zinc sulfide also can be oxidized to soluble 

sulfates by micro-organisms (Rudolfs and Helbronner, 1922).

Micro-organisms can also play a part in reduction reactions.

Under certain conditions, bacteria can precipitate native copper

(Levering, 1927) and copper sulfide (Arkhangelsk! and Soloviev,

1938) from copper-bearing solutions. The reduction of sulfate to

native sulfur in salt-dome cap rocks and the precipitation of pyrite in organic sediments apparently are also bacterial effects.

EMPIRICAL ESTIMATES OF MOBILITY OF ELEMENTS

In the preceding pages some of the more important factors

that affect the mobility of elements in the surficial environment

have been reviewed. The partition of elements between the mobile liquid phase and the relatively immobile solid phase is dependent on the interplay of these chemical and biological factors. In some environments and with some elements, the partition is

largely controlled by a single one, or a simple Combination, of 

these equilibria. In general, hOW6Ver, the relative mobility of

an element is tlie reauwant? ** ^^CK a^ i^VoiV6d combination Of

competing reactions that the net effect is extremely difficult tO 

predict. It is helpful, therefore, to consider the over-all tendency
PRINCIPLES OF GEOCHEMICAL PROSPECTING 263

of elements to move in the surface environment from a strictly 

empirical point of view, forgetting for the moment the physicochemical reasons for the relationships.

Mobility in normal environment. Goldich (1938) approximated a,n empirical evaluation of relative mobility by comparing 

the composition of residual soil with that of the parent rock, 

the difference being the fraction of the constituents that were 

removed in soluble, mobile forms. He concluded that sodium and 

calcium are lost early in the process of weathering, whereas potassium and barium are lost later; that is, sodium and calcium 

are more mobile than potassium and barium.

Another approach would be to determine the amount of an 

element carried by rivers in soluble form as compared with the 

total load, including suspended and bottom sediments. Inasmuch as all the products of weathering, both soluble and insoluble, 

are transported in the river systems, the ratio of these quantities 

should give a measure of the net tendency of an element to move 

in soluble form. The available data on the comparative composition of the soluble and insoluble load of rivers are not adequate 

for such computations.

Still another method of evaluating mobility involves the ratio 

of the composition of the total soluble residue of river waters 

to that of the unweathered rocks in the drainage basin. If weathering is at equilibrium, so that all material, solid and soluble, is 

being removed at the same rate, this method should give the 

same ratios as those based only on the load of rivers. If the residual, insoluble material is accumulating in the regolith faster than 

it is being removed or vice versa, the ratios would be somewhat 

different, although the relative order of mobility should be indicated by the order of increasing ratios.

Smyth (1913) and Polynov (1937) first pointed out the significance of these ratios as a measure of the mobility of the elements in the zone of weathering. Smyth computed the relative 

mobility of common elements using the composition of average 

crustal rocks, from data presented by Clarke (1924a). Polynov 

has obtained similar figures for mobility by comparing figures 

for the average composition of igneous rocks with figures for the 

composition of the mineral matter dissolved in rivers whose 

catchment basins are mostly in areas of massive igneous rocks. 

Both investigators found that the common elements could be arranged in order of increasing mobility as follows: iron-aluminum, 

silica, potassium, magnesium, sodium, and calcium. Reiche 

(1950), on the basis of further computations, concluded that this
264 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

order of mobility "may not hold in all situations, but if calcium, 

sodium, magnesium, and potassium be considered as a group, 

it is more mobile than silica, which in turn is more mobile than 

the sesquioxides A12 03 and Fe2 03 ."

Theoretically, it should be possible to extend the computations 

of Sniyth and Polynov by using the data of table 1 to derive the 

ratios of the minor element as well as the major-element content 

of river water to that in igneous rocks. Such computations do 

show the same general relationships that hold for the major 

constituents, where the elements that are commonly enriched in 

the soil during weathering, such as titanium, vanadium, and 

chromium, appear to have a lower mobility than elements like 

zinc and molybdenum, which are not characteristically enriched. 

For many of the minor elements, the reported data on the composition 'of fresh waters are not generally very reliable and 

cannot be used with confidence in computing relative mobility.

Mobility in a mineralized environment. In geochemical prospecting, attention is focussed on the dispersion of metals from 

decomposing ore bodies. In the vicinity of an oxidizing sulfide 

deposit, the chemical reactions dominating the mobility of elements may be quite different from those characteristic of normal 

environments. Large quantities of both sulfate and metals go into 

solution in the ground water, and extreme conditions of acidity 

are created by the free sulfuric acid resulting from the oxidation 

of pyrite and marcasite. As a result, the mobility of elements in 

a mineralized area will be somewhat different from that in a 

normal, unmineralized area.

Empirical observations have been.made by different workers

on the mobility of the ore metals in acid mine waters rich in

sulfate. Emmons (1917, p. 68-70) concluded that in the zone of 

secondary enrichment silver, in the absence of chloride, is more

mobile than lead or gold, that copper is relatively mobile under 

oxidizing conditions, and that zinc is mobile in an acid environment. In his study of the Breckenridge mining district, Colorado, 

Levering (1934) concluded that zinc is leached out of the surface 

material, whereas lead tends to be enriched, although some lead

apparently moves short distances as soluble compounds formed

by reaction with organic matter derived from the forest humus.

In later work on the metal content of efflorescences in underground workings of the mines of the Tintic district, Utah, LoverIng (1952)iIOUnd that where the country rocks consist of shale 

and quartzite, the ore metals could be arranged in the order of
PRINCIPLES OF GEOCHEMICAL PROSPECTING ' 265

increasing mobility as follows: lead, gold, copper, zinc, and silver. In fractures traversing carbonate rocks rather than shale 

and quartzite, silver is relatively immobile. His conclusions were 

based on the maximum distance from the nearest known ore that 

each of these metals had traveled in the solutions circulating 

through the capillary rock fissures. Work by the U.S. Geological 

Survey at the Union copper mine, Gold Hill district, North Carolina, showed that the Zn:Cu:Pb ratio of residual soil derived 

from the weathering of sulfide mineralization is about 10:10:30, 

whereas the ratio of the same elements in the unweathered ore 

is in the order of 10:0.6:2, with an absolute decrease in the zinc 

content from 4 to 0.04 percent (table 6).

From these and other data it seems safe to conclude that in 

acid waters rich in sulfate the order of increasing mobility of 

the common ore metals is lead, copper, and zinc. Lead in concentrations greater than 10 micrograms per liter is extremely unusual even in waters draining high-grade lead deposits. The 

relative immobility of lead in a mineralized environment may be 

partly the effect of the relative stability of galena as compared 

with other sulfides. Also, lead sulfate is much less soluble in dilute 

sulfate solutions than are zinc sulfate and copper sulfate. Copper is commonly an important constituent in waters draining copper deposits only where the pH is below 5.0. In normal surface 

waters where the pH is between 5.5 and 7.5, the content of copper 

is commonly below the sensitivity of the standard dithizone field 

method of analysis. Factors restricting the mobility of zinc do 

not make themselves felt until the solutions have passed well 

beyond the acid environment created by the oxidation of sulfides. 

However, as zinc-rich solutions come in contact with the finegrained material making up soils and stream sediments, much 

of the zinc is apparently removed from solution by exchange reactions with particles of clay or organic matter.

Much less is known regarding the mobility of other metals derived from the oxidation of ores. The mobility of molybdenum in 

neutral to mildly acid solutions is probably restricted by the 

stability of some of the insoluble products of hydrolysis such as 

molybdic ochre; under alkaline conditions, molybdenum is readily 

soluble as the molybdate ion. The mobility of cobalt, at least in 

central Idaho where for some reason the insoluble erythrite is 

not formed, is similar to that of zinc. The mobility of arsenic is 

dominated by the extreme stability and insolubility of the iron 

arsenates that form as secondary minerals.
266 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

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PRINCIPLES OF GEOCHEMICAL PROSPECTING 267 

SECONDARY DISPERSION

The factors that govern the partition of elements between the 

mobile aqueous phase and the immobile solid phase of the surface environment have been reviewed. The dispersion patterns 

that form as a result of this partition depend on the many different agencies that influence the patterns of movement of materials on the earth's surface.

Weathering, in the restricted sense of its definition, is only 

the first phase of the secondary geochemical cycle illustrated in 

figure 32. It is the phase dominated by the physical and chemical 

changes necessary to bring rocks into equilibrium with the new 

conditions at the surface of the earth. Movement of material in 

the weathering process is a minor consideration. In the later 

phase of the cycle, however, the physical and chemical changes 

that the products of weathering undergo as they are transported 

from their source to the site of sedimentation are influenced to 

a very considerable degree by the various transporting or "processing" agents. Here the patterns of flow of ice and particularly 

of water as it moves through soils, down drainage channels, and 

through the circulatory system of plants determine the dispersion 

patterns of the products of weathering. In presenting the principles responsible for the development of geochemical anomalies, 

therefore, it is more convenient to consider weathering processes 

first and to review the various kinds of dispersion patterns resulting from the transportation of weathering products in separate 

sections.

WEATHERING

Weathering has been defined by Polynov (1937, p. 12) as "the 

change of rocks from the massive to the clastic state." It includes the processes by which the parent rock is fragmented, 

and by which minerals stable in the subsurface environment 

are reconstituted to form new minerals that are stable in the 

surface environment.

The physics and chemistry of weathering have been reviewed 

by Reiche (1950) and for a more detailed treatment of the subject and for further bibliography the reader is referred to this 

excellent work.

Processes of iveathering. The dominant physical process of 

weathering is the disintegration of massive rocks into successively smaller fragments. Expansion of the rock due to unloading may cause cracks and joints to form. Differential expansion 

and contraction resulting from extremes of heat and cold at the
268 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

earth's surface may also cause cracking. Expansion due to freezing of water or the crystallization of salts .in cracks tends ,to 

rupture the rock further.. The penetration of roots into cracks 

and possibly other disruptive organic activity also serve to widen, 

the fractures already formed* : ,

Chemical reactions resulting from contact with the abundant, 

water, oxygen, and carbon dioxide of the surface environment 

are probably far more powerful in disintegrating massive rocks 

than the purely physical processes. Most primary minerals, being unstable in the surface environment, tend to be transformed \ 

into new minerals by hydrolysis, oxidation, and exchange reactions. In so doing, the grains expand differentially, and the 

rock tends to rupture along intergranular boundaries. The 

chemical action of micro-organisms and plant roots has a particularly destructive effect on many rock-forming minerals.

Products of weathering. The immediate products of, weathering take . three forms: residual primary minerals; secondary 

minerals, formed at or very close to the site of weathering; 

and soluble .material removed from the local site of weathering 

by circulating waters. : . * 

- Residual minerals are. the rock-forming minerals that are 

either, stable in the surface environment or unstable but react 

so slowly that they are not appreciably broken down. The only, 

common primary minerals that are truly stable in weathering 

are rock-forming clay minerals, muscoyite, and probably some 

Varieties Of chlorite. Most other minerals that can withstand'de-; 

composition in the secondary cycle are inherently unstable but

survive because they are chemically and physically refractory. 

Of theSC) Some minerals have a greater apparent stability than 

others. The common minerals o£ JgneoUS MkS MVC ''toWr '#?-' 

ranged in the following order of increasing resistance to weathering! Olivine; augite, hornblende, biotite, lime feldspar, soda 

feldspar, potash feldspar, and quartz (Goldich, 1938). A Similar"

order of increasing resistance to Weathering haS been WOfked 

OUt fOr heavy minerals Common to both igneous and metairiorphic rocks,. as follows! garnet, Staiirolite, hornblende, kyanite, 

monazite, sillimanite, and Zircon (Dryden and Dryden, lQ4fi^ 

These estimates are tossed <>niy o*x resistance to weathering1 and

do not indicate the ability of the minerals to withstand. me 

forces of physical abrasion in stream sediments, as wiii-w'?<Jig«

CUSS6CI later in the section on resistant minerals in gtreaHlS.

Thus, although sillimanite, is more Insistent than garnet. under 

purely chemical influences, it disintegrates much more. rapidly
-." . ;: PRINCIPLES OF;GEOCHEM'ICAL PROSPECTING, . . 269

than garnet when it enters the transportation phase, of the secondary cycle. . ' :

-Most vein-forming minerals are both unstable and extremely 

susceptible to. decomposition in the surficial environment. Few 

of them survive long enough to enter the, mineral, assemblage of 

stream sediments. Outstanding exceptions are vein quartz, chert, 

native gold and platinum, and. a few minerals of high-temperature., veins, particularly cassiterite, columbite, and probably 

beryl. Wolframite, scheelite, and barite can withstand the 

chemical .attack of weathering solutions relatively well, but disappear quickly during .transportation of the weathering products. Sulfide minerals are particularly vulnerable to attack in 

the-zone of weathering. The oxidation of pyrite and marcasite 

'results in the formation of free sulfuric acid, which has the 

strongest corrosive effect of any naturally occurring solution. 

'Silicates-and :the other sulfide minerals are attacked by'the 

strong acid at a rate far in excess of that'in a nonsulfide weathering environment. 'Some of the metal sulfates are readily 

soluble, and their removal in circulating ground water leaves 

voids and channels that provide further access to the system 

by weathering solutions. An important factor in the oxidation 

of siilfides is the electrochemical reaction developing in aggregates consisting of more than one electrically conducting sulfide 

mineral, whereby the oxidation of one mineral is favored over 

that of the others (Gottschalk and Buehler, 1912). 'Thus, in a 

'deposit consisting of chalcopyrite and pyrite, the chalcopyrite 

will be oxidized preferentially with respect to the pyrite. In fact, 

the overall mobility of the individual metals derived from an 

oxidizing complex .sulfide deposit is to a large extent 'prede^ 

termined by the relative stability of the parent sulfide minerals.

The/secondary minerals formed by the weathering of .primary 

rocks .are -principally the products of hydrolysis of the prhnary 

constituents. For this reason, they have been grouped together 

. as ;"hydroly sates"; .by many workers. They include the clay minerals, a few other hydrous silicates, such as chlorite and yermiculite, and the hydrous oxides. .Almost all are characterized 

by .extreme fineness. of crystal size that can usually foe resolved 

only under the electron microscope.1 -Clay minerals are composed, 

in addition to water, primarily of alumina and silica derived by 

the weathering of primary silicate minerals. .Kaolinite is a pure 

hydrated aluniinosilicate. Montmorillonite is ah aluminosilicate 

in which sortie of; aluminum ah the lattice, can be replaced by
270 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

iron, magnesium, or zinc. "Illite" requires potassium as a necessary constituent in addition to iron and magnesium. Iron not 

used in the formation of clay minerals is precipitated as a hydrated 

oxide; manganese may also be deposited as one or more of the 

black hydrated oxides.

The suite of secondary minerals that forms depends to a large 

extent on the physicochemical characteristics of the environment. One school of soil science holds that environment including climate, topography, and drainage conditions is the dominant factor controlling the chemical and physical characteristics 

of a soil and that composition of the parent rock is of strictly 

secondary importance. In tropical climates an extreme manifestation of this tendency may be seen in the contrast between 

the weathering profile in well-drained ground where the end 

product of weathering is lateritic iron and aluminum oxides and 

that in poorly drained areas where the end product consists 

largely of clay minerals.

Secondary minerals formed by the weathering of ores include 

not only hydrous iron oxides but a host of other secondary metalliferous minerals. Unlike the clay minerals, many of these are 

visibly crystalline, and occur in compact aggregates that are not 

readily dispersed as suspensions in flowing water. Different secondary minerals are formed under different chemical environments, leading to a great diversity of mineral species. Thus, of

the oxidized copper minerals, malachite will be the dominant 

copper-bearing product of weathering under some conditions, 

and ChrySOCOlla, brochantite, cuprite, or tenorite under others.

The conditions that control the stability of secondary ore minerals are principally the pH, Eh, and abundance of the reacting 

ions in the aqueous solutions with which they are in contact 

(Garrels, 1954).

The soluble products of rock weathering consist of the conStitUCntS that are released by the decomposition of primary minerals and that are not required in the formation of the new 

suite of stable secondary minerals. For calcareous rocks, lime

and magnesia may be the principal soluble products of weathering, whereas for granites, soda and potash may be dominant,

Similarly, the soluble products of the weathering of ores consist of elements which cannot be accommodated in stable secOfldcirV IIlillBralS. Maiiy Of the Secondary metalliferous minerals are

stable only in the presence of solutions containing relatively 

high concentrations of metals. If ground-water circulation is at 

all active, therefore, a substantial proportion of the metals can
PRINCIPLES OP GEOCHEMICAL PROSPECTING 271

leave the site of oxidation in soluble form. Other minerals, 

particularly those formed by hydrolysis under alkaline conditions, such as limonite, manganese oxides, and basic copper salts, 

are very sparingly soluble; where these minerals are stable, a 

correspondingly smaller fraction of the constituent metals will 

be removed in soluble form. Inasmuch as the specific reactions 

governing the solubility of metals near an oxidizing sulfide deposit is not generally known, it is helpful to depend on empirical observations of the mobility of metals in acid sulfate waters 

of the kind discussed in the section on mobility.

Relict structures and textures. The solid products of disintegration and decomposition of rocks, before they are moved by 

erosive agencies, generally maintain the same internal spatial 

relationships as the parent material. Traces of bedding, foliation, and vein structures can commonly be followed from bedrock well up into the disintegrated residual cover. The degree 

to which the structures of the parent rock are preserved in the 

residuum depend to a large extent on the amount of compaction 

and slumping resulting from reduction in volume by weathering, and on the amount of distortion due to gravity movement 

on sloping ground.

Granite and gneiss, for example, are made up of minerals 

that do not change volume greatly in weathering. Thus even 

in areas of extremely deep tropical weathering, the primary feldspar and mafic minerals of a granitic rock may be completely 

altered and disintegrated without any appreciable physical movement of the constituent grains with respect to each other. The 

solid products of weathering retain the primary structures and 

textures of the unweathered parent rock, although the aggregate can be shoveled or washed as easily as an unconsolidated 

sand.

Calcareous rocks, however, suffer a substantial reduction in 

volume due to the solution and removal of the carbonate minerals. The resultant slumping causes partial or total obliteration 

of the original rock structures. The compaction ratio may be estimated by determining the ratio. of the total volume of the 

original carbonate rock to the volume of the insoluble material 

contained in it. Where relict structures are still visible in the 

residuum, the compaction ratio may be approximated by observing the flattening of the dip of relict bedding or the thinning of individual beds. At the Friend's Station deposit in 

eastern Tennessee, a compaction ratio of 3:1 was estimated on 

the basis of the dip of vestigial bedding exposed along the banks
£72 CONTRIBUTIONS TO.GEOCHEMICAL PROSPECTING FOR MINERALS

,of gullies (Hawkes and Lakin, 1949). In the extreme weathering of rocks made up primarily of soluble, minerals, such,as pure 

limestone and saline deposits, the negligible amount of resulting 

residual material commonly shows no traces of original structures. ......

. Relict patterns of resistant minerals. Most rocks and some 

ores contain primary minerals that were not completely destroyed in the course of weathering. When one or more of these 

minerals has a unique association with its original host, a quantitative mineralogical analysis of the residual soil may be helpful in determining the identity, of the parent rock or ore. Many 

of the limestones of the southern Appalachians, for example,, contain distinctive and readily identified types of chert. Where 

rock exposures are lacking, systematic examination of surficial 

material for fragments of characteristic chert types has been 

used successfully as an aid in geologic mapping. More thorough 

quantitative determinations of heavy minerals in soils have been 

found equally useful in identifying the parent rock (Marshall 

and Jeffries, 1945).

In prospecting, the study of heavy minerals in residual soils 

is probably the oldest of all methods of locating a buried lode. 

.Gold and diamonds can be easily separated by panning, a process 

requiring no special training or expensive equipment. Other

minerals that are more difficult to identify may call for a more 

technical approach. For example, the relative abundance of 

scfyeelite in residual soils can be determined by counting the 

fluorescent specks under ultraviolet illumination with the. help 

of optical magnification (Sergeev, 1946b). A similar procedure 

has been described for prospecting deposits containing fluorescent corundum (Andreev, 1947). A systematic mineralogical

analysis of residual soil for cassiterite has been used in locating

bedrock deposits (Flerov, 1935, 1938).

 Relict patterns of secondary minerals. -The distribution of

secondary minerals in residual cover can be useful in identifying the parent rock, provided the secondary mineral Can be 

readily identified. In many deeply Weathered aMS, gGOlOglStS

depend heavily on the color of the soil to tell them what the

.underlying rock is likely to t>e. The color of a soil is usually related to'its .content of limonite, a secondary mme.ra.nnat may

reflect the iron content of the parent rock. '.

Prospectors in areas of residual cover are on the alert for 

.the- tell-tale red coloration of soil, representing limonite derived 

from the oxidation of iron sulfides. Similarly, the conspicuous
PRINCIPLES OF GEOCHEMICAL PROSPECTING 273

green color of secondary copper minerals is an important clue 

in the search for bedrock copper ore. The search for green copper in surficial material may profitably be put on a quantitative 

basis, as shown by C. H. White (1924) and Zenin (1935). The 

yellow iron arsenates, pink cobalt bloom, and many other conspicuous secondary minerals are identifying characteristics used 

by every seasoned prospector.

Geochemical anomalies in residual cover. In many residual 

soils, the diagnostic primary and secondary minerals, if present, are too fine grained for easy identification. Chemical analysis of residual material, however, may bring out latent images 

inherited from the parent rock that are not obvious from casual 

observation.

Little use has been made of chemical analysis of soils in geologic mapping, although experimental work shows that determination of the nickel content can be helpful in identifying soils 

derived from serpentine (Stevens and Lakin, 1949).

In prospecting, soil analysis for traces of metals has become 

the most widely used and successful of the geochemical methods 

of mineral exploration. A great many field surveys of the metal 

content of residual soils over sulfide deposits have been made, 

and with no important exceptions the dispersion pattern of 

metals in the soils was found to correspond closely with the 

distribution of metals in the underlying rock and hence probably 

with that in the rock from which the soil was derived. Details 

of some of these surveys have been published. See items numbered 4, 5, 22, 23, 26, 27, 36, 59, 66, 85, 94, 103, 104, 108, 110, 

and 117 abstracted by Harbaugh (1953) and also the following: 

Fersman, 1939; Gilbert, 1951, 1953; Hawkes, 1954; Huff, 1952; 

Kennedy, 1952; Nackowski, 1952; Pierce and Dias,. 1950; and 

Shima, 1953e, 195314

Much of the work, however, has been sponsored by private 

mining companies as part of their exploration program, where 

commercial considerations prevent the release of information to 

the public.

The absolute amount of metal in the soil as compared with 

that in the parent rock or ore depends on the mobility of the 

metal, or the ease with which it is removed in solution. Thus, 

although an ore deposit may contain equal concentrations of lead 

and zinc, the derived soil may contain many times as much lead 

as zinc. The lead is relatively immobile and is retained, whereas 

the zinc tends to be leached out. In general, it is found that

4 See also footnote 1 on p. 234.
274 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS >

lead, tin, arsenic and antimony are immobile and are held in 

the residual soil; zinc and cobalt tend to be impoverished; copper, tungsten, and molybdenum appear to be intermediate.

Although the major part of the mobile metals dissolved from 

the weathering products of a vein is entirely removed, a significant part may be transported in solution only for short distances and then reprecipitated locally. The effect is a lateral 

and downhill spreading of the dispersion pattern outward from 

the bedrock source. Zinc anomalies hundreds of feet wide have A 

been observed in residual soil associated with veins measuring 

only tens of feet in width. The lead anomalies over the same 

veins were not only much narrower but corresponded much 

more closely with the location of the vein. Over such a vein, 

samples spaced at 100- or 200-foot intervals would have been adequate for locating the zinc anomaly, whereas a 50-foot spacing ^ 

would have been necessary for the lead anomaly. It has been the 

writer's experience, therefore, that where complex ores contain- < 

ing two or more metals are sought, greatest economy is achieved 

when reconnaissance geochemical soil surveying is based on the 

more mobile metal and detailed work is based on the less mobile one.

The homogeneity of a metal pattern in residual soils is apparently also related to mobility. The characteristically homogeneous patterns formed by mobile metals such as zinc indicate that 

original local and erratic variations in the distribution in soils 

of the mobile metals tend to be smoothed by solution in rich 

spots and local redeposition in lean spots. With immobile metals,

solution is inhibited and the original spottiness of distribution is 

preserved. Thus Tikhomirov and Miller (1946) report that the 

molybdenum pattern over the Kounrad molybdenite deposit is 

less erratic than the tin patters commonly found over Cassiterite veins. Ttie relative homogeneity of a g-eochemicai anomaly is 

an important consideration in determining the most efficient 

spacing of samples in practical survey work. An anomaly defined by a mobile metal witk its more homogeneous pattern can 

be located and mapped with fewer sampi^ «.»» ~« anomaly defined by an Jrn^o^1 - z»et«*l.

Geochemical anomalies in residual cover may be distorted by 

downslope movement of the soil. The result is an asymmetrical curve in which the metal content fails off less rapidly OH the 

downhill side than in the Uphill side, as illustrated in the diagrams presented by Huff (1952). Asymmetry of this kind can 

also be caused by the action of metal-rich solutions depositing
PRINCIPLES OF GEOCHEMICAL PROSPECTING 275

metal in the soil on the downslope side, although the net effect 

is the same whatever the cause. In extreme cases of asymmetry 

owing to downslope movement, geochemical anomalies may be 

detected by sampling along the foot of a slope, hundreds of feet 

below the outcrop of the vein. Riddell (1954) describes reconnaissance exploration work in an area of high relief by systematic sampling of soils barely above the modern stream terraces.

Patterns in. residual soil may also be distorted by compaction 

slumping. At the Friend's Station deposit in eastern Tennessee, 

an average of 50 feet of residual clay overlies a gently dipping 

limestone sequence. The clay overburden was estimated to 

represent the weathering product of three times its volume of 

parent rock. The resulting flattening of the dip of the gently 

dipping ore caused the geochemical soil anomaly to come to the 

surface several hundred feet on the footwall side of the suboutcrop of the ore (Hawkes and Lakin, 1949).

Gossans. A gossan is the mass of residual limonitic material 

that remains behind after removal of the soluble products of 

weathering of a sulfide-bearing deposit. Being residual, gossans 

can be traced downward through successively less weathered 

zones into the unweathered primary sulfide minerals. Historically, gossans have been one of the best guides to the prospector in 

areas of residual cover and deep weathering.

At the surface, blocks of gossan material may be dislodged 

from the main mass and scattered over the immediate vicinity 

by frost action, slumping, and slope creep. If the fragments are 

sufficiently durable, they may on occasion be transported for 

substantial distances by glaciation or stream action. Studies of 

the dispersion pattern of limonitic fragments, particularly in 

alluvial material, have led many prospectors to the parent gossan 

mass and the hidden sulfide deposit beneath.

The necessary prerequisite for the formation of a gossan, in 

addition to deep weathering and an oxidizing environment, is 

the presence in the bedrock of iron as sulfide or carbonate to 

provide the raw material for the formation of limonite. The 

common gossan-making minerals are pyrite, marcasite, pyrrhotite, copper-iron sulfides, arsenopyrite, siderite, and ankerite. In 

general, the more iron is present in the primary ore, the more 

pronounced will be the gossan. The occurrence of economically 

valuable metals in the ore is only indirectly related to gossan 

formation, in that ore minerals are commonly associated with 

the gossan-making iron sulfides and carbonates. Thus not all
276 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

gossans indicate base-metal sulfides, and many base-metal sulfidc 

deposits do not weather to form gossans.

The mineralogy of gossans is limited to species that are stable 

in contact with acid sulfate solutions. The dominant minerals 

are limonite, quartz, and secondary silica. The overwhelming 

abundance of limonite is responsible for the conspicuous redbrown to black color of gossans, a feature difficult to overlook 

even in a casual reconnaissance of an arid terrane. Depending 

on the parent material and the maturity of the gossan, barite, 

gypsum, jarosite, secondary metalliferous minerals, and clay 

minerals resulting from the breakdown of the country rock may 

also be present. Secondary green copper minerals in a gossan 

may be a useful indication of the presence of copper in the 

primary ore.

The structure and texture of gossans, to a greater or less 

extent, reflect the original characteristics of the parent material. 

The primary ore minerals in the course of weathering may form 

minute, tabular veinlets of silica or limonite along crystal direc-

 tions. These systems of veinlets may remain behind after the 

original mineral has been completely destroyed, leaving a boxwork pattern that is characteristic of the primary mineral. 

Distinctive boxworks indicative of most of the common sulfide 

minerals have been identified and described by Blanchard and 

Boswell (McKinstry, 1948, pp. 268-276), and have been used 

widely in appraising leached outcrops in terms of the commercial grade of the primary sulfide deposit.

The chemical composition of gossans has received far less 

attention than their mineralogy and texture. What little evidence 

'has been reported to date, however, points to the conclusion

that the content of traces of the ore metals in the limonite Ot 

gossans can be used to indicate the relative abundance of those

metolS Jn the primary deposit. In the Nyeba district of Nigeria,

 samples of limonite from a gossan OVfiF fl dfipOSlt IfflOWH t9 

contain lead and zinc, contained on the order of 4,000 ppm lead 

and 500 ppm zinc. Similar samples from an undeveloped prospect

wkere . a geochemical soil survey Showed the presence of zinc 

but no lead contained on the order of 50 ppm lead and s,ooo

ppm zinc (Hawkes, 1054).

GLACIATION 

The grand scale of movement of the continental ice sheet is

attested by the identification of glacially transported erratics

that have been dropped hundreds of miles from their SOUTC8. 

Fragments of native copper derived from the Keweenaw
PRINCIPLES OF GEOCHEMICAL PROSPECTING 277

Peninsula of northern Michigan have been found as far south 

as southern Illinois, and a boulder of a distinctive norite gneiss 

from near the city of Quebec has been picked up in southern 

Ohio some 700 miles away (Flint, 1947, p. 118). The bulk of 

the material in glacial tills, however, is of relatively local origin. 

Chamberlin (1883) estimated that 90 percent of the material 

in the moraines of southern Wisconsin traveled less than 1 mile, 

and studies of the glacial boulders in northern New Brunswick' 

show that the most abundant rock type is a fairly reliable indication of the lithology of the bedrock directly beneath. Thus, 

although a few glacial erratics have traveled a very great distance from the source, the overwhelming majority of pebbles 

and boulders contained in glacial till are of local origin. It is 

possible that the bulk of the rock load of the continental ice mass 

was contained in a lower layer that moved relatively little and ; 

was overridden by a layer of cleaner ice carrying relatively few 

boulders but for far greater distances.

The direction of movement of continental ice during a single 

glacial epoch is generally outward from a central area in the 

heart of the ice mass. At any one locality, however, the direction 

may fluctuate somewhat around a mean value, with the result 

that glacial erratics are commonly distributed in the form of a 

fan spreading from the source in the direction of ice movement, 

rather than as a linear pattern. The prerequisite for the formation of a simple fan-shaped pattern of glacial dispersion is the 

existence of a relatively small area of outcrop of a unique, 

mechanically resistant, and readily identified rock type. In New 

England alone, well-defined glacial fans have been mapped in 

association with nine ocurrences of distinctive rock types (Flint, 

1947, p. 120). In Scandinavia, similar studies of glacial dispersion of rock fragments consistently reveal the same 

characteristic fan-shaped pattern (Lundqvist, 1935; Hogbom, 

1931).

Following the principle that the source of glacially transported boulders of an unusual rock type should be at the apex 

of a fan-shaped distribution pattern of similar boulders, prospectors in glaciated countries, especially in Scandinavia, have 

systematized the search for glacial ore boulders as an aid in 

exploration. A substantial number of important discoveries 

resulting partly or entirely from the use of this technique have 

been reported from Scandinavia (Grip, 1953; Hogbom, 1931; 

odman, 1947; Sauramo, 1924). In North America, the discovery 

of the Steeprock Lake iron deposit in western Ontario started
278 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

with the observation of glacial erratics of iron ore south of 

the point where the bedrock ore was later found (Bartley, 1940). 

If glacial movement can form a fan-shaped pattern of ore 

boulders, it is reasonable to expect that the chemically determined 

metal content of the fine-grained fraction of the till will show a 

similar pattern. Presumably, the sand and silt-sized fraction of 

till is derived in large part from the preglacial regolith which 

may contain gossan and other metal-rich preglacial dispersion 

patterns related to the ore. A variable amount of finely pulverized 

primary ore may also find its way into the fine-grained fraction 

of the till. This possibility is still largely in the realm of speculation, as glacially transported metals in the fine-grained fraction 

of tills have been identified in only a few areas. In the vicinity of 

the sulfide deposits of the Bathurst district of New Brunswick, 

the patterns, in addition to the strong homogeneous anomalies 

closely related to the ore, consist of extremely erratic, local areas 

of high metal content scattered in a crude fan-shaped arrangement lying to the east of the source. From this it may be assumed 

that the direction of ice movement was from west to east, although 

corroborative evidence is difficult to find. Between the local anomalies which are perhaps 50 feet across on the average, the 

metal content of the till is not appreciably above background level. 

Test pitting at one local geochemical anomaly in New Brunswick 

uncovered till containing a few cobbles and pebbles of massive 

pyrite, barite, and high-grade galena ore, together with the usual 

assortment Of locally derived unmineralized rocks. In the R0ros 

mining district of Norway, Vogt and Bergh (1946, 1948a, 1948b) 

have described a somewhat similar distribution pattern of copper, 

zinc, lead, iron, and manganese on the down-glacier side of a

known sulfide occurrence.

The source areas of alpine glaciers, in contrast to continental 

ice masses, are limited to the drainage basins within which they 

lie. For this reason, studies of terminal valley moraines might be 

a simple and rapid method of determining what kinds of rocks 

End OreS OCCUr Within a well-defined area of considerable extent.

Kreiter (1940, p. 170) mentions the occurrence of boulders of 

vein quartz in the moraine of a valley glacier at iak-su m Russia.

So far as tKe writer is aware, however, no USC has been made of

the distribution Of Chemically determined metals in valley morainal material as a method of prospecting.

FROST ACTION

The action of frost in moving and sorting surficial material 

involves a combination of movement by growing ice crystals and
PRINCIPLES OF GEOCHEMICAL PROSPECTING 279

by the water that forms the ice and is released when the ice melts. 

Experiments have shown that a growing frost crystal is fed by 

soil moisture moving upward from below, where temperatures 

are not sufficiently low to freeze the films of water on the surface 

of the clay minerals. The growing crystals thus act as collectors 

and concentrators of moisture gathered from a considerable 

volume of material. Any salts dissolved in the soil moisture are 

enriched in the aqueous phase as the water is removed to feed 

the frost crystals. As the crystals grow they exert pressure on 

the surrounding solid fragments, causing minor readjustments 

in the relative position of the fragments and keeping them in 

open packing. When the ice melts, the pressure is released and 

the water concentrated by the frost-forming process forms a 

mobile slurry with the silt and clay from the surrounding 

material. The total effect of this process repeated over a period 

of many years is a turbulent mixing of the surficial material to 

the maximum depth of the frost action. If the angle of slope is 

sufficient, a downslope movement is combined with the turbulent 

mixing, and the finer grained materials may be removed completely in the muddy water that drains out after the melting 

of the frost each spring. Under proper conditions the meltwater 

from the frost may mobilize a large mass of unconsolidated 

material, which then can move down the slope as a mudflow 

or landslide.

In geochemical prospecting, the turbulent mixing and downslope creep of surficial material owing to frost action is a factor 

deserving special consideration, at least in some areas. The 

Blackbird cobalt district of Idaho, where extensive experiments in 

geochemical prospecting methods were conducted by the Geological 

Survey, is in an unglaciated area of deep weathering where the 

zone of frost mixing extends commonly to a depth of about 4 feet.5 

The maximum intensity of frost activity probably coincided in 

time with periods of active glaciation elsewhere. Mineral exploration by conventional methods in this area was hampered by the 

scarcity of outcrops and especially by the virtual absence of 

fragments of oxidized ore or gossan in the surficial material overlying the cobalt deposits. Well-developed gossan, however, could 

be observed in the undisturbed weathered rock immediately below 

the zone of frost action. Very probably one of the effects of frost 

action was to disintegrate the soft limonitic fragments derived 

from the weathered rock into fragments too fine grained to be 

identified in the zone of frost mixing. Soil analysis for copper and

5 See footnote 1 on p. 234.
280 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

cobalt showed strongly developed and homogeneous dispersion 

patterns. Undoubtedly, the homogeneity of the patterns was at 

least in part the effect of the mixing action of the frost. On some 

of the steeper slopes, however, the patterns were difficult to 

interpret in terms of what was known about the distribution of 

bedrock ore. These were places where the topography indicated 

landslide activity, possibly resulting indirectly from frost action.

ANIMAL ACTIVITY

Although man, of all the animals, has assumed the most spectacular role in the transportation of surficial deposits, many other 

species have played an equally important part as far as the total 

effect is concerned. In many climates earthworms are continually 

churning the soil near the surface. Burrowing animals, such as 

foxes and woodchucks, bring material to the surface from deeper 

parts of the weathering profile. Ants and termites, especially in 

tropical countries, excavate huge labyrinths often extending to 

great depths, from which they carry the material to the surface. 

Although the transporting effect of any one individual or colony 

may be trivial, the effect of such activity over thousands of years 

may be a very substantial factor in the mixing of the components 

of the weathering profile.

In many areas of deep weathering, prospectors have profitably 

searched through the material brought to the surface by burrowing animals and insects for fragments of gossan or oxidized ore 

minerals. Analysis of ant heaps for traces of ore metals as a 

method of prospecting has foeen attempted in Afr^a and

Australia, but no report has yet been published on its SUCC6SS.

SOIL FORMATION 

Tll Upper few feet or the earth's surface comes under the

influence of a complex series of reactions that trangforHl tfl.6

raw fragmental material resulting from rock weathering into a 

medium that can support plant growth, The process, known as 

soil formation, is thought to be primarily the work of bacteria

and fungi that derive their vital energy from the oxidation of

(tefld plflnt remains. The result of the soil-forming process is the 

differentiation of the surficial material into distinctive lajBIS 01

son "horizons." The vertical section through the sequence of soil

hOriZOnS iS Commonly known as the soil "profile."

The principal horizons of the soil profile are the uppermost "A" 

horizon, or topsoil; the "B" horizon, or subsoil; and the "C" 

horizon, or parent material that has not been affected by soilforming processes. In detailed descriptions of soil profiles each 

of these horizons may be divided into smaller units on the basis
PRINCIPLES OF GEOCHEMICAL PROSPECTING 281

of local minor variations in color, texture, or composition. These 

subdivisions are commonly designated by subscripts; J5i and #2 

are thus subdivisions of the B horizon. The humus layer, which 

constitutes the topmost member of the A horizon, is commonly 

designated as the A0 horizon. The A horizon is characterized by 

a leaching of certain elements which move downward to be 

precipitated in the B horizon. The C horizon, or parent material, 

is usually weathered rock or residuum; the depth to the C horizon 

has no direct relation'to the depth to the unweathered bedrock.

Different elements take part in this process in different 

climates. In moist temperate climates, iron and aluminum oxides 

tend to be leached from the A horizon and reprecipitated in the 

B, a process known as podzolization. In moist tropical climates, 

silica as well as iron and alumina take part in the formation of 

the so-called lateritic soils. In arid climates, the leaching and 

reprecipitatidn of calcium within the soil profile is an important 

factor.

The importance of soil-forming processes in geochemical 

prospecting is that they may modify anomalies that have formed 

in either residual or transported cover. This effect is particularly 

apparent in temperate forest soils, where the topsoil or A horizon 

may be so leached that samples of this material cannot be 

effectively used for geochemical mapping. A zinc anomaly in 

residual soil over the Friend's Station deposit in Tennessee was 

clearly defined by samples taken from the B horizon at a depth 

of 4 feet; the same area sampled from the A horizon at a depth 

of 2 feet showed a very inhomogeneous and erratic pattern of zinc 

distribution. The difference was thought to be entirely the effect 

of leaching of the zinc from the upper topsoil horizon (Hawkes 

and Lakin, 1949). The copper, lead, and zinc contents of soil 

profile over ore and over barren ground at the Union copper 

mine, North Carolina, are given in table 6. The data for normal 

soil show leaching of copper and lead in the A horizons, an 

enrichment of lead in the B horizons, and an enrichment of 

zinc in both the A and B horizons as compared with the parent 

material. The almost consistent increase of all metals with depth 

in the anomalous profiles is noteworthy. These data confirm the 

general experience that the B horizon of forest soils is somewhat more reliable for geochemical sampling than the A horizon. 

Work in other types of soils, however, has not indicated any 

variations in the distribution of metals in the soil profile that 

need to be taken into account in geochemical survey practice, so 

that samples taken from any part of the soil profile can be used 

equally well in geochemical soil surveys. For example, Huff
282 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

(1952), in working with immature Rocky Mountain soils, found 

that samples of surface soil were just as satisfactory as deeper 

samples and were much easier to collect.

The data of table 6 also show the lateral variation of metal 

content within the same soil horizon. The distribution of metals 

in the A and B horizons is considerably more homogeneous than 

in the C horizon, indicating that the near-surface horizons are 

more suitable for geochemical surveying than the deeper material. 

The lateral variations within short distances are far greater 

than the variations of replicate determinations by the analytical 

methods used in this experiment but are roughly equivalent to 

the variations of replicate determination by the less precise 

rapid methods in general use in geochemical prospecting.

UNDERGROUND WATER MOVEMENT

The movement of water under the influence of gravity or of 

a hydrostatic head is a fairly simple matter of flow from a higher 

to a lower level, or from an area of higher to an area of lower 

pressure. Rainwater soaks into the soil and replaces the air in 

the pore spaces of the surficial material or rock; in the upper 

unsaturated section of the mantle it is known as vadose water. 

If the pore spaces extend to sufficient depth, the rainwater 

eventually reaches the water table, which is defined as the surface 

below which the air in the pore spaces has been completely 

replaced by water. The ground water, or water below the water 

table, then tends to move laterally in the direction of the easiest 

means of escape. It may emerge at the surface as springs and

as seepages along the banks or in the beds of streams. Under 

ordinary circumstances, a swamp, spring, or stream is in effect 

an "outcrop" of the water table. In climates with sufficient rainfall, the -water table slopes in essentially the same direction as 

the surface of the ground, and its contours are about parallel

with topographic contours. In some areas of deficient rainfall,

however, the river water may actually flow back into the ground,

with the effect that the water table slopes away from the riverbed

rather than toward it.

The gravity movement of ground water is impeded by the

material through which it flows. Fresh rainwater entering the

underground reservoir of the ground-water system cannot escape 

as fast as it is added and tends to pile up. The effect of this piling1

up is to raise the water table so that higher escape channels are

available, and new springs and seepages become active, Conversely, during a period of light rainfall, the water table will be 

lowered and springs will progressively dry up.
PRINCIPLES OF GEOCHEMICAL PROSPECTING 283

In areas of crystalline or metamorphic rocks which have 

negligible pore space, a true water table may not exist unless the 

cover of surficial material is deep enough. Here, rainwater that 

has soaked into the soil tends to flow along channels on the 

surface of bedrock. When a channel of this kind crosses a 

permeable zone of fracturing or shearing, the water may enter 

the fractures to emerge again at the surface of bedrock at a 

lower elevation.

Water and the salts dissolved in it can move against the force 

of gravity by capillary rise, by diffusion, and by migration of 

ions on the surface of minerals, as discussed in an earlier section. 

These effects are most pronounced in the unsaturated fringe zone 

of vadose water between the water table and the land surface. 

The net result of movement against the force of gravity is commonly a dispersion of the dissolved constituents both upward and 

laterally in the direction of decreasing concentration.

Upward dispersion of this kind may be accelerated by the 

pumping action of a periodically rising and falling water table. 

Water in the fringe zone moves downward as rainwater soaks 

in from above; in dry periods, the direction of movement is 

reversed in order to replenish the moisture removed nearer the 

surface by evaporation and transpiration. Thus the movement of 

moisture in the fringe zone pulsates with the weather, moving 

downward during rainy weather and upward during dry weather. 

At any given time, the direction of movement of this pulsation 

is thus the opposite of the movement of the water-table surface, 

which rises in rainy weather and falls in dry periods. The over-all 

effect of this pumping action is a spreading of dispersion 

patterns upward from the source in the bedrock.

The elements that can move readily in ground water and soil 

moisture are in general the elements of high mobility, such as 

zinc and cobalt. The dispersion patterns formed by them can, 

of course, be mapped directly by sampling and analysis of the 

water itself. They can also be mapped by measuring the exchangeable cations in the material through which the solutions percolate. 

Solutions containing metals derived from the weathering of a 

sulfide deposit, as they come in contact with permeable, unconsolidated sediments or residual soils, set up exchange reactions 

whereby the metal content of the matrix is increased at the 

expense of the metal content of the solutions. In the course of 

time, an equilibrium between the adsorbed ions in the matrix 

and the dissolved ions in the solutions will be reached. As this 

equilibrium is approached, the pattern of dissolved ions spreads 

farther from the source into fresh material, until that again is
284 CONTRIBUTIONS TO GEOCHEMIGAL PROSPECTING FOR MINERALS

saturated withf exchangeable metallic ions. In this way, a 

pattern of dispersion grows in the matrix that is an exact 

replica of the pattern in the wa,te'r. Because -patterns of this 

kind are superimposed upon whatever dispersion patterns were 

originally present in the matrix, they have been termed 

"superimposed" halos by Russian workers (Sergeev, 1941, p." 38 

of translation). -

In geochemical survey work, it is rarely practicable to collect 

soil moisture for analysis. Superimposed halos can be readily 

mapped by simple chemical analysis of the matrix, however. 

Inasmuch as the superimposed halos are fossilized replicas of 

the water pattern, they are extremely useful in tracing the 

channels followed by the soluble products of decomposition of 

ore bodies.

Geochemical anomalies developed by movement in underground 

water have somewhat different characteristics depending on 

whether they occur in' descending or laterally moving ground 

water, spring water and seepages, or vadose water.

Descending ground water. Descending ground water can be 

sampled conveniently only in the underground workings of mines. 

The composition of aerated water descending through cracks and 

fracture zones in the rock will in general reflect the chemical 

character of the rock or ore through which it has passed. 

Lovering (1952) has shown that the metal content of descending 

water in the relatively dry mines of the Tintic district, Utah, 

reflects the presence or absence of ore in the channels through 

which the water has passed. He found that the composition is 

modified by the chemical character of the rocks adjoining the

channels and by the distance traveled by the solutions. Japanese

workers found a correlation between the content of iron, zinc, 

and sulfate in fracture-zone waters, and the occurrence of

known ore above the underground WOrKmgS III WltiCR #16

were collected (Kimura, Fujiwara, and Morinagra, issi). On 

basis of data of this kind, at least one body of ore has foe, $11

discovered (T. Watanabe, oral communication, 1953). 

A commonly observed pattern formed by. descending ground

-water is the zone of secondary enrichment in large SUlfide

depOSltS. DOWnWard-mOVing Water above.tne water.table leaches 

copper from secondary copper minerals. As these copper-rich

Solutions pass downward into the zone of primary sulfide

minerals, the copper in the Solution reacts with ike primary 

chalcopyrite to form secondary copper sulfides, such as bornite 

or chalcocite. Zones of secondary enrichment make up the best
PRINCIPLES OF GEOCHEMICAL PROSPECTING ' 285

grade of ore in many of the western porphyry copper deposits 

(Emmoiis, 1933).

Laterally moving ground water. Many workers have made 

systematic studies of the metal content of well water, and some 

of them have reported positive correlation with known ore. 

Rarely, however, has it been possible to forecast the occurrence 

of an unknown body of sulfide ore from well-water data. Part 

of the difficulty is perhaps the almost universal presence of 

artificial contamination of the well water by copper and zinc 

from pumping equipment and other plumbing in contact with 

the water. Such contamination causes large erratic variations of 

.no significance that mask the minor variations in metal content 

due to increments from decomposing sulfide minerals. Another 

reason for failure in some areas is that the water has been 

sampled below the zone of oxidation where the metal from 

primary sulfide is not actively going into solution. Kennedy 

(1956) collected water from churn drill holes in and near an 

.undeveloped zinc deposit in southwestern Wisconsin and found 

that the zinc content was hardly above the background; the ore 

body there, however, is Well below the lowest level of the water 

table. In other areas, the pH of the ground water may account 

for the failure of metal to appear in well water. Levering, Huff, 

and Almond (1950) report that the copper content of water from 

.exploration holes cutting1 copper ore at the San Manuel deposit, 

'Arizona, was below the limit of detection. The pH of the water 

'averaged 9.0, well above the pH of hydrolysis of copper in dilute 

solutions (table 4). Although the results of experimental wellWater sampling have to date been uniformly discouraging, this 

approach perhaps should not be 'completely abandoned until more 

investigations have been made with proper respect for, the 

necessary precautions. :

Superimposed halos in the rocks or surficial material through 

which the ground water has passed have been observed in many 

i areas. At the Ray Copper deposit in Arizona, Clarke (1935) 

.described copper in the form of tenorite in the postore Wfcitetail 

conglomerate. The distribution pattern there indicates that the 

: tenorite was deposited from copper-rich ground, water derived 

from the oxidation of the main ore body. The maximum copper 

content of this secondary deposit is about 5 percent, or more 

than twice that of the better-grade ore in the mine. ..._'.

Sampling alluvial cover over a lead-zinc vein in the Abakaliki 

district of Nigeria (Hawkes, 1954) showed a well-defined zone of 

-lead- and zinc-rich material immediately above the surface of 

bedrock leading away from the suboutcrop of the ore in the
286 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

direction of the drainage channel; on the other side of the suboutcrop, away from the drainage channel, this pattern was 

lacking. Presumably the movement of ground water here was 

controlled largely by the bedrock surface, as the underlying 

shale was unweathered and relatively impermeable to percolating 

solutions.

Spring ivater and seepages. Analysis of water from cold 

springs and seepages has been considerably more successful than 

well-water studies in indicating unknown deposits of ore. The 

danger of artificial contamination of spring water is very slight, 

except for springs in limestone country where the spring is 

effectively the point of emergence of an underground stream. 

Also the water from springs is drawn from near the water-table 

surface, where oxidation and solution of primary sulfide minerals 

is most active, rather than from some unknown depth below the 

water table as is the case with well water. Many springs discharging metal-rich water have been correlated with known 

sulfide deposits within the source area. Other metalliferous 

spring waters occur in mineralized districts where the occurrence 

of sulfide ores is highly probable. In a few such areas, later 

exploration above the spring has uncovered sulfide occurrences. 

At least in noncalcareous terrain, no example of a metal-rich 

cold spring water has been reported where the absence of sulfide 

minerals in the bedrock has been definitely proved.

Superimposed patterns are commonly developed in the soil 

and muck around metal-rich springs or seepages where metal 

has been adsorbed in the solid material through which the solutions have percolated. Inasmuch as the pattern of exchangeable 

metal will be retained even when the seepage is inactive, soil 

analysis is a relatively dependable method of determining the

relative metal content of the solutions that have been in contact 

with it.

Seepages commonly OCClir On the edges Of modern alluvial flats,

where ground water containing the soluble products of weathering aisonargres into tKe surfaee drainage. Seepage areas also may

occur scattered on the hill slopes above the drainage channels

where they may be identified either by the nature of the son

or by characteristic types of vegetation. Trace-metal analysis of

SOU (UlCl fllUCK Ground ground-water seepages may indicate

Whether the water has passed through an area containing actively

oxidizing surfaces. Geochemical anomalies of this kind would, 

of course, indicate a source in a direction UP $6 fi]0pe pr the 

water table from the seepage rather than directly underneath.
PRINCIPLES OP GEOCHEMICAL PROSPECTING 287

Examples of what are probably superimposed seepage patterns 

have been reported by Bischoff (1954) in his work on geochemical 

soil sampling over base-metal deposits in eastern Canada. He 

found that the geochemical anomalies in samples of near-surface 

glacial material were commonly displaced as much as several 

hundred feet downslope from the suboutcrop of the sulfide vein. 

Presumably these anomalies represent the points of emergence 

of ground water that had been enriched in metal by passing 

through the oxidizing deposit.

Below the Chicago-Brown Bear ore zone at the Blackbird 

cobalt district of central Idaho surficial rubble has been cemented 

by limonite rich in copper and arsenic. The cementing material 

was most probably derived by precipitation from metal-rich 

ground waters that had filtered through the pyritic coppercobalt mineralized area. Very possibly many limonitic breccias 

generally included with gossans are in reality precipitated from 

ground waters.

Organic soils provide a particularly favorable host for superimposed halos. Under certain conditions the decay of dead 

vegetable remains is inhibited for one reason or another, and a 

considerable thickness of organic matter may accumulate. In 

northern climates, this process leads to the formation of peat 

deposits and muck bogs. Probably by a combination of adsorption and the formation of stable insoluble organic complexes, 

many elements are precipitated in the presence of organic matter. 

Any metallic ions that enter such an environment in ground or 

surface waters tend to be immobilized and strongly concentrated 

in the organic matrix.

At the Manning muck bog near Albion in western New York, 

Cannon (1955) describes a distribution of zinc along the edge of 

the bog and around springs that discharge through the central 

parts of the bog. The zinc is apparently precipitated from zincrich ground water at the point where it first comes in contact 

with the organic environment. The ultimate source of the zinc is 

the Lockport dolomite, which is locally enriched in sphalerite. 

Several million pounds of zinc have been precipitated in an area 

of less than 1 square mile. The average dry weight zinc content 

of the muck in this area is 0.5 percent, and maximum zinc contents of more than 10 percent have been reported.

Salmi (1950), in determining the metal content of peat from 

49 bogs, in Finland and Norway, found that the metal content 

of bogs in mineralized areas was significantly higher than in 

barren areas. He concludes that 0.1 percent copper and 0.6 

percent zinc in peat ash indicate rock mineralized respectively
288 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

with copper and zinc, and that 0.03 to 0.1 percent nickel could 

be regarded as an indication of nickel-bearing ore. The background copper, zinc, and nickel content of peat is, respectively, 

0.03, <0.03, and 0.01 percent.

Vadose ivater. The processes already described whereby dissolved salts move upward against the force of gravity can result 

in a pattern of dispersed metal in the surficial material directly 

over the source in the bedrock. Although ionic diffusion is 

probably only one of the mechanisms responsible for upward 

movement, it is convenient to refer to the resulting dispersion 

patterns as "diffusion patterns."

Diffusion patterns are best developed in a matrix containing 

a substantial proportion of clay-sized particles. The fine-grained 

matrix has both a higher retentivity for water and a higher 

exchange capacity, so that the dispersion patterns can be readily 

fixed as superimposed halos. Fine-grained alluvial and glacial 

deposits are relatively good hosts, whereas sand and loess are 

poor hosts. Diffusion halos undoubtedly form also in residual 

soils but are masked by the inherited patterns of residual metals.

In the Austinville zinc district of Virginia, Fulton (1950) 

reports a distribution of zinc in Tertiary river sediments that 

closely reflects the zinc content of the underlying mineralized 

bedrock. Patterns of this kind were lacking in the most recent 

river sediments, where presumably the shortness of time had 

not permitted the maturing of the diffusion pattern.

A well-defined example of a diffusion pattern was mapped in 

detail in the Abakaliki lead-zinc district, Nigeria, where relatively 

unweathered bedrock was overlain unconformably by a 6-foot 

deposit of alluvial silt (Hawkes, 1954), Sampling on a vertical

section through the silt as exposed in an exploration trench showed

an easily contoured distribution of zinc, falling off uniformly with

distance from the underlying source from a maximum of several

thousand parts per million directly over the ore to several hundred

at the surface. Historical evidence indicates that the silt in which

this pattern was formed was deposited about 400 years ago, so 

that an estimate of the time required for the evolution of a 

diffusion pattern can be made.

Somewhat similar patterns, although not as clearly developed,

have been" found in the course of experimental work in glaciated 

terrane inithe United States and Canada, White and Alien (1954)

report copper in glacial till over -what is probably a leakage halo

in the rocks overlying Ike fteadwoocl Camp deposit in British 

Columbia. Some of the anomalies in glacial till over mineralized
PRINCIPLES OF GEOCHEMICAL PROSPECTING 289

zones illustrated by Bischoff (1954) may be, at least in part, 

diffusion halos. Some of the best examples of diffusion halos in 

deep glacial cover have been found in the course of commercial 

exploration work, the results of which are not available.

Work by Kennedy (1956) in the driftless area of southwestern 

Wisconsin has failed to find any evidence for superimposed halos 

in the loess cover. A zone of mechanically mixed loess and residuum 

occurs commonly at the base of the loess blanket, where any 

anomalies present in the residuum are dispersed into the mixed 

zone. This, however, has been interpreted as a simple mechanical 

mixture of metal-rich residuum and barren loess, and not as 

the effect of migrating ions or solutions.

VEGETATION

The principles underlying chemical or botanical studies of 

vegetation as a method of locating buried ore deposits are basically 

simple. The root systems of trees can be portrayed as powerful 

sampling mechanisms, bringing representative solutions up from 

a large volume of ground below the surface. Then, as the water 

is removed by evaporation, the mineral content of these solutions 

is left behind and concentrated in the leaves.

In detail, however, the circulatory system of terrestrial plants is 

by no means simple. A vast and complex set of equilibrium relationships is active from the time the nutritive solution comes 

within the influence of the root tip until the water is discharged 

into the atmosphere. Whether or not a metal-rich nutrient solution 

will be reflected by an easily measured variation in the composition 

of the plant, or by a diagnostic variation in plant morphology or 

ecology, depends on the balance of these many relationships.

In reviewing the factors causing plant anomalies, it is pertinent 

to consider (1) the availability of elements in the soil, (2) the 

factors governing the movement of solutions into plants, (3) the 

movement of and nutritive effect of mineral matter within plants, 

that is, plant nutrition, and (4) the chemical and biological effects 

of this process that can be used as guides to the prospector. As a 

result of recent research, much of it aided by radiotracer techniques, the physics and chemistry of some of these reactions are 

beginning to be understood (Truog, 1951).

Availability of elements in so^.-^Agricultural scientists refer to 

"available" nutrients, which consist of ions either dissolved in the 

soil moisture or adsorbed on the clay minerals of the soil. These 

nutrients constitute the mineral content of the soil that is immediately available for uptake by the plant. They make up only a 

small proportion of the total mass of the soil, the remainder of
290 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

which consists of ions tightly bonded within the lattice structures 

of the stable soil minerals.

Availability of an element to plants is measured either by determining the amount of the element that can be removed from a soil 

by leaching with chemical reagents, or by growing a plant in the 

soil and determining the amount of the element taken up by the 

plant.

Availability is a concept closely related to mobility in the surface 

environment. It can be regarded as the mobility with respect to 

plant activity. The ratio of the availability to the total content of 

an element in the soil is a function principally of the soil pH, 

oxidation potential, exchange capacity, and presence of complexing 

agents. Artificial modification of one or more of these factors can 

under many conditions change the nutritive value of a soil. For 

example, the available molybdenum can be increased by adding 

lime and thus increasing the pH to a point where the molybdenum 

already present becomes soluble (Evans and others, 1951). The 

addition of lime has also been recommended as a cure for soils 

poisoned by an excess of available zinc, because of the lessened 

solubility of zinc at a high pH. Adding animal fertilizer to a soil 

in one experiment was also found to reduce the availability of zinc, 

probably by the formation of stable organic zinc complexes. The 

effect of complexing agents is illustrated by the use of synthetic 

metallo-organic complexes (specifically, the metal salts of ethylen ediamine tetraacetic acid) as an artificial source of minorelement nutrients; added to a soil, these complexes are just reactive 

enough to provide the plant with an adequate source of the 

element but not so unstable that the element is largely leached out 

with the first rain, as would happen if it were present as soluble

salts.

Movement of soil solutions into plants. According to currently

held Concepts, the Surface of the root tip of a plant and the

immediately surrounding solutions are characterized by ft high

concentration of hydrogen ions. This effect is SO local that it is not 

apparent from a measurement of the Pn of the soil as a whole

The cause of the enrichment of hydrogen ions is probably the 

hydrolysis of C02 , which escapes through the roots in substantial 

qua.ntitio8 <BWa. 1947). The effect of the H+ abundance is to set 

up active cation-exchange reactions ^etween ^* ^y «*_.,. Q£

the soil ana the surface of the roots, which have been shown to

have a high exchange capacity (Williams &M COlema

On the surface of clay minerals, hydrogen JOflS exchange

ions which then move through the soil to the roots, probably by a
PRINCIPLES OF GEOCHEMICAL PROSPECTING 291

combination of diffusion, surface migration, and contact exchange 

(Jenny and Overstreet, 1939). When the metal ions reach the 

outer surface of the root tip, they exchange for hydrogen ions, 

which are then released to repeat the process.

Empirical observations have shown that the local but extremely 

corrosive environment near the root tips of plants can extract 

mineral matter well in excess of what is present in readily 

exchangeable form. Even primary minerals such as feldspar can 

be broken down and their component cations made available to 

the plant (Keller and Frederickson, 1952). A spectacular example 

of the dissolving effect of roots is the "converter" plant which 

takes up selenium from stable and relatively insoluble selenium 

compounds in the soil (Beath and others, 1939, p. 266). With the 

death and decay of the plant, the selenium returns to the soil in 

soluble form and is then available for uptake by other plants that 

lack the power to dissolve selenium.

Movement into the plant of the cations adsorbed on the outer 

surface of the root tip is controlled by a selective restraining effect 

of the cell membranes. Some ions are freely admitted and others 

are impeded to a greater or lesser degree, an effect that is 

apparently due largely to the pH of the cell sap within the root 

tip. Lead, for example, is an element that is apparently largely 

immobilized by precipitation in the cell walls and nuclei of the roots 

of some plants (Hammett, 1928). Thus, toxic excesses of lead may 

not reach the active centers of growth in the upper parts of the 

plant. If the quantity of lead in the nutrient solution is too great, 

however, the precipitate apparently impedes the flow of solutions 

and the plant does not grow normally. Uranium and vanadium, 

elements which are also toxic, are apparently precipitated in the 

roots in the same way (Cannon, 1952).

Plant nutrition. The movement of mineral matter within 

plants is controlled by many factors including free and restrained 

diffusion, movement of the solvent, electrical and thermal effects, 

exchange reactions, and, perhaps most important, metabolic accumulation of mineral nutrients in the building of metallo-organic 

molecules (Broyer, 1947). Of the last type of reaction, the entrance 

of magnesium into the chlorophyll molecule is a classic example. 

Many other elements play a similar dominant role as components 

of enzymes and other catalysts that speed the many vital reactions 

in a growing plant.

Stated in a different way, the acceptance of inorganic salts into 

the circulatory systems of plants, and the distribution of those salts 

throughout the plant structure is a response to the plant's nutri-
292 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

tional requirements. In the upper part of the plant, the nutritive 

elements are commonly enriched in the actively growing cells, 

particularly in the seed structures and growing tips. As the cells 

mature, the concentration of these elements declines. .There is 

abundant evidence that the distribution of nutrient elements 

changes with changing requirements and that the circulatory 

systems of plants maintain a dynamic balance whereby inorganic 

material can be not only supplied to fulfill the nutritive needs but 

also removed when it is no longer needed. Each species of plant 

has its own individual nutritive requirements that differ somewhat from those of every other species. The nutritive or toxic effect of any one element may depend on the over-all composition of 

the nutrient solution. The uptake of one element in a plant thus 

may be suppressed or stimulated by the presence of other elements 

in the solution (Evans and others, 1951; Ahmed and Twyman, 

1953). The composition of plant organs has also been correlated 

with age of the plant, exposure to sunlight, and height above the 

ground.

For whatever reasons the elements are needed by plants, it has 

been definitely established that in addition to the common nutritive elements potassium, nitrogen, calcium, and phosphorus 

most plants require small quantities of many minor elements, 

including copper, zinc, iron, molybdenum, manganese, sulfur, and 

boron. If the nutrient solutions do not provide adequate quantities 

of these elements to the root system, the plant will be unhealthy 

or may not survive. Some workers have even postulated that plants 

require a certain,small amount of every element in the periodic

table, but perhaps in quantities so small that the need could never 

be demonstrated in greenhouse experiments.

At the Other extreme, an excess of any element above a critical 

level in the nutrient solution will impair the health of the plant

or may even kill it. The element here is present in SUCh Quantities

that it interferes with rather than assists the normal metabolism

of the plant and has an.Over-811 tOXIC rather than a nutritive effect.

For some elements there is an optimum range for the composition t?r tti« wwtriexxt solution, if the concentration of an element

in the solution is either greater than the upper limit of mis range 

or less than the lower limit, the plant will not grow normally.

BQron is perhaps an extreme example; very small Quantities are

necessary for the growth of many plants, whereas only slightly

higher Concentrations CaUSe injury. With many plants the range 

between these two levels is only a few parts per million of boron 

(Robinson, 1951). For some other elements, such as zinc and
PRINCIPLES OF GEOCHEMICAL PROSPECTING 293

arsenic, plants can tolerate a wider range without conspicuous 

damage. For still, others, the existence of either one or both of 

the limits has not been demonstrated. It is quite possible, however, 

that further research will eventually show that an optimum range 

of concentration exists for every element in the supporting 

solution.

Prospecting by plant analysis. If the metal content of a sample 

of plant material is to be useful in prospecting, it should bear a 

fairly simple correspondence to the metal content of the supporting 

soil. Considerations of availability in the nutrient solution, 

together with the many vital and nonvital processes affecting the 

movement of elements into and through the plant, indicate correctly that the correspondence may not be as simple as might be 

desired. In general, however, if other factors are held constant, a 

useful degree of correspondence will be found. The problem is to 

determine what irrelevant factors are most likely to mask the 

correlation between plant composition and soil composition.

First, the accumulating effect of plants is apparently not a 

critical factor. In earlier work, this effect was regarded as a 

highly important mechanism for enriching the metal content of a 

geochemical sample to a point within the range of sensitivity of 

the available analytical method. Thyssen (1942) pointed out that 

the degree of enrichment for each element can be expressed as 

an "enrichment factor," equal to the ratio of its content in the 

biosphere to its content in the lithosphere. He suggested that 

elements characterized by a high enrichment factor are to be 

recommended for prospecting by plant analysis.

With the high sensitivity of modern analytical methods, an 

enriched sample is no longer necessary. Furthermore, it has been 

found that elements that are highly enriched in plant material 

are not necessarily the ones that will best reflect the relative 

abundance of that element in the soil. Zinc is an element that may 

be very highly enriched in many plants. In dwarf birch, for 

example, the zinc content of the ash of mature twigs is commonly 

about 1 percent, representing a hundredfold enrichment factor 

over the 100 ppm zinc of normal soils (Warren and others, 1952b). 

The variation in the zinc content of most plants, however, is so 

sensitive to factors completely unrelated to mineralization, such 

as drainage and sunlight conditions, that the response to differences in the composition of the soil may be largely masked. Recent 

observations indicate that the content of toxic elements, like 

uranium and lead, may reflect the composition of the soil more 

accurately than the nutrient or neutral elements, even though the
294 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

absolute amount of the toxic element in the plant organ is extremely small. The term "accumulator" plant has been applied 

indiscriminately to all plants whose chemically determined metal 

content is useful in prospecting. In view of the dubious significance 

of the accumulating effect, it is suggested that the use of this term 

in discussing plant analysis as a prospecting method be discontinued.

The part of the plant selected for analysis is an especially critical 

factor. As a result of vital processes, the metal content of different 

organs of the same plant may be widely divergent. Furthermore, 

the organs of plants differ somewhat in the degree to which their 

composition reflects the composition of the supporting soil. The 

zinc and copper content of mature twigs and wood have generally 

been found to be more stable than the content in immature green 

tips, leaves, or seed structures in which the variations in coirfposition depend on the rate of metabolism of the actively growing 

part. The contrast between the metal content of stems and that 

of leaves or needles collected from the same individuals is illustrated in data collected by Warren, Delavault, and Irish (1952b) 

and summarized in table 7. The metal content of plant organs can 

be accurately interpreted in terms of geologic environment, therefore, only where they are based on samples of the same parts of 

the plant.

Different species of plants take up different amounts of inorganic material from the soil. The contrast in the uptake of copper 

and zinc by different species all living in essentially the same

climatic environment and all growing in unmineralized terrane is

also shown in table 7. Here, it would be extremely misleading to

attempt geologic interpretations of the metal content of plant

samples taken without regard to the identity of the species, In a 

given environment, a group of species may have similar response 

to certain elements, and where this can be established it is 

permissible to include two or perhaps more species in one set of 

comparable samples.

It is not practical to limit plant sampling to soils of identical pH,

drainage conditions, and exposure to sunlight. Variations due to

these factors may be minimized, however, by determining the ratio 

of two elements, such as copper and zinc, whose content in plants

responds to nongeologic factors in a similar way. Thus, under

normal conditions, a fairly constant copper-to-zinc ratio may be 

observed even though the absolute amounts of the two elements 

may vary greatly due to drainage, sunlight, and soil texture. Here 

a high copper-zinc ratio would indicate copper mineralization of
PRINCIPLES OF GEOCHEMICAL PROSPECTING 295

TABLE 7. Average copper and zinc content, in parts per million of dry .weight, of leaves 

or needles, and stems bearing them

[Compiled from data of Warren, Delavault, and Irish, 1952b]

Species

Douglas fir (Pseudotsuga taxlfolia) ...........

Lodgepole pine (Pinus contorta) .............

Yellow pine (Pinus ponderosa) ..............

Whitebark pine (Pinus albicaulis) ..........

Engelmann spruce (Picea Engelmanni) .......

Western red cedar (Thuja pUcata) .^. ........

Hemlock (Ttuga heterophylla) ...............

Willow (Salixtp.). ........................

Aspen (Populus tremuloidsg) ..._............

Cottonwood (Populus trichocarpa) ...........

Scrub birch (Betula glandulosa) ..............

Water birch (Betula occidentalis) ............

Mockorange (Philadelphus lewisii) ...........

Chokecherry (Prunus demissa) ..___. .......

Saskatoon ( A melanchier alnifolia) ...........

Mountain maple (Acer glabrum) .... .__._._.

Broombrush (Symphoricarpos racemosus) .....

Sagebrush (Artemisia tridentata) ............

Copper

Leaves or 

needles

3 

5

4 

4 

4 

3 

2 

12 

15 

11 

10 

11 

8 

10 

11 

13 

9 

17

Stem

5 

7 

3 

6 

10 

2 

7 

12 

11 

8 

8 

9 

7 

7 

7 

6 

8 

14

Zinc

Leaves or 

needles

24 

37 

34 

27 

41 

10 

12 

120 

120 

130 

170 

94 

23 

26 

31 

31 

24 

28

Stem

45

33 

29 

31 

C4 

14 

48 

120 

102 

75 

130 

110 

34 

36 

30 

24 

31 

20

the bedrock, and an unusually low ratio would similarly indicate 

zinc mineralization.

Subject to the several modifying factors previously discussed, 

variations in (the chemical composition of the upper parts of the 

plant correspond to variations in the composition of the solutions 

tapped by the root system. The roots of many plants extend to considerable depth even in moist climates where wrter is abundantly 

available near the surface. The root systems spread out and gather 

samples from a substantial volume of soil so that the material concentrated in the upper organs is the integrated effect of all the material within a considerable radius. In prospecting, therefore, the 

metal content of properly chosen samples of vegetation is an indication of the average composition of soil solutions at some depth 

and to a considerable lateral extent around the sample site. The 

roots of trees have been seen in tunnels 50 feet below the surface 

in the uranium mines of the Colorado Plateau. In British Columbia, plant anomalies ranging in width from 4 to 50 times the width 

of the ore deposit itself have been reported by White (1950). Plant
296 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

analysis as a method of prospecting is particularly useful in areas 

of deep transported cover where the ground-water and diffusion 

patterns do not reach the surface.

Palmqvist and Brundin of the Swedish Prospecting Co. 

pioneered in the use of plant analysis as a prospecting method by 

systematically sampling the leaves and needles of vegetation and 

making spectrographic analyses of the samples reduced to ashes. 

As a result of this work, they reported discoveries of small tin and 

tungsten deposits in Cornwall (Swedish Prospecting Co., 1939), a 

vanadium-bearing shale at Skane in Sweden, and a tungsten 

deposit at Yxsjoby in Sweden (Josef Eklund, oral communication, 

1948). Electrisk Malmletning, a Swedish geophysical company, 

has reportedly done some work on the chromium content of vegetation over chromite deposits in Greece, where they found a 

positive correlation (Josef Eklund, oral communication, 1948). 

Rankama (1940) conducted a similar investigation of nickel in the 

ash of birch leaves in the vicinity of known nickel deposits, where 

by contouring the nickel content of the plant ash he was able to 

show the location of ore buried beneath 10 feet of glacial cover. 

Hans Lundberg (oral communication, 1947) used the lead and 

zinc content of vegetation growing near geophysical anomalies in 

Newfoundland to determine whether the anomalies warranted 

drilling for lead-zinc ore. Vogt and Bugge (1943) found that the 

leaves of dwarf birch growing on covered outcrops of ore contained more copper than other species from the same locality, 

and also more copper than the same species growing on normal

soil. 

Beginning in 1945, Warren and coworkers at the University of

British Columbia have been active both in research into the 

biochemistry of copper and zinc in Canadian flora and in the application of plant sampling on a large scale as a prospecting method. 

They have gathered a vast amount of data to show the normal

distribution of copper and zinc in different species of plants and 

in different organs of the same species (Warren, Delavault, and

Irish, 1952b). Guided by these observed relationships, they concluded that stems of 1 full year's growth of gymnosperms, particularly Douglas firs and pines, provide the most useful samples.

Using Douglas fir stems, they consider as anomalous a content of

more than 9 pp>m (dry- weight) for copper, more than 6O ppm

(dry weight) for zinc, and outside the limits 0.07 to 0.23 for the 

copper-zinc ratio. They have applied these techniques on a commercial scale throughout Canada and have reportedly uncovered 

a number of mineralized areas. Warren and his colleagues have
PRINCIPLES OF GEOCHEMICAL PROSPECTING 297

also done some experimental work on the distribution of iron, 

manganese, gold, silver, and molybdenum in plants (Warren, 

and others, 1952a; Warren and Delavault, 1950a, 1953a).

In the Tri-State lead-zinc district, Harbaugh (1950) found that 

the zinc content of leaves and twigs of 24 species of trees over 

mineralized zones were respectively 38 and 25 percent greater than 

similar samples from barren areas. Twigs of blackjack oak collected within 300 feet of known ore contained 67 percent more 

zinc than similar samples collected in barren areas some miles 

distant.

Plant analysis for uranium and vanadium has become an effective method of prospecting for uranium ores in the Colorado 

Plateau area ('Cannon, 1952, 1953, 1954, 1957). The most useful 

samples come from the twigs and wood of sage, rabbitbrush, 

pifion, and juniper, which put down their roots to very great 

depths in search of water. A uranium content greater than 1 ppm 

on an ash basis indicates geologically favorable ground. It is 

noteworthy that the 1 ppm threshold for plant ash is less than the 

4 ppm normal background for unmineralized rock. Cannon points 

out that uranium and vanadium are largely precipitated within the 

root near the point of intake, so that only a relatively small fraction reaches the upper parts of the plant.

Experiments with analysis of plant material have also been 

reported from California6, Arizona (Lovering and others, 1950; 

Warren and others, 1951b), Missouri (Keller, 1949), Michigan 

(McKinstry, 1948, p. 218), eastern Canada (Riddell, 1952b; 

Warren and Delavault, 1953b), Poland (Bobrowski and Piechota, 

1949), Russia (Tkalich, 1938; Maliuga, 1947), and west Africa 

(Webb and Millman, 1950).

Prospecting by botanical observations. The effect of different 

concentrations of metals in the nutrient solution can go far beyond 

a simple variation in the composition of the plant organs. High 

concentrations of metal in the supporting soil may modify the 

morphology or color of the flora and even determine which species 

can live under the conditions imposed. Identification of the symptoms and species that are characteristic of the chemical environment thus can provide information that is directly helpful to the 

prospector without recourse to sampling and chemical analyses 

of plant material.

The abnormal colors and morphological features of a plant 

caused by a poisonous element in the nutrient solution are collec9 Roberts, E. E., 1949. Geochemical and geobotanical prospecting for barium and copper, 

Stanford Univ., unpublished thesis.
298 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

tively referred to as toxicity symptoms. Between the level where 

a plant can tolerate the concentration of a given element in the 

soil solutions and the level where it cannot live is a fringe zone 

where the plant can live but where it suffers from the poisoning 

effect of the toxic element. Most commonly, the toxemia takes 

the form of simple stunting of growth. A few plants, however, 

develop peculiarly diagnostic symptoms that can under favorable 

conditions be interpreted directly in terms of probable excesses 

of a toxic element in the soil. Excess quantities of available zinc 

in soils will cause a yellowing of the leaves or needles known as 

chlorosis. Somewhat similar chlorotic symptoms have been observed for excesses of copper, cobalt, and cadmium and for a 

deficiency of available iron (Hewitt, 1953).

The ecological assemblage of plants growing normally in a 

given environment is a response to the nutritive quality of the soil 

as well as to the soil texture, drainage, sunlight, and many other 

factors. Different species of plants have different nutritive requirements. Some grow best in acid soils and others in alkaline soils. 

Some can tolerate and may prefer deficiencies or excesses of certain 

elements. The most familiar example of an ecological assemblage 

characteristic of a particular chemical environment is the flora 

restricted to limestone soils of high pH. Flora characteristic of 

acid soils of abnormally low pH have been observed in areas of 

rock alteration and pyritization (Billings, 1950). A characteristic 

flora also distinguishes serpentine soils in most climates, although 

there is some doubt as to whether this is due to the restrictive

influence of the abundant nickel, magnesium, and chromium in

the soil or to some more indirect reflection of the parent rock. The 

tolerance of plants for excesses of minor elements also varies with 

the species, On metal-rich soil, plants with a low tolerance win

not survive, leaving the field free of competition to species with

high tolerance, In central Africa, search for bare places in the

bush caused by excesses of copper in the soil has been used successfully as a prospecting method (Guillemain, 1913; Ball and Shaler,

1914). Vogt (1924a, 1942b) in Norway has observed several

plant species thriving on outcrops of cupriferous pyrite to the

exclusion of many other common plants, which he explains on the 

assumption that these species have a high tolerance for copper

and hence are left without competitors on the wpper-r^h. son.

Ragweed, which is generally tolerant to heavy metals, is said to 

grow abundantly on outcrops of zinc ore in Arkansas (Robinson 

and Edgington, 1945).
PRINCIPLES OF GEOCHEMICAL PROSPECTING 299

Extreme examples of the nutritional response of plants are 

certain indicator plants that grow exclusively on soil containing 

an excessive amount of some element. In the Rocky Mountain 

states, Beath, Gilbert, and Eppson (1939) have shown that a 

group of plants, chiefly species of Astragalus, will grow only on 

soils containing an excess of selenium. This relationship is so 

consistent that it is possible to map seleniferous geologic formations by the distribution of the selenium indicators. Inasmuch as 

selenium-rich forage is highly toxic to sheep and other livestock, 

the recognition of seleniferous areas by means of the selenium 

indicator plants is of considerable economic importance. Selenium 

is also associated with the uranium ores of the Colorado Plateau, 

where selenium indicators have been used successfully in prospecting for uranium.

Indicator plants for other elements have been reported. In 

prospecting, the most famous is the calamine violet which thrives 

only on zinc-rich soils in the zinc districts of Silesia. This species 

is of only local occurrence. Sulfate indicators have been used in 

conjunction with the selenium indicators in prospecting on the 

Colorado Plateau (Cannon, 1957). At the San Manuel copper 

deposit, California poppies are apparently confined to copper-rich 

soil, and the population density of this species is closely proportional to the copper content of the soil (Lovering and others, 

1950). The distribution of a certain shrub that prefers a soil rich 

in iron has been useful in determining the extent of the Cerro 

Bolivar iron deposits in Venezuela (Buck, 1951). Other indicators 

for copper, lead, zinc, tin, mercury, silver, and gold, have also been 

reported as useful in local areas (Lidgey, 1897; Dorn, 1937).

The use of indicator plants in mineral exploration undoubtedly 

has been outstandingly successful in some areas. Such success, 

however, requires an unusual coincidence of a climatic environment where an indicator plant can thrive, together with the occurrence of ores of the metal to which the plants respond. An 

appropriate environment for an indicator plant may in reality be 

a marginal zone for the distribution of that species, where a 

relatively slight change in conditions will either make the species 

ubiquitous in its habitat or eliminate it altogether. Thus, although 

the distribution of the California poppy corresponds with the copper content of the soil at San Manuel, in neighboring areas of 

slightly different climate the California poppy can grow almost 

anywhere, whereas in other areas not too far distant it cannot 

grow at all. No indicator plants can be cited as being universally 

useful, therefore, and any application of indicator plants to pros-
300

pecting must be based upon careful preliminary studies of the 

local flora.

Role of plants in the secondary dispersion cycle. Plants may 

play an important part in the over-all movement of elements in 

the surficial environment. One phase is the decomposition of primary rock-forming minerals. Another is the modification of the 

mobility of elements, as seen in the action of converter plants on 

the mobility of selenium. Still another phase is the movement of 

nutrient solutions from the root tips of plants through ;the stem 

and into the leaves, a process that can account for the transfer of 

substantial amounts of inorganic matter (Goldschmidt, 1937). 

With the falling of leaves or the death and decay of the plant, 

the inorganic matter is returned to the surface soil in highly 

soluble form. A large proportion of these soluble salts is leached 

by rainwater and removed in the drainage. A part, however, can 

remain behind as organic complexes and adsorbed ions in the 

humus and other near-surface horizons of the soil.

The immobilized fraction of the mineral matter brought to the 

surface by plants can have an important effect in the development 

of geochemical anomalies in soils, particularly transported soil of 

glacial or alluvial origin. The subsoil, where iron and alumina 

tend to be enriched by soil-forming processes, is generally a locus 

of stable accumulation of metals. Soil samples collected from the 

B horizon may, therefore, show the same pattern of anomalies as 

the trees overhead. Inasmuch as the immediate source for this 

enrichment is the decaying humus overlying the subsoil, it is not 

uncommon to find that anomalous patterns in the B horizon of 

transported soils over ore deposits do not extend downward into 

the immediately underlying parent material.

STREAMS AND RIVERS

Surface water is by far the most important long-distance carrier 

of SUrfiCial materials. Products of weathering enter the surface 

drainage in part as solid particles and grains resulting from

mechanical erosion and in part as soluble matter. Once this material is caught up in the rapidly flowing water of streams and

rivers, it may move in a matter of hours distances that WOUld 

require days or years in the more sluggish environment Of the

soil mantle.

Dispersion patterns formed in running surface waters are 

restricted to drainage channels. The result is an essentially linear 

distribution of weathering products, as distinguished from the 

planar pattern resulting from other types of secondary dispersion 

and the three-dimensional arrangement of most primary disper-
PRINCIPLES OP GEOCHEMICAL PROSPECTING 301

sion patterns. For this reason, dispersion patterns in drainage 

systems Have' been referred to in the Russian investigations as 

dispersion "trains," in contrast to the halos and other nonlinear 

patterns formed in the soil cover.

All the products of weathering in a drainage basin must funnel 

down through the system of streams and rivers that flow out of 

the area. Thus the load carried by a stream at any given point is a 

sample of material composited from the area drained by the 

stream, and its composition will be a reflection of the average 

chemical composition of the rocks in the drainage basin. Particularly, the metal derived by the weathering of an ore deposit, if 

that deposit is sufficiently large, may be indicated by a higher than 

normal metal content of the material being carried away in the 

drainage water. Under favorable conditions, therefore, chemical 

analysis of either the soluble or solid load of stream waters can be 

used in appraising the mineral potentialities of the area drained 

by the stream.

The characteristic pattern of dispersion of any particular 

element in a drainage system is dependent on whether it moves 

as a resistant or stable mineral carried with the solid load of the 

stream, as an unstable component of the solid load that can readily 

go into solution with changing conditions, or as soluble matter.

Resistant minerals. Minerals that do not readily decompose in 

the surficial environment include both resistant residual minerals 

inherited from the parent igneous rocks and the clay minerals and 

.secondary oxides that comprise the hydrolysates formed by the 

weathering of primary minerals. The relative ability of primary 

minerals to resist decomposition by weathering agencies and the 

factors governing the formation of stable secondary minerals have 

already been reviewed in the discussion of weathering products.

Residual minerals commonly make up the bulk of the more 

coarse-grained fraction of the stream load, which moves primarily 

by traction, or rolling and bouncing along the streambed at a 

velocity much lower than that of the water. The clay minerals of 

the hydrolysate fraction, on the other hand, are commonly fine 

grained and in turbulently flowing water move in either mechanical or colloidal suspension at the same velocity as the water. When 

turbulence ceases in lakes and in quieter parts of the stream 

channel,, most of the suspended matter settles out as deposits of 

mud and silt.

The residual minerals of stream sediments include dominantly 

quartz, together with a suite of less common, heavier minerals. 

Near the source, the grain size of the residual minerals is rela-
302 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

Egyg

tively coarse. Transportation of the grains takes place by repeated 

erosion and resedimentation along the stream bed, during which 

abrasive forces are continually reducing the size of the grains. 

Freise (1931) has conducted laboratory experiments to determine 

the relative rate of disintegration of primary minerals under the 

abrasive action of flowing water. He arranged the important 

minerals of placer deposits in the following order of increasing transportation resistance: galena, quartz, zircon, ilmenite, 

sphalerite, cassiterite, magnetite, wolframite, rutile, chromite, 

pyrite, and tourmaline. This sequence does not necessarily represent the relative distance the minerals will travel from their 

source, as no account was taken of the relative rate of chemical 

decomposition of the minerals or the effect of shape of the mineral 

grains and the resulting differences in the buoyant effect of running water. By the time the residual minerals reach the larger 

rivers, even the most resistant of the grains may be reduced to 

the size of silt particles or smaller and may be carried in suspension along with the clay-mineral fraction.

The continual erosion and redeposition of silt and sand-sized 

grains can result in a gravity sorting of the minerals, whereby 

heavier minerals are concentrated in the bottoms of stream channels. Concentrations of this kind, where they contain economically 

valuable heavy minerals, such as native gold and cassiterite, are

known as placer deposits.

Stable secondary minerals under certain conditions can also 

occur in the coarse-grained fraction of stream sediment along with 

the more abundant resistant minerals. Chief among these is 

limonite. Manganese oxides and secondary copper and lead

minerals also may be observed in the sand and silt fraction of

stream sediments, provided an adequate source of these minerals 

is present.

The occurrence of certain diagnostic heavy minerals in stream

Sediments can provide a clue to the distribution of major rock types 

an<a to tKe general geologic setting of the drainage basin. A study 

Of the relative abundance Of the heavy minerals in sediments of

the James River in Virginia, for example, showed that the mineral 

assemblage could be correlated with the heavy minerals in the 

rocks of the areas through which the river flowed, as shown in 

table 8. Limonite derived from brown iron ores dominates the 

heavy mineral assemblage in the upper reaches of the river system

where it crosses the Valley and Kidge physiographic province. TUe

relative abundance of limonite decreases as the river passes pro-
PRINCIPLES OP GEOCHEMICAL PROSPECTING 303

TABLE 8. Heavy minerals of James River sands

[From Stow, 1939. F, flood; A, abundant; C, common; R, rare]

Minerals

Limonite. ____.______..__.

Ilmenite and magnetite. 

Zircon. __________ _______

Tourmaline. ______________

Rutile __ ________________

Leucoxene. ______-___---_.

Hornblende.. . ____________

Epidote.________ _______

Garnet. __________________

Muscovite.--.. . -------

Chlorite. _________________

Hypersthene. _-________-_.

Staurolite. .--_-__.__--_.

Andalusite.-..- __________

Kyanite____ ____ _______

Sillimanite. ___-_____--____

Sphene. __________________

Actinolite. ._-_____._--__.

Apatite. ________ ______

Biotite ___________________

Diopside .-_.._________-_

Monazite_.______ __.__.-_

Trernolite.-_.__ ___

Physiographic provinces 

Upstream to downstream

Valley and 

Ridge

F

C 

R 

R 

R

Blue Ridge

A 

C 

R 

R 

R 

C 

R 

R 

R 

C 

C 

R

Piedmont

C 

C 

A 

R 

R 

C 

A 

C 

R 

C 

C 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R

Coastal Plain

A 

C 

R 

R 

R 

C 

C 

C 

R 

R 

 R 

C 

R 

C 

C 

R

gressively through the Blue Ridge and Piedmont provinces, and 

new minerals of local origin appear.

Sampling of heavy minerals in the South Island of New Zealand 

showed a similar correlation with the geology of the drainage 

basins (Hutton, 1950). Three geologic provinces were identified, 

defined respectively by a zircon-scheeelite-thorite-uranothorite 

assemblage, a zircon-garnet-epidote-hornblende assemblage, and a 

zircon-hyacmth-monazite-xenotime-hornblende assemblage. In this 

work, the heavy-mineral studies provided an original source of 

geologic information, as the rocks from which many of the minerals were derived were unknown because of inaccessible terrane.

In prospecting for ore deposits, heavy-mineral studies have been 

used since prehistoric times. Instead of the heavy accessory 

minerals of igneous rocks, the prospector looks for heavy minerals
304 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

derived from the weathering of vein deposits. Many of these 

minerals occur only in hydrothermal deposits, and rarely or never 

are found as disseminated accessory minerals. Chief among these 

are gold, cassiterite, wolframite, scheelite, and cinnabar. The 

provenance of some of the other heavy minerals, such as platinum, 

columbite, barite, or pyrite may not be unique, as they can on 

occasion occur in unmineralized rock as minor accessories as well 

as in hydrothermal deposits. Thus, cassiterite in a heavy-mineral 

assemblage is more indicative of economic mineralization in the 

drainage basin than columbite.

Prospecting by heavy-mineral studies consists in determining 

the relative amounts of an economic mineral in stream sediments, 

and in tracing the drainage upstream to the source by following 

the pattern of increasing concentrations. Techniques of concentrating the heavy fraction and of mineral identification are beyond 

the scope of this report; they have been described in detail by 

others (Button, 1950; Raeburn and Milner, 1927; Sigov, 1939).

Chemical analysis, rather than mineral identification, may be 

helpful where abrasion has reduced the grain size to such an extent 

that the properties of the minerals can no longer be readily 

observed. Russian workers have made particular use of spectrographic analysis of stream sediments for tin as a method of 

prospecting for tin-bearing veins in the bedrock. (Flerov, 1935, 

1938). In the United States, trace analysis of sediments in the 

dry arroyos below the San Manuel copper deposits in Arizona 

showed a distribution of copper that could be correlated with the

occurrence of ore upstream (Lovering and others, 1950). The

copper content of alluvium in the modern streambed was soo PPm

at a point 1.4 miles downstream from the ore outcrop, as compared with a background of 30 ppm. In an ancient alluvial terrace 

at the Same location, the copper content was 140 ppm. Microscopic

studies showed that the copper was present in the sediment principally as ohrysocolla. The fine-grained fraction of the alluvium

contained somewhat more copper than the coarse fraction, probably because of abrasion of the soft chrysocolla as the sediments

were -washed downstream.

UnStMV Components Of sediments. Unlike the resistant primary minerals, many of the components of tKe solid load 01 streattlS 

can go readily into aqueous solution With changing Conditions,

Tliese unstable components of stream sediments include some finegrained products of abrasion of residual minerals, Unstable 

chemical or biological precipitates from aqueous solutions, and 

exchangeable ions.
PRINCIPLES OF GEOCHEMICAL PROSPECTING 305

The relative solubility of finely divided residual minerals is 

known mainly from inference. Barite, for example, which is a 

mineral rapidly comminuted by abrasion, might be expected to go 

into solution readily when present in finely divided form. The 

same may be true of finely divided cassiterite, which is known 

from experiment to be measurably soluble in water (Lundberg, 

1941). Much has been written on the solubility of finely divided 

gold, and although opinions differ it would be reasonable to expect 

that soluble gold complexes could form by reaction of native gold 

with natural solutions. Except for a few qualitative experiments, 

however, very little work has been done to determine the fate of 

fine-grained fragments of residual minerals in stream sediment.

The formation of precipitates in a stream system is most commonly related to changes in pH and Eh, and to biological activity. 

Iron hydroxide may be precipitated as limonitic coatings on 

pebbles where acid iron-rich waters derived from the oxidation 

of sulfates are neutralized in the surficial environment. Traces 

of many metals may at the same time be removed from solution by 

coprecipitation with the iron hydroxide. A study of minor elements 

in an ironstone gravel in Australia, for example, showed that 

gallium, molybdenum, lead, vanadium, and zinc are concentrated 

in the limonite (Oertel and Prescott, 1944). Lead in amounts as 

high as, 1 percent was found in the material coating pebbles near 

.the discharge of acid springs in Collar Gulch in the Judith Mountains area of Montana (L. C. Huff, written communication, 1951). 

A deposit of native copper has been observed in a peat bog near 

Jefferson City, Mont., where copper-rich water from neighboring 

mines entered the reducing environment of the peat muck 

.(Forrester, 1942). Lovering (1927), in seeking to explain a 

similar occurrence of native copper in peat muck, prepared laboratory cultures of the bacteria extracted from the muck. He showed 

that the reduction of the Cu+2 ion to metallic copper was effected 

by organic compounds resulting from the bacterial metabolism. A 

large part of the copper in fresh lake waters has been found tied 

up iboth in suspended organic matter and in free-floating microorganisms (Riley, 1939). Coatings of manganese oxides on the 

pebbles in streambeds have been observed in many areas. 

Ljunggren (1951), for example, reports active formation of manganese-rich pebble coatings in river water containing 0.05 ppm 

Mn. These reactions are all somewhat reversible. Thus, if for 

some reaspn the pH of the environment should change sufficiently, 

the immobilized material would become unstable, and the contained 

elements would tend to reenter the aqueous phase.
306 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

Exchangeable ions adsorbed to the surfaces of minerals in the 

finer grained fraction of stream sediments apparently make up 

the major part of the unstable component of the stream load. By 

exchange reactions, a balance is established between adsorbed ions 

and ions in aqueous solution. The content of an exchangeable 

element in the sediment thus may be an approximate measure of 

the average content of that element in the stream water. Very little 

information on the role of exchange reactions with metals in 

stream sediments has been published. Perhaps the most quantitative study of the problem was by Murata (1939), who found three 

forms of manganese in a fluvial environment: soluble manganese, 

exchangeable manganese, and nonexchangeable manganese. The 

soluble and exchangeable manganese were in apparent equilibrium. 

The ratio of the exchangeable and the total manganese was related 

to the intensity of reducing conditions resulting from the decomposition of organic matter, whereby the manganese of insoluble 

manganese oxides was reduced to form soluble and hence exchangeable manganous ions. Heide (1952) has found that important 

percentages of many other elements may travel downstream as 

exchangeable ions attached to the surfaces of fine-grained suspensoids. The notable exceptions are fluorine, chlorine, and bromine, 

which are not appreciably adsorbed to or otherwise held in the 

suspensoids. Saito (1951) reports that thorium is more readily 

adsorbed on suspended matter than radium; thorium is therefore 

precipitated in coastal waters, whereas radium reaches midocean.

No systematic geochemical prospecting surveys based on determination of the unstable components of stream sediments have 

been published, although a few writers have observed dispersion 

patterns in drainage channels that can 'probably foe attributed to 

this cause. Hawkes (1952) mentions cobalt in the sediments of

streams draining mineralized areas in the Blackbird cobalt district

of Idaho. White and Alien (1954) found more than 500 ppm 

copper in the soil of drainage channels below copper-rich dumps at 

Phoenix Camp, British Columbia. There the copper in the channels

-was pm.-otoa.lbly precipitated from, ooppejr in the -\vaters derived t>y

leaching of the mine dump,

Soluble matter. T<he soluble fraction of the stream load travels

faster than either the residual minerals or the hydrolysates.

wnereas sana- ana siit-sizea grains ana to a lesser extent tne

clay-sized fraction may remain immobilized for long periods of 

time as alluvial sediments, the soluble salts move actively with the 

water. As a result, dispersion patterns of elements dissolved in 

stream waters are relatively transitory phenomena and are
PRINCIPLES OF GEOCHEMICAL PROSPECTING 307

extremely susceptible to sudden changes in both time and space. 

The principal causes of such variations are: changes in the supply 

of soluble material at the source, changes along the stream course 

in the environmental factors governing the solubility of the different elements, and dilution by rain water and tributory streams. 

Spring water is the principal source of the soluble salts carried 

by streams. Changes in the salt content and discharge rate of 

springs, therefore, will cause corresponding changes in the salt 

content of the streams fed by them. Major changes in the quantity 

of soluble material discharged by springs can apparently result 

from the flushing action of rainwater moving through unsaturatecl 

surficial material in which soluble salts have had a chance to 

accumulate during the preceding period of dry weather. The rising 

water table resulting from an increase in rainfall may also contribute to the flushing effect. It has been reported that flash-flood 

waters can, under some conditions, have a higher salinity than 

waters of the same streams during dry periods. Bryant and Slater 

(1948) determined the leaching of soluble salts by runoff water 

in a series of systematic experiments over a year's period. They 

concluded that

. . . concentrations of solutes in runoff appeared to be increased by the salts 

brought to the soil surface by capillarity and evaporation and decreased 

by downward movement that accompanied infiltration. Because of the vertical 

movements of soil salts, flash runoffs that followed conditions favorable to 

capillarity and evaporation were highest in solute concentration. Additional 

runoff tended to dilute initial runoff and so lower the concentration of solutes, 

although the total amounts lost were necessarily increased.

A similar direct relationship of solute concentration and discharge rate has been observed for many minor constituents of 

stream water. The cobalt content of the water of many small 

streams in the Blackbird cobalt district of Idaho, after an unseasonal August rain, averaged about four times the cobalt content of the same waters measured 2 weeks previously, during a 

dry spell. The rate of .discharge of the streams here was also 

higher. An increase in the heavy-metal content of streams during 

rising water level has also been noted by workers in eastern 

Canada.

Webb and Millman (1950) report an initial decrease in the 

heavy-metal content of streams draining an area of lead-zinc 

mineralization in Nigeria after a heavy rain; this was followed 

by a marked increase in metal content after several days of heavy 

rainstorms. The initial decrease was ascribed to simple dilution by 

direct surface runoff and the later increase largely to increments 

of soluble metal flushed out of the deeper horizons of the soil. These
308 CONTRIBUTIONS <TO:GEOeHEMICAL PROSPECTING FOR MINERALS

observations'differ somewhat from. :the leaching cycle described 

by Bryaht and Slater. (1948),. possibly; because of differences 'in 

climatic effects. '' ;.-. ..- ':. . ;.-. ..:.- . . :' 

'' 'Heide (1952) found; however > that ^ although the iodine content 

of r the Elbe River varied; directly with; 'the ^discharge, the major 

constituents in the same'Silite of samples varied inversely. >:It is 

difficult to rationalize an opposite behavior of different soluble 

components o£the same water system with a single, simple process, 

such as leaching of salts- by rainwater. Other factors: not understood are involved in the process.

Inasmuch as short-term variations in the composition of stream 

water can apparently result from changes in the weather, several 

writers '('Huff j 1=948 ;-Webb and Millman, 1950) have recommended 

establishing base sampling stations, where the metal content of 

the water is rechecked' periodically'and the variations used in derivmg'a^correction factor to be applied to-the field data. In this 

way, it'may be'possible to' reduce the error due to 'short-term 

fluctuations-with" time.- ' - .: - ;. 

The supply of soluble metals derived from the oxidation of a 

sulfide deposit depends to a large extent on the rate of oxidation 

of the: deposit. The rate-of .oxidation 'varies somewhat with cli- 

: matic conditions; ' ; For example, in the relatively cool climate of 

the Pacific Northwest, spring water containing 0.005 ppm heavy 

metal has been considered a. promising indication of mineralization. (Warren and others, 1951a), whereas, in southwestern Wisconsin, spring water flowing from undeveloped sulfide deposits

contained as: niuch as.0.05,ppm heavy metal (Kennedy, 1956), and 

in Nigeria a similar spring .was found to contain 0.5 ppm (Webb 

and Millman, 1950). The rate of oxidation of sulfide material also 

depends on .the, aceessibility .of the material to oxidizing solutions.

This effect is ; especially pronounced where the deposit has been

ppened up with tes|; pits or underground workings, or where mined

ore has, been piled on the surface. Thus, ,an abandoned ; mine or

(pro.5pect in which the sulfide material has .been, exposed to accelerated oxidation may-discharge from 10 to 100 times as much

soluble metal into the stream water as the same deposit before it

had been ; worked. In :previously prospecited areas, therefore, .the

increments. of soluble .metal derived from undiscovered deposits 

may.be completely masked , ;by the contribution, ;frpm the knowii

prospects.. Water analysis, for this -reason may be .more/useful in 

locating1 forgotten prospects than in finding new prospects.

Changes in the chemical and physical environment can modify 

the composition of surface waters by: changing the mobility of
«'-. ''. PRINCIPLES OF GEOCHEMICAL PROSPECTING : '-. 309-

some elements. The-elements most sensitive to changes of this 

kind are the ones of intermediate mobility: The extremely mobile 

ions, such as sodium and sulfate, will not be precipitated by any 

normal variation in the environment. At the other end of the 

mobility scale, the extremely immobile elements such as chromium 

will remain in the solid phase throughout the normal cycle. Many 

intermediate elements, however, including copper and zinc, are 

very sensitive to changes in pH, the nutritive requirements of 

plant life, organic complexing agents, and the exchange capacity 

of bottom sediments, to mention a few of the disturbing factors. 

These effects can vary in both time and space.

Of the factors causing a time variation, perhaps biological activity has the most pronounced effect. Heide (1952) has noted that 

the nitrate content'of tne Elbe River <is inversely related to the 

temperature Of the water: He ascribes this to the increased metabolism of organisms in a warm environment with a resulting-increased removal of nitrates for nutritive purposes^ Riley (1939), 

in following'the biochemical/cycle of copper in a lake in Connecticut, found that in 'the autumn the copper content of some stream 

waters increased 'by a factor: of 10 when the copper was release'd 

by the decay of fresh plant litter.' . :; '. ;

Of the factors causing a variation in space, removal of ions by 

progressive adsorption to the solid suspensoids and sediments'in 

the stream appears to play an important role. Many workers have 

noted a rapid decrease in the metal content of stream water in 

passing downstream from an area of high metal discharge.

For example, Warren, Delavault, and Irish (1951a, p. 616) 

report that ".. . in a very short distance it is possible for a stream 

to lose its metal content, although the stream as a whole may 

exhibit no change in volume." L. C. Huff (written communication, 

1954), in measuring the metal content .of water draining mine 

workings at Jerome, Ariz., :noted that the zinc content fell off by 

a factor of 25 in flowing 3 miles through an irrigation canal, with 

no water entering the canal to cause dilution and no change in pH 

(table 9). Dilution, of course, cannot account for a decrease in 

metal content of this kind. The most probable explanation' is a 

progressive removal of metallic ions by. exchange .reaction's, 

together with perhaps some removal by biological, activity.., ,, . >.,''

A,variation in pH, particularly i^.acid waters issuing directly 

from an oxidizing sulfide mass* cajn cause major ^variations in,the 

metal content .of the water,... Copper tends to be r;emo,ved from 

solution as the pH rises above 5. Thus copper-rich acid, waters, as 

they, are .progressively' dflutecl and - neutralized in flowing ;:
310 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

TABLE 9. Heavy metal content of -water from irrigation ditch draining 

the U.V.X. mine, Jerome, Ariz.

[Samples collected and analyzed by L. C. Huff]

Distance from mouth 

of tunnel (miles)

0............ .

.3.............

0

1.4._________

pH

8.0

Heavy metal 

(ppm)

2.0

1.2

.6

Distance from mo'st'-i 

of tunnel (miles)

1.8

2.4.. _...._....

3.2 ....

3. 5_--._. ...---

,,H

8.0

Heavy metal 

(ppin)

0.4

.08

.08

.06

stream, will lose much of their copper content. This effect may be 

seen in the data on the copper content of the drainage below the 

mines at Butte, Mont., collected by Huff (written communication, 

1947) as shown in table 10. Here, if it is assumed that the zinc 

content falls off by a simple factor of dilution, the copper-zinc 

ratio will be a measure of the tendency of the copper to remain in 

solution. It is notable that the ratio remains constant until the 

pH exceeds 5.0 and then falls off rapidly, indicating that copper 

joins the solid load of the stream in some form.

TABLE 10. Metal content of water in drainat/e front copper mines at Butte, Mont.

[Samples collected by L. C. Huff; analyses by Norman Davidson and L. C. Huff]

Stream

Do

DO...... ._.-------

Do...... ._.._..._.

Deer Lodge River.

Do

Chirk Fork River. ...

Distance

below

mines 

(miles)

2 

6 

12

IS

27

41

82

1'H

4.5

4.8

4.8 

5.0

5.8

5.8

5.8

Parts per million

Cu

70

20 

15 

10

.5

.08

.Oo

Zn

400

iro 

100 

SO 

20 

10

3

.Fe

80

30 

11

2.5

.8

.4

. s

Cu:Zn

ratio

0.17

.13 

Jo

.12

. 02

.008 

. 01 R

r>ii«tioTx of a stream by increments of water from tributaries 

Of different COmpOSitiOn generally has a simple arithmetic effect,

provided the turbulence is adequate to cause complete flUXlng OV61' 

a short distance, and provided of course that no chemical reaction

K)6tW§§Di $15 tWO Waters causes a precipitate to form. With larger

streams and rivers, where laminar rather than turbulent flow predominates, many miles may be required for complete mixing of
PRINCIPLES OF GEOCHEMICAL PROSPECTING 311

water of contrasting compositions. For example, the chloride 

content of water from the left bank of the Elbe, just below the 

confluence of the chloride-rich Saale River, is 17 times higher 

than that on the right bank; 27 kilometers below the confluence, 

the chloride content of water from the left bank of the Elbe is 

still three times higher than that from the right bank (Heide, 

1952). In sampling the water of larger rivers, therefore, care 

should be taken either to obtain a true average sample composited 

from subsamples taken across the full width of the river or to 

collect and analyze separate samples from the two sides of the 

channel.

Prospecting methods based on chemical analysis of stream water 

have been investigated by many workers. The heavy-metal content of waters has been most widely used, probably because of the 

simplicity of the dithizone method of analysis (Sergeev, 1946a; 

Huff, 1948; Sokoloff, 1948; Webb and Millman, 1950; Riddell, 

1952a; Ohashi, 1952; Shima, 1953b, 1953c, 1953d, 1953e; Hayashi, 

and others, 1951). Work has also been done on copper alone (Vogt 

and Rosenqvist, 1943), gold (Konovalov, 1941), iron (Kimura, 

and others, 1950,1951; Shima, 1953c, 1953f), manganese (Shima, 

1953a, 1953c), and sulfate (Hayashi, and others, 1951; Kimura, 

and others, 1950, 1951; Shima, 1953f).

In tracing the dispersion train of an element in a drainage 

pattern, especially careful consideration must be given to the form 

in which the metal or other element is transported. A dynamic 

equilibrium exists between the unstable fraction of the solid load 

of streams and the soluble fraction. Whether the bulk of any 

particular element is traveling in the solid or the soluble fraction 

at any point in the drainage system depends on the balance of 

many factors that may be difficult to evaluate on the basis of 

theory alone. In any given set of field conditions, however, it 

should be possible to get at least an empirical idea of the partition 

of an element by carrying out determinations respectively of the 

total content of the element in sediments, the fraction readily 

extractable from sediments in weak reagents, and the soluble 

salts. The best material to be sampled in any reconnaissance 

exploration program and the most suitable analytical method can 

then be selected on the basis of this preliminary information.

LAKES

Fresh-water lakes may be considered temporary resting places 

during the transportation of weathering products, where the rapid 

movement of stream and river water gives way to a quiet environment dominated by sedimentation and biological activity. The bulk
312 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

of the solid fraction of the stream load is dropped at the inlets. 

Some of the soluble components of the streams entering a lake may 

enter the biological cycle of fresh-water organisms and be' deposited with the organic sediment that accumulates in the lake 

bottom. Copper in particular is known to be immobilized in this 

way (Riley, 1939; Nichols and others, 1946). ;

Soluble metals originating from the weathering of ore deposits 

also may be trapped in the bottom sediments of lakes; Vogt (1942c) 

describes lake deposits of bog manganese ore containing traces of 

zinc, copper, nickel, and cobalt derived from sulfide bodies in the 

tributary basins.

In addition to the metal introduced by streams flowing into a 

lake, some water can enter lakes directly by seepage of ground 

water around the shores. Chisholm (1950a) describes lake water 

collected offshore from a known mineralized vein, where he 

found that readily detectable amounts of heavy metals occurred 

within 5 feet of the shore. The heavy-metal content dropped 

rapidly more than 5 feet from the shore and in the absence of 

nearshore mineralized zones, the metal content of the water was 

negligible. This metal undoubtedly came into the lake from' 

seepages of metal-rich ground Water. ' '

MARINE BASINS

Deposition of sediments brought into marine basins by rivers is 

the final phase of the surficial geochemical cycle. On entering a

body of salt water, most of the minor elements dissolved in river 

waters are precipitated and deposited along with the sediments 

(Krauskopf, 1952). The material deposited is a sample of the 

terrane drained by the rivers that flow into the basin. The 

chemical peculiarities of some sedimentary rocks have been explained on the assumption of similar peculiarities in the rocks of

tributary land areas. For example, tke Lockport dolomite o£ the

Great Lakes area and the Mansfeld shale of Germany are unusually rich in base metals that are presumed to be syngenetic. These

metals may have originated from the weathering of a terrane 

particularly rich in those metals.

In addition tO the material brought into marine basins by rivers,

a small contribution may also be received from rocks cropping out

on tKe floor of the basin. Huff (1955) has correlated the copper

content of the basal sandstone of Cambrian age in the Jerome 

area of Arizona witk copper ore in 'tile Precambriaft ICOCk nOGF

of the sea during earliest Cambrian time. An oval-shaped area of 

sandstone containing more than 100 ppm copper extends for as 

much as 2 miles around the exposure of Precambrian rocks of the
PRINCIPLES OF GEOCHEMICAL PROSPECTING 313

United Verde ore body. Background copper content is less than 

50 ppm. This pattern is interpreted as the result of lateral dispersion of copper by water currents and waves washing back and 

forth over copper ore exposed in the floor of the shallow marine 

basins.

APPLIED GEOCHEMICAL PROSPECTING

In the preceding pages some of the laws governing the dispersion of the chemical elements in earth materials and the characteristics of the resulting dispersion patterns have been reviewed. 

The application of dispersion-pattern studies to practical problems 

of mineral exploration remains to be considered. After a review 

of the historical development of geochemical methods of prospecting, some comments are made on the selection of the most appropriate exploration method and on techniques of carrying out a 

geochemical survey.

HISTORICAL SKETCH

Early development. The basic principle upon which geochemical prospecting is based the following of dispersion patterns has probably been recognized and used since man first began 

his search for metal. The ancient prospector who panned gold upstream in quest of the mother lode or examined outcrops and 

stream beds for iron stains was looking for the same types of 

clues to buried ore as the modern prospector with his kit of chemical tests. The chief difference was in the use of mineralogical 

observations rather than chemical analyses.

Probably the first written record of the use of chemical analyses 

in prospecting is in Vannoccio Biringuccio's "Pirotechnia," (Biringuccio, 1540, p. 15) published in Venice in 1540, in which he 

says:-

There are some who praise highly as a good sign certain residues that 

waters make where they are still, and after having stood for several days, 

frequently warmed by the rays of the sun, they show in some parts of their 

residues various tinctures of metallic substances. There are others who 

usually take this water and cause it to evaporate or dry up entirely by 

boiling it in a vessel of earthenware, glass, or some other material, and they 

test the gross earthy substance that remains at the bottom by testing, by 

the ordinary fire assay, or in some other way that pleases them. In this 

way (although they do not have an exact proof) they approach some sort 

of knowledge of the thing.

During the 40-year period before 1935, many authors both 

on this continent and abroad have reported observations on the 

response of vegetation to underlying ore (Lidgey, 1897; Lungwitz, 1900; and references in Dorn, 1937), and on the distribution
314 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

of traces of metals in rocks associated with ores (Vogt, 1923; 

C. H. White, 1924; Wilson, 1935). They were the results of isolated 

projects, however, and did not represent large-scale or concerted 

research programs.

Russm. The first large-scale systematic investigation of chemical analysis as a method of prospecting was undertaken in 1932 

by Soviet geologists (Fersman, 1939; Sergeev, 1941). By 1935, 

the geological staff of the Central Geological and Prospecting Institute in Moscow had perfected spectrographic analytical equipment 

and sampling procedures suitable for routine geochemical soil 

surveys. Three field projects were undertaken in 1935, 8 in 1936, 

6 in 1937, and 3 in 1938. Seven of these projects depended upon 

semiquantitative spectrographic analyses of soil and stream sediment for tin, a procedure referred to in the Russian investigations 

as the "stannometric survey." The remainder of the Russian projects during this period were orientation and prospecting surveys 

for copper, lead, zinc, nickel, chromium, tungsten, molybdenum, 

and borates. Most of this work was based on spectrographic methods of analysis, although spot tests, flame tests, and coloriinetry 

were used in a few projects. In the course of these surveys a total 

of more than 45,000 samples were collected and analyzed. Welldefined chemical indications associated with known ore were obtained in all but 3 of the 20 areas investigated, and 5 new mineral 

discoveries were reported. In addition to the discoveries, many 

geochemical anomalies were found which had not been confirmed

by subsequent exploration at the time of the last comprehensive 

report (Sergeev, 1941) received in the United States.

Much of the analytical work in connection with these surveys 

was done in the field or in temporary field headquarters. A small 

spectrograph with a portable power supply was constructed for 

Use Under primitive conditions in the immediate vicinity of field

operations (Raisbaum, 1929). This unit could be disassembled for

transportation by truck or where necessary by pack animals.

In addition tO the SOil WOrK, Some experiments have been carried OUt in the Soviet Union with analysis of vegetation as a prospecting method (Tkalich, 1938; Maliuga, 1947); to date, no report O.t large-SCale prospecting activity based on plant sampling

has been received. It is perhaps worth noting that the1 publication

date of the paper by Tkalich antedates the earliest Scandinavian

reports on plant surveys by about a year. Preliminary investigfations of the metal content of surface water in relation to mineralization have also been reported from the Soviet Union (Sergeev, 

1946a).
PRINCIPLES OF GEOCHEMICAL PROSPECTING 315

Scandinavia. In 1936, Palmqvist and Brundin of the Swedish 

Prospecting Co. undertook experiments with spectrographic analysis of plant ash as a method of prospecting. Trial geochemical 

plant surveys in Cornwall °and Wales indicated abnormally high 

contents of tin, tungsten, lead, and zinc in the leaves of trees and 

shrubs growing over soils containing correspondingly large proportions of those metals (Swedish Prospecting Co., 1939). On 

the basis of these experiments, a patent (Brundin, 1939) was 

obtained to cover systematic sampling of plant material followed 

by spectrographic analysis of the plant ash as a method of prospecting. For several years, the Swedish Prospecting Co. conducted 

geochemical surveys in conjunction with its regular geophysical 

service to the mining industry, and many areas were systematically prospected by plant analysis. Because of the confidential 

nature of the exploration contracts, very little of the results of this 

work have been published. The company was dissolved during the 

early years of the war, and large-scale geochemical prospecting 

work in Sweden has not been resumed.

In 1939, Rankama (1940) made an experimental study of the 

nickel content of plant samples from a number of nickel deposits 

in the glaciated country of northern Finland. Within the last few 

years, additional experiments with geochemical dispersion patterns related to ore have been undertaken under the auspices of the 

University of Helsinki (Marmo, 1953) and the Geological Museum 

(Salmi, 1950).

Beginning in 1938, Vogt and coworkers at the Technical 

University of Norway have investigated the dispersion of 

weathering products of known sulfide deposits in soil, vegetation, 

and surface water, and have published a series of papers summarizing their results. (See Vogt and also Rosenqvist and Vogt).

Canada. In 1939 and 1940, Lundberg (1941), following the 

lead of the Swedish investigators, experimented with spectrographic analysis of vegetation for lead as a prospecting method. 

Tests were carried out at Buchans, Newfoundland, and at several 

other localities in eastern Canada. Although the results were 

generally promising, Lundberg's work was suspended because of 

wartime restrictions, and has not been resumed.

In 1945, H. V. Warren and his coworkers at the University of 

British Columbia undertook a research program on the metal 

content of vegetation as a method of prospecting and a few years 

later began applying the methods on a large scale to practical 

prospecting problems. (See references under Warren and others). 

This program has been maintained actively to the present time.
316 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

Widespread Canadian interest in all methods of geochemical 

prospecting has been growing rapidly since about 1950* and has; 

resulted in the publication of reports by many independent investigators (Chisholm, 1950a, 1950b; Bischoff, 1954; Riddell, 1950, 

1952a, 1952b, 1954; White, 1950; White and Alien, 1954). An, 

increasing number of Canadian mining companies and private 

consulting groups have organized their own geochemical prospecting units and, using primarily geochemical soil surveys, have had 

very successful results in integrating the geochemical work with 

their other exploration activities.

United States. Before the end of World War II, geochemical 

prospecting work in the United States was relatively sporadic 

(Campbell, 1941; Fowler, 1950; Jakosky and others, 1942). Largescale experimental work in the United States was begun in 1946 

with the initiation of geochemical prospecting research by the 

U. S. Geological Survey. Part of this program was directed toward 

developing chemical tests suitable for geochemical prospecting 

work and has resulted in the publication of rapid procedures for 

the determination of most of the ore metals (Lakin and others, 

1952; U. S. Geological Survey7 ). The remainder of the program 

was concentrated principally on experimental sampling surveys 

under a wide variety of geologic and climatic conditions to 

determine the characteristics of dispersion patterns of metals in 

rock, residual soil, vegetation, and natural water. (See reports by 

Cannon, Cooper, Hawkes, Huff, Kennedy, Lovering, and Morris 

in Literature Cited.) The Geological Survey program is being 

continued actively at the present time under the direction of T. &. 

Levering. ..'- 

In addition to the Geological Survey's program, many experimental projects have been carried out by .independent workers 

(Graf and Kerr, 1950; Harbaugh, 1950; Keller, 1949; Nackowski, 

1952),8

Geochemical methods have been applied by many of the large

mining companies to their exploration problems, particularly in 

the southern Appalachians and in the Pacific Northwest, with

favorable results. Descriptions of Some of this WOrk haV6 beGTl

published (Fulton, 1950; Gilbert, 1951, 1953; Kingnian, 1951), 

This represents Only a minute fraction of the total amount of 

work done, as very little information on the results of geochemical 

surveys by American mining interests has been released to the

public. Recent progress in the United States on the development 

T U. S. Geological Survey, 1953, Additional field methods used* in geoetamtdAl

by the U. S. Geological Survey: U. S. Geol. Survey open-file rept. 

8 See also footnote 3 on p. 242 and footnote 6 on p. 297.
..; ; PRINCIPLES OF GEOCHEMICAL PROSPECTING" 317

and application of geochemical prospecting methods has been summarized by Webb (1953).

Africa. In 1949, Roberts (1953) working in Nigeria carried 

out the first experiments with geochemical soil surveys in tropical 

terrane. Roberts' work was followed by further experiments in 

the same areas of Nigeria by Webb and Millman (1950, 1951) 

and Hawkes (1954). Beginning about 1952, several of the large 

mining companies undertook experimental soil sampling programs 

in Rhodesia and Tanganyika, many of. which are still in progress. 

. /apcw.^-Under the direction of Professor Kenjiro Kimura of 

the Department of Chemistry at the University of Tokyo, chemical 

tests were developed for the determination of copper, zinc, iron, 

manganese, and sulfates in water and for copper, zinc, lead, silver, 

nickel, manganese, cobalt, and sulfate in soils and rocks. Experiments in the vicinity of known Japanese deposits showed favorable results,.and Kimura's methods are now in current use by the 

majority of Japanese mining companies. A very large number 

of articles have appeared in Japanese publications. (See reports 

by 'Kimura, Shima, Fujihara, Hayashi, Ohashi, and Umemoto in 

Literature Cited). They are almost entirely in the Japanese 

language, and very few of them have been translated or otherwise 

made accessible to non-Japanese workers. Thus, at present, it is 

not possible to comment on either the scope or success of this work.

Other countries. Work in Australia began in 1948 with experimental investigations by Sokoloff (1949, 1950a, 1950b, 1950c, 

1951a, 1951b), and is currently being continued under the auspices 

of the government and private mining interests (Engineering and 

Mining Journal, 1953). A broad program of research on the application of geochemical prospecting methods to problems throughout the British Commonwealth is currently being conducted with 

government sponsorship under the direction of J. S. Webb at the 

Imperial College in London (Williams, 1954). A governmentsponsored program .has also been started in India. In Yugoslavia, 

research work on the relation of the composition of spring water 

to the age of faults and to geochemical provinces has been reported 

by Miholic (1948, 1949). Papers on geochemical prospecting have 

.also been published by workers in Germany (Fricke, 1953), Italy 

(Minguzzi and Vergnano, 1948), Poland (Gawel, 1947; Bobrowski and Piechota, 1949), and Portugal (Neiva, 1949).

CHOICE OF EXPLORATION METHODS

Mineral exploration may be considered the search for a target, 

on which the bull's-eye is the ore deposit. Just as the center of 

the marksman's target is surrounded by concentric rings, so most
318 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

ore deposits are closely related to a series of larger target areas, 

each characterized by some physical or chemical feature that is 

diagnostic of the ore environment. Some of these features, such 

as favorable host rocks or geologic structures, are related to the 

genesis and localization of the ore. Others, such as geophysical 

anomalies, are a direct response to some unusual property of the 

ore body itself. Still others, as for example the pattern of metals 

dispersed in surficial material near the ore, result from the breakdown of ore minerals by agencies of weathering. Each geologic, 

geophysical, and geochemical feature of the environment of an 

ore deposit defines a target area of characteristic size, shape, and 

relationship to the ore.

Some characteristics of the ore environment extend over large 

areas and form targets that are useful in broad-scale reconnaissance. Others are restricted to the immediate vicinity of the ore 

body and are of most value in detailed exploration. On entering a 

new field, the exploration geologist may make a reconnaissance 

geologic study, looking for regional criteria for mineral deposits 

to help him decide which parts of his territory show the best 

chances for the occurrence of ore and which other parts can be 

eliminated as relatively unfavorable. When he has selected regions 

that appear to be promising, he may then examine the geologic 

features within these large tracts in more detail using more restricted aspects of the ore environment to determine where intensive exploration is desirable. This process of elimination of unfavorable areas and of increasingly intensive study of the favorable areas is continued step by step up to the ultimate proving 

of the deposit by drilling and underground exploration. It is a 

process of progressively reducing the size of the target, where

at each step the target is the area having the highest probability

of containing ore.

The traditional prospector, before the days of modern exploration aids and modern concepts of economic geology, was guided 

to the target mainly by the distribution of known deposits, plus

a liberal amount of intuition. His next Step Was ttie tCCliOUS CXammation of every bedrock exposure for signs of mineral deposits. 

This was a job for a very patient man, for whom time had little

value. iP-mrtKex-more, ^^ ^vas almost entirely restrict/eel ill Ills

chances Of SUCCeSS to deposits that were exposed at the surface;

luaaen ore coma fee found only by the rarest accident. As a result 

of the conscientious work of prospectors of an earlier generation, 

very few major ore deposits remain to be found by simple outcrop

surveys.
PRINCIPLES OF GEOCHEMICAL PROSPECTING 319

The well-trained modern prospector, however, has a wide choice 

of methods of reducing his target area, both in the reconnaissance 

and in the detailed phases of his search. His selections of promising 

areas can be guided not only by the distribution pattern of known 

mines and prospects but also by considerations of favorable geologic structures, host rocks, and alteration patterns. His direct 

geologic observations can be reinforced and augmented by geophysical data, which will tell him not only more about the geologic 

setting, but will in many areas provide indications of the ore itself. 

Every method he uses in narrowing the target area increases the 

probability of success of the final and most expensive phase of 

exploration, the diamond drilling and underground exploration. 

The alert geologist is, therefore, ready to use any set of reliable 

criteria available to him as additional sources of evidence.

The choice of an exploration method should be guided by a consideration of size of target, probability of locating target, expected 

value of the ore deposit to be found, and cost per unit area for 

making the survey.

By size of target is meant the size of the favorable area that can 

be delimited by the method in question. Examination of regional 

structural trends on a geologic map of the United States, for 

example, may show that the Appalachian belt is a favorable area 

for mineralization. This presents a large target. Airborne 

magnetic surveys, on the other hand, will not indicate a magnetic 

anomaly much more than 1,000 feet from the magnetic body 

responsible for the anomaly, and ground magnetic observations 

must be made usually within 100 feet of the magnetic body to 

detect it. These are small targets.

The probability of locating a target means the probability of 

obtaining and recognizing indications of an ore body or mineralized district by the method being used. It depends on whether a 

target exists and, if so, how effective the exploration method is in 

locating it. A zinc deposit containing only the nonconducting 

mineral sphalerite is not likely to have an associated resistivity 

target; no method depending on resistivity could be expected to 

find it and the chances of finding a target are, therefore, extremely 

small. On the other hand, geochemical soil anomalies are present 

over virtually all base-metal deposits that are covered only by 

residual soil. Here the chances of finding a target are excellent 

if the survey is properly conducted.

The expected value of ores to be found in a given area can be 

determined by consideration of the value of known deposits in the 

area. or. if no deposits have been discovered, by comparison with
320 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

geologically similar areas where important deposits are known to 

occur.

The cost of the prospecting survey is the only one of the critical 

factors that can be computed quantitatively. It is important, however, to compare costs on a unit-area basis. High total cost does 

not necessarily imply a high unit-area cost. Airborne geophysical 

surveys, therefore, although they represent a high cost of overhead 

and hourly operation, are relatively inexpensive when computed in 

terms of cost per square mile.

The efficiency of any exploration method whether geologic, 

geophysical, or geochemical will depend on the balance of these 

four factors. Thus low cost of making the survey (airborne magnetic, for example) can offset small target size, poor chances of 

finding a target, or a low probability for the occurrence of large 

ore bodies. Conversely, a high-cost survey such as geochemical soil 

sampling is justified if large ore bodies are expected, and there is 

relatively little chance of passing by a deposit if one occurs in the 

area of the survey.

It should be apparent from the foregoing discussion that geochemical methods of mineral exploration have no unique claim to 

universal applicability. For any given problem, the pros and cons 

of any geochemical method must be weighed against those of the 

other available prospecting methods and a proper place assigned 

to each in the schedule of reducing the target size. 

PRELIMINARY ORIENTATION

Although the past record of effectiveness of geochemical prospecting methods is certainly helpful in planning exploration in a 

new area, there is no substitute for a preliminary orientation 

survey to determine which methods will work in the particular 

area under study. No two field problems are exactly alike.

Unexpected factors may locally modify the dispersion patterns of

ore metals and make them difficult or impossible to use as indications of buried ore.

The cost of a geochemical survey can also be estimated by preliminary experiments. If geochemical methods are to be economically feasible, techniques of field sampling and CnemlCal analySlS

must be both simple and cheap, so that the routine work of carrying

OUt a geOOliemical evil-ve^ can toe entrusted to relatively low-eos-fc

personnel. Quantitative accuracy may be sacrificed for the sate

of greater productivity as long as the methods are still adequate to

lOCate tile Significant anomalies. In applied prospecting work, the

aim is to find ore bodies rather than to make accurate geochemical 

maps. Many interfering and disturbing factors can be ignored
PRINCIPLES OF GEOCHEMICAL PROSPECTING 321

under certain conditions if experience shows that they do not 

materially alter the geochemical trail that is being followed. 

Whether or not they actually can be ignored in a particular 

exploration problem is a question that can only be answered by 

preliminary orientation surveys.

Orientation surveys in the vicinity of known ore are, in the 

writer's opinion, mandatory if any degree of success is to be 

expected from a geochemical survey. If possible, the experimental 

surveys should be conducted in the vicinity of deposits that have 

not been disturbed by previous exploratory work, so that the 

natural geochemical pattern as it existed before the advent of 

man can be observed. Many expensive sampling programs have 

failed either because the type of anomaly being sought did not 

exist in the area or because the samples were taken in the wrong 

places or of the wrong material. Many geochemical surveys were 

successful insofar as they served to delineate the anomalies, but 

they were so expensive and laborious as to be wholly uneconomic 

as a practical method of prospecting. In either case, preliminary 

work would have shown not only what kinds of anomalies could 

be expected but also what shortcuts could have been taken to 

eliminate unnecessary precautions and refinements. All practical 

exploratory work should be guided by the principle that the least 

expensive method of finding the ore body is the best.

LAYOUT OF SAMPLING PROGRAM

Two questions that must be answered before embarking on a 

geochemical survey are: what will be the most effective geometric 

pattern for sampling, and what is the maximum permissible spacing of samples. Both can be answered with preliminary experiments.

Sample pattern. Sampling of any material on a regional basis 

is not only easier but commonly more effective if it is laid out on 

a simple geometric pattern. In geochemical surveying, sample 

patterns should be made to fit the geometry of the expected 

anomalies. Most geochemical anomalies are the result of movement either through well-defined channels (dispersion trains), 

spreading predominantly to one side of the source (dispersion 

fans), or spreading upward or outward in all directions from the 

source (dispersion halos). Different sample patterns are needed 

for the most efficient delineation of anomalies of these different 

shapes.

The dispersion trains developed by flowing stream water assume 

a linear form determined by the drainage channels. Reconnaissance
322 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

geochemical work based upon the following of dispersion trains 

consists simply of collecting and analyzing samples from the larger 

streams; where the analytical data show an anomalous metal 

content, the trail of increasing metal content is followed upstream 

to the source. The maximum size of stream that will give a sure 

geochemical indication of mineralized zones in the drainage basin 

cannot generally be determined in advance without preliminary 

experimental sampling downstream from known but undisturbed 

deposits. The pattern of sampling to be followed in tracing an 

anomaly upstream is fixed by the pattern of tributaries entering 

the main stream. Sergeev (1946a) suggests a system of collecting 

three samples at each important confluence, two in the main 

stream respectively below and above the tributary, and one in the 

tributary itself. In practical work, it may be more convenient to 

sample the main stream at fixed intervals and to double back if 

the metal content falls off sharply in going upstream. In following 

dispersion trains, it is particularly desirable to have analytical 

methods that can be used on the spot.

Fan-shaped patterns are formed by glacial movement and by 

creep of surficial material down steep slopes. Generally, the concentration of metal in a fan apexing at an ore deposit decreases 

with distance from the source. Traverses designed to find dispersion fans with the least effort should be laid out at right angles to 

the direction of movement. Particularly on steep slopes, soilsample traverses parallel to the contours and transverse to the 

direction of slope movement have been recommended (Sergeev,

1941).

Dispersion halos due to spreading of material in all directions 

from a small source make up most of the anomalies found in 

Sampling residual soil and vegetation. A perfectly equidimensionai halo can best be located by means of an equal-spaced spread

Of Sample points. The shape of the halo, however, is rarely equidimensional, as it commonly mirrors to some extent the shape of the

SOUrce. Most Ore deposits are tabular, and the elongate pattern 

of the resulting anomalies in the overlying cover can be mapped

mOSt effectively by Collecting samples of soil and plants along

parallel traverse lines crossing the ore structure at right angles,

Traverse lines are commonly spaced a<t intervals of not more than

one-half the strike length, of tKe anticipated mineralized ZOneS.

This spacing permits at least One and Usually two linea to totem*

every important anomaly. Thus if a deposit must be at least 1,000 

feet in strike length to be of economic interest, a traverse spacing 

of 500 feet should be recommended.
PRINCIPLES OF GEOCHEMICAL PROSPECTING 323

One weakness of parallel sample traverses in soil and plant surveys is that samples from ridge crests, slopes of varying degrees 

of steepness, and valley bottoms, each subject to somewhat different interpretation, all appear on the same map. On ridge crests, 

the residual soil reflects the composition of the bedrock almost 

directly beneath, whereas on slopes, because of creep or landslide 

effects, it may reflect bedrock occurring a certain unknown distance upslope. Where distortion of this kind becomes a serious probJem, it may be desirable to lay out reconnaissance soil or plant 

traverses to conform with the topography rather than with a rigid, 

rectilinear system of coordinates. Topographically controlled 

sample patterns may be laid out along the crests and spurs of 

ridges, down the slope at right angles to contours, on hillsides 

parallel to contours, or on hillsides parallel to the ridge crest.

Where the strike of the mineralized structure is not known, it 

may be desirable to lay out an equal-spaced checkerboard pattern 

of samples. Here the spacing should be close enough that at least 

two and preferably three or four samples will fall within any 

anomaly that reflects a deposit large enough to be of economic 

interest.

Some geochemical anomalies do not fit the convenient classification of trains, fans, and halos. For these the most suitable 

sample pattern may be selected by considering the geometry 

peculiar to the anomaly. In most cases this is fairly obvious. If a 

geochemical province is manifested by the composition of diabase 

dikes, then diabase dikes should be sampled. Similarly, wells, 

springs, and seepages should be sampled if a ground-water pattern 

is sought. Sampling here must be guided by the distribution of 

the material sampled and cannot be laid out on a previously established geometrical grid.

Sample spacing. The spacing of samples should be close enough 

sc that no important anomaly could normally be overlooked, but 

no closer. If the anomaly is inhomogeneous, so that a proportion 

of the samples taken within an anomalous area will fail to indicate 

the anomaly, correspondingly more samples will be necessary than 

if the anomalous values are distributed uniformly. Also, if 

erratic high values of no economic significance occur outside the 

anomalous area, a closer spacing of samples will be called for. 

Here, a great deal depends on whether or not the analytical data 

are reported promptly, so that isolated anomalous values can be 

checked by local detailed work before the sampling party leaves 

the area. If so, it may be safe to use a wider spacing for the
'324 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

initial survey and to plan on immediate rechecking of all anomalous 

spots with detailed grids.

The above comments apply to any prospecting method involving 

systematic measurements or observations. More specifically, 

experience in most areas has shown that in sampling residual soil 

and plants, a spacing of 100 feet is both adequate and necessary. 

Anomalies in soils developed by ground-water movement are 

likely to be more restricted in area, requiring a spacing of from 

10 to 50 feet. In glacial soils, a spacing of as much as 500 feet 

may be effective in locating glacially dispersed patterns. Still 

larger targets, as for example in a stream system where an 

; anomalous metal content can be detected perhaps 10 miles from 

the source, can be sampled on a correspondingly wider spread.

SAMPLING TECHNIQUES

The technique of collecting samples will naturally depend on 

what is being sampled, whether rock, soil, vegetation, water, or 

stream sediment.

Rock. Elements occurring in rocks as primary dispersion patterns may be either evenly disseminated throughout the rock mass 

or- segregated as clots or swarms of minute fracture fillings. If it 

can be established that the rock is relatively homogeneous, single 

grab samples may suffice. If the composition is spotty and erratic, 

. however, it is safer to collect either channel samples or chip 

samples composited along sections of traverse as described by 

Cooper and Huff (1951). Split diamond-drill core is also suitable. 

The size of sample should be governed by the relative homogeneity 

of the. .material, a factor that can be determined, by. preliminary 

experiments. Ten grams is adequate for most analytical methods. 

Cloth sacks and cylindrical ice-cream cartons are suitable as containers for rock samples.

in working with, primary dispersion patterns, it is well to remefmber that the distribution of metals in residual soils may reflect the

'_ general pattern of the primary anomaly in the parent TOCk fairly 

accurately. In fact, the: averaging effect resulting from Weathering and soil formation may serve to give a more homogeneous

primary pattern than channel sampling of the rock itself, son

samples can be collected and analyzed more economically than

rock samples; thus if the soil anomalies are found to correspond

With the primary anomalies in the parent rock, a, soii-samr>iins

survey is to be recommended.

Soil. In stony soil it is usually easier to prepare sample holes 

with a pick and shovel. A geologic pick or a folding Army foxhole
PKINCIPLES OF GEQCHEMICAL PROSPECTING 325

shovel has been found satisfactory for shallow holes. In .clay soils, 

a soil auger is usually easier and faster than the pick-and-shovel 

technique. A suitable soil auger may be assembled by brazing or 

welding a large wood-auger bit to a section of light iron pipe, and 

attaching additional lengths of pipe as needed for greater depth; 

a T-shaped handle may then be fitted to the top section of pipe. It 

is found that the auger bit is more effective in cutting through soils 

if the leading screw point is cut out. If samples are to be taken at 

a predetermined 'depth, it may be easier to drive a crowbar into 

the soil for the required distance, remove the bar, and then extract 

the sample from the hole with an auger. Where deep holes are 

required, and where the terrane permits, the use of mobile power 

augers should be investigated.

The size fraction of soil used for analysis may make some difference in the significance of the data. In some problems it has 

been found that the metal content of the fine fraction was somewhat, but not greatly, higher than that of the coarse fraction. In 

other experiments, no significant variation with size was apparent. 

The standard procedure adopted for Geological Survey work has 

been to collect the fines (minus 80 mesh) for analysis and discard 

the coarse fraction. This avoids the need of grinding the sample 

before analysis and may cut down erratic data resulting from 

possible coarse fragments of oxidized ore minerals such as lead 

carbonate or malachite. An alternative procedure is to collect all 

sizes less than 2 mm in diameter and grind before analysis. This 

procedure may be preferable where the soil lacks an appreciable, 

proportion of fines or where the ore metal is concentrated in the 

coarser sizes.

It is sometimes possible in dry climates to sieve samples as they 

are collected. Usually, however, fresh samples are so damp that 

the fines cannot be separated by sieving until the samples have had 

a chance to dry. Most samples may either be collected without 

sieving or, if desirable, sieved to minus 2 mm on the spot. If 

paper containers are used, such samples should be dry enough for 

sieving to the desired size in a day or two of storage in a dry room 

or in the sun without opening the containers.

Harold Bloom of the Geological Survey has conducted comparative experiments on sieves composed of brass, stainless steel, and 

silk, and has found that contamination of the sample by copper 

and zinc from brass screening under extreme conditions is less 

than 10 ppm. Thus, except for very precise work, the use of standard brass sieves is permissible. The advantage of stainless steel 

besides being noncontammating is its strength and durability. It
326 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

is considerably more expensive than other materials. Silk sieves 

are by far the least expensive of the three but are easily damaged 

and must be replaced frequently. A very economical noncontaminating sieve can be made by knocking the paper disc out of the 

cap of a half-pint ice-cream container, and using the remaining 

band to clamp a piece of silk bolting cloth, to the bottom section 

of the container.

For the standard field tests, the analyst needs about 5 grams 

of prepared material (sieved or ground). This leaves enough of 

the sample for possible repeat determination and for tests for 

more than one element if desired.

Paper containers are most commonly used for soils. For 

standard, mass-production work either 2-ounce paper cylinders 

sold by drug houses for pills, or manila envelopes with a metal 

clasp are usually satisfactory. For larger samples, cylindrical icecream containers have been widely used. The advantages of paper 

containers are low cost, usually less than a cent apiece, and convenience in handling. A serious disadvantage of paper containers 

is that they tend to become unglued when used for very wet 

samples. When this happens, it is necessary either to repair the 

container with scotch tape, or transfer the sample to a new container after drying. Paper containers constructed with heavy 

kraft paper and waterproof glue should be used if available.

Vegetation. Samples of vegetation for chemical analysis should 

be taken far enough above the ground to be clear of contamination

from rain spatter. Experience has shown that it is important to 

confine a geochemical plant survey to samples taken of the same 

organs of the same species to be sure of obtaining comparable 

data. The collector must, therefore, be able to recognize the 

SDeCieS Of tree that iS tO be USed, Wood can be collected either from 

the main trunk with a carpenter's auger or from branches sawed

Or chopped off and stripped of leaves and bark. Where twigs are 

used, they may be removed eitker with a knife Or" a prillting d^VlCC

of some kind. Leaves and needles can most conveniently be removed from twigs by first allowing the sample to dry and then

stripping Off the brittle OUter foliage. The same way of removing 

needles can be used in surveys where the metal content of the 

needles alone is required. For most of the analytical procedures, a 5amPie of Bt ieast &

grams, dry weight, is required. The most commonly used containers are lightweight paper bags.

Water. The collection of water samples presents a special 

problem not found with other kinds of material in that the content
PRINCIPLES OF GEOCHEMICAL PROSPECTING 327

of traces of metals is relatively unstable. The most serious difficulty is the removal of ions from solution by adsorption to the 

walls of the vessel in which the water sample is stored. Metal may 

also be removed from solution by coprecipitation with the iron 

hydroxide precipitates that commonly form when water is stored 

for any length of time. It is reported that these effects can be 

minimized by acidifying the sample immediately after collection, 

in order to inhibit both exchange reactions and hydrolysis. If a 

soft-glass vessel is used, some of the metal contained in the glass 

may go into solution to contaminate the sample; this may be 

avoided by using containers made of either borosilicate glass or 

plastic. Polyethylene bottles with screw-cap tops are probably 

the most suitable, as they are not only free of contamination but 

also unbreakable.

Because of the serious difficulties in the storage of water 

samples, it is highly desirable to avoid these problems entirely by 

making the analyses on the spot using a portable analytical kit.

Stream sediments. Where the heavy-mineral content of sediments is to be measured, it is usually desirable to collect the sample 

from the surface of bedrock beneath the stream channel. This may 

require either digging a pit or augering a hole, if the bedrock is 

buried beneath a heavy cover of alluvial material. Where the 

unstable component of the stream load is being mapped, suitable 

samples can be obtained from deposits of silt either in the stream 

bed or exposed under the sod or forest litter on the banks of the 

stream. Under some conditions samples from older alluvial terraces may be suitable.

The general problems of determining the optimum size fraction 

are the same for sediments as for soils, which have already been 

discussed. As with soils, about 5 grams of prepared material is 

adequate for most types of analytical work. For sediment samples, 

waterproof containers of some kind are mandatory, as nonwaterproof paper containers will disintegrate in contact with the 

moisture in normal sediment samples. Heavy paper envelopes 

made with waterproof glue are probably most satisfactory, as they 

permit drying of the sample without transfer and also provide a 

convenient surface for notes. Small aluminum containers have 

been widely used for sediment samples, as they are unbreakable, 

noncontaminating, and easily stored. A plastic (styrene) cylindrical container fitted with a friction-held polyethylene cap used 

for dispensing drugs appears to be equally suitable. Tinned steel 

has been found unsatisfactory because of rusting and danger of 

contamination from minor constituents in the tin plating. Cloth
328 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

or polyethylene sacks would probably be satisfactory if rigid containers were not available.

Marking sample sites. It is almost always desirable to mark 

the sample site in such a way that it can be found again if the 

area is revisited. It is rarely necessary to mark more than one 

out of three or four sites in a large systematic survey. Marking 

may be done by marked stakes, marked rags tied on bushes, blazes 

on trees, or pieces of paper left in the hole and anchored under a 

stone. Waterproof and weatherproof crayon of some kind saves 

the embarrassment of finding the mark illegible when the site 

is revisited.

Numbering samples. In its geochemical prospecting work, the 

Geological Survey uses systems of simple accession number for 

each job so that samples are numbered consecutively with simple 

Arabic numerals in the order in which they are taken, regardless 

of the nature of the sample. Even so, skipped or duplicated numbers will turn up from time to time; when numbers are duplicated, 

both samples bearing the identical number become worthless and * 

have to be resampled, often at considerable cost. This may be 

avoided by printing or writing a consecutive series of numbers on 

gummed tape and then tearing off the appropriate number from 

the coil of tape and pasting it on the container when the sample 

is collected. If envelopes or other flat containers are used, the 

number may be marked on the empty containers in advance. In 

addition to the number, every sample container should adequately 

identify the project. This may be done easily with a hand-set 

rubber stamp showing name of project, location, name of collector,

and year.

CHOICE OF CONSTITUENTS TO BE DETERMINED

Choice of element. The mapping of dispersion patterns fCHuGd

by the major ore metals is the most straightforward approach. If 

zinc ore is sought, the distribution of traces of zinc would seem 

to give the most direct indication of the buried ore. A large part

of the geochemical prospecting work to date has been based on 

this premise, and its SUCess in finding ore justifies the assumption.

Not uncommonily, however, the ore metals themselves fail for

0116 reaSOri Or another to form a dispersion pattern that can be

readily detectoa and mapped. In this event, Consideration HlUSt

136 glVeil tO the distribution Of associated noneconomic elements, or 

"pathfinders," as denned by Warren and Delavault (1953a), Pathfinders may be elements present in the ore in major amounts but 

not of commercial value, such as iron and sulfur (in pyrite), 

barium (in barite), or antimony (in tetrahedrite); common ore
PRINCIPLES OF GEOCHEMICAL PROSPECTING 329

metals occurring in quantities too small to be commercially extractable, such as zinc (in most ores of copper and silver); or rare 

elements that are strongly enriched in certain ores, such as 

antimony, selenium, cadmium, and bismuth (table 3).

In a geochemical reconnaissance of a virgin area, where little 

or nothing is known about the kind of minerals in the area, the 

prospector must watch for all of the important ore metals. If 

every sample is analyzed for every one of these elements, the 

survey would almost certainly be an expensive undertaking and 

might turn out to be uneconomical. A less pretentious approach 

would be to analyze the reconnaissance samples only for a certain 

few selected elements that, taken together, occur in a wide variety 

of ore types. Zinc occurs as either a major or minor constituent of 

most base-metal ores and in some precious-metal deposits as well. 

Copper is associated with many ores of nickel, cobalt, molybdenum, 

and precious metals. Zinc and copper together, therefore, may be 

useful as indicators not only for zinc and copper deposits, but for 

many other types of ore. Other associations of metals that might 

be helpful in selecting key elements for reconnaissance are the tintungsten-niobium association in high-temperature veins and the 

rare elements in pegmatite deposits.

Most geochemical prospecting surveys, however, have been 

conducted in areas where it is possible to make an intelligent 

guess of the kinds of ore deposits that are likely to be found. In 

this event the plan of investigation can be guided by a knowledge 

of the characteristic dispersion patterns formed by the particular 

elements occurring in the type of ore that is expected. In the 

secondary dispersion cycle, immobile metals commonly form the 

most clear-cut patterns in residual soils, whereas the mobile metals 

tend to be dispersed more widely by movement in ground and 

surface waters and into the vegetation. Thus, where a mineral 

deposit is enriched in more than one metal, it may be most effective 

to test for the most mobile of the metals in the reconnaissance 

work and for the least mobile in the detailed soil survey. In prospecting for lead-zinc deposits, therefore, the reconnaissance may 

be based on zinc or total heavy metals and the detailed followup on 

lead. The cobalt ores of the Blackbird district of Idaho contain 

major amounts of both cobalt and arsenic. In weathering, arsenic 

is far less mobile than cobalt, with the effect that the arsenic 

patterns in residual soils delineate the mineralized areas far more 

sharply than the cobalt patterns.

In actual practice, the choice of the element to be determined 

is governed all too frequently by the availability of a suitable
330 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

analytical test. It is earnestly hoped that continuing chemical 

research will eventually provide adequate tests for all the important elements that occur in ore deposits

Choice of extraction method. Most geochemical prospecting 

work is based on the determination of either the total content of 

one or more elements in the sample or of an approximately proportional part of the total content a part that will show the same 

general pattern as the total values.

An occasion may arise, however, where an element is bound up 

in the sample in more than one way, and where the mechanism of 

binding is related to the source of the element, whether normal 

rock or a mineral deposit. Such a situation is found in glacial 

soil, where part of the metal content is tied up in the lattice 

structure of primary rock-forming silicate minerals of no economic 

interest, and part originates from nearby ores by ground-water 

circulation and is loosely held by adsorptive forces. Here it would 

be highly desirable to differentiate the metal according to its two 

modes of origin. A weak extraction procedure adequate to remove 

the exchangeable metal, but not strong enough to break up the 

primary silicates, might give a better indication of the economically important dispersion pattern than a method involving total 

extraction of the metal.

Lovering, Sokoloff, and Morris (1948) describe a relationship 

of this kind in their study of primary halos in the Tintic district 

of Utah. They report that a weak extraction of metals from altered 

volcanic rocks overlying a concealed ore body gave a significant 

geochemical pattern that was not brought out at all by a total

extraction method.

ANALYTICAL TECHNIQUES

In touching briefly upon the methods of chemical analysis used

in geochemical prospecting, it is perhaps worth pointing out again 

that the purpose of a geochemical prospecting survey is to find ore

deposits. The most economical method of chemical analysis that will provide the data by which ore deposits can be found is, almost

by definition, tHe best. Expressed in a different way, the most Suitat)le analytical procedure iS One that embodies a satisfactory balance of reliability, economy, and promptness in reporting results.

Meihods available. A full discussion of the many procedures

tticl't/ have been developed fox- g^eocKemical i3rosr>ecting' -work is beyond the scope of this report; details may be obtained by consulting the references. The following list contains the principal references to colorimetric methods of analysis:
PRINCIPLES OF GEOCHEMICAL PROSPECTING 331

Metal Material " °"""?3 References 

Antimony ____Soil and rocks... Ward and Lakin (1954) 

Arsenic. .____Soil.. .....-_.._Almond (1953b)

Cobalt. _....___Soil and rocks_ Lakin, Almond, and Ward (1952)

Soil... __..__Almond (1963a) 

Water..........._....._...U. S. Geological Survey, p. 13.»

Copper............ _Soil and rocks....._Lakin, Almond, and Ward (1952)

U. S. Geological Survey, p. 16.9 

Plants....... _._Warren and Delavault (1949)

Stevens and Lakin (1949)

Water..._... ..__Lakin, Almond, and Ward (1962) 

Rosenqvist and Vogt (1943) 

Huff (1948) 

Heavy metals...__Soil and sediment .Lakin, Almond, and Ward (1952)

Huff (1951) 

Water..............._...Lakin, Almond, and Ward (1952)

Warren, Delavault, and Irish (1951a) 

Riddell (1952a)

Warren, Delavault, and Irish (1953) 

Huff (1948) 

Lead_......_ ._Soil and rocks..__Lakin, Almond, and Ward (1952)

Water...__.____Huff (1948) 

Manganese___._.Soil..._.... _._U. S. Geological Survey, p. 82.9

Molybdenum _.Soil and rocks.. Lakin, Almond, and Ward (1952) 

Plants._._____Reichen and Ward (1951) 

Soil and rocks.__Ward (1951a)

Nickel .._____Soil and rocks..__Lakin, Almond, and Ward (1952) 

Plants _____Do.

Reichen (1951)

Niobium ._____Rocks. _____Ward and Marranzino (1955) 

Silver______-Soil and rocks....._.Lakin, Almond, and Ward (1952)

Almond, Stevens, and Lakin (1953) 

Tungsten______Soil... _____..-Lakin, Almond, and Ward (1952)

Ward (1951b) 

Uranium _........ Grimaldi, Ward and Fuyat (1954)

Vanadium-____Rocks.. .___.._U. S. Geological Survey, p. 39.9 

Zinc.._.. .___Soil ..._..___Lakin, Almond, and Ward (1952)

U. S. Geological Survey, p. 16.9 

Lakin, Stevens, and Almond (1949) 

Plants. . _..._Lakin, Almond, and Ward (1952)

Reichen and Lakin (1949) 

Water.. __._Lakin, Almond, and Ward (1952)

Warren, Delavault, and Irish (1951a) 

Huff (1948)

Spectographic methods of analysis were used widely for geochemical prospecting work during the prewar period. When determinations of more than two or three constituents are needed for 

each sample, semiquantitative spectrographic analysis is usually

* U. S. Geological Survey. 1953. Additional field methods used in reochemical prospecting: by 

the U. 8. Geological Survey: U. S. G«ol. Survey open-file rcpt.
332 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

more economical than the chemical methods. With the recent construction of a mobile spectrographic unit these methods may again 

have a wide application in geochemical prospecting, especially in 

reconnaissance work.

Methods employing paper chromatography have recently been 

developed for geochemical prospecting by chemists at the Chemical Research Laboratory of the National Physical Laboratory in 

Teddington, England. In preliminary experiments these methods 

show great promise, and it is possible that some of them will 

replace the rapid colorimetric methods now in common use.

Reliability. Accuracy and precision of analytical data are not 

so important as the reliability with which the figures reflect the < 

geochemical pattern. Most of the colorimetric procedures commonly used in geochemical prospecting were developed from the 

standard colorimetric methods of trace analysis by omitting or 

simplifying many of the steps needed for precise, quantitative work. 

As a result, the data contain errors that would.not be tolerated in 

the average analytical laboratory. With the relatively weak ex- > 

tractants used in the rapid tests, rarely more than 80 percent 

of the total metal present in the sample will be measured. Furthermore, the reproducibility may be within a factor of only 1.5 or 

even 2.0 of the mean of several replicate determinations. Most 

geochemical anomalies, however, show a contrast of anomalous 

values against a background equal to many times the errors in 

the analytical tests. Thus, even with relatively inaccurate methods, ,

as judged by usual chemical standards, the pattern should still 

appear.

One of the unavoidab]..- consequences of the many shortcuts used 

in the procedures for the sake of speed is that seriously erratic

analytical results will appear in a certain (usually small) proportion of the reported figures. The analyst has no way of knowing which of his figures may be questionable without running the 

entire lot in duplicate. The geologist familiar with his problem, 

however, is much better equipped to choose samples where the 

reported analysis does not seem to fit the geologic picture and to

ask for confirmatory repeat analyses. This should be done by the

geologist as a routine matter as soon as he receives an analytical

report.

Cost. With a properly equipped laboratory, one man can make

30 determinations per working day with most of the procedures 

developed by the Geological Survey. With a few of the procedures,

the rate may be as high as 100 per man-day. The cost of materials 

and glassware is negligible, so that the bulk of the cost is in labor.
PRINCIPLES OF GEOCHEMICAL PROSPECTING 333

Promptness. The promptness with which the field party needs 

analytical data varies with the nature of the exploration program. 

In the following drainage patterns, and particularly in analysis 

of stream water for metals, effective work almost requires that 

analyses be made on the spot. In experimental investigations preliminary to laying out a program of routine work, data are needed 

within a day or two of the time of collecting the sample and can 

best be provided by a mobile analytical unit at the base camp. 

Most of the colorimetric procedures can be set up under crude field 

conditions if necessary, and a few are adaptable for use at the 

sample site. In large-scale routine surveys where there is no call 

for immediate day-to-day decisions, however, samples can most 

efficiently be analyzed in some well-equipped central laboratory. 

Apart from the needs of the job for prompt data, the most efficient, reliable, and economical analytical work is done in an established laboratory.

PREPARATION OF MAPS AND DIAGRAMS 

Clear and concise graphic plots of geochemical data make the 

task of interpretation much easier. Profile curves, in which the 

relative position of the sample sites is plotted on the horizontal 

axis and the geochemical data are plotted vertically, are useful for 

isolated sample traverses. Where the values vary over an extremely wide range, the use of a logarithmic vertical scale serves 

to bring the entire range into a scale that can be readily handled. 

Data for more than one component can be shown on the same 

diagram by using different symbols for the lines of the curves; if 

only two components are shown, the data for each may be plotted 

in opposite directions from the centerline, taken as zero. Geologic 

or other information may be added either as notes or as a separate 

diagram directly beneath the geochemical curve.

Geochemical plans are desirable where more than a single traverse line has been sampled. Sample locations may be marked by 

a dot, cross, or circle. The analytical data can then be lettered on 

the plan next to the symbol for the sample site. The scale of the 

map should be chosen so that the figures on the map are not 

crowded; a minimum distance of ^ inch between symbols results 

in an attractive and legible map. Where more than one analytical 

figure must be shown for each sample, they can be plotted (1) on 

opposite sides of the symbol for sample location, (2) one over the 

other and separated by a horizontal line, or (3) in a consistent 

sequence separated by hyphens or semicolons. To save space and 

confusion on the map, it may be desirable to assign simple code 

numbers to represent ranges of values and to plot the code num-
bers in place of the figures reported by the analyst. Kennedy 

(1952) developed a particularly effective system of logarithmic 

code numbers to represent figures ranging from 50 to 50,000 ppm.

If possible, the geochemical data should be contoured by drawing 

"isograds," or lines of equal composition. When more than one set 

of figures is to be contoured on the same map, different styles of 

lines may be drawn for the different isograds. It is commonly 

found that the only useful contour that can be drawn on a 

geochemical plan is the threshold contour separating areas of 

anomalous values from areas of background values; additional 

contouring should be avoided as it congests the map and does not 

assist in the interpretation. However, lines connecting geochemical 

maximums should be drawn where possible to emphasize the axes 

of the anomalies.

In interpreting secondary dispersion patterns, consideration 

must be given to the slope of the surface and to the pattern formed 

by drainage divides and the drainage channels. The crests and 

spurs of ridges should be plotted on the geochemical map by a 

suitable symbol, and the pattern of streams, swales, springs, 

swamps, and alluvial flats by another set of symbols. The data of 

a geochemical survey of stream water or sediment can be generalized by shading in the basin upslope from any anomalous samples.

Simple geological information can be sketched directly on the 

geochemical map. If the geological patterns are complex, a transparent overlay is usually more suitable. Geochemical plans and 

diagrams should show (1) name and location of area, (2) scale

and orientation, (3) explanation of symbols, (4) nature of 

samples, (5) analytical procedures, (6) units used in expressing

analytical data, and (7) name of party chief, samplers, and 

analysts, 

The methods of plotting data mentioned above are illustrated

by the maps and diagrams published by Cannon (1952), Hawkes

(1954), Huff (1952), and Kennedy (1952, 1956),10

INTERPRETATION

Accurate interpretation of geochemical survey data is ttie final

step in effective geochemical prospecting, Effort expended in the

planning and execution of the sampling and analytical work is

if the results are not understood. Skill in interpreting geofltfl JllVlSt depend first upon general familiarity with the

many factors that contribute to the formation of geochemical 

anomalies as discussed in this report and, secondly, on a specific

1 See also footnote 1 on p. 234.
PRINCIPLES OF GEOCHEMICAL PROSPECTING 335

knowledge of the balance of these factors in the area under study, 

such as may be gained from local orientation studies over known 

deposits.

No hard-and-fast rules can be given for the interpretation of 

geochemical data. The personal factor plays a major role. The 

following suggestions represents the writer's approach to the 

problem of interpretation. This approach is based upon finding the 

answer to three questions: (1) how do the anomalies form? (2) 

what is the theshold value of the anomalies? and (3) what can 

cause false anomalies ?

More than one geochemical process can and usually does play a 

part in the formation of an anomaly. In residual soil, the pattern 

of residual metal owing to the weathering of ore in place is only 

one component of the pattern; metals may also be distributed in 

residual soils by solution and redeposition in ground water, by 

slumping, slope creep, frost action, and the activity of living 

organisms. Similarly, the pattern of metals in glacial till may combine the effects of glacial transportation, ground-water movement, 

ionic diffusion, and living organisms. An accurate interpretation 

of the significance of an anomaly, therefore, is not necessarily a 

simple matter. However, if the relative effect of each of the 

factors contributing to the formation of an anomaly is accuratelyo 

appraised, an accurate over-all interpretation is much more likely.

Knowing the threshold value separating anomalous areas from 

background is a prerequisite to recognizing an anomaly. Inasmuch 

as the threshold is simply the upper limit of the normal variation 

in background values, an accurate estimate of the background 

range is of prime importance. Establishing the background should 

be one of the principal objectives of the preliminary orientation 

survey.

False anomalies are areas of high metal content that cannot be 

used as guides to ore. Under special circumstances, natural enrichments of metal can occur that have no genetic connection with 

ore or mineralizing processes. The normal enrichment of zinc in 

the ash of dwarf birches in concentrations as high as 1.0 percent 

is an example (Warren and others, 1952b). With an adequate 

understanding of normal enrichment processes, however, unusual 

concentrations of this kind can be recognized as lying within the 

normal background range for the particular material. The same 

cannot be said for the effects of human activity. False anomalies 

due to human contamination are an ever-present threat, even in 

remote areas. Contamination can be caused by (1) fragments of 

ore scattered over the surface near mines or prospects, (2) metal-
336 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

rich mine water, causing false anomalies by ground- and surfacewater circulation, (3) mineralized waste rock from mines used for 

general construction purposes or as an agricultural fertilizer, (4) 

trash containing metallic objects, (5) industrial waste water, (6) 

metal-rich dust from mine-tailings piles, (7) smelter fumes, smoke 

and fumes from industrial and urban areas, and exhaust fumes 

from motor vehicles, and (8) insecticide sprays. Every one of the 

above sources of contamination has at one time or another caused 

either trouble or concern in connection with the interpretation of 

geochemical data. Preliminary experiments in areas of suspected 

contamination should make it possible to recognize these effects 

when they are found in geochemical survey data.

GLOSSARY

Accumulator plant. A plant that takes up a particular element in quantities 

considerably in excess of that in "normal" plants (Robinson and Edgington, 1945).

Alluvium. Detrital material deposited by running water.

Background. The abundance of an element or any chemical property of a 

naturally occurring material in areas where the chemical pattern has not 

been affected by the presence of a mineral deposit.

Biogeochemical prospecting. Synonymous with geochemical plant survey.

Blind deposit. A deposit that does not extend to the surface of bedrock.

Botanical anomaly. A geochemical anomaly in which the chemical composition, 

ecological assemblage, or morphology of plants indicates the presence of a 

mineral deposit.

Contrast. A ratio expressing the geochemical relief, computed as the ratio 

either of maximum value to threshold, of maximum to background, or of 

threshold to background values.

Converter plant. A plant that takes up an insoluble element from the soil, 

builds it into its living structure, and at death returns it to the soil in

soluble £orm.

Diffusion pattern. A dispersion pattern resulting from upward movement

of ions in vadose water,

Dispersion pattern. A pattern of distribution of chemical elements resulting 

from the movement of natural materials.

Ecology. The study of relationships between organisms and their environment.

Extractable metal. A metal that can be extracted from a sample by any 

given chemical treatment.

Fan. A dispersion pattern that spreads predominantly to one side of the

source of material.

Genetic Halo. A. g-eochemical anomaly resulting from primary dispersion. 

Geochemical anomaly. Area where the chemical properties of a naturally OCcurring material indicate the presence of a mineral deposit in the vicinity,

Geochemical prospecting. Mineral exploration based on systematic measurement of the chemical properties of a naturally occurring material.
PRINCIPLES OF GEOCHEMICAL PROSPECTING 337

Geochemical province. An apparent local variation in the original composition of the earth's crust.

Geochemical survey. A survey involving the chemical analysis of systematically collected samples of rock, soil, plants, or water; this expression 

may be further modified by indicating specifically the material sampled, 

as, for example, "geochemical soil survey."

Geochemistry. The study of the distribution of elements in the earth.

Halo. A nearly equidimensional dispersion pattern, spreading symmetrically 

upward or outward from the source of material.

Heavy metals. Metals that react readily with dithizone, principally zinc, 

copper, cobalt, and lead, but under special conditions including one or 

more of the following metals: bismuth, cadmium, gold, indium, iron, 

manganese, mercury, nickel, palladium, platinum, silver, thallium, and 

tin.

Hydrogeochemical prospecting. Synonymous with geochemical water survey.

Indicator plant. A plant that indicates by its presence the occurrence of an 

element in the soil upon which it grows (Beath, Gilbert, and Eppson, 1939).

Leakage halo. A dispersion pattern formed in the rock overlying a mineral 

deposit by the movement of ore-forming fluids through a well-defined 

system of channels.

Mobility. The tendency of an element to move in a given geochemical environment.

Pathfinder. A mineral .or element found in close association with the element 

being sought, which can be more readily found or which has more obviously anomalous features than the element which is the main object of 

search (Warren and Delavault, 1953a).

Pedogeochemical prospecting. Synonymous with geochemical soil survey.

Plant symptom. An abnormal growth habit of a plant indicative of a peculiarity in the chemical composition of the supporting soil.

Primary dispersion. Geochemical dispersion of elements by processes originating within the earth; opposite of secondary dispersion.

Regolith. Loose surface material overlying solid rock.

Secondary dispersion. Geochemical dispersion of elements by processes originating at the surface of the earth; opposite of primary dispersion.

Sediment. Solid material deposited by running or standing water.

Soil. In agriculture: loose surface material capable of supporting plant 

growth, and having properties resulting from the integrated effect of 

climate and living matter. In geology: any loose surface material overlying solid rock; synonymous with regolith.

Soil formation. The process whereby fragmental material resulting from 

rock weathering is transformed into a medium that can support plant 

growth.

Soil horizon. A layer of soil, approximately parallel to the surface, which 

differs from adjacent layers in chemical and physical properties; the 

principal horizons from the surface downward are (1) the topsoil, A horizon, or leached horizon; (2) the subsoil, B horizon, or horizon of accumulation; and (3) the parent material, C horizon, from which the upper 

horizons were formed.

Soil profile. The vertical sequence of soil horizons.
338 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

Suboutcrop. Area of intersection of a geologic feature with the surface of 

bedrock beneath the regolith.

Superimposed halo. A dispersion pattern formed in the regolith by the 

movement of material in subsurface waters.

Threshold. In geochemical prospecting: the limiting anomalous value below 

which variations represent only normal background effects and above 

which they have significance in terms of possible mineral deposits. In 

analytical chemistry: the limiting sensitivity of an analytical method.

Train. A linear dispersion pattern resulting from movement along welldefined drainage channels.

Wall-rock halo. A dispersion pattern formed in the rock adjoining mineral 

deposits where the chemical composition has been modified by the oreforming fluids.

UNITS OF MEASUREMENT

The units of measurement commonly found in the literature 

of geochemical prospecting are denned in tables 11, 12, and 13. 

The common unit of weight is the microgram, equal to a millionth of a gram and represented by the Greek letter gamma (y). 

For solid material the common unit of concentration is the part 

per million (ppm), equal to 0.0001 percent. In expressing data

on the composition of plants, the basis of measurement, whether 

ash or dry weight of the plant, should be specified. For aqueous 

solutions, concentrations may be expressed as parts per million

(micrograms per milliliter) or micrograms per liter. Parts per 

billion should be avoided because of the difference in the American and British usage of the term billion.

TABLB: 11. Units of weight

Unit

Kilosr&tn --_- _

Microgram, gamma.--.---. .-.._..__..- Short ton...... ...-- ' 

A-voiT-dvifiois ipOxind

Avoirdupois ounce...... .-.--.--.- -- - 

Troy ounce .._........--__.._--_._---..

Symbol

t 

kg 

g

*"S

7

ib

oz

s

Metric equivalent

(grams)

1,000,000 

1,000

1

.001 

.000001

907,180

453.6

28. 3S

SI. 10

29.166
PRINCIPLES OF GEOCHEMICAL PROSPECTING

TABLE V^. Units of concentration

339

Unit

Grams per gram.. _____

Percent ___ ______ ___ _ ____ ______

Milligrams per kilogram ... _. _________

Parts per million. __ _______ _________

Grums pur metric ton... _ _

Mierograms per liter. ._-__-.._ __ ___

Milliequivalents per 100 grains.. __ _ ___

Troy ounces per short ton __ _. ... _.

Symbol

g/g~ ---_. ___

%.. ' ....

ing/kg. __________

ppm. -.-.___._--.

K/t

7/liter. _.._.._-.

meq/lOOg. .......

oz/t

Proportionality

1

.01

. 000001

. 000001

. 000001

.000000001

. 00001 X eq '

. 000034

1 An equivalent (eq.) IB the weight in grams which in its reaction corresponds to a grain-atom of hydrogen. For our purposes, it is taken as being numerically equal to the atomic or molecular weight divided 

hy the valence. One thousand milliequivalents (men.) is equal to one equivalent.

TABLE 13. Conversion tahle, units of concentration l

^\ B

A ^x^

g/K

Percent.... _.

ppm........

ineq/lOOg.--.

oz/fc.. .__....

g/K

1

.01

10- 6

10-9

eq X 10-B 

3.4 X 10-6

Percent

100

i

10-4

10-7

eq X 10-3 

3.4 X 10-3

ppm

10«

104

1

10-1

eq X 10 

34

7 /liter

10»

107

10s

1

cq X 104 

3.4 X W

ineri/100 K

105 /oq

JOJ/eq

10-' eq

10-4 /eq

1

3.4/eq

oz/t

2.9 X 104

2.9 X W2.9 X 10-2

2.9 X 10-'

eq X 0.29 

1

1 To express concentration in terms ol "B," multiply concentration expressed us "A" by factor shown.

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342 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

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346 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

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Internat. Geol. Gong. London, 18th sess. Kept., pt. 2, p. 86-87.

some samples of plutonic rocks: Soc. chim. Belgrade

Bull., V. 14, p. 121-127 (from cnem. Ats., -. 46,

uzz{, fl.. and VergMnO, 0., 1948) Contribute alia conoscenza della 

distribUZlOne del niChel nella biosfera; il contenuto di nichel nelle ceneri

TH^'""" ^ oV""*/^0*^* !>«*«.: 'Soc. mineralog. Italians, Rend, anno 4,

1947, ^ 37-38. (From Geol. Soc. America, Biwioe^^ _^ T« d«^ of

Geology Exclusive of North America, v. 17, p. 301.)

, T. W., 1952, Indicator minerals, Coeur d'Alene silver belt: Econ.

MoiTlS, H. T., 19S2, SUpergeiie and hydrothermal dispereion ^r *^-^r «-t».i« 

i n wall rocks near ore bodies, Tintic district, Utah. II Primary dlSpCrSlON 

patterns of heavy metalS In Carbonate and quartz monzonite wall rocks :

Econ. Geology, YI ^/ p- 698-7ie.

Mortland, M. M., and Gieseking, J. E., 19rf, Infaft^ d! QlB SlMW W 

on potassium fixation: Soil Sci., v. 71, p. 381-885.
PRINCIPLES OF GEOCHEMICAL PROSPECTING 347

Moore, E. S., and Maynard, J. E.f 1929, Solution, transportation, and precipitation of iron and silica: Econ. Geology, v. 24, p. 272-203, 365-402, 

506-527.

Murata, K. J., 1939, Exchangeable manganese in river and ocean muds: 

Am. Jour. Sci., v. 237, p. 725-735.

Nackowski, M. P., 1952, Geochemical prospecting applied to the IllinoisKentucky fluorspar area: Univ. Microfilms (Ann Arbor, Mien.), pub. 

no. 3853.

Neiva, J. M. C., 1949, Prospec§ao geoquimica: Serv. fomento mineiro Portugal, Estudos, notas, e trabalho, v. 5, p. 91-98.

Nichols, M. S., Henkel, Theresa, and McNall, Dorothy, 1946, Copper in lake 

muds from lakes of the Madison area: Wisconsin Acad. Sci. Trans., 

v. 38, p. 333-350.

Odman, 0. H., 1947, Manganese mineralization in the Ultevis district, 

Jokkmokk, North Sweden; I Geology: Sveriges geol. undersokning, ser. 

C, no. 487.

Oertel, A. C., and Prescott, J. A., 1944, A spectrochemical examination of 

some ironstone gravels from Australian soils: Royal Soc. South Australia 

Trans., v. 68, p. 173-176.

Ohashi, Shigeru, 1952, Geochemical studies on the ore deposits in Ishikawa 

Prefecture (in Japanese): Chem. Soc. Japan Jour., v. 73, p. 353-355.

Peech, Michael, 1941, Availability of ions in light sandy soils as affected by 

soil reaction: Soil Sci., v. 51, p. 473-486.

Pierce, A. P., and Dias, M. B., 1950, Os metodos geoquimicos na prospecgao 

de jazigos minerals: Soc. Estudos da Col6nia de Mogambique Bol. 

(Lourenc.0 Marques), ano XX, no. 67, Oct.-Dec. 1950, p. 99-114.

Polynov, B. B., 1937, The cycle of weathering, London, Thos. Murby and Co.

Raeburn, C., and Milner, H. B., 1927, Alluvial prospecting, London, Thos. 

Murby and Co.

Rankama, K. K., 1940, On the use of trace elements in some problems of 

practical geology: Soc. ge"ol. Finlande Comptes rendus, v. 14, p. 92-106.

Rankama, K. K., and Sahama, T. G., 1950, Geochemistry, Chicago, Univ. 

Chicago Press.

Ratsbaum, E. A., 1939, Field spectroanalytical laboratory for servicing prospecting parties (in Russian): Razvedka Nedr, vol. 10, no. 1, p. 38-41. 

Translation by V. P. Sokoloff in "Selected Russian papers on geochemical 

prospecting for ores," U. S. Geological Survey, p. 1-6, Feb. 1950.

Reiche, Parry, 1950, A survey of weathering processes and products: New 

Mexico Univ. Pub. in Geology, no. 3.

Reichen, L. E., 1951, Geochemical field method for determination of nickel 

in plants: Anal. Chemistry, v. 23, p. 727-729.

Reichen, L. E., and Lakin, H. W., 1949, Field method for the determination 

of zinc in plants: U. S. Geol. Survey Circ. 41.

Reichen, L. E., and Ward, F. N., 1951, Field method for the determination 

of molybdenum in plants: U. S. Geol. Survey Circ. 124.

Riddell, J. E., 1950, A technique for the determination of traces of epiprenetic 

base metals in rocks: Quebec Dept. Mines, Prelim. Rept. 239.

 1952a, Preliminary report on hydrochemical analyses of streams ajid 

rivers in the Gasp£ peninsula: Quebec Dept. Mines, Prelim. Rept. 268.

 1952b, Anomalous copper and zinc values in trees in Holland Township, Gasp -North County: Quebec Dept. Mines, Prelim. Rept. 269.
348 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

 1954, Geochemical soil and water surveys in Lemieux Township,

Gaspe-North County: Quebec Dept. Mines, Prelim. Kept. 302. 

Riley, G. A., 1939, Limnological studies in Connecticut: Ecol. Mon. v. 9, p.

53-94. 

Roberts, R. 0., 1953, Geochemical investigations in Nigeria in 1948 and 1949:

Colonial Geol. and Min. Res. v. 3, no. 4, p. 347-357. 

Robinson, W. 0., 1951, The minor or trace elements in soils, plants, and

animals: U. S. Dept. Agr. (unnumbered leaflet). 

Robinson, W. 0., and Edgington, Glen, 1945, Minor elements in plants and

some accumulator plants: Soil Sci., v. 60, p. 15-28. 

Rosenqvist, A. M., and Vogt, Thorolf, 1943, Geokjemisk eg geobotanisk

malmleting. V. Bestemmelse av kobber i vannpr0ver, analysemetoden:

K. norske vidensk. selsk. Forh., v. 15, p. 83-86. 

Ruchhoft, C. C. and Setter, L. R., 1953, Application of biological methods

in the treatment of radioactive wastes: Sewage and Indus. Wastes, v.

25, p. 48-60.

Rudolfs, W. and Helbronner, A., 1922, Oxidation of zinc sulfide by microorganisms: Soil Sci., v. 14, p. 459-464. 

Saito, Nobufusa, 1951, The existence of radiocolloids in natural waters:

International Assoc. Hydrologists, Brussels, Assembly, August 1951

(from Chem. Abs. v. 47, column 11607). 

Salmi, Martti, 1950, Trace elements in peat: Geol. Tutkimuslaitos, Geotek.

julkaisuja, no. 51. 

Saukov, A. A., 1946, Geochemistry of mercury (in Russian): Akad. Nauk

SSSR, Inst. Geol. Nauk Trudy, v. 89, Mineral-Geol ser. no. 17. 

Sauramo, Martti, 1924, Tracing of glacial boulders and its application in

prospecting: Comm. geol. Finlande Bull. 67. 

Schmitt, Harrison, 1939, Outcrops of ore shoots: Econ. Geology, v 34 p.

654-673. ' ' 

Scott, Jean, Collins, G. A., and Hodgson, G. W., 1954, Trace metals in the

McMurray oil sands and other Cretaceous reservoirs of Alberta:

Canadian Inst. Min. Metallurgy Bull., v. 47, no. 501, p. 36-42. 

Seidell, Atherton, 1940, Solubilities of inorganic and metal organic compounds V. 1, 3rd edition, 1698 p., with supplement, 1952, 1254 p., New

York, D. VanNostrand Co., Inc. 

Sergeev, E. A., 1941, Geochemical method of prospecting for ore deposits

(In EUSSl&n) Materialy VsCSOiUZnogO Nauchno-Issledovatel'skogO Geologicheskogo Instituta, Geonzikfl, SbOmlK HO; p. 3-55. Translation by 

V. P. Sokoloff in "Selected Russian papers on geochemical pr6St)6Ctin£

for Oles,» v. s. Geol Survey, p. 15-87, Feb. 1950. 

_____ 1946a, Water analysis as a means ox P *>-«-« for metallic ore

deposits (in Russian): Razvedka Mt V, 12, HO, 2, p, 51-56. Translation 

by H. E. Hawkes in "Selected Russian papers on geochemical proSpfiCtlfl? 

for ores," v. s. GOOI. survey, p. 7_12, Feb. 1950.

1946b, A new lumillOSCOpe for field use (in R^W .. Ttazveaka Nedr,

v. 12, no. 5, p. 41-42. Translation by V. P. Sokoloff in "Selected Russian 

papers on geochemical prospecting for ores," U. S. Geol. Survey, p. 13-14, Feb. mo.

Shaw,, D. M., 1952, The geochemistry of Miflffl! ^Cto «s~~v,m^ at

Cosmochimica, v. 2, p. 118-154. 

Shcherbina, V., 1950, Concentration and dissemination of chemical elements
PRINCIPLES OF GEOCHEMICAL PROSPECTING 349

in the Earth's crust as a result of oxidation and reduction processes 

[abs.]: Internat. Geol. Cong. London, 18th sess. Rept., pt. 2, p. 139. 

Shima, Makoto, 1953a, Geochemical prospecting for manganese ore deposits 

(in Japanese): Repts. Sci. Research Inst. (Japan), v. 29, p. 99-110.

 1953b, Geochemical prospecting for gold, silver, copper, lead, and 

zinc ore deposits. I Prospecting for gold and silver ores (in Japanese): 

Repts. Sci. Research Inst. (Japan), v. 29, p! 111-115.

 1953c, Geochemical prospecting for gold, silver, copper, lead, and zinc 

ore deposits. II Prospecting for zinc and manganese ore deposits (in 

Japanese): Repts. Sci. Research Inst. (Japan), v. 29, pp. 116-120.

 1953d, Geochemical prospecting for gold, silver, copper, lead, and zinc 

ore deposits. Ill Distribution of copper, lead, and zinc in mine districts 

(in Japanese). Repts. Sci. Research Inst. (Japan), v. 29, p. 207-218.

 1953e, Geochemical prospecting for gold, silver, copper, lead, and 

zinc ore deposits. IV Gold (in Japanese): Repts. Sci. Research Inst. 

(Japan), v. 29, p. 245-248.

1953f, Geochemical prospecting for sulfur, pyrite, and limonite ore

deposits (in Japanese): Repts. Sci. Research Inst. (Japan), v. 29, p.

249-258. 

Sigov, A. P., 1939, Heavy mineral investigations (in Russian): Ural. Sci.

Res. Inst. of Geol. Prosp. and Econ. Mineralogy, trans. no. 4. 

Smyth, C. H., Jr., 1913, The relative solubilities of the chemical constituents

of rocks: Jour. Geology, v. 21, p. 105-120. 

Sokoloff, V. P., 1948, Geochemical prospecting for ore: Mines Mag., v. 38, no.

4, p. 21-24

 1949, Geochemical reconnaissance in the Wallaroo mining district: 

South Australia Dept. Mines, Min. Rev. no. 88, p. 32-64.

 1950a, Sampling and testing of soil and rock for copper, lead, and 

zinc in geochemical reconnaissance: Mines Mag., v. 40, no. 11, p. 15-22.

 1950b, Dispersion of gold in rock and soil: Chem. Eng. and Min. Rev., 

v. 43, no. 1, p. 7-10.

 1950c, Geochemical prospecting methods bring results in Australia: 

Min. World, April, 1950, p. 26-28; v. 12, no. 4, p. 26-28.

1951a, Geochemical exploration for copper in the Wallaroo mining

district, South Australia: Acta Geochimica et Cosmochimica, v. 1, p.

284-298. 

 1951b, Exploration for copper in Wallaroo mining district, South

Australia: Chem. Eng. and Min. Rev., v. 43, p. 331-341. 

Stevens, R. E., and Carron, M. K., 1948, Simple field test for distinguishing

minerals by abrasion pH: Am. Mineralogist, v. 33, p. 31-49. 

Stevens, R. E., and Lakin, H. W., 1949, The chromograph, a new analytical

tool for laboratory and field use."U. S. Geol. Survey Circ. 63. 

Stock, Alfred, and Cucuel, Friedrich, 1934, Die Verbreitung des Quicksilbers:

Naturwissenschaften, v. 22, p. 390-393.

Stoll, W. C., 1945, The presence of beryllium and associated chemical elements in the wallrocks of some New England pegmatites: Econ. Geology,

v. 40, p. 136-141. 

Stow, M. H., 1939, Reflection of provenance in heavy minerals of James

River, Va.: Jour. Sed. Petrol, v. 9, p. 86-91. 

Sullivan, E. C., 1907, The interaction between minerals and water solutions,

with special reference to geologic phenomena: U. S. Geol. Survey Bull.

312.
350 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

Swaby, R. J. and Passey, B. 1., 1953, Availability of trace elements from 

rocks and minerals: Australian Jour. Agr. Research, v. 4, p. 292-304 

(from Chem. Abs. v. 47, column 10164).

Swedish Prospecting Company, 1939, P. M. angaende v&r geokemiska prospekteringsmetod, Malmo, Sweden.

Thiel, G. A., 1925, Manganese precipitation by microorganisms: Econ. Geology, v. 20, p. 301-310.

Thyssen, Stephen von, 1942, Geochemische und pflanzenbiologische Zusammenhange in Lichte der angewandten Geophysik: Beitr, angew. Geophysik, v. 10, p. 35-84.

Tikhomirov, N. I., and Miller, S. D., 1946, On a physico-chemical method of 

prospecting for molybdenum in the semi-desert climate of the northern 

Lake Balkhash area (in Russian): Razvedka Nedr, 1946, no. 2, p. 34-39. 

Translation by H. E. Hawkes in "Selected Russian papers on geochemical 

prospecting for ores," U. S. Geol. Survey, p. 97-103, Feb. 1950.

Tkalich, S. M., 1938, Investigation of vegetation as a guide in prospecting 

(in Russian): Vest. Dal'nevostoch. Filiala Akad. Nauk (Vladivostok), 

no. 32, (5) p. 3-25.

Trenel, M., 1946, Nature and importance of the "exchangeable acidity" of 

soil: Pflanzenernahr. Diingung Bodenk., v. 37, p. 205-221 (from Chem. 

Abs., v. 42, col. 7469).

Truog, Emil, 1951, Mineral nutrition of plants: Madison, Wis., University 

Press.

Umemoto, Shunji, 1953, Studies on the chloride and sulfate content of 

waters and the amounts of chloride and sulfate fixed to the soil in 

the mineral spring district. VII Possibility of chemical prospecting 

of mineral springs (in Japanese): Repts. of the Balneological Laboratory, Okayama Univ., no. 10, March 1953, p. 1-2.

U. S. Geological Survey, 1952, Quality of surface waters of the United

States, 1947: U. S. Geol. Survey Water-Supply Paper 1102. 

Vinogradov, A. P., 1953, The elementary chemical composition of marine 

organisms, New Haven, Sears Foundation for Marine Research, Yale

University, 646 p.

Vogt, J. H. L., 1923, Nickel in igneous rocks: Econ. Geology, v. 18, p. 307-353. 

Vogt, Thorolf, 1939, "Kjemisk" og "botanisk" malmleting ved R0ros: K.

norske vidensk. selsk. Forh., v. 12, p. 81 84.

 1942a, Geojemisk og geobotanisk malmleting. II Viscaria, alpina (L.)

G. Don som "kisplante": K. norske vidensk. aelsk. Forh., v. 15, p. 5 8.

 1942b, Geokjemisk og geobotanisk malmleting. Ill Litt om plankeveksten ved R,0rosmalmene: K. norske vidensk. selsk. Fork, v. 15, p. 21-24. 

1942c, Geojemisk og geobotanisk malmleting. VII Sporelementer

i TO.ymn.alm off sjcimalm: K. norske vidensk. selsk. Forh., V. 15, p. 91 94.

Vogt, ThOI'Olf, and Bergh, H,, 1946, Geokjemisk og geobotanisk malmleting. 

X Bestemmelse av kobber i jordpr0ver: K. norske vidensk. selsk. Fork, 

v. 19, p. 76-79.

 1948a, Geokjemisk og geobotanisk malmleting. XI Sink og bly i

jordprtfver: K. norske vidensk selsk. Forh,, v, 20, p, 100-100,

 1948b, Geokjemisk og geobotanisk malmleting. XII Bestemmelse av 

jem og mangan i jordprtfver: K. norske vidensk. selsk. Forh., v. 20, 

p. 106-111. .
PRINCIPLES OF GEOCHEMICAL PROSPECTING 351

Vogt, Thorolf, and Braadlie, 0., 1943, Geokjemisk og geobotanisk malmleting. IV Plankevekst. og jordbunn ved R0rosmalmene: K.. norske 

vidensk. selsk. Forh., v. 15, p. 25-28.

Vogt, Thorolf, Braadlie, 0., and Bergh, H., 1943, Geokjemisk og geobotanisk 

malmleting. IX Bestemmelse Cu, Zn, Pb, Mn, og Fe i planter fra 

R0rosfeltet: K. norske. vidensk. selsk. Forh., v. 16, p. 55-58.

Vogt, Thorolf, and Bugge, Jens, 1943, Geokjemisk og geobotanisk malmleting. VIII Bestemmelse av kobber i planter fra R0rosfeltet ved 

kvantativ r0ntgenanalse: K. norske vidensk. selsk. Forh., v. 16, p. 51-54.

Vogt, Thorolf, and Rosenqvist, A. M., 1943, Geokjemisk og geobotanisk 

malmleting. VI Bestemmelse av kobber i vannpr0ver fra R0rosfeltet: 

K. norske vidensk. selsk. Forh., v. 15, p. 87-90.

Ward, F. N., 1951a, Determination of molybdenum in soils and rocks: Anal. 

Chemistry, v. 23, p. 788-791.

 1951b, A field method for the determination of tungsten in soils:

U. S. Geol. Survey Circ. 119. 

Ward, F. N., and Lakin, H. W., 1954, Determination of traces of antimony

in soils and rocks: Anal. Chemistry, v. 26, p. 1168-1173. 

Ward, F. N., and Marranzino, A. P., 1955, Field determination of microgram

quantities of niobium in rocks: Anal. Chemistry, v. 27, p. 1325-1328. 

Warren, H. V., and Delavault, R. E., 1948, Biogeochemical investigations in

British Columbia: Geophysics, v. 13, p. 609-624.

 1949, Further studies in biogeochemistry: Geol. Soc. America Bull., 

v. 60, p. 531-560.

 1950a, Gold and silver content of some trees and horsetails in British 

Columbia: Geol. Soc. America Bull., v. 61, p. 123-128.

 1950b, A history of biogeochemical investigations in British Columbia: 

Canadian Min. Metallurgy Bull., v. 43, p. 344-350.

 1952, Trace elements in geochemistry and biogeochemistry: Sci. 

Monthly, v. 75, p. 26-30.

 1953a, Geochemical prospecting finds widespread application in 

British Columbia: Min. Eng., v. 5, p. 980-981.

1953b, Biogeochemical investigations in eastern Canada (abst.): Geol.

Soc. America Bull., v. 64, p. 1487-1488. 

Warren, H. V., Delavault, R. E., and Irish, R. I., 1949, Biogeochemical researches on copper in British Columbia: Royal Soc. Canada Trans., v. 

43, p. 119-137.

 1951a, An improved dithizone field test for heavy metals in water: 

Geol. Soc. America Bull., v. 62, p. 609-618.

 1951b, Further biogeochemical data from the San Manuel copper 

district, Final Co., Ariz.: Geol. Soc. America Bull., v. 62, p. 919-929.

 1952a, Preliminary studies on the biogeochemistry of iron and manganese: Econ. Geology, v. 47, p. 131-145.

 1952b, Biogeochemical investigations in the Pacific northwest: Geol. 

Soc. America Bull., v. 63, p. 435-484.

1953, Acetonic dithizone in geochemistry: Econ. Geology, v. 48, p.

306-311. 

Warren, H. V., and Howatson, C. H., 1947, Biogeochemical pr.ospecting for

copper and zinc: Geol. Soc. America Bull., v. 58, p. 803-820. 

Webb, J. S., 1953, A review of American progress in geochemical prospecting

and recommendations for future British work in this field: Inst. Min.

Metallurgy Trans., v. 62, pt. 7, p. 321-348.
352 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

Webb, J. S., and Millman, A. P., .1950, Heavy metals in natural waters as

a guide to ore: a preliminary investigation in West Africa: Inst. Min. 

 Metallurgy Bull., no. 518, p. 3-16.

 1951, Heavy metals in vegetation as a guide to ore: Inst. Min. Metallurgy Trans., v. 60, pt. 2, p. 473-504. 

White, C. H., 1924, Prospecting for disseminated copper by a study of

leached croppings: Eng. and Min. Jour.-Press, v. 117, p. 483-488. 

White, W. H., 1950, Plant anomalies related to some British Columbia ore

deposits: Canadian Inst. Min. Metallurgy Bull. 459, p. 368-371. 

White, W. H., and Alien, T. M., 1954, Copper soil anomalies in the Boundary

district of British Columbia: Min. Eng., v. 6, p. 49-52. 

Williams, David, 1954, Geochemical prospecting research center at the Royal

School of Mines, Imperial College of Science and Technology: Inst.

Min. Metallurgy Trans., v. 64, pt. 2, p. 51-58. 

Williams, D. E., and Coleman, N. T., 1950, Cation exchange properties of

plant root surfaces: Plant and Soil, v. 2, p. 243-256. 

Wilska, Seppo, 1952, Trace elements in Finnish ground and mine waters:

Annales Acad. Sci. Fennicae, ser. A, II, no. 46, p. 7-76. 

Wilson, H. D. B., 1944, Geochemical studies of the epithermal deposits at

Goldfield, Nevada: Econ. Geology, v, 39, p. 37-55. 

Wilson, M. E., 1935, Rock alteration at the Amulet mine, Noranda district,

Quebec: Econ. Geology, v. 30, p. 478-492. 

Zenin, M. F., 1935, Experimental cuprometric survey in Almalike (in

Russian): from "Geology of Central Asia," v. 1, p. 58-75. 

ZoBell, C. E., 1946, Studies on redox potential of marine sediments: Am.

Assoc. Petroleum Geologists Bull., v. so, p. 477-513.
INDEX

Page 

A 

Absorption ..............1.......... 255 256

Abundance of elements in

earth materials .................. 227-230

Acknowledgments .................. 227

Adsorption ............ 254-255, 283, 306, 809

Aluminum:

distribution, in plants .......... 228

in rocks ................... 228, 236

in water ................... 229

mobility ........... 250, 251, 260, 263, 270

Analytical techniques, 

chromatographic .................. 332

colorimetric ................... 330-331

spectrographic ......... 314, 315, 331-332

Animal activity .................... 280

Antimony:

distribution, in rocks ........... 228

in residual cover ........... 274

mobility ....................... 274

Area! dispersion patterns ....... 240-241,244

Arsenic:

distribution, in plants .......... 292

in precipitates ............. 287

in residual cover ....... 234, 273, 274

in rocks ................... 228, 244

in water ................... 229

mobility ............... 253,259,265,274

B

Background ................ 227-230, 233, 335

Barium:

distribution, in detrital 

minerals ..................... 304-305

in plants .................. 228

in residual cover ........... 276

in rocks ................... 228

in water ................... 229

mobility ............... 262-254,263,269

Beryllium, distribution, in rocks ..... 228, 244

mobility ................... 250, 259, 269

Boron, distribution, in 

detrital minerals .................. 302

in plants ...................... 228,292

in rocks ....................... 228, 239

in sediments ................... 239

in water ...................... 229,239

Cadmium:

distribution, in plants .......... 298

in rocks ................... 228

mobility ....................... 250

Calcium:

distribution, in plants .......... 228, 292

in rocks ................... 228, 236

in water ................... 229

mobility ............... 262, 254, 265, 263

Page

Chromium :

distribution, in detrital minerals.. 802 

in plants .................. 296

in rocks ................... 228

in water .................. 229

mobility ....................... 250, 264

Cobalt:

distribution, in plants .......... 298

in precipitates ............. 312

in residual 

cover ........ 234, 241, 273, 274, 280

in rocks ............... 228, 236, 241

in sediments ............... 306

in water .................. 229, 307

mobility ........... 250, 253, 259, 265, 274

Colloidal solutions .................. 260

Complex ions, inorganic ............ 268

Contamination ..................... 335 336

Contrast of geochemical anomalies .. 234-235 

Copper:

distribution, in detrital minerals.. 304 

in plants ...... 228, 234, 292, 294-296,

298, 299 

in precipitates ..... 285, 287, 302, 305

in residual 

cover ............... 265, 266, 273,

274, 276, 279, 281 

in rocks ........... 228, 236, 241, 244

in sediments ............... 306, 312

in transported 

cover ........ 243, 278, 286, 287, 288

in water .............. 229,309-311

mobility .......... 250-253, 256, 258, 269,

261, 262, 266, 269, 270, 274,

305, 309

Coprecipitatlon ........ 253-264, 287, 805, 811

Definition of terms ................ 336-338

Dithizone method of analysis ........ 265, 311

E 

Exchange reactions.. 254-255, 283-289, 290, 330

F 

Fluorine:

distribution, in rocks .......... 228,236

in water .................. 229,306

mobility ....................... 262

Frost action ....................... 278-280

Gallium:

distribution,

in rocks

mobility ...

in precipitates 305

228

269

353
354 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

Page 

Gaseous dispersion ................. 245-246

Geochemical cycle .................. 230 232

anomalies ............. 227, 233-236, 273

provinces ...................... 237 239

Glacial dispersion .................. 276-279

Gold:

distribution, in detrital j

minerals .......... ....' ...... 302, 30 i

in plants .................. 297, 299

in rocks ..................... 228, 239

in water .............. 229, 305, 311

mobility ..............: 259, 264, 265, 269

Gossans ....................;... 275-276,287

H

Heavy metals. See Zinc. 

Homogeneity of geochemical 

anomalies ........................ 235-236

Hydrogen-ion concentration. See pH.

Iron:

distribution, in plants .......... 298,299

in rocks ............... 228,236, 242

in transported cover ........ 278

in water .......... 229, 284, 310, 311

mobility . . . 250, 255-258, 260-263, 270, 310

Lakes ............................. 311-312

Lead:

distribution, in detrital

minerals ..................... 302

in plants .......... 291, 293, 296, 299

in precipitates ............. 302,305

in residual 

cover ....... 265, 266, 273, 276, 281

in rocks .......... 228, 236, 243, 244

in transported cover.... 278,285,288

in water .................. 229

mobility .......... 250, 252, 253, 259, 261

264, 265, 273 

Leakage halos ..................... 241-243

M 

Magnesium:

distribution, in plants .......... 228, 291

in rocks ................... 228, 236

in water ................... 229

mobility ............... 250, 254, 255, 263

Manganese:

distribution, in plants .......... 292, 297

in precipitates ............. 305

in rocks ................... 228

in sediments ............... 306

in transported cover ........ 278

in water ............... 229, 306, 311

mobility . . . 2EO, 251, 256-258. 261. 262. 306 

Marine basins ..................... 312-313

Mercury:

distribution, in detrital 

minerals ..................... 304

in plants .................. 299

Page 

in rocks ................... 228, 246

in water ................... 229

mobility ....................... 246, 250

Microbiological factors

affecting mobility ............ 260-262, 312

Mobility ........................... 246-266

Molybdenum:

distribution, in plants ...... 278, 292, 297

in precipitates ............. 305

in residual cover ........... 274

in rocks ................... 228

mobility ........... 261, 264, 265, 274, 290

N 

Nickel:

distribution, in plants .......... 296

in residual cover ........... 273

in rocks ................... 228,239

in transported cover ........ 288

in water .................. 229, 312

mobility ....................... 250, 259

Niobium:

distribution, in detrital

minerals ..................... 304

in rocks ................... 228, 239

mobility ....................... 269

Ores, composition of ................ 235

Organic metal compounds ...... 259-260, 290

Oxidation potental

Eh .......... 256-258, 261-262, 270, 290, 305

Pathfinder elements ................ 328-329

Petroleum ......................... 245

pH, hydrogen-ion 

concentration .... 249-251, 252, 255, 257, 270,

285, 290, 298, 305, 309, 310 

Plant sampling, 

instructions .......... 293-297, 321-324, 326

Plants, geochemical

dispersion in ................ 228, 289-300

Potassium:

distribution, in plants .......... 228, 292

in rocks .............. 228, 236, 245

in water ................... 229

mobility ............... 254, 255, 262, 263

Primary dispersion ............. 232, 236-246

R

Rare earths:

distribution in detrital minerals . . 303 

in plants .................. 228

in rocks ................... 228,236

mobility ....................... 250

Resistant minerals ...... 268-269, 272, 301-304

Rock sampling instructions ........ 321-324 ,

Rocks, geochemical dispersion

in ...................... 227,228. 236-246
PRINCIPLES OF GEOCHEMICAL PROSPECTING 355

Sampling: instructions ..............

Secondary dispersion ........... 232,

Secondary enrichment of ores ......

Selenium:

distribution, in plants ..........

in rocks ...................

in water ...................

mobility .......................

Silicon:

distribution, in plants ..........

in rocks ............... 228,

in water ...................

mobility .......................

Silver:

distribution, in plants ..........

in rocks ............... 228,

in water ...................

mobility ....... 250, 252, 258, 259,

Sodium:

distribution, in plants ..........

in rocks ...................

in water ...................

mobility .......................

Soil sampling: instructions ..........

Soils and soil formation .... 230, 266,

Solubility of salts .............. 248,

Streams and rivers ................

Stream sediments, heavy 

minerals in ......................

sampling instructions .. 321-324, 

unstable components in ........

Sulfur, sulfate, distribution, 

in plants .................... 228,

in rocks .......................

in water ..................

Superimposed halos .............

Page

321-328

246-313

284

291, 299

228

229

291

228

236, 241

229

260, 263

297, 299

241, 243

229

264, 265

228

228, 236

229

254, 263 

321-326 

280-282 

251-253

300-311

301-304 

327-328 

304-306

292, 299 

228

284, 311 

284-289

Thorium:

distribution, in detrital minerals.. 303 

in rocks ................... 239,241

in sediments ............... 306

mobility ....................... 250

Threshold of geochemical 

anomalies ............... 233, 241, 243, 335

Tin :

distribution, in 

detrital mineraJs ............. 302,304

in plants .................. 302, 304

in residual cover ........... 272, 274

in rocks ............... 228,237-239

in sediments ............... 304

Page 

in water ................... 305

mobility ................... 250, 269, 274

Tungsten:

distribution, in 

detrital minerals ............. 302-304

in plants .................. 296

in residual cover ........... 272, 274

in rocks ................... 288

mobility ....................... 269, 274

U 

Units of measurement .............. 388-339

Uranium :

distribution, in

detrital minerals ............. 303

in plants .......... 234,291,293,297

in rocks ................... 241

mobility ....................... 250,256

Vanadium:

distribution, in plants ...... 228,291,297

in precipitates ............. 305

in rocks ................... 228

mobility .................. 256, 259, 264

Vegetation ................. 228,289-300,326

W

Wall-rock dispersion ........... 240, 243, 244

Water, geochemical dispersion 

in ............... 227-229,282-289,300-312

Water sampling instructions. . 321-324, 326-327 

Weathering ................ 230-232, 246-282

Zinc:

distribution, in detrital minerals.. 302 

in plants .............. 228, 292-299

in precipitates ............. 305,312

in residual 

cover ....... 242-243, 265, 266, 273,

274, 276, 281 

in rocks ........... 228. 236, 242-244

in transported

cover ............ 278, 285,287, 288

in water ...... 229,284,285,307-312

mobility ...... 250-253,255,258,269,261,

262, 264, 265, 270, 274, 290, 

309, 310 

Zirconium :

distribution, in 

detrital minerals ............ 302,303

in rocks ............... 228,236,241

mobility ....................... 250

. S. GOVERNMENT PRINTING OFFICE: 1957 413438