A Paleozoic Geochemical 

Anomaly Near Jerome 

Arizona

GEOLOGICAL SURVEY BULLETIN 1000-C

A CONTRIBUTION TO GEOCHEMICAL PROSPECTING

A PALEOZOIC GEOCHEMICAL ANOMALY 

NEAR JEROME, ARIZONA

By LYMAN C. HUFF

ABSTRACT

The pre-Cambrian copper deposits at Jerome, Ariz., and their enclosing metamorphic rocks are overlain unconformably by a thick sequence of Paleozoic 

formations. Immediately overlying the pre-Cambrian rocks and ores is a marine 

sandstone correlated tentatively with the Tapeats sandstone of the Grand 

Canyon region. Samples of this Tapeats (?) sandstone were collected and. 

analysed for traces of copper, zinc, and lead.

The analyses reveal that the basal sandstone unit of this formation contains 

anomalous copper concentrations of more than 100 ppm (parts per million) 

near Jerome and in an area extending about 2 miles southeast from Jerome.' 

Elsewhere the same basal unit contains about 20 ppm copper. Anomalous 

zinc concentrations of over 100 -ppm are distributed in roughly the same^ 

area, as the copper, but abnormal lead concentrations are. limited to the_ 

immediate vicinity of the ore bodies. It is concluded that the abnormal copper ' 

and zinc content of the basal sandstone represents ore metal eroded from the"' 

ore deposits and incorporated in the sand during deposition. " ;

Apparently geochemical prospecting techniques can be used to identify and 

trace heavy-metal anomalies like that present in the basal Tapeats(?) sandstone. 

The anomaly in this sandstone is much more extensive than most geochemical 

anomalies developed near ore in soil or alluvium. The broad extent of the 

basal Paleozoic anomaly probably results from the great dispersal power of wave 

action and shore currents in a marine environment. A search for other ancient 

anomalies may be helpful in prospecting large areas in which ore-bearing rocks 

are covered unconformably by younger sediments, whether marine or continental.

INTRODUCTION

Surficial dispersion of ore metals such as copper, lead, and zinc 

in water, soils, alluvium, and other sediment has been investigated 

in modern deposits and in those of fairly recent origin such as glacial 

till. However, the possibility that analogous geochemical anomalies 

exist in older rocks, such as basal sandstones or conglomerates, has 

not been investigated. If such anomalies do exist, it may be possible

321784 65 105
106 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING

to use them as drilling guides to prospect vast areas of concealed orebearing formations. This paper describes the investigation of such 

an ancient geochemical anomaly at Jerome, Ariz.

The geology and ore deposits of the Jerome area are being studied 

in detail by a U. S. Geological Survey party consisting of C. A. 

Anderson and S. C. Creasey. After the Geological Survey initiated 

geochemical prospecting investigations in 1946, the writer spent 

parts of several field seasons testing geochemical methods in the 

Jerome area. The initial geochemical investigations of the district 

concerned surface drainage, mine drainage, alluvium, and soils. 

The results of these studies will be incorporated in a detailed report 

concerning the geology and mineral resources of the area being 

prepared by Anderson and Creasey. The chemical investigation of 

the Tapeats(?) sandstone is described separately here because it is a 

new application of geochemical prospecting of possible economic 

significance.

The writer is indebted to H. E. Hawkes, C. A. Anderson, and other 

colleagues of the Geological Survey who suggested a chemical study 

of the Tapeats(?) sandstone and who encouraged and facilitated its 

progress. In addition the writer is indebted to Geological Survey 

chemists mentioned in the text for their painstaking analysis of the 

many samples involved. The Phelps Dodge Corporation kindly 

provided necessary background data and other useful information 

concerning the mines at Jerome.

This paper includes a brief description of the basal Paleozoic or 

Tapeats(?) sandstone and its relationship to the ore bodies at Jerome, 

an account of the sampling, analysis, and results of the geochemical 

study of the sandstone, and a consideration of the use of ancient 

geochemical anomalies as drilling guides.

GEOLOGIC SETTING OF THE BASAL PALEOZOIC

SANDSTONE

The basal Paleozoic formation or Tapeats(?) sandstone overlies

unconformabiy the pre-Cambrian rocks and ore bodies at Jerome. 

In general this formation consists of a well-sorted coarse red sandstone at the base, lenses of white and red sandstone above, and red 

or green siltstone and claystone at the top. The basal unit of this

formation is commonly an arkosic sandstone which contains a few 

small pebbles. The red Color of the basal Unit apparently is caused 

by a ferruginous gram coating and cement. The Tapeats(?) sandstone near Jerome is similar to the Tapeats sandstone at tke Grand 

Canyon, wkicH Has been studied in detail \)j Sharp (1940) and by 

several earlier writers. Sharp concluded that the Tapeats is a shallow-
A PALEOZOIC GEOCHEMICAL ANOMALY NEAR JEROME, ARIZ. 107

water marine deposit derived from a residual soil which was in turn 

derived by thorough chemical weathering of the underlying preCambrian rocks under humid conditions. These conclusions can 

apply equally well to the Tapeats(?)'sandstone of the Jerome area.

The thickness of the Tapeats (?) sandstone near Jerome averages 

about 50 feet but within short distances it ranges from less than a few 

inches to a maximum of about 100 feet. This variation in thickness 

is a consequence of gentle undulations of its base. Apparently this 

formation filled shallow depressions in the surface of the pre-Cambrian 

rocks as it was deposited so that it is thickest in these old depressions 

and thinnest over what must have been low knolls on the pre-Cambrian 

surface. Locally, over what must have been the highest knolls of 

the pre-Cambrian surface, the Tapeats(?) sandstone is missing.

The age of the Tapeats(?) or basal Paleozoic sandstone at Jerome 

is in doubt. Reber (1938) and McKee (1951) correlate this basal 

Paleozoic sandstone near Jerome with the Tapeats sandstone of 

Cambrian age of the Grand Canyon area. McNair (1951), however, 

correlates the basal sandstone at Jerome with the Martin lunestone 

of Devonian age. Until satisfactory index fossils are found in it the 

age of the basal sandstone in the Jerome area will remain doubtful. 

Following a suggestion by C. A. Anderson and S. C. Creasey (personal 

communication) the basal sandstone formation near Jerome is referred 

to here as the Tapeats (?) sandstone to indicate that its Cambrian 

age is not proven.

Near Jerome the Tapeats(?) sandstone is overlain by a thick 

sequence of formations in layer-cake arrangement including, from 

the Tapeats(?) upwards (1) 450 feet of Martin limestone (Devonian), 

(2) 290 feet of Redwall limestone (Mississippian), (3) about 370 feet 

of siltstone and shale of the Supai formation (Pennsylvanian and 

Permian), and (4) more than 1,000 feet of basalt (Tertiary). The 

Tapeats (?) and younger rocks cover much of Mingus Mountain, 

west of Jerome, and the broad valleys near Jerome contain extensive 

alluvial fill. Thus, throughout much of the area near Jerome, the 

pre-Cambrian rocks are concealed beneath younger sedimentary 

rocks (fig. 14).

Because the basal Paleozoic sandstone was derived from the underlying pre-Cambrian rocks and ores it seems probable that the chemical 

composition of these pre-Cambrian rocks and ores largely determined 

the chemical composition of the Tapeats. These pre-Cambrian rocks, 

formerly lumped together as the Yavapai schist (Lindgren, 1926), 

consist of metamorphosed lava flows, tuffs, and tuffaceous sediments 

which are intruded locally by quartz porphyry, diorite, diabase 

(Creasey and Anderson, 1948). About 15 miles south of Jerome, the 

pre-Cambrian Bradshaw granite underlies extensive areas.
108 CONTRIBUTIONS TO .GEOCHEMICAL PROSPECTING

EXPLANATION

Valley fill Paleozoic and

younger rocks

Pre-Cambrian rocks Sample locality

FIGURE 14. Simplified geologic map of Jerome and vicinity, showing where samples of the basal Paleozoi 

sandstone were collected. Geology modified from I/indgren (1926).

The principal mines of ike area are ike United Verde and United 

Verde Extension, both of which are located at Jerome. The United

Verde Extension is known locally as the U. V. X. The United

Verde ore is an irregular pipelike body localized along contacts between

diorite, quartz porphyry, and metamorphosed tuffaceous sediments 

(Reber, 1938). Chalcopyrite and sphalerite are the principal ore

minerals, and tennantite and galena are minor ones. In-addition,

to these ore minerals, the ore body contains quartz, pjrite, specularitGj

magnetite, dolomite, and ctlorite. WJien first discovered by Indians

and early prospectors, the ore body was covered with about 100 feet,

of a limonitic gossan containing oxidized copper minerals. The small 

amount of chalcocite beneath the gossan indicates only minor super-? 

gene enrichment of the ore..
A PALEOZOIC GEOCHEMICAL ANOMALY NEAR JEROME, ARIZ. 109

The U. V. X. ore contains primary minerals similar to those of the 

United Verde, but they have been .replaced largely by supergene 

chalcocite. A deep oxidized zone containing much malachite, chrysocolla, and azurite covers the U. V. X. ore body. This ore body and 

its oxidized zone are completely concealed beneath a cover of younger 

rocks; the story of the discovery of the U. V. X. ore body in 1914 is a 

dramatic chapter in the history of mining (Rickard, 1932, p. 365-379). 

Originally both the United Verde and U. V. X. ore bodies were completely covered by the basal Paleozoic sandstone. The relations of 

these ore deposits and the sandstone are shown in simplified form in 

figure, 15.

The United Verde and U. V. X. ore bodies have been interpreted 

as segments of what was once a single large ore body having a thick 

zone of supergene enrichment (Reber, 1938). According to this 

interpretation the zone of supergene enrichment, which became the 

U. V. X. ore body, was separated from the United Verde ore pipe by 

movement along the Verde' fault in late pre-Cambrian time and 

separated still farther by additional Tertiary movement along the 

fault. An alternative interpretation is that the United Verde and the 

U. V. X. have always been separate ore bodies. This problem is 

vital to interpreting the genesis of these ore bodies but is of only 

minor importance to this geochemical prospecting study. As far as 

the geochemical study is concerned, the important fact is that both 

of these ore bodies must have been undergoing weathering and 

erosion at the time the basal Paleozoic sandstone was deposited. 

Because these ore bodies are close to each other they can be considered 

for the purposes of this chemical investigation as a single concentration 

of copper, zinc, and lead.

A

7000'i

,Shale ^^_

____ t | ^ ^ ^Limestone

6000'-

4000'-

3000'-

2000'

K/Tapeats(?) sandstone

5000 Feet

FIGURE 15. Simplified geological cross section showing relationship of basal Paleozoic sandstone to ore 

deposits at Jerome. Modified from Rcber (1938).

321784 55 2
110 . .CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING

Reber (1938) states that over 99 percent of the ore production of 

the Jerome district has come from the United Verde and United 

Verde Extension mines. Other known ore bodies of the district, such 

as the Copper Chief and the Iron King, lie in the belt of pre-Cambrian 

outcrop extending southeast from Jerome along the east flank of 

Mingus Mountain. Some gold mines are near Cherry, about 12 

miles southeast of Jerome; one copper mine, the Yaeger, is located 

about 7 miles southwest of Jerome on the west flank of Mingus Mountain; other small mines and prospects are distributed throughout the 

the outcrop area of pre-Cambrian rocks. All of these mines are 

smaller than the mines at Jerome. According to Reber, many of 

these deposits were hardly adequate to supply the stockholders with 

ore specimens. Thus, it seems likely that the contribution of copper 

and zinc from these ore bodies to the Tapeats(?) sandstone was 

smaller than that of the United Verde and U. V. X. ore.

GEOCHEMICAL INVESTIGATION OF THE BASAL PALEOZOIC SANDSTONE

The geochemical investigation described here was made to determine whether a detectable amount of copper derived by erosion 

of the Jerome ore bodies was incorporated in and deposited with the 

Tapeats(?) sandstone. Both the vertical and horizontal distribution 

of copper and zinc within the Tapeats(?) sandstone were investigated. 

At 18 localities each lithologic unit of the formation was sampled. 

Depending upon the local thickness and lithologic variation of the 

Tapeats(?) the number of samples collected at each site ranged from 

2 to 7. Samples representing only the basal member were collected 

at 19 additional localities. The locations of all of the sample sites 

are shown in figure 14.

The sampling method consisted of knocking small chips from good

exposures with a prospecting pick. Each sample consisted of 6 to

10 chips from an area about 6 feet in diameter. Pint cardboard

cartons served as sample containers.

After the samples were ground to a powder on a bucking board,

they were analyzed by field-type tests for total heavy-metal content

(Huff, 1951) and. oopper (Stevens and Laltin, 1949). Tliese fieldtype analyses indicated that throughout a considerable area near and

south of Jerome the heavy-metal content in the basal sandstone 

member is higher than normal. Near Jerome the total heavy-metal

wm/ejnfc ranges from so \,v goo ppm, whereas it arerages less than 70

ppm elsewhere.

The field-type tests are not very suitable for detecting small differences in metal content. For this reason all or tne samples were

analysed for copper, lead, and zinc by a more accurate laboratory-
A PALEOZOIC GEOCHEMICAL ANOMALY NEAR JEROME, ARIZ. HI

type analysis (Holmes, 1945). The laboratory analyses permit a 

better discrimination between high and low samples than the fieldtype analyses (table 1). Duplicate analyses by the laboratory method 

were made for some of the samples (table 1). It is evident that the 

errors involved in analysing these samples by the laboratory method 

are small in comparison with the total range of metal content among 

the samples.

TABLE 1. Metal content, in parts per million, of the basal member of the Tapeats(?)

sandstone

[Samples listed in order of increasing copper content, with duplicate determinations given where available. 

Analyses made by H. E. Crowe and J. P. Schuch]

Sample no.

6... --------------

7__-- ----------

11---. -------

22---. -------

25- 

26. ---------------

10 

56 

20 

36 

38 

27... ----------

37. -

14 - 

3 

5_ 

15 

41..-- --------

4 _ 

42-.-. -------

44. ---------------

43 

24. -_---_---_-_.--

Field test

Total 

heavy 

metal a

75 

75 

75 

100 

50 

50 

75 

100 

50 

100 

50 

50 

75 

50 

100 

75 

75 

250 

225 

200 

100 

275 

225

Copper s

10 

10 

10 

10 

10 

10 

10 

10 

10 

10 

10 

10 

10 

10 

10 

10 

100 

10 

100 

50 

50 

100 

150

Laboratory analysis '

Copper

4, 10 

4, 10 

7, 10 

10, 13 

10, 15 

10, 15 

15, 15 

10, 20 

15, 25 

20, 24 

25, 27 

25, 29 

20, 50 

40, 44 

54 

54, 55 

60, 75 

70, 90 

90, 100 

110, 130 

130, 130 

140, 190 

250, 300

Lead

19 

25 

19 

31, 35 

31 

21 

25 

9, 30 

30 

12, 30 

16 

13 

20 

30 

120 

20 

40, 45 

18 

30 

40 

11, 35 

40 

35, 37

Zinc

17 

17 

80 

20, 20 

30 

24 

32 

18, 20 

30 

108, 110 

44 

42 

43 

54 

210 

28 

50, 60 

140 

160 

86 

150, 160 

160 

30, 40

Calculated 

total 

heavy 

metal

26 

27 

89 

34 

44 

35 

46 

32 

47 

124 

61 

59 

83 

83 

267 

60 

99 

184 

214 

156 

226 

252 

184

i Analytical method described by Holmes (1945).

> After digestion for 1 hour in dilute nitric acid; method B of HuS (1951).

 Determination by chromograph (Stevens and Lakin, 1949).

Abnormal copper concentrations within the Tapeats(?) sandstone 

are concentrated mostly in the basal ferruginous sandstone unit 

(table 2). Similar data, which are not given here, show that the 

same generalization can be made for zinc and lead.

The laboratory-type analysis revealed, much better than the fieldtype analyses, the systematic distribution of copper, zinc, and lead 

in the basal unit of the Tapeats(?) sandstone. The normal or background copper content of the basal unit ranges from 5 to 20 ppm, but
112 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING

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A PALEOZOIC -GEOCHEMICAL ANOMALY NEAR; JEROME; .'ARIZ. 113

throughout a large area near Jerome the copper content ranges from 

100 to 270 ppm (fig. 16). The area of abnormal copper content is 

somewhat asymmetric; it extends for 2 miles south of, Jerome and is 

very large in comparison with the cross section of the United Verde 

and U. y. X. ore bodies. In addition, there is one anomalous copper

R. 1 E. R.2 E.

I.;-.? 4 Mile

EXPLANATION

Less than 40 ppm 40 to 80 ppm More than 80 ppm 

FIGURE 16. Geochemical map showing concentration of copper in basal Paleozoic sandstone.

value of 275 ppm about 6 miles south of Jerome. Unfortunately, the 

writer has had no opportunity to collect additional samples at this, 

locality.

The zinc content of the basal Paleozoic sandstone unit has a pattern 

somewhat similar to that of copper with a normal or background concentration of. from 15 to 30 ppm and abnormally high concentrations 

of more ithanlOO ppm near Jerome (fig. 17). The small size of the, 

lead anomaly;as compared with copper and zinc is in conformity with
114 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING ,

R.J E. R.2E. R. 3 E.

.

_ V.KX.^h 

UNITED ^ll MINE ^1,

veaoE ^^^i-^"~ 

A «-- -"^^^ ^^ Jerome

if.

 A

* 

 

f /*

/o

r

*

EXPLANATION

Lees than 40 ppm 40 to 80 ppm More than 80 ppm 

17. Geochemical map showing concentration of zinc in basal Paleozoic sandstone.

the relative abundance of these metals in the ore deposits at Jerome 

(fig. 18).

The abnormal copper and zinc in the basal sandstone could have 

been derived in part from the ore bodies and in part from mineralized 

pre-Cambrian rock surrounding the ore. Dispersion of metals from

either of these sources could explain an anomaly asymmetric with 

respect to the ore bodies. The asymmetry of the anomaly might be

a consequence of southward movement of beach sand and eroded 

materials from the Jerome ore bodies during Tapeats( ?) tune. A zone

of hydrothermal alteration extends for two or three miles southeast

of Jerome. Widespread dissemination of metals in this zone is indicated by the metal content of the associated soil (unpublished

Survey data). Thus, the mineralized pre-Cambrian rocks of this zone 

could also have contributed to the asymmetry of the anomaly.
A PALEOZOIC GEOCHEMICAL ANOMALY NEAR JEROME, ARIZ. 115

Although the data available are inadequate to permit evaluation of 

the contribution of each source to the copper and zinc of the basal 

sandstone member, a discrimination may not be essential for geochemical prospecting.

The geochemical anomaly observed in the basal Paleozoic sandstone 

near Jerome is different ir several respects from geochemical anomalies 

that have been investigated elsewhere. Most copper, lead, or zinc 

anomalies in residual soil have maximum concentrations ranging 

from 1,000 to 10,000 ppm, but extend only several hundred feet. 

The low maximum of the basal Paleozoic sandstone anomaly and 

its broad extent may be the effect of the relatively great dispersing 

power of marine processes. This characteristic of broad areal extent 

and low maximum metal content indicates that anomalies of this

R.I E. R.2 E. R. 3 E.

UHlTtO 

VEKOE 

MINE

Jerome

4 Miles

EXPLANATION

 

Less than 40 ppm 40 to SO ppm More than 80 ppm

FIGURE 18. Qcochemical map showing concentration of lead in basal Paleozoic sandstone.
116 ^CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING

kind may be mapped by samples taken at comparatively broad intervals but that accurate analytical methods are required.

Geochemical anomalies have been classified as primary or secondary according' to whether they were formed in the rocks surrounding the ore at the tune of ore emplacement or whether they were 

formed much later by the weathering and erosion of the ore. According to these definitions, the geochemical anomaly in the basal 

Paleozoic sandstone is secondary in that it was derived by erosion of 

the pre-Cambrian ore bodies and rocks. On the other hand, the 

Paleozoic anomaly was formed long before development of the modern 

secondary anomalies in vegetation, soil, and alluvium that have received most attention hi geochemical prospecting investigations. 

It is possible that geochemical anomalies of secondary origin might 

occur elsewhere in the geologic column; for example, a geochemical 

anomaly of Tertiary age might be revealed by a chemical study of the 

Tertiary gravels near Jerome. In fact, buried anomalies might exist 

anywhere that ore-bearing rocks are overlain unconformably by basal 

conglomerates or sandstones which postdate the ore. This type of 

geochemical anomaly .may necessitate some revision of the simple 

twofold classification of prunary and secondary anomalies.

ANCIENT GEOCHEMICAL ANOMALIES AS DRILLING 

! GUIDES

The foregoing material describes the geochemical anomaly in the 

basal Paleozoic sandstone near Jerome and presents evidence supporting the conclusion that this anomaly was formed by weathering 

and erosion of the exposed ore deposits and neighboring mineralized 

rock at the time that the sandstone was deposited. This study will 

be completed by a consideration of the possible use of such ancient

anomalies in prospecting near Jerome and elsewhere.

The copper deposits of the United Verde and United Verde

Extension mines at Jerome provide good examples of the manner in 

which ore deposits can be concealed by younger rocks. The U. Y. X. 

ore body is completely covered by younger rocks and would very 

probably never have been found if it had not been near the United

Verde deposit. The United Verde deposit itself is less than 1,OQO

feet from the outcrop of the basal Paleozoic sandstone (fig. 15). An 

overlap of the Paleozoic formations extending 1,000 feet farther east

than it does would have covered the United Verde deposit, with the 

result that eyen this deposit might, never have been discovered.

Thus, the discovery of both of these ore deposits can be attributed to

the fortunate progress of erosion that stripped the cover from one of 

them. The situation leads to speculation concerning the possible 

existence of other covered ore deposits near Jerome. According to
A PALEOZOIC GEOCHEMICAL ANOMALY .NEAR : JEROME, ARIZ. 117

;Reber (1922, p. 25) the possibilities are good that additional ore 

.,deposits occur under the Paleozoic and younger rocks near Jerome. 

 Where ore-bearing rocks have a post-ore sedimentary cover, 'the 

.customary method of prospecting is to drill through the cover of the 

.ore-bearing rock. Such drilling, to be "successful, must rely upon 

fitting the sough t-f or ore body directly with "a drill hole or coming

 close enough ;to the ore that geologic evidence of mineralization in the

. core will encourage more detailed exploration. - An average ore tody 

and its mineralized periphery present a very small target to the 

exploration drill, commonly requiring a maximum spacing of holes

.of 100 to 200 feet.

If the drilling program were designed primarily to locate geochemical anomalies measuring at least 1 mile hi diameter, only 1 hole per

anile would be required. Thus, preliminary drilling at wide intervals

 to locate geochemical anomalies might avoid much closely'spaced

 drilling in the search for buried ore'.

The f ayorable results of one experiment .with an ancient geochemical 

anomaly, hardly justifies large-scale prospecting programs based upon 

their use. The use of such geochemical anomalies will be unpractical 

where there have been significant epigenetic changes in the metal

:content of the sedimentary cover. Although the geochemical

 anomaly at Jerome does not appear to have experienced any epigenetic modification in metal .content, without more data it is impossible to say whether the anomaly at Jerome represents the exception 

.jprithe rule. . . , ; 

Another deterrent to the application of geochemical anomalies

 like that of the basal Paleozoic sandstone at Jerome is the difficulty 

in obtaining reliable measurements of low metal concentrations. 

'Most geochemical prospecting investigations deal with'higher metal 

, concentrations, which are easier to measure: An accurate measurement of copper, zinc, and lead in the range of 10 to 200 ppm, as was

 necessary to detect the Jerome anomaly> is considerably more difficult and required a laboratory-type..'analytiqal method. If may 

be anticipated that working in such low ranges will require studies

( of errors involved in sampling and analysis to make.certain that 

these errors are small in comparison with significant variations.

 To balance these difficulties in the use of buried geochemical 

anomalies are the benefits which might possibly accrue through their 

use. Vast areas of pre-Cambrian rocks are overlain by Cambrian

.sandstones in the Eastern and Midwestern States. These areas 

could possibly be prospected by a search for buried geochemical 

anomalies.

The Basin and Range province offers other and perhaps better 

opportunities. Nolan (1950, p. 604) has made some rough estimates
118 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING

of the value of ore deposits concealed by gravel-filled valleys and 

relatively undisturbed lavas in the Basin and Range province. He 

estimates that from one-half to two-thirds of the province is concealed by the young gravels or lavas and that the exposed fraction 

of the province has yielded a production of metals in excess of one 

billion dollars. If it is assumed that the amount of ore is roughly 

proportional to the area (as Nolan does), then it follows that the 

concealed area must contain at least a billion dollars worth of undiscovered ore. Part of the covered area consists of rock pediments 

covered by a thin layer of gravel that could be sampled by shallow 

drilling and therefore seems especially amenable to the search for 

buried geochemical anomalies.

Buried geochemical anomalies might be useful for prospecting in 

many other areas. However, before any extensive prospecting for 

them is attempted we should have more data concerning anomalies 

near known ore bodies. Additional investigations of ancient or 

buried geochemical anomalies in the vicinity of known ore will permit 

a better evaluation of this technique.

LITERATURE CITED

Creasey, S. C., and Andersori, C. A., 1948, Pre-Cambrian stratigraphy and

structure of the Mingus Mountain quadrangle, Arizona [abs.]: Geol. Soc.

America Bull., v. 59, no. 12, pt. 2, p. 1369. 

Holmes, R. S., 1945, Determination of total copper, zinc, cobalt, and lead in

soils and soil solutions: Soil Science, v. 59, p. 77-84. 

Huff, L. C., 1951, A sensitive field test for detecting heavy metals in soil or

sediment: Econ. Geology', v. 46, no. 5, p. 524-540. 

Lindgren, Waldemar, 1926, Ore deposits of the Jerome and Bradshaw Mountains

quadrangles, Arizona: U. S. Geol. Survey Bull. 782. 

McKee, E. D., 1951, Sedimentary basins of Arizona and adjoining areas: Geol.

Soc. America Bull., v. 62, p. 481-506. 

McNair, Andrew H., 1951, Paleozoic stratigraphy of part of northwestern

Arizona: Am. Assoc. Petroleum Geologists Bull., v. 35, p. 503-541. 

Nolan. T. B., 1950, The search for new mining districts: Econ. Geology v. 45,

no. 7, p, 601-609. 

Reber, L. E., Jr., .1922, The geology and ore deposits of the Jerome district

[Arizona]: Am. Inst. Min. Met. Eng. Trans., v. 66, p. 3-26. 

 1938, Jerome.district, in Some Arizona ore deposits: Univ. Ariz. Bull.,

v. 9. no. 4, p. 41-65. 

Rickard, T. A., 1932, A history of American mining: New York, McGraw-Hill

Book Co., 419 p. 

Sharp, Robert P.,. 1940, Ep-Archean and Ep-Algonkian erosion surfaces, Grand

Canyon, Arizona: Geol. Soc. America Bull., v. 51, p. 1235-1270. 

Stevens, R. E., and Lakiri, H. W., 1949, The chromograph, a new analytical tool

for laboratory and field use: U. S. Geol. Survey Circ. 63.

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