Trace Elements in Magnetic 

Concentrates from Stream Sediments 

in Southwestern New MexicoA Potential Tool for Reconnaissance 

Geochemical Exploration in Arid Lands 

U. S. G E 0 L 0 G I CAL SURVEY B U L LET IN 1 56 6 

Trace Elements in Magnetic 

Concentrates from Stream Sediments 

in Southwestern New MexicoA Potential Tool for Reconnaissance 

Geochemical Exploration in Arid Lands 

By T. G. LOVERING and]. A. HEDAL 

U. S. G E 0 L 0 G I C A L S U R V E Y B U L L E T I N 1 5 6 6 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON:1987 
DEPARTMENT OF THE INTERIOR 

DONALD PAUL HODEL, Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

Library of Congress Cataloging·in-Publication Data 

Lovering, T. G. (Tom Gray), 1921-

Trace elements in magnetic concentrates from stream sediments in southwestern New Mexico. 

(U.S. Geological survey bulletin: 1566) 

Bibliography: p. 

Supt. of Docs. no.: I 19.3:1566 

1. Trace elements. 2. Ore deposits-New Mexico. 3. Magnetite-New Mexico. 4. Geochemical 

prospecting. I. Hedal, J. A. II. Title. III. Series. 

QE75.B9 no. 1566 557.3 s 85-600270 

[QE516.T85] [622'.13] 

For sale by the Books and Open-File Reports Section, U.S. Geological Survey, Federal Center, 

Box 25425, Denver, CO 80225 
CONTENTS 

Page 

Abstract ........................................................ . 1 

Introduction ..................................................... . 1 

Composition of magnetic concentrates ............................... . 3 

Sample localities, sampling, and analytical procedures .................. . 4 

Results of investigation ............................................ . 6 

Contact metasomatic deposits ................................... . 6 

Iron Mountain ............................................. . 8 

Copper Flat ............................................... . 9 

Hanover area .............................................. . 12 

Fissure vein deposits ........................................... . 15 

Chloride district ........................................... . 18 

Quartz monzonite intrusive ..................................... . 18 

Cuchillo Negro area ........................................ . 18 

Replacement deposit in limestone ................................ . 18 

Lake Valley district ........................................ . 18 

Discussion ....................................................... . 23 

Distribution of individual elements .................................. . 24 

Barium ...................................................... . 24 

Beryllium .................................................... . 24 

Bismuth ..................................................... . 25 

Chromium .................................................... . 25 

Cobalt ....................................................... . 25 

Copper ....................................................... . 26 

Lead ............................................... · · · · · · · · · · 26 

Manganese ................................................... . 26 

Molybdenum .................................................. . 27 

Nickel ......... · .............................................. . 27 

Strontium .................................................... . 27 

Tin .......................................................... . 27 

Tungsten ..................................................... . 28 

Vanadium .................................................... . 28 

Zinc ..................... · .. · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 29 

Zirconium .................................................... . 29 

Summary and conclusions .......................................... . 29 

References Cited .................................................. . 31 

III 
IV CONTENTS 

ILLUSTRATIONS 

Page 

FIGURE 1. Index map showing location of areas from which magnetic concentrates were collected . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 

2. Sketch map showing location of magnetic concentrate samples from 

the Iron Mountain district . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 

3. Sketch map showing magnetic concentrate sample localities in the 

Copper Flat area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 

4. Sketch map showing location of magnetic concentrate samples in the 

Chloride district . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 

5. Map showing location of magnetic concentrate samples in the Lake 

Valley area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 

TABLES 

Page 

TABLE 1. Median concentrations, anomaly thresholds, and concentration ranges 

of elements in magnetic concentrate samples from New Mexico 5 

2. Distribution of elements in magnetic concentrates from six areas in 

New Mexico . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 

3. Analyses of magnetic concentrates from stream sediments in the Iron 

Mountain district . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 

4. Analyses of magnetic concentrates from stream sediments in the 

Copper Flat area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 

5. Analyses of magnetic concentrates from stream sediments in the 

Hanover area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 

6. Analyses of magnetic concentrates from stream sediments in the 

Chloride district . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 

7. Analyses of magnetic and nonmagnetic heavy-mineral concentrates 

from Cottonwood Creek, Cuchillo Negro area . . . . . . . . . . . . . . 19 

8. Analyses of magnetic concentrates from the Lake Valley area . . . 22 
TRACE ELEMENTS IN MAGNETIC 

CONCENTRATES FROM STREAM SEDIMENTS 

IN SOUTHWESTERN NEW MEXICOA POTENTIAL TOOL FOR 

RECONNAISSANCE GEOCHEMICAL 

EXPLORATION IN ARID LANDS 

BY T. G. LOVERING AND J. A. HEDAL 

ABSTRACT 

Detrital magnetic concentrates were collected from stream sediments at several 

localities in southwestern New Mexico. The concentrates contain magnetite derived from 

the gangue of pyrometasomatic or hydrothermal base metal, tungsten, and tin deposits 

in carbonate host rock and accessory magnetite derived from felsic plutonic rocks that 

are genetically associated with these deposits. Magnetite from these environments commonly contains abnormally high concentrations of the ore metals. Samples were obtained with a hand magnet and were not panned. Analysis of the concentrates reveals 

geochemical anomalies that are traceable downdrainage for several miles under favorable 

circumstances. This study shows that detrital magnetic concentrates can be rapidly 

collected in the field and may provide a useful sample medium for reconnaissance 

geochemical exploration for certain types of mineral deposits in arid lands. 

INTRODUCTION 

The use of stream-sediment samples in reconnaissance geochemical 

exploration for metallic mineral deposits is standard procedure. However, there is less general agreement as to the most useful portion of 

the sediment sample to analyze. Sediment samples may be separated 

into various size fractions by sieving, into heavy- and light-mineral 

fractions by panning, or into magnetic and nonmagnetic mineral fractions with a hand magnet. The magnetic fraction obtained by this last 

operation normally consists of a nearly mohomineralic concentrate of 

detrital magnetite or "black sand," in contrast to the fine-size fraction obtained by sieving, or the heavy-mineral concentrate obtained 

by panning, both of which are composed of heterogeneous assemblages 

of detrital minerals. 

1 
2 TRACE ELEMENTS IN MAGNETIC CONCENTRATES 

Numerous studies of the distribution of ore and indicator elements 

in various size fractions of stream sediments collected downdrainage 

from known deposits have shown that the fine fraction ( -80 mesh) 

generally contains a greater concentration of these elements and a 

longer anomaly train below the deposit than do the coarser fractions, 

and furthermore, the fine fraction can be analyzed directly without 

requiring grinding in the laboratory. However, this sample medium 

may fail to show anomalies related to certain types of deposits such 

as gold-bearing quartz veins and cassiterite deposits, where the values 

tend to concentrate in coarser particles. Furthermore, in arid 

environments characterized by prevalent strong winds, the fine fraction may be so diluted with eolian dust particles as to obscure any 

locally derived anomalies. 

Bulk sediment samples collected at the same localities as the fine 

fraction samples and subsequently panned to yield a heavy-mineral 

concentrate will provide a sample medium that largely compensates 

for deficiencies of the fine-fraction samples, and will generally yield 

metal anomaly patterns more closely related to updrainage mineral 

deposits in arid lands than can be derived from the fine-fraction sediment samples. However, collecting and transporting the bulk samples 

to a water supply, then hand panning each sample to yield an adequate quantity of heavy-mineral concentrate for subsequent analysis 

requires a considerable amount of time and effort. 

Magnetic concentrates share the advantage of fine-fraction sieved 

sediments in that they can be obtained directly from dry sediment 

at the sample site, and they share the advantage of panned concentrates in being relatively free from contamination by windblown dust. 

However, in many areas the abundance of barren detrital magnetite 

derived from mafic igneous rocks or arenaceous sedimentary rocks 

can mask anomalies from magnetite that is genetically related to 

mineral deposits to such an extent that this sample medium is rarely 

used. Nevertheless, magnetite bodies associated with hydrothermal 

or contact metasomatic ore deposits commonly contain highly anomalous concentrations of ore metals (Freitsch, 1970, p. 75-89; Kisvarsanyi and Proctor, 1967; Theobald and Thompson, 1959). Anomalous 

concentrations of zinc and tungsten, reflecting ore deposits of these 

elements in the upstream drainage basin, have been found in detrital 

magnetite concentrates from stream sediments more than 32 kilometers (20 mi) downstream from their source (Theobald and Thompson, 1959). Accessory magnetite from quartz monzonite intrusives that 

are genetically associated with base-metal deposits may also contain 

anomalous concentrations of these metals (Hamil, 1967). 
COMPOSITION OF MAGNETIC CONCENTRATES 3 

This pilot study of detrital magnetite in stream sediments, derived 

from various types of deposits in an arid to semiarid environment, 

was undertaken to investigate the usefulness of detrital magnetic concentrates as a tool for reconnaissance geochemical exploration in arid 

lands of the western United States. The study involves three contact 

metasomatic deposits around felsic intrusives in carbonate rocks (Iron 

Mountain, Copper Flat, and Hanover), one area of fissure vein deposits 

in carbonate rocks (Chloride), one quartz monzonite intrusive 

genetically related to small base-metal deposits (Cuchillo Negro), and 

one lead-silver-manganese replacement deposit in carbonate rock (Lake 

Valley) (fig. 1). 

We are indebted to our colleagues A. V. Heyl and C. H. Maxwell 

who suggested the sample localities and provided background information on the geologic setting of the deposits. Sample analyses were 

performed by D. F. Siems. Map illustrations were prepared by Teresa 

Feder. 

COMPOSITION OF MAGNETIC CONCENTRATES 

Although "black sand" concentrates are composed predominantly 

of the mineral magnetite (Fe30 4), they commonly contain many other 

mineral impurities, which may be present as surface films and fracture coatings, small inclusions, or foreign particles cemented by and 

adhering to detrital magnetite grains. 

Elements, other than iron, which are determined by spectrographic 

analysis of these concentrates, may be either bound within the mineral 

lattice of the magnetite, substituting for ferrous or ferric iron or filling holes in the lattice; or else they may be important constituents 

of foreign minerals associated with the magnetite. These elements may 

be divided into four groups on the basis of their ability to substitute 

for iron in the magnetite lattice and their prevalence in associated 

minerals in magnetic concentrates. Group 1 elements, abundant in 

magnetite but not in accessory minerals, include V and Zn. Group 2 

elements, abundant both in magnetite and accessory minerals, include 

Co, Cr, Mg, Mn, Sn, and Ti. Group 3 elements with limited substitution in magnetite, but abundant in accessory minerals, include Be, Bi, 

Cu, Mo, Ni, Sc, and W. Group 4 elements, which are not concentrated 

in magnetite, but are present in accessory minerals, include Ag, As, 

Au, B, Ba, Cd, La, Nb, Ph, Sb, Sr, Y, and Zr. Table 1 shows the median 

concentrations and observed range of concentrations of 25 elements 

detected in one or more of the 30 samples collected in this study; 

elements are arranged in order of decreasing median concentration. 
4 TRACE ELEMENTS IN MAGNETIC CONCENTRATES 

SAMPLE LOCALITIES, SAMPLING, 

AND ANALYTICAL PROCEDURES 

All of the deposits that were sampled in this investigation are in 

Grant and Sierra Counties, N.Mex.; their approximate locations are 

shown on figure 1. Samples were collected downdrainage at 100-meter 

NEW 

MEXICO 

MAP LOCATION 

10 

1 

2 

3 

4 

5 

6 

10 20 MILES 

20 KILOMETERS 

EXPLANATION 

Iron Mountain 

Cuchillo Negro 

Chloride 

Lake Valley 

Copper Flat 

Hanover 

FIGURE I.-Index map showing location of areas from which magnetic concentrates 

were collected. 
SAMPLING AND ANALYTICAL PROCEDURES 5 

(330-ft) intervals in close proximity to the deposits and at intervals 

of about 2 kilometers (1.6 mi) farthest from the deposits. 

The sampling procedure consists of attaching one end of the keeper 

bar on a horseshoe magnet to one pole of the magnet and inserting 

the other end into a concentration of "black sand" (detrital magnetite) 

in dry stream sediment. The bar with magnetic particles clinging to 

it is then transferred to a sample container and the upper end of the 

bar is detached from the magnet, allowing the adhering particles to 

drop into the sample container. This process is repeated until an adequate sample (about 10 g) is obtained. The keeper bar is then wiped 

TABLE 1.-Median concentrations, anomaly thresholds, and concentration 

ranges of elements in magnetic concentrate samples from 

New Mexico 

[N = detection limit] 

Anomaly 

Element Median Threshold Range 

Percent 

Fe 30. 20-50 

Ca 1. 2. 2-3 

Ti 1. 2. .2->2 

Mg .5 1.5 .2-2 

Mn .3 .7 .1->1 

Zn .1 .2 .05-1 

Parts per million 

v 700 2,000 100-3,000 

Cr 200 1,000 100-3,000 

Zr 200 700 70-1,000 

Ba 200 500 <50-500 

Cu 150 500 15-2,000 

Sr <200 300 N-700 

Ni 100 200 30-500 

Pb 50 200 20-700 

La 50 100 N-100 

Co 50 100 30-100 

w N(<70) 70 N-1,000 

y 30 70 <20-100 

Sn N(<15) 30 N-700 

Sc 12 15 N-20 

Nb N(<30) 50 N-70 

B <20 20 <20-100 

Mo N( <7) 10 N-700 

Bi N(<15) 15 N-50 

Be 5 7 2-30 
6 TRACE ELEMENTS IN MAGNETIC CONCENTRATES 

clean and reattached across the poles of the horseshoe magnet. Sample containers are then sealed, appropriately labeled, and stored for 

transportation to the analytical laboratory, where they are ground to 

a fine powder with ceramic plates and analyzed semiquantitatively 

for 31 elements with a D.C. arc spectrograph. 

RESULTS OF INVESTIGATION 

Detrital magnetite samples, derived from each of the deposits 

investigated, show characteristic compositional features which differ 

from any of the other sample suites. Median concentrations and ranges 

for each element in the samples from each area are shown in table 2. 

CONTACT METASOMATIC DEPOSITS 

The three contact metasomatic deposits sampled differ from each 

other in their geologic setting and in the types of mineral deposits 

with which they are associated. The Iron Mountain deposit in Sierra 

County consists of contact metasomatic iron ore in Paleozoic sedimentary rocks that have been intruded by Tertiary granite, aplite, and 

porphyritic rhyolite. Contact metasomatic skarn zones consist 

dominantly of garnet, magnetite, and hematite as well as a large 

variety of accessory minerals. Minor Cu, Be, Mo, Sn, and W mineralization is associated with the iron. 

The Copper Flat deposit in the Central mining district, Grant 

County, consists of an unexposed granodiorite porphyry lacolith cut 

by a slightly younger quartz latite porphyry stock or plug intruded 

into Lower Mississippian Lake Valley Limestone and the overlying 

Middle and Upper Pennsylvanian Oswaldo Formation, a calcareous 

unit with a basal 9-meter (30-ft) thick shale unit. The stock or plug 

is surrounded by an irregular belt of alteration and replacement in 

the limestone and shale. The shale unit is altered to hornfels and the 

Oswaldo Formation to magnetite, sphalerite, and garnet with minor 

chalcopyrite adjacent to the stock. This deposit was first prospected 

for copper about 1900 and has since produced some iron ore and a 

considerable quantity of zinc. 

The Hanover area, also in Grant County, is characterized by a large 

northerly trending stock of granodiorite porphyry, intruded into the 

Oswaldo Formation at the southern end. The stock is cut by a complex network of granodiorite porphyry and quartz monzonite porphyry 

dikes. The Oswaldo Formation limestone, at the contact with the 

granodiorite stock, has been metasomatized to a calc-silicate skarn 
TABLE 2.-Distribution of elements in magnetic concentrates from six areas in New Mexico 

[n = number of samples, M = median concentration, R = concentration range, N = not detected) 

Iron Mountain Copper Flat Hanover Cuchillo Negro Chloride Lake Valley 

Element (n = 5) (n = 9) (n = 2) (n = 2) (n = 8) (n = 4) 

M R M R R R M R M R 

Percent 

~ 

Fe 50 30-50 30 20-50 50 30 20 20-30 40 30-50 tzj 

Mg 1.5 .7-2 .3 .2-.5 .2-1 .3-.7 .7 .5-1 .7 .5-1 00 

c: Ca .5 .3-3 1 .7-1.5 .3-.5 1-2 1.5 1.5-2 .5 .2-1 t'-4 

Ti .3 .2-1.5 .5 .2-1.5 .5-.7 1.5-2 2 1.5-2 >2 >2 t-3 

Mn >1 .7->1 .3 .2-.5 .3-.7 .1-.15 .3 .2-.5 .7 .7-1 00 

0 

Parts per million ~ 

~ 

z 

B 20 <20-20 20 <20-20 <20-20 N <20 <20-20 <20 <20 < 

Ba 150 <50-200 200 150-500 200-300 150-500 200 200-500 200 200-500 tzj 

00 Be 20 7-30 10 7-15 3-5 5-7 5 3-7 2 2-3 t-3 

Bi <20 N-50 N N-20 N N N N N N ~ 

Q 

Co 70 30-70 70 30-100 50 70 50 50-70 100 100 > 

Cr 100 100-200 200 150-700 150-300 3,000 1,500 700-2,000 1,000 700-1,000 t-3 

~ 

Cu 20 15-30 700 300-2,000 150-1,000 150 150 100-150 200 100-200 0 

La 50 N-100 70 50-100 <50 N 50 <50-100 50 N-100 z 

Mo 20 20-700 20 <10-70 N-10 N N N N N-10 

Ni 50 30-70 200 100-500 50-100 500 150 100-150 200 200 

Pb 30 20-50 500 200-700 30 150 70 50-100 200 100-700 

Sn 500 150-700 N N-300 N N N N-50 20 N-50 

Sr N N <200 <200-200 <200-200 200-500 300 200-700 <200 <200-200 

v 150 100-500 300 200-700 700-3,000 1,500 1,000 500-1,500 1,500 1,500 w N N-1,000 N N N N N N N N 

y 30 <20-100 50 50-70 20 <20-20 30 30-50 30 30-50 

Zn 10,000 700-10,000 3,000 2,000-5,000 500-700 1,500-2,000 1,000 1,000-1,500 1,000 1,000 

Zr 100 70-150 150 100-200 500-1,000 300 500 200-700 700 700-1,000 

-::J 
8 TRACE ELEMENTS IN MAGNETIC CONCENTRATES 

containing masses of magnetite garnet rock from which a considerable 

quantity of iron ore has been produced. Beyond the borders of this 

contact zone there are several large zinc-lead vein and replacement 

ore bodies in the Oswaldo Formation. 

IRON MOUNTAIN 

The Iron Mountain deposit is on the western flank of the north end 

of the range locally known as the Cuchillo Negro Mountains in northern Sierra County in sees. 35, 2, 3, 10, and 11, T. 9-10 S., R. 8 W. (fig. 

2). It extends about 5.6 kilometers (3 Y2 mi) north-south, and ranges 

in width from 0.4 to 0.8 kilometer ( Y4 to Y2 mi). An iron-rich skarn zone 

has developed at the upper contact of a Tertiary granitic intrusive 

and the overlying Paleozoic sedimentary rocks. Limestone beds near 

the contact have been converted to a massive tactite composed 

dominantly of coarsely crystalline magnetite, garnet, and hematite, 

cut by small fractures containing deuteric or hydrothermal fluorite, 

apatite, diopside, hornblende, quartz, feldspar, idocrase, spinel, biotite, 

chlorite, scheelite, powellite, willemite, helvite, bertrandite, pyrite, pyrrhotite, sphalerite, and galena. Massive tactite grades outward 

through a zone of "ribbon rock" consisting of alternating crenulated 

layers of magnetite and of fluorite mixed with a variety of silicate 

minerals, into an outer zone of coarsely recrystallized limestone with 

scattered inclusions of epidote and tremolite (Jahns, 1944). 

Iron ore was mined here in the early 1900's, and during the 1940's 

small deposits of beryllium and tungsten were mined and stockpiled. 

A dump sample of siliceous iron ore from a mine near the summit of 

the Iron Mountain ridge contains anomalously high concentrations 

of Be, Bi, Cd, Co, Cu, F, In, Mo, Ph, Sn, Te, V, W, and Zn. Nonmagnetic 

heavy-mineral concentrates from streams draining the Iron Mountain 

district give strong anomalies for tin and tungsten. 

Five magnetic concentrate samples were collected from a stream 

draining westward from the southern end of the Iron Mountain ridge 

(fig. 2). The results of spectrographic analyses of these five samples 

are shown in table 3. 

Sample 1, from the area of tactite just below a prospect pit, contains highly anomalous concentrations of Mn, Bi, Mo, Sn, W, and Zn. 

Concentrations of these elements in the samples collected farther 

downstream show an irregular fluctuation that cannot be readily 

explained, but the farthest downstream sample (5), taken nearly 3 

kilometers (2 mi) below the deposit, is still highly anomalous in Mn, 

Be, Sn, and Zn. 
RESULTS OF INVESTIGATION 9 

COPPER FLAT 

The Copper Flat deposit is in the Central mining district, Grant 

County, about 5 kilometers (3 mi) west of the old townsite of Santa 

Rita in sees. 19 and 30, T. 17 8., R. 12 W. (fig. 3). At Copper Flat a 

small irregular stock of quartz latite porphyry of probable Late 

Cretaceous age has intruded the basal shale unit and overlying impure limestones of the Middle and Upper Pennsylvanian Oswaldo 

107"40' 

~·~~IJ------------------~f··-------~--?~----·~·~~~~7~---~~~~--~~~~~+~--~:---+~' 

R B W 

1 KILOMETER 

EXPLANATION 

~ Granite intrusive 

---Boundary fault 

..,5 Sample locality 

X Prospect pit 

~ Mine shaft 

]!] 

1 MILE 

FIGURE 2.-Location of magnetic concentrate samples from Iron Mountain district. 
10 TRACE ELEMENTS IN MAGNETIC CONCENTRATES 

TABLE 3.-Analyses of magnetic concentrates from stream sediments in the 

Iron Mountain district 

[Ag, As, Sb, and Sr not detected. N, not detected. D. F. Siems, analyst, USGS] 

Element Sample Nos. 

1 2 3 4 5 

Percent 

Fe 50 30 30 50 50 

Mg 1.5 .7 2 1.5 1.5 

Ca 3 1.5 .3 .3 .5 

Ti .2 1.5 .3 .3 .5 

Mn >1 .7 >1 >1 >1 

Parts per million 

B <20 20 20 <20 20 

Ba <50 70 200 150 150 

Be 7 7 30 20 30 

Bi 20 N N 50 <20 

Co 70 70 30 50 70 

Cr 100 150 700 100 200 

Cu 20 30 15 15 30 

La N 50 100 N 100 

Mo 700 20 30 20 20 

Ni 50 70 30 50 50 

Pb 50 20 30 30 50 

Sc N 20 <10 <10 <10 

Sn 700 150 500 500 700 

v 100 500 100 150 150 

w 1,000 N N 100 N 

y <20 100 30 20 50 

Zn 10,000 2,000 10,000 700 10,000 

Zr 150 150 70 100 70 

Formation. This stock is approximately 0.6 kilometer (1,800 ft) long 

east-west by 0.3 kilometer (900 ft) wide at the surface, and is surrounded by a belt of metasomatically altered rock consisting of a 

silicate hornfels containing garnet, epidote, chlorite, actinolite, 

tremolite, quartz, and chlorite. Within this hornfels are tabular and 

lenticular bodies of magnetite and hematite, locally containing abundant marmatitic sphalerite with subordinate chalcopyrite and 

supergene chalcocite (Hernon and others, 1964; Hernon and Jones, 

1968). 
RESULTS OF INVESTIGATION 

1l!8'fJI':lG'' 

1 KILOMETER 

EXPLANATION 

1 MILE 

~ Quartz latite porphyry stock 

• 1 Sample locality 

!'l Mine shaft 

~ Open pit mine 

>- Mine adit 

11 

FIGURE 3.-Magnetic concentrate sample localities in the Copper Flat area. Base from 

U.S. Geological Survey 1:24,000, Fort Bayaud, 1947, and Santa Rita, 1951. 
12 TRACE ELEMENTS IN MAGNETIC CONCENTRATES 

The area was first prospected for copper about 1900, and later, iron 

ore was mined from surface deposits. Mining of zinc ore began about 

1942, and continued until the mines were closed in 1947. During this 

period, approximately 170,000 tons of zinc ore were produced from 

the deposits at Copper Flat (Muller and Storms, 1948). 

Samples of silicified rock (j asperoid) from the dump of one of the 

old mines contain small amounts of pyrite, sphalerite and galena, 

cuprite, smithsonite, and cerrusite in a gangue of quartz, hematite, 

garnet, tremolite, and actinolite. Analyses of these samples showed 

anomalously high concentrations of V and Mn plus slightly anomalous 

Cr, Cu, Ph, and Zn. 

Six magnetic concentrate samples were collected from Y ellowdog 

Gulch, which drains the western part of the Copper Flat mineralized 

area; and three additional samples were taken from Gold Gulch, which 

drains the eastern part of the area (fig. 3). Spectrographic analyses 

of these nine samples are shown in table 4. 

All of the samples from this area show anomalously high concentrations of Mn, Be, Cu, Ph, and Zn; and all, except sample 5 from 

Y ellowdog Gulch upstream from the mine area, are high in Mo. The 

three samples from Gold Gulch, east of Copper Flat, also show 

anomalously high concentrations of Ba, Ni, and Sn; this may reflect 

contributions from a different source, such as the Mountain Home 

Mine group on Humboldt Mountain at the head of the gulch. Sample 

6, farthest downstream on Y ellowdog Gulch, contains considerably 

more copper and molybdenum and somewhat more zinc than the next 

upstream sample. Sample 6 was taken just below the junction of a 

small tributary gulch on the north, which drains the unprospected 

western part of Copper Flat, and may indicate the presence of an 

undeveloped ore deposit in this area. 

HANOVER AREA 

The Hanover mining area is in sees. 21, 22, T. 17 S., R. 12 W. in 

the Central mining district, Grant County, about 2 to 5 kilometers 

(1 Y2-3 mi) east of Copper Flat. Here a large northerly trending pluton 

of Tertiary granodiorite porphyry was intruded into the Middle and 

Upper Pennsylvanian Oswaldo Formation at the southern end of the 

pluton and into older Paleozoic sedimentary rocks farther north. The 

stock is cut by numerous northerly trending dikes of quartz monzonite 

porphyry and granodiorite porphyry; and the sedimentary rocks, 

which the pluton intrudes, contain large sills of hornblende quartz 

diorite of probable Cretaceous age. A belt of contact metasomatic 

alteration, as much as 240 meters (800 ft) wide, is irregularly developed 
RESULTS OF INVESTIGATION 13 

TABLE 4.-Analyses of magnetic concentrates from stream sediments in the Copper Flat 

~ment 

Fe 

Mg 

Ca 

Ti 

Mn 

B 

Ba 

Be 

Bi 

Co 

Cr 

Cu 

La 

Mo 

Ni 

Pb 

Sc 

Sn 

Sr 

v 

y 

Zn 

Zr 

sw. 

6 

50 

.3 

1 

.5 

.3 

<20 

150 

7 

N 

100 

150 

2,000 

50 

70 

150 

200 

10 

30 

<200 

500 

50 

5,000 

150 

30 

.2 

.7 

.3 

.5 

20 

200 

10 

20 

50 

150 

300 

70 

15 

150 

500 

15 

N 

<200 

300 

50 

3,000 

150 

area 

[N = not detected; D. F. Siems, analyst] 

Yellowdog Gulch 

2 

20 

.2 

.7 

.3 

.3 

20 

200 

7 

N 

30 

150 

300 

70 

10 

100 

500 

15 

N 

<200 

200 

50 

3,000 

150 

Sample Nos. 

3 4 

Percent 

30 

.3 

1 

.7 

.3 

30 

.3 

.7 

.3 

.3 

Parts per million 

20 

200 

10 

20 

70 

300 

1,000 

70 

20 

200 

500 

20 

N 

200 

300 

70 

3,000 

200 

20 

200 

15 

N 

70 

200 

500 

100 

10 

200 

700 

15 

N 

200 

300 

70 

2,000 

200 

NE. 

5 

30 

.2 

.7 

.7 

.5 

<20 

200 

10 

N 

70 

200 

500 

70 

<10 

200 

500 

15 

N 

<200 

300 

50 

3,000 

100 

S. Gold Gulch N. 

7 

30 

.5 

1.5 

1.5 

.5 

20 

200 

10 

N 

70 

700 

2,000 

50 

50 

300 

700 

10 

300 

200 

700 

50 

2,000 

200 

8 

30 

.5 

1.5 

.7 

.3 

20 

500 

10 

N 

70 

300 

1,000 

70 

70 

500 

500 

10 

20 

<200 

500 

70 

2,000 

200 

9 

30 

.3 

1.5 

.2 

.2 

20 

300 

10 

N 

70 

150 

700 

100 

70 

500 

700 

10 

30 

<200 

300 

70 

3,000 

150 

in the Oswaldo Formation adjacent to the contact with the pluton. 

This belt of skarn consists of magnetite nearest the contact grading 

outward into garnet and epidote, and into pyroxene at the outer edge. 

Accessory minerals include quartz, calcite, pyrite, chlorite, actinolite, 

and tremolite. The porphyry adjacent to the contact has locally been 

converted into an aggregate of scapolite, zoisite, epidote, and garnet. 

Within the contact zone chalcopyrite, cubanite, pyrrhotite, and 

sphalerite locally form small ore bodies; larger replacement ore bodies 

of sphalerite and galena are present in the limestone beyond the contact metasomatic zone (Knopf, 1933; Hernon and Jones, 1968). 

Magnetic concentrate samples were collected at two localities in the 

Hanover area. Sample 1 comes from the mouth of a small gulch draining easterly into Hanover Creek about 800 meters (¥2 mi) north of 

Hanover. Sample 2 comes from the mouth of a small gulch that drains 
14 TRACE ELEMENTS IN MAGNETIC CONCENTRATES 

TABLE 5.-Analyses of magnetic concentrates from stream sediments in the Hanover 

Element 

Fe 

Mg 

Ca 

Ti 

Mn 

B 

Ba 

Be 

Co 

Cr 

Cu 

La 

Mo 

Ni 

Pb 

Sc 

Sr 

v 

y 

Zn 

Zr 

area 

[N = not detected; D. F. Siems, analyst] 

Sample 1 

Percent 

50 

.2 

.3 

.7 

.3 

Parts per mill ion 

<20 

300 

5 

50 

300 

150 

<50 

N 

100 

30 

<10 

<200 

3,000 

20 

500 

1,000 

Sample 2 

50 

1 

.5 

.5 

.7 

20 

200 

3 

50 

150 

1,000 

<50 

10 

50 

30 

N 

200 

700 

20 

700 

500 

westerly into Hanover Creek about 1,400 meters (4,000 ft) north of 

Hanover. Spectrographic analyses of these samples are shown in 

table 5. 

The high iron content of both samples indicates that they are relatively pure magnetite concentrates. The Mn, Ba, Cu, V, and Zr contents of sample 1 are somewhat higher than normal. Sample 2 is 

anomalously rich in manganese and copper, and slightly high in 

molybdenum. The absence of anomalous concentrations of zinc and 

lead in these samples is surprising in view of the abundance of zinc 

in the peripheral pyroxene-rich zone of contact metasomatic alteration, and of both zinc and lead replacement deposits in the unaltered 

limestone beyond the zone. Evidently, in this area, these elements 

either were not abundant when the magnetite formed, or were expelled 

from the early high-temperature magnetite zone at the contact, whereas copper was retained. 
RESULTS OF INVESTIGATION 15 

FISSURE VEIN DEPOSITS 

Although the main purpose of this study was to investigate the composition of detrital magnetite concentrates derived from contact 

metasomatic ore deposits, for purposes of comparison, some samples 

were also collected from an area where most of the ore has been derived from fissure veins. 

CHLORIDE DISTRICT 

The Chloride mining district lies largely in sees. 18, 19, 20, and 30, 

T. 11 S., R. 8 W., on the eastern flank of the Black Range in Sierra 

County, about 15 kilometers (10 mi) southwest of the Iron Mountain 

deposit (fig. 4). The rocks exposed in this district consist of isolated 

fault blocks of Pennsylvanian Magdalena Limestone and overlying 

Permian Abo Formation, capped by and locally overlying a thick pile 

of Tertiary andesite flows and tuffs in large gravity slide blocks. The 

andesite is also locally covered by erosion remnants of younger Tertiary rhyolite flows and tuffs. Ore deposits consist of Cu, Ph, Zn, Au, 

and Ag ore bodies in large westerly and northwesterly trending veins. 

Where these veins cut andesitic host rock, the ore is largely gold and 

silver with some copper in a quartz gangue, whereas those in limestone 

yield Ph, Zn, Cu, and Ag ore with little gold in a gangue of quartz 

and calcite. Primary ore mineral assemblages vary in different parts 

of the district. The most common are: free gold, auriferous pyrite, 

argentite, chalcopyrite, bornite, covellite, tetrahedrite, galena and 

sphalerite, that have accessory pyrite, chlorite, barite, and talc (Harley, 

1934, p. 82-84). 

This district produced about $200,000 worth of mixed base- and 

precious-metal ore prior to 1930, after which it was largely dormant 

until the 1981 increase in the price of precious metals stimulated 

renewed exploration and development of some of the old mines in the 

area. 

A panned concentrate of nonmagnetic heavy minerals collected 

about 500 meters (1,500 ft) down Chloride Creek below the old Nana 

Mine contained anomalously high concentrations of lead and copper. 

Another sample from about 300 meters (900 ft) farther downstream 

was anomalously high in lead. 

Four magnetic concentrate Saii}ples were collected from stream sediments along lower Mineral Creek in the northern part of the district, 

and another four along lower Chloride Creek, in and just east of the 

central part of the district (fig. 4). Spectrographic analyses of the eight 

samples collected in this area are given in table 6. 
16 TRACE ELEMENTS IN MAGNETIC CONCENTRATES 

11! w R8W 

1 KILOMETER 

EXPLANATION 

._ 1 Sample locality 

----Fault 

----Vein 

~ Mine shaft 

>- Mine adit 

1 MILE 

1i 

FIGURE 4.-Magnetic concentrate sample localities in the Chloride district. Base from 

U.S. Geological Survey Winston, 1:24,000, 1965. 

These samples are remarkably uniform in composition, the variation in concentration of both major and minor elements among the 

four samples from each of the two creeks is no more than could 

reasonably be expected from four replicate analyses of the same sample, with the exception of tin. The samples from Chloride Creek appear 
RESULTS OF INVESTIGATION 17 

TABLE 6.-Analyses of magnetic concentrates from stream sediments in the Chloride 

district 

[N = not detected; D. F. Siems, analyst] 

E. Mineral Creek w. E. Chloride Creek w. 

Element Sample Nos. 

2 3 4 5 6 7 8 

Percent 

Fe 20 20 20 30 20 30 20 20 

Mg • 5 .5 .5 .5 1 .7 .7 1 

Ca 1.5 1.5 1.5 1.5 2 1.5 1.5 1.5 

Ti 2 1.5 1.5 2 1.5 2 2 2 

Mn • 3 .2 .3 .3 .3 .5 .3 .3 

Parts per million 

B <20 20 <20 <20 <20 <20 20 20 

Ba 200 200 200 200 500 200 300 300 

Be 7 5 5 7 3 5 5 5 

Co 70 50 50 70 50 70 50 50 

Cr 1,000 1,000 700 _,500 1,500 2,000 1,500 1,500 

Cu 150 150 100 100 150 150 150 150 

La 50 100 70 70 <50 50 50 50 

Ni 150 150 100 150 100 150 100 150 

Pb 100 100 70 100 50 50 50 50 

Sc 20 20 15 20 20 20 20 20 

Sn N 30 N N 20 N N 50 

Sr 200 300 300 300 700 300 500 500 

v 1,000 1,500 1,000 1,000 500 1,000 1,000 700 

y 30 50 30 50 30 30 30 30 

Zn 1,000 1,000 1,000 1,000 1,000 1,500 1,000 1,000 

Zr 500 500 700 700 200 300 300 300 

to contain slightly more Mg, Ba, Cr, and Sr, whereas those from 

Mineral Creek are slightly richer in La, Pb, V, and Zr. Tin-bearing 

hydrothermal veins are present in the upper drainage basins of both 

streams about 10 kilometers (6 mi) to the west, and may account for 

the sporadic occurrence of tin in these magnetic concentrates. The 

uniformity in composition of these samples is all the more remarkable 

in view of the fact that they consist of very impure magnetic concentrates, as shown by their low iron content. 

Although these samples contain slightly higher than normal 

amounts of copper and zinc, the uniformity in their composition suggests that they consist of detrital accessory magnetite derived from 

the volcanic rocks, rather than hydrothermal magnetite associated 

with the vein deposits. This conclusion is further supported by the 

observation that magnetite is not a common gangue mineral in the 

veins. 
18 TRACE ELEMENTS IN MAGNETIC CONCENTRATES 

QUARTZ MONZONITE INTRUSIVE 

CUCHILLO NEGRO AREA 

A large quartz monzonite stock on Cuchillo Mountain intrudes Pennsylvanian Magdalena Limestone. Several small contact metasomatic, 

vein and replacement deposits of Cu, Ph, and Zn with a little Ag, have 

been developed in the limestone close to its contact with this intrusive. 

These deposits appear to be genetically related to the quartz monzonite 

stock. Two magnetic concentrate samples were collected from the 

upper basin of Cottonwood Creek in theSE~' sec. 29, T. 11 S., R. 

7 W. from the southern and northern forks of this creek, close to their 

confluence. The drainage basins of both tributaries are entirely within 

the stock, so the magnetic concentrates should represent detrital 

accessory magnetite derived from the stock. Nonmagnetic heavymineral concentrates were also collected at the same localities for comparison. Spectrographic analyses of these samples are shown in table 7. 

Both of the magnetic concentrate samples consist of rather impure 

magnetite as shown by their relatively low iron content. They have 

very similar compositions, suggesting that the magnetite in both 

samples is probably derived from accessory magnetite in the stock. 

The Zn, Ph, and Ni content of these samples is anomalously high, and 

the Cu content slightly high. The corresponding nonmagnetic heavymineral concentrates are much higher in copper and lead than the 

magnetic concentrates, and contain comparable amounts of zinc. These 

metals probably have been derived from small base-metal sulfidebearing veins cutting the stock in the upstream drainage basins of 

the streams. There is considerably more variation in composition between the two nonmagnetic heavy-mineral concentrates than between 

the corresponding magnetic concentrates, probably reflecting the more 

heterogeneous mineralogical composition of the former. 

Although the contact metasomatic magnetite around the Iron 

Mountain stock, a few miles to the northwest, is rich in Mo, Sn, W, 

and Be, the accessory igneous magnetite in these samples shows no 

detectable Mo, Sn, or W, and only small amounts of Be, despite the 

fact that the igneous intrusives in both places are similar. 

REPLACEMENT DEPOSIT IN LIMESTONE 

LAKE VALLEY DISTRICT 

The old Lake Valley mining district is in sec. 21 and the NW~ sec. 

28, T. 18 S., R. 7 W. on Apache Hill, approximately 24 kilometers 

(15 mi) south of Hillsboro in southern Sierra County (fig. 5). It was 
RESULTS OF INVESTIGATION 19 

TABLE 7.-Analyses of magnetic and nonmagnetic heavy-mineral concentrates from 

Cottonwood Creek, Cuchillo Negro area 

Element 

Fe 

Mg 

Ca 

Ti 

Mn 

Ag 

Ba 

Be 

Co 

Cr 

Cu 

La 

Ni 

Pb 

Sc 

Sr 

v 

y 

Zn 

Zr 

[N = not detected; D. F. Siems, analyst] 

S. Fork Cottonwood Creek N. Fork Cottonwood Creek 

Magnetic Nonmagnetic Magnetic Nonmagnetic 

concentrates concentrates concentrates concentrates 

30 

.3 

1 

1.5 

.1 

N 

150 

5 

70 

3,000 

150 

N 

500 

150 

10 

200 

1,500 

<20 

2,000 

300 

0.5 

.15 

20 

1.5 

.05 

Percent 

30 

.7 

2 

2 

.15 

Parts per million 

N 

500 

<1 

<5 

70 

1,000 

1,000 

10 

2,000 

10 

500 

500 

700 

2,000 

>2,000 

N 

500 

7 

70 

3,000 

150 

N 

500 

150 

15 

500 

1,500 

20 

1,500 

300 

2 

.2 

20 

2 

.07 

3 

50 

<1 

10 

200 

700 

1,000 

10 

20,000 

10 

700 

2,000 

700 

700 

>2,000 

discovered in 1878 and produced about 5.8 million ounces of silver 

and some lead prior to 1893. The district was then largely dormant 

until the second World War, when about 50,000 tons of siliceous 

manganese ore was mined. 

The rich silver ore came from irregular replacement mantos in Lower 

Mississippian Lake Valley Limestone on the north side of the southeasterly trending Lake Valley fault. This limestone forms the low 

northerly trending ridge of Apache Hill, and dips easterly. To the west, 

a valley is cut into the underlying Upper Devonian Percha Shale, and 

is flanked by a higher ridge (Quartzite Ridge) on the west side that 

is composed of the Ordovician El Paso Limestone and Lower and Middle Silurian Fusselman Dolomite, which are on the hanging wall side 

of the large northeasterly trending Berenda fault. To the east of the 

mining district, the Lake Valley Limestone is unconformably overlain 
20 TRACE ELEMENTS IN MAGNETIC CONCENTRATES 

107"35' 

2 KILOMETERS 

EXPLANATION 

2 MILES 

e1 Magnetic concentrate sample 

---- Fault, dashed where inferred 

1!1 Mine shaft 

-< Mine adit 

FIGURE 5.-Location of magnetic concentrate samples in the Lake Valley area. Base 

from U.S. Geological Survey Lake Valley, 1:62,500, 1962. 

by Tertiary andesite. South of the Lake Valley fault, the Tertiary 

andesite, on the foot wall side of the fault, is overlain by a large mass 

of upper Tertiary rhyolite, which forms Town Mountain. 

The Lake Valley Limestone has been subdivided into three members, 

the basal Andrecito Limestone Member overlying the Percha Shale 

is barren. The ore bodies are localized at the contact of the middle 

(Alamogordo) member with the upper (Nunn) member, and are largely 
RESULTS OF INVESTIGATION 21 

in the basal part of the upper member. The contact between the middle and upper members has been extensively silicified. In the southern 

part of the district, close to the Lake Valley fault, this siliceous floor 

has been fractured, brecciated, and recemented by ore, which 

penetrates downward about 1 meter (3.3 ft) into the underlying 

Alamogordo. Farther north, the silicified contact zone marks the base 

of the ore. Large barren siliceous replacement bodies (j asperoid) are 

also extensively exposed in the lower Paleozoic carbonate rocks on 

Quartzite Ridge to the west of the district. 

The main ore minerals were cerrusite and cerargyrite with minor 

embolite, native silver, vanadinite and wulfenite and very sparse 

hypogene galena, pyrite, and ankerite, in a gangue of manganiferous 

calcite, limonite, and manganese oxides. There are some small hot 

spring deposits of travertine in the southern part of the district, close 

to the Lake Valley fault. 

The ore deposits are unique in this region, and their origin is still 

controversial. They were long regarded as supergene deposits derived 

from primary sulfide deposits in the Lake Valley Limestone to the 

west, before it was removed by erosion, and that the ore metals were 

transported by ground water to the present site; or possibly, primary 

lead-silver sulfide ore bodies formed· at the present site and subsequently oxidized and slightly redistributed by supergene solutions. 

An alternative explanation is that they are of primary hydrothermal 

origin, formed near the surface by solutions related to those which 

formed the hot spring travertine deposits in Quaternary time (C. H. 

Maxwell, U.S. Geological Survey, oral commun., 1982). 

Samples of red and grayish-green j asperoid from the top of the 

Alamogordo Member in the main district are enriched in silver and 

lead, and some j asperoid bodies in the Fusselman Dolomite close to 

the Lake Valley fault west of the main district also contain 

anomalously high concentrations of silver, molybdenum, lead, and zinc 

(Young and Lovering, 1966, p. D15-D16). A sample of hydrothermal 

calcite from the dump of a small prospect on the southwest side of 

the boundary fault, about 150 meters (450ft) west of the road junction and about 400 meters (Y-1 mi) west of the Lake Valley district, 

contains anomalously high concentrations of lead and zinc. Nonmagnetic heavy-mineral concentrates from the stream valley followed 

by N. Mex. Highway 27, west of Apache Hill, contain anomalously 

high concentrations of lead. Similar samples from the wash followed 

by the Lake Valley fault show sporadic zinc anomalies upstream from 

the district and strong lead and silver anomalies adjacent to the 

district and downstream for at least 1 Y2 kilometers ( 1 mi) beyond it. 

Four magnetic concentrate samples were collected from stream 

sediments in the vicinity of the Lake Valley district (fig. 5). Spectrographic analyses of these samples are given in table 8. 
22 TRACE ELEMENTS IN MAGNETIC CONCENTRATES 

TABLE B.-Analyses of magnetic concentrates from the Lake Valley area 

[N = not detected; D. F. Siems, analyst] 

Sample Nos. 

Element 1 2 3 4 

Percent 

Fe 50 50 30 30 

Mg .7 .5 1 .7 

Ca .3 .2 1 .7 

Ti >2 >2 >2 >2 

Mn .7 1 .7 .7 

Parts per mill ion 

B <20 <20 <20 <20 

Ba 200 200 500 200 

Be 2 2 3 2 

Co 100 100 100 100 

Cr 1,000 700 1,000 1,000 

Cu 200 100 200 200 

La 70 100 <50 N 

Mo N N 10 N 

Nb 50 50 50 70 

Ni 200 200 200 200 

Pb 150 700 200 100 

Sc 20 15 15 10 

Sn 30 50 N N 

Sr <200 <200 200 <200 

v 1,500 1,500 1,500 1,500 

y 30 50 30 30 

Zn 1,000 1,000 1,000 1,000 

Zr 700 700 700 1,000 

All of the samples from this area contain unusually high concentrations of titanium and manganese. Samples 1 and 2 both appear to consist of relatively pure magnetite, as shown by their high iron content. 

The detrital magnetite collected from the stream south of the Lake 

Valley district is probably derived from the Tertiary volcanic rocks 

on the south side of the fault that bounds the district, ~d the 

anomalously high concentrations of some elements in these samples 

may represent leakage from buried mineralization along the strong 

northwest-trending fault zone, which is locally followed by this stream 

(fig. 5). Magnetite is not present in the gangue of the ore deposits nor 

is it an accessory mineral in the host rock. These samples are high 

in lead, particularly sample 2, which was collected just south of the 
DISCUSSION 23 

mining district. A nonmagnetic heavy-mineral concentrate from the 

same locality contained 10,000 ppm (1 percent) lead, and also 3,000 

ppm silver, although silver was below the limit of detection in the corresponding magnetic concentrate. This sample was collected from the 

main drainage on the south side of the andesite-covered hill south of 

the Lake Valley fault, so the high lead and silver values could hardly 

have been derived from the mineralized area of the mines in the Lake 

Valley district on the north side of the main Lake Valley fault. It must 

represent leakage of concealed mineralization along the southern split 

of this fault in the highly altered andesitic volcanic rocks, probably 

from concealed ore bodies in carbonate rocks below these volcanic 

rocks. All of the samples, except this one, also run high in copper, and 

samples 1 and 2 show measurable amounts of tin, although samples 

3 and 4, upstream from the district, do not. 

DISCUSSION 

The suites of elements that are enriched in the majority of magnetic 

concentrate samples are different for each of the areas sampled. The 

two contact metasomatic iron deposits in which magnetite forms the 

gangue of the base-metal mineralization (Iron Mountain and Copper 

Flat) both showed extensive suites of anomalous minor elements 

including those of associated ore. The third, Hanover, showed 

anomalous copper but lacked anomalous zinc, despite large zinc 

deposits in the outer zone of the contact metasomatic belt, but outside the magnetite zone. Concentrates of detrital primary magnetite 

derived from the quartz monzonite stock in the Cuchillo ~ egro area, 

which is related to contact metasomatic deposits of copper, lead, and 

zinc showed anomalously high concentrations of lead, but not copper 

although copper is the predominant base metal in the associated contact metamorphic deposits. Magnetic concentrates from streams 

draining the area of base-metal vein deposits in the Chloride district 

did not reflect this mineralization, as anticipated because magnetite 

is not a gangue mineral of the ore in this district. However, magnetic 

concentrates from the stream that follows the main fault south of the 

Lake Valley district does show a variety of anomalous ore elements 

including lead and manganese, although there is no magnetite 

associated with the replacement ore deposits of manganese and lead 

in limestone in this district. However, this stream follows a fault zone 

with Tertiary andesite on both walls, and is separated from the carbonate rocks containing these deposits by a low andesite-capped hill 

south of the district. Thus, the metal suite in these magnetic concentrates probably is derived in part from accessory rock magnetite in 

the andesite, and in part from magnetite related to concealed 

mineralization at depth along the Lake Valley fault. 
24 TRACE ELEMENTS IN MAGNETIC CONCENTRATES 

The suites of minor elements that are present in higher-than-normal 

amounts in the majority of magnetic concentrate samples from each 

of the areas sampled, are shown below. 

CONTACT METAMORPHIC IRON DEPOSITS 

1. Iron Mountain (5 samples)- Mn, Be, Bi, Mo, Sn, (W?), Zn 

2. Copper Flat (9 samples)- Cu, Mo, Ni, Ph, Sn, Y, Zn 

3. Hanover (2 samples) - Cu, V, Zr 

PRI~ARY MAGNETITE DERIVED FROM QUARTZ MONZONITE ASSOCIATED WITH CONTACT DEPOSITS 

4. Cuchillo Negro (2 samples) - Ti, Cr, Ni, Ph, Sr, V 

BASE-METAL FISSURE VEINS LACKING ACCESSORY 

MAGNETITE 

5. Chloride district (8 samples) - Ti, Cr, Sc, (Sn?), Sr 

SILVER-LEAD-MANGANESE REPLACEMENTS IN CARBONATE ROCKS, LACKING ACCESSORY MAGNETITE 

6. Lake Valley district (4 samples)- Ti, Mn, Co, Cr, Nb, Ni, Ph, Sn, 

V, Zr 

DISTRIBUTION OF INDIVIDUAL ELEMENTS 

BARIUM 

This element has too large an ionic radius to substitute for either 

ferrous or ferric iron, so that in magnetic concentrates it reflects the 

presence of detrital mineral impurities, generally grains of barite, 

mechanically trapped with the magnetite. In none of the sample suites 

did a majority of the samples contain anomalously high barium concentrations, and the samples that were high in barium all show less 

than 50 percent iron indicating that the sample contained a high proportion of foreign mineral particles. 

BERYLLIUM 

Beryllium can substitute to a limited extent for iron in magnetite. 

The only area in which the majority of magnetic concentrates show 

unusually high amounts of beryllium is Iron Mountain, where the 

mineral helvite, an iron-manganese-beryllium silicate, occurs in a 

magnetite gangue in the mineral deposit. Many samples from the Copper Flat area also appear to be slightly enriched in beryllium, although 

no known beryllium minerals are associated with this deposit. 
DISTRIBUTION OF INDIVIDUAL ELEMENTS 25 

BISMUTH 

Bismuth is not commonly detected in detrital sediment samples of 

any kind. Its ability to enter the mineral lattice of magnetite is 

extremely limited, and it most commonly occurs as a minor constituent of complex silver and base-metal sulfide minerals. Yet bismuth 

is reported in three of the five magnetic concentrates from the Iron 

Mountain area in concentrations as high as 50 ppm; and it also occurs 

in detectable amounts in two of the nine samples from the Copper Flat 

area. Our limited sample information suggests that detectable bismuth 

in magnetic concentrates is indicative of magnetite closely associated 

with base-metal mineralization, exposed in the upstream drainage 

basin. 

CHROMIUM 

Chromium Cr+3 can readily substitute for ferric iron in magnetite; 

and magnetic concentrates commonly contain as much as 1,000 ppm 

of Cr. One would normally expect that high chromium content would 

be indicative of magnetite derived from mafic or ultramafic igneous 

intrusives, such as those with which chromite deposits are associated. 

It is, therefore, quite startling that the two magnetic concentrates 

with the highest chromium content are those composed of accessory 

magnetite which was derived from the quartz monzonite stock in the 

Cuchillo Negro area, both samples from this locality contained 3,000 

ppm Cr. On the other hand, none of the samples consisting of magnetite derived from contact metasomatic iron deposits contained as 

much as 1,000 ppm Cr. Thus, the only conclusion justified by the data 

is that magnetic concentrates with high chromium are unlikely to 

reflect magnetite associated with contact metasomatic deposits 

around felsic intrusive bodies. 

COBALT 

Cobalt is capable of substituting to a limited extent, for ferrous iron 

in magnetite, and is commonly present in magnetic concentrates in 

amounts of several tens of parts per million; however, concentrations 

of 100 ppm or more are unusual. The only area in which the majority 

of samples showed this much cobalt is the Lake Valley district. The 

source of this magnetite is not definitely known, so the significance 

of the high cobalt concentration here is also open to speculation. 
26 TRACE ELEMENTS IN MAGNETIC CONCENTRATES 

COPPER 

The Cu+2 ion is comparable in size to the Fe+2 ion, and the copper 

content of magnetite increases during the late stage of magmatic differentiation as much as 150 ppm in hydrothermal and contact metasomatic deposits (Freitsch, 1970, p. 77). Higher concentrations are apt 

to reflect the presence of primary copper minerals in the magnetic concentrates. Magnetic concentrates from the Copper Flat area are consistently high in copper, as is one of the two samples from Hanover. 

Copper concentrations of 500 ppm or more appear to reflect copper 

mineralization associated with a contact metasomatic magnetite 

gangue in the upstream drainage basin, and may also indicate detrital 

cubanite mixed with the magnetite. 

LEAD 

The ionic radius of lead is too large for it to substitute for iron in 

magnetite. Although contact metasomatic magnetite with lead content greater than 100 ppm has been reported (Hegemann and Albrecht, 

1954), amounts greater than 100 ppm in magnetic concentrates 

generally reflect the presence of lead mineral impurities derived from 

mineralized rocks. High lead values characterize magnetic concentrate 

samples from Copper Flat, Lake Valley, and Cuchillo Negro. At both 

Lake Valley and Cuchillo Negro, nonmagnetic concentrates collected 

at the same localities contain much higher amounts of lead than do 

the magnetic concentrates. 

MANGANESE 

The Mn+2 ion is similar in size to the Fe+2 ion and manganese can 

substitute to a considerable extent for ferrous iron in magnetite; 

however, manganese minerals such as siderite and various manganese 

oxides are also closely associated with magnetite in detrital mineral 

concentrates. The normal manganese content of our magnetic concentrates ranges from 0.1 to 0. 7 percent, manganese values of 1 percent 

or more are considered anomalous. Samples from Iron Mountain and 

Lake Valley are rich in manganese, which is abundant in the replacement deposits of the latter area. Although these deposits could not 

have yielded the magnetite in the magnetic concentrates, their 

manganese content may reflect an earlier episode of mineralization 

and primary manganese concentration genetically related to the Lake 

Valley deposits. 
DISTRIBUTION OF INDIVIDUAL ELEMENTS 27 

MOLYBDENUM 

Molybdenum, as Mo+4, is capable of substituting to a limited 

extent for ferric iron in magnetite, although its ionic radius is 

somewhat larger. It is most abundant in accessory magnetite derived 

from felsic plutonic rocks (Freitsch, 1970, p. 76). Sample suites from 

the Iron Mountain and Copper Flat areas both contain unusually large 

amounts of molybdenum. Although no molybdenum deposits have 

thus far been discovered at either place, its presence in magnetic concentrates may be indicative of base-metal mineralization. 

NICKEL 

Nickel, like cobalt is capable of limited substitution for ferrous iron 

in magnetite. It normally ranges from about 50 to 250 ppm, although 

amounts as high as several percent have been reported from magnetite 

derived from ultramafic intrusive rocks (Freitsch, 1970, p. 57, 75). Both 

of the samples of detrital accessory magnetite derived from the 

Cuchillo Negro quartz monzonite, as well as two samples from Gold 

Gulch, in the Copper Flat area, contain abundant nickel (500 ppm). 

The significance of these high values is not known, although Freitsch 

(1970, p. 13) points out that the presence of sulfides, such as pyrite 

and pyrrhotite, may produce high nickel values. 

STRONTIUM 

Like barium and lead, strontium is unable to enter the' crystal lattice of magnetite because of its large ionic radius; hence, high strontium values in magnetic concentrates are indicative of contamination 

by nonmagnetic detrital minerals such as barite and calcite. Only the 

-samples from Chloride Creek show consistently high strontium values, 

and these do not appear to have any economic significance. 

TIN 

Tetravalent tin has an ionic radius comparable to that of ferric iron, 

for which it may substitute in magnetite, and it is reported to be particularly abundant in some contact metasomatic iron deposits 

(Freitsch, 1970, p. 86). This is well illustrated by the high tin content 

of the magnetic concentrates from Iron Mountain, and some of those 
28 TRACE ELEMENTS IN MAGNETIC CONCENTRATES 

from Copper Flat. The sporadic occurrence of detectable tin in samples 

from the Chloride district is probably attributable to a different source, 

possibly reflecting the presence of cassiterite-bearing veins in the headwater drainage basins, about 10 kilometers (6.2 mi) upstream. Implications of tin in the two downstream samples from the Lake Valley area 

are unknown, as these magnetic concentrates could not have been 

derived from the replacement deposits in the mining district. It may 

indicate leakage from buried deposits along the Lake Valley fault 

which cuts altered andesite along the stream valley. Tin may also 

reflect contamination from the leaching of old tin cans. 

TUNGSTEN 

We were unable to locate any published reports on the tungsten content of magnetite; however the w+4 ion has the same radius as Mo+4, 

which is very close to that of ferric iron, so tungsten should also be 

capable of substituting to some extent for Fe+3 in the crystal lattice 

of magnetite. According to Rankama and Sahama (1950, p. 629) 

hydrated tungsten oxide, in the weathering zone of tungsten ore, goes 

into solution in alkaline waters, and will react with calcium to 

precipitate secondary scheelite. Tungsten was reported in magnetic 

concentrates only from the Iron Mountain area, where the upstream 

sample closest to the ore deposits contains 1,000 ppm tungsten. This 

suggests contamination of the sample with scheelite, which is an 

accessory mineral in the magnetite ore. Another sample downstream 

from this locality has 100 ppm tungsten. The presence of tungsten 

in magnetic concentrates appears to indicate the existence of tungsten 

deposits exposed in the upstream drainage basin. 

VANADIUM 

Trivalent vanadium has an ionic radius similar to that of ferrous 

iron, for which it substitutes in the magnetite lattice. It is particularly 

abundant in titaniferous magnetite of mafic and ultramafic rocks, 

where it may be present in amounts of 1 percent or more. In contact 

metasomatic iron deposits, it is commonly found in concentrations 

ranging from a few hundred to about 2,000 ppm (Freitsch, 1970, p. 81). 

Only a few of the magnetic concentrates obtained in our study contain more than 1,000 ppm V. One of the two samples from the Hanover 

area has 3,000 ppm V, but the other contains only 700 ppm. All four 

of the magnetic concentrates from the Lake Valley area exhibit 

1,500 ppm V. This consistently high value for all of the samples is 

unusual, but its significance relative to ore mineralization, if any, is 

unknown. 
SUMMARY AND CONCLUSIONS 29 

ZINC 

The Zn +2 ion has the same ionic radius as Fe +2 for which it can 

readily substitute in magnetite. It is most abundant in the magnetite 

of contact metasomatic iron deposits, and in accessory magnetite of 

certain late-stage mafic intrusive rocks (Freitsch, 1970, p. 79-80). Zinc 

is commonly present in magnetic concentrates in amounts ranging 

from several hundred ppm to as much as 10,000 ppm. However, only 

samples containing 3,000 ppm or more Zn are considered to be 

anomalously rich in this element. Three of the five samples from the 

Iron Mountain area contain 10,000 ppm Zn, and six of the nine samples 

from the Copper Flat area run 3,000 ppm or more in Zn. In both areas, 

primary zinc minerals are present in a magnetite gangue in the ore 

deposits. However, the two magnetic concentrates from the Hanover 

area both contain less than 1,000 ppm Zn, despite the fact that one 

of these samples was collected from a short tributary of Hanover Creek 

whose upper drainage basin includes some large zinc deposits. However, these deposits are in or adjacent to an outer zone of contact 

metasomatic alteration characterized by pyroxene-bearing rock that 

is separated from the magnetite zone at the intrusive contact by a belt 

of garnet and epidote-bearing rock. It appears that either most of the 

zinc in this area was expelled from the magnetite zone during metasomatic alteration or that zinc was not abundant in the early intrusive. 

Thus, the presence of high zinc values in magnetic concentrates appears 

to indicate proximity to contact metasomatic iron deposits in which 

zinc minerals are intimately associated with magnetite. 

ZIRCONIUM 

Zirconium is a strongly oxyphile element which does not occur in 

magnetite to any appreciable extent. It is chiefly present in magnetic 

concentrates in the form of detrital zircon impurities. Although some 

samples from Lake Valley and one from Hanover contain 700 to 

1,000 ppm Zr, this only indicates that zircon is an abundant accessory 

mineral in the rocks from which the sediments were derived, and has 

no apparent significance relative to mineral deposits. 

SUMMARY AND CONCLUSIONS 

Detrital magnetic concentrate samples from stream sediments in 

southwestern New Mexico show considerable variation in their minor 

element content. Their composition is a mixture of magnetite and 

associated nonmagnetic mineral impurities. Detrital magnetite from 

skarn zones in c,arbonate rock adjacent to intrusive bodies in which 
30 TRACE ELEMENTS IN MAGNETIC CONCENTRATES 

magnetite is a major gangue mineral for associated mineral deposits 

exhibits an extensive suite of anomalous minor elements including 

those of the associated ore deposits (Iron Mountain and Copper Flat). 

Detrital magnetite derived from skarns in which the magnetite is 

separated from associated ore deposits because of primary zoning may 

not reveal anomalous concentrations of the ore metals (Hanover). 

Detrital magnetite derived from accessory magnetite in an igneous 

intrusive that is genetically associated with mineral deposits around 

its margins may contain anomalous concentrations of some of the ore 

metals (Cuchillo Negro). Detrital magnetite derived from hydrothermal magnetite along fault zones cutting volcanic rocks may also contain an extensive suite of anomalous minor elements that might reflect 

deep seated mineralization along the fault (Lake Valley). Detrital 

magnetite from streams draining areas of barren volcanic rocks, even 

in close proximity to vein deposits that are devoid of accessory 

magnetite, show no anomalies related to the ore deposits (Chloride 

district). 

Anomalously high concentrations of Zn, Ph, Cu, Mo, and Sn in 

magnetic concentrates from stream sediments in this region appear 

to most consistently indicate proximity to mineralized areas. Bismuth 

and tungsten, if present in detectable amounts, are also good 

indicators of mineral deposits. Minor element anomalies in detrital 

magnetic concentrate samples collected during this study suggest the 

possibility of concealed ore mineralization west of Copper Flat and 

also along the Lake Valley fault south of the Lake Valley mining 

district. 

Detrital magnetic concentrates can be readily collected from dry 

stream sediment, and may provide a useful sample medium for reconnaissance geochemical exploration. 
REFERENCES CITED 31 

REFERENCES CITED 

Freitsch, Rudyard, 1970, Trace elements in magnetite and hematite mainly from northern Sweden: Sverges Geologiska Underskoning Arsbok 64, no. 3, 136 p. [in English]. 

Hamil, B. M., 1967, Trace elements in magnetite from Basin and Range quartz monzonites: Ann Arbor, Mich., University of Michigan Ph. D. thesis, 229 p. 

Harley, G. T., 1934, The geology and ore deposits of Sierra County, New Mexico: New 

Mexico School of Mines Bulletin 10, 220 p. 

Hegemann, F., and Albrecht, F., 1955, Zur geochemie oxydischereisenerze: Chemie der 

Erde, v. 17, p. 81-103. 

Hernon, R. M., and Jones, W. R., 1968, Ore deposits of the Central mining district, Grant 

County, New Mexico, in Ridge, J. D., ed., Ore deposits of the United States 1933-

1967: New York, American Institute of Mining, Metallurgical and Petroleum 

Engineers, p. 1211-1237. 

Hernon, R. M., Jones, W. R., and Moore, S. L., 1964, Geology of the Santa Rita 

quadrangle, New Mexico: U.S. Geological Survey Geologic Quadrangle Map GQ306, scale 1:24,000. 

Jahns, R. H., 1944, Beryllium and tungsten deposits of the Iron Mountain district, Sierra 

and Socorro Counties, New Mexico: U.S. Geological Survey Bulletin 945-C, p. 45-79. 

Kisvarsanyi, Geza, and Proctor, P. D., 1967, Trace element content of magnetites and 

hematites, southeast Missouri iron metallogenic province, U.S.A.: Economic 

Geology, v. 62, no. 4, p. 449-471. 

Knopf, Adolph, 1933, Pyrometasomatic deposits, Hanover, New Mexico, in Ore deposits 

of the Western States: New York, American Institute of Mining, Metallurgical and 

Petroleum Engineers, p. 541-542. 

Muller, D. H., and Storms, W. R., 1948, Copper Flat zinc deposit, Central mining district, 

Grant County, N.Mex.: U.S. Bureau of Mines Report of Investigations 4228,8 p. 

Rankama, Kalervo, and Sahama, Th. G., 1950, Geochemistry: University of Chicago 

Press, 912 p. 

Theobald, P. K., and Thompson, C. E., 1959, Reconnaissance exploration by analysis 

of heavy-mineral concentrates [abs.]: Mining Engineering, v. 11, no. 1, p. 40. 

Young, E. J., and Lovering, T. G., 1966, Jasperoids of the Lake Valley mining district, 

New Mexico: U.S. Geological Survey Bulletin 1222D, 27 p. 

1:r U.S. GOVERNMENT PRINTING OFFICE: 1987-773-047/46,062 REGION NO.8