Gold Investigations in 

Precambrian Clastic and 

Pelitic Rocks, Southwestern 

Colorado and Northern 

New Mexico

GEOLOGICAL SURVEY BULLETIN 1272-F

Gold Investigations in 

Precambrian Clastic and 

Pelitic Rocks, Southwestern 

Colorado and Northern 

New Mexico

By FRED BARKER

CONTRIBUTIONS TO ECONOMIC GEOLOGY

GEOLOGICAL SURVEY BULLETIN 1272-F

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1969
UNITED STATES DEPARTMENT OF THE INTERIOR 

WALTER J. HICKEL, Secretary

GEOLOGICAL SURVEY 

William T. Pecora, Director

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D.C. 20402 - Price 25 cents (paper cover)
CONTENTS

Page

Abstract._______________________________________________________ Fl

Introduction- _____________________________________________________ 1

Needle Mountains, Colo__________________________________________ 2

Geologic relations.____________________________________________ 2

Vallecito Conglomerate_______________________________________ 3

Uncompahgre Formation_______________________________________ 10

Tusas Mountains, N. Mex_______________________________________-___ 14

Geologic relations.____________________________________________ 14

Sampling results_____________________________________________ 17

Picuris Range, N. Mex___________________________________________ 18

Geologic relations.____________________________________________ 18

Sampling results_____________________________________________ 19

Comparison with the Central Rand goldfield, South Africa.____________ 19

References cited.__________________________________________________ 21

ILLUSTKATIONS

[All figures are geologic maps]

Page 

FIGURE 1. Needle Mountains, Colo., and index map for figures 2, 3, 4,

and 5__-__-__--___--___-_____------__--_-_-___-_---_- F4

2. Vallecito Conglomerate, Needle Mountains, Colo____________ 6

3. Snowdon Peak area, Needle Mountains, Colo_______________ 11

4. Part of the canyon of the Animas River near Molas Creek,

Needle Mountains, Colo______________________________ 12

5. Uncompahgre Formation, Needle Mountains, Colo__________ 13

6. Tusas Mountains, N. Mex________________________________ 16

7. Picuris Range, N. Mex_________________________________ 20

TABLES

Page 

TABLE 1. Localities and descriptions of samples analyzed for gold.-____ F7

2. Analyses of slates, phyllites, and siltstones of the Uncompahgre

Formation.._ _________________________________________ 14

3. Stratigraphic column of Precambrian rocks in the Tusas

Mountains, N. Mex__________________________________ 18

4. Stratigraphic column of Precambrian rocks in the Picuris

Range, N. Mex___________.____.___._______. _...__ 19

in

CONTRIBUTIONS TO ECONOMIC GEOLOGY

GOLD INVESTIGATIONS IN PRECAMBRIAN CLASTIC AND 

PELITIC ROCKS, SOUTHWESTERN COLORADO AND 

NORTHERN NEW MEXICO

By FEED BARKER

ABSTEACT

A search was made to find fossil placer deposits of gold in the Precambrian 

clastic rocks of southwestern Colorado and northern New Mexico. In Colorado, 

the Vallecito Conglomerate and conglomerates of the Uncompahgre Formation 

of the Needle Mountains were sampled. In New Mexico, the Ortega Quartzite, 

the Big Rock Conglomerate Member, the Jawbone Conglomerate Member, and 

the upper quartzite member of the Kiawa Mountain Formation in the Tusas 

Mountains, and the lower quartzite member of the Ortega Quartaite and the 

conglomerate member of the Vadito Formation of Montgomery (1953) in the 

Picuris Range were sampled. These rocks contain less than 0.1 part per million 

gold, and they apparently were derived from a terrane of quartzite, jasper, 

argillite, and iron-formation that contained virtually no gold.

In addition, carbonaceous slate and schist of the Uncompahgre Formation 

were sampled and analyzed for gold and for 29 other metals. These rocks are 

predominantly low in metals.

INTRODUCTION

This report describes a reconnaissance search for gold in Precambrian clastic and politic rocks of the Needle Mountains of southwestern Colorado and of the Tusas and Picuris Mountains of northern 

New Mexico. The possibility of finding fossil placers in pebbly quartzites and conglomerates, and deposits of very fine grained precipitated 

vanadium and gold in carbonaceous slates and schists, provided inducement for this work as part of the U.S. Geological Survey's search for 

heavy metals. Analyses show low amounts of gold less than 0.1 part 

per million in these rocks, and consequently no geochemically anomalous amounts of gold or commercially important deposits are indicated. The three areas involved are discussed separately.

Fl
F2 CONTRIBUTIONS TO ECONOMIC GEOLOGY 

NEEDLE MOUNTAINS, COLO. 

GEOLOGIC RELATIONS

The Needle Mountains, which lie in La Plata, San Juan, and Hinsdale Counties, Colo., form the southwestern part of the San Juan 

Mountains and include the Grenadier Kange, the Needle Mountains 

group, the West Needle Mountains, and adjacent peaks. They are 

underlain largely by Precambrian rocks.

The geology of the Needle Mountains was studied intensively in 

the period 1895-1910 by Cross, Howe, and Kansome (1905), Cross 

and Howe (1905), and Cross and Hole (1910). Keports of these 

studies included geologic maps at 1:62,500 scale. Later the geology 

was summarized by Cross and Larsen (1935) and Larsen and Cross 

(1956), whose reports included geologic maps at 1:250,000 scale. The 

Precambrian Uncompahgre Formation in illncompahgre Gorge, about 

14 miles north of the Needle Mountains area, was described by Kelley 

(1946),Luedke and Burbank (1962), and Burbank and Luedke (1964). 

Kecent studies by the author (Barker, 1968a, b; 1969) have revealed 

a geologic history of the Precambrian rocks of the Needle Mountains 

that is somewhat different from that described by Cross and his associates and that consists of:

1. Deposition of the Vallecito Conglomerate.

2. Deposition of the largely metavolcanic Irving Formation, 

which comprises Cross and Howe's Irving Greenstone and 

Archean schist and gneiss.

3. Folding along north to northeast trends, metamorphism to 

high rank, and formation of the Twilight Gneiss and the 

Tenmile and Bakers Bridge Granites.

4. Deep erosion.

5. Unconformable deposition of sediments of the Uncompahgre 

Formation now quartzite, slate, schist, and conglomerate.

6. Isoclinal folding along east to southeast trends, and metamorphism of low to medium rank.

7. Intrusion of the Eolus and Trimble Granites and the Electra 

Lake Gabbro.

8. Deep erosion, followed by deposition of sediments in Cambrian time.

These various geologic units are shown on the geologic map (fig. 1), 

but the older and younger intrusive rocks are shown undivided.

Kadiometric studies by Silver and Barker (1968), using the uranium-lead method, and by Bickford, Barker, Wetherill, and Lee-Hu 

(1969), using the rubidium-strontium method, indicate that the Twi-
GOLD INVESTIGATIONS, PRECAMBRIAN ROCKS F3

light Gneiss is about 1,780 m.y. (million years) old, the Tenmile and 

Bakers Bridge Granites are about 1,720 m.y. old, and the Eolus 

Granite and the Electra Lake Gabbro are about 1,460 m.y. old.

The Vallecito Conglomerate, the basal conglomerate of the Uncompahgre Formation, and the pebbly quartzite and pyritic pelitic 

rocks stratigraphically higher in that formation were sampled and 

analyzed for gold, with negative results. Descriptions of these units 

follow.

VALLECITO CONGLOMERATE

The Vallecito Conglomerate is found only in the southeastern 

Needle Mountains, along the lower valleys of Vallecito Creek and 

Pine River and underlying much of the complex ridge between these 

streams (fig. 2). This conglomerate forms many cliffs and is well 

exposed.

In outcrop the Vallecito Conglomerate is mostly gray, but locally 

it is pink or purple. It is thin to very thick bedded, and it shows 

conspicuous cross-stratification of the trough type described by McKee 

and Weir (1953, p. 387) or the pi type described by Alien (1963, p. 

109), except that the cross-strata are lithologically heterogeneous; 

hematite laminae are interlayered with pebble conglomerate. The Vallecito contains randomly distributed beds of coarse-grained quartzite 

1-18 inches thick and a few scattered, much thicker, beds of quartzite. 

Joints cut both clasts and matrix.

A few folds that have amplitudes of one hundred to several hundred 

feet were found, but folds that have amplitudes of a few inches to 

several feet are extremely sparse.

The Vallecito Conglomerate is overlain by amphibolite, metavolcanic rocks of intermediate composition, mica schists, quartzite, gneisses, and chlorite schists of the Irving Greenstone of Cross and Howe 

(1905), here termed the Irving Formation. The contact between the 

Vallecito and the overlying rocks has little or no angular discordance, 

and the sequence of deposition was determined from cross-stratification. The lower contact of the Vallecito is not exposed, and therefore 

neither the thickness of the formation nor the nature of rocks underlying it is known. However, at Granite Peaks Ranch in Pine River valley 

(fig. 2), good top and bottom control by cross-stratified beds enables 

measurement of a 2,400-foot thickness of the stratigraphically lowest 

part of the Vellecito Conglomerate. Larsen and Cross (1956, p. 24) gave 

"an estimated exposed thickness of more than 3,000 feet west of Pine 

River." This formation may well be more than 5,000 feet thick.

The Vallecito Conglomerate is metaconglomerate and pebbly quartzite that contains subangnlar to rounded fragments of milky quartz,
F4 CONTRIBUTIONS TO ECONOMIC GEOLOGY

107M5' 107°30'

Area shown

Area shown in figure 3- 

in figure 5

12 MILES

FIGURE 1. Generalized geologic map of the Needle Mountains, Hinsdale, La 

Plata, and San Juan Counties, Oolo., and index to location of areas shown 

in figures 2-5.
GOLD INVESTIGATIONS, PRECAMBRIAN ROCKS 

EXPLANATION

F5

Post-Precambrian rocks

Younger intrusive rocks

Include Trimble Granite, Electra Lake Gabbro, and Eolus

Uncompahgre Formation

Stipple, quartzite

Solid black, slate and schist

Older intrusive rocks

Include Tenmile and Bakers Bridge Granites and

Irving Formation

Dashes show trend of foliation

oa a ~ n o

Vallecito Conglomerate

Contact

Fault

381-385 O 69 2
F6 CONTRIBUTIONS TO ECONOMIC GEOLOGY

v 107*30'

R. 7W. R.6 W. R. 5W.

4 MILES 

I

FIGURE 2. Geologic map showing Vallecito Conglomerate (ruled areas) and 

sample (localities, Needle Mountains, Oolo.

red and black jasper, chert, gray argillite, ferruginous quartzite and 

iron-formation, intermediate volcanic rocks, epidote-rich greenschist, 

and muscovite schist. The clasts range in maximum dimension from 

less than 1 mm to about 12 inches, but very few are larger than 4 

inches. The quartz clasts are polygranular, and most grains are equant 

and polygonal to irregular in shape and %-l mm in size; grains 1-2 

mm in size and shaped like the smaller ones form 10-20 percent of 

many of the clasts. Such a fabric suggests that these clasts were 

derived from quartzite in which larger detrital grains were set in a 

finer matrix. Ovoid aggregates of sericite, sericite + quartz + albite,
GOLD INVESTIGATIONS, PRECAMBRIAN ROCKS F7

and sericite + epidote + biotite + quartz are interpreted as metamorphosed grains of feldspar or of relatively fine grained quartzose 

f eldspathic rocks, probably volcanic rocks of intermediate to rhyolitic 

compositions, in which original potassic feldspar has been hydrolyzed 

to sericite and original plagioclase has been converted to albite and 

epidote. The matrix is a poorly sorted aggregate of quartz and sericite 

with minor hematite, leucoxene, garnet, albite, biotite, and epidote. 

It is mostly gray, but locally it is pink to purple; most grains are 

y$-l mm in size. The rock was completely recrystallized during metamorphism: quartz, both in the matrix and in the various types of 

clasts in which it occurs, has grown into polygranular mosaic fabrics; 

the sericite is mostly well alined and gives a schistose aspect to the 

matrix; the sparse garnets all lie enclosed in sericite and may be 

metamorphic rather than detrital; and epidote grains only rarely 

show rounded outlines, suggesting detrital origin and later recrystallization. Dark laminae 1-3 mm thick are abundant in much of the 

formation. These are largely hematite, commonly with accessory 

ilmenite and rutile. The hematite commonly shows octahedral forms, 

indicating derivation from magnetite by oxidation (Barker, 1968b). 

No gold was found in the Vallecito Conglomerate within the limits 

of detectability.

Sampling of the Vallecito Conglomerate involved collecting a 170- 

Ib sample (No. 107 in table 1 and fig. 2) in the canyon of Vallecito

TABLE 1. Localities and descriptions of samples analyzed for gold

Analyses showed that all samples, except first sample listed, contained less than 0.1 part per million of gold. 

All samples, except first sample listed, are chip samples. Analysts: W. L. Campbell, R. L. Miller, M. 8. 

Rickard, and T. A. Roomer]

Sample locality

Formation Remarks 

Tig. Loc.

__________________No. No.________________________________

Needle Mountains, Colo.

Vallecito Conglomerate. _..-.- 2 107 170-lb sample collected in canyon of Vallecito Creek

Description and analysis given in text.

123,124, 5-lb composite chip samples taken west of the Lake 

127-129 Fork of Pine River. 

ITncompahgre Formation:

Basal conglomerate...-.-. 3 192 3-4 ft above base (base not exposed here).

193 Basal 6 in.

194 6 in. to 4 ft above base.

195 4-8 ft (top) above base.

196 Laterally 8 ft along base and in lowermost 2 in.

199 Basal 12 in.

200 1-8 ft (top) above base.

201 Basal 12 in.

202 1-8 ft (top) above base.

203 2J4-3 ft above base (base not exposed here).

(North side of formation, 4 197 0-18 in. above base of pebbly layer, about 20 ft verwhere basal conglom- tically above railroad tracks.

erate is 1J4-3 ft thick). 204 18-in.-thick conglomerate overlain by pebbly quartzite.

206 4-in.-thick layer of conglomerate in a 2}£-ft-thick layer 

of pebbly quartzite (equivalent to the basal conglomerate).
F8 CONTRIBUTIONS TO ECONOMIC GEOLOGY

TABLE 1. Localities and descriptions of samples analyzed for gold Continued

Formation

Sample locality

Fig. 

No.

Loc.

No.

Remarks

Uncompahgre Formation Con. 

Pebbly quartzite and 

conglomerate (body of 

formation).

143 4-in.-thick pebble conglomerate.

144 Pebble quartzite lens 3-6 in. thick.

168 12-ft-thick pebbly conglomerate and quartzite.

169 3-ft-thick layer of conglomerate.

174 5- to 6-in.-thick lens of conglomerate.

175 2- to 4-in.-thick lens of conglomerate'.

185 Across a 15-ft-thick conglomerate layer with 1 in. 

pebbles of quartz and jasper; layer lies hi 300-ft thick 

unit of coarse-grained to pebbly quartzite.

187 lO-in.-thick conglomerate.

188 4- to 5-in-.thick conglomerate in sparsely pebbly 

quartzite; 9 ft north of sample 187.

189 6-in.-thick conglomerate lens; 100 ft north of sample 188.

191 2- to lO-in.-thick conglomerate lenses hi 2-ft-thick

pebbly quartzite. ____ ___

Tusas Mountains, N. Meat.

Kiawa Mountain Formation: 

Big Rock Conglomerate 

Member.

Jawbone Conglomerate 

Member.

Upper quartzite member .

12 SWJiSEW sec. 22, T. 27 N., R. 8 E.; Las Tablas quadrangle. Massive conglomerate with 1- to 4-in. clasts; 

muscovitic schistose matrix. Sampled across a 10-ft 

breadth normal to schistosity, bedding not visible. 

Lowermost conglomerate exposed on northeast flank 

of Big Rock syncline, sample within about 20 ft of 

base of this member.

13 200 ft N. 70° W. of sample 12 locality, SEJiSWJi sec. 22, 

T. 27 N., R. 8 E. Lithology like that of sample 12. 

Chipped across a 40-ft breadth normal to schistosity; 

bedding not visible.

14 SWJiNWJi sec. 27, T. 27 N., R. 8 E., Las Tablas 

quadrangle. Lithology similar to that of samples 12 

and 13. Chipped across a 50-ft breadth normal to 

schistosity. Lowermost exposed conglomerate on 

southwest flank of Big Rock syncline. Bedding not 

visible hi sampled section but is apparent hi folded 

pebbly quartzite immediately to the northeast, which 

suggests that the conglomerate, also, contains minor 

folds.

15 1,650 ft southeast of sample 14 locality, also on southwest 

flank of Big Rock syncline; SEJ£NWJ£ sec. 21, T. 27 

N., R. 8 E., Las Tablas quadrangle Chinrwd across 

a 4-ft thickness of a small outcrop

6 NEJiNEM sec. 24, T. 29 N., R. 6 E., Cebolla quadrangle, south ridge of Jawbone Mountain at 10,340-ft 

elevation. Chipped across a 10-ft thickness of mixed 

conglomerate and pebbly quartzite, each with hematite-rich laminae. Pebbles mostly H-l in. in maximum dimension and consist of about 80 percent 

quartz and 20 percent red and dark-gray jasper. The 

heavy minerals of 354 grains of this sample were 

separated with bromoform and yielded 56 grams of 

hematite, kyanite, rutile, and ilmenite.

7 NEJiNWJi sec. 19, T. 29 N., R. 7 E., Burned Mountain 

quadrangle, 10,400-ft elevation on southwest slope of 

east summit (10,601-ft elev.) of Jawbone Mountain. 

Chipped across a 3-ft thickness of conglomerate with 

Ji- to 1-in. pebbles of milky and pink quartz and red 

and dark-gray jasper. Underlying rocks not exposed; 

overlying rocks are cross-stratified fine-grained conglomerate and quartzite.

8 SEJtfNEJi sec. 7, T. 28 N., R. 7 E., Burned Mountain 

quadrangle, 9,650-ft elevation. Chipped across a 30-ft 

thickness of poorly sorted conglomerate with >£- to 2- 

in. pebbles of quartz and jasper.

20 SWMNEJi sec. 24, T. 29 N., R. 6 E., Cebolla quadrangle, small knob at 10,200-ft elevatidn. Chipped 

across 8-ft thickness of about 80 percent of conglomerate with Ji-in. pebbles and 20 percent of fine-grained 

quartzose conglomerate and quartzite.

9 West end of hill near 9,727-ft elevation, Burned Mountain quadrangle. Sample, largely of float, chipped 

across 30 ft of folded quartz pebble conglomerate that 

probably is 5-10 ft thick.

10 200 ft east of sample 9 locality. Chipped across 12 ft of 

intricately folded quartzite that contains 25-30 percent conglomerate in layers 4-8 in. thick.

11 About 525 ft east and 75 ft north of sample 9 locality. 

Chipped across 15 ft of mixed bedrock and float of a 

layer of conglomerate that is probably 10-15 ft thick.
GOLD INVESTIGATIONS, PRECAMBRIAN ROCKS F9 

TABLE l.< Localities and descriptions of samples analyzed for gold- Continued

Sample locality

Formation Remarks 

Fig. Loc. 

No. No.

Picnris Ranee, N. MM.

Ortega Quartzite, lower 7 6 NWJ£NWJ£ sec. 21, T. 23 N., E. 11E., Trampas quadquartzlte member, rangle. southeast side of Cooper Hill at 7,470-ft

elevation. Chipped across a 2-ft thickness of gray 

hematitic quartzite with kyanite and staurolite.

8 NWJiNEJi sec. 15, T. 23 N., E. 12 E., Peflasco quadrangle, north end of summit of Picuris Peak. Chipped 

across 5-ft thickness of slightly rusty, massive quartzite that contains 10-15 percent of garnet and staurolite 

but no hematite or other opaque minerals.

9 NWJtfSWJi sec. 24, T. 24 N., E. 11 E., Taos SW quadrangle, north side of Hondo Canyon at 7,090-ft elevation. Chipped across 5-ft thickness of sillimanitemuscovite quartzite with laminae of hematite and 

ilmenite spaced 8 mm to 8 cm apart; rock is not crossstratified.

(10-13) NEJiNEJi sec. 12, T. 23 N., E. 10 E., Trampas quadrangle, Glen Woody prospect (Jones, 1904, p. 158-161; 

Lindgren and others, 1010. p. 82, 01), east of Glen 

Woody bridge, about 6,070-ft elevation.

10 Kyanite-bearing quartzite that contains disseminated 

hematite and ilmenite; from walls of shallow old adit.

11 15 ft northeast of sample 10 locality. Eed altered quartzite containing sericite, limonite, and leucoxene. 

Chipped across a 7-ft-thick altered zone that is subparallel to bedding.

12 Interlayered quartz pebble conglomerate and quartzite 

with hematitic laminae. From talus blocks that fell 

from cliffs above old adit; from 5-in.-thick layer of 

conglomerate in a 2-ft-thick block.

13 Same as sample 12, except from conglomerate and

quartzite from 6 talus blocks.

Vadito Formation of Mont- 7 1 SWJiSWJi sec. 24, T. 23 N., B. 10 E., Trampas quadgomery (10S3) conglomerate rangle, south side of Canada de Piedra Lumbre, at 

member. 6,620-ft elevation. Chip of matrix across startigraphically lowest 3 ft of unit, here consisting of 70-80 percent 

pebbles and cobbles of milky quartz and felsite in 

matrix of quartz and muscovite with minor hematite, 

ilmenite, kyanite, and chlorite.

2 From next 25 ft of strata above sample 1, and of similar 

conglomerate.

3 NWKNEJi sec. 30, T. 23 N., E. 10 E., readout on north 

side of State Highway 75 in Arroyo del Ploma. Sample 

largely of matrix across a 10-ft-thick layer of conglomerate with about 00 percent by volume clasts of milky 

quartz as large as 12 in., and 10 percent clasts of pink 

felsite as large as 8 hi. set hi schistose gray matrix of 

quartz, muscovite, hematite, and minor chlorite and 

tourmaline.

4 NEJiSWJi sec. 22, T. 23 N., E. 11 E., Trampas quadrangle. Chipped across 7-ft thickness of peblby and 

cobbly quartzite, with 10-15 percent by volume of 

clasts of milky quartz.

6 NWJiSEJi sec. 15, T. 23 N., E. 12 E., Peflasco quadrangle, about 1,100 ft east of 9,315-ft elevation summit 

on south ridge of Picuris Peak (area contains only 

small scattered outcrops). Chip sample of 6 small 

outcrops in 20-ft thickness of pebble conglomerate and 

pebbly quartzite.

Locality of sample 6; chip sample of conglomerate from 

a 2- by 5-ft outcrop, the largest found hi this area.

Creek and collecting five 5-lb composite chip samples (Nos. 123, 124, 

127, 128, and 129 in table 1 and fig. 2) west of the Lake Fork of Pine 

Kiver. The five smaller samples were analyzed for gold, and no gold 

was detected. The large sample was crushed and processed through 

bromoform. The heavy fraction contained no visible gold and, moreover, showed an unusually sparse heavy mineral population that con-
F10 CONTRIBUTIONS TO ECONOMIC GEOLOGY

sists chiefly of hematite with minor amounts of subangular to subrounded zircon. A split of this heavy fraction was sieved, and the 

resulting four size fractions were analyzed for gold as shown in the 

folio wing table:

Size fraction 

(mesh)

+ 20 

-20, +100 

-100, +200 

-200

Weight (grams)

0.89 

15.0 

10.0 

2.2

Fire assay .

Cyanide at< 

Fire assay.

-____do__._

Method of analysis l Gold 

(ppm)

__... <0. 3

_____ <. 02

_____ <. 02

..... <. 1

1 Fire assays by L. B. Riley, O. M. Parker, and Claude Huffman, Jr.; cyanide-atomic absorption analysis by J. A. Thomas.

UNCOMPAHGRE FORMATION 

BASAL CONGLOMERATE

The Uncompahgre Formation unconf ormably overlies the older Twilight Gneiss and Irving Formation (fig. 1). Lying in gradational to 

abrupt contact with these older formations at and west of the Animas 

River (figs. 1,3,4) is an unusual rock, 4 to about 40 feet thick, that consists of about 10-50 percent 14- to 4-mm single grains and polygranular 

aggregates of quartz set hi a schistose matrix of sericite and minor 

hematite, limonite, and leucoxene. This rock, which could be classified 

as quartz sericite schist, apparently is a phyllonite formed from the 

older rocks, in which the original quartz grains were not comminuted 

but were first severely strained and then recrystallized, and in which 

the original iron was oxidized. A granite dike in the Irving Formation, 75 feet north of the unconformity, shows similarly strained and 

recrystallized quartz and therefore is a possible source of such quartz 

in the basal Uncompahgre. The phyllonite is mostly in gradational 

contact with the underlying granitic and metamorphic rocks; its 

sohistosity is parallel to bedding of the overlying metasedimentary 

rocks; and it is free of chert and jasper granules that are present in 

the overlying conglomerate.

The basal unit of the Uncompahgre Formation is a V/2- to 8-foot 

thick bed of interlayered quartzose conglomerate and pebbly quartzite. 

This rock is gray, and it is poorly stratified and sorted; it is crossstratified in only a few places. Its matrix is largely recrystallized 

quartz, mostly of %0- to 14-mm grain size, with variable amounts of 

sericite and hematite; and its clasts are predominantly quartz, with 

red and black jasper, gray chert, and dark-gray argillite. The clasts 

range in size from 2-mm granules to 6-inch'cobbles, but most are in 

the 1- to 8-cm range. Some of the quartzose clasts are quartzite and
GOLD INVESTIGATIONS, PRECAMBRIAN ROCKS Fll

have a fabric in which y2- to 2-mm original detrital quartz grains are 

set in a recrystallized matrix of %0- to %0-mm quartz grains, but 

others show irregular fabrics and perhaps were derived from quartz 

veins. The clasts, like those in the Vallecito Conglomerate, indicate 

that the source data contained much quartzite, jasper, chert, and ironformation. This basal conglomerate grades upward for several feet 

through pebbly quartzite into about 1,000 feet of pale-violet to white 

sparsely laminated and cross-laminated rarely pebbly quartzite at 

Snowdon Peak (fig. 3) and into 300-600 feet of similar quartzite in 

the canyon of the Animas River (fig. 4).

The basal conglomerate was sampled hi its three areas of exposure: 

west of Snowdon Peak, on the east bank of the Animas River, and 

below the west rim of the canyon of the Animas River. None of the 

samples contained detectable gold, with the limit of detection at 0.1 

ppm. Descriptions and localities of samples are given in table 1 and in 

figures 3 and 4.

PEBBLY QTTARTZITE AND CONGLOMERATE

The quartzite layers in the Uncompahgre Formation, for the most 

part, are well sorted, pale violet to light gray, thick bedded, sparsely

1 MILE 

J

Contact

EXPLANATION

40 87

Strike and dip of beds Strike and dip of foliation

W

Water

FIGURE 3. Geologic map of the Snowdon Peak area, Needle Mountains, Colo., 

showing sample localities 192-196 and 199-203. p-Ct (diagonally ruled), Twilight 

Gneiss; p-Cu (no pattern), Uncompahgre Formation, here quartzite with an 

8-foot-thick basal conglomerate, both of Precambrian age; Qtr (stippled), 

Holocene talus and rock glaciers. Base from U.S. Geological Survey, Snowdon 

Peak, 1:24,000.
CONTRIBUTIONS TO ECONOMIC GEOLOGY

107MO' f SILVERTON 3,5 M'

1 MILE I

EXPLANATION

Contact 

Dashed where approximately located

 K »

Fault

Dashed where approximately located. U, 

upthrown side; D, downthrown side; 

query, further extent unknown

W 

Water

Strike and dip of beds 

Strike and dip of vertical beds

83^7

Strike and dip of beds and bearing 

and plunge of lineation

73

Strike and dip of foliation

FIGURE' 4. Geologic map of part of the canyon of the Animas River near Molas 

Creek, Needle Mountains, Colo., showing sample localities 197, 204, and 205. 

p ag (diagonally ruled), amphibolite and granitic rocks, and p-Cu (no pattern), 

Uncompahgre Formation (here quartzite, slate, siltstone, and conglomerate), 

both of Preambrian age; Pzr (vertically ruled), Paleozoic rocks; Qt (stippled), 

Holocene talus deposits. Base from U.S. Geological Survey, Snowdon Peak, 

1:24,000.

laminated with hematite, and sparsely cross-laminated. Pebbly layers 

are sparse, and, of the 13 found and sampled, none showed detectable 

gold with the limit of detection at 0.1 ppm. Details of sampling are 

given in table 1.

SLATE AND SCHIST

The widespread pelitic rocks of the Uncompahgre Formation were 

sampled at the 13 localities shown in figure 5 and were analyzed for 

gold and other metals (table 2). These rocks are mostly carbonaceous
GOLD INVESTIGATIONS, PRECAMBRIAN ROCKS F13

351-385 O 69 3
F14 CONTRIBUTIONS TO ECONOMIC GEOLOGY

TABLE 2. Analyses of slates, phyllites,

[All values are in parts per million except those for Ca, Fe, Mg, and Ti, which are in percent. Numbers in 

parentheses below element symbols are limits of detection. N, looked for but not detected; n.a. not looked 

for. Analytical errors, of values given, are +100 percent, 50 percent for spectrographic analyses and ±30

Sample

loc. No.1 Semiquantitative spectrographic analyses 2 

(fig- 5)

Ag As B Ba Be Bi Ca Cd Co Cr Cu Fe La Mg Mo Mn 

(0.5) (200) (10) (20) (1) (10) (0.05) (20) (5) (5) (2) (0.05) (20) (0.02) (2) (20)

125B

125D

125F

125G

125H

125J

125K

125L

125M

125N

125Q

142

145

146

148

153

154

155

156

157

186

190

198

N

N

N

N

1

.5

.7

.5

.7

.5

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

30

150

150

200

200

30

150

100

50

100

150

50

30

150

150

100

100

50

50

20

70

70

50

700

500

1,500

700

500

700

700

1,000

700

700

700

500

200

200

300

150

300

200

500

500

200

200

200

3

2

1

N

1

N

N

1.5

N

N

N

1

1

2

1

1

1

1

1

1

1

1

1

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

0.05

.05

.15

.07

.7

.5

.3

1.5

.5

.7

.7

.2

.2

.05

.05

.05

N

N

.5

N

N

.1

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

50

30

20

N

N

10

5

N

N

N

30

N

N

5

N

5

N

5

N

5

50

N

N

150

150

150

30

30

50

30

30

30

30

50

100

100

70

50

70

150

150

30

50

50

20

100

20

30

50

15

50

70

5

30

10

20

150

70

50

50

20

20

10

30

20

50

150

30

5

15

15

15

2

7

5

.7

2

1.5

3

7

5

3

2

1

7

3

5

1

5

7

1.5

5

50

30

N

30

20

N

30

20

20

20

20

N

20

50

N

30

100

30

30

20

20

20

30

1.5

1.5

3

.7

2

1

.5

1.5

1

.7

1.5

1

1

.5

.5

1

.7

1

.5

1

1

.7

1

N

N

N

50

70

30

30

70

50

50

10

N

N

N

N

N

N

N

15

N

N

20

N

1,500

1,000

500

200

700

500

70

300

300

150

500

500

300

20

30

150

100

500

50

500

200

100

200

1 Samples 125B-125Q were collected, by T. A. Steven, in a layer of black slate and siltstone about 145 ft 

thick; individual samples were collected above the base (north margin of this layer) as follows: 125B, 8 ft; 

125D, 21 ft; 125F, 39 ft; 125G, 49 ft; 125H, 55 ft; 125J, 90 ft; 125K, 105 ft; 125L, 120 ft; 125M, 126ft; 125N, 131 ft; 

and 125Q, 139 ft. Sample 155 was collected 10 ft east of sample 154 locality.

and pyritic compositionally layered dark-gray to black slate, phyllite, 

and siltstone. None of the samples showed detectable gold by atomic 

absorption analysis, with 0.02 ppm as the limit of detection. These 

analytical results indicate that the pelites of the Uncompahgre Formation generally are not metalliferous.

TUSA8 MOUNTAINS, N. MEX. 

GEOLOGIC RELATIONS

The Tusas Mountains of Eio Arriba County, N. Mex., lie immediately 

west of the Rio Grande valley, and are a southeastern continuation of 

the San Juan Mountains of Colorado. Slightly more than 200 square 

miles of Precambrian rocks are exposed in this area.

The hydrothermal ore deposits of the Tusas Mountains, including 

the gold placers of Hopewell, were described by Lindgren, Graton, 

and Gordon (1910), and the geology of the Precambrian rocks was
GOLD INVESTIGATIONS, PRECAMBRIAN ROCKS F15

and siltstones of the Uncompahgre Formation

percent for atomic absorption analyses. Gold was not detected in any of the samples, by atomic absorption 

analysis, with 0.02 ppm as the limit of detection]

Atomic absorption

Semiquantitative spectrographic analyses 3 Continued analyses, by colorimetric methods,3 

(parts per million)

Nb Ni Pb Sb Sc Sn Sr Ti V W Y Zn Zr Cu Mo Pb Zn 

(10) (2) (10) (100) (5) (10) (60) (0.002) (5) (50) (5) (200) (10,200) (10) (4) (25) (20)

20

15

15

10

10

15

15

15

15

15

15

n.a.

n.a.

n.a.

n.a.

n.a.

n.a.

n.a.

n.a.

n.a.

n.a.

n.a.

n.a.

100

150

30

10

30

30

15

15D

15

50

30

15

15

30

N

15

10

15

N

15

50

10

5

100

50

70

30

50

N

N

N

N

30

70

15

10

N

10

N

20

10

10

10

70

N

10

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

30

20

30

15

15

15

7

7

10

7

7

30

20

20

15

15

50

30

30

20

20

10

30

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

50

50

50

N

N

N

N

N

N

N

N

50

1

1

1

.3

.5

.3

.2

.3

1

.5

.3

.7

.7

1

.7

.7

.5

.5

.7

.3

.2

.3

.5

200

200

500

700

700

300

300

500

700

500

300

100

100

100

200

50

150

100

200

50

50

200

150

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

50

70

15

20

30

10

15

20

30

15

15

20

20

20

20

30

30

50

50

15

50

30

30

200

N

N

N

1,000

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

N

200

> 1,000

300

150

150

150

100

150

70

100

150

700

300

300

200

500

150

200

200

150

200

200

200

24

59

92

18

67

22

N

12

N

12

100

4

N

N

44

60

16

40

60

60

56

8

40

70

70

40

110

N

N

N

N

35

N

160

89

100

67

510

340

200

92

100

20

180

2 Analysts: samples 125B-125Q, Arnold Parley, Jr.; samples 142-198, K. C. Watts. 

a Analysts: for Cu, Pb, and Zn, S. L. Noble and Elizabeth Mart Inez; for Mo, W. L. Campbell and Z. C. 

Stephenson.

described by Just (1937), Barker (1958), and Bingler (1965). The 

study by Just was reconnaissance in nature; the stratigraphic sequence 

(table 3) and structural features were first determined by Barker 

(1958, p.10-36).

The rock units pertinent to this investigation are the Ortega 

Quartzite and the Big Rock Conglomerate and Jawbone Conglomerate 

Members, and the upper quartzite member of the Kiawa Mountain 

Formation. The lithology and thickness of each of these is given 

in table 3, and areal distributions are shown in figure 6. The clasts 

in the pebbly quartzite and conglomerates of this area are identical 

with those in the rocks of the Needle Mountains, which suggests a 

common provenance. Also, there may be a general correlation of these 

rocks of the Tusas Mountains with the Vallecito Conglomerate and 

Irving Formation of the Needle Mountains.

The Precambrian rocks of the Tusas Mountains are intensely folded 

(see Barker, 1958), and the fold axes plunge to the northwest and 

west-northwest. The major folds are a syncline whose axial surface
F16 CONTRIBUTIONS TO ECONOMIC GEOLOGY

106° 15' 106°00'

10 MILES 

_I

FIGUBE 6. Geologic sketch map of the Tusas Mountains, N. Mex. Geology 

adapted from Barker (1958) for area north of lat 36°30' N., and from Bingler 

(1965) for area south of lat 36°30' N.

is approximately vertical, called the Kiawa syncline, which passes 

through Kiawa Mountain and is delineated by the upper quartzite 

member of the Kiawa Mountain Formation (fig. 6); and an inferred 

anticline, the Hopewell anticline, whose axial surface lies close to
GOLD INVESTIGATIONS, PRECAMBRIAN ROCKS 

EXPLANATION

F17

Post-Precambrian rocks

Other Precambrian rocks

Upper quartzite member

Jawbone Conglomerate Member

Big Rock Conglomerate Member

Predominantly Ortega Quartzite

Contact

Fault

.6

Sample locality and number

Hopewell. The Big Rock Conglomerate Member is folded into a minor 

syncline and anticline, as indicated by the pattern in figure 6.

SAMPLING RESULTS

The Ortega Quartzite in the Tusas Mountains is sparsely pebbly, 

and only one sample was taken from it. That sample was collected 

in the SE%SWi/4 sec. 10, T. 26 N., R. 8 E. (La Madera quadrangle),
F18 CONTRIBUTIONS TO ECONOMIC GEOLOGY

TABLE 3. Stratigraphic column of Precambrian rocks in the Tusas Mountains,

N. Mex.

[In part from Barker (1958, p. 10)]

Formations (from Character Thickness, in feet 

youngest to oldest)

Kiawa Mountain Formation:

Upper quartzite Quartzite, light-gray to blue, vitreous, massive, with 5,000-10,000; 

member. sparse pebbly layers; contains laminae of kyanite sCnd of uppermost part 

hematite (commonly both) along bedding planes; cross- not exposed, 

laminated.

Amphibolite member Amphibolite and quartzite, interlayered. Amphibolite 35 to about 2,000. 

consists largely of hornblende, oligoclase-andesine, chlorite, quartz, and ilmenite; it is basaltic in composition. 

Lower quartzite Quartzite, light-gray to blue, vitreous, massive; contains Several hundred.

member. muscovite in the Petaca pegmatite district.

Jawbone Conglomer- Quartzose conglomerate and quartzite, gray, fine-grained, 500-2,000(7). 

ate Member. interlayered, vitreous, massive. A few pebbly layers with

clasts of quartzite and jasper 6-25 mm in size.

Big Rock Conglom- Quartzose conglomerate and pebbly quartzite, interlay- 50-200. 

erate Member. ered, gray; clasts are of quartzite and jasper, J£-5 in. hi

size; secondary muscovite is present; cross-laminated.

Moppin Metavolcanic Qreenschist and amphibolite, ranging hi composition from Several thousand. 

Series. olivine basaltic to andesitic; minor phyllite, conglomerate, schist, and gneiss.

Ortega Quartzite-......... Quartzite, light-gray, pink, or blue, vitreous, massive; with 14,000-20,000; lowlaminae of kyanite and of hematite (commonly both) ermost part not 

along bedding planes; cross-lamination is common. exposed.

across a 15-foot thickness of gray schistose muscovitic quartzite containing 3-10 percent by volume of i/£- to 3-inch pebbles of quartz and 

dark-gray jasper. The Big Rock Conglomerate and Jawbone Conglomerate Members, and the upper quarzite member of the Kiawa Mountain Formation were sampled. ('See table 1 for localities and descriptions of samples.) None of the rocks collected was found to contain 

gold, with 0.1 ppm as 'the limit of detection.

PICURIS RANGE, N. MEX. 

GEOLOGIC RELATIONS

The Picuris Range, which is east of the Rio Grande River and 

southwest of Taos, is underlain largely by Precambrian metasedimentary rocks. Its geology was studied by Just (1937, p. 9-40) and, in 

much greater detail, by Montgomery (1953). The economic geology 

of the Copper Hill or Picuris district and of the Glen Woody area, 

both in the Picuris Range, was discussed by Lindgren, Graton, and 

Gordon (1910, p. 82,89-91).

The Stratigraphic units of the Precambrian rocks of the Picuris 

Range are described in table 4. These units are intensely folded and 

are generally eastward trending.
GOLD INVESTIGATIONS, PRECAMBRIAN ROCKS F19

TABLE 4. Stratigraphic column of Precambrian rocks in the Picuris Range, N. Mex.

[From Montgomery (1953, p. 8)]

Formations Character Thickness, in feet 

(from youngest to oldest)

Vadito Formation:

Schist member........ Quartz-muscovite schist and phyllite, quartz-btotite 2,500.

granolite; lower part quartz-muscovite schist interlayered with plagioclase amphibolite.

Conglomerate Quartzose conglomerate and quartzite, both muscovitic; 2,000. 

member. interlayered felsite, meta-dacite, meta-andesite, and

amphibolite. 

Unconformity. 

Ortega Formation:

Filar Phyllite Gray to black carbonaceous quartz-muscovite phyllite.... 2,300.

Member. 

Rinconada Schist Phyllite, quartzite, staurolite schist and gneiss and andalu- 800-1,850.

Member. site-biotite hornfels.

Lower quartzite Coarse-grained quartzite with minor hematite and ilme- 2,500; lowermost 

member. nite, including thin beds of sillimanite and (or) fcyanite, part not exposed, 

and sparse lenses of quartz-pebble conglomerate.

SAMPLING RESULTS

In this study the lower quartzite member of the Ortega Quartzite 

and the conglomerate member of the Vadito Formation of Montgomery (1953) were sampled, as shown in figure 7, and no gold was 

found. Sample localities and descriptions are given in table 1.

COMPARISON WITH THE CENTRAL, RAND GOL.DFIBLD,

SOUTH AFRICA

The quartzites and conglomerates examined in this study may be 

compared with the auriferous conglomerates of the Central Rand 

goldfield of South Africa. The gold-bearing conglomerates of the 

Central Rand are found in the Precambrian Witwatersrand System, 

which is about 24,000 feet thick and lies on a basement complex of 

granite, gneiss, and schist. These conglomerates were deposited 2,100- 

3,000 m.y. ago, and they contain about 8 percent conglomerate beds 

(Pretorius, 1964, p. 69-86). The economically important deposits are 

in many thin layers of pebble conglomerate that lie in the upper 9,400 

feet of the Witwatersrand System. The pebbles are mostly vein quartz, 

quartzite, and chert, with lesser amounts of quartz porphyry, shale and 

schist, jasper, and tourmaline-bearing rock. The matrices are predominantly quartz, pyrite, muscovite, sericite, and pyrophyllite, with 

minor chlorite, chloritoid, rutile, tourmaline, carbon, zircon, calcite, 

dolomite, pyrrhotite, galena, sphalerite, chalcopyrite, chromite, gold, 

uraninite, ilmenite, leucoxene, platinum metals, and other minerals
F20

36°20'

CONTRIBUTIONS TO ECONOMIC GEOLOGY

105"45' TAPS 5.5 Ml.

36° 10'

10 MILES

EXPLANATION

Tertiary and Precambrian rocks

Conglomerate member of Vadito Formation

Lower quartzite member of Ortega Quartzite.

Contact

Fault

.8 

Sample locality and number

FIGURE 7. Geologic sketch map of the Picuris Range, N. Mex., showing 

areas underlain by the lower quartzite member of the Ortega Quartzite 

and the conglomerate member of the Vadito Formation. (From Montgomery, 1953.)
GOLD INVESTIGATIONS, PRECAMBRIAN ROCKS F21

(Pretorius, 1964, p. 94r-95). Average values of ore of the 17 largest 

mines in the Central Rand have ranged from about 1/3 to 1 ounce of 

gold per ton (Pretorius, 1964, p. 105). The varied and unusual suite of 

minerals in these conglomerates partly results from a postdepositional 

hydrothermal event in which the detrital quartz, feldspars, magnetite, 

gold, uraninite, platinum, and other minerals were partly recrystallized and were moved short distances or otherwise altered, and in 

which the mica, pyrophyllite, and sulfides were formed.

In contrast to these rich beds of the upper Witwatersrand System, 

the quartzites, shales, and minor conglomerates of the lower parts of 

that system are largely barren. These quartzites are orthoquartzites, 

whereas the quartzose sedimentary rocks of the upper part of the 

Witwatersrand System are largely graywackes (Fuller, 1958, p. 27- 

30). Thus the quartzites of the Ortega, Kiawa Mountain, and Uncompahgre Formations in Colorado and New Mexico, all orthoquartzites, are lithologically similar to the lower, barren quartzites of the 

Central Rand goldfield.

In summary, the clastic rocks of Colorado and New Mexico discussed in this report differ from the auriferous conglomerates of the 

Central Rand in their lack of detrital gold, platinum group minerals, 

and uraninite; in being free of carbon; in having escaped hydrothermal alteration in which pyrite, sphalerite, galena, and other sulfides 

were formed; and probably in containing much less detrital vein 

quartz. Also, the American rocks are at least 300 m.y. younger than 

the African sediments and apparently were derived from a terrane 

much poorer in granitic and gneissic rocks.

REFERENCES CITED

Alien, J. R. L., 1963, The classification of cross-stratified units, with notes on

their origin: Sedimentology, v. 2, no. 2, p. 93-114. 

Barker, Fred, 1958, Precambrian and Tertiary geology of Las Tablas quadrangle,

New Mexico: New Mexico Bur. Mines and Mineral Resources Bull. 45,104 p.

 1968a, Precamibrian geologic history in the Needle Mountains, Colorado, 

in Abstracts for 1966: Geol. Soc. America Spec. Paper 101, p. 385.

 1968b, Occurrence and genesis of hematite in Precambrian clastic rocks 

in southwestern Colorado and northern New Mexico [abs.] : Geol. Soc. America, Cordilleran sec., Program 64th Ann. Mtg., p. 33-34.

 1969, Precambrian geology of the Needle Mountains, southwestern Colorado : U.S. Geol. Survey Prof. Paper 644-A (in press).

Bickford, M. E., Barker, Fred, Wetherill, G. W., and Lee-Hu, Chin-nan, 1969, Precambrian Rb-Sr chronology in the Needle Mountains, southwestern Colorado : Jour. Geophys. Research, v. 74, p. 1660-1676.

Bingler, E. C., 1965, Precambrian geology of La Madera quadrangle, Rio Arriba 

County, New Mexico: New Mexico Bur. Mines and Mineral Resources Bull. 

80,132 p.
F22 CONTRIBUTIONS TO ECONOMIC GEOLOGY

Burbank, W. S., and Luedke, R. G., 1964, Geology of the Ironton quadrangle,

Colorado: U.S. Geol. Survey Geol. Quad. Map GQ-291. 

Cross, Whitman, and Hole, A. D., 1910, Description of the Engineer Mountain

quadrangle, Colorado: U.S. Geol. Survey Geol. Atlas, Folio 171, 14 p. 

Cross, Whitman, and Howe, Ernest, 1905, Description of the Needle Mountains

quadrangle [Colorado] : U.S. Geol. Survey Geol'. Atlas, Folio 131, 13 p. 

Cross, Whitman, Howe, Ernest, and Ransome, F. L., 1905, Description of the

Sllverton quadrangle [Colorado]: U.S. Geol. Survey Geol. Atlas, Folio 120,

34 p. 

Cross, Whitman, and Larsen, E. S., Jr., 1935, A brief review of the geology of

the San Juan region of southwestern Colorado: U.S. Geol. Survey Bull. 843,

138 p.

Fuller, A. O., 1958, A contribution to the petrology of the Witwatersrand system [with discussion] i South Africa Geol. Soc. Trans. and Proc., v. 61,

p. 19-45. 

Jones, F. O., 1904, New Mexico mines and minerals: Santa Fe, New Mexican

Printing Co., 349 p. 

Just, Evan, 1937, Geology and economic features of the pegmatites of Taos and

Rio Arriba Counties, New Mexico: New Mexico School Mines Bull. 13, 73 p. 

Kelley, V. C., 1946, Geology, ore deposits, and mines of the Mineral Point,

Poughkeepsie, and Upper Uncompahgre districts, Ouray, San Juan, Hinsdale Counties, Colorado: Colorado Sci. Soc. Proc., v. 14, no. 7, p. 287-466. 

Larsen, E. S., Jr., and Cross, Whitman, 1956, Geology and petrology of the

San Juan region, southwestern Colorado: U.S. Geol. Survey Prof. Paper

258,303 p. 

Lindgren, Waldemar, Graton, L. C., and Gordon, C. H., 1910, The ore deposits

of New Mexico: U.S. Geol. Survey Prof. Paper 68, 361 p. 

Luedke, R. G., and Burbank, W. S., 1962, Geology of the Ouray quadrangle,

Colorado: U.S. Geol. Survey Geol. Quad. Map GQ-152.

McKee, E. D., and Weir, G. W., 1953, Terminology for stratification and crossstratification in sedimentary rocks: Geol. Soc. America Bull., v. 64, no. 4,

p. 381-389.

Montgomery, Arthur, 1953, Pre-Cambrian geology of the Picuris Range, northcentral New Mexico: New Mexico Bur. Mines and Mineral Resources Bull.

30,89 p. 

Pretorius, D. A., 1964, The geology of the Central Rand goldfield, p. 63-108 in

Haughton, S. H., ed., The geology of some ore deposits in Southern Africa:

South Africa Geol. Soc., v. 1, 625 p. 

Silver, L. T., and Barker, Fred, 1968, Geochronology of Precambrian rocks of

the Needle Mountains1 , southwestern Colorado Pt 1, U-Pb zircon results,

in Abstracts for 1967: Geol. Soc. America Spec. Paper 115, p. 204.
Contributions to 

Economic Geology 

1968_________

GEOLOGICAL SURVEY BULLETIN 1272

This volume was published 

as separate chapters A-F
UNITED STATES DEPARTMENT OF THE INTERIOR 

WALTER J. HICKEL, Secretary

GEOLOGICAL SURVEY 

William T. Pecora, Director
CONTENTS

[Letters designate the separately published chapters]

(A) Phosphate rock in Colombia A preliminary report, by James B. Cathcart 

and Francisco Zambrano O., with a section on The phosphate occurrence 

at Turmeque1 , by Pedro E. Mojica G.

(B) Geology of magnesite deposits in northern Okanogan County, Washington 

A preliminary report, by Kenneth F. Fox, Jr., and C. Dean Rinehart.

(C) Fluorite deposits of the Quinn Canyon Range, Nevada, by C. L. Sainsbury 

and F. J. Kleinhampl.

(D) New talc deposit in St. Lawrence County, New York, by C. Ervin Brown. 

(E) Stratigraphy of the Morrison Formation and structure of the Ambrosia

Lake district, New Mexico, by Elmer S. Santos. 

(F) Gold investigations in Precambrian clastic and pelitic rocks, southwestern

Colorado and northern New Mexico, by Fred Barker.

US. GOVERNMENT PRINTING OFFICE: 1969 O 351-385




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