Nye County, Nevada

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1287

Huebnerite Veins near 

Round Mountain, 

Nye County, Nevada

By DANIEL R. SHAWE, EUGENE E. FOORD, and NANCY M. CONKLIN 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1287

A study of the geology, mineralogy, and 

chemistry of huebnerite-bearing veins 

suggests their formation during two 

major episodes of mineralization

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1984
UNITED STATES DEPARTMENT OF THE INTERIOR 

WILLIAM P. CLARK, Secretary

GEOLOGICAL SURVEY 

Dallas L. Peck, Director

Library of Congress Cataloging in Publication Data

Shawe, Daniel R., 1925-

Huebnerite veins near Round Mountain, Nye County, Nevada.

(Geological Survey Professional Paper ; 1287)

Bibliography: 40 p.

Supt. of Docs. No.: 119.16:1287

1. Huebnerite. 2. Mineralogy Nevada Nye County.

I. Foord, Eugene E. II. Conklin, Nancy M. III. Title. IV. Series

QE391.H84S53 1984 549'.74 82-600307

For sale by the Branch of Distribution

U.S. Geological Survey

604 South Pickett Street

Alexandria, VA 22304
CONTENTS

Abstract ...............

Introduction and acknowledgments . 

Geologic setting of the veins ....

Distribution and form of the veins

Alteration related to the veins . . .

Description of the vein minerals . .

Primary gangue minerals ....

Quartz ............

Muscovite ..........

Allanite ...........

Fluorite ...........

Barite ...........

Calcite ............

Chalcedony .........

Monazite ..........

Primary ore minerals ......

Huebnerite .........

Scheelite ..........

Tetrahedrite-tennantite . .

Page

1

1

2

4

4

4

6

6

9

10

10

13

14

14

14

14

14

15

16

Description of the vein minerals Continued 

Primary ore minerals Continued

Sulfides ........................

Secondary minerals ....................

Sulfides ........................

Oxides, tungstates, carbonates, sulfates, phosphates, 

and silicates ...................

Remobilized minerals ................

Summary of textures and paragenesis .........

Chemical composition of the huebnerite ...........

Iron-manganese composition ...............

Tungsten-manganese composition ............

Growth zones .......................

Trace-element composition ................

Variations in tungsten mineralization ............

Geochemistry of the huebnerite veins ............

Discussion ...........................

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

References cited ........................

Page

17

19

19

20

21

21

23

23

25

25

27

28

29

30

39

40

ILLUSTRATIONS

FIGURE 1. Geologic map of Round Mountain area ..............

2. Geologic map of tungsten area ..................

3. Diagrammatic sketch of huebnerite-bearing quartz vein ....

4. Sketch of thin section showing vein wall ............

5. Drawing of huebnerite crystals .................

6. Drawing of quartz with fluid inclusions .............

7. Photomicrograph showing zoned huebnerite with fluorite ....

8. Drawing of quartz-vein selvage ..................

9. Photomicrograph showing transitional vein margin .......

10. Photomicrograph showing late-stage veinlet ...........

11. Drawing of barite after pyrite .................

12-28. Photomicrographs showing:

12. Zoned huebnerite ......................

13. Zoned and fractured huebnerite, sample DRS-79-67 . .

14. Zoned and fractured huebnerite, sample DRS-79-68 . .

15. "Milled" huebnerite .....................

16. "Milled" and "mixed" huebnerite .............

17. Huebnerite, veined and replaced by scheelite ......

18. Huebnerite veined with scheelite .............

19. Scheelite filling vug in quartz ..............

20. Tetrahedrite-tennantite filling vug, sample DRS-78-2A

21. Tetrahedrite-tennantite filling vug, sample DRS-78-2B

22. Copper minerals filling vug ................

23. Pyrite (to limonite) filling vugs ..............

24. Vug in quartz vein .....................

25. Fractured and "milled" sphalerite ............

26. Galena replaced by covellite ................

27. Sphalerite with exsolved chalcopyrite ..........

28. Tetrahedrite-tennantite ...................

Page

3

5

7

7

8

9

12

12

13

13

14

15

16

16

17

17

18

19

19

20

20

21

22

23

24

25

26

26

in
IV CONTENTS

Page

FIGURE 29. Scanning electron micrograph showing manganese oxide on huebnerite ....................... 27

30-33. Photomicrographs showing:

30. Tetrahedrite-tennantite replaced by stibiconite ................................. 28

31. Secondary minerals in vein quartz ........................................ 28

32. Vug in vein quartz ................................................. 29

33. Late veinlet in quartz ............................................... 29

34. Paragenetic diagram of huebnerite veins ......................................... 30

35-38. Graphs of:

35. Spectrographic vs. microprobe analyses of iron in huebnerite ......................... 34

36. Correlation between huebnerite iron and altitude ................................ 35

37. Comparison of FeO and MnO in huebnerites .................................. 35

38. Comparison of MnO and W03 in huebnerites .................................. 37

TABLES

TABLE 1. Description of huebnerite-bearing quartz-vein samples .............................

2. Chemical analyses of muscovite ..........................................

3. Spectrographic analyses, minerals from huebnerite-bearing quartz veins ...................

4. Approximate lower limits of determination for elements analyzed by the six-step Spectrographic method

5. Electron microprobe analyses of huebnerite ...................................

6. Spectrographic analyses of huebnerite ......................................

7. Spectrographic analyses of quartz-vein material .................................

8. Other analyses of quartz-vein material ......................................

10

11

11

31

32

38

38
HUEBNERITE VEINS NEAR ROUND MOUNTAIN, 

NYE COUNTY, NEVADA

By DANIEL R. SHAWE, EUGENE E. FOORD, and NANCY M. CONKLIN

ABSTRACT

Small huebnerite-bearing quartz veins occur in and near Cretaceous 

(about 95 m.y. old) granite east and south of Round Mountain. The 

veins are short, lenticular, and strike mostly northeast and northwest 

in several narrow east-trending belts. The quartz veins were formed 

about 80 m.y. ago near the end of an episode of doming and 

metamorphism of the granite and emplacement of aplite and pegmatite dikes in and near the granite. An initial hydrothermal stage 

involved deposition of muscovite, quartz, huebnerite, fluorite, and 

barite in the veins. Veins were then sheared, broken, and recrystallized. A second hydrothermal stage, possibly associated with emplacement of a rhyolite dike swarm and granodiorite stock about 35 m.y. 

ago, saw deposition of more muscovite, quartz, fluorite, and barite, 

and addition of scheelite, tetrahedrite-tennantite, several sulfide minerals, and chalcedony. Finally, as a result of near-surface weathering, 

secondary sulfide and numerous oxide, tungstate, carbonate, sulfate, 

phosphate, and silicate minerals formed in the veins.

Depth of burial at the time of formation of the veins, based on 

geologic reconstruction, was about 3-3.5 km. The initial hydrothermal 

stage ended with deposition of quartz at a temperature of about 210°C 

and pressures of about 240-280 bars (hydrostatic conditions) from 

fluids with salinity of about 5 weight percent sodium chloride. Fluorite then was deposited at about 250°-280°C from solutions of similar 

salinity and containing a small amount of carbon dioxide. During 

shearing that followed initial mineralization, quartz was recrystallized 

at a temperature of 270°-290°C and in association with fluids of about 

5 weight percent sodium chloride equivalent and containing carbon 

dioxide. Late-stage fluorite was deposited from fluids with similar 

salinity but devoid of carbon dioxide at a temperature of about 210°C.

Huebnerite in the veins is of nearly end-member composition in 

the huebnerite-wolframite-ferberite series; iron content increases 

with altitude in the system. The present veins are interpreted to 

be near the bottom of the original system. A postulated upper part, 

now removed by erosion, may have formed in granite cupolas where 

deposits were richer and the tungstate much more iron rich.

INTRODUCTION AND 

ACKNOWLEDGMENTS

Small huebnerite-bearing quartz veins in granite just 

east of Round Mountain, Nye County, Nev., have been 

known since 1907 (Ferguson, 1921, p. 388-390). The 

veins have produced only a small quantity of tungsten 

since their discovery, and residual surface material near 

the veins also has produced a little tungsten, in 1915. 

According to Schilling (1963), the total production of 

tungsten from the Round Mountain district is between 

1,000 and 10,000 units of W03 (1 unit equals 20 Ibs).

H. K. Stager (oral commun., Sept. 1983) indicated that 

recorded production is 500-1,000 units, mostly from residual surface material. Some of the tungsten veins 

have been prospected for uranium (Krai, 1951, p. 154).

The Round Mountain district is better known as a 

gold district, having produced a little more than 0.5 

million oz of gold through 1959 (Koschmann and 

Bergendahl, 1968, p. 194), both from placer deposits 

and from lode deposits in Tertiary rhyolite. A 

stockwork gold deposit in Tertiary rhyolite was reactivated in 1976, and during the first 2 years of renewed 

mining more than 50,000 oz of gold was produced (R. 

J. Leone, written commun., 1978). About 50,000 oz of 

gold per year has been produced since then (Russell 

Wood, oral commun., Dec. 1980) for a total production 

of about 200,000 oz during the present phase of mining. 

Production of the deposit and development of new reserves are continuing. Newly discovered reserves in a 

nearby ore body of 8.4 million oz gold and 15.7 million 

oz silver were announced recently (Wall Street Journal, 

Jan. 5, 1982).

Despite the apparent economic insignificance of the 

huebnerite veins, their study is important for several 

reasons. First, the huebnerite is of nearly end-member 

composition, a rarity worldwide. Second, the veins appear to have been formed many millions of years following emplacement (in Cretaceous time) of a granite pluton with which they are associated. Commonly, such 

tungsten-bearing veins are interpreted to have formed 

as a final event related to magmatic emplacement of 

granite. Third, tourmaline in the granite pluton is not 

related genetically to the tungsten-bearing veins as is 

common the world over, but instead it is related to 

an Oligocene granodiorite stock that invades the granite 

and is substantially younger than the huebnerite veins. 

Finally, the huebnerite veins present evidence of two 

major episodes of mineralization. The first episode saw 

deposition of huebnerite along with quartz, muscovite, 

and fluorite closely following invasion in Late Cretaceous time of the granite by aplite and pegmatite dikes. 

The second episode of mineralization was introduction 

into the huebnerite veins of several sulfide minerals,
HUEBNERITE VEINS NEAR ROUND MOUNTAIN, NYE COUNTY, NEVADA

tetrahedrite-tennantite, barite, and chalcedony, and 

formation of scheelite, in a zone spatially associated 

with the Oligocene granodiorite stock, and at a time 

probably shortly following emplacement of the stock.

This study is part of a broad investigation by the 

U.S. Geological Survey of the geology and mineral deposits of the Round Mountain and Manhattan 71/2-minute quadrangles, Nye County, Nev.

We wish to thank Charles M. Taylor of C. M. Taylor 

Microprobe Co. for examining one of the huebnerite 

specimens (DRS-79-68) by electron microprobe to 

measure iron content of color-zoned crystals. The late 

Graham R. Hunt of the U.S. Geological Survey performed optical-spectral studies of several huebnerite 

specimens. Discussions with C. G. Cunningham and J. 

T. Nash of the Geological Survey proved helpful in our 

interpretation of the fluid inclusion data, and discussions with G. A. Desborough and B. F. Leonard, III, 

of the Geological Survey aided our microprobe and 

other mineralogic studies. Comments on the manuscript 

by G. P. Landis and W. H. Raymond improved our 

interpretations of some of the data.

GEOLOGIC SETTING OF THE VEINS

The huebnerite veins near Round Mountain occur in 

and near Cretaceous granite that forms a large pluton 

extending 23 km southeast across the Toquima Range 

from Round Mountain to a long-inactive silver camp at 

Belmont (fig. 1). The granite is emplaced in Paleozoic 

sedimentary and metamorphic rocks. A swarm of Oligocene rhyolite and andesite dikes and a granodiorite 

stock intrude granite about 3 km east and southeast 

of Round Mountain. Miocene silicic volcanic rocks overlie both granite and sedimentary rocks locally in the 

area, and Quaternary alluvium fills the intermontane 

valleys that flank the Toquima Range (Ferguson, 1921; 

Shawe, 1977a).

The Paleozoic rocks are marine sedimentary rocks: 

quartzite, silty argillite, and limestone of Cambrian 

(possibly in part latest Precambrian) age, and argillite, 

limestone, dolomite, chert, and quartzite of Ordovician 

age. Aggregate thickness of the Paleozoic rocks, in part 

probably the result of repetition by thrust faulting, is 

at least 1.5 km. Locally the argillite has been 

metamorphosed to phyllitic shale, and near the contact 

with granite it consists of knotted (chloritoid) schist and 

muscovite-biotite schist. In places the limestone is tremolitized strongly, although not necessarily in proximity to the granite contact. In only a few places does 

limestone contain epidote and garnet, possibly as a result of contact metamorphism adjacent to granite.

"The granite typically is a coarse-grained, granulartextured, light-gray rock that contains quartz, microcline, orthoclase, sodic plagioclase, biotite, and muscovite. Accessory minerals are monazite, apatite, [zircon,] 

and iron-titanium oxide minerals. Fluorite and tourmaline are present locally. Some rocks of the pluton 

are quartz monzonite and granodiorite rather than 

granite" (Shawe, 1977a). An apparently early phase of 

the granite pluton present 8 km south-southeast of 

Round Mountain and extending to Belmont is porphyritic and contains large microcline crystals mostly 2-8 

cm long.

Much of the granite is foliated, especially near the 

border of the pluton. Foliation that is manifested chiefly 

by alined biotite and muscovite flakes, and locally by 

lensoid quartz and feldspar grains, is conformable with 

the contact. The moderately outward dipping contacts 

of the granite pluton and the conformable foliation in 

the granite impart a domelike form to the pluton. The 

pluton is cut by numerous aplite and pegmatite dikes 

and by quartz veins. Aplite and pegmatite commonly 

occur together in individual dikes, and thus are coeval, 

although some dikes locally are cut by younger dikes 

of the same composition. Some foliated dikes are cut 

by unfoliated dikes. Quartz veins everywhere cut the 

aplite and pegmatite dikes. The veins include many that 

are barren and some that are sulfide-bearing in addition 

to those with huebnerite. In places iron-oxide stain in 

granite is intense; numerous limonite pseudomorphs 

after cubic pyrite suggest that most of the iron-stained 

rock is hydrothermally altered granite that has been 

weathered.

The date of emplacement of the granite was 90-100 

m.y. ago (Shawe, 1977a). Several potassium-argon ages 

on muscovite and biotite from foliated granite, pegmatite dikes, and quartz veins are about 80 m.y., indicating that doming and metamorphism of the granite, and 

emplacement of pegmatite and aplite dikes and quartz 

veins, took place in a single episode many millions of 

years after emplacement of the pluton.

The Oligocene dike swarm east and south of Round 

Mountain trends northeast and is about 1.5 km wide 

and 11 km long. The Oligocene stock intrudes the 

swarm near its northeast end. The intrusives are dated 

as about 35 m.y. old (Shawe, 1977a). Mineralization that 

formed tourmaline along with andalusite and dumortierite in granite and tourmaline in rhyolite dikes, is spatially associated with, and apparently genetically related to, the granodiorite stock. Surprisingly the tourmaline mineralization is in no way related to the much 

earlier episode of huebnerite mineralization, but as described later, did involve a small degree of tungsten 

mineralization.
GEOLOGIC SETTING OF THE VEINS

117" 00'

38° 45' 

38" 3D1

KNOWN ZONE OF TUNGSTEN MINERALS

QUATERNARY ALLUVIUM

TERTIARY VOLCANIC ROCKS

CRETACEOUS GRANITE

CRETACEOUS PORPHYRITIC GRANITE

PALEOZOIC SEDIMENTARY AND METAMORPHIC ROCKS

MINE

FIGURE 1. Geologic map of the area near Round Mountain, showing zones of tungsten minerals east and south of Round Mountain.
HUEBNERITE VEINS NEAR ROUND MOUNTAIN, NYE COUNTY, NEVADA

DISTRIBUTION AND FORM 

OF THE VEINS

The huebnerite veins east of Round Mountain are 

found in an area that covers about 25-35 km2 (fig. 2). 

Despite this broad distribution, the veins occur in only 

a few clusters that are narrow east-trending zones no 

more than 200 m wide and 4 km long (fig. 2). The 

huebnerite veins have been found in a vertical interval 

of about 500 m, between altitudes of about 2,125 m 

and 2,625 m (6,800 ft and 8,400 ft). Geologic reconstruction of the granite pluton prior to erosion suggests that 

veins in the core of the pluton were 1.5-2 km below 

its apex. There is no evidence that individual veins extend for more than about a hundred meters vertically 

and most probably are much less than that. Veins within the east-trending clusters are narrow (mostly no 

more than 30 cm wide) and short (generally less than 

30 m long). According to Brown (1911), numerous 

quartz stringers and veins that ranged in thickness 

from 2.5 cm to 1 m extended across the principal easttrending belt. Mostly tabular, the veins pinch and swell 

locally and may vary greatly in thickness in a short 

distance. They occur singly in most places within the 

east-trending clusters, although in a few places they 

appear to occur as very short, en echelon segments. 

Ferguson (1921, p. 389) stated that the veins locally 

"are close enough together to give a banded appearance 

to the granite." Some of the thicker veins split along 

strike into several thin, nearly parallel veinlets. Most 

of the veins are in granite where they tend to strike 

northeast and dip moderately to steeply southeast 

(table 1). A few veins 5 km south of Round Mountain 

occur in muscovite-biotite schist close to the granite 

contact. These veins lie in the schist foliation and dip 

away (southwestward) from the granite contact at low 

to moderate angles. One vein is known in quartzite 

north of the granite contact and east of Round Mountain.

At the time of tungsten mining in 1911, as reported 

by Brown (1911), workings consisted of three tunnels 

in granite. Tunnel No. 1 followed veins and stringers 

for 60 m across the belt, with a crosscut extending 60 

m west that exposed "a large body of milling ore, varying in width from three to ten feet [1-3 m]." Tunnel 

No. 2 was "a drift on the strike of the belt for a distance 

of 400 feet [120 m], exposing large bodies of good milling ore, varying in width from four to twelve feet [1.2 

to 3.7 m]." Tunnel No. 3 was also "a drift on the belt 

for a distance of 390 feet [120 m], cross-cutting many 

veins and stringers," with two drifts from it following 

separate veins 30 m in length. These workings exposed 

"very good ore bodies***having a width of from five 

to fourteen feet [1.5 to 4.3 m]." The locations of these 

tunnels are not certain now, but probably they are the

same as the workings known near the bottom of 

Shoshone Canyon at and near the Darrough prospect 

(fig- 2).

ALTERATION RELATED TO THE VEINS

The huebnerite-bearing quartz veins are bounded by 

a selvage of hydrothermally altered rock. This selvage 

is most evident in granite and is inconspicuous in schist. 

Granite adjacent to veins has been strongly altered so 

that virtually all feldspar crystals have been replaced 

by sericite. Biotite commonly has been converted to 

muscovite, and coarse muscovite crystals have developed locally in masses of sericite within replaced 

feldspar crystals. Quartz, pyrite, chalcopyrite, fluorite, 

and huebnerite have been added to wall rocks locally. 

According to Brown (1911) huebnerite crystals occurred 

in bunches in clay selvages adjacent to the larger veins 

and in the enclosing granite walls. Our studies were 

not adequate to determine the thickness of the altered 

granite selvage adjacent to huebnerite veins. The granite in some places has been widely altered mainly 

sericitized and pyritized probably by mineralizing 

events other than the tungsten episode, and this fact 

has prevented our distinguishing the altered rocks related only to tungsten mineralization. Schist wall rocks 

adjacent to huebnerite veins contain finely crystallized 

muscovite and biotite, but so does all the schist in the 

vicinity of the granite contact. Some of the schist wall 

rocks contain tiny cubes of pyrite (weathered to limonite) and minor huebnerite. We were unable to determine alteration products related solely to the emplacement of the huebnerite veins.

Locally, within the area of huebnerite veins, the 

granite has been strongly greisenized with development 

of much muscovite and some fluorite. Greisen is here 

defined as altered granite consisting of dominant muscovite and containing significant fluorite; quartz, feldspar, 

and other minerals may be present. In places the 

greisen bounds quartz veins not known to contain 

huebnerite but probably of the same mineralizing 

episode, and in other places greisen forms small pipes 

not closely associated with quartz veins.

DESCRIPTION OF THE VEIN MINERALS

Minerals of the huebnerite veins comprise three 

groups: primary (hydrothermal) gangue minerals, primary (hydrothermal) ore minerals, and secondary (alteration) minerals formed as a result of weathering of 

the veins. Primary gangue minerals are quartz, muscovite, allanite, fluorite, barite, calcite, and chalcedony. 

Monazite may be a gangue mineral, but we have no 

direct evidence that it is. Primary ore minerals are 

huebnerite, scheelite, tetrahedrite-tennantite, pyrite,
117° 05'

DESCRIPTION OF THE VEIN MINERALS

117° 02'3D" 117° 00'

38° 42' 30" 

38" 40' 

FIGURE 2. Generalized geologic map of the tungsten area near 

Round Mountain, showing localities of samples described in this 

report. Open circle is locality where huebnerite was identified in 

vein material; only collected samples are labeled with sample numbers. Open circle with X is locality referred to in text. Thin solid 

line, contact, ftsm, Paleozoic sedimentary and metamorphic rocks; 

Kgp, Cretaceous porphyritic granite; Kg, Cretaceous granite; Tgd, 

Tertiary granodiorite stock; TV, Tertiary volcanic rocks; Qa, 

Quaternary alluvium. Cross-lined areas, tungsten-mineralized zones

(0.005-1.0 percent W or visible huebnerite); shaded areas, baseand precious-metal-mineralized zones (as much as 3.0 percent Cu, 

10.0 percent Pb, 5.0 percent Zn, 0.00036 percent Au, and 0.15 percent Ag). Dashed lines are generalized topographic contours, in 

feet, labeled with iron content (in percent, determined by spectrographic analysis) in huebnerite at sample localities (see table 6): 0.2 

percent Fe approximates 6,800 ft, 0.3 approximates 7,000, 0.7 approximates 7,400, 1.0 approximates 7,600, 2.0 approximates 7,800, 

3.0 approximates 8,400 (see fig. 36). (1 ft=0.3 m.)
HUEBNERITE VEINS NEAR ROUND MOUNTAIN, NYE COUNTY, NEVADA

TABLE 1. Description of huebnerite-bearing quartz-vein samples collected east and south of Round

Mountain

[Localities shown on figure 2; leader (--), not determined]

Sample No. 

DRS67-30

67-33

73-17

73-19

73-21

73-27

73-168

74-64

74-66

74-70

74-72

74-76

74-105

74-193

74-194

74-200

74-218

74-221

74-252A.B

78-1

78-2

79-67A.B

79-68

Strike and dip of

N.

N.

N.

N.

N.

N.

N.

N.

N.

N.

N.

N.

N.

N.

N.

N.

15°

60°

15°

30°

40°

40°

18°

42°

_

35°

19°

30°

10°

_-i

45°

15°

35°

15°

W.

E.

E.

E.

E.

W.

E.

E.

E.

E.

E.

E.

E.

E.

E.

W.

35°

55°

70°

50°

60°

_

_

30°

61°

51°

_

16°

39°

85°

80°

_,

_.

65°

79°

-

67°

-.

40°

vein

E.

SE.

E.

SE.

SE.

_

_

NE.

E.

SE.

_

SE.

E.

SE.

E.

_

_

SE.

W.

-

SE.

-

W.

Host rock

Granite

 do 

 do 

 do 

 do 

 do 

 do 

 do 

 do 

 do 

 do 

 do 

 do 

 do -

 do 

 do 

 do 

 do - 

 do 

Quartzite

Granite

Schist

 do 

Scheellte

no

sparse

no

no

no

no

no

abundant

no

no

sparse

no

sparse

no

no

abundant

sparse

no

abundant

sparse

abundant

Sulflde or 

sulfosalt

no

no

no

no

no

no

no

yes

no

no

no

no

yes

yes

no

no

yes

yes

yes

yes

no

yes

Barlte

no

yes

no

no

no

no

no

no

no

yes

no

no

no

no

no

no

no

yes

no

no

yes

no

no

galena, sphalerite, chalcopyrite, pyrrhotite, covellite, 

and blaubleibender covellite (a variety of covellite that 

remains blue in polarized light under the reflecting 

microscope). Secondary minerals are covellite, blaubleibender covellite, chalcocite, stromeyerite, acanthite, 

stibiconite, azurite, malachite, chrysocolla, cerussite, 

anglesite, brochantite, limonite, jarosite, plumbojarosite, autunite, pyrolusite, psilomelane, other manganese 

oxides, tungstite(?), ferritungstite, jixianite(?), stolzite, 

calcite, and opaline silica (chalcedony).

PRIMARY GANGUE MINERALS

QUARTZ

Alpha quartz is the principal component of the veins. 

It tends to fill the vein space as a solid mass of intergrown crystals that individually are as much as 10 cm 

long and 2 cm wide. In places vugs remain, and a few 

veins have much open space in their cores into which 

euhedral, commonly slightly tapered quartz crystals 

penetrate (fig. 3). Crystals here tend to grow perpendicular to the vein walls and may develop forms resembling cockscomb structure. However, many quartz 

crystals are randomly oriented, and large open spaces 

within veins may be lined with doubly terminated 

quartz prisms that have grown transversely on crystals

that penetrate the vugs (fig. 3). Most of the quartz is 

milky white but tends to be only slightly milky or clear 

and colorless where crystals penetrate vugs. Locally 

clear quartz crystals that penetrate vugs are smoky 

gray.

Shears parallel to the walls of the veins are common, 

and shear surfaces generally are slickensided. Only 

rarely has quartz in parts of the veins been strongly 

broken and sheared, and then refilled with younger 

quartz. For example, in one place (sample DRS-74-193) 

vein quartz has been brecciated, the breccia filled with 

chalcedony, and the chalcedony-filled breccia veined 

with clear mosaic quartz (grains less than 1 mm in size) 

that shows mild strain but is virtually free of fluid inclusions. However, some veins are composite, such that 

part of the vein consists of quartz that filled an initial 

open-space fracture that was again opened and filled 

with quartz. The reopened fracture in some places is 

one wall of the original vein and in other places it is 

within the original vein. Massive quartz of the older 

and younger parts of a vein generally seems to merge 

owing to recrystallization, as described below.

Massive, milky-white vein quartz may be extensively 

recrystallized, and virtually all of it is strained. As seen 

in thin sections, this material appears as dominantly 

anhedral intergrown crystals (mosaic structure; locally,
DESCRIPTION OF THE VEIN MINERALS

10 cm

FIGURE 3. Diagrammatic sketch of huebnerite-bearing quartz vein 

(sample DRS-79-68) in quartz-mica schist. Sample is from prospect 

dump; attitude of schist foliation at prospect is N. 15° W., 40° W. 

Wavy dash pattern, schist wall rock; sparse stipple, massive milky 

quartz; clear colorless quartz crystals project into vugs (solid 

white); cross lining, muscovite selvages and seams; solid black, 

huebnerite; close stipple, fluorite.

almost mortar structure) with uneven extinction, 

mostly 1-5 mm across (fig. 4), but locally also as strungout aggregates of tiny crystals that average about 0.1 

mm in size (fig. 5). Leonard, Mead, and Conklin (1968, 

p. 56) described similar quartz in a tungsten lode at 

the New Snowbird deposit, Idaho. In places the finer 

grained aggregates occur in zones that parallel vein 

walls, and they probably resulted from shearing. The 

recrystallized quartz in places contains very abundant, 

minute, somewhat cymoidal fractures 0.03-0.15 mm 

long that are arranged in narrow elongate zones parallel 

to the vein walls. The zones of minute fractures vary 

according to the crystallographic orientation of the 

quartz crystals. Where the c axis is parallel to the vein 

walls, the fractures are nearly parallel and on end. 

Where the c axis is oblique or normal to the vein walls, 

the fractures are arranged en echelon in the elongate 

zones, which themselves are parallel to the vein walls. 

Commonly, alternating zones of fractures have alternating orientations of the contained fractures, such that 

the direction of zone elongation bisects the acute angle 

formed by the alternating fracture orientations, producing a crude herringbone effect.

Fluid inclusions are present in much of the quartz. 

As seen in thin sections, most of the inclusions occur 

in strings or trains that commonly transgress grain 

boundaries (fig. 6). Most sets of subparallel fluid inclusion trains are alined with vein walls, but other orientations are common (fig. 5). In places, sets of subparallel 

fluid inclusion trains seem restricted to small fields or 

cells that show an orientation different from those of 

adjacent fields, as though the fields became rotated unevenly following formation of the trains of inclusions. 

Fluid inclusions tend to be absent from quartz near free 

crystal faces that border vugs in the massive vein

1 cm

FIGURE 4. Sketch of thin section of sample DRS-79-68B showing 

locally transgressing contact between huebnerite-bearing quartz 

vein (right) and quartz-mica schist wall rock (left). Wall rock schist 

(subparallel dashes) contains abundant tiny pyrite cubes weathered 

to limonite (black specks); some schist septa are almost wholly muscovite (unoriented dashes) locally with some pyrite (black blebs); 

other septa contain clear unstrained quartz (solid white) and minor 

huebnerite (high relief, close-stippled mineral) in muscovite. Quartz 

vein (no huebnerite present in this thin section) has muscovite 

(bladed) selvage and contains wisps and flakes of muscovite. Quartz 

(solid white) is strained, and near vein selvage shows well-developed mosaic structure. A thin, limonite-filled fracture (near top 

of thin section) extends from a schist septum across vein wall and 

into muscovite selvage of the vein.

quartz (figs. 6, 19, 20). Quartz prisms that penetrate 

voids and are almost wholly surrounded by space appear to be almost totally devoid of fluid inclusions (figs. 

18, 21). Thus, as seen in hand specimens, quartz crystals that penetrate vugs appear to be clear and colorless, whereas massive quartz is opaque and white as 

the result of diffusion of light caused by millions of 

microscopic fluid inclusions.

The fluid inclusions vary in shape and size. Extremely small (<0.01 mm) inclusions tend to be 

equidimensional and to show negative quartz crystal 

forms. Medium-size (0.02-0.05 mm) inclusions are somewhat oblong and slightly irregular, with stubby spurs 

extending from some corners. Large (as much as 0.1 

mm) inclusions tend to be quite ragged and irregular, 

some being weblike in form. All three forms of inclusions occur mostly in trains, although all also may occur 

randomly scattered. There seem to be no criteria evident by which any of the fluid inclusions could be identified as primary; virtually all may be secondary. However, J. T. Nash of the U.S. Geological Survey (written 

communs., January 1969 and March 1980) reported 

sparse primary fluid inclusions in clear, colorless 

quartz. Most of the fluid inclusions contain a single gas 

bubble whose diameter is about half the diameter of 

the inclusion, but sizes of bubbles relative to apparent 

volume of the fluid in the inclusions vary. Some inclu-
HUEBNERITE VEINS NEAR ROUND MOUNTAIN, NYE COUNTY, NEVADA
DESCRIPTION OF THE VEIN MINERALS

1 mm

FIGURE 6. Quartz charged with fluid inclusions (black specks), thin 

section of sample DRS-78-2A. Small vug (center) is partly lined 

with botryoidal chalcedony (on upper left quartz prism face) and 

filled with fibrous chalcedony; core of vug is granular chalcedony. 

Note the dominant subparallel orientation of trains of fluid inclusions, some of which transgress boundaries of quartz crystals, 

and the lack of fluid inclusions near the vug.

sions contain a second bubble, consisting of liquid 

carbon dioxide, within which the gas bubble is suspended. The diameter of this carbon dioxide bubble varies substantially among different inclusions, from 

slightly longer to perhaps twice as long as the diameter 

of the enclosed gas bubble.

Fluid inclusions that contain only a single bubble are 

much more abundant than those that also contain liquid 

carbon dioxide. The carbon dioxide-bearing inclusions

are irregularly distributed; most thin sections examined 

in this study contain very few. Locally, however, the 

carbon dioxide-bearing inclusions are quite abundant, 

but still unevenly distributed. One thin section of quartz 

vein material from sample DRS-67-30 shows abundant 

carbon dioxide-bearing fluid inclusions in one large area 

that is defined by a set of subparallel trains of fluid 

inclusions, whereas another part of the thin section that 

is defined by another set of trains of fluid inclusions 

is almost devoid of carbon dioxide-bearing inclusions.

According to J. T. Nash (written communs., January 

1969 and March 1980), massive milky quartz of the 

veins contains small fluid inclusions that have filling 

temperatures of 250°-270°C. Liquid carbon dioxide is 

present in many of these fluid inclusions. Nash estimated that original fluids contained about 2-10 mol percent (5-20 weight percent) carbon dioxide. Freezing 

temperatures of fluid inclusions in this quartz indicate 

a salinity of 5.2 weight percent sodium chloride equivalent. Fluid inclusions in clear quartz crystals that penetrate vugs give filling temperatures of about 190°C. The 

fluid inclusions in clear quartz contain no liquid carbon 

dioxide. Freezing temperatures of fluid inclusions in 

clear quartz indicate a salinity of 5.7 weight percent 

sodium chloride equivalent.

MUSCOVITE

Muscovite is a common component of the huebnerite 

veins, and although it makes up perhaps only 1-5 percent of the vein material, it is everywhere present (figs. 

3, 4, 5). The muscovite is colorless, very pale silvery 

gray, or very pale yellowish green. It almost universally forms a thin selvage 1-5 mm thick on the vein 

walls. Muscovite flakes tend to grow perpendicular to 

the vein margins (figs. 4, 5). Although the c axes of 

the crystals commonly are nearly parallel to the margin, 

their orientation otherwise appears to be random so 

that the muscovite forms a feltlike layer viewed normal 

to the vein wall. In places the muscovite in the vein

FIGURE 5 (facing page). Zoned huebnerite crystals (dense stipple)grown on vein wall (black), thin section of sample DRS-79-68A. 

Compound (twinned?) crystal at right displays simple growth zone 

pattern. Note that crystal touches the vein wall locally, and otherwise has grown upon quartz (solid white) or muscovite (bladed) 

selvage. Complexly zoned huebnerite crystal at left commenced 

growth at the left end of the compound crystal, near the vein wall. 

Note that growth zones are grossly different above and below a 

growth boundary that extends diagonally toward the upper left 

of the crystal; uniform extinction under the microscope indicates 

crystallographic continuity across the growth boundary of the two 

differently zoned segments. The complex growth zonation of the 

huebnerite suggests a possibly complex history of crystal growth,

partial dissolution, and regrowth of a differently zoned segment. 

Fluorite (high-relief, patterned, labeled F) forms two small crystals, one between quartz and huebnerite crystals near the initiation 

point of the complexly zoned huebnerite crystal, and one near the 

middle of the upper edge of that crystal. Barite (high-relief, patterned, labeled B) forms an irregular patch on the upper right point 

of the complexly zoned huebnerite crystal. Muscovite (plumose and 

bladed) has grown on huebnerite crystals and in a vug (upper left). 

Quartz (solid white, and marked with numerous strings of fluid 

inclusions) is strained; at the left, shapes of original growth prisms 

remain; at the right, quartz has recrystallized and displays mosaic 

and mortar structure.
10 HUEBNERITE VEINS NEAR ROUND MOUNTAIN, NYE COUNTY, NEVADA

selvage shows a slightly plumose habit (figs. 4, 5). Thin 

lensoid layers of muscovite 1-2 mm thick are found locally within quartz veins, oriented parallel to the vein 

walls (fig. 3). Originally these may have been selvages 

on veins that were reopened and again filled with 

quartz so that the selvage that clung to the original 

vein quartz then formed a layer enclosed within vein 

quartz. Muscovite flakes in some of these internal 

lenses have a pronounced "rake" (fig. 3) as though the 

flakes were dragged out of their normal perpendicular 

alinement by shearing within the vein. Irregular small 

patches and clusters of muscovite flakes are found intergrown with quartz and huebnerite throughout the 

veins.

As seen in thin sections, muscovite also occurs as 

crystals 0.1-1 mm long that fill thin shears in quartz 

that parallel the vein walls (fig. 4). Unlike the muscovite crystals in thicker lensoid layers that are oriented 

normal to the muscovite layers, the muscovite crystals 

in the thinner shears are parallel to the vein walls. 

These thin, muscovite-filled shears are closely associated with parallel streaks of finely crystallized 

quartz.

A purified portion1 of muscovite selvage from sample 

DRS-79-68 was analyzed by J. E. Taggart of the U.S. 

Geological Survey using X-ray fluorescence techniques. 

Results of the analysis, in weight percent, are given 

in table 2. Muscovite separated from samples DRS-79- 

67 and DRS-79-68 was analyzed spectrographically; results are given in table 32. These samples were handpicked but not carefully purified mechanically, and the 

analytical results show evidence of minor impurities.

The unusually high magnesium content of the muscovites shown by both X-ray fluorescence and spectrographic analyses, and the abnormally high silica and 

abnormally low alumina shown by the X-ray fluorescence analysis, indicate that the muscovites are phengitic. In phengite the octahedral Al is replaced by Mg 

and (or) Fe + 2 and the tetrahedral Al is replaced by 

Si. Data for a phengite of similar composition from a 

pegmatite at Amelia, Va. (Glass, 1935), are given for 

comparison in table 2.

Substantial amounts of silver, copper, molybdenum, 

lead, and zinc in sample DRS-79-68 (table 3) are likely 

present in sulfide impurities, and abnormally high 

amounts of tungsten in samples DRS-79-67 and DRS79-63 (table 3) are probably present in huebnerite or 

scheelite. Most of the other minor elements shown in

1Purification of the muscovite entailed trimming of the selvage with adiamond saw, crushing, grinding, and sieving. A 35-60 mesh fraction was treated with magnetic separation 

and heavy liquids; bromoform (D 2.85) floated quartz, and methylene iodide-bromoform mixture (D 3.10) sank heavy minerals. The sample was finally hand picked to assure a virtually 

pure concentrate (0.80 g).

Approximate lower limits of determination for elements analyzed by the six-step spectrographic method, data for which are presented in tables 3, 6, and 7, are given in table 4.

TABLE 2. Chemical analysis of muscovite from. Round Mountain 

huebnerite vein compared with chemical analysis of phengite from 

Amelia, Va., pegmatite (Glass, 1935)

[Leaders ( ), not looked for]

Muscovite from 

Round Mountain 

huebnerite vein

Phengite from 

Amelia, Va. , 

pegmatite

Si °2

A1 2°3

Fe (as Fe-jO-j)

FeO

MgO

CaO

Na 2 0

K2 0

Ti°2

P2°5 

MnO

S

Loss on ignition

H20- 

Other

Totals

49.5

30.0

.17

2.94 

.05

<.2 

11.10 

.09

<.05 

.60

<.02

3.91

98.36

49.16

30.81

1.43

2.22

.48

10.90

4.73 

.15 

.19

100.07

! 30 minutes at 900°C.

the spectrographic analyses could be present in the 

muscovite structure. Amounts of lithium and barium 

in muscovite from sample DRS-79-68 are sufficiently 

high that, if added to the components analyzed by X-ray 

fluorescence, they would raise the total to nearly 100 

percent.

Muscovite collected from vein material at the Darrough tungsten prospect (sample DRS-67-122, same location as DRS-73-168) has a potassium-argon age of 

79.2 ±2.2 m.y. (Marvin and Dobson, 1979, p. 23).

ALLANITE

A few small elongate prisms of a brown, pleochroic 

mineral showing inclined extinction, high relief, and 

moderate birefringence were identified optically as 

allanite in sample DRS-78-2B. The allanite crystals are 

enclosed in vein quartz (fig. 21) and are inferred to have 

been deposited during the initial main phase of vein 

formation.

FLUORITE

Fluorite is widely but irregularly distributed through 

the huebnerite veins. Where present it is generally 

sparse and may make up less than 1 percent of a vein;
DESCRIPTION OF THE VEIN MINERALS 11

TABLE 3. Semiquantitative spectrographic analyses, in weight percent, of some minerals from huebnerite-bearing quartz veins (sample

localities shown on fig. 2)

[Analyses by Nancy M. Conklin. N, not detected at limit of detection or at value shown (see table 4). L, detected, but below limit of determination or below value shown. Also

looked for but not found: Au, Co, La, Pd, Pt, Te, U, Zr, Ce, Ge, Hf, In, Re, Ta, Th, Tl]

Mineral 

Sample No. 

Si

Al

Fe

Mg

Ca

Na

K

Ti

Mn

Ag

As

B

Ba

Be

Bi

Cd

Cr

Cu

Ga

Li

Mo

Nb

Ni

Pb

Sb

Sc

Sn

Sr

V

W

Y

Yb

Zn

Muscovite 

DRS-79-67

>10

>10

.7

3

1.5

.3

7

.07

.3

N

N

.003

.07

.007

N

N

.0002

.0015

.003

.07

N

.0015

.0015

.003

N

.0007

N

.03

.007

.3

N

N

N

Muscovite 

DRS-79-68

>10

>10

1.5

3

.05

.3

10

.07

.3

.01

N

.003

.7

.007

.0015

N

.0003

.07

.007

.15

.07

.0015

N

.7

N

.001

.001

.003

.007

.02

N

N

.03

Fluorite 

DRS-79-67

0.03

.07

.1

.005

>10

N .05

N

N

.15

N

N

N

.0015

N

N

N

N

N

N

N

N

.005

N

N

N

N

N

.7

N

.3

.015

.0015

N

Barite 

DRS-74-221

0.07

L .001

.07

L .001

.007

N

N

N

.003

.002

N

N

>10

.0003

N

N

L

.0015

N

N

N

N

N

.01

N

N

N

.5

N

N

N

N

N

Tetrahedritetennantite 

DRS-78-1

1

.015

.7

.001

1.5

.2

N

N

.02

>2

>10

N

.05

N

.15

.15

N

>10

N

N

N

N

N

.1

>10

N

N

.007

.0015

.03

N

N

7

Tetrahedritetermantite 

DRS-78-2

3

.015

1

.007

3

.1

N

N

.005

>2

>10

.015

.7

N

.7

.07

N

>10

N

N

N

N

N

.15

>10

N

N

.07

.0015

N

N

N

5

Galena 

DRS-74-221

0.3

.015

.003

L .001

.003

N .05

N

N

.0007

.3

N

N

.007

N

.3

N

N

1

N

N

N

N

N

>10

.07

N

N

.0015

N

N

N

N

N

TABLE 4. Approximate lower limits of determination for elements 

analyzed by the 6-step spectrographic method (in percent)

Si

Al

Fe

Mg

Ca

Na

K

Ti

P

Mn

Ag

As

Au

B

Ba

Be

Bi

Cd

Ce

Co

Cr

Cu

Dy

Er

Eu

0.002

.001

.001

.002

.002

.05

.7

.0002

,2

.0001

.00005

.1

.002

.002

.00015

.0001

.001

.002

.015

.0003

.0001

.0001

.005

.005

.01

Ga

Gd

Ge

Hf

Ho

In

Ir

La

Li

Lu

Mo

Nb

Nd

Ni

Os

Pb

Pd

Pr

Pt

Re

Rh

Ru

Sb

Sc

Sn

0.0005

.005

.001

.01

.002

.001

.005

.003

.005

.003

.0003

.001

.007

.0005

.005

.001

.0001

.01

.003

.003

.0002

.001

.015

.0005

.001

Sr

Sm

Ta

Tb

Te

Th

Tl

Tm

U

V

U

Y

Yb

Zn

Zr

0.0005

.01

.02

.03

.2

.02

.005

.002

.05

.0007

.01

.001

.0001

.02

.001

locally, however, such as where wall rocks are schist, 

it may constitute as much as 25 percent of short segments of a vein. It is mostly white but also pale green 

and pale to deep purple; Ferguson (1921, p. 389) described "complex delicate pink crystals" in many veins; 

color varieties occur both separately and together. Typically, fluorite is a late vein mineral, filling vugs. Locally, the tabular interior parts of veins that were open 

space following quartz deposition are lined or filled with 

fluorite (fig. 3). Crystals that line vugs commonly have 

cubic form. Also, fluorite occurs in minor amounts associated with both early and late vein minerals. Tiny 

crystals are seen under the microscope in or adjacent 

to huebnerite (fig. 5), and fluorite is found enclosed in 

some growth layers in zoned huebnerite (fig. 7). Locally 

it is found intergrown with muscovite in vein selvages 

(fig. 8), where it apparently formed during initial stages 

of vein formation. Where quartz has been recrystallized, traces of fluorite may occur together with muscovite and pyrite in small patches interstitial to quartz
12 HUEBNERITE VEINS NEAR ROUND MOUNTAIN, NYE COUNTY, NEVADA

0.5 mm

FIGURE 7. Part of a zoned huebnerite crystal, plane-polarized light, 

thin section of sample DRS-79-68A. Crystal faces on the inner 

part of the huebnerite crystal (lower right) are coated with a thin, 

uneven layer of fluorite. Zoned and partly broken layers of huebnerite that contain blebs of quartz and fluorite overlie the inner 

fluorite layer. Quartz is molded against the corroded exterior of 

the huebnerite crystal (upper left).

grains (fig. 9). Fluorite occurs also in trace amounts 

as a postvein mineral, within parts of veins that were 

strongly sheared following vein formation (fig. 8).

Examination of sample DRS-79-67 with an ultraviolet lamp indicated the presence of both phosphorescent and nonphosphorescent fluorite, suggesting 

the possibility of two separate episodes of fluorite deposition that resulted in fluorites of slightly different 

trace-element composition. Also, some fluorite in the 

huebnerite veins shows bluish-white fluorescence under 

short-wave ultraviolet radiation, and some does not.

A six-step semiquantitative emission spectrographic 

analysis of the pale fluorite in DRS-79-67 is presented 

in table 3. Minor impurities suggested by the data are 

pyrite (iron), muscovite (silicon and aluminum), and 

huebnerite (manganese and tungsten). Strontium, yttrium, and ytterbium likely are present in the fluorite 

structure.

1 mm

FIGURE 8. Edge of huebnerite-bearing quartz vein (above) and 

sheared wall rock (below), thin section of sample DRS-79-68C. 

Sheared wall rock consists of muscovite (subparallel dashes), pyrite weathered to limonite (black cubes and blebs), and a trace 

of fluorite (high relief, patterned, labeled F); the sheared zone 

(2-5 mm thick) laterally (beyond the field of view) transgresses 

the margin of the vein and may be enclosed wholly in vein material or wholly in wall rock. Tetrahedrite-tennantite and its oxidation products occur in the sheared zone elsewhere. Vein selvage 

is muscovite (bladed and plumose), randomly oriented against the 

vein wall, and inward tending to be plumose, locally intergrown 

with fluorite that constitutes about 20 percent of the selvage. 

Huebnerite (high relief, dense stipple) and strained quartz (solid 

white, marked by fluid inclusions) fill the interior of the vein.

Fluid inclusions are present in fluorite. According to 

J. T. Nash (written communs., January 1969 and March 

1980), fluorite that fills vugs in quartz vein material 

contains fluid inclusions that have filling temperatures 

of 230°-260°C. Freezing temperatures of fluid inclusions 

in this fluorite indicate a salinity of 5.8-6.0 weight percent sodium chloride equivalent. Some of the fluorite 

that has fluid inclusions with a filling temperature of 

260°C contains no visible carbon dioxide but decrepitates on heating, suggesting the presence of some carbon dioxide dissolved in the aqueous phase of the inclusions. Freezing temperatures of fluid inclusions in this 

fluorite indicate a salinity of 4.5 weight percent sodium 

chloride. Late-stage fluorite, also occurring as vug fillings, gives filling temperatures of about 190°C. No liquid carbon dioxide is evident in fluid inclusions in the 

late-stage fluorite.
DESCRIPTION OF THE VEIN MINERALS 13

0.5 mm

FIGURE 9. Transitional vein margin, plane-polarized light, thin section of sample DRS-67-33D. Field of view includes quartz (upper 

right) that contains fluid inclusions and is similar in appearance 

to vein quartz, plagioclase (upper left) that shows limonite-filled 

cleavages, and randomly oriented bladed muscovite (lower left); all 

three minerals are intergrown in lower right. Pyrite cube (center) 

that is oxidized to limonite and contains small blebs of quartz is 

abutted by an elongate grain of fluorite on its upper left face. Massive vein quartz lies just below the field of view.

BARITE

Barite is present only locally and in very small 

amounts in the huebnerite veins. Rare, small, irregular 

patches that are aggregates of tabular crystals have 

grown on huebnerite (fig. 5), where barite probably was 

an early vein mineral. Barite occurs also as white crystals less than 1 mm across in places intergrown with 

quartz and elsewhere penetrating vugs where free surfaces show characteristic tabular orthorhombic form. 

Locally, tabular barite crystals as large as 3 cm across 

and 0.5 cm thick occur in vugs in vein quartz. A thin 

section of sample DRS-74-70 as seen under the microscope contains late-stage barite (fig. 10). In this sample 

"milled" granite lies in a matrix of vein quartz that contains huebnerite and is itself veined by thin (about 1

1 mm

FIGURE 10. Late-stage veinlet in huebnerite-bearing quartz vein, 

plane-polarized light, thin section of sample DRS-74-70. Quartz 

(right, and upper left) is strained, and is crowded with fluid inclusions, some of which contain liquid carbon dioxide; note subparallel 

trains of abundant fluid inclusions. Irregular late-stage veinlet 

(lower left to upper right) is chalcedony that contains barite 

pseudomorphs after cubic pyrite (light-gray, squarish crystals), 

muscovite (randomly oriented, bladed crystals), and scattered 

dustlike limonite (black). Note that some barite pseudomorphs and 

muscovite crystals occur in vein quartz outside the chalcedony veinlet. Beyond the field of view, clear quartz veinlets that contain 

barite cut chalcedony veinlets.

mm or less), irregular veinlets of chalcedony that contain muscovite and barite. The barite appears to have 

replaced pyrite inasmuch as it occurs as aggregates of 

barite crystals pseudomorphous after a cubic mineral 

(fig. 10). The cores of some such pseudomorphs contain 

limonite, probably oxidized from original pyrite (fig. 

11).

Barite separated from sample DRS-74-221, collected 

from a huebnerite- and sulfide-bearing quartz vein (fig. 

2), was analyzed spectrographically (table 3). Of the elements detected, barium, and probably calcium, lead, 

and strontium, are present in the barite structure; 

other elements may be present in mineral impurities 

within the analyzed barite.
14 HUEBNERITE VEINS NEAR ROUND MOUNTAIN, NYE COUNTY, NEVADA

1 mm

FIGURE 11. Barite pseudomorphous after pyrite in quartz vein, 

thin section of sample DRS-74-70. Variously oriented barite crystals (white, patterned) replace periphery of pyrite cube (center), 

core remnant of which has been oxidized to limonite (black). Unidentified high-relief, moderately birefringent, pale-yellow (color 

not shown) mineral (labeled J) at lower edge of pseudomorph may 

be jarosite. Pseudomorph lies in strained vein quartz (white) that 

shows mosaic and mortar structure and contains abundant trains 

of fluid inclusions (dark specks, mostly alined subparallel). Muscovite (bladed) forms individual crystals and short stringers scattered in quartz.

CALCITE

Calcite occurs in minor amount and only locally as 

tiny (0.03 mm and less) crystals associated with scheelite, pyrite (oxidized), and muscovite, and it is considered to be hydrothermal in origin in those places.

CHALCEDONY

Chalcedony is found in late-stage veinlets in the 

huebnerite-bearing quartz veins; because it contains 

minerals such as muscovite, barite, and pyrite (weathered to limonite), it is interpreted to be a hydrothermal 

mineral in these occurrences.

MONAZITE

We have no direct evidence of the occurrence of 

monazite in the quartz veins, although Ferguson (1921, 

p. 389) reported recovery of monazite along with huebnerite from residual surface material near a vein 3 km 

southeast of Round Mountain. Ferguson (1921, p. 389- 

390) inferred that the monazite and huebnerite were

derived from a pegmatitic quartz vein. Monazite is an 

accessory mineral of the granite locally, for example 

in Shoshone Canyon along the vein where sample DRS73-168 was collected.

PRIMARY ORE MINERALS

HUEBNERITE

Huebnerite is the principal primary ore mineral of 

the tungsten-bearing quartz veins. Small local concentrations may exceed 10 percent of the vein material 

(these parts have been prospected or mined), but the 

huebnerite content of much of the veins ranges from 

but a few percent down to substantially less than 1 

percent. Huebnerite content varies as much within a 

vein as from vein to vein. The huebnerite is dark brownish black on fresh cleavage surfaces, showing deep-bloodred internal reflection in bright light. Cleavage 

is well developed on {010}, and cleavage (parting) less 

developed on {100}. Huebnerite occurs as stubby, tabular to prismatic crystals, generally subhedral to euhedral, either singly or as composite clusters. Single crystals are as much as 5 cm long, although commonly 1 

cm or less in size. In granite huebnerite tends to occur 

in the cores of quartz veins where it is intergrown with 

quartz as subhedral crystals and as aggregates of crystals. In this environment tabular, somewhat tapered 

crystals are common. In schist huebnerite tends to 

occur as stubby, euhedral crystals growing from one 

wall of flat veins (fig. 3). Vein material with huebnerite 

growing from one wall was not observed in place in 

schist, but was noted in material from prospect dumps. 

Presumably the huebnerite is on the footwall of these 

flat veins, analogous to the example from Panasqueira, 

Portugal, illustrated by Kelly and Rye (1979, fig. 9). 

A thin (3 cm), northeast-striking, nearly vertical quartz 

vein in granite at the locality marked with an open circle and X on figure 2 displays prismatic crystals that 

grow perpendicularly into the vein from its northwest 

wall.

Where huebnerite has grown from vein walls, crystals commonly fan or flare outward from their base in 

the direction of growth (fig. 3). The center of the base 

of such a crystal is in direct contact with the wall, and 

outward the crystal rests on a progressively thicker selvage of muscovite, which shows thickest development 

on the walls between separate huebnerite crystals (fig. 

3). This relationship indicates simultaneous deposition 

of huebnerite and muscovite beginning with the onset 

of vein mineralization. Inclusion of flakes of muscovite 

within huebnerite also indicates synchronous crystallization of huebnerite and muscovite.

Many of the subhedral to euhedral crystals of huebnerite show growth zones that, as seen in thin sections
DESCRIPTION OF THE VEIN MINERALS 15

1 mm 0.25 mm

FIGURE 12. Zoned huebnerite crystal, plane-polarized light, thin section of sample DRS-79-68. Rectangular outline in A shows area of B.

and less plainly in polished sections, are alternating 

lighter and darker brown zones that reflect the crystallographic form of the growing crystals (figs. 12-14). 

Some euhedral huebnerite crystals have been fractured, 

dismembered, or otherwise deformed during growth 

(fig. 14). Growth zones may be truncated or separated, 

and the resulting fracture space filled by later stage 

huebnerite or by quartz (figs. 13, 14). This dismemberment resulted from brecciation rather than replacement, as can be shown locally by the fact that segments 

of huebnerite can be fitted together if interstitial later 

huebnerite and quartz are removed. The "milling" of 

some huebnerite crystals as a result of excessive deformation of the vein material was accompanied by recrystallization of quartz, as evidenced by the fact that the 

dispersed "milled" fragments of huebnerite are embedded in fine-grained mosaic quartz (figs. 15, 16).

In places where quartz shows pronounced mosaic 

structure and is sheared (for example, samples DRS67-33 and DRS-74-221), huebnerite may appear "worm 

eaten" and is intergrown with granular quartz crystals. 

Locally this huebnerite may have lighter colored, mottled patches against quartz. Some huebnerite crystals

show evidence of solution etching where they are adjacent to voids in the vein material, as well as where 

they are embedded in recrystallized quartz. BeddoeStephens and Fortey (1981) reported that, in the Carrock Fell tungsten deposit in the English Lake district, 

wolframite that occurs in quartz veins near vugs tends 

to be veined and replaced by scheelite, arsenopyrite, 

pyrite, carbonate minerals, and less commonly by 

quartz.

The density measured by Herman balance of three 

samples of huebnerite from Round Mountain quartz 

veins ranges from 7.24 to 7.26. Calculated density of 

pure MnW04 is 7.234.

Chemical data for Round Mountain huebnerites are 

presented in a later section of this report.

SCHEELITE

Scheelite is a widespread but sparse component of 

the huebnerite veins. It is restricted, however, to a 

specific environment and is therefore present in some 

veins and virtually absent from others (table 1). It is 

associated with sulfides and sulfosalts within the areas
HUEBNERITE VEINS NEAR ROUND MOUNTAIN, NYE COUNTY, NEVADA

-ffr

5mm

FIGURE 13. Zoned and fractured huebnerite crystal, plane-polarized 

light, thin section of sample DRS-79-67. White patches in lower 

half of view are areas plucked during grinding of thin section. 

Upper part of crystal lies along an irregular boundary against 

strained quartz (also white). Irregular corrosion of the outer part 

of the huebnerite crystal before crystallization of quartz is implied. 

Note converging growth zones in huebnerite crystal that suggest 

diminished and arrested growth of the crystal periodically along 

some faces, and that imply a directional influx of material that 

formed the growing crystal. Some growth zones have been truncated (upper left), but the mechanism of truncation is not evident. 

Note also fractured growth zones at top center where fractures 

are filled by light-colored huebnerite, and corroded huebnerite 

growth zones at right center filled by light-colored huebnerite. 

Scale is approximate.

of base- and precious-metal mineralization of the tungsten-bearing veins, and it occurs in some veins devoid 

of sulfides and sulfosalts but close to the areas of baseand precious-metal mineralization. With one known exception, scheelite is absent from veins more distant 

from these zones of mineralization (compare table 1 and 

fig. 2). Within scheelite-bearing veins the mineral occurs in sparse to trace amounts. On a microscopic scale 

it is seen to occur closely associated with huebnerite, 

and there it ranges from a few percent to perhaps 50 

percent of the tungsten-bearing mineral present in a 

thin section (sparse to abundant in table 1).

White to very pale yellowish green scheelite occurs 

as irregular patches and blebs on the margins of and 

within huebnerite crystals, and as small veinlets or fracture fillings a fraction of a millimeter wide in huebnerite 

(figs. 17, 18). Locally, veinlets of scheelite as much as 

1 mm wide fill fractures that extend through huebnerite 

and into adjacent vein quartz. Small specks, patches, 

and veinlets of scheelite occur in quartz near concentrations of huebnerite. The veinlets, some of which are 

aggregates of scheelite and muscovite (fig. 17), appear 

to fill late shears; the patches commonly are fillings of 

vugs in quartz (fig. 19). These relations of scheelite to

5mm

FIGURE 14. Zoned and fractured huebnerite crystal, plane-polarized 

light, thin section of sample DRS-79-68. White patches within crystal are areas plucked during grinding of thin section. Quartz (white, 

upper right) has grown on huebnerite. Note segment of zoned 

huebnerite (center) that was fractured and displaced upward (so 

that growth zones are offset) and then overgrown with continuous 

layers of huebnerite. Bleaching or filling of huebnerite has occurred 

along the margins of the fractured and displaced segment. Scale 

is approximate.

other minerals are similar to those described for scheelite in a tungsten-bearing quartz lode at the New Snowbird deposit, Idaho, by Leonard, Mead, and Conklin 

(1968, p. C6).

Microprobe examination of scheelite associated with 

huebnerite in sample DRS-74-193 revealed the presence of about 0.045 percent MnO, 0.35 percent FeO, 

81.64 percent WO3, 18.80 percent CaO, and 0.00 percent MoO3 (total, 100.83 percent; average of two 

analyses). Examination of the scheelite under ultraviolet light using a scheelite fluorescence analyzer 

manufactured by Ultra-violet Products, Inc., Los 

Angeles, Calif. 1 , showed that the scheelite fluoresces 

bright blue and contains virtually no molybdenum.

TETRAHEDRITE-TENNANTITE

Tetrahedrite-tennantite (referred to as tetrahedrite 

by Ferguson, 1921, p. 389-390) is present in some of 

the huebnerite veins where it is generally sparse but 

may locally make up a few percent of the vein material. 

These veins are found in zones of base- and preciousmetal mineralization indicated on figure 2. Tetrahedrite-tennantite forms small grains as much as 5 mm 

across in milky white quartz. Under the microscope the 

grains are seen to fill vugs in quartz (figs. 20-22).

'Brand or manufacturers' names used in this report are for descriptive purposes only 

and do not constitute endorsement by the U.S. Geological Survey.
DESCRIPTION OF THE VEIN MINERALS 17

1 mm

FIGURE 15. "Milled" huebnerite crystal, plane-polarized light, thin 

section of sample DRS-79-68C. Original huebnerite crystal (dark 

gray) has been broken and is dispersed in strained and recrystallized quartz (white) that contains large numbers of fluid inclusions 

(tiny dark specks). Irregular patches of muscovite and fluorite (light 

gray) are intermingled with very fine grained mosaic quartz and 

fragments of huebnerite to the right of the large crystal of huebnerite.

Tetrahedrite-tennantite separated from samples 

DRS-78-1 and DRS-78-2, collected from huebneritebearing veins (fig. 2), was identified optically in 

polished sections and by X-ray diffraction, and analyzed 

spectrographically. The spectrographic analyses are 

given in table 3. The substantial amounts of copper, 

antimony, arsenic, zinc, and silver indicated in the 

analyses show that the sulfosalt is zincian tetrahedritetennantite. Also, appreciable amounts of silicon, calcium, barium, and tungsten given in the analyses suggest 

the presence of some impurities in the analyzed sulfosalts such as quartz, calcite, barite, and a tungsten 

mineral. The small amounts of aluminum given rule out 

the presence of much feldspar. Also, the low aluminum 

contents rule out a large number of sodium-bearing 

minerals to account for the sodium that is present; possibly a secondary iron-sodium sulfate such as natrojaro1 mm

FIGURE 16. "Milled" and "mixed" huebnerite fragments, planepolarized light, thin section of sample DRS-79-68E. Extremely disrupted huebnerite (dark gray) consists of a large number of disoriented fragments of different sizes, color shades, and degrees of 

zoning, embedded in strained mosaic quartz (white) that contains 

large numbers of fluid inclusions (dark specks).

site or copper-sodium sulfate such as krohnkite or natrochalcite could account for the presence of sodium. 

Elements such as iron, bismuth, cadmium, and lead 

may be present mostly in the sulfosalt structure, or 

otherwise in minor amounts of sulfide impurities.

Minor amounts of tetrahedrite-tennantite are found 

along with pyrite, chalcopyrite, and fluorite dispersed 

as small crystals (less than 1 mm) in wall rock near 

huebnerite veins at the Darrough prospect (fig. 2).

SULFIDES

Sulfides are found in only trace to minor amounts 

(probably less than 1 percent) in most of the vein material from the tungsten-bearing veins. Local concentrations in vein material of hand-specimen size may reach 

several percent. Like tetrahedrite-tennantite, sulfides 

occur in the tungsten-bearing veins within the zones 

of base- and precious-metal mineralization shown on figure 2.
18 HUEBNERITE VEINS NEAR ROUND MOUNTAIN, NYE COUNTY, NEVADA

1 mm 1 mm

FIGURE 17. Huebnerite, veined and partly replaced by scheelite, 

plane-polarized light, thin section of sample DRS-78-2B. Rectangular outline in A shows area of B. A, Quartz (white) that is locally 

sheared, strained, and universally crowded with fluid inclusions 

(dark specks) in variously oriented trains. Mosaic structure is developed only locally in quartz, and apparent original prismatic form 

of much of the quartz is still evident. Enclosed in quartz is a central 

patch of huebnerite (dark gray), irregularly veined and largely replaced by scheelite (medium gray). Quartz prism faces surround

Pyrite is by far the most abundant and widespread 

sulfide. It and other sulfides such as sphalerite, galena, 

covellite (CuS), chalcopyrite, and pyrrhotite characteristically are late-stage minerals in the veins. Both 

covellite and blaubleibender covellite are present in the 

veins, but not everywhere together. The sulfides occur 

in shears in quartz, filling vugs in quartz in the fashion 

of tetrahedrite-tennantite (figs. 20-22), and in latestage veinlets of chalcedony (fig. 10). Figure 23 shows 

pyrite (altered to limonite) filling vugs in quartz and 

partly replacing quartz prisms that penetrate vugs. Pyrite also forms crystals about 1 mm in diameter that, 

along with quartz prisms, line vug walls, and that appear to have grown contemporaneously with the late 

quartz (fig. 24). Pyrite occurs also as cubes disseminated locally in vein quartz (fig. 9) and widely in wall

some of the patch and suggest that the scheelite may be in part 

a vug filling. Veinlet in quartz (lower part of view) contains scheelite and muscovite (bladed, light gray). B, Scheelite (light gray) 

appears to replace huebnerite (medium gray) irregularly; also it 

fills cracks where huebnerite has been fractured and separated, 

as for example in the upper right where a Z-shaped fracture separated slightly and slipped in a left-lateral sense to provide an opening that was filled with scheelite.

rocks (figs. 4, 8). Sulfides also occur as irregular grains 

enclosed in mosaic quartz where they may have crystallized simultaneously with mosaic quartz but are probably younger than the initial stage of quartz mineralization. Sphalerite that is enclosed in mosaic vein quartz 

near vugs has been fractured, "milled," and dispersed 

apparently simultaneously with recrystallization of 

quartz (fig. 25). Figure 26 shows examples of covellite 

that apparently replaced galena, and figure 27 shows 

chalcopyrite exsolved from sphalerite. Molybdenite has 

not been recognized within huebnerite veins, although 

spectrographic analyses of a few samples (DRS-79-68, 

table 3; DRS-67-33, table 6; DRS-74-194, DRS-74- 

221, DRS-74-252A, table 7) show minor amounts of molybdenum.

Some late shearing in the veins postdated deposition 

of sulfide and sulfosalt minerals.
DESCRIPTION OF THE VEIN MINERALS 19

1 mm

FIGURE 18. Huebnerite veined with scheelite, plane-polarized light, 

thin section of sample DRS-79-68A. Fractured and somewhat 

granulated huebnerite (dark gray) has been veined and otherwise 

filled with late-stage scheelite (medium gray). Huebnerite and 

scheelite are veined and surrounded by strained quartz (white) that 

displays mosaic structure. Quartz is crowded with fluid inclusions 

(dark specks).

A spectrographic analysis of galena from DRS-74-221 

is given in table 3. Silver, bismuth, and antimony probably are held in the galena structure, copper is present 

mostly in covellite, and silicon, aluminum, barium, and 

strontium are present in minor mineral impurities.

SECONDARY MINERALS

Secondary minerals in the huebnerite veins near 

Round Mountain are mostly oxidation products that resulted from near-surface weathering. They occur as alteration halos around primary vein minerals, particularly the ore minerals, and in fractures and vugs near 

the primary vein minerals. A few secondary minerals 

appear to be low-temperature precipitates that resulted 

from solution and redeposition of vein or wall rock components by near-surface ground waters.

1 mm

FIGURE 19. Vug in quartz (white) filled with scheelite (medium 

gray), plane-polarized light, thin section of sample DRS-79-68A. 

Quartz that bounds the vug consists of well-formed prisms, is only 

slightly strained, and contains few fluid inclusions. Elsewhere the 

quartz has well-developed mosaic structure, is strongly strained, 

and contains numerous fluid inclusions (dark specks). Huebnerite 

(dark gray, at top) is part of a grain that has been partly broken 

and filled with quartz locally. Muscovite (bladed, light gray) is randomly oriented in a clot in quartz 1 mm above the scheelite-filled 

vug, and elsewhere forms plumose bunches in and near huebnerite 

and in the vug. Some of the larger black blebs in quartz are limonite 

probably oxidized from pyrite.

SULFIDES

Sulfides have formed commonly as initial breakdown 

products of weathering of primary sulfide and sulfosalt 

minerals. As shown on figure 28, chalcocite (Cu2S), 

acanthite (Ag2S), and stromeyerite ((AgCu)2S), identified by optical properties, X-ray diffraction, and the 

scanning electron microscope, have formed as an initial 

breakdown of tetrahedrite-tennantite. In places covellite and blaubleibender covellite appear to be alteration 

products of primary copper-bearing sulfide minerals, 

and in addition appear to be alteration products of the 

initial alteration minerals chalcocite and stromeyerite 

(fig. 28).
20 HUEBNERITE VEINS NEAR ROUND MOUNTAIN, NYE COUNTY, NEVADA

0.5 mm

FIGURE 20. Tetrahedrite-tennantite (black) filling vug in quartz 

(white), plane-polarized light, thin section of sample DRS-78-2A. 

Quartz contains abundant fluid inclusions (dark specks); inclusions 

tend to be least abundant where quartz prisms penetrate the vug. 

Irregular, light-gray veinlets near top of view are muscovite. 

Chrysocolla fills a minute vug at upper left.

OXIDES, TUNGSTATES, CARBONATES, SULFATES, 

PHOSPHATES, AND SILICATES

Oxide minerals have formed directly from weathering 

of some ore minerals such as huebnerite, or are further 

breakdown products of weathered sulfide and sulfosalt 

minerals. Manganese oxides, including pyrolusite 

(Mn02), psilomelane (colloidal Mn02), and probably 

other manganese oxides, are common alteration products 

of huebnerite (fig. 29). Some of the manganese 

oxide minerals contain significant barium, as indicated 

by scanning electron microscope studies. Weathered 

huebnerite has a dull-black appearance as a result of 

the presence of manganese oxide minerals. Black and 

dark-brown manganese oxide and manganese-iron oxide 

mixtures commonly line vugs or coat fractures in the 

quartz veins near the sites of primary ore minerals. 

Manganese oxide dendrites coat fracture surfaces in 

many places in and near the veins.

1 mm

FIGURE 21. Tetrahedrite-tennantite (black) filling vug in quartz 

(white), plane-polarized light, polished thin section of sample DRS78-2B. White blebs within tetrahedrite-tennantite, some of which 

contain bubbles, are areas plucked during grinding of the thin section. Dark-gray areas within the large vug and in smaller nearby 

vugs are weathering products, mostly malachite. Quartz contains 

abundant fluid inclusions (dark specks) that are sparse or absent 

in small quartz prisms that penetrate the vug. Small, dark-gray, 

needlelike prisms at center right and above tetrahedrite-tennantitefilled vug are allanite. Light-gray vug filling at lower right edge 

of view is chalcedony.

Stibiconite (Sb306(OH)) has formed both as an early 

(fig. 30) or late (fig. 28) weathering product of tetrahedrite-tennantite.

Limonite is almost ubiquitous in and near the huebnerite veins. It has been derived mostly from the oxidation of pyrite, and it occurs commonly as pseudomorphs 

after pyrite (figs. 4, 8, 9, 10, 11, and 19), fracture fillings (figs. 4 and 33), and as a wash or in dustlike form 

permeating vein material and wall rocks. Tungstite, a 

hydrous oxide, occurs as a minor buff-yellow alteration 

product on the surfaces of and in fractures in huebnerite 

crystals. It is generally associated with other secondary 

tungsten minerals and (or) stibiconite.

Chrysocolla is the only silicate weathering product 

identified in the huebnerite veins. It may have formed
DESCRIPTION OF THE VEIN MINERALS 21

1 mm

FIGURE 22. Copper minerals (shades of gray) filling vug in quartz 

(white), plane-polarized light, polished thin section of sample DRS78-2B. Island remnants of original vug filling are irregular blebs 

of tetrahedrite-tennantite; these are surrounded by secondary copper and antimony oxides (in the photomicrograph these minerals 

are indistinguishable and together appear as nearly black patches); 

surrounding the tetrahedrite-tennantite and associated oxides and 

filling the arm of the vug in the lower three-fourths of the view 

are green secondary copper minerals (mostly malachite?) and minor 

brown secondary antimony(?) and arsenic(?) minerals (dark gray); 

the other arms of the vug (upper left and upper right) contain 

azurite (medium gray) that shows concentric growth layers. Beyond 

the area of the view, azurite is bounded by crystal faces in open 

space of the vug. Note that the quartz prisms that penetrate the 

vug are nearly devoid of fluid inclusions (dark specks) that abound 

in the remaining quartz. Small vug in lower right is lined with 

chalcedony.

early in the weathering of copper-bearing sulfides inasmuch as it lines vugs that were later filled with 

malachite (fig. 31). Chrysocolla also was deposited before or contemporaneously with the precipitation of 

chalcedony that fills vugs (fig. 32). It fills late fractures, 

and itself is veined by very late chalcedony (fig. 33).

The tungstates, ferritungstite ((W,Fe +3)2O4(OH)2 - 1/2- 

H2O Machin and Susse, 1975 yellow tungstic ochre, 

sample DRS-74-221), jixianite(?) (Pb(W,Fe +3)2- 

(O,OH)7, brownish-red tungstic ochre), and stolzite

(PbWO4, orange-yellow tungstic ochre), are minor alteration products found associated with the primary 

tungsten minerals. Because ferritungstite, jixianite, 

and stibiconite are all reported to have pyrochlore-type 

structure, conventional X-ray diffraction techniques 

cannot readily distinguish them with certainty, particularly when they are known to occur as mixtures. Jixianite is still an incompletely described mineral and discrepancies exist in the published descriptions (Jianchang, 1979; Hogarth and Chao, 1979, p. 1330).

Several carbonates azurite, malachite, cerussite, 

and calcite and sulfates anglesite, brochantite, and 

jarosite-plumbojarosite are common alteration products in the vicinity of primary vein sulfides. According 

to Krai (1951, p. 154), the phosphate autunite occurs 

in trace to small amounts in the tungsten veins east 

of Round Mountain; the mineral presumably is a weathering product of an unidentified primary uranium mineral.

REMOBILIZED MINERALS

Two minerals appear to have been in part simply remobilized from earlier vein minerals and deposited in 

very late stages. The silica of chalcedony probably was 

derived mainly from preexisting vein quartz; it appears 

to have been deposited in several late stages of 

mineralization (see fig. 34), the earlier ones probably 

low-temperature hydrothermal and the later ones possibly during weathering by cold ground waters. Opaline 

silica that fluoresces bright yellowish green under both 

shortwave and longwave ultraviolet radiation, probably 

owing to the presence of the uranyl ion, commonly coats 

fracture surfaces. Calcite that fluoresces pale salmon 

to orange pink and that may be slightly phosphorescent 

sparsely coats fractures in the veins along with other 

secondary minerals, particularly chalcedony. The calcite 

may have been reworked from earlier primary vein calcite or from calcium-bearing wall rocks.

SUMMARY OF TEXTURES AND PARAGENESIS

The huebnerite-bearing quartz veins near Round 

Mountain were filled with gangue and ore minerals to 

form nearly solid lenticular-tabular masses that locally 

contain vugs. Most vein walls are sharp and bounded 

by muscovite selvages, but in places veins merge with 

country rocks as if formed in part by replacement, and 

locally near veins some vein minerals impregnate the 

country rocks.

Figure 34 shows the interpreted paragenesis of mineral deposition, and events of deformation and recrystallization. The paragenesis is based on the previously 

described detailed interrelations of minerals local sequences of mineral deposition, and correlations of specific mineral deposition from place to place.
22 HUEBNERITE VEINS NEAR ROUND MOUNTAIN, NYE COUNTY, NEVADA

1 mm

FIGURE 23. Pyrite (altered to limonite) filling vugs in quartz and 

partly replacing quartz prisms that penetrate vugs, plane-polarized 

light, thin sections of samples DRS-74-252A! (A) and DRS-74- 

252A2 (B). A, Quartz prisms (white) that penetrate vugs contain

The paragenetic diagram (fig. 34) shows that an initial hydrothermal phase witnessed deposition of major 

amounts of quartz and lesser amounts of muscovite, 

huebnerite, fluorite, barite, and pyrite. A period of 

shearing and recrystallization followed in which much 

quartz was reconstituted; some new muscovite, huebnerite, fluorite, and pyrite were added at this stage, and 

muscovite and huebnerite were in part mechanically redistributed. Some scheelite and tetrahedrite-tennantite 

may have formed in the later part of this stage. A second hydrothermal stage saw deposition along shears 

and in the earlier vugs of small additional amounts of 

muscovite, quartz, fluorite, and barite; formation of 

minor calcite, scheelite, tetrahedrite-tennantite, and 

several sulfides; and finally precipitation of chalcedony. 

In places more than one younger episode of hydrothermal remineralization is evident. Near-surface weathering of the veins resulted in formation of small amounts 

of calcite, covellite, chalcedony, chalcocite, stibiconite, 

chrysocolla, malachite, azurite, manganese oxide, and 

jarosite.

bleblike grains of limonite after pyrite (black). B, Granular pyrite 

in upper right (orbicular forms) has altered to concentric layers 

of limonite, jarosite, and chalcedony.

Some uncertainty exists regarding part of the relations shown on figure 34. Muscovite is associated with 

chalcedony in some late veinlets that cut earlier vein 

minerals; the muscovite appears to have grown in place 

although it is possible that the muscovite crystals were 

mechanically emplaced in the chalcedony veinlets. More 

than one major episode of shearing may have affected 

the veins: an earlier episode that took place when 

quartz was recrystallized at the time carbon dioxidebearing solutions moved through the veins, and a later 

(perhaps much later) episode that preceded and (or) accompanied scheelite, tetrahedrite-tennantite, and sulfide mineralization.

The paragenetic diagram (fig. 34) has been simplified 

inasmuch as several minerals of the veins are not 

shown. The positions of some minerals in the paragenetic sequence are uncertain, although most of the deleted 

minerals can be placed in their appropriate positions. 

Allanite probably was contemporaneous with early vein 

quartz. Chalcopyrite probably belongs with sphalerite; 

blaubleibender covellite with covellite; acanthite and
DESCRIPTION OF THE VEIN MINERALS 23

1 mm

FIGURE 24. Vug in quartz vein, under crossed nicols, thin section 

of sample DRS-74-252B2. Pyrite crystals (black) and quartz prisms 

(white and shades of gray) line vug and are coated with chalcedony 

(fine grained, mottled gray). The core of the vug is filled with 

granular quartz (white, black, and shades of gray).

stromeyerite with chalcocite; and cerussite, anglesite, 

brochantite, limonite, jarosite-plumbojarosite, autunite, 

tungstite, ferritungstite, jixianite(?), and stolzite with 

stibiconite, chrysocolla, malachite, azurite, manganese 

oxide minerals, or jarosite.

CHEMICAL COMPOSITION OF 

THE HUEBNERITE

Chemical data were acquired to establish the ironmanganese compositions, 'Jie compositional variations, 

if any, in visible growth zones, and the trace-element 

compositions of the huebnerites, for the purpose of better defining the environment of their deposition.

Samples of huebnerite from 20 localities (shown on 

fig. 2) were analyzed using electron microprobe and 

emission spectrographic techniques. Synthetic huebnerite standards were made for use in the electron microprobe determinations. Stoichiometric proportions of 

Mn02 , W02 , and Fe metal were fused to a melt and

allowed to crystallize. The resulting material was entirely crystalline, and only slight iron-manganese variation was found in the 95 mol percent MnW04 standard. 

Natural huebnerite was prepared for analysis by hand 

picking crushed material selected from the vein samples. Examination of cleavage fragments under the 

microscope revealed no other mineral phases nor fluid 

inclusions, although it was evident that oxidation and 

replacement by iron-manganese oxides along cleavage 

planes, fractures, and other irregular surfaces have occurred in various degrees.

Conditions for microprobe analysis were 15 kilovolts 

operating voltage, 30 nanoamperes sample current, 10 

micrometer beam diameter, and counting times of about 

10 seconds on samples and standards using integrated 

beam current. Data were reduced by a computer program utilizing a linear least-squares best-fit line. No 

elements other than iron, manganese, and tungsten 

were detected above background. Results of the microprobe analyses of 19 samples are given in table 5.

Polished thin sections of four huebnerite-bearing samples (DRS-73-17, DRS-74-221, DRS-79-67, and DRS79-68) were prepared for microprobe study of growth 

zones. The polished thin sections of huebnerite were 

examined under the microscope, in both transmitted 

and reflected light, and under the SEM, and no other 

mineral phases that might define the growth zones were 

detected.

Six-step semiquantitative emission spectrographic 

analyses of 23 samples of huebnerite are presented in 

table 6. Details of the six-step method, its precision, 

and comparison with other analytical methods were discussed by Myers, Havens, and Dunton (1961). In spite 

of the fact that the crushed huebnerite samples were 

carefully hand picked to remove other visible mineral 

phases before analysis, it is believed from the analytical 

data, as discussed later, that minor impurities were 

contained in some of the analyzed huebnerites.

IRON-MANGANESE COMPOSITION

The analytical data (tables 5 and 6) show that the 

mean iron contents of the huebnerites range from about 

0.1 to 3.0 weight percent (recorded as Fe for spectrographic analyses and as FeO for microprobe analyses; 

the high value of 7.0 percent Fe (spectrographic) in 

sample DRS-74-221A is discounted, being attributed 

provisionally to pyrite). A comparison of the analytical 

data for iron (fig. 35) shows that iron values determined 

spectrographically are somewhat higher on average 

than those determined by microprobe.

Variations in the iron content of the Round Mountain 

huebnerites suggest the possibility of compositional zoning in the vein system. Indeed, the iron content (deter-
24 HUEBNERITE VEINS NEAR ROUND MOUNTAIN, NYE COUNTY, NEVADA

1 mm 1 mm

FIGURE 25. Sphalerite that has been fractured, "milled," and dispersed in recrystallized mosaic quartz, under crossed nicols, thin 

section of sample DRS-74-252B2. A, Strongly broken and dispersed 

sphalerite (black) in mosaic quartz (white and shades of gray). Broken sphalerite at left center has been filled with chalcedony (fine 

grained, mottled gray). Note vug at lower right filled with chalmined by spectrographic analyses, which we believe to 

be more representative of the bulk compositions than 

are the microprobe analyses) appears to be a sensitive 

indicator of altitude within the vein system, increasing 

from values of about 0.2 percent Fe at an altitude of 

2,125 m (6,800 ft) to about 3.0 percent Fe at an altitude 

of 2,625 m (8,400 ft) (figs. 2 and 36). It should be noted, 

however, that although the altitude correlation of 

microprobe-determined FeO is similar to that of spectrographically determined Fe (recalculated to FeO), 

sample DRS-74-221B is anomalous in its FeO (recalculated)-FeO ratios (see fig. 35). As discussed later, the 

vertical compositional zoning of the vein huebnerites is 

thought to reflect change in the pressure-temperaturecomposition conditions upward through the vein system.

A comparison of the FeO and MnO contents of the 

huebnerites as determined by microprobe analysis (fig. 

37) reveals two fields of composition. A field of huebnercedony (fine grained to fibrous, mottled gray). B, Fractured sphalerite (black) filled with chalcedony (fine grained, mottled gray). 

Note that quartz (white and shades of gray) penetrates fractures 

a short distance, suggesting that quartz recrystallized and molded 

itself against sphalerite as the fractures in sphalerite opened. Chalcedony deposition likely was the latest event.

ites with highest MnO to FeO ratios includes only 

huebnerites with which sulfides are associated in the 

veins. A field of huebnerites with lowest MnO to FeO 

ratios includes only huebnerites with which no sulfides 

are associated in the veins. In this comparison, sample 

DRS-74-221B does not appear anomalous. Assuming 

that the huebnerites and sulfides were deposited simultaneously in the vein system, we could explain the low 

content of iron in the sulfide-associated huebnerites by 

its preferential deposition in pyrite. Assuming that the 

sulfides were deposited in the veins later than the 

huebnerites, as the geological and mineralogical evidence indicates, we could explain the low content of 

iron in the sulfide-associated huebnerites by movement 

of iron out of huebnerite to be deposited as pyrite at 

the time of sulfide mineralization. We note the "reworked" character of the huebnerites that developed 

following their initial deposition but that predated (or 

accompanied?) deposition of sulfides.
DESCRIPTION OF THE VEIN MINERALS 25

FIGURE 26. Galena partly replaced by covellite, reflected light, 

polished sections of sample DRS-74-221. A, Galena (white) partly 

replaced by covellite (shades of gray) in irregular patches and along

TUNGSTEN-MANGANESE COMPOSITION

The variations in tungsten contents of 75.9 to 78.9 

percent W03, as determined by microprobe analysis 

(table 5), compared to an ideal composition for huebnerite of 76.6 percent W03, led to the calculation of the 

molecular proportions of the components based on the 

microprobe data (structural formulas given in table 5). 

The results indicate compositions near stoichiometry 

and suggest that the compositional variations resulted 

largely from an instrumental factor, most likely variation in sample current, and are not real variations in 

tungsten composition.

We also plotted the MnO versus W03 compositions 

of the analyzed huebnerites (fig. 38) to evaluate further 

the compositional variations. Here again two distinct 

fields are shown, one of huebnerites with associated sulfides in the veins and one of huebnerites without associated sulfides in the veins. An exception is sample 

DRS-73-17 (queried on fig. 38), a huebnerite without 

associated sulfides that falls in the field of huebnerites

crystallographic planes. B, Galena (white) intergrown with or 

partly replaced by covellite (gray). Dark-gray areas near top and 

at right are quartz (high-relief fragments) and mounting medium.

with associated sulfides. The tendency for positive correlation of MnO and W03 within the separate fields 

suggests instrumental variation, probably in sample 

current during the time the analyses were made.

GROWTH ZONES

Because of the extremely low total iron contents, 

microprobe analyses of visible growth zones in huebnerite were inconclusive. Sample DRS-79-68 was 

examined by Dr. Charles M. Taylor (oral commun., 

1979) and darker colored zones were found to contain 

very slightly more iron than lighter colored zones (0.2 

versus 0.15 weight percent Fe). However, our studies 

failed to show convincing variations in iron content between darker and lighter parts of the huebnerite crystals, possibly because of the very thin character of the 

dark growth layers compared to the microprobe beam 

diameter employed. Nevertheless, local variation in the 

iron contents of the huebnerites (table 5) is evident despite our inability to correlate such with color variation.
26 HUEBNERITE VEINS NEAR ROUND MOUNTAIN, NYE COUNTY, NEVADA

0.1 mm

FIGURE 27. Sphalerite (medium gray) that contains exsolved blebs 

of chalcopyrite (light gray), reflected light, polished section of sample DRS-74-252B.

Iron-manganese zonation within huebnerite single 

crystals has been described by a number of authors (for 

example, Takla, 1976; Bird and Gair, 1976). The growth 

layers described by Bird and Gair (1976) for Hamme, 

N.C., huebnerites are similar in appearance to those 

observed in Round Mountain huebnerites, except that 

in the Round Mountain examples, growth layers appear 

to be much thinner. Patchy and random iron-manganese 

distribution in wolframite was reported by Moore and 

Howie (1978). Clark (1970) pointed out that many wolframites contain small but significant amounts of ferric 

iron and that this feature has received little attention 

in most recent studies. In crystals where the total iron 

is only 1.0 weight percent or less, small variations in 

amounts of ferrous (Fe +2) and ferric (Fe +3) iron might 

produce color zonation (Fe +2 producing lighter colored 

zones and Fe +3 producing darker colored zones). Moore 

and Howie (1978) reported appreciable excess ferrous 

oxide in some analyzed Cornish wolframites. Study of 

the stability relations of the wolframite series by Hsu 

(1976) has shown that wolframite of any composition

0.25 mm

FIGURE 28. Tetrahedrite-tennantite (light gray to white) partly replaced by a narrow halo of chalcocite, acanthite, and stromeyerite 

(mottled light to medium gray) and by intervening patches of gray 

isotropic mineral (stibiconite?) and covellite (mottled medium gray), 

reflected light, polished section of sample DRS-74-252A. Dark-gray 

areas are quartz (except mounting medium at lower right).

can remain stable under the oxidation states prevailing 

in hydrothermal environments. The stability of ferberite and huebnerite does not differ appreciably in the 

presence of both oxygen and sulfur. Apparently neither 

f02 nor /S2 exerts any noticeable influence on the 

composition of wolframite. Optical spectral studies 

(Graham R. Hunt, oral commun., 1980) were not able 

to distinguish Fe+2 from Fe+3 in several Round Mountain heubnerites (DRS-73-17, DRS-74-66, DRS-79-68) 

because of very low total iron content.

Moore and Howie (1979) in a study of cassiterite from 

Cornwall suggested that alternating color zones in that 

mineral resulted from other than chemical variation. 

They found that small variations in iron content did 

not correlate with color zones. Banerjee (1969) and 

Banerjee, Johnson, and Krs (1970) could not show conclusively by Mossbauer spectral studies of the cassiterite that color variation was related to differences in the 

Fe +2:Fe +3 ratio. We note, however, that the extremely
DESCRIPTION OF THE VEIN MINERALS 27

60 ^

FIGURE 29. Manganese oxide weathering product of huebnerite, sample DRS-79-68. A, oxide (pyrolusite?) coating a substrate of huebnerite; 

B, closer view of the manganese oxide mineral. Scales are 60 and 6 ^m (micrometers), respectively.

low concentration of iron in the cassiterite would make 

detection of variation in the Fe +2:Fe +3 ratio difficult.

TRACE-ELEMENT COMPOSITION

In light of the fact that the Round Mountain huebnerites were cleaned by hand picking, rather than by thorough mechanical and chemical means, the mineral residence of many of the minor elements detected is uncertain. Spectrographic analyses of huebnerite from Japan 

that was carefully purified by electromagnetic and 

heavy liquid separations and by acid treatment (Lee, 

1955, p. 2, 49) revealed traces of titanium, magnesium, 

silicon, calcium, aluminum, zinc, copper, and silver. 

These trace elements may have been present in the 

huebnerite structure, in consideration of Lee's careful 

and effective methods of removing mineral impurities 

from the material that was analyzed. The minor 

amounts of elements detected by spectrographic 

analyses of the Round Mountain huebnerites thus may 

be held, in part, in the huebnerite structure rather than 

in mineral impurities. The character of our data, however, suggests that much of the minor elements detected are present as "impurities," that is, separate 

mineral phases; possibly some extraneous minor elements reside in fluid inclusions.

Spectrographic data given in table 6 suggest the identity of some "impurities" present in the analyzed huebnerites. Four samples contained greater than 0.5 percent 

Si, probably as quartz. Unusually high amounts (0.03- 

0.07 percent) of calcium and magnesium were detected 

in some huebnerites, and these elements in part may 

be present in carbonate minerals; some calcium may 

be present in scheelite (see, for example, Grubb, 1967). 

Certain elements, such as lead, zinc, copper, bismuth,

silver, molybdenum, and cadmium, occur in amounts 

perhaps sufficient to indicate the presence of sulfides 

and sulfosalts, or weathering (secondary) products derived from them. The huebnerites that presumably contain sulfides or sulfosalts are widely and apparently randomly scattered throughout the tungsten-mineralized 

area. However, those with the highest amounts of sulfide- or sulfosalt-related metals were collected within 

the zones of base- and precious-metal mineralization (for 

example, samples DRS-74-221 and DRS-78-2; compare 

table 6 and fig. 2), although some huebnerite samples 

collected within the base- and precious-metal mineralization zones (for example, samples DRS-79-67 and 

DRS-79-68) contain no unusually high amounts of metals that could be attributed to sulfides or sulfosalts. 

Nickel and cobalt were detected and chromium was 

found in amounts perhaps anomalously high in a few 

huebnerite samples. The mineral residence of these elements is uncertain. Barium is present in significant 

quantities (0.03-0.1 percent) in some samples, probably 

reflecting admixed barite or barium-manganese oxides. 

Small amounts of strontium are present in the samples 

that contain unusually high amounts of barium. Small 

amounts of the yttrium-group rare-earth elements along 

with lanthanum, cerium, neodymium (in one sample), 

beryllium, niobium, scandium, and titanium were found 

in a few huebnerites; the mineral residence of these 

elements also is uncertain. Because of interference between the spectra of tungsten and niobium, niobium 

was determined on an emission line with a sensitivity 

less than that of the line normally used.

Judged from the total of elements present other than 

the major elements comprising huebnerite (see table 6), 

most of the huebnerite samples analyzed were reasonably free of "impurities."
28 HUEBNERITE VEINS NEAR ROUND MOUNTAIN, NYE COUNTY, NEVADA

0.5 mm

FIGURE 30. Tetrahedrite-tennantite (light gray) partly replaced by 

stibiconite (medium gray) along irregular fractures, reflected light, 

polished section of sample DRS-78-2. Dark-gray grain in upper 

right is quartz.

VARIATIONS IN TUNGSTEN 

MINERALIZATION

One east-trending zone of tungsten mineralization 

that extends 2.5 km eastward from a point 3 km due 

east of Round Mountain (fig. 2) appears to be virtually 

devoid of well-defined huebnerite-bearing quartz veins. 

Instead, the zone contains local areas of tungstenmineralized rock that are tourmalinized granite, ironand quartz-mineralized fractures in granite, sheared 

and iron-mineralized argillite, or iron- and quartzmineralized fractures in Oligocene rhyolite. The tungsten content of mineralized samples collected at these 

occurrences is low and ranges from 0.005 to 0.01 percent; identity of the tungsten mineral or minerals here 

is not known. Despite their low tungsten content, the 

occurrences contain substantially more tungsten than 

other nearby mineralized rocks. The tungsten-bearing 

deposits in this east-trending zone contain, in weight

. \

0.5 mm

FIGURE 31. Secondary minerals in vein quartz (white), planepolarized light, thin section of sample DRS-78-2A. Irregular veinlets are filled with growth layers of chrysocolla (medium gray). 

Vug bounded by sharp quartz prism faces (left center) is lined with 

layers of chrysocolla (medium gray), in part colloform, and filled 

with malachite (black). Small, sharp-cornered vug below (lower left) 

is lined with colloform chalcedony (nearly white) and filled with 

chrysocolla. Fluid inclusions (dark specks) form variously oriented 

trains in vein quartz.

percent, as much as 0.02 Ag, 0.3 As, 0.007 Bi, 3.0 Cu, 

0.002 Mo, 0.2 Pb, 0.5 Sb, and 1.0 Zn. Because some 

of these mineral occurrences are in Oligocene rhyolite 

or tourmaline-mineralized granite near the Oligocene 

stock east of Round Mountain, it is clear that there 

was a Tertiary tungsten-mineralizing event substantially younger than the emplacement of the huebnerite 

veins in Late Cretaceous time. In view of the small 

amount of tungsten involved in the younger (Tertiary) 

mineralization, the tungsten conceivably was remobilized from the earlier formed (Cretaceous) veins. 

The paragenetic data that show significant deposition 

of scheelite during a second hydrothermal stage, possibly derived by remobilization of huebnerite, indicate the 

availability of tungsten during hydrothermal activity
GEOCHEMISTRY OF THE HUEBNERITE VEINS 29

0.5 mm

FIGURE 32. Vug in vein quartz (white with numerous trains of fluid 

inclusions black specks) lined with chrysocolla (gray) and filled 

with chalcedony (white, faintly layered), plane-polarized light, 

polished thin section of sample DRS-78-2B. Alternating layers of 

chrysocolla and chalcedony form a colloform mass on quartz prism 

face (below center). Stibiconite (black, lower right) is a selvage 

on tetrahedrite-tennantite (outside field of view).

that took place at some time following initial vein formation.

GEOCHEMISTRY OF THE 

HUEBNERITE VEINS

Semiquantitative spectrographic and other analyses 

of five samples of tungsten-bearing quartz vein material, given in tables 7 and 8, provide information on 

variations in mineralization of the veins that are indicated by the varied distributions of minerals described 

previously. The samples are part of a group of several 

hundred collected throughout the area of figure 2 for 

the purpose of determining patterns of metal distribution (Shawe, 1977b). Those samples were collected with 

an effort to obtain the most intensely mineralized material within a local area, and consisted of visibly

!-%\

V" 4

0.5 mm

FIGURE 33. Late veinlet of secondary minerals cutting quartz 

(white) and huebnerite (dark gray), plane-polarized light, thin section of sample DRS-78-2A. Principal veinlet, extending across 

view, is filled with chrysocolla (light gray) that within the huebnerite crystal is partly replaced or filled with chalcedony (white). Thinner veinlets of chrysocolla follow cracks in huebnerite and along 

huebnerite-quartz contact. A thin, late veinlet of chalcedony follows 

the right margin of the principal chrysocolla veinlet; in the huebnerite crystal the chalcedony veinlet locally merges with chalcedony 

that replaced or filled chrysocolla. Outside the field of view the 

chalcedony veinlet is seen to transgress the chrysocolla veinlet to 

its left margin, indicating that it postdates the chrysocolla veinlet. 

Tiny grains of iron oxide (limonite) or sulfate (jarosite) dark 

specks are present within the late chalcedony veinlet.

mineralized rocks such as strongly iron-stained rocks, 

quartz and iron oxide-coated fracture surfaces, thin 

quartz and iron oxide veinlets, and quartz vein material 

containing sulfide and other ore minerals. Three of the 

samples listed in tables 7 and 8 (DRS-74-194, DRS-74- 

221, and DRS-74-252A) were collected within zones of 

base- and precious-metal mineralization as determined 

by the geochemical survey, and two samples (DRS-74- 

64 and DRS-74-200) were collected outside of those 

zones.

Highest amounts of a number of metals, including 

mercury, gold, silver, arsenic, bismuth, copper, molyb-
30 HUEBNERITE VEINS NEAR ROUND MOUNTAIN, NYE COUNTY, NEVADA

MINERAL INITIAL HYDROTHERMAL 

STAGE

SHEARING AND 

RECRYSTALLIZATION

YOUNGER HYDROTHERMAL 

STAGE

Manganese 

oxide

Jarosite

WEATHERING

(SECONDARY)

STAGE

FIGURE 34. Paragenesis of huebnerite veins. Thicknesses of bars suggest relative abundance of minerals in each stage of

mineralization.

denum, lead, antimony, and zinc, were detected in the 

three samples collected within zones of base- and precious-metal mineralization. On the other hand, tungsten 

and a few elements such as manganese, iron, barium, 

fluorine, and niobium appear to be randomly concentrated through all five samples. Two elements, germanium and selenium, are more abundant in veins outside 

the zones of base- and precious-metal mineralization 

than within them.

DISCUSSION

Huebnerite has been reported from a large number 

of occurrences worldwide, but nearly end-member 

huebnerite, as in Japan (Lee, 1955, p. 49), Egypt 

(Takla, 1976; Takla and others, 1977), Mexico (Ramdohr, 1966, p. 1068), and western Transbaikal 

(Shnuraeva, 1972), is uncommon. In the United States 

substantial amounts of huebnerite have been mined
DISCUSSION 31

TABLE 5. Electron microprobe analyses, in weight percent, of 19 samples of huebnerite from quartz-vein samples collected east and south

of Round Mountain (localities shown on fig. 2)

[Analyses by E. E. Foord; variation in total and some of the variation in component values resulted from variation in conditions of the microprobe analyses. Leaders (-), not applicable]

Sample No. 

DRS67-30

67-33

73-17

73-19

73-21

73-27

74-66

74-70

74-72

74-76

74-105

74-193

74-200

74-218

74-221

78-1

78-2

79-67

79-68

FeO

1.6

1.9

.5

1.4

1.5

1.0

.4

.6

.4

2.1

2.9

.5

.4

.2

.3

.1

.1

.3

.3

Min 

FeO

1.23

1.38

.22

1.05

.84

.22

.00

.04

.00

.84

.17

.00

.32

.19

.00

.10

.30

.24

Max 

FeO

1.97

2.41

.94

1.57

2.07

1.80

1.08

.92

.87

3.57

5.94

.48

.39

.29

.43

.12

.35

.30

MnO

21.8

21.7

22.9

21.9

21.8

22.9

23.0

22.5

22.7

21.1

21.6

23.3

22.6

22.9

22.9

23.0

23.1

23.0

23.3

W03

77.6

77.8

76.6

77.2

77.0

78.9

75.9

77.5

78.4

76.3

76.7

77.7

78.2

76.9

76.7

77.2

76.7

76.9

77.4

Total

101.0

101.4

100.0

100.5

100.3

102.8

99.3

100.6

101.5

99.5

101.2

101.5

101.2

100.0

99.9

100.3

99.9

100.2

101.0

No. of 

analyses

6

4

5

5

5

7

5

5

4

9

6

3

2

3

6

1

2

2

3

Structural formulas 

(basis of 4 oxygens)

(Mn.92Fe .07 ) 0.99W 1.00°4

(Mn>91 Fe >08 ) 0e99W 1>0004

< Mn.98Fe .02>1.00W 1.0004

(Mn.93 Fe .06 ) 0.99W 1.00°4

< Mn.93Fe .06>0.99W 1.00°4

(Mn.95Fe .04 ) 0.99W 1.00°4

< Mn.99Fe .02>1.01W 1.0004

< Mn.96 Fe .03>0.99w 1.01°4

< Mn.96Fe .02>0.98w 1.01 04

( Mn.91 Fe .09>1.00w 1.00°4

(Mn.92Fe .12 ) 1.04W0.99°4

(Mn.98Fe .02 ) 1.00W 1.00°4

< Mn.95Fe .02>0.97W 1.01°4

(Mn<98Fe >01 ) 0>99W 1>0004

( Mn.98Fe .01 ) 0.99W 1.00°4

( Mn.98Fe .004 ) 0.98W 1.00°4

< Mn.99 Fe .004>0.99W 1.00°4

(Mn>98Fe >01 ) 0!99W 1<0004

( Mn.98Fe .01 ) 0.99W 1.00°4

from veins at the Hamme (Tungsten Queen) Mine, N.C. 

(White, 1945; Bird and Gair, 1976), and small amounts 

have been mined from or recognized in veins at Butte, 

Mont., in the San Juan Mountains, in Boulder, Chaffee, 

Gunnison, Park, and Summit Counties, at Leadville, 

and at Cripple Creek, Colo. (Eckel, 1961), in Lincoln 

County, N. Mex., in Valley County (Leonard and 

others, 1968) and in Lemhi County, Idaho, .and near 

Round Mountain, and from pegmatites in the Black 

Hills, S. Dak. (see, for example, Palache and others, 

1951, p. 1064, 1068-1070). Elsewhere in Nevada huebnerite occurs near Austin (first reported occurrence of 

the mineral, in 1865) and near Osceola (Palache and 

others, 1951, p. 1064, 1070) in quartz veins similar to 

those near Round Mountain. Huebnerite also was found 

in quartz gangue of epithermal veins of the Tonopah

district, associated with sulfides and sulfosalts (Melhase, 1935). Despite the description of the Tonopah 

veins as epithermal, they were probably deposited at 

temperatures (350°C-200°C; Bonham and Garside, 1979, 

p. 107) similar to those of the Round Mountain huebnerite veins. Of the deposits in the United States, only 

those at the Hamme Mine and near Round Mountain 

are reported to contain end-member huebnerite (^1 

weight percent FeO) (Bird and Gair, 1976; Shawe and 

others, this report).

The huebnerite veins near Round Mountain are similar to those at the Hamme Mine in their mineralogy, 

rock associations, and conditions of formation. At the 

Hamme deposit quartz veins that contain huebnerite, 

fluorite, sulfides, and tetrahedrite occur in a northnortheast-trending linear belt nearly 6 km long, mostly
32 HUEBNERITE VEINS NEAR ROUND MOUNTAIN, NYE COUNTY, NEVADA

TABLE 6. Semiquantitative spectrographic analyses, in weight percent, of 23 samples of huebnerite from quartz-vein samples collected

east and south of Round Mountain (localities shown on fig. 2)

[Analyses by Nancy M. Conklin. N, not detected at limit of detection or at value shown; L, detected, but below limit of determination or below value shown; G, greater than 10 

percent. Also looked for but not found: Na, K, P, As, B, Pd, Pt, Sn, Te, U, V, Zr, Ga, Ge, Hf, In, Li, Re, Ta, Th, Tl. (--), not looked for. Approximate lower limits (in 

percent) of determination for elements analyzed by six-step spectrographic method as shown in table 4, except for Ag (0.0002), Ba (0.0003), Be (0.0002), Cd (0.005), Co (0.0005), 

Cr (0.00015), Dy (0.003), La (0.005), Mo (0.0005), Nb (0.02), Ni (0.0002), Sr (0.001), Y (0.002), Yb (0.0005), Zn (0.03)]

Sample No. -

Si

Al

Fe

Mg

Ca

Ti

Mn

Ag

Ba

Be

Bi

Cd

Ce

Co

Cr

Cu

Dy

La

Mo

Nb

Nd

Ni

Pb

Sb

Sc

Sr

W

Y

Yb

Zn

DRS-67-30

0.03

N .015

1

.03

.015

.0015

G

N

.015

N

.007

N

N

N

N .0005

.007

.01

N

N

.02

N

N

.03

N

.003

N

G

.02

.01

N

DRS-67-33

0.7

N .015

2

.015

.015

.007

G

.002

.015

.0003

.003

N

.015

N

N .0005

.015

.005

.007

.001

.02

.007

N

.07

N

.0015

N

G

.007

.005

N

DRS-73-17

0.7

N .015

.7

.003

.03

.007

G

N

.05

N

N

N

N

N

N .0005

.015

.005

N

N

.03

N

N

.15

N

.0007

.002

G

.007

.005

N

DRS-73-19

0.07

N .015

1.5

.007

.03

.0015

G

N

.07

N

N

N

N

N

N .0005

.015

.003

N

N

N .02

N

N

N .01

N

.0015

.002

G

.007

.003

N

DRS-73-21

0.15

N .015

1.5

.015

.07

.005

G

N

.1

N

N

N

N

.002

N .0005

.02

.005

N

N

N .02

N

N

.15

N

.003

.0015

G

.007

.007

N

DRS-73-27

0.05

N .015

1.5

.007

.01

.0015

G

N

.015

N

N

N

N

N

.0007

.001

.003

N

N

N .02

N

N

N .01

N

.0015

N

G

.003

.002

N

DRS-73-168

0.1

N .015

.7

.007

.03

.003

G

N

N .0003

N

N

N

N

N

N .0003

.0015

.007

N

N

.03

N

N

N

N

.0015

N

G

.007

.007

N

DRS-74-66

0.07

N .015

.7

.015

.015

.001

G

N

.005

N

N

N

N

N

.0015

.0015

N .003

N

N

.03

N

N

.01

N

.003

N

G

.003

.002

N

DRS-74-70

0.15

N .015

1

.015

.03

.0015

G

N

.007

N

N

N

N

N

.0003

.0007

N .003

N

N

N .02

N

N

.015

N

.0015

N

G

.003

.003

N

DRS-74-72

0.03

N .015 .7-

.015

.02

L .001

G

N

.0015

N

N

N

N

N

.00015

.0002

N .003

N

N

N .02

N

N

N

N

.002

N

G

.003

.003

N

DRS-74-76A

0.05

N .015

1.5

.015

.015

.003

G

.0007

.005

N

N

N

N

N

.0005

.007

N .003

N

N

N .02

N

N

.02

N

.0015

N

G

.003

.003

N

DRS-74-76B

0.15

N .015

1.5

.03

.0015

G

.0007

.0015

N

N

N

N

N

N .0003

.007

.003

N

N

N .02

N

N

N

N

.003

N

G

.007

.005

N

in a granitic (granodioritic-tonalitic) pluton but extending a short distance into phyllite wall rocks. The huebnerite contains about 0.2-1.2 percent FeO and shows 

growth zoning similar to, although coarser than, that 

of the Round Mountain huebnerites. Microprobe 

analyses of the zoned huebnerites showed that dark-colored growth layers commonly contain 0.1-0.4 percent 

more FeO than do the light-colored growth zones. Depositional temperatures of the Hamme deposit probably 

were less than 350°C (summarized from Bird and Gair, 

1976).

The significance of variations in manganese and iron 

contents of wolframites, commonly stated as the huebnerite-ferberite molecular ratio (H:F), as an indication 

of conditions of deposition is controversial. Early work 

in western Europe and Africa by Oelsner (1944, 1952, 

1954), Leutwein (1952), Bolduan (1954), Varlamoff 

(1958), and de Magnee and Aderca (1960) indicated that 

huebnerite has been deposited at higher temperatures 

than ferberite. More recently, in the Soviet Union and 

elsewhere, Churikov (1959), Ganeev and Sechina (1960), 

and Taylor and Hosking (1970) presented data to 

suggest that the opposite has been true. Clark's (1970) 

data on Cornwall deposits indicated that wolframite in

pegmatitic veins contained more iron than that in associated "normal" (presumably lower temperature) 

lodes. Nevertheless, Hollister (1970) pointed out that 

Bolivian tin districts and Peruvian and North American 

molybdenum porphyry districts are zoned outward from 

huebnerite-rich cores to ferberite-rich peripheral zones. 

Landis and Rye (1974) noted zonation outward from 

wolframite to ferberite in the Pasto Bueno tungstenbase metal district, Peru. Other studies in Tasmania, 

Europe, and the United States by Edwards and Lyon 

(1957), Baumann and Starke (1964), Bird and Gair 

(1976), Amosse (1978a), and Moore and Howie (1978), 

indicated more complex relations between H:F and environment. The studies of Groves and Baker (1972) in 

northern Tasmania showed that regional variations in 

H:F probably reflect regional compositional differences 

among ore fluids, these differences being much greater 

than variations in the ratio within local ore areas. This 

conclusion is supported by the experimental data of Hsu 

(1976). Amosse (1978b) has suggested, by thermodynamic considerations applied to wolframite from 

the Borralha Mine, Portugal, that H:F cannot be used 

as a geothermometer, but rather indicates direction 

toward the source of mineralization. Hsu (1976) also
DISCUSSION 33

TABLE 6. Continued

Sample No. DRS-74-105 DRS-74-193 DRS-74-200 DRS-74-218 DRS-74-221A DRS-74-221B DRS-78-1 DRS-78-2 DRS-79-67A DRS-79-67B DRS-79-68

Si 0.05 0.07 0.15 1 0.3 0.15 0.05 3 0.2 0.07 0.15 

Al N .015 N .015 N .015 N .015 N .015 N .0015 N .015 N .015 N .015 N .015 N .015 

Fe 1.5 .3 1.5 .7 7 3 .15 .3 .3 .3 .2 

Mg .007 .005 .005 .005 .0015 .002 .007 .003 .007 .002 .005 

Ca .005 .015 .05 .005 .03 .005 .07 .05 .01 .03

Ti L .001 .007 .002 .005 .003 .003 N .007 .03 .03 .007 

Mn GGGGG G GGGGG 

Ag N N N N .005 .0007 N .0007 .005 NNN 

Ba .03 .0015 .05 .0007 .03 .007 .001 .015 .01 .007 .007 

Be NNNNN N NNNNN

Bi .0015 N N N L N NNNNN 

Cd NNNNNNN .015 N N N 

Ce NNNNN N NNNNN 

Co N N .0015N N N NNN N N 

Cr .0007 .0002 .0002 .00015 .0002 N .0003 N .0005 N .0005 .0003 .0002 .0003

Cu .0015 .03 .02 .0007 .07 .03 .02 .3 .0007 .0015 .007 

Dy N .003 N .003 .003 N .003 N .003 N .003 N .003 N .003 N .003 N .003 N .003 

La NNNNN N NNNNN 

Mo NNNNN N NNNNN 

Nb N .02 .03 N .02 N .02 .02 .02 N .02 .05 .03 .03 .07

Nd NNNNN N NNNNN 

Ni N N .0003 .0002 .0003 N N N .0007 .0015 .002 

Pb .003 .05 .007 .03 .2 .05 N .03 N N N .003 

Sb N N N N .15 N NNN N N 

Sc .001 .003 .0005 .007 .007 .007 .005 .007 .003 .003 .0015

Sr .002 N .001 N .001 N N .003 .001 N .002 

W GGGGG G GGGGG 

Y .003 .002 .003 N .002 N .002 N .002 .002 .002 N .002 N .002 N .002 

Yb .003 .002 .003 .0007 .0007 .0007 .002 .002 .0007 .0007 .0005 

Zn N N N N .03 .07 N N N N N

concluded that H:F is of little value as a clue to temperature, pressure, and oxygen and sulfur fugacity during 

ore formation. Wiendl (1968, p. 265-279) showed that 

pH of mineralizing fluids generally is more important 

than temperature in determining the manganese-iron 

content of wolframite; a lateral increase in iron results 

from neutralization of ore fluids by wall rocks. Homer's 

(1979) theoretical and experimental data indicated that 

huebnerite should form at temperatures above 200°C 

from neutral to weakly alkaline solutions, whereas ferberite should form through a wide temperature range 

but from acidic solutions. Studies by Vinogradova, 

Barabanov, and Sorokin (1980) suggested that ferruginous wolframites precipitated at low pH were richer in 

scandium and niobium than crystals precipitated from 

more alkaline (manganiferous) media. Niobium was not 

detected in less ferruginous wolframites formed in a 

less acid medium. Moore and Howie (1978) indicated 

that the uneven distribution of manganese and iron may 

be controlled not only by the concentration of these elements in ore fluids but by rapid changes in the composition of ore fluids, by competing mineral phases (for example, sulfides) if present, and by subsequent remobilization of manganese and iron. Voyevodin (1981) emphasized the influence of varied complex factors on composition of wolframites. 

Oscillatory zoning of iron and manganese in wolframite crystals may be controlled by local concentration

gradients at the crystal-liquid interface, or by periodic 

supercooling of the liquid, or by "constitutional" supercooling as proposed for oscillatory zoning in plagioclase 

feldspars by Sibley and others (1976), or to the thermodynamic changes proposed by Amosse (1980). Major 

compositional changes in broad growth zones may be 

due to changes in external conditions.

Lawrence (1961) attempted to correlate the habit of 

wolframite with temperature of crystallization. He concluded that stout prismatic crystals grew at higher temperatures, whereas platy crystals grew at lower temperatures; iron-composition differences (0.5 weight percent between the two types) were slight, however. 

Landis and Rye (1974) showed at Pasto Bueno, Peru, 

that early-stage wolframite (75 weight percent MnW04) 

formed stubby bladed crystals and was deposited at a 

temperature of about 235°C and late-stage ferberite (<5 

weight percent MnW04) formed elongate crystals and 

was deposited at a temperature of about 180°C. We 

note in the huebnerite veins near Round Mountain a 

tendency for stubby crystals to form where wall rock 

is schist, which also is at the lowest altitude of vein 

exposure and where huebnerite contains only about 0.2 

weight percent FeO. In granite and at higher altitudes, 

huebnerite may occur more commonly as tapered tabular crystals, and the mineral in this part of the vein 

system contains 0.7-3.0 weight percent FeO. We do
34 HUEBNERITE VEINS NEAR ROUND MOUNTAIN, NYE COUNTY, NEVADA

0.5 1.0 1.5 2.0 

PERCENT FeO, MICROPROBE ANALYSES

2.5 3.0

FIGURE 35. Comparison of iron (recalculated as FeO) in huebnerite samples determined by six-step spectrographic 

analyses, and by microprobe analyses. Numbers are sample numbers.

not have adequate data to indicate whether or not there 

was a temperature difference between deposition of the 

two forms of huebnerite.

An assessment of the geologic setting of the huebnerite veins near Round Mountain permits an estimate of 

depth of burial of the veins at the time of their formation and an estimate of some of the parameters of the 

hydrothermal fluids that deposited the veins. A reconstruction of the domed granite, based on attitudes of 

granite contacts and of foliation within the granite, 

suggests that the apex of the pluton was about 1.5-2 

km above the present erosional level. Perhaps another 

1.5 km of Paleozoic sedimentary rocks lay above the 

dome at the time of its formation, interpreted to be

the time of tungsten mineralization. Erosional stripping 

of some or all of the Paleozoic rocks during doming cannot be evaluated easily, and we discount it in this assessment. Thus the depth of formation of the present 

huebnerite veins was likely about 3-3.5 km beneath the 

surface. Fluid pressure at the time of vein formation 

is difficult to assess. Hydrostatic rather than lithostatic 

pressure may have prevailed, because of the evidence 

of some brittle deformation at the time of vein formation, and because locally much open space in the veins 

implies through-going solution flow. However, at times 

during the course of vein deposition, deformation took 

place under high confining pressure. Such deformation 

is evidenced by the recrystallization of prismatic quartz
DISCUSSION 35

8400

8200

8000

7800

LU 

LU 

LL

z 7600

LU" 

Q

b 7400 

<

7200

7000

6800

660Q'0 1.0 2.0 

Fe, IN PERCENT

3.0

FIGURE 36. Positive correlation between spectrographically determined iron composition of huebnerite samples and altitude 

in the vein system.

crystals to form massive mosaic vein quartz that contains carbon dioxide-bearing fluid inclusions, and by the 

fact that along some vein walls partial replacement of 

wall rocks rather than open-space filling took place. Uncertainties as to the amount of carbon dioxide present 

in vein fluids, the temperature of the vein fluids at the 

level of and above the present huebnerite veins, and 

the height of the column of fluids in the vein system 

above the present veins also make an evaluation of fluid 

density uncertain. We use the assumptions that hydrostatic pressure prevailed and that the column of fluids 

extended upward to the surface. Like Landis and Rye 

(1974, p. 1043), we have arbitrarily selected an average 

density of 0.8 g/cm3 (80 bars/km) as possible and reasonable. Maximum fluid pressures at depths of'3-3.5 km 

thus would have been about 240-280 bars. If lithostatic 

pressure is assumed (granite density =2.65 g/cm3), 

maximum pressure would have been about 640-740 

bars.

We believe that clear quartz crystals that penetrate 

vugs, on which J. T. Nash (written commun., March 

1980) determined filling temperatures of about 190°C 

and which contain no liquid carbon dioxide, were

formed near the end of the initial episode of mineralization during which huebnerite was deposited. Temperatures at the beginning of this stage may have been 

much higher. Following this stage of vein formation, 

the veins were deformed, quartz was recrystallized except where quartz prisms penetrated vugs, and fluid 

inclusions, some bearing carbon dioxide, were formed 

in the recrystallized quartz. Nash determined filling 

temperatures of 250°-270°C for these fluid inclusions. 

Fluorite that fills vugs penetrated by clear quartz crystals contains fluid inclusions that have filling temperatures of 230°-260°C, according to Nash, and he indicated that some of the fluid inclusions with filling temperature of 260°C contain carbon dioxide dissolved in 

the aqueous phase. Younger fluorite contains fluid inclusions that have filling temperatures of about 190°C, 

and these inclusions contain no liquid carbon dioxide. 

These temperatures, corrected for estimated maximum 

pressures at about 5 weight percent equivalent NaCl 

(Lemmlein and Klevtsov, 1961, fig. 4), are about 210°C 

for early quartz and late fluorite, 270°-290°C for recrystallized quartz, and 250°-280°C for early fluorite, at 

pressures of about 240-280 bars. At pressures of about 

640-740 bars, they are about 245°C for early quartz 

and late fluorite, 310°-330°C for recrystallized quartz, 

and 290°-320°C for early fluorite.

A fluid under pressure of 240-280 bars (hydrostatic 

conditions) and with about 5 weight percent NaCl 

should boil at about 380°^80°C, and a fluid under pressure of 640-740 bars (lithostatic conditions, considered 

improbable) should boil at about 515°-545°C 

(Takenouchi and Kennedy, 1965, fig. 5). Perhaps the 

uneven distribution of carbon dioxide in fluid inclusions 

in recrystallized vein quartz suggests the possibility of 

boiling during the formation of these secondary inclusions. However, the pressure-salinity data that indicate 

boiling in the range 380°^80°C, well above the estimated temperature of formation (270°-290°C) of the carbon dioxide-bearing fluid inclusions in recrystallized 

quartz, argue against boiling. The variation in carbon 

dioxide contents of these secondary fluid inclusions 

suggests instead a variation with time in carbon dioxide 

contents of the depositing fluids through the period of 

quartz recrystallization.

J. T. Nash's estimate (written commun., March 1980) 

of 2-10 mol percent (5-20 weight percent) C02 in fluids 

that were trapped in inclusions in the recrystallized 

(milky) quartz seems reasonable. According to 

Takenouchi and Kennedy (1965, fig. 2), in the temperature range of 270°-290°C and pressure range of 240-280 

bars, at which the recrystallized quartz formed, 6 

weight percent NaCl solution could contain a maximum 

of 6-7 weight percent CO2 . At 210°C and the same pressures and salinity, the maximum carbon dioxide content
36 HUEBNERITE VEINS NEAR ROUND MOUNTAIN, NYE COUNTY, NEVADA

24.0

23.0 A

22.0

21.0

o 

79-68

->74-193 

cA

/ . - __ L-Huebnerites with associated sulfides 

/ Low-altitude field /

/ 78-2 / 

I ° xj^-High-altitude field 

78-1 79-67 X/XTTRR 

o o ^'b-^'74-66

Huebnerites without associated sulfides

FeO, IN WEIGHT PERCENT

FIGURE 37. Comparison of FeO and MnO in huebnerites analyzed by microprobe. Numbers are sample numbers.

would be 5 weight percent; Nash detected no carbon 

dioxide in quartz and fluorite that were deposited at 

210°C.

The huebnerite veins near Round Mountain probably 

represent the lower part of a mineralized system, the 

bulk of which has been eroded away. Wolframite-bearing vein systems that are spatially associated with 

granitic rocks commonly appear to have maximum development that is, show the greatest concentration of 

rich and large veins at and near the crests of cupolas. 

Examples are Panasqueira, Portugal (Kelly and Rye, 

1979), Borralha, Portugal (Amosse, 1978b); several 

localities in Thailand (Shawe, personal observations,

1974); Pasto Bueno, Peru (Landis and Rye, 1974); Las 

Guijas, Arizona (Sheikh, 1970); several localities in Tasmania (Groves and Baker, 1972); and Cligga Head, 

Cornwall, England (Moore and Jackson, 1977). If the 

Round Mountain vein system had reached as high as 

cupolas near the apex of the granitic pluton, it would 

have had a vertical extent of 1.5-2 km. However, G. 

P. Landis (written commun., 1980) suggested to us that 

a chemically integrated continuum of wolframite deposition possibly could not be maintained through such a 

vertical extent. The fact that nearly end-member 

huebnerite was deposited in the Round Mountain veins 

also suggests that they are near the base of a tungsten
DISCUSSION 37

79.0

78.0

77.0

76.0

Huebnerites without associated sulfidesLow-altitude fiekk./ 74-193

High-altitude field

Huebnerites with associated sulfides

21.0 22.0 

MnO, IN WEIGHT PERCENT

23.0

FIGURE 38. Comparison of MnO and W03 in huebnerites analyzed by microprobe. Numbers are sample numbers; query indicates 

that the position of sample DRS-73-17 in the field of huebnerites with associated sulfides is anomalous.

vein system. Once huebnerite started to precipitate, as 

hydrothermal fluids rose through fractures, solution 

compositions changed so that huebnerites deposited 

higher in the system were more iron rich. Thus, where 

end-member huebnerite is present in a vein system that 

shows systematic increase upward in the iron content

of the huebnerites, we interpret that the end-member 

huebnerite indicates the lowest part of the vein system. 

Assuming that huebnerite compositions changed toward that of ferberite with increasing altitude in the 

vein system, the diagram of iron versus altitude of the 

Round Mountain veins (fig. 36) suggests that at a level
38 HUEBNERITE VEINS NEAR ROUND MOUNTAIN, NYE COUNTY, NEVADA

TABLE 7. Semiquantitative spectrographic analyses, in weight percent, of five samples of tungsten-bearing quartz vein material 

(sample localities shoum on fig. 2)

[Analyses by Harriet G. Neiman. N, not detected at limit of detection. G, greater than 

10 percent. Also looked for but not found: Au, B, Co, La, Ni, Pd, Pt, Sc, Sn, Te, 

U, Y, P, Ce, Ge, Hf, In, Li, Re, Ta, Th, Tl, Eu]

Sample No. DRS-74-64 DRS-74-194 DRS-74-200 DRS-74-221 DRS-74-252A

Si02

A1 20 3

Fe 2 0 3

CaO

K20

86

4.3

.88

<.l

1.4

100

1.8

.54

.13

.42

100

.65

.47

.25

.23

88

<.5

.53

.56

.24

98

<.5

.66

<.l

.20

.44 

.42

.05 <.04

.01 .002

.000117 <. 000005

.175 .0105

.00007 <. 00001

.0432

.00021

.0111

<.00001

.0168

.00018

.0035

.00001

1.5-2 km higher in the system that is, the interpreted 

level of cupola formation at the apex of the granite pluton the composition of the tungstate mineral would be 

about 18 percent Fe, or virtually end-member ferberite. 

The uncertainty of the slope of the curve as controlled 

by the data points of figure 36, as well as the uncertainty of slope above the segment of the vein system 

represented in the diagram, make that value of iron 

content rather uncertain. Nevertheless, the extrapolation suggests that the wolframite would contain substantially more iron than that present in the huebnerites of the Round Mountain veins, and the composition 

of wolframite would be closer to compositions of wolframites in the cited cupola environments elsewhere in the 

world.

Trace element components of wolframites have been 

reported by a number of authors (Lee, 1955; Churikov, 

1959; Ganeev and Sechina, 1960; Zuyev and others, 

1966; Mineev, 1968; Takla and others, 1977; Vinogradova 

and Barabanov, 1978; Moore and Howie, 1978; 

Vinogradova, Barabanov, and Sorokin, 1980). With the 

exception of Lee (1955, p. 5) and Ganeev and Sechina 

(1960) none of these workers presented details on 

methods or effectiveness of purification of the analyzed 

minerals. Takla and others (1977) and Zuyev and others 

(1966) reported inclusions of other minerals in the wolframites they analyzed for trace elements. We believe

TABLE 8. Analyses, in weight percent, for several components of 

five samples of tungsten-bearing quartz vein material (sample 

localities shown on fig. 2)

[Si02, A1203 , Fe203 , CaO, K20, Ti02, P206, MnO, S, and Cl by X-ray fluorescence method 

by J. S. Wahlberg and J. W. Baker; F. by specific ion electrode method by Johnnie 

Gardner and Patricia Guest; Hg by wet oxidation plus atomic absorption method by 

J. A. Thomas; Au by fire assay plus atomic absorption method, and Ag by difference, 

by A. W. Haubert, L. B. Riley, and J. G. Crock; Sn, Sb, Ge, As, and Se by X-ray 

fluorescence by J. S. Wahlberg, J. 0. Johnson, and J. W. Baker]

Sample No. DRS-74-64 DRS-74-194 DRS-74-200 DRS-74-221 DRS-74-252A

1.5 

.2 

.03

.05

.5

.15

.00015

.0007

0.3 

.1 

.02 

.03

N

N

.005

.05

.005

.01

N

.002

0.2 

.07 

.015 

.2

N 

N

.001 

.15

G

0.2 

.1

.015 

.3

N

N

.001

.2

.1

.07

.02

N

.003

.003

.0001

.15

N 

.003

.005

N

.005

G

0.15 

.15 

.005 

.002

N

N

.0005

.0015

.01

.002

N

.15

N

.003

.0005

.07

that the presence of small amounts of other minerals 

enclosed in the analyzed wolframites was likely in many 

of the reported studies of trace elements in wolframites, 

and in some cases therefore speculations on the residence and absolute amounts of trace elements in the 

wolframite structure are not valid. The association with 

wolframite of minor amounts of minerals of certain compositions, however, as suggested by the analytical data, 

undoubtedly has geochemical significance. Noting, then, 

the uncertainty of residence of many of the trace elements associated with the Round Mountain huebnerites, we can point out some perhaps meaningful associations. Yttrium-group rare-earth elements dominate 

over cerium-group rare-earth elements, a relation also 

described for wolframites from the Soviet Union 

(Mineev, 1968; Vinogradova and Barabanov, 1978). We 

detected yttrium and ytterbium values as high as 0.007 

percent each in Round Mountain huebnerites, whereas 

Ganeev and Sechina (1960) reported as much as 0.08 

percent Y and Vinogradova and Barabanov (1978) reported as much as 0.036 percent Y in wolframites of 

the Soviet Union. Scandium was found in Round Mountain huebnerites in amounts as high as 0.07 percent,
SUMMARY AND CONCLUSIONS 39

whereas Ganeev and Sechina (1960) found as much as 

0.032 percent Sc and Vinogradova and Barabanov 

(1978) found as much as 0.11 percent Sc in wolframites 

from the Soviet Union. A microprobe study of five 

zoned wolframite crystals from vein-type deposits (Vinogradova, Barabanov, and Sorokin, 1980) showed a 

range of 0.17 to 1.04 percent Sc203 . Beddoe-Stephens 

and Fortey (1981) detected as much as 0.03 percent 

Sc203 in wolframite from the Carrock Fell tungsten deposit in the English Lake district. Ganeev and Sechina 

(1960) suggested close correlations between scandium 

and iron and between yttrium and manganese in the 

Soviet Union wolframites, but we see no such correlations in the Round Mountain huebnerites, possibly 

owing to their narrow iron-compositional range. Niobium was undetected above 0.02 percent in most Round 

Mountain huebnerites, but it ranges as high as 0.07 percent in those in which it was found. Takla and others

(1977) reported 0-0.05 percent Nb in Egyptian huebnerites, Ganeev and Sechina (1960) reported 0-0.1 percent 

Nb in Soviet Union wolframites, and Moore and Howie

(1978) reported as much as 0.5 percent Nb in Cornwall 

wolframites. Vinogradova, Barabanov, and Sorokin 

(1980) reported as much as 0.56 weight percent Nb205 

in zoned wolframites from the U.S.S.R. Zuyev and 

others (1966) showed by means of selective chemical 

extraction and electron microprobe studies that practically 100 percent of the tantalum and niobium in 

epithermal wolframite from quartz veins is due to the 

isomorphous entry of these elements into the mineral. 

Examination of hypothermal wolframite (from albitized 

and greisenized granite) showed that only part of the 

tantalum and niobium is an isomorphous admixture, the 

remainder occurring in inclusions of columbite and 

microlite. An average of 0.19 percent Ta205 was found 

to enter isomorphously into the wolframite structure. 

Beddoe-Stephens and Fortey (1981) detected (by electron microprobe) as much as 0.98 percent Nb205 in wolframite from quartz veins in the Carrock Fell tungsten 

deposit in the English Lake district; minute amounts 

of columbite are associated with the wolframite. Where 

other minerals have replaced the Carrock Fell wolframite, no concentration of niobium at mineral contacts 

was detected, suggesting that the niobium content of 

the wolframite was primary. Moreover, microprobe 

analyses showed that niobium enrichment occurred in 

zones in wolframite close to primary crystal faces, 

suggesting original growth zoning. A niobium-rich wolframite (20.25 weight percent Nb205) was reported by 

Saari, von Knorring, and Sahama (1968) from the 

Nuaparra pegmatite, Zambezia, Mozambique. The wolframite also contained 5.35 percent Ta205 , 2.68 percent 

Ti02 , 1.52 percent Sn02 plus Sb203 , and significantly, 

8.43 percent Fe203 compared to 7.43 percent FeO.

We have interpreted that much of the calcium detected in analyses of Round Mountain huebnerites is 

actually resident in scheelite or calcite impurities. 

Phase equilibria studies by Chang (1967) have shown 

only a limited solid solution between CaW04 and 

MnW04 and even less between CaW04 and FeW04. 

Zinc was detected in huebnerite from only one locality 

(DRS-74-221), where the huebnerite-bearing quartz 

vein also contains appreciable sphalerite. Although a 

complete series of solid solutions forms in the system 

ZnW04-MnW04 above 840°C (Chang, 1968), it seems 

unlikely that a phase of this system is present in the 

Round Mountain material.

The magmatic-metamorphic episode that was accompanied by tungsten mineralization near Round Mountain about 80 m.y. ago may have been widespread in 

the region. For example, we interpret that the Jurassic 

Snake Creek pluton in the southern Snake Range in 

eastern Nevada was metamorphosed and invaded by 

aplites and pegmatites and mineralized by tungstenbearing quartz veins at various times following 

emplacement; one such episode took place about 71-78 

m.y. ago (data from Lee and Van Loenen, 1971; Lee 

and others, 1970). At Tungsten, site of an important 

scheelite-producing district in northwestern Nevada, 

granitic rocks were metamorphosed about 74-79 m.y. 

ago and tungsten mineralization took place about 72-76 

m.y. ago (Tingley, 1975). Near the site of large production of scheelite ores at Pine Creek, Calif., about 200 

km southwest of Round Mountain, plutonic rocks 

yielded K-Ar (biotite) ages of 70-80 m.y. in contrast 

to surrounding plutonic rocks that yielded K-Ar 

(hornblende) ages of 80-100 m.y. (Evernden and Kistler, 1970). Possibly these relations indicate metamorphism of the plutonic rocks in the vicinity of Pine Creek 

at the time of tungsten mineralization. At the Old 

Woman Mountains in southeastern California, tungsten 

mineralization took place in granitic rocks that yield a 

Rb-Sr (whole rock) age of 80 m.y. (Miller, 1977).

SUMMARY AND CONCLUSIONS

Huebnerite-bearing quartz veins were deposited 

about 80 m.y. ago near Round Mountain, mostly in Cretaceous granite (emplaced about 95 m.y. ago), when the 

granite was invaded by pegmatite and aplite dikes, was 

domed, and was metamorphosed. Depth of burial at the 

time of vein formation was probably about 3-3.5 km, 

based on geologic reconstruction. Through the initial 

stage of vein deposition, pressures were probably about 

240-280 bars or only slightly higher, and salinity of the 

fluids persisted at about 5 weight percent NaCl. Muscovite, quartz, and huebnerite were the principal minerals 

of early-stage deposition in the veins. Quartz crystals
40 HUEBNERITE VEINS NEAR ROUND MOUNTAIN, NYE COUNTY, NEVADA

deposited near the end of this initial phase were precipitated from solutions at a temperature of about 210°C 

and contained little if any carbon dioxide. Following the 

precipitation of quartz, fluorite was deposited at temperatures of about 250°-280°C, from solutions that contained small amounts of carbon dioxide (about 5 weight 

percent?). Also, after initial precipitation of vein quartz, 

the veins were deformed, and the quartz was recrystallized and permeated by solutions at a temperature of 

about 270°-290°C that contained carbon dioxide (5-20 

weight percent?). Probably following this deformation, 

additional fluorite was deposited at a temperature of 

about 210°C from solutions that contained little or no 

carbon dioxide. Foose, Slack, and Casadevall (1980) 

documented post-mineralization deformation at the 

Tungsten Queen (Hamme) deposit, North Carolina. 

Casadevall and Rye (1980) presented evidence that 

metamorphic temperatures exceeded earlier primarymineralization temperatures at the Tungsten Queen 

deposit.

During the initial stage of vein deposition at Round 

Mountain, some pyrite was deposited along with the 

other vein minerals. Possibly other sulfides and sulfosalts were deposited in the veins or in altered rocks 

adjacent to the veins at that time, but the amounts 

were likely quite small.

After the initial hydrothermal stage of vein deposition, the veins were sheared and reopened, possibly at 

the time of widespread recrystallization of vein quartz, 

but more likely at a later time. A second stage of hydrothermal mineralization then took place, involving minor 

deposition of muscovite, quartz, and fluorite, but 

characterized mainly by deposition of sulfides, tetrahedrite-tennantite, scheelite (altered from initial-stage 

huebnerite), and near the end of the stage, barite and 

chalcedony. Although we have no direct evidence of the 

age of this mineralization, its dominant spatial association with 35-m.y.-old intrusive rocks (southwest end of 

rhyolite dike swarm and vicinity of granodiorite stock) 

leads us to believe that the younger hydrothermal stage 

of mineralization was related to a geologic episode that 

saw emplacement of those igneous rocks. Moreover, 

sulfide and minor tungsten mineralization took place in 

35-m.y.-old rocks in the vicinity of the granodiorite 

stock. The mineralization of Tertiary rocks and the 

presence of chalcedony in late phases of the younger 

hydrothermal stage suggest that the younger hydrothermal stage took place at a shallower level at lower 

temperatures and pressures than did the initial hydrothermal stage.

We note that Leonard, Mead, and Conklin (1968, p. 

C19-C20) interpreted the New Snowbird, Idaho, tungsten-bearing quartz lode, somewhat similar to the 

Round Mountain huebnerite veins, to be the product

of a single (although complex) episode of mineralization, 

even though they admitted that it might consist of two 

principal stages: early higher temperature tungsten 

mineralization and late lower temperature sulfide 

mineralization, as Schneider-Scherbina (1962) had interpreted for so-called telescoped mineralization of the 

Bolivian tin-silver deposits.

Following uplift and erosion of the Round Mountain 

huebnerite vein system in late Tertiary and Quaternary 

times the veins were weathered, with the development 

of numerous secondary minerals derived from the 

breakdown of primary vein minerals.

Possibly the huebnerite veins near Round Mountain 

represent the lower part of a vein system that when 

formed extended to a much higher level and resulted 

in mineralization of cupolas at the apex of the granite 

pluton. By analogy with wolframite deposits known 

elsewhere in the world that are associated with granite 

cupolas, the richest part of the Round Mountain vein 

system may have formed at that level, and thus was 

destroyed by erosion long ago. If the zonation of the 

iron content of the huebnerites in the Round Mountain 

vein system, increasing with altitude, is valid, we are 

led to believe that any such eroded deposits in cupolas 

must have contained wolframites with iron compositions 

much higher than those in the Round Mountain veins. 

Cupolas of granite plutons in the Basin and Range province in Nevada and adjacent States that have had deformation and metamorphic histories similar to the 

granite near Round Mountain, and that have not been 

unroofed by erosion, seem to be likely sites for 

undiscovered wolframite vein deposits, perhaps of large 

size. Such postulated deposits, as well as known ones, 

may have formed dominantly during a major regional 

event of tungsten mineralization about 80 m.y. ago.

REFERENCES CITED

Amosse, Jean, 1978a, Variation in wolframite composition according 

to temperature, at Borralha, Portugal, and Enguyales, France: 

Economic Geology, v. 73, no. 6, p. 1170-1175.

 1978b, Physicochemical study of the huebnerite-ferberite 

(MnW04-FeW04) zonal distribution in wolframite (MnxFe(i_X)- 

W04> deposits; Application to the Borralha Mine (Portugal): 

Physics and Chemistry of Minerals, v. 3, p. 331-341. 

-1980, Physicochemical interpretation of the mechanism of the

oscillatory zoning in wolframite crystals: International Mineralogical Association, Collected abstracts, 12th General Meeting, Orleans, France (July 4-6, 1980), p. 29.

Banerjee, K. S., 1969, Origin of weak ferromagnetism and remanence 

in natural cassiterite crystals: Journal of Geophysical Research, 

v. 74, p. 3789-3795.

Banerjee, K. S., Johnson, C. E., and Krs, M., 1970, Mossbauer study 

to find the origin of weak ferromagnetism in cassiterite: Nature, 

v. 225, p. 173-175.
REFERENCES CITED 41

Baumann, L., and Starke, R., 1964, Beitrag zur verteilung der H/Fkoeffizienten innerhalb der wolframitlagerstatte Pechtelsgrun auf 

grund neuer rontgenographischer untersuchungen: Bergakademie 16, p. 79-82.

Beddoe-Stephens, B., and Fortey, N. J., 1981, Columbite from the 

Carrock Fell tungsten deposit: Mineralogical Magazine, v. 44, 

p. 217-223.

Bird, M. L., and Gair, J. E., 1976, Compositional variations in wolframite from the Hamme (Tungsten Queen) Mine, North Carolina: 

U.S. Geological Survey Journal of Research, v. 4, no. 5, p. 583- 

588.

Bolduan, Helmut, 1954, Genetische untersuchung der wolframitlagerstatte Pechtelgriin (Vogtland) und besonderer berucksichtigung der verteilung des H/F-koeffizienten und der 

spurenelemente niob und tantal in wolframit: Freiberger 

Forschungshefte, ser. C, no. 10, p. 46-61.

Bonham, H. F., Jr., and Garside, L. J., 1979, Geology of the Tonopah, Lone Mountain, Klondike, and northern Mud Lake quadrangles, Nevada: Nevada Bureau of Mines and Geology Bulletin 

92, 142 p.

Brown, G. C., 1911, Round Mountain tungsten mine: The Salt Lake 

Mining Review, August 15, 1911, p. 16.

Casadevall, Tom, and Rye, R. 0., 1980, The Tungsten Queen deposit, 

Hamme district, Vance County, North Carolina A stable 

isotope study of a metamorphosed quartz-huebnerite vein: 

Economic Geology, v. 75, no. 4, p. 523-537.

Chang, L. L. Y., 1967, Solid solutions of scheelite with other RHW04- 

type tungstates: American Mineralogist, v. 52, nos. 3-4, p. 427- 

435.

 1968, Subsolidus phase relations in the system ZnW04- 

ZnMo04-MnW04-MnMo04: Mineralogical Magazine, v. 36, p. 

992-996.

Churikov, V. S., 1959, Certain features of the chemical composition 

of wolframites Materials relating to the geology, petrography, 

mineralogy and geochemistry of ore deposits: Academy of Sciences of the U.S.S.R., p. 235-250. [In Russian.]

Clark, A. H., 1970, Manganese-iron ratios in wolframite, South 

Crofty Mine, Cornwall A discussion: Economic Geology, v. 65, 

p. 889-892.

de Magnee, I., and Aderca, B., 1960, Contribution a la connaissance 

du tungsten belt Ruandais (aspects geologiques, geochemique, 

metallogenique): Academie Royale Sciences Outre-Mer, c. 1, Sci. 

Nat. Mem., In. 8°, n.s.t, 11, f. 7, 56 p.

Eckel, E. B., 1961, Minerals of Colorado, a 100-year record: U.S. 

Geological Survey Bulletin 1114, 399 p.

Edwards, A. B., and Lyon, P. J., 1957, Mineralization at Aberfoyle 

tin mine, Rossarden, Tasmania: Proceedings of the Australian 

Institute of Mining and Metallurgy, v. 181, p. 93-145.

Evernden, J. F., and Kistler, R. W., 1970, Chronology of emplacement of Mesozoic batholithic complexes in California and western 

Nevada: U.S. Geological Survey Professional Paper 623, 42 p.

Ferguson, H. G., 1921, The Round Mountain district, Nevada: U.S. 

Geological Survey Bulletin 725-1, p. 383-406.

Foose, M. P., Slack, J. F., and Casadevall, Tom, 1980, Textural and 

structural evidence for predeformation hydrothermal origin of the 

Tungsten Queen deposit, Hamme district, North Carolina: 

Economic Geology, v. 75, no. 4, p. 515-522.

Ganeev, I. G., and Sechina, N. P., 1960, The geochemical peculiarities 

of wolframites: Geochemistry, v. 6, p. 617-623.

Glass, J. J., 1935, The pegmatite minerals from near Amelia, Virginia: 

American Mineralogist, v. 20, p. 754-756.

Groves, D. I., and Baker, W. E., 1972, The regional variation in 

compositions of wolframites from Tasmania: Economic Geology, 

v. 67, p. 362-368.

Grubb, P. L. C., 1967, Solid solution relationships between wolframite and scheelite: American Mineralogist, v. 52, p. 418-426.

Hogarth, D. D., and Chao, G. Y., 1979, Jixianite, in New mineral 

names: American Mineralogist, v. 64, p. 1330.

Hollister, V. F., 1970, Manganese-iron ratios in wolframite, South 

Crofty Mine, Cornwall a discussion: Economic Geology, v. 65, 

no. 5, p. 592.

Horner, C., 1979, Solubility and hydrolysis of FeW04 and MnW04 

in the 25°-300°C range, and the zonation of wolframite: Chemical 

Geology, v. 27, p. 85-97.

Hsu, L. C., 1976, The stability relations of the wolframite series: 

American Mineralogist, v. 61, p. 944-955.

Jianchang, Liu, 1979, Jixianite, Pb(W,Fe +3)2(0,OH)T a new tungsten mineral: Acta Geologica Sinica, v. 53, p. 46-49.

Kelly, W. C., and Rye, R. 0., 1979, Geologic, fluid inclusion, and 

stable isotope studies of the tin-tungsten deposits of Panasqueira, 

Portugal: Economic Geology, v. 74, no. 8, p. 1721-1822.

Koschmann, A. H., and Bergendahl, M. H., 1968, Principal gold-producing districts of the United States: U.S. Geological Survey Professional Paper 610, 283 p.

Krai, V. E., 1951, Mineral resources of Nye County, Nevada: Nevada 

University Bulletin, v. 45, no. 3, Geology and Mining Series 50, 

223 p.

Landis, G. P., and Rye, R. 0., 1974, Geologic, fluid inclusion, and 

stable isotope studies of the Pasto Bueno tungsten-base metal 

ore deposit, northern Peru: Economic Geology, v. 69, no. 7, p. 

1025-1059.

Lawrence, L. J., 1961, Crystal habit of wolframite as an indication 

of relative temperature of formation: Neues Jahrbuch fur 

Mineralogie. Monatshefte, p. 241-247.

Lee, D. E., 1955, Mineralogy of some Japanese manganese ores: Stanford University Publications, University Series, Geological Sciences, v. 5, 64 p.

Lee, D. E., and Van Loenen, R. E., 1971, Hybrid granitoid rocks 

of the southern Snake Range, Nevada: U.S. Geological Survey 

Professional Paper 668, 48 p.

Lee, D. E., Marvin, R. F., Stern, T. W., and Peterman, Z. E., 

1970, Modification of potassium-argon ages by Tertiary thrusting 

in the Snake Range, White Pine County, Nevada, in Geological 

Survey research 1970: U.S. Geological Survey Professional Paper 

700-D, p. D92-D102.

Lemmlein, G. G., and Klevtsov, P. V., 1961, Relations among the 

principal thermodynamic parameters in a part of the system 

H20-NaCl: Geokhimiya, 1961, no. 2, p. 133-142 (in Russian); 

translated in Geochemistry, no. 2, p. 148-158, 1961.

Leonard, B. F., Mead, C. W., and Conklin, Nancy, 1968, Silver-rich 

disseminated sulfides from a tungsten-bearing quartz lode, Big 

Creek district, central Idaho: U.S. Geological Survey Professional Paper 594-C, p. C1-C24.

Leutwein, F., 1952, Die chemische zusammensetzung des wolframit 

und ihre lagerstattenkundliche bedeutung: Acta Geologica 

Akademiae Scientiarum Hungaricae, v. 1, p. 133-141.

Machin, M. P., and Susse, P., 1975, On the crystal structure of ferritungstite, (W,Fe +3)204(OH)2-1/2H20: Fortschritte der 

Mineralogie, v. 53, p. 50 [abs.].

Marvin, R. F., and Dobson, S. W., 1979, Radiometric ages Compilation B, U.S. Geological Survey: Isochron/West, no. 26, p. 3-32.

Melhase, John, 1935, Nevada, the mineral collector's Mecca: 

Mineralogist, v. 3, no. 4, p. 9-10, 37-38.

Miller, C. F., 1977, Muscovite granite with high initial Sr^/Sr86, Old 

Woman Mountains, California; a product of upper crustal 

anatexis?: Geological Society of America Abstracts with Programs, v. 9, no. 4, p. 466.
42 HUEBNERITE VEINS NEAR ROUND MOUNTAIN, NYE COUNTY, NEVADA

Mineev, D. A., 1968, Average composition of lanthanoids in minerals: 

Geochemistry, no. 7, p. 825-835. [In Russian, English abs.]

Moore, F., and Howie, R. A., 1978, On the application of the huebnerite:ferberite ratio as a geothermometer: Mineralium Deposita, v. 

13, p. 391-397.

 1979, Geochemistry of some Cornubian cassiterites: Mineralium

Deposita, v. 14, p. 103-107. 

Moore, J. M., and Jackson, N., 1977, Structure and mineralization

in the Cligga granite stock, Cornwall: Journal Geological Society

of London, v. 133, p. 467-480. 

Myers, A. T., Havens, R. G., and Dunton, P. J., 1961, A spectrochemical method for the semiquantitative analysis of rocks and

ores: U.S. Geological Survey Bulletin 1081-1, p. 207-229. 

Oelsner, Oscar, 1944, Uber Erzgebirgische wolframit: Freiberger

Geologischen Gesellschaft Bergbau, v. 20, p. 44-49.

 1952, Die pegmatitisch-pneumatolytischen lagerstatten des 

Erzgebirges mit ausnahme der kontakt-lagerstatten: Freiberger 

Forschungshefte, ser. C, no. 4, 80 p. 

-1954, Bemerkungen iiber die anwendbarkeit des H/F-koeffizienten zur deutung der genese von wolframiten: Freiberger 

Forschungshefte, ser. C, no. 10, p. 62-67.

Palache, Charles, Berman, Harry, and Frondel, Clifford, 1951, The 

system of mineralogy, 7th ed., vol. II: New York, John Wiley, 

1124 p.

Ramdohr, Paul, 1966, The ore minerals and their intergrowths, English translation of 3d ed.: Oxford, Pergamon Press.

Saari, E., von Knorring, 0., and Sahama, Th. G., 1968, Niobian wolframite from the Nuaparra pegmatite, Zambezia, Mozambique: 

Lithos, v. 1, no. 2, p. 164-168.

Schilling, J. H., 1963, Tungsten mines in Nevada: Nevada Bureau 

of Mines Map 18.

Schneider-Scherbina, Alexander, 1962, Uber metallogenetische 

epochen Boliviens und den hybriden charakter der sogenannten 

Zinn-Silber-Formation: Geologische Jahrbuch, v. 81, p. 157-170 

[1964].

Shawe, D. R., 1977a, Preliminary generalized geologic map of the 

Round Mountain quadrangle, Nye County, Nevada (with text): 

U.S. Geological Survey Miscellaneous Field Studies Map MF833.

 1977b, Geochemical and generalized geologic maps showing distribution of iron, copper, lead, zinc, molybdenum, silver, antimony, arsenic, tungsten, barium, potassium, and boron in the Round 

Mountain quadrangle, Nye County, Nevada (12 separate maps): 

U.S. Geological Survey Miscellaneous Field Studies Maps MF835A-I.

Sheikh, A. M., 1970, Geology and ore deposits of Las Guijas tungsten 

district, Pima County, Arizona: Economic Geology, v. 65, no. 

7, p. 875-882.

Shnuraeva, L. Ya., 1972, The typomorphism of heubnerite of the 

Bom-Gorkonsk tungsten deposit (western Transbaikal): Zapiski 

Vsesoyuznevo Mineralogichestvo Obshchestvo 101, p. 118-122. 

[In Russian.]

Sibley, D. F., Vogel, T. A., Walker, B. M., and Byerly, G., 1976, 

The origin of oscillatory zoning in plagioclase A diffusion and 

growth controlled model: American Journal of Science, v. 276, 

p. 275-284.

Takenouchi, Sukune, and Kennedy, G. C., 1965, The solubility of 

carbon dioxide in NaCl solutions at high temperatures and pressures: American Journal of Science, v. 263, p. 445-454.

Takla, M. A., 1976, Electron microprobe of zoned wolframite from 

Elba, Egypt: Neues Jahrbuch fur Mineralogie Monatshefte, v. 

11, p. 477-483.

Takla, M. A., Sharkawi, M. A., and Fawzi, E., 1977, The geochemistry of Egyptian wolframites: Chemie der Erde, v. 36, p. 10-19.

Taylor, R. G., and Hosking, K. F. G., 1970, Manganese-iron ratios 

in wolframite, South Crofty Mine, Cornwall: Economic Geology, 

v. 65, p. 47-53.

Tingley, J. V., 1975, K-Ar dates on granodiorite and related scheelitebearing quartz veins at Tungsten, Pershing County, Nevada: 

Isochron/West, no. 12, p. 3-4.

Varlamoff, N., 1958, Les gisements de tungestene au congo beige 

au Ruanda-Urundi, materiaux pour 1'etude de leur geologic et 

de leur classification: Academic Royale Sciences, Colon. Brussels, 

nov. ser., 8, fasc. 2.

Vinogradova, L. G., and Barabanov, V. F., 1978, On the question 

about the chemistry of wolframite: Zapiski Vsesoyuznevo 

Mineralogichestvo Obshchestvo 107, no. 5, p. 585-590. [In Russian.]

Vinogradova, L. G., Barabanov, V. F., and Sorokin, N. D., 1980, 

On the distribution of iron, manganese, niobium, and scandium 

in wolframites: Zapiski Vesesoyuznovo Mineralogischestvo Obshchestvo, v. 109, p. 351-358. [In Russian.]

Voyevodin, V. N., 1981, The relation between chemical composition 

of wolframites and the geological conditions of their formation: 

International Geology Review, v. 23, no. 5, p. 561-570.

White, W. A., 1945, Tungsten deposit near Townsville, North 

Carolina: American Mineralogist, v. 30, p. 97-110.

Wiendl, Ulrich, 1968, Zur geochemie und lagerstatten kunde des wolframs: Technischen Universitat Clausthal, Disertation zur erlangung des grades eines Doktor-Ingenieurs, 295 p. (Genehmigt von 

der Fakultat fur Bergbau. Hiittenwesen und Maschinenwesen).

Zuyuv, V. N., Zubkov, L. B., Zubynina, K. B., UtWna, T. F., and 

Chistov, L. B., 1966, New data on the modes of occurrence of 

tantalum and niobium in wolframite: Doklady of the Academy 

of Sciences of the U.S.S.R., v. 166, no. 106, p. 105-107.

 tt U.S. GOVERNMENT PRINTING OFFICE: 1984 776-041/4030 REGION NO. 8