DEPARTMENT OF THE INTERIOR 

U.S. GEOLOGICAL SURVEY

Geologic map of the Belmont West 7 1/2-minute quadrangle, 

Nye County, Nevada

By

Daniel R. Shawe1

Open-File Report 92-0186 

1992

This map is preliminary and has not been reviewed for conformity with U.S. 

Geological Survey editorial standards or with the North American stratigraphic code. 

Any use of trade, product, or firm names is for descriptive purposes only and does 

not imply endorsement by the U.S. Government.

Denver, Colorado
DESCRIPTION OF MAP UNITS

Qmf Manmade fill (Modern)-Chiefly mine dumps and mill tailings; includes some 

bulldozed areas in northwest part of quadrangle

Qa3 Alluvium (Holocene)-Active alluvium in drainage courses. Characterized by 

braided veinlike strands of freshly deposited gravel, sand, and silt. Qa3b, 

alluvium with abundant strands of freshly deposited alluvium; Qa3a, slightly 

older alluvium with less abundant freshly deposited alluvium. Qa3a 

commonly stands higher than Qa3b along sides of drainage courses; the two 

may merge. Thickness 0-a few meters

Qf Alluvial fans (Holocene)-Alluvial fans commonly formed at the foot of short

drainages that enter deeply incised courses in older alluvium, and fronting 

steep escarpments. Qf may merge with Qa3a or Qa3b. Thickness 0-several 

hundred meters

Qt Talus (Holocene)-Active talus on steep slopes. Thickness 0-a few tens of meters

Qsw Slope wash (Holocene)-Slope wash, more or less stabilized. Qsw may merge 

upslope with Qt and downslope with Qa3a. Thickness 0-several meters

Qls Landslide deposits (Holocene and Pleistocene(?))--Qls, undifferentiated landslide 

material. Qls2, younger landslide; Qlsl, older landslide, possibly 

Pleistocene. Thickness 0-several tens of meters

Qa2 Older alluvium (Holocene and Pleistocene(?))--Stabilized alluvium that occurs in 

flats and terraces higher than Qa3, and is presently being eroded. Clasts 

generally are only slightly weathered. Qa2b is a lag deposit on only slightly 

eroded flat surfaces; Qa2a is extensively eroded and is laced with numerous 

incised strands of active alluvium too small to map; older parts may be as 

old as Pleistocene. Thickness 0-several tens of meters

Qal Old alluvium (Pleistocene(?))-Stabilized old alluvium, in part pediment gravel, 

that occurs in flats and terraces higher than Qa2; it also is presently being 

eroded. Locally contains boulders from a proximal source. Larger clasts, 

especially of volcanic rocks, may be significantly weathered. Thickness 0- 

several hundred meters

Tva Volcanic ash (Miocene)-Light-gray glass-shard tuff. Underlies two adjacent small 

knobs on the east side of Silver Creek near its mouth. Zircon fission-track 

age 12.0+2.6 Ma (Shawe and others, 1987). Thickness about 20 m

Tit Ash-flow tuff (Miocene?)--Light-lavender-gray moderately crystal-rich biotitebearing rhyodacitic ash-flow tuff. Caps the middle knob of five westnorthwesterly aligned knobs underlain by Trt, Tg, and granite west of 

Belmont. Remnant thickness about 5 m
Trt Ash-flow tuff (Miocene?)-Light-gray crystal-rich rhyolitic ash-flow tuff. Caps five 

west-northwesterly aligned knobs underlain by Tg and granite west of 

Belmont. Remnant thickness 25-30 m

Tg Boulder gravel (Miocene?)-Granite-boulder gravel that contains abundant cobble 

and pebble clasts of Paleozoic rocks such as siliceous argillite, schist, chert, 

and limestone. Underlies Trt and overlies granite west of Belmont. 

Thickness 0-30 m

Tea Crone Gulch Andesite (Miocene)-Olive-brown, brown-weathering porphyritic 

andesite. Forms thick sills emplaced in Bald Mountain Formation at 

northwest edge of the quadrangle, and in Trls and between Tdks and Trus 

northeast of lower Bald Mountain Wash, and thin dikes near west edge of 

the quadrangle 1 km north of East Manhattan Wash. Plagioclase K-Ar age 

22.6+1.4 Ma (Shawe and others, 1986)

Tld Latite dike (Upper Oligocene)~Gray biotite-bearing latite dike. Lithologically 

similar to a nearby dike in the Manhattan quadrangle that has a biotite KAr age of 24.2+0.8 Ma (Shawe and others, 1986)

Tbs Ash-flow tuff (Upper Oligocene)~Light-greenish-buff and buff quartz-latitic to 

rhyodacitic ash-flow tuff. Caps hills at northwest edge of the quadrangle. 

Biotite K-Ar age 24.6+0.8 and 24.8+0.8 Ma (Shawe and others, 1986). 

Remnant thickness 110 m

Tr Rhyolite plugs (Upper Oligocene)-Gray flow-layered biotite-bearing rhyolite

intruded as plugs into Trus in northwest corner of the quadrangle and into 

Trus, Trub, and Kbgp in west-central part of the quadrangle

Tql Quartz-latite plugs (Upper Oligocene)-Gray biotite-bearing quartz latite intruded 

as plugs into Tru3 and Kbgp in west-central part of the quadrangle

Tbm Bald Mountain Formation (Upper Oligocene)-Lacustrine laminated buff

claystone and siltstone composed of volcanic materials. Underlies Tbs and 

is intruded by Tea on hills in northwest part of the quadrangle. Thickness 

25-60 m

Diamond King Formation (Upper Oligocene)-Interlayered welded ash-flow tuffs 

and volcanic sandstone. Crops out widely in hills along northwest margin 

of the quadrangle. Maximum exposed thickness about 65 m

Tdku Upper member-Gray to buff moderately welded, moderately crystal-rich 

rhyolitic ash-flow tuff. Characterized by smoky quartz dipyramids. 

Maximum exposed thickness about 15 m

Tdks Sandstone units-Buff coarse-grained quartz-rich sandstone composed of 

volcanic materials. Water laid or base-surge origin. Present locally at base 

of Tdkl, and interlayered in Tdku and Tdkl. Thickness of individual units 

0-30 m
Tdkl Lower member-Buff moderately to densely welded, crystal-rich rhyolitic ashflow tuff. Characterized by smoky quartz dipyramids. Maximum exposed 

thickness about 30 m

Tdks Sandstone units-Described above

Round Rock Formation (Upper Oligocene)--Inter layered ash-flow and ash-fall 

tuffs, megabreccia, tuff-breccia, and sandstone, and intruded by thin tuffbreccia dikes. Widely distributed in western part of the quadrangle. 

Inferred thickness within the quadrangle about 600 m (Shawe and Snyder, 

1988, plate 1)

Trtb Tuff-breccia dikes-Gray, brown-weathering, rhyolitic tuff that contains

abundant small angular lithic fragments mostly less than 1 cm long; flow 

laminated adjacent to dike walls. Intruded only into the Round Rock 

Formation at the southeast margin of the Manhattan caldera near lower 

Bald Mountain Wash

Tru Upper member undivided-Poorly consolidated ash-flow and ash-fall tuff.

Biotite K-Ar age 25.0+0.8 Ma (Shawe and others, 1986). Thickness about 

200m

True Chert and sinter-Gray to brown, bedded to thinly laminated, porous to

massive chert and hotsprings sinter, locally with abundant plant remains, in 

places with thin interlayers of buff tuff. Unit caps hills on the east side of 

lower Bald Mountain Wash. Maximum remnant thickness about 20 m

Tru3 Unit 3 of the upper member-Greenish-buff partially welded crystal-poor 

rhyodacitic ash-flow tuff. Widely distributed in west-central and northwest 

parts of the quadrangle. Thickness 40-110 m

Trus Megabreccia unit of Silver Creek-Small to large (10 m) clasts of mostly 

Cretaceous granite of the Belmont lobe of the granite of Shoshone 

Mountain in an eruptive matrix of comminuted granite and dacitic to 

rhyodacitic volcanic ash. Widely exposed in the west-central and northwest 

parts of the quadrangle. Thickness 0-50 m where the unit is outflow 

interlayered between overlying Tdkl and underlying Tru3; incised to depths 

as great as 150 m where the unit is inferred to be vent facies

Trss Sandstone units-Buff volcanic sandstone, water laid or base-surge

origin. Present in northwest part of the quadrangle, interlayered in Trus as 

thin lenses (thickness 0-10 m)

Trub Tuff breccia-Granite clasts (to several centimeters across) in a welded 

ash-flow tuff matrix; locally consists of megabreccia that contains granite 

boulders as large as 4 m in size. Present in northwest part of the 

quadrangle where it forms thin layers and lenses (thickness 0-10 m) near 

the top of Tru3, near the base of Trus, and between these units
Tru2 Unit 2 of the upper member-Pinkish-brown partially welded crystal-poor 

rhyodacitic and quartz-latitic ash-flow tuff. Caps knobs southwest of Bald 

Mountain Wash. Thickness 0-35 m; absent locally between Tru3 and Trul

Trul Unit 1 of the upper member-Buff partially welded crystal-poor rhyodacitic 

ash-flow tuff. Exposed between Bald Mountain Wash and west edge of the 

quadrangle. Maximum thickness about 60 m

Trm Middle member-Megabreccia of autobrecciated small to large (10 m) clasts of 

reddish-brown rhyolite (both welded tuff and lava) and gray hornblende- or 

biotite-bearing andesite (and types intermediate between rhyolite and 

andesite) in an eruptive matrix of buff to gray poorly welded ash-flow tuff. 

In small exposures north of East Manhattan Wash near west edge of the 

quadrangle, and just northeast of Bald Mountain Wash. Thickness 15-20 m

Trl Lower member-Buff partially welded crystal-poor to crystal-rich quartz latitic 

to rhyodacitic ash-flow tuff. Present near East Manhattan Wash and lower 

Bald Mountain Wash. Inferred intracaldera thickness within the 

quadrangle 450 m (Shawe and Snyder, 1988, plate 1); thickness of two 

lenses interlayered with Trls as outflow each 30-35 m

Trls Megabreccia unit of Sloppy Gulch-Small to immense (as much as 600 m) 

clasts of granite and Paleozoic rocks including argillite, limestone, quartzite, 

chert, and schist in an eruptive matrix of buff rhyodacitic ash-flow tuff. 

Contains some mesobreccia and tuff-breccia layers. Present near East 

Manhattan Wash and lower Bald Mountain Wash. Inferred thickness of 

outflow 0-200 m (Shawe and Snyder, 1988, plate 1)

Trie Siltstone-claystone-Buff lacustrine(?) volcanic siltstone and claystone 

layers and lenses interlayered in megabreccia of Trls east of lower Bald 

Mountain Wash. Thickness of individual units 0-10 m

Trp Rhyolite plugs (Upper Oligocene) Buff porphyritic rhyolite. Small plugs near 

Monarch in the southeast corner of the quadrangle. Zircon fission-track 

age 25.1+2.3 Ma (Shawe and others, 1987)

Tos Ash-flow tuff (Upper Oligocene)-Light-gray moderately welded crystal-rich

rhyolitic ash-flow tuff; characterized by small veinlet- and cavity-fillings of 

white opaline silica. Caps east-northeast-trending ridge in the southeast 

corner of the quadrangle as three small remnant patches a few meters thick 

overlying Trdu

Trdu Ash-flow tuff, upper member (Upper Oligocene)--Light-lavender-gray moderately 

to densely welded crystal-poor rhyodacitic ash-flow tuff. Characterized by 

clinopyroxene as the dominant mafic mineral. Constitutes the principal 

capping unit atop the east-northeast-trending ridge in the southeast corner 

of the quadrangle. Thickness about 50-85 m
Trdl Ash-flow tuff, lower member (Upper Oligocene)--Light-lavender-gray moderately 

to densely welded crystal-poor rhyodacitic ash-flow tuff. Characterized by 

clinopyroxene as the dominant mafic mineral; distinguished from overlying 

Trdu by fewer crystals and a lower proportion of plagioclase and mafic 

minerals. Underlies Trdu on the east-northeast-trending ridge in the 

southeast corner of the quadrangle. Thickness about 60-70 m

Tap Andesite plugs and flows (Upper Oligocene)--Gray to lavender-gray porphyritic, 

in part flow-layered, biotite and hornblende-biotite andesite; intruded into 

or overlying Tbql, Us, and Tat. Exposed at the southeast edge of the 

quadrangle. Biotite K-Ar ages 26.8-1-1.0, 26.6-1-1.0, and 26.3-»-0.9 Ma 

(Shawe and others, 1987)

Tat Ash-fall tuff (Upper Oligocene)-White bedded biotite-bearing quartz latitic ashfall tuff. Widespread in southeast corner of the quadrangle. Biotite K-Ar 

age 27.0-1-1.0 Ma (Shawe and others, 1987). Thickness about 110-130 m

Tatc Conglomerate (Upper Oligocene)-Light-gray pebble conglomerate with clasts 

of light-reddish-brown rhyolite, gray latite or andesite, coarse-grained 

biotite granite, and Paleozoic chert; local black-sand layers. Forms lenses 

0-10 m thick at or near top of the white ash-fall tuff unit (Tat) on southeast 

slope of the east-northeast-trending ridge in the southeast corner of the 

quadrangle

Us Limestone (Upper Oligocene)-Light-gray algal limestone that contains local

lenses of hotsprings sinter and chert-rich conglomerate with some volcanic 

clasts. Underlies Tat and overlies Tbql in southeast corner of the 

quadrangle. Locally domed around small andesite plugs. Thickness about 

10m

Tbql Ash-flow tuff (Upper Oligocene)-Greenish-gray moderately crystal-rich biotite 

quartz latitic partially welded ash-flow tuff. Small area of outcrop in 

southeast corner of the quadrangle. Exposed thickness about 130 m

Tcs Claystone, siltstone, and sandstone (Upper Oligocene)-Buff platy volcanic

claystone, siltstone, and sandstone, quartz-latitic to rhyolitic in composition; 

probably mostly lacustrine; minor pebble conglomerate lenses. Underlies 

white ash-fall tuff in southeast corner of the quadrangle. Exposed thickness 

about 40 m

Tcsb Tuff-breccia and megabreccia (Upper Oligocene)-Buff-gray ash-flow tuff with 

abundant clasts (to 5 cm), mostly Paleozoic shale and chert, and 

megabreccia that contains clasts as large as 2 m in size mostly of ash-flow 

tuff, some flow-layered rhyolite, and black phenocrystic vitrophyre. Thin 

(to a few meters) lenses and layers in Tcs
Granite of Pipe Spring (Upper Cretaceous)--Coarse-grained two-mica granite 

pluton intruded by thin aplite dikes; fine-grained granodiorite forms 

irregular dikes near the east contact. Crops out in southwest corner of the 

quadrangle

Kpgd Granodiorite-Light-gray fine-grained biotite granodiorite, and hornblende 

granodiorite characterized by abundant sphene. Locally tourmalinized. 

Forms irregular dikes as thick as 10 m just east of the east contact of the 

Pipe Spring pluton. Biotite K-Ar age 76.1+2.7 Ma; K-feldspar K-Ar age 

76.5+2.8 Ma (Shawe and others, 1987)

Kpa Aplite-Pale-gray to pale-buff biotite-bearing aplite; locally grades into

pegmatite. Forms thin (to 10 m wide) dikes emplaced widely in the Pipe 

Spring pluton, and thin dikes and larger masses as apophyses penetrating 

wallrocks of Paleozoic age. Biotite K-Ar age 76.1+2.7 Ma (Shawe and 

others, 1987)

Kpg Granite-Pale-gray to pale-buff coarse-grained two-mica granite. Granite

exposed in the southwest corner of the quadrangle is part of a large pluton 

extending about 12 km farther southwest. Whole-rock isochron Rb-Sr age 

80.2+2.4 Ma (John and Robinson, 1989), and whole-rock-biotite isochron 

Rb-Sr age 80.1+1.0 Ma (Shawe and others, 1986)

Belmont lobe of the granite of Shoshone Mountain (Upper Cretaceous)-Coarsegrained two-mica granite grading up into sparsely porphyritic granite 

grading up into porphyritic granite, in an oval-shaped, domed pluton whose 

long axis trends northwestward and that occupies much of the north half of 

the quadrangle. The porphyritic upper shell of the pluton is widely 

intruded by fine-grained granite masses and aplite dikes, some of which 

penetrate into adjoining wallrocks

Kba Aplite-Pale-gray to pale-buff biotite-bearing aplite; locally grades into

pegmatite. Forms thin (to 10 m wide) dikes emplaced widely in Kbgp, and 

thin dikes and larger masses as apophyses penetrating wallrocks of 

Paleozoic age. Biotite K-Ar age of pegmatite 80.2+1.6 Ma (M.L. 

Silberman, written commun., 1968; corrected to new decay constants, 

Dalrymple, 1979)

Kbgf Fine-grained granite-Pale-gray to pale-buff fine-grained granite. Forms small 

to large (several hundred meters across) irregular masses, dikes, and sills 

intruded into Kbgp and Paleozoic wallrocks near the pluton margin in 

northeast part of the quadrangle

Kbgp Porphyritic granite-Pale-gray to pale-buff coarse-grained two-mica granite

that contains abundant (about 15 percent or more) large phenocrysts (1 to 

8 cm long) of orthoclase. Forms an annular shell 1-2 km wide around the 

Belmont pluton. Contacts against intruded Paleozoic rocks dip gently to 

steeply outward. Pedimented surface with discontinuous thin gravel veneer 

in east-central part of the quadrangle shown as Kbgp (ped)
Kbgs Sparsely porphyritic granite-Pale-gray to pale-buff coarse-grained two-mica 

granite that contains 0-about 15 percent large phenocrysts of orthoclase. 

Forms an annular shell 1-2 km wide within the peripheral porphyritic shell 

that surrounds the core of the pluton

Kbg Granite-Pale-gray to pale-buff coarse-grained two-mica granite that forms the 

core of the Belmont pluton in north part of the quadrangle. Rb-Sr wholerock isochron age 84.2+2.3 Ma; 84.8+4.4 Ma (John and Robinson, 1989)

Pzg Greenstone (Paleozoic, undivided)-Greenish-gray to olive-brown fine- to

medium-grained diabase-textured to schistose amphibolitic greenstone, 

probably a mafic intrusion. Intruded as several oval-irregular masses into 

Ordovician argillite and limestone on southwest side of the mouth of Bald 

Mountain Wash

Osa Siliceous argillite (Ordovician, undivided)-Dark-gray locally brown-weathering

argillite with minor interlayered limestone. In thrust contact with Pzmg and 

Pzmm northeast of Monarch near east boundary of the quadrangle

Toquima Formation (Middle Ordovician)-Generally thin-bedded interlayerd 

argillite, siliceous argillite, limy argillite, argillaceous limestone, limestone, 

siltstone, and quartzite. Near granitic plutons limestone is metamorphosed 

to marble and calc-silicate mineral-bearing rock, and argillite is 

metamorphosed to schist. Locally elsewhere limestone commonly has been 

jasperized and argillite has been silicified. Exposed on either side of East 

Manhattan Wash in southwest corner of the quadrangle, in northeast 

corner of the quadrangle, and along margin of the Belmont pluton north of 

Monarch. Forms a thrust plate overlying the Zanzibar Formation. 

Thickness unknown because of repetition of section by thrust faults, 

thickening that resulted from isoclinal folding, and thinning that resulted 

from laminar shearing; original thickness probably several hundred meters

Otl Limestone-Light-gray to dark-gray, thin-bedded to laminated (laminae due 

mostly to tectonic shearing related to deformation that resulted in thrust 

faulting). Metamorphosed in places near granite plutons to pale-gray and 

white marble

Otlj Jasperized limestone-Dark gray, commonly showing reddish- or yellowishbrown iron stain. Most abundant either as beds laterally continuous for 

several hundred meters, or as irregular masses that grade along bedding 

from unaltered limestone. Present on both sides of East Manhattan Wash 

in southwest corner of the quadrangle

Otic Calc-silicated limestone-pale-buff to pale-greenish-gray calc-silicate 

mineral assemblages that resulted from metasomatic replacement of 

limestone near or adjacent to plutons; typical minerals are diopside, 

tremolite, wollastonite, idocrase, and (or) garnet
Otq Quartzite Medium-gray fine-grained quartzite, locally bleached white in 

patches or interstitially in breccia zones. Forms a thin (1-20 m) layer 

medially in the formation; a few thin lenses are present that may represent 

remnants of boudinaged layers. Dark-gray argillite both above and below 

quartzite commonly contains graptolites. Quartzite is correlative with the 

Eureka Quartzite of eastern and southern Nevada

Otla Limestone with interbedded argillite 

Otal Argillite and limestone, interlayered

Ota Argillite Medium- to dark-gray somewhat phyllitic or fissile laminated to 

massive and faintly bedded argillite or shale; locally silty. Adjacent to 

principal quartzite layer in the Toquima Formation, argillite contains 

abundant graptolites of Mohawkian age

Ots Schist-Medium- to dark-gray, brown weathering in places, micaceous

schist; locally has wavy foliation. Locally contains siltite interlayers; locally 

is, in part, hornfels. Most abundant north of Monarch adjacent to Belmont 

pluton, near east edge of quadrangle

Zanzibar Formation (Ordovician)-Generally thin- to medium-bedded interlayerd 

argillite, siliceous argillite, limy argillite, argillaceous limestone, limestone, 

and siltstone. Near granitic plutons limestone is metamorphosed to marble 

and calc-silicate mineral-bearing rock, and argillite is metamorphosed to 

schist. Locally elsewhere limestone commonly has been jasperized and 

argillite has been silicified. Exposed southwest of East Manhattan Wash in 

southwest corner of the quadrangle and in northeast corner of the 

quadrangle. Forms a thrust plate overlying the Gold Hill and Mayflower 

Formations and underlying the Toquima Formation. Thickness unknown 

because of repetition of section by thrust faults, thickening that resulted 

from isoclinal folding, and thinning that resulted from tectonic shearing; 

original thickness probably several hundred meters

Ozl Limestone Light-gray to dark-gray, medium-bedded to laminated limestone 

(laminae due mostly to tectonic shearing related to deformation that 

resulted in thrust faulting). Locally contains dark-gray nodular to layered 

chert. Metamorphosed in places near granite plutons to pale-gray and white 

marble

Ozlc Calc-silicated limestone-pale-buff to pale-greenish-gray calc-silicate 

mineral assemblages that resulted from metasomatic replacement of 

limestone near or adjacent to the Belmont pluton in northeast corner of the 

quadrangle; typical minerals are diopside, tremolite, wollastonite, idocrase, 

and (or) garnet

Ozal Argillite and limestone, interlayered
Oza Argillite-Gray to dark-gray, noncalcareous to limy, locally faintly laminated or 

phyllitic argillite or shale

Ozs Schist-Medium- to dark-gray, brown-weathering schist. Locally contains 

thin siliceous argillite and (or) siltite layers. Occurs close to the Belmont 

pluton contact in northeast corner of the quadrangle

Gold Hill Formation (Cambrian)--Phyllitic schist and quartzite and minor 

interlayered limestone. Exposed southwest of East Manhattan Wash in 

southwest corner of the quadrangle. Forms a thrust plate overlying the 

Mayflower Schist and underlying the Zanzibar and Toquima Formations. 

Thickness unknown because of tectonic deformation. Original thickness 

probably several hundred meters

 Ggs Schist-Light-olive-brown to buff phyllitic argillite and mica schist. Contains 

minor interlayered quartzite and limestone. The dominant lithology in the 

Gold Hill Formation

 Cgq Quartzite-Buff to light-olive-gray mostly fine-grained thin- to mediumbedded quartzite. Interlayered in schist as lenses and layers a few 

centimeters thick to several tens of meters thick

 Cgl Limestone-Buff and light-brownish-gray to gray, massive and thin-bedded to 

laminated limestone. Locally consists of white marble near pluton contacts. 

Forms layers a few meters to 40 meters thick interlayered between and 

within schist (Cgs) and schist-quartzite (Cgqs) units

 Cglc Calc-silicated limestone-Pinkish-buff, pale-greenish-gray, and nearly white 

calc-silicate mineral assemblages that resulted from metasomatic 

replacement of limestone; characterized by minerals such as diopside, 

tremolite, wollastonite, idocrase, and garnet. Present near margin of the 

granite of Pipe Spring

 gqs Quartzite and schist-Interlayered quartzite and schist that constitute most of 

the unit adjacent to the granite of Pipe Spring

Rocks of the Monarch area (Paleozoic, undivided)-Greenstone, chert, 

metasomatite, argillite-schist, dolomite, and serpentinite, in part 

interlayered and (or) tectonically intermixed, that make up a unit, probably 

a thrust plate, near Monarch in southeast part of the quadrangle. Partial 

lithologic similarity to Cambrian units in the region suggest a possible 

Cambrian age

Pzmg Greenstone-Dark-greenish-gray to brownish-gray, brown-weathering, aphanitic 

to porphyritic greenstone. Locally vesicular. Fragmental (brecciated to 

agglomeratic) layers a few meters thick interlayerd with massive greenstone 

layers several tens of meters thick. Extensive outcrops northeast and 

southeast of Monarch
Pzmc Chert-Greenish-gray to brownish-gray chert lenses a few meters thick 

interlayered in greenstones

Pzma Argillite and chert-Gray to light-brown thin-bedded and interlayered siliceous 

argillite and chert. Interlayered with or intruded by lenses and irregular 

masses of greenstone. Exposed on a low hill south of Monarch. Aggregate 

thickness of argillite and chert about 400-500 m

Pzmm Metasomatite--Yellowish-brown carbonate rock, mostly calcite, locally 

dolomitic and locally brecciated. Contains gray jasperoid in places. 

Probably formed by metasomatic replacement of an unknown protolith. 

Crops out north of Monarch near east-central edge of the quadrangle, and 

at southeast end of a low hill southwest of Monarch

Pzmd Dolostone-Light-brown, reddish-brown, and pinkish-brown sugary dolostone. 

Associated with metasomatite and serpentinite at the southeast end of a 

low hill southwest of Monarch. Thickness about 30-150 m

Pzms Serpentinite-Grayish-green and greenish-gray dense, massive, locally schistose 

or brecciated serpentinite. Studied and placed in a regional context by 

Poole and Desborough (1973). In places silicified and iron mineralized. 

Underlies most of low hill southwest of Monarch

Cms Mayflower Schist (Cambrian)--Gray to olive-gray phyllitic to knotted schist. In 

thrust contact with overlying Gold Hill, Zanzibar, and Toquima Formations

REFERENCES

Dalrymple, G.B., 1979, Critical tables for conversion of K-Ar ages to new constants: Geology, 

v. 7, p. 558-560.

John, D.A., and Robinson, A.C., 1989, Rb-Sr whole rock isotopic ages of granitic plutons in the 

western part of the Tonopah 1° by 2° quadrangle, Nevada: Isochron/West, no. 53, p. 

20-27.

Poole, F.G., and Desborough, G.A., 1973, Alpine-type serpentinites in Nevada and their tectonic 

significance: Geological Society of America Abstracts with Programs, v. 5, no. 1, p. 90-91.

Shawe, D.R., Marvin, R.F., Andriessen, P.A.M., Mehnert, H.H., and Merritt, V.M., 1986, Ages 

of igneous and hydrothermal events in the Round Mountain and Manhattan gold 

districts, Nye County, Nevada: Economic Geology, v. 81, p. 388-407.

Shawe, D.R., Naeser, C.W., Marvin, R.F., and Mehnert, H.H., 1987, New radiometric ages of 

igneous and mineralized rocks, southern Toquima Range, Nye County, Nevada: 

Isochron/West, no. 50, p. 3-7.

Shawe, D.R., and Snyder, D.B., 1988, Ash-flow eruptive megabreccias of the Manhattan and 

Mount Jefferson Calderas, Nye County, Nevada: U.S. Geological Survey Professional 

Paper 1471, 28 p.

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