Middle Buttes (Cactus) Deposit

Past Producer in Kern county in California, United States with commodities Gold, Silver, Copper, Lead

Sections on this page

Identification information
Geographic coordinates
Site location context
Geographic areas
Public Land Survey System information
Commodities
Materials information
Alteration
Mineral occurrence model information
Host and associated rocks
Nearby scientific data
Geologic structures
Ore body information
Controls for ore emplacement
Economic information about the deposit and operations
Mining district
Land status
Ownership information
Bibliographic references
General comments
Reporter information

Geologic information

Identification information

Deposit ID	10310650
Record type	Site
Current site name	Middle Buttes (Cactus) Deposit
Alternate or previous names	Cactus, Cactus Queen, Blue Eagle, Shumake, Winkler, Silver Prince, Crescent, Ella, Trent, Burton-Brite-Blank, Middle Butte

Comments on the site identification

The other names listed above represent individual historical properties within Middle Buttes. Of these, the Cactus Queen Mine was by far the most significant historic producer. The modern-day Cactus Mine encompassed all of Middle Buttes. Although the deposit produced substantially more silver than gold, the modern exploitation of the deposit has been for gold.

Geographic coordinates

Geographic coordinates:	-118.28937, 34.95778 (WGS84)
Elevation	1040
Location accuracy	100(meters)
Relative position	About 9 miles southwest of Mojave.

Site location context

Political divisions (FIPS codes)

Kern(county)

California(state)

United States(country)

North America(continent)

Land(continent)

USGS map quadrangles

Willow Springs(quadrangle 1:24,000 scale)

Lancaster(quadrangle 1:100,000 scale)

Los Angeles(quadrangle 1:250,000 scale)

Hydrologic units (watersheds)

Antelope-Fremont Valleys(hydrologic unit)

Northern Mojave(hydrologic accounting unit)

Northern Mojave-Mono Lake(hydrologic subregion)

California(hydrologic region)

Geographic areas

Country	State	County
United States	California	Kern

Public Land Survey System information

Meridian	Township	Range	Section	Fraction	State
San Bernardino	010N	013W	08,09,16,17		California

Comments on the location information

The main ore bodies of the deposit are in sections 16 and 17. The location point selected for latitude and longitude is the approximate location of the original Cactus Queen Mine on the west side of Middle Buttes. The deposit is accessible west off State Highway 14 via the paved Backus Road then north on Tehachapi-Willow Springs Road.

Commodities

Commodity	Importance
Gold	Primary
Silver	Primary
Copper	Secondary
Lead	Secondary

Comments on the commodity information

Commodity Info: Ore in the Cactus Queen-Shumake area is silver-rich. Ore in the Middle Butte Mine area is gold-rich. In 1941-43, 7,500 pounds of copper and 2,500 pounds of lead were recovered from the Cactus Queen Mine. Ore grade in the modern operations reportedly ranged from 0.039 oz/ton Au in the Silver Prince ore body to 0.185 oz/ton in the Winkler ore body (Blaske and others, 1991).
Ore Materials: Native gold, electrum, cerargyrite, argentite, proustite, chalcopyrite, galena
Gangue Materials: Quartz, alunite, kaolinite, iron oxide, adularia, pyrite, marcasite, arsenopyrite

Materials information

Materials	Type of material
Gold	Ore
Electrum	Ore
Cerargyrite	Ore
Argentite	Ore
Proustite	Ore
Chalcopyrite	Ore
Galena	Ore
Alunite	Ore
Kaolinite	Ore
Adularia	Ore
Pyrite	Ore
Marcasite	Ore
Arsenopyrite	Ore
Quartz	Gangue

Alteration

(Local) Silicic (early phase, pervasive)
Phyllic; sericite (envelopes up to 5m thick surrounding massive quartz veins)
Advanced argillic; alunite, kaolinite (peripheral to main ore zones)
Potassic; adularia
Propylitic; chlorite, pyrite, sericite, calcite (affects basement granitic rocks)
Oxidation; hematite

Mineral occurrence model information

Model code	104
USGS model code	25a
Deposit model name	Hot-spring Au-Ag
Mark3 model number	45
Model code	151
USGS model code	25d
Deposit model name	Epithermal vein, Sado
Mark3 model number	28

Host and associated rocks

Host or associated

Host

Rock type

Volcanic Rock (Aphanitic) > Felsic Volcanic Rock > Rhyolite

Rock type qualifier

Porphyritic

Rock unit name

Bobtail Quartz Latite Member

Stratigraphic age (youngest)	Early Miocene

Host or associated

Host

Rock type

Volcanic Rock (Aphanitic) > Pyroclastic Rock > Volcanic Breccia (Agglomerate)

Rock type qualifier

vent breccia

Rock unit name

Gem Hill Formation

Stratigraphic age (youngest)	Early Miocene

Nearby scientific data

(1)	-118.28937, 34.95778	ListMap

Economic information

Geologic structures

Type of structure	Local
Structure description	Both NE- and NW-trending normal faults that cut the volcanic-dome complex are significant in their control of the district?s ore bodies. Most important are the NE-trending Blue Eagle-Cactus Queen fault in the western area and an unnamed NW-trending fault in the eastern area. The Blue Eagle-Cactus Queen fault was traceable for several thousand feet.
Type of structure	Regional
Structure description	San Andreas Fault; Garlock Fault

Ore body information

General form Tabular; irregular

General form	Tabular; irregular

Controls for ore emplacement

The Blue Eagle-Cactus Queen vein and Shumake vein were the dominant pathways for metalliferous hydrothermal fluids. The Blue Eagle-Cactus Queen vein formed along a fault between the granitic basement rock and the volcanic dome complex. The Au-Ag-bearing fluids migrated through dilatant fault zones during episodic movements associated with regional tectonism. Repeated rupture-rehealing events, without boiling, are interpreted as having created secondary zones of permeability. These zones were the sites of stockworks composed of quartz-adularia-sericite. Alunite is an important guide to ore, although it is rare in the Shumake ore body.

Comments on the geologic information

INTRODUCTION

This part of California consists of a complex intersection of three geomorphic provinces: the Mojave Desert province forms a west-pointing wedge between the Sierra Nevada province on the north and the Transverse Ranges province on the south. Within this region of intersection are various precious-metal deposits, a few of which are considered significant. Most important is Soledad Mountain, which is situated within the Mojave Desert province. About 9 miles southwest of Soledad Mountain is the Middle Buttes deposit.

REGIONAL SETTING

Several generations of geologic study have been applied to this region of California. Earlier work by Simpson (1934) and Dibblee (1963, 1967) established a regional framework of stratigraphy and structure upon which later, more detailed local studies have been conducted. One of these important local studies, which centered on the volcanic features of Soledad Mountain, is that of McCusker (1982) who mapped the mountain at a scale of 1:6,000. At Middle Buttes, Blaske and others (1991) and Bottaro (1987) conducted detailed studies. Other older technical papers also present information on the geology of Middle Buttes (Bateson, 1907; Simpson, 1934; Julihn and Horton, 1937; Dibblee, 1963). On a broader scale, many papers have been published in the last 20 years that attempt to reconstruct this region?s geologic history in the light of plate tectonics; among these are papers or volumes by Dickinson (1981, 1997), Burchfiel and others (1992), Dokka and Ross (1995), Atwater (1989), and Atwater and Stock (1998).

Stratigraphy

The rocks of the western part of the Mojave Desert province can be generalized as topographic ?islands,? or inliers, that are surrounded by plains of Quaternary alluvium. These inliers consist of Mesozoic plutonic basement with pendants of older metamorphic rock, which are overlain by an eroded Tertiary cover. The Mesozoic plutonic basement ranges in composition from quartz diorite to granite and is present beneath the alluvial plains. The Tertiary cover consists of volcanic and sedimentary rocks. Simpson (1934) originally mapped the Tertiary cover as the ?Rosamond series,? but Dibblee (1963, 1967) later remapped it as the ?Tropico Group.? Within the Tropico Group, Dibblee (1963, 1967) mapped a volcanic unit known as the Gem Hill Formation, which includes a subunit at Soledad Mountain called the Bobtail quartz latite member. Dibblee placed the pyroclastic phases at Soledad Mountain in the Gem Hill and the hypabyssal and lava phases in the Bobtail.

Structure

Although the basement complex is part of the Sierra Nevada plutonic arc, which was associated with subduction tectonics during the Mesozoic, it is regional tectonism during the Late Cenozoic that was important in the development of the ore deposit at Soledad Mountain. Tectonics of this region during the Late Cenozoic were first dominated by subduction of plates to the west of this region and then by subsequent movements along the northwest-trending right-lateral San Andreas Fault System, which progressively formed when the Farallon-Pacific spreading center collided with the subduction zone (Atwater, 1989). This tectonic activity was part of the larger interaction of the North American Plate, Pacific Plate, and intervening Farallon Plate (and its subsidiary plates, which formed upon breakup of the Farallon within subduction zones) as they collided along the west coast of North America. With shutting off of subduction along the coast and resultant development of a slab window inboard of the newly developed San Andreas transform boundary that replaced the trench, magma may have ascended from the mantle to fill the void between the transform fault system and the broken-off slab that was still descending to the east of the system. The volcanism at Soledad Mountain may have been a local expression of this process.
The western Mojave Desert is part of what is termed the ?Mojave Desert block.? the geologic history of this structural block, particularly the western part, is still controversial. The western area is considered by Dokka (1989) to be part of what he termed the Mojave Extensional Belt (MEB), an approximately E-W-trending zone that is inferred to underlie much of the western two-thirds of the Mojave Desert including Soledad Mountain. The westernmost part of the belt, which includes Soledad Mountain, was termed the Edwards Terrane by Dokka (1989). In this model, the upper and middle crust of the MEB was extended in early Miocene (24 to 21 Ma) by low- and high-angle normal faulting accompanied by intrusion and eruption of intermediate to silicic magmas (Dokka and others, 1998). According to Dokka and Ross (1995), the MEB was overprinted about 20-18 Ma by a zone of dextral shear known as the Trans-Mojave-Sierran shear zone. This zone produced clockwise vertical-axis rotation of both the western Mojave Desert and the southernmost Sierra Nevada. Dokka and Ross (1995) believed that interaction of the Pacific and North American plates during this period of time was directly responsible for regional extension in the western Mojave Desert. The interaction may have been highlighted by transtensional pulling away of the Pacific Plate from the North American Plate (Atwater, 1989) which caused the edge of the North American Plate to extensionally collapse, perhaps by gravitational failure. This inferred extensional activity between 24 and 18 Ma overlaps the known ages of all Cenozoic volcanic activity at Soledad Mountain as determined by McCusker (1982).

Based on surface mapping and seismic-reflection surveys, Dokka (1989) concluded that the inliers discussed above are tilted upper-plate normal-fault blocks that are floored by detachment faults in the subsurface. The current orientation of structural features indicate that the extensional direction for the MEB is NE-SW; however, Dokka and Ross (1995) cited paleomagnetic evidence that suggests the western part of the Mojave Desert block may have been rotated clockwise since extension in the early Miocene such that the true extensional direction was originally N-S. Glazner and others (1996) believed, however, that the observations cited by Dokka and Ross (1995) were not convincing evidence of extension and rotation in the western Mojave Desert. Indeed, the tectonic history and causes of the Cenozoic magmatism are still not satisfactorily understood; several tectonic models have been proposed over the last few decades for this region as well as the western U.S., but none have yet satisfactorily explained all observable features and events.

Metallogeny

Albers (1981) and Albers and Fraticelli (1984) interpreted the westernmost part of the Mojave Desert geomorphic province to be underlain by a composite terrane of oceanic and island-arc crust with a few localized areas that are geologically favorable terrane for gold deposits; Soledad Mountain is one of these terranes. Various silicic eruptive centers of Tertiary age in this region have been the sites of epithermal precious-metal mineralization. Besides Soledad Mountain, other deposits of a similar epithermal nature within these volcanic centers include Standard Hill, Middle Buttes, and Tropico Hill.

The determination of whether extension, as described above, has taken place in this region is important regarding metallogeny of the region. Extensional environments are favorable for the migration of magmas and associated metal-bearing hydrothermal fluids. The potential for future discoveries of ore deposits in this region may depend largely on exploration beneath the alluvial fringes adjacent to the known deposits or in areas that may have formed in extensional environments.
GEOLOGY AT MIDDLE BUTTES DEPOSIT

Middle Buttes is composed of a rhyolite to quartz latite flow-dome complex that was intruded into and erupted upon Mesozoic quartz monzonite basement during the early Miocene. Some workers believed that Middle Buttes is on the northwest rim of a ring-fracture zone associated with a caldera (Burnett and Brady, 1990).

Overlapping with the Miocene volcanism at Middle Buttes were episodes of fracturing and hydrothermal alteration that resulted in gold and silver mineralization. Hypogene alunite from the altered pyroclastic rocks yielded a K-Ar age of 18.36 ? 0.55 Ma.

In brief, gold and silver ores occur within massive and brecciated epithermal quartz veins that follow NW- and NE-trending faults, and intersections thereof. They are also along basement contact zones associated with advanced argillic alteration and potassic alteration contemporaneous with the Miocene volcanism. Nearly all of the rocks at Middle Buttes have been hydrothermally altered. The alteration assemblages are zoned. The Shumake ore body contains mercury, arsenic, and antimony (Blaske and others, 1991), which are indicative of epithermal conditions.

Economic information about the deposit and operations

Operation type	Surface-Underground
Development status	Past Producer
Commodity type	Metallic
Deposit size	Medium
Significant	Yes
Discovery year	1934

Mining district

District name	Mojave District

Land status

Ownership category	Private
Area name	Kern County Planning Department
Ownership category	BLM Administrative Area
Area name	Ridgecrest Field Office (BLM)

Ownership information

Type Owner-Operator

Owner Cactus Gold Mines Company

Type	Owner-Operator
Owner	Cactus Gold Mines Company

Comments on the workings information

Early exploitation of the gold and silver ore bodies at Middle Buttes was through standard underground workings (shafts, adits, drifts, and crosscuts), which cumulatively amounted to many thousand feet at several mines. Of greatest extent were those at the Cactus Queen Mine, the most productive property in Middle Buttes. Other significant workings were on the eastern side of Middle Buttes at the Middle Butte Mine.

During the modern era of gold mining in California, the ore bodies at Middle Buttes were exploited through open-pit, heap-leach mining techniques. In the late 1980s and early 1990s, the mining operations consisted of one large open pit (Shumake) and several smaller ones (Silver Prince, Winkler, Alunite, Ella, and Trent). The Shumake Pit reached a depth of 640 feet below the ground surface. It eventually merged with the Silver Prince Pit to form a single pit about 1,300 feet wide and 2,500 feet long.

Comments on other economic factors

Troxel and Morton (1962) reported the value of total production from the Cactus Queen Mine at more than $5 million (gold + silver). Blaske and others (1991) reported that the Cactus Queen produced 92,000 oz Au and 2,320,700 oz Ag between 1934 and 1962. Production of gold at the modern Cactus Gold Mine operations from 1986 to 1996 is estimated to be less than 500,000 oz.

Comments on development

Gold was discovered at Middle Buttes in 1934 initially on the eastern side of the buttes at the Trent and Burton-Brite-Blank mines. Later that year, gold was discovered at the Cactus Queen Mine. By 1936, a 1,000-foot 45o inclined shaft was sunk at the Cactus Queen, which produced 125 tons/day of ore. All mines were closed in 1942 by the War Production Board.

Activity commenced for a short time during the 1950s at the Cactus Queen Mine by the Burton Cactus Mines Company. Ore was processed at nearby Tropico Hill until 1956 when the mine was closed.

In 1979, the Congdon & Carey Partnership (later CoCa Mines, Inc.) initiated a reconnaissance campaign at Middle Buttes. In 1980, an 11-hole diamond drilling program resulted in discover y of the Winkler ore body, which was initially estimated to contain 200,000 tons of 0.200 oz/ton ore. Open-pit mining of this body began in 1986. Subsequent exploration and drilling defined reserves at the Ella, Trent , and Alunite ore bodies in 1987 and 1988. Also during this period, drilling defined reserves at the Shumake and Silver Prince ore bodies, and mining began in 1988 at the Shumake, the largest of the entire group.

Gold recovery at the Middle Butte (eastern) operations, which included the Trent, Ella, Alunite, and Winkler, utilized heap leaching with a Merrill-Crowe system rinse. The final ore at this facility was processed in 1991. Gold recovery at the Shumake (western) operations, which included the Shumake and Silver Prince ore bodies, utilized heap leaching with an activated carbon system.

Active mining at all sites ceased in 1992. Heap-leaching of stockpiled ore at the Shumake operation continued until 1996. As of 2001, it appeared that the property was still being decommissioned.

Comments on the environmental information

Middle Buttes is an isolated group of low hills in the Mojave Desert southeast of the Tehachapi Mountains. It is within a broad alluvial plain punctuated by buttes and isolated mountains. Vegetation is a typical high-desert xerophytic assemblage of creosote, Joshua trees, sagebrush, and grasses. The climate is arid with a mean annual precipitation of less than 20 cm. The annual temperature ranges from -1o C during the winter to over 40oC during the summer; the mean annual temperature is 19oC. The region is sparsely populated.

Reference information

Bibliographic references

Deposit

Albers, J.P., 1981, A lithologic-tectonic framework for the metallogenic provinces of California: Economic Geology, v. 76, no. 4, p. 765-790.
Deposit

Albers, J.P. and Fraticelli, L.A., 1984, Preliminary mineral resource assessment map of California: U.S. Geological Survey Map MR-88, scale 1:1,000,000.
Deposit

Atwater, T., 1989, Plate tectonic history of the northeast Pacific and western North America, in Winterer, E.L. and others, editors, The eastern Pacfic Ocean and Hawaii: Geological Society of America, The Geology of North America, v. N, p. 21-72.
Deposit

Atwater, T. and Stock, J, 1998, Pacific-North America plate tectonics of the Neogene southwestern United States: An update, in Ernst, W.G. and Nelson, C.A., editors, Integrated earth and environmental evolution of the southwestern United States: Geological Society of America, Clarence A. Hall, Jr. volume, p. 393-420.
Deposit

Bateson, G.E.W., 1907, The Mojave Mining District of California: Transactions of American Institute of Mining Engineers, v. 37, p. 160-177.
Deposit

Blaske, A.R., 1990, Alteration, mineralization, and geochemistry of the Shumake deposit: A volcanic dome-hosted epithermal precious metal deposit, Kern County, California: Michigan Technological University, M.S. thesis, 247 p.
Deposit

Blaske, A.R. and others, 1991, The Shumake volcanic dome-hosted epithermal precious metal deposit, western Mojave Desert, California: Economic Geology, v. 86, p. 1646-1656.
Deposit

Bottaro, J.L., 1987, Geology of the Middle Buttes volcanic complex, Mojave District, Kern County, California: San Jose State University, M.S. thesis, 94 p.
Deposit

Burchfiel, B.C. and others, 1992, The Cordilleran Orogen: Conterminous U.S.: Geological Society of America, The Geology of North America, v. G-3, 724 p.
Deposit

Burnett, J.L. and Brady, J., 1990, Cactus gold mine, Kern County, California: California Geology, v. 43, no. 4, p. 85-88.
Deposit

Christiansen, R.L. and Yeats, R.S., 1992, Post-Laramide geology of the U.S. Cordilleran region, in Burchfiel, B.C. and others, editors, The Cordilleran Orogen: Conterminous U.S.: Geological Society of America, The Geology of North America, v. G-3, p. 261-406.
Deposit

Dibblee, T.W., Jr., 1963, Geology of the Willow Springs and Rosamond quadrangles, California: U.S. Geological Survey Bulletin 1089-C, p. 141-253.
Deposit

Dibblee, T.W., Jr., 1967, Areal geology of the western Mojave Desert: U.S. Geological Survey Professional Paper 522, 153 p.
Deposit

Dickinson, W.R., 1981, Plate tectonic evolution of the southern Cordillera, in Dickinson, W.R. and Payne, W.D., editors, Relations of tectonics to ore deposits in the southern Cordillera: Arizona Geological Society Digest, v. 14, 288 p.
Deposit

Dickinson, W.R., 1997, Tectonic implications of Cenozoic volcanism in coastal California: Geological Society of America Bulletin, v. 109, no. 8, p. 936-954.
Deposit

Dokka, R.K., 1989, The Mojave Extensional Belt of southern California: Tectonics, v. 8, no. 2, p. 363-390.
Deposit

Dokka, R.K. and Ross, T.M., 1995, Collapse of southwestern North America and the evolution of early Miocene detachment faults, metamorphic core complexes, the Sierra Nevada orocline, and the San Andreas fault system: Geology, v. 23, no. 12, p. 1075-1078.
Deposit

Dokka, R.K. and others, 1998, The Trans Mojave-Sierran shear zone and its role in early Miocene collapse of southwestern North America, in Holdsworth, R.E. and others, editors, Continental transpressional and transtensional tectonics: Geological Society of London Special Publication 135, p. 183-202.
Deposit

Glazner, A.F. and others, 1996, Collapse of southwestern North America and the evolution of early Miocene detachment faults, metamorphic core complexes, the Sierra Nevada orocline, and the San Andreas fault system: Comment, Geology, v. 24, no. 9, p. 858-859.
Deposit

Julihn, C.E. and Horton, F.W., 1937, The Golden Queen and other mines of the Mojave District, California: U.S. Bureau of Mines Information Circular 6931, 42 p.
Deposit

McCusker, R.T., 1982, Geology of the Soledad Mountain volcanic complex, Mojave Desert, California: San Jose State University, M.S. thesis, 113 p.
Deposit

Simpson, E.C., 1934, Geology and mineral deposits of the Elizabeth Lake quadrangle, California: California Journal of Mines and Geology, v. 30, no. 4, p. 371-415.
Deposit

Skillings, D.N., 1989, CoCa opens Shumake mine and plant for production at Cactus Gold Mines: Skillings? Mining Review, v. 78, no. 4, p. 4-8.
Deposit

Troxel, B.W. and Morton, P.K., 1962, Mines and mineral resources of Kern County, California: California Division of Mines and Geology County Report 1, 370 p.
Deposit

Tucker, W.B., 1923, Kern County, Mojave Mining District: California State Mining Bureau 19th Report of the State Mineralogist, p. 156-164.
Deposit

Tucker, W.B., 1935, Mining activity at Soledad Mountain and Middle Buttes - Mojave Mining District: California Journal of Mines and Geology, v. 31, no. 4, p. 465-485.
Deposit

Tucker, W.B. and others, 1949, Mineral resources of Kern County: California Journal of Mines and Geology, v. 45, no. 2, p. 220-223.
Deposit

Miscellaneous information on the deposit is contained in File Number 330-5154 (CGS Mineral Resources Files, Sacramento) and in files of the Anaconda Geological Documents Collection at the University of Wyoming.

General comments

Subject category	Comment text
Deposit	Middle Buttes is a volcanic complex composed of a series of overlapping and coalescing flows and lava domes interbedded with vent breccias and pyroclastic flows of quartz latite to rhyolite composition (Blaske and others, 1991). The complex was erupted upon Cretaceous quartz monzonite basement rocks similar to the granitic rocks of the southern Sierra Nevada Batholith exposed to the north. The age of the complex is interpreted to be between 16.9 ? 0.7 Ma and 21.5 ? 0.8 Ma based on correlation with similar rock sequences at nearby Soledad Mountain (Blaske and others, 1991). There are two areas of Middle Buttes that differ in both types of alteration and mode of occurrence. On the east side is the Middle Butte Mine area. On the west side is the Cactus Queen-Shumake area. The Middle Buttes MIne area includes the Winkler, Ella, Trent, and Crescent-Alunite ore bodies. These bodies are associated with NW-trending, east-dipping epithermal quartz veins up to 5 feet thick as emplaced within the flow-dome complex. The veins are situated at the intersection of NE- and NW-trending faults. They are also enveloped by locally intense, pervasive advance argillic alteration, which mainly consists of alunite and kaolinite. The Cactus Queen-Shumake area includes the Shumake and Silver Prince ore bodies. The Shumake body is at the contact between quartz monzonite basement and a vent breccia facies of the volcanic dome complex. It comprises the lower contact of Cactus vein, which strikes N45E and dips 30SE, and the higher Shumake vein, which strikes N70E and dips 20-70NW. Both veins are 2-5 meters thick. The Shumake vein is strongly fractured and has massive, granular, interlocking quartz. The deposit also has an intermediate zone of vuggy stockworks that consist of quartz-adularia-sericite. The stockwork veinlets are several tens of microns to 10 mm thick. The basement rocks are propylitically altered to chlorite-pyrite-sericite. Sericite (muscovite-illite) alteration is also present both in the basement immediately below the Cactus vein and as massive 5-m pods that envelop the thick quartz veins. The Shumake body differs from the other ore bodies, which are characterized by alteration assemblages of alunite, kaolinite, and silicification (Blaske and others, 1991). Hypogene alunite from altered pyroclastic rocks in the deposit yielded a K-Ar age of 18.36 ? 0.55 Ma (Bottaro, 1987).

Subject category

Comment text

Deposit

Middle Buttes is a volcanic complex composed of a series of overlapping and coalescing flows and lava domes interbedded with vent breccias and pyroclastic flows of quartz latite to rhyolite composition (Blaske and others, 1991). The complex was erupted upon Cretaceous quartz monzonite basement rocks similar to the granitic rocks of the southern Sierra Nevada Batholith exposed to the north. The age of the complex is interpreted to be between 16.9 ? 0.7 Ma and 21.5 ? 0.8 Ma based on correlation with similar rock sequences at nearby Soledad Mountain (Blaske and others, 1991).

There are two areas of Middle Buttes that differ in both types of alteration and mode of occurrence. On the east side is the Middle Butte Mine area. On the west side is the Cactus Queen-Shumake area.

The Middle Buttes MIne area includes the Winkler, Ella, Trent, and Crescent-Alunite ore bodies. These bodies are associated with NW-trending, east-dipping epithermal quartz veins up to 5 feet thick as emplaced within the flow-dome complex. The veins are situated at the intersection of NE- and NW-trending faults. They are also enveloped by locally intense, pervasive advance argillic alteration, which mainly consists of alunite and kaolinite.

The Cactus Queen-Shumake area includes the Shumake and Silver Prince ore bodies. The Shumake body is at the contact between quartz monzonite basement and a vent breccia facies of the volcanic dome complex. It comprises the lower contact of Cactus vein, which strikes N45E and dips 30SE, and the higher Shumake vein, which strikes N70E and dips 20-70NW. Both veins are 2-5 meters thick. The Shumake vein is strongly fractured and has massive, granular, interlocking quartz. The deposit also has an intermediate zone of vuggy stockworks that consist of quartz-adularia-sericite. The stockwork veinlets are several tens of microns to 10 mm thick. The basement rocks are propylitically altered to chlorite-pyrite-sericite. Sericite (muscovite-illite) alteration is also present both in the basement immediately below the Cactus vein and as massive 5-m pods that envelop the thick quartz veins. The Shumake body differs from the other ore bodies, which are characterized by alteration assemblages of alunite, kaolinite, and silicification (Blaske and others, 1991).

Hypogene alunite from altered pyroclastic rocks in the deposit yielded a K-Ar age of 18.36 ? 0.55 Ma (Bottaro, 1987).

Reporter information

Type	Date	Name	Affiliation	Comment
Reporter	24-JUN-2005	Koehler, Bret M. (Higgins, Chris T.)	California Geological Survey CGS (Formerly CDMG)
Editor	01-SEP-2007	Schruben, Paul G.	U.S. Geological Survey	Converted from S&A FileMaker format to Oracle. Edit checks on rocks, units, and ages with Geolex search, and other fields.

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