Hasloe Mine

Site Name

Primary: Hasloe Mine
Secondary: Funk
Secondary: Coward
Secondary: Hasloe and Centuary
Secondary: Gentry Gulch

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Commodity

Primary: Gold
Secondary: Silver

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Location

State: California
County: Mariposa
District: Kinsley District

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Land Status

Not available

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Holdings

Not available

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Workings

Not available

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Ownership

Not available

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Production

Not available

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Deposit

Record Type: Site
Operation Category: Past Producer
Deposit Type: Hydrothermal vein
Operation Type: Underground
Discovery Year: 1851
Years of Production:
Organization:
Significant: Y
Deposit Size: S

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Physiography

Not available

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Mineral Deposit Model

Model Name: Low-sulfide Au-quartz vein

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Orebody

Form: Tabular

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Structure

Type: R
Description: Sonora Fault

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Alterations

Alteration Type: L
Alteration Text: None reported in documents researched

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Rocks

Name: Slate
Role: Host
Age Type: Host Rock
Age Young: Mesozoic
Age Old: Paleozoic

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Analytical Data

Not available

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Materials

Ore: Chalcopyrite
Ore: Tetrahedrite
Ore: Arsenopyrite
Ore: Gold
Ore: Pyrite
Ore: Galena
Gangue: Quartz

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Comments

Comment (Commodity): Commodity Info: Ore shoots typically averaged about 0.5 to 0.6 ounces of gold per ton. In addition to the standard native gold and auriferous sulfides, some pockets contained beautiful specimen gold.

Comment (Commodity): Ore Materials: Native gold, auriferous sulfides (pyrite, galena, chalcopyrite, tetrahedrite, and arsenopyrite).

Comment (Commodity): Gangue Materials: Quartz, fault gouge

Comment (Deposit): The deposit at the Hasloe Mine consists of a typical gold- and sulfide-bearing hydrothermal quartz vein within metamorphic wall rock. The vein is reportedly in slate and quartz-biotite hornsfels, with a series of associated dikes, one of which is intruded along the strike of the vein for about 200 feet. The vein strikes either N76W or N50W, according to different reports, and it dips 28-30NE. It is remarkably consistent in attitude, with walls that are exceptionally flat and smooth. Vein width varies from six inches to five feet. Vein matter is milky quartz mingled with wallrock gouge and in places is ribboned by parallel inclusions of slate. Almost all of the gold has been found near the walls of the vein and on the footwall in particular. Gold is present both in native form and in sulfides; the presence of tetrahedrite is considered an indicator of gold content. Pockets of specimen gold are present in places; in some specimens, the gold is spread as a polished, sometimes striated, slickenside over many square inches by movement of the wall rock against vein material in which the gold was deposited. Rock without copper sulfides is generally barren of gold.

Comment (Development): Opened in either 1851, 1852, or 1857, this mine was worked sporadically to at least 1956 when new development work was underway. Clark (1970) stated that the Hasloe Mine had been ?worked intermittently in recent years.? Amalgamation processes were used at this mine.

Comment (Economic Factors): Clark (1970) reported a production value of $3 million for this mine.

Comment (Geology): REGIONAL GEOLOGY The Hasloe Mine is within the Sierra Nevada Mountains, where bedrock consists of northerly trending tectonostratigraphic belts of metamorphosed sedimentary and volcanic rocks and associated intrusive rocks that range in age from Paleozoic to Mesozoic. The structural belts, which extend about 235 miles along the western side of the Sierra, are flanked to the east by the Sierra Nevada Batholith and to the west by sedimentary rocks of the Cretaceous and Jurassic Great Valley sequence. The structural belts are internally bounded by the Melones and Bear Mountains fault zones and are characterized by extensive faulting, shearing, and folding (Earhart, 1988). From El Dorado County southward into Mariposa County, lode gold deposits occur in three distinct belts - the West Belt, the Mother Lode Belt, and the East Belt. The Mother Lode Belt is responsible for most of the gold produced. However, there has also been substantial gold production from the West Belt and East Belt. The West Belt in Mariposa County consists of widely scattered gold deposits located west of the Mother Lode vein system, which represents the Mother Lode Belt. Gold occurs in irregular quartz veins and stringers in schist, slate, granitic rocks, altered mafic rocks, and as gray ore in greenstone. The West Belt is cut by the northwest-trending Bear Mountains Fault Zone, which separates an assemblage of metavolcanic and metasedimentary rocks of Jurassic age on the southwest from a more disrupted and diverse assemblage of metavolcanic, metasedimentary, plutonic, ultramafic, and melange rocks on the northeast. The metavolcanic rocks consist generally of volcanic and volcanic-sedimentary rocks of island-arc affinity. These rocks are mostly mafic to intermediate in composition and include flows, breccias, and a variety of layered pyroclastic rocks. Some silicic rocks are present also. Various formation names assigned to the metavolcanic assemblages include Gopher Ridge, Copper Hill, Logtown Ridge, and Penon Blanco. The metasedimentary rocks are dominantly distal turbidites and hemipelagic sequences of black slate. Assigned formation names include Mariposa, Salt Spring Slate, and Merced Falls Slate. The northwest-trending Mother Lode Belt traverses western Mariposa County and is associated with the Melones Fault Zone. The rocks of this belt are typically metavolcanic, metasedimentary, and ultramafic, some of which have been hydrothermally altered to assemblages as described below. Mother Lode Belt mineralization is characterized by steeply dipping gold-bearing quartz veins and bodies of mineralized country rock adjacent to veins. Mother Lode veins are characteristically enclosed in Mariposa Formation slate with associated greenstone. The Mother Lode belt vein system ranges from a few hundred feet to a mile or more in width. Within the zone are numerous discontinuous or linked veins, which may be parallel, convergent, or en echelon. The veins commonly pinch and swell. Few can be traced more than a few thousand feet. Mother Lode type veins fill voids created within faults and fracture zones and consist of quartz, gold and associated sulfides, ankerite, calcite, chlorite, limonite, talc, chromium-bearing mica, and sericite. Stringer veins are commonly found in both adjacent footwall and hanging walls. Mother Lode ores are generally low- to moderate-grade (1/3 ounce of gold or less per ton), but ore bodies can be large. Ore shoots are generally short, 200-300 feet being the average stope length. However, they persist at depth, some having been mined to several thousand feet (Clark and Lydon, 1962). Ore shoots are commonly localized at bulges in veins, shear zones, vein intersections, or near abrupt changes in strike or dip.

Comment (Geology): Wall rocks have invariably been hydrothermally altered, having been partially to completely converted to ankerite, sericite, quartz, pyrite, arsenopyrite, chlorite, and albite with traces of rutile and leucoxene (Knopf, 1929). The mineralization is generally adjacent to the veins in ground that has been fractured and contains small stringers and lenses of quartz. Locally, greenstone bodies adjacent to the quartz veins contain enough disseminated auriferous pyrite in large enough bodies to constitute what has been called "gray ore.? Altered slate wall rock commonly contains pyrite, arsenopyrite, quartz, chlorite, and sericite with or without ankerite (Zimmerman, 1983). Large bodies of mineralized schist also form low-grade ore bodies throughout the Mother Lode. This ore consists of amphibolite schist that has been subjected to the same processes of alteration, replacement, and deposition that formed the greenstone gray ores. The altered schist consists mainly of ankerite, sericite, chlorite, quartz, and albite. Gold is associated with the pyrite and other sulfides that are present. Pyrite comprises about 8 percent of the rock. The average grade of mineralized schist is about 0.1 oz per ton. The Melones Fault Zone separates the Mother Lode Belt from the East Belt. The East Belt is dominantly argillite, phyllite and phyllonite, chert, and metavolcanic rocks of Paleozoic-Mesozoic age. Carbonate rocks (marble) are also present locally. The phyllite and phyllonite are dark to silvery gray. The chert is mostly thin-bedded with phyllite partings. The Upper Paleozoic-Lower Mesozoic metasedimentary and metavolcanic rocks of the East Belt have been assigned to the Calaveras Complex by most investigators (Earhart, 1988). The Lower Paleozoic metamorphic rocks farther east have been assigned to the Shoo Fly Complex. More recently, some geologists have reinterpreted certain assemblages along and immediately east of the Melones Fault Zone as separate Jurassic units (Schweickert and others, 1999). The metamorphic complexes are intruded in places by Mesozoic plutonic rocks. Lode deposits of the East Belt consist of many individual gold-bearing quartz veins enclosed in metamorphic rocks of possible Jurassic age, metamorphic rocks of the Calaveras Complex, metamorphic rocks of the Shoo Fly Complex, or in granitic rocks. Most of the veins trend northward and dip steeply. An east-west set of intersecting faults may be a controlling factor in controlling deposition of ore. Ore deposits of the East Belt are smaller and narrower than those of the Mother Lode, but commonly are more chemically complex, and richer in grade. Gold is generally associated with appreciable amounts of pyrite, chalcopyrite, pyrrhotite, galena, sphalerite, and arsenopyrite.

Comment (Workings): Principal workings at this mine consist of a 700-foot main drift adit and a 500-foot main shaft. At least six levels of drifts from the shaft, aggregating more than 1,750 feet, were present in 1956. At this time, most of the ore above the main drift had been stoped; the deepest reported workings were 540 feet down-dip.

Comment (Geology): LOCAL GEOLOGY The Hasloe Mine is situated in the East Belt of gold mineralization of the Sierra Nevada and is similar in its origin and setting to the nearby Bandarita Mine. The deposit consists of a main gold-bearing quartz vein in slate that is part of the Paleozoic-Mesozoic Calaveras Complex. Regionally, this complex also includes phyllite, metachert, schist, metavolcanic rock, and metacarbonate rock. Other reported rocks associated with the deposit include quartz-biotite hornfels and dikes, one of which is intruded along the strike of the vein for a length of about 200 feet. The vein strikes N76W according to Julihn and Horton (1940); Bowen and Gray (1957) reported a strike of N50W. It dips 28-30NE and is remarkably consistent in attitude. The walls of the vein are exceptionally flat and smooth. Its width varies from six inches to five feet. Vein matter is milky quartz mingled with wallrock gouge and in places is ribboned by parallel inclusions of slate. Almost all of the gold has been found near the walls of the vein and on the footwall in particular. Ore minerals are native gold, pyrite, galena, arsenopyrite, and tetrahedrite. Tetrahedrite is commonly associated with concentrations of gold and is believed to be an indicator of good ore. Reportedly, chalcopyrite is dominant in the upper levels, while tetrahedrite is dominant in the lower levels. Rock without copper sulfides is generally barren of gold. Pockets of specimen gold are present in places; in some specimens, the gold is spread as a polished, sometimes striated, slickenside over many square inches by movement of the wall rock against vein material in which the gold was deposited.

Comment (Identification): The Hasloe Mine, as discussed here, exploited this gold deposit as a single operation. Various other mining claims are also present in the immediate area.

Comment (Location): Location selected for latitude and longitude is the Hasloe Mine symbol on the USGS 7.5-minute Buckhorn Peak quadrangle.

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References

Reference (Deposit): 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.

Reference (Deposit): Logan, C.A., 1935, Mother Lode gold belt of California: California Division of Mines Bulletin 108, 240 p.

Reference (Deposit): Schweickert, R.A., Hanson, R.E., and Girty, G.H., 1999, Accretionary tectonics of the Western Sierra Nevada Metamorphic Belt in Wagner, D.L. and Graham, S.A., editors, Geologic field trips in northern California: California Division of Mines and Geology Special Publication 119, p. 33-79.

Reference (Deposit): Strand, R.G., 1967, Mariposa Sheet: California Division of Mines and Geology Geologic Map of California, scale 1:250,000.

Reference (Deposit): Wagner, D.L., Bortugno, E.J., and McJunkin, R.D., 1990, Geologic map of the San Francisco-San Jose Quadrangle, California: California Department of Conservation, Division of Mines and Geology Regional Geologic Map Series, Map No. 5A, scale 1:250,000.

Reference (Deposit): Zimmerman, J.E., 1983, The geology and structural evolution of a portion of the Mother Lode Belt, Amador County, California: Unpublished M.S. thesis, University of Arizona, 138 p.

Reference (Deposit): Bowen, O.E., Jr. and Gray, C.H., Jr., 1957, Mines and mineral resources of Mariposa County, California: California Journal of Mines and Geology, v. 53, nos. 1-2, p. 35-343.

Reference (Deposit): Castello, W.O., 1921, Mariposa County: California State Mining Bureau, 17th Annual Report of the State Mineralogist, p. 86-143.

Reference (Deposit): Clark, W. B., 1970, Gold districts of California: California Division of Mines and Geology Bulletin 193, p. 85.

Reference (Deposit): Clark. W. B., and Lydon, P.A., 1962, Mines and mineral resources of Calaveras County, California: California Division of Mines and Geology County Report No. 2, p. 72-73.

Reference (Deposit): Earhart, R.L., 1988, Geologic setting of gold occurrences in the Big Canyon area, El Dorado County, California: U.S. Geological Survey Professional Paper 1576, 13 p.

Reference (Deposit): Julihn, C.E., and Horton, F.W., 1940, Mineral industries survey of the United States - Mines of the southern Mother Lode Region, Part II - Tuolumne and Mariposa counties: U.S. Bureau of Mines Bulletin 424, 179 p.

Reference (Deposit): Knopf, A., 1929, The Mother Lode system of California: U. S. Geological Survey Professional Paper 157, 88 p.

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