Mary Harrison-Malvina Group

Site Name

Primary: Mary Harrison-Malvina Group
Secondary: Potosi
Secondary: Mahoney
Secondary: Douglass
Secondary: D. Cook
Secondary: Merced
Secondary: Louise (Louisa)

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Commodity

Primary: Gold
Secondary: Silver
Secondary: Copper
Secondary: Lead

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Location

State: California
County: Mariposa
District: Coulterville District

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Land Status

Land ownership: Private
Note: the land ownership field only identifies whether the area the mine is in is generally on public lands like Forest Service or BLM land, or if it is in an area that is generally private property. It does not definitively identify property status, nor does it indicate claim status or whether an area is open to prospecting. Always respect private property.
Administrative Organization: Mariposa County Planning Department

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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 and replacement; hydrothermal stockwork
Operation Type: Underground
Discovery Year: 1852
Years of Production:
Organization:
Significant: Y
Deposit Size: M

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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, irregular

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Structure

Type: R
Description: Main and subsidiary branches of the Melones Fault Zone

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Alterations

Alteration Type: L
Alteration Text: At the Mary Harrison group (from Hehnke, 1990, and Evans and Bowen, 1977): Carbonate; ankerite, quartz, sericite, Cr-mica, pyrite, albite (10-30% carbonate, up to 75% sericite, and < 2% albite all in greenstone; massive ankerite, 10-50% quartz veinlets, and several percent Cr-mica all in serpentinite). Chloritic; chlorite, talc; all in serpentinite

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Rocks

Name: Schist
Role: Host
Description: Amphibolite
Age Type: Host Rock
Age Young: Late Jurassic

Name: Serpentinite
Role: Host
Age Type: Host Rock
Age Young: Late Jurassic

Name: Slate
Role: Host
Age Type: Host Rock
Age Young: Late Jurassic

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Analytical Data

Not available

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Materials

Ore: Pyrite
Ore: Gold
Ore: Galena
Ore: Pyrite
Gangue: Ankerite
Gangue: Talc
Gangue: Quartz

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Comments

Comment (Economic Factors): Clark (1970) reported a production value of $1.5 million for the Mary Harrison group and $1 million for the Malvina group. Most of the production from the Malvina was in the periods 1897-1903 and 1938-1942. About 250,000 tons of 0.2-ounces gold/ton ore were reportedly present in the Malvina group in the 1930?s. In the 1980?s, a resource of 5.5 million tons of ore at 0.057 ounces per ton gold was calculated based on exploratory work and computer modeling.

Comment (Geology): LOCAL GEOLOGY The Mary Harrison-Malvina Group is situated in the Mother Lode Belt of gold mineralization of the Sierra Nevada. The original Mary Harrison group is on the main branch of the Mother Lode vein system, while the Malvina group is on what is termed the ?west branch? of the system, about a mile to the west. The Mary Harrison group of workings exploited the Mary Harrison vein, which is clearly traceable for several miles. The vein strikes N50W and dips 60-75NE. It is characterized by a prominent, massive sheet of milky quartz 4 to 20 feet thick between irregular ribboned masses of quartz--ankerite-mariposite (QAM) rock that contains pyrite. Oxidation of the pyrite to produce sulfuric acid has converted some of this rock to porous, earthy masses of yellowish brown oxides of iron and silica. In places, high-grade ore was taken from these masses, but in other places the masses are barren. Adjacent to the vein, wall rocks, which are chiefly slate, serpentinite, and greenstone, are impregnated with large irregular patches of pyrite. In the early days of mining, this altered material may not have been rich enough to constitute ore. The entire width of the vein complex (quartz plus QAM rock) varies from 50 to 100 feet; north of the Mary Harrison group the vein complex reaches a width of 300 feet. Large horses of schistose serpentinite are incorporated in the complex also. Wagner and others (1991) show the wall rocks along the Melones Fault Zone here as Jurassic Mariposa Formation on the footwall (west) and Jurassic metavolcanic rock on the hanging wall (east). During mining, the most extensive ore shoot at the Mary Harrison was on the footwall side of the massive sheet of quartz. It had a strike length of at least 300 feet. Ore was not obtained from the massive sheet itself, but some ore was also found on the hanging wall side. As part of an exploratory program at the Mary Harrison group during the 1980?s, Hehnke (1990) reported that all significant gold mineralization in the group is hosted by hydrothermally altered greenstone (?gray ore? described previously); high-grade mineralization is associated with brecciation and stockwork quartz-carbonate veining. Locally, high-grade mineralization is also found in QAM rock adjacent to massive quartz veins and in association with swarms of porphyritic dikes. Ore-grade material reportedly always contains > 2% pyrite. The Malvina group exploited the Malvina vein, which is almost continuously traceable for a distance of about 2-1/2 miles. The vein strikes N45-50W and dips 56-75NE. Its thickness ranges from 2-20 feet, with an average of about 10 feet. Ore minerals are principally native gold and auriferous pyrite present in a vein complex of milky quartz and slate; the Malvina deposit is notable for the extensive ribbon-vein, or banded, structure of this complex, which likely resulted from several episodes of alteration/hardening and re-fracturing/quartz-filling of the rock. Quartz-ankerite-mariposite rock is locally present. Wall rocks are chiefly slate of the Mariposa Formation; the vein is also within a few hundred feet of the contact between the Mariposa Formation and the metavolcanic rocks of the Penon Blanco Formation to the west. Hydrothermal alteration at the Mary Harrison was reported by Hehnke (1990) as follows: In coarse-grained greenstone, 10-30% carbonate and several percent sericite. In fine-grained greenstone, up to 75% sericite and minor carbonate. In serpentinite, coarse-grained ankerite and massive ankerite + talc; several percent Cr-mica; and quartz veinlets and replacement. In slate, generally little altered, but where present it consists of sericite and small masses of ankerite.

Comment (Geology): REGIONAL GEOLOGY The Mary Harrison Mine and Malvina Group are 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 (Identification): Two separate groups of mines, the Mary Harrison and Malvina, were operated by the same company at one time. Together, these mines comprised many individual patented claims. The Malvina is on a subsidiary vein system west of and subparallel to the main Mother Lode vein system on which the Mary Harrison was developed. Because of this separation, it may be more appropriate to treat these groups as two distinct deposits geologically.

Comment (Commodity): Commodity Info: In the late 1930?s, mill heads contained $7.50 to $8.00 per ton in gold; some $10.00 ore was also discovered at this time. Ore was believed to generally average about $4.00 gold per ton overall. There was a report of ?light green talc frequently coated with leaf gold.?

Comment (Commodity): Ore Materials: Native gold, auriferous sulfides (pyrite, galena) Sulfides averaged about 1% according to an unpublished report. Ore-grade material contains > 2% pyrite (Hehnke, 1990).

Comment (Commodity): Gangue Materials: Quartz, ankerite, talc

Comment (Development): Typical of most gold mines in the region, the Mary Harrison-Malvina group was operated intermittently by various owners after discovery of the ore bodies in the 1800?s. The most important periods of production were 1897-1903 and 1938-1942. For many years, the Mary Harrison and Malvina groups were operated by the same company (Merced Gold Mining Company). The main ore sheet along the massive sheet of quartz was stoped between the 400- and 700-foot levels. Most of the ore was of milling grade at $5-12 per ton during the 1890?s and early 1900?s. In the 1930?s, an extensive exploration program was undertaken at the Malvina group by the Boston-California Mining Company to sample a reported 250,000 tons of 0.2-ounce/ton ore that was believed to be present according to old mine records. By 1934, the exploration revealed a substantial quantity of $10 ore. From 1938 to 1942, the company milled about 121,000 tons of ore, which yielded 13,197 ounces of gold, 1,460 ounces of silver, 4,988 pounds of lead, and 24,548 pounds of copper; the ore averaged $3.82 per ton in gold. Between 1942 and the mid-1950?s, the property was idle. In the 1980?s, Kennecott Exploration investigated the Mary Harrison group through sampling and drilling. At Louise Point, just south of Coulterville, the company delineated an elliptical ore body 50-170 feet thick and 1,000 feet long on strike. A resource calculation done by software indicated a mineable resource of 3.6 million tons at 0.061 ounces per ton gold and a total geologic resource of 5.5 million tons at 0.057 ounces per ton gold. Milling for both groups was done at the nearby Potosi Mine. Concentrates were shipped to the smelter at Selby for processing. Amalgamation processes were used at the Mary Harrison-Malvina group and cyanidation processes were used at the Malvina group during the exploration program of the 1930?s.

Comment (Deposit): The Mary Harrison-Malvina group consists of a low-sulfide quartz-vein complex typical of those formed in greenstone-slate-serpentinite wall rock along the southern Melones Fault Zone. The Mary Harrison group is on the main branch of the zone, while the Malvina group is on what is termed the ?west branch? of the zone in this area. Both the Mary Harrison and Malvina groups were developed in deposits characterized by large quartz veins, quartz veinlets, and hydrothermally altered wall rock. The large quartz veins are typical of the Mother Lode Belt, characterized by milky quartz. There is evidence of at least two and possibly three or more generations of quartz deposition. The dominant hydrothermal alteration is of the carbonate type and has produced masses of quartz-ankerite-mariposite rock in serpentinite and masses of carbonate-sericite rock in greenstone. Both types of altered rock contain gold as does the quartz veining. Sulfides averaged about 1% overall, but according to recent exploration, pyrite reportedly comprises 2% or more of the rock that is considered ore-grade material. Locally, some concentrations of gold are associated with dikes.

Comment (Geology): REGIONAL GEOLOGY (continued) 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 (Geology): LOCAL GEOLOGY (continued) Kistler and others (1983) reported a potassium-argon age of about 108 million years from a sample of mariposite rock obtained at the Mary Harrison Mine. They concluded that formation of gold-bearing quartz-mariposite veins along the Mother Lode Belt between Sonora and the Coulterville area took place during the Early Cretaceous between approximately 127 and 108 Ma.

Comment (Workings): The Mary Harrison and Malvina groups were developed by standard shafts, crosscuts, drifts, raises, and stopes. Principal workings at the Mary Harrison group consisted of a 1,200-foot vertical shaft and a second inclined shaft, both with levels at 100-foot intervals. There is a reported minimum of 5,000 feet of drifts. The Malvina was mainly developed through a 1,010-foot vertical shaft and a 3,000-foot haulageway tunnel. There are more than 2,200 feet of drifts and 1,200 feet of crosscuts on five levels.

Comment (Location): Location selected for latitude and longitude is the northernmost Mary Harrison Mine shaft symbol on the USGS 7.5-minute Coulterville quadrangle.

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References

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): California, in Seedorff, E., editor, Geology and ore deposits of the Sierra Nevada and foothills: Geological Society of Nevada, Special Publication No. 11, 1990 Fall Field Trip Guidebook, 134 p.

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. 41-42.

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): Evans, J.R. and Bowen, O.E., 1977, Geology of the southern Mother Lode, Tuolumne and Mariposa counties, California: California Division of Mines and Geology Map Sheet 36, scale 1:24,000.

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): Landefeld, L.A., 1990, The geology of the Mother Lode gold belt, Foothills metamorphic belt, Sierra Nevada, California, in Landefeld, L.A. and Snow, G.G., editors, Yosemite and the Mother Lode gold belt: Geology, tectonics, and the evolution of hydrothermal fluids in the Sierra Nevada of California: American Association of Petroleum Geologists, Pacific Section, Guidebook 68, p. 117-124.

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

Reference (Deposit): Moore, L., 1968, Gold resources of the Mother Lode Belt, El Dorado, Amador, Calaveras, Tuolumne, and Mariposa counties, California: U.S. Bureau of Mines Technical Progress Report 5, p. 1-22.

Reference (Deposit): Hehnke, C.A., 1990, Geology and mineralization of the Mary Harrison prospect, Mariposa County,

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): Kistler, R.W., Dodge, F.C.W. and Silberman, M.L., 1983, Isotopic studies of mariposite-bearing rocks from the south-central Mother Lode, California: California Geology, v. 36, no. 9, p. 201-203.

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

Reference (Deposit): Newton, M.C., III, 1990, Structural control of gold mineralization in the southern Mother Lode region in Seedorff, E., editor, Geology and ore deposits of the Sierra Nevada and foothills: Geological Society of Nevada, Special Publication No. 11, 1990 Fall Field Trip Guidebook, 134 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): 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.

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