Ferguson Mine

Site Name

Primary: Ferguson Mine
Secondary: Anderson
Secondary: Clearinghouse
Secondary: Original and Ferguson
Secondary: Golden Rule
Secondary: Moonstone

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Commodity

Primary: Gold
Secondary: Copper
Secondary: Silver
Secondary: Lead
Tertiary: Zinc

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Location

State: California
County: Mariposa
District: Clearinghouse 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
Operation Type: Underground
Discovery Year: 1860
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: Calaveras-Shoo Fly Thrust

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Alterations

Alteration Type: L
Alteration Text: None reported

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Rocks

Name: Granodiorite
Role: Host
Age Type: Host Rock
Age Young: Early Cretaceous

Name: Tonalite
Role: Host
Age Type: Host Rock
Age Young: Early Cretaceous

Name: Metamorphic Rock
Role: Host
Description: Metapelite
Age Type: Host Rock
Age Young: Triassic
Age Old: Paleozoic

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Analytical Data

Not available

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Materials

Ore: Galena
Ore: Sphalerite
Ore: Gold
Ore: Arsenopyrite
Ore: Pyrite
Gangue: Quartz

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Comments

Comment (Geology): LOCAL GEOLOGY The Ferguson-Original (Clearinghouse) 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 Hite Mine. The Ferguson and Original mines are on opposite sides of a mass of tonalite/granodiorite (Bass Lake Tonalite) that intrudes slate. The portion of the deposit at the Ferguson workings consists of a gold-bearing quartz vein in both the slate and tonalite/granodiorite. The slate is part of a complex zone that Bateman and Krauskopf (1987) mapped as a "carbonaceous metapelite" unit of uncertain age. This narrow (about one mile wide), north-northwest-trending unit separates their "phyllite and chert of Hite Cove" unit of Triassic age on the west from their "quartzite of Pilot Ridge" unit of Paleozoic (?) age on the east. The Hite Cove unit is likely equivalent to the Paleozoic-Mesozoic Calaveras Complex, while the Pilot Ridge unit is tentatively correlated with the Paleozoic Shoo Fly Complex as described by Schweickert and others (1999). Regionally, the Calaveras Complex includes slate, phyllite, metachert, schist, metavolcanic rock, and metacarbonate rock. The Shoo Fly Complex includes quartzite, schist, phyllite, and lesser amounts of metachert, metacarbonate rock, and metavolcanic rock. The intervening metapelite unit also locally contains small masses of metabasalt, metagabbro, limestone, and quartzite. Bateman and Krauskopf (1987) believed that this unit may be a tectonic rather than stratigraphic unit and could be a local segment of the Calaveras-Shoo Fly Thrust (Schweickert and others, 1999). The various lithologies present in the unit could represent the tectonic mixing of the two adjacent units along the thrust zone. The Ferguson Vein, which lies on the west side of the body of Bass Lake Tonalite, strikes about N21E and dips about 70NW. In general, it follows the contact between the tonalite/granodiorite (footwall) and the metasedimentary rocks of the ?carbonaceous metapelite? unit (hanging wall). The vein averages about 3 feet wide, but ranges from less than one foot to more than 6 feet. Three lateral quartz veins (Spanish, Golden Rule, Moonstone) join the Ferguson Vein at various angles from a northwesterly direction; the first two are on contacts with parallel dikes. Ore in the Ferguson Mine consists of ribbon quartz that contains native gold, arsenopyrite, pyrite, galena, and sphalerite. Although the ore minerals of the Ferguson and Original are similar, there is much arsenopyrite on the borders of the ore shoots in the Ferguson, and its ore has about twice as much sulfide content as that of the Original Mine. Based on the reported 2% sulfide content of the Original Mine, this observation suggests that the sulfide content of the Ferguson is about 4%. Five ore shoots were discovered in that part of the vein north of the main underground shaft and four ore shoots were worked to the south of the shaft. All pitch north at angles of 40-70 degrees. The northern shoots average 4 to 5 feet thick and are 100 to 150 feet wide. Two of the shoots were mined to depths exceeding 1,000 feet as measured on the axis of pitch.

Comment (Location): The Ferguson Mine is on the north side of the Merced River at Clearinghouse, across from State Highway 140. Location selected for latitude and longitude is the adit symbol just northwest of ?Clearing House? on the USGS 7.5-minute El Portal quadrangle. Workings are west of the Original Mine workings, but there is some uncertainty regarding the actual location.

Comment (Geology): REGIONAL GEOLOGY The Ferguson 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): 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 (Development): The Ferguson Mine was discovered about 1860 and operated fairly continuously until 1880. During this period, it achieved its main production. From 1881 to 1934, the mine was largely inactive. About 1925, claims of the mine were acquired and patented by the Original Mining and Milling Company, which also operated the adjoining Original Mine. Production was recorded at the Ferguson Mine between 1935 and 1940. During this period, the mine was operated by the San Juan Ramsey Company under lease from Original Mining and Milling Company. After a flood along the Merced River in 1937, the Original Mine workings were closed, and the Ferguson workings became the sole focus of operations. The mine likely did not operate after 1942 because of World War II restrictions. Amalgamation and flotation processes were used at this mine.

Comment (Economic Factors): Bowen and Gray (1957) reported total production of the Ferguson Mine at approximately $1,357,000. In combination with the Original Mine as the Clearinghouse Mine, Bowen and Gray (1957) determined the total production to be in excess of $3,350,000. The Ferguson had a recorded production of $107,000 between 1935 and 1940.

Comment (Environment): The Ferguson Mine is situated in a rugged river canyon, with workings distributed along a steep south-facing slope that descends to the Merced River. Vegetation is grass and brush with small areas of outcrop.

Comment (Deposit): The deposit at the Ferguson Mine is a low-grade hydrothermal-vein type typical of the Sierra Nevada foothills. It consists of ribbon quartz with native gold and auriferous sulfides. The sulfides include arsenopyrite, pyrite, galena, and sphalerite; based on reported percentages of sulfides in the Original Mine, concentrations in the Ferguson may be about 4%. The Ferguson Vein was emplaced along the steeply dipping contact where a body of tonalite/granodiorite intruded dominantly pelitic metasedimentary rocks. The vein strikes about N21E, dips about 70NW, and ranges from about one to 6 feet in width.

Comment (Workings): There are extensive workings along the Ferguson Vein, although they are less than in the Original Mine. These consist of five adit levels (100, A, B, C, D from lowest to highest), which are driven into the steep south-facing canyon wall of the Merced River. The 100 and A levels are about 1,200 feet long. A main underground shaft and a few other minor winzes were driven from these two levels. Several ore shoots have been stoped for hundreds of feet. A 1,200-foot crosscut connects the Ferguson Vein with the workings of the Original Mine. About 1,800 feet north of and 1,350 feet above the portal of the A-level is a group of workings (Spanish) that consist of several short drifts.

Comment (Commodity): Commodity Info: In 1871, ore reportedly averaged about $44 gold per ton and reached as much as $100 per ton in 1879. Fifty pounds of specimen gold-quartz from this mine was sold in 1880.

Comment (Commodity): Ore Materials: Native gold, auriferous sulfides (arsenopyrite, pyrite, galena, sphalerite)

Comment (Commodity): Gangue Materials: Quartz

Comment (Identification): Operated together with the adjacent Original Mine in later years, the Ferguson Mine has been described in some reports as either the Clearinghouse Mine or Anderson Mine, and in other reports as associated with the Original Mine.

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References

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): 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.

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): Bateman, P.C. and Krauskopf, K.B., 1987, Geologic map of the El Portal Quadrangle, west-central Sierra Nevada, California: U.S. Geological Survey Miscellaneous Field Studies Map MF-1998, scale 1:62,500.

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. 37-38.

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.

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