Original Mine

Site Name

Primary: Original Mine
Secondary: Original and Ferguson

---

Commodity

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

---

Location

State: California
County: Mariposa
District: Clearinghouse District

---

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

---

Holdings

Not available

---

Workings

Not available

---

Ownership

Not available

---

Production

Not available

---

Deposit

Record Type: Site
Operation Category: Past Producer
Deposit Type: Hydrothermal vein
Operation Type: Underground
Discovery Year: 1908
Years of Production:
Organization:
Significant: Y
Deposit Size: S

---

Physiography

Not available

---

Mineral Deposit Model

Model Name: Low-sulfide Au-quartz vein

---

Orebody

Form: Tabular

---

Structure

Type: R
Description: Calaveras-Shoo Fly Thrust

---

Alterations

Alteration Type: L
Alteration Text: None reported

---

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

---

Analytical Data

Not available

---

Materials

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

---

Comments

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 (Identification): Operated together with the adjacent Ferguson Mine, the Original Mine was discovered much later than the Ferguson. Nevertheless, it became the more extensively developed and productive of the two properties.

Comment (Development): Discovered in 1908, the Original Mine operated almost continuously from 1911 to 1937, when flooding along the Merced River forced closure of the mine. For most of this period, the mine was operated by the Original Mining and Milling Company. In the mid-1930?s, it was operated in conjunction with the adjacent Ferguson Mine. The mine is located on claims patented in 1925. Ore was milled at the mine site. In addition, there were several other buildings in the mine complex. Amalgamation and flotation processes were used at this mine.

Comment (Economic Factors): Julihn and Horton (1940) reported total production of the Original Mine at approximately $2 million. Between 1911 and 1937, the Original Mine yielded about 80,000 ounces of gold, 25,000 ounces of silver, 340 pounds of copper, and 134 pounds of lead, all from about 175,000 tons of ore. In combination with the Ferguson Mine as the Clearinghouse Mine, Bowen and Gray (1957) determined the total production to be in excess of $3,350,000.

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

Comment (Commodity): Commodity Info: the ore milled from the Original Mine from 1911 to 1934 averaged 0.454 ounces of gold per ton, 0.14 ounces of silver, and a small amount of copper and lead. Over an 8-year period, the average recovery from the Original Mine was 0.67 ounce gold per ton. The concentrates contained 5-6 ounces per ton.

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

Comment (Commodity): Gangue Materials: Quartz

Comment (Geology): REGIONAL GEOLOGY The Original 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 (Deposit): The deposit at the Original 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; sulfide content is about 2%. The Original Vein was emplaced along the steeply dipping contact where a body of tonalite/granodiorite intruded dominantly pelitic metasedimentary rocks. The vein strikes either NW or N7-10E, dips about 78NE, and ranges from about one to 10 feet in width with an average of two feet.

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 Original and Ferguson mines are on opposite sides of a mass of tonalite/granodiorite (Bass Lake Tonalite) that intrudes slate (metapelite). The portion of the deposit at the Original workings consists of a gold-bearing quartz vein in both the slate and tonalite/granodiorite. The slate may be 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. Alternatively, the slate described above may be part of the ?quartzite of Pilot Ridge? unit. The uncertainty is caused by the extent of the body of Bass Lake Tonalite as mapped by Bateman and Krauskopf (1987) relative to descriptions of the locations and wallrocks of the mines as reported by Bowen and Gray (1957). The Original Vein, which reportedly lies on the east side of the body of Bass Lake Tonalite, strikes about N7-10E and dips about 78NE according to Bowen and Gray (1957); some earlier reports indicate a NW strike. In general, it follows the contact between the tonalite/granodiorite (footwall) and the metasedimentary rocks of either the ?carbonaceous pelite? unit or ?quartzite of Pilot Hill? unit (hanging wall). To a depth of about 400 feet the vein is entirely within the metasedimentary rocks, but below that depth it is in the tonalite/granodiorite body. The vein averages two feet in width, but ranges from less than one foot to 10 feet. Ore in the Original Mine consists of ribbon quartz that contains native gold, arsenopyrite, pyrite, galena, and sphalerite. Sulfide content in the ore is about 2%. Four ore shoots were developed, the longest 100 to 125 feet in length and the others 50 to 75 feet. All pitch north at about 45 degrees.

Comment (Location): The Original Mine is on the north side of the Merced River near Clearinghouse, across from State Highway 140. Location selected for latitude and longitude is the adit symbol just east of BM 1506 on the USGS 7.5-minute El Portal quadrangle. Workings are east of the Ferguson workings, but there is uncertainty regarding the actual location. It is believed to be at or near the settlement of Incline, somewhere between BM 1506 and BM 1553 on the El Portal quadrangle. Bowen and Gray (1957) reported that the portal of the main adit is ?on the west side of a ravine at an elevation of approximately 1600 feet.?

Comment (Workings): There are extensive workings along the Original Vein. Main entry to the mine was through a west-trending crosscut adit, which intersects the vein 180 feet below the outcrop. A main winze near the end of this adit reached an inclined depth of 1,170 feet and served nine levels; in all, the mine has 11 levels. Total vertical depth explored in the Original workings is about 1,530 feet. There is extensive stoping of the ore bodies, which were developed from drifts. Two faults encountered on both the 900-level and 1100-level, cut off the vein for a distance of 110 feet. A 1,200-foot crosscut connects the Original Vein with the workings of the Ferguson Mine. Little timbering was required in this mine.

---

References

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): Bateman, P.C. and Krauskopf, K.B., Geologic map of the El Portal Quadrange, 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.

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): 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): 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.

---

California Gold

"Where to Find Gold in California" looks at the density of modern placer mining claims along with historical gold mining locations and mining district descriptions to determine areas of high gold discovery potential in California. Read more: Where to Find Gold in California.