Mammoth Mine (Mammoth Copper Company; Anderson Mine; Mayflower Mine; Sheridan Mine; Gillispie Mine), Copper Crest group, Mammoth Butte, Backbone District, West Shasta Copper - Zinc Mining District, Klamath Mountains, Shasta County, California, USAi

Regional Level Types
Mammoth Mine (Mammoth Copper Company; Anderson Mine; Mayflower Mine; Sheridan Mine; Gillispie Mine)	Mine
Copper Crest group	- not defined -
Mammoth Butte	Table/Butte
Backbone District	Mining District
West Shasta Copper - Zinc Mining District	Mining District
Klamath Mountains	Mountain Range
Shasta County	County
California	State
USA	Country

A former Cu-Au-Ag-S-Zn-Pb-Cd-Fe mine located in sec. 32, T34N, R5W, MDM, 1.5 km (4,800 feet) E of Mammoth Butte (coordinates of record), on the divide between Shoemaker Gulch and Little Backbone Creek, on private land (patented claim). Discovered 1880. First production 1890. Produced principally during the period 1905-1925. Owned by U.V. Industries (100%), California (1978). Later Owner-Operator was the U.S. Smelting, Refining and Mining Company. MRDS database stated accuracy for this location is 1,000 meters. Location point selected as adit symbol on USGS 7.5-minute quadrangle map, which represents 470-level adit (main haulage level for mine). Access route to mine not determined at this time. Quadrangle map shows unpaved road to mine.

NOTE: Early reports of the California State Mineralogist make unclear reference to a Mammoth Mine about 6 miles to the south in the Old Diggings District. The 29th Report of the State Mineralogist contains a map of the Old Diggings District, which shows that the Mammoth Mine there is distinct from the Mammoth Mine in the West Shasta District. U.S. Smelting, Refining and Mining Company also owned patented claims in the Old Diggings District.

Mineralization is a Late Devonian replacement massive sulphide deposit (Deposit model: code 184; USGS model code 28a; Massive sulfide, kuroko), hosted in the Balaklala Rhyolite (Late Devonian). The ore body is tabular and strikes S60W and dips 14W at a thickness of 33.53 meters and a width of 304.8 meters and a length of 1,280 meters. Ore bodies also include a tabular, disseminated tabular body and a lenticular ore body. Primary mode of origin was hydrothermal with a secondary mode of contact metasomatic. Pyrite is major ore component. Local rocks include Paleozoic metavolcanic rocks, unit 1 (Eastern Klamath Mountains).

Ore control was folding and faulting; stratigraphic control, foliation, main arch and minor flexures and location of feeder fissures (faults and shear zones). Kinkel and Hall (1952) believed the ore bodies occur along the crest of a broad arch marked by steep cleavage, which is absent elsewhere. District-wide, Albers and Bain (1985) identified three main linear trends, N23?E, N37?E, and N60?E defined by faults, clusters of ore bodies and the long axes of ore bodies. Furthermore they noted that most of the large ore bodies occur at the intersections of these trends and surmised that the faults, especially at the intersections, provided conduits for emanating ore fluids. Post-mineral normal faults disrupt the lateral continuity of the ore. The massive sulfide occurs with sharp contact within the upper unit of the Balaklala Rhyolite. The coarse phenocryst unit of the Balaklala Rhyolite consistently overlies the ore.

Moderate wall rock alteration is present (interm. argillic, sericitic & pyritization). Sericitic alteration: quartz, sericite, pyrite, chlorite hematitic (gossan); hematite gossan and minor supergene enrichment are present locally. Oxidation is known to extend up to 150 feet in from the present erosion surface. Throughout the district, hydrothermal alteration, pervasive below the ore zone and absent above, developed a quartz-sericite-pyrite+/-chlorite assemblage (Kistler and others, 1985 and Reed, 1984).

At the Mammoth Mine, the ore consisted of copper ore and zinc ore. Between 1905-1925, 3,311,145 tons of copper ore and 84,000 tons of zinc ore were mined. Lydon and O'Brien (1974) reported the copper ore averaged 3.99% Cu, 4.20% Zn, 2.24 oz/ton Ag, and 0.038 oz/ton Au. The zinc ore averaged 21.1% Zn, 2.40% Cu, 5.79 oz/ton Ag, and 0.078 oz/ton Au. Similarly, Kinkel and Hall (1952) reported the copper ore averaged 4-5% Cu, 2-3 oz/ton Ag, and 0.03-0.04 oz/ton Au. The zinc ore consisted of 27-37% Zn, 1-2% Cu, 1.4-6.5 oz/ton Ag, and 0.02-0.4 oz/ton Au. Howe (1985) divided the mineralization into six stages, as follows: 1) Precipitation of framboidal and colloform pyrite and sphalerite; 2) Deposition of fine-grained arsenopyrite and coarse-grained pyrite; the latter encloses tiny inclusions of pyrrhotite; 3) Precipitation of chalcopyrite, sphalerite, galena, tennantite, pyrrhotite, bornite, and idaite; and replacement of stage 2 minerals; 4) Recystallization and remobilization of previous stage minerals; 5) Deposition of quartz, sericite, and calcite; 6) Supergene enrichment.

Ore minerals were pyrite, chalcopyrite, sphalerite, galena, tetrahedrite-tenantite, arsenopyrite, bornite, idaite, digenite, bornite, covellite, chalcocite, unknown gold, unknown silver. The gangue minerals were quartz, sericite, calcite, and chlorite.

Balaklala rhyolite in the mined area consists of porphyritic and non-porphyritic rhyolite flows and intercalated coarse and fine rhyolitic pyroclastic material. The ore zone is in the uppermost part of the middle unit, immediately under the base of the upper unit. The lower unit consists mainly of light grayu to light green non-porphyritic rhyolite and rhyolitic tuff and volcanic breccia. The middle unit ranges in thickness from 150 - 300 feet. It consists of light gray to green porphyritic rhyolite flows and pyroclastic rocks. The upper unit is coarse porphyritic rhyolite containing quartz and feldspar phenocrysts. It is 1,400 feet thick at Mammoth Butte but thins rapidly toward the east. The upper unit forms the "cuprock" for the ore deposits.

Local structures include folds and faults. The principal faults are the California fault, the 12 Drift fault, the Schoolhouse fault, the Gossan fault, the Eureka Fault, the Yolo Fault, the 313 Fault, the Friday fault and the Clark fault. In all these faults, the North or East side has moved down relative to the South or West. The horizontal component is only known for the California. It is 250 feet. All faults are post-ore normal faults that offset the orebodies.

Workings included underground openings. The mine area was extensively developed by thousands of feet of workings appended to nine princpal adits. •Several levels of tunnels with raises and winzes amounted to at least 60,000 feet of development. Nine principle adits were driven at altitudes between 2,426 and 3,096 feet. A few short, unconnected adits were driven at altitudes up to 3,250 feet. Depth was principally gained by tunneling lower on the hillsides. Maximum vertical depth was 800 feet. The main haulage level was the 470-foot-level adit, at an elevation of 2,820 feet, driven a little north of west for about 3,500 feet. Plan view of the workings displays a dominant E-NE trend following the orebodies. Only the Gossan orebody deviates from this trend.

Production data are found in: Kinkel, et al (1956). Between 1905-1925, 3,311,145 tons of copper ore and 84,000 tons of zinc ore were mined at Mammoth Mine. Lydon and O?Brien (1974) reported the copper ore averaged 3.99% Cu, 4.20% Zn, 2.24 oz/ton Ag, and 0.038 oz/ton Au. The zinc ore averaged 21.1% Zn, 2.40% Cu, 5.79 oz/ton Ag, and 0.078 oz/ton Au. Total silver production was 7,416,965 ounces. Total zinc production was about 313,711,000 pounds, including 84,000 tons of ore mined 1914-1915 that averaged 21.10% zinc. Several thousand pounds of cadmium were recovered at the electrolytic zinc plant in Kennett. Kinkel and Hall (1952) reported the copper ore averaged 4-5% Cu, 2-3 oz/ton Ag, and 0.03-0.04 oz/ton Au. The zinc ore consisted of 27-37% Zn, 1-2% Cu, 1.4-6.5 oz/ton Ag, and 0.02-0.4 oz/ton Au.

Assay data in 1925: ^40.4% S, 34.3% Fe, 4.2% Zn, 3.99% Cu, 2.24 ounces/ton Ag, and 0.038 ounces/ton Au.

Additional narrative: The Mammoth Mine is one several copper-zinc mines in the eastern Klamath Mountains. The two copper-zinc districts of Shasta County are the East Shasta and West Shasta Districts. Mammoth Mine is in the West Shasta District. The Klamath Mountains geomorphic province consists of four imbricate, fault-bounded, east-dipping plates of oceanic affinity, which have been further subdivided into several terranes (Irwin, 1994; Irwin and Mankinen, 1998). Lithologies include variably metamorphosed volcanic and sedimentary rocks and ultramafic masses, intruded locally by post-amalgamation plutons. Volcanic rocks range in composition from mafic through silicic. Sedimentary rocks are chiefly pyroclastic beds, graywacke, and shales with minor cherty and calcareous layers. The plates, from west to east, are the Western Jurassic, Western Paleozoic and Jurassic, Central Metamorphic, and Eastern Klamath (Irwin, 1981). Both the West Shasta and East Shasta Districts are within the Eastern Klamath plate. On a regional scale, the terranes are progressively younger to the west. Within individual plates, however, the east-dipping stratigraphy places stratigraphically higher units east of older units. Consequently, Permian to Triassic rocks of East Shasta District rocks lie east of the Devonian rocks of the West Shasta District. Origin of the massive sulfide ore of the West Shasta District has been the subject of geologic debate for years. The most comprehensive and recent evaluation of the deposits is found in a special issue of Economic Geology and the Bulletin of the Society of Economic Geologists, volume 80, number 8. As presented in this volume, the West Shasta Copper-Zinc district is now generally considered to represent stratabound Kuroko-type volcanogenic massive sulfide deposits. The deposits developed during the Early Devonian within a very depleted (exceedingly more depleted in light rare earth elements than in heavy rare earth elements), ensimatic island-arc regime. The arc formed a submarine volcanic pile consisting of a bimodal suite of low-potassium volcanic rocks, represented by the Copley Greenstone and the overlying Balaklala Rhyolite (Bence and Taylor, 1985). Interpretations of trace-element geochemistry of these rocks vary. Bence and Taylor (1985) infer a calc-alkaline trend, whereas Lapierre and others, (1985) infer a tholeiitic trend. Further explanation of this tectonic model is offered below. PRINCIPLE FORMATIONS The original fabrics and petrography of the two main rock units of the Mammoth area have been obscured by regional greenschist-facies metamorphism (probably during the Mesozoic) and hydrothermal alteration associated with mineralization. Some sedimentary structures are preserved in the pyroclastic units. Primary fabrics or structures within the massive sulfide unit are lost, however. Both units display large lateral variation in thickness and an abundance of breccia and conglomerate indicating that the depositional environment was topographically irregular. The oldest unit, the Copley Greenstone, is a 1,800-meter thick sequence of pillow basalts, andesites, and pyroclastic flows with high-Mg andesites near the top. It underlies the Balaklala Rhyolite. The high-Mg andesites compare favorably to boninites recovered from the Marianas arc. Boninites, found in present-day arcs, represent the first stages of back-arc development. Therefore, the high-Mg andesites of the upper Copley Greenstone probably represent the development of an extensional regime and progression to silicic volcanism represented by the Balakala Rhyolite (Lapierre and others, 1985; and references therein).
•The contact between the Balaklala Rhyolite and the Copley Greenstone is locally gradational; in places, rounded clasts of Balaklala-like rhyolite are found in a tuffaceous, andesitic matrix. A few thin flows of Copley-like greenstone are interlayered with the lower part of the Balaklala rhyolite suggesting that the Copley Greenstone and the Balaklala Rhyolite are roughly coeval. Additionally, Copley-like pillow basalts occur within the Balaklala Rhyolite (Albers and Bain, 1985). The 1,000-meter thick Balaklala Rhyolite hosts the massive sulfide ores and consists of siliceous flows, conglomerates, and tuffs (Lapierre and others, 1985). Discontinuous lenses of water-laid tuff overlie nearly all the ore bodies. Some of the tuff beds are ripple-marked, and one contained a fish plate of Devonian age. The lack of intercalated sediments within the volcanic pile suggests a deeply submerged arc (Doe and others, 1985, Lapierre and others, 1985), although apparent contamination of Pb (Lapierre and others, 1985) and Sm-Nd (Kistler and others, 1985) indicates some pelagic input. The Balaklala Rhyolite and the nearby Mule Mountain trondhjemite stock are remarkably similar in petrologic and rare-earth element characteristics, and isotopic age. These similarities and corroborative field relationships imply that stock and rhyolite are probably comagmatic (Albers and Bain, 1985). The Mule Mountain stock has been dated at 400 Ma (K-Ar, hornblende and U-Pb, zircon). The Balaklala Rhyolite is subdivided into three units. The upper unit, distinguished by the presence of dark quartz phenocrysts in excess of 4mm in diameter, consists of massive volcanic flows overlying pyroclastic material. The middle unit consists of rhyolite flows, containing quartz phenocrysts 1-4 mm in size, and a complex assortment of tuffs, breccias, and pyritic massive sulfide bodies. The sulfide ore bodies are stratabound and restricted to the upper part of the middle unit. The lowermost unit consists of non-porphyritic to slightly porphyritic tuffs and breccias (Kinkel and others, 1956). EXTENSION AND VOLCANISM Extension (perhaps back-arc spreading) and coeval Balaklala volcanism, resulted in a half dozen silicic eruptive centers (Kinkel, 1966; Albers and Bain, 1985), a series of NW-NE-dipping extensional faults, and abundant NE-trending rhyolitic dikes that intrude the Copley Greenstone. Lindberg (1985) postulated that the extensional faults represent graben-like structures that both localized hydrothermal activity and captured volcanic flows and sediments. Field evidence of graben formation is sparse. The proliferation of breccia and conglomerates in the volcanic units and the extreme variation in unit thickness suggests irregular topography, however. Albers and Bain (1985) identified three main linear trends, N23?E, N37?E, and N60?E defined by faults, clusters of ore bodies, and the long axes of ore bodies. Furthermore, they noted that most of the large ore bodies occur at the intersections of these trends and surmised that the faults, especially at the intersections, provided conduits for emanating ore fluids. Apparently, submarine fumaroles exhaled the ore fluids, which upon mixing with seawater precipitated sulfide minerals. During either a lull in volcanism or a brief interval of radically accelerated ore formation, sulfide precipitation dominated over volcanic sedimentation. The sulfide minerals accumulated as a conformable massive sulfide horizon within the strata of the contemporaneous Balaklala Rhyolite. Earlier interpretations of the deposits described them as a nearly thorough replacement of a highly favorable stratum of unknown original composition (Kinkel and Hall, 1952).
•Kinkel and others (1956) identified two probable volcanic centers and estimated the location of several others. The best-defined center, interpreted to represent a cumulo-dome, is just west of Mammoth Mine. Its roughly oval-shaped body is about 425 meters thick and 2.5 kilometers across. It consists of a body of coarse-phenocryst rhyolite porphyry intruded as vertical dikes, lenses, and a stockwork into shattered wall rocks of non-porphyritic rhyolite. The intrusion contains xenoliths of the non-porphyritic rock. This center probably was a major source of all three units of the Balaklala Rhyolite because, adjacent to the dome, they form thick arcuate belts that contain large amounts of coarse- and fine-grained pyroclastic rocks (Albers and Bain, 1985). The second volcanic center is submerged beneath Shasta Lake, except on the south, where it is characterized by a jumble of rhyolitic breccia. The fragment size in the breccia decreases to the south for a mile where sparse, small fragments are found in greenstone tuff (Kinkel and others, 1956). Four other probable centers have been identified, but are poorly defined (Albers and Bain, 1985). This volcanic pile formed over oceanic lithosphere that by mid-Devonian began subducting under the North American continent. The progressive subduction of the oceanic plate lead to the arc's eventual convergence with the continent and ultimate accretion. As noted above, the younger (Pennsylvanian-Permian) arc of the East Shasta District lies east of the Devonian arc. Hutchinson and Albers (1992) suggested that the Pennsylvanian-Permian island arc formed in a back-arc basin between the continent and the Devonian arc. In this case, the younger arc would have accreted first. This implies that either prior to or after its accretion, the Permian arc was underthrusted by the Devonian arc. This suggests that stratigraphic superposition of the Permian strata is structural not depositional. Available geologic maps of this region do not show a tectonic boundary between these arcs (Fraticelli and others, 1987; Strand, 1962). Whether the two arcs accreted independently or as one package, the accretion occurred after Pennsylvanian-Permian time. The validity of a back-arc basin model is challenged by regional biostratigraphy that suggests prohibitively large distances between the Eastern Klamath plate and North American craton in the Permian. The eastern Klamath area is crossed by a side-by-side pair of N-S trending biostratigraphic belts, defined by the unique McCloud fauna and Tethyan fauna. Both faunal assemblages are Pennsylvanian-Permian in age and distinct from contemporaneous North American fauna. The western belt is defined by the McCloud fauna, which is found in the McCloud Limestone. Stratigraphically, the McCloud Limestone occurs between the Devonian and Permian volcanic arc sequences. Tethyan fauna defines the eastern belt. These distinct faunas suggest that their host rocks are far traveled (5,000 km or more) (Stevens and others, 1990), an interpretation that is incompatible with a simple back-arc basin model. The origin of these faunal assemblages is controversial, however. Opponents to an exotic origin of these terranes suggest that the fauna developed in an offshore arc close to (within 1,000 km) but biologically isolated from North America. Similarities between Middle Ordovician to Middle Devonian faunas of the Eastern Klamath Terrane and cratonal North America suggest relative proximity (< 1,000 km) (Potter and others, 1990). Furthermore, the presence of continentally derived sediments in related formations supports that suggestion (Miller and others, 1992; and references therein).
•HYDROTHERMAL SYSTEM During deposition of the middle unit of the Balaklala Rhyolite, rifting formed submarine basins or grabens (Lindberg, 1985) concomitant with the development of a hydrothermal system. This system circulated heated (100- 425?C; Taylor and South, 1985), acidified (pH 3-5; Reed, 1984) seawater through the volcanic pile. The hydrothermal fluids leached sulfur and base metals from the surrounding rocks. The metals eventually were discharged at hot springs and precipitated on the seafloor, accumulating in the downfaulted basins. Mass balance considerations and isotopic analysis suggest that greater than 95% of the sulfur in the ore deposits could have been leached from the Copley Greenstone during hydrothermal alteration (Taylor and South 1985). MASSIVE SULFIDE ORE The best description of the ore throughout the district is found in Kinkel and others (1956) from which the following is derived. The massive sulfide occurs with sharp contact within the upper unit of the Balaklala Rhyolite. The coarse-phenocryst unit consistently overlies the ore. Deformation and recystallization of the ore has erased primary textures or sedimentary structures. The ore consists of a chaotic mixture of breccia, crystal aggregates, and minor crosscutting veins. The ore is generally localized along fold axes, but it also occurs along the flanks. It is most common in synformal basins, but also occurs along anitformal structures. Pre-mineral and post-mineral faults are common. Some pre-mineral faults served as feeder channels, some of which show wallrock alteration. Others show only localized mineralization within the fault plane. Post-mineral normal faults offset the orebodies from several centimeters to 90 meters (Kinkel and others, 1956). At Mammoth Mine, the orebodies form large lenses of copper- and zinc-bearing pyrite ore within a diffuse, widespread ore zone. The ore zone is elongate NE-SW, plunges slightly to the south, and is 1,280 meters long. It crops out on the northeast in a canyon wall, where it projects into the sky. It is thickest (up to 300 meters) in the central portion. The orebodies occurred along the crest of a broad upright arch. The crest is marked by steep foliation that is absent elsewhere. The zone is moderately disrupted by a series of NE-NW dipping normal faults. Ore was mined down to 213 meters, although the workings reached 243 meters. The largest stopes observed by Kinkel and Hall (1952) measured 274 meters by 152 meters horizontally and 33.5 meters vertically (Kinkel and Hall, 1952). At Mammoth Mine, thin (less than 3 meters) gossan formed in three locations. In other parts of the district, large and well-developed gossan formed. These were oxidized and enriched. A comparison of the production figures from one of the gossan, the Gossan Orebody, and average grades of the primary ore showed a two-fold enrichment of gold and silver. Covellite and chalcocite were reported present in the gossan (Kinkel and Hall, 1952).

•Presumably, the deposit was discovered before 1890. No significant mining had occurred prior to 1904 when U.S. Smelting, Refining and Mining Company purchased the property. Large-scale production began in 1905 and continued until 1919, when operations ceased until 1923. Operations resumed in 1923 and ultimately ceased in 1925. Between 1905-1925, 3,311,145 tons of copper ore and 84,000 tons of zinc ore were mined. Ore was transported to the smelter in Kennett. Some exploration has occurred since, but no mining. Hassemer (1983) presented preliminary findings of a reconnaissance geochemistry study of the West Shasta District. The report evaluated various media and the effectiveness of various techniques. Water samples and stream-sediment samples (pan-concentrated and bulk) were collected. Pan concentrates were divided into three fractions (one non-magnetic and two magnetic fractions) by heavy liquid separation and electromagnetic separation. The bulk stream-sediment samples were divided into three fractions based on sieve size. Various analytical methods were employed. The results of the water analysis show that that copper and sulfate concentrations and specific conductance were useful values for reconnaissance. The coarse fraction of the stream sediments (-20 to +80 mesh) proved to be the best fraction for reconnaissance work. Lastly, the non-magnetic fraction proved to have the most intense values with the greatest contrast. The U.S. Geological Survey also tested the use of near-infrared spectroscopy (Raines and others, 1985) and electrical geophysical exploration methods (Horton and others, 1985) in the West Shasta District. Near-infrared spectra (800-2,500 nm) proved to define gossans within the district. The gossans showed distinctive spectral characteristics of goethite (~900 nm) and diaspore (1,400-2,500 nm). Furthermore, spectral differences between gossans correlated with the size of the massive sulfide deposits. The shape and depth of conductive bodies were defined by the application of combined induction techniques. The conductive Hornet orebody was successfully detected within resistive rhyolite by each of the induction surveys employed. However, shale units and various fault zones in the vicinity are also conductive, which confounds interpretation. Differentiation of various conductors required the integrated use of several conduction methods.

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