Royal Mountain King Mine

Site Name

Primary: Royal Mountain King Mine
Secondary: Butcher Shop
Secondary: Hodson Fault
Secondary: Dublin Property
Secondary: McCarty
Secondary: Snowstorm
Secondary: Skyrocket
Secondary: Gold Knoll
Secondary: Wilbur Womble
Secondary: Lillian
Secondary: Pine Log

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Commodity

Primary: Gold
Secondary: Silver
Tertiary: Antimony
Tertiary: Arsenic
Tertiary: Lead
Tertiary: Iron
Tertiary: Zinc
Tertiary: Copper

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Location

State: California
County: Calaveras
District: Hodson (Madam Felix) District

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Land Status

Land ownership: BLM Administrative Area
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: Folsom District.

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Holdings

Not available

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Workings

Not available

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Ownership

Owner Name: Meridian Gold Inc.

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Production

Not available

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Deposit

Record Type: Site
Operation Category: Past Producer
Deposit Type: Hydrothermal stockwork; hydrothermal vein and replacement
Operation Type: Surface-Underground
Discovery Year: 1851
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; lens

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Structure

Type: L
Description: Hodson Fault, Hilltop Fault, Littlejohns Fault Zone, McCarty Ranch Fault Zone

Type: R
Description: Bear Mountains Fault Zone

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Alterations

Alteration Type: L
Alteration Text: Carbonate; ankerite, quartz, sericite, calcite, pyrite, mariposite Oxidation; hematite, goethite, limonite

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Rocks

Name: Serpentinite
Role: Associated
Age Type: Associated Rock
Age Young: Mesozoic
Age Old: Paleozoic

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

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

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Analytical Data

Not available

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Materials

Ore: Tetrahedrite
Ore: Pyrite
Ore: Gold
Ore: Electrum
Ore: Sphalerite
Gangue: Chalcopyrite
Gangue: Galena
Gangue: Sericite
Gangue: Hematite
Gangue: Goethite
Gangue: Calcite
Gangue: Ankerite
Gangue: Quartz
Gangue: Arsenopyrite

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Comments

Comment (Geology): Royal Mountain King Mine General Structure Nevadan and Laramide deformation prepared the ground for ore deposition at Royal Mountain King Mine by first folding the host rock, which was then pervasively sheared in the BMFZ. Ore formed during active faulting in the BMFZ, which was most active from Late Jurassic to Early Cretaceous. Only very limited Cenozoic extensional faulting occurred within the fault zone. The regional extent of gold in the Foothills Fault System suggests that deposition occurred during robust activity prior to the limited and regionally insignificant Cenozoic faulting. Below is a summary of fault structure related to the deposit. The Royal Mountain King Mine consists of three open-pits, aligned along the NNW-trending Hodson Fault, a western splay of the BMFZ. From north to south, the pits are referred to as the North, Skyrocket, and Gold Knoll Pits. South of the mine, the Hodson Fault closely parallels and adjoins a poorly understood fault zone, informally named the Littlejohns fault zone. The Hodson Fault varies from a single break with moderate dips to a system of low-angle splays. A ramp-and-flat profile was revealed during mining. Drag folds, slickensides and offsets of early quartz veins indicated SW-directed thrusting. Gold in all three ore bodies occurred within or adjacent to the Hodson Fault or its splays. The fault defines a generally sharp contact between a metavolcanic hanging-wall and metasedimentary foot-wall. However, deformation extended 50-200' into the walls. Ore grades increased in more intensely deformed areas. Post-mineralization faulting on the Hodson Fault and its splays sheared the ore and created abrupt ore-to-waste boundaries. Additionally, late (probably Cenozoic) NE-trending normal faults further disrupted the deposits with displacements up to 150 feet (Lechner and Kuhl, 1990; Kuhl and Garmoe, 1989). The N-trending Littlejohns fault zone is barren and has not been studied in detail. The zone dips steeply to the east and consists of serpentine and metavolcanic rocks that have been intensely brecciated and locally mylonitized. The implications of these steep shear zones regarding mineralization and structural development of the Hodson Fault are unknown (Lechner and Kuhl, 1990; Meridian Gold Inc., unpublished geologic map). South of the mine, the Hodson Fault, dips 45-60? NE and parallels and even adjoins the Littlejohns fault zone to the east. However, at the Gold Knoll Pit, the Hodson Fault flattened (dipping 10-30?) and split into several splays creating two distinct ore horizons (Meridian Gold Inc., unpublished geologic map). Kuhl and Garmoe (1989) reported that 1) hanging wall rocks were sheared, brecciated, and altered up to 100' from the fault; 2) footwall rocks (carbonaceous phyllite) were weakly brecciated for 5-20' adjacent to the fault, and contorted up to 50' from fault; and 3) a 1-3' thick layer of gouge and veins of ribbon quartz and calcite occupied the fault zone. North of the Gold Knoll Pit, the Hodson Fault steepens somewhat and loses its ancillary splays. In the upper 300' of the Skyrocket Pit, the fault dipped approximately 45NE with prominent ramps and flats. Deeper, it steepened to 60?, again parallel with the Littlejohns Fault Zone (Meridian Gold Inc., unpublished geologic map). The fault zone was 10-50' wide, highly sheared and brecciated, and consisted of black carboneous phyllite and clayey gouge with slivers of mylonitized greenstone (Kuhl and Garmoe,1989). Conglomeratic lenses parallelled the foliation and were composed of rip-up clasts of the black carboneous phyllite (Carpenter, in press).

Comment (Geology): Farther north, the Hodson Fault diverges from the Littlejohns Fault Zone. In the North Pit, it became a shallow dipping system of imbricate faults forming multiple ore zones. The complicated structure in this pit caused problems with grade control and exploration, as did large stopes associated with historic mining. The original Mountain King and Royal mines followed two prominent quartz veins in this area. Kuhl and Garmoe (1989) described three distinct structural styles in the North Pit as follows: 1) In the SE 1/3 of the pit, near the historic "Glory Hole", the Hodson Fault and vein associated with the Royal Mine were parallel, striking N45?W. 2) In the center of the pit was a complex area, known as the "Gut Area". A 200-300' wide, N70W-trending shear zone offset the N45W-trending "Glory Hole" structures with an apparent left lateral displacement of 700'. At least 5 anastomosing and en echelon low-angle faults composed the shear zone, dipped N-NE, and cut the ore body into lenses. 2) North of the "Gut Area," a NW-trending vein (mined in the Mountain King Mine) and a N-trending fault splay (the Hill Top Fault) extended from the "Gut Area". Gold mineralization developed predominantly in the metavolcanics forming the hanging wall of the Mountain King vein. Metasediments formed the footwall, were highly contorted, and locally mineralized. Both walls of the Hill Top Fault were mineralized, but too inconsistently for development. Mineralization Better ore grades were associated with 1) the presence of euhedral pyrite, 2) increased quartz veining and alteration, and 3) proximity of the Hodson Fault. Gold and pyrite occurred primarily within quartz veins in the Gold Knoll and Skyrocket orebodies. In the North Pit orebody, however, the gold and pyrite were generally restricted to the margins of veins. In the Gold Knoll Pit, both the footwall and hanging wall were mineralized about 300' down-dip. Grades in the metavolcanics that formed the hanging wall were more continuous and higher than in the metasediments that formed the footwall. In both walls, gold was found chiefly in tuff beds. Free gold formed along late NE-trending faults that cut the Hodson Fault indicates some remobilization. The free gold and either pyrite or sphalerite were visible along margins of quartz veins. Ag-poor electrum occurred as inclusions and microveinlets within pyrite and sphalerite grains. Chalcopyrite was present but barren. Auriferous quartz veins occurred both as lenticular pods of brecciated stockworks and as gash veins with medium-grained, euhedral pyrite. Individual quartz veins were 0.04- 4" thick and formed composite veins that were usually 1-5' thick, but up to 10' locally. Overall, veins composed 5-50% of the host rock (Lechner and Kuhl, 1990; Kuhl and Garmoe, 1989). In the Skyrocket Pit, mineralization extended 2,000' along strike and 750' down-dip. The pit reached a maximum depth of 360', which was 100' short of the bottom of mineralization; deeper mining was not economical. Ninety percent of the mineralization was restricted to brecciated phyllite in the footwall. The remainder of the mineralization occurred in the NE part of the pit in a sequence of intercalated metasediments and metavolcanics. Brecciated stockworks of quartz veinlets pervaded the footwall and penetrated into the fault zone. The stockworks contained coarse-grained euhedral pyrite and free gold. Gold predominantly occurred as microscopic (5-50 microns) inclusions and veinlets in the pyrite. Pyrite ore composed 0.5-5.0% of the host rock and carried 0.10 opt. Twenty-five per cent of the gold was free, but was rarely visible in hand samples (Lechner and Kuhl, 1990; Kuhl and Garmoe, 1989).

Comment (Deposit): The gold deposit is hosted in Jurassic metasedimentary and metavolcanic rocks along a thrust fault. In map view, the Jurassic rocks form slivers and blocks of mafic, ultramafic, and marine sedimentary rocks, interpreted to represent island arc, flysch, and ophiolite sequences accreted and deformed during the Nevadan Orogeny. Prior to ore deposition, the host rocks were regionally metamorphosed to greenschist facies and then complexly faulted along ductile and brittle shear zones of the Foothills Fault System. Ore fluids invaded these shear zones. Massive veins and stockworks of quartz formed within fractures. Ribbon quartz and crosscutting quartz veins indicate repeated faulting and ore-fluid invasion. The gold and pyrite formed within and along the margins of quartz veins and as low-grade disseminations in the wall rock. Local high-grade pockets also formed. A suite of other metals (most notably silver, copper, lead, and arsenic) were also deposited at the same time. The majority of gold was deposited as electrum, although native gold and silver also formed. The grains of gold and electrum were typically microscopic but are occasionally visible. The metavolcanic host rocks were intensely altered to a quartz-sericite-ankerite-mariposite assemblage.

Comment (Geology): REGIONAL GEOLOGY The mesothermal gold ore deposits at Royal Mountain King Mine formed within a western splay of the Bear Mountains Fault Zone (BMFZ). The BMFZ along with the Melones Fault Zone define the Foothills Fault System of Clark (1964). The BMFZ hosts the West Gold Belt. The Melones Fault Zone hosts the Mother Lode Gold Belt. At Royal Mountain King Mine, brittle thrust faulting provided the necessary ground preparation for ore fluid transport and deposition. The ore bodies developed during multiple episodes of continued faulting. Thrust faulting along the southern BMFZ was active from 155-123 Ma (Saleeby and others, 1989). The Royal Mountain King deposit (now largely mined-out) was located within the Jurassic rocks of the western Sierra Nevada metamorphic belt. The Jurassic rocks form slivers and blocks of mafic, ultramafic, and marine sedimentary rocks interpreted to represent island arc, flysch, and ophiolite sequences accreted and deformed during the Nevadan Orogeny. Diachronous metamorphism is ubiquitous and generally low-grade except in minor areas of amphibolite and blueschist grades. These higher-grade rocks generally represent older lithologies, possibly basement (Day, 1992). The structural and stratigraphic histories of these juxtaposed terranes of diverse origins and lithologies have been obscured by polyphase deformation, metamorphism, and poor exposure. The fabric of the region is dominated by the generally steeply east-dipping faults of the Foothills Fault System and generally parallel penetrative cleavage. Bedding is generally subparallel to the faults and cleavage, but dips less steeply (Clark, 1964). Belts of serpentinite and melange locally occur along the faults. The above conditions result in a regional map pattern of northerly trending tectonostratigraphic units. On a regional scale, the terranes are progressively younger to the west. However, within individual terranes, the east-dipping stratigraphy places stratigraphically higher units east of older units. This reversal of younging direction is typical in zones of underthrusting (Landefeld, 1990). Interpretations vary regarding the regional tectonic setting, the significance and extent of faults, the sense of displacement along some of the faults, and stratigraphic correlations. Several schemes divide the rocks into a variety of fault-bounded terranes. Some enlist the two major strands of the Foothills Fault System, the Melones and Bear Mountains fault zones, as major structural boundaries, dividing the region into three subparallel tectonostratigraphic belts. These are generally referred to, from east to west, as the Calaveras belt, the central or Placerville belt, and the western belt. Interpretations vary regarding the extent to which these belts represent terranes. Graymer and Jones (1994, 1997) have subdivided a portion of the Placerville belt into five terranes based on biostratigraphic controls coupled with structural interpretations. They suggested that the faults of the Foothills Fault System may not be continuous, 300-km long structures as generally accepted. Instead, in their study area, they characterized the Foothills Fault System as a composite of small, incidentally aligned faults bounding many unrecognized terranes that comprise the region.

Comment (Development): Gold in the district was discovered in placers in 1851. Lode mining began in 1857. Production was minor until the 1880's when extensive deposits were discovered at the Royal and Mountain King mines. Historic productivity reached its peak in the 1890's and early 1900's, with sporadic production until the late 1940's. The Royal Mine was operated extensively between 1895 and 1905, closed until 1914, idle between 1916 and 1919, and operated off and on from 1929 to 1949. Substantial development occurred in 1931. The Mountain King Mine was operated from 1900 to 1948. Mining operations ceased in the 1940's. From then until the 1980's, nine mining companies conducted drilling programs outlining bulk deposits of low-grade ore. About 560 holes were drilled. In 1984, Meridian Gold leased the Gold Knoll and Wilbur Womble properties and conducted geologic mapping, a drilling program, soil geochemistry, and magnetic studies. In 1986, Meridian entered into an exploration option with Mother Lode Gold Mines Consolidated and initiated an accelerated exploration program. Permitting and feasibility studies were conducted in 1987. Construction began in January of 1988. Open-pit mining began in May of 1988 (Lechner, 1988) and continued until 1995. Chaffee and Hill (1989) conducted a soil geochemistry survey in the Hodson District. They found that Ag, As, Au, Ca, Hg, Mg, Sb, and W concentrations were elevated and Ca and Mg concentrations were depressed. Tungsten proved to effectively delineate mineralized zones. The anomalies were greatest along mineralized faults and extended as much as several hundred meters laterally. King (1986) regarded As as the best pathfinder element for gold mineralization, based on soil and drill-core geochemistry. Historically, several stamp mills existed at various underground operations. The Royal Mill, completed in 1903, was the largest mill in the country at that time and consisted of 120 stamps. The pulp of the stamp mills was passed over mercury-coated amalgamation plates. The tailings from the plates were then purified on a circuit of flotation tanks, vibration tables, and vanners. The gold was separated from the concentrates by a chlorination process. The mills processed ore from other mines, including copper ore during the war years. The vast majority of the ore produced by the Meridian Gold Inc. operation was processed on-site in a multistage mill. Processing included crushing, grinding, flotation, cyanidation, activated carbon filtration, and electroplating. Recovery rates averaged about 78%. About 250,000 tons of oxide ore were cyanide heap-leached, but recovery rates were poor due to migrating fines, channeling, and compacting of the lower lifts by truck traffic. Reclamation is still under way. The mill was dismantled in 1996, and the Gold Knoll Pit has been backfilled. The Skyrocket and North pits have been allowed to fill with naturally occurring water flow. The Sky Rocket Pit encompassed a portion of Littlejohns Creek, which has been diverted around the pit. Where the original downstream channel leaves the pit, a detention dam was constructed to prevent pit water from flowing into the old channel. Reclamation of the flotation tailings reservoir has not been approved yet.

Comment (Environment): The area consists of sparsely populated low-relief, rolling foothills covered with oak woodland-grasslands. Ranges and valleys generally follow a NW strike; the mine is located in the southern end of Salt Springs Valley, one of these strike valleys. Annual precipitation is generally between 25-30? and occurs mostly as rain during the winter months. Temperatures reach freezing in the winter and exceed 100 degrees (F) in the summer. Two of the open pits (North and Skyrocket) have filled with water, while the third (Gold Knoll) is backfilled.

Comment (Identification): The Royal Mountain King Mine is a large open-pit operation that encompassed both the Royal and Mountain King mines and several smaller mines.

Comment (Location): Location point selected as shaft symbol for Skyrocket Mine on USGS Copperopolis 7.5-minute quadrangle map. Mine is accessible by paved road from Copperopolis.

Comment (Geology): In the North Pit, mineralization extended about 3,000 feet along strike and 560' down-dip, reaching a maximum vertical depth of 210'. The maximum depth of the pit reached 120'. About 80% of the mineralization developed in the metavolcanics. Ore grade was directly proportional to the intensity of silicification. For example, in the highest-grade areas, quartz and calcite veins composed 10-50% of the host rock. The presence of late-stage translucent quartz also indicated higher grades. The quartz veins were typically 0.04-2.0" wide with thin calcite margins. The quartz was low-grade, but auriferous pyrite and free gold were disseminated along vein margins. The gold was microscopic (1-50 microns) and occurred as inclusions in very fine to medium-grained pyrite, sphalerite, and tetrahedrite, in association with a barren assemblage of arsenopyrite, galena, and chalcopyrite (Lechner and Kuhl, 1990; Kuhl and Garmoe, 1989). Alteration The relative permeabilities of the wall rocks seem have to controlled the degree of alteration. For example, alteration of the metavolcanics of the hanging wall was much stronger than in the metasediments of the footwall. Additionally, alteration varied somewhat between the three principal ore bodies as described below. Hanging wall alteration at the Gold Knoll Pit was zoned, consisting of a core of quartz-sericite-pyrite where the highest grades were found. This zone was enveloped by an ankerite-quartz-mariposite (sometimes with pyrite) zone, which was in turn surrounded by a halo of weak carbonate alteration. However, in the footwall phyllites, the pyrite was disseminated and carbonate alteration was weak. The phyllites appeared bleached due to leaching of organic carbon. Surface oxidation (hematite, goethite, and limonite) was very intense in the mineralized metavolcanics extending to a depth of at least 100 feet in the southern portion of the deposit (Lechner and Kuhl, 1990; Kuhl and Garmoe, 1989; Chaffee and Sutley, 1994). In the Skyrocket orebody, the positive correlation between the degree of alteration and higher ore grades did not hold. In this area, the fault zone is dominantly brecciated phyllite that was favorable for mineralization but less susceptible to alteration than the metavolcanics. Alteration of the footwall and fault zone phyllites was subtle with weak sericitization, local silicification, and late-stage carbonate veinlets. Remobilization of organic carbon produced a silky, sericitic sheen in the phyllites. In contrast, the hanging-wall metavolcanics were intensely altered to quartz-sericite-ankerite-mariposite along a 10-200' wide zone adjacent to the fault. Oxidation was shallow, reaching a maximum depth of 20-30'. In the North Pit, alteration was dominantly in the hanging walls along faults. Silicic alteration extended for 20-50' from the faults; whereas, carbonate alteration extended to 250'. In the footwall, carbonate alteration was limited to 60' from faults. The type of alteration at the North Pit was similar to the Gold Knoll Pit, except silicic alteration and sericite development were more strongly developed here than in the other ore bodies. As in the Skyrocket Pit, remobilization of organic carbon produced a silky, sericitic sheen in the phyllites. Oxidation extended to 80' below ground level (Lechner and Kuhl, 1990; Kuhl and Garmoe, 1989; Chaffee and Sutley, 1994).

Comment (Geology): BEAR MOUNTAINS FAULT ZONE The westernmost of the major Foothills Fault System, the BMFZ separates the Copper Hills Volcanics on the west from a belt of melange and serpentinite on the east. Edelman and Sharp (1989) and Behrman (1978) interpreted the melange belt to represent a disrupted ophiolite, that they called the Bear Mountains Ophiolite. Conversely, Miller and Paterson (1991) broadened definition of the fault into a wide shear zone that includes the belts of melange and serpentinite. In their model, essentially the entire Central Belt is a fault zone that separates a footwall of Copper Hills Volcanics and the Salt Springs Slate from the possibly equivalent rocks of the Logtown Ridge volcanics and the Mariposa Formations. Locally, stratigraphically lower rocks of the Penon Blanco Formation (Late Triassic-Early Jurassic) compose the hanging wall. They noted that correlations of the Salt Springs Slate with the Mariposa Formation and of the Copper Hills Volcanics with the Logtown Ridge are more circumstantial than definitive. Farther north, in the Placerville area, Graymer and Jones (1994, 1997) dispute the existence of the Bear Mountains Ophiolite and regard the Bear Mountains Fault Zone in their study area to be relatively young and of little apparent regional significance. They doubt the existence of the fault zone as a continuous single tectonic entity. CHARACTER OF REGIONAL DEFORMATION In a regional analysis, Schweickert (1999) defined three major episodes of deformation: 1) Middle Jurassic contraction with thrusting, expressed in the eastern belt, 2) Late Middle Jurassic extension, expressed in the western belt, and 3) Late Jurassic Nevadan contraction, expressed as the Foothills Fault System and regional folds. The second and third phases affected the Copper Hill Volcanics and the Salt Springs Slate. As noted above, Nevadan structures and Cretaceous units are deformed by the Foothills Fault System. They considered indications of sinistral-slip, as reported by others and summarized below, to reflect later fault reactivation that does not bear on their interpretations of earlier events. Thus in their analysis, this strike-slip reactivation constitutes yet another deformational episode. Below are summaries of detailed structural analyses conducted across the southern section of the BMFZ, approximately 80-100 miles south of the Royal Mountain King Mine. Steep SE-plunging stretching lineations and subparallel fold axes indicated to Miller and Paterson (1991) and Newton (1990a, b) that fault movement was a combination of sinistral and reverse slip. However, their interpretations differ concerning which was the dominant component of slip. The former considered reverse slip as dominant and, conversely, the latter concluded that slip was dominantly sinistral. Saleeby (1992) analyzed the structure of mafic dike swarms that occur along the Bear Mountains Fault Zone to determine the timing and pattern of deformation (see below). He concluded that slip was dominantly sinistral.

Comment (Geology): Miller and Paterson (1991) described the Bear Mountains Fault Zone as a 5-km wide, steeply east-dipping shear zone of complex brittle and ductile deformation and polyphase metamorphism. Stretching lineations dominantly plunge steeply SE. Within the shear zone are narrow, subparallel belts of tectonic melange containing exotic blocks of ultramafic rock and limestone showing no affinity to the wall rocks. The blocks imply large degrees of mixing and displacement. The authors? transects across the fault show no change in metamorphic grade and a significant increase, from E-W, in strain intensity. They proposed that these conditions could not have developed along a steeply dipping fault zone but instead are compatible with a low-angle fault. The increase in strain to the west indicates an east-over-west arrangement. From this, they concluded that the fault was originally an east-dipping, low-angle, thrust fault. The SE-plunging stretching lineations reflect an added component of minor sinistral slip. They contend that the fault zone and enclosing rocks were later rotated to the current steep dip by continued contraction. Newton's (1990a, b) study incorporated fault and fold geometries, and relative plate motions into his structural analysis. He described asymmetric drag folds that indicate counterclockwise rotation of wall rocks. He viewed the various splays or segments of the BMFZ as a right-stepping en echelon system. In the crossover zones between fault segments, he finds NE-trending thrusts. These findings suggest sinistral displacement, which is also indicated by the plate motion reconstruction models and paleomagnetic interpretations of others (references found therein). Saleeby (1992) determined that the Folsom (164 Ma) and Smartville (162 Ma) dike swarms in the northern regions of the fault predate the Nevadan Orogeny. In the central and southern sections, the Sonora (158 Ma), and the Owens Mountain dike swarms formed during the Nevadan Orogeny -in part coeval with the Jurassic-Cretaceous Independence Dike Swarm near Owens Valley. The Owens Mountain dike swarm, the southernmost, is south of the originally recognized terminus of the fault zone, but Wolf and Saleeby (1996) found structures that they consider a southern continuation of the BMFZ. The mafic dikes all indicate extension and show left-lateral shear. Saleeby (1992) suggested that the mafic dike swarms reveal alternating cycles of transpression and transtension. Furthermore, he suggested that the reverse slip revealed by Miller and Paterson (1991) may represent only the most recent sense of movement. Earlier sinistral slip fabrics may have been obliterated. TIMING OF REGIONAL DEFORMATION AND TERRANE ACCRETION The timing of accretion is controversial. Accretion probably occurred episodically during the Paleozoic and Mesozoic. Edelman and Sharp (1989) described the Upper Jurassic (159-151 Ma) Mariposa Formation as an overlap sequence; hence, suggesting that accretion predates those strata. Conversely, Schweickert and others (1988, 1999) considered these flysch deposits to be subduction trench fill. This interpretation suggests accretion occurred after deposition of the Mariposa Formation. As mentioned above, the Foothills Fault System cuts Upper Jurassic strata and deformed Lower Cretaceous rocks. Latest movement therefore postdates accretion and occurred either in the Early Cretaceous or later. Along southern portions of the fault system, Saleeby and others (1989) indicated that penetrative ductile deformation, metamorphic recrystallization, and magmatism (Guadalupe Igneous Complex) occurred about 150-135 Ma. In northern sections, latest low-grade metamorphism occurred during the Nevadan Orogeny between 152-162 Ma. A multitude of earlier metamorphic events are recognized in the various terranes. Some of the individual terranes reveal unique pre-Nevadan metamorphic history, which presumably predates accretion (Day, 1992).

Comment (Commodity): Commodity Info: Early mining concentrated on very fine-grained free gold present in placers or in quartz veins and veinlets. The gold ranged from 627-700 fine. Some high grade pockets were found. Recent mining exploited invisible gold disseminated in carbonate-altered metasedimentary and metavolcanic rocks. The gold is initimately associated with euhedral pyrite, sometimes as a coating or as microveinlets in the pyrite. These deposits were low grade, ranging from 0.025-.074 ounces of gold per ton. The ore mineral was principally electrum, with a fineness of 500 to 750.

Comment (Commodity): Ore Materials: Electrum, native gold, pyrite, sphalerite, tetrahedrite.

Comment (Commodity): Gangue Materials: Quartz, ankerite, calcite, sericite, chalcopyrite, galena, arsenopyrite, hematite, goethite

Comment (Geology): LATE JURASSIC ROCK UNITS The Upper Jurassic Salt Springs Slate and Copper Hill Volcanics host the deposits of Royal Mountain King Mine. Important coeval units are the Mariposa Formation and Logtown Ridge Volcanics. The Salt Springs Slate (Clark, 1964) is considered by most workers as an equivalent to the Mariposa Formation (Miller and Paterson, 1991; Edelman and Sharp, 1989). Both formations, considered collectively as the Mariposa Formation, consist of thin-bedded slates, tuffs, greywackes, and conglomerates. The Copper Hills Volcanics conformably overlie and intertongue with the Mariposa Formation. Most workers equate the Copper Hills Volcanics with the Logtown Ridge Volcanics, although the former is more silicic. These formations consist of andesitic tuffs, volcanic breccias, and flows with some pillow lava. A series of late folds, some overturned, plunge gently to the S-SE (Clark, 1964, 1970). Edelman and Sharp (1989) described these Jurassic units as an overlap sequence depositionally resting above already amalgamated Paleozoic- early Mesozoic terranes. FOOTHILLS FAULT SYSTEM The role of the Foothills Fault System during terrane subduction, accretion, and deformation is controversial. It was clearly active after the terrane amalgamation because it cuts the Upper Jurassic strata, truncates the regional folds, and deforms Lower Cretaceous plutons of the Sierra Nevada Batholith. The Foothills Fault System extends 300 km N-S. Most recently published research has focussed on the northern and southern ends of the system. Interpretations regarding the structure and role of the Foothills Fault System vary between workers. These variations may be a consequence of regional or local changes along the system. Landefeld (1990) proposed that the fault system is more deeply exposed in the south, thus explaining the prevalence of 1) ductile structures in the south and 2) brittle structures in the north. In the northern portions of the system, Day and others (1985) and Moores and Day (1984) concluded that the Foothills Fault System consists of east-vergent thrust faults. Gefell and others (1989) found shear sense indicators in the Feather River Perioditite, which they attributed to a northern continuation of the Melones Fault Zone. Here, older ductile fabrics record sinistral reverse faulting and younger brittle structures record dextral normal faulting. In central sections of the region, Edelman and others (1989) defined the system as west-vergent faults with dip-slip displacements of less than 10 km. Schweickert and others (1988, 1999) and Ernst (1983) described the system as reverse faults active during the Nevadan Orogeny related to east-dipping subduction. Landefeld (1990) proposed that initial motion consisted of ductile thrusting followed by poorly constrained, brittle, lateral slip. In its southern region, Miller and Paterson (1991) and Barry (1993) interpreted movement along the BMFZ as east-over-west low-angle thrusting with large displacements. Saleeby (1981) and Newton (1986) concluded, however, that the fault zone exhibits sinistral transpression with large displacements.

Comment (Workings): At the Royal Mine, the main shaft reached 1,500' depth along the 20-25? incline. Drifts were extended at every 100-foot level. At the 700-foot and 1200-foot levels drifts were extended along strike for 1,000' and 600', respectively. Numerous stopes are located between the 1000-foot and 1200-foot levels, many with 80-foot backs. By 1905, the area between the 700-1200 levels was reportedly mined out. The room-and-pillar method was employed for support. Some of the ore was processed at the Royal Mill, one of the largest in state. At one time, it consisted of 120 stamps. Constructed in 1905, it operated for only 18 months (Logan and Franke, 1936). By 1925, the main shaft of the Mountain King Mine had reached 1,044' in depth along the 28? incline. Six levels, the deepest at 800', were extended from the main shaft at irregular intervals. A 300' long drift, at Level 6, was the longest at the time. A 10-stamp mill was operated on the premises (Logan, 1925). Immediately after the war, mining was begun at Mountain King Mine in the Hobo and Hill Top open pits. By 1947, 250,000 tons of ore were milled. Operations ceased later that year due to rising costs. From 1988 to 1995, Meridian's Royal Mountain King Mine encompassed the above mines, as well as lesser mines. It consisted of thee open pits; from northwest to southeast these were the North Pit, Skyrocket Pit, and Gold Knoll Pit. The Skyrocket Pit, which was the largest, reached a maximum depth of 360' by 2,200 feet by 1,000 feet, covering 24 acres.

Comment (Economic Factors): the total production of the district is estimated to be 467,800 to 504,300 ounces of gold and 75,000 to 100,000 ounces of silver from 5.7 million tons of ore and 50 million tons of overburden. The average grade was 0.05 ounces of gold per ton. By 1936, 800,000 tons of ore had been mined with an average grade of 0.20 ounces of gold per ton. The historic Mountain King Mine, alone, produced 20,000 to 35,000 ounces of gold. The deposit is essentially mined out, although scattered ore-grade pockets remain. Mineralization extends deeper than the pit bottoms, but was uneconomical to mine. Although some reserves (30,000-40,000 oz. Au) exist in ponded leach-concentrate, extraction of gold from the concentrate is not economically feasible at this time.

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References

Reference (Deposit): Lechner, M.J. and Kuhl, T., 1990, Geology of the Royal Mountain King Mine: Unpublished report presented at the 96th Annual Northwest Mining Association Meeting, 19 p.

Reference (Deposit): Paterson, S.R. and Wainger, L., 1991, Strains and structures asociated with a terrane bounding stretching fault: the Melones fault zone, central Sierra Nevada, California: Tectonophysics, v. 194, p. 69-90.

Reference (Deposit): Paterson, S.R. and others, 1987, Post-Nevadan deformation along the Bear Mountains fault zone: implications for the Foothills terrane, central Sierra Nevada, California: Geology, v. 15, p. 513-516.

Reference (Deposit): Saleeby, J.B., 1981, Ocean floor accretion and volcano-plutonic arc evolution of the Mesozoic Sierra Nevada, California, in Ernst, W.G., editor, Geotectonic development of California: Rubey Volume 1, Prentice-Hall, Englewood Cliffs, New Jersey, p. 132-181.

Reference (Deposit): Logan, C.A., 1925, Calaveras County: California State Mining Bureau 21st Report of the State Mineralogist, p. 155-156.

Reference (Deposit): Miller, R.B. and Paterson, S.R., 1991, Geology and tectonic evolution of the Bear Mountains Fault Zone, central Sierra Nevada , California: Tectonics, v. 10, p. 995-1006.

Reference (Deposit): Moores, E.M. and Day, H.W., 1984, An overthrust model for the Sierra Nevada: Geology, v. 12, p. 416-419.

Reference (Deposit): Newton, M.C., 1986, The southern part of the Bear Mountains fault zone, Foothills terrane, western Sierra Nevada, California: Geologic Society of America Abstracts with Programs, v. 18, p. 164.

Reference (Deposit): Newton, M.C., 1990a, Structural control of gold mineralization in the southern Mother Lode region, in Seedorf, E., editor, Geology and ore deposits of the Sierra Nevada and foothills: Mary Harrison Prospect, Royal Mountain King Mine, Spanish Mine: Geological Society of Nevada Special Publication No. 11, p. 84-92.

Reference (Deposit): Newton, M.C., 1990b, Tectonostratigraphic history of the southern Foothills terrane: Ph.D dissertation, University of Arizona, Tucson, 203 p.

Reference (Deposit): Kuhl, T.O., 1990, The Royal-Mountain King project, Calaveras County, California, in Landefield, L.A. and Snow, G., editors, Yosemite and the Mother Lode Gold Belt: geology, tectonics, and the evolution of hydrothermal fluids in the Sierra Nevada of California: Pacific Section, AAPG Volume and Guidebook, p. 155-170.

Reference (Deposit): Landefeld, L.A., 1990, The geology of the Mother Lode Gold Belt, Foothills Metamorphic Belt, Sierra Nevada, California, in Landefield, L.A. and Snow, G., editors, Yosemite and the Mother Lode Gold Belt: geology, tectonics, and the evolution of hydrothermal fluids in the Sierra Nevada of California: Pacific Section, AAPG Volume and Guidebook, p. 117-124.

Reference (Deposit): Logan, C.A. and Franke, H., 1936, Calaveras County: California Journal of Mines and Geology, v. 32, p. 285-287.

Reference (Deposit): Barry, T.F., 1993, Structure and tectonics of the Bear Mountains fault zone and western Foothills terrane between Lake Don Pedro and Lake McSwain, central Sierra Nevada: M.S. thesis, San Jose State University, 56 p.

Reference (Deposit): Schweickert, R.A. and others, 1988, Deformational and metamorphic history of Paleozoic and Mesozoic basement terranes in the western Sierra Nevada metamorphic belt, in Ernst, W.G., editor, Metamorphism and crustal evolution of the western United States: Rubey Volume VII, Prentice-Hall, Inc., Englewood Cliffs, New Jersey, p. 789-820.

Reference (Deposit): Saleeby, J.B., 1992, Petrotectonic and paleogeographic setting of U.S. Cordilleran ophiolites, in Burchfiel, B.C. and others, editors, The Cordilleran Orogen: Conterminous U.S.: Geological Society of America, The Geology of North America, v. G-3. p. 653-682.

Reference (Deposit): Saleeby, J.B. and others, 1989, Isotpoic systematics of Pb/U (zircon) and 40-Ar/39-Ar (biotite-hornblende) from rocks of the central Foothills terrane, Sierra Nevada, California: Geologic Society of America Bulletin, v. 101, p. 1481-1492.

Reference (Deposit): Berger, B.R., 1987, Descriptive model of low-sulfide au-quartz veins, in Cox, D.P and Singer, D.A, editors, Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 239.

Reference (Deposit): Behrman, P.S., 1978, Pre-Callovian rocks, west of the Melones Fault Zone, central Sierra Nevada foothills, in Howell, D.G. and McDougall, K.A., editors, Mesozoic paleogeography of the western United States: Pacific Coast Paleogeography Symposium 2, Society of Economic Paleontologists and Mineralogists, Pacific Section, p. 303-310.

Reference (Deposit): Chaffee, M.A. and Hill, R.H., 1989, Soil geochemistry of Mother Lode-type gold deposits in the Hodson mining district, central California, U. S. A.: Journal of Geochemical Exploration, v. 32, p. 53-55.

Reference (Deposit): Burchfiel, B.C. and others, 1992, Tectonic overview of the Cordilleran orogen in the western United States, in Burchfiel, B.C. and others, editors, The Cordilleran Orogen: Conterminous U.S.: Geological Society of America, The Geology of North America, v. G-3. p. 407-479.

Reference (Deposit): Schweickert, R.A. and others, 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): Edelman, S.H. and Sharp, W.H., 1989, Terranes, early faults, and pre-Late Jurassic amalgamation of the western Sierra Nevada metamorphic Belt, California: Geological Society of America Bulletin, v. 101, p. 1420-1433.

Reference (Deposit): Ernst, W.G., 1983, Phanerzoic continental accretion and metamorphic evolution of northern and central California: Tectonophysics, v. 100, p. 287-320.

Reference (Deposit): Engebretson, D.C. and others, 1985, Relative motions between oceanic and continental plates in the Pacific basin: Geological Society of America Special Paper 206, 59 p.

Reference (Deposit): Fuller, W.P. and others, 1996, Madam Felix?s gold: the story of the Madam Felix Mining District, Calaveras County, California: Calaveras Historical Society and Foothill Resources, Ltd., 166 p.

Reference (Deposit): Gefell, M.J. and others, 1989, Ductile and brittle shear sense for the ?Melones Fault Zone?, northern Sierra Nevada, California: Geological Society of America Abstracts with Programs, v. 21, no. 5, p. 83.

Reference (Deposit): Graymer, R.W., 1992, Structural evolution of the central part of the Foothills Terrane, Sierra Nevada, California: Unpublished Ph.D dissertation, University of California, Berkeley, 173 p.

Reference (Deposit): Graymer, R.W., 1997, Geologic history of the Placerville Belt, in Jones, D.L. and Lawler, D., editors, Northern Sierra Nevada region geological field trip guidebook: Northern California Geological Society, October 11-12, 1997.

Reference (Deposit): Clark, L.D., 1970, Geology of the San Andreas 15-minute Quadrangle, Calaveras County, California: California Division of Mines and Geology Bulletin 195, 23 p.

Reference (Deposit): Clark, L.D., 1976, Stratigraphy of the north half of the westen Sierra Nevada Metamophic Belt: U. S. Geological Survey Professional Paper 923, 26 p.

Reference (Deposit): Clark, W.B., 1970, Gold districts of California: California Division of Mines and Geology Bulletin 193, 186 p.

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 2, 217 p.

Reference (Deposit): Chaffee, M.A. and Sutley, S.J., 1994, Analytical results, mineralogical data, and distributions of anomalies for elements and minerals in three Mother Lode-type gold deposits, Hodson Mining District, Calaveras County, California: U.S. Geological Survey Open-File Report 94-640-A, 216 p.

Reference (Deposit): Clark, L.D., 1964, Stratigraphy and structure of part of the western Sierra Nevada metamophic belt, California:

Reference (Deposit): U.S. Geological Survey Professional Paper 410, 70 p.

Reference (Deposit): Day, H.W., 1992, Tectonic setting and metamorphism of the Sierra Nevada, California: in Schiffman, P. and Wagner, D. L., editors, Field guide to the geology and metamorphism of the Franciscan Complex and Western Metamorphic Belt of northern California, p. 12-28.

Reference (Deposit): Day, H.W. and others, 1985, Structure and tectonics of the northern Sierra Nevada: Geological Society of America Bulletin, v. 96, p. 436-450.

Reference (Deposit): Edelman, S.H. and others, 1989, Structure across a Mesozoic ocean-continent suture zone in the northern Sierra Nevada, California: Geological Society of America Special Paper, v. 224, p. 1-56.

Reference (Deposit): Graymer, R.W. and Jones, D.L., 1994, Tectonic implications of radiolarian cherts from the Placerville Belt, Sierra Nevada Foothills, California: Nevadan-age continental growth by accretion of multiple terranes: Geological Society of America Bulletin, v. 106, p. 531-540.

Reference (Deposit): Graymer, R.W. and Jones, D.L., 1997, Stratigraphic and structural significance of new 40Ar/ 39Ar dates from the Placerville Belt, Sierra Nevada Foothills, California, in Jones, D.L. and Lawler, D., editors, Northern Sierra Nevada region geological field trip guidebook: Northern California Geological Society, October 11-12, 1997.

Reference (Deposit): Julihn, C.E. and Horton, F.W., 1938, Mines of the southern Mother Lode region, Part I - Calaveras County: U.S. Bureau of Mines Bulletin 413, 140 p.

Reference (Deposit): Ingersoll, R.V. and Schweickert, R.A., 1986, A plate-tectonic model for Late Jurassic ophiolite genesis, Nevadan orogeny and forearc initiation, northern California: Tectonics: v. 50, p. 901-912.

Reference (Deposit): King, D.A., 1986, Controls of gold mineralization in the southern portion of the Hodson Mining District, west Mother Lode Gold Belt: Unpublished Master?s thesis, University of Montana, 60 p.

Reference (Deposit): Sharp, W.H., 1988, Pre-Cretaceous crustal evolution in the Sierra Nevada region, in: Ernst, W.G., editor, Metamorphism and crustal evolution of the western United States: Prentice-Hall, Englewood Cliffs, New Jersey, p. 824-864.

Reference (Deposit): Taylor, G.C. and others, 1993, Mineral land classification of the San Andreas 15-minute Quadrangle, Calaveras County, California: California Division of Mines and Geology Special Report 169, 77 p.

Reference (Deposit): Wagner, D.L. and others, 1981, Geologic map of the Sacramento quadrangle, California: California Division of Mines and Geology Regional Map Series Map 1A, scale 1:250,000.

Reference (Deposit): Tobisch, O.T. and others, 1989, Nature and timing of deformation in the the Foothills terrane, central Sierra Nevada, California: its bearing on orogenesis: Geological Society of America Bulletin, v. 101, p. 401-413.

Reference (Deposit): Lechner, M.J., 1988, Royal Mountain King Mine Project: Unpublished report for Meridian Gold Company, 15 p.

Reference (Deposit): Kuhl, T.O. and Garmoe, W.J. , 1989, Geology of the Royal-Mountain King Mine Hodson District, Calaveras County, California: Unpublished paper presented at Society of Mining Engineers annual meeting, 11 p.

Reference (Deposit): Hershey, O.H., 1933, Geologic report on the Royal Mine: Unpublished report, Hershey and White Consulting Engineers, 17 p. (CDMG Library, Sacramento).

Reference (Deposit): Wolf, M.B. and Saleeby, J.B., 1995, Late Jurassic dike swarms in the southwestern Sierra Nevada Foothills Terrane, California: implications for the Nevadan Orogeny and North American Plate motion, in Miller, D.M. and Busby, C., editors, Jurassic magmatism and tectonics of the North American Cordillera: Geological Society of America Special Paper 299, p. 203-228.

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California Gold

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