Sleeper mine, Awakening Mining District, Humboldt County, Nevada, USAi

Regional Level Types
Sleeper mine	Mine
Awakening Mining District	Mining District
Humboldt County	County
Nevada	State
USA	Country

Structure: In the northern Slumbering Hills, Triassic sedimentary rocks are weakly folded and form a N20E-trending monocline that dips 45 east. The Sleeper Deposit occurs within a N20E-striking range front fault zone that dips 45-85 and terminates the NW side of the range. This fault zone hosted extensive hydrothermal alteration and mineralization and localized the Sleeper Gold Deposit. A normal fault which strikes N50W and dips 72 south intersects the range front fault zone in the vicinity of the Sleeper Deposit.

Alteration: Alteration of rhyolitic host rock consists predominantly of silicification, argillic alteration, acid leaching, and supergene alteration. Replacement and open-space filling by silica minerals are the most prominent and diagnostic alteration styles at Sleeper. Early silicification, accompanied by pyrite, resulted in pervasive replacement of plagioclase phenocrysts and groundmass by opaline silica. Alunite occurs in some early silicified rocks, but possibly was a later addition. Silicification of several types accompanied ore stages. Late-stage silicification in the form of opal is controlled by post-ore faults and fractures and is barren of gold. This late opal typically contains abundant light-colored alunite, kaolinite, or jarosite. Small amounts of native sulfur are enclosed in the late silica. Hypogene argillic alteration occurs peripheral to zones of early silicification; commonly there is a transition zone from 3 to 50 m wide of clay-altered plagioclase in silicified groundmass. The broad argillized zones are barren of Ag and Au, and contain little sulfide and no silica veinlets. Feldspar phenocrysts and aphanitic groundmass in argillized zones commonly are altered to clay minerals, most commonly kaolinite, smectite, and illite. Plagiocalse phenocrysts have been replaced by fine-grained clay minerals and alunite. Sanidine is locally altered to sericite or kaolinite. Groundmass is generally altered to very fine grained silica-clay mixtures. Thoroughly acid-leached rocks with sponge-like texture of more than 90% silica occur in local zones along post-ore faults. Subsequently, opal, alunite, and jarosite were deposited in the porous rocks. The prominent red coloration of upper pit walls reflects supergene destruction of sulfides and local redistribution of iron into fractures. Pyritic tuffs have been oxidized to tan alunite+jarosite+limonite-bearing mixtures. Feldspars are altered to white clays along open fractures and voids later filled by phases of unusual composition, some rich in Cl (as NaCl and AgCl), and various combinations of Al, Mn, and Co As oxides or sulfates. Propylitically altered tuffaceous sediments, andesitic lava flows, and metasedimentary basement rocks underlie the rhyolitic host rock.Ore was mined from high-grade veins and lower grade stockwork and breccia ores. The Sleeper deposit formed at about 15-16 Ma in a volcanic field during Basin-and-Range extension. Bonanza veins of uncommonly high gold grade are the most important ore type, but widespread zones of quartz stockwork and zones of breccia contain a sizable portion of bulk-mineable material. Both types of ore exhibit strong structural control in a brittle, formerly glassy rhyolite. The deposit is a combination of three superimposed ore types: 1) very high-grade bonanza veins, 2) medium grade breccias, and 3) lower grade stockworks. Multiple high-grade, banded quartz+adularia+Au veins are semi-continuous for more than 1200 m along strike and more than 500m down dip and comprise > 60% of reserves. The veins range up to 3m wide and generally dip 60-70W. Commonly, there is a zone comprised of many parallel and splaying veins spanning >30m with intervening breccias. Breccias cemented by silica, pyrite, and minor adularia typically contain 0.1 to 1 opt au with Au:Ag ratios ranging 3:1 to 6:1. Breccia ore generally is within 5m of high-grade veins but also occurs as discrete zones several meters wide in both footwall and hangingwall rocks. Approximately half of the breccia ore, chiefly that near veins, is processed through the mill. Stockwork ore containing numerous 1 to 10 mm wide quartz+pyrite veinlets generally grades <0.1 opt Au with Ag:Au ratios of 10:1. Stockwork ore is bulk mined for heap leaching. A small placer deposit has developed downslope from the ore deposit. Banded gold-silver veins at Sleeper exhibit similar textural features as veins at the National district. The gold content of the veins averages >20 opt and ranges to >170 opt. The veins contain more gold than silver. Hydrothermal breccias and stockwork veinlets formed after the high-grade veins and contain more silver than gold.

Commodity: Ore Materials: native gold Gangue Materials: quartz, adularia, stibnite, pyrite, marcasite, opal, cristobalite, sericite, alunite, kaolinite, smectite, barite, illite, jarosite.

Deposit: Mining will probobly stop some time in 1996 As ore is deplete leach pad and milling will proceed till all ore is processed. "lowest cost gold producer in u.s." randol 93-94

Deposit type: Epithermal vein, Comstock

Development: During a 1982 aerial reconnaissance program conducted by AMAX Exploration, Inc., geologist John Wood spotted an iron-oxide stained scarp which was the focus of follow-up mapping and sampling that indicated a large continuous geochemical anomaly in a zone 50-300m wide and more than 1000m long that was bounded on the east by a large normal fault and was covered by alluvium to the west. Within this zone 65 rock chip samples averaged about 0.2 ppm Au, 200 ppm As, and 100 ppm Sb with anomalous metals such as Ag, Hg, Tl, and Ba. This geochemical anomaly was characteristic of epithermal precious metal mineralization. Vegetation sampling outlined a large gold anomaly 50 m downslope from the orebody and several other anomalies probably reflecting placer gold accumulations at the bedrock surface. Resistivity, induced polarization, ground magnetics and gravity were used to delineate drill targets. Subsequently, 3536m of core and reverse circulation drilling over a two year span outlined a zone of low-grade (0.04 opt gold) mineralized volcanic rock. Hole 34, a step-out drilled through alluvial cover west of the pediment, intersected 102m of silicified breccia that averaged 28 g/t gold and 62 g/t silver, and one vein containing visible, very high-grade gold. Drilling activity was accelerated and within 6 months a "probable" mining reserve of 1.45 million tons grading 0.32 opt Au and 0.90 opt Ag was defined. Overburden stripping started June, 1985, mining in January, 1986, and milling began in February, 1986. The original Sleeper Mine was developed and brought to production by Amax Gold and was mined through 1996.AMAX was later taken over by Kinross Gold, and in 2004, X-Cal bought out Kinross' remaining interest in the property and established a 50/50 joint venture with New Sleeper Gold Corporation to reevaluate and develop the mine property, deeper targets, and adjacent areas. IN 2002, X-Cal reported that eighty holes 35 feet deep had been completed by Sonic Drilling into 6.6 million tons of Sleeper tailings. The objective of the work was to better quantify some of the above-ground gold at the site as a possible offset to bonding and reclamation costs. in 2004, X-Cal reported an extensive program of geophysics, geochemistry, satellite imagery, and soil sampling as well as 3-D modeling and a thorough review of all data from Amax Gold. Past and recent drilling programs seem to verify the potential of multiple Sleeper-like and other major Nevada-type deposits. The company has identified above-ground resources of value and has also measured, indicated and inferred resources in the immediate vicinity of the existing Sleeper Pit. X-Cal has identified six favorable project domains within the 20,000 acre Sleeper Project: Sleeper Mine and vicinity (SM), Sleeper Ring - Rose Domal Uplift (SR),West Pediment (WP), Breccia Hill and South Pediment (BH), ZZ Top igneous center (ZZ) and Southeast igneous center (SE). The Sleeper deposit produced 1,685,500 ounces of gold and 2,334,400 ounces of silver from high-grade veins and lower grade stockwork and breccia ores. Ninety percent of the these ore mined was hosted by the Sleeper Rhyolite, a volcanic unit that is covered by alluvial gravels . The New Sleeper Gold joint venture controls approximately 27 square miles centered on the old Sleeper open pit. New Sleeper is aggressively exploring their ground for additional reserves and our claims are located on trend just 1.5 miles to the south

Geology: Nash, et al. (1991) do not classify Sleeper as a hot springs deposit because ore spans a vertical distance of >500m. However, the setting was shallow (probably 50-500m depth).

Ore(s): Brittle rocks (mainly rhyolite porphyry) were required for deposition of gold in open tension fractures and as stockwork veins and hydrothermal breccias.

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Link to USGS MRDS:	10310319

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