Summary:
Deposit Types
The Copper King deposit is thought by some to be a Proterozoic porphyry gold-copper deposit (Hausel, 1992, 1997; Carson, 1998), and is included in a list of undeveloped porphyry copper deposits by Long (1995). Others (Klein, 1974) categorized the Copper King deposit as a structurally controlled base and precious metal deposit in a Precambrian shear zone.
The presence of stockwork and disseminated mineralization, the uniformity of metal content in the mineralized intercepts, and the association of propylitic and potassic alteration zones do suggest a similarity to the porphyry copper model. However, the apparent lack of an associated large porphyry intrusion, the rather small size of both the mineralized and altered zones, the Proterozoic age, and the apparent structural control exerted by the associated shear zone suggest that the appropriate model may be one of shear-zone related mineralization. In determining the mineral resource for Compass Minerals in 1995, MDA had modeled higher-grade shear-zone related mineralization within a larger shell of disseminated and stockwork mineralization (Ristorcelli et al., 1995).
Mineralization
According to Klein (1974) Copper King is a structurally controlled base-precious metal deposit in silicified portions of a Precambrian shear zone in granodiorite. According to Soule (1955), most of the primary gold-copper mineralization is in relatively fine-grained, equigranular gneiss (foliated granodiorite) composed of quartz, orthoclase, microcline, oligoclase, biotite, and hornblende with occasional epidote, hematite, and magnetite. Although most of the mineralization is in silicified, rehealed, mylonitic granodiorite, lesser amounts of primary copper minerals are present in aplitic quartz monzonite and hybrid felsic rocks (Klein, 1974). The mineralization tends to occur proximally to the monzonite dikes (Shrake, 1988). The deposit is elongate and ovoid in shape.
According to Nevin (1973) and Hausel (1982, 1997), and visually confirmed by the Saratoga drill hole geology, alteration zoning is evident, with a central zone of quartz veinlets and silicification extending outward into a narrow zone of potassic alteration (secondary biotite and K-spar with muscovite, sericite, epidote, and sulfides), enclosed outward by a zone of propylitic alteration (secondary epidote, chlorite, sulfides, and quartz). The zone of silicified foliated granodiorite that is the primary host for mineralization is about 762m long with an average width of 152m (Hicks, 1972). It appears that the hydrothermal alteration overprinted regional retrogressive metamorphism that had produced widespread greenschist alteration in the Silver Crown district (Hausel, 1997). Carson (1998) studied the mineralogy of six rock samples from Copper King and concluded it “possesses all the features of a weakly to moderately deformed and recrystallized small, low-grade, sub-economic porphyry copper system” or that it could “represent leakage from a larger and similar but higher-grade porphyry system related to a quartz monzonite porphyry stock at depth.” Carson (1998) identified potassic, propylitic, and phyllic- argillic alteration in the samples he studied. He proposed that the potassic and propylitic alteration are related to the porphyry system, whereas the phyllic alteration is later and related to structurally controlled alteration and mineralization. Although the deposit has been deformed and recrystallized, most of the mylonitic foliation and deformation appear to be pre-mineralization (Carson, 1998). In the better mineralized areas, quartz occurs as numerous veinlets, and there is a direct quantitative relationship between the quartz veinlets, chalcopyrite, and gold content (Soule, 1955).
Mineralization is present as disseminated sulfides and quartz/sulfide stockworks with malachite and chrysocolla and native copper present at the surface and chalcopyrite, pyrite, minor bornite, primary chalcocite, pyrrhotite, and native copper at depth (Soule, 1955; Hausel, 1997; and Clark, 2008). The mineralization is low in pyrite and high in magnetite (Nevin, 1973). Spectrographic analysis identified traces of lead, zinc, tungsten, and titanium dioxide in the mineralization (Hausel, 1997). Covellite and molybdenite have also been reported by Klein (1974). Little to no molybdenum analyses exist for the project; however, those assays that do exist from early in the project history showed low values. Sphalerite is present in intervals enriched in Zinc. Precious metal concentrations are directly proportional to sulfide content, particularly chalcopyrite (Klein, 1974). Gold occurs as free gold in grains 10 to 250 microns in size (Mountain Lake Resources Inc., 1997) or as electrum grains (F.L. Schmidt, 2021). Although mineralization is in general low grade, supergene ores with rich masses of chalcocite were selectively mined in the past (Ferguson, 1965, cited in Hausel, 1997).
Oxidation occurs within the upper 100ft. (30m) below the topographic surface and a mixed zone of weak oxides and remnant sulfide, often associated with increased metal grades, occurs within the core of the deposit up to 250ft. (75m) below the oxide boundary. Chalcopyrite is the dominant sulfide mineral though chalcocite and native copper are enriched within the mixed oxide/sulfide zone and oxide zones, respectively.
The Copper King deposit consists of a near-surface, central core of high-grade (>1.71g Au/t) mineralization, 575ft. (175m) long, 160ft. (50m) wide, and 500ft. (150m) thick, associated with moderate to pervasive silicification and near-vertical thin, sulfide-bearing quartz veins and stockwork. The highgrade core is surrounded by a large envelope of low-grade disseminated mineralization, 760m long along its N60oW strike, up to 1,000ft. (300m) wide at the widest part, and over 1,100ft. (330m) in thickness. The low-grade mineralization is open along strike, both to the northwest and southeast, and also at depth, where historic core holes have encountered mineralization to a depth of at least 1,000ft. (305m). Gold and copper mineralization within the lower-grade portion of the deposit is uniformly consistent in tenor both along strike and at depth. Historic and Saratoga drill holes have intercepted > 820ft. (250m) of continuous gold and copper mineralization in which over 90% of the individual gold assays range between 0.3g Au/t and 1g Au/t. grade and the copper values range between 0.1% Cu and 0.3%Cu.