Mammoth Prospect, Admiralty District, Juneau Borough, Alaska, USA
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Geology: The Mammoth prospect, which was discovered in the 1890's, consists of gold and disseminated and massive sulfides in quartz-carbonate-mariposite schist, graphitic schist, and mafic tuff. The sulfides include sphalerite, galena, tetrahedrite, and pyrite. The volcanic units are intruded by serpentinized diorite-gabbro and pyroxene plugs (Miller and Barnett, 2000). From 1976 to 1988, Bear Creek Mining Company explored the Mammoth prospect by soil and stream-silt sampling, geologic mapping, and ground geophysics. Surface samples that assayed up to 0.085 ounce of gold per ton and 53.75 ounces silver per ton led to diamond drilling. Four holes in the quartz-carbonate-mariposite unit were completed in 1987 and one in 1988. Holes MRD-1 to MRD-4 encountered significant lead-zinc-silver-gold mineralization that had up to 0.4 percent lead, 3.8 percent zinc, 1.77 ounces of silver per ton, and 0.237 ounce of gold per ton. Hole MRD-1 intersected a 54-foot interval of 0.435 percent zinc, and hole MRD-2 intersected 40 feet of 0.51 percent zinc, There is an adit on the Mammoth prospect and numerous surface pits and trenches. Recent mapping by Kennecott Greens Creek geologists indicate intense sericite alteration and ubiquitous sulfides throughout the workings. Kennecott geologists suggested that the mineralization may be similar to that at the Greens Creek mine (JU253) (Miller and Barnett, 2000). The Greens Creek mine is Late Triassic based on fossils found in argillite intercalated with massive sulfides (Crafford, 1989). The Mammoth claims are patented and owned by Herman Meiners of Juneau, Alaska. The prospect is currently (2001) under lease to Red Diamond Mining Company, also of Juneau. The rocks in the general area are mainly Ordovician and Devonian to Triassic, clastic units, mafic-intermediate volcanic rocks, and subordinate limestone. The bedded rocks are intruded and locally metamorphosed by Cretaceous granodiorite (Gehrels and Berg, 1994).
Workings: The Mammoth prospect was discovered in the 1890's. From 1976 to 1988, Bear Creek Mining Company explored the Mammoth prospect by soil and stream-silt sampling, geologic mapping, and ground geophysics. Surface samples that assayed up to 0.085 ounce of gold per ton and 53.75 ounces silver per ton led to diamond drilling. Four holes were completed in 1987 and one in 1988. There is an adit on the Mammoth prospect and numerous surface pits and trenches.
Age: The Mammoth prospect is probably similar in age and origin to the nearby Greens Creek Mine that is Late Triassic based on fossils found in argillite intercalated with massive sulfides (Crafford, 1989).
Alteration: Intense quartz-sericite alteration.
Commodities (Major) - Ag, Au, Pb, Zn
Development Status: No
Deposit Model: Kuroko massive sulfide deposit (Cox and Singer, 1986; model 28a)
7 entries listed. 6 valid minerals.
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Crafford, T.C., 1989, The Greens Creek Ag-Au-Pb-Zn massive sulfide deposit, Admiralty Island, southeast Alaska: Alaska Miners Association, Juneau, April 20-21, 1989, Program with Abstracts, p. 27-29 Gehrels, G.E., and Berg, H.C., 1994, Geology of southeastern Alaska, in Plafker, George, and Berg, H. C., eds., The geology of Alaska: Geological Society of America, DNAG, The geology of North America, Vol. G-1, p. 451-467. Miller, L.D., and Barnett, J.C., 2000, The Mammoth claim group: Unpublished report for Red Diamond Mining Company, 14 p.