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Gold/Mining/Energy : Gold and Silver Juniors, Mid-tiers and Producers -- Ignore unavailable to you. Want to Upgrade?

To: E. Charters who wrote (19935)	9/3/2006 5:26:50 PM
From: teevee	Read Replies (1) \| Respond to of 78408

gac.esd.mun.ca Geology of the Greens Creek Mining District, Northern Admiralty Island, southeast Alaska Duke, N.A., University of Western Ontario, London, ON, N6A 5B7, West, A., Kennecott Greens Creek Mining Co., P.O. Box 32199, Juneau, AK, 99803-2199, and Lindberg, P.A., 205 Paramount Dr., Sedona, AZ, 86336 The Greens Creek deposit occurs within the core of the Admiralty Subterrane of Alexandria. The host tectonostratigraphic assemblage constitutes late Paleozoic back arc basement and its upper Triassic flood basalt cover sequence. The Admiralty back arc basin was volcanically active into the Devonian, giving rise to Retreat Group greenstones. The Mississippian through Permian Cannery Group includes older deep-marine siliciclastics and a younger shallow-marine dolomite-chert facies. The uppermost Pybus Chert signals the termination of back arc sedimentation through shoaling accompanying the amalgamation of Alexandria and Wrangellia in the mid-Permian. The post-amalgamation unconformity ended with late Triassic rifting driven by the Nikolai plume. The Greens Creek deposit is hosted in Karnian/Norian-age black argillite occurring below the Hyd flood basalts. Protracted compressional tectonism attended the suturing of Wrangellia to North America during the Laramide. Cretaceous subduction caused fold and thrust-style imbrication, and severe strike-slip dislocation accompanied dextral-transpression on the Tertiary Denali system. The back arc succession and its cover were decoupled; inversely metamorphosed Hyd Group thrusts are stacked south of the mine. The Greens Creek deposit occurs in low grade phyllites making up the lowest thrust plate. This domain is bound by major ductile shears along Hawk Inlet and Young Bay. Brittle fault/fracture sets are common, with the Maki Fault dextrally offsetting mineralization about 500 meters. The Hyd Group is subdivided into basal growth-fault breccia/conglomerate, medial Mine Argillite and upper Basalt members. At the mine, Retreat greenstone interleaved with sheets of serpentinite and lesser gabbro is intensely hydrothermally altered, forming Mine Phyllite in the stratigraphic footwall of the ore. Occurrence of barian mariposite ties hydrothermal alteration to the time of serpentinite injection. High grade laminated ores at the base of Mine Argillite stratigraphically overlie carbonate-barite replacement ores within Mine Phyllite. Exhalative ores are capped by bedded pyrite, and bands of Mn-dolomite persist into overlying slaty argillite. Greens Creek is unique in that it comprises high-grade Zn-Pb-Ag ores at a major unconformity in a juvenile oceanic arc setting. The deposit is linked to an active rift segment plumbed by sepentinite/gabbro and filled with euxenic argillite. Gabbro sills intruding Mine Argillite have the same geochemistry as Hyd Basalt, thus tying rifting to the Nikolai plume. Although somewhat of a VMS/SEDEX hybrid, the Greens Creek setting lacks the felsic volcanics that characterise polymetallic Kuroko-type VMS districts. The evident link to a growth-fault controlled, starved, sedimentary trough favours placing Greens Creek in the SEDEX class.