GEOLOGY, LITHOGEOCHEMISTRY, AND ALTERATION OF THE BATTLE VOLCANOGENICMASSIVE SULFIDE ZONE, BUTTLE LAKE MINING CAMP, VANCOUVER-ISLAND, BRITISH-COLUMBIA

Volcanogenic, poly-metallic massive sulfide deposits within the Buttle Lake mining camp occur within the felsic volcanic and volcaniclastic rocks of the Myra formation that immediately overlies Price formation andesite. These units comprise the lower exposed part of the Paleozoic Sicker Group in tile Buttle Lake uplift in central Vancouver Island. The Sicker Group represents a volcanic island al-c that forms the base of the allochthonous Wrangell terrane. The Battle Main zone contains 2.3 million tons (Mt) of proven and probable reserves grading 1.3 g/t Au, 25.3 g/t Ag, 2.5 percent Cu, 0.5 percent Pb, and 13.2 percent Zn. Overall, the Buttle Lake camp hosts geologic about 12.5 Mt. The Battle Main massive sulfide zone occurs nil hin the H-W horizon, tile lowest member of the Myra formation, immediately above tile Price formation andesite. Price formation andesite is over 300 m thick in the vicinity of the camp and consists of feldspar +/- pyroxene porphyritic basalti c andesite flows. Synvolcanic block faulting of this unit formed the r egional-scale Buttle Lake camp basin with a strike length of at least 10 lull. Local sub-basins in this major structure contain the sulfides and felsic volcanic rocks of the H-W horizon. The H-W horizon is a 15 - to 200-m-thick felsic package that extends throughout the basin. It consists of eight members, three of which represent periods of massive sulfide deposition. From the stratigraphic base to the top of these m embers are (1)the Battle Main massive sulfide lens, (2) fine rhyolitic tuffaceous deposits, (3) H-W mafic sills, (4) Gap massive sulfide len s; (5) coarse rhyolite pyroclastic deposits, (6) rhyolite tuffaceous a nd cherty sediments, (7) Battle Upper massive sulfide lenses, and (8) a tripartite rhyolite flow-dome complex consisting of quartz porphyrit ic rhyolite, quartz-feldspar porphyritic rhyolite, and green quartz-fe ldspar porphyritic rhyolite. Volcaniclastic units in the felsic packag e evolved with interfingering of subaerial and submarine pyroclastic p rocesses. Plow-dome units evolved by fractionation of quartz and felds par. Alteration, evaluated petrographically and with Pearce element ra tios, is most intense close to synvolcanic and synmineral feeder fault s that channeled solutions through the Price formation andesite proxim al to the Battle Main massive sulfide lens. Envelopes to tile feeder f a;lts have distinctive Mg addition anomalies and contain the mineral a ssemblage pyrite > sericite > quartz > chlorite. Discharge feeder stoc kworks immediately below the Battle Main massive sulfide lens contain varying proportions of sericite, quartz, and pyrite but lack significa nt chlorite. Deposition of tile H-W horizon rhyolitic units on top of tile Battle Main massive sulfide lens did not halt mineralization. Rat her, fluids continued to percolate upward through tile newly deposited rhyolitic units and deposited the Battle Upper lenses close to tile n ew sediment-water interface. Alteration below the Battle Upper lenses consists of quartz, sericite, and pyrite with minor galena, sphalerite , and tennantite. Overall, hydrolysis of feldspar in both tile Price f ormation and the II-SV horizon resulted in a halo surrounding the ore lenses marked by addition of I(and concomitant Na and Ca depletion.