Physical Volcanology, Hydrothermal Alteration and Massive ...

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32003000280026002400220020001800FE 1600ET1400120010008006004002000LEGEND OF GEOLOGICAL UNITS( INTCf')No Nome Lake Success lotiL Sl,lGCe9S 101Upper L - Ouortz o~d ploQiocIQ'" crYS'ol ic breccia (t.4esobrecl;jo)(ULPYF)(LSED)(8RDL. 8RrL)(hlLPYF)(8ROL)(LLPyF.L .....T)(MT ..... )(MTC)( TLDFS)(TLA)(HLPyn~~t~~~Jackpot L(Jl
HYDROTHERMAL ALTERATIONHydrothermal solutions, both ore-forming and non-ore-forming, have altered thevolcanic rocks associated with the Sturgeon Lake Caldera Complex. Following alteration,these rocks were metamorphosed to greenschist facies. Therefore, the alteration mineralsnow present are, in part, metamorphosed equivalents of the alteration minerals formed inthe hydrothermal system.Hydrothermal fluids formed five distinct, mappable massive sulphide ore-associatedalteration assemblages in the area. From least- to most-altered, these assemblages are:a) widespread, semiconformable carbonatization and silicification; b) widespread,semiconformable iron carbonate ± iron chlorite; c) widespread, semiconformable chloritoid± iron carbonate and/or iron chlorite; d) lens- to pod-like, locally linear zones of aluminumsilicate (pyrophyllite, andalusite, and/or kyanite) + chloritoid; and e) linear cross-cutting,and stratiform zones of aluminum silicate.alteration locally overprints these five alteration assemblages.Late sericite and/or magnesium-rich chloriteIron formation-associatedalteration composed of patches to cross-cutting veinlets of iron carbonate + iron chlorite+ magnetite ± garnet ± grunerite is present in the uppermost sections of the L succession.Iron carbonate ± iron chlorite assemblage rocks contain at least 10% iron carbonate+ iron chlorite with less than 5% chloritoid or aluminum silicate minerals. Outcrops whichcontain abundant iron carbonate are easily identified by their orange to orange-brownstained, commonly pitted surfaces. Staining varies from irregular, lens-shaped patchesup to 15 cm in diameter, to veins and veinlets 1-15 mm in width that are aligned parallelto the foliation. Pumice that has been replaced by carbonate can be recognized asrounded to oval, orange-brown stained pits up to 5 cm in diameter which commonly containrounded to lens-shaped quartz-filled amygdules (10-60%). In thin section, thisassemblage contains iron carbonate ± iron chlorite (10-60%), sericite (up to 30%), Mg-richchlorite (0-50%), and locally, traces of chloritoid or aluminum silicate minerals.Chloritoid ± iron carbonate and/or iron chlorite assemblage rocks contain greaterthan 5% chloritoid, and are characterized by the presence of 1-3 mm dark green to blackchloritoid prisms and rosettes. The presence of the chloritoid commonly gives the rocksa "salt and pepper" appearance. Locally, chloritoid porphyroblasts occur with sericite (10-17
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Page 39 and 40: REFERENCESBusby - Spera, C., 1984,
Page 41: associated with the Lyon Lake massi

Physical Volcanology, Hydrothermal Alteration and Massive ...

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