Abstract

The Huanzala mine is a zinc and lead mineral deposit found in the Lower Cretaceous Santa Formation limestone and has associated copper and accessory polymetallic minerals. Early-stage mineralization began with pyritization and was followed by middle-stage zinc and lead mineralization, occasionally accompanied by skarnization. The lead and zinc mineralization stage was followed by late-stage copper ore deposition, together with small amounts of silver-tin-tungsten and miscellaneous minerals.The pyrite orebodies can be grouped by texture into two kinds: compact and fine-grained, and loose and coarse-grained ore. The zinc ores are composed of two types: iron-rich sphalerite and iron-poor sphalerite. The iron-rich sphalerite contains only a few blebs of copper minerals, whereas the iron-poor sphalerite is characterized by many inclusions of copper minerals.The copper-bearing hydrothermal solution of the late-stage mineralization permeated the grain boundaries and cracks of the iron-rich sphalerite and converted it into iron-poor sphalerite. Petrographic observations suggest that iron-poor sphalerite was produced by a process involving extraction of iron from iron-rich sphalerite, and the combination of this iron with copper in the hydrothermal solution, resulting in precipitation of chalcopyrite and bornite.The compact, fine-grained pyrite ore was changed into the loose, coarse-grained type by the same hydrothermal solution which transformed the iron-rich sphalerite into the ironpoor type.Late-stage copper ores were produced by mineralization ofchalcopyrite, bornite, tennantite, and enargite, followed by scheelite, cassiterite, stannite, canfieldite, hocartite, argentite, and other miscellaneous minerals. Mineralization of enargite was accompanied by bornite and was followed by chalcopyrite and tennantite. In several stages tennantite was deposited simultaneously with bornite and also with chalcopyrite.Studies of these paragenetic relationships, together with consideration of the orebody formation temperature and thermochemical treatment of the ore-forming minerals, suggest that with a decline in temperature the mineralization proceeded toward low f (sub S 2 ) and low f (sub O 2 ) .

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