The tops and bottoms of high-sulfidation epithermal ore deposits

摘要

High-sulfidation (HS) epithermal Cu-Au-(Ag) deposits form in a proximal position relative to volcanic vents of various styles. The characteristics of the near-surface portion of HS systems are influenced strongly by the paleogroundwater table and relief. Hypogene silicic (vuggy quartz) and advanced argillic (quartz-alunite) alteration forms where magmatic vapor condenses into groundwater. HS systems can be covered by a blanket of steam-heated acidic alteration; crater lake sediments are also common. The roots of HS alteration are typically controlled by structures, and these estend into narrow to broad zones of sericite +- pyrophyllite alteration, in places coupled in time and origin to underlying porphyry Cu-Au deposits.