Abstract

Bladed quartz frequently is observed in low-sulfidation, epithermal gold deposits. Bladed calcite also has been documented in boiling zones of some active epithermal systems, and boiling in these systems has been directly linked to gold mineralization. In the Hishikari low-sulfidation epithermal gold deposit, the distribution and texture of fluid inclusions within bladed quartz reveal a similar relationship to gold precipitation.

The formation of bladed quartz at Hishikari involves several stages: (1) deposition of bladed calcite; (2) precipitation of fine-grained adularia and quartz on the surface of calcite blades; (3) dissolution of calcite blades, leaving cavities in the interstices between aggregates of adularia and quartz; and (4) infilling of the cavities by later quartz (i.e., pseudomorphs of the original bladed calcite). Bladed quartz is present largely in the deeper part of the vein system, beneath the high-grade gold ore zone at Hishikari. This distribution may be explained by the fact that the original bladed calcite formed at depth in the system, where boiling and loss of CO2 initially caused the precipitation of the calcite, and quartz formed as pseudomorphs of the original calcite blades.

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