Hydrothermal alteration geochemistry of the Qianhe gold deposit in western Henan Province

Abstract：Hydrothermal alteration is caused by fluid-rock interaction in the migration process of the ore-bearing hydrothermal fluids. The hydrothermal alterations of the Qianhe gold deposit might be divided into seven types, namely potash feldspathization, propylitization, sericitization, silicification, pyritization, carbonation and fluoritization. The alteration-mineralization process and the alteration zones can be divided respectively into six stages and three zones, in order of botite-potash feldspar stage→propylite stage→phyllic stage→pyrite-quartz stage→quartz-pyrite stage→carbonate-halide stage, forming outer, central and inner zones. Analyses of major and trace elements for five typical altered rocks indicate that, during phyllic alteration, Si, K, Pb increased considerably and HREE concentrated a bit with the slight decrease of REE. Negative anomalies of δEu and δCe were present in each alteration-mineralization stage. These factors might be responsible for gold precipitation. The metasomatic characteristics of fluid-rock interaction at every ore-forming stage are also reflected in chemical composition variation of chlorite.