The Genetic Mineralogical Study Of Pyrite In The Huanxiangwa And Fancha Gold Deposits,Western Henan Province

The Xiaoqinling-Xiongershan area is one of the most important gold districts in China. There are mainly two gold mineralization types in this district: auriferous quartze vein and structural alteration type gold deposits. The auriferous quartze vein type gold deposits are dominant throughout the Xiaoqinling area, while the structural alteration type gold deposits are widely distributed in the Xiongershan area. Therefore, a detailed study on the two type deposits in the Xiaoqinling-Xiongershan district would give a clue to understand the geological causes for the separation of this two mineralization types, and provide new evidence for enrichment of the metallogenic theory of gold deposits and further summarize regional metallogenic regularity. A detailed geological, pyrite genetic mineralogical, and isotopic study has been carried out on the Fancha auriferous quartze vein type gold deposit and Huanxiangwa structural alteration type gold deposit, with a focus on an analysis of the ore-forming and separation mechanism of the two deposits.In the Fancha deposit, ore texture is granular, and structure is vein type; ore minerals include pyrite, chalcopyrite, galena, sphalerite, telluride and native gold, and gangue minerals are quartz and calcite. Gold minerals occur mainly as intergranular gold and inclusive gold. In the Huanxiangwa deposit, ore texture is metasomatic relicts, and structure is disseminated type; ore minerals include pyrite, chalcopyrite, galena, and sphalerite, and gangue minerals are k-feldspar, quartz, and minor biotite, chlorite, and calcite. Gold mineral occurs mainly as inclusive gold in pyrite. Wall rock alteration is similar in the two deposits, from the center to both sides of the orebody, and shows the following sequence: beresitization, silicification, potassic, and chloritization. The size and extent of wall rock alteration in the Huanxiangwa deposit are stronger than those in the Fancha deposit. The pyrites in the two deposits are mainly S-depleted pyrites, and show enrichment in large ion lithophile elements and LREE, and depletion in HFSE. The sulfur and lead isotope values, and trace elements of pyrites in the two deposits are consistent with those of Tahua group metamorphic rocks, but are different from those of Yanshanian magmatic rocks, suggesting the ore-forming materials originated from Tahua group metamorphic rocks. The study shows that the two deposits have similar physical and chemical condition, ore mineral assemblages, mineralogical characteristics of pyrite, ore-forming fluids, isotopic composition, and ore-forming materials, implying that the two deposits may belong to the similar metallogenic system. The metamorphic fluid moved upward along fractured zone, and replaced the wall rocks to form Huanxiangwa gold deposit. On the other hand, the metamorphic fluids moved upward the shallow crust and filled in open-space to form the Fancha gold deposit. Additionally, the differences in mineralization type, forming process, and temperature between the two deposits may be associated with tectonic environment.