Zhengminghuaite:A new mineral from Carlin-type gold deposits in southwest-ern Guizhou and its metallogenic significance
Zhengminghuaite is a new sulfosalt mineral recently found in the Zimudang Carlin-type gold deposit in southwestern Guizhou. Based on an overview of occurrence,physical and optical properties,chemical composition and crystal structure of the new mineral,the major purpose of this contribution is to document the geological background,microtextures,and relations to other mineral species of isotypic series,and combined with paragenetic sequence,to discuss the formation condition of the new mineral. Zhengminghuaite occurs in fault-controlled brec-ciated gold ores and is paragenetically associated with the late ore-stage quartz,realgar,calcite,and minor to trace amounts of As-Sb-Hg-Tl sulfides and sulfosalts. Zhengminghuaite is opaque and brittle with a metallic luster. It shows no cleavage and has a Mohs hardness of～4. In reflected light,zhengminghuaite is whitish gray,with no to weak bireflectance and reflection pleochroism,very weak anisotropy,and a reflectance of 23％～29％ (546 nm).Zhengminghuaite is trigonal,with space group R3 and unit-cell parameters of a=13.5373(17) Å,c=9.2354(13) Å,and V=1465.7(4) Å3 (Z=3). It belongs to a new member of the nowackiite isotypic series with an ideal formula of Cu6Fe3As4S12. Paragenetic relationships indicate that zhengminghuaite precipitated after the deposition of aurifer-ous arsenian pyrite and arsenopyrite,but was prior to the bulk deposition of realgar,during which the sulfur fugac-ity (f(S2)) of the ore fluid increased by 1～2 log units and the temperature decreased by 60～100℃.
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