Gold occurrence and pyrite trace elements in the Xiejiagou gold deposit, Jiaodong Peninsula, China: Implications for the mineralization process

Te–Bi bearing minerals are commonly present in many hydrothermal gold deposits and can provide important physicochemical constraints on their mineralization. The gold mineralization in the Xiejiagou gold deposit is hosted in the Mesozoic Linglong granite and consists of auriferous quartz veins and subordinate disseminated ores in the vein-proximal alteration zone. Three types of pyrite were identified that formed in stage I, II, and III. Gold occurs mostly as native gold and electrum (Ag > 20 wt.%) inclusions in or filling microfractures in pyrite. The abundant auriferous pyrite-quartz veins contain an assemblage of tsumoite and hessite. The tsumoite occurs as irregular inclusions in the Py₁ and is intergrown with the chalcopyrite. The hessite occurs as irregular inclusions or along the margins of the Py₂, and it coexists with the gold and galena. The tellurium fugacity continually decreased from stage I (log fTe₂ = −8.8 to −10.7) to stage III (log fTe₂ = −13.8 to −17.0). The sulfur fugacity increased from stage I (log fS₂ = −8.6 to −11.4) to stage II (log fS₂ = −7.2 to −11.4), and then, it decreased from stage II to stage III (log fS₂ = −9.8 to −13.0). These data indicate the conditions of the gold precipitation during the ore formation process. A detailed study of gold distribution in texturally different pyrite and the paragenetic association of tellurides provide valuable information on the distribution pattern of gold and in understanding the processes of gold deposition and evolution.