CHAI Peng;ZHANG Zhiyu;HOU Zengqian;Institute of Geology, Chinese Academy of Geological Science;
Institute of Geology, Chinese Academy of Geological Science;
The Dayingezhuang gold deposit, hosted mainly by Late Jurassic granitoids on Jiaodong Peninsula in eastern China, contains an estimated 170 t of gold and is one of the largest deposits within the Zhaoping fracture zone. The orebodies consist of auriferous altered pyrite–sericite–quartz granites that show Jiaojia-type(i.e., disseminated and veinlet)mineralization. Mineralization and alteration are structurally controlled by the NE-to NNE-striking Linglong detachment fault. The mineralization can be divided into four stages:(K-feldspar)–pyrite–sericite–quartz, quartz–gold–pyrite, quartz–gold–polymetallic sulfide, and quartz–carbonate, with the majority of the gold being produced in the second and third stages. Based on a combination of petrography, microthermometry, and laser Raman spectroscopy, three types of fluid inclusion were identified in the vein minerals: NaCl–H2 O(A-type), CO2–H2 O–NaCl(AC-type), and pure CO2(PC-type).Quartz crystals in veinlets that formed during the first stage contain mainly AC-type fluid inclusions, with rare PC-type inclusions. These fluid inclusions homogenize at temperatures of 251°C–403°C and have low salinities of 2.2–9.4 wt%NaCl equivalent. Quartz crystals that formed in the second and third stages contain all three types of fluid inclusions, with total homogenization temperatures of 216°C–339°C and salinities of 1.8–13.8 wt% NaCl equivalent for the second stage and homogenization temperatures of 195°C–321°C and salinities of 1.4–13.3 wt% NaCl equivalent for the third stage. In contrast, quartz crystals that formed in the fourth stage contains mainly A-type fluid inclusions, with minor occurrences of AC-type inclusions; these inclusions have homogenization temperatures of 106°C–287°C and salinities of 0.5–7.7 wt%NaCl equivalent. Gold in the ore-forming fluids may have changed from Au(HS)0 as the dominant species under acidic conditions and at relatively high temperatures and f O2 in the early stages, to Au(HS)2– under neutral-pH conditions at lower temperatures and f O2 in the later stages. The precipitation of gold and other metals is inferred to be caused by a combination of fluid immiscibility and water–rock interaction.
fluid inclusion;;gold deposition;;Dayingezhuang gold deposit;;Jiaodong Peninsula