Ore-forming fluids associated with granite-hosted gold mineralization at the Sanshandao deposit,Jiaodong gold province,China

【摘要】：正The Sanshandao gold deposit,with total resources of more than 60 t of gold,is located in the Jiaodong gold province,the most important gold province of China.The deposit is a typical highly fractured and altered.disseminated gold system,with high-grade, quartz-sulphide veinveinlet stockworks that cut Mesozoic granodiorite.There are four stages of veins that developed in the following sequence:(1)quartz-K-feldspar -sericite;(2)quartz-pyrite±arsenopyrite;(3)quartzbase metal sulfide;and(4)quartz-carbonate.Fluid inclusions in quartz and calcite in vein veinlet stockworks contain C-O-H fluids of three main types.The first type consists of dilute CO_2-H_2O fluids coeval with the early vein stage.Molar volumes of these CO_2-H_2O fluid inclusions,ranging from 50-60 cm~3/mol,yield estimated minimum trapping pressures of≥3 kbar. Homogenization temperatures,obtained mainly from CO_2-H_2O inclusions with lower CO_2 concentration, range from 267-375℃.The second inclusion type,with a CO_2-H_2O±CH_4 composition,was trapped during the main mineralizing stages.These fluids may reflect the CO_2-H_2O fluids that were modified by fluid/rock reactions with altered wallrocks.Isochores for CO_2- H_2O±CH_4 inclusions,with homogenization temperatures ranging from 204-325℃and molar volumes from 55 to 70 cm~3/mol,provide an estimated minimum trapping pressure of 1.2 kbar.The third inclusion type, aqueous inclusions,trapped in cross-cutting microfractures in quartz and randomly in calcite,are post-mineralization, and have homogenization temperatures between 143-228℃and salinities from 0.71-7.86 wt% NaCl equiv.Stable isotope data show that the metamorphic fluid contribution is minimal and that ore fluids are of magmatic origin,most likely sourced from 120- 126 Ma mafic to intermediate dikes.This is consistent with the carbonic nature of the fluid,and the crosscutting nature of those deposits relative to the host Mesozoic granitoid.