Characteristics And Sources Of The Ore-forming Fluids Of Jiuqu Gold Deposit In Linglong Jiaodong

The Linglong Jiuqu gold deposit in Jiaodong is a quartz vein type gold deposit.In this paper,the geological characteristics,fluid inclusions and isotopic geochemistry of the typical"quartz vein type"gold deposit are studied in detail,and the ore-forming fluid,material source and fluid evolution mechanism are discussed:(1)According to the characteristics of mineral interpenetration,wall rock alteration and mineral assemblage,the gold mineralization of Linglong Jiuqu gold deposit can be divided into four metallogenic stages:pyrite-quartz-sericite stage(I),quartz-pyrite stage(II),quartz-polymetallic sulfide stage(III),quartz-carbonate stage(IV).(2)By calculating and analyzing the micro temperature measurement data of inclusions,it is found that the ore-forming fluid of Linglong Jiuqu gold deposit is characterized by medium low temperature and low salinity.The temperature and salinity of ore-forming fluid gradually decrease from early to late mineralization,and the fluid pressure also decreases.The salinity,pressure and temperature of fluid are positively correlated during mineralization,and the density is negatively related to temperature.The ore-forming fluid is H₂O-Na Cl-CO₂system as a whole,and the content of CO₂gradually decreases in the late stage of mineralization.(3)The Sr-Nd and S isotopic characteristics of pyrite indicate that the ore-forming materials of Linglong Jiuqu gold deposit are mainly derived from the enriched lithospheric mantle,and a small amount from Jiaodong Group and basic dikes,with the characteristics of crust mantle mixing;The H-O isotopic characteristics of quartz indicate that the ore-forming fluid was derived from deep magmatic fluid,and a small amount of meteoric water was mixed in the late stage of mineralization;The C-O isotopic characteristics of calcite are very close to that of mantle source,indicating that mantle source material was added into the gold deposit.(4)Based on the above research results,the magmatic fluid enriched from lithospheric mantle metasomatized with Linglong granite formed before mineralization in the process of upward migration to the crust,forming early potassium alteration.During the metallogenic period,the tectonic setting gradually changed from compression to extension,and the ore-forming fluid became immiscible with the decrease of pressure,gold began to accumulate and precipitate,and the temperature and salinity of the fluid gradually decreased,In the late stage of mineralization,a small amount of meteoric water was mixed in,which made the fluid temperature and salinity to the lowest.The whole mineralization ended,and finally the quartz vein type Linglong Jiuqu gold deposit was formed.