FLUID INCLUSION STUDY OF THE LINGLONG GOLD DEPOSIT, SHANDONG PROVINCE, CHINA

Abstract

The Linglong gold deposit is located in the east of Zhao-Ye Metallogenic Zone, which is in the northwest of Jiaodong Peninsula. It is one of the most typical super-large scale gold-bearing quartz vein type deposits. Metallogenic process can be divided into three stages, i. e. the early, meddle and late stages. The composition of fluid inclusion evolved in such a tendency that there are pure CO2(LCO2 + VCO2 > 90%) and CO2-rich type (10≤LCO2 + VCO2 ≤90%) in the early stage, and pure CO2, CO2-rich and CO2-bearing type (LCO2 + VCO2 <10%) in the middle stage, H2O-rich type in the last stage. Homogenization temperature of fluid inclusion in the three stages was 240°C ∼ 360°C, 220°C ∼ 340°C, 180°C ∼ 260°C and 80°C ∼ 180°C respectively; and the salinities are 3.4% ∼ 10.4%, 3.0% ∼ 10.2%, 4.0% ∼ 14.6% and 2.4% ∼ 5.0% NaCl eqv, respectively. The salinities of fluid increase gradually with the decrease of temperature during the, early and middle stages. Main metallizing process of Au took place from 320°C to 220°C. According to coexisting of CO2-rich and H2O-rich fluid inclusions, a boiling event is presumed in the late middle stage. From the early to the late stage, the tectonic events were recorded in various fluid inclusions. Especially, the inclusions which were sealed along the X-type fissures in the early stage quartz, not only recorded the tectonic events, but also reflected the characteristics of fluid when the events took place. Considering the fact that pyrite-quartz vein filled with extensional cracks during the main stage, it indicates the stress transformed from compressive to extensional condition. Decompressional boiling is assumed to be the main factor resulting in gold precipitation. Fluid pressure data show that their change was hysteretic than tectonic strain's. Considering orogenic event that occurred in Jiaodong peninsula, the stress transformed from compressive to extensional condition, and the characteristics low salinity, CO2-rich in ore fluid, Linglong gold deposit is assured a typic orogenic gold deposit.