TRANSPORTING STYLE AND DEPOSITIONAL MECHANISM OF GOLD IN THE QINGSHAN GOLD DEPOSIT, SHAANXI PROVINCE

The small-medium sized Qingshan gold deposit in Shaanxi Province, hosted in the Carboniferous sedimentary rocks, is of micro-fine dissemination type. The fluid inclusion is examined by atomic absorption spectrometry and gas chromatograph. Based on geochemical thermodynamics theory, the physical-chemical conditions of mineralization and the transportation style and deposition mechanism of the deposit are studied. The result shows that the metallogenic fluid is in weakly acid and reduced, belonging to calcium bicarbonate type, generally regarded as CO₂-H₂O-NaCl system, mainly derived from ancient meteoric water, and mixed with the meteoric water during later period. The gold in the metallogenic fluid transported as Au-Cl complexAu (HS)₂-in early mineralization stage, while as Au-S complexAu (HS)₂-in main and late stages. Change of physical-chemical conditions, such as temperature, salinity, pH, Eh and oxygen fugacity, as well as the mixing of meteoric water, water-rock reaction and sulfate reducing bacteria are the main factors causing the precipitation of gold.