Abstract:

Chaganhua porphyry molybdenum deposit is a newly discovered large-scale deposit in central Inner Mongolia. Ore bodies are mainly hosted in the greisenizated and silicified granite. Molybdenum mineralization is closely associated with greisenization and silicification and is characterized by quartz-molybdenum-muscovite and quartzmolybdenum stockwork veins. Fluid inclusions in quartz of the major metallogenic stage and late molybdenum mineralization are mainly two-phase vapor-liquid inclusions with small amount of CO₂ phase. The homogenization temperatures and salinities of inclusions in major stage vary from 147℃ to 387℃, 2.6% to 8.6 % NaCl equivalent, and in late molybdenum mineralization vary from 161℃ to 322℃, 0.4% to 6.5% NaCl equivalent, respectively. The oxygen isotopic fractionation temperatures in quartz and muscovite associated with molybdenum mineralization vary from 384℃ to 653℃, which represent the mineralization temperatures and are higher than the homogenization temperatures of fluid inclusions. Studies show that the molybdenum began to deposit at 653℃, 200 MPa (approximately 7.4 km of lithostatic pressure) and mainly deposit from 416℃ to 384℃, 65 MPa to 40 MPa (approximately 6.5 km to 4 km of hydrostatic pressure). The inclusions data, together with H-O isotope data, record an evolution path of the hydrothermal fluid of degassed magma water source from high temperature, pressure and moderately low salinity to low temperature, pressure and salinity, which resulted in Chaganhua porphyry molybdenum deposit.

Key words: porphyry, molybdenum deposits, fluid inclusion, H-O isotopes, oxygen isotopic fractionation temperatures, Chaganhua, Inner Mongolia