Abstract:

The Liangshan molybdenum is one of molybdenum deposits recently discovered in central Jiangxi Province. Its major molybdenite ore bodies are situated within the tectonic fissures of Nanhua system low-grade metamorphic rocks, and molybdenite-quartz veins are the main mineralization types.Fluid inclusions in quartz veins suggest that these inclusions are distributed in groups or scattered stars randomly with long axes of 2-15 microns.There are four types of fluid inclusions, including pure liquid inclusions, gas-rich two-phase inclusions, liquid-rich two-phase inclusions and liquid phase CO₂-bearing three-phase inclusions. Liquid-rich two-phase inclusions are the main type of fluid inclusions.The homogenization temperatures range from 136 to 298 ℃, the salinities range from 1.22% to 10.11% NaCleqv and the density range from 0.78 to 0.99 g/cm³, indicating medium-low temperature, low salinity and lower density.The ore-forming pressure is estimated at 13 to 70 MPa, and the depth is about 0.5 to 2.6 km. The inclusions in gas and liquid ingredients all are mainly composed of H₂O with a small amount of CO₂ and CO in gases by the test of Laser Raman spectroscopy. The hydrogen and oxygen isotopic compositions of the ore-forming fluids show that δD values of the ore-forming fluid are between -61‰ and -57.9‰, and δ¹⁸OH₂O are between -3.32‰ and -0.52‰, which indicates that the ore-forming fluids were derived from the mixing of magmatic water and meteoric water.The sulfur isotope compositions of ore-forming fluid show that δ³⁴S values of the ore-forming fluid are between -1.8‰  and +1.9‰, which indicates that the sulfur of ore-forming fluid has the characteristics of the sulfur of magma source. Our comprehensive studies suggest that the ore-forming fluid of the Liangshan molybdenum deposit is related with the Yanshannian magmatic activities, the mixing of magma fluid with the meteoric water and later potassic alternation are two main factors to ore-forming material enrichment and precipitation. Therefore, it is proposed that the Liangshan molybdenum deposit is a typical hydrothermal filling quartz vein type deposit related with magmatic activities.

Key words: Liangshan molybdenum deposit, fluid inclusion, ore-forming fluid, Laser Raman spectroscopy, quartz vein type molybdenite deposit, Jiangxi