Characteristics of ore-forming fluids and sources of ore-forming materials in the Dongyuan W-Mo deposit, southern Anhui Province

Abstract：Lying in Qimen City of Anhui Province, the Dongyuan W-Mo deposit is the largest W-Mo deposit so far discovered in this region. Its major W-Mo ore bodies are mainly hosted in granodiorite porphyry and near the contact zone, and mineralization is mainly of veinlet dissemination and dissemination types. Geochemical study of fluid inclusions shows that gas components of fluid inclusions are mainly H2O and CO2, with minor amounts of such components as C2H4, N2 and CH4. Liquid components of fluid inclusions are mainly Ca2+, Na+, SO2-4 and Cl-, with subordinate K+ and F- and small amounts of Mg2+, NO-3 and Br-. Studies of hydrogen, oxygen, sulfur and lead isotopes show that δ18Owater‰ values of the inclusions in quartz range from -0.498‰ to 3.102‰, and δDwater‰ values of quartz range from -85‰ to -66‰, suggesting that the ore-forming fluid was mainly derived from the mixed meteoric water and magmatic water. δ34SV-CDT‰ values of pyrite range from 2.6‰ to 5.8‰, implying that sulfur might have been derived from the Dongyuan granodiorite intrusion as a result of the leaching of ore-forming fluids. The lead isotope have a small range of values, and its source has obvious mixing characteristics. The ore-forming fluids in the metallogenic process experienced immiscibility or boiling and mixing with heated meteoric water, and thus changed the physical and chemical conditions of the ore-forming fluid system, causing unstableness of W and Mo complexes in the system and resulting in the precipitation, precipitation and enrichment of large quantities of ore-forming materials to form the ore deposit.