On The Ore-forming Fluid In The Xikuangshan Antimony Deposit, Central Hunan

Abstract:The Xikuangshan antimony deposit is the largest antimony deposit throughout the world. Lots of researches had been undertaken on this deposit, but there still exist many different opinions on its sources of ore-forming fluids and ore-forming materials, as well as the ore genesis and metallogenic mechanism. Based on fluid inclusion geochemistry, combined REE geochemistry and stable isotope geochemistry the ore-forming fluids of the Xikuangshan deposit are systematically studied in this dissertation, and its metallogenic mechanism is further discussed. The major achievements have been obtained as follows:(1)The fluid inclusions in the stibnite can be divided into I-type(parallel to the axis) and Ⅱ-type(perpendicular to the axis) fluid inclusions. The fluid inclusions in gangue minerals including quartz, calcite, barite and fluorite were divided into liquid-rich and pure liquid fluid inclusions.(2)The ore-forming fluid in the Xikuangshan antimony deposit was characterized by low temperature (150-250℃), low salinity (<5wt%NaCl) and low density (<1g/cm5). Stibnite was easy to be deposited under the hypoxic fugacity, acidic environments.(3)REE distribution pattern of fluorite in the studied deposit is characterized by obvious LREE-depletion, MREE-and HREE-enrichment, and a weak negative Eu anomaly. MREE3+and HREE3+substituting Ca2+into fluorite are mainly controlled by their ionic radius, and REE distribution behaviors between fluorite and hydrothermal fluid are irrelevant with the stabilities of REE complexes in the ore-forming fluid. In addition, it is concluded that the fluorite formed under the reduced condition, and fluorite precipitation is predominately caused by the drastic variations in temperature and pressure. Ca and F in the fluorite should be derived from the host limestone and deep-seated magmatic rock in the mining district, respectively.(4)Early ore-forming fluid was of magmatic origin, but the late ore-forming fluid was mainly derived from meteoric water. (5)The mineralization mechanism of the Xikuangshan deposit can be summarized as follows:a Sb-and S-rich magmatic hydrothermal solution extracted the ore-forming element from the basement. When ore-forming fluid ascended near the surface, due to silicification alteration and the abrupt changes of physicochemical conditions including temperature, pressure and pH, stibnite precipitation took place in Devonian strata.