Mineralization Of The Huangshui'an Carbonatite Mo Deposit In East Qinling

The carbonatite Mo deposit,located in the East Qinling molybdenum belt,is a unique and new deposit type.A few carbonatite Mo deposits have been discovered in recent years,while the magmatism and metallogenesis are not well studied.To solve this problem,the large Huangshui'an deposit was selected as an object for this study.Hopefully,a comprehensive understanding of the carbonatite Mo deposit will be formed by studying magmatism and mineralization.The Huangshui'an Mo deposit is hosted in the gneiss of the Archean Taihua Group.The orebodies is composed mainly of mineralized carbonatite dykes.Molybdenite,with main types of disseminated mineralization distributes in the carbonatite dykes.Ore-related hydrothermal alteration includes K-feldspathization,silicification,carbonatization etc.Four mineralization stages have been recognized:silicate-sulfide stage???,carbonatite-sulfide-sulfate stage???,sulfide-telluride stage???and carbonate stage???.The carbonatite-sulfide-sulfate stage is the main molybdenite mineralization stage,and the sulfide-telluride stage is represented by the mineral assemblage of carbonate,sulfides,tellurides and bismuthide.The Huangshui'an carbonatites occur as dykes,mainly consisting of pink calcite.The C and O isotope composition of calcite from the Huangshui'an carbonatite is remarkably uniform(?¹³C_PDB=-4.7 to-5.3‰and?¹⁸O_SMOW=7.1 to 8.2‰),indicative of a mantle source.The geochemistry of whole rock is similar with that of calcite from the Huangshui'an carbonatite.Calcite and barite in Huangshui'an carbonatites have ⁸⁷Sr/⁸⁶Sr ratio of 0.7060962-0.7062713 and 0.7060376⁰.7062310,respectively,closing to that of EM1 mantle region.Hydrogen and oxygen isotopic compositions indicate that magma fluid is the main ore forming fluid.The fluid inclusions in the Huangshui'an deposit is abundant and characterized by plenty of CO₂-rich and daughter miners-bearing fluid inclusions,indicative of carbonic fluid.The ore forming fluid derived from the Huangshui'an carbonatites.The original ore forming fluid belongs to a SO₄^2--NaCl?KCL?-CO₂-H₂O system,with high temperature,high salinity and rich CO₂.Phase separation of CO2and aqueous is occurred in the main mineralization stage and considered as the dominant fator for molybdenite precipitation.The deposit has the?³⁴S_?S of 1‰,indicative of a mantle source.The remarkably homogeneous lead isotope compositions of pyrite and galena,approach that of a EM1-like mantle region,which is well coincident with that of calcite from the Huangshui'an carbonatite.Synthetical carbon,oxygen,sulfur and lead isotope compositions show that rock-forming and ore-forming materials are derived from an analogous EM1-like mantle region.Eight molybdenite-bearing samples yielded model ages ranging from?207.9±3.0?Ma to?210.9±3.8?Ma,indicative of the mineralization in Late-Triassic.The deposit formed in the extensional period of post-collision orogenic process between North China and Yangtzi cratons.