南大别山地区白石山高纯石英矿床成因研究OA

Objectives:High-purity quartz is an extremely important strategic mineral resource and plays an important role in multiple high-technology fields.The Baishishan deposit in the south Dabie Mountains is a renowned vein-type quartz deposit within the Tongbai—Dabie metallogenic belt of China.Previous beneficiation experiments on quartz ore from this deposit have yielded a purified product with a SiO2 content of 99.996％,which meets the criteria for high-purity quartz.An investigation into the genesis of the Baishishan deposit therefore has indicative significance for the prospecting of vein-type quartz deposits that could serve as sources of high-purity quartz raw materials. Methods:This study conducted fluid inclusion microthermometry to measure and calculate homogenization temperatures,freezing temperatures,and salinities,combined with quartz hydrogen—oxygen isotope analyses,to investigate the source of ore-forming materials and the ore-forming processes of the Baishishan deposit in the south Dabie Mountains.We selected samples with well-developed muscovite for electron microprobe analysis to determine the muscovite composition,and performed Rb—Sr isotopic dating of muscovite to constrain the metallogenic age of the Baishishan deposit in the south Dabie Mountains. Results:Fluid inclusions in vein quartz from the Baishishan deposit are predominantly primary gas—liquid two-phase inclusions.Microthermometric measurements yielded homogenization temperatures ranging from 164.8 ℃to 330℃,with the majority ranging from 190℃ to 250℃ and an average of 220.15 ℃.Freezing temperatures range from-20.1℃ to-0.2℃,with the majority ranging from-12℃ to-4℃ and an average of-8.74 ℃.Based on these freezing temperature measurements,we calculated salinities ranging from 0.35％to 22.4％NaCleqv,with an average of 11.87％NaCleqv.The homogenization temperatures and salinities of fluid inclusions in the Baishishan deposit show a certain negative correlation.The δD—δ18O diagram of quartz from the Baishishan deposit reveals that the data points of ore-forming fluids exhibit a linear distribution,falling between the metamorphic water line and the meteoric water line.The δDV-SMOW values range from-69‰ to-27‰,with an average of-41‰,which fall within the range of typical metamorphic water(-70‰ to-20‰).Oxygen isotope compositions are relatively stable,with δ18OH2O values ranging from-1.1‰ to-0.1‰ and an average of-0.6‰.Electron microprobe analyses confirm that the muscovite coexisting with quartz in the Baishishan deposit is common muscovite and formed contemporaneously with quartz.Rb—Sr isotopic dating of muscovite yielded a metallogenic age of 190.6±1.5 Ma. Conclusions:The Baishishan High-purity quartz deposit in the south Dabie Mountains formed during the late Indosinian period.We interpret its formation as closely related to dehydration reactions that occurred during the retrograde metamorphism of ultra-high-pressure metamorphic rocks,such as eclogite,as they were exhumed.The ore-forming fluids of the Baishishan deposit was primarily derived from metamorphic hydrothermal fluids.The fluids were likely dominated by metamorphic water during the early stage,with subsequent influx of meteoric water or other external fluids during the later evolution of the ore-forming system,resulting in significant fluctuations in hydrogen isotopic compositions.Such variations in geochemical characteristics may be closely related to ore-forming processes including hydrothermal circulation mechanisms,fluid boiling phenomena,or fluid—wallrock metasomatic reactions.