Chemical and boron isotopic compositions of tourmaline in the Longtoushan hydrothermal gol

Chemical and boron isotopic compositions of tourmaline in the Longtoushan hydrothermal gold deposit, Guangxi, China:implications for gold

mineralization

Lihua Qian;Jianqing Lai;Shugen Zhang;Lifang Hu;Rong Cao;Shilong Tao

【期刊名称】《中国地球化学学报（英文版）》 【年(卷),期】2024(038)002

【摘要】The Longtoushan hydrothermal gold deposit is located in the southwestern region of the Dayaoshan Uplift.Tourmaline is widespread in the Longtoushan gold deposit and is mainly distributed in the rhyolite porphyry and associated cryptoexplosive breccia.The spatial distribution of tourmaline enrichment is similar to that of the gold orebody.Feldspar has been largely replaced by tourmaline in the rhyolite porphyry and cryptoexplosive breccia.Electron microprobe analysis revealed that tourmalines in the Longtoushan deposit belong mainly to the alkali group and partly to the X-vacant group;they mostly fell in the schorl-dravite series field.Two distinct sets of dominant substitutions were observed:MgFe-1 and Al□(NaR2+)-1,where R =Fe,Mg.In addition,minor substitutions include (CaMg)(NaA1)-1 and FeAl-1.The calculated δ11B value for the mineralizing fluids ranged from-12.8 to-9.7％,which is typical of S-type granites,and boron-enriched fluids predominantly derived from rhyolitic melt.Part of the