Chemical and boron isotopic compositions of tourmaline in the Longtoushan hydrothermal gold deposit,

• 作者: Lihua Qian Jianqing Lai Shugen Zhang Lifang Hu Rong Cao Shilong Tao
• 学科: 地球科学
• 关键词: Longtoushan gold deposit Tourmaline Oreforming fluids Boron isotopes
• 年，卷（期）: 2022,（2）
• 页码范围: 277-291
• 页数: 14页
• 语种: 英文
• DOI: 10.1007/s11631-018-0292-5

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 Alh(NaR2□)-1, where R = Fe, Mg. In addition, minor substitutions include (CaMg)(NaAl)-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 tourmaline from the rhyolite porphyry crystallized during the magmatic-hydrothermal stage, whereas most tourmalines from the deposit formed in the post-magmatic hydrothermal stage. The tourmalines were deposited from a relatively reduced and acidic fluid system, and the gold predominantly precipitated during the post-magmatic hydrothermal stage in the Longtoushan deposit.