Enrichment Mechanism of Gold in the Yanlinsi Gold Ore Concentration Area, Northeastern Hunan: Evidence from Fluid Inclusions and Isotopes
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摘要: 湘东北雁林寺金矿集区是湖南重要的独立金矿产基地之一, 一直以来众多学者对于矿集区内金的沉淀富集机制争论不休。本文通过对金矿成矿流体包裹体及同位素组成研究, 反演了成矿流体演化过程和流体地球化学条件变化, 了解了金富集成矿的关键机制。研究结果表明: 矿集区内的金矿床流体包裹体类型有含CO2 包裹体(C 型)和水溶液包裹体(W 型), 包裹体均一温度范围主要为143～231 ℃, 盐度主要分布在(2～9) wt% NaClequiv, 成矿流体为中低温、低盐度的CO2-H2O-NaCl 体系。矿集区的成矿流体δ18O 值范围为4.5‰～9.7‰, δD 值的变化范围为–66.8‰ ～ –46‰。方解石 δ13CVPDB 为–4.7‰ ～ –3.7‰, δ18OSNOW 为10.6‰～15.0‰。矿集区的C-H-O 同位素组成表明成矿流体性质可能为变质水, 与流体包裹体特征反应的结果一致。矿集区内Au 以 络合物形式赋存于低温、低盐度的CO2-H2O-NaCl 变质流体体系进行迁移, 流体的不混溶作用是金矿富集成矿的关键。Abstract: The Yanlinsi gold ore concentration area, located in northeastern China, remains one of the single gold deposit bases in Hunan Province. The mechanism of gold precipitation and enrichment in this area has been widely debated among scholars, and determining the metallogenic mechanism of gold deposits is crucial for guiding the prospecting of precious metal gold. This study identifies the evolution process of ore-forming fluids and the key mechanism of changes in fluid geochemical conditions that restrict gold enrichment and mineralization in the area by examining the temperature, pressure, gas-liquid phase composition, and isotopic compositions of fluid inclusions. Petrography and microthermometry of the fluid inclusions revealed the presence of CO2-containing inclusions (C-type) and aqueous inclusions (W-type) in the gold deposits of the study area. The homogenization temperature range of the inclusions in Tuanshanbei and Yanlinsi deposits is 143–231 ℃ and the salinity range is (2–9) wt%, indicating that the ore-forming fluid is a CO2-H2O-NaCl system with low temperature and low salinity. The δ18O value of the ore-forming fluid in the gold ore concentration area range from 4.5‰ to 9.7‰, and the δD value range from –66.8‰ to –46‰. The δ13CVPDB value of the calcites range from –4.7‰ to–3.7‰, and δ18OSNOW value range from 10.6‰ to 15.0‰. The δD-δ18O binary diagram of the gold ore concentration area suggests that the ore-forming fluid may be metamorphic water or magmatic water. The C-H-O isotope composition of the ore concentration area indicated that the ore-forming fluid is likely metamorphic water, consistent with the results of the fluid inclusion characteristics. Au exists and migrates in the form of an complex within the low-temperature and low-salinity CO2-H2O-NaCl metamorphic fluid system, with the addition of atmospheric water, and Au deposits are formed by fluid immiscibility.
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