Genesis of the Baimadong carbonate-hosted uranium deposit, Guizhou, SW China: Constrains from geology, fluid inclusions, and C-O isotopes
Genesis of the Baimadong carbonate-hosted uranium deposit, Guizhou, SW China: Constrains from geology, fluid inclusions, and C-O isotopes
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DOI：
10.1016/j.oregeorev.2021.104487
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发表时间：
2021-12
影响因子：
3.3
通讯作者：
Yanyan Li;Chengjiang Zhang;J. Duo;Fangfang Zhang;Hao Song;Baojian Zhang;Yifei Xing
中科院分区：
文献类型：
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作者：
Yanyan Li;Chengjiang Zhang;J. Duo;Fangfang Zhang;Hao Song;Baojian Zhang;Yifei Xing
白马洞铀存款矿床位于中国西南部扬子江上，是中国最具代表性的碳酸盐岩型铀矿床之一。铀矿化与黑色和红色蚀变具有空间和成因关系，这已被先前的研究所证实。然而，签名，来源和评价的成矿流体产生的蚀变和矿化仍然知之甚少。对不同世代热液方解石中的流体包裹体进行了分析，包括Cal 1（成矿前阶段）、Cal 2（成矿早期阶段）和Cal 3（主成矿阶段）。三种类型的流体包裹体被确定为：以液体为主的双相，以蒸汽为主的双相，只有蒸汽单相。流体包裹体显微测温结果表明，与Cal 2有关的流体具有较高的温度（~ 243 ℃）和盐度（5.3wt%NaCl当量）。与Cal 1相关流体（Th= 1.221 ℃;盐度= 1.9wt%NaCl当量）相比，和Cal 3（Th= 144 ℃;盐度= 2.5 wt% NaCl当量）。稳定同位素的结果成矿前流体中的碳主要来源于容矿的海相碳酸盐岩（δ 13 C流体-PDB = −3.0至0.5 ‰; δ 18 O流体-SMOW = 4.8 ~ 11.3 ‰），早期成矿流体中的碳、硫主要来源于牛蹄塘组，少量来自地壳深部（δ 13 Cfluid-PDB = −11.2 ‰ ~ −8.4 ‰; δ 18 Ofluid-SMOW = 7.9 ‰ ~ 11.4 ‰; δ 34 Sv-CDT = −11.3 ‰ ~+ 2.1 ‰），成矿流体主要来自大气降水（δ 13 Cfluid-PDB = −8.6 ‰ ~ −4.9 ‰; δ 18 Ofluid-SMOW = 0.4 ‰ ~ 8.6 ‰）。这些结果表明，氧化还原反应和流体-岩石反应是白马洞大规模铀成矿的重要控制因素。结合这些观察、地质背景和前人的地球化学特征，我们认为构造体系和黑色、红色蚀变叠加带是华南乃至世界碳酸盐岩型铀存款找矿的标志。
The Baimadong uranium deposit is situated in the Yangtze Craton, SW China, and is one of the most representative carbonate-hosted uranium deposits in China. Uranium mineralization has spatial and genetical relationships with black and red alterations that has been documented by previous studies. However, the signature, source, and evaluation of ore-forming fluids producing the alterations and mineralization remain poorly understood. Fluid inclusions hosted in different generations of hydrothermal calcite have been analyzed in this study, including Cal 1 (pre-ore stage), Cal 2 (early ore stage), and Cal 3 (main ore stage). Three types of fluid inclusions were identified: liquid-dominated biphase, vapor-dominated biphase, and vapor-only monophase. Based on fluid inclusion microthermometry using the FIA method, the fluids associated with Cal 2 are characterized by relatively higher temperature (∼243 ℃) and salinity (5.3 wt% NaCl equiv.) compared with fluids associated with Cal 1 (Th= ∼221 ℃; Salinity = 1.9 wt% NaCl equiv.) and Cal 3 (Th= ∼144 ℃; Salinity = 2.5 wt% NaCl equiv.). The results of stable isotopes (C, O, and S) indicate that the carbon in pre-ore stage fluids was dominantly originated from host marine carbonate rocks (δ13Cfluid-PDB= −3.0 to 0.5 ‰; δ18Ofluid-SMOW= 4.8 to 11.3 ‰), the carbon and sulfur in early ore-forming fluids were mainly derived from the Niutitang Formation with minor from deep crust (δ13Cfluid-PDB= −11.2 to −8.4 ‰; δ18Ofluid-SMOW= 7.9 to 11.4 ‰; δ34Sv-CDT= −11.3 to + 2.1 ‰), whereas the main ore-forming fluids were sourced from meteoric fluids (δ13Cfluid-PDB= −8.6 to −4.9 ‰; δ18Ofluid-SMOW= 0.4 to 8.6 ‰). These results reveal that redox reaction as well as fluid-rock reaction are key factors controlling the large-scale uranium mineralization at Baimadong. Combined with these observations, geological setting, and previous geochemical features, we suggest that tectonic system together with overprinting zone of black and red alterations are indicators for exploration of carbonate-hosted uranium deposit in South China and elsewhere worldwide.