地质学
闪长岩
地球化学
磷灰石
矿化(土壤科学)
热液循环
黄铁矿
矿物学
锆石
古生物学
土壤科学
土壤水分
作者
Hongjun Chen,Xiaoming Sun,Dengfeng Li,Rong Yin,Zida Tong,Zhongwei Wu,Yu Fu,Qiaofen Liu,Xian Chen,Jianzhou Yi,Xueguo Deng
标识
DOI:10.1016/j.oregeorev.2022.104811
摘要
Mineralization age dating is essential for understanding orogenic-type gold metallogeny, but suitable minerals for dating are not always available. Apatite can incorporate considerable amount of U and Th, making it a potential U-Pb geochronometer to study hydrothermal alteration and mineralization processes. The newly-discovered Nianzha is a large orogenic Au deposit (∼25 t @ 3.08 g/t Au) and located in the contact fault zone between ultramafic rocks and diorite in the Renbu tectonic mélange of southern Tibet. Two different types of apatite were identified in the Nianzha gold deposit: type I magmatic apatite hosted in diorite and syenite, and intergrown with other magmatic minerals; type II hydrothermal apatite hosted in mineralized diorite. These apatite grains are coarse euhedral granular and closely associated with auriferous sulfides (e.g., pyrite, chalcopyrite, galena). Type I apatite is F- and SO3-rich, whereas type II apatite is distinct from type I apatite by its significantly higher Cl, Mn, rare earth elements (REE), U, Th, and As contents, indicative of a hydrothermal origin. Thus, formation age of type II apatite reflects the timing of gold mineralization. Two type I magmatic apatite samples yielded similar discordia U-Pb ages of 80.35 ± 1.56 Ma (MSWD = 1.3; n = 86) and 79.53 ± 1.27 Ma (MSWD = 0.91; n = 72), respectively, whilst type II hydrothermal apatite yielded a discordia age of 44.60 ± 1.45 Ma (MSWD = 1.2; n = 64). The gold mineralization age is consistent with that of nearby orogenic gold deposits (e.g., Mayum, Bangbu, Zhemulang, and Juqu) in the region. Therefore, we suggest that hydrothermal apatite U-Pb dating can effectively constrain the timing of orogenic Au mineralization events.
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