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China's First Independent Cobalt Deposit and its Metallogenic Mechanism: Evidence from Fluid Inclusions and Isotopic Geochemistry
Author(s) -
Chengyou FENG,
Feng QI,
Dequan ZHANG,
Daxin LI,
Hongquan SHE
Publication year - 2011
Publication title -
acta geologica sinica ‐ english edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.444
H-Index - 61
eISSN - 1755-6724
pISSN - 1000-9515
DOI - 10.1111/j.1755-6724.2011.00595.x
Subject(s) - geochemistry , geology , meteoric water , hydrothermal circulation , pyrite , fluid inclusions , sedimentary rock , metamorphic rock , mineralization (soil science) , magmatic water , ore genesis , mineralogy , seismology , soil science , soil water
The Tuolugou cobalt deposit is the first independent large‐scale Co‐ and Au‐bearing deposit discovered in northwestern China. It is located in the eastern Kunlun orogenic belt in Qinghai Province, and occurs conformably in low‐grade metamorphic volcano‐sedimentary rock series with well‐developed Na‐rich hydrothermal sedimentary rocks and typical hydrothermal sedimentary ore fabrics. Fluid inclusions and isotopic geochemistry studies suggest that cobalt mineralizing fluid is dominated by NaCl‐H 2 O system, accompanied by NaCl‐CO 2 ‐H 2 O‐N 2 system responsible for gold mineralization. Massive, banded and disseminated pyrite ores have similar compositions of He and Ar isotopes from the mineralizing fluid, with 3 He/ 4 He range between 0.10 to 0.31Ra (averaging 0.21Ra), and 40 Ar/ 36 Ar between 302 and 569 (averaging 373), which reflects that Co mineralizing fluids derived dominantly from meteoric water deeply circulating. δ 34 S values of pyrite approaches to zero (δ 34 S ranging from –4.5‰ to +1.5‰, centering around ‐1.8‰ to ‐0.2‰), reflecting its deep source. Ore lead is characterized by distinctly high radiogenesis, with 206 Pb/ 204 Pb>19.279, 207 Pb/ 204 Pb>15.691 and 208 Pb/ 204 Pb>39.627, and its values show an increase trend from country rocks, regional Paleozoic volcanic rocks to ores. This may have suggested that high radiogentic ore Pb derived mainly from country rocks by leaching meteoric water‐dominated hydrothermal fluid during its circulation at depth. Cobalt occurs mainly in sulfide phase (such as pyrite), but cobalt enrichment, and presence and increasing contents of Co‐bearing minerals have a positive correlation with metamorphic degree. The Tuolugou deposit and other typical strata‐bound Co‐Cu‐Au deposits have striking similarities in the geological features and metallogenic pattern of primary cobalt All of them are syngenetic hydrothermal exhalative sedimentation in origin.