The origin of the Tongkeng-Changpo tin deposit,Dachang metal district,Guangxi, China: clues from fluid inclusions and He isotope systematics |
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| Authors: | Cai Minghai Mao Jingwen Liang Ting Franco Pirajno Huang Huilan |
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| Institution: | (1) Faculty of Resource and Environment, Guangxi University, Daxue Road 100, Nanning, 530004 Guangxi, China;(2) Institute of Mineral Resources, Chinese Academy of Geological Sciences, 26 Baiwanzhuang Road, Beijing, 100037, China;(3) Department of Geology and Mineral Resources, Chang’an University, Cuihua Road, Xi’an, 710054 Shaanxi, China;(4) Geological Survey of Western Australia, 100 Plain Street, East Perth, WA 6004, Australia;(5) Yichang Institute of Geology and Mineral Resources, China Geological Survey, Guangyao Road 37, Yichang, 443003 Hubei, China |
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| Abstract: | Tongkeng-Changpo is the largest tin deposit within the giant Dachang polymetallic tin ore field in Guangxi, southern China,
which is part of a large skarn system associated with Cretaceous granitoids. The Tongkeng-Changpo mineralization consists
of veins and stockworks in the upper levels and replacement stratiform orebodies (mantos) at lower levels. Based on textural
relationships, three major mineralizing stages can be recognized: stage I with cassiterite, sulphides, stannite, tourmaline,
and quartz; stage II with cassiterite, sulphides, sulphosalts, quartz, and calcite; and stage III with calcite as the main
phase. The study of fluid inclusions has shown that there are two main fluid types: CO2 and NaCl-H2O. Homogenization temperatures are 270 to 365°C, 210 to 240°C, and 140 to 190°C for stages I, II, and III, respectively. Salinities
range from 1 to 7 wt.% NaCl equiv. in the early ore stage and 3 to 10 wt.% NaCl equiv. in the late stages. Laser Raman Spectroscopy
indicates that the inclusion fluids in stages I and II were of carbono-aqueous composition, with minor amounts of CH4 and H2S, whereas those in stage III were aqueous. Helium isotopic analyses of inclusion fluids indicate that the 3He/4He ratios in the ore veins are in between 1.2 to 2.9 Ra (Ra = 1.4 × 10−6, modern atmospheric ratio), and range from 1.6 to 2.5 Ra in the stratiform orebodies. This range of 3He/4He ratios is significantly higher than that of crustal fluids (0.01–0.05 Ra). The similar characteristics of fluid inclusions
and their He isotopic composition, as well as age constraints, indicate that the ore veins and stratiform orebodies of the
Tongkeng-Changpo deposit formed from the same hydrothermal system, likely related to granite intrusions of the Mesozoic Yanshanian
tectono-thermal event. In addition, the high R/Ra ratios indicate a mantle contribution in the ore fluids. |
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| Keywords: | Tin Mineralization fluid Inclusions He Isotopes Tongkeng-Changpo Polymetallic tin Dachang Guangxi China |
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