Ore geology and fluid inclusion study of the Donggebi giant porphyry Mo deposit, Eastern Tianshan, NW China

Abstract

The Donggebi giant porphyry Mo deposit in Hami city, Xinjiang Province, NW China, was formed in the Triassic in the Jueluotage metallogenic belt of Eastern Tianshan. Mo mineralization is associated with the Donggebi porphyritic granite, occurring as numerous stockworks in the altered wall rocks. The hydrothermal ore‐forming process can be divided into four stages, from early to late, characterized by veinlets composed of (1) quartz + K‐feldspar ± beryl ± pyrite ± tourmaline; (2) quartz + molybdenite ± K‐feldspar ± tourmaline ± fluorite ± beryl; (3) quartz + polymetallic sulphides ± fluorite; and (4) quartz + calcite ± fluorite. Three types of fluid inclusions (FIs) are distinguished in this study based on petrographic and microthermometric criteria, i.e. carbonic (C‐type), aqueous (W‐type) and solid‐bearing fluid inclusions (S‐type). All three types of FIs can be observed in the quartz, beryl and fluorite formed in stages 1, 2 and 3, while the stage 4 minerals only contain aqueous inclusions. The FIs in minerals of stages 1, 2, 3 and 4 yield homogenization temperatures of 261–443, 210–385, 152–304 and 159–263 °C, respectively, and salinities of ≤9.3 wt.% NaCl equiv., without consideration of the contribution from daughter minerals. The maximum estimated pressure decrease from 193 MPa in stage 1, through 182 MPa in stage 2, to 129 MPa in stage 3, suggesting the maximum mineralizing depths decreased from 8.4, through 7.9, to 5.6 km, and possibly occurred at 5.6–7.9 km. Therefore, the ore‐forming fluids at Donggebi are characterized by high‐temperature, CO2‐bearing and NaCl‐poor and then progressively evolved to CO2‐poor and lower‐temperature. Copyright © 2014 John Wiley & Sons, Ltd.

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