科研之友
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摘要
The Gangcha gold deposit in Hezuo, Gansu, China, is a newly discovered medium-scale (19 tons) epithermal deposit occurring within the western Qinling orogenic belt. The Daguanshan Formation, represented by metamorphosed volcanic-clastic rock suite, is the main ore-bearing strata. Gold occurs mainly as submicroscopic inclusions in sulphides and quartz. The hydrothermal alteration is characterized by mid- to low-temperature mineral assemblages such as pyrite, arsenopyrite, and fluorspar. We report results from Rb-Sr isotopic dating of pyrites in the main orebody, which yield an isochron age of 225.3 +/- 3.4 to 229.9 +/- 4.7Ma suggesting that the mineral deposit formed during the middle Triassic within a collisional orogenic setting. The initial Sr-87/Sr-86 value of pyrite (0.710326 to 0.710349) is lower than that of the continental crust and higher than that of the mantle. The S isotope data of pyrites from the deposit show a narrow range from 0.6 parts per thousand to 1.3 parts per thousand with an average of 0.975 parts per thousand. Their Pb isotopes exhibit characteristics of a crust-mantle mixed source with a (U-238/Pb-204) of 9.39 to 9.53 and a (Th-232/Pb-204) of 36.81 to 38.14. The S and Pb isotopic composition indicates that ore-forming materials were derived from a magma sourced in the lower crust, which also incorporated mantle components.
- 出版日期2018-10
- 单位中国地质大学（北京）; 西北大学
