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External fluids cause alteration and metal redistribution in the granite-hosted Tangziwa Sn Cu deposit, Gejiu district, China
Lithos ( IF 3.5 ) Pub Date : 2021-02-01 , DOI: 10.1016/j.lithos.2020.105937 Rong Xu , Rolf L. Romer , Johannes Glodny
Lithos ( IF 3.5 ) Pub Date : 2021-02-01 , DOI: 10.1016/j.lithos.2020.105937 Rong Xu , Rolf L. Romer , Johannes Glodny
Abstract The granite-hosted Tangziwa Sn Cu deposit in the Gejiu district shows variable alteration of the granite with associated mineralization. In this paper, we used whole rock chemistry mass balance calculations and Sr, Nd, Pb, Li, and B isotope data to constrain the source of metals and fluids in different alteration stages. The δ7Li and δ11B values of unaltered and weakly altered (Type I) granite samples fall in narrow ranges of −0.70 to 3.61‰ and −14.87 to −12.82 ‰, respectively, which is typical for granites. The Li and B isotopic composition of moderately (Type II) to strongly altered (Type III-1 and Type III-2) granite samples are shifted toward higher δ7Li (up to 13.61‰) and lower δ11B values (as low as −31.32‰). These extreme values reflect the addition of Li and B via an external fluid. Petrographic observations and isocon mass balance calculations demonstrate that early stage, magmatic fluids altered biotite and plagioclase to muscovite and clay minerals, respectively, and led to loss of Ca, Na, Fe, and Cs. The later stage, external fluids caused the destruction of feldspar and the precipitation of calcite, anhydrite/gypsum, fluorite, and sulfide minerals (pyrite, chalcopyrite, arsenopyrite, and stannite). This alteration is associated with an increase in the contents of Ca, S, Fe, Co, Cu, Sb, Cd, and Sn and a reduction of the contents of Pb, Sr, Cs, and LREEs. The high contents of Cu and S, which are not typically abundant in granite, could be added by the external fluids characterized by high δ7Li and low δ11B. The weakly and moderately altered granites have lower Sn contents than the unaltered granite. This indicates that late magmatic or external fluids may have leached Sn from weakly and moderately altered granite and thar sulfide minerals in the strongly altered granites eventually scavenged this mobilized Sn.
更新日期：2021-02-01
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