Sulfur and copper isotopic signatures of chalcopyrite at Kalatongke and Baishiquan: Insights into the origin of magmatic Ni-Cu sulfide deposits

摘要

Sulfide Cu isotope systematic has been used as a metallogenic tracer in various deposits; however, only rarely in magmatic Ni-Cu sulfide deposits. Here we present chalcopyrite delta S-34 and delta Cu-65 data for the Kalatongke and Baishiquan Ni-Cu sulfide deposits in the Central Asian Orogenic Belt. The Kalatongke deposit yields delta S-34 of -3.99 parts per thousand to 3.30 parts per thousand and delta Cu-65 of -1.32 parts per thousand to 0.07 parts per thousand, whereas chalcopyrite from the Baishiquan deposit has delta S-34 values ranging from 1.70%e to 4.98%e and delta Cu-65 from -0.40 parts per thousand to 0.59 parts per thousand. These isotopic ratios show no correlation with intrusion/orebody shape, location of sample in the orebody, lithofacies or type of mineralization. Based on Kalatongke and Baishiquan delta S-34 data, our multicomponent modeling suggests that, with an increase in the relative crustal component contribution, the measured delta S-34 values in sulfide ores approach the value of the contaminant. Mass ratios (R') of silicate magma/(xenomelt + sulfide xenomelt + resitite + crystalline olivine) of 250-800 in the Kalatongke and 10-1000 in the Baishiquan deposit, yield delta S-34 values of -1.78 parts per thousand to 1.74 parts per thousand and 1.70 parts per thousand to 4.98 parts per thousand in these deposits. Contamination by host tuff and shale material with delta S-34 values of -7.2 parts per thousand to 3.3 parts per thousand reasonably explains the negative delta S-34 in the Kalatongke ores. A lack of correlation between the Kalatongke and Baishiquan chalcopyrite delta Cu-65 values and Cu or S contents (or Cu/Ni ratios) indicates that Cu isotopic fractionation was not controlled by sulfide fractional crystallization, but instead by contamination and the mantle source. Multicomponent modeling shows that an R' factor between 10 and 1000 can reproduce most delta Cu-65 signatures in sulfide ores from the Kalatongke and Baishiquan deposits, with the exception of a few negative delta Cu-65 values. Undetected contamination and heterogeneous mantle resulting from different degrees of partial melting and metasomatism in the mantle source may explain these negative values and the wide range of delta Cu-65 noted in magmatic sulfide deposits worldwide. The Cu and S isotopes in sulfide from the magmatic Ni-Cu sulfide deposits can be utilized as indicators of crustal contamination and the nature of the mantle source. (C) 2020 Elsevier Ltd. All rights reserved.