Variation of trace elements in chalcopyrite from worldwide Ni-Cu sulfide and Reef-type PGE deposits: implications for mineral exploration

Chalcopyrite from 13 worldwide representative Ni-Cu sulfide and Reef-type PGE deposits were investigated using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) to evaluate its potential as an indicator mineral for exploration. Trace element data were investigated with PLS-DA (partial least square-discriminant analysis) which, combined with discriminant binary diagrams, allows identification of geochemical criteria for discrimination of deposit type (Ni-Cu sulfide vs. Reef-type PGE) and ore type (Cu-rich vs. Fe-rich). A first PLS-DA model (using Bi, In, Se Sn and Te ) discriminates chalcopyrite by deposit type; those from Reef-type PGE have higher Se relative to Ni-Cu sulfide deposits, as a result of higher R factors, whereas chalcopyrite from Ni-Cu sulfide deposits is higher in Te, Bi and Sb. Platinum Group Mineral (PGM) crystallization in Reef-type PGE deposits typically deplete Te, Bi and Sb in co-existing chalcopyrite, enhancing the differences between these two deposit types. The second PLS-DA model (based on Sb, Se, Sn, Tl and Zn) discriminates by ore type, showing that chalcopyrite from Cu-rich samples is enriched in Sn, Se and Zn relative to Fe-rich/unzoned samples, mainly as a result of sulfide fractionation. Complementary discriminant diagrams Se/(Te+Bi) vs. Se and 2Zn/(3Se+5Sn) vs. Se are proposed to discriminate chalcopyrite by deposit type and ore type, respectively. This study demonstrates that the trace element composition of chalcopyrite enables its use as an indicator mineral for exploration.