The effects of post-cumulus alteration on the distribution of chalcophile elements in magmatic sulfide deposits and implications for the formation of low-S-high-PGE zones: The Luanga deposit, Carajás Mineral Province, Brazil

ABSTRACT Most of the World's platinum-group element ore deposits occur as thin stratiform layers within layered intrusions. These generally contain disseminated base-metal sulfides or chromite. However, cryptic also without chromite in what are known low-S-high deposits. The origin these is not clearly understood. Luanga Complex hosts largest elements resource South America (i.e., 142 Mt at 1.24 ppm Pt + Pd Au and 0.11% Ni) both a deposit containing (style 1) 2). It therefore offers opportunity to compare two types same overall geological setting consider how could have formed. first style termed Sulfide zone consists 10–50 meter-thick interval with base metal sulfides, whereas second named low-S-high-Pt-Pd 2–10 discontinuous lenses 1–5 sulfide- oxide-free harzburgite orthopyroxenite discrete minerals. Secondary assemblages commonly replace primary igneous minerals variable extent throughout deposit, thus allow for investigating effects post-cumulus alteration on distribution wide range chalcophile magmatic sulfide whole-rock mineral scale. This study presents S, elements, Te, As, Bi, Sb, Se mineralization styles concentration trace from zone. has Pt/Pd ratios around 0.5 high concentrations Se, low-S-high-platinum-group greater than 1 much lower Bi concentrations, but comparable As Sb contents. reflected assemblage, comprising bismuthotellurides mostly arsenides antimonides low-S, Moreover, anomalously contents (50–500 ppm), which suggest that liquid segregated very As-rich silicate magma, possibly illustrated by an average komatiitic basalt assimilated mixture upper continental crust black shales. We interpret product S loss during Complex. Selenium, were lost together expelled structures combined form minerals, suggesting they may play role fixating alteration. remobilization located Carajás Mineral Province represent potential source hydrothermal found region.