A mineralogical and fluid inclusion study of modified, contact-style Ni-Cu-PGE ores in the #1 and #4 shear zones, Garson Mine, Sudbury, Ontario, Canada

Abstract

The Garson deposit is a structurally and hydrothermally modified contact-style nickel-copper-platinum-group element ('PGE') magmatic sulphide deposit, located in the South Range of the Sudbury Igneous Complex, Ontario, Canada. The ores are hosted mainly in shear zones and are exceptionally enriched in arsenic, platinum, and palladium. Bulk rock arsenic is controlled by the abundance of cobaltite-gersdorffite solid solution (CGSS) and nickeline in the ore assemblages. Laser ablation-ICPMS analyses show that exceptionally high concentrations of PGE are found in these sulfarsenides and arsenides with high PPGE/IPGE ratios (avg. >30). In contrast, the base metal sulphides are consistently depleted in PGE and arsenic (rarely >1 ppm). The arsenic-rich phases are also rich in PGE mineral inclusions. The arsenic-rich phases (i) may represent the accumulation of phenocrysts from arsenic-saturated sulphide melt, or (ii) may have formed during metamorphic reheating, recrystallization or partial melting of originally arsenic-rich sulphide ore bodies.