Geochemical evidence for a magmatic contribution to the metal budget of the Windy Craggy Cu-Co(±Zn) volcanogenic massive-sulfide deposit, northwestern British Columbia

Abstract

Volcanogenic massive-sulfide (VMS) deposits may have had metal contributions from magmatic degassing and leaching of footwall rocks. The Windy Craggy Cu-Co-Zn VMS deposit in northwestern British Columbia may include magmatic contributions, based on laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) of fluid inclusions (enriched in Sb, Sn, and Bi) and lithogeochemistry. Sulfide-mineral trace-element abundances in the massive-sulfide orebody, underlying stockwork zone, gold zone, and altered and unaltered mafic rock and argillite were analyzed by LA-ICP-MS. Elevated Au, W, As, Bi, Sb, Se, Te, Tl, Ag, Co, and Mo contents occur within the gold and/or stockwork zones. Increasing 'magmatic metals' with increasing Co/Ni values suggest direct magmatic contribution to the deposit. Covariation of Co with these so-called 'magmatic elements' indicates that it, too, may be of magmatic origin, sourced via fluids exsolved from a crystallizing magma; however, evidence from the composition of rocks and sulfide minerals from Windy Craggy and other VMS deposits suggests that there is probably no meaningful distinction between hydrothermal leaching and direct magmatic contributions and that most - if not all - fluids that form VMS deposits should be termed 'magmatic-hydrothermal'.