Assessment of pyrite composition by LA-ICP-MS techniques from massive sulfide deposits of the Bathurst Mining Camp, Canada: From textural and chemical evolution to its application as a vectoring tool for the exploration of VMS deposits

Abstract

PYRITE is ubiquitous throughout the massive sulfide deposits of the Bathurst Mining Camp, Canada. Pyrite locally preserves primary, pseudo-primary textures, as well as secondary textures, that formed in response to the hydrothermal, metamorphic, and deformation processes to which the host sequence was exposed. In the Bathurst Mining Camp most forms of pyrite are arsenian (up to 3.13 wt% As), with considerable enrichment in Tl, Sb, Sn, Bi, Ag, Se, and to a lesser extent Cd, Ga, Te, Hg, Ge, In, and Au. LA-ICP-MS analyses of primary pyrite show significant enrichment in fluid-mobile elements, in particular, Tl, Sb, As, and Hg, as well as Bi, Pb, and Sn. In contrast, secondary pyrite (syn-to post-deformation varieties) is not enriched in these elements. Superimposed metamorphism typically causes loss of fluid-mobile elements to different degrees, except for Se.Pyrite chemical variations have the potential to monitor ore petrogenesis at inter- and intra-deposit scales. Pyrite from the Cu-zone is enriched in Se relative to pyrite from Zn-Pb zone, in which Tl is elevated. Throughout the host sequence fluid-mobile element concentrations of pyrite vary by several orders magnitude, with the highest fluid-mobile element abundances in footwall rocks immediately proximal to the deposit. Moreover, elevated fluid-mobile element concentrations of pyrite are recognized in footwall felsic volcanic and sedimentary rocks as much as several hundred metres away from the deposit. Hanging-wall zones contain pyrite with fluid-mobile element contents comparable to pyrite from sulfide horizon. The fluid-mobile element concentrations of pyrite are higher in exhalative sedimentary rocks than pyrite from the sulfide mineralization itself.The spatial variation in fluid-mobile element concentrations in pyrite as identified using LA-ICP-MS can be used to identify otherwise cryptic deposit-related haloes. Ultimately, this technique, when combined with traditional exploration tools, can be used to vector toward VMS mineralization in the Bathurst Mining Camp and possibly a useful indicator in a prospect-scale base metal exploration.