Selwyn Basin magmatism and relationship to sediment-hosted Zn-Pb deposits

Abstract

Paleozoic volcanic and intrusive rocks from the Selwyn Basin are being investigated to establish if there is genetic relationship between volcanism and sediment-hosted massive sulphide (SEDEX) mineralization with the aim of improving mineral exploration models. The spatial and temporal distribution of dominantly highly alkalic magmatism and SEDEX deposits in the Selwyn Basin are similar, but traditional models for SEDEX deposit formation have excluded any role of magmatism in their genesis. This study is testing whether magmatic systems supply heat and possibly metals and/or volatiles to the ore system. Herein we report preliminary petrological and geochemical data for samples from the Keno Hill, Anvil and MacMillan Pass districts, and Misty Creek Embayment. Most of the volcanic rocks in the Anvil and MacMillan Pass districts are alkalic and mafic, although Paleozoic volcanic rocks and later dykes in the Keno Hill district are subalkalic. Significantly, most volcanic rocks in all districts are enriched to highly enriched in Ba, Cs, Nb and Th, and show a positive relationship between barium and thallium, similar to the Howards Pass SEDEX deposit, suggesting either the volcanic rocks have been altered by similar hydro-thermal fluids as those that generated SEDEX mineralization or that the volcanic rocks formed from magmas that may have contributed metals and metalloids (e.g. Ba, Tl) to ore-forming magmatic-hydrothermal fluids. Thallium, strontium, carbon and oxygen isotopic analysis, combined with U-Pb dating are planned to constrain the connections between alkalic volcanism and SEDEX formation in the Selwyn Basin.