Glacial dispersal of gahnite from the Izok Lake Zn-Cu-Pb-Ag VMS deposit, northern Canada

Abstract

The Izok Lake Zn–Cu–Pb–Ag volcanogenic massive sulphide (VMS) deposit in the Arctic region of Canada is one of the largest undeveloped Zn–Cu VMS resources in North America. In 2009, the Geological Survey of Canada initiated a detailed glacial dispersal study of the deposit focused on documenting its associated indicator mineral and till geochemical signatures. Glacial dispersal from the deposit is fan-shaped and was formed by an older SW ice flow and younger NW ice flow phases. Till samples contain chalcopyrite, sphalerite, galena, and pyrite up to 1.3 km down-ice and gahnite at least 40 km down-ice. Gahnite (ZnAl 2 O 4 ) is an ideal indicator mineral in till because of its visually distinctive bluish green colour combined with its high specific gravity (4–4.6) for recovery using density-based separation methods, moderate hardness (physical durability during glacial transport), chemical stability in oxidizing surficial environments (resistance to post-glacial weathering), and its occurrence in highly metamorphosed VMS deposits such as Izok Lake. Most gahnite grains in till down-ice are 0.25–0.5 mm in size. Coarser gahnite (0.5–2.0 mm) occurs only in till proximal to the deposit (<3 km down-ice) and thus is an indicator of proximity to a gahnite-bearing bedrock source. Ore (Cu, Pb, Zn, Ag) and pathfinder element (As, Cd, Bi, Hg, In, Sb, Sb, Tl) contents in the <0.063 mm fraction of till reflect glacial dispersal up to a maximum of 6 km down-ice. A 15–20 km till indicator mineral sample spacing is sufficient to detect a gahnite glacial dispersal train such as that from the Izok Lake VMS deposit.