Till geochemical signatures of volcanogenic massive sulphide deposits: an overview of Canadian examples

Abstract

Volcanogenic massive sulphide (VMS) deposits are an important source of Cu, Pb, Zn and Ag in Canada. These deposits formed on the paleo-seafloor in volcanic or volcano-sedimentary rocks. On the glaciated landscape of Canada, the bulk composition of till (so-called ‘till geochemistry’) is an important exploration method for VMS deposits. Herein we provide an overview of the 50-plus year history of the application of till geochemical methods to VMS exploration in Canada, and summarize best practices, including appropriate size fractions of till to analyse, analytical techniques and indicator and pathfinder elements. Till geochemical methods are now well-developed and used widely, most commonly employing the <0.063 mm till fraction and an extensive suite of VMS indicator elements Cu, Pb, Zn, Au, and Ag, as well as pathfinder elements Ag, Au As, Bi, Cd, Ga, Ge, Hg, In, Sb, Se, Sn, Tl. In order to detect the clastic glacial dispersal signal down-ice of a VMS deposit, unoxidized to weakly oxidized till should be collected and analysed, and not B-horizon soil. Case studies and examples of glacial dispersal patterns associated with known VMS mineralization in major mining camps and deposits across Canada are highlighted.