Hydrothermal History and Gold Mineralization at the Lalor Volcanogenic Massive Sulphide Deposit, Snow Lake Camp, Manitoba, Canada

The Lalor deposit is a newly developed Volcanogenic Massive Sulphide (VMS) deposit in the Snow Lake camp, Manitoba. The deposit is hosted in a complexly deformed and metamorphosed rock package referred to as the Lalor volcanic succession and located in the VMS-prospective Chisel sequence of the Snow Lake arc assemblage. The Lalor deposit consists of stratigraphically and structurally stacked Zn-rich, Au-rich and Cu-Au-rich ore lenses gently dipping toward the NNE. The Lalor volcanic succession has undergone extensive syn-VMS hydrothermal alteration and subsequent polyphase deformation and amphibolite grade metamorphism. Metamorphosed hydrothermal alteration styles have been classified into chemical associations (K, K-Mg-Fe, Mg-Fe and Mg-Ca). Mapping of the host volcanic rocks, chemical associations and ore lenses at Lalor indicates that: 1) the Zn-rich massive sulphide lenses are preferentially associated with K and Mg-Ca alteration zones, 2) the Zn-rich massive sulphide lenses formed at two distinct stratigraphic positions as a result of protracted seafloor/sub-seafloor hydrothermal activity, 3) the Cu-Au-rich zones at depth are associated with transposed discordant Mg-Fe altered rocks and presumably represent footwall feeders, and 4) Au was introduced as part of the VMS-forming event, probably during a late, low-temperature pulse and was locally remobilized into sulphide-poor ore zones during the main deformation events.