The Paleoproterozoic Lalor auriferous VMS deposit, Snow Lake, Manitoba: geology and geochemistry of the host rocks and hydrothermal alteration zones.
2013
Lalor is a recently discovered Au-Zn-rich volcanogenic massive sulphide (VMS) deposit
located in the Paleoproterozoic Snow Lake arc assemblage in northern Manitoba. The
Snow Lake camp is host to numerous past producing Cu-Zn, Zn-Cu and Au-Zn-Cu VMS
deposits. Lalor is the largest VMS deposit of the Snow Lake camp with reserves of 15.1
Mt at 7.2% Zn, 0.6% Cu, 1.9 g/t Au and 23.3 g/t Ag and resources of 12 Mt at 2.6% Zn,
0.9% Cu, 4.0 g/t Au and 27.8 g/t Ag. The major gold endowment (approximately 2.6 Moz
Au) and the unique geologic characteristics of the Lalor deposit represent an ideal case to
document and better understand gold enrichment processes in the VMS environment. The
deposit consists of highly-strained, stacked massive to semi-massive Zn-Cu±Au, Au-Cu
and Au zones that are hosted in highly altered volcanic and intrusive rocks. Most primary
features in the footwall succession were obliterated by superimposed hydrothermal and
tectonometamorphic events. However, using mineral assemblages, extensive whole-rock,
isotopic and mineral geochemistry accompanied with detailed structural analysis of
sections and underground maps, it is possible to precisely map the lithological units and
the nature and distribution of hydrothermal alteration zones. This should allow for a wellconstrained
3D representation the deposit’s current and primary architecture. Preliminary
results indicate that several distinct mafic to felsic units of tholeiitic to calc-alkaline
affinities are present in the host succession. These units were subjected to multiphase
hydrothermal events responsible for the complexity of the zoned Mg-, Fe-, K- and Cabearing
hydrothermal alterations and later Ca metasomatism.
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