Paper No. 3
Presentation Time: 9:30 AM


DUFF, Shamus, Department of Earth Sciences, University of Ottawa, 140 Louis Pasteur Pvt, Ottawa, ON K1N 6N5, Canada, HANNINGTON, Mark, Department of Earth Sciences, University of Ottawa, Marion Hall, 140 Louis Pasteur Street, Ottawa, ON K1S 0X7, Canada and MERCIER-LANGEVIN, Patrick, Geologic Survey of Canada, Natural Resources Canada, 490 De la Couronne Street, Quebec, QC G1K 9A9, Canada,

The Lalor Deposit is a newly discovered gold rich volcanogenic massive sulfide (VMS) deposit located on the East end of the Paleoproterozoic Flin Flon belt within a tectonostratigraphic sequence known as the Snow Lake Arc (SLA) assemblage. At nearly 30 Mt, Lalor stands out as an anomalously large VMS deposit on a global scale as well as the largest deposit within the SLA assemblage. Considering the abnormal size, it is notably enriched in Au-Ag-Cu-Zn. Currently, grades are estimated at 2.79 g/t Au, 25.29 g/t Ag, 4.83% Zn and 0.74% Cu. Polyphase deformation (D1-D3) and metamorphism to the middle amphibolite facies has produced a series of assemblages that are atypical to what is predicted by conventional VMS models. During the 2012 and 2013 field seasons, core was logged along three planar sections and 150 ore samples were collected of which 70 were analyzed for 67 elements. Using this data, four main ore types (labelled types 1-4) were identified based on geochemistry and mineralogy. Type 1 massive sulfide (Zn±Cu±Ag) is the most commonly observed ore type, it is characterized by coarse grained pyrite-sphalerite with trace galena. Type 2 stringer sulfide (Au-Cu) contains chalcopyrite veins hosted in chlorite with sporadic patches of coarse biotite and almandine garnets. Although recrystallization and remobilization has taken place to some degree, these two assemblages are typical of VMS mineralization as they respectively represent the low and high temperature zones of the most commonly followed VMS models. Type 3 mineralized chlorite carbonate schist (Ag-Au±Pb±Zn) contains stringers of galena with trace amounts of freibergite, electrum and native gold hosted in a chlorite-dolomite matrix rich in calc-silicates. Type 4 low sulfide ore (Au±Ag) is recognized as a sparsely mineralized assemblage with unpredictably high Au grades. This assemblage is dominated by quartz-biotite-staurolite with no more than 10% pyrite. These latter two ore types are not typical to VMS deposits and are the result of extensive reworking during prograde metamorphism. Using these four ore types, the goal of this project is to understand their genetic relationship to the original hydrothermal system as well as unravelling what role metamorphism played in concentrating these metals.