Willian Valentin Coqueiro Sanches, MSc
W.V. Coqueiro Sanches1, A. Voinot2, P.M. de Paula Garcia3, D. Layton-Matthews1, M.B. McClenaghan2, L. Moore2, J. Kidder2
1Department of Geological Sciences and Geological Engineering, Queen's University, Kingston, ON, Canada
2Geological Survey of Canada, Ottawa, ON, Canada
3Universidade Federal do Mato Grosso, Cuiabá, MT, Brazil
The Cu-PGE Marathon Deposit (Northwestern Ontario) is situated within the Coldwell Complex which is part of the Midcontinent Rift in North America. The deposit is hosted by the Two Duck Lake Gabbro, which is subdivided into three main mineralized zones: 1) the Footwall Zone, characterized by net-textured disseminated pyrrhotite with minor chalcopyrite and trace platinum-group minerals (PGM); 2) the Main Zone, the thickest and most continuous zone, has disseminated chalcopyrite with less pyrrhotite and PGM, mainly kotulskite [Pd(Te,Bi)2] and sperrylite [PtAs2]; and 3) the W-Horizon, which exhibits lower overall sulfide abundance, (bornite and chalcopyrite) and a diverse assemblage of PGM including common keithconnite [Pd20Te7], zvyagintsevite [Pd3Pb], and isoferroplatinum [Pt3Fe].
This study systematically compares the mineral chemistry of the mineralized bedrock and that of the till overlying the deposit. Petrographic characterization of the deposit is integrated with analytical methods, such as scanning electron microscope (SEM), electron microprobe (EPMA), and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), to assess mineral-chemistry variation across the various mineralized zones. Chalcopyrite trace-element mineral chemistry data were obtained exclusively from analyses of bedrock thin sections, whereas magnetite and clinopyroxene were evaluated in both bedrock and till.
Multivariate statistics, principal component analysis (PCA), and element-ratio biplots show that clinopyroxene and magnetite exhibit systematic trace-element variations across the Footwall Zone, Main Zone, and W-Horizon. Proximal till grains consistently overlap with mineralized bedrock compositional fields, whereas background till defines a separate geochemical population (e.g. background clinopyroxenes have elevated Mg concentrations >75,000 ppm, and generally lower Fe, Zn, and Co than samples from mineralized zones). Our results demonstrate that silicate- and oxide-mineral chemistry may complement traditional PGM and sulfide indicator-mineral approaches.These results offer new approaches to discriminate mineralized zones from the background and vector toward Cu–PGE anomalies in glaciated terrain, with direct implications for brownfield and greenfield exploration and surficial geochemical targeting of similar deposits.