Ore mineralogy of Cu-PGE mineralized gabbros, Coldwell Alkaline Complex, Midcontinent rift: supporting databases, scanning electron microscope, and mineral chemistry

Abstract

In the Midcontinent rift-related Coldwell Alkaline Complex, a series of co-genetic gabbroic to ultramafic intrusions host Cu and Pd in the 97.4 Mt Marathon deposit (0.27% Cu, 0.75 ppm Pd, 0.23 ppm Pt, and 0.09 ppm Au) the 32.42 Mt Geordie Lake deposit (0.3 g/t Pd), and in numerous occurrences. This report presents a number of mineralogical databases that are the result of work undertaken to characterize the Cu-Pd mineralization of 4 gabbro-hosted ore zones within the Coldwell Alkaline Complex. More than 40 ore and host rock samples from Geordie Lake, Area 41, and the Marathon Main and W Horizon orebodies were included in the petrographic study of textures and mineral associations allowing for in situ characterization of minerals of interest. The database of the of twelve, 0.5 to 12 kg mineralized drillcore sample concentrates contain sample locations, more than 200,000 Scanning Electron Microscope (SEM) semi-quantitative mineral analyses, and SEM scans and images. Over 140,000 ore mineral grains from the three ore zones yielded more than 70 different ore minerals, of which at least five phases from the W Horizon orebody, Marathon deposit are unknown or unnamed. The electron microprobe mineral-chemical database lists more than 300 analyses for a range of precious metal minerals and unknowns, including Pd-Au-Ag-Cu, Pd-Ag-S, Pd-S, Pd-Ni-As, Pd-As-Sb, Pd-Te-As-Ge, Pd-Pb-Sn, Pd- Ag-Te, unknown Rh-rich and Rh-bearing pentlandite-like sulphides, Ru-Rh-As-S, and Cd-S phases from the PGE-enriched W Horizon orebody. The principal ore minerals that account for the Pd, Pt, Rh, and/or Ru metal budget of the Main and W Horizon orebodies, Marathon deposit and the Area 41 Cu-Pd mineralized zone are useful in discriminating high-value PGE exploitable mineralization.