Electronic Thesis and Dissertation Repository


Doctor of Philosophy




Robert Linnen


The Eastern Gabbro forms the northern and eastern margin of the Coldwell Alkaline Complex. It contains three magma series: the barren meta-basalt, the Layered Series, and the Marathon Series which hosts all known PGE mineralization. The Marathon Series can be distinguished from other Series using the combination of portable X-ray fluorescence (pXRF) and benchtop scanning electron microscope (bSEM). Whole-rock Ba, Mg# (molar Mg/(Mg+Fe)*100), Zr and V/Ti values acquired from pXRF, and Mg#s of olivine and clinopyroxene, and anorthite content (molar Ca/(Ca+Na)*100) of plagioclase acquired from bSEM-EDS are key parameters. The Layered Series generally contains higher Ba and lower V/Ti than the Marathon Series and presents relatively smooth normal and reverse differentiation trends, whereas the Marathon Series exhibit strong compositional changes over short distances.

Reverse and normal lithogeochemical and mineral chemical evolution are observed for the Layered Series at Four Dams and Area 41. Olivine-clinopyroxene Fe/Mg exchange disequilibrium is also observed, and is interpreted to reflect crystallization in an open dynamic system. Geochemical modeling shows that the Layered Series magma is more evolved than the Coubran basalts, but the former contains lower Pd+Pt contents than the latter. Cu-rich & PGE-poor mineralization is also recognized in the Layered Series at Four Dams. This is interpreted to reflect an early sulfide saturation of the Layered Series.

Area 41 is a newly discovered zone of mineralization at the northern edge of the Eastern Gabbro. Three types of mineralization are identified. Type 1 is Cu-rich but PGE-poor mineralization. Type 2 contains PGE mineralization and has mantle-like Cu/Pd ratios, suggesting that it likely formed in a relatively closed system, similar to the Main zone mineralization at the Marathon deposit. Type 3 mineralization is the most PGE-enriched and has low Cu/Pd ratios. This, together with average S/Se ratios of 1200 is evidence of S loss, which suggests that it formed by multi-stage dissolution upgrading, similar to the W-horizon mineralization at the Marathon deposit. 3D modeling of the igneous stratigraphy and mineralization indicate that Area 41 is a magma conduit, similar to the Marathon deposit. Thus, the Coldwell may also contain additional conduit-related mineralization