Constraining alteration in the footwall of the Sudbury igneous complex: a case study of the alteration footprint to the Podolsky, Cu(-Ni)-PGE deposit, Sudbury

Abstract

The footwall environment of the Sudbury Igneous Complex (SIC) host high-grade Cu-(Ni)-PGE deposits that have become a prime exploration target due to increases in metal prices and depletion of traditionally mined contact-style deposits that are high-grade Ni-Cu rich deposits. Understanding and constraining footwall deposits has been underway for some time, still, several aspects of these deposits that need to be constrained. With respect to alteration the nature, origin, relevance, and significance of these hydrothermal minerals have not yet been constrained. A detailed study of the homogeneous grey gabbro unit that is hosted in the Podolsky 2000 deposit host’s sharp-walled sulfide veins, rich in copper and PGEs was an ideal study area to look at alteration leading up to sharp-walled sulfide veins and its association to mineralization as the vein is approached. The initial step is to define and understand what the composition of the least altered grey gabbro with respect to its petrogenetic, spatial, and chronological relationship. Once the least altered grey gabbro is characterized alteration associated to these veins can be explored in detail. Alteration assemblages associated to these sharp-walled veins could potentially be implemented into an exploration tool for mining companies local to the area in search of such footwall deposits. The least altered grey gabbro unit was not as homogenous as previously thought, after careful review of petrography, SEM-DES, geochemical bulk-rock data, isotope work, and U-Pb age dating; a suitable petrographic summary of the grey gabbro was achieved. Once a least altered summary was achieved, comparing this data to transects leading up to these sharp-walled sulfide veins and various samples of most altered grey gabbro were petrographically, geochemically, isotopically, compared to the least altered samples available. Generally, understanding footwall deposits and unravelling the relevance and significance of these hydrothermal minerals was summarized in this thesis, unfortunately, these alteration trends are rather small and can only be observed <30 cm away from the vein, and are most obvious against the vein. This indicated that alteration signatures are not very strong outside of these sharp-walled sulfide veins, despite these veins ~1 m thick.