Abstract Sulfide-poor deposits of platinum-group elements (PGE) occur in two main types: silicate-type and oxide-type. In the silicate-type mineralization PGE form discrete platinum-group minerals (PGM) that occur as inclusions in various silicate minerals. In the oxide-type mineralization PGM may have different modes of occurrence. They may be associated with silicates or they may occur as inclusions in chromite, magnetite or ilmenite, for example. In some cases they may even be associated with base metal sulfides. The approach chosen in this work is mainly a mineralogical one. PGM parageneses, their modes of occurrence and associations with other minerals were studied from different deposits. These are then compared to some well-recorded examples of PGE deposits. The case studies presented, the Duluth Complex in Minnesota, U.S.A., the Hanumalapur Complex in Karnataka, India, and the Penikat Layered Intrusion in northern Finland, are examples that illustrate the multitude of possibilities regarding PGE mineralization versus the traditional approach where any significant quantities of PGE are supposed to occur only in association with base metal sulfides. As the traditional orthomagmatic and hydrothermal models cannot explain the genesis of some sulfide-poor PGE occurrences, a new theory of PGE mineralization was developed. This “redox theory” is an attempt at explaining the association of PGE with various oxide minerals, most importantly chromite.

<p> Sulfide-poor platinum-group element (PGE) mineralization occurs within the Archean Boston Creek Flow ferropicrite, Abitibi greenstone belt, Canada. The PGE mineralization (∑PGE+Au = up to 1000 ppb) is manifest as metre-scale platinum-group mineral-bearing pods of disseminated chalcopyrite and pyrite (< 1 modal%) within titaniferous magnetite-rich gabbroic rock at the base of its central gabbroic layer. This mineralization is distinct in character from well known PGE mineralization associated with massive Fe-Ni-Cu sulfides at the base of komatiite flows at Kambalda, Western Australia and elsewhere. Exploration strategies presently used to search for PGE in mafic and ultramafic volcanic rock terrains are based on the geological and geophysical characteristics of sulfide-rich PGE mineralization. Consequently, refinements in exploration strategies are required if economic concentrations of sulfide-poor PGE mineralization are to be discovered in volcanic terrains.</p> <p> To begin development of such exploration criteria, ground-based magnetic and VLF surveys were conducted over the PGE mineralization along a single cross-section through the BCF. Drill core samples were collected along this transect to characterize the volume magnetic susceptibility and natural remanent magnetization (NRM) of the mineralization. Magnetic highs ranging in intensity from 64000 to 65000 nT were recorded for the base of the gabbroic layer, including mineralized outcrops. Susceptibilities of up to 9700 cgs and high remanence values with variable directions were determined. VLF, as expected, was not useful in identifying the mineralized horizons. The peridotite at the base of the flow appears to be the only conductive rock in the BCF.</p> <p> The magnetic highs associated with the base of the gabbroic layer define a positive anomaly that appears to be podiform in outline and up to ten metres in maximum dimension. This result suggests that the titaniferous magnetite-rich rock is itself podiform, like the enclosed PGE mineralization. This magnetic anomaly is not extensive enough to be evident on a regional scale aeromagnetic map as a separate anomaly within the BCF, and is not evident through VLF techniques. The rocks hosting the PGE mineralization is defined by the paleomagnetic results but this is not a practical field method.</p> <p> The geophysical characterization of the PGE mineralization host rocks, and of the BCF in general, demonstrates the potential of detailed magnetic and susceptibility mapping, together with petrographic and petrologic studies, in the search for economic PGE concentrations of sulfide-poor PGE mineralization in other volcanic and possibly plutonic rocks as well. Specifically, the results suggest that podiform magnetic anomalies within titaniferous magnetite-rich pyroxenites and gabbroic rocks may have potential use in the exploration for economic sulfide-poor PGE mineralization. Although the paleomagnetic methods used in this study are probably not of direct use in exploration, they were able to distinguish the different lithologies in the BCF. This substantiates the results of the susceptibility measurements in characterizing PGE mineralized, titaniferous magnetite-bearing rocks. The results of the paleomagnetic study also show that the NRM of the Ghost Range intrusive complex is not primary and therefore the Archean apparent polar wander path as it is currently defined is incorrect.</p> / Thesis / Bachelor of Science (BSc)