Joshua Buosi Honours Thesis Abstract
The Sharpsand River IOCG prospect is located within the southern Algoma district, of the western Abitibi terrane, in the Archean Superior province. This study integrates field mapping, petrography and x-ray diffraction analysis to determine; mineralogy, the controls on mineralization, the paragenesis of the prospect and to constrain an appropriate deposit model for the Sharpsand River prospect. It has had previous exploration work completed in 1962 consisting of trenching, magnetometer surveys and 297 m of diamond drilling. Assay results from the trenches and diamond drill holes averaged 1.18% Cu throughout, and a maximum value of 5.40%.
Five lithologies were identified within the study area, consisting of Algoma monzogranite, Keweenawan diabase intrusives, quartz veins, silicified breccia and quartz/diabase breccia. The Algoma monzogranite is the host rock in the study area and is comprised of weakly foliated, coarse- to medium-grained plagioclase, microcline, quartz and minor biotite. The Keweenawan diabase dikes consist of 5 to 50 m vertical dikes intruding the monzogranite at a northwest-southeast trend, and are related to the Mackenzie dike swarm. The dikes are comprised of fine-grained, massive plagioclase, pyroxene and finely disseminated magnetite. After the intrusion of the Keweenawan dikes, the area underwent regional greenschist metamorphism, altering pyroxenes to clincochlore, forming selectively pervasive sericite alteration and causing recrystallization of primary quartz and magnetite. The quartz veins occur in a northeast-southwest trending fault zone through the topographic low in the middle of the study area. Silicification of the fault zone occurred penecontemporaneously to faulting. The quartz veins consist of coarse-grained, euhedral quartz with minor clinochlore and chalcopyrite, with common open filling textures. The silicified breccia unit represents the area between the intersections of diabase dikes and the barren quartz vein, characterized by 60-90% quartz by modal composition, with strongly altered diabase fragments and shear textures. The quartz/diabase breccia occurs at the intersections of the diabase dikes and quartz veins, and is comprised of equal proportion of vein fill, dominated by quartz, and angular diabase clasts. This unit hosts the strongest chalcopyrite and hematite mineralization. The chalcopyrite and hematite mineralization was precipitated by late stage hydrothermal fluids, which intruded the fractured quartz veins and through oxidation of primary magnetite in the Keweenawan dikes, concentrated the mineralization in the quartz/diabase breccia unit. Controls on the mineralization have been determined to be the presence of magnetite bearing diabase dikes, the northeast-southwest trending fault zone, silicification of the fault zone and the hydrothermal fluids to concentrate the mineralization.
The IOCG deposit model in the broadest sense is applicable to the Sharpsand River prospect. The prospect fits the IOCG deposit model due to: (1) presence of copper and trace gold, (2) hydrothermal ore styles and strong structural controls, (3) abundant magnetite and hematite and (4) no clear spatial associations with igneous intrusions. To constrain a specific IOCG deposit subtype, more research should be conducted through geochemical analysis to determine (1) the presence of LREE enrichment and low S sulphides, (2) the range in depth of formation of the prospect and (3) the Fe/Ti ratios of the Fe oxides. Further exploration work would also be required to determine if the copper and gold are present in economic quantities.