Geology

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Browsing Geology by Subject "Abitibi greenstone belt"

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    Can magnetic susceptibilities measured on outcrops be used for modelling (and constraining inversions of) aeromagnetic data?
    (2019-09-07) McNeice, William John
    Magnetic susceptibilities measured on outcrop and drill-core samples using hand-held instruments have been shown in the literature to be useful for identifying mineralogical changes. It is not yet clear how useful these measurements are for constraining magnetic modelling and inversion. We have generated estimates of the apparent magnetic susceptibility of the ground by mathematical transformation of an aeromagnetic data and assumed that these values can be used to model the magnetic data. In the same area we have a large number of measurements on outcrop and have compared these two independent estimates. When the measured values are below 1x10-3 S.I., there is a no correlation between the measured and apparent values, interpreted to be likely due to the influence or interference from nearby or underlying magnetic sources. Hence, in this case the measured values cannot be used to constrain modelling and inversion. When the measurements are above this value there is a limited correlation, with values only agreeing to within a factor of about 10, so these values can be used as very rough constraints. The poor correlation is interpreted as due to the presence of remanent magnetization or heterogeneity of the magnetic susceptibility within the rock. A large database of outcrop measurements gives an indication of the range of the variation in magnetic susceptibility values that could be used in modelling.
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    Characterization of alteration and mineralization at the Archean Grey Fox and Hislop magmatic-hydrothermal gold deposits, Matheson, Ontario
    (2021-06-30) Kelly, Christopher Hugh
    The Abitibi Greenstone belt (AGB) is host to some of the world’s largest gold deposits and their study has led to various gold deposit models and classifications. The latter includes a syenite- associated deposit type, which was first recognized in the early 2000s. This type of mineralization is present at the Grey Fox and Hislop deposits, which are located 80 km east of Timmins, Ontario. A study of their geologic setting, alteration, mineralogy, mineral chemistry, veining styles, and metal associations, suggest that these deposits, as well as others in the area, developed in different zones of a larger magmatic-hydrothermal system associated with alkalic intrusions of probable Timiskaming age (i.e., <2680 Ma). As such, they formed relatively early in the deformation history of the belt and predate the formation of the more common orogenic or greenstone-hosted quartz- carbonate vein deposits, such as the nearby Black Fox, which make up much of the gold budget in the AGB. A strong host-rock control is present at both deposits and their complex alteration histories provide insights on the formation of multiple mineralization styles within a single system. These different mineralization styles are described here to provide guidelines for mineral exploration for this deposit type in the Abitibi greenstone belt, as well as in other greenstone belts globally.
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    Mobilization of komatiite-associated Ni-Cu-(PGE) mineralization in the Southern Manneville fault zone, Southern Abitibi subprovince, Quebec
    (2020-03-25) Shirriff, Danielle; Shirriff, Danielle
    The Cubric showing and Marbridge deposit occur in the 2714 ± 2 Ma La Motte-Vassan Formation, 20-25 km north of Malartic, Québec. Mineralization at the Cubric showing is hosted by a silicate-magnetite facies iron formation as well as gabbro, but the high Ni/Cu and Ir/Pd ratios of the mineralization suggest that it formed from a komatiitic magma, similar to the mineralization at the historic Marbridge deposit. Normal abundances of most metals in the mineralization in the gabbro suggest that it was mechanically mobilized into the gabbro as a high-temperature monosulfide solid solution, whereas low abundances of Cr and Ir-Ru-Rh in the mineralization in the iron formation suggest that Ni-Cu-Pt-Pd-Au and other metals were mobilized into the iron formation by metamorphic-hydrothermal fluids. The host rocks and country rocks have experienced two phases of deformation during regional metamorphism, and it is likely that the mineralization was mobilized from unexposed/eroded mineralized cumulate komatiites during this deformation and metamorphism, which occurred after emplacement of the younger 2680 ± 1.5 Ma gabbro.