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Browsing by Author "Steele-MacInnis, Matthew"

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    Basin scale evolution of zebra textures in fault-controlled, hydrothermal dolomite bodies: insights from the Western Canadian Sedimentary Basin
    (2023) McCormick, Cole A.; Corlett, Hilary; Clog, Matthieu; Boyce, Adrian; Tartèse, Romain; Steele-MacInnis, Matthew; Hollis, Cathy
    Structurally controlled dolomitization typically involves the interaction of high-pressure (P), high-temperature (T) fluids with the surrounding host rock. Such reactions are often accompanied by cementation and recrystallization, with the resulting hydrothermal dolomite (HTD) bodies including several ‘diagnostic’ rock textures. Zebra textures, associated with boxwork textures and dolomite breccias, are widely considered to reflect these elevated P/T conditions. Although a range of conceptual models have been proposed to explain the genesis of these rock textures, the processes that control their spatial and temporal evolution are still poorly understood. Through the detailed petrographical and geochemical analysis of HTD bodies, hosted in the Middle Cambrian strata in the Western Canadian Sedimentary Basin, this study demonstrates that a single genetic model cannot be applied to all the characteristics of these rock textures. Instead, a wide array of sedimentological, tectonic and metasomatic processes contribute to their formation; each of which is spatially and temporally variable at the basin scale. Distal to the fluid source, dolomitization is largely stratabound, comprising replacement dolomite, bedding-parallel zebra textures and rare dolomite breccias (non-stratabound, located only proximal to faults). Dolomitization is increasingly non-stratabound with proximity to the fluid source, comprising bedding-inclined zebra textures, boxwork textures and dolomite breccias that have been affected by recrystallization. Petrographical and geochemical evidence suggests that these rock textures were initiated due to dilatational fracturing, brecciation and precipitation of saddle dolomite as a cement, but significant recrystallization occurred during the later stages of dolomitization. These rock textures are closely associated with faults and carbonate-hosted ore deposits (e.g. magnesite, rare earth element and Mississippi Valley–type mineralization), thus providing invaluable information regarding fluid flux and carbonate metasomatism under elevated P/T conditions.
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    Mixing of brine with oil triggered sphalerite deposition at Pine Point, Northwest Territories, Canada
    (2021) Szmihelsky, Marko; Steele-MacInnis, Matthew; Bain, Wyatt M.; Falck, Hendrik; Adair, Robin; Campbell, Brandon; Dufrane, S. Andrew; Went, Ashley; Corlett, Hilary
    Hydrocarbons are commonly invoked as triggers for the precipitation of sphalerite in carbonate-hosted Pb-Zn deposits, but direct evidence for the presence of petroleum during sulfide mineralization is rarely documented. Here, we report evidence of fluid mixing between basinal brines and oil during deposition of coarse sphalerite at a classic carbonate-hosted Pb-Zn district, Pine Point, Northwest Territories, Canada. The brines contain high concentrations of Pb, detectable aqueous sulfate, and hydrocarbons that attest to chemical interaction with oil. The oil inclusions in sphalerite contain much less Pb relative to the brines and no evident H2S, suggesting that the principal role of hydrocarbons was as a reductant. Mixing of brine with oil enabled the conversion of aqueous sulfate to sulfide, and thereby triggered sphalerite deposition.