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Publication Type:

Journal Article


Ore Geology Reviews, p.105916 (2024)






diagenesis, Hematization, Ore system, Polaris district, Quartz cement, Redbed copper


<p>Red sandstone of the Proterozoic Aston Formation (Nunavut, Canada) is exposed in the same geographic area as the Storm Cu showing in the Paleozoic-carbonate-hosted Polaris Zn-Pb district (Arctic Canada). The ∼800-m-thick Aston Formation experienced successive burial and exhumation episodes, with maximum burial (&gt;3 km) at the time of the Devonian Ellesmerian orogeny. A petrographic and in situ SIMS oxygen isotope study identified redbed diagenetic events, associated fluid types and temperatures, and their relative timing. The first hematite coat (Hem1) developed in the Proterozoic. Intrusion of Proterozoic dykes and sills heated local formation water to high temperatures (130–223 °C), resulting in precipitation of patchy Qz1 cement in a shallow-burial environment. The Fe and Si were probably derived through alteration of non-quartz silicate detritus. In the Paleozoic, a bleaching (reducing) event removed most Hem 1; the reduced fluid may have been related to regional Zn mineralisation throughout the Polaris district during the mid-Paleozoic Ellesmerian orogeny. Ensuing pressure-solution during maximum burial was probably also Ellesmerian. A second hematisation episode (Hem 2) encloses the pressure-solved quartz-grain contacts. Coeval with Hem 2 was pervasive Qz2 cementation from a low- to mid-latitude, meteoric-derived, oxidised hydrothermal (140–180 °C) fluid that supplied externally derived Si and Fe, probably in the Early Carboniferous. The nature and timing of the fluid events indicated by the Aston Formation’s diagenetic history closely match the fluid history recorded in both Cu and Zn mineralisation in the Polaris district. This relationship strongly supports the concept that Cu in sedimentary-rock-hosted ore deposits can be sourced from redbeds, even those whose depositional age and environment is much older than, and geodynamically unrelated to, the fluid event(s) that caused diagenetic reddening and Cu transfer from source rock to mineralising site.</p>