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Publication Type:

Journal Article


Precambrian Research, Volume 406, p.107394 (2024)






Ament Bay assemblage, Neoarchean, Orogenic gold, Sturgeon Lake greenstone belt, Timiskaming basin


<p>The Neoarchean conglomeratic Timiskaming assemblage is considered to be one of the most gold-endowed rock associations in the Abitibi greenstone belt of the southern Superior craton. Identifying Timiskaming-like basins, therefore, may facilitate new discoveries of gold deposits in other Archean greenstone belts. This study focuses on the conglomeratic Ament Bay assemblage (ABA) in the Neoarchean Sturgeon Lake greenstone belt of the western Wabigoon terrane of the western Superior craton. Geologic mapping and petrographic analysis show that the ABA consists of a&nbsp;≥1000&nbsp;m thick conglomerate-arenite lithofacies and a conformably overlying&nbsp;≥200&nbsp;m thick greywacke-mudstone lithofacies, which are interpreted to indicate a sub-aerial fan delta that transitioned into subaqueous turbidites. The depositional age is constrained to be between 2697.5&nbsp;±&nbsp;1.2 and 2693.2&nbsp;±&nbsp;0.9&nbsp;Ma by the statistically defined minimum age of the ABA detrital zircons and igneous zircons of an alkalic intrusion within the ABA, respectively. Detrital zircons from seven ABA samples are characterized by ca. 2930, 2780–2770, and 2750–2690&nbsp;Ma age populations along with minor zircons of ca. 3300–3000&nbsp;Ma, which are consistent with proximal sources mostly in the western Wabigoon terrane and secondarily in the adjacent Winnipeg River terrane. Petrography of conglomerate clasts and sandstone supports these provenances and reveals additional sources from proximal mafic volcanic rocks. The ABA is interpreted to result from uplift and erosion associated with the late-stage convergence between the western Wabigoon and Winnipeg River terranes and to be partially controlled by a regional fault zone and accompanied by broadly coeval alkalic magmatism. Overall, the ABA is similar to the typical Timiskaming assemblage in lithofacies, depositional environments, structural setting, and syn-depositional alkalic magmatism, but dissimilar to the latter in gold endowment. The apparent lack of gold in the ABA is likely due to assimilation of crustal components into the coeval alkalic melts and a shallow-penetrating fault zone, in contrast to the juvenile nature of alkalic magmatism and deep-penetrating fault zones associated with the Timiskaming assemblage. This study suggests that Timiskaming-like basins similar in geology are not necessarily equivalent to the typical Timiskaming assemblage in gold endowment.</p>