Formation of a late-orogenic conglomeratic sequence in the Neoarchean western Wabigoon terrane, Superior craton

• Published in: Precambrian research 2024-06, Vol.406, p.107394, Article 107394
• Main Authors: Tamosauskas, Michael, Ma, Chong, Haugaard, Rasmus, Lodge, Robert W.D., Sherlock, Ross, Hamilton, Mike, Marsh, Jeffery
• Format: Article
• Language: English
• Subjects: Ament Bay assemblage; Neoarchean; Orogenic gold; Sturgeon Lake greenstone belt; Timiskaming basin
• ISSN: 0301-9268
• DOI: 10.1016/j.precamres.2024.107394

•The study reveled the formation of the Neoarchean conglomeratic Ament Bay basin.•The basin is similar to the Timiskaming assemblage in sedimentation and setting.•The basin is dissimilar to the latter in crustal architecture and gold endowment.•The lack of gold in the basin is due to existence of underlying gneissic basement.•Timiskaming-like basins similar in geology may not contain similar gold endowment. 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 ≥1000 m thick conglomerate-arenite lithofacies and a conformably overlying ≥200 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 ± 1.2 and 2693.2 ± 0.9 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 Ma age populations along with minor zircons of ca. 3300–3000 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 fa