Geologic-tectonic setting of the gold-endowed Kilo Terrane in the eastern Central Kibalian Superterrane, northeastern Democratic Republic of Congo

Abstract

Solid geological mapping, granite geochemistry and robust U-Pb SHRIMP geochronology confirm our subdivision of the eastern Central Kibalian Superterrane (ECKS) into two terranes: the ca 2570–2552 Ma Western Ituri Terrane and the ca 2680–2570 Ma Kilo Terrane. The ECKS is part of the Central, Northern and Southern Kibalian Superterranes, first-order interpretative crustal blocks, which constitutes the Kibalian Greenstone Region in the Bomu-Kibalian craton. The Kilo Terrane comprises: 1) the lower Kibalian lithostratigraphic units of deep-sea facies mafic–ultramafic volcanic rocks, interlayers of pelitic-sedimentary rocks and mafic granite and diorite-tonalite complexes in the Galaya-Kilo Sub-Terrane; and 2) the upper Kibalian lithostratigraphic units of intermediate-felsic volcanic-sedimentary, mafic–ultramafic intrusive rocks and widespread quartz-dioritic, tonalitic to granodioritic granites in the Balazana-Bunia Sub-Terrane.Mafic granite and diorite-to-tonalite magmatism in the Kilo Terrane is demonstrated by: 1) the ca 2680–2640 Ma syn-volcanic mafic-dioritic granite magmatism, including the ca 2650–2640 Ma albitic granites extensive in the Nizi-Tsi Belt; 2) the ca 2640–2600 Ma syn-volcanic hornblende tonalite-to-granodiorite magmatism in the Kilo and Moto-Zani Terranes; and 3) a ca 2600–2570 Ma syenite, quartz-monzonite and felsic granite intrusions along extensional zones and reactivated major terrane boundaries. The coincidence between the ca 2603 Ma tectonic uplifting and ca 2605–2590 Ma hydrothermal activity in the Kilo Terrane is associated with the gold mineralization.The 2711–2790 Ma xenocryst ages point to potential existence of the > 2790 Ma basement rocks extending from underneath the Western Ituri Terrane into underneath the Bunia West Domain. It’s absence in the gold-hosting domains of the Kilo Terrane does not exclude the existence of > 2.8 Ga basement, but instead it invokes on the existence of an unconformity separating the basement rocks from rootless, ca 2680–2570 Ma complexly folded and faulted juvenile granite-greenstone domains, sutured together by first- to second-order fault/shear zones. Protracted periods of Archean to post-Archean tectonic uplifting and inversion were responsible for preservations and erosion of upper crustal-level granite greenstone belts, including orogenic gold depositsThe ca 2680–2570 Ma juvenile crustal addition in the Kilo Terrane occurred some 30 m.y. after the ca 2850–2600 Ma juvenile crustal addition events in well-researched Archean cratons, worldwide.