Lithology, petrography and Cu occurrence of the Neoproterozoic glacial Mwale Formation at the Shanika syncline (Tenke Fungurume, Congo Copperbelt; Democratic Republic of Congo)

Abstract

The Mwale Formation that constitutes the base of the Nguba Group in the Neoproterozoic Katanga Supergroup has recently attracted renewed interest for copper mineral exploration. We present new field observations combined with detailed logging and petrography of MWAS0001 drill hole at Shanika syncline in the Tenke Fungurume Mining District. Our study has enabled us to subdivide the Mwale Formation into 7 distinct sequences. This succession is host to glaciogenic, glaciomarine, glaciofluvial and glaciolacustrine deposits. Glaciomarine beds are typically a deposit by debris flow in deep water marine environment, induced by basin wide tectonics and glaciation influence. Glaciofluvial beds were deposited in shallow water, fluvial deltaic environment. The glaciolacustrine environment is indicated by dropstones occurring in the laminated mudstone and rhythmites with dispersed clasts observed in the siltstone and conglomerate. These beds are interlayered within the glaciogenic beds, and are characterised by variable clast composition (felsic, mafic and metamorphic). The clasts are very poorly sorted, angular, rounded to moderately rounded, faceted or striated, and supported in a sandy argillaceous or mud matrix.Two main episodes of sulphide mineralisation are distinguished in the Mwale Formation. The diagenetic episode consists of disseminated euhedral and framboidal pyrites. The hydrothermal episode is associated with Mg-metasomatism and characterised by low grade copper mineralisation that occurs (i) in veins filled with carbonate-chlorite and carbonate-quartz-chlorite-Cu sulphides, such as chalcocite, chalcopyrite and bornite, and (ii) as disseminated sulphides within the host rock. This second episode is late to post-orogenic and can be correlated with late brittle tectonics within the Lufilian arc. The other alteration types include silicification and potassic alteration; however, these alterations are not associated with mineralisation.

Sedimentary evolution and stratigraphy of the ~765–740 Ma Kansuki-Mwashya platform succession in the Tenke-Fungurume Mining District, Democratic Republic of the Congo

“…2). Although, the glacial origin of these diamictites is still debated due to recent observation of submarine gravity sliding of unconsolidated sediments (Kennedy et al, 2019;Twite et al, 2019) on one hand, and the presence of glaciogenic, glaciofluvial, glaciolacustrine or glaciomarine deposits recognized within these diamictites on the other hand (Binda & Van Eden, 1972;Wendorff & Key, 2009;Master & Wendorff, 2011;Mambwe et al, 2017a). The age of the Mwashya Subgroup is younger than the U-Pb SHRIMP age of 765 ± 5 Ma and 763 ± 6 Ma measured on zircon grains from volcanic rocks in the Kansuki Formation (Key et al, 2001;Cailteux & De Putter, 2019).…”

“…The Kitana Syncline is the only one in the area that has a normal sequence starting from the Fungurume Subgroup up to the Ngule Subgroup. The Mutaka and Pumpi synclines are located south of the Fungurume Fault and Cailteux et al, 2018) and location of the Tenke Fungurume Mining District (from Mambwe et al, 2017a). the Pumpi Overthrust Fault, which consist of a normal succession of Nguba and Kundelungu rocks (Fig.…”

“…In the western part of TFMD, mega-fragments observed in the Pumpi region form rafts consisting of Nguba and Kundelungu rocks (e.g., Kabwe and Lukonde rafts). In the central part of TFMD, a window into the Roan shows tectonic megabreccias of the Cu-Co-mineralized Mines Subgroup and the Mwale Formation (e.g., Shanika Raft) (Jackson et al, 2003;François, 2006;Mambwe et al, 2017aMambwe et al, , 2019b.…”

Mobility of copper and cobalt in metalliferous ecosystems: Results of a lysimeter study in the Lubumbashi Region (Democratic Republic of Congo)

“…Katanga is known for Cu and Co ore deposits. Several world class deposits are exploited for these elements as the Tenke-Fungurume deposits (Fay and Barton, 2012;Mambwe et al, 2017). Over a century, mining has disseminated large quantities of waste in the environment and created secondary metalliferous substrates with elevated concentrations of Cu and Co (Pourret et al, 2016;Faucon et al, 2016).…”

“…The mineralogical composition of samples was further determined by optical microscopy, scanning electron microscopy (SEM) and energy dispersion spectrometry (EDS). Samples were examined under a Leica DRM-XP polarizing microscope in transmitted and reflected light and subsequently studied under a Hitachi S3400 SEM equipped with a ThermoNORAN NSS Ultradry EDS (Pourret et al, 2016) and further refined using previous studies from literature (Fay and Barton, 2012;Schuh et al, 2012;Decrée et al, 2015;Mambwe et al, 2017).…”