Genesis of sediment-hosted stratiform copper–cobalt mineralization at Luiswishi and Kamoto, Katanga Copperbelt (Democratic Republic of Congo)

Abstract

The sediment-hosted stratiform Cu-Co mineralization of the Luiswishi and Kamoto deposits in the Katangan Copperbelt is hosted by the Neoproterozoic Mines Subgroup. Two main hypogene Cu-Co sulfide mineralization stages and associated gangue minerals (dolomite and quartz) are distinguished. The first is an early diagenetic, typical stratiform mineralization with finegrained minerals, whereas the second is a multistage synorogenic stratiform to stratabound mineralization with coarse-grained minerals. For both stages, the main hypogene Cu-Co sulfide minerals are chalcopyrite, bornite, carrollite, and chalcocite. These minerals are in many places replaced by supergene sulfides (e.g., digenite and covellite), especially near the surface, and are completely oxidized in the weathered superficial zone and in surface outcrops, with malachite, heterogenite, chrysocolla, and azurite as the main oxidation products. The hypogene sulfides of the first Cu-Co stage display δ 34 S values (−10.3‰ to +3.1‰ Vienna Canyon Diablo Troilite (V-CDT)), which partly overlap with the δ 34 S signature of framboidal pyrites (−28.7‰ to 4.2‰ V-CDT) and have Δ 34 S SO4-Sulfides in the range of 14.4‰ to 27.8‰. This fractionation is consistent with bacterial sulfate reduction (BSR). The hypogene sulfides of the second Cu-Co stage display δ 34 S signatures that are either similar (−13.1‰ to +5.2‰ V-CDT) to the δ 34 S values of the sulfides of the first Cu-Co stage or comparable (+18.6‰ to +21.0‰ V-CDT) to the δ 34 S of Neoproterozoic seawater. This indicates that the sulfides of the second stage obtained their sulfur by both remobilization from early diagenetic sulfides and from thermochemical sulfate reduction (TSR). The carbon (−9.9‰ to −1.4‰ Vienna Pee Dee Belemnite (V-PDB)) and oxygen (−14.3‰ to −7.7‰ V-PDB) isotope signatures of dolomites associated with the first Cu-Co stage are in agreement with the interpretation that these dolomites are by-products of BSR. The carbon (−8.6‰ to +0.3‰ V-PDB) and oxygen (−24.0‰ to −10.3‰ V-PDB) isotope signatures of dolomites associated with the second Cu-Co stage are mostly similar to the δ 13 C (−7.1‰ to +1.3‰ V-PDB) and δ 18 O (−14.5‰ to −7.2‰ V-PDB) of the host rock and of the dolomites of the first Cu-Co stage. This Editorial handling: H. Frimmel Electronic supplementary material The online version of this article

Petrography and geochemistry of the Shilu Fe–Co–Cu ore district, South China: Implications for the origin of a Neoproterozoic BIF system

“…S CDT values ranging from +11.1 to 17.5‰ (average +15.97‰; Xu et al, 2009), comparable to a mean δ 34 S value of +17.5‰ ± 3‰ for Neoproterozoic seawater at the time of deposition of the Shilu Group, but distinctly different from those of the Zambian Copperbelt (El Desouky et al, 2010;Sweeney et al, 1986). Nevertheless, the previous study (Xu et al, 2013) has indicated that the tectonic, metamorphic and hydrothermal reworking which most likely was related to the multistage orogenies in South China has significantly modified the Shilu district resulting in enrichment and upgrading of Fe-and Co-Cu ores and secondary mineralization.…”

Reactive transport modelling of ore mineral zoning and the paragenesis of copper sulfides in sediment-hosted stratiform ore deposits, the Katanga Copperbelt (DRC)

“…Bartholomé et al, 1972). This replacement of pyrite by chalcopyrite is followed by the replacement of chalcopyrite by bornite, bornite by digenite and finally digenite by chalcocite (El Desouky et al, 2010). Chalcopyrite, bornite and chalcocite can also occur as direct precipitates or replacement of anhydrite in nodules and lenses (Muchez et al, 2008).…”

“…This early pyrite was replaced by chalcopyrite (Bartholomé et al, 1972). At Kamoto and Luiswishi (Katanga Copperbelt), this replacement is followed by a general succession of chalcopyrite, bornitecarrollite and chalcocite (El Desouky et al, 2010). A vertical and lateral distribution pattern from copper-rich minerals (chalcocite) to pyrite has been described for many deposits in the Katanga Copperbelt (Oosterbosch, 1962;Lefebvre, 1989;Cailteux et al, 2005).…”

“…A multiphase origin has been proposed by many authors during the last decade (Cailteux et al, 2005, Selley et al, 2005Dewaele et al, 2006;El Desouky et al, 2010), and is characterized by several hypogene phases, ranging from early diagenetic up to syn-orogenic, followed by an important supergene phase .…”

Fluid evolution of the Paleoproterozoic Hujiayu copper deposit in the Zhongtiaoshan region: Evidence from fluid inclusions and carbon–oxygen isotopes

“…2B). The interaction between the oxidized Cu-bearing brines and reduced carbonaceous shales would have resulted in the oxidation of organic matter El Desouky et al, 2010), which may be the main reason for the significant variation of carbon isotope values.…”