Orebody characterisation and structural features that govern copper and cobalt mineralisation in the eastern limb of the Lufilian Arc, Democratic Republic of Congo

[摘要] The Central African Copperbelt is located in the Lufilian Arc which straddles the border betweenZambia and the Democratic Republic of Congo (DRC). Mineralisation of the cupriferous Arc is foundin basal Neoproterozoic Katangan Supergroup sedimentary rocks, which in DRC are termed theMines Series Subgroup. The Mines Series is divided into the dolomitic and carbonaceous GRAT,DStrat RSF, RSC, SD and CMN units. The composition of the units is homogeneous across theLubumbashi district and potentially across the Katangan basin. This study focussed on the Kinsevereand Ruashi deposits in the Lubumbashi district, which are approximately 50 km apart.The study confirmed that relative eustatic sea level changes resulted in the non-deposition of theRSF and RSC stratigraphic units at Kinsevere. Sedimentation was followed by early pervasive potassicalteration and silicification at the diagenetic stage whilst a magnesian dolomitisation event resultedin alteration of potassic feldspars and recrystallisation of carbonates. Albitisation was veincontrolledand late-stage scapolitisation altered evaporitic nodules. Finally, haematisation by lateiron-rich fluids circulating through the Roan Group strata resulted in oxidation of sulphides.The structural analysis of Kinsevere Central pit indicates E-W and N-S shortening whereas the Ruashipit 1 deposit underwent NE-SW and N-S shortening. Initial shortening, associated with Kolweziandeformation (D1), resulted in the formation of NE-thrust folds and a primary set of joints. TheKolwezian deformation event (D2), reoriented the shortening direction from E-W to N-S, creatinginterference folds and possibly a second set of joints. The final phase in the structural evolution ofthe Kinsevere and Ruashi deposits was late-stage brittle deformation (faulting).Mineralisation was a multi-stage process. Disseminated chalcopyrite and carrollite were depositedfrom formation waters during diagenesis in a stable basin environment. Chalcopyrite, carrollite,chalcocite and bornite are predominantly located at the base of the DStrat, whereas chalcopyriteand pyrite dominate the stratigraphically higher portions of the deposits. Hypogene veinmineralisation began at the syn- to late- orogenic stage with carrollite and chalcopyrite in beddingparallelveins. Possible changes in the compression direction created the perpendicularly orientedveins that host chalcopyrite, carrollite, bornite, covellite, digenite and chalcocite. Finally a late stageof chalcopyrite and pyrite deposition occurred in and around the evaporites, indicating a strongcorrelation between mineralisation, evaporites and scapolitisation.iiiNear-surface supergene alteration of hypogene sulphide ores, resulted in Cu-Co carbonates andoxides, such as malachite, azurite, cobaltiferous malachite, chrysocolla, kolwezite andsphaerocobaltite being deposited in vugs and pore spaces above the meteoric water line. Faultedand brecciated zones tend to have deeper supergene alteration. Between the sulphide facies atdepth and the supergene oxide facies at surface is a transition zone which marks the depth to whichoxidation has penetrated.Sulphur isotope analysis from the Kinsevere and Ruashi deposits suggests a sulphur contributionfrom a continental Red-Bed sedimentary source and from an evaporitic source.

[发布机构] University of the Witwatersrand