Abstract
The origin of giant, sedimentary rock-hosted copper-cobalt (Cu-Co) provinces remains contentious, in part due to the lack of precise and reliable ages for mineralisation. As such, no consensus has been reached on the genetic model for ore formation, and the relationships between tectonism, palaeo-fluid circulation and mineralisation. Here, we link the timing of Cu-Co mineralisation in the Central African Copperbelt to compressional tectonics during the Lufilian Orogeny by using new ca. 609–473 Ma ages given by rhenium-osmium (Re-Os) isotope data for individual Cu-Co sulphides (carrolite and bornite) from the Cu-Co Kamoto deposit. The initial Os isotope composition of carrolite is compatible with the leaching of Os and Cu(-Co) from Mesoproterozoic Cu sulphide deposits hosted in fertile basement. In contrast, the ca. 473 Ma Cu-Au mineralisation stage, which is coeval with late- to post-compressional deformation, may be a distal expression of fluid flow and heat transfer caused by magmatic intrusions in the core of the collisional orogen. The Re-Os ages support a model for mineralisation driven by evaporite dissolution and percolation of large volumes of dense brines in the Katangan Basin during the Lufilian Orogeny.
Highlights
The most important source of copper (Cu), beyond that of giant and supergiant porphyry Cu deposits, is sedimentary rock-hosted stratiform and vein-type Cu deposits
We present new Re-Os isotope geochemistry and geochronology data from mineral separates of individual sulphide species from fifteen mineralised samples from the sedimentary horizons comprising the Upper and Lower Orebodies at the Cu-Co Kamoto deposit, in the western part of the Central African Copperbelt, Katanga province, DRC
We discuss the possible roles of the demise of mid-Neoproterozoic ice ages followed by the building of the Lufilian fold-and-thrust belt with known linkages to salt tectonics, for the formation of the giant, sedimentary rock-hosted Cu-Co ores of the Central African Copperbelt[20] based on the new geochronological data
Summary
A total of 15 carrolite- and/or bornite-mineralised samples from the Upper Orebody, Lower Orebody and evaporitic breccia from the Cu-Co Kamoto deposit, DRC, were processed prior to Re-Os isotope geochemistry (Details of sample characterisation in the Supplementary Data Table). Polished thin sections of the 15 samples were studied by means of transmitted and reflected light microscopy in order to establish, prior to mineral separation, the paragenetic relationships between sulphides and gangue minerals, as well as the relative timing between carrolite and bornite. The mounts were studied by scanning electron microscopy (SEM) using a Hitachi SU-70 FEG SEM operated in backscattered electron mode (SEM-BSE, beam conditions of 20 kV) To further this quality control of mono-mineralic sulphide separates, these qualitative observations were complemented by point wavelength-dispersive spectroscopy (WDS) analyses of carrolite and bornite in the mounts using the following suite of elements: S, Fe, Co, Ni, Cu, Cd, and Te
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