A càrrec de Prof. Philippe MUCHEZ (Geodynamics and Geofluids Research Group, Katholieke Universiteit Leuven, Bèlgica)
Organitzat conjuntament CSIC-UB

Data: 01-06-2011
Hora: 12:00
Lloc: Sala d'actes de l'Institut Jaume Almera

Descripció:
The Central African Copperbelt is one of the largest and richest Cu-Co metallogenic provinces in the world. A recent consensus suggests these high-grade stratiform deposits resulted from multiple mineralization/remobilization stages. During initial rifting, Cu and Co sulfides formed due to convective circulation of brines in the underlying rock pile including the pre-Katangan basement, from which metals were leached. Interaction of these brines with bacteriogenic sulfide resulted in early diagenetic, stratiform mineralization. This stage occurs in the DRC, but is absent or obscured in Zambia. Ore events then occurred during the Lufilian Orogeny at ~583-526 Ma. In Zambia, layer-parallel veins formed at lithostatic pressures during basin inversion. Subsequently, rocks and layer-parallel veins were folded, concentrating minerals in the hinge zones of the folds. Highly irregular veins formed at high pressures during the main phase of the orogenesis. Unfolded massive veins cr

To unravel this complex metallogenesis, mineralogical and geochemical studies must be carried out on individual stages. ∂34S increases from early diagenetic stratiform sulfides to syn-orogenic sulfides, reflecting the evolution from early bacteriogenic sulfides to sulfur derived from thermochemical sulfate reduction. Fluids associated with the first Cu-Co mineralization stage had moderate temperature (115° to ≤220°C) and salinity (11.3 to 20.9 eq.wt% NaCl). In the DRC [4], the second Cu-Co stage is related to a hydrothermal fluid with a higher temperature (>270°C) and salinity (35 - 45 eq. wt% NaCl). Although, the barren host-rock carbonates show Sr isotope signatures compatible with Neoproterozoic marine seawater, carbonates associated with all the mineralization/remobilization stages in Zambia and with the early diagenetic mineralization stage in the DRC are significantly more radiogenic, reflecting the interaction of the fluids with basement rocks or basement-derived s