Carbonate dykes associated with Archaean lode-Au mineralisation, Barbertongreenstone belt, South Africa

Carbonate dykes, exposed within the Barberton greenstone belt, display geoc hemical signatures similar to altered carbonatite. The trace element signat ure normalised to primordial mantle, and the chondrite-normalised REE trend s of the Ulundi Dyke display geochemical similarities to carbonatites. In a ddition, stable isotope results from the Ulundi Dyke (delta(13)C(whole rock ) and delta(18)O(whole rock) range from -3.7 to -4.9 parts per thousand and 12.8 to 13.2 parts per thousand, respectively) are similar to values found for samples of wall rock and vein carbonate from Archaean Au-quartz-carbon ate-sulphide vein systems studied in the Barberton greenstone belt. Althoug h the data do not plot in the field of primary igneous carbonatite, they ar e similar to data of deuterically-altered carbonatite. These associations s trengthen the deduction that lode-Au mineralised fractures and shear zones in the Barberton greenstone belt were open to mantle-tapping fundamental fa ults. (C) 2000 Elsevier Science Limited. All rights reserved.