The Albert Silver Mine Revisited: Toward a Model for Polymetallic Mineralization in Granites of the Bushveld Complex, South Africa

Exploration & Mining Geology, Vol. 3, No. 3, 1994

L.J. ROBB and V.M. ROBB, Department of Geology, University of the Witwatersrand, Johannesburg, Republic of South Africa. F. WALRAVEN, Geological Survey of South Africa, Pretoria, Republic of South Africa

The old Albert Silver Mine is a polymetallic deposit comprising concentrations of Cu-Pb-Zn-Ag-U-F within a set of sub-parallel quartz-hematite veins which occur within the fine-grained apical phase of the 2050 Ma old A-type Bushveld granites. Mineralization occurs as an early pyrite-chalcopyrite-arsenopyrite-galena-sphalerite-(argentiferous) tetrahedrite paragenesis followed by a later, more oxidized assemblage comprising chlorite-hematite-fluorite-pitchblende. Accumulation of metals appears to have taken place at the interface between a coarse-grained porphyritic granite and an overlying fine-grained phase: veins occur in the latter and represent leakage of magmatic fluids from the differentiated, water-saturated, subjacent granite. Mineralization processes in the Bushveld granites are believed to be related to long-lived circulation of dominantly magmatic fluids stimulated by the high heat productive capacity of the host rocks. Endo- and exogranitic tin-tungsten and base metal mineralization formed during an evolving hydrother-mal system that lasted for several hundred million years, forming innumerable small- to medium-scale polymetallic deposits. At the Albert Silver Mine, unroofing of the cover sequences at circa 1600 Ma to 1700 Ma resulted in the incursion of lower-temperature, high-fO2 meteoric fluids which remobilized the earlier sulfides and introduced the paragenetically late U-F mineralization.