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