Nature 357, 677 - 680 (25 June 1992); doi:10.1038/357677a0

Ages of altered granites adjoining the Witwatersrand Basin with implications for the origin of gold and uranium

L. J. Robb^*, D. W. Davis^†, S. L. Kamo^† & F. M. Meyer^*

^*Department of Geology, University of the Witwatersrand, 1 Jan Smuts Avenue, Johannesburg 2050, Republic of South Africa
^† Jack Satterley Geochronology Laboratory, Royal Ontario Museum, Toronto, Ontario M5S 206, Canada

ONE of the main problems in understanding the origin of the Witwatersrand Basin mineralization concerns the source of the prodigious concentrations of gold and uranium in the basin; another problem is the age and nature of the rocks in the source area. Recent data^1,2 indicate that the source area was largely 3,200–2,900 Myr old, becoming progressively younger as the basin evolved. Granites adjoining the basin are commonly overprinted by pervasive and vein-related hydrothermal alteration, which resulted in an enrichment of both gold and uranium^3,4. Here we report uranium-lead data demonstrating that these hydrothermally altered granites were intruded sporadically, both before and during the 360-Myr period⁵ constraining Witwatersrand sediment deposition, and that hydrothermal alteration was associated with granitoid intrusion and subsequent cooling. Thus, 'fertilization' of the crust occurred during basin evolution, a feature that supports the idea¹⁹ that gold and uranium mineralization occurred simultaneously with sediment deposition.

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