Paper Number: 21
Precambrian gold-bearing Nemui Conglomerates, eastern Siberia: Possible analogue to the Witwatersrand Basin and a new emerging gold province
Kepezhinskas, P.K.
1Mineral Investments Resources plc, London, United Kingdom (pavel_k7@yahoo.com)
______________________________________________________________________________
The Witwatersrand basin is a unique geologic structure that is believed to hold about 40% of the world’s gold resources and historically produced nearly one-half of all gold ever mined on planet Earth. Witwatersrand mineralization is hosted in a system of flat-dipping reefs that originated through a prolonged accumulation of detrital gold in a major sedimentary basin, a basin also characterized by prolific volcanic activity and intense hydrothermal alteration. The sheer size of Witwatersrand gold-bearing structure suggests that such an incredible geologic phenomenon could have only been the result of a unique set of conditions that probably were never reproduced anywhere else in the course of geologic history. However, geologic basins resembling Witwatersrand, at least in some characteristics, have been described in the Amazon, Guyana, Kuloi (NW Russia), and Pilbara cratons. Possibly the closest analogue to Witwatersrand is the newly discovered, Precambrian gold-bearing Nemui sedimentary basin in eastern Siberia (Table).
| GEOLOGIC PARAMETERS | |
|---|---|
| Witwatersrand (3.1-2.7 Ga) | |
| Nemui (Mesoarch.-Paleoprot.) | |
| Petrographic features of sedimentary rocks | |
| Abundant pyrite, mica in the shaly matrix | |
| Pyrite, mica in the shaly matrix | |
| Geochemical features of sedimentary rocks | |
| Elevated Th, Ta, Ti, Y, W, and REE (igneous provenance) | |
| Elevated Th, Ta, Nb, Y, Bi and REE (igneous provenance) | |
| Associated greenstone belt and possible provenance rocks | |
| Barberton greenstones and hydrothermally altered granitoids geochemically anomalous in Au and U | |
| Batomga greenstones and hydrothermally altered granitoids geochemically anomalous in Au and U | |
| Mineralization | |
| Gold, uranium, rare diamonds | |
| Gold, uranium, rare diamonds | |
| Mineralized structures | |
| Stacked, sub-horizontal reefs, late-stage faulting, mafic dikes | |
| Stacked, sub-horizontal reefs, late-stage faulting, mafic dikes | |
| Gold occurrence and shape | |
| Mostly free, predominantly disclike with some toroidal forms, extreme flattening | |
| Mostly free, re-mobilized intergrowth with quartz pebbles; predominantly disclike, flat oval, and circular with extreme flattening | |
| Possible formation model | |
| Detrital, syn-sedimentary and (or)hydrothermal, with inputs from ancient volcanic activity and Archean biological processes | |
| Currently unclear, but most probably detrital (paleo-placer) with later hydrothermal alteration |
Although the Nemui basin is currently experiencing early stages of exploration history, it is already famous for its modern alluvial gold operations that routinely produce unique flattened gold nuggets, the largest of which (7.6 kg) is hosted in the State Diamond Fund of Moscow Kremlin’s Treasury. The current gold resource for a single isolated deposit within the Nemui paleo-clastic system stands at 14 Moz of contained gold grading 3 g/t Au or higher, with an overall potential to host several major world-class, detrital gold deposits.