Back to Abstract Index
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).
| 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.
