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Details van artikel 5 van 11 gevonden artikelen
| Titel: |
Evidence for the origin of hydrothermal alteration in granitoids after witwatersrand basin deposition, South Africa |
| Auteur: |
Klemd, R. Wulbers, A. Hallbauer, D. K. Barton, J. M. |
| Verschenen in: |
Australian journal of earth sciences |
| Paginering: | Jaargang 41 (1994) nr. 2 pagina's 131-140 |
| Jaar: |
1994-04 |
| Inhoud: |
In order to help resolve the controversy of whether hydrothermal alteration in granitoids associated geographically with the gold-bearing metasediments of the Witwatersrand and Ventersdorp Supergroups is deuteric or the result of later hydrothermal activity, a study was made of the carbon isotopic and fluid inclusion compositions of alteration products in two typical examples of altered granitoid and in the gold-bearing Kimberley Reef of the Central Rand Group (Witwatersrand Supergroup) and the unconformably overlying Ventersdorp Contact Reef. The δ13C values of hydrothermal carbon nodules in altered granitoids (-25.7 to -36.0‰) and of nodular carbon (fly-speck) in the Ventersdorp Contact Reef (-20.6 to -32.4‰) are light, consistent with an organic origin and inconsistent with a magmatic origin. Fluid inclusions in quartz of the altered granitoids and in quartz of shear zones in the gold-bearing reefs display almost identical populations of at least two types. One type, which occurs in all altered granitoid bodies and in the shear zones of the gold-bearing strata, contains H2O, CH4, no daughter minerals, high salinities (up to 30 equivalent wt % NaCl) and low homogenization temperatures (normally between 90 and 250° C), with Na and Ca as the dominant cations, characteristics of diagenetic formation brines and/or retrograde metamorphic fluids. The fluid and stable isotope characteristics in the hydrothermally altered granitoids and the gold-bearing strata are inconsistent with the hydrothermal alteration of the granitoids being exclusive of a deuteric origin. These data are consistent with major parts of the alteration being a result of sediment dewatering affecting both the granitoids and gold-bearing horizons. Therefore, the hydrothermally altered granitoids do not support their role as a possible source for the sulphides, gold and carbon nodules of the Witwatersrand Basin as suggested by Klemd and Hallbauer (1987) and Robb and Meyer (1987, 1990). |
| Uitgever: |
Taylor & Francis |
| Bronbestand: |
Elektronische Wetenschappelijke Tijdschriften |
Details van artikel 5 van 11 gevonden artikelen
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