The Bien Venue massive sulphide deposit is associated with a felsic volcanic succession
developed in the north-eastern part of the Barberton Greenstone Belt, Eastern Transvaal. The
deposit is situated 8km east-north-east of Louw's Creek between the Lily Syncline to the south
and the Stentor Pluton to the north. The stratigraphy of the Onverwacht, Fig Tree and
Moodies Groups in the vicinity of the deposit is poorly documented, and the exact stratigraphic
position of the host felsic volcanics is not known. They are tentatively correlated with the felsic
volcanics from the Theespruit Formation, Onverwacht Group.
The felsic volcanics have undergone low-grade greenschist facies metamorphism and occur as
quartz-sericite schists. Detailed petrography enables sub-division of the volcanic succession into
distinct units. A lapilli metatuff unit hosts the base metal and precious metal mineralisation.
The sulphides are best developed in the upper part of this unit, together with intercalated
barite-rich horizons and cherts. A series of structural events have modified the attitude of the
lithological units and disrupted the continuity of the orebody.
The orebody comprises stratabound lenses of massive to semi-massive and often banded
sulphides, as well as disseminated sulphide mineralisation. The dominant base metal mineralogy
consists of pyrite, sphalerite, chalcopyrite, galena and tennantite. Native silver and various
copper-silver sulphides are also associated with the base metal sulphides. A vertical zonation
of the mineralisation exists, from pyrite-chalcopyrite-rich ore in the footwall, to pyrite -
chalcopyrite-sphalerite-galena-barite-rich ore towards the hanging wall.
Geochemical studies indicate that the Bien Venue lithologies are rhyolitic to rhyodacitic in
composition and show a calc-alkaline affinity. The mobility of some elements at Bien Venue
has been clearly demonstrated. This is believed to be associated with hydrothermal alteration
that has led to SiO2 and MgO enrichment, as well as K2O depletion, in the wall rocks of the
deposit.
The geological setting and nature of the mineralisation at Bien Venue suggest that it is an
example of a volcanogenic exhalative sulphide deposit. In terms of the classification scheme
suggested by Hutchinson (1973, 1980), Bien Venue would best be described as a Primitive type
deposit that contains barite. / Thesis (M.Sc.)-University of Natal, 1990
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/646 |
| Date | January 1990 |
| Creators | Murphy, Philip William. |
| Contributors | Harwood, A., Kerr, Alan. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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