Barberton Barite Drilling Project – BBDP
Summer 2008, we completed diamond drilling of ~200m of sedimentary and volcanic rocks from the Barberton Greenstone Belt in South Africa.
Reasons for drilling
The BBDP core was obtained on the west limb of the Barite Syncline, which provides some of the best exposures of the transition from a system dominated by tectonic quiescence, the deposition of komatiitic volcanic units and deep-water carbonaceous black cherts forming the top of the Mendon Formation (Onverwacht Group), to one dominated by active tectonics, felsic volcanism and the deposition of shallow-water terrigeneous and volcanoclastic units of the Mapepe Formation (Fig Tree Group). The Mapepe Formation consists of a complex clastic and cherty sequence barite beds, spherule beds, thin jasper layers and a variety of greenish cherts representing silicified felsic ash, which contain disseminated barite, cherty sandstones containing detrital barite and jasper grains and chert pebble conglomerates. This succession is thought to have been deposited as a complex fan delta and coastal association along the flank of the tectonically exhumed underlying Mendon Formation and penecontemporaneous felsic volcanic rocks as indicated by the occurrence of several terrigeneous beds enriched in black chert and felsic sand in the upper part of the core. Radiometric age constraints of felsic tuff at the base of the Mapepe Formation indicate that felsic volcanism occurred between 3.22 and 3.24 Ga. The Barite Syncline stratigraphy closely resembles the 3.49 Ga old Chert-Barite Unit of Dresser Formation, Pilbara Craton, Western Australia for which we have obtained two drill cores as part of Pilabra Drilling Project (PDP2). In this respect, it was of great value to obtain a new drill core from such a stratigraphic unit that was located some 1000 km away from the Pilbara terrane during deposition. Detailed petrography and geochemical studies of drill cores from this unit can therefore greatly expand our insight in the Early Archean environment and associated evolution of early life.
Site Location
The dr
illing site was chosen in the west limb of the barite syncline (25°54’24.8”S and 31°03’23.9”E) where bedded sedimentary rocks of the Mapepe Formation dip 40° to 55° to the southeast. The drillhole was sited to the east of the surface outcrops, in the stratigraphic hangingwall, and were oriented at 50° towards 288°, in order to intersect the bedding at about right angle. The hole was drilled with HQ core (75.7 mm diameter) and NQ core (47.6 mm diameter) to a depth of 182.4 m depth. A preliminary stratigraphic log of the drill core obtained is shown beneath. The diamond drillcore was oriented.
Synthetic stratigraphic log of the Barberton Barite drill hole. Stratigraphic legend: 1, Shales. 2, Felsic volcanoclastic tuff grading into sandstone, local barite and jasper beds (3). 4, Bedded barite. 5, Black chert. 6, Komatiites cut across with black and white chert veins. After Philippot et al, 2012.
Drilling team
The BBDP was performed in continuation of the Barberton Scientific Drilling Project organized by Maarten de Wit from the Africa Earth Observatory Network at the University of Cape Town and Harald Furnes from Center for Geobiology in Bergen. Many thanks to both of them and to Eugene Grosch and Nicola McLoughlin for their collaboration and great field excursions. André van Wyk and Grant Innes of “Drilling in Training” (DiT) and their crew are thanked for their professional work and enthusiasm in obtaining the drillcore. The drilling research team consisted of Pascal Philippot, Mark van Zuilen and Yoram Teitler.
Funding
This project was supported by funds from the Centre National de la Recherche Scientifique and the Institut de Physique du Globe de Paris as part of the !Khure Africa project.