Provenance analysis and thermo-dynamic studies of multi-type Holocene duricrusts (1700 BC) in the Sua Salt Pan, NE Botswana

• Published in: Journal of African earth sciences (1994) 2014-08, Vol.96, p.79-98
• Main Authors: Dill, Harald G., Dohrmann, R., Kaufhold, S., Techmer, A.
• Format: Article
• Language: English
• Subjects: Botswana; Heavy minerals; Light minerals; Multi-type duricrusts; Physical–chemical regime; Provenance analysis
• ISSN: 1464-343X; 1879-1956
• DOI: 10.1016/j.jafrearsci.2014.03.014

•It is a Holocene environment of geogenic and anthropogenic impact.•Kaolinite, illite-smectite, and zeolites are key to the physical-chemical changes.•Calcite is abundant in the salt pan and a tool for age dating.•Geogenic heavy minerals accumulated from fluvial and eolian transport.•Anthropogenic heavy minerals derived from archeometallurgical processes. Multi-type duricrusts, composed of silcretes, calcretes, halcretes and sulcretes developed during the Holocene at the northern rim of the Sua Salt Pan, NE Botswana. They were investigated for their light (quartz/chalcedony, feldspar, analcime, clinoptilolite, calcite, kaolinite/halloysite, illite–smectite mixed-layers, halite) and heavy minerals (baryte, clinozoisite–epidote s.s.s., amphibole, corundum, tourmaline, ilmenite, rutile, sphene, kyanite, andalusite, staurolite, garnet, zircon, apatite, monazite, cassiterite, garnet, biotite) using petrographic microscopy, X-ray fluorescence and diffraction analyses, radio-carbon dating, scanning electron microscopy equipped with an EDX-system, cation exchange capacity and infrared spectroscopy. Detrital minerals predominantly derived from the erosion of rocks belonging to the Archaean Basement Complex, the Stormberg Volcanites and the Kalahari sediments. Of particular interest to exploration geologists, geikielite-enriched ilmenite fragments are a hint to kimberlitic pipes. Biodetritus was derived from invertebrates and from vertebrates (fish bones?). A man-made impact on the heavy mineral suite has to be invoked from small fragments of cassiterite fragments that derived from processing of sulfidic and pegmatitic Sn-bearing ore. In the salt-pan-derived duricrusts mainly the aeolian and to a lesser degree fluvial inputs were responsible for the concentration of clasts in these multi-type duricrusts. Moreover, their variegated mineralogy enables us to constrain the physical–chemical regime, prevalently as to the pH and the chemical composition of the major constituents. All duricrusts developed in a self-sufficient chemically closed system where quartz and feldspar provided the elements Si, Na, K, Ca, and Ba to produce the encrustations. The spatial and temporal trend in the Sua Salt Pan rim encrustations may be described as follows: (1) sulcrete–silcretes, (2) silcretes with kaolinite-group minerals towards more recent stages at the rim and smectite-illite mixed-layers and clinoptilolite towards the basin center, (3) calcretes with analcite towards the basin ce