G. J. Beukes

Petrochemical evidence on the probable origin of ferriferous metasediments in western Bushmanland

The mineralized Proterozoic metasediments of Bushmanland are characterized by the presence of ferriferous rocks. This includes banded and unbanded iron formations and various types of gossans. These units are not laterally extensive and occur in different stratigraphic levels. The prevalent minerals in the ferriferous rocks are hematite, magnetite, quartz, garnet, muscovite, biotite and sillimanite, but less common occurrences of graphite, alunite, plumbojarosite, gahnite and dufrenite have been noted. The chemical variation (wt%) is extensive: total Fe2O3 (1.3–93.5), SiO2 (4–93), Al2O3 (0.2–14.0), CaO (0.02–20.7), MnO (0.0–14.3), MgO (0.0–5.7), TiO2 (0.0–4.4), Na2O (0.0–2.0), K2O (0.0–1.5) and P2O5 (0.1–7.0). The preliminary nature of the data set precludes, however, firm conclusions regarding stratigraphic control of the chemical composition. The trace-element contents (ppm) extend over several orders of magnitude: Zn (0–7,000), Ba (0–5,200), Cu (0–1,400), Pb (0–1,070) and Ni (6–540). Collectively, the data indicate that most of the ferriferous rocks represent highly metamorphosed sediments.

The composition of descloizite-mottramite in relation to the trace-element distribution of Pb, Zn, Cu and V in the Otavi Mountain Land, South West Africa/Namibia

Abstract The carbonate rocks of the Otavi Group (ca. 800 Ma) in the northeastern part of South West Africa/Namibia are known to contain Pb, Zn and Cu sulphide deposits with the mining activities at Tsumeb, Kombat and Berg Aukas being the most prominent. Vanadium mineralisation, associated with karst development, is often associated with the sulphide deposits, but occurrences without a sulphide association are also present. The distribution of Pb, Zn, Cu and V in the dolomite and limestone of the Otavi Mountain Land delineates geochemical regions which coincide with the above mineralisation. This coincidence is also manifest in the type of V mineralisation; where high concentrations of Zn occur in the country rocks, descloizite predominates, whilst mottramite occurs when the Cu values are higher.

The Jacomynspan copper-nickel prospect — a study of secondary dispersion in the calcretes of the Northern Cape Province, South Africa

Abstract Large parts of the Northern Cape Province in South Africa are blanketed by Quaternary calcrete under which potential base-metal ore-deposits may occur. In an attempt to examine the distribution of ore-related elements in a calcrete environment, the copper-nickel prospect at Jacomynspan was investigated and both calcrete and soil samples were studied. The Cu, Ni and Co values decrease in the profiles from the bedrock upwards, but remain anomalous up to 2 m above the bedrock. Lateral dispersion of these elements reveals limited but intense anomalies in the calcrete as opposed to wider but subdued anomalies in the soils covering the ore-body. Pedogenic calcrete, where the in situ weathering products (soil and gossan) of a sulphide ore-body are calcretised at a later stage, presents an ideal medium for followup and detailed geochemical exploration in the secondary environment.

Secondary ZnPbCu minerals, an aid to mineral exploration in the Aggeneys area, Bushmanland, South Africa

Abstract A close spatial association exists between secondary and primary CuPbCu minerals in the Aggeneys area, Bushmanland, South Africa. A wide variety of metamorphic and non-metamorphic indicator mineral assemblages occur within this area which may successfully be utilized in mineral exploration programmes. The mode of occurrence, associations and parageneses of secondary silicates, oxides, sulphates, phosphates, carbonates, carbonate-sulphates and chlorides are described, while their importance as indicators of mineralization is stressed.