The stanniferous granites of the Zaaiplaats Tin Field are part of the A-Type Lebowa Granite Suite, within the greater Bushveld Igneous Complex of northeast South Africa. The tin field comprises three granites: (1) the Nebo, a leucocratic, equigranular biotite granite; (2) The brick-red hypidiomorphic Bobbejaankop granite, which is extensively microclinized with chloritized biotite and characteristic synneusis-textured quartz; and (3) The variably altered roof facies of the Bobbejaankop granite known as the Lease microgranite. The Bobbejaankop and Lease granites were both extensively mined for cassiterite until 1989. The cassiterite is hosted in disseminations, miarolitic cavities, and within large hydrothermal, tourmalinized, and greisenized pipes and lenticular ore-bodies. An extensive petrological and whole-rock XRF and ICP-MS geochemical study, has provided new insight into the magmatic and magmatic-hydrothermal mineralization processes in these granites. Trace elements and Rayleigh Fractionation modelling suggest the sequential fractionation of the Nebo granite magma to be the origin of the Bobbejaankop granite. Incompatible elemental ratios, such as Zr/Hf and Nb/Ta, record the influence of internally derived, F-rich, hydrothermal fluid accumulation within the roof of the Bobbejaankop granite. Thus, the Lease granite resulted from alteration of the partially crystallized Bobbejaankop granite, subsequent to fluid saturation, and the accumulation of a magmatic-hydrothermal, volatile-rich fluid in the granite cupola. The ratio of Nb/Ta, proved effective in distinguishing the magmatic and magmatic-hydrothermal transition within the Bobbejaankop granite. Elemental ratios reveal the differences between pre- and post-fluid saturation in the mineralizing regimes within the same pluton. Thus highlighting the effect that the location and degree of hydrothermal alteration have had on the distribution of endogranitic tin mineralization.

New SHRIMP U-Pb zircon and titanite data are presented for two amphibolites from the Central Zone of the Damara Orogen, Namibia. These data (the first ages for amphibolites in the Central Zone) show that amphibolites are derived from both Palaeoproterozoic (2026.9 ± 2.3 Ma – sample ACAM-1) and Pan-African (557.2 ± 7.4 Ma – sample LKR021) precursors emplaced into the Palaeoproterozoic Abbabis Complex basement in the Central Zone. The younger amphibolites are interpreted as part of a mafic to dioritic phase of magmatism in the Central Zone (the Goas Suite), and major- and trace-element geochemistry from a suite of amphibolites from the southwestern Central Zone confirms this relationship. This phase of mafic to dioritic magmatism is contemporaneous with the onset of collision between the Congo and Kalahari Cratons. It is suggested that delamination of dense mafic lower crust and underplating of mantle-derived magmas following crustal thickening may have led to partial melting of pre-Pan-African mafic lower crust, generating this mafic to dioritic suite of rocks. Metamorphic zircon overgrowths in sample LKR021 give an age of 520 ± 6.9 Ma, consistent with recent estimates for the age of peak metamorphism in the southwestern Central Zone. Titanites from LKR021 give an age of 493.4 ± 6.4 Ma, and this is interpreted as a cooling age for the Central Zone.

We present the first in-situ Sr isotopic and mineral geochemical results for plagioclase in mafic to ultramafic rocks of the Waterberg Project of the far northern Bushveld Complex. Initial strontium isotopic compositions of plagioclase are dominantly in the range of ⁸⁷Sr/⁸⁶Sr_i (Sr_i) 0.7065 to 0.7075, differing from the rest of the Northern Lobe, which has higher values with an average Sr_i values of 0.708. Based on mineralogy and geochemistry, the intrusion was previously interpreted to consist of two main pulses. However, the Sr isotopic data exhibit relatively little stratigraphic variation over a wide range of rock types. The results of this study, therefore, represent a paradox: Compositionally clearly different magmas have nearly identical initial Sr ratios, whereas the compositionally somewhat similar magmas of the Northern Lobe display statistically significantly different initial Sr ratios. We suggest, therefore, that the observed Sr values represent a proxy for the residence time and concomitant country rock assimilation of magma in the lower crust and in the case of the Waterberg Project, indicate one common staging chamber for all magmas. Furthermore, the data presented here, together with recently published studies support a disconnect between rocks north and south of the Hout River Shear Zone, and indicate two separate, mineralized, magmatic basins.

Zircon U-Pb, Hf- and O-isotopic results from granites and basement rocks from the southwestern Central Zone of the Damara Belt (Namibia) are used to decipher the process of remobilization during collision in this Pan African (ca. 580 to 500 Ma) orogeny between the Congo and Kalahari cratons. The lack of juvenile Damaran magmatism highlights that little new crust was generated and, consequently, that there was little or no oceanic subduction preceding collision. Basement rocks from the Damara Central Zone have Archaean model ages, consistent with them being a southerly extension of the Congo Craton; however, Damaran granites formed in response to the collision tend to have model ages younger than those for the Congo Craton. It is argued that this indicates reworking of younger crust belonging to the leading edge of the Kalahari Craton and that the Congo Craton basement experienced only limited mid- to lower-crustal heating. We therefore invoke initial underthrusting of the Kalahari Craton below the Congo Craton during the collision of these two cratons, leading to mantle lithosphere eclogitization and delamination, and heating of the mafic lower crust of the Kalahari Craton. This produced the mafic to granitic Goas Suite at 560 to 540 Ma. Subsequent lithospheric thinning further heated the underthrust Kalahari Craton material, resulting in granulite-facies LPHT metamorphism and widespread granitoid magmatism at 520 to 510 Ma. This is consistent with geophysical transects of the orogen showing that the lithosphere below the Damara Belt is thinned, in contrast to the Congo Craton which has a thick, cold, lithospheric root and a lower geothermal gradient. This model is also consistent with petrological evidence which shows no evidence for deep burial of the Central Zone, and a near-isobaric heating path to granulite facies.

The Zaaiplaats tin field is host to two of the historically most significant tin mines in South Africa. The geological maps of Zaaiplaats and Groenfontein have not been updated since the 1980s and 1950s respectively and warrant a renewed investigation. Cassiterite is hosted in the Bobbejaankop and Lease granites, of the Zaaiplaats and Groenfontein tin mines, which are part of the Lebowa Granite Suite of the Bushveld Complex. Tin mineralisation is primarily hosted as low-grade disseminations and within networks of high-grade hydrothermal pipes and lenticular ore-bodies. One difficulty in mapping such formations arises from the limited lithological variability between mineralised and unmineralised granitic facies. In order to map the granitic lithologies and discriminate alteration zones, an integrated approach is applied by combining remote sensing and in situ portable X-ray fluorescence (pXRF) mapping. The pXRF large ion lithophile (LIL) element distribution mapping, specifically correlating Rb, Sr and Ba with Sn, points to the concentration of late-stage magmatic-hydrothermal fluids, which are associated with endogranitic mineralisation. The use of the Rb/Ba ratio highlights regions of late-stage magmatic-hydrothermal alteration, effectively delineates granitic facies and identifies zones of potential tin mineralisation. Spectral image processing techniques were used as tools to support the mapping of these granites, their variable degrees of magmatic-hydrothermal alteration and regions of endogranitic disseminated mineralisation. We thus exemplify that an expert-based and synergic approach, combining inexpensive in situ pXRF and freely available satellite remote sensing data, supports the mapping and identification of endogranitic mineralisation in early exploration stages. Furthermore, due to its versatility, this approach can easily be applied to other styles of plutonic mineralisation.