Elisha Mutum Shemang

Continental rifts preferentially initiate in orogenic belts and avoid cratons as old, cold cratonic lithosphere resists deformation. Recent earthquakes in eastern Botswana unveil an active incipient rift zone within the Kalahari Craton that hosts ∼80‐km long, >100‐m high fault scarps of the Khurutshe Graben. We investigate the rift structure, stratigraphy, and long‐term evolution to understand the rift‐timing and initiation mechanisms. We utilize 2‐D electrical resistivity imaging, borehole logs, and observations in excavation trenches across the Khurutshe Fault (KF) to delineate fault structure and relationships with subsurface stratigraphy. The resistivity tomography reveals three geoelectrical layers: a shallow ∼10‐m thick resistive unit representing Holocene Kalahari Formation (EL1) which thickens toward and terminates on the KF, an underlying ∼80‐m thick highly‐discontinuous moderate‐to‐low resistivity Jurassic (“Karoo”) unit (basalts and siliciclastics; EL2) which also thicken toward the KF, and basal highly‐resistive Precambrian basement (EL3). Borehole isopach maps confirm a ubiquitous pattern of hanging wall stratigraphic thickening toward the KF. Fault trenching reveals highly cemented Karoo sandstones hosting slickensided calcite‐altered slip surfaces. These observations indicate: (a) normal faulting with syn‐tectonic deposition of Jurassic sequences evidence Karoo rifting in southeast Botswana, and (b) initial phase of rift faulting followed by magmatism, and rift dormancy. Absence of magmatism during “Karoo” rift inception and the development of the rift zone near an intra‐cratonic suture may reflect early structural inheritance. The rift exploited a mechanical weakness in southern Africa's cratonic lithosphere, and is now reactivated at the tip zone of the Southwestern Rift of the Cenozoic African Rift System.

The minerals sector continues to draw attention from policy makers who would want to see both old and new mineral projects add value to the minerals in the host country. The current technological development in the leaching of manganese oxide ores to produce a high-purity manganese sulphate monohydrate, a compound that is used in the manufacture of batteries for electric vehicles or long-life storage cells for the renewable energy market, has led to junior mining companies spearheading this technology in new projects across the globe. In this paper, we researched the high-purity manganese sulphate monohydrate project pipeline and used projected production volumes and C1 cash costs to construct the industry supply curve for six projects, including the K.Hill project owned by Giyani Metals Corporation near Kanye, in the southern part of Botswana. The aim was to determine the ideal conditions that would provide a comparative advantage for further local value addition to high-purity manganese sulphate monohydrate and to the end user product. The results showed that while the estimated C1 cash costs would place the K.Hill project as the second highest cost producer from among five projects, it would nonetheless have healthy profit margins due to the high projected price of high-purity manganese sulphate monohydrate. The study recommended policy options, which, if implemented, could further encourage the exploitation and value addition of battery metals in Botswana.

Continental rifts commonly develop in orogenic belts and avoid cratons as cratonic crust agedness and cooler geotherms inhibit strain localization. Recent earthquakes in Eastern Botswana unveil an active incipient rift zone within the Kalahari Craton featuring ~80-km long fault scarps of the Khurutshe Graben. Here, we investigate the rift structure, syn-rift stratigraphic architecture and long-term evolution, to understand the timing and rift initiation mechanisms. We utilize 2-D DC-resistivity imaging, borehole logs, and field observations in excavations of the Khurutshe Fault (KF) scarps to delineate its fine-scale structure and relationships with subsurface stratigraphy. Borehole-constrained resistivity tomography reveals four geoelectrical layers: a shallow ~10-m thick resistive wedge unit representing the Holocene Kalahari Formation which thickens towards and terminates on the KF, overlying ~100-m thick highly-discontinuous moderate-to-very high resistivity Jurassic (Karoo) basalts and siliciclastics which also thicken towards the KF, and basal highly-resistive Precambrian crystalline basement. Borehole isopach maps confirm a ubiquitous pattern of stratigraphic thickening on the KF hanging walls. Excavations of the fault zone reveal highly cemented Karoo sandstones hosting slickensided calcite-altered slip surfaces. These observations indicate: 1) concurrent fluid-involved normal faulting with syn-tectonic deposition of the Jurassic sequences, providing for the first time, evidence of Karoo extension in southeast Botswana, and 2) that the Phanerozoic cratonic rift initiation was first accommodated by magmatic diking and normal faulting. We propose that this ancient, failed rift zone constitutes a mechanical weakness in the cratonic lithosphere that is now being reactivated again by the lithospheric buoyancy tectonic forces of the African Superplume.

Hydrothermally altered granitoids in the Batouri district host gold mineralization. Gold and associated metals occur as disseminated, stockwork and veins. The granitoids range from quartz-alkali granitoids sensu stricto to diorite with various types of wallrock alterations including K-feldspar alteration, sericitization, silicification, and sulphidation/ferruginization. Most gold-bearing samples are extensively brecciated. Gold mineralization is accompanied with sericitization, silicification, and sulphidation/ferruginization alterations. Gold concentrations reach a high of 103.7 ppm. The granitic rocks are sub-alkaline. They show enrichment in the LREE, a negative Eu anomaly and a depletion in the HREE reflecting the breakdown and mobility of the initial plagioclase feldspar bearing HREE during fluid-rock interaction. On multielement variation diagrams, spikes at K, Ba, Pb, and Th are depicted resulting from selective enrichment during alteration. Mass gains/losses during alteration calculated using the immobile element method indicate, amongst others, gains in SiO ₂ (silicification), K ₂ O (K-feldspar alteration), SO ₃ and Fe ₂ O ₃ (sulphidation/ferruginization) with losses in Na ₂ O linked to sericitization. The samples show Pd and Pt as high as 2 ppm. Gold mineralization is associated with wallrock alteration zones with elevated contents of As-Ba-Cu-Pb-Rb-Sr-Zn and Zr due to the neominerals developed during hydrothermal alteration. Au-Ag-Zn defines a potential pathfinder element cluster in the Batouri district.

Lode‐gold mineralization in the Bétaré Oya gold district is related to a series of quartz–sulphide veins that define a steeply dipping NNE–SSW‐trending brittle–ductile shear zone. The veins transect metasedimentary sequences in the vicinity of small granitic intrusions. Quartz veins range from barren (massive quartz) to mineralized with textures that vary from foliated, sheared, vuggy, fractured, and sugary to brecciated with inclusions of altered wall rock. They contain gold, pyrite, and galena in addition to chalcopyrite and both hypogene and supergene haematite and covellite. Parameters that consistently define primary gold mineralization in the area include silicification, sulphidation, sericitization, K‐feldspar alteration, haematitization, and carbonatization. Gold grains recovered from heavy mineral concentrate and grains that occur as inclusions in pyrite were characterized by microchemical methods. The gold grains are zoned and exhibit a simple internal structure of partly deformed and leached rims and high‐purity intragranular veinlets. Gold is alloyed with Ag; gold fineness varies between 859 and 877 in the core and from 958 to 997 in the leached rims. Inclusions of gold in pyrite cluster between 875 and 900. Pyrite has up to 0.59 wt% Au, and other trace elements occur in low quantities but for Pb (0.13 wt%), Ag (1.36 wt%), and Sb (1.63 wt%). The bulk trace element signature of the veins is characterized by Au, Ag, As, Bi, Ba, Cr, Cu, Mn, Pb, Sb, Sr, V, W, Zn, and Zr. This depicts a geochemical association of Au ± Cu ± Bi ± As ± Pb. The occurrence of Au as well as elevated Pb and Zn could suggest a granitic source for the ore‐bearing fluid. The auriferous quartz veins are characterized by a widespread in δ³⁴S from 2.8 to 14.9‰ pointing to multiple sources of sulphur in the system, perhaps a mixture of sulphur from the metasedimentary and the granitic rocks.

On 3 April 2017, a M_w 6.5 earthquake struck Moiyabana, Botswana, nucleating at >20 km focal depth within the Paleoproterozoic Limpopo‐Shashe orogenic belt separating the Archean Zimbabwe and Kaapvaal Cratons. We investigate the lithospheric structures associated with this earthquake using high‐resolution aeromagnetic and gravity data integrated with Differential Interferometric Synthetic Aperture Radar (DInSAR) analysis. Here we present the first results that provide insights into the tectonic framework of the earthquake. The ruptured fault trace delineated by DInSAR aligns with a distinct NW striking and NE dipping magnetic lineament within the Precambrian basement. The fault plane solution and numerical modeling indicate that the cause of the earthquake was 1.8 m displacement along a NW striking and NE dipping normal fault, rupturing at 21–24 km depth. We suggest that this seismic event was due to extensional reactivation of a crustal‐scale Precambrian thrust splay within the Limpopo‐Shashe orogenic belt.

A combination of petrography, whole-rock geochemistry, geochronology and compositional variation in magnetite is employed in this study to elucidate the nature and origin of enigmatic magnetite mineralisation hosted within gneissic rocks in the Nyong Unit in southern Cameroon. The mineralisation occurs as magnetite-bearing calc–silicate gneisses. The host rock mineral assemblage comprises quartz–plagioclase–biotite–amphibole–chlorite–clinopyroxene–garnet that provides evidence of medium-grade metamorphism and retrograde alteration. Textural and chemical analyses of the magnetite grains show variable textural and trace element chemical characteristics attributed to metamorphic-hydrothermal overprint and weathering. Magnetite occurs as disseminations and stringers commonly intergrown with amphiboles. It is also observed to show vermiforms wrapped around quartz and clinopyroxenes within a biotite–chlorite- plagioclase groundmass. Massive-granoblastic magnetite is rare and mainly observed within vein-like domains. On backscattered secondary electron images the magnetite grains are anhedral, with minor spinel exsolution lamellae. Electron microprobe analysis on magnetite suggests both a hydrothermal skarn and banded iron formation (BIF) affinity. The lack of negative Ce anomalies excludes a Proterozoic BIF setting, but it is in agreement with Archaean BIF. Sensitive high resolution ion microprobe U-Pb isotope data on zircon in the magnetite gneiss define an identical Wetherill concordia and Tera–Wasserburg Neoarchaean age of 2699 ± 7 Ma (1σ; MSWD (mean square weighted deviation) = 1.3; n = 13), and Pan-African disturbance at about 500 ± 200 Ma. The Neoarchaean age is in accordance with the known onset of BIF deposition at the northern edge of the Congo Craton and therefore constrains the maximum age of formation of the Nyong magnetite gneisses.