Berg Aukas Research Articles

The new small emballonurid (Emballonuridae, Chiroptera, Mammalia) from the Miocene of Africa: its phylogenetic and palaeogeographic implications

ABSTRACT The fossil Afrillonura namibensis gen. et sp. nov. from the late Middle Miocene (12–13 Ma) site of Berg Aukas I, Namibia was a medium-sized emballonurid with a gracile dentition. It shows a mosaic combination of dental features of extant Emballonurini and distinct plesiomorphies suggesting its basal phylogenetic position close to the root of the extant clades of the tribe. It shares many odontological characteristics with Coleura and Paremballonura but also with some species of Emballonura. Afrillonura namibensis gen. et sp. nov. differs from most members of the tribe Emballonurini particularly in the presence of a vestigial paracrista on M1, resembling the state in the Palaeogene genus Dhofarella. Together with other available fossils, the new material from Namibia supports the hypothesis of the African origin of the family Emballonuridae. Further phylogenetic conclusions and biogeographic scenarios of emballonurid ancestral distribution are discussed.

Minerals of Berg Aukas, Otavi Mountainland, Namibia

“[Berg Aukas is] without question the world's best locality for crystallized specimens of descloizite” (Moore 2016, p. 473). This comment is confirmed by the inventory of most major private and ins...

Vanadium in slags from smelting of African Pb-Zn vanadate ores: Mineralogy, extractability and potential recovery

Slags originating from the metallurgical processing of Pb-Zn vanadate ores at Berg Aukas (Namibia) and Kabwe (Zambia) contain interestingly high concentrations of V (3750–6140 mg/kg) and can be considered potential sources of this metal. We focused on the mineralogical determination of the major V-bearing phases in these slags using a combination of mineralogical methods (XRD, SEM/EDS, EPMA) and found that V is mainly bound in clinopyroxene (Berg Aukas) and glass/vanadates (Kabwe). The abiotic extraction tests, simulating a hydrometallurgical recovery via agitation leaching, were carried out in 0.5 mol/l sulfuric acid (25 °C and 70 °C, pulp density of 1%) to determine the release of V (and other metals: Pb, Zn) from these slags. The leaching of the metals attained a steady state after 24 h and was systematically higher for the high-temperature trials. There was an incomplete dissolution of V-bearing clinopyroxene from the Berg Aukas slags, as opposed to the much higher extractabilities of V (>80%) observed for the Kabwe slags. Compared to the relatively high Zn extractabilities (>72%), lower yields were observed for Pb due to massive formation of secondary Pb sulfate (anglesite) as confirmed by the PHREEQC-3 calculations and the mineralogical investigation of the slag residues. Due to the high expenses related to the mechanical sample treatment and chemical extraction and low prices of V and Zn, the recovery of these metals from the studied slags is currently non-economical. However, the Kabwe slags have a much higher potential for secondary metal recovery in the future, because they are relatively fine-grained and the extraction could potentially be carried out on the as-is materials without expensive comminution processes (crushing/milling).

New insights into the genesis of willemite (Zn2SiO4) from zinc nonsulfide deposits, through trace elements and oxygen isotope geochemistry

Willemite is a common mineral mainly occurring in the so-called “hypogene” nonsulfide Zn-Pb mineralizations, deposited from what have been interpreted as high temperature hydrothermal or metamorphic fluids. The literature is currently lacking a comprehensive compilation of geochemical data on willemite so the aim of this study was to elucidate specific geochemical signatures for willemites of contrasting genesis. For this work, we analyzed a range of specimens from the Mineralogy Collection of the Natural History Museum in London. The specimens are from several deposit-types: 1.Stratiform hypogene deposits: Franklin and Sterling Hill (USA);2.Structurally-controlled hypogene deposits: Star Zinc, Excelsior, Surprise (Lusaka area, Zambia), Kabwe (Zambia), Berg Aukas and Tsumeb (Namibia);3.Supposedly supergene deposits: Mumbwa area (Zambia), and Altenberg-Vieille Montagne (Belgium).Textures and structures of the willemite-bearing specimens were initially investigated by scanning electron microscope energy dispersive analysis (SEM-EDS). Trace element concentrations were later measured in situ on selected willemite crystals by laser ablation (LA)-ICP-MS. Statistical analyses (principal component analysis-PCA, multivariate analysis of variance, post hoc Tukey HSD test), conducted on the data obtained by LA-ICP-MS, showed that significant differences exist between willemites derived from the various deposit types studied. High-T, stratiform willemite samples contain significant amounts of Mn and Mg, and are statistically different from all the other analyzed specimens. Structurally-controlled hypogene willemites, characterized by lower Mn and Mg concentrations, and by higher Pb, Cu, As, B, Ge contents, are statistically inhomogeneous, both at the district and at the deposit scale. High-T willemite from the Lusaka area contains more Mn than the low-T hydrothermal deposits, with the latter showing higher concentrations of other elements (e.g. Pb, Cu, Ge). Among the willemite generations associated with the supposedly supergene mineralization, only the Mumbwa willemites form a cluster that is significantly displaced from the other deposits. The δ18O isotopic compositions match the mentioned trace element distribution: willemites with similar origin are characterized by similar oxygen isotopic ratios. On the basis of the present work, willemite-types can be distinguished as follows:•High-T willemites are characterized by high Mn + Mg concentrations (between 100 ppm to unit wt%) and by low, positive δ18O compositions (around 3 to 5‰ V-SMOW);•Low-T hydrothermal willemites show Mn + Mg concentrations below 50 ppm and are associated with high Pb + Cu + As + Ge concentrations (above 100 ppm). They also have high, positive δ18O compositions (between 9 and 15‰ V-SMOW);•Willemites derived from (either cold or warm) meteoric fluids have generally low concentrations of the above elements and negative δ18O compositions (−3 and −9‰ V-SMOW). The supposedly supergene Altenberg-Vieille Montaigne willemite, having low Mn + Mg and high Pb + Ge + As concentrations, and showing δ18O compositions between 11 and 12.5‰, likely formed from low-T hydrothermal fluids.

Vanadium-rich slags from the historical processing of Zn–Pb–V ores at Berg Aukas (Namibia): Mineralogy and environmental stability

The historical mining and processing of Zn–Pb–V ores at Berg Aukas in northern Namibia left large amounts of various wastes. This study focuses on the mineralogical and geochemical investigation of the V-rich slags issued from the processing of the local ores in the Waelz kiln, which was operational between 1968 and 1980 and left ca. 500 kt of slag deposited on the adjacent dump. A combination of mineralogical methods, bulk chemistry, leaching tests and speciation-solubility modeling was used to understand the binding of the major contaminants (Zn, Pb, V) in the solid phase and their potential release under the changing environmental conditions. The average concentrations of the metal(loid) contaminants in the slags are 3.78 wt% Zn, 3370 mg/kg Pb, 5880 mg/kg V, 767 mg/kg Cu, 578 mg/kg As and 92 mg/kg Sb. The mineralogy is dominated by high-temperature silicates (clinopyroxene, melilite, olivine-family phases) and Zn-bearing phases (willemite, zincite). All the primary silicates and oxides are Zn-rich, but vanadium is mainly concentrated in clinopyroxene (up to 5 wt% V2O3). Metallic Fe inclusions, formed under highly reducing conditions in the kiln, are highly weathered. Secondary Fe(III) (hydr)oxides, corresponding to the main weathering products in the slag, efficiently sequester the metal(loid)s (mainly As and Sb). The EU regulatory leaching tests indicated that the release of the metal(loid) contaminants is quite low at the natural pH (deionized water extract: 8.5–10.4) obtained by extraction in the deionized water and only Sb in all the slag samples exceeds the EU limits for the landfilling of inert waste. The pH-static leaching tests revealed up to 5 orders of magnitude higher release of Pb and Zn under acidic conditions (up to 38% and 63% of their total concentration, respectively), compared to the natural pH. In contrast, V exhibits relatively flat pH-dependent leaching patterns with only <1.6% of the total V leached. Using the slag re-processing costs by acidic (bio)leaching and the current metal prices, the recovery of V, being the most important critical metal in the Berg Aukas slags, seems to be non-economical.

Oral bioaccessibility of metal(loid)s in dust materials from mining areas of northern Namibia

Ore mining and processing in semi-arid areas is responsible for the generation of metal(loid)-containing dust, which is easily transported by wind to the surrounding environment. To assess the human exposure to dust-derived metal(loid)s (As, Cd, Cu, Pb, Sb, Zn), as well as the potential risks related to incidental dust ingestion, we studied mine tailing dust (n = 8), slag dust (n = 5) and smelter dust (n = 4) from old mining and smelting sites in northern Namibia (Kombat, Berg Aukas, Tsumeb). In vitro bioaccessibility testing using extraction in simulated gastric fluid (SGF) was combined with determination of grain-size distributions, chemical and mineralogical characterizations and leaching tests conducted on original dust samples and separated PM10 fractions. The bulk and bioaccessible concentrations of the metal(loid)s were ranked as follows: mine tailing dusts < slag dusts ≪ smelter dusts. Extremely high As and Pb bioaccessibilities in the smelter dusts were caused by the presence of highly soluble phases such as arsenolite (As2O3) and various metal-arsenates unstable under the acidic conditions of SGF. The exposure estimates calculated for an adult person of 70 kg at a dust ingestion rate of 50 mg/day indicated that As, Pb (and also Cd to a lesser extent) grossly exceeded tolerable daily intake limits for these contaminants in the case of slag and smelter dusts. The high risk for smelter dusts has been acknowledged, and the safety measures currently adopted by the smelter operator in Tsumeb are necessary to reduce the staff's exposure to contaminated dust. The exposure risk for the local population is only important at the unfenced disposal sites at Berg Aukas, where the PM10 exhibited high levels of bioaccessible Pb.

Depositional ages and provenance of the Neoproterozoic Damara Supergroup (northwest Namibia): Implications for the Angola-Congo and Kalahari cratons connection

The Damara Orogen is composed of the Damara, Kaoko and Gariep belts developed during the Neoproterozoic Pan-African Orogeny. The Damara Belt contains Neoproterozoic siliciclastic and carbonate successions of the Damara Supergroup that record rift to proto-ocean depositional phases during the Rodinia supercontinent break up. There are two conflicting interpretations of the geotectonic framework of the Damara Supergroup basin: i) as one major basin, composed of the Outjo and Khomas basins, related to rifting in the Angola-Congo-Kalahari paleocontinent or, ii) as two independent passive margin basins, one related to the Angola-Congo and the other to the Kalahari proto-cratons. Detrital zircon provenance studies linked to field geology were used to solve this controversy. U-Pb zircon age data were analyzed in order to characterize depositional ages and provenance of the sediments and evolution of the succession in the northern part of the Outjo Basin. The basal Nabis Formation (Nosib Group) and the base of the Chuos Formation were deposited between ca. 870Ma and 760Ma. The upper Chuos, Berg Aukas, Gauss, Auros and lower Brak River formations formed between ca. 760Ma and 635Ma. It also includes the time span recorded by the unconformity between the Auros and lower Brak River formations. The Ghaub, upper Brak River, Karibib and Kuiseb formations were deposited between 663Ma and 590Ma. The geochronological data indicate that the main source areas are related to: i) the Angola-Congo Craton, ii) rift-related intrabasinal igneous rocks of the Naauwpoort Formation, iii) an intrabasinal basement structural high (Abbabis High), and iv) the Coastal Terrane of the Kaoko Belt. The Kalahari Craton units apparently did not constitute a main source area for the studied succession. This is possibly due to the position of the succession in the northern part of the Outjo Basin, at the southern margin of the Congo Craton. Comparison of the obtained geochronological data with those from the literature shows that the Abbabis High forms part of the Kalahari proto-craton and that Angola-Congo and Kalahari cratons were part of the same paleocontinent in Rodinia times.

Stratigraphy of the Neoproterozoic Damara Sequence in northwest Namibia: Slope to basin sub-marine mass-transport deposits and olistolith fields

The Neoproterozoic Damara Sequence (>1000m thick) is composed of siliciclastic and carbonate rocks that crop out in the Damara Belt, Namibia. In Damaraland (including the Vrede, Bethanis, Austerlitz and Toekoms farms), these rocks were deformed and metamorphosed under greenschist facies (biotite zone) conditions during the Damara Orogeny. The stratigraphy and paleoenvironments of the Damara Sequence rocks are debated by the scientific community. We use field data, including detailed 1:25,000 geological mapping, elaboration of stratigraphic profiles and observation of preserved primary structures, textures and composition, to identify lithofacies and lithofacies associations, and to interpret lateral stratigraphic relations.The Nosib and Otavi/Swakop groups of the Damara Sequence in the study area are herein interpreted as gravitational deposits, including up to 150m thick slide blocks, related to the opening of the Outjo Basin. Debrites of the Nabis Formation (Nosib Group) are basement derived, and were developed in alluvial fan setting. Siliciclastic, carbonate and mixed successions of the Otavi/Swakop groups reflect slope to basin deposits and can be grouped in two tectonic sequences. The lower sequence consists mainly of slope and proximal submarine fan successions; medium to distal fan deposits characterize the upper sequence. A U–Pb SHRIMP zircon dating of a dacite layer yielded a 757±5Ma age for the base of the lower sequence. In the study area these sequences are limited by an unconformity. This unconformity records basin margin onlap and was later partially reactivated as a thrust fault during Pan-African compression.The Chuos and Ghaub formations, considered by several authors as Sturtian and Marinoan glaciogenic deposits, are interpreted alternatively as gravitational subaqueous mass flows. Rudstone beds similar to those of the Ghaub Formation occur in the Berg Aukas and Karibib formations and reinforce this interpretation. Large blocks, locally containing stromatolites are interpreted as olistoliths and isolated blocks (pebble to boulder size), are interpreted as sieved from gravitational flows, leaving a non glacial interpretation for these formations as a distinct possibility.

The endostructural pattern of a middle pleistocene human femoral diaphysis from the Karain E site (Southern Anatolia, Turkey).

The human femur from Karain E Cave (Turkey) exhumed from a Mousterian level provided the opportunity to make an incursion into the structural morphology of a late adolescent, or a young adult, femoral shaft from the late Middle Pleistocene of Anatolia. Considering the chrono-ecogeographical context, this study focuses particularly on the endostructural morphological similarities between Karain and Neanderthal fossils. Comparative analysis shows that some femoral features of the Karain specimen are frequently observed in Neanderthals, in comparison to some Middle Pleistocene Homo and Middle/Upper Paleolithic modern humans. In particular, we note a high degree of circularity and a strong midshaft posteromedial reinforcement of cortical thickness on the medial side. According to the mapping of cortical thickness, this latter feature can be related to the medial spiral distribution pattern of cortical thickness in the mid-proximal shaft, which is present at Karain and in all Neanderthals available for this study. This spiral distribution was not identified in recent modern humans and may be absent from ancient Homo with femoral pilaster. The endostructural signature of Karain could indicate a similar biomechanical strain system to that of Neanderthals that could be linked to body shape. However, the presence of posteromedial reinforcement in Berg Aukas may point to an ancestral feature and may be independent of latitude. A larger comparative sample should further clarify the taxonomical, biomechanical, and chrono-ecogeographical origins of the structural femoral features observed in an evolutionary Neanderthal context from MIS 7-9 in Karain.

Formation of secondary hematite and its role in attenuation of contaminants at mine tailings: review and comparison of sites in Zambia and Namibia

Mine tailings in African countries Zambia and Namibia have been investigated with an objective to determine the role of secondary hematite in immobilization of contaminants. Two sites, Chambishi and Mindolo, are located in the Copperbelt in Zambia with relatively humid climates and two sites, Berg Aukas and Kombat, are in Namibia, where the climate is semiarid. At the Chambishi site which is about 40 years old, a hardpan composed of hematite and gypsum has formed at a depth of about 60 cm and large amounts of Cu and Co have been deposited. At the much younger Mindolo site (30 years old, but most V remains in primary descloizite, embedded in a carbonate matrix while a relatively small amount of released V is incorporated into hematite. In contrast, released Zn and Pb are incorporated mainly into smithsonite and cerussite, which are less stable from an environmental viewpoint. Finally, at the Kombat mine tailings (< 5 years old), As released from pyrite is also incorporated into hematite, but Cu released by dissolution of chalcopyrite and bornite has precipitated as malachite, which is less stable than hematite. Water-leached concentrations of contaminants such as Cu, Zn, and Pb (also present in some carbonate phases) are an order of magnitude higher than water-leached concentrations of V and As which are bound to crystalline ferric minerals such as hematite and soluble only in the aqua regia fraction of sequential extraction. It seems that rapid formation of hematite under tropical climate conditions and incorporation of contaminants into this mineral phase is favourable for attenuation of released contaminants. These findings have implications at other mining sites with similar climates in Africa, South America and Asia.

Geochemistry and mineralogy of vanadium in mine tailings at Berg Aukas, northeastern Namibia

Vanadium-rich mine tailings at Berg Aukas, site with a world-known vanadium mineralization in northeastern Namibia, were investigated using a combination of solid phase and mineralogical analyses, leaching tests and speciation modeling. Principal objective of the study was to determine, if vanadium can be released into the environment. In spite of >30y of weathering and oxidation of tailings material to a maximum sampling depth of 2.4m, a large portion of V still remains in the primary mineral descloizite, (Pb, Zn)2(OH)VO4.A part of V was mobilized and adsorbed/co-precipitated with ferric oxyhydroxides. Based on sequential extraction and 57Fe Mössbauer spectroscopy, a large amount of ferric iron is present in insoluble hematite and goethite, where V is effectively bound. Other potential contaminants are Zn, present mostly in the primary mineral willemite, Zn2SiO4, descloizite and also in secondary smithsonite, ZnCO3; and Pb, which was transferred from completely dissolved galena to cerussite, PbCO3 and is also partly present in primary descloizite. Conditions in the mine tailings are alkaline (pH generally >8.2) and oxidizing during dry period, but mobility of V is low due to low solubility of descloizite and secondary crystalline ferric phases such as hematite. In contrast, Zn and especially Pb in secondary carbonates, probably represent more serious environmental and health risks.

The Social and Economic Challenges of the Namibian Children of the Liberation Struggle at Berg Aukas Camp in Grootfontein, Otjozondjupa Region

Despite efforts to address the economic challenges and provide a social safety net for orphans and vulnerable children, Namibia is still faced with social and economic challenges. The aim of this study is to explore the developmental context that underpins the social and economic challenges of the Namibian children of the liberation struggle at the Berg Aukas camp in Grootfontein in the Otjozondjupa Region. Data were collected by means of in-depth interviews with the Namibian Children of the Liberation Struggle and analysed by means of a case- and content-oriented analysis. The results of the study show that Children of the Liberation Struggle are faced with social and economic hardships. The social hardships include dropping out of school, teenage pregnancies and traumatic events such as illness, stigma and discrimination, isolation and loneliness, poor family structures, and lack of adult support and guidance. The economic hardships relate to lack of financial assistance to further their studies and follow aspired careers. The socio-economic challenges refer to lack of social support, lack of counseling, lack of personal income to sustain career development and unfamiliarity with Namibian government policies. The study recommended psychosocial counselling and re-orientation of supportive policies that would provide social safety nets for these children.

Environmental stability of the processing waste from sulfide mining districts of Namibia — A model rhizosphere solution approach

Kinetic batch leaching of the flotation wastes from Berg Aukas and Kombat mining districts (northern Namibia) in 500μM solutions of citric, oxalic and acetic acids was performed to simulate the release of trace metals and As in the rhizosphere-like environment. The obtained data demonstrate that citric acid may significantly contribute to mineral waste alteration accompanied by contaminant mobilization; the maximum dissolution rates corresponded to 7% (Cu), 3% (As), 2% (Cd), 0.8% (Pb) and 0.3% (Zn) of their total amounts. In contrast, the role of oxalic and acetic acids in the complex process of contaminant leaching was usually negligible and/or comparable with water. The precipitation of newly formed Fe (hydr)oxides followed by the adsorption of Pb, Cd and eventually Zn from the model solutions seems to be the key mechanism which led to the metals' stabilization, as predicted by speciation modeling. Considering the neutral and slightly alkaline (and lowly organic) character of soils around the investigated flotation waste dams, Cu and As, present as neutral or anionic species, are suggested to be contaminants with the highest potential for rhizospheric mobilization and subsequent vertical mobility in local soils and/or transfer to plants.

Southern African Minerals Photo-Essay

10.1080/00357529.2012.709172-F0001 Figure 1. Descloizite is one of my personal favorite collectible species. Berg Aukas is the acknowledged king of localities for this mineral and, during its tenur...

Potential human health risks associated with historic ore processing at Berg Aukas, Grootfontein area, Namibia

Health risks to people living at Berg Aukas have been identified through a geochemical study of mine dumps and soils at Berg Aukas. Berg Aukas once served as a mining town, where ores of Pb, V, and Zn were mined and roasted on site until 1979. Roasting of ores produced an unintended hazardous risk in the surrounding area. For this study, soil, crops, and water from the Berg Aukas area were analysed for various pollutants. The main pollutants are metals like Pb, Zn, Cu, Cd, As, Hg and Mo. They are bound to layered silicates, to easily soluble sulphide minerals, or occur in native form. The analytical results show severe heavy metal contamination of the surface soils south and east of Berg Aukas. Crops grown at the National Youth Service, like sweet potatoes, cabbage, and Irish potatoes, accumulate heavy elements that are deleterious to health. Prolonged exposure to As and heavy metals in concentrations as found in the soils and some crops in Berg Aukas can cause severe health problems like diabetes, skin lesions, bladder problems, neurological effects, as well as skin, kidney or lung cancer. Pb affects mental development of children and Pbs to brain retardation. The study aims to help the local community to delineate no-go areas for agricultural use and to either diversify the crops grown on contaminated soils or to grow crops that are less vulnerable to high heavy metal contents in soils or transfer the crops grown on contaminated soils to areas that are not contaminated.

Willemite (Zn 2SiO 4) as a possible Rb–Sr geochronometer for dating nonsulfide Zn–Pb mineralization: Examples from the Otavi Mountainland (Namibia)

The zinc silicate willemite (Zn 2SiO 4) is the main carrier of zinc in a number of high-grade, carbonate-hosted nonsulfide deposits located in the southern hemisphere that have been recently reinterpreted to be of hypogene–hydrothermal origin. The timing of willemite mineralization in these deposits is only poorly constrained. In this pilot study, willemite has been evaluated as a potential Rb–Sr geochronometer that can be used to directly date nonsulfide ore deposits. We have analyzed samples of economic-stage willemite from the Berg Aukas and Abenab West deposits, Otavi Mountainland (Namibia), which are hosted by Neoproterozoic, dolomitized and tectonized carbonate rocks. Rb–Sr elemental concentration levels and ranges of 87Rb/ 86Sr and 87Sr/ 86Sr ratios in these willemite samples are comparable to those observed for the Zn sulfide sphalerite, which has been already successfully used for direct Rb–Sr dating of carbonate-hosted (MVT) deposits. This reflects similar Rb–Sr partitioning mechanisms into Zn ore minerals that precipitate either as sulfides from reduced or as silicates from oxidized hydrothermal fluids, respectively. The Rb–Sr results on willemite presented here reflect mostly low, but variable 87Rb/ 86Sr ratios, sufficient to generate radiogenic 87Sr over time. This clearly shows that willemite is suitable as an Rb–Sr geochronometer and should be further evaluated for direct Rb–Sr dating of nonsulfide Zn deposits. Isochron regressions combining samples from Berg Aukas and Abenab West willemites yield Rb–Sr ages in the range of ca. 500 to 560 Ma. These values are geochronologically doubtful at first sight due to high excess data scatter (MSWD = 2000 to 3000). Massive, fine-grained willemite samples from Abenab West alone ( n = 3) give a – still statistically unacceptable (MSWD = 60) – isochron regression corresponding to an Rb–Sr age of 574 ± 84 Ma. More reliable ages are obtained from two statistically adequate small-scale Rb–Sr isochron regressions for samples of coarse-grained, well-crystallized Berg Aukas willemite, which yield 499 ±63 Ma (MSWD = 2.6) and 493 ± 2 Ma (MSWD = 1.2), respectively. Regardless of the quality of isochron regressions in terms of MSWD, the Rb–Sr ages obtained in this study are fully compatible with other available geochronological data that reflect distinct tectonothermal events in the study area. Therefore, on a regional scale, they appear to be at least geologically reasonable, which has yet to be verified by further studies. Comparable mineralization ages in the range of ca. 490 to 550 Ma are also reflected by the few other known economic, hypogene willemite deposits in the southern hemisphere, for which direct geochronological information is mostly lacking. This may point to a global period of hydrothermal activity in the Cambrian to Lower Ordovician under conditions that favored the formation of hypogene nonsulfide Zn mineralization.

Genesis of Vanadium Ores in the Otavi Mountainland, Namibia

Zn-Cu-Pb vanadate ores (descloizite, mottramite, and vanadinite) in the Otavi Mountainland, Namibia, once were considered the greatest vanadium deposits in the world, with resources estimated at several million tons of vanadium ore. The deposits, now mostly exhausted, occurred in collapse breccias and solution cavities related to a karstic network associated with the post-Gondwana land surfaces in carbonate rocks of the Neoproterozoic Otavi Group, which already contained primary sulfide orebodies. Although a supergene, post-Damaran origin has been generally accepted, the timing and genesis of this mineralization style remains controversial. Mottramite and Cu descloizite are particularly abundant around Cu sulfide deposits (Tsumeb type), whereas descloizite occurs in the areas surrounding primary sphalerite-willemite orebodies (Berg Aukas type). The V deposits the Otavi Mountainland represent a special low-temperature, weathering-related, non-sulfide ore type, also fairly widespread in other areas of southern Africa (e.g., Zambia, Angola). Here we describe the geologic setting of the main V deposits and their ore mineralogy, present some comprehensive major and trace element data for the vanadate ore minerals and gangue carbonates, as well as fluid inclusion microthermometry, O, C, Sr, and Pb isotope analyses, and direct (U-Th)/He descloizite thermochronometry. The vanadates are considered to have formed during a late phase in the depositional history of the post-Damaran supergene ores. Calcite and dolomite gangue are paragenetically coeval with the vanadates, occurring with the vein- and breccia-related ores and as cement in the deeper parts of the recent karst infills. The acidic conditions of sulfide alteration, coupled with a low Eh caused by the influence of organic matter, could have been favorable for vanadate precipitation. Geochemical results and isotope data indicate that most vanadate deposits were formed at temperatures of ~40° to 50°C by meteoric waters interacting with Neo-proterozoic shales, carbonates, and related primary sulfide ores, which were subjected to multiple weathering events in a karst environment. The age of most deposits appears to be generally confined to the Tertiary, with a distinct period of descloizite formation dated at 24 to 33 Ma. The V ores are genetically related to post-Gondwanan erosional episodes, controlled by tectonomorphological evolution following rifting phases in the Atlantic realm and spanning the period from the end of the Cretaceous to Pleistocene.

Stratigraphy and base metal mineralization in the Otavi Mountain Land, Northern Namibia—a review and regional interpretation

Sediment-hosted base metal sulfide deposits in the Otavi Mountain Land occur in most stratigraphic units of the Neoproterozoic Damara Supergroup, including the basal Nosib Group, the middle Otavi Group and the uppermost Mulden Group. Deposits like Tsumeb (Pb–Cu–Zn–Ge), Kombat (Cu–Pb–Zn), Berg Aukas (Zn–Pb–V), Abenab West (Pb–Zn–V) all occur in Otavi Group dolostones, whereas siliciclastic and metavolcanic rocks host Cu–(Ag) or Cu–(Au) mineralization, respectively. The Tsumeb deposit appears to have been concentrated after the peak of the Damara orogeny at around 530 Ma as indicated by radiometric age data. Volcanic hosted Cu–(Au) deposits (Neuwerk and Askevold) in the Askevold Formation may be related to ore forming processes during continental rifting around 746 Ma. The timing of carbonate-hosted Pb–Zn deposits in the Abenab Subgroup at Berg Aukas and Abenab is not well constrained, but the stable (S, O, C) and Pb isotope as well as the ore fluid characteristics are similar to the Tsumeb-type ores. Regional scale ore fluid migration typical of MVT deposits is indicated by the presence of Pb–Zn occurrences over 2500 km 2 within stratabound breccias of the Elandshoek Formation. Mulden Group siliciclastic rocks host the relatively young stratiform Cu–(Ag) Tschudi resource, which is comparable to Copperbelt-type sulfide ores.

The role of evaporites in the genesis of base metal sulphide mineralisation in the Northern Platform of the Pan-African Damara Belt, Namibia: geochemical and fluid inclusion evidence from carbonate wall rock alteration

The Otavi Mountain Land is a base metal sulphide ore province in northern Namibia where deposits are hosted by platform carbonates of the Otavi Group in a foreland fold-and-thrust belt on the northern edge of the Pan-African Damara Belt. Deposits have been classified as the Berg Aukas- or Tsumeb-types, based on differences in ore association, stratigraphic position and geochemistry of ores and gangue carbonates. Mineralisation at these deposits is accompanied by carbonate alteration in the form of dolomite and calcite veins, carbonate recrystallisation, calcitisation and carbonate silicification. Based on cathodoluminescence imaging, trace and rare earth element (REE), O and C isotope, and fluid inclusion data, a series of carbonate generations, constituting wall rock alteration around the Tsumeb and Kombat (Tsumeb-type) and Berg Aukas (Berg Aukas-type) deposits, was established. Similar data obtained on the recently discovered Khusib Springs deposit indicate a strong affinity to Tsumeb-type deposits. Tsumeb-type deposits are distinguished from Berg Aukas-type deposits by having trace element and REE concentrations that are significantly higher in the alteration products compared to the carbonate host rocks. Only around Tsumeb-type deposits a relative enrichment in light REE is noted for the hydrothermal carbonate generations that are cogenetic with the main stage of mineralisation. Microthermometric results from fluid inclusions in carbonate alteration phases and associated quartz indicate relatively high salinity (17–23 wt% NaCl equivalent) for the main mineralising and subsequent sulphide remobilisation stages at the deposits investigated. Estimated mineralisation temperatures are significantly higher for Tsumeb-type deposits (370–405 °C) with early sulphide remobilisation in Tsumeb at 275 °C, whereas they are lower at Berg Aukas (up to 255 °C). Fluid inclusion leachate analysis suggests that most of the observed salinity can be ascribed to dissolved, predominantly Ca- and Mg-carbonates and chlorides with subordinate NaCl. Na-Cl-Br leachate systematics indicate a derivation of the fluid salinity from the interaction with evaporitic rocks en route. Tsumeb-type mineralisation is interpreted to be derived from fluids expelled during Pan-African orogeny in the more intensely deformed internal zones of the Damara Belt further south. When the high salinity fluids reached the carbonate platform after having scavenged high concentrations of base metals, base metal sulphide precipitation occurred in zones of high porosity, provided by karst features in the carbonate sequence. Results obtained for the Berg Aukas-type deposits emphasise their derivation from basinal brines, similar to Mississippi Valley-type deposits, and confirm that mineralisation of the Berg Aukas- and Tsumeb-types are both spatially and temporally distinct.

The anomalous archaic Homo femur from Berg Aukas, Namibia: a biomechanical assessment.

The probably Middle Pleistocene human femur from Berg Aukas, Namibia, when oriented anatomically and analyzed biomechanically, presents an unusual combination of morphological features compared to other Pleistocene Homo femora. Its midshaft diaphyseal shape is similar to most other archaic Homo, but its subtrochanteric shape aligns it most closely with earlier equatorial Homo femora. It has an unusually low neck shaft angle. Its relative femoral head size is matched only by Neandertals with stocky hyperarctic body proportions. Its diaphyseal robusticity is modest for a Neandertal, but reasonable compared to equatorial archaic Homo femora. Its gluteal tuberosity is relatively small. Given its derivation from a warm climatic region, it is best interpreted as having had relatively linear body proportions (affecting proximal diaphyseal proportions, shaft robusticity, and gluteal tuberosity size) combined with an elevated level of lower limb loading during development (affecting femoral head size and neck shaft angle).