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Jim Gibson, Gavin Lamont and Manfred Marx next to an early evaluation pit on 2125A/K01 (photo Lamont 1967)
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Bechuanaland/Botswana has a long and colourful history in exploration and mining. Here these activities are subdivided into three phases: pre-historic, historic and modern. Quarrying stone in Botswana was ongoing 500,000 years ago during the Early Stone Age (ESA). Actual mining of stones probably only started during the Middle Stone Age (MSA) i.e....
Citations
... Kimberlite is an intrusive igneous rock (injected in a plastic state, into cavities or hosting rock layers), ultramafic (composed predominantly of mafic minerals, rich in iron and magnesium, with little or no feldspar), granulated to irregular, which can be classified as peridotite rich in volatiles (mainly carbon dioxide), composed of serpentinized olivine, with variable amounts of phlogopite, clinopyroxene (diopside), orthopyroxene, carbonates, chromite, apatite, zircon, titaniferous spinel and ilmenite (Deer et al., 1963;Akella et al., 1979;Clement & Skinner, 1979, 1985Scott Smith et al., 1983;Agee et al., 1982;Clement et al., 1984;Giuliani, 2018;Fitspayne et al., 2019). Important contribution have been made lately to understand and interpret chemical results of mineral xenoliths occurrences in kimberlite from the mantle (Buerger & Prewitt, 1961;Aullbach et al., 2017;Moore & Cistin, 2016;Kargin et al., 2017;Howarth, 2018;Giuliani, 2018;de Wit, 2018;Bussleiler et al., 2018;Fitzpayne et al., 2018Fitzpayne et al., , 2019Fitzpayne et al., , 2020 Kimberlites can be diamonds fertile and, together with olivine-lamproites, are the main primary sources of diamonds (de Wit, 2018;Moore & Costin, 2016). The term kimberlite was proposed by Lewis (1888) to describe such ultrabasic volcanic rocks in a diatreme in the city of Kimberley, South Africa. ...
... Kimberlite is an intrusive igneous rock (injected in a plastic state, into cavities or hosting rock layers), ultramafic (composed predominantly of mafic minerals, rich in iron and magnesium, with little or no feldspar), granulated to irregular, which can be classified as peridotite rich in volatiles (mainly carbon dioxide), composed of serpentinized olivine, with variable amounts of phlogopite, clinopyroxene (diopside), orthopyroxene, carbonates, chromite, apatite, zircon, titaniferous spinel and ilmenite (Deer et al., 1963;Akella et al., 1979;Clement & Skinner, 1979, 1985Scott Smith et al., 1983;Agee et al., 1982;Clement et al., 1984;Giuliani, 2018;Fitspayne et al., 2019). Important contribution have been made lately to understand and interpret chemical results of mineral xenoliths occurrences in kimberlite from the mantle (Buerger & Prewitt, 1961;Aullbach et al., 2017;Moore & Cistin, 2016;Kargin et al., 2017;Howarth, 2018;Giuliani, 2018;de Wit, 2018;Bussleiler et al., 2018;Fitzpayne et al., 2018Fitzpayne et al., , 2019Fitzpayne et al., , 2020 Kimberlites can be diamonds fertile and, together with olivine-lamproites, are the main primary sources of diamonds (de Wit, 2018;Moore & Costin, 2016). The term kimberlite was proposed by Lewis (1888) to describe such ultrabasic volcanic rocks in a diatreme in the city of Kimberley, South Africa. ...
In exploratory programs for kimberlites focused at discovering diamond deposits, it is important to identify tools that define their fertility. The observation of mineral indices such as garnet and ilmenite is the first indication of the proximity of kimberlite intrusion, and the possibility of using these minerals as fertility proxys through mineral chemistry allows us to characterize the presence of diamonds in kimberlite. In this work, mineral chemistry data in garnets and ilmenites concentrated in streams and soil were carried out to investigate the kimberlite intrusion from Ariquemes, State of Rondônia, northern Brazil, is reported. Ilmenite occurred exhibiting reaction bands for leucoxene, suggesting two phases in evolution during kimberlite ascension and inplacement. All garnets formed in rocks in the presence of clinopyroxene present a composition consistent with the G9 group. In these terms, it is concluded that the studied body is non-fertile and that the results reported here of the chemical compositions with respect to both garnets and ilmenites, indicate the sterility of the Ariquemes kimberlite intrusion.
Drafted as part of a Debswana 55th Anniversary Publication, the following text outlines the historical roots of how Botswana emerged as a leading player in the global diamond supply chain.
An understanding of the regional geomorphic framework of BotswanaBotswana played a critical role in the discovery by De BeersDe Beers of economic kimberliteKimberlite pipes in the OrapaOrapa area in central Botswana. Early prospecting in the eastern Botswana hardveldHardveld in the late 1950s to early 1960s resulted in the recovery of a train of diamondsDiamonds in the east-flowing MotloutseMotloutseRiverRiver, extending to the headwaters of this drainageDrainage line. De Beers concluded that the MotloutseMotloutse had previously extended further west, based on an appreciation that the eastern Botswana watershed represented an axisAxis of epeirogenicEpeirogenic flexure, which had beheaded the former headwaters. The implication was that the source of the diamonds recovered in this riverRiver could be located in the Kalahari sandveldSandveld to the west of the drainage divide. Subsequent extension of sampling to the west into the Kalahari was rewarded by the discovery of the OrapaOrapakimberlitesKimberlite in 1967, a year after BotswanaBotswana achieved independence. We discuss how these sampling programmes in turn provided a feedback loop, making it possible to refine understanding of the regional geomorphic evolution. Because kimberlite pipes typically taper in size with depth, they also provide a gauge for estimating the depth of post-emplacement erosionErosion, providing an important constraint on landscape evolution. SoilSoil sampling in the Kalahari environment demonstrated that bioturbationBioturbation has translocated kimberliteKimberlite indicator minerals (KIMs) vertically from sub-Kalahari kimberlite pipes, resulting in their concentration in the Kalahari surface sandSand directly above the buried kimberlite. A consequence of this vertical mixing of the Kalahari sedimentary section is that luminescence dating of Kalahari quartz grains may produce spurious “mixed” ages. In the south of Botswana, mid-Cretaceous sub-Kalahari kimberlitesKimberlite are overlain by fluvial conglomeratesConglomerate, while in the northeast of the country, pipes of comparable age are overlain by a calcretized silcreteSilcrete, which has been linked to the developmentDevelopment of the African erosionErosion surface. The basal conglomeratesConglomerate and African Surface duricrustsDuricrust are unconformably overlain by semi-consolidated Kalahari sandKalahari Sand. However, both conglomerate clasts and fragments of the duricrustDuricrust have been identified within craters sedimentsSediment forming the upper section of the respective kimberliteKimberlite pipes. This implies that deposition of the conglomerates, and development of the African surface overlapped the episode of kimberliteKimberlite eruption. This, in turn, provides an important mid-Cretaceous temporal constraint on initiation of Kalahari deposition, and of the African erosionErosion cycle.
Controversies surround the origin of kimberlite megacrysts, including whether and how they are genetically related to their host kimberlites, the relationship between the Cr-poor and Cr-rich suites and the dominant processes responsible for elemental and isotopic variations of megacrysts from a given kimberlite. We present new in-situ major and trace element and Sr isotopic results for clinoyroxene and garnet megacrysts from four southern African kimberlites: Colossus and Orapa (Group 1 kimberlites on the Zimbabwe craton), and Kalkput and Bellsbank (Group 2 kimberlites on the western Kaapvaal craton), that include both Cr-poor and Cr-rich megacryst varieties. Cr-poor megacrysts are present at Colossus, Orapa and Kalkput and the data exhibit tight, well-defined trends on major element diagrams as well as incompatible and rare earth element abundances similar to those previously reported for Cr-poor megacrysts. Cr-rich megacrysts, which are also present at Orapa and are the only variety present at Bellsbank, generally have higher Mg# values, lack well-defined major element trends and show stronger incompatible element enrichments as well as more radiogenic ⁸⁷Sr/⁸⁶Sri ratios than Cr-poor megacrysts from the same kimberlite group. Thermobarometry indicates that the Cr-poor megacrysts equilibrated at temperatures of ≈1200 to 1450 °C and pressures of 4.5 to 7.5 GPa. Cr-rich megacrysts, in contrast, extend to temperatures and pressures as low as 700 °C and 3 GPa, respectively. This indicates that, in the studied suites, Cr-poor megacrysts equilibrated at high temperatures in the lower lithosphere (>135 km), whereas Cr-rich megacrysts typically equilibrated at lower temperatures and pressures. Within the Cr-poor megacrysts from Group 1 and Group 2 kimberlites, there is a clear correspondence between kimberlite group, diagnostic incompatible element ratios (e.g., Nb/La) and Sr isotope ratios that parallel the differences noted between whole-rock Group 1 and Group 2 kimberlites. In the case of Cr-poor megacrysts, similar calculated melt compositions in equilibrium with garnet and clinopyroxene from the same kimberlite were obtained using recent high-pressure mineral‑carbonated melt partition coefficients. This suggests formation in conditions close to trace element equilibrium, and is consistent with crystallization from primitive melts with kimberlite-like trace element compositions. In the case of Cr-rich megacrysts, differences in the compositions of melts in equilibrium with clinopyroxene and garnet tend to be larger, and melts in equilibrium with Cr-rich clinopyroxene tend to show significantly greater incompatible element enrichments than those of estimated near-primary kimberlite melts. This could be due to the different behaviour of clinopyroxene and garnet during metasomatic melt-rock interaction, but the apparent disequilibrium between clinopyroxene and garnet could also be due to some of the Cr-rich megacrysts actually being peridotitic xenocrysts. We propose a model for the origin of southern African megacrysts in which carbonated protokimberlite melts formed stockwork-like bodies of variable size in the deep lithosphere (> 130 km), which fed networks of melt-filled veins extending into the surrounding and overlying mantle. Crystallization of larger melt bodies resulted in megacryst assemblages dominated by Cr-poor megacrysts, and the incompatible element and isotopic characteristics of these dominantly reflect those of the protokimberlite melt. In contrast, crystallization of smaller melt bodies and their vein networks resulted in megacryst assemblages dominated by Cr-rich megacrysts, which formed as a result of extensive assimilation and metasomatic melt-rock interaction between protokimberlite and peridotite wallrock at low melt/rock ratios, particularly in the middle to shallow lithosphere where pre-existing potassic metasomatic heterogeneities are prevalent. The Cr-rich nature and enrichments in incompatible elements and radiogenic Sr in the Cr-rich megacrysts reflect extensive interaction of their parental magmas with this metasomatized peridotite.
3 ABSTRACT Botswana, like many developing countries, seeks to take advantage of the advent of the fourth industrial revolution or 4IR, and like other resource dependent countries, 4IR poses both challenges and opportunities to its mining landscape. These relate to the use of 4IR in the improvement of safety and efficiency in mines, more so in the diamond mining industry which is the main economic activity in the country. The purpose of the study was to investigate and obtain insights on the effective mining safety work practices in the fourth industrial revolution in Debswana Diamond Mining Company Jwaneng, owing to the lack of prior experience of the mines in dealing and managing safety in a digital environment. Moreover, there is a need to establish the effectiveness of safety work practices in terms of systems, tools, measures, processes, procedures and technologies in the context of 4IR technologies. The study made use of a mixed methods methodology through the utilization of an online questionnaire administered to 76 participants at Debswana Mining Company. The data collected was then analysed using Ordinary Least Squares Regression (OLS), Binary Logistic Regression and thematic analysis. From the study results, Debswana Jwaneng Mine is faring well with regards to the adoption of the latest technologies. However, the results also noted a need for improved change management processes as a means of enhancing employee engagement and communication, which have been noted to play a crucial role in the success of adoption of 4IR. Consequently, the study notes the need for a more inclusive approach to 4IR adoption which seek to enhance the mine's preparedness at an individual and organizational level, putting forth recommendations in the way of review of change management processes, utilization of machine learning and big data analytics in automation of slope stability monitoring as well as adoption of wearable devices.
Kimberlites are the main source of natural gem-quality diamonds. The intrepid diamond explorer faces three major problems. First, finding a small, usually less than 300 m diameter, kimberlite, which is often highly weathered. Second, evaluating the quantity of diamonds within a kimberlite that often consists of multiple phases of intrusive and extrusive kimberlite, each with potentially different diamond grades. Third, evaluating the rough diamonds, the value of which is dependent on carat-weight, shape, colour, and clarity. Modern advances in mantle petrology, geophysics, geochemistry, geomorphology, and geostatistics now complement historical exploration knowledge and aid in selecting prospective target areas, resource estimation, and evaluating kimberlite-hosted diamond deposits.
Important implications for the interior workings, constituent, circulation between crust and mantle, convection between core and mantle of the Earth can be drawn by studying diamonds and their hosted rocks. Based on the geological comparison of metallogenic kimberlites from super-giant deposits in Botswana and Mengyin and Wafangdian deposits in China, some exploration suggestions and prospecting clues are present as follows: (1) Kimberlite is an unique diamondiferous rock in Botswana. Whereas, lamproite is main hosted-rock in South China craton including two important lamproite zones along the Jiangnan orogenic belt and northern margin of South China craton. Kimberlite is dominantly distributed in the North China craton, which is composed of three kimberlitic zones along Tanlu fault, Trans-North China orogen and Northern margin of North China. Two industrial value diamondiferous kimberlite deposits are distributed in the Tanlu zone. (2) In-situ U-Pb age and Sr, Nd isotopic data of perovskites show that 86-97 Ma Orapa kimberlites and 456-470Ma Mengyin and Wafangdian kimberlites have low 87Sr/86Sr ratios of 0.703-0.705, medium εNd(t) values ranging from -0.09 to 5, indicating that primary kimberlitic magmas were likely derived from primitive mantle or convective lower mantle. (3) Primary kimberlite morphology in Botswana dominantly occur as pipes, while in China mainly occur as irregular fissures, expressed as dykes and lesser extent sills. Crater facies are pervasively observed in Orapa and Jwaneng kimberlite pipes in comparison with hypabyssal (or root zone) facies in Mengyin and Wafangdian pipe clusters. (4) Orapa A/K1 and Jwaneng mines are few dimonderious kimberlitic pipes yielding predominantly eclogitic xenoliths and E type diamond. In constract, Letlhakane, Damtshaa and Karowe mines also in Orapa cluster, Mengyin and Wafangdian mines from the Tanlu kimberlite belt have mainly peridotite xenoliths, P type and E type diamonds. (5) Some exploration suggestions and prospecting clues of diamondiferous kimberlites are represented as follows: (A) Deep faults cutting through on-craton and off-craton subcontinental lithospheric mantle play role in the emplacement of kimberlites; (B) Soil sampling for kimberlite indicator minerals such as picroilmenite and garnet, Cr-rich rutile, Cr-spinel and Cr-diopside is primary exploration tool; (C) Geophysical surveys such as aeromagnetic mothed should be combined with soil sampling for better prospecting results. (6) Diamondiferous prospecting target areas in the Tanlu kimberlite zone, Jiangnan lamproite zone and Tarim block should be further intensified. Illuvial type diamond deposits in China have great potential for mineralization.
