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Windhoek, Namibia

Burke A.,Namdeb Diamond Corporation | Newton R.,Wakehurst Place Ardingly | Boyce D.,Imperial College London | Kolberg H.,National Botanical Research Institute | Brunner I.,Swiss railway company BLS AG
Ecological Restoration | Year: 2011

Beach hummocks are important ecological components of coastal ecosystems. Although hummocks are naturally adapted to harsh conditions, reestablishing them in arid areas poses great challenges. During a collaborative project, researchers from Namdeb Diamond Corporation and the Millennium Seed Bank Partnership investigated practical methods to reestablish saltbush (Salsola nollothensis) beach hummocks to restore areas disturbed by alluvial diamond mining. Withfocus on simple methods that can be implemented over large areas, collecting seed-containing debris, placing windbreaks, and seeding these with debris are some of the means currently investigated. Preliminary findings indicate that seed quality may deteriorate quickly if seeds are stored in ambient conditions, and storage under controlled conditions and/or seed harvesting shortly before restoration is recommended. Laboratory tests indicate a naturally high proportion of empty seeds, possibly short seed longevity, and that seeds must not be buried too deeply for seedling emergence. Further, seasonal and site-related variation in seed production influences the quality and amount of viable seeds available. All this suggests a complex set of environmental conditions that have to be met to achieve natural recovery or restoration goals. This project illustrates the benefits of partnerships in restoration that made it possible to investigate practical field questions with scientific sophistication, making an international initiative relevant to applied restoration ecology in a developing country. © 2011 by the Board of Regents of the University of Wisconsin System. Source

Prins C.F.,Anglo American | Jacob J.,Namdeb Diamond Corporation
Journal of the Southern African Institute of Mining and Metallurgy | Year: 2014

At Namdeb, submerged beaches are earmarked for sampling and future mining and various sampling configurations are tested for optimality through the use of spatial simulations. For the creation of these virtual orebodies, basic statistics and variograms are needed, but in this specific instance no data exists from which the necessary parameters can be determined. The best that can be done is to use proxy data from onshore beaches, with adaptations where needed. The reworking of raised beaches during periods of rising and falling sea levels in some cases destroyed the internal beach structures, and it is very difficult to determine the variograms. A method is proposed whereby simulated annealing is used to adjust the sample locations to align the data pertaining to beach crests or cliff lines, thus improving the variogram structure along the shoreline in the direction of the highest geological continuity. © The Southern African Institute of Mining and Metallurgy, 2014. Source

Jacob J.,Namdeb Diamond Corporation | Prins C.,Anglo American | Oelofsen A.,Namdeb Diamond Corporation
Journal of the Southern African Institute of Mining and Metallurgy | Year: 2014

Diamondiferous linear beaches in Mining Area No. 1 have been the mainstay of Namdeb's diamond production for more than 80 years. Most of the onshore beaches have been mined out, but in recent years mining has been extended offshore into the surf zone through a process of beach accretion. A total of 61.6 million carats has been produced from the gravel beaches since their discovery in 1928, and Mining Area No. 1 is considered to have great remaining potential from areas currently submerged under water. To date, the surf zone has remained largely unexplored due to the consistently strong winds, currents, and large waves which make access to this area extremely difficult. This paper describes the processes used in developing a practical methodology for exploration of the surf zone in a domain extending approximately 22 km long in a northwest-southeast direction and 0.3 km wide in a perpendicular direction adjacent to the current Mining Area No 1. The vigorous surf zone poses multiple technical challenges in terms of obtaining geological and diamond information. In order to access the area for sampling, a jack-up walking probe drill platform (PDP) with a 5-inch diameter reverse-circulation drill has been developed to carry out exploration drilling in the dynamic surf zone. The hydraulically driven platform has eight legs, each of which is 18 m long. Four of the legs are in fixed positions on the fore and aft sides of the platform. The other four moveable legs are fitted to sliding frames attached to the port and starboard sides of the platform. The sets of fixed and moveable legs can be raised and lowered by hydraulically powered jacking stations. By alternately lifting and lowering the sets of fixed and moveable legs in conjunction with the frames moving back and forth horizontally, a walking action is performed by the PDP. The platform can walk at a speed of 10-15 m/h, depending on weather and footwall conditions. Optimization of sampling for diamondiferous gravel occurrence in Mining Area No.1 was undertaken through creation of a virtual orebody on which different sample configurations were tested. The input data for the construction of a virtual orebody comprises a set of drilling data, collected from recently accreted areas directly adjacent to the 22 km × 0.3 km target domain. The input drilling data covers only 34% of the domain, and for the purpose of this study, a single realization is deemed to be sufficient. The texture obtained from using only the drilling data to construct a simulation did not make geological sense; hence it was necessary to make use of analog data in order to improve the simulation. The first analog data used consists of the gully patterns found in the metasedimentary Precambrian bedrock footwall. Gullies are, in general, gravel filled and it is fair to assume that gully patterns form a subset of the total gravel occurrence. Total gravel occurrence includes marine terraces (governed by sealevel stands) above bedrock peaks, together with gravel within gullies below bedrock peaks. The second analog 'data' introduced is through the use of 'expert interpretation'. The indicator drilling data is interpreted by expert opinion and the 2-dimensional result is hand-sketched, digitized, and then pixelated. The pixelated data set is then used as input for variogram calculation. This study cannot provide a single definite optimization result as the nature of the data does not permit this. The use of different validation approaches (conditioning data, where available; expert interpretation; and gully pattern data), however, can give a very good indication of how to balance sampling effort with de-risking aspects related to geological continuity. Work undertaken by sampling the simulation will give an assessment of the relative probabilities of determining gravel occurrence in the study area. This study showed that a 50 m × 400 m cross-configuration will be a good initial sample spacing for highlighting areas where gravel may be absent, and further infill drilling may be required. The relative efficiency of a 50 m × 400 m cross off-set sampling configuration has been demonstrated using a trumpet curve versus sampling effort when using kriging as the estimation method. © The Southern African Institute of Mining and Metallurgy, 2014. Source

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