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Wimpey Environmental, Hargreaves Road, Groundwell, Swindon, Wiltshire SN2 5AZ, UK
The assessment of reserves in a stratified deposit should define the areal extent of the mineral, the spatial variation of thickness and quality and the ratio of mineral to waste. The assessment of reserves at opencast coal mines in Great Britain also involves the estimation of the extent of areas where coal is absent or of reduced quality due to old mining activity, washout, alteration by igneous intrusions, lime burning and faulting. The most appropriate estimation technique will vary from site to site and, within an individual site, from seam to seam. Conventional non-spatial statistics can be used where the extent of areas of lost coal is not definable. Area-of-influence approaches such as Thiessen polygons are routinely used to estimate the spatial extent of old workings from point observations at boreholes. The use of indicator kriging may provide a refinement to this deterministic approach. Delaunay triangulations are used by popular mine design software for area and volume calculations. Kriging may also be used to model the variation of seam thickness and quality. Whatever method of estimation is used, poor quality input data will result in poor estimates. Metadata such as how, when and by whom information was collected should be used to decide whether or not a particular piece of information should be retained. Experience shows that each site must be treated as a unique entity with techniques and software being modified to suit the site circumstances. A black box ‘expert system’ approach would fail to identify site specific features and result in misleading estimates.
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  4. Assessment Geological Society, London, Engineering Geology Special Publications, 1999; 16: 107 - 141. [Abstract] [PDF]
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