Resource and reserve evaluation in the presence of imprecise data

Several sources of information often contribute to the comprehension of an ore deposit, for instance samples from diamond drill holes, reversed-circulation drill holes, or blast holes. Even if all the available information comes from the same drill hole type, it may have been collected through several campaigns, sampled with different protocols, or analyzed by different laboratories. In general, these sources of information do not have the same quality, therefore, they constitute different statistical populations for mineral resource/ore reserve estimation studies.This work examines the impact of data imprecision in resources and reserves evaluation through two case studies on simulated deposits. The first one is a porphyry copper deposit represented by blocks 15 m by 15 m by 12 m in size; the copper grades are conditioned to real exploration and production data (diamond drill holes and blast-holes) and show gradational transitions. The second case study consists of a bench of a gold deposit simulated without any conditioning data, with 5 m by 5 m blocks, for which there is a clear-cut discontinuity between the waste and the ore. In each deposit, a set of exploration samples is defined to estimate the block grades. These samples are divided into two subsets standing for two different sampling campaigns: a set of hard (error-free) data and a set of imprecise data obtained by altering the true grade values. Two types of imprecision are examined: measurements with multiplicative errors (each measured value is the true value times a random number lying between 0.75 and 1.25) and measurements defined as intervals. Additionally, two reference situations are considered: the block model obtained using the complete exploration dataset without data imprecision and the one obtained using the hard data subset exclusively. The results are compared to the simulated block grades from a statistical and an economic viewpoint, by assessing the true and expected profits associated with the block estimated models.Five geostatistical techniques are used to estimate the block grades: 1) ordinary kriging, for which all the data are pooled together as if they belonged to a single statistical population; 2) separate kriging, where each data subset originates its own block model (the models are then unified by a weighted average); 3) ordinary cokriging, consisting of a joint estimation of both types of data; 4) lognormal kriging associated with a filtering procedure; and 5) indicator kriging to determine the e-type estimate of the grades.The study concludes that the kriging techniques are not very sensitive to the level of sampling error, and that the quantity of data prevails over their quality. Only the reference estimation from the hard data subset shows a significant loss of precision with respect to the other situations. Therefore, the imprecise measurements should never be discarded in the estimation paradigm, despite their poor quality. Furthermore, in the examples under study, simple methods perform well: a kriging with all the data pooled together or a separate kriging with each type of measurement are efficient for estimating the block grades, although they are theoretically not perfectly sound. There is no need to seek more complicated techniques such as cokriging or indicator kriging.In practice, determining whether a sampling campaign is deficient or not requires further information, in particular, taking sampling duplicates or re-assaying existing pulps. Comparing the grade distributions of two campaigns via quantile-quantile plots is generally not enough to conclude on the existence of data imprecision. Comparing their sample variograms is a more powerful tool, since a measurement error is reflected by a higher nugget effect. Calibration samples (for which both the error-free and imprecise measurements are available) or twin drill holes are required to model the type of imprecision.
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Summary: Surface subsidence and sinkhole development over abandoned and collapsing underground mine workings are major environmental and public safety hazards in some areas. Small-scale undocumented workings are particularly problematic because their presence is often unknown until infrastructure has been developed over them and there is an unexpected subsidence event, often requiring expensive site stabilization or abandonment. Surface wave imaging is a relatively new seismic technique that generates...
Publication: CIM Bulletin
Author(s): S.D. Butt, C. Xu, M.D. Vance, G.C. Corbett
Issue: 1089
Volume: 98
Year: 2005
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Summary: Following initial discovery in 1991, BHP Diamonds Inc. (now part of BHP Billiton) opened Canada’s first diamond mine, the EKATI Diamond Mine, in the Northwest Territories, on October 14, 1998. Four short years later, on November 29, 2002, saw the opening of North America’s first underground diamond mine—the Koala North mine. Nestled between the original Panda open pit and the new Koala pit, which is now in production, Koala North represents the first underground kimberlite...
Publication: CIM Bulletin
Author(s): P. Harvey
Issue: 1089
Volume: 98
Year: 2005
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Summary: The preparation of a long-term plan requires an understanding of all the facets of a mine, among them, the access and other infrastructures; the general layout; the geology, reserves, and extraction plan of every sector; and the productivity of the workers. The planner combines all these elements, often in an intuitive way, into a number of alternative plans, trying to identify the most likely outcomes and problems. The final plan that is compiled is functional, but there is no certainty that...
Publication: CIM Bulletin
Author(s): G. McIsaac
Issue: 1089
Volume: 98
Year: 2005
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Summary: Underground coal production at the Hustas mine, west of the village of Eynez, was from the KM2 seam, which lies at an average depth of 200 m and ranges from 15 m to 25 m in thickness with an average extractable thickness of about 18 m. The underground lignite mining methods employed in Turkey are mostly non-mechanized longwall methods. At the Hustas mine, the method used is a manual double-slice longwall method. The face area is maintained at about 2 m high using hydraulic steel props...
Publication: CIM Bulletin
Author(s): C.O. Aksoy
Issue: 1089
Volume: 98
Year: 2005
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Summary: The Ambatovy Nickel Project involves the proposed recovery of nickel and cobalt from a laterite deposit in Madagascar. The project has the potential to produce 60,000 t of nickel and 5,600 t of cobalt annually. In support of the bankable feasibility study, laboratory and mini pilot plant testwork was carried out at the Dynatec laboratory in Fort Saskatchewan. This paper describes the major findings of the test program.The Ambatovy ore is primarily ferralite (limonite). Saprolite is...
Publication: CIM Bulletin
Author(s): M.J. Collins, L.A. Barta, K.R. Buban, R. Kalanchey, G. Owusu, R. Raudsepp, J. Stiksma, I.M. Masters
Issue: 1089
Volume: 98
Year: 2005
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Summary: Load-haul-dump vehicles (LHDs) are extensively used in underground mining, however, equipment design and operating conditions contribute to restricted operator sight lines. The inability to clearly see people, objects, or hazards around the machine has contributed to a number of accidents including fatal injuries. In order to identify vehicle design characteristics resulting in restricted and blocked sightlines, line-of-sight assessments are traditionally completed in the field. However,...
Publication: CIM Bulletin
Author(s): T. Eger, A. Jeffkins, P. Dunn, I. Bhattacherya, M. Djivre
Issue: 1089
Volume: 98
Year: 2005
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