Slide 1: Application of a Localised Direct Conditioning Mineral Resource Modelling Technique
Application of a Localised Direct Conditioning Mineral Resource Modelling Technique for Medium and Long-term Mine Planning of Underground Mining Operations August 2015 Winfred Assibey-Bonsu Charles Muller Hendrik Pretorius 1
Slide 2: Content
Content • Introduction • Background • LDC Metodology • LDC as applied by South Deep Gold Mine • Conclusions 2
Slide 3: Introduction
Introduction • For new mining projects or for medium to long-term areas of existing mines, drilling data are on a relatively large grid. • Direct estimates for SMU and also of much larger block units will then be smoothed due to the information effect and the high error variance of the estimate. • D
Slide 4: Introduction
Introduction • Various post-processing techniques have been proposed to correct for the smoothing effect where data is widely spaced and sparse: – Spectral-processor(Journel et all 2000) – Conditional simulations – Indirect post-processing (Assibey-Bonsu and Krige 1999, Marcotte and David 1985) – Un
Slide 5: Background
Background • The LDC methodology has been developed for Gold Fields South Deep underground mine, where stope designs using probability recoverable estimates on indirect basis, have practical limitations. • South Deep mines the Upper Elsburgs which comprise multiple stacked reef horizons that form pa
Slide 6: Background
Background • Both Ordinary (OK) and Simple Kriging (SK) techniques are applied in developing SMU blocks (30x30x1) estimation grade models. • SK panel grades are used for the post-processing of recoverable resources which are used for mine planning – higher kriging efficiencies observed for SK panel
Slide 7: Background
Background • In providing the mean value, historical mined out information is taken into account. • It is critical that the SK input means are analysed for robustness. • Mine planning requires a single block value and therefore development of LDC rather than the indirect method which provide a propo
Slide 8: LDC Methodology - Definitions
LDC Methodology - Definitions Dispersion variances of conditionally unbiased estimates for direct SMU’s = BVs - 2se1 (at exploration stage) [1] = BVs - 2se2 (at final production stage) [2] 8
Slide 9: LDC Methodology
LDC Methodology • LDC estimates are derived from initial direct smooth kriged estimates. • The initial Direct Conditioning (DC) is derived by super-imposing on the kriged estimate for each SMU block, a simulated lognormal distribution of expected ‘actual’ values with a variance equal to the differen
Slide 10: LDC Methodology
LDC Methodology • The LDC methodology referred to in this paper extends the Localised UC technique as proposed by Abzalov (2006). • Abzalov uses the grade-tonnage functions from the large panel indirect estimates (derived from UC) and then decomposes the panel-specific grade-tonnage data into a suit
Slide 11: LDC Technique as Applied by South Deep
LDC Technique as Applied by South Deep • Derive Simple Kriging (SK) estimates of SMUs. • Estimate the local conditional probability distribution (lcpd) of non-smoothed grade estimates. – The lcpd uses each smoothed SMU kriged estimate as the mean of the distribution and associated variance parameter
Slide 12: LDC Technique as Applied by South Deep
LDC Technique as Applied by South Deep • Agglomerate individual SMU grade-tonnage results into a ‘panel’ (in this case 120mx120m). • Decompose the resultant ‘panel’ grade-tonnage function above to yield unsmoothed SMU grades; the linkage of these grades to SMU is obtained through ranking of the orig
Slide 13: LDC Technique as Applied by South Deep
LDC Technique as Applied by South Deep • The direct post-processing techniques effectively provides the average proportion of ore and corresponding grade, which can be expected to be selected for mining when grade control data becomes available. • These unsmooth post-processed estimates can then be
Slide 14: Comparison between Initial SK and LDC
Comparison between Initial SK and LDC 14
Slide 15: Reconciliation of LDC Estimates
Reconciliation of LDC Estimates • LDC recoverable estimates compared with follow-up Grade Control estimate Cut-off Mean grade above cut-off Proportion above cut-off (g/t) (g/t) (%) LDC Grade Control LDC Grade Control 0 16.89 17.85 100.0% 100.0% 3 17.39 17.86 97.14% 99.95% 4 17.39 17.86 97.14% 99.95%
Slide 16: Analysis of MCF following the Introduction of LDC
Analysis of MCF following the Introduction of LDC • Although there are several direct and indirect production and modifying factors which affect the MCF, the paper presents the observed MCF changes pre and post LDC • The observed improved correlation of MCF following LDC does not necessary provide c
Slide 17: Mine Call Factor on six months basis
140% 120% os Oo 100% 80% 60% Mine Call Facto 40% 20% Mine Call Factor on six months basis Jul-08 to Jan-09 Jul-09 to Jan-10 Jun-10 Dec-10 Jun-11 Dec-11 Jun-12 Dec-12 Jul-13 to Dec-08 to Jun- Dec-09 to May- to Nov- to May- to Nov- to May- to Nov- to Jun- Dec-13 09 10 10 11 11 12 12 Periods (6 monthly
Slide 18: Conclusions
Conclusions • Reconciliations to date at South Deep show encouraging results following the introduction of LDC. • It is important that the mine strives to maintain and keep abreast of the necessary grade control programmes, which will improve local scale estimation, as LDC is aimed at medium to long
Slide 19: END
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