Geostatistical modelling in presence of trend – a test case of a bauxite deposit in Jharkhand,India

Abstract

A bauxite deposit located in the state of Jharkhand in India has been studied for geostatistical modelling in the presence of trend. The deposit is a blanket type formed by residual enrichment of aluminium oxides and selective leaching of oxides of iron, titanium, silicon, sodium and potassium among others. Population modelling of six major variables (Al₂O₃, loss on ignition, Fe₂O₃, SiO₂, TiO₂ and thickness) revealed the presence of a log-normal distribution in all cases. Experimental semi-variograms when computed exhibited presence of trend in the sample values. An attempt to fit a trend surface reflected the presence of a third degree trend. Sample values were then made free from the trend by subtracting the trend component from the sample values thereby yielding residual values (i.e. deviations from the trend). Semi-variograms computed for the residuals exhibited regionalised phenomena. Estimates of residuals have been obtained employing block kriging. The trend component has then been added to each of the block kriged residual estimates in order to yield estimates of block grade values. A comparison of block kriged estimates and values of the nearest drill composite samples made for reconciliation of results exhibited a high degree of match as evidenced by the correlation coefficient value (r = 0·83).

Keywords

BAUXITE DEPOSIT GEOSTATISTICS TREND ANALYSIS SEMI-VARIOGRAM KRIGING

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