In mathematical statistics, a sampling variogram is a graph that shows where a significant degree of causality (in this context, spatial dependence in sample spaces or sampling units) dissipates into randomness. A sampling variogram is obtained by plotting statisticallly significant variance terms of a temporally or in situ ordered set of measured values against the variance of the set and the lower limits of its asymmetric 95% and 99% confidence ranges. Corrected sampling variograms derive from uncorrected ones when extraneous measurement variances are subtracted before spatial dependence is verified. Bre-X's bogus gold grades for crushed, salted and in situ ordered core samples of Borehole BSSE198 in Busang's South-East zone give the following uncorrected sampling variogram.
The corrected sampling variogram for Bre-X's bonanza borehole, its primary data set and test statistics are posted on this page. A temporally ordered set of on-stream data for mill feed to a mineral processing plant, its test statistics and sampling variogram are given in Appendix D of Sampling in Mineral Processing. The variogram or semi-variogram, unlike the above sampling variogram, does not show where spatial dependence in a sample space dissipates into randomness simply because the kriging variance of a set of kriged estimates is an invalid measure for variability, precision and risk.
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