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812Re: AI-GEOSTATS: re CLT and mixtures

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  • Digby Millikan
    Jan 2, 2003
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      Francis,
      On topic in "Lognormal-de Wijsian Geostatistics for Ore Evaluation"
      D.G.Krige pp5. points out that the slope of the log-probability plot
      provides an estimate of the variance which Rendu 78 and Storrar 77
      also published information on. The graph paper in the book actually
      has a variance slope scale on it from which you can estimate the
      variance. There is also a graph which gives the realtionship between
      mean value, pay limit, pay value and percentage pay for lognormal
      distributions. I will take a look and see how this relates to the 50th
      percentile. It is interesting that your mill grade was related to the
      50th percentile as this would depend on the pay limit or cutoff grade
      which we call it in Australia which is entirely based on economic
      factors and hence should show no relationship unless at operations
      of similar commodity type and operating costs and revenues.
      Overestimating gold grade used to be due to a reluctance to cut grades
      so operators would hear the figures they wanted to, in regards to
      nugget effect, I am a mining engineer, on what basis do geologists
      select core size? is it e.g. hole depth, mineralization type etc.

      Regards Digby Millikan
      Geolite Mining Systems
      digbym@...
      http://www.users.on.net/digbym


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