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419Re: AI-GEOSTATS: Cracks in the foundations?

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  • dwmccarn@aol.com
    Oct 27, 2001
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      Dear Chuck:

      On reflection, I guess that I should have been less "absolute" in my
      statement (You never know how your own words may come back to haunt you!). A
      number of companies (including COGEMA) have very successfully applied
      geostatistical techniques to the evaluation of ore zones in roll-front
      environments. One of the approaches is to use a curvilinear block which
      matches the sinuosity of the ore body geometry (a significant handicap if you
      can't model the shape). Although it doesn't directly overcome the problem of
      leading-edge discontinuity of the ore body, with practice, well justified
      estimates can be obtained. I am intrigued, however, by your suggestion of
      using a well-fitting non-linear probability model. But for two companies
      that I've worked with, other means to obtain ore reserve estimates have been
      applied. In other sandstone U environments besides roll-fronts, the ore
      tends to be more or less continuous, and spatial statistical models are quite
      appropriate. One of these ore bodies, however, had a disappointingly very
      "flat" variogram which had very little spatial structure over a large range
      and direction. This more or less justified their use of an "average" grade
      adjusted by windsorising the high outliers when specific criteria are met.

      R = Thickness * Grade * Area * density * probability of encountering ore
      zones in the area

      I think that the above is "out of the book" for Russian & Kazakh
      practitioners.

      Regards,

      Dan ii

      In a message dated 10/27/2001 5:18:11 PM Mountain Daylight Time,
      chuckre@... writes:

      << "For roll-front uranium deposits, a geostatistical approach is avoided
      because of the deposit characteristics. The leading edge of the roll has
      generally the highest concentration of uranium and is bounded by a very
      distinct discontinuity on the reduced side. The trailing edge displays a
      more gradual tapering of grade on the oxidized side." >>


      Dan W. McCarn, AIPG CPG #10245, Wyoming PG#3031
      10228A Admiral Halsey NE
      Albuquerque, NM 87111
      +1 (505) 822-1323
      +1 (505) 710-3600
      http://resumes.yahoo.com/dwmccarn/geologist
      11 Sept 2001

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