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AI-GEOSTATS: Block size - estimation variance - resource category.

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  • Digby Millikan
    Hello, Is use of estimation variance for classification of resource confidence e.g the AusIMM s resource categories of Measured, Indicated and Inferred common
    Message 1 of 2 , Mar 15, 2001
      Hello,
      Is use of estimation variance for classification of resource confidence e.g the AusIMM's resource
      categories of Measured, Indicated and Inferred common and is this good practice. Also how is this
      effected by block size in that should a reasonable block size be chosen e.g. 1/4 drillhole spacing.
      Thanks in advance.
      Regards Digby Millikan.
      Geolite Mining Systems


      [Non-text portions of this message have been removed]
    • Isobel Clark
      Digby, at last a real question! ... Depends on how you use it, whether your estimates and errors have Normal distributions, how many samples you can find
      Message 2 of 2 , Mar 16, 2001
        Digby, at last a real question!

        > Is use of estimation variance for classification of
        > resource confidence e.g the AusIMM's resource
        > categories of Measured, Indicated and Inferred
        > common and is this good practice.
        Depends on how you use it, whether your estimates and
        errors have Normal distributions, how many samples you
        can find within your search radius plus a whole can of
        other worms.

        There are as many different ways of using the kriging
        variance as there are major mining houses and
        consultancy groups. If you want to classify on a
        block-by-block basis, the following seems to work
        pretty well. As professional engineers with 30 years
        of experience specialising in resource and reserve
        estimation, we have found this acceptable to most
        Western Banks:

        Measured resource: kriging variance less than ordinary
        statistical sample variance (or total sill if you have
        one)

        Indicated resource: not measured but within the range
        of influence of at least 4 samples (not sure how you
        would apply that if you have no sill!)

        Inferred resource: anything that a competent geologist
        can justify on the grounds of physical continuity.

        In plain words: measured is something that you can
        have some confidence in; indicated is within range but
        the local average is a better estimator than the
        kriging; inferred is a can of worms.

        > Also how is this
        > effected by block size in that should a reasonable
        > block size be chosen e.g. 1/4 drillhole spacing.
        The 'sample variance' referred to in the measured
        category should be reduced by the within block
        variance to be meaningful. This means the bigger the
        block the better the estimate must be to be measured.

        Drillhole spacing is not the issue in classification
        or confidence measurements -- the range of influence
        or distance scaling parameters are.

        Hope this helps
        Isobel Clark
        http://uk.geocities.com/drisobelclark

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