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Re: GEOSTATS: kriging weighted values?

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  • P.V. RAO
    2th Oct., 2000 Dear Dr Isobel Clark, Thanks for your advice on iron ore deposit. I have a further quiery to you on the same subject. You may appreciate that
    Message 1 of 7 , Oct 27, 2000
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      2th Oct., 2000

      Dear Dr Isobel Clark,

      Thanks for your advice on iron ore deposit. I have a further quiery
      to you on the same subject.

      You may appreciate that when we take samples (let us say 3m length)
      along the vertical boreholes for each 12m bench height, different
      ore types with varying lengths willb e encountered. In such a case,
      when the mid-slice plans are prepared, usually the maximum length of
      ore (core length) is designated in the slice plans. When the variogram
      has to be calculated for 12m samples how to composite the radicals
      for a given ore type? if all the samples falling within 12m bench
      height are taken for compositing, then the sample assay value don't
      truly represent the designated ore type in the slice.

      I seek your advice on this please. You may please note that I do not
      have access to internet at my place of work, which is definitely a
      constraint in reviewing the published literature.


      Dr P.V. RAO
      Dy. Divisional Manager (planning)
      Tata Steel, India
      ----------------------------------------------------------------------


      On Thu, 26 Oct 2000, [iso-8859-1] Isobel Clark wrote:

      > Dear Dr Rao
      >
      > How lovely to hear from you.
      >
      > In dealing with an area with several sub-populations
      > of different geology, it is always best to use only
      > the samples of the relevant geology.
      >
      > It would improve the estimation further if you can:
      >
      > (a) produce a semi-variogram model for each ore type
      >
      > (b) allow for the skewed nature of the data by using
      > (say) a modified lognormal transformation.
      >
      > We have followed this pattern successfully in iron ore
      > deposits in South Africa and in the USA.
      >
      > Let me kno wif I can be of any more help. Perhaps you
      > would also like to visit our 'professional' Web pages
      > at http://www.stokos.demon.co.uk
      >
      > With best regards
      > Isobel Clark
      >
      >
      >
      > ____________________________________________________________
      > Do You Yahoo!?
      > Get your free @... address at http://mail.yahoo.co.uk
      > or your free @... address at http://mail.yahoo.ie
      >

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    • Isobel Clark
      ... The semi-variogram should always be calculated on your basic core section length. Represent a block (discretisation) by four points in the vertical
      Message 2 of 7 , Oct 27, 2000
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        > Thanks for your advice on iron ore deposit. I have
        > a further quiery to you on the same subject.

        The semi-variogram should always be calculated on your
        basic core section length. Represent a block
        (discretisation) by four 'points' in the vertical
        direction when it is estimated. All software which
        does block estimation should allow you to specify the
        number of points in each direcion.

        If you have more than one type of ore in a particular
        block, the most reliable process is as follows:

        (1) krige a value for that block for each ore type
        which is present, using only the samples from that ore
        type.

        (2) use an indicator to krige the proportion of the
        block in each ore type. For example, if you have two
        ore types, each intersection with ore type A sould be
        given a value of 1. Intersections with B should be
        given a value of 0. Semi-variograms can then be
        constructed on these indicator values and the kriging
        result will be an estimated proportion of the block
        which is in type A.

        If you have more than two ore types, you can start
        with A being 1 and all others 0. Then you remove the A
        samples, call B 1 and the others 0. This is often
        called multiple nested indicators.

        We have used this successfully in ore deposits with
        several mineralisation types which cannot be separated
        geographically.

        If (as with other iron ore mines I know) your software
        is only operating in two dimensional slices, you can
        approximate the best answer by compositing only within
        the specific ore types and weighting by length or
        physical weight, in the same way that South African
        gold miners do with 'accumulation' values in reef
        deposits.

        I hope this helps. Indicator kriging is illustrated in
        Practical Geostatistics 2000, in Chapter 12.

        Isobel Clark






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      • P.V. RAO
        Dear Dr Isobel Clark, It seems I am learning more now than what I could do sofar through reading books/ periodicals. Thanks for your kind response. I ahve to
        Message 3 of 7 , Oct 31, 2000
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          Dear Dr Isobel Clark,

          It seems I am learning more now than what I could do sofar through reading
          books/ periodicals. Thanks for your kind response.

          I ahve to querries to make:

          1) What is "Practical geostatsics 2000?" Is it a book published by you?
          May I have the details of it please? I stay, first of all in India and
          then in a remote place like Noamundi (75 year old iron ore mine producing
          over 6 mtpa!) where access to internet and other modern means of
          communications are yet to be made available.

          2) When the directional variograms are made, one finds that sill value
          do not reach the total variance of the smaples. Even then, when the
          variogram parameters are used in kriging, we try to nullify the
          variation in range by giving anisotropy factors in 3 dimensions. However,
          the same is not accomodated for sill value in different directions as
          there is provision to give only one C0 and one C1 value unless we have
          nested variograms.

          I hope I could explain my query.

          3) Madam, will it be possible to share your worked out examples on
          indicator kriging on iron ore deposits?

          Thanks

          P.V. Rao
          ---------------------------------------------------------------------
          On Fri, 27 Oct 2000, [iso-8859-1] Isobel Clark wrote:

          > > Thanks for your advice on iron ore deposit. I have
          > > a further quiery to you on the same subject.
          >
          > The semi-variogram should always be calculated on your
          > basic core section length. Represent a block
          > (discretisation) by four 'points' in the vertical
          > direction when it is estimated. All software which
          > does block estimation should allow you to specify the
          > number of points in each direcion.
          >
          > If you have more than one type of ore in a particular
          > block, the most reliable process is as follows:
          >
          > (1) krige a value for that block for each ore type
          > which is present, using only the samples from that ore
          > type.
          >
          > (2) use an indicator to krige the proportion of the
          > block in each ore type. For example, if you have two
          > ore types, each intersection with ore type A sould be
          > given a value of 1. Intersections with B should be
          > given a value of 0. Semi-variograms can then be
          > constructed on these indicator values and the kriging
          > result will be an estimated proportion of the block
          > which is in type A.
          >
          > If you have more than two ore types, you can start
          > with A being 1 and all others 0. Then you remove the A
          > samples, call B 1 and the others 0. This is often
          > called multiple nested indicators.
          >
          > We have used this successfully in ore deposits with
          > several mineralisation types which cannot be separated
          > geographically.
          >
          > If (as with other iron ore mines I know) your software
          > is only operating in two dimensional slices, you can
          > approximate the best answer by compositing only within
          > the specific ore types and weighting by length or
          > physical weight, in the same way that South African
          > gold miners do with 'accumulation' values in reef
          > deposits.
          >
          > I hope this helps. Indicator kriging is illustrated in
          > Practical Geostatistics 2000, in Chapter 12.
          >
          > Isobel Clark
          >
          >
          >
          >
          >
          >
          > ____________________________________________________________
          > Do You Yahoo!?
          > Get your free @... address at http://mail.yahoo.co.uk
          > or your free @... address at http://mail.yahoo.ie
          > --
          > *To post a message to the list, send it to ai-geostats@....
          > *As a general service to list users, please remember to post a summary
          > of any useful responses to your questions.
          > *To unsubscribe, send email to majordomo@... with no subject and
          > "unsubscribe ai-geostats" in the message body.
          > DO NOT SEND Subscribe/Unsubscribe requests to the list!
          >

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