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Re: GEOSTATS: kriging weighted values?

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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 1 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 2 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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