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Re: GEOSTATS: kriging weighted values?

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  • P.V. RAO
    26th Oct., 2000 Dear Dr Isobel clark, I was made part the list of geostats from yesterday only and it is my good fortune to see your reply in my first
    Message 1 of 7 , Oct 26, 2000
      26th Oct., 2000

      Dear Dr Isobel clark,

      I was made part the list of geostats from yesterday only and it is my
      good fortune to see your reply in my first message. I had the opportunity
      of corresponding with you on geostatistics during 1983-86.

      Currently I am working with iron ore mines of Tata Steel in India. The
      ore is won by opencast mining method with 12m high benches. The iron
      ore consists of several types of ores each having definable quality
      in terms of Fe, Al2O3 and SiO2; and physical characterisics such as
      hard ore, soft ore, flaky ore, bluedust etc. making them to be
      processed in wet and dry methods. In such a case, using all the iron ore
      samples in kriging is leading to over=estimation of lean grade ores
      and under-estimation of high grade ores if one sees block-wise. This
      type of estiamtes are not acceptable to the production staff. Hence
      I used variogram parameters of the entire iron ore samples to specific
      ore type estimation for 12m benches with 100mx100m blocks using the
      core smaples of that specific ore type, which satisfied the production
      staff. Is the procedure correct? If not, can you please suggest a better
      method?

      In anticipation of your valuable advice.

      With regards

      Dr P.V. Rao


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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 2 of 7 , Oct 27, 2000
        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 3 of 7 , Oct 27, 2000
          > 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 4 of 7 , Oct 31, 2000
            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.
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            > "unsubscribe ai-geostats" in the message body.
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            >

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