Hi Digby, The variance of a sum of random variables is not equal to the sum of their variances, except if they are independent.. Consequently, the kriging variances cannot be simply combined to compute the variance of the global estimator, see Mining Geostatistics, Page 323 (Journel and Huijbregts, 1978). The most flexible approach is to use stochastic simulation to generate a set of realizations of the block values, aggregate them, and use the empirical distribution of aggregated block values as a model of uncertainty. You can find an example in my publication http://home.comcast.net/~goovaerts/karen.pdf and there is a whole book devoted to the use of stochastic simulation in mining. Journel and Kyriakidis. 2004. Evaluation of Mineral reserves. A simulation approach. Oxford University Press.
Cheers, Pierre -----Original Message----- From: Digby Millikan [mailto:[EMAIL PROTECTED] Sent: Mon 11/7/2005 1:09 AM To: AI Geostats mailing list Cc: Subject: [ai-geostats] Adding kriging variances. Dear list, If you had a set of blocks is it possible to add their kriging variances together, to get a standard error for the mine head grade, is this something that is done in practice or has been done in the past to estimate possible deviations from a kriged head grade? Digby
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