812Re: AI-GEOSTATS: re CLT and mixtures
- Jan 2, 2003Francis,
On topic in "Lognormal-de Wijsian Geostatistics for Ore Evaluation"
D.G.Krige pp5. points out that the slope of the log-probability plot
provides an estimate of the variance which Rendu 78 and Storrar 77
also published information on. The graph paper in the book actually
has a variance slope scale on it from which you can estimate the
variance. There is also a graph which gives the realtionship between
mean value, pay limit, pay value and percentage pay for lognormal
distributions. I will take a look and see how this relates to the 50th
percentile. It is interesting that your mill grade was related to the
50th percentile as this would depend on the pay limit or cutoff grade
which we call it in Australia which is entirely based on economic
factors and hence should show no relationship unless at operations
of similar commodity type and operating costs and revenues.
Overestimating gold grade used to be due to a reluctance to cut grades
so operators would hear the figures they wanted to, in regards to
nugget effect, I am a mining engineer, on what basis do geologists
select core size? is it e.g. hole depth, mineralization type etc.
Regards Digby Millikan
Geolite Mining Systems
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