Francis, 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 [EMAIL PROTECTED] http://www.users.on.net/digbym -- * To post a message to the list, send it to [EMAIL PROTECTED] * As a general service to the users, please remember to post a summary of any useful responses to your questions. * To unsubscribe, send an email to [EMAIL PROTECTED] with no subject and "unsubscribe ai-geostats" followed by "end" on the next line in the message body. DO NOT SEND Subscribe/Unsubscribe requests to the list * Support to the list is provided at http://www.ai-geostats.org
