MINE-PRODUCT VARIABILITY ESTIMATORS WITH EMPHASIS ON THE CASE OF COAL

Two estimators are derived for the variability of small lots, such as barges or trains, around the mean of all small lots shipped in some fi xed time frame such as a month or a quarter. These estimators are desi gned to account for simultaneous mining from any number of mining mach ines dispersed over a property and depend on the in situ spatial autoc orrelation expressed by exploratory drill cores and in-mine sampling a nd on variability in mining-machine productivity. The two estimators, both approximations, are referred to as the expanded form and the redu ced form. The reduced form is considerably easier to apply than the ex panded form, although it requires more restrictive assumptions. A sens itivity analysis is provided that demonstrates the reasonableness of t hese stricter assumptions for mine plans and variograms typical of coa l. Comparisons of estimated and actual mine-output variability are pro vided.