Abstract

A new method (FINDER) that uses the area of influence and Bayesian statistics to aid in selection of target areas on the basis of one or more variables and multiple observations was tested with drill hole data. A previously defined bimodal distribution of Na 2 O with the low sodium group confined to a 1.5 X 3.0-km zone beneath the cluster of deposits at Fukazawa was used as a control area for one test of FINDER. Using the Na 2 O means and standard deviations for the control area and minimum Na 2 O values from 174 drill holes, a probability map of centers of sodium depletion is produced for the Hokuroku district. High probability areas correspond to the known deposits that should have been rediscovered and to several areas without known deposits.Use of X-ray data from 165 drill holes, some of which also have chemical analyses, led to the identification of two additional variables, sericite and gypsum plus anhydrite, that allow more drill holes to be used and that expand the areas of influence around drill holes. Sericite is enriched up to 2.15 km and gypsum plus anhydrite up to 3.5 km from the centroid of the control area Fukazawa deposits. For the deposit groups with X-ray data nearby, Fukazawa, Shakanai, and Furutobe, a pattern of sericite enrichment, kuroko deposits, and gypsum plus anhydrite enrichment over 4 or 5 km is shown.With sodium, sericite, and gypsum plus anhydrite, FINDER's high probability areas include each of the four groups of kuroko deposits that should have been rediscovered and only one known deposit that is much smaller than Fukazawa is missed. Several large areas that are favorable centers of undiscovered deposits and other areas that are unlikely centers of deposits are also identified.

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