Of the various geochemical techniques tested in the Upper Mississippi Valley Zinc-Lead District, and particularly in its Southwest Wisconsin portion, spring sampling appears to solve most satisfactorily the difficulties inherent in the search for ore bodies of moderate size in carbonate rocks.Spring sampling, initially tried by the U. S. Geological Survey during 1948-51, was developed in the present investigation into a technique of regional coverage, permitting a rapid and economical evaluation of hydrologic and mineral potentials of large areas. Coverage completed in Southwest Wisconsin between June, 1965, and September, 1966, amounted to 410 square miles and 3,766 springs were sampled.Computed values of 75-percentile and 75-50 percentile ranges of overall, sectional and stratigraphic zinc distributions are used as criteria for evaluating economic merits of sections of the southwest Wisconsin area and of individual geological formations. Among the 56 zinc anomalies indicated by the survey, 26 were found to coincide with known zinc deposits; drill testing of a small number of the remaining anomalies confirmed the presence of zinc ore of commercial grade in their vicinity. Validity of the method depends on an overlap of the oxidation zone and primary halos of base-metal deposits. Quality of coverage and accuracy are found satisfactory. Prerequisites for a successful use of the method in areas outside Wisconsin are suggested.

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