John Warvelle Harbaugh
Biogeochemical investigations in the Tri-State District
Economic Geology and the Bulletin of the Society of Economic Geologists (September 1950), 45(6):548-567

Abstract:
Samples of various plants were collected at seven areas in the Tri-State Mining district. These samples were analyzed colorimetrically for zinc and copper and analyzed spectrographically for lead, nickel, tin, silver and cobalt. Higher average zinc concentrations were found in plants growing near mineralized zones less than 100 feet in depth. Analyses of 56 samples of twigs of the blackjack oak, Quercus marilandica, from trees growing above or near mineralized zones, showed an average zinc concentration 29 percent greater than 101 similar samples gathered in the same area, but at a distance of 300 feet or more from mineralized zones. In addition, the samples from above or near mineralized zones showed an average zinc concentration 67 percent greater than 23 similar samples collected in areas presumably barren of mineralization and lying some miles distant.Samples of 24 species of trees, collected above mineralized zones, showed an average zinc concentration 38 per cent greater (in leaves) and 25 percent greater (in twigs) than similar samples from areas barren of mineralization. Samples of 16 species of grasses and herbaceous plants, gathered above mineralized zones, showed an average concentration of zinc 30 percent greater than similar samples from barren areas.In a two square mile area, the geographical distribution of zinc concentration in samples of Quercus marilandica twigs showed moderate correlation with known mineralized zones. Other metals showed much less correlation.Biogeochemical surveys based upon average zinc concentrations from large numbers of plant analyses appear to offer promise in prospecting for concealed mineralization in the Tri-State district, particularly within the outcrop area of the "Boone" limestone.