ENZYME LEACH ANOMALIES ASSOCIATED WITH DEEP MISSISSIPPI VALLEY-TYPE ZINC ORE BODIES AT THE ELMWOOD MINE, TENNESSEE

Deeply buried Mississippi Valley-type deposits that have been or are c urrently being mined in North America were initially discovered by dri lling. Conventional geochemical methods are ineffective for detecting these 'blind' deposits when they occur deep within sequences of stable -platform carbonates and shales, The 'enzyme' leach is a selective ana lytical technique for determining trace elements associated with amorp hous Mn oxide coatings in soils, In many areas of the world, the enzym e leach method is useful for detecting low-level geochemical anomalies in soils, which are associated with blind mineral deposits. Enzyme le ach analysis of soils, collected at the Elmwood Mine, Tennessee, revea led high-contrast anomalies over ore bodies 370 m below the surface. I n areas where the soils are in chemical equilibrium, 'combination' ano malies occur over Zn ore bodies. These are characterized by asymmetric al halogen halos which occur around a halogen 'central low'. Commodity metals (Zn and Pb) and trace elements associated with the ore (Cd, Ba , and Mn) form apical anomalies, which occur over the ore bodies and w ithin the halogen halo. Under most circumstances, agricultural practic es do not affect enzyme leach results. However, agricultural activity in central Tennessee appears to have altered the proportion of amorpho us Mn oxides in the soils in some locations. Where the MnO2-form equil ibrium of the soil has been disturbed, enzyme leach data are erratic. In the one instance where this was encountered, ratioing the data to M n reveals anomalies which bracket the blind ore bodies. (C) 1998 Elsev ier Science B.V. All rights reserved.