A Pb isotope synthesis of Mississippi Valley-type ores in the midcontinent U.S.A.: trends and ore metal source(s)

Abstract

High concentrations of Ga and Ge, two strategic metals vital to modern technology and industry, have been noticed in ores from various Mississippi Valley-type deposits in midcontinent U.S.A. [1]. These deposits also account for a substantial amount of worldwide Pb and Zn resources. A variety of crustal rocks, including basement rocks, shales, and carbonate aquifers, have been suggested as potential source(s) of ore metals [2, 3, 4, 5, 6]. MC-ICP-MS Pb isotope analysis of ores and rocks have been carried out to re-evaluate these source(s). Lead isotope values of ores define two collinear, parallel trends: Tri-State (TS) and Central Missouri (CM) ores are collinear with Southeast Missouri (SM) and Northern Arkansas (NA) ores; Upper Mississippi Valley (UMV) and Illinois-Kentucky (IK) ores are collinear with Central Appalachian (CA), Southern Appalachian (SA), East Tennessee (ET), Central Tennessee (CT), and South-Central Kentucky (SCK) ores (Figs. 1, 2). Ores from Ozark region (CM, SM, TS, and NA districts) are characterized by 208 Pb-depleted Pb compared to Pb in UMV,