Se. Kesler et al., LEAD-ISOTOPE GEOCHEMISTRY OF MISSISSIPPI VALLEY-TYPE MINERALIZATION IN THE CENTRAL APPALACHIANS, Economic geology and the bulletin of the Society of Economic Geologists, 89(7), 1994, pp. 1492-1500
Lead isotope compositions of sulfide minerals from Mississippi Valley-
type deposits in Cambrian, Ordovician and Silurian rocks in the centra
l Appalachians plot in distinct groups, one for each major district. D
ata for deposits in the Nittany Arch and Shawangunk districts form cir
cular clusters, whereas data for the Timberville and Friedensville dis
tricts form more elongated fields. Comparison of these data to isotopi
c compositions of possible source rocks suggests that lead in the Nitt
any Arch, Shawangunk, and Timberville clusters came largely from Paleo
zoic igneous rocks or sediment derived from these rocks, whereas lead
in the Friedensville deposits came from Grenville-age basement rocks.
Additional lead from the Timberville district appears to have come fro
m Triassic diabase, suggesting that as least some mineralization there
is unusually young. These results contrast strongly with those for th
e southern Appalachians, where different Mississippi Valley-type distr
icts have similar isotopic compositions over large areas. Only lead fr
om the Ordovician-hosted Timberville deposits in the central Appalachi
ans has an isotopic composition similar to that of any of the southern
Appalachian deposits, and its composition is similar to that of depos
its in the Lower Cambrian paleoaquifer of the southern Appalachians, r
ather than the Ordovician paleoaquifer. These relations indicate that
although Mississippi Valley-type brines in the central Appalachians pa
rticipated in significant cross-formational flow, they were not as reg
ionally extensive as those in the southern Appalachians, a factor that
might account for the relative scarcity of large Mississippi Valley-t
ype deposits in the central Appalachians area.