EPIGENETIC SULFIDE MINERALIZATION ASSOCIATED WITH PENNSYLVANIAN PALEOKARST IN EASTERN IOWA, USA

Paleokarst-associated, sulfide-bearing mineral deposits are wide-sprea d in the Paleozoic carbonate rocks of eastern Iowa. Minerals occur in nodules enclosed in karst-filling mudstones, as sandstone cements, and as surface coatings on, and fracture fillings in, foundered carbonate rock clasts. Mineralogy and paragenetic sequence vary among the occur rences. Sulfur isotopic compositions exhibit wide variations within an d among deposits (deltaS-34 = -33.8 to +35.1 parts per thousand). Oxyg en isotopic compositions of fracture-filling calcite spars (deltaO-18 = -8.41 to +3.60 parts per thousand) are similar to the isotopic compo sitions of their carbonate rock hosts. Calcite spars are somewhat depl eted in deltaC-13 relative to host rock [deltaC-13 (spars) = -5.66 to +0.24 parts per thousand vs. -1.54 to +1.21 parts per thousand (host r ock) 1. Results of mineralogic, paragenetic and isotopic investigation s suggest that: (1) minerals are products of multiple events operating on a local, rather than a regional scale; (2) spatially-disjunct frac ture-filling mineral deposits exposed in the same quarries are probabl y not cogenetic with paleokarst-associated deposits; (3) paleokarst-fi lling calcite spars formed at near-surface temperatures; and (4) paleo karst-associated deposits are probably not cogenetic with Upper Missis sippi Valley Zn-Pb pitch-flat deposits.