Tens-of-centimeter scale calcite crystals concentrically zoned with sulfide minerals and growing within meter-scale solution cavities along NW-trending fractures were recently discovered in Kane County, NE Illinois in the Ordovician Galena Group limestone (Trenton). On the basis of plane-light and cathodoluminescent petrography and scanning electron microscopy, a series of diagenetic events are identified within the cavities that consist of dissolution followed by dolomite, marcasite, pyrite, and calcite precipitation, and later hydrocarbon migration. The paragenetic sequence, in conjunction with changes in delta 13C, delta 18O, and 87Sr/86Sr concentrations in calcite growth zones, reflect changes in the fluid chemistry and the source of the subsurface diagenetic waters migrating through the midcontinent. Isotopic values suggest the existence of at least two distinct fluids that flowed through fractures following the development of solution cavities. Isotopic values in calcite zones record each fluid getting heavier in delta 13C and lighter in delta 18O with respect to time. The youngest calcite zones record significantly lighter delta 18O (-9.27 to -5.24 ppm) and delta 13C (-10.58 to -3.27 ppm) than the older zones implying a warmer fluid and a possible genetic relationship to hydrocarbon generation and/or migration. The paragenesis revealed in this study is comparable to that of the world famous Upper Mississippi Valley Zn-Pb mining District in northwest Illinois, suggesting that migrating warm fluids were widespread throughout northern Illinois and surrounding areas, resulting in the formation of massive solution cavities, dolomitization, and the subsequent deposition of Mississippi Valley-type minerals. However, on the basis of the paragenetic sequence and the isotopic values for diagenetic calcite cements precipitated within solution cavities in northeastern Illinois, at least two paleo-fluids are identified that may be genetically related to the fluids that were responsible for the Upper Mississippi Valley ore deposits and cavernous porosity development at the productive Albion Scipio hydrocarbon reservoirs in the Michigan Basin. Determining the paragenetic sequence coupled with geochemical characterization of the solution cavity calcite and associated minerals in the Galena carbonates in northeastern Illinois will assist in mapping paleo-fluid flow throughout the midcontinent and aid in mineral and hydrocarbon exploration.
|Original language||English (US)|
|Title of host publication||Abstracts: Annual Meeting - American Association of Petroleum Geologists|
|Place of Publication||Tulsa, OK|
|Publisher||American Association of Petroleum Geologists|
|State||Published - 2011|