Mineralized Veins and Sand Injectites in the Utica Formation, New York State: Implications for Fluid Flow and Fracture Development
Bruce Selleck, Nicole MacDonald, and Kristen Meisner
Department of Geology, Colgate University, Hamilton, NY 13346 [email protected]
Cm-scale calcite veins and sand injectites occur in the basal Utica Formation (Upper Ordovician, Flat Creek Member) in the proximal portion of the Taconic foreland basin in east-central New York State. E-W striking veins contain zoned calcite spar with multiple generations of 2- phase aqueous and hydrocarbon gas inclusions. Wellcrystallized authigenic illite occurs within veins. Homogenization and ice melt temperatures indicate vein development took place when temperatures exceeded ~80oC and persisted to ~130oC. Stable isotopic data from calcite suggest fluids were derived from dewatering of adjacent mud, consistent with the near sea water salinity of fluid inclusions. The relatively low salinity of the vein-forming fluids indicates that mud dewatering was an unlikely source of fluids that caused dolomitization of underlying Trenton- Black River carbonates. Calcite veining in the Utica Formation is generally restricted to the eastern Mohawk Valley. Filled fractures are uncommon in the type area near Utica, New York and the Tug Hill Plateau region.
Sand injectites hosted by the Utica Formation are 2-10 cm thick, sharp-walled, and dike-like in aspect. The injectites consist of angular fine sand- to coarse silt-size quartz, feldspar, and volcanic clasts. The texture and petrology of the sand injectite are most consistent with internal derivation from host Utica Formation during compaction dewatering and fluid explusion. This origin contrasts with sand injectites developed at the Paleozoic-Proterozoic contact in the Mohawk Valley, where fluidized, mature quartz-rich sands were injected downward into basement rock. Fluid inclusions in carbonate veins associated with basement-hosted injectites have salinities to 25% NaCl equivalent.
AAPG Search and Discovery Article #90095©2009 AAPG Eastern Section Meeting, Evansville, Indiana, September 20-22, 2009