ORIGIN OF CARBONATE-HOSTED CELESTINE DEPOSITS OF THE FINDLAY ARCH REGION: NEW EVIDENCE FROM SOLID AND FLUID INCLUSIONS

Large deposits of celestine are abundant in rock quarries along the crest and flanks of the Findlay Arch in NW Ohio, SE Michigan, and SW Ontario. They occur in Middle Silurian to Middle Devonian dolostones as open space fillings and replacements of evaporites. An early generation of bladed celestine and a later generation of prismatic crystals occur together with fluorite, sphalerite, and other epigenetic minerals. The areal distribution of celestine correlates closely with Late Silurian and Middle Devonian bedded and nodular gypsum in near surface rocks and inferred extensions in rocks eroded from the Findlay Arch. The former presence of evaporites at many sites is indicated by inclusions of anhydrite in celestine.

Homogenization temperatures (Th) and last ice melting temperatures (Tm) were measured for primary and secondary inclusions in celestine. Liquid/vapor ratios of fluid inclusion assemblages in celestine were highly variable, most variability being attributed to necking down. Average Th values in celestine are estimated to lie between 60 and 90^oC based on the abundance of metastable one-phase liquid inclusions. Values of Tm for fluid inclusion assemblages showed less variability. For all inclusions, values of Tm ranged from –24 to 0^oC. The lowest temperature records the salinity of basinal brine, whereas higher temperatures represent various stages of dilution with meteoric water. Bladed celestine has lowest values of Tm (mean=-5.9^oC) whereas prismatic celestine has higher values (mean=-1.6^oC).

The following genetic model is proposed for the genesis of Findlay Arch celestine. It is similar to the model of Hanor (2004) with the addition of evidence from fluid inclusions. Downward moving meteoric water resulted in secondary porosity and karst features that provided depositional sites for celestine. Strontium was introduced from brine driven out of the Appalachian Basin during the Late Paleozoic, and sulfate from dissolution of local evaporites by meteoric water. Mixing of brine with meteoric water resulted in the precipitation of most celestine, while some formed from the replacement of evaporites.