Abstract

Mineral aggregates consisting of celestite, dolomite, calcite, and very small amounts of sphalerite, anhydrite, and pyrite occur in the uppermost beds of the Glen Dean limestone, of upper Mississippian age, which crops out along the slopes of Buffalo Cove. Proportions of minerals range widely in adjacent aggregates; maximum content of strontium sulphate is about 96 per cent. The aggregates are spherical to nearly flat, and are regular to irregular in outline; a few coalesce. The maximum dimensions of those examined range from 0.04 to 1.35 feet, and their known vertical range in the Glen Dean limestone is from 7 to 20 feet or more downward from the contact with the overlying Pennington shale. The aggregates in the uppermost beds commonly contain chert and are somewhat hollowed as a result of weathering. Those in the lower beds contain no chert, and, where unweathered, no cavities. Celestite also occurs as isolated crystals and groups of crystals embedded in the limestone. The limetone is fine-grained, brownish gray, argillaceous, and un-fractured. The isolated crystals probably were precipitated from connate water as the limestone consolidated. During subsequent erosion of the Pennington shale to a level only 200 feet above the Glen Dean limestone, meteoric water probably gained access to the upper Glen Dean beds and dissolved cavities in them. The dense, unjointed limestone prevented downward percolation of the water, which became saturated with strontium sulphate and calcium carbonate, and deposited celestite and calcite in the solution cavities. As the dolomite in the aggregates has no apparent local source, it is believed to have been introduced from depth, probably with the small amounts of sphalerite and pyrite, by hydrothermal solutions in post-Mississippian time. Although no veins were seen in the few exposures examined around the cove, it is inferred by analogy with other mineralized areas that the solutions rose along fissures and were deflected by the overlying shale, spreading laterally through the partly filled cavities in the limestone without impregnating the limestone itself. Meteoric water still present in the cavities probably promoted deposition without attack on the limestone by lowering the temperature of the solutions.The celestite zone is being developed at the Youngs quarry. Reserves in the block of ground that contains the quarry are estimated to be 2,822 tons of the mineral aggregates, or strontium ore, containing 2,148 tons of celestite. The celestite constitutes 5.89 per cent by weight of the combined rock and aggregates in the block. Four out of seven exposures examined elsewhere in the ore zone suggest that other roughly comparable blocks may be developed. Underground quarrying is not practicable because of the overlying shale, but a dozen or more similar open quarry sites might be found on the divides between the numerous ravines that drain the sides of the cove.

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