Abstract

Bedded barite deposits in northeastern Washington occur as distinct beds, from 1 to 45 feet thick, interbedded with quartz siltstones, argillites and limestone that may range in age from Ordovician to Carboniferous. Six of 9 known bedded barite deposits were selected for field and laboratory study. They are similar in many respects to other bedded and presumably marine sedimentary barite deposits in Nevada and Arkansas, including: 1) their conformity with the bedding of enclosing quartz siltstones, argillites and limestone, 2) their thin laminae (<1.0-10.0 mm), 3) their very fine grain (0.02-0.60 mm), 4) their mosaic texture, 5) their essentially monomineralic constitution, 6) their content of disseminated euhedral pyrite and amorphous organic matter, 7) their strong fetid odor when crushed, 8) their lack of control by fractures or other potential channelways of ingress, 9) their lack of wall rock alteration, and 10) their lack of zoning with respect to nearby granitic intrusives.The uranium content of the bedded barite ranges from about 3 ppm to 17 ppm, whereas the uranium content of hydrothermal vein barite from Stevens County is generally less than 3 ppm. This is compatible with the findings of others who have compared the uranium content of marine barite nodules with that of vein barite.Both the conformable bedded barite and enclosing strata display two generations of folds, an early isoclinal and recumbent and a later upright fold set with accompanying slip or crenulation cleavage.Post-folding recrystallization is indicated by loss of undulatory extinction, coarsening of grain in low pressure areas and in the purer beds, and the presence of 120 degrees triple junctions. The age of the bedded barite is probably Middle to Late Paleozoic, the folding is Late Jurassic or Early Cretaceous, and the recrystallization may be related to the emplacement of granitic batholiths in Cretaceous time.

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