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Abstract

The recently-opened stratiform lead-zinc deposits at Pine Point in northwestern Canada are situated in gently-dipping, middle Devonian carbonate sediments roughly 20 to 50 miles from the edge of the Pre-cambrian Shield. Projections of major Precambrian faults underlie the many ore bodies. Although nearly dormant in post-Precambrian times, the faults are believed to have provided the locus for a chain of geologic events including the development of a great barrier reef in Devonian times, subsequent shattering and recrystallization of the reef and the deposition of lead, zinc and iron sulfides in ore bodies of substantial size and grade. Though conclusive evidence is not available, it nevertheless seems probable that the deposition of ore and possibly the solution and redeposition of the sedimentary dolomite (recrystallization) was brought about by thermal waters arising from, but not necessarily originating" at, great depth.

At Pine Point the relation between the basement structures and the overlying facies variations, metamorphism and mineralization can be observed. It is postulated that in some other areas of stratiform lead-zinc deposition, where the basement structures cannot be visualized, similar zones of repeated crustal strain may exist. Such zones may not be the site of great faults but rather, narrow belts of pronounced differential movement between a stable highland and an adjacent sedimentary basin or between adjacent areas where there have occurred prolonged periods of respectively positive and negative radial crustal movement.

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