Abstract

Base metal occurrences in the Mississippian Windsor Group (Nova Scotia, Canada) are commonly associated with carbonate breccias in the Macumber Formation. Based on sedimentologic, structural, and diagenetic data, three types of temporally distinct breccias are recognized near the top of the Macumber Formation: early synsedimentary, synburial tectonic, and late, postburial karstic. Early breccias originated as rotational slides on a Visean deep-water slope and host mineralization such as the Walton deposit (Ba-Cu-Pb-Zn-Ag). Later tectonic breccias of Westphalian age are a manifestation of the Ainslie detachment, a regional flat-lying extensional fault, and host the Jubilee deposit (Zn-Pb). Finally, an irregularly distributed postburial, karstic solution-collapse barren breccia is designated as the Pembroke breccia. The recognition of three temporally and genetically distinct breccias is significant for comprehension of the breccia-hosted mineralization in the Mississippian section in eastern Canada. The synsedimentary and tectonic breccias are pre- to synore, respectively, and both have played a key role in localizing mineral deposition through enhanced permeability. The late karstic breccia was not involved in the mineralization and, where present, subaerial exposure leading to the formation of this breccia has removed significant portions of the orebodies.

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