PROSPECTIVE TRENDS FOR PB-ZN ORE DEPOSITS IN CAMBRIAN CARBONATES, SOUTHEASTERN BRITISH COLUMBIA

Miogeoclinal, Cambrian carbonates in southeastern British Columbia host numerous Pb-Zn orebodies ranging from minor showings to major deposits with extensive exploration and production histories. The sulphides are concentrated in three belts: 1) shelf-to-basin facies transitions along the eastern margin of the extensional, Cambrian to Late Silurian White River Trough, 2) the western side of the latter trough, where Cambrian carbonates onlap the Windermere High, and 3) the Paleozoic Lardeau Trough, developed along the western flanks of the Windermere High and Montania. Major east-west and north-south lithofacies changes, significant to base-metal exploration, occur within the region's Cambrian successions. It is anticipated that the study of the carbonate-hosted lead-zinc deposits will lead to a more detailed understanding of the Cambrian facies changes and, hopefully, new discoveries of lead-zinc mineralization.

Mississippi Valley-Type orebodies appear to predominate in the Cambrian carbonates but vein deposits, deeply oxidized ore zones and tectonized, stratabound orebodies containing stratiform deposits that resemble sedimentary-exhalative deposits are common. The metamorphic grade of the sulphides increases westward from lowest greenschist in the Rockies to lower amphibolite grade in the central to northern Kootenay Arc. Orebodies east of the Windermere High preserve original fabrics and show little tectonic deformation but most of those in the Kootenay Arc north of the Metaline district in northeastern Washington State display isoclinal folding, penetrative deformation and effects of regional and contact metamorphism.

The age of the lead-zinc mineralization in most of the carbonate-hosted orebodies is poorly constrained because of the lack of radiometric dates. There were several episodes of mineralization ranging from early Paleozoic to post Middle Jurassic. Two important episodes of Paleozoic mineralization occurred: an early one resulting from Early Cambrian to Silurian extension and alkaline intrusion, and a subsequent phase during deformation and magmatism related to the Late Devonian to Mississippian Antler Orogeny.