Abstract

Copper in the Helikian Grinnell Formation, Alberta, occurs in "cyclic quartz arenite units," produced by short-lived fluvial to lacustrine episodes in a semi-arid region. Each cyclic unit consists of a 2- to 3-foot-thick red argillite overlain by a mineralized, cross-bedded-fluvial quartz arenite (2 in to 6 in thick) capped by a mineralized (1 in to 2 in thick) lacustrine quartz arenite. This environmental cycle of prolonged oxidation (argillites) followed by organically induced reduction (quartz arenites) was repeated several times. The copper sulphides occur intergrown with silica cement and may be an integral product of the sedimentary cycle.

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