Early proterozoic tectonics and metallogeny of the lake huron region of the Canadian shield

Abstract

Abstract Deposition of the Huronian Supergroup, dominantly fluvial clastic sediments with local basal volcanic accumulations, began at ∼2.49 Ga in a broad trough that extended far south of the present Lake Huron area atop a large Archean continent that was assembled at ∼2.7 Ga and broken up at ∼2.15 Ga after intrusion of widespread gabbro sheets and dykes including Nipissing diabase. The Wyoming Province, which contains sequences similar in age and stratigraphy to the distinctive Huronian Supergroup, may be a fragment of this continent; the Superior Province is a much larger fragment. Tectonic controls of deposition of the Huronian and its paleoplacer uranium deposits, and of the pre-2.2 Ga deformation of these strata, were probably unrelated to processes that controlled deposition of the Animikie and Marquette Range sequences in the Lake Superior region at ∼2.0 Ga. The Huronian, Animikie, and Marquette Range sequences were deformed during the ∼1.85 Ga Penokean orogeny which occurred when an assembly of island arc terranes collided with the Superior block. The Sudbury structure, including the Whitewater Group and its contained sedex deposits and the Sudbury igneous complex and its NiCuPGE ores, were also formed at ∼1.85 Ga. The Elliot Lake pyritic paleoplacer uranium ores, myriad lenses of radioactive pyritic gravels, were deposited by early Huronian fluvial systems. Other endogenic Huronian mineral deposits include disseminated NiCu sulphides in gabbros, Cu in red beds high in the Huronian succession, and silica in quartz arenites. Intrusions of Nipissing gabbro near Sudbury contain minor NiCu mineralization. These intrusions also caused recycling of metals from Archean and Huronian rocks to form concentrations of Cu, Au, Ag, Fe and W in veins and other epigenetic deposits. Most important of these are the unconformity-related Ag veins of the Cobalt area which had particularly complex, still undeciphered, histories that probably included pre-Huronian weathering. Metallogenic patterns in the Early Proterozoic rocks were controlled by a complex interplay of factors including the distribution of mineral deposits in the Archean basement, tectonically controlled variations in Huronian deposition and deformation, and oxyatmoversion, the transition from anoxic to oxygenic atmospheric conditions that occurred during deposition of the Huronian Supergroup.