ANCIENT RIFTED LAURENTIAN MARGIN CONTROLS ON MESO-CENOZOIC CORDILLERAN METALLOGENY (Invited Presentation)

The provinciality of mineral deposits emphasizes crustal and lithospheric-scale controls on metal tenor and fertility, or on the processes that form them. The diversity of crustal blocks underlying the North American Cordillera is a fundamental control on its metallogenic diversity and distribution of mineral deposits. The Cordillera’s accreted terranes are backstopped against the previously (Neoproterozoic) rifted western Laurentian miogeoclinal margin which is metallogenetically characterized by the strataform and stratabound base metal deposits that formed during punctuated periods of unpassive Paleozoic margin extension.

These same regions also host anomalous Mesozoic magmatism, including lamphrophyres, and related tungsten and gold deposits that formed from fluids exsolved from moderately reduced, felsic intrusions. These regional metallic features are particular to Yukon and Nevada, and are within and characterize the upper plates of the ancient rifted continental margin and their bounding transform zones. Much of the metal budget is related to magmas which were derived from the upper plate’s previously metasomatized, sub-continental lithospheric mantle. The metasomatism is ancient and has no direct relationship to Mesozoic subduction. Rifted lower plate margins do not display similar metallogenic associations.

Carlin-type gold deposits are also features that are particular to the previously-rifted upper plate miogeoclinal margin and related ancient rifts and transform zones that underlie Nevada. Recent Carlin-type gold discoveries in the Yukon indicate that tectonic features of the ancient rifted upper plate are also essential to their localization. Although enigmatic, Carlin-type deposits in Nevada are associated (temporally and potentially genetically) with late Eocene voluminous magmatism which potentially indicates another link between gold and magmas from an enriched lithospheric mantle. However, the Yukon Carlin-type gold mineralization lacks significant contemporaneous magmatism and emphasize that such magmatic contributions are not essential, and that the ancient features of its upper plate setting are fundamental, despite their formation in the uppermost crust.