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UBC Theses and Dissertations

The geology of the Indin "Break", N.W.T. Hodgson, Alexander G.


This thesis presents the results of a general geological study of a belt of Archean rocks in the Indin Lake district, N.W.T. The summary results of a summer's field work are incorporated with a brief petrographical investigation of different rock types. Intermediate to acidic lava flows and pyroclastic rocks overlain conformably (?) by a succession of clastic sediments are invaded by minor acidic intrusives and a plexus of basic dykes and sills. Isoclinal folds in sediments, broader flexures in volcanics, bedded shear zones, and regional foliation and lineation are all attributed to a single system of powerful tangetial forces that affected all stratiform rocks in the area. Zones of weakness at contacts are imputed, to differential competence between volcanic and sedimentary rocks, and a. theory of folding of rock units of differing competency is applied in modified form to the origin of the Indin "break" - a gold-bearing shear zone close to a major contact. Evidence is presented to suggest that “cross-faults” clean-cut dislocations that transect the regional structural trend - and emplacement of late basic intrusives are quasi-contemporaneous events that progressed over a protracted interval of time and may have been consequent upon a single deformational-pattern. An attempt to explain the propinquity, and thus the possible structural relation, of gold mineralization to cross-faults is embodied in a theory relating the control of mineralization "by channeling of ore-solutions in structures developed during the period of strain accumulation that culminated in cross-faulting. An almost completely reconstituted mineral assemblage is ascribed to a moderate grade of regional metamorphism consisting of dynamic metamorphism during orogeny and relatively minor effects of superimposed thermal and retrograde metamorphism. Metacrysts of ankeritic carbonate, believed to be hydro-thermal, are discussed, and their superficial genetic or structural association with gold mineralization is offered as a possible guide to future ore discovery. Rather detailed descriptions are submitted of ankeritic carbonate, an unusual "hornblende" occurring in amphibolite, and a green mica, tentatively called phengitic-muscovite, from a carbonate zone.

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