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Distribution of district-scale hydrothermal alteration, vein orientations and white mica compositions in the Highland Valley Copper district, British Columbia, Canada : implications for the evolution of porphyry Cu-Mo systems

University of British Columbia

This thesis presents a multi-layer lineament mapping method that integrates topography, geophysical data and geological observations to interpret faults at surface, and demonstrates how magnetic intensity data can be used to estimate the dip of fault-related magnetic anomalies by performing 2D inverse modeling along profiles extracted from a magnetic intensity grid. Dip modeling of magnetic anomalies created in a synthetic 3D magnetic susceptibility model shows that the method is accurate to better than 5° for input dips >60°. Comparison between fault orientations modeled from magnetic data and measured in the field in the Guichon Creek batholith (GCB) confirms that the methodology can be successfully applied to brittle faults in real, albeit relatively simple geological environments. Alteration mapping across the Highland Valley Copper (HVC) district defined zones of K-feldspar-bearing and muscovite-bearing veins, and later and more extensive zones of veins bearing sodic-calcic and propylitic mineral assemblages. A palinspastic reconstruction of the GCB to its Late Triassic geometry shows that: 1) potassic alteration forms a westerly-elongated ~12 x 2 km zone that overlaps with the Valley–Lornex and Highmont deposits, 2) sodic-calcic alteration forms discontinuous zones that cover an area ~17 km by 11 km (southwest) and <1 km (northeast), and 3) propylitic alteration is ubiquitous but a 10 km diameter zone of higher vein intensity (>5 cm/m) is located in the center of the batholith. Permeability within the batholith was dominantly the result of local stresses induced by magma or magmatic fluid overpressure (i.e., radial aplite and K-feldspar-bearing vein patterns around porphyry deposits), and by thermal contraction (i.e., sodic-calcic and propylitic veins perpendicular and parallel to intrusive contacts). The Late Triassic regional sinistral stress regime only locally contributed to the batholith-scale permeability along favourably-oriented west to west-northwest-trending structures. White mica compositional variations, determined by short-wave infrared (SWIR) spectroscopy, define footprints associated with porphyry mineralization. Sodic-calcic and propylitic alteration are characterized by a zone of increased muscovitic white mica abundance that is detectable within 3 km of the HVC deposits, and a zone of increased phengitic white mica abundance detectable to distances up to ~5 km from the HVC deposits.

Text

2020-02-28

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/73624

Geological Sciences

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/