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Detailed bedrock geology of the brenda copper- molybdenum mine, peachland, b.c. Oriel, William Michael

Abstract

Detailed mapping of the bedrock geology of the Brenda copper-molybdenum deposit has revealed a consistent sequence of geological events. Consolidation of the quartz diorite host rock that forms Brenda stock was followed by intrusion of small pegmatite and aplite dikes that probably relate to a residual fraction of the parent magma. Age dating of various quartz diorites (White and Harakal, unpublished) indicates that magma solidification occurred about 176 m.y. A concentration of biotite model ages at about 146 m.y. seems best interpreted as the time of ore mineralization. Mineralization occurred at the beginning of a continuous sequence of related structural events. All mineralized ore fractures and younger shears, faults and intramineral dikes exhibit similar, strongly preferred orientations that are unlike orientations of felsic dikes or primary foliations in the quartz diorite host rock. The ore occurs entirely in fractures as products of three sequential overlapping phases of mineralization and consists almost entirely of the ore minerals chalcopyrite and molybdenite with quartz gangue predominanting. Hydrothermal alteration products exist mostly as thin envelopes of potassium feldspar and/or biotite and propylitic alteration. Large argillic alteration zones also exist, however, and are associated commonly with extensively sheared zones. An effort was made at finding a zoning pattern of ore minerals, minor elements and alteration minerals. Ore mineral zoning in the classical sense appears to be absent at Brenda. Metal grades show a crude zonal distribution that correlates directly with density of ore fractures, Hydrothermal alteration minerals and minor elements in chalcopyrite also lack any obvious systematic zonation pattern on the scale of the mine pit. Intramineral dikes of various textures and compositions have been dated at about 130 m.y. They formed after ore mineralization yet before late minor veining not associated with ore-producing veins.

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