Open Collections

Johnston, Russell James

University of British Columbia

The Galore Creek porphyry deposit is a major alkalic porphyry deposit hosted in latest Triassic silica-saturated to silica-undersaturated volcanic rocks of the Stikine Terrane of northwestern British Columbia. The deposit is bordered to the west by an anomalous, approximately north-south striking, steeply west-dipping zone of high strain (referred to as the Ridgeline Deformation Corridor or RDC) that contains penetrative cleavages, stretching lineations and folds. The genesis of the corridor and its relationship to the Galore Creek deposit is poorly understood but has been recognized by previous workers as an important structure in the area. The genesis and structural history of the RDC, and overall deformation history of the Galore Creek area was investigated through field mapping coupled with petrography, scanning electron microscope (SEM) and micro-X-ray fluorescence (μXRF) analyses. It was determined that the cross-cutting relationships between the RDC and mineralization/alteration associated with the Galore Creek deposit are inconclusive, and that, given how wide-spread the deformation corridors are, it is unlikely that the RDC and the Galore Creek deposits formed synchronously. It is proposed that the RDC formed during regional mid-Cretaceous compression, either as a function of localization of strain along the margin of the relatively rigid Galore Creek deposit, or, that both the Galore Creek deposit and the RDC formed due to localization of fluids through a deep-seated seated, pre-existing structure underlying the RDC and the Galore Creek deposit. Previous models of tilting that suggested the deposit had been tilted >45° towards the south-southwest were assessed and rejected as they are not compatible with the orientation of bedding. The rocks that comprise the RDC contain pseudoleucite and analcime after albite pseudomorphs, some of which are deformed, and some of which are not. A series of igneous, surficial, and metamorphic reactions involving the breakdown of leucite to analcime, and analcime to albite were interpreted based on mineral textures. It was determined that the speed at which analcime reacts to form albite is a key control on strain partitioning in analcime-bearing rocks during deformation and metamorphism, which is controlled by the availability of silica.

Text

2025-04-24

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/90758

Geological Sciences

University of British Columbia

UBCV

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