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TitleDetecting buried porphyry Cu mineralization in a glaciated landscape: a case study from the Gibraltar Cu-Mo deposit, British Columbia, Canada
AuthorPlouffe, AORCID logo; Kjarsgaard, I M; Ferbey, T; Wilton, D H C; Petts, DORCID logo; Percival, J BORCID logo; Kobylinski, C; McNeil, R
SourceEconomic Geology 2022 p. 1-24, Open Access logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20210117
Mediapaper; on-line; digital
File formatpdf; html
ProvinceBritish Columbia
Lat/Long WENS-139.5000 -112.0000 60.0000 48.0000
Subjectsmineralogy; Science and Technology
Illustrationslocation maps; photographs; diagrams; tables
ProgramTargeted Geoscience Initiative (TGI-6) Ore systems
Released2022 02 01
AbstractAt the Gibraltar porphyry Cu-Mo deposit in south-central British Columbia, geochemical and mineralogical anomalies in till, around a cluster of mineral occurrences, form amoeboid dispersal patterns controlled by three phases of ice movements. The dispersal patterns defined by elevated concentrations of ore (Cu, Mo) and pathfinder (Ag, Zn) elements, and alteration oxides (Al2O3, K2O) in the till matrix (clay and silt plus clay fractions) extend over areas of 6 to 36 km2 and are centered on the main economic mineralization. The abundances of sulfides (chalcopyrite, pyrite), sulfate (jarosite) and silicates (titanite, epidote) in the till were determined optically in the 0.25-0.50 mm size range, and the 2.8-3.2 and >3.2 specific gravity (SG) fractions, and by mineral liberation analysis (MLA) and scanning electron microscopy (SEM) in the 0.125-0.180 mm and >3.2 SG fraction. The dispersal trains are defined by the high abundances of these minerals derived from the mineralization and associated oxidized and alterated zones. The areal extent of these mineralogical anomalies in till reaches approximately 30 km2 for chalcopyrite, 62 km2 for jarosite, and up to 136 km2 for epidote. Epidote grains in till with a trace element composition of >10 ppm As, >4 ppm Sb, <200 ppm Sigma-REE, <45 ppm Y, <100 ppm Sc + Cr + Y, and/or <2 ppm Th + Hf are interpreted as being principally derived from intrusive rocks or the hydrothermal alteration associated with the porphyry mineralization at the Gibraltar deposit. Rare epidote grains with >30 ppm Cu are interpreted to be related to porphyry Cu mineralization and are detected in till at up to 7 km down-ice from the economic mineralization. A limited number of zircon grains from till yielded Ce/Nd ratios >19 which might relate to the high oxidation state and potentially the ore fertility potential of the intrusion. Till geochemistry and mineralogy along with geochemical analyses of specific minerals such as epidote and zircon represent an efficient method to establish porphyry Cu mineralization potential in terrains covered with glacial sediments.
Summary(Plain Language Summary, not published)
Porphyry deposits are found in intrusive rocks (like granite) and contain large quantities of copper. The discovery of new copper deposits, a low-cost conductor, is necessary for the development of a green economy based on renewable energy such as hydro-electricity. This paper presents data on the geochemical and mineralogical composition of glacial sediments and how it can be used to discover copper deposits buried under glacial deposits of the last glaciation.

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