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TitleUnravelling tourmaline in mineralized porphyry systems: assessment as a valid indicator mineral
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AuthorBeckett-Brown, C E; McDonald, A M; McClenaghan, M B
SourceTargeted Geoscience Initiative: 2018 report of activities; by Rogers, N (ed.); Geological Survey of Canada, Open File 8549, 2019 p. 345-351, (Open Access)
PublisherNatural Resources Canada
Documentopen file
Mediaon-line; digital
RelatedThis publication is contained in Rogers, N; (2019). Targeted Geoscience Initiative: 2018 report of activities, Geological Survey of Canada, Open File 8549
File formatpdf
Subjectseconomic geology; igneous and metamorphic petrology; geochemistry; surficial geology/geomorphology; mineral deposits; porphyry deposits; copper; gold; molybdenum; mineral exploration; exploration methods; ore mineral genesis; mineralization; tourmaline; petrogenesis; paragenesis; hydrothermal systems; mineral zoning; petrographic analyses; electron microscope analyses; trace element geochemistry; textural classifications; major element geochemistry; mass spectrometer analysis; glacial deposits; tills; till samples; stream sediment samples; ore systems approach; indicator minerals; redox sensitive elements; large-ion lithophile elements (LILE); rare earth element analyses
Illustrationstables; photographs; photomicrographs; ternary diagrams
ProgramTargeted Geoscience Initiative (TGI-5), Knowledge Management Coordination
ProgramTargeted Geoscience Initiative (TGI-5), Intrusion/Porphyry ore systems - porphyry processes - mineral markers
Released2019 03 01
AbstractTourmaline has long been regarded as a petrogenetic indicator of its host environment, but its genesis in mineralized porphyry systems is poorly understood. Based on chemical and physical properties, tourmaline possesses essential features to be an effective indicator mineral. These properties, along with its abundant occurrence in mineralized copper-gold-molybdenum porphyry systems, make it potentially a key recorder of hydrothermal fluid composition, evolution and potential mineralization. A suite of tourmaline-bearing, barren and mineralized porphyry samples have been analysed as part of a broader study, including those from the Canadian Cordillera (Casino, Schaft Creek, High-land Valley and Woodjam) plus others, have been studied. Paragenetically, tourmaline is observed to be an early hydrothermal phase, predating both sulphide formation and any alteration. Tourmaline is observed to exhibit multiple growth zones, based on petrographic and electron microscope observations, which are also reflected in distinct trace-element variations. Three distinct textural types are recognized: breccia-style, vein-style and disseminated-style. Ma-jor element analyses based on SEM-EDS show a range between schorl (Na-Fe2+-rich) to dravite (Na-Mg-rich) with some minor povondraite (Na-Fe3+) component. Trace element analyses of porphyry related tourmaline via LAM-ICP-MS show distinct characteristics in comparison to that from non-porphyry settings, including redox sensitive elements (Mn, As and Sb) and large-ion lithophile elements (Sr, Ba). Elements not observed in significant concentrations include the light elements (Li, Be) and REEs, which commonly were below limit of detection. Current trace element analysis of tourmaline derived from surficial sediments points to tourmaline originating from the local porphyry system rather than an external source.