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TitreLinking porphyry deposit geology to geophysics via physical properties: six porphyry deposits in British Columbia, Canada
AuteurEnkin, R J; Mitchinson, D E
Source23rd World Mining Congress 2013, proceedings; par World Mining Congress; 2013 p. 1-11
Année2013
Séries alt.Secteur des sciences de la Terre, Contribution externe 20130330
ÉditeurWorld Mining Congress
Réunion23rd World Mining Congress 2013; Montreal; CA; août 11-15, 2013
Documentlivre
Lang.anglais
Medianumérique
Formatspdf
ProvinceColombie-Britannique
SNRC93
Lat/Long OENS-128.0000 -120.0000 56.0000 52.0000
Sujetssusceptibilité magnétique; porphyres; altération; minéralisation; gisements porphyriques; anomalies magnétiques; argilisation; résistivité; porosité; sulfures; interprétations géophysiques; Groupe de Takla ; pétrologie ignée et métamorphique; minéraux métalliques; géophysique
Illustrationsanalyses
ProgrammeDeveloppements methodologie, Initiative géoscientifique ciblée (IGC-4)
Résumé(disponible en anglais seulement)
Modern mineral exploration depends on multidisciplinary 3-dimensional integration of geological and geophysical data. Identification of the geological sources of geophysical anomalies requires knowledge of the physical property fingerprint of rock types, formations and their alteration products. Understanding how and why physical rock properties vary within the Earth's subsurface ensures that appropriate geophysical exploration methods can be chosen, and allows for more efficient and effective surveys to be designed. Physical property knowledge is integral to geophysical modeling - measured data or values estimated based on geological understanding are used to produce realistic forward calculations and to constrain inversion models.
Mira Geoscience and the Geological Survey of Canada, in collaboration with industry and academe, are building a Rock Properties Database System (http://rpds.mirageoscience.com). It compiles the most valuable physical properties for mineral exploration (density, porosity, magnetic susceptibility and remanence, electrical resistivity and chargeability) linked with location and lithological metadata.
A critical knowledge gap, addressed in this study, concerns the dependence of physical properties on alteration and mineralization processes. We report on the results of a Geoscience British Columbia project, "Integrated Geological & Geophysical Porphyry Models: Adding Value to Geoscience BC Geophysical Data". As part of the QUEST and QUEST-West geophysical initiatives, Geoscience BC focused detailed geophysical surveys on a suite of six known porphyry deposits: Mount Milligan, Endako, Huckleberry, Bell, Granisle, and Morrison. Physical properties for a set of 272 samples of characteristic host rocks and their altered equivalents were measured. The causes of physical property variations were investigated through their correlations with ore and alteration mineralogy determined from thin-section observations and geochemical measurements.

Physical properties of variably altered host-rocks and intrusive rocks vary significantly between different BC porphyry deposits. No specific unifying geophysical model exists that can be uniformly applied during exploration. Knowledge of local background geology and local physical property variations is necessary as host-rocks and intrusive rock compositions vary depending on magmatic affinities, and alteration styles will vary reflecting magmatic affinities, crustal depth and influence of meteoric water. A district-scale exploration strategy requires location of intrusive bodies, which are commonly magnetic, resistive and low in density. Correlations should not be expected between density and magnetic susceptibility, because alteration may lead to magnetite destruction or to secondary magnetite development. Deposit-scale ground geophysics might image potassic alteration zones that can be magnetic in both alkalic and calcalkalic systems. Low magnetic susceptibilities, resistivities and densities might aid in locating the typically more porous phyllic and argillic zones. All geophysical data must be interpreted with background knowledge of local rock types and in light of the expected deposit model and associated magmatic and hydrothermal processes.
The most effective means to building physical property knowledge prior to geophysical investigation remains collecting physical rock property measurements. The cost of rock property data collection is low, relative to the overall costs of running a mineral exploration program, and can provide an important framework for design of geophysical surveys, survey method selection, geophysical modelling, and data interpretation.
Résumé(Résumé en langage clair et simple, non publié)
L'Initiative géoscientifique ciblée 4 (IGC-4) est un programme fédéral de collaboration dans le domaine des géosciences dont le mandat consiste à fournir à l'industrie la prochaine génération de connaissances géoscientifiques et de techniques novatrices qui lui permettront de cibler plus efficacement les gisements minéraux enfouis. La Colombie-Britannique détient la majorité des gisements minéraux porphyriques du Canada, et elles produisent le plus de cuivre du pays. Exploration pour ce type de dépôt, en particulier dans les milieux profonds ou à distance des routes, s'effectue à l'aide de levés géophysiques. Afin de lier l'analyse de levé géophysique pour les types de roches qui forment ces dépôts, des échantillons ont été prélevés à partir de 6 gisements porphyriques en Colombie-Britannique. Les propriétés physiques et minéralogie ont été mesurées sur les mêmes échantillons pour chercher le contrôle minéralogique sur les propriétés physiques. Recommandations de quels outils géophysiques sont efficaces dans des contextes différents sont proposés.
GEOSCAN ID293333