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TitreLinking physical rock properties to porphyry alteration and mineralization: examples from the QUEST and QUEST-West project areas
AuteurMitchinson, D E; Enkin, R J
SourceAMEBC Roundup 2013, abstract volume; par Association for Mineral Exploration BC; 2013 p. 23-25
LiensOnline - En ligne (Abstracts, PDF, 3.99 MB)
LiensOnline - En ligne (Presentation, PDF, 3.81 MB)
Année2013
Séries alt.Secteur des sciences de la Terre, Contribution externe 20130329
ÉditeurAssociation for Mineral Exploration British Columbia
RéunionMineral Exploration Roundup; Vancouver; CA; janvier 28-31, 2013
Documentlivre
Lang.anglais
Mediaen ligne; numérique; papier
Formatspdf
ProvinceColombie-Britannique
SNRC93
Lat/Long OENS-128.0000 -120.0000 56.0000 52.0000
Sujetsaltération; gisements porphyriques; minéralisation; susceptibilité magnétique; résistivité; porosité; gîtes sulfureux; pétrologie ignée et métamorphique; minéraux métalliques
Illustrationsgraphs; tables; plots; location maps
ProgrammeDeveloppements methodologie, Initiative géoscientifique ciblée (IGC-4)
Résumé(disponible en anglais seulement)
As part of the QUEST and QUEST-West geophysical initiatives, Geoscience BC focused detailed electromagnetic and magnetic surveys on a suite of six porphyry deposits to identify characteristic geophysical footprints for these economically important deposit types. The deposits chosen for investigation included Mount Milligan, Endako, Huckleberry, Bell, Granisle, and Morrison. To aid the interpretation of the collected geophysical data, a project was initiated to investigate physical rock properties of the host and mineralized rocks associated with the deposits surveyed. The primary objectives of the research were to 1) identify physical property data distributions and ranges for characteristic host rocks and their altered and mineralized equivalents, 2) understand the causes of physical property variations, and 3) provide a synopsis of physical property criteria defining altered and mineralized rocks in specific BC porphyry settings to help reduce risk during geophysical exploration within these regions.
The deposits studied share features typical of calc-alkalic and alkalic porphyry deposits. The deposits are generally characterized by an association with porphyritic intrusions, by overprinting potassic, phyllic, and propylitic alteration, and by sulfides controlled by fracture and vein systems. Despite these similarities, geophysical responses vary from one deposit to another. Whereas some differences in geophysical response are expected between calc-alkalic and alkalic porphyry systems due to differing alteration mineralogy and deposit geometries, dissimilarities between similar porphyry types can also be expected. Physical property analyses on sample suites from BC porphyry deposits has shown that changes in physical properties between background and mineralized rock arise predominantly from mineralogical and textural variations.
The Mount Milligan and Endako deposits provide contrasting examples of the effect of porphyry-related alteration on magnetic susceptibility and magnetic signatures. At Mount Milligan, secondary magnetite forms in association with potassic alteration increasing magnetic susceptibilities of altered rocks proximal to mineralized zones. At Endako, primary magnetite in host monzonitic rocks is destroyed by overprinted phyllic and argillic alteration.
Sericite and clay dominated alteration at Endako also brings about increases in porosity and correlated decreases in density. Alteration of feldspars to sericite and clay causes the rock to become friable and weak, allowing increased fluids to permeate the rock, lowering electrical resistivities. Phyllic and argillic alteration is similarly related to decreased resistivities at several Babine Lake Cu-Au porphyry deposits.
Sulfide abundance and distribution also affect electrical rock properties. If sulfides are disseminated, the rock may be chargeable, but not necessarily conductive. Connected networks of sulfides enhance conductivities but may not result in high chargeabilities. The variety of sulfide and oxide minerals which occur also influence electrical rock properties, with some minerals being inherently more chargeable or conductive than others.
Although knowledge of the geology of the area being explored will allow physical property trends to be anticipated to some degree, the most effective means of building physical property knowledge prior to geophysical investigation remains collecting physical property measurements. Ideally data is collected at a range of scales, from hand sample to outcrop. 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 the 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 ID293332