| Title | Linking porphyry deposit geology to geophysics via physical properties: six porphyry deposits in British Columbia, Canada |
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| Author | Enkin, R J ;
Mitchinson, D E |
| Source | 23rd World Mining Congress 2013, proceedings; by World Mining Congress; 2013 p. 1-11 |
| Image |  |
| Year | 2013 |
| Alt Series | Earth Sciences Sector, Contribution Series 20130330 |
| Publisher | World Mining Congress |
| Meeting | 23rd World Mining Congress 2013; Montreal; CA; August 11-15, 2013 |
| Document | book |
| Lang. | English |
| Media | digital |
| File format | pdf |
| Province | British Columbia |
| NTS | 93 |
| Area | Prince George; Williams Lake; Terrace |
| Lat/Long WENS | -128.0000 -120.0000 56.0000 52.0000 |
| Subjects | igneous and metamorphic petrology; metallic minerals; geophysics; magnetic susceptibility; porphyries; alteration; mineralization; porphyry deposits; magnetic anomalies; argillization; resistivity;
porosity; sulphides; geophysical interpretations; Mount Milligan deposit; Takla Group; Huckleberry mine |
| Illustrations | analyses |
| Program | Targeted Geoscience Initiative (TGI-4) Methodological Development |
| Abstract | 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. |
| Summary | (Plain Language Summary, not published)
The Targeted Geoscience Initiative 4 (TGI-4) is a collaborative federal geoscience program that provides industry with the next generation of geoscience
knowledge and innovative techniques, which will result in more effective targeting of buried mineral deposits. British Columbia holds the majority of Canada¿s porphyry mineral deposits which produce most of the country¿s copper. Exploration for
this deposit type, especially in deep or remote settings, is done using geophysical surveys. In order to link geophysical survey analysis to the rock types which form these deposits, samples were collected from 6 porphyry deposits in British
Columbia. The physical properties and mineralogy were measured on the same samples to reveal the mineralogical control on the physical properties. Recommendations of which geophysical tools are effective in different settings are
proposed. |
| GEOSCAN ID | 293333 |
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