Insights for Porphyry Exploration from Rock Properties Data: Examples from the QUEST and QUEST-West Project Areas Dianne Mitchinson Mira Geoscience Exploration Undercover Geoscience BC/BC Geophysical Society shortcourse Vancouver, BC Oct 12-14, 2011
Acknowledgements Geoscience BC, and Mineral Deposit Research Unit, UBC for support; Endako Mines, Huckleberry Mines Ltd, Pacific Booker Minerals, Terrane Metals Corp., Xstrata for access to their properties, drillcore and data, and for logistical support during 2009, 2010 fieldwork; Randy Enkin, D. Gilmour, A. Severide, A. Tkachyk, and R. Raynor, GSC Pacific Paleomagnetism and Petrophysics Laboratory; Elisabetta Pani, Jenny Lai, and Mati Raudsepp (UBC X-Ray diffraction lab)
Why should we care about physical rock Magnetic susceptibility model from magnetics inversion properties? Understanding rock properties will improve our interpretations of geophysics and geophysical models High mag sus, low density Low mag sus, high density Density model from gravity inversion X-section location Plan view Variations in apparently homogeneous rock? Not only that...geophysical method selection, geophysical survey design, forward modelling, constraining inversions...
Relating geology to geophysics through physical properties Potassic Mt. Milligan - predicted magnetic susceptibility Develop expectations by considering: Pyrr Hem Mag Geological setting Mineralization Deposit model Geological processes.. Geological processes control: Minerals formed Mineral distribution Rock textures/porosity.. MAGNETIC SUSCEPTIBILITY Felsic minerals Carbonates Mafic minerals Pyrite Modified from Williams (2008) DENSITY
Quest and Quest-West case studies - tools and methods Data presented: Magnetic susceptibility - KT- 9 Kappameter susceptibility meter : outcrop, core and hand sample Resistivity modelled from spectral impedance data Randy Enkin, GSC-Pacific: core and hand sample (porosity geometric and hydrostatic methods; chargeability - from spectral impedance data ) XRD, petrography KT-9 Kappameter Impedance/ phase analyzer
Geoscience BC geophysical surveys QUEST-West QUEST
Mount Milligan Cu-Au deposit
Susceptibility at Mount Milligan Potassic 6109500 433500 434000 Monz. DWBX WBX 434500 Monz. Basaltic rks MBX 435000 435500 Monzonite Basalt Propylitic (Chl+Ep+Cb) Potassic Sodic-calcic Sodiccalcic 6109000 6108500 6108000 6109500 6109000 433500 Basaltic rocks 434000 Monz. 66 Southern Star DWBX WBX 434500 MBX 66 435000 435500 6108500 Magnetics useful for distinguishing potassic alteration and monzonites from background; scale of survey important 6108000 ZTEM magnetics, Geotech Ltd, 2009 Southern Star
Resistivity at Mount Milligan Potassic 6109500 433500 Monz. 434000 DWBX WBX 434500 Monz. Basaltic rks MBX 435000 435500 Monzonite Basalt Sodiccalcic Propylitic (Chl+Ep+Cb) Potassic Sodic-calcic 6109000 6108500 6108000 6109500 433500 Basaltic rocks 434000 DWBX WBX Southern Star Monz. 66 MBX 435000 435500 6109000 66 Propylitic/Na-Ca altered rocks are most conductive of QUEST porphyry suite due to sulfides. EM surveys detect sulfides related to propylitic alteration, and/or faults 6108500 6108000 ZTEM, 180Hz, phase rotated; Geotech Ltd, 2009
Sulfides vs resistivity Pyrite + chalcopyrite (%) Resistivity (Ohm-m) Oldenburg et al. (1997)
Endako Mo deposit
Susceptibility at Endako Casey Granite Endako Quartz Monzonite Kaol overprnt Leastaltered Potassic alteration Kaol overprnt Phyllic (Quartz-sericitepyrite) Argillic (Kaolinite) Least-alt d Casey Granite Magnetics useful for locating alteration within Endako Quartz Monzonite hosts AeroTEM magnetics; Aeroquest Surveys, 2009
Resistivity at Endako Casey Granite Endako Quartz Monzonite Least-altered Potassic alteration Phyllic (Qtz-ser-py) Argillic (Kaolinite) Least-alt d Casey Granite The highest conductivities correlate with phyllic-argillic alteration these samples have increased porosities AeroTEM Late time Tao; Aeroquest Surveys, 2009
Phyllic/argillic alteration = porosity = lower conductivity Porosity (%) 6 5 4 3 2 EK_Monz_Unalt EK_Monz_Pot_dom EK_Monz_Qsp_dom EK_Monz_Kaol EK_Bas_dike EK_Casey_Gran Ser+Clay 1 Unalt d monz 0 System core? 10 100 1000 10000 100000 Py halo Resistivity (Ohm-m) Unalt d monz Strong K (+ser/clay) Py halo Endako alteration map; plan view (after Selby et al., 2000)
Huckleberry Cu-Mo deposit
Susceptibility at Huckleberry Granodiorite Andesite Andesite outside hornfelsed area Hornfelsed andesites (Bt-mag-act) Ore-proximal potassic/bt-mag-qtz altn Least-alt d Sericite-carb altered Potassic.- altered Ore proximal alteration/mineralization doesn t stand out from hornfelsed rocks, but hornfels distinct from andesite volcanoclastics; granodiorites low-mod susceptibility AeroTEM magnetics; Aeroquest Surveys, 2009
Resistivity at Huckleberry Granodiorite Andesite Andesite outside hornfelsed area Hornfelsed andesites Ore-proximal potassic/bt-magqtz altn Least-alt d Ser-carb alt d Str. kaolinite alt d Potassic - alt d MacIntyre (1985) Silicified and hornfelsed andesitic rocks near ore zone, most resistive rocks of collection but directly within ore zone sulfides are fracture controlled (conducive to conductivity) AeroTEM Late time Tao; Aeroquest Surveys, 2009
Bell Cu+/- Au+/-Mo deposit
Susceptibility at Bell Lower Cret. seds Biotite-Feldspar Porphyry BFP pit Lower Cret. volcanics Lower Cret. rhy Sediments Good distinction between susceptibilities of potassic and phyllic altered rocks. Magnetics useful for imaging BFP intrusives/bt-mag altered BFP/ bt-mag altered sedimentary rocks. Some alternately magnetic and nonmagnetic volcanic/sedimentary rocks to east. AeroTEM magnetics; Aeroquest Surveys, 2009 pit pit
Resistivity at Bell Lower Cret. seds Biotite-Feldspar Porphyry Sedimentary Rks BFP pit Lower Cret. Alk rhy Lower Cret. rhy Bt-mag altered rocks have high resistivities these zones are overwhelmed by lower resistivities related to phyllic altered rocks. Phyllic altered BFP s (with sulfide veins) are some of the lowest resistivity samples of the QUEST-West suite. Background sediments are relatively resistive pit AeroTEM Late time Tao; Aeroquest Surveys, 2009
Photomicrographs resistive and conductive samples from Bell Biotite-quartz-magnetite altered sediments Sericite-carbonate-quartz-pyrite altered BFP qtz Qtz in veins bt Sulfides in veins PPL PPL (2696 Ohm-m) (88 Ohm-m) qtz Ser+qtz+cb halo bt cb XPL For all, field of view ~ 8mm XPL
Resistivity vs. sulfide distribution vs. porosity Patchy/domainal Veins+voids+disseminated Veins+disseminated Veins Disseminated Size proportional to porosity 0.1 1 10 100 1000 10000 100000 1000000 Resistivity (Ohm-m)
Chargeability vs. sulfide abundance 25 20 >1 ms generally some amount of sulfide? Pyrite + chalcopyrite (%) 15 10 5 0 0.001 0.01 0.1 1 10 100 1000-5 Chargeability (milliseconds)
Chargeability vs. sulfide + magnetite abundance 25 Pyrite + chalcopyrite + magnetite (%) 20 15 10 5 >1 ms generally some amount of sulfides +/- magnetite 0 0.001 0.01 0.1 1 10 100 1000-5 Chargeability (milliseconds)
Chargeability vs. sulfide + magnetite vs. sulfide distribution 25 Pyrite + chalcopyrite + magnetite (%) 20 15 10 5 Size proportional to sulfide distribution Patchy/domainal Veins Veins+dissem 0 0.001 0.01 0.1 1 10 100 1000-5 Chargeability (milliseconds)
Messages No unifying porphyry geophysics model Do background reconnaissance (historical data, public data, deposit models) and think in physical properties! Important considerations for geophysical exploration: Hornfelsing, adding magnetite? Later phyllic alteration? Sulfides Disseminated? Connected? Porosity + faulting? Scales of alt n/sulfide zones? Tilting? Depth of erosion? Key to getting the most out of any geophysics data: communication and collaboration between geologists and geophysicists
Thanks!