Presentation on theme: "3D ZTEM inversion, interpretation and integrated exploration at the Silver Queen project, British Columbia Patrick B. M. van Kooten, Peter L. Kowalczyk."— Presentation transcript:
3D ZTEM inversion, interpretation and integrated exploration at the Silver Queen project, British Columbia Patrick B. M. van Kooten, Peter L. Kowalczyk & Dianne E. Mitchinson KEGS Symposium 2012: Exploration 07 - Plus 5: A Half-Decade of Mineral Exploration Developments Saturday 03 March 2012
Acknowledgements For granting permission to show select results from the Silver Queen Project, sincere thanks are due to: Ellen Clements (Director, President & CEO) New Nadina Explorations Ltd. (NNA: TSX-V) The authors would also like to acknowledge: Geotech Airborne (www.geotech.ca) Quantec Geoscience (www.quantecgeoscience.com)
Outline Inverting ZTEM Data ZTEM Basics ZTEM Processing Workflow QA/QC & Data Preparation Topography: A Cautionary Tale ZTEM Inversion Silver Queen Case Study Overview Geologic Setting ZTEM Survey and Data Preparation Targeting Criteria ZTEM Inversion Results Titan 24 Survey & Results Choosing targets Summary & Outlook Questions / Contacts
ZTEM Basics: Factsheet ZTEM = Z-axis Tipper EM Airborne AFMAG EM System developed by Geotech Ltd. Frequency Range: 30 Hz to 720 Hz Number of frequencies (typical survey): 6 (compared to 1 for commonly used EM16 systems) Depth of penetration: ~20 times greater than EM16 Polarizations measured: both along-line (X) and cross-line (Y) components (vs. 1 for EM16) Number of ZTEM data channels (typical survey): 6 frequencies x 2 polarizations x 2 components (real & imaginary) = 24 This problem is best suited to 3D inversion!
ZTEM Basics: Some Details ZTEM data do not include an E-Field measurement. The ZTEM system is sensitive to channelling of natural magnetotelluric (MT) currents in the subsurface. Large skin-depth in resistive terrains means ZTEM map geology to a greater depth and detect lower conductivity anomalies than active-source airborne EM systems. ZTEM response is independent of flight direction (2 polarizations measured).
ZTEM Processing Workflow Survey data 1 Check projections & datums 2 Adjust coil Z to geoid Z from GPS ellopsiod Z 3 Flag or delete bad data 4 Design mesh 5 Build topo model in mesh 6 Run single frequency inversions 7 Review results (optionally: adjust errors and edit data) 8 Run multi-frequency inversion 9 Review results (optionally: modify & run again)
ZTEM Data: QA/QC and Preparation Data QA/QC Confirm projections and datums are consistent. Interpolate flight line data onto regular grid to visualize each channel in ZTEM database and identify regions of poor data. Confirm tilt-angle cross-overs have correct sense. Data Preparation Ensure that all data are in a consistent coordinate system. Assign appropriate error to each component of the ZTEM data. Flag or remove bad data. Design inversion meshes best suited for survey data. ZTEM data are transformed to the MT3Dinv EM sign convention for inversion. Obtain suitable topographic data
Topography: A cautionary tale Default discretization of topography Ground surface downward biased, increasing effective flight height. We can do better! Aircraft flight path Actual topographic surface
Topography: A cautionary tale Modified discretization of topography Ground surface better estimates topography but flight lines could clip steep topography. Only use inversion points over cell centres. Aircraft flight path Actual topographic surface Inversion data point
ZTEM Inversions Inversions are done with the UBC-GIF MT3Dinv program which derives from UBC-GIF EH3Dinv (adapted by Elliot Holtham and Doug Oldenburg to incorporate ZTEM tipper data). Inversion process is iterative. Begin with one or more single frequency inversions (used to assess the quality of the data and appropriateness of the errors assigned). Single frequency inversion models provide a starting model for the multifrequency inversion(s) At each stage results are reviewed. Data, errors, models and parameters may be edited and further inversions may be done before an acceptable conductivity model is obtained.
Silver Queen Case Study (Overview) The Silver Queen polymetallic vein system is a high grade past producer south of Houston, British Columbia. Abundant small veins and showings around the old underground mine suggest further prospectivity Current exploration around the old Silver Queen mine by New Nadina Explorations Ltd has been driven by a conceptual model, targeting a blind, buried bulk tonnage deposit near the old mine and deeper in the mineralized system. In the 2011 field season: ZTEM, airborne magnetic and Titan24 (IP / MT) surveys completed and data were inverted. Drilling, directed by integrated geology/geophysics, led to discovery of new porphyry-style zone of mineralization. AGIC provided data analysis, 3D inversion, modeling, visualization, and interpretation services
Silver Queen Vein Silver Queen: Vein system and Geology Cretaceous andesitic volcanic rocks Lower Cretaceous sedimentary rocks Late Cretaceous Bulkley Intrusive Suite Eocene basaltic volcanic rocks Eocene felsic intrusive rocks
Silver Queen: Data QC 45 Hz) Region of bad data
Silver Queen: Data QC 720 Hz) Region of bad data
Silver Queen: Exploration targeting criteria CriteriaEvidence layers Proximity to known mineralizationOld mine workings plotted in 3D, with a corroborating resistive feature seen near surface in the ZTEM inversion. Proximity to intrusive bodyIntrusive boundaries were interpreted using ZTEM conductivity isosurfaces and magnetic susceptibility isosurfaces, all derived from the 3D inversions. In a regional structure, preferably spatially related to a kink, or a dilational zone of accommodation Linear zones of higher conductivity from ZTEM inversion, associated with linear features in airborne magnetic data, map out regional structures. In a zone of increased brecciationBrecciated rock interpreted from local zones of increased conductivity in the ZTEM inversion model.
Silver Queen: Inversion results NS section through ZTEM inversion model 0.02SI isosurface defining magnetic phase of Silver Queen intrusive stock ZTEM buried target Silver Queen Vein
Silver Queen: Titan24 survey location Titan 24 survey 4 lines across target area 150m dipoles, 300m traverse line separation IP (Resistivity & Chargeability) & MT)
Silver Queen: Titan24 results (3D View from South) Titan A Titan B Titan C DH S11-13 Top of End of 777M 693 metres of mineralization! IP Chargeability anomaly shell from 2011 Titan24 inversion Titan 24 identified deep chargeable body (Titan B) which was drilled
Silver Queen: Summary and Outlook The airborne survey, data inversion and interpretation, Titan24 data acquisition, data inversion and interpretation and drilling were done in one field season! Drilling intersected a significant, previously unknown, porphyry style molybdenum deposit. Keys to success: application of well-chosen geophysical methods integrated interpretation of geophysical and geological data ZTEM proved to be cost effective; ZTEM results used to focus follow-up ground exploration and shortened the time necessary to explore the project area work planned / underway: More Titan24 work north and south of the discovery 3D inversion of Titan24 MT data plus integration with geology from drilling Continued program of deep drilling to define the mineralization and identify additional zones of mineralization
Exploration Eye-candy Core photographs (courtesy New Nadina Explorations Ltd.) showing molybdenum mineralization and stock- work veining. Thank you! Questions?
Contacts Patrick B. M. van Kooten Peter L. Kowalczyk Dianne E. Mitchinson