The Continuity Challenge Dr. Wayne Barnett
The Interpretation! Great geological continuity? Huge potential?
The Reality Not what it might seem... Not what it might seem...
Presentation Objective Highlight the importance of understanding geological continuity. and to describe techniques for getting better constraint on continuity. for resource and engineering reasons. Geological continuity is a fundamental characteristic of any geological interpretation. The difference between actual and interpreted continuity directly impacts the risk to any decision based on the interpretation, often with huge financial implications. Unfortunately, continuity is the characteristic of a sub-surface 3-D geological model that is typically the hardest to interpret with certainty.
Structures and Mineralization Continuity Structural geology may directly control the style and continuity of mineralization. Blast hole gold assays Intersection pattern, kinematics and fluid permeability (fault zone properties)
Structures and Mineralization Continuity Structure may directly control continuity of the high grade mineralization. Grade continuity should make sense relative to deformation Mineralization can be deformed by Brittle deformation: commonly understood Ductile deformation: Often overlooked
Modelling Structural Continuity How did I justify this interpretation? What are the data constraints? Where is the model confident? Resource Geologist Geotechnical Engineer Investor
Geology is not straight lines Geological systems are complex with variable properties. How do you communicate this pattern and continuity? West Claims Mine, Ortlepp,1997
3-D Modelling Continuity Interpreted continuity has large impact on a resource or on mine stability. How far? Requires understanding of patterns from mapping and tectonic environment. Often comes down to Segmented? How well does it line up?? What is your interpretation confidence? How do you communicate this?
Resource Continuity evidence is sufficient to imply but not verify geological and grade or quality continuity. evidence is sufficient to assume geological and grade or quality continuity between points of observation. evidence is sufficient to confirm geological and grade or quality continuity between points of observation. From CIM DEFINITION STANDARDS, 2014
Structural Constraints on Geotechnics (A) weak or sheared lithological contact (B) weak foliation, (C) failure on basal fault surface, (D) failure on basal surface with fault tensile release plane, (E) damage zone around a fault, Murphy & Barnett, 2018 (F) toppling failure associated with steeply dipping fault system, (G) stable slope with favourable oriented folds and rock fabric, (H) 3-D perspective with unfavorable fold plunge, Structural deformation patterns and continuity are fundamental input factors in assessing slope failure risks
Increasing continuity Structural Continuity on Geotechnics From Sullivan, 2013 Fault zone orientation and continuity can constrain the slope angle
The Continuity Problem How can we try constrain continuity?
(1) Identify and Describe the Patterns Structural geology is recognition and understanding of patterns Large scale Patterns help define the possible continuity. Map the Patterns!!! Pattern Recognition Small scale Motion tablet 213 / 27
Typical Tectonic Structural Patterns Extensional Compressional Strike-slip Combined Patterns Conjugate Riedel
Fault Network Linked arrays of faults: Basin linkage in the North Sea, off Norway (top right) Main faults in the Pannonian Basin, Hungary (bottom right) Global oceanic plate fault system (bottom) NORTH SEA HUNGARY
Realistic Patterns and Continuity Understand real patterns. Look for relationships between different scale structures, as well as crosscutting relationships. Realistic Not realistic
3-D Modelling Interpretation of Patterns Modern computer modelling software can import represent structural data in 3-D. 3-D data can be selected and queried on stereonets, to unravel complex patterns. Fold patterns Structural sets Leapfrog Geo TM
Fault Heterogeneity - Damage Zones Patterns include zones of complexity. Damages zone commonly occur where faults intersect and/or change orientation. From Peacock et al. 2017 These zones control mineralizing fluids. The pattern and extent of damage influences mineralization continuity.
Fault Zone Domains How do the damage zone vary along strike and down-dip? Sericite-altered Damage Zone Fault Core Damage Zone
(2) Structural Timing / Deformation History Mapping patterns and noting relative timing / cross-cutting relationships help define continuity. Pit mapping typically helps constrain continuity Young Fault
Structural Timing / Deformation History Mapping patterns and noting relative timing / cross-cutting relationships help define continuity. 500 m Snap Lake Map - From Barnett, 2013 >
Continuity and Brittle Faulting What is the spacing of faults and typical displacement? Post-mineralization faulting can significantly reduce local continuity of the resource. It can also duplicate stratigraphy and mineralization.
Ductile Deformation Patterns Impact Continuity 2.1 Ga orogenic belt Relative timing? When does mineralization occur? < 200 ka orogenic belt
Continuity and Partitioned Strain
Continuity and High Ductile Strain High grade may not have continuity or geometry expected
Continuity and Transposition Folded gold, Rainy River Gold project, Ontario. Continuity can be different in different directions and scales
Continuity and Transposition Signs of transposition what does this mean on the large-scale? ±10 km
Continuity Clues Be careful of continuity!! Quartz veins associated with gold! These veins are deformed, and so is the gold distribution Old Gold S2 S1
(3) Surface Traces of Continuity Aerial photographs Aeromagnetic images Surface mapping Orthophotographs Lidar topography lineaments
(4) Continuity Evidence from Drillholes clay Clay or alteration Fracture Frequency North Structural Codes Flt, Bx, etc Oriented?! BH / DH assays RQD % shell in Leapfrog
(5) Lithological Pattern Changes Lithological offsets and thickness changes Interpreted fault trace along offset
(6) Form Line Interpretation Pattern Changes From Geoff Owen, SRK 34 0 500
(7) LiDAR Data Continuity Traces Surface or pit LiDAR, photogrammetry and other remote sensing data can help trace continuity. Mapped Faults Fracture Pattern
Photogrammetry Continuity Traces Like LiDAR, photogrammetry can help trace continuity. Faults The full trace of a discontinuity is very rarely observed!
(8) Geostatistical Geostatistical analysis of sampled rock properties, e.g. assays, can be used to mathematical explore continuity within a geological domain. Grade Estimation Variography used to define estimation search ellipse continuity CIM Conference Montreal 2017
(9) Integrated Geological Interpretation Final interpretation of pattern and continuity is built based on all evidence, integrated in 3D.
Geological Foundation The single most important factor in Resource/Reserve estimation is an understanding of the geology of the deposit This cannot be emphasized too strongly. Without a sound geological understanding, and a sensible application of that understanding, an estimation exercise becomes merely a mathematical treatment of sample results with no practical value Commonly the potential errors associated with an incorrect or inappropriate geological interpretation are orders of magnitude larger than the potential errors associated with grade estimation. Changes in the fundamental understanding of the geological controls on mineralization can dramatically alter an assessment of tonnage (Stephenson and Vann, 2001)
Example Red Lake Northern Miner, January 13, 2016 Phoenix Project Geology, 2013 TR Red Lake Geology D 1 -D 2 Relationships, F2 deposit, 2013 TR
Examples Red Lake Evolution of the Litho-structural model, Phoenix Project, 2016 TR The 2016 model benefited from and extra 94,575 m of infilled drilling and 10 km of underground development. Gold mineralization examples, Phoenix Project, 2016 TR The nature of these uncharacterized faults and their timing relative to gold mineralization is not understood. Rubicon Phoenix 2013 Technical Report
Conclusions Continuity is important for geological resources and geotechnical studies. One of the best tools for understanding continuity is structural geology, which constrains possible interpretations and often brings realistic expectations back into a geological model. Modern 3-D modelling tools and the ability to integrate multiple old and new technologies into one decision making environment also helps improve interpretation of continuity. IF founded on Sound Geological Understanding
This presentation is protected by copyright vested in SRK Consulting (Canada) Inc. Neither the entire presentation or any part therein, including any images, graphs or tables, may be reproduced or transmitted in any form or by any means whatsoever to any person without the written permission of the copyright holder. This presentation is for informational purposes only and is not the provision of a professional service. SRK accepts no responsibility for any liability which may arise from reliance upon the contents of this presentation. Thank you Wayne Barnett, PhD, PrSciNat. wbarnett@srk.com