by R.N. Monteiro, P.Geo., M.Sc., FSEG, Ph.D., President and Chief Structural Geologist at Vektore Exploration Consulting Corporation
Why are we still struggling to apply structural geology in target exploration and development? Aren’t the tools and required skills currently available in the industry sufficient for such an application?
In 2023, we still see mineral exploration ventures debunked in the industry by a lack of knowledge about the structural controls of their targets. A memorable example is the Rubicon Minerals that in 2016 had their gold resources slashed by 88%, signaling that untapped structural controls were a significant player. This article explores some of the challenges we face to uncover the structural controls of mineral targets, and it introduces successfully tested solutions.
At Vektore, we understand that mineral exploration comprises a complex integration of many methods and tools in which a particular sequence will have an impact on its outcome. The Structural geology exploration component is slowly coming back to exploration thanks to a major paradigm shift evidenced by a stream of developments of core orientation tools attached to the core barrel — allowing orienting core while drilling. The BallMark was the first of its kind — conceptualized and developed by Les Anderson (1999), and later followed up by more sophisticated electronic tools. Modern core orientation tools are noticeably present in the industry, with more than five brands available on the market. Tools for reading structural features from oriented core have also evolved from sandbox/rocket launcher to electronic devices and ortho-corrected images from core boxes. Nevertheless, workflow segmentation associated with misuse of tools and processes represents a major obstacle. Figure 1 shows how Vektore views the borehole structural logging supply chain space, its segments, and inefficiencies that lead to inconsistent communication/engagement between domains and unreliable information transfer.
Two major problems arising at the drill rig are the core orientation process handling and the reference mark transfer to the core. In 2018, Vektore compiled core orientation programs from four distinct exploration programs (juniors and majors) in a period of 16 months. In total, 3385 runs were completed. However, by following the +/- 15 degree mismatch between two contiguous runs (Holcombe, 2014) — which seems to be the current industry standard — only 980 (around 30%) of the total runs were useful. This pattern seems to be present throughout the industry and it warrants further investigation. Therefore, a significant number of incorrect orientation runs are transferred to the core shack. In the public domain, Holcombe (2014) proposed the logging of the reference line mismatch to properly assess the core orientation-misorientation. Later in 2016, Myers et. al. presented the Bamboo diagram, based on Holcombe’s method, as a visualization tool for the mismatch problem. However, a solution for the correction of such errors was not presented.
At the core shack, reading structural features is limited to what the industry standard alpha-beta-gamma method can provide. This method was likely developed in the 1950s, but it has been upgraded significantly with the use of more modern tools, including electronic ones. Nevertheless, it falls short when measuring lines and their attributes (fold axis/vergence/facing, fault kinematics, vectors, etc.), which are prime features to unravel structural controls in mineralized bodies.
Aiming at addressing the above-mentioned problems, Monteiro (2002) developed a new reading method, the Structural Vectoring Log (SVL), in which the parameters to be read for structures in the core are the piercing points of plane’s dip/dip-direction and the piercing points of lines independently, making high-accuracy/precision vectorization of such piercing points possible. In addition, it allows for reading attributes associated with such structures, and with the provision of the drilling vector or survey, remapping them into their world coordinates. SVL has been successfully applied in various projects since its inception – including Inco Ltd (2002), Vale (2007), AngloGold Ashanti (2014), Nexa (2015) and on a short course promoted by Vektore during PDAC 2016. Since 2018, SVL and new developments have been embedded into the Ore.node® software.
Figure 2 summarizes the solutions developed by Vektore to address the drilling rig, core shack domains and Geolloger’s gap limitations. An integration of methods, tools, and software addresses each of the problems indicated in this article. The Ore.node has the capability to recover structural information not only from misoriented core (Structural Convergence) but also from non-oriented core (Structural Inversion) in real-time. Structural Convergence and Inversion are the cornerstones for Vektore’s Quality Optimization (QO) process for data recovery. QO will be discussed in depth in a future article.
vStructure and vSTAR are Vektore’s newest products. vStructure software is a more agile and simplified version of the Ore.node software, designed with the general geologists in mind. vSTAR is an AR-based reader software that brings speed, high-accuracy, high-precision, and universal reading of structures to the core shack. It provides real-time logging and visualization within the vStructure and Ore.node softwares. This is a significant innovation in structural logging designed with geologists and technicians in mind. The integration of Ore.node, vStructure and vSTAR will significantly improve the core logging process by generating trustworthy data to provide a sound framework for more robust 3D modeling.
Here we present two significant case studies applying Vektore’s SVL method – both in Brazil: (a) ore shoots in a IOCG deposit (Figure 3); and (b) orebody extension in a Copper-rich norite deposit (Figure 4). Figure 3 shows the outcome of a structural analysis in which off-plane mineralization-related lineations (chalcopyrite and bornite) and grade distribution analysis determined the new drilling direction that unraveled 95 Mt of additional resources. Figure 4 shows the outcome of a structural analysis of non-oriented core in which Structural Inversion was applied. Contrary to the Client’s drilling design, the collar coordinates, the drilling vector, and the range in which the mineralization should be intersected were generated by Structural Inversion analysis. The mineralization was intersected as proposed.
Figure 5 shows the GUI – graphical user interface of the vStructure software with the vSTAR module’s viewport. The core and Augmented reality (AR) handle are presented to the computer camera for measuring structural features (full, half, quarter core – planes, lines and attributes independently) on the vSTAR viewport. The readings are sent directly to the structural logging table, as well as the 3D and 3D Stereonet viewports. Since this is a real-time process, the user can experience spatial awareness of the target’s architecture.
The integration of the tools and methods presented here, and briefly demonstrated in the case studies, resolve key problems along the borehole structural logging supply chain that have been limiting the development of sound 3D models of mineral targets.
For more information visit: www.vektore.com for details on the upcoming live presentations of the vStructure-vSTAR or check out Vektore’s LinkedIn.
References
- Holcombe; R. (2014) Oriented drillcore: measurement, conversion, and QA/QC procedures for structural and exploration geologists – last updated in 2023.
- Les Anderson (1999) Core orientation. Patent AUPQ074299A0 – https://patents.google.com/patent/AUPQ074299A0/ en?q=(Les+Anderson+drilling)&assignee=Shelljet+Pty+Limited
- Myers; R, et. al. (2016) An Inexpensive Way to Maximize and Preserve the Value of Oriented Core: The Orientation Log. SEG Discovery (2016) (107): 1–19.
- The Northern Miner (2016) Rubicon’s F2 deposit is uneconomic. Volume 101, number 49 on January 13th.
- https://www.northernminer.com/financial-matters/rubicon-minerals-f2-deposit-is-uneconomic/1003746846/
- Monteiro, R. N., (2002). Structural Analysis of Borehole Data and Structural Scenario Design. Inco Internal Peer Reviewed Report. 20 pg.
- Monteiro; R. (2016) Structural Vectoring in mineral exploration: What it is and how, when and why we should use it. PDAC 2016 short course.
