Elements from the Meter to the Micron: Multiscale Analysis Workflows for Elemental and Derivative Mineral Data
Jonathan Knapp; Toti Larson, Ph.D.
Methods/Procedures/Processes: Decision-makers in oil and gas and mineral exploration use data to form and test a hypothesis. These high-risk, high-reward experiments include the drilling of exploration wells and the completion of mining projects. Rock imaging and high resolution data collection are emerging tools for providing decision-makers with actionable intelligence to reduce risk and find more resources. Geochemical visualization, the systematic qualitative or quantitative imaging of elements from geologic samples, provides a pathway to translate imaging data into a scalable workflow.
The workflow for collecting, analyzing, and utilizing data visualization across multiple scales requires re-examination within the context of scientific decision-making for exploration. We propose a multi-scale approach that combines sample down-selection with robust sample classification. Down-selection based on robust characterization allows results to be translated up-scale. We will examine three elemental geochemical visualization technologies to demonstrate how this workflow can be applied: (1) XRF scanning with imaging, (2) micro-XRF elemental mapping, and (3) automated mineralogy.
Bulk geochemical analysis of core, RC chips, and cuttings with XRF was revolutionized with the development of portable XRF scanning. Advances in detector technology and automation have empowered analysis at the speed of drilling. In oil and gas, depth-registered elemental data from core and cuttings can be used for chemostratigraphy, an environment of deposition analysis, geosteering, and the calculations of petrophysical attributes. In mining, this data can assist in lithologic logging, the identification of target zones and indicator minerals, and mapping cut-off grade. Remote analysis and geologically-informed interpretation has been empowered by the innovation of combining elemental data with classification technology like clustering and high-resolution photography. The resulting chemofacies classifications empower a scheme for sample down-selection that is inclusive, robust, and heuristic.
Micro-XRF scanning utilizes polycarpellary x-ray optics and rapid stages to make elemental visualizations within the context of mineral distribution and texture. Elemental maps with down to 18µm resolution can be displayed as relative intensity maps, quantified concentration maps, or the XRF spectra matched to mineral databases to make mineral maps. Samples do not require coatings and can be measured as core or scatter mounts of cuttings, sediment, or RC chips. In addition to mineral and lithological characterization, this tool can identify and target datable minerals with LA-ICPMS, geochemical, and mineral vectoring for mining and quick-look lithology from cuttings and selecting samples locations for higher-resolution analysis.
Scanning electron microscopes remain a critical part of the lithologic characterization workflow. Sub-micron resolution and the ability to standardize measurements enables data to be collected systematically at the scale of rock and mineral formation. Automated mineralogy automates the collection of BSE images and EDS x-rays from an SEM with spectral matching to generate mineral maps. This mineral information can be used to create more objective lithologic logs using lithotyping workflows, validation of rock-physics workflows, rapid identification of pathfinder or indicator minerals, and characterization of ore or resource mineralogy, allowing ongoing assessment of viability or during exploration.
All three scales of analysis can contribute to exploration model thinking. The utilization of workflows that select higher resolution samples from lower-resolution but more comprehensive analysis empowers a systematic expansion of analysis results up-stream. Hardware innovations have allowed all three levels of analysis to be deployed on mine-sites or drill rigs. These technologies work across scales for a complete understanding of lithology, mineralogy, and geochemistry.
