2024 Q1 technical highlights

This episode features the following technical highlights:

• Bar Coding Metallogenesis; and our
• Downhole Swept Frequency EM Tool

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BAR CODING METALLOGENESIS

Contact our Project Leader: Marnie Forster (ANU)

With innovative new instrumental methodologies, we extract highly detailed age spectra from small samples of drill core and/or rock fragments. Purpose-built computer codes for modelling and simulation then delineate temperature-time histories mapping fluid-rock interaction, cryptic metasomatism, and paleodepth variation.

MinEx CRC developed this workflow to allow characterisation of the later stages of the geological history (from 500-150°C) of terranes being drilled into by the National Drilling Initiative (or NDI). New information is provided about basement rocks under sedimentary and regolith cover. Mineral explorers should be able to examine patterns in a National Argon Map reinvigorated with the ability to show palaeodepth variation through critical times, barcoding the tectonic signature of Metallogenesis.

We work in collaboration with mineral explorers and the geological surveys, for the public good. The explorers allow access to rock samples providing a regional coverage that would be unavailable without their help. With these samples, and those of the geological survey, a set of samples is collected that is specifically targeted to allow the ‘barcoding’ of events associated with metallogenesis on a regional scale.

Common rock forming minerals contain potassium and thus allow argon geochronology and thermochronology, as potassium radioactively decays to argon at a predictable rate. Our approach involves first developing a careful link between geological processes and the microstructures in the mineral sample sent off for irradiation. Several hours of neutron bombardment converts ³⁹K into ³⁹Ar. On return from the reactor, the sample is loaded into a unique gas extraction system, specifically designed for the problem at hand. No other lab possesses this capability. The sample can be warmed for up to 24 hours, driving out contaminants and adsorbed gases, leading to an unprecedented level of cleanliness, and improved data quality.

Through carefully controlled furnace step-heating, in a succession of steps over a 24 hour period, Agnes the argon robot (named after Marnie’s grandmother) produces age spectra with a remarkable level of detail and precision, enabling patterns to be recognised that hitherto were lost in the scatter caused by contaminants and different measurement strategies. The hidden benefit of the method is that each heating-step in itself acts as a diffusion experiment, thus allowing identification of the essential characteristics of different gas reservoirs within the grains. In turn, these characteristics, identified through Arrhenius data, allow correlation of the measured ages with the already recognised microstructural components. Modelling and simulation then allow inversion, producing a Temperature-time curve identifying the timing of individual mineral growth events, and distance from the heat source. The Temperature-time curve can also be interrogated to yield paleodepth – how deeply the rock was buried when it was at the measured temperature.

In collaboration with the National Drilling Initiative we are able to produce event sequence diagrams that can be used to barcode potentially fertile metallogenic sequences. The workflow was developed during an earlier project aimed at “Getting the best out of your date” and has been successfully tested in several NDI campaigns. The current project is aimed at upscaling capacity and providing an ongoing legacy.

The project has already identified otherwise unrecognised but now thought to be widespread patterns of cryptic metasomatism associated with fault and shear zone movement, sometimes with fluid percolation up to 5 km from the active structure. Moving forward, we will refine and apply this workflow, both on legacy samples and during NDI campaigns. The National Argon Map will be revigorated with the ability to show palaeodepth variation through critical times: we will bar-code the tectonic signature of metallogenesis, with the dynamic aspects of new code able to show and delineate brief flashes of potentially mineralising fluids. This is a powerful method to add to the toolkit being developed in the NDI to allow us to rapidly characterise the mineral potential of buried frontier terranes.

DOWNHOLE SWEPT FREQUENCY EM TOOL

Contact our Project Leader: Brett Harris (Curtin University)

MinEx CRC has developed a unique borehole electromagnetic (EM) sensor system which will measure multiple petrophysical parameters during a single deployment to push towards new frontiers of rock characterization from drilling.

MinEx CRC recognizes the critical role of drilling in mineral discovery and mine development.  An objective of MinEx CRC is to deliver new cost effective technologies that add value to every meter drilled.  Conventional borehole EM sensors are part of the mineral exploration toolkit but deployment in angled, unstable holes is problematic and their functionality is limited to single, or sometimes dual, frequency settings. MinEx CRC’s Curtin University-based research team has developed and are patenting  an entirely new way of making in-hole multifrequency measurements that will enable logging-while-tripping and logging-while-drilling deployment (significantly reducing the risks associated with hole collapse).

Compared to conventional induction logging, the MinEx EM sensor has potential to deliver; (i) multiple geophysical parameters, (ii) greater depth penetration and (iii) greater resolution.  The MinEx EM tool will have broad application for geophysical characterization for up to tens of meters around a borehole with direct application in identifying and characterizing high electrical conductivity ores such as massive sulfides.c

Compared to conventional induction logging, the MinEx EM sensor has potential to deliver; (i) multiple geophysical parameters, (ii) greater depth penetration and (iii) greater resolution.  The MinEx EM tool will have broad application for geophysical characterization for up to tens of meters around a borehole with direct application in identifying and characterizing high electrical conductivity ores such as massive sulfides.

Based on test results so far we believe that the new multifrequency EM tool has the potential for significant impact in the mineral exploration drilling market – enabling multifunction EM logging as part of routine drilling practice.

A patent application has been submitted to protect this innovative new technology and MinEx CRC are working with our Participants to define and facilitate a pathway to market that will provide the best opportunity for widespread utilization of the tool.

In the meantime, our researchers are assessing the potential for new in-hole time-domain EM tools with potential to impact the market. Stay tuned for future developments in this space.