Our ability to measure the mineral and chemical composition of rocks while still in the ground is tantalizingly close, but just out of reach. When will routine downhole geochemistry become a reality?
By Kylie Williams
Mapping the mineral and chemical composition of recovered drill material requires a geologist to log and send drill samples to a laboratory for analysis, and wait weeks or months until results are available. However, over the last decade, the lab has been inching closer and closer to the drill site as technologies become smaller, more sensitive (to detect lower concentrations of a wider range of elements) and tough enough for field conditions. Still, safe, reliable, cost-effective downhole measurements remain just out of reach.
“No one is measuring geochemistry in the drill hole… yet,” said geochemist, Britt Bluemel, “In the last five years, service providers and applied researchers have not only increased the speed that we acquire geochemistry from the drill hole, such as the REFLEX Lab-At-Rig, but also the speed at which we can drill, like the DET-CRC coiled tube drilling system. We’ve also improved the way we detect gold using handheld instruments, such as Chrysos’ Gamma Activation Analysis, but I don’t know of any downhole geochemistry tools used by industry at this time.”
Downhole geophysical probes are used more often in mineral exploration to measure the physical properties of rocks, including density, magnetic properties or electrical conductivity. They are much more common in oil & gas exploration where rock samples are rarely retrieved, so downhole tools are the only way to examine the rock properties at depth.
Cost is a limiting factor on the use of downhole geophysical tools in mineral exploration where drill operators need to be on stand-by while geophysical operators deploy the tools downhole. It remains difficult to reliably locate and orient geophysical features recorded downhole and this casts a shadow on the reliability of the models generated from the results. Drilling and measuring a cluster of holes may generate a more reliable model, but cost is a huge factor. Many exploration companies still choose to invest exploration dollars in drilling more holes, rather than rely on sending probes down fewer holes.
“Similar issues would exist for downhole geochemistry tools” said Bluemel, “At the moment the technology is still too big to fit in the drill hole, but geochemistry is very forgiving compared to structural measurements, for example, because the geologist doesn’t need to collect oriented drill core to confidently use the geochemistry; they only need the collar and survey data, which is being consistently and routinely collected already.”
“We are getting quicker at measuring X–ray fluorescence (XRF) on core and cuttings at the rig as soon as the rock is out of the ground,” said Bluemel, “But the real quantum leaps in geochemistry and mineralogy on drill core have been in the hyperspectral arena.”
Bluemel joined Corescan, a global company specializing in automated mineralogical and textural analysis of drill core, rock chips and other geological samples, earlier in 2018. She said that using Short Wave Infra Red (SWIR) technology is changing the way we understand alteration systems, not just in porphyry deposits where it is commonly used, but also in epithermal, Volcanic Massive Sulphides (VMS), skarn, and even intrusion-related or ‘orogenic’ deposits.
Incremental innovation has bought geochemical equipment closer to the rig to analyse rock samples and see results within a few minutes of recovery. Who will be first to send geochemical measuring tools downhole? For now, here is a roundup of the industry-leaders performing near-real-time geochemical analysis at the top of the hole.
Boart Longyear uses TruScan™ for elemental and photo scanning of core at the exploration site. Boart geochemists collect samples from the hole and send them to a lab to calibrate the on-site XRF technology, which is able to analyze for the elements between sodium and uranium on the periodic table. TruScan also takes high-definition wet, dry, and spot-scan photos of the retrieved rock core. This information can be quickly viewed by the geologist – on or off-site – and aids in the logging and interpretation of the geology.
Developed in Australia by the Deep Exploration Technology Cooperative Research Centre (DET CRC) and licenced to Imdex in 2015, is the Lab-At-Rig – a system that uses XRF to determine geochemistry and XRD (X-Ray Diffraction) to determine mineralogy at the surface immediately after rock is drilled. According to the DET CRC Legacy Book, a prototype Lab-at-Rig has also been demonstrated for the coarser and wetter coiled tubing drill samples, and in 2017 Imdex and Barrick Gold began working on an automated version of the technology.
Corescan’s Hyperspectral Core Imager Mark III (HCI-3) integrates reflectance spectroscopy, visual imagery and 3D laser profiling to map the mineralogy and geochemistry of drill core, rock chips and other geological samples. Designed in-house and proprietary to Corescan, the system offers ultra-high spectral and spatial resolution. The hyperspectral and photographic data collected on core compliments the geologist’s own qualitative assessment of core with quantitative mineral assemblage and mineral compositional data. Corescan opened an office in Vancouver in June 2018.
Swedish company, Minalyze, have the Minalyzer Core Scanner that provides rapid and non-destructive analysis of drill core in trays as well as chips, pulps and pressed pellets using an XRF scanner which gives multi-elemental chemical information on the sample. In August 2017, Minalyzer and SGS announced they had joined forces to provide near real-time geochemical based analysis on drill core through the Minalyzer CS scanner. The Minalyzer CS scanner ‘generates a variety of data including continuous chemical XRF analysis, core photography, specific gravity estimation, rock quality designation and digital structural logging, assisting clients to make real-time decisions relating to drilling and exploration activities’.
A team of researchers from Germany and Australia published an abstract for the 35th International Geological Congress in 2016 describing “a novel type of downhole logging probe has been developed that is capable to register continuously the chemical composition of borehole walls by combining XRF techniques with downhole logging.” No additional news could be sourced for this technology.
Have we missed something? Are there other techniques that AME members are working on or have heard of that you would like to discuss? Add a comment on AME social media and we will follow up with a second post on this topic soon.
Boart Longyear, Corescan and SGS are Corporate Members and are exhibiting at Roundup 2019.
Barrick Gold Corporation is a Corporate Member.
Barrick and SGS are Roundup 2019 Conference Sponsors.