Focus no. 6, 2023. Hyperspectral imaging of drill cores at NGU

HYPERSPECTRAL IMAGING OF DRILL CORES AT NGU

NGU FOCUS 02.02.23 / WRITTEN BY TOBIAS KURZ & NOLWENN COINT

INNOVATIVE MINERAL MAPPING

Hyperspectral imaging - also termed imaging spectrometry - is an emerging method for mineral identification and mapping and is increasingly applied in rock laboratories and for mapping in geosciences. This non-destructive and semi-quantitative method is based on the diagnostic reflectance and absorption properties of minerals and other materials within the visible and infrared light.

Hyperspectral imaging, in contrast to photographs and multispectral imaging, measures the reflected light with a higher number, commonly hundreds of very narrow spectral bands, resulting in a continuous reflectance curve per image pixel. The pixel spectra can be analysed for diagnostic mineral properties or by comparing with reference spectra from spectral libraries. The image nature of these data also enables data exploitation with various image processing methods including pixel or object-based image classifications or machine learning methods. Diagnostic reflectance properties of minerals occur within different spectral ranges and include beside the visible also the infrared and thermal-infrared spectral range.

PORTABLE HYPERSPECTRAL LABORATORY AT NGU

NGU operates a mobile hyperspectral laboratory using a SisuRock core scanning system from Specim Spectral Imaging Ltd (Oulu, Finland) equipped with two high performance hyperspectral cameras as well as a high resolution full-frame photo-camera. The hyperspectral cameras measure within the wavelength ranges 400-1000 nm (visible to near-infraredVNIR) and 1000-2500 nm (shortwave-infrared - SWIR). These spectral ranges are suitable to identify and map many rock- and ore-forming minerals or key minerals related to alteration processes.

The SisuRock system is designed to scan entire core boxes to enable fast turnarounds and scan capacities of couple of hundreds of core-metres per day. With this imaging method, the mineral composition can be efficiently determined, and thus mineral variations and trends can be disclosed over the entire core lengths with a spatial resolution of approximately 1 mm. The laboratory at NGU is installed in a container and can transported and temporarily set up at core repositories or drill sites when shipment of the drill cores is not feasible.

Hyperspectral mineral classifcation superimposed on a core box photo. Tobias Kurz (NGU).

INNOVATIVE CORE LOGGING WITH HYPERSPECTRAL IMAGING ENABLES:

• Mineral identification and distribution over entire core length with high spatial resolution

• Non-destructive, non-contact, semi-quantitative mineral mapping

• Guiding representative sampling

• Analysis of spatial mineral distributions at the core surface

• Framework for integrative core analysis

• Fast turnaround time

• Valuable information for many different

applications and geological settings

REFERENCES

Websites:

Reports and publications:

Ongoing projects at NGU:

• Application of hyperspectral imaging for logging carbonatites and assess the distribution of Rare Earth Elements mineralization in cores from the Fen alkaline and carbonatite complex.

• Basement Fracturing and Weathering On- and Offshore Norway projects (BASE 2 and 3)

• Clay mapping in drill cores

FOR MORE INFORMATION, PLEASE CONTACT:

Figure 1: Mobile hyperspectral laboratory at NGU

Table 1: Main specifcations of the hyperspectral cameras from Specim used at NGU’s mobile hyperspectral laboratory.

Figure 3: Hyperspectral core imagery showing core box photos, hyperspectral auto-cluster images, hyperspectral mineral classifcation and derived hyperspectral core logs (form left to right: kaolinite, montmorillonite, chlorite) showing mineral trends over the entire core length.

Figure 2: Hyperspectral core laboratory at NGU equipped with a SiSuRock core scanning system and a VNIR and SWIR hyperspectral camera.