HYPGEO – New Methods for the Exploration of Mineral Resources

Country / Region: Study site: Iberian Pyrite Belt (Spain)

Begin of project: August 1, 2016

Status of project: March 31, 2019

Exploration methods for mineral resources: hyperspectral remote sensing – gradient magnetometry – gamma ray spectrometry and further geophysical methods

WorldView-3 satellite image covering the eastern Iberian Pyrite Belt (IPB) in southern Spain, with the open pits of Aznalcóllar and Los Frailes (RGB: 14,8,2) Source: BGR

Aim of project: Development of application-oriented, generic methods for the detection and 3D characterisation of mineral resources based on the synergistic application of hyperspectral remote sensing and geophysical data

HYPGEO is a project of the Federal Institute for Geosciences and Natural Resources (BGR) in Germany with the contribution of the Remote Sensing Unit and the Airborne Geophysics and Aeronautical Operation Unit. In the course of this project, application-oriented and generic methods for the exploration of different types of mineral resources are further developed which will be implemented in the conception of a new synergistic exploration strategy. Using hyperspectral data allows point-by-point and spatial mineralogical mapping of areas of interest permitting the characterisation and detection of mineral resource deposits. Hyperspectral spectrometer acquire spectrally high resolved data to identify different materials and distinguish between them based on their spectral characteristics. In the geological and mineralogical context, data covering the visible and near infrared (VNIR, 0.4 µm – 1.0 µm), the short-wave infrared (SWIR, 1.0 µm – 3.0 µm) and long-wave infrared wavelength range (LWIR, 8.0 µm – 15.0 µm) allow the detection of different minerals, such as iron-(hydr-)oxides, phyllosilicates and carbonates.

Imaging spectrometer (AisaOWL in the foreground, AisaFENIX in the background) in the open pit of Los Frailes for the analysis and identification of characteristic mineral distributions in the rock Source: BGR

In addition to the hyperspectral data, airborne geophysical data are acquired. The gamma-ray spectrometry detects naturally occurring radioactivity from up to 30 cm depth caused by potassium, uranium and thorium or their isotopes and daughter products, respectively. The identified surface information gained from the hyperspectral and gamma-ray data are complemented by gradient magnetometry data to obtain information on the subsurface. State-of-the-art and highly sensitive SQUID systems (superconducting quantum interference device), which measure the gradient tensor of the Earth’s magnetic field with very high accuracy, are used for the airborne survey. They provide detailed 3D models as well as inputs for new ideas in the development of exploration methods and will be implemented in the exploration concept.
The use of these hyperspectral and geophysical systems allows a precise characterisation of the surface and subsurface of the area of interest. The hyperspectral and gamma-ray data, giving information on the Earth’s surface, and the gradient magnetic data, representing magnetic characteristics of the subsurface, are synergistically analysed and evaluated. This focused combination of different physical data und their assessment for a modern exploration strategy will be evaluated by the German Mineral Resources Agency (DERA) for the practical implementation and application in the exploration process.

In the course of the project HYPGEO, Cu-Pb-Zn mineralisations from massive sulphide complexes in the Iberian Pyrite Belt in southern Spain are analysed. Due to hydrothermal alteration that are associated with the massive sulphide ore body, characteristic mineral patterns have developed. Thus, they are indicative for potential mineral resource occurrences. These mineral distributions can be detected using hyperspectral remote sensing methods due to mineral-diagnostic absorption features. Field-based and airborne hyperspectral data are acquired with the sensors AisaFENIX and AisaOWL (SPECIM), covering the solar-reflective (0.4 µm – 2.5 µm) and thermal (7.7 µm – 12.3 µm) wavelength range. With the help of the hyperspectral point spectrometer ASD FieldSpec4 Hi-Res, a drill core, defined profiles and reference areas are analysed for calibration and validation of the imaging spectrometer data as well as for a quick capture of spectral features of the minerals and rocks. Furthermore, rock samples are collected for the hyperspectral analysis in the laboratory. The spectral results are validated by geochemical and mineralogical data.

The BGR helicopter at the start of the geophysical survey, measuring the naturally occurring radioactivity with a NaI-scintillator (within the helicopter) and the gradient magnetometry with the SQUID-sensor (on the left) Source: BGR

The naturally occurring radioactivity is measured with a NaI-scintillator and gives indication of the abundance of the natural radionuclides K, Th and U in the rocks and soils. The gamma-ray spectrometer RS-500 of the company Radiation Solutions Inc. consists of one upward looking and four downward looking detectors and is mounted on the BGR helicopter. The distribution of the radionuclides on the Earth’s surface (from up to 30 cm depth) allows the characterisation of the rocks regarding their mineralogy, structure and weathering patterns. The results can be used as a validation and supplement of the hyperspectral data and vice versa.
The geophysical exploration of the subsurface (up to 200 m depth) allows the spatial and structural description of the deposit. Based on this, a 3D concept can be developed to characterise and evaluate the deposit. The data are acquired using a SQUID-system measuring the gradient tensor of the Earth’s magnetic field. The sensor is also installed on the BGR helicopter. The data reveal magnetic anomalies, which indicate structure, position and shape of magnetic bodies (e.g. fault zones, ore bodies/veins). Additionally, the structural and spatial description allows an assessment regarding where mining activities are actually economic.

The synergistic use of hyperspectral and geophysical data is a new procedure, which increases the accuracy of the exploration of mineral resources. This combination shows the potential to minimise cost and time consumption, e.g. by allowing more focused field and laboratory work such as sampling, drilling and geochemical and mineralogical analyses. Due to the investigation of both the Earth’s surface and subsurface, the deposit can be interpreted more accurately and allows the development of a continuative exploration concept to identify and analyse unknown mineral deposits. Thus, this project aims to contribute to the securing of the mineral resources supply of the Federal Republic of Germany.