Mineral exploration is carried out in stages, typically moving from basic desktop studies to more advanced field investigations and analysis. A typical workflow looks like this:
1. Preparations
Geologists review and compile publicly available historical data, core samples, geological maps, and digital databases. This is often provided by the National Geological survey (like the Geological Survey of Sweden – SGU). Areas of interest are selected based on improved geological understanding, mineral potential and/or historic mining activity, though new, unexplored areas are also evaluated. This forms the basis for an exploration permit application.
2. Review & Sampling of Historic Drill Cores
When available, historical drill cores are stored at the Geological Survey of Sweden’s (SGU) national drill core archive in Malå, Västerbotten. These cores are frequently revisited, logged, and sometimes re-sampled to obtain additional information.
There is no general legal requirement to hand over drill cores to SGU; deposits are often made voluntarily by companies. However, once cores are stored in the SGU archive, they can be re-examined by industry, researchers, and other stakeholders. If material from the archive is sampled for analysis, the results must be reported back to SGU within six months so that the data becomes publicly available.
3. Fieldwork and mapping
Geologists visit the field to investigate the bedrock. They map geological features such as faults, layering, and signs of mineralization, and collect samples from soil, rock (boulders and outcrops), and water.
4. Geophysical surveys
Instruments are used to measure the geophysical properties below the surface by airborne or ground surveys that include:
- Magnetometry (magnetic fields)
- Resistivity (electrical conductivity)
- Electromagnetics (a combination of magnetic and electrical properties)
- Seismic and gravity surveys (waves and gravitational variations)
These data sets are commonly used to create conceptual 3D geological models including potential mineralized domains.
5. Drilling
Drilling is the only exploration method which can confirm that there is mineralization of interest in the subsurface. If earlier stages of exploration are promising and the work plan is approved, test drilling is carried out. The most common techniques are:
- Diamond drilling, which produces cylindrical rock samples (core) for detailed geological analysis
- Reverse circulation (RC) or hammer drilling, which produces crushed rock samples and is faster but less precise
All drill cores are logged and selected intervals of drill core are analyzed in laboratories to determine metal content and rock characteristics.
6. Evaluation and modelling
All data collected is compiled and analyzed. Findings are often presented in the form of 3D geological models that illustrate the subsurface conditions and potential mineralized domains.
7. Consultation and environmental assessments
For more extensive work, consultation is required with landowners, local authorities, and environmental agencies. Environmental, cultural, and social factors must be considered.
Source: SGU, “Hur en gruva blir till”,
https://www.sgu.se/mineralnaring/mineralnaring-och-samhalle/hur-en-gruva-blir-till/