Controls on the high-grade gold-cobalt mineralisation at Rajapalot, Finland

Cobalt is one of the crucial metals needed for the energy transition as cobalt is found in batteries in e.g. electric vehicles. Gold, in turn, remains a key economic commodity but it is also an important metal in non-corrosive electronic components. The Rajapalot area in Finnish Lapland hosts several high-grade Au-Co prospects with an inferred resource estimate of 887 koz of gold and c. 4800 tonnes of cobalt, based on extensive drilling.
The Au-Co mineralisation occurred in two phases. The earlier, Co-only mineralisation is likely to be syngenetic; whilst the latter Au-Co event is structurally controlled with hydrothermal fluids circulated through extensive fracture systems. For the gold, the grade control is only partially understood, and the controls on the high cobalt grades in the Au-Co phase are unresolved. Previous studies, however, imply different processes for the enrichment of the two elements.

The grade controls of Au and Co need to be constrained further with a detailed mineralogical, trace element, and textural study. The main aim, therefore, is to investigate what controls the precipitation of Au and Co. There is also potential to address wider scientific questions on the partitioning of Co and various trace elements into sulphides in a hydrothermal system. In particular, the study provides an opportunity to study how trace metal partitioning and Co deposition may be controlled by chemical and physical processes during fracturing and fluid flow.

Establishing zoning in sulphides is needed to understand element partitioning and possible fluctuation in the depositional conditions; a detailed paragenetic analysis is also needed to investigate the number and character of fluid pulses/generations that were involved in the mineralisation. Therefore, your main tools will be the Scanning Electron Microscope (SEM) for textural and paragenetic studies; and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) with a Time-of-Flight capability for trace element mapping in sulphides.

Additional data and information can be gained to aid interpretation of the textural and element data: e.g., dating the Au-Co mineralisation may help in understanding the geological context of the mineralisation; or using Leapfrog 3D modelling to understand the spatial context of the mineralisation. You may also have an opportunity for a more regional study, comparing gold alloy compositions and mineral inclusions in gold particles from the deposits with those from placer, using LA-ICP-MS, SEM/BSE and Electron Microprobe Analyser EMPA.