Geochemical and mineralogical investigations of waste rock from the historic mines at Håkansboda in Bergslagen, Sweden

Historic mines at Håkansboda located in western part of the Bergslagen mining district in west-central Sweden were selected as one of the pilot studies within the FUTURAM, a HORIZON EUROPE Research and Innovation project (2022-2026). FUTURAM’s main objectives is to map the supply of Critical Raw Materials (CRM) obtained from recycling of six waste streams: batteries, electrical and electronic equipment, vehicles, mining waste, slag and ash, and construction and demolition waste, and to develop a standard methodology for resource assessment, reporting structure, and guidance to improve the raw materials knowledge base up to 2050. Apart from building a database with Secondary Raw Materials (SRM) in Europe, several case studies were carried out to test different methods and approaches in order to evaluate the mineral potential and economic value of historic and current mining waste volumes. Additionally, UNFC was applied to SRM projects to test, develop, validate and demonstrate the procedures in line with UNFC requirements to enable fact-based decision making for their future exploitation.

In the Håkansboda historic mines, Cu and Co ore was mined since the XV century. Håkansboda deposit is located in the Guldsmedshytte syncline, folded during the Svecofennian orogeny with the stratigraphic sequence of metasedimentary and felsic metavolcanic rocks typical of central Bergslagen mining province. The Håkansboda polymetallic Cu-Co+Ag sulphide deposit is a SVALS-type, a stratabound Cu-Co (Fe, Sb, As, Bi, Ag and Au) mineralisation hosted in the so-called Håkansboda marble. The Håkansboda mineralisation occurs as disseminated sulphides of varying abundance in the marble horizon. It contains massive chalcopyrite-pyrrhotite rich ore bodies with surrounding less massive mineralization zones with various textures and composition. The main mineralogy is represented by chalcopyrite, pyrrhotite with subordinate arsenopyrite, pyrite, tetrahedrite-tennantite, sphalerite, molybdenite, cobaltite and Fe-Co sulphides. Native bismuth and gold can also be found.

Several groups of methods have been tested at Håkansboda: sampling routines, geochemical and mineralogical methods, and waste beneficiation methods. Geochemical methods including geochemical maps gave an overview of the chemical composition of the waste rocks with special emphasis on metals and critical raw materials and their spatial distribution in waste heaps. Mineralogical methods were used to identify the metal-bearing minerals and their parageneses/associations. The preliminary beneficiation tests helped to predict best possible extraction and processing technologies and validate the potential of waste for further extraction, including economic-related factors, such as the grade which can be obtained. At last, UNFC classification was developed upon the basis of quality of the parameters/controlling factors as well as their uncertainties supporting the level of confidence.