Exploration for magmatic Ni–Cu–Co sulphide deposits in a convergent tectonic setting – a case study in southeast Sweden

ered have been falling for decades. In addition, the demand for gold is increasing, especially where there is a growing consumer market in developing countries such as China and India. This makes it crucial to discover new gold deposits; however, the vast majority of surface deposits have been discovered, which means it is harder and more expensive to find deposits in the subsurface. Norway lies on the Fennoscandian shield, which contains an extensive wealth of minerals. This is explained by the geological evolution of this region, including the development of Precambrian supracrustals, intrusive rocks and Devonian intrusions that formed in major rift and orogenic settings. There are exploitable resources of gold in Norway, indicating that this country could be a significant supplier of gold (Eilu 2011). The quartz veins at the Bleka Mine in the Telemark region have reported grades of 35 g t Au, 45 g t Ag, 0.5% Bi and 1.5% Cu (NGU 2017). Other studies have estimated a reserve of 60,000 tonnes of ore with grades of 11 g t Au that could produce 233,000 oz of Au (Horvath 1943). These veins form the Bleka Main Vein System (BMVS) where they are hosted by the Svartdal Metagabbro, a large Proterozoic gabbroic sill complex. Another set of quartz veins, known as the Espelid vein system, is located 3 km north of the Bleka Mine; these veins are smaller, but are more numerous and may have a significant amount of gold that could be utilised. Scheelite, an important ore mineral of tungsten, was observed at Bleka and might be of economic importance, depending on its abundance (Dahlgren 2015). It is currently known that scheelite is abundant within the BMVS; however, it is unknown if it is abundant in the Espelid vein system or other quartz systems in the area as it superficially appears similar to quartz although it can be easily distinguished in darkness using short wave UV light (Søren and Tonny 1998). The project area, located northwest of the Bleka mine, contains the Svartdal Metagabbro that hosts the gold bearing quartz veins and scheelite. This gives the opportunity to explore the area for scheelite in the Espelid vein system or other gold bearing quartz veins. Geological mapping of the project area confirms the presence of quartz veins, along with their location, orientation and relationship with the Svartdal Metagabbro. A detailed petrographic and geochemical analysis of the quartz veins along with the Svartdal Metagabbro is currently being undertaken to better characterise the formation of the host rock and the quartz veins. Interpretation of data gathered from a geophysical survey of the Svartdal Metagabbro using an EM31 and magnetometer will show the location of quartz veins and their strike in the subsurface.