Förnätra mine

The body of ore at Förnätra (also known as the Bolag mina and Eckhoff mine) was discovered back in 1789 and copper was claimed there in 1839. From 1855-1857 nickel and copper ore were mined, and then processed nearby at Frösdals Kopparverk.

The western ore body is biggest, with an estimated ore area of about 700 m². The ore mineralisation appears in primorogenic mafic to intermediate abyssal rock with transitions from gabbro via quartz diorite to tonalite. The abyssal body extends to the west-north-west with a slope of about 30° to the east-north-east. The ore mineralisation consists partly of massive magnetic pyrites, impregnated by pentlandite and copper pyrites. In and by the ore zone there is a fine grained amphibolite as a dyke or sheet. Additionally, there is greywacke gneiss in a line that comes in from the north-west. The largest mine opening is sited at 7014550/1636800, where there are large dump heaps. About 100m north-east of this mine opening, several test ditches have been dug. At the end of the 1990s[clb1]   , in association with the construction of a new forest road about 100m east of the largest mine opening, rusty weathered gabbro rock impregnated by pentlandite, magnetic pyrites and copper pyrites was found in the ditch. Boliden Mineral AB investigated the find in the 1940s. According to Grip¹, analyses showed:     - 15-24% S      - 38% Fe      - 0.08% Co      - 0.4-0.8% Ni      - 0.2-1% Cu     - 0.09% As.

According to investigations carried out by T. Du Rietz in 1943, a sulphide-rich phase has been separated out of a dioritic to quartz-dioritic parent magma, which has intruded into older rock along level fissure zones. Later prospecting work by the Geological Survey of Sweden has estimated the average metal and sulphur content at:

     - 0.5% Ni     - 0.9% Cu      - 0.06% Co     - 18% S.

The known assets of nickel and copper are estimated at 125 and 225 tonnes² respectively. Copper and iron are important base metals with broad areas of use. Nickel is particularly useful as an alloy in steel, with primary usages in stainless steel, Ni-alloys and nickel-plating.Copper is used in Co-based plating when manufacturing tools and hardening surfaces.

¹ Grip, E. 1961. Geology of the Nickel Deposit at Lainijaur in northern Sweden and a summary of other nickel deposits in Sweden. SGU, series C no 577.² Nilsson, G. 1985. Nickel-copper deposits inSweden. I "Nickel-copper deposits of the Baltic Shield and Scandinavian Caledonides", H. Papunen and G.I. Gorbunov (ed.). - Geological Survey of Finland, Bulletin 333, pages 313-362.