The Tverrfjellet deposit is a 1.8 km long orebody which has was operation from 1968 until 1993 producing circa 15 Mt at 1.0% Cu, 1.2% Zn, 0.2% Pb and 36% sulphur. In addition, the deposit contained about 4% magnetite, 10 g/t Ag and 0.1 g/t Au. At its time, the Tverrfjellet minewas the largest producer of pyrite concentrate, chalcopyrite and sphalerite in Norway.
The deposit occurs as three (3) almost vertical lenticular ore bodies, plunging to the east to a depth of approximately 650 m below the surface. To the east the ore body is cut off by a major east-dipping fault zone, which down-throws the mineralised orebody by more than 300 m, which was considered to be too low grade and too small to be mined at the time. The thickness of mineralisation was on the average 15 m, but up to 60 min places. The deposit is hosted by a rock series consisting of greenstone, mica schist, quartzite and conglomerate, and is thought to be an equivalent to the Støren Group, situated about 100 km to the NNW. The deposit lies on the edge of an inverted part of the Trondheim Nappe Complex, and consequently it is structurally complex with tight folding and repetition of lithologies. These structures are responsible for the lenticular shape and the almost separated three ore bodies. The main ore minerals are pyrite, chalcopyrite, sphalerite and magnetite.