Mining mitigation in Norway and future improvement possibilities

Abstract

Norway has a long history of mining dating back to the Akersberg silver mine in Oslo about 1000 years ago. Larger-scale mining for copper and sulfur became common in the early 1600s. There is no active mining of massive sulfide deposits in Norway today; but the operations have left behind tailings, waste rocks and adits that in many cases discharge low-pH, metal-laden waste streams. Three of the Norwegian sulfide mines (Røros, Råna, and Sulitjelma) where mitigation has taken place, but metal release is still evident are discussed in this paper. The Røros Mining District consists of many massive sulfide deposits mined primarily for Cu with minor lead and zinc. Some of the tailings dam s have been reclaimed, while others have been left open exposed to weathering. Evidence of oxidation appears in the upper % meter in one of the uncovered tailings dams, closed 30 years ago, where pH is 2.5 at the surface increasing to a pH 6 at70 cm depth. These tailings contain silicate minerals that most likely have a neutralizing potential. The Råna mining area consist of a few smaller massive deposits an d a recently closed (2002) nickel deposit associated with a mafic intrusive. Tailings from the nickel mine were emplaced along the shore line. Closure of the tailings included a soil cover 10-20 cm thick. Preliminary investigations indicate that this cover is not efficiently reducing the oxidation of sulfide minerals. Magnesium silicate minerals are most likely, however, neutralizing the acid generated from pyrrothite, the main sulfide in the ore. The Sulitjelma Mining District also consists of many massive sulfide deposits mined until 1991. Reclamation of the mining district includes a one meter cover on the tailings dam and the discharge of ARD into old underground mine workings. This has resulted in a mass loading reduction of 80-90%. Characterization of these sites has primarily focused on surface water quality, and in some instances, groundwater quality. The water quality data combined with mineralogical, geochemical, and hydrogeological data of the ore deposit and waste material can be used to improve mitigation, resulting in better control of metal release.