New Mexico Geological Society Annual Spring Meeting — Abstracts

The Sulitjelma mining district, located in Northern Norway, consists of more than twenty deposits that were mined from 1860 to 1991 and produced some 26 million tons of ore. The mining district was closed and partly mitigated in the mid 1990’s, based on very little characterization data, by leading adit water into the larger underground mine areas and plugging lower portals. A thin layer of soil was also applied to one of the larger exposed tailings piles. This closure has failed in its intent to reducing the concentration of copper to less than 10 μg/L in the receiving environment. The ore deposits within the district are classified as volcanogenic massive sulfide (VMS) hosted in an ophiolite complex. The long Lake Langvatn divides the district in a north and south section. The sulfide deposits were predominantly mined for sulfur, copper, and zinc. Ore processing and exposed waste rock dumps scattered around the district has resulted in A/NRD and soil contamination. As a consequence of A/NRD, there is heavy metal leaching from waste rock into surrounding streams leading into the Lake. In addition to waste rock contamination contribution, there is discharge from several of the mine adits. Thus, determining the sources of the contamination load on the receiving lake is more complicated than siting a single source. Implications of waste rock weathering and the impact on the surrounding water sources is being examined. Most waste dumps were sampled (solids and seep water when available), while four major mine areas were sampled more extensively during the summer 2016. The focus of this research is on the south side of the Langvatn, but the study also includes one waste dump on the North side. Waste rock and water samples were taken from each site and analyzed. The majority of sites yielded a low soil pH, and high total dissolved solids. Water samples from numerous creeks and drainages were sampled and tested for copper, zinc, iron, and sulfate. The data shows a wide spread of values, with highest copper concentrations (35 mg/L) near a small open pit mine, Furuhagen (the westernmost sampling point). When evaluating overall copper loading on the Lake, an adit on the North side is found to contribute 2.09 mg/L at a rate of 1033 L/sec. Ten waste rock samples selected from the four zones will be used in kinetic column tests to determine mineral reactions and further leaching potential together with mineralogy, acid base accounting, and sequential chemical extraction. This information will be combined with streamflow data to estimate contaminant load to the Langvatn. The Norwegian government has a regulation that the acceptable copper levels leaving Lake Langvatn have to be under 10 μg/L Cu. Upon measuring water at the end of the Lake, the copper level was ten times this, at 112 μg/L Cu. Without this more extensive mineralogical and geochemical characterization of the district any remediation/mitigation of such a large variable mining area is likely to fail.

References:

1. [1] Tom V. Segalstad, (2002) Mining at Sulitjelma[2] Ingar Walder, (2017) Metal leaching from the Sulitjelma VMS mining district, Norway[3] The project is funded by Kjeøy Research & Education Center and Norwegian science foundation