Pollution monitoring at the Black Angel legacy mine in West Greenland using in-situ portable X-Ray Fluorescence (pXRF) measurements

In Greenland, mining has been undertaken in remote areas for more than 150 years and long before legislation for environmental protection was implemented. The Black Angel mine by the Affalikassaa fjord in Central West Greenland served as a marble quarry, known as Maarmorilik, operating in the 1930s when a metal-sulphide ore body was discovered in the ‘Black Angel’ mountain on the other side of the fjord. This discovery led to establishment of the Black Angel lead-zinc mine, operating from 1973-1990 with a total of 13.5 million tons of ore produced from an ore body located 600 meters up a vertical mountain side and only accessible via cable cart spanning 1500 meters across the fjord. Mining was done by the “Room-and-Pillar” method, where ore was crushed inside the mine before being transported via cable cart to the processing facility. Large amounts of pyrite and sphalerite bearing waste rock were dumped directly out of mine tunnel openings at approx. 600 meters altitude onto the steep mountain slopes below as well as and onto the “Tributary Glacier” towards the Greenland Ice Sheet. Since deposition, the waste rock has been exposed to the elements with significant leaching of heavy metals and dispersion of fine particles into the terrestrial and marine environments. Environmental monitoring since mine-closure in 1990 has documented a widespread pollution of Pb in the area. However, the knowledge on the geochemical composition of the different waste rock dumps, their relative contributions to both historical, current and future releases of heavy metals to the environment as well as future risk due to permafrost thaw and surface erosion is limited by a lack of widespread geochemical characterization of deposited waste rock.

In the current study we present the first large scale in-situ pollution monitoring at the legacy Black Angel mine, using portable X-Ray Fluorescence spectrometry (pXRF). pXRF has been shown to provide fast, accurate and cost-effective results for many heavy metals in sediment and soil, enabling effective in-situ identification of pollution hot-spots. Results from this study show significant variation in heavy metal content between different waste rock dump sites. The highest concentrations of Pb, Zn and Cd are found in the North Face Dump and 17xCut established early in the mine's history, and lower, yet still significant concentrations are found in the much younger Tributary Glacier dump. We find that the waste rock from the Tributary glacier has been reworked and transported downstream where we measure increased concentrations of heavy metals. This highlights the large environmental risks associated with depositing mine waste on dynamic landforms. Current surface and bank erosion of fine particles from waste rock dumps will likely continue in the future as a warmer climate may increase erosion potential in response to large precipitation events as well as changes in snow cover. The remaining environmental risk is generally dominated by the mine closure strategy of leaving waste rock exposed to the environment, with only limited impacts from future warming and thawing permafrost.