Interaction of submarine tailings with natural sediments in three northern Norwegian coastal areas. Sedimentological, mineralogical and geochemical constraints

Abstract

Submarine tailings placements (STPs) is an alternative practice of handling mine waste, which involves deposition of tailings into submarine environments. However, the environmental impacts of STPs remain poorly understood. This thesis is a contribution to improve the understanding of how submarine tailings placements interact with natural sediments. It is based on multi-proxy analyses of 10 sediment cores from three northern Norwegian coastal areas with submarine tailings histories: the fjords Bøkfjorden and Ranfjorden, as well as the sound Stjernsundet. The tailings in Bøkfjorden and Ranfjorden are associated with extraction of iron ore, whereas Stjernsundet is associated with extraction of nepheline syenite. The applied proxies included physical properties (e.g. magnetic susceptibility), geochemical properties (qualitative and quantitative element geochemistry), bulk mineral assemblages and lithological analyses. Three depositional environments are distinguished: a natural depositional environment (endmember 1), tailings depositional environment (endmember 2) and transitional depositional environment (mix of endmember 1 & 2). Endmember 1 is defined by alternating grainsize, low magnetic susceptibility and stable geochemistry. Endmember 2 is defined by fine-grained sediments, high magnetic susceptibility and elevated levels of tailings associated elements. Transitions are defined by gradual increase (tailings-dominance) or decrease (natural dominance) in grainsize, magnetic susceptibility and tailings associated elements. The relation and composition of the identified depositional environments reflect either gradual or abrupt changes in sediment supply, sedimentary and depositional processes. Ranfjorden and Bøkfjorden show a large lateral extent of tailings (> 15 km) due to a high sediment input of fine-grained tailings, bed load transportation and associated submarine meandering channel systems. Stjernsundet shows a limited lateral extent of tailings (< 2 km) due to a low sediment input of relatively coarse-grained tailings. The analyzed material from Ranfjorden and Stjernsundet reflects a gradual evolving dominance of tailings, whereas the material from Bøkfjorden reflect an abrupt evolving dominance of tailings.