Magnus Land

Mobility of rare earth elements during weathering of till in northern Sweden

Abstract Continuous, volume-controlled sampling from the surface down to a depth of 130 cm was conducted at two stations on weathered till (typic haplocryods). All the samples were analysed for major and trace elements including the rare earth elements (REE). Eight thousand seven hundred years of weathering since the glacial ice left the area, has resulted in a strong depletion of REE in the E-horizon. This loss decreases as atomic number increases, so that 80–85% of the La and 54–60% of the Yb have been lost. Europium has been lost to a greater degree than have the neighbouring elements. Possible explanations for the release of REE are: weathering of common silicates such as hornblende and epidote (and plagioclase in the case of Eu); weathering of apatite; weathering of rare but REE-rich minerals such as allanite and monazite; and release of REE adsorbed on clay minerals. Further studies on various size fractions and minerals are needed to quantify the importance of the various possible mechanisms of REE release. The release of REE continues within and below the Bs1-horizon, but the results from one station show that light REE can be enriched in the Bs1-horizon. This secondary enrichment could be caused by adsorption on secondary oxy-hydroxides, on clay minerals or on organic material. However, the net result of the weathering is that all REE have been released to the groundwater.

Seasonal variations in the geochemistry of shallow groundwater hosted in granitic till

The groundwater chemistry in a small catchment in northern Sweden has been studied for a period of 15 months, including two snowmelt events. The groundwater was sampled from two wells in a slope ...

Redistribution of trace metals in a mineralized spodosol due to weathering, Liikavaara, northern Sweden

The till east of the Liikavaara Ostra ore deposit in northern Sweden is in some parts rich in Cu and other sulphide-associated metals. Groundwater flowing in this till has higher concentrations of Cu than groundwater in a reference area where the till has low concentrations of Cu and other metals. To understand the processes that release metals from the mineralized till at Liikavaara into the groundwater, the authors performed a detailed study of the <2 mm fraction of a till profile where the highest metal concentrations in the Liikavaara area occur. The geochemistry and mineralogy of the till were determined, and the soil water was sampled by tension lysimeters. The importance of local diffusion of Cu-bearing airborne dust from the adjacent Aitik mine tailings impoundment was quantified and solid speciation of metals in airborne material was performed by sequential extraction. The results from Liikavaara were compared to results from the reference area. Glacial ice picked up sulphide-rich material from the Liikavaara Ostra Cu ore during its flow. This material was deposited in the till east of the ore body when the ice melted. The sulphides have been dissolved in the <2 mm fraction during 8.7 ka of weathering since the glacial ice retreated. After dissolution of the sulphides, Cu was redistributed and secondarily retained in association with Fe-oxyhydroxides and altered biotite. Other sulphide-associated elements such as Co, Ni and Zn show the same pattern in the till profile as Cu, though the concentrations are much lower. Uptake of Cu2+ in the biotite through ion exchange with K+ may be an important mechanism for Cu-enrichment in biotite at Liikavaara. The airborne dust is not the source of Cu in the till. Although the soil water at Liikavaara has higher concentrations of Cu and other metals than the soil water at the reference area, the Cu-concentration is too low for infiltrating soil water to explain the high Cu-concentrations observed in groundwater. The high metal concentrations in the till, of Cu in particular, cause the increased concentrations in the local groundwater. A fluctuating groundwater table washes out Cu and other metals from the till. It is possible that increased Cu concentration in the local groundwater is caused by dissolved organic complexes, or by colloids (<0.45 μm) rich in organic matter and/or Fe-oxyhydroxides.