Abstract-Wehave analyzed the trace-element and isotopic composition of a series of lavas and their constituent pyroxenes and calcite from near the town of Skien in the Permo-Carboniferous Oslo Rift. The series decreases in alkalinity upsection: the lowermost layaS are n~heli~t~, followed by basanites and finally alkali basalts. This sequence is accompanied by decreasing light ram earth element (LREE), Th, Nb and U concentrations. Nd isotopic change is strongly correlated with the petrologic and chemical evolution. The nephelinites are characterized by cNd (300 Ma) of 1.0 to 1.6, the basanites 1.9 to 2.2 and the alkali basalts 2.4 to 3.9. cSr (300 Ma) ranges from -10 to -15 and shows little change from one group to the next. Calcite segregations in the basaltic rocks show 6'-'C = -2.825, 6'*0 = 7.7 to 9.6%, tsr = -6.5 to -9.9 and Q.+, = 0 to +2, values which are compatible with formation from magmatic CO, exsolved from a mantle-derived silicate melt.The Sr isotope values are unradiogenic relative to Nd for the nephelinites, causing these samples to fall to the lefthand side of most rn~tl~~y~ rocks on a eNd vs. 6sr diagram. They are similar to rocks from "high p" (HIMU) sources and the recently proposed "LoNd array" f HART et al., 1986). The alkali basal&, with their higher cNd, lie close to the mantle array for 300 Ma ago and resemble tholeiitic magmatism in the Oslo Rift. We interpret these trends as representing evolution in which the earliest magmas were derived from a source with HIMU-LoNd characteristics, and successive magmas gradually acquired the more dominant mantle isotopic composition. Model age calculations permit either 1) that the nephelinite source was originally depleted then subsequently re-enriched in LREE or 2) that the nephelinite source was primitive with respect to Nd but had undergone Rb depletion. The nearby Fen carbonatite complex is about 250 Ma older than Skien and its em is slightly more positive. A direct ~~tion~ip between Fen and Skien would favor the first hypothesis.
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 dams have been reclaimed, while others have been left open exposed to weathering. Evidence of oxidation appears in the upper ½ 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 at 70 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 and 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.
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