No abstract

In search for a source for a slow-releasing K fertilizer, the plant availability of mineral K in selected crushed rocks and mine tailings was investigated by growing Italian ryegrass for six months in small volumes of peat, loamy sand or silt loam mixed with different K-sources. The K supplied as K-feldspar was nearly unavailable to the plants, whereas nearly 60% of the K supplied as biotite and nepheline in a carbonatite, was recovered in harvested plants parts. The carbonate content of the rocks and tailings seemed to be more important for the availability of the K than the specific surface of the mineral particles. It is concluded that a rock-based fertilizer containing biotite as its main K-bearing mineral and between 5 and 20% carbonate, will release K at a slower rate than soluble K fertilizers do and still supply considerably more K to the plants than is supplied from the fraction of non-exchangeable K in the soil.

Strike, dip, and thickness were measured for 504 sheets (inclined sheets and dykes) in the 4-6 Ma old Hafnarfjall central volcano in southwest Iceland. The average dip of sheets is 65°, 80% are less than 1.2 m thick, and the thickness tends to decrease with decreasing dip. In 0.5 km long traverses perpendicular to the average strike of sheets, the percentage of sheets ranges from about 6 to 11.Of 140 chemically analysed sheets most are quartz-tholeiites; a few are intermediate or acid. The sheets are chemically more evolved than the host rock and were generated by a shallow crustal magma chamber at a mature stage of the central volcano, whereas the host rock was generated earlier before the chamber was established. Trace element results suggest that the sheet magmas evolved by lowpressure fractional crystallization as well as by mixing of primitive magmas and crustal melts.A model is proposed where most of the sheets are generated by a growing shallow magma chamber. As the chamber grows its shape changes, and so does the local stress field associated with it. Because the sheets follow the stress trajectories of the local stress field, the potential pathways of the sheets change with the growth of the chamber, which may explain the common occurrence of cross-cutting sheets. From the evolved chemistry of the sheets, as well as from the pattern of the stress trajectories, it is concluded that the bulk of the sheets were injected from the upper part of the shallow magma chamber.

No abstract

There are three provinces in Northern Norway in which occurrences of graphite are abundant; the Island of Senja, the Vesterålen archipelago, and the Holandsfjorden area. From these provinces, we report graphite resources from 28 occurrences. We use a combination of airborne and ground geophysics to estimate the dimensions of the mineralized areas, and, combined with sampling and analysis of the graphite contents, this gives us inferred resources for almost all the occurrences. The average TC (total carbon) content is 11.6%, and the average size is 9.3 Mt or 0.8 Mt of contained graphite. We demonstrate that the Norwegian graphite occurrences have grades and tonnages of the same order of magnitude as reported elsewhere. The graphite-bearing rocks occur in a sequence that encompasses carbonates, meta-arenites, acid to intermediate pyroxene gneisses, and banded iron formations metamorphosed into the granulite facies. Available radiometric dating shows that the graphite-bearing rocks are predated by Archean gneisses and postdated by Proterozoic intrusions of granitic to intermediate compositions.