US 5,030,675 Fire retardant polycarbonate moulding compounds

Abstract

The 1.9–1.86 Ga ensialic belt of western Bergslagen, Sweden, comprizes a > 12 km thick felsic volcano-sedimentary sequence intruded by syn-volcanic granitic plutons and mafic dykes and sheets, developed in a rifted continental setting. Regional, low-temperature alteration of the supracrustal sequence produced greenschist to low amphibolite facies mineral assemblages. Localized, cross-cutting zones of intense alteration are developed in felsic volcanics which have been affected by the regional alteration, producing drastic changes in both mineralogy and chemistry. These zones are found close to the Hjulsjö granite-granophyre intrusive complex, most probably the heat source for the hydrothermal system, and related to the exhalative Sirsjöberg-Osjöberg Fe-oxide deposits.The Hjulsjö zones are subdivided into inner and outer zones, based on differences in mineralogy and chemistry resulting from the variable intensity of alteration. While the degree to which most elements are leached increases from the outer into the inner zones, Mg increases with alteration intensity, and Si and Al stay unchanged, although they were mobilized during alteration. Initially K, Rb, Fe and Mn increase in the outer zones, but are depleted in the inner zones. Rare earth elements (REE) are depleted, with the light REE being more depleted than the heavy REE. A pronounced negative Eu anomaly is generally present. The hydrothermal fluid was enriched in ore-forming metals during alteration and leaching. REE patterns of exhalative minerals indicate that the Fe-oxide deposits were derived from these hydrothermal fluids.