摘要:

Rb-Sr whole rock isochron dating of Svecokarelian prekinematic granitoids from a single outcrop ca. 20 km NNE of Ludvika, south central Sweden, gives an age of 1799 ± 10 Ma. Zircons separated from one of the granitoid samples yield a U-Pb discordia age of 1869+9-8Ma. Regional sampling of similar granitoids in the Ludvika area results merely in a Rb-Sr whole rock errorchron of 1770 ± 10 Ma, thus emphasizing the importance of restricting sampling in older metamorphic terrains to a small area with good geological control. Rb-Sr whole rock dating of Svecokarelian metarhyolites (leptites) from the Yxsjöberg area, WSW of Ludvika, fails to give a meaningful age.

ISSN:0016-786X    

DOI:10.1080/11035898509454636

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035898509454637

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

It has been postulated that during the formation of an impact crater, fragments from the bedrock mainly move radially with respect to the impact center. The result of rock counts in the Ordovician basal conglomerate from five localities in the Siljan Ring structure is consistent with this hypothesis. The distribution of rock types occurring as pebbles in the allochthonous conglomerate varies from locality to locality, reflecting the Proterozoic bedrock of each radial sector from the impact center.

ISSN:0016-786X    

DOI:10.1080/11035898509454638

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

This paper deals with the formation of magnetite in connection with sulphurization and serpentinization of skarn iron ores in Early Proterozoic (1.9 Ga) metasediments and mafic metavolcanics in northern Sweden. The ores contain Ca-Mg and Mg silicates which are characterized by a high Mg/(Mg + Fe) ratio, being mainly higher than 0.8. This feature is possibly due to an original high content of sulphur in the chemically precipitated ore material. During regional metamorphism involving heat transfer and recrystallization there occurred internal reactions. Sulphur reacting with primary, more Fe-rich silicates, gave rise to more Mg-rich silicates and a simultaneous formation of iron sulphides and magnetite. Calculations made on the Stora Sahavaara ore show, however, that the sulphide-silicate reactions could only have attributed to relatively restricted amounts of magnetite. The magnetite of the ores often contains small amounts of magnesium, at maximum 6 weight% Mg. The magnesium-bearing magnetite is mostly associated with serpentine which is an alteration product of olivine, tremolite and diopside. The occurrence of the magnesium-bearing magnetite is attributed to serpentinization which released iron from the silicates, and their high magnesium/iron ratio could in part be related to this process. However, the formation of magnetite in connection with serpentinization is only known in some deposits, and it is therefore plausible that serpentinization, in similarity with the sulphide-silicate reactions, has given rise to restricted amounts of magnetite in comparison to the amount of magnetite (or its precursor) which was deposited as a primary chemical precipitate.

ISSN:0016-786X    

DOI:10.1080/11035898509454639

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The distribution of uranium in kolm from Upper Cambrian alum shales has been studied using backscattered electron imagery, and found to be concentrated in discrete mineral phases. Authigenic minerals in kolm include pyrite, galena, and a cerium-bearing mineral referable to monazite. Uranium occurs within the monazite and generally shows a close relationship with phosphorus. Uranium bearing monazite has also been identified within the host alum shale.

ISSN:0016-786X    

DOI:10.1080/11035898509454640

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Economic sulfides occur in metasedimentary rocks in a Proterozoic supracrustal formation surrounded by granitoid massives at Saxberget in the province of Bergslagen, south central Sweden. The occurrences of high grade metamorphic minerals indicate that the Saxberget Formation has been subjected to temperatures above 600°C and pressures exceeding 300 MPa. Present temperature measurements, combined with analyses of ore elements, indicate that the present mineralization could be the surviving remnant of a formerly overlapping larger system of ZnS-PbS-precipitations which have since been lost to erosion. During deformation, the Saxberget Formation developed chevron folding, during which the thin sulfide mineralized layer flowed from the straight limb into the sharp hinge.

ISSN:0016-786X    

DOI:10.1080/11035898509454641

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The sillimanite bearing quartzite occurring at Enåsen has been found to carry high amounts of gold together with Bi, Sb, Tc and Se. Cation distribution between Fe-Mg silicates in the regionally metamorphosed country rocks (gneisses) yields temperatures of 600–700°C and pressures of 4–6 kb with an estimated XH2O= 0.5. The temperatures indicated by the arsenopyrite geothermometer, 385–435°C, are assumed to show retrograde equilibrium conditions. The present study shows the gold to occur in two different modes, as elementary gold associated with sulphides and as elementary gold and gold-antimony tellurides together with complex graphic intergrowths of tellurides and sulphides. The presence of Te, Bi, Sb, Se and abundant rutile and topaz suggests that hydrothermal activities provided for the original deposition of ore minerals.

ISSN:0016-786X    

DOI:10.1080/11035898509454642

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The supracrustal sequence at Garpenberg, south central Sweden, consists mainly of felsic gneisses with subordinate intercalations of amphibolites and stratabound sulfide and iron deposits. During the Svecokarelian orogeny this sequence was isoclinally folded, metamorphosed and intruded by synorogenic granitoids. The history of these supracrustals is characterized by at least two successive stages of metamorphism, followed by a stage of alteration at low temperature and pressure. A first stage (M1) of regional, low pressure, deformative metamorphism in the amphibolite facies was followed by retrogressive, low pressure, non-deformative metamorphism in the greenschist facies (M2). M1is considered to be related to the Svecokarelian orogeny, whereas M2represents a late or post Svecokarelian event. Later low temperature, low pressure, alteration is represented by cross-cutting fractures filled with mineral assemblages such as prehnite-epidote-calcite or chloriteprehnite. Petrologic and mineralogic evidence supports a metamorphic temperature for M1of ca 550°C and a total pressure lower than 3.5 kbar.

ISSN:0016-786X    

DOI:10.1080/11035898509454643

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035898509454644

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The Cambro-Ordovician alum shales in Scandinavia have anomalously high contents of certain trace elements, among them U, V and Mo, when compared to other black shales in the world. Variations in the contents of these elements within the formation show a clear correlation with the stratigraphy. The geochemical signature of the different levels of the stratigraphy is apparent over vast areas of the Baltoscandian Platform but has also proved to be valid for fossiliferous black phyllites in the Caledonian autochthon, the lower nappes and one of the higher nappes. Investigation of the content of U, V and Mo in graphitic phyllites of the Stikke Nappe in the Seve-Köli Nappe Complex of the Stekenjokk area has identified the presence of anomalously high contents of these elements compared to average black shales. The content of these elements in the graphitic phyllites correlates clearly with that found in the Early OrdovicianDictyonema-bearing shales in eastern Trøndelag and on the Baltoscandian Platform; it is, therefore, suggested that these metasediments in Stekenjokk are of the same age.

ISSN:0016-786X    

DOI:10.1080/11035898509454645

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor