摘要:

Vein deposits containing fluorite, quartz, calcite, galena, pyrite, marcasite, sphalerite and chalcopyrite occur in steep, N-S or NW-trending faults in Cambrian sandstones in southeast Skåne, southern Sweden. They are of late Variscan (probably late Carboniferous) age, related to the transcurrent faulting of the Tornquist-Teisseyre lineament and the subsidence of the Danish-Polish Trough. A relation to intracontinental holspot magmatism and incipient rifting in the Oslo Graben may also be suggested. Carbon isotopes in eight calcite samples from the Scanian veins show a δ13C-range of −3 to −5 per mil versus PDB, while oxygen isotope values fall in two groups, one with δ18O around + 11 to + 12 per mil versus SMOW in the calcite and another with δ18O around + 16 per mil. Sulfur isotope data on sulfides in the veins show a large spread towards rather light values. δ34S of eleven sulfide samples from the veins thus ranges between −2 and −19 per mil versus CDT. Heavier sulfur (+ 5.2 and + 25.5 per mil, respectively) is found in two samples of marcasite occurring in fragments of alum shale. No linear relation between lead and sulfur isotopes in galena exists for the Scanian veins. In their carbon and sulfur isotope geochemistry, the Scanian veins differ markedly from the sandstone-hosted Pb-Zn impregnation deposits of Laisvall and Vassbo. The geological setting and mineralogy of the Scanian veins instead suggest a relationship to the fluoritic ‘Rosiclare-Pennine’ subtype of Mississippi Valley-type deposits.

ISSN:0016-786X    

DOI:10.1080/11035898509454653

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035898509454654

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The stratabound Zn-Pb sulfide ores of Vindfall occur in a series of Precambrian metavolcanic rocks, bordered to the east by younger granites. Skarns form the host rocks of the mineralisation. Major ore minerals are sphalerite, galena, pyrite, magnetite and chalcopyrite; the most important Ag minerals are native silver and Ag-bearing tetrahedrite. A primary chemical zonation is mainly characterised by the regional separation of Bi and Sb, both present as minor elements in galena and as Bi- and Sb-bearing minerals. Bi is characteristic for the inner part of the mineralised zone. It is concluded that this zonal pattern appears to be consistent with an exhalative sedimentary origin of the ore. The distribution of Ag shows a relation with ore composition: Pb-rich ores show high Ag contents, Zn-rich ores are very poor in Ag. Retrograde metamorphism of high-grade clinopyroxene skarns resulted in the widespread formation of tremolite- and chlorite-bearing rocks. The ores reacted to this retrogression by recrystallisation, Fe-depletion of sphalerite and simultaneous formation of magnetite. Several stages of Fe-depletion, well demonstrated by discolouration of the original brown-coloured sphalerite, starting along polygonal cracks, indicate a gradual transformation of Fe-rich sphalerite into recrystallised, nearly iron-free sphalerite. Remobilisation is supposed to be responsible for the formation of local Ag- and Bi-rich ores in a final post-retrograde stage.

ISSN:0016-786X    

DOI:10.1080/11035898509454655

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035898509454656

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Dating of zircons with the U-Pb method in southeastern Sweden gives ages of 1837 Ma on volcanics, considered as postorogenic to the Svecokarelian, and 1825 Ma on an arkose (possibly a sheared synorogenic granite). These figures coincide with previous U-Pb ages in southeastern Sweden. Zircons from an older preorogenic gneiss and a metasediment do not fit a U-Pb discordia line but imply a previous history back to 2500 Ma ago. Zircons from a dike porphyry intruding the ‘younger’ volcanics do not yield a meaningful age, probably due to contamination. When compiling the presented U-Pb data with previous Rb-Sr and K-Ar ages the orogenic activity from synorogenic through postorogenic times seems to be continuous in southeastern Sweden.

ISSN:0016-786X    

DOI:10.1080/11035898509454657

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035898509454658

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The Götemar massif, located in south-eastern Sweden, consists mainly of a coarse-grained homogeneous alkali feldspar granite with subordinate fine-grained varieties. A multi-radiometric dating approach gives a variety of discordant data depending on method and material. The coarse-grained Götemar granite is believed to have intruded and crystallized between 1400 and 1350 Ma ago. The isotopic data, together with Ti, Zr, Y and Nb ratios, strongly resemble those of the Jungfrun granite which represents another anorogenic intrusion in the area. This suggests a common origin for these two granites. Rb-Sr dating of the fine-grained aplitic varieties of the Götemar granite gives an age of 1255 Ma. It is not clear whether these represent late differentiates, or if their age is lowered by late-stage hydrothermal activity.

ISSN:0016-786X    

DOI:10.1080/11035898509454659

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035898509454660

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The study deals with a group of small, originally subaquatic ridges on the eastern side of Pohjankangas, a large fluvioglacial esker formation, which has been accumulated in a glacial estuary between passive and active ice in the western parts of Finland. The directions of the ridges differ from most other moraine fields north of Hämeenkangas and seem to reflect an ice recession to the northeast. The morphology and dimensions of the ridges are of the De Geer type, but the composition and structure of the material are somewhat different and refer to possible transportation from both longitudinal and transversal directions. The average distance between the ridges is more than 170 m, which clearly exceeds normal values for De Geer moraine areas in Finland. It is concluded that the moraines have been deposited at or near the ice margin on the wider eastern side of the embayment at Pohjankangas. Their shape and distribution have been affected by abundant meltwaters and the formation of crevasses in the marginal zone.

ISSN:0016-786X    

DOI:10.1080/11035898509454661

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035898509454662

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor