Lead isotope systematics in the Langban deposit and adjacent sulphide mineralisations in western Bergslagen, Sweden
2009 (English)In: GFF, ISSN 1103-5897, Vol. 131, no 3, 215-227 p.Article in journal (Refereed) Published
The Langban mines and the investigated sulphide deposits are situated in the westernmost part of the Bergslagen ore province, where it borders the voluminous, younger intrusives of the Transscandinavian igneous belt (TIB) in south-central Sweden. We report thermal ionisation mass spectrometer (TIMS) lead isotope data from the Langban Mn-Fe-(As-Ba-Pb-Sb) deposit and from Pb-Zn-(Cu-Fe-As-Ag) sulphide mineralisations in the region. Based on a systematic study of lead isotopic compositions of minerals from different assemblages and paragenetic stages (galena, native lead, arsenates, arsenites, oxychlorides, silicates, carbonates) from Langban, we propose that c.1.89-1.88Ga (Svecofennian) volcanic-hydrothermal processes supplied the predominating lead component to this complex deposit. Regional amphibolite facies metamorphism, the intrusion of younger granitoids, as well as a succession of ductile to brittle deformation episodes, led to multiple stages of remobilisation of the pre-existing, syngenetic components. During these stages, variable mixing with a minor component of presumed sedimentary origin, comparatively rich in 207Pb and 208Pb, resulted in a temporally unsystematic variability in lead isotopic compositions in the Langban deposit. Contrary to previous suggestions, our lead isotope data suggest that a significant input from, or overprinting by, fluids derived from post-Svecofennian granitic magmatism is unlikely to have affected the Langban mineralisation. By contrast, such processes were probably locally significant in sulphide +/- oxide deposits situated in the immediate vicinity of 1.78Ga intrusives (e.g. at Lahall and northern Myssberget). Here, the lead isotopic compositions of galena are more radiogenic, which is interpreted to be the result of mixing between Svecofennian ore +/- evolved host-rock lead and a later overprinting lead component related to the intrusion of c.1.78Ga granitoids (Filipstad-type TIB, Hyttsjo intrusive suites). Presently, we cannot unambiguously distinguish whether the source of the major overprinting lead component in some of the sulphide mineralisations was derived from the 1.78Ga magmas themselves, or from evolved Svecofennian metasupracrustal whole-rock lead remobilised at that time, although our data lean towards the latter.
Place, publisher, year, edition, pages
2009. Vol. 131, no 3, 215-227 p.
lead isotopes, Fe-Mn oxides, Pb-silicates, arsenates, oxychlorides, sulphides, native Pb, hydrothermal ore deposit, remobilisation, Langban, Bergslagen, Sweden
Earth and Related Environmental Sciences
IdentifiersURN: urn:nbn:se:su:diva-59658DOI: 10.1080/11035890903189751ISI: 000272026200001OAI: oai:DiVA.org:su-59658DiVA: diva2:432183
authorCount :22011-08-012011-07-052011-08-01Bibliographically approved