Synvolcanic mixing of ore lead and the development of lead isotopic provinces in the Skellefte district,Sweden |
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| Authors: | K Billström W Vivallo |
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| Institution: | (1) Laboratory for Isotope Geology, Swedish Museum of Natural History, Box 50007, S-10405 Stockholm, Sweden;(2) Department of Geology and Geochemistry, Stockholm University, S-106 91 Stockholm, Sweden;(3) Present address: Department of Geology, University of Chile, Santiago, Chile |
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| Abstract: | Ore lead isotope ratios have been analysed in galenas and sulphosalts from nineteen massive sulphide deposits hosted by Svecofennian (1.9 Ga) supracrustals in the Skellefte ore district, northern Sweden. The ore lead data can be grouped on the basis of their geographical distribution. Most probably, this feature is reflecting a number of lead isotopic provinces which correspond to crustal blocks. The obtained ore lead data define linear trends in conventional Pb-Pb plots. The ore lead signatures are due to synvolcanic mixing processes as lead was leached from mafic and acid volcanic sources. The relationships inferred for initial ratios in source rocks at 1.89 Ga require a pre-Svecofennian crustal history. It is suggested that magmatic processes at c. 2.0 Ga involved recycling of Archean sedimentary material into the mantle and the formation of a crystalline, felsic basement. The metasomatized mantle and the basement melted at the time of Svecofennian magmatism (1.89 Ga) which created mafic and acid magma sources. Subsequently, basalts and rhyolites were extruded onto the sea floor. Ore was formed as hot solutions penetrated isotopically different levels of the volcanic pile. |
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