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Geochronology and geochemical evidence for a magmatic arc setting for the Ni-Cu mineralised 1.79 Ga Kleva gabbro–diorite intrusive complex, southeast Sweden

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posted on 17.03.2015 by Karolina Bjärnborg, Anders Scherstén, Ulf Söderlund, Wolfgang D. Maier

Magmatic Ni-Cu sulphide deposits are commonly associated with mafic rocks within the marginal areas of Archean or Proterozoic cratons. The Kleva Ni-Cu sulphide deposit in southeast Sweden is hosted by gabbro–diorite rocks and is sandwiched between two Palaeoproterozoic magmatic arcs: the Transscandinavian Igneous Belt (TIB) and the Oskarshamn–Jönköping Belt (OJB). Major and trace element data corroborate an arc origin for the Kleva intrusive complex. The variety of rocks and geochemical signatures suggest that it formed from several magmatic pulses. Despite the occurrence of supracrustal xenoliths, there is a lack of trace element evidence for significant assimilation. Mafic intrusions are abundant in southeast Sweden and are generally inferred to be synchronous with the TIB. Of these, Kleva is the only known Ni-Cu deposit, and it is unclear if it is associated with the OJB or TIB. Here, we present zircon and baddeleyite U-Pb dates of 1788 ± 4 Ma, 1788 ± 5 Ma and 1792 ± 3 Ma. We interpret a 1790 Ma date to be the best estimate of the crystallisation age of the Kleva intrusive complex, indicating that the emplacement of mafic magma is coeval with the voluminous arc-related TIB magmatism in the area.