Facies architecture of the Palaeoproterozoic VMS-bearing Maurliden volcanic centre, Skellefte district, Sweden

摘要

The four Maurliden massive to network sulphide deposits are hosted by a silicic volcanic succession in the Palaeoproterozoic Maurliden domain in the central part of the Skellefte district, northern Sweden. The,bedrock in the Maurliden domain can be divided into primary volcanic rocks and volcaniclastic sedimentary rocks. The primary volcanic rocks comprise coherent rhyolitic, dacitic, andesitic and mafic volcanic facies and their related autoclastic and pumiceous breccia facies. The volcaniclastic sedimentary rocks, include monomict to slightly polymict breccia-conglomerates, which are related to terrestrial to shallow marine erosion of domes, and sandstone turbidites and mudstones, which indicate submarine settings below wave base. The primary volcanic rocks and volcaniclastic sedimentary rocks collectively define a submarine volcanic centre. This volcanic centre was characterized by the emplacement of rhyolitic, domes and cryptodomes, accompanied by subordinate explosive activity. It was developed in the ensialic back-arc or intra-arc basin of the Skellefte district. The facies architecture shows that prior to massive sulphide deposition, feldspar porphyritic rhyolitic volcanism, and both terrestrial/shallow marine and below wave base environments characterized the volcanic centre. At the time of massive sulphide deposition the Maurliden volcanic centre was characterized by quartz-feldspar porphyritic rhyolite volcanism and below wave base environment. This volcanism resulted in strongly quartz-feldspar porphyritic rhyolite cryptodomes, domes and quartz-feldspar porphyritic pumice breccia-sandstone (QFP pumice unit). The QFP pumice unit erupted explosively and was rapidly sedimented on the sea floor as a series of subaqueous mass-flows. All four Maurliden sulphide deposits are hosted within this QFP pumice unit, which suggest a genetic connection between eruption of the QFP pumice unit and formation of the sulphide deposits.