Redistribution of minor and trace elements in ore minerals in metamorphosed VMS deposits, Rävliden North, Skellefte district, Sweden

Abstract

The Rävliden North volcanogenic massive sulfide (VMS) deposit, in northern Sweden underwent polyphase deformation and greenschist to lower amphibolite facies metamorphism during the Svecokarelian orogeny. This caused remobilisation and recrystallisation of ore minerals, whose composition was analysed using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and electron probe microanalysis (EPMA). Sphalerite, chalcopyrite, and pyrrhotite chemistry mirrors zonation of undeformed VMS deposits. Chalcopyrite-rich mineralisation contains higher Cu, Co, In, and lower Mn concentrations than sphalerite-rich mineralisation. Besides galena, Ag occurs in sulfosalts, tellurides, antimonides, and amalgams, which possibly formed through exsolutions from α-galena in syn- to post-tectonic structures. LA-ICP-MS imaging shows Ag-rich minerals in early syngenetic pyrite, in contrast to syn-metamorphic pyrite, indicating remobilisation during deformation. Despite sampling effects accounted for through linear mixed effects (LME) modelling, the results indicate that syn-metamorphic recrystallisation and remobilisation did not lead to substantial compositional changes in ore minerals. Instead, these processes partitioned Ga between sphalerite and chalcopyrite and enriched Ag, Cd, and Sb in minerals associated with younger parageneses. Zeolite-bearing veins in the hanging wall host sphalerite with the highest Ga, Ge, Cu, and Sb contents and galena with the lowest Bi, Te, and Tl contents. An origin potentially linked to far-field effects of the opening of the Iapetus Ocean or waning Timanian orogeny is discussed based on similarities to other vein- and breccia-hosted ZnPb deposits in Northern Sweden. This study provides the first multiple-mineral in-situ trace element dataset for a VMS deposit in the Skellefte district, enhances understanding of element redistribution during metamorphism, and identifies remobilised elements potentially vectoring mineralisation at depth. Moreover, this study enables tracing of penalty and by-product elements in downstream beneficiation processes.