Mineralogy of the sulphide deposits at Sulitjelma, northern Norway

Abstract

The pyritic VMS deposits at Sulitjelma, northern Norway have been regionally metamorphosed at amphibolite facies during the Caledonide Orogen. The deposits contain a wide diversity of sulphide, sulphosalt and related minerals, which are systematically discussed with reference to their occurrence, paragenesis and mineral chemistry. Most of these minerals are, however, rare to absent within the massive deposits, which are dominantly composed of pyrite with subordinate chalcopyrite, sphalerite and pyrrhotite. Galena, arsenopyrite, cubanite, molybdenite, stannite and tetrahedrite occur in minor amounts. Syn-metamorphic mobilisation has, however, resulted in the redistribution of a range of elements, including Cu, Pb, Sb, As, Ni and Au. These elements have been reconcentrated into mobilised segregations, where they have crystallised, under retrograde conditions, into a range of discrete phases. Ore mobilisation, which took place along tectonically-controlled pathways is, however, of a highly localised nature, with a considerable range in mineral textures and parageneses observed in different samples. Typical associations within these mobilisates include a range of CuPbSb and CuPbAs sulphosalts, including bournonite, meneghinite, seligmannite and jordanite, breithauptite, nisbite, costibite, arsenopyrite and gudmundite. Co-existing galena is characterised by elevated concentrations of Ag, Bi and Se. Argentian tetrahedrite (9–17 wt% Ag), the chief Ag-carrier in the deposits, as well as other Ag-bearing phases, including pyrargyrite, hessite and empressite, are strongly enriched in the mobilisates. Gold, as electrum (50–75 wt% Au), and more rarely as aurostibite, is also relatively enriched in the mobilisate samples over those from more massive parts of the deposits. A further range of minerals, including native antimony, native arsenic, allargentum, dyscrasite, argentite, mckinstryite (?), jalpaite (?) and native silver occur as low temperature breakdown products of earlier-formed minerals. Preserved textures do not contradict a model involving more than a one phase of mobilisation during the metamorphic evolution.