Distribution of ore-forming elements in sediment-hosted massive sulphide mineralisations in the Rana region, Norway

Frie emneord: Sulfidmalmforekomst Ore-element ratio analysis of 67 sulphide occurrences from two meta- sedimentary units in the Scandinavian Caledonides, has shown that the proportional distribution of Zn and Pb are similiar in the two groups, whereas the distribution of Cu, Ag and Au vary between them. One of the units, known as the Mofjelet Group, is relatively enriched in Au and Ag whereas the Plurdalen Group is enriched in Cu. The average zinc ratio (100Zn/(Zn+Pb) in both groups is 86. Assuming that the ore-bearing solutions were saturated with Zn and Pb, this ratio may suggest relatively low temperatures of the ore-forming solutions, a salinity in excess of ca 2 M NaC1 and/or partial complexing of Zn by bisulphide ions. Proportionally higher concentrations of Cu in the Plurdalen Group are due to increased stability of bisulphide complexes which, selectively, would enhance and/or maintain the Cu solubility in the ore-bearing solutions and lower the concentration of Zn and Pb. This study also imply that a Zn-Pb deposit discovered in the Mofjellet Group might benefit from recoverable concen- trations of Ag and Au, whereas a deposit in the Plurdalen Group, besides Zn and Pb, potentially could benefit from econoic concentrations of Cu.

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