The mineral system of magmatic sulfide deposits: an experimental approach

The Mineral System Approach is a concept in which the formation of ore deposits is viewed as a series of source, pathway, and sink processes. In the context of magmatic sulfide deposits, the main source of metals is in the mantle, the pathway is a translithospheric network of intrusions and dykes, and the sink is a physicochemically suitable crustal segment, where the metals are ultimately concentrated and deposited. The ability to decipher the signs of these processes in rocks is useful for identifying prospective areas for mineral exploration. With petrological experiments, we can simulate many of the processes occurring within the mineral system in a controlled laboratory environment. Experiments conducted in mantle conditions reveal how different mantle lithologies melt and what is the role of each phase in releasing the metals. Sulfide saturation state of the melt is one of the main variables in controlling the faith of the chalcophile metals and hence it has been intensively studied experimentally. The presence of dense sulfides in the mantle source or their precipitation along the translithospheric pathway tends to inhibit effective metal transportation to the upper crustal levels. However, experiments have shown that sulfides have a strong tendency in attaching to low-density fluid bubbles and carbonate melts, which may aid in their transport within the silicate melt in certain situations. Finally, observations from many ore deposits indicate that magmatic assimilation of sedimentary sulfur is important in triggering early sulfide saturation, which favors efficient metal enrichment to the sink. Experiments enable us to characterize the physicochemically complex magma-sediment interactions in detail and identifying the reaction pathways, which promote sulfide saturation. From source to sink, the key processes affecting the metal budget leave geochemical and mineralogical fingerprints to rocks, which we can detect with the experiments and use to evaluate the exploration potential of magmatic suites. An application to the magmatic Cu-Ni-PGE sulfide deposits of the Central Lapland Greenstone Belt will be presented.