Fig. 4

Geochemistry of El Hierro sulphides compared to sulphides from MORB, back-arc and arc settings. a Ternary diagram showing the composition (in molar fractions) of El Hierro sulphides (circles) and sulphides from MORB (blue symbols), back-arc (purple symbols) and arc settings (pink symbols)²⁶. Different symbols are used for mss (crosses), iss (x’s) and mss–iss intergrowths or zoned sulphides where phases were not separately measured (stars). El Hierro group 1 sulphides have pyrrhotite-like (po) mss compositions with increasing Ni content towards group 2. The mss and iss phases in group 2 sulphides were analysed separately (orange and beige circles, respectively), hence the bulk compositions of those globules would fall on a straight mixing line between the two. Common sulphide mineral compositions are also shown for comparison: pyrrhotite (po), pentlandite (pn), cubanite (cub) and chalcopyrite (cpy). Bold triangle in inset shows the region of the Fe–Ni–Cu ternary used for the plot. b Ni/Cu and Fe/S ratios (wt.%/wt.%) of mss as in ref. ²⁶., showing that the early group 1 sulphides have a strong affinity with arc sulphides and plot near the upper Ni/Cu end of the arc trend. The apparent extension of the MORB trend by group 3 sulphides is likely an artefact of their lower S content due to S degassing