LA-ICPMS investigation of base and precious metal contents in rock-bearing sulfides from the Troodos Ophiolite, Cyprus: implications for the cycle of metals during hydrothermal alteration of oceanic crust

Abstract : The Troodos ophiolite in Cyprus, formed in a Cretaceous (92 Ma) supra-subduction zone setting, is considered to be one of the best-preserved ophiolite complexes in the world. This ophiolite hosts several dozen Volcanogenic Massive Sulfide (VMS) deposits that are up to ~20 Mt in size and were exploited for both sulfur and base metals. VMS deposits have been shown to originate through leaching of metals during hydrothermal alteration of the sheeted dike complex. A recent study [1], has performed mass balance calculations by considering the protolith composition and the secondary mineral assemblages, and thus was able to quantitatively constrain the release of base metals from the altered sheeted dikes. These authors report bulk metal contents of basaltic andesite glass protoliths and variably altered facies rocks from the epidosite zone of the Troodos ophiolite, and suggest that Cu was totally lost during the early stages of alteration owing to complete breakdown of igneous sulfides originally present in the protoliths, whereas the release of other base metals (Ni, Zn, Mn, Co) towards mineralizing fluids was controlled by the secondary mineral assemblage, i.e., the relative abundance of epidote and chlorite ± amphibole. This interpretation stresses the role of silicate minerals in the redistribution of metals during hydrothermal alteration of the sheeted dike complex, and contrasts with the common assumption that accessory phases, such as sulfides, control base metal concentrations within mineralizing fluids in VMS systems. Here we propose to test this hypothesis by providing measurements of the metal contents of sulfide minerals contained in various lithologies from the Troodos ophiolite. We report laser-ablation ICPMS analyses of 14 base and precious metals (Ti, Cr, Mn, Co, Ni, Cu, Zn, Zr, Mo, Ag, W, Pt, Au, and Pb) in sulfides present in samples representative of different stratigraphic levels and chronological stages of the hydrothermal alteration within the ophiolite complex. Preliminary results show a large variability of metal concentration and behavior depending on the lithology. Igneous sulfides present in least-altered metabasalts from the upper part of the crust are notably enriched in Co, Ti, Cu, Pb, Mn and Ag. They likely contain most of the bulk metal budget of the primary lavas. Importantly, numerous sulfides are still preserved in the epidotized sheeted dike complex, and remain enriched in Co, Ti, Pb, Mn (while Cu and Ag appear to have been remobilized). The sulfide-bearing quartz veins corresponding to the discharge upwelling of hydrothermal fluids show very low metal concentrations, with the exception of Ni, Pb and Cu. Finally, the massive sulfide deposits are made of Cu-, Zn-, and Co-rich pyrite and Pb-, Mo-, Zn- (and Ti-) rich chalcopyrite. These observations suggest that sulfides may have a significant role in controlling the progressive release of some metals during the different steps of hydrothermal alteration, and need to be considered in conjunction with the secondary silicate minerals. [1] Jowitt S.M. et al. (2012). J. Geochem. Explor., 118, 47-59.
Complete list of metadatas

https://hal-insu.archives-ouvertes.fr/insu-01143267
Contributor : Nathalie Pothier <>
Submitted on : Friday, April 17, 2015 - 11:00:13 AM
Last modification on : Friday, May 10, 2019 - 1:54:16 PM

Identifiers

  • HAL Id : insu-01143267, version 1

Collections

Citation

Sébastien Jégo, Michel Pichavant, Gabriel Coelho, Claire Ramboz, Stanislas Sizaret, et al.. LA-ICPMS investigation of base and precious metal contents in rock-bearing sulfides from the Troodos Ophiolite, Cyprus: implications for the cycle of metals during hydrothermal alteration of oceanic crust. International Mineralogical Association IMA 2014, Sep 2014, Johannesburg, South Africa. pp.EG9 - SULPHIDE MINERALOGY AND GEOCHEMISTRY - ORAL. ⟨insu-01143267⟩

Share

Metrics

Record views

194