Gold and sulfide-bearing listvenite in the mantle section of the Tays ophiolite in the Arabian Shield, Saudi Arabia

The mantle section of the Late Neoproterozoic Tays ophiolite in the Arabian Shield consists principally of thoroughly serpentinized peridotite with characteristics typical of depleted mantle protoliths from a fore-arc environment. The serpentinite is altered along shear zones and thrust planes to gold-bearing listvenite bodies of various sizes. These bodies are divided into carbonate listvenite and silica‑carbonate listvenite; they may be dyke-like or lenticular in form, and are yellowish-brown, reddish-brown, or greyish in outcrop. Carbonate listvenite expresses schistose deformation fabrics concordant to fabric in the host serpentinite, whereas silica‑carbonate listvenite is undeformed at field scale and contains a generation of undeformed minerals at thin-section scale. Silica‑carbonate listvenite contains Cr-rich muscovite (fuchsite) and base-metal sulfides and is enriched in Zn, Pb, Cu, Ag, and Au along with SiO2. The transformation of serpentinite along shear zones to different types of listvenite reflects successive episodes of fluid-mediated metasomatism. Carbonate listvenite develops first, driven by infiltration of CO2–bearing fluids during serpentinization of the original fore-arc peridotite. Silica‑carbonate listvenite marks a later episode associated with infiltration of K-bearing, SiO2-saturated fluids released during emplacement of the ophiolite. Listvenitization in the Tays serpentinite concentrated gold in sub-economic to economic extents, with concentrations increasing from host serpentinite (2–4 ng/g) to carbonate listvenite (267–937 ng/g) to silica‑carbonate listvenite (1717–3324 ng/g).