Chalcophile and Siderophile Elements in Mantle Rocks: Trace Elements Controlled By Trace Minerals

Abstract

Since V.M. Goldschmidt’s pioneering work, chalcophile elements have been identified as showing the greatest affinity for sulfur. Goldschmidt (1954) attempted to chart the distribution of these elements between the silicate (lithophiles), metal (siderophiles) and sulfide (chalcophiles) portions of meteorites by using sulfidation curves of metal 2M + S2 ⇌ 2 MS. Using a similar approach, Arculus and Delano (1981) suggested the following decreasing order of chalcophilic behavior: Ga >Cu>Mo >Fe >Ni >W >Co >Sn >Pb >Ag >Pt >Ir >Os >Sb >Ge >Re. Clearly such classifications are not suitable for discussing mantle chalcophiles. Siderophile and chalcophile elements have intermediate electronegativities and tend to form covalent or metallic bonds that are predominant in sulfide structures. Most elements that are siderophile are usually also somewhat chalcophile and vice versa. For example, highly siderophile elements (HSE) such as platinum-group elements (PGEs: Os, Ir, Ru, Rh, Pt, Pd), Re and Au are strongly concentrated in the sulfide phases, compared to nominally chalcophile elements (e.g., Pb, Ga, Ni) in terms of mass balance. Highly siderophile elements are assumed to be controlled by sulfide phases in the source of most mantle rocks and mantle-derived melts examined so far, because the uppermost mantle is not saturated with respect to Fe–Ni metal (Rohrbach et al. 2007). For this reason, the broad definition of chalcophile elements in the mantle should include all of the elements that are collected into sulfides, i.e., including highly siderophile elements (HSE), i.e., the platinum-group elements (PGE), Re, Au, Ag and the chalcogenides Se and Te. One way of sorting chalcophiles is by considering their sulfide melt/silicate melt partitioning behavior ( D sulfide melt/ silicate melt = the weight fraction of metal in sulfide melt/ the weight fraction of metal in silicate melt). Empirically and experimentally determined D sulfide melt/ silicate melt increase from …