Can the Ni-Cu-PGE signatures of sulphide inclusions in diamond help to constrain diamond formation processes?

摘要

Fe-Ni-Cu sulphides are the most common syngenetic mineral inclusion found within diamonds. Silicate mineral inclusions have been split into two major parageneses: peridotitic (P-type) and eclogitic (E-type). The chemistry of sulphide inclusions broadly divides into Ni-rich types (found in association with P-type silicates) and Fe-rich, Ni-poor types (often found in association with E-type silicates). Analyses for platinum-group elements (PGE) have been carried out on Ni-rich sulphides from Siberian and South African diamonds and Ni-poor sulphides from Botswana (Orapa) diamonds. More recently, Re-Os isotope analyses have been performed on a number of Siberian and African sulphide inclusions, which have indicated a range of formation ages for the sulphides (and, presumably, the diamonds that host them). What remains uncertain is how these different sulphides formed (via a sulphide melt or via a S-rich fluid) and whether sulphide formation is linked in any way to diamond formation (e.g via the action of a C-S-H-O-N-bearing fluid).