Platinum-group elements-bearing pyrite from the Aguablanca Ni-Cu sulphide deposit (SW Spain): a LA-ICP-MS study

Abstract

Despite the fact that pyrite is a relatively common phase in Ni-Cu-PlatinumGroup Elements (PGE) magmatic sulphide deposits, it has been neglected in the studies on PGE distribution in favour of pyrrhotite, pentlandite and chalcopyrite. An example of this is the Aguablanca deposit, where although pyrite is an important phase in the semi-massive ore and an early study has revealed that it hosts traces of PGE, the presence and origin of PGE into the pyrite has not been investigated in detail. With this in mind, we have measured by laser ablation ICP-MS the content of these and other chalcophile elements (Au, Ag, Co, Ni, Cu, Se, Sb, As, Bi and Te) in pyrite exhibiting different textures. The results show that 1) large idiomorphic pyrite is compositionallyzoned with Os-Ir-Ru-Rh-As-rich layers and Se-Co-rich layers; 2) some idiomorphic pyrites contain unusually high PGE contents (up to 32 ppm Rh and 9 ppm Pt); 3) ribbon-like and small-grained pyrites host IPGE (i.e., Iridium-group PGE, Os, Ir, Ru and Rh) in similar contents (100-200 ppb each) to the host pyrrhotite; and 4) pyrites replacing to plagioclase are depleted in most metals (i.e., PGE, Co, Ni and Ag). Overall, the different textural types of pyrite have similar abundances in Pd, Au, Se, Bi, Te, Sb and As. Mineralogical and compositional data suggests that pyrite is the result of the activity of late magmatic/hydrothermal fluids that triggered the partial replacement of pyrrhotite and plagioclase by pyrite, probably due to an increase in the sulphur fugacity during cooling. During this episode, pyrites inherited the IPGE content of mineral to that was replaced, whereas other elements such as Pd, Au and semi-metals were likely partially introduced into pyrite via altering fluids. These results highlight that pyrite can host appreciable amounts of PGE and therefore it should not be overlooked as a potential carrier of these metals in Ni-Cu-(PGE) sulphide deposits.

Extreme enrichment of Se, Te, PGE and Au in Cu sulfide microdroplets: evidence from LA-ICP-MS analysis of sulfides in the Skaergaard Intrusion, east Greenland

“…The Te contents of magmatic sulfides are generally in the range of a few ppm (e.g., Dare et al 2010;Djon and Barnes 2012;Piña et al 2013, Prichard et al 2013Smith et al 2014). Our data show that around the Au zone, Te concentrations are in the tens to a few hundred ppm (Table 2; Fig.…”

“…Queffurus and Barnes 2015). For comparison, Se is generally present in sulfide minerals in the range of tens of ppm, up to around 250 ppm in some sulfide minerals (e.g., Dare et al 2010;Piña et al 2013, Prichard et al 2013Smith et al 2014) and up to 455 ppm in sulfides of the Lac des Isles Complex (Djon and Barnes 2012). The S/Se ratios of the Platinova Reef (mostly 190-800) are lower than any other magmatic sulfide deposit currently recorded (see review by Queffurus and Barnes 2015; Fig.…”

“…Laser ablation-ICP-MS is one of the most effective and advanced tools in determining the fine scale mineralogy and composition of minerals in general, and the application to determining the base, precious and semimetal contents of sulfide minerals has become a standard tool in characterizing magmatic sulfide ores (e.g., Ballhaus and Sylvester 2000;Holwell and McDonald 2007;Godel et al 2007;Godel and Barnes 2008;Hutchinson and McDonald 2008;Dare et al 2010;Holwell et al 2011;Piña et al 2013, Prichard et al 2013Smith et al 2014). In addition to determining the bulk compositions of sulfides, the technique also allows for the identification of whether elements are present in solid solution, or as discrete minerals or microinclusions.…”

Chalcophile and platinum-group element distribution in pyrites from the sulfide-rich pods of the Lac des Iles Pd deposits, Western Ontario, Canada: Implications for post-cumulus re-equilibration of the ore and the use of pyrite compositions in exploration

“…In contrast, the presence of pyrite in magmatic Ni-Cu-PGE deposits is less common. Recent studies have demonstrated that pyrite in these magmatic deposits contain PGE (Oberthür et al, 1997;Barkov et al, 1997;Dare et al, 2011;Djon and Barnes, 2012;Piña et al, 2012Piña et al, , 2013aOsbahr et al, 2013Osbahr et al, , 2014Smith et al, 2014). However, because pyrite is not abundant, very little attention has been paid to the processes that control the distribution of PGE in pyrite.…”

“…Furthermore, pyrite may remain stable under the highest grades of metamorphism owing to its high temperature stability and durability during deformation (Craig and Vokes, 1993). During its formation, pyrite can incorporate a large number of minor and trace elements as structure substitutions in the crystal lattice (Abraitis et al, 2004) that in some cases show compositional zoning (Chouinard et al, 2005;Craig and Solberg, 1999;Craig et al, 1998;Large et al, 2009;Piña et al, 2013a;Thomas et al, 2011). The compositional and textural features of pyrite are closely related to the conditions of pyrite formation and chemical characteristics of its host environment.…”