Platinum-group and trace elements in Cu-sulfides from the Loolekop pipe, Phalaborwa: implications for ore-forming processes

Three-dimensional textural investigation of sulfide mineralisation from the Loolekop carbonatite–phoscorite polyphase intrusion in the Phalaborwa Igneous Complex (South Africa), with implications for ore-forming processes

“…Sulphide layer textures do not show homogeneous characteristics, consistent with operation of several independent but similar ore-forming events (Mao et al 2008). Bras et al, 2021). The presence of elongated sulphide assemblages with diameters of ~1 mm implies coalescence between sulphide droplets (Lesher and Groves, 1986;Robertson et al, 2015).…”

“…These sulphide networks are classified as disseminated grains in this study due to the size of the fractures allowing hydrothermal fluids to circulate which is below the microCT resolution. Bras et al (2021).…”

“…Chalcopyrite, as part of this mineralisation, is commonly associated with cubanite, the latter being present either as exsolution lamellae or grains (Lombaard et al, 1964;Palabora Mining Company Ltd Staff, 1976;Le Bras et al, 2021). The second chalcopyrite type occurs as disseminated grains (50 to 500 µm) associated with small modal amounts of bornite within banded carbonatite and phoscorite, and is present in minor amounts relative to chalcopyrite (Palabora Mining Company Ltd. Staff, 1976).…”

“…The corresponding 3D model does not show any link between such alignments and the hydrothermal vein itself. The absence of disseminated grains and cumulates suggests that such preferred orientations may have resulted from the filling of fractures with sulphides within the gangue, possibly by hydrothermal fluid precipitation associated with mineral dissolution (Le Bras et al, 2021).…”

“…Yet, primary ore-forming and late-stage alteration processes have not been entirely characterised (Heinrich et al, 1970;Palabora Mining Company Ltd Staff, 1976;Vielreicher et al, 2000). Stable isotope (Fe and Cu) and trace element analysis on Cu-sulphides revealed the presence of a magmatic monosulphide solid solutionintermediate solid solution (iss -mss) system in the Loolekop carbonatite -phoscorite intrusion (Le Bras, 2020;Le Bras et al, 2021), but the mechanisms responsible for magmatic sulphide textures operating during the late stages of magma ascent remain unclear. Previous detailed research was made on the basis of optical and electron microscope observations, as well as electron microprobe analysis of Cu-sulphides on epoxy mounts and thin sections (Rudashevsky et al, 2004;Giebel et al, 2017).…”