Very good but very technical but in layman's terms this extraction seems to fit the language and story form management
Comparison with other layered intrusions
In comparison to the Bushveld Complex of South Africa (Teigler and Eales
1996; Roelofse and Ashwal
2012; Barnes’ unpublished data), olivine from the Jameson Range crystallised from a significantly more evolved magma than olivine from the Lower Zone (Fig.
6a). Moreover, plagioclase and orthopyroxene compositions indicate that the Jameson Range is broadly equivalent to the most evolved parts of the Main Zone or the lower part of the Upper Zone of the Bushveld Complex (Fig.
6b). Magnetite from the Jameson Range is highly enriched in Fe, V and Cr relative to magnetite from the well-studied Emeishan layered intrusions in SW China described by Liu et al. (
2015). Moreover, the highest V concentrations in magnetite from the Upper Zone of the Bushveld Complex (∼10,000 ppm V, Tegner et al.
2006) are also lower than in magnetite from the Jameson Range (Fig.
7b). The highest Cr concentrations in magnetite from the Emeishan layered intrusion were reported for the Hongge intrusion which hosts a number of magnetite layers in clinopyroxenites rather than **broic rocks (Bai et al.
2012). The compositional range of the Jameson Range magnetite clearly suggests a magmatic origin of magnetite. Tegner et al. (
2006) showed that the V concentrations in magnetite from the Upper Zone of the Bushveld Complex decrease dramatically with stratigraphic height, whereas V concentrations in magnetite from the Emeishan layered intrusions decrease gradually (Fig.
7b, c). Hence, the evolution of the magnetite chemistry in the Jameson Range strongly resembles that of the Bushveld Upper Zone.
In the Bushveld Complex, P-rich layers occur together with a suite of magnetitites in the upper third of the Upper Zone (e.g. Cawthorn et al.
2006). Tegner et al. (
2006) reported six nelsonite (magnetite-ilmenite-apatite) layers within the western Bushveld Complex, some of which are currently being explored in the northern limb of the Bushveld as they could have economic significance. In the Jameson Range, P-rich layers already occur in the lower half of the Upper Zone, i.e. at a lower stratigraphic level than in the Bushveld Complex. Their P grade is significantly lower than that of the nelsonites from the Bushveld Complex, but the relatively poor exposure constitutes significant added exploration potential.
Another remarkable occurrence of massive magnetite layers hosted by an Emeishan layered intrusion is the **broic Panzhihua intrusion (Zhou et al.
2005; Zhou et al.
2013). Multiple lenses and layers of massive magnetite in layered (melano-)**bro occur in the lower portion of the intrusion. Zhou et al. (
2005) reported up to 0.87 wt% V
2O
5 and 15.5 wt% TiO
2, respectively, which is significantly lower compared to the PGE-rich magnetitite from the Jameson Range. However, P
2O
5 concentrations in the Panzhihua intrusion are comparable with up to 2.59 wt%.
In some cases, magnetite-rich lithologies in the upper parts of layered intrusions also show an enrichment in PGE. Globally, this reef-type PGE mineralisation can be broadly subdivided into two groups: (1) PGE mineralisation hosted by magnetitites, such as in the Stella intrusion in South Africa (Maier et al.
2003), the Rio Jacaré intrusion in northeastern Brazil (Sá et al.
2005), the Coldwell Complex in Ontario (Barrie et al.
2002) and the Bushveld Complex (von Gruenewaldt
1976), and (2) PGE mineralisation in magnetite-**bros, such as the Koitelainen intrusion in northern Finland (Mutanen
1997), the Rincón del Tigre intrusion in Bolivia (Prendergast
2000), the Sonju Lake intrusion in Minnesota (Joslin
2004) and perhaps the Skaergaard intrusion in east Greenland, even though in the latter the spatial association to magnetite enrichment is not as clear (Andersen et al.
1998; Holwell and Keays
2014).
All of these reefs are characterised by relatively low modal abundances of sulphides, reaching 1 to 2 % at most.
The mineralogy of the mineralisation is also exceptional as most of the intrusions, except for Rio Jacaré and Stella, are dominated by Cu-rich sulphides with high Cu/Fe ratios, including bornite and chalcopyrite, whereas pyrrhotite is often absent.
The only other known magmatic occurrence of bornite hosted by mafic-ultramafic lithologies is in the Okiep district of Namaqualand, South Africa (Cawthorn and Meyer 1993; Maier 2000).
Another important characteristic of the PGE-mineralised magnetitites is the Ni depletion which is generally attributed to the prolonged fractionation of olivine and pyroxene prior to sulphur saturation (Leeman and Lindstrom
1978).
Geochemically, these reefs can be recognised by a sharp increase in Cu/Pd ratios above the PGE-rich interval and Pt/Pd ratios mostly above unity.
The basal magnetitite from the Jameson Range exhibits very similar characteristics in terms of mineralogy and geochemistry compared to the reefs described above (Figs. 4 and 10a, b). Hence, the Jameson Range magnetitite meets all criteria to be considered a “Stella-type” reef as defined by Maier et al. (2003).
In contrast, the magnetitite intersected in drill hole WMTD2 exhibits no enrichment in PGE and the mineralogy is dominated by a typical magmatic sulphide assemblage comprising pyrrhotite, chalcopyrite and minor pentlandite.
(20min delay)