This might explain our rising price people are getting excited about the Komatiites. they are associated with Fe,Co,Ni,Au,Cu,TI,Bi, and PGE's and can be strongly enriched in Ni, Cu, Au, PGEs and other chalcophile elements,whichmay accumulate to form ore deposits directly or be dispersed in the komatiites.
Another interesting aspect of komatiitic magmas is their importance in ore forming processes. They are among the few mafic/ultramafic lavas types that are S-undersaturated at the time of magma formation and do not reach S- saturation until a late stage in their ascent from the mantle. This S- undersaturation is due to the high temperature of these magmas produced by large degrees of partial melting of upper mantle source regions that were already depleted in S through earlier partial melting events. S-saturation of magmas leads to depletion in the chalcophile metals, in contrast komatiitic magmas retain the full complement of chalcophile elements (including Fe, Co, Ni, Au, Cu Tl, Bi and PGEs) that the magma derived from the mantle source. When they become S-saturated they may form sulphides, strongly enriched in Ni, Cu, Au, PGEs and other chalcophile elements, which may accumulate to form ore deposits directly or be dispersed in the komatiites (Keays, 1995). Platinum-group element (PGE) abundances including Os, Ir, Ru, Pt, Pd have been reported in komatiites (Table 4). PGEs are present at higher levels in komatiites than in basalts making komatiites better probes of mantle PGE abundances (Puchtel and Humayun, 2000). In accordance with these authors, the spinifex-textured (MgO = 25 - 28%) and cumulate (MgO = 34 - 37%) komatiites are moderately enriched in Pt and Pd relative to Os and Ir with (Pt/Os)N = 2.5±0.4, and exhibit chondritic (Os/Ir)N = 0.98±0.06 ratios. Generally it is observed that, in ultramafic magmas, PGEs are very strongly and roughly equally enriched in any sulphide or metallic minerals that are present. They can provide unique information on the important role that sulfur plays during magmatic processes, a role still ignored by most petrochemists. It has been observed in many geological shields (e.g. Yilgarn, Perseverance, Pilbara, Zimbabwe, Kambalda, Abitibi terrains) that abundant komatiites host magmatic sulphide deposits rich in nickel (Barnes et al., 1995; Moore et al., 2000; Lahaye et al., 2001; Barnes, 2004; Hill et al., 2004and show high content of Ni. Almost all of the largest known concentrations of komatiite- hosted Ni sulfide deposits (but also Fe-Cu-PGE deposits) formed during the Archean. However, some komatiites of Permian-Triassic age (Northwestern Vietnam) are also associated with Ni-Cu-(PGE) bearing deposits (Glotov et al., 2001). Magmatic Ni-Cu sulphides strongly influence the precious metal contents of komatiites because they are greatly enriched in these metals relative to crustal rocks (Keays, 1982). Most komatiite-associated magmatic Ni-Cu-(PGE) sulfide deposits formed from sulfide undersaturated magmas and are interpreted to have formed in dynamic lava channels or magma conduits by incorporation of crustal sulfur. They commonly exhibit geochemical and isotopic evidence of crustal contamination (e.g., Th-U-LREE enrichment, negative Nb-Ta-Ti anomalies) and chalcophile element depletion on the scale of individual cooling units (Lesher et al., 2001). Thermal erosion and incorporation of sulphur-rich sea-floor sediments have been proposed as a mechanism by which the komatiites were brought to sulphide saturation (Huppert et al., 1984; Groves et al., 1986; Lesher and Groves, 1986). Among the chemical analyses for determining PGE abundance in komatiites, osmium has been studied in detail, particularly its isotopic composition. As with modern plumes, the sources of Archean and Proterozoic komatiites exhibit a large range of initial 187Os/188Os ratios. Most komatiites are dominated by sources with chondritic Os isotopic compositions (e.g. Song La, Norseman-Wiluna, Pyke Hill, Alexo), though some (e.g. Gorgona) derive from heterogeneous sources (see Table 4). Some komatiites are enriched in 186Os and 187Os (Brandon et al., 2003; Gangopadhyay et al., 2003). The coupled enrichments of 186Os/188Os and 187Os/188Os are very similar to those displayed by the Hawaiian and Siberian plumes. Such enrichments could originate from the addition of ancient hydrothermally altered or metalliferous sediments into the source of plumes (Ravizza et al., 2001). But this is contradicted by mixing models and another explanation for the Os isotopic variations involves Os transfer from the outer core to the lower mantle in the late Archean (Puchtel et al., 2001; Brandon et al., 2003).
Finally, one of the last attractive discoveries about komatiites has been the report of diamonds (Capdevila et al., 1999). Abundant diamonds ranging from microdiamonds size up to 4 mm were found in a volcaniclastic komatiite from the Proterozoic Dachine island arc in French Guiana, South America. This recent discovery was quite unexpected as the tectonic setting is distinct from that of all other currently exploited diamond deposits. It places significant constraints on the origin of komatiite magmas and the manner in which they interact with hydrated mantle in subduction zones. Capdevila et al. (1999) proposed that a primary, anhydrous komatiite magma formed by deep melting, then penetrated hydrated lithosphere beneath the ancient island arc where it collected both water and diamonds. As komatiite magma interacted with the relatively cool hydrated base of the mantle wedge, it become hydrous, its temperature and density decreased dramatically and it was ejected to the surface, bringing with it diamonds. The discovery implies also that some komatiites must have originated at depths of ~250 km or greater. It has been proposed that diamonds can be natural time capsules, preserving information about the cycling of sulfur between Earth's crust, atmosphere, and mantle some 3 billion years ago (Farquhar et al., 2002). These authors report that diamonds from a region in Botswana, Africa contain a distinctive ratio of three isotopes of sulfur. The presence of this ratio indicates that the sulfur in these diamonds went through a nearly complete geochemical cycle. Thus, diamonds are valuable crystals through which geologists and atmospheric chemists can peer to gain insights into the Earth's atmosphere as it existed billions of years ago. Whereas the petrological features of komatiites have been the purpose of a wide range of studies, relatively little is known about their volatile abundances because of significant alteration of rocks and lack of fresh glasses. Despite claims to the contrary, some komatiites display evidence of being volatile- bearing like hydromagmatic amphiboles (Stone et al. 1997), and degassing structures i.e. segregation structures and vesicles/amygdales (Beresford et al., 2000). Studies of melt inclusions in olivines provide information about volatile contents of komatiites (McDonough and Ireland, 1993; Woodhead et al.,2005). For example, melt inclusions found in nearly fresh Belingwe komatiites contain up to 1.1 wt% of water, detectable CO2(up to 200 ppm), sulfur (500-750 ppm), chlorine (400-700 ppm) and Cl with Cl/K2O ratios ∼0.8 – 1.5 (Woodhead et al., 2005). In many komatiite sequences worldwide, there is a strong spatial correlation between volatile-rich phases or vesicles/amygdales, and different styles of komatiite-hosted Ni-Cu-(PGE) sulphide mineralisation. However, it is unclear whether the volatile content of mineralised sequences plays a role in the genesis of komatiite-hosted NiS mineralisation, either in the control of sulphur solubility or/and in the concentration of sulphide blebs (Fiorentini et al., 2005).
all the best
FireflyOne The writer's opinions are his own and do not constitute financial advice in any ways.Nothing here constitutes an investment recommendation nor should anything written here or published by myself be relied upon for any investment activities.I strongly recommend that you perform your own independent research and/or speak with a qualified investment professional before making any financial decisions.
SGQ Price at posting:
7.8¢ Sentiment: Hold Disclosure: Held
and show high
