The 1.88 Ga Kotalahti and Vammala nickel belts, Finland: Geochemistry of the mafic and ultramafic metavolcanic rocks

Abstract

The mafic and ultramafic volcanic rocks within the Svecofennian (1.88 Ga) Kotalahti and Vammala Nickel Belts, Finland, are spatially associated and coeval with a suite of mineralized mafic-ultramafic intrusions. They have been divided into five suites based on major element geochemistry and spatial distribution: the Rantasalmi high-and low-Mg suites, the Vammala high-Mg suite, and the Rantasalmi, Kestilä and Pielavesi low-Mg suites. The Rantasalmi and Vammala high-Mg suites are very similar and probably comagmatic, and the Kestilä and Rantasalmi low-Mg suites are derived from them by a combination of fractionation and crustal assimilation. The Pielavesi suite is interpreted as an unrelated suite of island-arc affinity. On the basis of their trace element contents, the Kotalahti Belt intrusions are comagmatic with part of the analyzed volcanic rocks. In the Vammala Belt it is likely that the parent magmas to the intrusions and picrite magmas have a common mantle source but have evolved along distinct paths, and the picrites probably do not represent parent magmas tapped directly from the intrusions. Platinum-group element data show localised evidence for depletion by sulfide extraction. Vammala picrites are predominantly S-undersaturated, with the exception of lavas in the Stormi area. In the Kotalahti Belt the volcanic rocks are predominantly S-undersaturated, while the volcanic rocks in the more northern part of the Belt are predominantly S-saturated. These spatial differences imply that the PGE contents of the metavolcanic rocks can be used as regional area selection criteria for intrusive nickel-copper-(PGE) deposits within the Finnish Svecofennian.

Petrogenesis of the ∼2·77 Ga Monts de Cristal Complex, Gabon: Evidence for Direct Precipitation of Pt-arsenides from Basaltic Magma

“…Such levels are at the upper end of Pd contents in global basalts (Fiorentini et al, 2010;Maier et al, 2013). Other examples of Pd rich basalts include Finnish 2.45 Ga tholeiitic dykes having up to 30-35 ppb (Guo et al, 2012), and Svecofennian basalts reaching 25 ppb (Barnes et al, 2009). In contrast to Pd, the measured Pt contents of the MdC cumulates are far too high to be explained by a trapped liquid component.…”

Petrography, geochemistry, and geochronology of the Sc-enriched Kiviniemi ferrodiorite intrusion, eastern Finland

“…Fe-Ti-P-enriched mafic intrusions in the western parts of the CFGC area (post-kinematic and synorogenic) include a quartz diorite-wehrlite layered intrusion, ilmenite gabbros, and apatite-ilmenite-magnetite gabbros (Rämö 1986;Kärkkäinen and Appelqvist 1999;Rämö et al 2001;Kärkkäinen and Bornhorst 2003). In the eastern parts of the CFGC, the focus of exploration has been on Ni-Cu-enriched intrusions along the Proterozoic-Archaean boundary zone (Barnes et al 2009). In general, the small mafic intrusions of the area are amphibole-and pyroxene-bearing gabbros and diorites; rare ultramafic rocks are present as inclusions or as small igneous bodies.…”

The mineral system approach applied to magmatic Ni–Cu–PGE sulphide deposits

“…Compressional settings are implicated in the deposits of the northern Appalachian Belt in Maine (Thompson and Naldrett, 1984), the Svecofennian Raahe-Ladoga and Vammala Belts in Finland (Peltonen, 1995, Barnes et al, 2009, Eilu et al, 2012, Aguablanca in Spain (Ortega et al, 2004, Pina et al, 2006 and possibly Jinchuan in China (Lehmann et al, 2007) among others.…”