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Magmatism and Geodynamics in the Archaean
Published in O.A. Bogatikov, R.F. Fursenko, G.V. Lazareva, E.A. Miloradovskaya, A. Ya, R.E. Sorkina, Magmatism and Geodynamics Terrestrial Magmatism Throughout the Earth’s History, 2020
Granite–gneiss areas occupy 70–90% of the granite–greenstone terranes and are composed of polygenetic granitoid complexes of varying ages. The majority of them appear to be formed by the tonalitic–trondhjemite gneisses. The rest is considered to be a component of the greenstone belts themselves, in which migmatization, metasomatism and secondary melting of earlier granitoids play an important role. As shown by Samsonov et al. (1993), using the example of the Middle Dnieprov’e area (the Ukrainian Shield), endogenetic activities within the GGST and the granite–gneissic areas nearly coincided in time.
Formation of Cu–Au porphyry deposits: hydraulic quartz veins, magmatic processes and constraints from chlorine
Published in Australian Journal of Earth Sciences, 2023
G. N. Phillips, J. R. Vearncombe, J. D. Clemens, A. Day, A. F. M. Kisters, B. P. Von der Heyden
The host rocks for porphyry Cu–Au deposits span a variety of settings in the crust and mantle. The dominant minerals that link the main, unaltered host rocks of diorite, quartz diorite, monzodiorite and granodiorite are plagioclase, lesser K-feldspar and minor to moderate quartz contents, with additional biotite and hornblende. Granodiorites that are not associated with Precambrian trondhjemite–tonalite–granodiorite series can have a variety of origins. These origins include fractionation from enriched mantle parental magmas, such as K-rich diorites, and possibly magma mixing, although this is disputed (e.g. Frost & Mahood, 1987). Brown (2001) pointed out that granitic magmas (granites to granodiorites) are the necessary complements to the melt-depleted granulites commonly formed in the deep crust (e.g. Arth & Hanson, 1972; Otamendi et al., 2009). For the majority of granodiorites (and other I-type granitic rocks), Clemens et al. (2011) showed that the only mechanism that simultaneously explains their major-element, trace-element, isotopic and mineralogical characteristics is partial melting of pre-existing meta-igneous crustal rocks, with variable entrainment of the solid products of the melting reactions. Recent summaries of the evidence can be found in Clemens (2012) and Brown (2013). Some of the more mafic plutonic rocks (such as diorites and monzodiorites), which also host Cu–Au porphyry deposits, are likely to represent magmas produced largely through partial melting of enriched mantle and subsequent differentiation or hybridisation (e.g. Shaw et al., 1993).
Mapping geological configuration using geophysics data: an investigative approach in targeting iron ore, gold mineralization and other commodities, a case study of Toko-Nlokeng area (Nyong Greenstone Belt, SW Cameroon)
Published in Applied Earth Science, 2023
Yannick Saturnin Evina Aboula, Joseph Mvondo Ondoa, Paul-Désiré Ndjigui
The discovered Toko-Nlokeng IFs deposits are located in the Nyong Complex. The geological sketch map of the deposit is presented in Figure 2(b). The Toko-Nlokeng area hosts mainly gneissic basement, schist, amphibolite, garnetite, eclogitoid, quartzite, tonalite trondhjemite-granodiorite (TTG) granitoid, orthopyroxene-garnet (charnockitic) gneiss, mafic-ultramafic intrusion, dolerite and IFs (Odigui et al. 2019; Swiffa Fajong et al. 2022; Evina Aboula et al. 2023a, 2023b). These rocks have a general E–W-trending S1 foliation and SW–NE-trending S2 foliation (Binam et al. 2018) associated with numerous intrusions (granodiorite, tonalite, syenogranite and serpentinites). Its morphology is marked by horsts and grabens (Binam et al. 2018; Odigui et al. 2019). Some studies point out the alluvial gold potential of the study site, more precisely in Abiete and Toko-Nlokeng, where the gold grade in some streams varied from 0.35 to 3.7 g t–1 (Milési et al. 1980; Binam et al. 2018; Kouankap Nono et al. 2021; Evina Aboula et al. 2023b). The quantitative chemical analyses of this alluvial gold could originate from the mobilization of primary vein minerals (Ngo Bidjeck 2004; Binam et al. 2018; Kouankap Nono et al. 2021). Previous studies of iron deposits in this area were limited in morphological, lithostratigraphic, geochemical and mineralogical studies of soil profiles developed on the IFs (Odigui et al. 2019; Swiffa Fajong et al. 2022; Evina Aboula et al. 2023a, 2023b) and mining exploration results by Caminex/IMIC.
Mafic dykes of the southeastern Gawler Craton: ca 1564 Ma magmatism with an enriched mantle source
Published in Australian Journal of Earth Sciences, 2022
A. J. Reid, C. E. Wade, E. A. Jagodzinski
The Daly Head Metadolerite represents tholeiitic gabbros formed in an intraplate, continental to back arc setting (Figure 12a). Enriched lithospheric trace elements such as high Ba, Pb and La are common in continental flood basalts, which reflect a contribution from the continental lithosphere (Baker et al., 2000). Low to moderate combined Nb/La–La/Yb ratios suggest the source region for Daly Head Metadolerite is a mixed asthenospheric–lithospheric mantle source (Figure 12b). The trend in the data on Figure 12b suggests a mixing array with tonalite–trondhjemite–granodiorite (TTG) or GLOSS in the lithospheric mantle source. The overall SiO2 content of the Daly Head Metadolerite is relatively low, negative anomalies of Nb and Ta are modest and negative Ti anomalies are insignificant, suggesting the degree of crustal assimilation must be proportionally small, and therefore the geochemical enrichment could have been present within the mantle source prior to melt extraction.