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Lexicon of lithostratigraphic units for the Sudan
Published in J.R. Vail, Lexicon of Geological Terms for the Sudan, 2022
In the Sudan the term has been applied (Almond et al. 1969) to most ring-complexes although Almond (1979) attempted to distinguish between late-orogenic and anorogenic (the true Younger Granite) igneous intrusions. The dominant rock types are alkaline and peralkaline granites, quartz syenites, and more rarely gabbros. Extrusive phases may be preserved. Ring-dykes, cone-sheets and radial dykes are also characteristic.
Geological, geochemical and geophysical characteristics of geothermal fields
Published in D. Chandrasekharam, Jochen Bundschuh, Low-Enthalpy Geothermal Resources for Power Generation, 2008
D. Chandrasekharam, Jochen Bundschuh
The Olkaria volcanic complex consists of about 80 volcanic centers. Both central and fissure eruptive styles of volcanism have given rise to pyroclastic cones and thick lava flows (Clarke et al. 1990). The volcanic rocks include peralkaline rhyolites. A simplified volcanic stratigraphy of Olkaria geothermal field is shown in Figure 5.27.
Geophysical and geochemical characteristics of western Xar Moron suture zone
Published in Petroleum Science and Technology, 2019
Xianli Du, Xuanlong Shan, Xiaojuan Dai, Jian Yi, Rongsheng Zhao, Tiantian Du, Jiayi Wu, Xianfang Du, Hongbo Shi, Qingfa Meng
In the K2O-SiO2 discriminant diagram (Figure 5a), the rock samples in the study area fall on the high potassium series, except for the Jurassic syenogranite falling in the potassic series and the Carboniferous quartz diorite falling in the calc-alkaline series. In the discriminating diagram of the main elemental tectonic environment of the granite (Figure 5b), the samples are belonging to the island arc granite, continental arc granite and continental collision granite, except for a Permian monzonitic granite which is related to the rift valley and the continental uplift and a sample of Jurassic syenogranite fall apart from post-orogenic granite. Combined with the Harker diagram of the magmatic rock sample in the study area (Figure 7), it is shown that the magmatic rock samples are not homologous, which indicates that the magma source has a mixed source of oceanic crust and mantle. In the granite Rb-(Y + Nb) discriminant diagram (Figure 5c), all the samples are belonging to the volcanic arc granite (VAG), the range of Rb varies greatly, indicating that the continental material pollution is serious, suggesting that the granite formed under the subduction environment. In the granite A/NK-A/CNK discriminant diagram (Figure 5d), seven of the samples are belonging to the peraluminous area, one Permian volcanic sample is belonging to the peralkaline area, and the Jurassic sample is belonging to the metaluminous area, it indicates the post-subduction conversion mechanism and the magmatism of the mixed source of crust and mantle in the continental collision environment.
Carbonatites: related ore deposits, resources, footprint, and exploration methods
Published in Applied Earth Science, 2018
George J. Simandl, Suzanne Paradis
Alkaline-carbonatite complex-related ore deposits represent large resources in terms of REE (Figures 21(a, b) and 22(a), e.g. Bayan Obo, China; Maoniuping, China; Mountain Pass, USA; and Mount Weld, Australia). Most of these deposits are strongly enriched in LREE and have a high LREE/REE(total) ratio relative to peralkaline intrusion-related, and ion adsorption clay deposits (Mariano 1989a, Simandl 2014; Verplank et al. 2016); however, they also contain significant resources of heavy rare earth elements (HREE; Figure 22(b)). Under current market conditions, concentrates of REE-bearing minerals from typical alkaline-carbonatite complex related deposits are the main source of LREE. The ion adsorption clay deposits are low grade relative to alkaline–carbonatite intrusion-related- and peralkaline intrusion-related deposits and can't compete effectively against high-grade-carbonatite-related deposits as a source of LREE (Figure 22(a, b)). However, because peralkaline complex-related REE deposits are metallurgically challenging (Verbaan et al. 2015), and carbonatite concentrates have a high LREE/REE(total) ratio, the REE-bearing ion adsorption deposits which benefit from simple and cost-effective metallurgy are currently the main source of HREE (Simandl 2014). With the exception of the LREE-enriched, loparite and eudialyte–bearing, nepheline-feldspar-aegirine pegmatite at Lovozero (Russia), there is currently no production of REE from peralkaline intrusion-hosted deposits.
Occurrence, geochemistry and provenance of REE-bearing minerals in marine placers on the West Coast of the South Island, New Zealand
Published in New Zealand Journal of Geology and Geophysics, 2021
Stephanie L. Tay, James M. Scott, Marshall C. Palmer, Malcolm R. Reid, Claudine H. Stirling
Three REE-bearing phosphates were identified: apatite, monazite and xenotime. Apatite REE abundance is sensitive to the igneous rock alumina saturation. Apatites from a peraluminous source (such as an S-type granite) typically have flat REE patterns with pronounced negative Eu anomalies (Bea 1996; Sha and Chappell 1999; Chu et al. 2009), whereas metaluminous granite-derived apatite characteristically has a positive slope in the LREE, moderate negative Eu anomaly and a mostly flat HREE pattern (Bea 1996). Apatite with a negative slope from relative LREE enrichment and HREE depletion could come from either a peralkaline source (Bea 1996) such as an A-type granite (e.g. Foulwind Granite (Tulloch et al. 2009)) or a metaluminous granitoid (Sha and Chappell 1999; Chu et al. 2009) such as the Separation Point Suite (Muir et al. 1995) or parts of the Hohonu Batholith (Waight et al. 1998b). If there is little variation in apatite composition in different potential source rocks (e.g. compositions not affected by evolution of host magma), then Hector and Little Wanganui have at least one grain each with a REE pattern indicative of derivation from a metaluminous or peralkaline granite, and have therefore been supplied from the Separation Point Suite and/or Foulwind Granite. Although the trace element compositions for metamorphic apatite have been less studied compared to magmatic apatite, metamorphic apatite is thought to be depleted in Th and REE including Y (Henrichs et al. 2018). Nineteen apatite analyses with low concentrations of Y, La, Ce, Nd, Yb and Th may therefore be from metamorphic, mainly metasedimentary, rocks of the Alpine Schist (Figure 4c).