PDF Publication Title:
Text from PDF Page: 189
REE Mineralogy and Resources Chapter 279 153 Kimberlite is thought to form at depth less than 300 km, and CO2-rich kimberlite and carbonatite may be produced by partial melting of carbonated lherzolite. Although kimberlite geochemistry is complex and because of its hybrid nature, it is difficult to determine the compositions of original melt, like carbonatite, kimberlite is enriched in LREEs, suggesting garnet was a residual phase in their source regions (Table 4 and Fig. 14) (Winter, 2010). Alkaline rocks occur not only in the rift zones, but also in other tectonic settings such as continental and oceanic intraplate settings and subduction zones, particularly in backarc setting or in the waning stages of magmatic activ- ity (Winter, 2010). Alkaline rocks are deficient in SiO2, with respect to Na2O, K2O, and CaO to the extent that they become undersaturated in SiO2. On the other hand, some rocks may be deficient in Al2O3 so that Al2O3 may not be able to accommodate the alkalis in normative feldspars. Such rocks are called peralkaline and may be either silica undersaturated or silica oversaturated. In the continental rift zones, high volume and short duration alkaline mag- matism are recognized. These zones are characterized by ascending astheno- spheric mantle, which form various types of alkaline magmas in addition to tholeiitic magmas at shallow depths (as shallow as 50 km) by partial melting at the beginning of the rifting (Winter, 2010). The primitive alkali basalt magmas are generally interpreted to form by small degree (1–3%) of batch melting of a source mantle at the base of continental lithosphere that is scarce in garnet, resulting in a slightly more enrichment of HREEs compared with carbonatite and kimberlite (Fig. 14). Large peralkaline plutonic complexes cluster in the older-age eroded con- tinental rift zones, represented by Kola Peninsula in Russia, Northern South Africa, and northeastern Canada (Ernst and Bell, 2010). These peralkaline complexes are heavily differentiated and commonly include carbonatite units (eg, Downes et al., 2005; Ernst and Bell, 2010; Femenias et al., 2005; Harmer, 1999). The origin of the nepheline syenite, major constituent of these peral- kaline complexes, is interpreted as the result of fractional crystallization from alkaline ultramafic magmas. Such nepheline syenite at Kola Peninsula, Russia, has LREE-enriched patterns, which are similar to those of carbonatite, kimberlite, and alkali basalt in the same region, although total concentration of REE of nepheline syenite is quite variable because of extensive fractional crystallization and accumulation of the magma (Downes et al., 2005). 2.4 Magmatic Crystallization and REE Enrichment The REE concentrations of the primitive magmas for various rock types are not high enough to reach typical ore grades that are found in economical mineral deposits, even in the case of carbonatites which commonly contain up to a few thousand ppm of REEs. The magmatic processes subsequent to melt forma- tion, ie, (1) accumulation, (2) immiscibility, and (3) fractional crystallization are important to increase REE concentration to the economic grades.PDF Image | HANDBOOK ON THE PHYSICS AND CHEMISTRY OF RARE EARTHS
PDF Search Title:
HANDBOOK ON THE PHYSICS AND CHEMISTRY OF RARE EARTHSOriginal File Name Searched:
Chemistry-Rare-Earths-49.pdfDIY PDF Search: Google It | Yahoo | Bing
Sulfur Deposition on Carbon Nanofibers using Supercritical CO2 Sulfur Deposition on Carbon Nanofibers using Supercritical CO2. Gamma sulfur also known as mother of pearl sulfur and nacreous sulfur... More Info
CO2 Organic Rankine Cycle Experimenter Platform The supercritical CO2 phase change system is both a heat pump and organic rankine cycle which can be used for those purposes and as a supercritical extractor for advanced subcritical and supercritical extraction technology. Uses include producing nanoparticles, precious metal CO2 extraction, lithium battery recycling, and other applications... More Info
CONTACT TEL: 608-238-6001 Email: greg@infinityturbine.com (Standard Web Page)