Geology and rare-earth element geochemistry of highly evolved, molybdenite-bearing granitic plutons, Southeastern Desert, Egypt

Abstract

The field relations, mineralogy, and major and trace elements (including REE analyses of whole-rock samples and minerals) of granites and their associated molybdenite + uranium mineralized aplites in Southeastern Desert, Egypt, have been studied. The granites are leucocratic and mostly peraluminous in nature with muscovite increasing at the expense of biotite. The chemical and mineralogical characteristics of the granitic rocks indicate that their melts originated from the LILE-enriched mantle wedge by partial melting and are contaminated by crustal melts, followed by thermogravitational processes. Leucogranites with higher Na 2 O/K 2 O ratios from Um Dargag and Um Maiat crystallized under H 2 O-saturated equilibrium conditions in which the exsolved vapor continuously migrated away. The REE patterns of the granites studied are characterized by LREE enrichments and negative Eu anomalies. In comparison, the potassic aplites and the more sodic leucogranites are depleted in LREE, enriched in HREE and show more remarkable negative Eu anomalies. Allanite and monazite are the most important REE carriers in the granites. These minerals are strongly enriched in LREE, whereas fluorite and xenotime, which are more abundant in the aplites, are enriched in HREE. The average Lu/Ce ratio represents the fractionation trend with respect to HREE. It is 0.71 for radioactive fluorite, and it increases to 1.22 for non-radioactive fluorite. The high REE contents of molybdenite represent re-deposition of the mobilized Mo and REE. Due to the strong control of accessory minerals, the REEs are of limited use in petrogenetic modelling of highly evolved granitic systems.

Folate and homocysteine metabolisms and their roles in the biochemical basis of neuropsychiatry

“…Geochemically, these layers display the highest concentrations of Ca and Sr, as expected from the abundance of carbonates, but also of La. The relatively high La concentrations may be related to the supply of minerals such as monazite [(Ce, La, Pr, Nd, Th, Y)PO 4 ], allanite [(Ce, Ca, Y, La) 2 (Al, Fe +3 ) 3 (SiO 4 ) 3 (OH)] and bastnasite (Saleh 2007), a heavy mineral that is habitually deposited with coarse terrigenous particles. Lanthanum and Sc have significant negative Pearson correlations in this core.…”

Geochemistry of pyroxenites, amphibolites and their weathered products in the Nyong unit, SW Cameroon (NW border of Congo craton): Implications for Au–PGE exploration

“…The positive Ce anomalies in some samples are similar to those of unusual tridymite-hercynite xenoliths (Ce/ Ce ⁎~1 .2-2.5) in middle Miocene Niutoushan tholeiites from the southeast coastal area of China (Zou et al, 2004). The negative Eu anomalies could result from the high degree of plagioclase Coarse-garnet type Fine-garnet type Non-garnetiferous type Amphibolites fractionation (Lee et al, 2009;Saleh, 2007). According to Lee et al (2009), voluminous plagioclase growth removes significant Eu 2 + from the system during magma crystallization and this reduction of total Eu limits the Eu 3 + available to zircon, resulting in progressively more negative Eu anomalies in later grown zircon.…”

Geochemical Characterization of Vertisols Developed on Granites from Kaele, North-Cameroon: Implications for REE Exploration

“…The positive or absence of Eu anomalies could be linked to the stability of Eu rich minerals. Definitely and despite the variable values, the low REE contents in general may result from depletion of REE rich-minerals [39,48] as confirmed by petrographycal observation.…”

“…Several authors [44,46,47] have explained that the high LREE concentrations in granite suggest that the liquid mantle might have been enriched in light REE. In general, accessory minerals such as monazite, apatite and zircon control the REE contents in granitoids [48]. Monazite is responsible for most of LREE abundance while zircon controls most of HREE [39].…”

“…The negative europium anomalies may result from high degree of plagioclase fractionation at the early stage of weathering, notably in reducing conditions [48]. The positive or absence of Eu anomalies could be linked to the stability of Eu rich minerals.…”