Geochemical and genetical constraints on rare metals mineralization at the central Eastern Desert of Egypt.

Abstract

Rare metals mineralization in Jabal Gattar, N. E. Egypt, occurs at the sheared tectonic contact between a younger granite and Hammamat sediments. The contact is affected by a local reverse fault directed N75°E and dipping 45°SSE. The Hammamat sediments consist substantially of rhythmic siltstones and immature greywackes. The paragenetic history of the mineralized sediments involves many types of alteration, such as dissolution of primary quartz (episyenitization), sericitization, albitization, hematization, pyritization, silicification, kaolinization and bleaching. The calculation of the mass-balance indicates preferential mobilization of REE, Rb, Cs, Be and S from Gattar granite to Hammamat sediments in the alteration zone. The elements; U, Y, W, Nb, Cu, Pb, Sb and Zn are enriched in both granite and sediments, but with higher magnitude for the latter. The hematized sediments are generally better accumulators for rare metals.The Gattar granite is classified as a meta-aluminous leucogranite, containing low Ca and high alkali. The low Ba and Sr and the high REE + Y reflect a highly fractionated (low P) A-type granite. The mineralized granite is affected by several metasomatic alterations. The mineralization causes enrichment in the content of U, Nb, W, Y and the chalcophile elements. The REE content displays portioning towards preferential mobilization of the LREE to the adjacent mineralized Hammamat sediments while higher quotient of the HREE is adopted within the secondary fluorite. The volume loss of granite due to leaching reactions (e.g., episyenitization) causes apparent enrichment of the immobile elements such as Sc, Th and Zr.The mineralization was caused by alkaline and oxidizing hot fluids, with contribution of meteoric water volume heated by convection. The hot fluids flowed up along ENE-WSW and NE-SW faults to cause a rather complicated series of metasomatic reactions. The rare metals were mobilized from the younger granite pluton of Gattar and concentrated in the sheared tectonic contact. The reaction of the mineralizing solutions with the wall rocks and the pseudomorphic oxidation of pyrite caused reduction and fixation of uranium. The study area can be considered as a possible potential deposit for U, REE + Y and other rare metals as well.wide spread in Sinai and the Eastern Desert of Egypt. They represent the magmatic activity making the end of the cratonization process of the PanAfrican orogeny and many of them are affected by post magmatic deuteric and hydrothermal alterations associated in many places by rare metals mineralization. These post-orogenic discordant massive younger granite plutons are high in SiO 2 , low in Ca and Mg and have low 87 Sr/ 86 Sr (Rogers and Greenberg, 1983). The younger gran-

Mineralogical, REE-geochemical and fluid inclusion studies on some uranium occurrences, Gabal Gattar, Northeastern Desert, Egypt

“…This means that surface water could be a favourable factor for secondary uranium concentration in the study area. El-Kammar et al (2001) gave the same conclusions about the secondary uranium deposits at the GV occurrence. During the pluvial period, the underground water level was raised and consequently the underground water can also play a role in the formation of secondary uranium under suitable conditions of temperature and pH.…”

“…The relative enrichment in the HREE (Tm, Yb and Lu) can be attributed to the presence of the high contents of xenotine and zircon which are traditionally known as HREE accumulators (El-Kammar et al, 2001;Mahdy and El Kammar, 2003;Abla et al, 2005. The negative Eu anomaly (Eu/Eu * ) increases markdly from ratio of 0.22 in the altered granite at the GII occurrence to 0.02 at the GV occurrence.…”

“…1). In this occurrence uranium mineralization is mainly confined to the Hammamat sediments rather than the granitic rocks, in which few sporadic uranium mineralizations of spotty nature were recorded (El-Kammar et al, 2001).…”

“…The mineralogical composition of these deposits is dominated by secondary U-minerals (Dawood and Abdel-Naby, 2001). Gabal Gattar was geologically investigated by El Rakaiby and Shalaby (1992), Roz (1994), and El-Kammar et al (2001), among others. Hussein and Sayyah (1992) estimated as much as 4000 tons of uranium in the mineralized granites in the G. Gattar area.…”

Mineralogy and geochemistry of Nb-, Ta-, Sn-, U-, Th-, and Zr-bearing granitic rocks from Abu Rusheid shear zones, South Eastern Desert, Egypt

“…Irber (1999), and Vuorinen and Hålenius (2005) emphasized the role of alkali metasomatism as an efficient mechanism for the separation between the two isovalent cations, i.e., Nb and Ta. This mechanism seems to be effective in the study area, as well as in many other occurrences of younger granites in the Eastern Desert of Egypt (El-Kammar et al, 2001). The Nb/Ta ratios of two mineralized granites are about 9.02 in the northern zone and 8.94 in the southern shear zone, respectively.…”