Origin and hydrothermal alteration of rare-metal granites in the Al-Hamra area, northeastern Arabian Shield, Saudi Arabia

Abstract

The Jabal Hamra (538 Ma) and Jabal Abu ad Dud plutons in northeast Saudi Arabia are epizonal bodies consisting of alkali feldspar granite and alkali feldspar syenite. Fracture-controlled zones of highly altered granites are recorded along the margins of the plutons. The granites intrude metamorphosed volcano-sedimentary successions of the Matran Formation. The rocks of the two plutons are chemically indistinguishable. They are characterized by above-average Th, Nb, Y, Ta, Hf and Zr, very low CaO, TiO 2 , MgO, FeO and MnO, and by high contents of rare earth elements (REE). Tectonic discrimination diagrams suggest an intra-plate environment, with many geochemical and mineralogical features resembling post-orogenic A-type granites. Numerous local and regional geologic constraints indicate that the plutons were intruded in an extension-related setting following the cessation of Neoproterozoic arc-related magmatism. Geochemical data are consistent with their derivation by partial melting of depleted crust followed by fractional crystallization of feldspars, ferromagnesian minerals and REE-rich accessory phases. The radiogenic isotope data [eNd (T) values are +3.5 to +4.2] indicate that the granite magma was generated from a 'juvenile' source, which is typical of the rocks making up most of the Arabian-Nubian Shield. Rare-metal mineralization is associated with the fracture-controlled alteration zones that occur at Jabal Al Hamra and Jabal Abu ad Dud. The altered rocks are characterized by higher TiO 2 , Fe 2 O 3 , SiO 2 and lower Al 2 O 3 , CaO, Na 2 O, than the unaltered rocks. They show high and wide range in the total REE contents (804-15579 ppm), , Nb (51-3483 ppm), Hf (13-368 ppm), Zr (394-14887 ppm), Th (16-572 ppm) and U (4-143 ppm). Field observations and further petrographic and chemical studies suggest that the altered rocks and the rare metal enrichment are the products of hydrothermal-metasomatic alteration of the quartz alkali feldspar syenite and the alkali feldspar granite. The rare-metal enrichment was explained by orthomagmatic fluid transport of these elements as fluoride complexes, and their subsequent deposition as a result of mixing with externally derived Fe-rich fluids.

The Geochemistry, Petrogenesis, and Rare-Metal Mineralization of the Peralkaline Granites and Related Pegmatites in the Arabian Shield: A Case Study of the Jabal Sayid and Dayheen Ring Complexes, Central Saudi Arabia

“…The A1 subgroup is associated with rare-metal-bearing granitoids, similar to the Al-Ghurayyah granitoids in Saudi Arabia. On the other hand, the A2 subgroup aligns with the overall assumption of peralkaline granites in the ANS, where many peralkaline granites of crustal origin have been recognized, such as Al-Hamra granites, Saudi Arabia [51]; Feinan granites, Jordan [52]; and Um Taghir granites, Egypt [53].…”

Geochemical Constraints on the Evolution of Late- to Post-Orogenic Granites in the Arabian Shield, with a Specific Focus on Jabal Al Bayda Area in the Central Hijaz Region, Saudi Arabia

“…The Th/Ta ratio vs. Yb diagram helps to outline the tectonic environment of magmatism (Figure 8b). It is suggested that the alkali granites formed in an ensimatic rift setting, comparable to the alkaline granites of Saudi Arabia, e.g., the alkali feldspar granite from the Al-Hamra area [39], Jabal Sayid area [40], Idah area [37], and Jabal az Zuhd area [38]. On the other hand, the monzogranites are regarded as subduction-related arc granitoids at an active continental margin setting, similarly to Egyptian monzogranites from the El Fereyid area [33], Wadi Um Sidra area [48], and Wadi Al-Baroud area [43].…”

“…The Zr vs. (Nb/Zr) N diagram enables a clear discrimination between two magmatic series (Figure 8c). The early magmatic series, represented by the Jabal Al Bayda monzogranites, is plotted in the subduction-related field, similarly to the Egyptian monzogranite from the Sukari area [42], Wadi Um Sidra area [48], Um Taghir area [32], and Feinan area, Jordan [41], whereas the late magmatic series of alkali granites falls within the field of intraplate granites, except three samples that belong to the collision-related granites, similarly to the alkali feldspar granites from Saudi Arabia, e.g., the Jabal Sayid area [40], Al-Hamra area [39], and Jabal az Zuhd area [38]; A2 alkaline granites from Sahara area, Sinai [45]; and alkali feldspar granite from Egypt, e.g., the Qash Amir area [44] and Um Taghir area [32]. There are similarities between the studied granitoids and the 559 ± 6 Ma Sukari monzogranite of [51]), the 556-572 Ma Feinan Ghuweir Magmatic Suite of [41], the 593 ± 2.4 Ma Jabal Sayid alkali granite of [52], the 564 ± 140 Ma Jabal az Zuhd alkali feldspar granite of [38], and the 608-578 Ma Sahara alkaline granites of [45].…”

“…Ref. [75] suggested that the source of the Al Ghurayyah granite could be either the mantle or juvenile crust. In Egypt, studies by [33,43,48] focused on different areas such as Wadi Um Sidra, Wadi Al-Baroud, and El Fereyid.…”