Understanding Critical Mineral Enrichment in the Mineralized Al-Ghurayyah Granite Pluton and Associated Pegmatites, NW Saudi Arabia: Insight on Mineral Exploration in the Arabian Shield
Authors: Sulistyohariyanto Faris , Whattam Scott , Chattopadhyay Sabyasachi , Pilia Simone , Stern Robert , Seo Jieun , Yi Keewook 
Published: March 2024

The Arabian-Nubian Shield (ANS) comprises the largest tract of juvenile, mantle-derived continental crust on Earth. ANS granitoids thus record the major development and evolution of this juvenile Neoproterozoic continental crust and extensive distribution of A-type granitoids. Whereas 900 &#8211; 630 Ma I-type granitoids dominate the early plutonic evolution of the ANS, within-plate A-type granitoids dominate 630 &#8211;570 Ma plutons and provide a record of the final collision between eastern and western Gondwana. Some transitional A/I-type granitoids are highly mineralized in HFSEs and REEs. The Al - Ghurayyah granitoid complex represents a small but highly mineralized pluton exposed in the Midyan terrane of NW Saudi Arabia, the easternmost of a belt of similar bodies in Egypt (Stern et al. in press). Four components of the intrusion are identified: Arfvedsonite granite, amphibole-free porphyritic coarse and medium-grained granite, and microgranite. Peripheral melt-rock interaction generated albitite and marginal units adjacent to host Neoproterozoic metavolcanics. The granitoids are highly fractionated Fe-rich metaluminous to peraluminous A-type, suggesting within-plate affinity. Chondrite and primitive mantle-normalized patterns are similar for granite components. Abundances of HFSE and REE from the different components suggest comagmatic evolution with extreme HREE fractionation (La/YbN=0.034 &#8211; 1.752) and negative Eu anomalies (Eu/Eu*=0.046 &#8211; 0.375). U-Pb SHRIMP dating of zircons provides an age of 647 &#177; 9.3 Ma, in the range of 692-628 mineralized A/I-type granites in Egypt. Average &#8721;REEs from the main intrusion is 1,162 &#181;g/g, with a maximum value of 1,917 &#181;g/g housed within zircons and other accessory phases of the marginal unit. Nb and Ta mineralization (mean of 303 &#181;g/g Nb, 25 &#181;g/g Ta) is strongly correlated (R2=0.74), concentrated in columbite. Tungsten (W) concentration increases towards the marginal unit. Granite REEs tetrad effects (TE1,3) are from 1.25 &#8211; 1.67 and display a weak negative correlation with Zr/Hf (R2=0.08) and Y/Ho (R2=0.14), suggesting primary enrichment as a result of extreme fractionation with subsequent fluid&#8211;rock interaction. Three types of pegmatites are documented: (1) northern pegmatites (type 1), emplaced into metavolcanics, exhibit complex mineral zonation and highly elevated &#8721;REEs (436 &#8211; 13,115 &#181;g/g) and Li (13&#8211;3,010 &#181;g/g), but low concentration of U (2.82 &#8211; 94.3 &#181;g/g) and Th (25.3 &#8211; 600 &#181;g/g); (2) southwestern pegmatites (type 2) emplaced into microgranite exhibits simple mineral zonation with anomalous abundance of zircon (up to 10% of the mode), high &#8721;REEs (up to 6,000 &#181;g/g), and extremely high radioactive element abundances&#160; (1,160 &#181;g/g Th and 348 &#181;g/g U). The main HFSEs- and REEs-bearing phases for type 1 and 2 are zircon, pyrochlore, columbite, rutile, xenotime, and cassiterite; (3) southeastern non-zoned pegmatites (type 3) emplaced into the contact of arfvedsonite bearing granite, with low &#8721;REEs and radioactive elements, but abundances of Li (up to 1,775 &#181;g/g) housed within the mica. We conclude the critical mineral enrichment is primarily magmatic controlled by F- ligands in the melt for the granite. Different types of pegmatite are attributed to different processes and conditions.&#160; Exploration for rare metal mineral deposits should concentrate along and around the reconstructed E-W trending Egypt-Arabia 630-690 Ma mineralized granite belt.
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