The Petrogenesis of the Neoproterozoic Granodiorite Hosting Porphyry Cu‐Au Mineralization in the Anagulu District, Western Eritrea: Implications for Tectonics and Porphyry Cu Mineralization in the Arabian‐Nubian Shield

ABSTRACT The Arabian‐Nubian Shield (ANS) is part of a Neoproterozoic accretionary orogen at the northern part of the East African Orogen (EAO), however, only few arc‐related porphyry Cu deposits have been found. In order to understand the rarity of arc‐related porphyry Cu deposits in this belt, we focused on the newly‐discovered Anagulu porphyry Cu‐Au deposit. In this paper, zircon U–Pb, trace element and Hf isotopic, whole‐rock major and trace element, and apatite major and trace element study of the Anagulu ore‐bearing granodiorite of western Eritrea, are reported to study the petrogenesis and implications for the tectonics and porphyry Cu mineralisation in the Arabian‐Nubian Sheild. The zircon U–Pb dating of the Anagulu granodiorite yields from 815.2 ± 4.8 to 814.6 ± 4.6 Ma, belonging to Mozambique oceanic crust subduction stage. The Anagulu granodiorite has geochemistry patterns resembling those of high‐Mg adakite, with high SiO 2 (64.02~64.98 wt.%), Al 2 O 3 (15.21~15.89 wt.%), Sr. (241~298 ppm), Sr/Y (19.2~24.7), Mg# values (48~51, ≥ 45), and relatively low, Y (11.9~13.6 ppm), Yb (1.25~1.55 ppm). Combined with the positive ε Hf (t) values (7.5~13.8), the Anagulu granodiorite is supposed to be generated by the partial melting of subducted oceanic crust mixed with sediments, followed by interaction with the overlying mantle peridotite. The concentrations and ratios of incompatible elements in the Anagulu granodiorite, prove evidence for the intra‐oceanic island arc affinity. The Anagulu granodiorite has the high zircon log( fO2 ), Eu N /Eu N *, Ce 4+ /Ce 3+ , (Ce/Nd)/Y and Eu/Eu* ratios, and high whole rock Fe 2 O 3 /FeO, V/Sc, Al 2 O 3 /TiO 2 and Sr/Y ratios, with the relatively low zircon Dy/Yb ratios. These features indicate that it is water‐rich and oxidised, which are fertile for porphyry Cu mineralisation. Moreover, the Anagulu granodiorite exhibits high apatite contents of Sr, U, Ba, Th, Pb, Sr., Zr, and low contents of Y and Pb, with the relatively high Ce/Pb ratios, and low Sr/Eu, Sr/Ce, Sr/Y, Th/U ratios, corresponding to these of typical porphyry Cu ore‐bearing rocks worldwide. Preservation of such shallowly formed Neoproterozoic porphyry Cu mineralisation in the Arabian‐Nubian Shield mainly attributed to burial beneath thick post‐amalgamation volcano‐sedimentary basinal cover, collision‐generated thrust sheets, and later Phanerozoic strata. Therefore, the Arabian‐Nubian Shield has the exploration potential for the porphyry Cu deposits, and the future exploration targets possibly be the fertile volcano‐sedimentary rocks area in Arabian‐Nubian Shield if these rocks covered the subduction‐related porphyry Cu deposits.