Apatite in granite as a fingerprint of gold mineralization: A case study from the Jiaodong goldfield, North China Craton

Abstract The relationship between granitoids and gold mineralization, particularly as a prospecting indicator, is a topic of longstanding debate. In this context, the world-class deposits of Jiaodong in the North China Craton provide a good window for exploring the spatio-temporal association between granite and gold mineralization. The Jiaodong goldfield is the largest gold-producing region in China, with mineralization ages concentrated at 130–110 Ma. The Guojialing granodiorite in this area was formed between 126 Ma and 120 Ma, while the Linglong granite was formed between 160 Ma and 150 Ma. The Guojialing pluton is spatially and temporally related to the gold mineralization, whereas the Linglong pluton formed 30 million years before the gold mineralization. In this contribution, we present results from a study of the cathodoluminescence (CL) color imaging and spectroscopy and in situ elemental and Sr-Nd isotopes of apatite in the Guojialing and the Linglong plutons. Our purpose is to unravel the different characteristics of apatite in granitic plutons with varying relationships to gold deposits, and to utilize the characteristics of apatite as an indicator of gold mineralization. The Guojialing apatite (Ap-G) displays alternating yellow to green and blue to bluish violet color zoning under CL. We correlate these features with rare earth elements (REEs) such as Ce3+, Dy3+, and Sm3+, which suggests that the magma source of the Guojialing pluton has high-REE contents. The chemical compositions of the different color zones (Ce/Y, light REE-middle REE-heavy REE ratio) of Ap-G are consistent with those of the I-type granites. The Sr-Nd isotopes (87Sr/86Sr = 0.7106–0.7108, εNd [128 Ma] = −15.9 to −12.9) indicate the involvement of mantle-derived materials. Analysis of the different color zones in Ap-G shows that the blue to bluish violet zone has higher REEs, Y, and Si contents than the yellow to green zone. This variation in the chemical composition of different zones records the change in magma composition of the Guojialing pluton, which was caused by multipulse mixing and the differentiation of a hot mafic magma derived from a mixture of mantle and felsic crustal sources. However, the Linglong apatite (Ap-L) shows a uniform bright yellow color under CL that is mainly attributed to Mn2+ rather than REEs, which suggests that the magma source of Linglong pluton had low REE contents. The chemical composition and Sr-Nd isotopes of Ap-L (87Sr/86Sr = 0.7107–0.7113, εNd [160 Ma] = −22.6 to −21.2) indicate that the Linglong pluton is an S-type granite derived from crustal sources. The elements sensitive to redox environments in apatite, such as S, Eu, and Ce, indicate that the Guojialing pluton formed in a relatively oxidized environment, whereas the Linglong pluton formed in a relatively reduced environment. Our results reveal that apatite in the Guojialing pluton (Ap-G) reflects high REE content, mantle-crust magma mixing, and an oxidizing environment, all of which are conducive to gold mineralization. In contrast, apatite in the Linglong pluton (Ap-L) displays uniform CL coloration, low REE content, crustal magma origins, and a reducing environment, which are unfavorable for gold deposition. Our research demonstrates that the Guojialing pluton is closely related to the gold deposit, and apatite's composition and redox-sensitive elements can effectively indicate granitoids that are associated with gold mineralization.