Rutile grains often occur in different types of gold deposits, and their U-Pb ages have been widely used to determine the formation time of gold mineralization. However, the origin of rutile grains in the gold deposits remains controversial. In this paper, laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analyses of U-Pb ages and trace elements on rutile grains were applied to investigate the metamorphic and hydrothermal processes of the Baiyun gold deposit (70 t Au, avg grade: 3 g/t) in the Liaodong Peninsula in the northeastern part of the North China craton. Rutile grains in the hydrothermal altered gold schist from the Baiyun deposit yielded two group ages of 1924 ± 18 and 237.0 ± 1.8 Ma, respectively. Combined with our systematic U-Pb zircon geochronological results of the ore-hosting schists and post-ore dikes, we suggest these rutile ages record a Paleoproterozoic metamorphic event and a Triassic hydrothermal gold mineralization event, respectively. The metamorphic and hydrothermal rutile grains have no obvious textural differences, but they show distinct trace element contents of Zr, W, Nb, and Ta. Combined with previous published data, we propose that high W (>1,000 ppm) and low Zr (<200 ppm) contents in rutile can be used to distinguish hydrothermal rutile from metamorphic and magmatic rutile. The newly identified ca. 237 Ma hydrothermal event is much older than the ca. 227 to 210 Ma Triassic magmatic rocks in the region, which precludes a temporal and genetic link between the Baiyun gold mineralization and the regional Mesozoic magmatism. Rather, the ca. 237 Ma gold mineralization may be associated with the Triassic orogenic metamorphism, and Baiyun is an orogenic gold deposit. The Triassic gold deposits in the northern margin of the North China craton formed by orogenesis between the Siberian craton and the North China craton. After a hiatus, the large-scale gold deposits formed during the Early Cretaceous in the North China craton due to a westward subduction of the paleo-Pacific plate beneath the craton since the Early Jurassic. Our study highlights that rutile in gold deposits may be inherited from the host rocks and/or formed by hydrothermal fluids. Distinguishing between these two different rutile generations requires a combination of in situ age dating and trace element geochemistry in petrogenetic context.

Palaeozoic granitoids in the Chinese Altai are important for understanding the evolution of the Central Asian Orogenic Belt (CAOB). The Xiaodonggou granitic intrusion, situated in the Chinese Altai (southern CAOB), is composed of two intrusive phases, medium-grained granite intruded by porphyritic granite. Zircon LA-ICP-MS U–Pb analyses of medium-grained granite and porphyritic granite yield ages of 409 ± 2 Ma and 400 ± 1 Ma, respectively, indicating that these formed in Early Devonian time. Medium-grained granite and porphyritic granite have similar geochemical features and Nd–Hf isotopic compositions. Arc-like geochemical characteristics (e.g. enrichment of LILEs and negative anomalies of Nb, Ta, Ti, and P) show that both phases are volcanic arc granites (VAGs). Geochemical and isotopic characteristics suggest that these magmas originated from melting older crust. Based on their near-zero or negative ε_Nd(t) values (−1.4to 0) and positive ε_Hf(t) values (+1.4 to +7.8), together with Nd model ages of 1.15–1.26 Ga and zircon Hf model ages of 0.90–1.30 Ga, we suggest that the Xiaodonggou granites were derived from a mixture of juvenile and old crustal components. Some other Devonian granitic intrusions were recently identified in the Chinese Altai with ages between 416 and 375 Ma. These Devonian granites have similar geochemical characteristics and petrogenesis as Xiaodonggou granites. The formation of these Devonian granites was in response to subduction processes, suggesting that Chinese Altai was an active continental margin in Early Devonian time.

Extensive Permian mafic–ultramafic intrusions crop out within the eastern Tianshan, southern part of Central Asian Orogenic Belt (CAOB). Most of these mafic–ultramafic complexes are associated with Cu-Ni-Co deposits. However, Cihai, located in the southern part of the eastern Tianshan, is a large Fe deposit hosted in the Early Permian mafic rocks. The mafic to intermediate rocks are composed of gabbro, diabase, and monzodiorite. Geological and geochemical characteristics suggest that their parental magmas might have been generated by interaction between the depleted asthenospheric mantle and the metasomatized lithospheric mantle. Iron ores of the Cihai iron deposit are hosted in the diabase, and all Fe–Ti oxides in the ore-hosted diabase are ilmenite, instead of magnetite as previously reported. Chondrite-normalized REE patterns show that the magnetite separates from disseminated, banded, and massive iron ores, which are distinct from those in magmatic Fe-Ti deposits. Geological and chemical features suggest that the main ore bodies in the Cihai iron deposit are of hydrothermal origin, rather than magmatic as previously suggested. Numerous other Early Permian mafic rocks were recently identified in the Tarim basin and the eastern Tianshan with ages between 301 and 269 Ma. The mafic rocks in the Tarim basin exhibit characteristics of Oceanic Island Basalt (OIB), whereas the mafic rocks in the eastern Tianshan show island arc basalt (IAB) affinity. In addition, the presence of skarn iron deposit instead of Fe–Ti oxide deposit in the eastern Tianshan during the Early Permian time also lends little support for a plume-related environment. These features, together with a lack of verified anomalous high-temperature magmas in the eastern Tianshan, suggest that the Permian Tarim mantle plume may not account for the formation of the mafic rocks in the eastern Tianshan area, and that the Tarim LIP does not extend to the eastern Tianshan area.