Rare-metal and rare earth element mineralizations in the eastern Liaoning-southern Jilin tectonic zone in Northeast China: A review

The eastern Liaoning-southern Jilin tectonic zone (also referred to as the Liao-Ji tectonic zone), a potential zone for rare-metal and REE mineralizations in China, hosts over 10 rare-metal and REE deposits and ore occurrences with varying scales and mineralization characteristics, which establish this zone as an ideal target for research on the metallogenic regularities of rare-metal and REE mineralizations.The study area resides in the northern part of the East Asian continental margin, lying on the overlapping part of the North China and the Western Pacific Plates, is located in the northeastern North China Plate, consisting of the North China Craton and the north margin orogen of the North China Plate. This area serves as a critical large-scale copper-gold and polymetallic mineral resource base in China, also providing favorable geologic conditions for the enrichment and mineralization of rare metals and REEs. So far, many rare-metal and REE deposits and ore occurrences have been discovered in the Liao-Ji tectonic zone, including two large Nb-Be-Zr-REE deposits (i.e., Lijiapuzi and Pianshishan), two medium-sized Rb-Be-Nb-Ta-REE deposits (i.e., Saima and Gangshan), one small Nb-Ta-REE deposit (i.e., Shijia), and over 10 rare metal-REE ore occurrences (e.g., Xiaolizi, and Baiqi), suggesting considerable mineralization potential. Most of the deposits in the Liao-Ji tectonic zone are closely associated with alkaline rocks.

Extensive field surveys and geochemical studies of the above deposits reveal that the ore-forming rock masses of the Pianshishan, Gangshan, and Lijiapuzi deposits include alkaline granites and pegmatites and those of the Shijia and Saima deposits are quartz syenites and aegirine nepheline syenites, respectively. The Pianshishan (67±2.2 Ma) and Gangshan (110±1.2 Ma) deposits were formed during the Yanshanian, the Shijia (226.3±2.4 Ma) and Saima (224.4±6.1 Ma) deposits originated from the Late Indosinian magmatism, while the formation of the Lijiapuzi deposit (2501±11 Ma) was associated with the Lvliang Movement. Therefore, the study area underwent three stages of regional rare-metal and REE mineralizations: the Late Yanshanian (Mesozoic), Late Indosinian (Mesozoic), and Proterozoic Lvliangian mineralizations. The petrogeochemical analysis indicates that the ore-forming rock masses of several typical deposits all belong to the metaluminous, alkaline - calc-alkaline, and tholeiitic basalt series, sharing similarities with the elemental geochemical characteristics of intraplate rift rock series and rocks in an extensional environment under plate subduction. The rare-metal and REE mineralizations in the study area were primarily governed by the evolution and crystallization differentiation of alkaline magmas. Given that the alkaline magmatic rocks were all formed by crust-mantle contamination, this study posits that the enrichment and mineralization processes of rare metals and REEs in the Liao-Ji tectonic zone are intimately associated with the highly evolved alkaline magmas. Under the action of water and volatile constituents, magmas underwent intense fractional crystallization, leading to the migration and accumulation of ore-forming elements. With changes in ore-forming conditions such as temperature and pressure, ore-bearing fluids became enriched and mineralized in the late stage of magmatism with the crystallization of primary rock-forming minerals.