Geologic Characteristics and Age of Beryllium Mineralization in the Jiulong Area, the Southeast Edge of the Western Kunlun–Songpan–Ganzi Rare Metal Metallogenic Belt

Abstract

Rare metals such as lithium and beryllium are strategic mineral resources that play a highly significant role in the national aerospace, defense, and new energy industries. The western Kunlun–Songpan–Ganzi metallogenic belt is an important rare metal metallogenic belt in China that mainly consists of granite–pegmatite-type lithium–beryllium deposits with uncommon beryllium-only deposits. In the Jiulong area on the southeastern edge of this metallogenic belt, several deposits, including the Daqianggou lithium–beryllium, Luomo beryllium, Baitai beryllium, and Shangjigong beryllium deposits, have been identified. Unlike the northern areas of Jiajika, Ke’eryin, Zawulong, and the western regions of Dahongliutan and Bailongshan, this area contains beryllium-only deposits. In this paper, we examine representative beryllium deposits in the Jiulong area, including detailed petrographic observations and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb isotope dating of cassiterite and columbite–tantalite, to define the metallogenic age and summarize the spatiotemporal characteristics of the beryllium mineralization in this area. The research results show that the Daqianggou lithium–beryllium deposit is dominated by spodumene and beryl mineralization, while the Luomo and Baitai beryllium deposits primarily feature beryl mineralization. The dating results indicate that the U-Pb ages of the cassiterite and columbite–tantalite in the Daqianggou lithium–beryllium deposit are 157.3 ± 1.7 Ma and 164.1 ± 0.8 Ma, respectively. For the Luomo beryllium deposit, the U-Pb ages of the cassiterite and columbite–tantalite are 156.1 ± 1.5 Ma and 163.3 ± 0.8 Ma, respectively. For the Baitai beryllium deposit, the U-Pb age of the columbite–tantalite is 188.8 ± 1.1 Ma. Therefore, the Jiulong area experienced two pegmatite-type rare metal metallogenic events: a beryllium–niobium–tantalum–molybdenum event at 197~189 Ma and a lithium–beryllium–niobium–tantalum–rubidium event at 164~156 Ma. Based on the reported metallogenic ages, we suggest that the western Kunlun–Songpan–Ganzi rare metal metallogenic belt experienced three rare metal metallogenic events at 210~200 Ma, 200~180 Ma, and 170~150 Ma. Regarding exploration directions, early Yanshanian beryllium mineralization predominates in the Jiulong area along the southeastern edge of the belt, and deep exploration of the early Yanshanian rare metal mineralization within this belt should be strengthened to facilitate new breakthroughs.

1. Introduction

Beryllium is the lightest alkaline earth metal by atomic weight and is an exceptional rare metal. It is characterized by a low density, high melting point, large specific heat capacity, low thermal expansion coefficient, high elastic modulus, high specific rigidity, and high strength. Due to its excellent nuclear and physical properties, beryllium is widely used in the aerospace, defense, and nuclear industries and in the industrial components, electronic information systems, automotive, and home appliance sectors. It is known as an important strategic and critical engineering material, and it has been dubbed a strategic critical metal, super metal, and cutting-edge metal, and it is used as a protector of nuclear reactors [1,2].

Beryllium resources are abundant worldwide. They are primarily located in the United States, Brazil, Russia, and India, and 60% of global reserves are concentrated in the United States [3]. In China, beryllium mines are primarily located in Xinjiang, Neimenggu, Yunnan, and Sichuan, with major deposits being found in the Koktokay mine, Baiyanghe beryllium mine, Xianghualing mine, and Zhelimu League 801 mine. The beryllium reserves in Xinjiang account for about one-third of the national total [2,3,4,5]. Beryllium deposits can be classified into those related to magmatic–hydrothermal processes and those unrelated to magmatic–hydrothermal processes [1,6]. Magmatic–hydrothermal-related beryllium deposits mainly include volcanic-type, highly differentiated granite–pegmatite-type, greisen–quartzite-type, alkaline-rock-type, skarn-type, and carbonatite-type beryllium deposits, while non-magmatic–hydrothermal deposits mainly consist of beryllium formed through tectonic metamorphism and sedimentation [1,2,3,6]. At present, highly differentiated granite–pegmatite-type beryllium deposits are the main sources of China’s beryllium resources, such as the pegmatite-type deposits in the Songpan–Ganzi area, Altay, and Xinjiang and the highly differentiated granite-type deposits in southern Tibet [1,7,8,9].

The western Kunlun–Songpan–Ganzi rare metal metallogenic belt is located on the northeastern margin of the Tibetan Plateau and extends from the Songpan–Ganzi area through Kekexili to the western Kunlun Tianshuihai region [10,11,12,13]. This rare metal metallogenic belt is characterized by a dense distribution of lithium–beryllium deposits and the coexistence of various associated resources (Nb, Ta, Cs, and Rb). The major ore districts include Jiajika, Ke’eryin, Zhawulong, Dahongliutan, and Bailongshan [13]. In recent years, significant progress has been made in terms of mineral exploration in this metallogenic belt, and major and super-large rare metal deposits have been recently discovered, including the Jiajika X03, Zhawulong Caolong, Yajiang Murong, Xinjiang Dahongliutan, and Bailongshan veins [13,14,15,16,17,18]. The western Kunlun–Songpan–Ganzi rare metal metallogenic belt has become a global research hotspot.

The Jiulong area is located at the southeastern edge of the western Kunlun–Songpan–Ganzi rare metal metallogenic belt, and the main deposits are pegmatite-type Be (Li, Nb, Ta, and Rb) deposits (Figure 1c,d). Notable deposits include the medium-sized Daqianggou lithium–beryllium deposit, the medium-sized Luomo beryllium–niobium–tantalum deposit, the small Baitai beryllium deposit, and smaller beryllium occurrences in Shangjigong, Ruodeng, and Yanshuitang [19,20,21,22,23]. The region is characterized by well-developed pegmatite veins, with a concentration of deposits (occurrences), and it is thus a potential resource base for rare metals, including beryllium, lithium, tantalum, niobium, and rubidium. However, research on the beryllium deposits in the Jiulong area is relatively limited, and previous with studies have mainly focused on the mineral chemistry and rock geochemistry of the Daqianggou lithium–beryllium deposit [21,23,24,25]. This has resulted in an inadequate understanding of the beryllium metallogenesis in the Jiulong area, restricting exploration advancements in this region.

With the advancement of zircon, cassiterite, and columbite–tantalite U-Pb dating techniques, there has been a breakthrough in dating pegmatite-type rare metal deposits, making the metallogenic age characteristics of the western Kunlun–Songpan–Ganzi rare metal metallogenic belt clearer. Studies have shown that the metallogenic age of the Jiajika ore district is primarily concentrated between 216 and 192 Ma [12,26,27,28,29]. The metallogenic age of the Ke’eryin ore district is primarily concentrated between 216 and 192 Ma [30,31,32,33,34,35]. The metallogenic age of the Zhawulong ore district is primarily concentrated between 210 and 204 Ma [15,36,37,38,39]. The metallogenic age of the Dahongliutan ore district is primarily concentrated between 218 and 205 Ma [40,41]. The metallogenic age of the Bailongshan ore district is mainly concentrated between 223 and 207 Ma [18,42,43,44,45]. These dating results offer detailed chronological evidence for exploring regional magmatic activity, mineralization, and tectonic evolution, showing that pegmatite-type rare metal mineralization in the western Kunlun–Songpan–Ganzi region primarily occurred during the Late Triassic to Early Jurassic. Research on the mineralization age of pegmatite-type rare metal deposits in the Jiulong area is relatively sparse. Only the zircon U-Pb dating of the Daqianggou Li-Be deposit yielded an age of 147 Ma [25], while the Re-Os age of molybdenite in the beryl-bearing pegmatite veins at the Yansuitang Be deposit was 197 Ma [19], and the Re-Os age of molybdenite in the Mawo area pegmatite veins was 189 Ma [46]. To further investigate the beryllium mineralization age in the Jiulong area, this study performed petrographic observations, LA-ICP-MS columbite–tantalite U-Pb dating, and cassiterite U-Pb dating on the Daqianggou lithium–beryllium deposit, Luomo beryllium deposit, and Baitai beryllium deposit in Jiulong. The mineralization ages were accurately defined, and the beryllium mineralization characteristics were summarized, offering a foundation for assessing the rare metal mineralization mechanism and resource potential in the Jiulong area. In addition, comparative research was conducted with typical deposits from the western Kunlun–Songpan–Ganzi rare metal mineralization belt to categorize the mineralization stages of the belt, providing data support for the study of the mineralization patterns in the western Kunlun–Songpan–Ganzi rare metal mineralization belt.

Figure 1. (a) Map showing the location of the western Kunlun–Songpan–Ganzi ore-forming belt inside China. (b) Regional geological map showing the distribution of the main tectonic zones in central and southern Eurasia (from [22,47]), (CAOB = Central Asian orogenic belt, IC = Indochina, Tar = Tarim, EA = rare metal pegmatites in eastern Afghanistan, WK = rare metal pegmatites in western Kunlun, SG = rare metal pegmatites in Songpan–Ganzi). (c) Map showing the distribution of the major rare metal deposits in the western Kunlun–Songpan–Ganzi ore-forming belt (from [18,22,48,49,50]), (BNS = Bangong–Nujiang suture, JS = Jinsha suture, AKMS = Ayimaqin–Kunlun–Matztagh suture, SQS = southern Qilian suture, GLS = Ganzi–Litang suture, WKO = western Kunlun orogenic belt; XEBL = Xiaoerbulong, HSTS = Huoshitashi, MLC = Mulinchang, XFL = Xuefengling, DHLT = Dahongliutan, BLS = Bailongshan, TGM = Tugeman, CK = Chaka, ZWL = Zhawulong, CL = Caolong, XBD = Xuebaoding, KEY = Ke’eryin, JJK = Jiajika, BT = Baitai, LM = Luomo, DQG = Daqianggou). (d) Geological map of the Jiulong region (from [22,46,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68]), (1 = Daqianggou, 2 = Luomo, 3 = Baitai, 4 = Shangjigong, 5 = Ruodeng, 6 = Yanshuitang, 7 = Hede, 8 = Mawo, 9 = Ziershj).

Figure 1. (a) Map showing the location of the western Kunlun–Songpan–Ganzi ore-forming belt inside China. (b) Regional geological map showing the distribution of the main tectonic zones in central and southern Eurasia (from [22,47]), (CAOB = Central Asian orogenic belt, IC = Indochina, Tar = Tarim, EA = rare metal pegmatites in eastern Afghanistan, WK = rare metal pegmatites in western Kunlun, SG = rare metal pegmatites in Songpan–Ganzi). (c) Map showing the distribution of the major rare metal deposits in the western Kunlun–Songpan–Ganzi ore-forming belt (from [18,22,48,49,50]), (BNS = Bangong–Nujiang suture, JS = Jinsha suture, AKMS = Ayimaqin–Kunlun–Matztagh suture, SQS = southern Qilian suture, GLS = Ganzi–Litang suture, WKO = western Kunlun orogenic belt; XEBL = Xiaoerbulong, HSTS = Huoshitashi, MLC = Mulinchang, XFL = Xuefengling, DHLT = Dahongliutan, BLS = Bailongshan, TGM = Tugeman, CK = Chaka, ZWL = Zhawulong, CL = Caolong, XBD = Xuebaoding, KEY = Ke’eryin, JJK = Jiajika, BT = Baitai, LM = Luomo, DQG = Daqianggou). (d) Geological map of the Jiulong region (from [22,46,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68]), (1 = Daqianggou, 2 = Luomo, 3 = Baitai, 4 = Shangjigong, 5 = Ruodeng, 6 = Yanshuitang, 7 = Hede, 8 = Mawo, 9 = Ziershj).

2. Geologic Setting

The western Kunlun–Songpan–Ganzi metallogenic belt is a key rare metal metallogenic region in China. It is distinguished by strong magmatic activity, a complex tectonic background, and favorable geological conditions for metallogenesis. The metallogenic belt stretches from the Songpan–Ganzi region, westward through Kekexili to the western part of the orogenic belt in the western Kunlun–Tianshuihai region, with an east–west span of~2800 km and an inverted triangular shape [11,18,22,69,70]. The eastern part is sutured with the Yangtze block along the Longmenshan tectonic belt, the northern part is connected to the north Chin–Tarim block through the Animaqing–eastern Kunlun and Mazha–Kangxiwa suture zones, and the southwestern edge is connected to the Qiangtang block by the Jinsha River Ancient Tethys suture zone [11,71]. The metallogenic belt is extensively developed, with shallowly metamorphosed sedimentary rocks consisting of sandstone and slate, which are referred to as the Xikang Group in western Sichuan and the Bayankala Mountain Group in Qinghai. The western Kunlun–Songpan–Ganzi orogenic belt has experienced significant tectonic and magmatic events, resulting in the extensive development of granite bodies [72]. The magmatic activity in the metallogenic belt primarily occurred between 230 and 200 Ma, with additional magmatic events at 170~150 Ma, ~100 Ma, and 18~14 Ma, exhibiting a multi-phase intrusion characteristic [19]. The dominant types of granite are S-type and I-type granites, as well as a small proportion of A-type granite. The S-type granite is spatially closely related to the pegmatites. The rare metal deposits in the belt are mainly LCT-type pegmatite deposits, forming over 70 rare metal mineralized sites, which primarily contain lithium, with associated beryllium, niobium, and tantalum [11]. The main rare metal ore districts include Dahongliutan, Bailongshan, Caolong, Ke’eryin, Jiajika, and Jiulong.

The Jiulong region is situated on the southeastern edge of the Songpan–Ganzi block at the junction between the Yidun island arc and the residual Yajiang basin. The area is mainly controlled by northeast–southwest- and nearly north–south-trending faults, and the Bawolong–Yunongxi fault is the primary fault structure. The exposed strata mainly belong to the Triassic Xikang group, including the Zhagashan, Zagunao, Zhuwo, and Xinduqiao formations, which are composed of shallowly metamorphosed rocks such as sandstone, metamorphosed sandstone, slate, and phyllite. The Jiulong region has a well-developed magmatic rock formation, with 15 exposed intrusive bodies covering an area of ~1300 km² and dozens of smaller intrusions. It underwent two episodes of magmatic activity in the Indosinian and Yanshanian (Figure 1d). The Indosinian magmatism primarily occurred in the northern region, while the Yanshanian magmatism mainly occurred in the southern part of Jiulong. The predominant rock type is felsic rocks, with minor amounts of intermediate and mafic rocks. According to previous studies on magmatic rocks in this region, extensive magmatic activity occurred in the southeastern margin of the Songpan–Ganzi orogenic belt in the Jiulong region during the Late Indosinian (220~205 Ma) [19,22,52,53,54,62,63,64,65,67,68]. This magmatic activity led to substantial mineralization of rare metals, tungsten, tin, and molybdenum [19,22,53,73]. These magmatic activities reflect the dynamic processes of compressional thickening followed by extensional thinning after the collision of the Songpan–Ganzi orogenic belt [22,52,62,64,65]. Since the Yanshanian, S-type granites formed at 202 Ma, during the transition from compression to extension, accompanied by lithospheric thickening, detachment, and subsidence processes [46]. A-type granites formed during the extensional phase (175~155 Ma) [19,51,53,55,56,57,58,59,60,61,66]. Numerous pegmatite veins, quartz veins, and aplite veins are developed along the peripheries of some of the intermediate–felsic rock. The formation of these veins is closely related to the intrusive rocks and was strongly controlled by the rock bodies and structural features, often occurring along the external contact zones and joints in the surrounding strata. Some of the pegmatite veins are mineralized with rare metals, primarily lithium and beryllium, while the quartz veins are characterized by tungsten, tin, lead, and zinc mineralization. The Indosinian and Yanshanian granites in this area are closely related to the genesis of the lithium–beryllium rare metal deposits, and the lithium and beryllium deposits are mainly distributed in the pegmatite veins around the intrusive bodies, especially in the external contact zones of the Yanshanian granites where the lithium–beryllium mineralization is concentrated. The Jiulong region hosts mineral deposits containing W, Sn, Pb, Zn, Au, Cu, Li, Be, and other metals, including the Liwu-type copper–zinc deposit, Zigangping lead–zinc deposit, Hede tungsten–tin deposit, Dagianggou lithium–beryllium deposit, and Luomo beryllium deposit [21,22,25,73,74,75].

3. Geologic Characteristics of Deposits

3.1. Daqianggou Lithium–Beryllium Deposit

The Daqianggou lithium–beryllium deposit is located in the southeastern part of Jiulong County, Naqu Township, in the core of the Jiulong anticline. It exhibits a relatively simple structural form. The exposed strata in the mining area are primarily in the Triassic Xinduqiao formation, mainly consisting of gray to dark gray and gray–black silty slates, carbonaceous phyllites, and intercalated gray thinly to thickly bedded calcareous metamorphosed sandstones and quartz siltstone–mudstone (Figure 2). The magmatic activity was intense in the mining area, and a large-scale Indosinian late-stage Yangfanggou quartz monzonite intruded into the northwestern periphery. The deposit itself consists of the Yangfanggou quartz diorite, dated to 205 Ma [67]. In addition to the intrusive bodies, numerous granite pegmatite veins occur, mainly including microcline pegmatite (I), albite–microcline pegmatite (II), albite pegmatite (III), and albite–lithium-bearing pegmatite (IV). The microcline pegmatite, mainly located in the western periphery of the mining area, consists of quartz (40%~50%), microcline (30%~40%), tourmaline (10%~15%), and a small amount of albite. It is characterized by weak mineralization and typically does not have industrial value. The albite–microcline pegmatite is predominantly distributed in the Luomo region on the western periphery of the mining area. It mainly consists of quartz (30%~35%), microcline (35%~45%), albite (15%~25%), and lesser quantities of minerals such as beryl, muscovite, and tourmaline. It exhibits beryllium, niobium, and tantalum mineralization. The albite pegmatites are more abundant in the mining area and are mainly composed of quartz (40%~50%), albite (30%~35%), microcline (5%~10%), muscovite (5%~10%), spodumene (5%~10%), and a small amount of tourmaline. These pegmatites are primarily mineralized with lithium, beryllium, niobium, and tantalum and represent the main form of beryllium mineralization in the area. The albite–spodumene pegmatite is the most abundant and widespread type in the mining area. It mainly consists of albite (30%~40%), quartz (20%~35%), spodumene (10%~20%), microcline (10%~20%), and small amounts of lithium-rich muscovite and albite. Lithium and beryllium mineralization are dominant.

The Daqianggou lithium–beryllium deposit is hosted within a quartz diorite body. It is strictly controlled by northeast and nearly east–west-oriented joints and the joints in the biotite quartz schist of the Triassic Xinduqiao formation. The ore bodies are mainly vein-shaped, and there are also some lens-shaped bodies, and the ore bodies follow the main orientation of the pegmatite veins. The Daqianggou lithium–beryllium deposit includes one lithium–beryllium ore body, five lithium ore bodies, and eight beryllium ore bodies (Figure 3) [21]. The lithium ore bodies are primarily located in the albite–spodumene pegmatite veins within the biotite quartz schist of the upper Triassic Xinduqiao formation (Figure 4a). Branching is prominent, and the main and branch veins are nearly parallel after branching, with local deflections caused by topographic influences. The lithium ore bodies within the albite pegmatite veins in the quartz diorite are abundant but small in size, exhibit irregular mineralization, and are primarily lens-shaped. The beryllium ore bodies are predominantly clustered within the albite pegmatite veins in the quartz diorite and are oriented nearly parallel to each other.

The Daqianggou deposit is primarily composed of albite, quartz, microcline, muscovite, and tourmaline, as well as rare metal minerals such as spodumene, beryl, and columbite-tantalite. The accessory minerals include cassiterite, monazite, rutile, magnetite, ilmenite, garnet, apatite, and titanite. The spodumene is categorized into primary and replacement types. The beryl is predominantly located in areas with well-developed albite and occurs in two forms: coarse-grained beryl and fine-grained beryl. The coarse-grained beryl occurs as short columns or incomplete hexagonal prisms and blocky forms (Figure 4d,g). It has diameters of 1~3 cm and lengths of 3~4 cm. The fine-grained beryl is difficult to identify without a microscope and mostly occurs in association with albite. Mineralogical analysis revealed that as the pegmatite evolved, the mineral types in the area changed. The rare metal minerals transitioned as follows: beryl → beryl + spodumene → spodumene → spodumene + lepidolite. The mica changed from muscovite to lepidolite, the tourmaline transitioned from iron-rich to lithium-rich, the feldspar minerals changed from microcline + albite to albite, and the quartz changed from primary quartz to later hydrothermal quartz [21]. The mineralization process of the pegmatite minerals in the area included multiple evolutionary stages, which can be divided into a crystallization differentiation stage, replacement stage, and hydrothermal stage. The crystallization differentiation stage was characterized by crystallization of early pegmatitic melt fluids, forming coarse-grained albite, microcline, and spodumene. In the replacement stage, the residual melt fluids from the crystallization differentiation phase replaced the albite and spodumene formed earlier, undergoing self-replacement crystallization. In the early replacement phase, the spodumene was interspersed with the primary spodumene. In the middle replacement phase, spodumene was interspersed with those formed in the previous two stages. In the late replacement phase, the spodumene was replaced by sericite to form cymatolite. In the hydrothermal stage, the residual fluids crystallized and further modified the minerals crystallized earlier, causing processes such as albitization and silicification, which had minimal impacts on the deposit. Eventually, the ore bodies were exposed at the surface after structural uplift and erosion, revealing that the spodumene had been altered into cymatolite.

3.2. Luomo Beryllium Deposit

The Luomo beryllium deposit is situated 15 km to the south of Luomo Village, Xia’er Township, Jiulong County. The mining area is characterized by intense tectonic activity, and the faults and interlayer folds are the main mineralization-controlling structures. This deposit is situated in the northwest–western limb of the Jiulong syncline and the northeast–eastern limb of the Baitai anticline, and the main fault structures are the northwest-striking Zhari–Nari fault group and the northeast-striking Longxigou fault. The Zhari–Nari fault zone is characterized by brittle–ductile deformation and has an echelon distribution, forming a reverse fault zone with a complex network-like structure, which consists of linear strong strain zones and relatively weak strain zones. The Longxigou fault extends in the north–northwest to south–southeast direction along the Longxigou valley and exhibits a strike–slip transcurrent fault characteristic, with clear striations visible on the surfaces of the rock layers. The main strata exposed in the mining area are the metamorphosed fine-grained feldspar–quartz sandstone interlayered with sandy slate and biotite–quartz schist in the Zagunao group (T₃z), followed by the metamorphosed feldspar–quartz sandstone, fine sandstone, siltstone, and sandy slate with variable thicknesses in the Zhuwo group (T₃zw), and there are different levels of contact metamorphism near the intrusions. The magmatic rocks are mainly biotite two-mica granites, which have a fine-grained phaneritic structure and an equigranular texture and primarily consist of microcline (20%~25%), plagioclase (25%~30%), quartz (35%~40%), biotite (3%~5%), and muscovite (2%~3%).

The Luomo beryllium deposit is located on the eastern edge of the Qiaopengzi granite and primarily occurs in the pegmatite veins within the internal and external contact zones of the intrusion (Figure 5). Fifty pegmatite veins have been identified in the mining area, predominantly consisting of microcline pegmatite and albite–microcline pegmatite. Thirty of these veins are mineralized with rare metals. The pegmatite veins have lengths of 40~600 m (with most measuring between 100 and 150 m) and thicknesses of 1~80 m (typically around 4 m). The veins within the internal contact zone of the intrusion are predominantly fine-veined and regular, while the veins in the external contact zone of the strata tend to follow schistosity planes and can expand into lens-shaped bodies in areas with favorable structural development. The pegmatite exhibits clear zoning. From the core to the edge, there is a massive zone, a medium-to-coarse-grained zone, and a fine-grained or graphic zone, and the massive and medium-to-coarse-grained zones are the most pronounced. There are two mineralized pegmatite veins with industrial value in the mining area. Vein 101 is 227 m long and 3.25 m thick, and it has an average BeO content of 0.326%. Vein 102, which is 120 m long and 3.95 m thick, has an average BeO content of 0.233% [51]. The primary ore mineral is beryl, which occurs in coarse-grained, large crystal prismatic forms, with grain sizes ranging from several centimeters to tens of centimeters (Figure 4b,e). A small quantity of columbite–tantalite is present, and the beryl is more concentrated in the massive and medium-to-coarse-grained zones. The main alteration and replacement processes in the mining area included sodic feldspathization, muscovitization, and kaolinization, and the sodic feldspathization was closely related to the mineralization.

In the outer area of the Luomo mining region, around the ShitiziLandiao belt, numerous pegmatite veins are developed, which occur in the internal and external contact zones of the Shitizi and Landiao plutons and gradually extend toward the Daqianggou and Xinshangou areas. Within the granite body, 49 pegmatite veins with widths of 10~100 cm have been identified. These veins are mainly oriented between 240° and 270°, have dips of 70°~90°, and exhibit poor zoning. The majority are medium-to-coarse-grained quartz–microcline pegmatites, with some localized quartz zones, and beryl crystals with diameters of 1~10 cm occasionally occur [51]. The pegmatite veins in the surrounding rocks are predominantly oblique or vertically aligned with the schistosity. The surrounding rocks are mainly quartz schist and a small amount of slate. The pegmatite veins have lengths of 2~100 m, and 19 of the veins have lengths of between 50 and 200 m. The longest veins exceed 300 m in length, and the lengths of 44% of the veins range from 10 to 50 m. In terms of the thickness, the majority are between 1 and 5 m, accounting for more than 50%. The strike is primarily northwest to north–northwest, followed by northeast, and the dip angles are mainly concentrated between 50°~70° and 20°~40°. Based on field investigations, Tan et al. (2023) [51] summarized the structural characteristics of the pegmatite veins in the region and proposed that two phases of intrusive activity may have occurred and that the intrusion directions were oriented nearly north–south and northwest–southeast, consistent with the local structural directions.

3.3. Baitai Beryllium Deposit

The Baitai beryllium deposit is situated in Baitai Village, Bawolong Township, Jiulong County. In the western part of the mining area, the northeast–southwest-striking Bawolong–Yunongxi fault is developed, which is one of the major fault structures in the Jiulong region. The deformation is more intense in the northeastern section of the fault than in the southwestern section. The mining area is characterized by strong tectonic activity, which has resulted in the formation of a series of northeast-striking folds, such as the Baitai anticline. Influenced by tectonic activity, the pegmatite veins are predominantly northeast-trending, and these veins are the main ore-controlling structures. In this region, the strata of the Triassic Xinduqiao formation are exposed, mainly consisting of intercalated calcareous slate and black sandy slate interspersed with metamorphosed sandstone and other shallow-metamorphic rocks. The main magmatic rock exposed in the mining area is the Baitai granite, covering an area of ~90 km². This granite intrudes into the Xinduqiao formation and is situated in the central part of the Fangmaping–Sanyanlong granite. The Baitai granite is a biotite monzonitic granite with a fine-to-medium grain size, porphyritic texture, and massive structure. The primary mineral composition includes plagioclase (30%~40%), quartz (25%~30%), microcline (25%~30%), and biotite (5%~10%). In the northern part of the mining area, the Baitai granite has undergone muscovitization, resulting in fine-grained muscovite granite. The joints and fractures in the granite body are predominantly oriented north–northeast, with strikes of 110°~120° and dips of 30°~85°. A significant number of granite pegmatite veins have intruded along the fractures, and a few fine-grained veins and quartz veins are present. The beryllium mineralization occurs within the granite pegmatite veins.

In the Baitai mining area, 154 granite pegmatite veins have been discovered. These veins are hosted within the granite and display relatively straight boundaries, with occasional local undulations (Figure 4c). The majority of the veins are 1~15 m wide, a few are 30~50 m wide, and they extend approximately 50~500 m. Their dominant orientation is northeast, but a few trend north–northeast. According to the distribution of the pegmatite veins, the mining area is classified into two groups of veins: the southern and northern vein groups. The southern vein group primarily occurs in biotite monzonitic granite, forming vein-like and branching structures with larger sizes. The veins are approximately 5~30 m wide, extend for 100~300 m, and exhibit better beryl mineralization. The northern vein group mainly occurs in the northern part of the biotite monzonitic granite and is characterized by regular vein structures with smaller sizes and weaker mineralization.

The main type of pegmatite vein in the mining area is microcline–albite, and there is also a small amount of microcline pegmatite. The microcline–albite-type pegmatite primarily consists of microcline (20%~40%), albite (15%~35%), quartz (25%~35%), and muscovite (1%~5%), and the accessory minerals include zircon and cassiterite. The beryl mainly occurs in the microcline–albite-type pegmatites with higher microcline contents, predominantly located in the southern part of the mining area. The albite contents of the veins vary significantly due to differences in the degree of albite alteration. In particular, in the northern part of the mining area, where the albite alteration is intense, the veins are mainly composed of albite pegmatite. The granite pegmatite exhibits distinct zoning. Based on the mineral composition and structural features, the veins can be divided into five zones from the core to the edge. (1) The massive zone is mainly composed of massive quartz and microcline, and some of the veins consist solely of quartz. The beryl mainly occurs in this zone, and the beryl crystals can reach 10~20 cm. (2) The coarse-grained zone is mainly composed of coarse-grained quartz and microcline, and coarse beryl crystals are occasionally present. (3) The medium–coarse-grained zone is primarily composed of medium–coarse-grained quartz, microcline, and albite, with small amounts of muscovite. Beryl crystals are also visible. (4) The medium-grained zone mainly consists of medium-grained quartz, microcline, and albite, and fine-grained beryl crystals are present. (5) The fine-grained zone is mainly composed of fine-grained quartz and albite, and fine-grained beryl crystals are occasionally present. In most of the veins, the massive and coarse-grained zones are more developed, and the medium-grained and fine-grained zones are absent in some veins.

The mining area contains 115 beryllium-mineralized veins, and 13 beryllium ore bodies have been delineated (Figure 6). The ore bodies are controlled by the zoning of the veins and are mostly located in the massive zone in the central part of the veins. Their strikes are consistent with those of the pegmatite veins, and their dip angles mainly range from 60° to 80°, with some between 20° and 40°. The lengths of the ore bodies vary from 50 to 200 m, and they are 1~5 m thick. The extension varies considerably, with most being between 20 and 100 m and a few extending up to 150 m.

The primary ore mineral in the area is beryl, with associated columbite–tantalite. The beryl mostly occurs with quartz, microcline, and other minerals, forming coarse or giant crystals with sizes of greater than 10 cm and good crystal habits (Figure 4f,i). Based on the mineral occurrence characteristics, the beryl can be classified into two stages. (1) The primary beryl is green or light green, opaque, and hexagonal columnar in shape, it has longitudinal striations on the crystal faces, and the crystals are typically coarse-to-giant crystals. (2) The alteration-stage beryl is light green, transparent-to-translucent, and hexagonal columnar in shape, and the grains are usually smaller than 1 mm. The alteration-stage beryl is closely associated with albite alteration and muscovitization, and stronger albite alteration corresponds to a higher concentration of beryl. The gangue minerals mainly include quartz, microcline, albite, and muscovite. The ore structures include pegmatitic, subhedral-to-anhedral granular textures, and alteration-corroded structures. The ore structure is relatively simple, consisting primarily of massive and impregnated textures. The surrounding rocks exhibit alteration such as albite alteration, tourmalinization, and greisenization, and the albite alteration is closely linked to the rare metal mineralization. Albite alteration is widespread and becomes more intense from south to north across the mining area. It is particularly prominent in the medium-grained and medium–coarse-grained zones where the albite occurs in tabular, leaf-like, and granular forms. It has often replaced early minerals such as microcline, muscovite, beryl, and columbite, resulting in the formation of fine-grained beryl and needle-like columbite–tantalite. The muscovitization is less intense, primarily occurs in the medium-grained and medium–coarse-grained structure zones, and is commonly found in aggregates containing quartz.

4. Sampling and Analytical Methods

4.1. Sampling

To accurately determine the formation ages of the beryllium rare metal deposits in the Jiulong region, fresh and unaltered granite pegmatite samples (PM046-9, 22052802, 22052901, 22052907, and 21062620) were collected from typical veins in the Daqianggou lithium–beryllium deposit, Luomo deposit, and Baitai deposit. The sampling locations are shown in Figure 2, Figure 5 and Figure 6. After specimen observations and thin section examination, columbite–tantalite and cassiterite grains were selected from the samples for geochronological analysis. Sample PM046-9 was collected from the No. 1 lithium–beryllium ore body in the Daqianggou lithium–beryllium deposit and was an albite–lithium spodumene-type pegmatite. The main minerals included albite (20%~30%), spodumene (25%~30%), quartz (25%~35%), and muscovite (5%~10%), as well as a small amount of beryl, which was present as fine needle-like crystals that were less than 1 mm in size. The accessory minerals included zircon, cassiterite, columbite–tantalite, and apatite. Sample 22052802 was collected from the No. 13 beryllium ore body in the Daqianggou lithium–beryllium deposit and was a beryl–microcline–albite-type pegmatite. The main minerals were microcline (30%~35%), albite (20%~30%), quartz (20%~25%), muscovite (5%~10%), and beryl (1%~2%), as well as a small amount of biotite (1%). The accessory minerals included cassiterite, apatite, and zircon, and the beryl occurred as idiomorphic crystals with sizes of 1–2 cm. Sample 22052901 was collected from the No. 1 beryllium ore body in the Luomo beryllium deposit, which is located in the inner contact zone at the edge of the Qiaopengzi biotite granite body. It was a beryl–microcline–albite-type pegmatite, in which the beryl occurred as light green hexagonal columns that were approximately 0.5% ~2 cm in size. The main minerals were microcline (30%–35%), albite (25%~30%), quartz (30%~35%), beryl (1%~2%), and muscovite (3%~5%). Sample 22052907 was collected from the No. 5 beryllium ore body in the Luomo beryllium deposit, which is located in the outer contact zone at the edge of the Qiaopengzi biotite granite body. It was a beryl–microcline–albite-type pegmatite that contained approximately 5% beryl, which occurred as light green idiomorphic crystals approximately 1~5 cm in size. The main minerals were microcline (40%~45%), quartz (20%~25%), albite (20%~25%), and beryl (1%~2%), as well as small amounts of columbite–tantalite and cassiterite. Sample 21062620 was collected from the No. 19 beryllium ore body in the Baitai beryllium deposit, which is located inside an old mine shaft. It was a microcline–albite-type pegmatite, and the pegmatite veins occurred within a biotite two-mica granite. The tourmaline crystals were light green, hexagonal prisms with grain sizes of approximately 1~2 cm. This sample also contained well-developed columbite–tantalite, which occurred in granular and prismatic forms. The minerals were deep red to black and coexisted with microcline and quartz.

4.2. Analytical Methods

4.2.1. Mineral Selection and Target Fabrication

The mineral selection was performed at Guangzhou Tuoyan Analytical Technology Co., Ltd. (Guangzhou, China). After the samples were manually crushed, they were washed with clean water, and then gravity and electromagnetic separation techniques were used to isolate the columbite–tantalite and cassiterite. The minerals were observed under a binocular microscope to ensure that only particles without alteration, impurities, and cracks were selected. The chosen columbite–tantalite and cassiterite were fixed in epoxy resin, polished, and prepared for thin-section analysis. Transmitted reflection, cathodoluminescence (CL), and backscattered electron (BSE) imaging were conducted to observe the internal structures of the mineral grains. Based on these images, appropriate analysis points were selected for laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb dating analysis.

4.2.2. U-Pb Dating of Cassiterite

The LA-ICP-MS U-Pb dating of the cassiterite was performed at Yanduzhongshi Geological Analysis Laboratories Ltd. The analysis was conducted using an Analytikjena Plasma Quant MSQ inductively coupled plasma mass spectrometer and an NWR193nmAr-F excimer laser system (Electro Scientific Industries Inc., Portland, OR, USA). For each analysis, blank gas was introduced for 20 s, and the ablated particles were carried out of the chamber by the He carrier gas at a rate of 0.55 L/min, which flowed through a polyvinyl chloride (PVC) pipe, was mixed with Ar gas, and was delivered to the plasma mass spectrometer for analysis. The laser ablation analysis was performed for 50 s, with a background collection time of approximately 15 s, a laser energy density of 4 J/cm², a laser spot diameter of 40 μm, and a frequency of 8 Hz. For every 10 sample points analyzed, NIST610, Yankee, AY-4, and Cligga Head standards were analyzed once, twice, once, and once, respectively, for calibration purposes. The Yankee standard is composed of cassiterite from the Yankee tin–tungsten deposit in New England, eastern Australia, and it has a thermal ionization mass spectrometry (TIMS) U-Pb age of 246.48 ± 0.51 Ma [76]. The Cligga Head standard is composed of cassiterite from the Cligga Head tin deposit in Cornwall, southwest England, and it has a TIMS U-Pb age of 285.14 ± 0.25 Ma [77]. For the U-Pb isotope dating of cassiterite, the Yankee standard was used for isotopic fractionation correction. The AY-4 [76,78] and Cligga Head standards were used as data-quality-control standards, and NIST610 was used for the U and Pb content calculations. The analysis times for the measured elements were as follows: ²⁰⁴Pb (8 ms), ²⁰⁶Pb and ²⁰⁸Pb (15 ms), and ²⁰⁷Pb, ²³²Th, and ²³⁸U (20 ms). The data reduction was performed using the ZSkits and ICPMSDataCal programs [79,80], and the age of the cassiterite was calculated from the lower intercept of the U-Pb Tera–Wasserburg concordia plot. The U-Pb age calculations and the creation of the Tera–Wasserburg plot were conducted using the IsoplotR (v.3.3) software [81,82,83,84].

4.2.3. U-Pb Dating of Columbite–Tantalite

The in situ micro-region U-Pb dating of the columbite–tantalite was completed at Yanduzhongshi Geological Analysis Laboratories Ltd. Columbite–tantalite samples with good optical properties were selected for LA-ICP-MS analysis, which was conducted using an NWR193nmAr-F excimer laser system and an Analytikjena PlasmaQuant MSQ inductively coupled plasma mass spectrometer. The laser ablation spot size was 33 μm in diameter, the frequency was 6 Hz, and the energy density was 1.8 J/cm². The analysis times for the measured elements were as follows: ²³²Th and ²³⁸U (10 ms), ²⁰⁴Pb, ²⁰⁶Pb, and ²⁰⁸Pb (15 ms), ²⁰⁷Pb (30 ms), and other elements (6 ms). For every 10 sample points analyzed, NIST610, ZTA01, Coltan 139, and LCT02 standards were analyzed once, twice, once, and once, respectively. The U-Pb isotope dating analysis was conducted using ZTA01 (isotope dilution (ID)-TIMS age of 263.67 ± 1.71 Ma; [85]) as an external standard for isotope fractionation correction, Coltan139 (from the Rubicon pegmatite in Namibia, ID-TIMS age of 506.2 ± 5.0 Ma; [86,87]) as a quality-control standard, and NIST610 as an external standard. The data processing was carried out using the ICPMSDataCal 10.1 software [79,80], and the creation of the concordia plot and weighted average age calculation were performed using the IsoplotR software [84].

5. Analytical Results

5.1. U-Pb Ages of Cassiterite

The dated cassiterite from sample PM049 from the Daqianggou lithium–beryllium deposit is highly idiomorphic, typically occurs as subhedral-to-idiomorphic crystals with grain sizes of 90~120 cm, is dark brown, and mostly exhibits oscillatory zoning (Figure 7a). A total of 34 points were analyzed. The results are presented in Table S1. Six points with anomalies were discarded. The remaining points yielded ²⁰⁶Pb/²³⁸U ratios of 0.02464 to 0.02766 and ²⁰⁷Pb/²⁰⁶Pb ratios of 0.045815 to 0.06201. The Tera–Wasserburg isochron lower intercept age of the Daqianggou lithium–beryllium deposit (PM049) is 157.3 ± 1.7 Ma (MSWD = 1.0) (Figure 7a).

The dated cassiterite from sample 22052907 from the Luomo beryllium deposit is mostly dark brown and typically occurs as subhedral-to-idiomorphic crystals with grain sizes of 120~180 μm. It exhibits oscillatory zoning (Figure 7b), has a simple mineral structure, and has clean surfaces. Its structural and distribution characteristics suggest a magmatic crystallization origin. A total of 30 points were analyzed. The results are shown in Table S1. The ²⁰⁶Pb/²³⁸U values range from 0.02488 to 0.0557, and the ²⁰⁷Pb/²⁰⁶Pb values range from 0.06019 to 0.41953. The Tera-Wasserburg lower intercept age of the Luomo beryllium deposit (22052907) is 156.1 ± 1.5 Ma (MSWD = 0.59) (Figure 7b).

5.2. U-Pb Ages of Columbite–Tantalite

The columbite–tantalite samples selected for dating are well formed, typically occurring as subhedral-to-idiomorphic prismatic crystals with lengths of 100~200 μm. Most exhibit oscillatory zoning, and the BSE images of the columbite–tantalite are dark (Figure 8a,c,e). Columbite–tantalite grains without inclusions and fractures were selected for analysis. The LA-ICP-MS U-Pb isotope dating results are presented in Table S2.

For the columbite–tantalite from sample 22052802 from the Daqianggou lithium–beryllium deposit, the Th contents range from 1.13 × 10⁻⁶ to 7.12 × 10⁻⁶ (with an average of 2.44 × 10⁻⁶), the U contents range from 60 × 10⁻⁶ to 272 × 10⁻⁶ (with an average of 123 × 10⁻⁶), and the Th/U ratios range from 0.014 to 0.039. U-Pb isotope dating was conducted on 30 columbite–tantalite samples from this sample, and 27 valid data points were obtained. The ²⁰⁶Pb/²³⁸U ages are distributed along the concordia curve, and the weighted average ²⁰⁶Pb/²³⁸U age is 164.1 ± 0.8 Ma (MSWD = 2.3) (Figure 8a,b).

For the columbite–tantalite from sample 22052901 from the Luomo beryllium deposit, the Th contents range from 1.15 × 10⁻⁶ to 10 × 10⁻⁶ (with an average of 3.52 × 10⁻⁶), the U contents range from 84 × 10⁻⁶ to 524 × 10⁻⁶ (with an average of 221 × 10⁻⁶), and the Th/U ratios range from 0.008 to 0.031. U-Pb isotope dating was conducted on 30 columbite–tantalite samples from this sample, and 21 valid data points were obtained. The ²⁰⁶Pb/²³⁸U ages are distributed along the concordia curve, and the weighted average ²⁰⁶Pb/²³⁸U age is 163.3 ± 0.8 Ma (MSWD = 0.94) (Figure 8c,d).

For the columbite–tantalite from sample 21062620 from the Baitai beryllium deposit, the Th contents range from 0.58 × 10⁻⁶ to 38.9 × 10⁻⁶ (average 6.48 × 10⁻⁶), the U contents range from 15.1 × 10⁻⁶ to 239 × 10⁻⁶ (average 116 × 10⁻⁶), and the Th/U ratios range 0.009 to 0.213. U-Pb isotope dating was conducted on 20 columbite–tantalite samples from this sample, and 17 valid data points were obtained. The ²⁰⁶Pb/²³⁸U ages are distributed along the concordia curve, and the weighted average ²⁰⁶Pb/²³⁸U age is 188.8 ± 1.1 Ma (MSWD = 1.4) (Figure 8e,f).

6. Discussion

6.1. Timing of Mineralization

London [88] proposed that the formation of pegmatite-type rare metal deposits is linked to large-scale orogenic events. Therefore, determining the formation age of a deposit is a prerequisite for studying the deposit’s origin and discussing metallogenesis and tectonic–magmatic processes. It is also crucial for understanding the metallogenesis of rare metals and for resource exploration, investigating the regional orogenic evolution. In past studies, dating of granitic pegmatite-type rare metal deposits has typically relied on conventional U-Pb zircon dating and K-Ar dating of biotite. However, in granitic pegmatites, zircons are anomalously enriched in Th and U, which disrupts their U-Pb system. Zircons are often altered by the radioactive effects of Th and U, resulting in the formation of bent crystals, making it challenging to accurately date their formation [89,90,91]. The closure temperature of the biotite K-Ar isotope system is relatively low, and it is easily influenced by later hydrothermal fluids, which often leads to younger age results that do not accurately reflect the formation time of the pegmatite they were obtained from. These ages are typically interpreted as being related to later hydrothermal activity [36]. In recent years, to enhance the accuracy of determining the timing of the mineralization of rare metal pegmatite deposits, LA-ICP-MS U-Pb dating of accessory minerals such as columbite–tantalite, cassiterite, garnet, and monazite has been gradually adopted. These minerals are frequently present in rare metal granitic pegmatites and have been extensively used in pegmatite dating studies [39,92,93,94,95,96].

In this study, we utilized U-Pb isotope dating of cassiterite and columbite–tantalite to determine the ages of three deposits containing beryl–microcline–albite-type granitic pegmatite veins. Cassiterite is a common accessory mineral in granitic pegmatites. It has a relatively stable structure and high uranium content and is not easily influenced by late-stage hydrothermal fluids [97,98]. The U-Pb isotope system of cassiterite is generally stable, and it remains closed after crystallization, thus allowing it to accurately reflect the formation time of the pegmatite. Its age can be used as the mineralization age of the deposit. The U-Pb isotope system of columbite–tantalite is less influenced by alterations [87,91], and its low content of common Pb makes it a suitable mineral for U-Pb isotope dating. Our results reveal that the U-Pb ages of the cassiterite and columbite–tantalite from the Daqianggou lithium–beryllium deposit are 157.3 ± 1.7 Ma and 164.1 ± 0.8 Ma, respectively; the U-Pb ages of the cassiterite and columbite–tantalite from the Luomo beryllium deposit are 156.1 ± 1.5 Ma and 163.3 ± 0.8 Ma, respectively; and the U-Pb age of the columbite–tantalite from the Baitai beryllium deposit is 188.8 ± 1.1 Ma. The formation ages of the cassiterite and columbite–tantalite from the Daqianggou lithium–beryllium deposit and the Luomo beryllium deposit differ by 7 Ma but are largely consistent within the error range. Thus, these ages represent their emplacement and mineralization ages. The Daqianggou lithium–beryllium deposit was formed at 164~157 Ma, the Luomo beryllium deposit was formed at 163~156 Ma, and the Baitai beryllium deposit was formed at 189 Ma. The results show that the Daqianggou lithium–beryllium deposit and the Luomo beryllium deposit are substantially coeval, while the Baitai beryllium deposit formed 25 Ma earlier. All three deposits formed during the Early Yanshanian metallogenic period in the Early Jurassic.

Research on the metallogenic ages of granitic pegmatite-type rare metal deposits in the Jiulong area is relatively underdeveloped. The beryllium-bearing pegmatite veins in the Saltwater Pond beryllium deposit in the northern part of Baitai have a Re-Os age of 197 Ma [19], while the Re-Os age of molybdenite from pegmatite veins in the Mawo area is 189 Ma [46], both of which indicate that multiple magmatic–hydrothermal events occurred in the Early Yanshanian in the Jiulong area. Based on this study, the Saltwater Pond beryllium deposit formed at 197 Ma, the Baitai beryllium deposit and Mawo molybdenite formed at 189 Ma, and the Daqianggou lithium–beryllium deposit and Luomo beryllium deposit formed between 164 and 156 Ma. These findings suggest that two periods of granitic pegmatite-type rare metal metallogenesis occurred in the Jiulong area: a Be-Nb-Ta-Mo metallogenic event during 197~189 Ma and a Li-Be-Nb-Ta-Rb metallogenic event during 164~156 Ma.

6.2. Mineralization Characteristics

The granitic pegmatite-type beryllium deposits in the Jiulong area display a roughly concentric regional zonation. Based on geological field surveys and the dating results presented in this paper, the beryllium metallogenic events in the Jiulong area can be categorized into two periods: 197~189 Ma and 164~156 Ma (referred to as the early and late stages in this paper).

The Baitai beryllium deposit, Yanshuitang beryllium occurrence, Ruodeng beryllium occurrence, and Shangjigong beryllium occurrence are products of the early beryllium mineralization event and are primarily located in the Baitai–Yanshuitang region in the western part of Jiulong County. The beryllium deposits associated with this event are primarily controlled by the northeast-trending Bawolong–Yunongxi compressional–tectonic faults and their secondary fractures. The granitic pegmatite veins primarily occur along structural fractures, and the veins predominantly strike NNE and NE. The Baitai beryllium deposit, Yanshuitang beryllium occurrence, and Ruodeng beryllium occurrence are located to the east of the Bawolong–Yunongxi fault, while the Shangjigong beryllium occurrence is located to the west of the Sanyanlong fault. Regarding the occurrence characteristics of the pegmatites, the early beryllium deposits mainly have pegmatite veins in the inner and outer contact zones of the Late Indosinian (220~205 Ma) biotite granite and biotite monzogranite bodies, but a few occur in the Triassic strata. Limited research has been conducted on the genesis of the early beryllium deposits. Based on the occurrence features and diagenetic and mineralization ages of the Baitai beryllium deposit, we suggest that the beryllium mineralization was likely genetically related to the Late Indosinian granites. These granites are products of early magmatic crystallization. The related late residual melts ascended, differentiated, and crystallized along the structural fractures in the previously emplaced granite, resulting in the formation of pegmatite-type beryllium deposits [21].

In contrast to the early beryllium mineralization event, the late beryllium mineralization event was simultaneously associated with lithium and rubidium, resulting in the formation of a wider variety of pegmatite types. The main deposits formed during this period were the Daqianggou lithium–beryllium deposit and the Luomuo beryllium deposits, which are located in the east of the Tiechanghe anticline. The deposit is controlled by dorsal folds and secondary fracture structures. In both deposits, the pegmatite veins occur in the inner and outer contact zones of the Yanshanian Qiaopengzi highly differentiation granite (168~164 Ma; [51]), and the Daqianggou deposit is located farther away. Based on the mineral assemblages, the types of pegmatites in the Luomuo and Daqianggou deposits exhibit a gradual transition relationship. In terms of the temporal and spatial relationships, the Daqianggou lithium–beryllium deposit and the Luomuo beryllium deposit are associated with the Qiaopengzi granite and its surrounding satellite intrusive bodies [21,23,25,51]. The pegmatites exhibit a clear zoning pattern centered around the Qiaopengzi high-differentiation granite, and the mineralization characteristics vary in sequence from Be to Be-Nb-Ta to Li-Be-Nb-Ta, which is consistent with the magmatic crystallization differentiation features of Li-Ce-Ta (LCT)-type pegmatites [99]. The mineralization ages of the Daqianggou lithium–beryllium deposit and the Luomuo beryllium deposit are generally consistent, but the Luomuo deposit is slightly younger than the Daqianggou deposit. This may indicate that both deposits resulted from crystallization and differentiation of the same magmatic source. The magma transported further away underwent a higher degree of differentiation, leading to the formation of the lithium and beryllium deposits in Dajinggou, which is distant from the granite. In contrast, the magma transported closer to the granite experienced a lower degree of differentiation, resulting in the formation of the Luomo beryllium deposit near the granite.

6.3. Regional Significance of Mineralization

The Songpan–Ganzi orogenic belt hosts rare metal mining districts, such as the Jiajika, Ke’eryin, Jiulong, and Zhawulong mining districts [2], positioning it as a key granite pegmatite-type rare metal mineralization belt in China. As a result of the new discovery of vein X03 in the Jiajika mining district, the increase in the estimation of the reserves in the Li Jiagou and Dangba deposits in the Ke’eryin district, and the new prospecting findings in the Zhawulong Kalong and Caolong regions, the Songpan–Ganzi rare metal metallogenic belt has attracted global attention and has led to a surge in exploration for rare metals in granite pegmatites. Some researchers have proposed that the western Kunlun orogenic belt could be an extension of the Songpan–Ganzi orogenic belt to the west [48,100,101,102], and both belts are situated within the ancient Tethys tectonic domain. In the Tianshuihai region in western Kunlun, large and super-large granite pegmatite-type lithium–beryllium rare metal deposits, such as the Dahongliutan and Bailongshan deposits, have been discovered [16,17,44,103], leading to the proposal of the western Kunlun rare metal metallogenic belt. Based on studies of the metallogenic age, deposit genesis, metallogenic background, and isotope fractionation characteristics, Yan et al. (2022) [44] argued that the rock formation and metallogenic processes of the western Kunlun rare metal metallogenic belt were similar to those of the Songpan–Ganzi rare metal metallogenic belt, suggesting that both are part of a larger metallogenic belt within the ancient Tethys tectonic domain. This culminated in the concept of the western Kunlun–Songpan–Ganzi granite pegmatite-type large rare metal metallogenic belt [10,18,44].

The western Kunlun–Songpan–Ganzi rare metal metallogenic belt contains a large number of medium-to-large rare metal deposits, and research on these deposits is well developed, particularly research on the rock formation and metallogenic ages. This research aids in establishing the causal relationship between the tectonic setting, magmatic evolution, and metallogenesis. In this study, we systematically compiled data on the metallogenic ages of rare metals and the ages of the granites associated with the mineralization in the western Kunlun–Songpan–Ganzi rare metal metallogenic belt (

Table 1. Compilation of geochronological data of western Kunlun–Songpan–Ganzi rare metal metallogenic belt.

Ore Field	Location	Lithology	Dating Method	Age (Ma)	References
Western Kunlun rare metal pegmatite metallogenic belt
Kalawala-Mulinchang	Kalawala granite	Granite	Zircon U-Pb	207.5 ± 1.1	[94]
	Qiate granite	Granite	Zircon U-Pb	206.8 ± 1.1	[44]
	Qiate granite	Granite	Zircon U-Pb	205.9 ± 1.7	[44]
	Xiaoerbulong Be ore spot	Pegmatite	Zircon U-Pb	204.8 ± 0.7	[94]
	Xiaoerbulong Be ore spot	Pegmatite	Columbite U-Pb	204.7 ± 1.8	[94]
	Xiaoerbulong Be ore spot	Pegmatite	Columbite U-Pb	204.6 ± 2.1	[44]
	Huoshitashi Li deposit	Pegmatite	Monazite U-Pb	204.2 ± 0.8	[44]
	Huoshitashi Li deposit	Pegmatite	Columbite U-Pb	205.7 ± 2.7	[44]
	Mulinchang granite	Granite	Zircon U-Pb	208.4 ± 2.8	[44]
	Mulinchang Mica deposit	Pegmatite	Columbite U-Pb	206.4 ± 2.0	[44]
Dahongliutan	Dahongliutan granite	Granite	Zircon U-Pb	214 ± 1.8	[107]
	Dahongliutan granite	Granite	Zircon U-Pb	220 ± 2.2~217.4 ± 2.2	[108]
	Dahongliutan granite	Granite	Zircon U-Pb	209.6 ± 1.3	[109]
	Dahongliutan granite	Granite	Zircon U-Pb	216.7 ± 1.8	[109]
	Dahongliutan Li deposit	Pegmatite	Columbite U-Pb	211.9 ± 2.4	[40]
	Dahongliutan Li deposit	Pegmatite	Cassiterite U-Pb	218 ± 12	[40]
	Dahongliutan Li deposit	Pegmatite	Muscovite Ar-Ar	189.4 ± 1.1	[36]
	Dahongliutan Li deposit	Pegmatite	Muscovite Ar-Ar	187.0 ± 1.1	[36]
	Eastern Dahongliutan Li deposit	Pegmatite	Zircon U-Pb	205.2 ± 1.4	[41]
	Eastern Dahongliutan Li deposit	Pegmatite	Zircon U-Pb	205.0 ± 2.6	[41]
Bailongshan	Bailongshan granite	Granite	Zircon U-Pb	212.3 ± 1.6	[18]
	Bailongshan granite	Granite	Zircon U-Pb	210.8 ± 1.7	[44]
	Bailongshan granite	Granite	Zircon U-Pb	209.3 ± 1.3	[44]
	Bailongshan granite	Granite	Zircon U-Pb	208.3 ± 1.5	[44]
	Bailongshan granite	Granite	Zircon U-Pb	213.7 ± 2.0	[110]
	Bailongshan granite	Granite	Zircon U-Pb	214.7 ± 2.0	[42]
	Bailongshan granite	Granite	Zircon U-Pb	214.5 ± 2.8	[42]
	Bailongshan Li deposit	Pegmatite	Cassiterite U-Pb	211 ± 4.2	[43]
	Bailongshan Li deposit	Pegmatite	Cassiterite U-Pb	212.9 ± 3.6	[43]
	Bailongshan Li deposit	Pegmatite	Columbite U-Pb	208.1 ± 1.5	[18]
	Bailongshan Li deposit	Pegmatite	Monazite U-Pb	207.4 ± 0.6	[44]
	Bailongshan Li deposit	Pegmatite	Muscovite Ar-Ar	171.36 ± 1.87	[111]
	Bailongshan Li deposit	Pegmatite	Biotite Ar-Ar	172.39 ± 1.66	[111]
	Bailongshan Li deposit	Pegmatite	Columbite U-Pb	212.3 ± 0.9	[42]
	Bailongshan Li deposit	Pegmatite	Columbite U-Pb	213.7 ± 0.7	[42]
	Dahongliutan 505 Li deposit	Pegmatite	Cassiterite U-Pb	223 ± 11	[103]
	Xuefenling Li deposit	Pegmatite	Columbite U-Pb	208.4 ± 1.7	[44]
	Xuefenling Li deposit	Pegmatite	Columbite U-Pb	208.2 ± 2.1	[45]
	Xuefenling Li deposit	Pegmatite	Cassiterite U-Pb	208 ± 15	[45]
Songpan–Ganzi rare metal pegmatite metallogenic belt
Zhawulong	Zhawulong granite	Granite	Zircon U-Pb	211.6 ± 5.2	[36]
	Zhawulong granite	Granite	Monazite U-Pb	211.1 ± 0.46	[37]
	Zhawulong granite	Granite	Monazite U-Pb	212.3 ± 0.39	[37]
	Zhawulong granite	Granite	Monazite U-Pb	213.2 ± 0.23	[37]
	Zhawulong Li deposit	Pegmatite	Columbite U-Pb	204.5 ± 1.8	[36]
	Zhawulong Li deposit	Pegmatite	Muscovite Ar-Ar	179.6 ± 1	[36]
	Zhawulong Li deposit	Pegmatite	Muscovite Ar-Ar	174.3 ± 0.9	[36]
	Zhawulong Li deposit	Pegmatite	Monazite U-Pb	210.5 ± 0.3	[37]
	Zhawulong Li deposit	Pegmatite	Monazite U-Pb	205.1 ± 1.4	[37]
Caolong	Caolong granite	Granite	Zircon U-Pb	205.0 ± 1.2	[38]
	Caolong granite	Granite	Zircon U-Pb	207.4 ± 1.9	[38]
	Caolong granite	Granite	Zircon U-Pb	212.5 ± 1.1	[38]
	Caolong pegmatite	Pegmatite	Columbite U-Pb	204.3 ± 1.8	[38]
	Caolong pegmatite	Pegmatite	Columbite U-Pb	205.2 ± 7.2	[38]
	Caolong pegmatite	Pegmatite	Columbite U-Pb	201.1 ± 2.3	[38]
	Caolong pegmatite	Pegmatite	Cassiterite U-Pb	206.8 ± 3.4	[38]
	Caolong pegmatite	Pegmatite	Cassiterite U-Pb	200.6 ± 2.2	[38]
	Caolong pegmatite	Pegmatite	Cassiterite U-Pb	196.4 ± 2.2	[38]
	Caolong pegmatite	Pegmatite	Cassiterite U-Pb	208.5 ± 3.1	[38]
	Caolong pegmatite	Pegmatite	Muscovite Ar-Ar	169.9 ± 0.4	[38]
	Caolong pegmatite	Pegmatite	Muscovite Ar-Ar	167.6 ± 0.4	[38]
	Caolong pegmatite	Pegmatite	Monazite U-Pb	204.0 ± 0.7	[39]
	Caolong pegmatite	Pegmatite	Monazite U-Pb	200.4 ± 0.9	[39]
Gaduo-Zhaduo	Gaduo-Zhaduo granite	Granite	Zircon U-Pb	212.2 ± 1.1	[38]
	Gaduo-Zhaduo granite	Granite	Zircon U-Pb	217.9 ± 1.0	[38]
	Gaduo-Zhaduo granite	Granite	Zircon U-Pb	211.5 ± 1.2	[38]
	Gaduo-Zhaduo granite	Granite	Zircon U-Pb	216.1 ± 1.3	[38]
	Gaduo-Zhaduo granite	Granite	Zircon U-Pb	214.1 ± 1.0	[38]
	Gaduo-Zhaduo granite	Granite	Zircon U-Pb	214.9 ± 1.3	[38]
	Gaduo-Zhaduo granite	Granite	Zircon U-Pb	217.1 ± 0.8	[38]
	Gaduo-Zhaduo pegmatite	Pegmatite	Cassiterite U-Pb	194 ± 2	[39]
	Gaduo-Zhaduo pegmatite	Pegmatite	Columbite U-Pb	188 ± 1	[39]
	Gaduo-Zhaduo pegmatite	Pegmatite	Columbite U-Pb	178 ± 1	[39]
	Gaduo-Zhaduo pegmatite	Pegmatite	Muscovite Ar-Ar	153.6 ± 0.4	[39]
	Gaduo-Zhaduo pegmatite	Pegmatite	Cassiterite U-Pb	185 ± 3	[39]
	Gaduo-Zhaduo pegmatite	Pegmatite	Columbite U-Pb	188 ± 1	[39]
	Gaduo-Zhaduo pegmatite	Pegmatite	Muscovite Ar-Ar	158.4 ± 1.2	[39]
Keryin	Keryin granite	Granite	Zircon U-Pb	212.5 ± 2.2	[30]
	Keryin granite	Granite	Zircon U-Pb	207.8 ± 1.5	[30]
	Keryin granite	Granite	Zircon U-Pb	200.3 ± 2.7	[30]
	Keryin granite	Granite	Zircon U-Pb	200.1 ± 1.2	[30]
	Keryin granite	Granite	Zircon U-Pb	211.9 ± 2.4	[30]
	Keryin granite	Granite	Zircon U-Pb	219.2 ± 2.3	[33]
	Keryin granite	Granite	Zircon U-Pb	212.8 ± 1.1	[35]
	Keryin granite	Granite	Zircon U-Pb	209.1 ± 0.7	[35]
	Keryin granite	Granite	Zircon U-Pb	212 ± 2.8	[115]
	Keryin granite	Granite	Zircon U-Pb	213 ± 2.7	[115]
	Keryin granite	Granite	Zircon U-Pb	205 ± 4.5	[115]
	Keryin granite	Granite	Zircon U-Pb	200 ± 2	[116]
	Keryin granite	Granite	Zircon U-Pb	208 ± 2	[116]
	Redamen granite	Granite	Zircon U-Pb	223.6 ± 2.2	[30]
	Redamen granite	Granite	Zircon U-Pb	218.9 ± 8.6	[30]
	Redamen granite	Granite	Zircon U-Pb	206.4 ± 1.4	[117]
	Taiyanghe granite	Granite	Zircon U-Pb	206.7 ± 1.3	[117]
	Muzu granite	Granite	Zircon U-Pb	219.5 ± 0.7	[35]
	Genze granite	Granite	Zircon U-Pb	217 ± 2.8	[33]
	Feishuiyan granite	Granite	Zircon U-Pb	226.6 ± 2.5	[30]
	Keryin pegmatite	Pegmatite	Zircon U-Pb	210.1 ± 2.6	[30]
	Keryin pegmatite	Pegmatite	Zircon U-Pb	209.4 ± 2.5	[30]
	Keryin pegmatite	Pegmatite	Zircon U-Pb	198.6 ± 1.5	[30]
	Keryin pegmatite	Pegmatite	Zircon U-Pb	197.7 ± 1.7	[30]
	Keryin pegmatite	Pegmatite	Zircon U-Pb	196.3 ± 1.4	[30]
	Keryin pegmatite	Pegmatite	Zircon U-Pb	194.0 ± 1.9	[30]
	Keryin pegmatite	Pegmatite	Zircon U-Pb	190.8 ± 1.6	[30]
	Keryin pegmatite	Pegmatite	Zircon U-Pb	190.1 ± 1.3	[30]
	Dangba Li deposit	Pegmatite	Columbite U-Pb	213.5 ± 1.2	[31]
	Dangba Li deposit	Pegmatite	Cassiterite U-Pb	208.1 ± 1.9	[32]
	Dangba Li deposit	Pegmatite	Cassiterite U-Pb	199.3 ± 1.6	[32]
	Dangba Li deposit	Pegmatite	Muscovite Ar-Ar	159 ± 1	[36]
	Lijiagou Li deposit	Pegmatite	Cassiterite U-Pb	211.4 ± 3.3	[33]
	Lijiagou Li deposit	Pegmatite	Columbite U-Pb	211.1 ± 1.0	[33]
	Lijiagou Li deposit	Pegmatite	Zircon U-Pb	202 ± 4.9	[33]
	Lijiagou Li deposit	Pegmatite	Zircon U-Pb	200.1 ± 4.6	[33]
	Lijiagou Li deposit	Pegmatite	Zircon U-Pb	198 ± 3.4	[33]
	Jiada Li deposit	Pegmatite	Columbite U-Pb	204.7 ± 1	[35]
Jiajika	Majingzi granite	Granite	Zircon U-Pb	223 ± 1	[13]
	Majingzi granite	Granite	Zircon U-Pb	208.4 ± 3.9	[113]
	Majingzi granite	Granite	Zircon U-Pb	212.9 ± 5.9	[114]
	Majingzi granite	Granite	Zircon U-Pb	206 ± 3.2	[114]
	Jiajika Li deposit	Pegmatite	Cassiterite U-Pb	192.4 ± 7.3	[26]
	Jiajika Li deposit	Pegmatite	Cassiterite U-Pb	199.4 ± 3.3	[26]
	Jiajika Li deposit	Pegmatite	Columbite U-Pb	213.3 ± 1.9	[26]
	Jiajika Li deposit	Pegmatite	Cassiterite U-Pb	198.1 ± 3.8	[26]
	Jiajika Li deposit	Pegmatite	Columbite U-Pb	207.7 ± 1.5	[26]
	Jiajika Li deposit	Pegmatite	Cassiterite U-Pb	195.0 ± 12.0	[26]
	Jiajika Li deposit	Pegmatite	Cassiterite U-Pb	194.9 ± 4.1	[26]
	Jiajika Li deposit	Pegmatite	Columbite U-Pb	208.2 ± 1.9	[26]
	Jiajika Li deposit	Pegmatite	Cassiterite U-Pb	196.2 ± 2.4	[26]
	Jiajika Li deposit	Pegmatite	Cassiterite U-Pb	197.8 ± 2.6	[26]
	Jiajika Li deposit	Pegmatite	Columbite U-Pb	209.3 ± 1.7	[26]
	Jiajika Li deposit	Pegmatite	Zircon U-Pb	216 ± 2	[13]
	Jiajika Li deposit	Pegmatite	Columbite U-Pb	214 ± 2	[13]
	Jiajika Li deposit	Pegmatite	Muscovite Ar-Ar	198.9 ± 0.4	[27]
	Jiajika Li deposit	Pegmatite	Muscovite Ar-Ar	195.7 ± 0.1	[27]
	Jiajika Li deposit	Pegmatite	Zircon U-Pb	217 ± 0.84	[28]
	Jiajika Li deposit	Pegmatite	Cassiterite U-Pb	210.9 ± 4.6	[28]
	Jiajika Li deposit	Pegmatite	Cassiterite U-Pb	198.4 ± 4.6	[28]
	Jiajika Li deposit	Pegmatite	Cassiterite U-Pb	203.7 ± 4.6	[29]
	Jiajika Li deposit	Pegmatite	Zircon U-Pb	186.7	[114]
	Jiajika Li deposit	Pegmatite	Muscovite Ar-Ar	182.9 ± 1.7	[113]
	Jiajika Li deposit	Pegmatite	Biotite Ar-Ar	169.9 ± 1.6	[113]
Jiulong	Qiaopengzi granite	Granite	Zircon U-Pb	168.2 ± 0.9	[51]
	Shitizi granite	Granite	Monazite U-Pb	154.6 ± 0.6	[51]
	Landiao granite	Granite	Zircon U-Pb	157.1 ± 1.6	[51]
	Landiao granite	Granite	Monazite U-Pb	152.5 ± 0.5	[51]
	Baitai granite	Granite	Zircon U-Pb	212.6 ± 3.3	[22]
	Baitai granite	Granite	Zircon U-Pb	213.5 ± 1.7	[22]
	Baitai granite	Granite	Zircon U-Pb	212.6 ± 1.8	[22]
	Luomo Be deposit	Pegmatite	Cassiterite U-Pb	156.1 ± 1.5	This study
	Luomo Be deposit	Pegmatite	Columbite U-Pb	163.3 ± 0.8	This study
	Daqianggou Li-Be deposit	Pegmatite	Cassiterite U-Pb	157.3 ± 1.7	This study
	Daqianggou Li-Be deposit	Pegmatite	Columbite U-Pb	164.1 ± 0.8	This study
	Baitai Be deposit	Pegmatite	Columbite U-Pb	188.8 ± 1.1	This study

). In the western Kunlun region, the closure of the ancient Tethys Ocean occurred at around 240 Ma, and from 234 to 217 Ma, the region was in an extensional environment following a compressional orogeny [40,104,105,106]. In the Dahongliutan mining district, the rare metal pegmatites and granites mainly formed between 220 and 205 Ma [36,40,41,107,108,109], while in the Bailongshan mining district, they mainly formed between 223 and 207 Ma [18,42,43,44,45,110,111]. These rare metal pegmatites and granites are products of the stable intraplate extensional environment that formed after the closure of the ancient Tethys Ocean [40,43]. In the Songpan–Ganzi region, the closure of the Ganzi–Litang Ocean occurred at around 216 Ma [112], representing a compressional orogeny. The metamorphic ages of the mafic rock intrusions in the Jianglang dome in the southeastern margin of the Songpan–Ganzi region are between 214 and 206 Ma [74], while the ages of many of the post-collision granites are concentrated between 215 and 205 Ma, and thus, they represent the post-collision environment following compressional orogeny. In the Jiajika mining area, the rare metal pegmatites mainly formed between 216 and 192 Ma [13,26,27,28,29], and the associated Majingzi granite formed between 223 and 206 Ma [13,113,114]. In the Ke’eryin mining area, the rare metal pegmatites mainly formed between 216 and 192 Ma [30,31,32,33,34,35,36], and the Taiyanghe and Ke’eryin granite bodies formed between 232 and 200 Ma [30,33,34,115,116,117]. In the Zhawulong mining area, the rare metal pegmatites mainly formed between 210 and 204 Ma [36,37], and the related granites formed between 213 and 211 Ma [36,37]. The newly discovered rare metal pegmatites and granites in the Caolong and Kalong regions near Zhawulong formed between 208 and 196 Ma and between 212 and 205 Ma, respectively [15,38]. In the Gaduo–Zaduo region, the main rare metal pegmatites formed between 194 and 178 Ma [39], and the granites in these regions formed between 218 and 212 Ma [38]. It is evident that most of the granites in the western Kunlun–Songpan–Ganzi rare metal metallogenic belt formed between 220 and 205 Ma, and the formation of pegmatites can be divided into two phases: 210–200 Ma and 200–180 Ma. The rare metal pegmatites in areas such as Jiajika, Dahuangliutan, Bailongshan, Zhaowulong, and Caolong mainly formed during 210–200 Ma, while those in Gaduo–Zaduo, Ke’eryin, Jiqika, Jiulong, and other areas are mainly from 200–180 Ma. The 210–200 Ma stage corresponds to magma intrusion forming granites in a post-collision tectonic setting, with residual magma crystallization and differentiation leading to rare metal mineralization in pegmatites; the 200–180 Ma phase is a product of the lithospheric stability and extension after the collision (Figure 9).

The two phases of the formation of rare metal pegmatites in the Jiulong area are related to the Early Yanshanianian mineralization. The second phase (164~156 Ma) was significantly different from the Late Indosinian mineralization observed in rare metal mining districts such as the Jiajika, Ke’eryin, Zhawulong, Dahongliutan, and Bailongshan. In the Jiulong area, the rare metal mineralization primarily involved Be, which differs from the LCT-type Be, Be-Nb-Ta, and Li-Be-Nb-Ta evolutionary sequences identified in districts such as the Jiajika district. Most of the Jiulong deposits lack a Li evolution stage. Tan et al. (2022, 2023) believe that this feature may be linked to the strong erosion in the Jiulong area, that is, the Li-Be-Nb-Ta pegmatites at the top of the Be mineralized pegmatites have been almost completely eroded [19,51]. In the Jiulong area, intermediate–felsic magmatic rocks are widely exposed, covering an area of around >1300 km². In comparison, the exposed area of the Majingzi intrusion in the Jiajika mining area is ~4 km², the area of the Ke’eryin granite in the Ke’eryin mining area is ~188 km², and the exposed area of the Taiyanghe granite is ~42 km². The erosion in the Jiulong area is more intense than that in the Jiajika and Ke’eryin mining areas, indicating that the Jiulong area has undergone stronger erosion, which has resulted in the exposure of deep granites at the surface.

Through analyzing the rare metal mineralization and rock formation ages in the western Kunlun–Songpan–Ganzi rare metal metallogenic belt, along with the two-phase mineralization characteristics in the Jiulong area, we conclude that the development of the metallogenic belt consisted of three rare metal mineralization events associated with the pegmatites: 210~200 Ma (representative areas include Jiajika, Dahongliutan, Bailongshan, and Zhawulong), 200~180 Ma (representative areas include Ke’eryin, Gaduo-Zaduo, and Jiulong Baitai), and 170~150 Ma (representative areas include Jiulong Luomuo, and Daqianggou). The first rare metal mineralization event during 210~200 Ma mainly took place in the late orogenic stage, i.e., in a post-collision tectonic environment. The 200~180 Ma and 170~150 Ma mineralization events occurred in lithospheric extension environments. The metallogenic belt contains a large number of similar metallogenic bodies, which have considerable rare metal mineralization potential. The rare metal mineralization event in Jiulong during 170~150 Ma indicates the possible formation of rare metal resources during this period. Based on a comparison of the levels of erosion, it is recommended that exploration in the metallogenic belt focuses on deeper exploration of rare metals.

7. Conclusions

(1) The Jiulong area is located on the southeastern edge of the western Kunlun–Songpan–Ganzi rare metal metallogenic belt, which primarily consists of pegmatite-type beryllium (lithium–niobium–tantalum) deposits. The major deposits include the medium-sized lithium–beryllium deposit in Daqianggou, the small beryllium–niobium–tantalum deposit in Luomo, the small beryllium deposit in Baitai, and beryllium occurrences in Shangjigong, Ruodeng, and Yanshuitang. The type of pegmatite associated with the mineralization is microcline–beryl pegmatite, and beryl is the ore mineral. Spodumene has not been found, except for in the Daqianggou deposit.

(2) LA-ICP-MS U-Pb dating of cassiterite and niobium–tantalum ores revealed that the Daqianggou lithium–beryllium deposit formed between 164 and 157 Ma, the Luomo beryllium deposit formed between 163 and 156 Ma, and the Baitai beryllium deposit formed at 189 Ma. These deposits were formed in the Early-to-Middle Jurassic, corresponding to the Early Yanshanianian, and they formed through two stages of beryllium mineralization.

(3) The western Kunlun–Songpan–Ganzi rare metal metallogenic belt is characterized by multiple stages of mineralization from the Late Indosinian to the Early Yanshanianian, including three rare metal mineralization events at 210~200 Ma, 200~180 Ma, and 170~150 Ma. In the southeastern part of the belt, the Jiulong region primarily hosts Early Yanshanianian beryllium mineralization, and exploration efforts within the metallogenic belt should prioritize the identification of deep-seated rare metal mineralization events that occurred during the Early Yanshanianian.