Southwest China broadly experienced three mineralization phases: the Precambrian, Paleozoic, and Meso-Cenozoic phases. Among them, the Meso-Cenozoic mineralization phase shows the closest relationship with REEs.
(1) During the Precambrian, the Yangtze region had a relatively thin crust. Ancient mantle plume activity may have led to the formation of the SN-trending Xichang-central Yunnan rift basin. These conditions, accompanied by intense magmatic-volcanic processes, resulted in frequent mantle-crust material exchange, dominant minerals like Cu, Fe, and Au, and magmatic-volcanic-metamorphic mineralization in the region. As a result, the Yangtze region formed distinctive sedimentary-metamorphic reworked copper-iron deposits associated with marine volcanic extrusion, such as the Dahongshan, Lala, and Yi’nachang deposits. Moreover, this mineralization style is also observed in the basement sporadically exposed along the periphery of the Upper Yangtze block. Transitioning into the Meso- to Neoproterozoic and the Early Paleozoic, the ancient Upper Yangtze block took shape, and the geological process shifted to a prolonged period of stable cap rock evolution. During this stage, material exchange primarily occurred within the crust, potentially inheriting early mantle-derived materials. The subsequent intensified sedimentary mineralization led to the formation of iron/manganese/paleo-sandstone-hosted copper deposits closely linked to sedimentation, such as the Laniping-type paleo-conglomerate-hosted copper deposit, the Dongchuan sedimentary-metamorphic reworked copper deposit, and the Manyingou-Baozipu-type weathering-sedimentary iron deposit. During the Late Neoproterozoic, particularly in the Sinian-Cambrian transitional stage, the transport of polymetallic elements in basement rocks by contemporaneous deep faults on continental/platform/basin margins, in relatively enclosed restricted basins or platform-to-basin transition zones, resulted in sedimentation in carbonate formations and the formation of high-abundance layers of polymetallic elements like Pb, Zn, Ag, Hg, and Au. These laid a primary foundation for the final enrichment of the lead-zinc-mercury deposit within the Sinian-Early Paleozoic carbonate formation on the northeastern margin of the Upper Yangtze block and the lead-zinc deposit within the Sinian Dengying Formation-Early Cambrian carbonate formation on the western margin of the Upper Yangtze block. The Mesoproterozoic-Neoproterozoic Qingbaikouan witnessed significant extensive copper mineralization in the Yangtze block, represented by many large and medium-sized copper deposits distributed in the Yinmin and the Luoxue formations of the lower subgroup of the Kunyang Group on the eastern margin of the central Kangdian rift. These copper deposits include the Tangdan, Yinmin, Luoxue, and Xintang deposits in the Dongchuan area and the Tongshi, Shishan, and Sanjiachang Fengshan deposits in the Yimen area. Qiu et al. determined two quartz samples from the Dongchuan-type Luoxue copper deposit, obtaining the 40Ar-39Ar isochron ages ranging from 810 to 770 Ma, possibly suggesting the mineralization age or the enrichment and modification age of the copper deposit from the Jinningian to the Chengjiangian [
131]. In the Nujiang-Lancangjiang-Jinshajiang region (also referred to as the Sanjiang region) in Southwest China, the mineralization events associated with the Proterozoic volcanic rocks occurred principally in the Shuangjiang continental margin arc zone in the Lincang area. The mineralization in the region was provided by the metamorphic intermediate-mafic volcanic formation in the Huimin Formation of the Mesoproterozoic Lancang Group. The iron deposit-hosted metamorphic terrane in the Lancang Group is primarily composed of the siliceous and argillaceous formations in the lower part, the volcanic-sedimentary formation in the middle, and the argilloarenaceous flysch formation in the upper part. Among them, the middle metamorphic intermediate-mafic volcanic-sedimentary rock assemblage is essentially a ferrosilicon formation. Its iron-rich mafic volcanic rocks carried a large amount of magnetite along with volcanic materials into the volcanic basin, providing a material source for the formation of iron ore beds. Additionally, elements like Fe, Si, S, P, and CO
2 brought by volcanic activity entered the oceanic basin via gas emission and thermal springs during the intermission of volcanic activity, providing a rich material basis for the sedimentation of siderite and magnetite ore beds. Most ore beds within the deposits formed during the eruption intervals of the mafic eruption cycle. In the middle-late stage of volcanic activity (i.e., the late mafic eruption cycle), volcanic activity peaked, leading to the extrusion of substantial mafic lavas and the subsequent overflow of iron ore molten lava, forming a thick and large iron ore body at the leading edge of mafic lavas. Therefore, the Huimin iron deposit is identified as a typical marine volcanic eruptive-sedimentary iron deposit, with a Mesoproterozoic metallogenic epoch and mineralization ages ranging approximately from 1600 to 1000 Ma.
(2) The Paleozoic witnessed the formation and evolution of the Yangtze block, which exhibited relative internal stability, intense marginal extension, basalt eruption, and the emplacement of mafic-ultramafic rocks. During the Chengjiangian, the Yangtze block took shape, accompanied by large-scale intrusion of granitic magmas on its western margin and extensional rifting in the southeastern Guizhou region, leading to the formation of Mn-Fe-bearing sediments in the marginal sea basin and its margins. During the Caledonian, the Yangtze block developed an epicontinental sea. The Late Sinian-Early Cambrian neritic carbonate formations hosted lead-zinc/phosphate/gold deposits, whereas the Early-Middle Cambrian carbonate formations in the southeastern Yunnan region hosted copper-lead-zinc-tungsten-tin-silver polymetallic deposits. Moreover, the Caledonian structural modification contributed to the enrichment and mineralization of the tectonic-hydrothermal vein antimony deposit and the altered-rock gold polymetallic deposit hosted in the Meso- to Neoproterozoic epimetamorphic rock series in the southeastern Guizhou region. The Hercynian manifested weak magmatic activity in the early stage and basalt extrusion and the emplacement of ultramafic-mafic magmas in the late stage, generating vanadium-titanium-magnetite/copper-nickel-platinum-palladium/lead-zinc deposits. Due to the rise of the mantle plume during the Hercynian, extremely thick Devonian and Carboniferous sediments occurred in the Liupanshui rift trough, which formed due to crustal thinning, extension, and subsidence in the initial stage. Moreover, the possible circulation of Pb-Zn-rich hydrothermal fluids in deep faults along the rift trough boundary might have led to the sedimentation in the carbonate formation and the formation of a high-abundance layer of polymetallic elements like Pb, Zn, and Ag, providing an initial foundation for the final enrichment of the Huize-type lead-zinc deposit in the Late Paleozoic carbonate formation. The lead-zinc deposits might have formed concurrently with the sedimentation and diagenesis of Devonian carbonate formations. During the Late Hercynian, the activity of the Emeishan mantle plume reached its peak, marking another significant mineralization event in Southwest China, forming Panzhihua-type magmatic fluids vanadium-titanium-magnetite deposits, volcanic rock-hosted copper deposits, and lead-zinc deposits. In the early Late Permian, Southwest China exhibited tropical rainforests with lush vegetation, contributing significantly to coal formation. Bauxite deposits within the Middle Permian Liangshan Formation and the Upper Triassic Xuanwei Formation were associated with the littoral-swamp facies. From the Neoproterozoic to the Early Paleozoic, the marginal active zone on the east side of the Sichuan-Yunnan rift zone along the western margin of the ancient Yangtze block evolved into a significant lead-zinc metallogenic belt. These deposits are distributed within dolomites with algal layers in the second member of the Sinian Dengying Formation, frequently associated with the anhydrite layers. Based on the attitudes of ore bodies, the deposits can be categorized into stratiform and vein deposits, with the latter type being larger-scale, exemplified by the Daliangzi, Tianbaoshan, and Tuanbaoshan deposits [
132]. The Early Paleozoic mineralization in the Sanjiang region in Southwest China occurred primarily on the passive margins of the Zhongza and the Baoshan blocks, which are located on the east and west sides of the Qamdo-Pu’er block, respectively. It was predominately characterized by lead-zinc mineralization, thus forming sedimentary exhalative lead-zinc deposits. Such lead-zinc deposits are hosted by the Early Paleozoic marine carbonate rocks and exemplified by the Najiaoxi lead-zinc deposit in the Zhongza block in Batang County and the Mengxing lead-zinc deposit in the Baoshan block. Specifically, the Najiaoxi lead-zinc deposit is situated within the Paleozoic carbonate platform, with a model age of lead-zinc ores at 552 ± 73 Ma, which is comparable to the age (615 to 520 Ma) of the Cambrian and the ore-hosting surrounding rocks. Therefore, the Cambrian units can be considered the synsedimentary ore source layers, with their mineralization closely associated with hydrothermal sedimentation. Based on the information above, the Paleotethys Ocean can be understood as an archipelagic ocean that developed from the continental margin system of the Prototethys Ocean. It was an oceanic system characterized by alternative distributions of multiple blocks, oceanic basins, and island arcs, along with a complex continental margin. Zhong et al. regarded the Paleotethys Ocean as an archipelagic ocean system due to its archipelagic ocean pattern [
133]. However, Pan et al. highlighted the continental margin system, terming the Paleotethys Ocean as a multi-island arc basin tectonic system [
134]. Zhong et al. revealed that the Changning-Menglian (Lancang River) between Gondwana- and Yangtze-affiliated blocks served as the main oceanic basin, whereas the Jinsha River—Ailao Mountains, Ganzi-Litang, and the South Kunlun Mountains—Aemye Ma-chhen Range were considered as subsidiary oceanic basins [
133]. Pan et al. systematically analyzed five ophiolite melange belts and four arc-basin systems in the Sanjiang region and compared them with the arc-basin tectonic system in Southeast Asia [
134]. They proposed that the prototype basins represented by the Paleozoic ophiolite melange belts in the Sanjiang region were predominantly back-arc oceanic basins, interarc basins, and marginal sea basins. During the Paleotethys Ocean evolutionary stage, the coexisting arc chains (frontal/island/volcanic arcs), the back-arc, interarc, and marginal sea basins in an alternative distribution, and microblocks constituted a complex continental margin tectonic system. Driven by the subduction of back-arc basins and their oceanic crusts, the archipelagic orogenesis involving arc-arc and arc-continent collisions resulted in the Southeast Asia-type orogenic process during the Mesozoic. The Jinshajiang arc-basin system is characterized by the Qiangtang-Jitang-Chongshan-Lancang remnant arc as its frontal arc along the western margin of the Qamdo-Simao Block. Simultaneously, the Lancangjiang back-arc basin expanded northeastward of this remnant arc. The Yidun arc-basin system resulted from the westward subduction of the Ganzi-Litang oceanic basin, which formed through back-arc spreading [
135]. The Qamdo-Simao Basin, nestled between the Jinshajiang suture zone and the northern Lancangjiang fault zone, is recognized as a composite back-arc foreland basin formed on the Proterozoic-Lower Paleozoic basement from the Late Paleozoic to the Mesozoic. Based on the above, during the Late Paleozoic in the Sanjiang region in Southwest China, the successive closure of paleo-oceanic basins that opened from the Carboniferous to the Early Permian and the subduction-induced orogenic processes resulted in an archipelagic arc-basin system. This system produced the Tongchangjie copper deposit (typical of Cyprus-type deposits) associated with the Permian ocean basalt series and the Laochang lead-zinc-silver polymetallic deposit (typical of volcanogenic massive sulfide (VMS) deposits) associated with the slightly alkaline intermediate-mafic volcanic series. The Late Paleozoic mineralization events were characterized by submarine hydrothermal exhalative-sedimentary mineralization, forming various VMS deposits in three significant metallogenic environments. Specifically, the Changning-Menglian oceanic basin environment developed the Tongchangjie copper deposit (typical of Cyprus-type deposits) associated with the Permian ocean-bridge basalt series and the Laochang lead-zinc-silver polymetallic deposit (typical of VMS deposits) associated with the slightly alkaline intermediate-mafic volcanic series [
136,
137]. The Carboniferous-Permian volcanic arc (Tenasserim) environment, created by the eastward subduction of the Changning-Menglian oceanic basin, produced the Dapingzhang-type VMS deposit in the Carboniferous marine quartz keratophyre series (360 Ma; [
138,
139]) and the Sandashan-type massive sulfide copper deposit in the Late Permian marine intermediate-felsic volcanic series [
140]. The intra-oceanic arc environment, caused by the westward subduction of the Jinshajiang oceanic basin, developed massive sulfide deposits associated with the Permian arc volcanic series, exemplified by the Yangla copper deposit [
141]. Overall, the Late Paleozoic mineralization phase was dominated by copper, lead, and zinc mineralizations, succeeded by iron mineralization, predominantly forming large-scale VMS deposits, showing promising exploration potential. The Changning-Menglian rift oceanic basin exhibited different mineralization types in various evolutionary stages. In the early rift development stage, volcanic activity resulted in highly alkaline rift basalts, which, combined with hydrothermal fluid mineralization, led to the VMS deposits represented by the Laochang deposit. In the late oceanic basin stage, volcanic activity reduced the alkalinity of volcanic rocks, resulting in ocean-ridge basalts. The ocean-ridge basalts under volcanic-sedimentary mineralization formed the CVHMS deposits represented by the Tongchangjie deposit. Although the volcanic activity in the rift basin was generally controlled by the rift valley—oceanic basin system, the resulting deposits were significantly dictated by volcanic edifices and fault structures. The early hydrothermal fluid mineralization was dominated by metallic elements including Ag, Pb, and Zn, associated with S and Cu. Individual ore bodies featured upper black ores (massive silver-lead-zinc ore body) and lower yellow ores (Cu-bearing pyrite ore body). The copper ore body exhibited a veinlet-disseminated structure at the lower part, with a concealed porphyry mass in the deep part. The late volcanic-sedimentary mineralization showed primary metallic elements including Cu and Zn. The Carboniferous-Permian volcanic arc environment, produced by the eastern subduction of the Lancangjiang oceanic basin, developed the massive sulfide copper deposits (e.g., the Sandashan copper deposit) associated with the Carboniferous-Permian marine intermediate-felsic volcanic series and the volcanic-sedimentary iron deposits (e.g., the Manyang iron deposit) associated with the marine mafic volcanic rocks. Although the mineralization in the Yunxian-Jinghong rift basin was generally controlled by the rift zone, the deposits and orefields were primarily distributed in volcanic edifices and depressions along fault zones, with the deposit types and chemical structures varying with rift segments. For instance, the volcanic-sedimentary mineralization in the southern segment formed the Sandashan volcanic-hosted massive sulfide (VHMS) deposit with a dominant metallic element of Cu, while the mafic volcanic rocks in the rift basin formed the volcanic-sedimentary Manyang iron deposit. The Late Triassic mineralization events occurred principally in the magmatic arc environment and partially in the superimposed basin environment above magmatic arcs, resulting in various VMS deposits and porphyry copper deposits. In the Yidun island arc belt, the slab tearing and differential subduction of the Ganzi-Litang oceanic basin caused the arc segmentation. Specifically, the northern segment developed the Changtai extensional arc due to the steep subduction of the oceanic crust slab, hosting interarc rift basins. The southern segment developed the Zhongdian compressional arc due to the gentle subduction of the oceanic crust slab, developing significant intermediate-acid porphyry systems [
142]. The interarc rift basins in the Changtai extensional arc developed the VMS zinc-lead-copper deposits like the super-large Gacun deposit [
143]. The bimodal volcanic series associated with VMS mineralization showed ages ranging from 220 to 218 Ma [
135]. The Re-Os ages of the sulfide ores ranged from 218 to 217 Ma [
142]. The porphyry magmatic system within the Zhongdian compressional arc developed porphyry and skarn deposits, exemplified by the large Pulang porphyry copper deposit and the Hongshan skarn copper polymetallic deposit. For the Pulang porphyry copper deposit, the copper-bearing porphyry showed ages ranging from 216 to 213 Ma [
144], and the molybdenite yielded a Re-Os age of 213 ± 3.8 Ma [
145]. In the southern segment of the Jiangda-Weixi continental margin arc, the Late Triassic extension led to the formation of a volcanic-rift extensional basin, which was superimposed upon the Permian continental margin arc terrane [
146]. The basin developed massive sulfide deposits associated with the Late Triassic bimodal rock assemblages. Furthermore, the deep-water marine felsic volcanic series (Rb-Sr age: 230 Ma) produced the Luchun-type copper polymetallic deposit, while the shallow-water intermediate-acid volcanic series produced the Chuzhage-type iron-silver polymetallic deposit. During the contraction and extinction stage of the volcanic rift basin, hydrothermal-sedimentary mineralization generated large barite and gypsum deposits [
146,
147]. The superimposed basin located in the northern segment of the Jiangda-Weixi continental margin arc holds massive sulfide deposits associated with the Late Triassic intermediate-acid volcanic series in shallow-water volcanic environments, such as the Zhaokalong and the Dingqingnong iron-silver polymetallic deposits. Moreover, the superimposed basin hosts submarine hydrothermal-sedimentary deposits associated with the Late Triassic basalt series and extensional basins, for example, the Zuna silver-lead-zinc deposit in the Shengda Basin [
147]. In summary, the Late Paleozoic mineralization in the Sanjiang region in Southwest China is principally associated with the archipelagic arc-basin systems. The hydrothermal exhalative sedimentation and arc volcanism in rift valleys/basins primarily led to copper, lead, and zinc mineralizations, followed by iron mineralization. The resulting deposits are dominated by VMS deposits, succeeded by hydrothermal deposits, showing overall large scales.
(3) During the Mesozoic Indosinian (260–205 Ma), the subduction, collision, and rifting of block margins resulted in Carlin-type gold deposits. Frequent and intense magmatic activity enhanced metamorphic clastic-rock gold-iron-manganese deposits in the Barkam region on the Western Sichuan Plateau. Due to the subduction of the Pacific plate beneath the Yangtze block, the Cathaysia block moved further towards the Yangtze block, enriching the fine disseminated gold deposits through structural modification. In the folding and uplifting stage of continental blocks during the Mesozoic Yanshanian (205–80 Ma), the subduction of the Pacific plate toward the Chinese continent caused regional folding and uplifting, shifting the structural line from EW to NE-NNE directions. This led to the modification and enrichment of the initial lead-zinc protore beds, forming lead-zinc vein deposits. Furthermore, the Yanshanian magmatic activity in the southeastern Yunnan region played a significant role in the modification, enrichment, and localization of the copper-lead-zinc-tungsten-tin-silver polymetallic deposits, and sedimentary (sandstone-hosted) copper-iron deposits formed in the Mesozoic red-bed basins. During the Triassic, the structural framework characterized by alternating continental-margin island arcs and basins emerged. The Barkam-Xiangcheng and Yushu-Zhongdian areas in the north inherited the active basin environment that had formed since the Late Paleozoic. Flysch basins and island arc volcanic-sedimentary basins formed in the east and the west, respectively. In the early stage of the Late Triassic, typical bimodal volcanic formations were extensively developed in the Yidun island arc belt, and syn-collisional arc granite and diorite porphyries were developed in the northwestern Yunnan region, along with large-scale submarine volcanic exhalation and porphyry mineralization. During the Jurassic, seawater receded to the Tibet and western Yunnan regions due to the impacts of the Indosinian movement on the Chinese paleogeographic environment, surviving the Tethys-type sea area. The Riwoqe-Lhorong area in the northwestern Sanjiang region still developed metastable marine basins and flysch formations. The Shiqu-Xinlong-Muli area also developed similar sedimentary rocks in unconformable contact with the underlying Late Triassic volcanic rocks, suggesting that the Tethyan marine sedimentation had extended to the Ganzi area in the western Sichuan region. During the transition from the plate collisional orogeny in the Indosinian cycle to the intracontinental orogeny in the Yanshanian-Himalayan cycle, the Songpan-Ganzi orogenic belt transitioned into a relatively stable postcollisional stage. At the end of magmatic activity, large-scale intrusion of intermediate-felsic magmas occurred in the relatively stable and closed environment, laying the foundation for the post-magmatic pegmatite rare metal mineralization. During the Cretaceous, the Sanjiang region seldom received sediments, except for the Qamdo-Lanping-Simao basin and the southern side of the Bangonghu-Nujiang suture zone. During the Late Cretaceous, subjected to the subduction of the Bangonghu-Nujiang Ocean and the collisional orogeny, the granites formed in a back-arc thrusting setting in the Tengchong area were significantly associated with tungsten-tin mineralization. In the Baoshan area, the mountain belt subjected to intracontinental deformation developed post-orogenic A2-type granites, which played a vital role in the localization of lead-zinc polymetallic deposits. In addition, constrained by the large Longmenshan-Daxueshan-Jinpingshan nappe structure and magmatism, post-collisional granites/granite porphyries formed in the Songpan-Ganzi and Yidun-Zhongdian areas, dominating the Yanshanian copper polymetallic mineralization.