Critical Metal Occurrence, Enrichment, and Application

Typical stratiform-like cassiterite–sulfide orebodies formed at 160–150 Ma cut by a steep hydrothermal vein-type orebody were discovered in the Xianghualing tin–polymetallic orefield, which implied a new phase of magmatism and mineralization later than the Late Jurassic stage. Hence, a systematic study of the characteristics and genesis of the concealed Laohuya granite, including U–Pb age, trace elements, Lu–Hf isotopes of zircons, and whole-rock major- and trace-elements, is examined in this paper. The zircon U–Pb dating yielded a Concordia age of 87.75 ± 1 Ma, confirming the existence of Late Cretaceous magmatism in the Xianghualing tin–polymetallic orefield. The Laohuya granite is classified as syenogranite and belongs to the peraluminous, high K calc-alkaline series. It is a highly evolved A₂-type granite with ε_Hf(t) values ranging from −14.97 to −7.59 and two-stage model ages (T_DM2) ranging from 2939 to 2280 Ma. Combining chronology, petrochemistry, isotopic geochemistry, and previous tectonic studies, we believe that the Laohuya granite originated from the partial melting of a reworked ancient crust composed of TTGs, and its weathered sediments formed in subduction or collision zones at 2.5 Ga, controlled by the reactivation of the Chenzhou–Linwu deep fault in the extensional setting of South China during the Late Cretaceous. Full article

The Xiawolong gold deposit, located in the Muping–Rushan gold metallogenic belt (eastern Jiaodong Peninsula), is a newly discovered deposit that developed in the late Early Cretaceous as fine-grained granite. Gold mineralization, which mainly occurs in the middle of fresh fine-grained granite dikes, consists of stockwork-style and disseminated ores. They are characterized by middle-high-temperature mineral assemblages, such as molybdenite and magnetite, associated with gold-bearing pyrite. Four types of primary fluid inclusions, contained within the quartz grains from the gold-bearing disseminated and stockwork-style fine-grained granitic ores, were identified based on microthermometry and Raman spectroscopy. The types identified were type 1 aqueous inclusions with middle-high temperature (201 to 480 °C) and middle-low salinity of 0.18 to 17.00 wt.% NaCl equiv.; type 2 H₂O–CO₂ inclusions, which show middle-high temperatures (218 to 385 °C), middle-low salinities (1.23 to 13.26 wt.% equiv. NaCl), and variable XCO₂ (0.031 to 0.044); type 3 daughter mineral-bearing inclusions with high temperature (416 to 446 °C) and relatively constant and high salinity (28.59 to 32.87 wt.% NaCl equiv.); and type 4 CO₂ fluid inclusions, which possess a bulk density of 0.405 to 0.758 g/cm³ and a constant XCO₂ (0.952 to 0.990) (according to the decreasing abundance of fluid inclusions). The δ¹⁸O_water range is between 3.4 and 5.9‰, and the range of the δD is from −97.1 to −77.4‰, which indicates that the ore-forming process is of a magmatic water origin. The δ³⁴S values possess a narrow range between 4.5 and 9.3‰, indicating the source of the Mesozoic Kunyushan granitoids. The Pb isotopic compositions of pyrite show that the Mesozoic Kunyushan granitoids are the main lead source for pyrites. Types 1, 2, and 3 fluid inclusions coexist in the same view field of the quartz grain, which are suggested to occur as the result of fluid immiscibility because of the boiling of a single homogeneous NaCl-CaCl₂-KCl-CO₂-H₂O system. The fluid immiscibility, rather the fluid mixing and wall-rock sulfidation, is the mechanism of gold precipitation in the Xiawolong deposit. Compared with both the “Linglong-type” and “Jiaojia-type” gold deposits in the Jiaodong Peninsula in terms of geological–petrographic evidence and all of the available geochemical data, it can be concluded the Xiawolong gold deposit is of magmatic hydrothermal origin, having a genetic relation to the fine-grained granite. Full article

Zircon Hf-isotopic mapping can be regarded as a useful tool for evaluating the coupling relationship between lithospheric structure and metallic mineralization. Hence, this method shows important significance for mineral prediction. To explore this potential, the published granite zircon Hf isotope data from the Sanjiang Tethyan Orogen were systematically compiled. This study uses the Kriging weighted interpolation in the Mapgis software system to contour Hf isotopes, revealing a relation between the crustal structure and metallogenesis. The mapping results suggest that the Changning–Menglian suture zone is the boundary between ancient and juvenile crust, viz., the western terranes have ancient crust attributes, whereas the eastern terranes exhibit the properties of new juvenile crust. In addition, this study also found that the mineralization and element types in the Sanjiang Tethyan Orogen have a coupling relationship with the crustal structure. The distribution of porphyry Cu-Mo-Au deposits is mainly controlled by the new juvenile crust, whereas the magmatic-hydrothermal Sn-W and porphyry Mo-W(-Cu) deposits are closely related to the reworked ancient crust. The results of zircon Hf isotope mapping prove that the formation and spatial distribution of deposits are related to the composition and properties of the crust. Hf isotope mapping can reveal the regional metallogenic rules and explore metallogenic prediction and metallogenic potential evaluation. Full article

The Oligocene to Miocene Baiyangping Cu–Co and Pb–Zn mineralization was deposited during the collision of the India and Asia continents. The mineralization is hosted in veins in faulted carbonate and clastic rocks, which act as fluid pathways. A detailed fluid-inclusion analysis and C–O–S isotopic study are reported, focusing on the origin of the mineralizing fluids and mineralizing processes. The microthermometry of fluid inclusions hosted in quartz and carbonates indicate that the fluid peak temperature for both Cu–Co and Pb–Zn mineralizations ranges from 160 to 200 °C and from 120 to 160 °C, respectively. During these metallogenic hydrothermal events, salinity evolved from 2.7 wt% NaCl equiv to 24.8 wt% NaCl equiv. The δ³⁴S values measured on sphalerite and tennantite range from +5.2‰ to +9.5‰, which indicates that sulfur originated from a reservoir characterized by thermochemical sulfate reduction (TSR). The C–O isotopic values obtained from the carbonate samples suggest that the fluid mainly originates from basinal brines. The combination of C and S isotopic values of the Cu–Co and Pb–Zn mineralization indicate the sedimentary source of the basin. Mineralization is controlled by faults, thermochemical sulfate reduction, and the physicochemical conditions of the fluid. Full article

Rutile is an important ore mineral to meet the increasing demand of critical metal Ti in various sectors. Here we report a rare example of rutile deposits hosted within the Baishugang–Wujianfang amphibolite-facies metamorphic rocks in the East Qinling Orogen, central China. The rutiles are mostly located within or along the margins of biotite and show 94.6 to 99 wt% TiO₂. Rutiles occur as chains, thin layers along the foliation, and dense clusters. The grains are coexisted with magnetite. Based on Zr-in-rutile thermometer the estimated crystallisation temperature is at 630 °C at 7.0 kba. Based on Cr/Nb ratio, the source of the rutile is correlated with Ti-bearing silicate minerals such as biotite from aluminous sedimentary protoliths. The rutile deposit formed during lower amphibolite-facies metamorphism, and is distinct from the eclogite- and granulite-related types elsewhere in the orogen. The LA-ICP-MS U–Pb analyses of rutiles from the deposit yield lower intercept ²³⁸U/²⁰⁶Pb ages of 386 ± 16 Ma at the Baishugang–Wujianfang district. These ages correspond to a Devonian arc–continent collisional event between the South and North Qinling domains in the East Qinling Orogen. Full article