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The southwestern South China Block, composed of southwestern China and northeastern Vietnam, is one of the most important Sn-polymetallic ore districts in the world. The Dulong skarn Sn-polymetallic deposit, which is closely related to Late Cretaceous granitic magmatism, contains 5.0 mt Zn, 0.4 mt Sn, 0.2 mt Pb, and 7 kt In, and is one of the largest Sn-polymetallic deposits in the region. Sn mineralization occurs mainly as cassiterite at the contact zone between the Laojunshan granitic pluton and carbonates of the Cambrian Tianpeng Formation. The Laojunshan granitic pluton consists of three: medium- to coarse-grained two-mica monzonitic granite, medium- to fine-grained two-mica monzonitic granite, and granite porphyry, with zircon U–Pb ages of 87.5 ± 0.6 Ma, 85.3 ± 1.1 Ma, and 82.8 ± 1.6 Ma, respectively. Zircon grains from these three phases show eHf(t) values from −9.5 to −2.5, typical of a mantle origin. All samples exhibit strongly peraluminous and high-K calc-alkaline affinities, and show trace element patterns characterized by enrichment in Rb, Ta, La, Zr, and Hf, and depletion in Ba, Nb, and Ti, typical of S-type granites. Three main alteration/mineralization stages are recognized within the mineralized contact zones: (1) skarn stage; (2) sulfide mineralization stage; and (3) supergene stage. Cassiterite grains from the skarn alteration stage yield a 207Pb/206Pb–238U/206Pb concordia age of 89.4 ± 1.4 Ma, suggesting that mineralization was associated with the Laojunshan granitic pluton. Regionally, the Sn-polymetallic mineralization in the southwestern South China Block took place within a narrow time span from 97 to 79 Ma. The causative granitic magmas can be produced by partial melting of the Paleoproterozoic–Mesoproterozoic pelitic basement rocks during large-scale lithospheric thinning and asthenospheric upwelling.

The Dunde deposit, which is located in the Awulale Fe metallogenic belt, Xinjiang, China, is a uniquely large Fe-Zn deposit and also contains considerable Au resources. We present the results of a comprehensive study of this deposit based on fieldwork, mineralogy, and mineral geochemistry to constrain the Au mineralization. Our study indicates that the mineralization of Fe, Zn, and at least some Au precipitated in the same hydrothermal system. The Au mineralization, which occurs in the sulfide stage, is characterized by invisible Au at high temperatures and by electrum at low temperatures. Unusual sulfide is recognized in the deposit, such as cobaltite and bismuth minerals. Pyrrhotite compositions indicate that the early precipitation of sulfide generated in high temperatures (410–570 ℃) and high sulfur fugacities (−2.47 to −6.68). Arsenopyrite compositions indicate that the late precipitation of sulfide formed in low temperatures (326–393 ℃) and low sulfur fugacities (−7.41 to −12.00). Bismuth minerals exhibit a close relationship with the Au mineralization. In high temperatures and high oxygen fugacities, bismuth dissolved in the hydrothermal fluid as Bi3+ and precipitated as galenobismuthite and cosalite accompanying precipitation of the invisible Au. Accompanying the decrease of oxygen fugacities and temperatures, the Bi melt directly separated from the hydrothermal fluid and scavenged Au. The reduced condition further enriched Au in Bi melts through the decomposition of the invisible Au-bearing Bi-Pb sulfide. The decrease of temperatures caused the decomposition of the Bi-Au melt and the formation of native bismuth, bismuthinite, and electrum. In addition to the mineralization of Fe, Zn and Au, considerable Cu-, Co-, and Mn-bearing sulfide precipitated in the Zn ores. Integrated utilization of the Zn ores may get greater economic values.

The relationship between gold mineralization and magmatism within the Youjiang Basin of SW China remains poorly constrained as a result of the lack of outcropping igneous units in this region. This study presents new geological, geochronological, and geochemical data for recently discovered dolerite dykes associated with the Nibao gold deposit, which is located within the NW Youjiang Basin of SW China. Zircon laser ablation-inductively coupled plasma-mass spectrometry (LA–ICP–MS) U-Pb dating of these dykes yielded an age of 213.6 ± 2.5 Ma, indicating that these dykes were emplaced during the Late Triassic and providing new evidence for Late Triassic magmatism within the study area. The dykes also represent an opportunity to investigate the petrogenesis of mafic rocks and the tectonic setting of the Late Triassic magmatism in the Youjiang Basin. These Nibao dolerite dykes contain relatively low concentrations of SiO2 (46.03–47.66 wt%), have moderate total alkali contents (K2O + Na2O = 2.71–3.15 wt%) and high total Fe as Fe2O3 (TFe2O3) contents (13.49–14.96 wt%). Their trace element compositions are indicative of an OIB-like geochemical affinity barring depletion in the high field strength elements (HFSE) such as Nb, Ta and Th. The Nibao dolerites have homogeneous Lu-Hf and Sr-Nd isotopic compositions with (87Sr/86Sr)i and (143Nd/144Nd)i values of 0.70562–0.70677 and 0.51233–0.51239, respectively. These dykes have a narrow range in associated eNd(t) and eHf(t) values from –0.70 to +0.51 and from +0.04 to +3.24, respectively. These geochemical data indicate that the dolerites associated with the Nibao gold deposit were derived from an enriched region of the asthenopheric mantle (>90 km depth) and the magmas that formed these dykes were generated by 5–10% partial melting of ∼75% garnet peridotite and ∼25% spinel peridotite material. The ascending magmas underwent both crustal contamination and the fractional crystallization of olivine, clinopyroxene and Fe oxides (e.g., magnetite or ilmenite) prior to emplacement. The Nibao dolerites are geochemically distinct from mafic rocks related to the Emeishan large igneous province, suggesting that they are not linked to this mantle plume event. Instead, they formed in an extensional setting generated by the subduction of the Song Ma oceanic plate beneath South China Block and the subsequent collision between the Indochina and South China blocks. The breakoff of the Song Ma oceanic slab caused the partial melting of the mantle source region for the Nibao dolerite dykes. These relationships suggest that the post-collision extensional environment associated with this breakoff contributed to the deeply sourced, mantle-derived Late Triassic magmatism in this area and, perhaps as well, the gold mineralization in the Youjiang Basin. Most importantly, combining the new geochronological data presented in this study with the timing of extension in this region and the results of previous research suggest that the Carlin-like gold deposits in the Youjiang Basin formed at around 213 Ma (i.e., the Late Triassic).

The Lanping basin is a significant Pb–Zn–Cu–Ag mineralization belt in the Sanjiang Tethyan metallogenic province. A series of sediment-hosted Himalayan Cu–Ag–Pb–Zn polymetallic deposits have been discovered in the western part of the basin, controlled by a thrust–nappe system. In the thrust–nappe system, the Cu orebodies mainly occur in the western and relatively deep part of the mineralization system (the root zone), whereas the Pb–Zn–Ag (± Cu) orebodies occur in the eastern and relatively shallow part of the system (the front zone), both as vein-type mineralization. In this paper we present new data, combined with existing data on fluid inclusions, isotopes and geologic characteristics of representative deposits, to provide the first study that contrasts mineralizing fluids in the Cu–Ag (Mo) and Pb–Zn–Ag (Cu) polymetallic deposits. Fluid inclusion and isotope studies show that the Cu–Ag (Mo) mineralization in the root zone formed predominantly from deep crustal fluids, with the participation of basinal brines. The deep crustal fluids are marked by high CO2 content, relatively high temperatures (280 to 340 °C) and low salinities (1 to 4 wt.% NaCl equivalent), whereas the basinal brine shows relatively low temperatures (160 °C to 220 °C) and high salinities (12 to 22 wt.% NaCl equivalent), containing almost no CO2. In comparison, hydrothermal activity associated with the Pb–Zn–Ag (± Cu) deposits in the front zone is characterized by basinal brine, with relatively low temperatures (130 °C to 180 °C), high salinities (9 to 24 wt.% NaCl equivalent), and low CO2 concentrations. Although evolved meteoric waters have predominantly been proposed as the source for deep crustal fluids, magmatic and metamorphic components cannot be completely excluded. The basinal brine was predominantly derived from meteoric water. The δ34S values of sulfides from the Cu–Ag (Mo) deposits and Pb–Zn–Ag (± Cu) deposits range from − 17.9 to 16.3‰ and from 2.5 to 11.2‰, respectively. These ranges may relate to variations in physicochemical conditions or compositional variation of the sources. Lead isotope compositions indicate that the ore-forming metals were predominantly derived from sedimentary rocks of the Lanping basin.