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Metal migration and precipitation in hydrothermal fluids are important topics in economic geology. The Hongling polymetallic deposit comprises one of the most important parts of the Huanggangliang–Ganzhuermiao polymetallic metallogenic belt, which is in eastern Inner Mongolia. Except for lead–zinc skarn, minor cassiterite in the skarn and disseminated W–Sn mineralization in granitic rocks have also been found. The dominant Sn–W mineralization is in the northern part of the deposit, occurring as disseminated wolframite and cassiterite in aplite hosted in Mesozoic granite porphyry. The aplite together with pegmatite K-feldspar–quartz comprises vein dikes hosted in the granite porphyry, providing evidence for the transition from melt to fluid. The veins, dikes, and Sn–W mineralization in the aplite provide an opportunity to investigate fluid exsolution and the mechanics of metal precipitation. Based on field observations, the micrographic and scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) results of the vein dikes, chronology, and the whole-rock geochemistry of the host rock, together with the fluid inclusion results, this paper discusses the characteristics of the causative magma, the mechanics of fluid exsolution and W–Sn precipitation. Our results show that the causative magma is of highly fractionated A-type granite affinity and has an intrusive age of late Mesozoic (133.3 ± 0.86 Ma). The magmatic evolution during shallow emplacement led to immiscibility between highly volatile, high-silica, and W- and Sn-enriched melts from the parent magma, followed by fluid exsolution from the water-rich melt. The alkaline-rich fluid exsolution led to a change in the redox state of the magma and the chilling of the melt. Fluid boiling occurred soon after the fluid exsolution and was accompanied by the degassing of CO2. The boiling and escape of CO2 from the fluid led to changes in fluid redox and W and Sn precipitation; thus, the W and Sn mineralization are mostly hosted in causative intrusions or peripheral wall rocks, which can be used as indicators for Sn–W exploration in the area. [ABSTRACT FROM AUTHOR]

The Chaihulanzi area in eastern Inner Mongolia is tectonically situated on the northern margin of the North China Craton (NCC). The main Precambrian lithologies of the area have been referred to the Archean Jianping Group meta‐supracrustal sequences. Based on field observations, petrographic, whole‐rock geochemical, and zircon U‐Pb geochronological results, a magmatic origin for the units is proposed. Our results show that the Chaihulanzi gneisses are mainly of granitic, dioritic and granodioritic compositions, and show typical magmatic rock textures and mineral assemblages. The dioritic and granodioritic gneisses show Na‐rich tonalite–trondhjemite–granodiorite (TTG)‐like affinity with zircon U‐Pb dates of ca. 2.57–2.59 Ga, representing a juvenile continental growth for the northeastern NCC. The granitic gneiss is indeed potassic granite and yielded a zircon U‐Pb date of ∼2.50 Ga, which is contemporaneous with the Jining–Jiaoliao microblock collision (2.53–2.49 Ga), implying another crustal growth event. The well‐developed gneissosity in 2.57–2.59 Ga dioritic and granodioritic gneisses together with the 2.5 Ga potassic granite, which crosscuts the gneissosity implies a 2.57–2.50 Ga (mainly 2.53–2.51 Ga) collisional orogeny, probably related to the Jining–Jiaoliao microblock collision. Our new geology and chronological results provide new evidence for the early Precambrian tectonic evolution of the NCC. [ABSTRACT FROM AUTHOR]

[Display omitted] • Late-Permian and Late-Mesozoic Au mineralization was identified in Chaihulanzi. • Mineralization stages are differentiated by sericite-actinolite and quartz-carbonate alteration. • Late-Permian Au mineralization has genetic link with aplite. • The aplite is sourced from NCC basement under post-collision setting. The Chaihulanzi is a Precambrian metamorphic rock-hosted gold deposit in the northern margin of the North China Craton (NCC). The local outcropping lithologies include mainly Archean metamorphic rock, Paleoproterozoic carbonatite, and Phanerozoic diorite, granite, aplite and mafic to felsic dikes. Due to the lack of data, the deposit was variably proposed to be orogenic, intrusion-related, or mesothermal type, and the mineralization was loosely constrained to be Paleozoic or Mesozoic. Based on field geology, petrological/mineralogical observations, whole-rock geochemistry, and zircon U-Pb-Hf isotopes of ore-related aplite, and sericite Ar-Ar dating of gold-ore veins, we discussed the ore-causative magmatism, and the age and tectonic setting of gold mineralization. Our results show the presence of an early (native gold-dominated) and a late (gold-silver telluride-dominated mineralization) stage: The early-stage gold mineralization was genetically linked to the Middle-Late Permian aplite (LA-ICP-MS zircon U-Pb age: 264.5 ± 1.3 Ma), whose ages are similar to the gold ore veins (sericite Ar-Ar age: 263.67 ± 0.99 Ma). The distinct negative zircon εHf (-18.31 to -15.45) and model age (T DMC = 2.1–2.4 Ga) indicate a crustal magma source, probably from partial melting of the NCC basement. The whole-rock trace element compositions and zircon U-Pb ages, together with the tectonic evolution of northern NCC margin imply a post-collisional extension setting (after the Paleo-Asian ocean closure) for the gold mineralization. The newly-discovered late-stage quartz-carbonate ore veins occur as fracture infill, and crosscut early-stage quartz-sericite veins and Mesozoic volcanic wallrocks, implying that the late-stage mineralization occurred in the Mesozoic or after. The two-stage gold mineralization overprinting makes Chaihilanzi and its periphery highly prospective for gold exploration. [ABSTRACT FROM AUTHOR]