The Kangxiwa–Dahongliutan pegmatite field in the Western Kunlun Orogen, China contains numerous granitic pegmatites around a large granitic pluton (the Dahongliutan Granite with an age of ca. 220 to 217 Ma), mainly including barren garnet-, tourmaline-bearing pegmatites, Be-rich beryl-muscovite pegmatites, and Li-, P-rich albite-spodumene pegmatites. The textures, major element contents, and trace element concentrations of columbite-group minerals (CGM) and cassiterite from three albite-spodumene pegmatites in the region were investigated using a combination of optical microscopy, SEM, EPMA and LA-ICP-MS. The CGM can be broadly classified into four types: (1) inclusions in cassiterite; (2) euhedral to subhedral crystals (commonly exhibiting oscillatory and/or sector zoning and coexisting with magmatic cassiterite); (3) anhedral aggregates; (4) tantalite-(Fe)-ferrowodginite (FeSnTa₂O₈) intergrowths. The compositional variations of CGM and cassiterite are investigated on the mineral scale, in individual pegmatites and within the pegmatite group. The evolution of the pegmatites is also discussed. The variation of Nb/Ta and Zr/Hf ratios of the cassiterite mimics the Nb-Ta and Zr-Hf fractionation trends in many LCT pegmatites, indicating that these two ratios of cassiterite may bear meanings regarding the pegmatite evolution.

Submarine volcanic-hosted iron deposits are important sources of iron ore in northwestern China. Here we present the petrological characteristics and coupled Fe-O, C, and Si isotope data of iron ores from the Shikebutai submarine volcanic-hosted hematite deposit in the Western Tianshan region. Several stratiform and lenticular hematite-dominated orebodies occur in Carboniferous submarine volcano-sedimentary sequences in this region. The ores are mainly composed of hematite, quartz, and minor siderite with distinct alternating iron-rich and silica-rich bands. The hematite shows δ⁵⁶Fe and δ¹⁸O values in the range of –0.31 to 0.80‰ and 2.2 to 7.0‰, respectively, and the jasper yields δ³⁰Si values of –1.90 to –1.20‰. Iron and Si were both derived from hydrothermal fluids related to submarine magmatism/volcanism. The Fe-bearing minerals in the Shikebutai deposit define distinct formation pathways. Hematite is the primary dehydrated Fe(III) oxyhydroxide, and the Fe isotope data indicate fractionation resulting from the partial oxidation of Fe(II). The O isotope data reflect inheritance from the submarine hydrothermal fluids source. Jasper was produced during coprecipitation of silica adsorbed onto the Fe(III) oxyhydroxides. The siderite-rich iron ore/volcaniclastic rock samples with a high and variable total organic carbon content (0.14–5.57%) show negative δ¹³C values (–3.0 to –1.1‰) and light δ⁵⁶Fe values (–1.11 to –0.84‰). Our isotope data, together with the common occurrence of hematite inclusions in siderite, suggest that siderite was mainly produced by microbial dissimilatory iron reduction during diagenesis. The geologic, petrological, and isotopic data suggest that the Carboniferous Shikebutai deposit was precipitated through chemical and biogenic processes.

The Kalu’an-Azubai pegmatite field, one of the most important rare-metal metallogenic regions in China, contains a large number of pegmatite dikes belonging to spodumene and lepidolite subtypes. Columbite-group minerals (CGMs) collected from three spodumene subtype pegmatites (No. 802, No. 803, and No. 805 pegmatites) were analyzed for major element contents using EPMA (electron probe micro-analyzer) and dated using LA-ICP-MS (laser ablation-inductively coupled plasma mass spectrometer). The crystallization ages of the CGMs from No. 802, No. 803, and No. 805 pegmatites are 209.5 ± 1.4 Ma (2σ), 198.3 ± 2.0 Ma (2σ), and 224.3 ± 2.9 Ma (2σ), respectively. Oscillatory zoning and/or sector zoning along with the associated mineral assemblages suggest that the dated columbite is of magmatic origin. The crystallization ages of the columbite grains thus represent the emplacement ages of the Li pegmatites. Therefore, our dating results indicate that there were three emplacement events of the Li-rich pegmatite-forming melts in a timeframe of ~30 Ma. In combination with previous studies, we conclude that the Li pegmatites were formed before the Be-Ta-Nb pegmatites (~194–192 Ma), which precludes the genesis of rare-metal pegmatites via fractional crystallization of a granitic magma in the Kalu’an-Azubai region.