The accuratein situU–Pb age of scheelite can be determined using our proposed methods in normal ablation settingsviaLA-SF-ICP-MS.

Bastnaesite is an important mineral geochronometer to record the REE mineralization time for REE deposits. As the only reliable primary standard for in situ U–Th–Pb dating, bastnaesite K-9 is inhomogeneous and nearly out of supply. The accurate in situ U–Th–Pb dating of bastnaesite and its wide application are still constrained by the lack of reliable reference materials. Therefore, a potential primary standard was proposed and assessed in thirty-one ablation settings in this paper. The normalized ²⁰⁶Pb/²³⁸U and ²⁰⁸Pb/²³²Th ratios (i.e., ²⁰⁶Pb/²³⁸U and ²⁰⁸Pb/²³²Th fractionation) of xenotime XN01 are respectively similar or slightly different from those of bastnaesite K-9 in most ablation settings. The average value (i.e., calibration factor) of ²⁰⁶Pb/²³⁸U and ²⁰⁸Pb/²³²Th ratios for XN01 is consistent with those for K-9 with the offsets of <2.4% in the same ablation setting when using the ratio-of-the-mean intensity method for data reduction. Thus, the most obtained ages of K-9 calibrated by XN01 are consistent with its reference age of 118 ± 1 Ma with the offsets of 4500 ppm) and Th/U ratios (>400), the Th–Pb ages of these young samples are acceptable and agree well with their respective published Th–Pb ages within uncertainty. Therefore, the matrix effect between xenotime XN01 and bastnaesite can be neglected normally. Xenotime XN01 is more uniform than K-9 and can serve as a primary reference material for the in situ U–Th–Pb dating of bastnaesite. Moreover, bastnaesite Zagi has a sufficient reservoir, uniform Th–Pb, corrected U–Pb ages, and can serve as a secondary reference material for quality control.

Precious metals can be mobilized during supergene processes, which are important for the formation of high-grade or high-purity ores. The world-class Linglong gold deposit has high-grade ores that have undergone supergene processes in the near-surface zone. Under which conditions the supergene modification occurred and how Au and Ag behaved during the supergene processes have been poorly studied in this deposit. Here, we performed scanning electron microscope (SEM) and laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) analyses on samples from the supergene enrichment zone of the Linglong gold deposit. The results show that secondary minerals were formed sequentially from magnetite-goethite-limonite to marcasite-acanthite, and finally to siderite after the primary minerals of pyrite-pyrrhotite-chalcopyrite. These mineral assemblages and variations indicate that the supergene modification by groundwater occurred under oxidative and weakly acidic conditions in the near-surface zone and evolved to reductive and near neutral conditions in the supergene enrichment zone. The newly formed marcasite has much higher Au (0.003–23.5 ppm, mean of 1.33 ppm) and Ag (81.7–6021 ppm, mean of 1111 ppm) concentrations than those of the primary pyrite (Au of 0.004–0.029 ppm and Ag of 0.22–4.14 ppm), which together with the formation of independent Ag–S mineral (acanthite), indicates that Au and Ag were significantly mobilized and fractionated during the supergene processes. These processes improved the Au and Ag grades in the supergene enrichment zone and thus facilitate their extraction.

The Baishitouwa deposit is a medium-scale quartz–wolframite vein-type deposit in the southern Great Xing’an Range tungsten (W) belt. The W mineralization occurs mainly as veins and dissemination within the mica schist of the Mesoproterozoic Baiyunebo Group. The formation of the deposit can be divided into four stages. The wolframite yielded a lower intercept ²⁰⁶Pb/²³⁸U age of 221.0 ± 3.4 Ma (1σ, MSWD = 2.0), which records a late Triassic W mineralization event in the Baishitouwa deposit. In combination with previous geochronological data, we suggest that NE China may have an enormous potential for Triassic W mineralization and more attention should be given to the Triassic ore prospecting in the region. This work highlights that the chemical composition of wolframite is controlled by both the crystallochemical parameters and the composition of the primary ore-forming fluid. Trace-element compositions suggest that wolframite (I) was controlled by the substitution mechanism of 4^A(Fe, Mn)²⁺ + 8^BW⁶⁺ + ^B□ ↔ 3^AM³⁺ + ^AN⁴⁺ + 7^B(Nb, Ta)⁵⁺ + 2^BN⁴⁺, whereas wolframite (II) was controlled by the substitution mechanism of ^A(Fe, Mn)²⁺ + ^A□ + 2^BW⁶⁺ ↔ 2^AM³⁺ + 2^BN⁴⁺. Wolframite (I) contains higher concentrations of Nb, Ta, Sc, and heavy rare earth elements (HREEs), and lower Mn/(Mn + Fe) ratios than wolframite (II). Both wolframite (I) and (II) have similar trace elements and left-dipped REE_N patterns, and analogical Nb/Ta ratios. They have similar Y/Ho ratios to Mesozoic highly fractionated W-mineralized granitoids in NE China. These data indicate that the W mineralization at Baishitouwa is genetically related to an underlying highly fractionated granite, and the compositional variation of fluids is likely driven by crystallization of wolframite during the processes of fluid evolution. A change of the ore-forming fluids from an oxidized to a relatively reduced state during the evolution occurred from stage 1 to 2.