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The Naozhi deposit of northeast China comprises intermediate-sulfidation epithermal-style veins and subeconomic, porphyry-style Cu mineralization hosted by dioritic to granitic plutons, which formed at ca. 130 Ma. These intrusive phases were fed by magmas that ponded at mid- to upper-crustal levels and were finally emplaced at < 0.6 kbar based on amphibole geobarometry. The magmas were moderately oxidized (∆NNO − 0.35 to 2.21; with NNO being the nickel–nickel–oxide buffer) and water-rich (mostly > 4 wt. %), and likely experienced a relatively prolonged evolution in the shallow crust rather than at depth. Magma devolatilization and fluid exsolution at shallow-crustal levels lead to decreases in both oxygen fugacity (log ƒO2 − 10.96 to − 14.13) and water content (6.53 to 2.26 wt. %) at < 2.5 kbar pressures. Thermochronological data of zircon and apatite, thermal history modeling, and geological preservation record complex time–temperature histories of the mineralized intrusive rocks, from the cooling of the parent magma itself through burial by younger volcanic rocks to protracted erosion with time. It is estimated that < 2 km of pre-mineralization material was removed from the top of the Naozhi magmatic–hydrothermal system from the Early Cretaceous to present. A 108 ± 2 Ma volcanic event possibly tilted the hydrothermal system, but buried the ores, protecting them from extensive erosion. [ABSTRACT FROM AUTHOR]

Garnet is a common U-bearing mineral in various magmatic and metamorphic rocks with a high U–Pb closure temperature (> 850 °C), rendering it a potentially valuable U–Pb geochronometer. However, a high U (> 10 ppm) garnet reference material that suits both quadrupole and/or multi-collector inductively coupled plasma mass spectrometry (ICP-MS) is yet to be established. This study evaluates a potential reference material for in situ garnet U–Pb analysis with anomalously high U content from the Prairie Lake alkaline complex, Canada. The PL57 garnet, occurring in a calcite ijolite, has high TiO2 (6.5–15.0 wt%, average 12.7 wt%) and Fe2O3 (17.1–21.3 wt%) contents and is a member of the andradite (26–66 mol.%)-morimotoite (18–41 mol.%)-schorlomite (16–35 mol.%) solid solution series. Four samples were dated by U–Pb ID-TIMS to assess reproducibility. Twelve TIMS analyses produced concordant, equivalent results. Garnet PL57 yielded a concordant age of 1156.2 ± 1.2 Ma (2σ, n = 10, MSWD = 1.0), based on ten analyses with two results discarded due to possible mineral inclusions (if included, the concordia age is 1156.6 ± 1.8 Ma; n = 12, MSWD = 2.0). PL57 had 27–76 ppm (average 41 ppm) U with Th/U of 0.51–0.68 (average 0.63). The total common Pb content ranged from 0.4 to 3.9 pg (average 1.1 pg). Laser ablation coupled with ICP-MS and high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) imaging provide direct evidence that U is incorporated and homogeneously distributed within the garnet lattice rather than as defects or pore spaces. Published garnet samples and standards were then tested by calibrating the Willsboro, Mali, Qicun, and Tonglvshan garnet against PL57, which gave accurate ages within the recommended values. Case studies of garnet from the Archean Musselwhite orogenic gold deposit in Canada and the Cenozoic Changanchong and Habo skarn deposits in China yield reliable ages. This suggests that PL57 is a robust U–Pb isotope reference material. The limited variations of U and Pb isotopic ratios, together with the high U concentration and extremely low initial common Pb, make PL57 an ideal calibration and monitor reference material for in situ measurements. [ABSTRACT FROM AUTHOR]

The Zhuangzi Au deposit in the world-class Jiaodong gold province hosts visible natural gold, and pyrite as the main ore mineral, making it an excellent subject for deciphering the complex hydrothermal processes and mechanisms of gold precipitation. Three types of zoned pyrite crystals were distinguished based on textural and geochemical results from EPMA, SIMS sulfur isotopic analyses and NanoSIMS mapping. Py0 has irregular shapes and abundant silicate inclusions and was contemporaneous with the earliest pyrite-sericite-quartz alteration. It has low concentrations of As (0-0.3 wt.%), Au and Cu. Py1 precipitated with stage I mineralization shows oscillatory zoning with the bright bands having high As (0.4-3.9 wt.%), Au and Cu contents, whereas the dark bands have low contents of As (0-0.4 wt.%), Au and Cu. The oscillatory zoning represents pressure fluctuations and repeated local fluid phase separation around the pyrite crystal. The concentration of invisible gold in Py1 is directly proportional to the arsenic concentration. Py1 is partially replaced by Py2 which occurs with arsenopyrite, chalcopyrite and native gold in stage II. The replacement was likely the result of pseudomorphic dissolution-reprecipitation triggered by a new pulse of Au-rich hydrothermal fluids. The δ34S values for the three types of pyrite are broadly similar ranging from + 7.1 to + 8.8‰, suggesting a common sulfur source. Fluid inclusion microthermometry suggests that extensive phase separation was responsible for the gold deposition during stage II mineralization. Uranium-Pb dating of monazite constrains the age of mineralization to ca. 119 Ma coincident with a short compressional event around 120 Ma linked to an abrupt change in the drift direction of the subducting Pacific plate. [ABSTRACT FROM AUTHOR]