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Coesite- and microdiamond- bearing ultra-high pressure (UHP) eclogites in the North Qinling terrane have been widely retrogressed to amphibolites. Previous geochronological studies on these UHP rocks mainly focused on the timing of peak eclogite facies metamorphism. The Kanfenggou UHP metamorphic domain is one of the best-preserved coesite-bearing eclogite occurrences in the North Qinling terrane. In this study, mafic amphibolites and host schists from this domain were collected for 40Ar/39Ar dating to constrain their retrograde evolution. Two generations of amphibole are recognized based on their mineral parageneses and 40Ar/39Ar ages. A first generation of amphibole from garnet amphibolites yielded irregularly-shaped age spectra with anomalously old apparent ages. Isochron ages of 484–473 Ma and initial 40Ar/36Ar ratios of 3695–774 are obtained from this generation of amphibole, indicating incorporation of excess argon. Second generation amphibole occurs in epidote amphibolites yielded flat age spectra with plateau ages of 464–462 Ma without evidence for excess argon. These ages suggest that the amphibolite-facies metamorphism has taken place as early as 484 Ma and lasted until 462 Ma for the North Qinling UHP metamorphic rocks. Phengite from the country-rock schists yielded 40Ar/39Ar plateau ages of 426–396 Ma, with higher phengite Si contents associated with the older the plateau ages. Based on our new 40Ar/39Ar ages and previous zircon U[sbnd]Pb geochronological data, we construct a new detailed pressure-temperature-time (P-T-t) path illustrating the retrograde metamorphism and exhumation rate of the North Qinling eclogites and host schists. The P-T-t path suggests that these UHP metamorphic rocks experienced initial medium-to-high exhumation rates (ca. 8.7 mm/yr) during the Early Ordovician (489–484 Ma), which was mainly derived from buoyancy forces. Subsequently, the exhumation rate decreased gradually from ~0.8 to 0.3 mm/yr from 484 to 426 Ma, which was probably governed by extension and/or erosion.

The Jinchang gold deposit has been extensively studied, but precise dates for its formation are debated. Native gold mainly occurs as inclusions within pyrite and quartz. In this study, we analysed quartz crystals coeval with gold precipitation from two different types of mineralization using the ArgusVI multi-collector noble gas mass spectrometer by the stepwise crushing technique to resolve the timing and genesis of gold mineralization. 40Ar/39Ar dating of quartz samples (J12Q) from breccia ore yields a plateau age of 109.87 ± 0.86 Ma, and an inverse isochron age of 109.87 ± 0.88 Ma. Quartz samples (J18Q) from vein ore yields a slightly younger plateau age of 107.76 ± 0.85 Ma, with an inverse isochron age of 107.76 ± 0.92 Ma. These dates place the ore-forming age of the Jinchang gold deposit at 107~110 Ma, much younger than previously published radiometric ages, suggesting the gold mineralization is spatio-temporally associated with the granite porphyry. The formation of the Jinchang gold deposit is consistent with the regional late Mesozoic porphyry-epithermal gold mineralization event in the Yanbian-Dongning area. Finally, our study shows that 40Ar/39Ar of quartz can be used as a powerful tool to date the formation ages of hydrothermal ore deposits.

The West Qinling orogen in central China contains several dozens of gold deposits. However, absolute ages of gold mineralization and its relations to regional tectonism, magmatism, and metamorphism remain not tightly constrained for most of these gold deposits. Here we integrate 40Ar/39Ar dating of sericite from various hydrothermal alteration assemblages and U-Pb dating of zircon grains from magmatic rocks within and surrounding the Liziyuan gold deposit in the northern belt of the West Qinling orogen to provide new insights into the age and tectonic setting of gold mineralization. The Liziyuan gold deposit consists of six ore camps (Yuzigou, Liushagou, Jiancaowan, Kuangou, Suishizi, and Yingfang) that are hosted in Ordovician greenschist facies metamorphosed sedimentary-volcanic rocks and, less significantly, the Middle Triassic Tianzishan monzogranite pluton intruding the metamorphic rocks. Gold mineralization consists of auriferous quartz-pyrite veins and subordinate sulfide disseminations in hydrothermally altered wall rocks, with minor calcite-polymetallic sulfide veins in the monzogranite-hosted orebodies. Ore-related alteration assemblages are dominated by quartz, sericite, pyrite, chlorite, and calcite, with gold occurring mostly as native gold grains enclosed in or filling microfractures of pyrite and quartz. Barren alteration assemblages, dominated by K-feldspar, quartz, sericite, and pyrite, are locally developed along eastern margin of the Tianzishan monzogranite. Two sericite aggregates extracted from gold ores in the Liushagou camp yield well-defined 40Ar/39Ar plateau ages of 200.1 ± 1.2 and 198.8 ± 1.1 Ma (2σ), whereas those from barren alteration assemblages in the Tianzishan monzogranite, which hosts the Suishizi ore camp, give rise to older 40Ar/39Ar plateau ages of 211.9 ± 1.2 and 211.3 ± 1.3 Ma (2σ). The Tianzishan monzogranite pluton and several dioritic to granitic stocks and dykes in and surrounding the gold mines have zircon U-Pb ages ranging from 241.3 ± 1.2 to 212.4 ± 0.9 Ma (2σ). These new isotopic ages suggest that the Liziyuan gold deposit formed at the Triassic-Jurassic boundary, arguably representing the youngest orogenic-type gold mineralization event over the northern belt of the West Qinling orogen. Gold mineralization postdates magmatism in the Liziyuan gold deposit at least by about 10 million years, precluding a possible genetic relation between the two. Rather, the ore genesis was likely related to metamorphic fluids released from Paleozoic sedimentary and volcanic rocks in relation to the Qinling orogenesis. In contrast, the barren hydrothermal alteration assemblages were likely caused by fluids exsolved from a magma presumably represented by the ca. 212 Ma diorite dyke. Results presented here, when combined with independent geological and geochemical data, suggest that the Liziyuan gold deposit formed most likely under a post-collisional extensional setting related to the West Qinling orogeny.

The Qinzhou Bay–Hangzhou Bay metallogenic belt (QHMB), South China, contains numerous variable deposits, including Au, Cu, Pb, Zn, Ag, W, Sn, U-polymetallic ore deposits. The Tianjingshan gold deposit is located in the northern segment of the QHMB and is a typical large-scale lode gold deposit. Auriferous quartz veins occur along the contact zones between the Neoproterozoic greenschist-facies metamorphic rocks and gneissic granite and are structurally controlled by brittle faults. Mineralization-related hydrothermal alteration mainly includes silicification, pyritization, sericitization, and chloritization. Four stages of alteration and mineralization are recognized: quartz (I), quartz–pyrite (II), quartz–polymetallic sulfide (III), and quartz–carbonate–fluorite (IV) stages. Gold mineralization occurs mainly in stages II and III, as visible gold. Sericite that formed in association with mineralization stages II and III has well-defined step heating plateau 40Ar/39Ar ages of 243.4 ± 2.3 and 239.5 ± 2.3 Ma, respectively, suggesting that the gold mineralization took place during the Middle Triassic, consistent with the timing of the regional Indosinian intra-continental orogeny. In contrast, the Hanjia gneissic granite and Mi’ao monzogranite in the Tianjingshan deposit have zircon U–Pb ages of 789 ± 7 and 147 ± 2 Ma, respectively, which indicates that both intrusions were not involved directly in the gold mineralization. δ18O and δD values from fluid inclusions of auriferous quartz range from −1.1 to +2.6‰ and from −76.4 to −62.8‰, respectively, suggesting that the mineralizing fluid was likely of metamorphic origin. Gold-bearing sulfide minerals have δ34S values ranging from +0.6 to +9.8‰ with a mean of +7.1‰, which are similar to δ34S values of Neoproterozoic greenschist-facies metamorphic rocks and of typical orogenic gold deposits; therefore, we suggest that sulfur is derived mainly from regional metamorphic country rocks. The above mentioned characteristics, together with geological features, suggest that Tianjingshan is a typical orogenic Au deposit that formed during the Indosinian orogeny. Combined with knowledge of other similar deposits, the age and characteristics of the Tianjingshan gold deposit imply that Middle Triassic orogenic gold deposits in the QHMB could be common and of high economic potential.

Chrome chlorites are usually found as secondary phases formed by hydrothermal alteration of chromite deposits and associated mafic/ultramafic rocks. Here, we report the 40Ar/39Ar age of chrome chlorites separated from the Luobusa massive chromitites which have undergone secondary alteration by CO2-rich hydrothermal fluids. The dating results reveal that the intermediate heating steps (from 4 to 10) of sample L7 generate an age plateau of 29.88 &plusmn, 0.42 Ma (MSWD = 0.12, plateau 39Ar = 74.6%), and the plateau data points define a concordant inverse isochron age of 30.15 &plusmn, 1.05 Ma (MSWD = 0.08, initial 40Ar/36Ar = 295.8 &plusmn, 9.7). The Ar release pattern shows no evidence of later degassing or inherited radiogenic component indicated by an atmospheric intercept, thus representing the age of the hydrothermal activity. Based on the agreement of this hydrothermal age with the ~30 Ma adakitic plutons exposed in nearby regions (the Zedong area, tens of kilometers west Luobusa) and the extensive late Oligocene plutonism distributed along the southeastern Gangdese magmatic belt, it is suggested that the hydrothermal fluids are likely related to the ~30 Ma magmatism. The hydrothermal fluid circulation could be launched either by remote plutons (such as the Sangri granodiorite, the nearest ~30 Ma pluton west Luobusa) or by a similar coeval pluton in the local Luobusa area (inferred, not found or reported so far). Our results provide important clues for when the listwanites in Luobusa were formed.

To observe and assess the cognitive changes of mild cognitive impairment (MCI) in the elderly.A cohort study design was conducted among 47 patients with MCI and 21 control selected from the same convalescent camp, Montreal cognitive assessment (MoCA), mini mental state examination (MMSE) and clock drawing test (CDT) were performed to all subjects at the onset of study and 12 months later.The score of MMSE, CDT, MoCA and its subitems including visuospatial skill and delayed recall of MCI group were lower than the baseline after 12 months, with significantly decline in the score of MoCA (P = 0.041) and delay recall (P = 0.003). There was no obvious difference in the score of control between the baseline and that after 12 months.The decline of delayed recall occurred early and significantly, which may be a predictor in the conversion of mild cognitive impairment to dementia.