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Shuangqishan and Xiaoban Au deposits: chromian sericite is related to gold mineralization and the product of the late stage of Late Jurassic (ca. 153–146 Ma) magmatism. [Display omitted] • 40Ar/39Ar ages of chromian sericite in Shuangqishan and Xiaoban gold deposits are (146.21 ± 1.59 Ma) and (149.28 ± 1.26 Ma) respectively. • The gold mineralization is related to the late stage of Late Jurassic (ca. 153–146 Ma) magmatism. • The granite porphyry, chromian sericite, and Cr elements anomaly are the significant gold ore-prospecting indicators. The shuangqishan and Xiaoban are the two largest gold deposits in the Dehua-Youxi-Yongtai (DYY) mineral concentrated area of central Fujian Province. They are located adjacent to each other and show similarities in geological background, metallogenic characteristics and mineral assemblage. The orebodies are hosted in the Caledonian alaskite and the metamorphic rock of Neoproterozoic Daling Formation. Gold mineralization is closely related to pyritization, silicification, and micatization, with native gold mostly occurring in the cracks of pyrite, which formed slightly later than pyrite. In this paper, geochronologic work has been conducted on the granite porphyry and chromian sericite related to gold mineralization in the two deposits to determine the age of mineralization and discuss the genesis of the deposits. The chromian sericite is a hydrothermal alteration product of granite porphyry, and is a main indicator of gold enrichment. The plateau 40Ar/39Ar isotopic dating of chromian sericite indicates the mineralization ages of the two deposits were 146.21 ± 1.59 Ma and 149.28 ± 1.26 Ma respectively, similar to the LA-ICP-MS zircon U-Pb age(149.0 ± 1.0 Ma) of granite porphyry in the mining district. The ages of the chromian sericite and granite porphyry point to a close link with a large-scale magmatism event at the late stage of Late Jurassic in central Fujian. Based on the geology, alteration, mineralization and chronology characteristics, the Shuangqishan and Xiaoban gold deposits can be classified as the magmatic hydrothermal type gold deposits. [ABSTRACT FROM AUTHOR]

Shitouban Au deposit is a vein-type deposit, which located in the Dehua-Youxi area (Fujian Province, southeast China) and hosted by late Jurassic volcanic-sedimentary rocks. In this study, a detailed investigation on fluid inclusions, multiple isotopic compositions (H-O-S-Pb-Sr) and Rb Sr isotope dating of quartz have been carried out in an attempt to constrain the ore-forming processes and ore genesis. The deposit shares a characteristic of low-sulfidation epithermal Au deposit, such as low-temperature (peak T h 160–180 °C, average 168 °C) and low-salinity (2-3 wt% NaCl equiv., average 2.47). The hydrogen and calculated oxygen isotope values for fluids are −64 to −54‰ (average − 60‰) and - 0.95 to 0.76‰ (average 0.15‰) respectively, indicating that the ore-forming fluid was a mixture of dominant meteroric water and subsidiary magmatic fluid. Pyrite from the deposit shows a δ34S range from - 4.5 to - 1.2‰ (average −2.4‰), indicating a magmatic sulfur. The lead isotope ratios of pyrite, 206Pb/204Pb (18.399–18.494), 207Pb/204Pb (15.695–15.841), 208Pb/204Pb (38.842–39.297), are more radiogenic than the Jurassic magmatic rocks in the area, indicating a mixing metal source of magmatic and basement rocks. Based on the Rb Sr isotopic isochron age of Au-bearing quartz, the metallogenic epoch of Shitouban Au deposit is 157 ± 1 Ma, and consistent with the Jurassic volcanism in the Dehua-Youxi area. It is proposed that the primary hydrothermal fluids may have exsolved from the late Jurassic magma chamber and subsequently ascent into the shallower crust level near paleosurface to mix with meteoric water, which cause precipitation of Au and sulfides in the epithermal environment due to a decrease in metal solubility triggered by fluid boiling, cooling, and mixing. [Display omitted] • Shitouban Au deposit is a late Jurassic epithermal deposit in Dehua-Youxi area, Southeast China. • The ore-forming fluids show low-temperature and low-salinity characteristics. • H O isotopes indicate a mixture of dominant meteoric water with magmatic fluid. • Pb isotopes indicate a mixing metal source of magmatic and basement rocks. • Rb Sr geochronology of Au-bearing quartz yielded an age of 157 ± 1 Ma. [ABSTRACT FROM AUTHOR]

Qingyunshan Cu-Au deposit: an intermediate-low temperature IS epithermal deposit. [Display omitted] • Qingyunshan Cu-Au deposit in Fujian province is a vein-type epithermal deposit. • H-O isotopes indicate a dominant meteoric water for ore fluids. • S-Pb isotopes indicate a major magmatic source for ore metals. • Pyrite Re-Os dating yielded an age of 158.1 ± 9.3 Ma. • Zircon U-Pb dating yielded an age of 162 ± 1.0 Ma for the Nanyuan Formation volcanic rock. The Qingyunshan Cu-Au deposit, located in the Dehua-Youxi area (Fujian Province, southeastern China), is a vein-type deposit that occurs along fractured zones in the Late Jurassic volcanic-sedimentary rocks and Early Silurian intrusions. Three mineral paragenetic stages are identified, including the pyrite-quartz veins (stage I), polymetallic sulfide-quartz-calcite veins (stage II), and calcite (±siderite)-chalcedony-comb quartz veins (stage III). The stage II is the main mineralization stage, dominated by pyrite, chalcopyrite, and galena as well as two generations of Fe-poor sphalerite with average Fe content of 0.84 wt% in the early sub-stage and 0.31 wt% in the late sub-stage. Fluid inclusion studies indicate that the stage I has a temperature of 220–240 °C and salinity of 3.00–3.50 wt% NaCleq., whereas the stage II has lower temperature (140–160 °C), but similarly low salinity (2.50–3.00 wt% NaCleq.), suggesting it is an intermediate-low temperature epithermal deposit. Hydrogen and oxygen isotope data indicate the fluids of stage I has a δD value of −72.5 to −69.5‰ and δ18O w value of −2.96 to −0.46‰, whereas the stage II fluids show similar or slightly higher δD value (−68.0 to −66.5‰), but significantly lower δ18O w value from −6.96 to −6.26‰, which suggest meteoric water predominated in the ore-forming fluid and shows an increasing trend from stage I to II. The δ34S values of sulfide minerals are between −3.7 and −2.3‰, consistent with a major magmatic sulfur source. The lead isotope data show a relatively narrow range with 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb values of 18.392–18.513, 15.642–15.758, and 38.497–39.043, respectively. These Pb-isotope data are similar to those of the Late Jurassic intrusions, but quite different from those of the surrounding rocks of Early Silurian quartz diorite. Pyrite from the ores yielded a Re-Os isochron age of 158.1 ± 9.3 Ma, which is similar to the zircon U-Pb age (162.0 ± 1.0 Ma) of the host dacite crystal tuff in the Nanyuan Formation. Therefore, we concluded that the Late Jurassic magmatic activity (ca. 160 Ma) has a genetic relation with formation of the Qingyunshan vein-type Cu-Au deposit, for which the ore metals were mainly derived from the magma, but ore-forming fluids evolved from a mixing of magmatic fluids and meteoric water with the later playing a major role in the main stage of ore formation. [ABSTRACT FROM AUTHOR]

As an ordinary alteration mineral in the process of fluid–rock interaction, chlorite (most especially its chemical composition) has the potential to become an effective tool to reveal the physicochemical conditions during alteration and help exploration. However, its elemental characteristics during the chloritization process are yet to be clearly understood. The Dehua‐Youxi‐Yongtai (DYY) ore district in south‐east China is one of the potential areas of gold and polymetallic deposits. Lying in the north‐west section of the DYY ore district, the Donghua area is notable for its remarkable metallogenic potential, and porphyry‐epithermal systems might have developed in the area. This study focuses on the elemental characteristics of chlorite in the Donghua area as footprints of the alteration process and mineralization vectoring. According to the geological features and occurrences, the chlorite from Donghua can be divided into two generations: (a) Chlorite I is closely related to chloritization developed in intrusive and volcanic rocks (Permian quartz monzobiorite and Jurassic volcanic rocks of Changlin Formation), and (b) chlorite II is accompanied by superimposed hydrothermal overprinting. The alteration process suggested by overprinting chlorite II can be regarded as almost coeval with the ca. 154–153 Ma magmatic event, and chlorite II is later than chlorite I generation. According to the geothermometry of the chlorite in Donghua, chlorite I might have crystallized on the temperature of 180–240°C with a peak of ~200°C, and the overprinting chlorite II might have experienced two episodes of hydrothermal/epithermal fluid pulsing. The mineral geochemistry of the trace elements in the two generations of the chlorite in Donghua shows different characteristics. The replacement of Mg2+ by Fe2+ plays an important role for ionic substitution in the octahedral position, especially for chlorite II. The other occasion might be Mg and Fe jointly entering the octahedral position as well as Mg‐ and Fe‐AlVI substitution mechanisms. The enrichment of Mg especially in chlorite II suggests low‐grade oxidation and acid conditions, which might be beneficial for the transportation of metallogenic substances. The obvious differences of Co and Ni are remarkable aspects of the trace elements of chlorite in Donghua, resulted by the ion substitution and function of different octahedral site preference energy. The mineral chemistry of chlorite II from Donghua can be helpful for targeting and exploration vectoring in the DYY ore district. [ABSTRACT FROM AUTHOR]

• The Tieshan complex body (TCB) is actually a potassic metamorphic complex. • The K-feldspar in TCB is mainly microcline, indicating its hydrothermal origin. • Hydrothermal quartz and melanite, combining K-feldspar, confirmed the origin of TCB. • Massive potassic metasomatism indicates huge potential of rare earth oxide resources. • The 39Ar-40Ar age of feldspars is 108 – 126 Ma, suggesting the Mesozoic alteration event. Tieshan complex body (TCB) is located in Zhenghe County on the border of Zhejiang and Fujian, covering an area of about 5.7 km2. Tieshan complex body (TCB) is the most developed metasomatised area in the southeast of China, which was misunderstood as a syenite intrusion. Much Study has carried on at Shizigang in the southwest of the TCB. The alkali metasomatites are composed of feldspar, pyroxene, amphibole, biotite and melanite et al. Potassic feldspars in Complex body have four kinds of forms and can be separated into three stages: (1) one in facial alkali alteration and one in alkali alteration with melanites, (2) one in light alkali feldspar veins, and (3) one in dark alkali feldspar veins and. Pyroxenes had three kinds of forms: some in breccias, some in feldspar and some accompanied with amphiboles. Amphiboles had two kinds of forms: in breccias and scatter in feldspars in the veins, its mineral compositions are composed of basaltic hornblende, ferrous pargasite, actinolite and ferroactinolite, all belong to calcic amphibole subgroup. Biotites are scattered in breccias and in the veins or which is the product of metasomatised pyroxenes. The compositions of biotites show low-Ti and Fe, but high-Mg, which were the thermal products of a higher oxygen fugacity. Melanites occurred as layers and belts, which were metasomatised by feldspars and epidotes and amphiboles and carbonates and sericites and diopsides, their ingredients are solid solution series between andradite and Grossular and reflect the melanites were formed in the relative oxidative, alkaline environment. X-ray powder diffraction and infrared spectrum analyses of K-feldspar from early alkali feldspar provide degrees of ordering of 0.71–0.80, structural parameters of 1.27–1.61, triclinicities of 0.23–0.29, T1 (o) + T1 (m) of 0.86–0.90 degrees of ordering of 0.67–0.88 from late K-feldspar, its structural parameters of 1.10–1.91, triclinicities of 0.30–0.70, T1 (o) + T1(m) of 0.84–0.93. Both two kinds of alkali feldspars are microcline, most adularia. Their structure temperatures vary from 200 to 370 °C which are the highest temperatures at which K-feldspars were formed. Thus, it is concluded the K-feldspars in Tieshan is originated from thermal fluid, and the fluid was potassium-rich and a little rich in sodium at the later stage. The 39Ar-40Ar age of feldspars shows 118.68 ± 7.70 Ma and 114.61 ± 6.74 Ma, which represent the ages of early stage facial alkali alteration and late stage dark alkali feldspar veins respectively. It is obvious that an original granites were formed at about 250 to 255 Ma, but all the rocks were considered to be strongly metasomatised by alkali fluid later, most occurred during 108–126 Ma in Yanshanism. Metasomatism of the TCB reflected that complex history of the region. The metasomatised rocks include fenite and amphibole feldsparite. Fenite, especially apatite-rich fenite is associated with REE mineralization, which is helpful to understand the mechanism of a large scale of rare earth deposits in the region. [ABSTRACT FROM AUTHOR]

The Dehua Au-polymetallic ore cluster, as one of the most important area in the Wuyi Au-Cu-Mo metallogenic belt, consists of many large to middle sized epithermal Au deposits and recently discovered porphyry Cu-Mo deposits. We first study the geochronology and geochemistry characteristics of the Cu-Mo mineralization-related Xianyang granite porphyry to constrain its petrogenesis, tectonic setting and metal endowment. LA-ICP-MS zircon U-Pb dating yield a precise age of 157.2 ± 0.8 Ma for the Xianyang granite porphyry, indicating that the granite porphyry was emplaced during the Late Jurassic. The Xianyang granite porphyry was suggested to be generated under continental arc setting, associated with subduction of the paleo-Pacific slab beneath the South China Block. The Xianyang granite porphyry belongs to the high-K calc-alkaline series, with SiO 2 of 71.16–72.02 wt% and K 2 O of 4.28–4.69 wt%. It shows light rare earth element-enriched distribution patterns with (La/Yb) N of = 9.74–13.93, enrichment in large ion lithophile elements, but depletion of high field strength elements, with negative Nb, Ta and Ti anomalies, suggesting an arc magma geochemical affinity. It has lower initial 87Sr/86Sr ratios of 0.7079–0.7086 and relatively higher ε Nd (t) and ε Hf (t) values of −8.03 to −7.69 and − 8.86 to −5.48, respectively, than those of basement rocks of the Cathaysia block, suggesting that it was most likely generated by partial melting of the regional ancient crustal materials, with the involvement of asthenosphere mantle-derived materials. The Xianyang granite porphyry has remarkably high zircon Ce4+/Ce3+ values of 119–404 (mean = 245) and Eu N /Eu N * values of 0.37–0.60 (mean = 0.51), indicating a high oxygen fugacity, which is favor of the formation of the Xianyang porphyry Cu-Mo mineralization. Combining with published research results for regional subvolcanic rocks-related epithermal Au deposits, the porphyry Cu-Mo deposits and epithermal Au deposits in the Dehua ore cluster share similar petrogenetic-metallogenic ages and magma sources in the continental arc setting during the Late Jurassic period. The identification of the coeval porphyry-epithermal Cu-Mo-Au metallogenic system in the Dehua ore cluster highlights the possibility of finding the hidden porphyry Cu-Mo orebodies beneath the discovered epithermal Au deposits. [Display omitted] • The Xianyang granite porphyry were formed during the Late Jurassic. • The Xianyang granite porphyry was generated under continental arc setting. • The Xianyang granite porphyry had high oxygen fugacity. • The porphyry-epithermal Cu-Mo-Au metallogenic system was proposed. [ABSTRACT FROM AUTHOR]

• The ca. 154 ~ 154 Ma magmatic/hydrothermal episode is recognized. • The granitoids in Donghua exhibit characteristics of both A-type and I-type. • Favorable environment for mineralization in Donghua is distinguished. Located in the southern section of the Wuyi Mountain metallogenic belt, the Dehua-Youxi-Yongtai (DYY) ore district is one of the potential areas of gold deposits in the Fujian province, Southeast China. Gold mineralization is widely distributed in this district, including Qiucun, Shuangqishan, Ancun, and Dongyang gold deposits. However, the DYY ore district is still at a low degree of exploration and research. This paper focuses on the Donghua area in the northwest of the DYY ore district as its typical and integrated volcano-magma mechanism revealed in this study. Combined approaches including zircon SHRIMP U-Pb geochronology, Rb-Sr isochron dating and mineral chemistry of pyrite, and hyperspectral remote sensing are employed, aiming to identify the magmatism, alteration, geological setting, and metallogenic potential of the Donghua area. The zircon SHRIMP U-Pb ages of the granite porphyritic dykes in Donghua are 154.6 ± 1.1 Ma and 153.2 ± 1.2 Ma, respectively, indicating that the dykes were formed in the late Jurassic. The Rb-Sr geochronological age of hydrothermal/epithermal pyrite in Donghua is 153.7 ± 2.4 Ma, which is almost coeval with that of the granite porphyritic dykes within error, and consistent with the regional volcanic-magmatic activity and the metallogenic age of the regional metallogenic event. The granitic dykes in Donghua exhibit the characteristics of both A-type and I-type granitoids, thus indicating the presence of transitional geochemical characteristics. As a result of the subduction of the Pacific Plate towards the Eurasia, the ca. 154–153 Ma magmatic event in the Donghua area occurred at the beginning of large-scale delamination of the continental crust. The zoning distribution of the mineral alteration of chlorite, dickite, kaolinite, and gypsum, the interpretation of volcanic activity from the annular structure of hyperspectral remote sensing, and the inferred deep-seated intrusion emplacing from northwest to southeast are in agreement, thus displaying the volcano-magma-alteration mechanism developed in the Donghua area. The magmatism, dykes, faults, and Neoproterozoic metamorphic rock provide favorable advantages for the mineralization in Donghua, suggesting metallogenic potential. [ABSTRACT FROM AUTHOR]