The Age of Hubi Copper (Cobalt) Ore Mineralization in the Zhongtiao Mountain Area, Southern Margin of the Trans-North China Orogen: New Constraints from U-Pb Dating of Rutile and Monazite

The Hubi copper (cobalt) ore district, one of the largest typical examples of the sediment-hosted stratiform type in the Zhongtiao Mountain area, is located on the southern margin of the Trans-North China Orogen within the North China Craton (NCC) and has a copper reserve of 0.79 Mt. Mineralization is mainly hosted by the Zhongtiao Group, a sequence of metasedimentary rocks deposited from ~2168 Ma to ~2059 Ma. Subsequently, a collisional orogeny (Trans-North China Orogen) occurred at ~1.85 Ga. The absolute age of mineralization has not been well constrained due to the lack of suitable minerals for dating. Rutile and monazite are common accessory minerals and are intergrown with Cu mineralization in Cu-bearing veins in the Hubi-type copper (cobalt) deposits. This study presents the first new LA-ICP-MS U-Pb ages of hydrothermal rutile and monazite for the Tongmugou and Laobaotan copper (cobalt) deposits in the ore district, which yield lower intercept rutile U-Pb ages of 1815 ± 30 Ma (Mean Squared Weighted Deviation, MSWD = 5.0) and 1858 ± 27 Ma (MSWD = 5.2) for Tongmugou and 1876 ± 30 Ma (MSWD = 5.9) for Laobaotan. Monazite crystals separated from Cu-bearing carbonate veins within the orebody of Tongmugou yield a weighted mean 207Pb/206Pb age of 1856 ± 14 Ma (MSWD = 1.9), which is close to that of rutile within error. Mineralogical observations and geochemical characteristics suggest that both monazite and rutile crystallized in the hydrothermal fluid system and are closely related to Cu sulfide mineralization. Therefore, their nearly identical U-Pb isotope age of ca. 1850 Ma directly reflects the timing of metamorphic hydrothermal Cu mineralization. This age is indistinguishable from that of metamorphism during the collisional orogeny (Trans-North China Orogen) that led to the final amalgamation of the Eastern and Western Blocks. According to previous studies, the primary sedimentary mineralization of the Hubi-type copper (cobalt) deposits was synchronous with the deposition of the Zhongtiao Group. From the perspective of mineralization age, both the Congolese–Zambian Copperbelt and the Hubi copper (cobalt) ore district experienced early preorogenic sedimentary diagenetic mineralization and late metamorphic hydrothermal mineralization related to orogenesis, and the Hubi-type copper (cobalt) deposits may also be some of the oldest sediment-hosted stratiform-type deposits in the world. Moreover, this metamorphic hydrothermal Cu mineralization spread throughout the Zhongtiao Mountain area

Geochemistry, Zircon U–Pb Age, and Lu–Hf Isotope of the Granite Porphyry in Leimengou Mo Deposit in the East Qinling Molybdenum Ore Belt, China

The Leimengou Mo deposit is one of the typical porphyry deposits in the East Qinling molybdenum ore belt. The Mo mineralization mainly hosts in the Leimengou intrusion, with minor by the gneiss of Archean Taihua Group. The Leimengou intrusion is composed of granite porphyry and monzonitic granite porphyry. Zircon U–Pb LA-(MC)-ICP-MS dating of the two rocks yield the same age of 131 ± 0.6 Ma (N = 23, MSWD = 1.6), consistent with 132 ± 2 Ma of Mo mineralization age obtained by the Re–Os method. The Leimengou intrusion is peraluminous (A/CNK = 1.06–1.28) and high-K calc-alkaline series (K2O + Na2O = 7.84%–9.07%). The REE and trace elements are enriched in large ion lithophile elements (LREE, K, Rb, Ba, Sr, Th and U), and depleted in high-field strength elements (HREE, Nb, Ti and P), with moderately negative abnormal of Eu. Both granite porphyry and monzonitic granite porphyry show a large variation in zircon Hf isotopic compositions with εHf(t) values of −27.9 to −16.9 and −26.0 to −15.2, and two-stage model ages of 2259 to 2946 Ma and 2149 to 2827 Ma, respectively. Whole rock geochemistry and zircon Lu–Hf isotopic compositions suggest that the Leimengou intrusion was derived mainly from an ancient continental crust (probably Archean Taihua Group), with the addition of mantle-derived components

Genesis of the Huoshenmiao Mo deposit in the Luanchuan ore district, China: Constraints from geochronology, fluid inclusion, and H–O–S isotopes

The Huoshenmiao deposit is Mo skarn deposit, located in the western part of the Luanchuan ore district. Mineralization process can be divided into a skarn and a quartz-sulfide episodes with six stages: prograde (I), retrograde (II), quartz-K-feldspar (III), quartz-molybdenite (IV), quartz-pyrite (V), and quartz-calcite (VI). A combined study of geochronology, fluid inclusion (FI), and stable isotopes was conducted to constrain the mineralization age, source of ore materials, as well as the origin and evolution of the ore-forming fluids. Molybdenite Re–Os dating indicates that the deposit was formed in the Late Jurassic (∼145 Ma). The δ34S values of sulfides range from 3.0‰ to 7.1‰, implying that the ore materials in the deposit are magmatic in origin. Three types and six subtypes of FIs are distinguished, namely, aqueous two-phase (W1- and W2-type), daughter mineral-bearing multiphase (S1- and S2-type), and CO2-bearing three-phase (C1- and C2-type). In stages I and II, the W1-type FIs display homogenization temperatures (Th) from 496 °C to >600 °C, with salinities of 14.9–18.3 wt.% NaCl eqv. The FIs in stages III, IV and early stage V composed of coeval S-, C- and W-types, respectively homogenize at similar Th, suggesting the occurrence of boiling. The W1-type FIs in late stage V and stage VI, yield Th of 102–406 °C and salinities of 0–4.7 wt.% NaCl eqv. The δDH2O and δOH2O18 values of the ore-forming fluids in quartz-sulfide episode vary from −112‰ to −76‰, and 11.0‰ to 1.0‰, respectively. All these above observations reveal that the early ore-forming fluids are magmatic in origin, and characterized by high temperature and moderate to high salinity, and gradually evolve to low temperature, low salinity meteoric water. The Huoshenmiao Mo deposit is associated with the magmatism event induced by the protracted subduction of the Izanagi plate beneath the eastern China continent. The decrease in temperature, salinity and f(O2), as well as change of pH due to boiling and fluid-rock interaction, are the main factors controlling Mo deposition. Keywords: Molybdenite Re–Os age, Fluid inclusion, H–O–S isotopes, Huoshenmiao Mo deposit, Luanchuan ore distric

Genesis of the Dianfang breccia-hosted gold deposit, western Henan Province, China: Constraints from geology, geochronology and geochemistry

The Dianfang gold deposit, located in Songxian, western Henan province, China, is one of two breccia-hosted gold deposits in the Xiong'ershan-Waifangshan region. Previous studies suggest that the breccia and host volcanic rocks of the Xiong'er Group formed coevally. The deposit consists of seven vein-type orebodies, occurring within the southern and hanging wall margins of the breccia pipe, as well as in fractures in the rhyolites of the Jidanping Formation, and are structurally controlled by ENE-trending faults. Their mineral assemblage includes K-feldspar, quartz, sericite, chlorite, epidote, carbonate, adularia, and sulfides formed from hydrothermal alteration related to mineralization. Pyrite is the dominant ore mineral, and is associated with minor galena, sphalerite, and chalcopyrite. The trace minerals include magnetite, rutile, cervelleite, matildite, and bismuthinite. Gold occurs as native gold, and electrum inclusions in pyrite, or along microfractures in sulfides and quartz. Four stages of hydrothermal mineralization have been identified: quartz K-feldspar (I), quartz pyrite (II), polymetallic sulfide (III), and carbonate-adularia (IV). Zircon U-Pb geochronology of the granitic matrix of the breccia constrains the timing of breccia pipe formation to 145.8 Ma, indicating it formed at the end of the Late Jurassic, rather than the Paleoproterozoic, as suggested by previous studies. Hydrothermal sulfides from the main orebody yield a Rb-Sr isochron age of 121.5 +/- 1.7 Ma, placing gold mineralization at the end of the Early Cretaceous. The sulfur and lead isotope data suggest that the ore-forming materials have a close connection with magmatic fluid. The initial Sr-87/Sr-86 value of the sulfides is 0.71056 +/- 0.00012, suggesting an ancient crustal source, likely the Archean Taihua Group, mixed with a juvenile mantle component. The trace element characteristics of pyrite indicate the mineralizing fluid was magmatic in origin, sourced from a magma derived from the partial melting of the Taihua Complex, and may have been affected by water-rock interaction at high temperatures under reducing conditions. Geological, geochronological, and geochemical data suggest the Dianfang ore deposit is genetically related to a hidden late Mesozoic granite, and forms part of an intrusion-related auriferous system. Gold deposits of similar ages are widespread at the southern margin of the North China Craton, and are coeval with the emplacement of felsic and mafic intrusions, exhumation of a metamorphic core complex, and formation of extensively faulted basins. This suggests that the Dianfang gold deposit formed under conditions of lithospheric extension caused by crustal thinning, and the destruction of the lithosphere mantle beneath the craton during the Late Jurassic to Early Cretaceous

Molybdenite Re/Os dating, zircon U–Pb age and geochemistry of granitoids in the Yangchuling porphyry W–Mo deposit (Jiangnan tungsten ore belt), China: implications for petrogenesis, mineralization and geodynamic setting

The Yangchuling W–Mo deposit, located in the Jiangnan porphyry–skarn (JNB) tungsten ore belt, is the first recognized typical porphyry W–Mo deposit in China in the 1980's. Stockworks and disseminated W–Mo mineralization occur in the roof pendant of a 0.3 km2 monzogranitic porphyry stock that intruded into a granodiorite stock, hosted by Neoproterozoic phyllite and slate. LA-ICPMS zircon U–Pb analyses suggest that of the monzogranitic porphyry and granodiorite were formed at 143.8 ± 0.5 Ma and 149.8 ± 0.6 Ma, respectively. Six molybdenite samples yielded a Re–Os weighted mean age of 146.4 ± 1.0 Ma. Geochemical data show that both granodiorite and monzogranitic porphyry are characterized by enrichment of large ion lithophile elements (LILE) relative to high field strength elements (HFSE), indicating a peraluminous nature (A/CNK = 1.01–1.08). Two granitoids are characterized by a negative slope with significant light REE/heavy REE fractionation [(La/Yb)N = 8.38–23.20] and negative Eu anomalies (Eu/Eu* = 0.69–0.76). The P2O5 contents of the Yangchuling granitoids range from 0.12% to 0.17% and exhibit a negative correlation with SiO2, reflecting that they are highly fractionated I-type. They have high initial 87Sr/86Sr ratios (0.7104–0.7116), low negative εNd(t) (−5.05 to −5.67), and homogeneous εHf(t) between −1.39 and −2.17, indicating similar sources. Additionally, two-stage Nd model ages (TDM2) of ~1.3–1.4 Ga and two-stage Hf model ages (TDM2) of ~1.2–1.3 Ga are consistent, indicating that Neoproterozoic crustal rocks of the Shuangqiaoshan Group could have contributed to form the Yangchuling magmas. Considering the two groups of parallel Late Mesozoic ore belts, namely the Jiangnan porphyry–skarn tungsten belt (JNB) in the south and the Middle–Lower Yangtze River porphyry–skarn Cu–Au–Mo–Fe ore belt (YRB) in the north, the Nanling granite-related W–Sn ore belt (NLB) in the south, the neighboring Qin–Hang porphyry–skarn Cu–Mo–hydrothermal Pb–Zn–Ag ore belt (QHB) in the north, as well as the Southeastern Coast porphyry–skarn Cu–Mo–Au ore belt (SCB) recognized in South China in this paper,we propose that the latest Jurassic to earliest Cretaceous granitoids and associated ores were formed during a tearing of the subducting Izanagi slab. This tearing of the subduction slab caused the upwelling of asthenosphere and the resulting mantle–crust interaction. The granitoid-related Wore systems in JNB resulted from the remelting of the Proterozoic crust. The mafic–ultramafic volcanic rocks of the Shuangqiaoshan Group intercalated with phyllite and slate, ophiolitic mélange and magmatic arc rocks, mainly comprising I-type granite, basalt, andesite, rhyolite, pyroclastics, togetherwith subduction-relatedmetasomatized lithosphericmantle, would have provided additional mantle material. In this case, the partial melting of rocks of the Shuangqiaoshan Group can produce S-, I- and transitional type granitoids. After strong differentiation it formed tungsten-bearing granitoids characterized by enrichment of high alkali, silicon and volatile components. In the Yangchuling mine area the smallmonzogranitic porphyry stock has stronger fractionation, volatile content and ore-forming components than the older granodiorite, resulting in the development of the porphyry W–Mo ore system

Application of EPMA and LA-ICP-MS to Study Mineralogy of Arsenopyrite from the Haoyaoerhudong Gold Deposit, Inner Mongolia, China

BACKGROUND: The composition of major and trace elements in arsenopyrite can be used to identify the occurrence of elements and explore the remobilization and migration behaviour of elements in different stages. The Haoyaoerhudong gold deposit in Inner Mongolia is a super large gold deposit hosted in the black shales of the Bayan Obo Group. Gold-bearing minerals such as arsenopyrite and loellingite are present. Previous researchers have used the traditional powder dissolution method to analyze the isotope of the ore and discussed the source of ore-forming materials, but the migration and enrichment mechanism of gold has not been unraveled.OBJECTIVES: To understand the gold migration and enrichment process of this deposit.METHODS: Based on mineralogy, different types of arsenopyrite were analyzed by electron probe microanalyzer (EPMA) and inductively coupled plasma-mass spectrometry (ICP-MS). The data measured by EPMA was corrected by ZAF program, and the data measured by LA-ICP-MS was quantitatively calculated by "no internal standard-matrix normalized calibration".RESULTS: The results showed that loellingite was developed in arsenopyrite. They can be divided into Apy-Ⅰ1, Apy-Ⅰ2, Lo-Ⅰ in progressive shear deformation stage and Apy-Ⅱ1, Apy-Ⅱ2 and Lo-Ⅱ in post shear deformation stage. The major element composition of arsenopyrite in different generations was stable, with a small amount of Co and Ni and a trace amount of Sb, Te, Bi, Pb, Au and Ag. Cobalt was higher in Apy-Ⅱ1 and Apy-Ⅱ2, whereas Au, Bi, Pb and Te were obviously enriched in Apy-Ⅰ1. Loellingite was rich in As (64.06%-67.87%), Co (0.33%-4.98%), Ni (1.23%-6.37%). Trace elements such as Au, Te, Bi, Pb and Ag were more enriched in Lo-Ⅱ.CONCLUSIONS: Lo-Ⅱ is the most important gold-bearing mineral. The changes of temperature and sulfur fugacity lead to the precipitation of loellingite and native gold. Native gold is precipitated by remobilization and migration of "invisible gold" in early arsenopyrite and loellingite

UV-fs-LA-ICP-MS Analysis of CO2-Rich Fluid Inclusions in a Frozen State: Example from the Dahu Au-Mo Deposit, Xiaoqinling Region, Central China

The recently developed technique of ultraviolet femtosecond laser ablation inductively coupled plasma mass spectrometry (UV-fs-LA-ICP-MS) combined with a freezing cell is expected to improve the analysis of CO2-rich fluid inclusions by decreasing their internal pressure and avoiding the common problem of uncontrolled explosive fluid release on ablation. Here, we report the application of this technique through the case study of CO2-rich fluid inclusions from the quartz vein-style Au-Mo deposit of Dahu in the Xiaoqinling region of central China. The concentrations of Li, B, Na, Al, K, Ca, Mn, Fe, Cu, Zn, Rb, Sr, Mo, Ag, Te, Cs, Ba, Au, Pb, and Bi were analyzed in 124 (not all for Al and Ca) fluid inclusions, which have low to moderate salinity and multiphase composition (liquid H2O + liquid CO2  ± vapor CO2  ± solids). The Dahu fluids are dominated by Na and K. The concentrations of Mo are always below the detection limit from 0.005 to 2 ppm (excluding values obtained from fluid inclusions with accidentally trapped solids). The Dahu ore fluids differ from metamorphic fluids in compositions and most likely represent two separate pulses of spent fluids evolved from an unexposed and oxidized magmatic system. The UV-fs-LA-ICP-MS analysis of fluid inclusions in a frozen state improves the overpressure problem of CO2-rich fluid inclusions during laser ablation. The transformation of gaseous and liquid CO2 into the solid state leads to a significant decline in the internal pressure of the fluid inclusions, while femtosecond laser pulses generate a minimal heat input in the sample and thus maintain the frozen state during ablation. Transient signals of CO2-rich fluid inclusions obtained in this study typically had one or multiple peaks lasting for more than 15 seconds, without an initial short signal spike as obtained by ns-LA-ICP-MS analysis of CO2-rich fluid inclusions at room temperature

Age and fluid source constraints of the Haoyaoerhudong orogenic gold deposit, North China: Evidence from geochronology and noble gas isotopes

The Haoyaoerhudong gold deposit, located in the northwestern part of the North China craton (NCC), has produced over 120 metric tonnes (t) of gold since 2007. It has a total reserve of > 240 t at average gold grade of 0.62 g/t, making it one of the largest open pit gold mines in China. The steeply dipping, large-tonnage, low-grade, vein- or veinlet-type gold orebodies are hosted in strongly-deformed Mesoproterozoic carbonaceous schist of the Bayan Obo Group. The laminated/boudinaged veins/veinlets in the sinistral ductile–brittle shear zones are dominated by quartz, biotite, gold-bearing löllingite, pyrrhotite, (arseno)pyrite, with minor native gold, titanite and xenotime. In this paper, we present new in situ U–Pb geochronological data on magmatic zircon from the pre-ore dikes, on metamorphic and hydrothermal xenotime, and on hydrothermal titanite from the hydrothermally altered carbonaceous schist and auriferous quartz–sulfides veins/veinlets, as well as He-Ar isotopic analysis on gold-bearing (arseno)pyrite in the syn-ore stage. The metamorphic xenotime U–Pb age of 426 ± 6.0 Ma (2σ) records a regional metamorphic event, possibly related to the accretion of the Bainaimiao arc onto the NCC. Two pre-ore andesitic dikes yielded similar emplacement ages at ∼ 278 Ma constrained by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U–Pb zircon data. Hydrothermal xenotime grains from the altered carbonaceous schist and auriferous quartz–sulfides veins yielded U–Pb ages of 256.0 ± 4.1 Ma (2σ) and 254.4 ± 2.1 Ma (2σ), respectively, overlapping with that of the hydrothermal titanite at 255.4 ± 0.8 Ma (2σ) from the laminated quartz–sulfides veinlets. This indicates that the gold mineralization occurred at ca. 255 Ma. The ∼ 255 Ma gold mineralization age is much younger than the previously reported Early–Middle Permian regional magmatic activity (ca. 291 Ma to 268 Ma), and may be associated with the regional sinistral strike-slip event in the late orogenic cycle related to the collision between the Siberian craton and the NCC. The 3He/4He (R/Ra) and 40Ar/36Ar values of the gold-bearing (arseno)pyrite are 0.04 to 0.09 (average = 0.07) and 375.8 to 2023 (average = 1045), which reveal the ore-forming fluids dominantly originated from the crustal rocks, with limited involvement from the mantle. Collectively, our new geochronological data, noble gas isotopic analyses, and geological evidence support a typical orogenic gold deposit model at Haoyaoerhudong