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... Therefore, the exact formation time of these pegmatite dykes need to be further verified. Furthermore, the study of the pegmatites can also yield new information on the metamorphism history of the southern margin of the NCC, which is still controversial despite of lots of studies (Shi et al., 2011;Liu et al., 2009;Xu et al., 2009;Yang, 2008;Li et al., 2007;Wan et al., 2006;Ni et al., 2003). ...
... The Taihua Group rocks also occurred in the other old terranes, i.e., Xiaoshan, Xiong'ershan, Lushan and Wuyang, which all scatter along the southern margin of the NCC. Previous researchers have reported various ages for the Taihua Group ranging from the Late Archean to the Paleoproterozoic using different methods such as paleontology, Rb-Sr, Sm-Nd, Ar-Ar, and zircon Pb-Pb dating (Ni et al., 2003;Zhou et al., 1998;Ding 1996;Xue et al., 1995;Kröner et al., 1988). Recently, the application of SHRIMP and LA-ICP-MS to in situ U-Pb zircon geochronology confirmed the Late Archean to Paleoproterozoic ages of the Taihua Group (Yu et al., 2013;Diwu et al., 2010Diwu et al., , 2007Liu et al., 2009;Xu et al. 2009;Yang, 2008;Li et al., 2007;Wan et al., 2006). ...
... Xu et al. (2009) preferred 2.1 Ga as the metamorphism age at the Xiong'ershan and Xiaoqinling areas and they found no evidence for a ~1.85 Ga metamorphic event in this area. Ni et al. (2003) believed 2.3-2.4 Ga as the metamorphic age of the Xiong'ershan area. ...
In this study, we carried out petrography, zircon U-Pb geochronology and Hf isotopic analyses on a granitic pegmatite dyke in the Xiaoqinling area in southern margin of the North China Craton (NCC). Our study suggests that the pegmatite dyke likely crystallized from a volatile-rich pegmatitic magma. Different from most other pegmatite elsewhere, zircon from this pegmatite dyke does not contain unusually high U and Th concentrations and suffered no evident radioactive damage, therefore we successfully obtained a zircon U-Pb dating using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), which yields an average 207Pb/206Pb age of 1 814±6 Ma, representing the intrusive age of the granitic pegmatite dyke. Zircon ɛ
Hf(t) values are between −8.3 and −3.0, corresponding to Hf depleted mantle model ages from 2 649 to 2 991 Ma with an average of 2 881 Ma. These data indicate that this granitic pegmatite dyke may have been derived from partial melting of Meso-Neoarchean metamorphic rocks from the Xiaoqinling basement. Granitic pegmatite magma may have emplaced within the Taihua Group wall rocks during the last stage of the middle to high grade metamorphism. Furthermore, according to the petrographic observation, the 1.81 Ga pegmatite dyke and the 1 800–1 750 Ma Xiong’er Group rocks were not undergone middle to high grade metamorphism, indicating 1.81 Ga as the termination of the latest regional metamorphism in the southern margin of the NCC.
... The Taihua metamorphic complex exposes at the southern terminal of the TNCO and is traditionally termed the "Taihua Group" in Chinese literature (e.g., Zhang et al., 1985;Zhang and Li, 1998). Meta-volcanic rocks and meta-sedimentary sequences expose widespread in the complex (Guan, 1996;Zhang and Li, 1998;Ni et al., 2003). The Taihua metamorphic complex consists of five discrete metamorphic terranes, i.e., the Mts. ...
... The protolith of the amphibolites and TTG gneisses were dated to be 2.91-2.07 Ga (Zhang and Li, 1998;Ni et al., 2003;Huang et al., 2012;Jiang et al., 2011), but the metamorphism was controversially dated, ranging from 2.37 Ga to 1.54 Ga (Zhang and Li, 1998;Ni et al., 2003;Jiang et al., 2011). Therefore, we conducted detailed metamorphic and geochronological studies on this terrane in order to provide more accurate data. ...
... The protolith of the amphibolites and TTG gneisses were dated to be 2.91-2.07 Ga (Zhang and Li, 1998;Ni et al., 2003;Huang et al., 2012;Jiang et al., 2011), but the metamorphism was controversially dated, ranging from 2.37 Ga to 1.54 Ga (Zhang and Li, 1998;Ni et al., 2003;Jiang et al., 2011). Therefore, we conducted detailed metamorphic and geochronological studies on this terrane in order to provide more accurate data. ...
Garnet-bearing amphibolites and metapelites of the Luoning metamorphic terrane, Taihua metamorphic complex, southern terminal of the Palaeoproterozoic Trans-North China Orogen (TNCO), preserve different metamorphic mineral assemblages formed at three metamorphic stages in the Palaeoproterozoic. The prograde mineral assemblages (M1) comprise of hornblende + plagioclase + quartz ± biotite inclusions preserved in the garnet porphyroblasts in the amphibolites or quartz + biotite + plagioclase inclusions preserved in the garnet porphyroblasts in the metapelites. The metamorphic peak mineral assemblages (M2) are represented by the garnet porphyroblasts as well as the matrix minerals plagioclase + hornblende ± biotite + quartz in the amphibolites or quartz + biotite + plagioclase ± hornblende in the metapelites, respectively. The retrograde mineral assemblages (M3) are the worm-like, fine-grained “white-eye socket” symplectitic assemblages formed between the relict garnet porphyroblasts and the matrix minerals, consisting of plagioclase + hornblende ± biotite intergrowths in the amphibolites or plagioclase + biotite + quartz intergrowths in the metapelites, respectively. Geothermobarometric computation shows that the Luoning terrane records clockwise P-T trajectories including near isothermal decompression (ITD) processes, from 630-790 °C/5.3-8.9 kbar through 720-820 °C/8.9-10.7 kbar to 690-740 °C/7.1-7.7 kbar. SIMS U-Pb dating of zircons separated from the amphibolites and metapelites presents that the age of the protolith of the amphibolites is ∼2.32 Ga and the metamorphism occurred during 1.97-1.94 Ga, suggesting that the subduction-collision and the subsequent exhumation occurred in the late Palaeoproterozoic. Combined with the literature data of the different discrete terranes within the Trans-North China Orogen, it is further deciphered that the tectono-metamorphic event of the Trans-North China Orogen started as early as 1.97 Ga and lasted as late as 1.80 Ga, suggesting that the tectono-metamorphic event of the orogen is a long and complex history.
... The Taihua Group consists mainly of amphibolite, felsic gneiss, and migmatite with zircon U-Pb ages of 2.8-2.3 Ga (Kröner et al., 1988;Xue et al., 1995;Ni et al., 2003;Xu et al., 2009). The Xiong'er Group, ranging in thickness from 3000 to 7000 m, is mainly composed of basaltic andesite, andesite, dacite, and rhyolite (Zhao et al., 2004). ...
... Multiple lines of evidence suggest that the monazite, apatite, and rutile from the studied samples precipitated from the mineralizing fluids, rather than having been derived from the ore-hosting rocks. In the Xiong'ershan district, metamorphic rocks of the Taihua Group have accessory minerals dominated by zircon, ilmenite, and titanite (Ni et al., 2003;Jiang et al., 2011;Huang et al., 2012;Diwu et al., 2014;Chen et al., 2015). Accessory minerals in volcanic rocks of the Xiong'er Group consist mainly of zircon, magnetite, and ilmenite (Zhao et al., 2002b). ...
The North China craton was stabilized in the late Paleoproterozoic but experienced significant removal of ancient lithospheric keel in the late Mesozoic that resulted in the formation of numerous world-class gold deposits with combined reserves of more than 7000 t of gold. However, it remains uncertain whether the North China craton contains older gold deposits formed during generation and final stabilization of the craton. Here, we show that the Shanggong gold deposit (105 t Au at 5.31 g/t) on the southern margin of the North China craton formed in the late Paleoproterozoic during the collision between the Eastern and Western blocks that led to formation of the Trans−North China orogen and final stabilization of the craton. The Shanggong deposit is hosted in amphibolite-facies rocks of the Neoarchean to early Paleoproterozoic Taihua Group and overlying volcanic rocks of the late Paleoproterozoic Xiong’er Group. Gold mineralization is structurally controlled by NE-striking faults and occurs in four segments: the Liuxiugou, Hugou, Shanggong, and Qiliping segments. The ores consist mainly of quartz-ankerite-sulfide stockworks and sulfide disseminations in hydrothermally altered wall rocks. Gold is mostly contained in arsenian pyrite that is variably associated with minor sphalerite, galena, and chalcopyrite. Ore-related alteration assemblages comprise mainly quartz, ankerite, K-feldspar, sericite, and tourmaline. Both the stockworks and mineralized alteration assemblages contain hydrothermal accessory minerals, including monazite, apatite, and rutile. Paragenetic relations and textural data show that these accessory phases precipitated synchronously with gold-bearing sulfides. Laser ablation−inductively coupled plasma−mass spectrometry spot analyses of monazite and apatite from the Shanggong segment yielded reproducible U-Pb dates of 1747 ± 20 Ma (2σ, mean square of weighted deviates [MSWD] = 0.46) and 1788 ± 200 Ma (2σ, MSWD = 11.3), respectively. These dates are indistinguishable within errors from an apatite U-Pb date of 1743 ± 79 Ma (2σ, MSWD = 1.6) at the Liuxiugou segment and a rutile U-Pb date of 1804 ± 52 Ma (2σ, MSWD = 0.77) at the Hugou segment. These new dates suggest that the Shanggong deposit formed at ca. 1.80−1.74 Ga, coeval with or immediately after formation of the Trans−North China orogen and final stabilization of the North China craton. Sulfides from the Shanggong gold deposit have δ34S values ranging from −18.5‰ to −6.9‰, whereas the coexisting ankerite has δ13CPDB of −6.81‰ to −1.61‰ and δ18OSMOW of 15.70‰−17.62‰. The stable isotope data are distinctively different from values of the Early Cretaceous gold deposits in the southern North China craton, indicating contrasting hydrothermal systems responsible for these two categories of gold deposits. The results presented here, combined with independent geologic evidence, allow Shanggong to be the first confirmed Paleoproterozoic orogenic gold deposit in the North China craton. Recognition of Paleoproterozoic orogenic gold mineralization provides significant new insights into the gold metallogeny of the well-endowed North China craton and has implications for future gold exploration along the three Paleoproterozoic orogenic belts in this craton.
... The Taihua Group consists of biotite plagiogneiss, amphibole plagiogneiss, amphibolite, quartzite, and marble [42]. These rocks probably formed in the Neoarchean and have been subjected to amphibolite-facies metamorphism in the Paleoproterozoic [43][44][45]. The Archean rocks were intruded by Paleoproterozoic pegmatite [45,46], Paleoproterozoic and Early Cretaceous mafic dikes [47][48][49], and Proterozoic and Mesozoic granitic intrusions. ...
... Due to the higher repetition rate and the larger sample volumes, the calculated detection limits are expected to decrease significantly and the observed signal intensities and durations are expected to increase compared to the fixed spot ablation technique. Thus, it is possible to increase the sample time for the 20 measured elements ( 7 Li, 11 B, 23 Na, 27 Al, 39 K, 44 Ca, 55 Mn, 57 Fe, 65 Cu, 66 Zn, 85 Rb, 88 Sr, 95 Mo, 107 Ag, 125 Te, 133 Cs, 137 Ba, 197 Au, 208 Pb, and 209 Bi) to 10 ms per line with 4 lines per peak, resulting in a total sweep time of 707 ms. ...
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 CO 2-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 CO 2-rich fluid inclusions from the quartz vein-style Au-Mo deposit of Dahu in the Xiaoqinling region of central China. The concentrations of were analyzed in 124 (not all for Al and Ca) fluid inclusions, which have low to moderate salinity and multiphase composition (liquid H 2 O + liquid CO 2 ± vapor CO 2 ± 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 CO 2-rich fluid inclusions during laser ablation. The transformation of gaseous and liquid CO 2 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 CO 2-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 CO 2-rich fluid inclusions at room temperature.
... Gold deposits are mainly hosted within the Archean amphibolite-facies metamorphic rocks, which consist of biotite plagiogneiss, amphibole plagiogneiss , amphibolite, quartzite, and marble (Cai and Su, 1985). These rocks probably formed in the Neoarchean and have been subjected to amphibolite-facies metamorphism in the Paleoproterozoic (Zhou et al., 1998; Ni et al., 2003; H.M. Li et al., 2007b). The Archean rocks were intruded by pegmatite sills and dikes in the Paleoproterozoic (1955 ± 30 Ma: H.M. Li et al., 2007b), mafic dikes in the Paleoproterozoic (1851 ± 18 to 1719 ± 21 Ma: T.H. Wang et al., 2008; Bi et al., 2011b; J.W. Li et al., 2012b) and Early Cretaceous (130 ± 4 to 126 ± 1 Ma: T.H. Wang et al., 2008; H.J. Zhao et al., 2010; J.W. Li et al., 2012b), and granitic plutons in the Proterozoic and Mesozoic. ...
... Second, the refractory Archean Taihua rocks have a low content of volatiles (0.75–2.6 wt % LOI; Luan et al., 1985). Most volatiles of these rocks probably have been released during the regional amphibolite-facies metamorphism in the Paleoproterozoic (Zhou et al., 1998; Ni et al., 2003; H.M. Li et al., 2007b). Based on the Sr-Nd isotope data, Ni et al. (2012) proposed that the ore-forming fluids directly originated from devolatilization of a subducting oceanic slab, and by interaction of the ore-forming fluids with the radiogenic Archean Taihua rocks yielding an enriched mantle-like Sr-Nd isotope signature. ...
The Dahu Au-Mo deposit is located in the Xiaoqinling region and belongs to the Qinling-Dabie orogen of central China. The quartz vein-style Dahu Au-Mo deposit (31 t Au, average grade: 4.7 g/t; 30,000 t Mo, average grade: 0.13 %) formed in four stages, i.e., an early quartz-K-feldspar stage (I), a pyrite-molybdenite stage (II), a sulfide-telluride-sulfosalt-gold stage (III), and a late carbonate-barite stage (IV). Abundant tellurides and sulfosalts occur in stage III: altaite, tellurobismuthite, buckhornite, hessite, petzite, calaverite, aikinite, kupcikite, lindstromite, salzburgite, wittichenite, and tetradymite. The system is characterized by carbono-aqueous fluids of low to moderate salinity and high oxygen fugacity. Total homogenization temperatures of the H2O-CO2 fluid inclusions in stage I and stage III quartz range from 230 degrees to 440 degrees C and 198 to 320 degrees C, respectively. The variation in CO2/H2O ratios and microthermometric data of the H2O-CO2 fluid inclusions results from a combination of fluid unmixing and sequential trapping of fluid inclusions, but also from postentrapment reequilibration. Abundant minerals are present as solid phases in H2O-CO2 fluid inclusions in stage I quartz: Cu1.6.5S, covellite, chalcopyrite, bornite, molybdenite, pyrite, colusite, anhydrite, and celestine. delta O-18(qartz) values of stage I quartz range from 10.2 to 12.0 parts per thousand, with calculated delta O-18(fluid) values ranging from 5.6 to 7.4 parts per thousand. The delta D values of fluid inclusion waters (thermal decrepitation) in stage I quartz range from -117 to -54 parts per thousand. The low and scattered delta D values reflect a mixture of ore-forming fluids trapped by the H2O-CO2 fluid inclusions at deep crustal levels and postmineralization fluids, possibly meteoric waters, trapped by secondary aqueous fluid inclusions at higher crustal levels during uplift of the Xiaoqinling core complex. Four molybdenite samples yield an Re-Os isochron age of 206.4 +/- 3.9 Ma (MSWD = 0.88), suggesting ore formation in the Late Triassic. Metal signature, mineral association, fluid characteristics, and isotope data of the Dahu deposit, together with the tectonomagmatic setting, imply that the ore-forming fluids were derived from an unexposed and oxidized Magmatic system, which likely stems from partial melting of enriched lithospheric mantle beneath the North China craton in a postcollisional extensional setting.
... The formation ages of Taihua group were approximately 2.8, 2.5, 2.3, and 1.97-1.80 Ga [32,34,59], reflecting the multi-stage cyclic evolution of the crust in this area. The formation age of the early Taihua group (approximately 2.8 Ga) is much older than that of the later U-rich granitic pegmatite and is very close to the two-stage model age (T DM2 ) of the zircon Hf isotope (3.10-2.76 ...
The Huayangchuan uranium deposit, located in the west of the Xiaoqinling belt on the southern margin of the North China Craton, is a large U–Nb–Pb deposit accompanied with rare–earth elements. The Huayangchuan uranium deposit, discovered in the 1950s, has long been known as a carbonatite–type uranium deposit. Recently, new geological work has found uranium mineralization in many granitic pegmatite veins in the Huayangchuan deposit and adjacent areas. Here, we report a systematic investigation of the petrography, whole–rock geochemistry, zircon U–Pb ages, and in situ Lu–Hf isotopic characteristics of newly discovered U–rich granitic pegmatite veins in the west of Huayangchuan deposit. The petrological results showed that the lithology of the samples is granite pegmatite. The U–Pb ages of zircon were 1826.3 ± 7.9 and 1829 ± 11 Ma. Microscopically, the paragenetic characteristics of zircon, betafite, and uraninite exist in the intergranular fissures of K–feldspar and quartz, reflecting metallogenic phenomena in the rock formation process. Almost all whole–rock samples were rich in SiO2 (64.37−70.69 wt.%), total alkalis (K2O + Na2O = 8.50–10.30 wt.%), and Al2O3 (12.20–14.41 wt.%) but poor in TiO2 (0.23–0.73 wt.%), MgO (0.38–0.90 wt.%), CaO (1.23–2.22 wt.%), P2O5 (0.14–0.83 wt.%), and MnO (0.04–0.57 wt.%). Additionally, they showed enrichment of LILEs (such as Rb, Ba, Th, U, and K), depletion of HFSEs (such as Ta, P, Ti, and Hf), and no alkaline dark minerals, and the characteristics are intraplate A1–type granite. The A1–type granite displayed low zircon εHf(t) values (−19.42–−15.02) with zircon two–stage Hf model aged 3.10–2.76 Ga, indicating that the U–rich granitic pegmatite was derived predominantly from partial melting of the ancient continental crust (such as the early Taihua group formed in Archean–Neoarchean). Combined with the above results and regional geological data, the U–rich granitic pegmatite discovered in the Huayangchuan deposit was formed in a post–collisional regime after the Luliang movement in the late Paleoproterozoic. This study suggests that future uranium prospecting work in this area should focus on late Paleoproterozoic U–rich granitic pegmatites.
... The district primarily comprises amphibolite-facies rocks from the lower Paleoproterozoic Taihua Group and intermediate-felsic volcanic rocks from the upper Paleoproterozoic Xiong'er Group, along with minor Mesoproterozoic clastic and carbonate rocks. The Taihua Group comprise a variety of rock types, including biotite-plagioclase gneiss and granulite, dated between 2.5 and 2.3 Ga (Ni et al., 2003;Xu et al., 2009;Diwu et al., 2010;Huang et al., 2012;Li et al., 2015). The Xiong'er Group volcanic succession, unconformably overlying the Taihua Group, varies in thickness from 3.0 to 7.6 km and includes basaltic andesite and dacite-rhyolite, with an eruption age younger than 1.85 Ga Wang et al., 2010). ...
... Regional geology is dominated by metamorphic crystalline basement of the Neoarchean-early Paleoproterozoic Taihua Group and metavolcanic rocks of the Mesoproterozoic Xiong'er Group . The Taihua Group (2.8-2.1 Ga) is mainly composed of amphibole, felsic gneiss, and migmatite (Kröner et al., 1988;Ni et al., 2003;Xu et al., 2009), and is unconformably overlain by the Xiong'er Group. The Xiong'er Group comprises the Xushan, Jidanping, Majiahe and Gaoshanhe Formations, and is mainly composed of basaltic-andesite to rhyolite (Zhao et al., 2004;Zhao et al., 2001b). ...
... The formation ages of Taihua Group were approximately 2.8, 2.5, 2.3 and 1.97-1.8 Ga [32,34,60], reflecting the multi-stage cyclic evolution of the crust in this area. The formation age of the early Taihua Group (approximately 2.8 Ga) is much older than that of the later U-rich granitic pegmatite and is very close to the two-stage model age (TDM2) of the zircon Hf isotope (3.10-2.76 ...
The Huayangchuan uranium deposit, located in the west of the Xiaoqinling belt on the southern margin of the North China Craton, is a polymetallic deposit dominated by U, Nb, Pb, and rare earth elements. The Huayangchuan uranium deposit, discovered in the 1950s, has long been known as a carbonatite-type uranium deposit. Recently, new geological work has found uranium mineralisation in many granitic pegmatite veins in the Huayangchuan deposit and adjacent areas. Here, we report a systematic investigation of the petrography, whole-rock geochemistry, zircon U-Pb ages, and in situ Lu-Hf isotopic characteristics of newly discovered U-rich granitic pegmatite veins in the west of Huayangchuan deposit. The petrological results showed that the lithology of the samples is equivalent to that of granite. The U-Pb ages of zircon were 1826.3 ± 7.9 and 1829 ± 11 Ma. Microscopically, the symbiotic characteristics of zircon, betafite, and uraninite exist in the intergranular fissures of K-feldspar and quartz, reflecting metallogenic phenomena in the rock formation process. Almost all whole-rock samples were rich in SiO2 (64.37–70.69 wt.%), total alkalis (K2O+Na2O = 8.50–10.30 wt.%), and Al2O3 (12.20–14.41 wt.%), but poor in Ti2O (0.23–0.73 wt.%), MgO (0.38–0.90 wt.%), P2O5 (0.14–0.83 wt.%), MnO (0.04–0.57 wt.%). Additionally, they showed enrichment of LILEs (such as Rb, Ba, Th, U, and K), depletion of HFSEs (such as Ta, Nb, P, Ti, and Hf), no alkaline dark minerals, and the characteristics are typical of intraplate A1-type granite. The A1-type granite displayed low zircon εHf(t) values (-19.42– -15.02) with zircon two-stage Hf model aged 3.10–2.76 Ga, indicating that the U-rich granitic pegmatite was derived predominantly from partial melting of the ancient continental crust (such as the early Taihua group formed in Archean-Neoarchean). Combined with the above results and regional geological data, the U-rich granitic pegmatite discovered in the Huayangchuan deposit was related to granite magma activity that formed in a post-collisional regime after the Luliang movement in the late Palaeoproterozoic. This study suggests that future uranium prospecting work in this area should focus on late Palaeoproterozoic U-rich granitic pegmatites.
... The Taihua Group, the main host rocks for gold deposits, consists of tonalite-trondhjemite-granodiorite (TTG) gneisses and amphibolites. The rocks underwent amphibolite facies metamorphism (partially reached granulite facies) in the Paleoproterozoic (Luan and Chen, 1991;Ni, 2003). Zircons from the tonalite gneiss yield U-Pb ages from 2841 ± 16 to 2806 ± 7 Ma (Kröner et al., 1988;Sun et al., 1994), which were interpreted as the formation age of the Taihua Group. ...
The ore genesis of gold deposits in Xiaoqinling, located in the south margin of the North China Craton (NCC), remains highly debated. Either a magmatic source or a metamorphic origin has been advocated for the ore-forming fluids. In this paper, we report new ⁴⁰Ar/³⁹Ar dating, in-situ pyrite trace elements and C-H-O isotopic data for the Cangzhuyu deposit, hosted in quartz veins within the Archaean metamorphic rocks to constrain the ore-forming processes. Four stages of mineralization and alteration can be recognized in the deposit, including Stage I: quartz-pyrite veins; Stage II: pyrite-quartz-ankerite veins; Stage III: polymetallic sulfides-ankerite-quartz veins; Stage IV: quartz-carbonate veins. Sericite from stage III gold-bearing veins has a ⁴⁰Ar/³⁹Ar plateau age of 130.7 ± 1.3 Ma, which is synchronous with the regional gold mineralization event in the Xiaoqinling district. Laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) trace element analysis shows that Stage I and Stage IV pyrite show similar compositions and rarely contain lattice gold. In contrast, gold mostly occur as native gold or Au-Te-Bi mineral inclusions within Stage III pyrite, which are consistent with their high Ni, Te, Bi contents. The ore-forming fluids equilibrated with ankerite have C-O isotopes of −6.6 to −4.1‰ and 8.8 to 10.8 ‰, respectively. They are consistent with H and O isotopes of sericite that δDfluid ranges from −61.1 to −60‰ and δ¹⁸Ofluid ranges from 8.2 to 7.2 ‰, implying a magmatic source. We hence suggest that the Cangzhuyu gold deposit was formed from mantle-derived magmas in a setting of the destruction of NCC and lithospheric thinning.
... In the southern margin of North China Block, the mid-late Cretaceous (120-100 Ma) granites also have large variations in zircon ε Hf (t) values (ranging from −26.3 to −13.5) and two-stage model age(ranging from 2040 to 2860 Ma) [12], which is consistent with the Leimengou granitic rocks. Previous studies on the zircon U-Pb and Ar-Ar geochronology of the crystalline basement Taihua Group on the southern margin of the North China Block indicate that the formation time of the Taihua Group was about 2700 Ma, and the metamorphism occurred within the range of 2200 to 2300 Ma [36,37].It can be concluded that the Taihua Group is probably the main source region of the Leimengou intrusion. However, the Leimengou granitic rocks show large variations in zircon ε Hf (t) values (11 ε units), suggesting more than one sources. ...
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.
... The Shanxian TTG gneisses, Sihe granitic gneisses and Muce monzonitic gneisses are located in the Taihua Complex, which lies on the southern terminal of the TNCO and consists of metavolcanic rocks and metasedimentary sequences (Zhang et al., 1985;Guan, 1996;Zhang and Li, 1998;Ni et al., 2003) exposing in the discrete metamorphic terranes, e.g., the Mts. Huashan, Shanxian, Luoning, Yiyang, Lushan and Wugang terranes, from the northwest to the southeast. ...
... Based on a whole rock Sm-Nd isochron age of 2766 ± 29 Ma (Xue et al., 1995) for an amphibolite and single-grain zircon evaporation Pb-Pb ages of 2841 ± 6 Ma and 2806 ± 7 Ma for its TTG rocks (Kröner et al., 1988), it was suggested that the Taihua Complex was formed during the Archean. Others, however, attributed it to Paleoproterozoic or Archean to Paleoproterozoic by paleontology, Sr-Nd, Rb-Sr or Ar/Ar dating (Chen et al., 1980;Hu et al., 1988;Huang et al., 1995Huang et al., , 2012Ding, 1996;Zhou et al., 1998;Ni et al., 2003;Xu et al., 2009;Diwu et al., 2010;Jiang et al., 2011;Lu et al., 2013Lu et al., , 2014Lu et al., , 2015Yu et al., 2013;Wang et al., 2014). ...
... The strata exposed in the Xiaoqinling region are dominated by Archean medium-grade metamorphic rocks of the Taihua Group, which consists of biotite plagiogneiss, amphibolite gneiss, amphibolite, quartzite, and marble (Cai & Su 1985). These rocks probably formed in the Neoarchean and have been subjected to amphibolite-facies metamorphism in the Paleoproterozoic (Zhou et al. 1998, Ni et al. 2003, Li et al. 2007. ...
The Xiaoqinling vein-style gold district (reserves of >630 t Au) has a very pronounced tellurium signature. The Yangzhaiyu gold deposit is one of the largest gold deposits in this district. The ore-mineral assemblage consists of pyrite, chalcopyrite, galena, bornite, sphalerite, gold, and native tellurium together with a wide variety of telluride and Bi-sulfosalt minerals. The telluride mineral assemblage comprises Phase A, sylvanite [(Au,Ag)2Te4], hessite [Ag2Te], petzite [Ag3AuTe2], calaverite [AuTe2], stützite [Ag5-xTe3], rucklidgeite [PbBi2Te4], altaite [PbTe], volynskite [AgBiTe2], tellurobismuthite [Bi2Te3], tetradymite [Bi2Te2S], and buckhornite [AuPb2BiTe2S3]. The Bi-sulfosalt minerals observed are Phase B, aikinite [PbCuBiS3], felbertalite [Cu2Pb6Bi8S19], and wittichenite [Cu3BiS3]. We observed two unnamed phases: Phase A and Phase B. Phase A, with the empirical formula of AgTe3, occurs in small intergrowth aggregates with sylvanite and chalcopyrite, and locally with bornite, galena, and altaite. Phase A and its associated minerals occur along healed micro-fractures in pyrite. It has a distinctly golden reflection color, without discernable reflectance pleochroism or anisotropy. AgTe3 was synthesized in 1982, but its natural occurrence has not been reported to date. Phase B, with the empirical formula of Cu20FePb11Bi9S37, was observed in an intergrowth aggregate together with hessite, galena, chalcopyrite, bornite, and buckhornite. It has a pinkish grey reflection color, without discernable reflectance pleochroism or anisotropy. The telluride and gold mineralization took place at or below ca. 220 ° C and evolved towards decreasing fTe2. The ore-forming fluids and components of the Yangzhaiyu gold deposit may ultimately stem from refertilized upper mantle, either directly from devolatilization or from a magmatic system resulting from partial melting.
We present in situ LA-ICP-MS U-Pb dating of xenotime and monazite in assemblages with native gold and Au (Ag) tellurides from the Xiaoqinling lode gold district in central China. Composite xenotime and monazite grains formed through coupled dissolution-reprecipitation reactions reveal two discrete gold mineralization events. The first gold mineralization event, recorded by monazite (158.6 ± 3.3 Ma, Tera-Wasserburg lower intercept age) and xenotime cores (157.11 ± 0.83 Ma, weighted mean 206Pb/238U age), is characterized by the mineral assemblage of lingbaoite (AgTe3)-sylvanite ([Au,Ag]2Te4)-stützite (Ag5–xTe3)/native tellurium-sylvanite-stützite. The second gold mineralization event, recorded in the rims of xenotime (135.46 ± 0.93 Ma, weighted mean 206Pb/238U age), is characterized by the mineral assemblage of native gold-calaverite (AuTe2)-petzite (AuAg3Te2)-tellurobismuthite (Bi2Te3). Our study implies that the large-scale Jurassic mineralization event in eastern China, related to flat subduction of the paleo-Pacific plate beneath the eastern China continent, also caused widespread gold mineralization in the Qinling-Dabie Orogen, in addition to production of its world-class porphyry Mo deposits. The fact that only a few Jurassic gold mineralization ages have been reported before, may be due to the lack of suitable geochronometers to record the earlier Jurassic hydrothermal processes, which have been overprinted by the better-recognized Early Cretaceous gold mineralization event. This study also presents a rare example of xenotime compositional alterations and resetting of U-Pb ages induced by low to moderate salinity carbono-aqueous fluids at low temperatures. The textural relationships between gold minerals in contact with such composite xenotime crystals demonstrate that they could have precipitated before, coeval with, or after the dated domains. Since low to moderate salinity carbono-aqueous fluids are commonly involved in the formation of lode gold deposits, it is crucial to examine xenotime textures and recognize potential alteration textures before carrying out isotopic dating of xenotime collected from these deposits. Without prior compositional and textural characterization, attempts to date such composite crystals could yield mixed dates and meaningless ages.
The Jinqu Au deposit is located in the central Xiaoqinling gold field along the southern margin of the North China Craton. Ore-bearing auriferous quartz veins in the deposit are controlled by E–W trending structures within amphibolite facies metamorphic rocks of the Archean Taihua Group. The ore-forming process in this deposit can be divided into four stages represented by feldspar-quartz, pyrite-quartz, polymetallic sulfide-quartz, and carbonate-quartz veins and veinlets. Here we present fluid inclusion and isotopic data of the Jinqu Au deposit. Four types of fluid inclusions in quartz and calcite are identified, including carbonic-aqueous inclusions (type-1), aqueous inclusions (type-2), solid-bearing inclusions (type-3) and pure carbonic inclusions (type-4) varieties, based on petrography and laser Raman spectroscopy. Quartz in stage I contains type-1 fluid inclusions (FIs) which homogenized to aqueous or carbonic phase at temperature 361 to 406 ℃ and 385 to 400 ℃ respectively, and have salinities of 10.3 to 17.9 wt.% NaCl equiv. Type-2 FIs show homogenization temperatures of 347 to 410 ℃ into the liquid phase, with high salinities of 11.6 to 18.6 wt.% NaCl equiv. Quartz in stage II is the major host of type-1 FIs, with minor type-4 FIs, the former showing homogenization at temperatures of 305 to 390 ℃ into the carbonic phase and 280 to 410 ℃ into the aqueous phase , with variable salinities of 4.5 to 19.8 wt.% NaCl equiv. The stage III quartz contains all the four types of FIs (homogenizing to carbonic or aqueous phase at temperature 309 to 360 ℃ and 295 to 400 ℃, with salinities of 6.6 to 19.9 wt.% NaCl equiv for type-1, and homogenizing to liquid at temperature 308 to 326 ℃ with salinities of 12.5 to 13.2 wt.% for type-2 Fls). In stage IV, type-2 FIs are the major type in quartz and calcite with total homogenization temperatures of 213 to 280 ℃ into the liquid phase and variable salinities of 5.3 to 18.6 wt.% NaCl equiv. Our data show that the ore-forming fluids of the Jinqu Au deposit are generally characterized by moderate to high homogenization temperatures and variable salinities, belonging to the CO2-H2O-NaCl±CH4 system. Based on fluid inclusion data, we infer that fluid immiscibility occurred in stages II and III, and the estimated trapping pressures for stages II and III fluids are between 81 to 275 MPa.
The C-H-O isotopic values of fluids (δ¹⁸Owater = 1.2 to 6.4‰; δDV-SMOW = − 68.5 to − 56.0‰; δ¹³CCO2 = − 12.4 to − 3.4‰) in stage I to IV and δ¹³CV-PDB values for calcite (δ¹³CV-PDB = − 7.6 to − 4.3‰) in stage IV suggest that the ore-forming fluids were composed of a mixture of metamorphic water and mantle-derived fluids with minor involvement of meteoric water. Fluid inclusions in pyrite of stage II and III yield ³He/⁴He ratios of 0.88 to 1.39 Ra, and considerable ⁴⁰Ar/³⁶Ar ratios range from 2287.6 to 5669.9, suggesting the mixing of mantle and crustal components. The δ³⁴SV-CDT values of sulfide samples in stages II and III range from − 5.8 to 4.5‰ (except for a pyrite grain within calcite that shows − 28.5 ‰). The values of ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb of pyrite samples in stages II and III are from 16.919 to 17.321, 15.340 to 15.539, and 37.303 to 37.971 respectively. Our data suggest that the Taihua Group was possibly a major source for the ore-forming metals of the Jinqu Au deposit. Integrating the data from ore geology, fluid inclusions, isotope geochemistry and regional setting, we propose that the Jinqu Au deposit is an orogenic-type deposit which formed within the continental collision setting of the North China and Yangtze Cratons.
The North China Craton is well endowed with numerous Early Cretaceous gold deposits that are mainly hosted in Archean to early Paleoproterozoic metamorphic rocks and late Mesozoic granitoid intrusions intruding the former. Whether or not gold was sourced from those metamorphic rocks remains hotly debated. Here we present trace element and S-Pb isotope data of pyrite from the Neoarchean to early Paleoproterozoic metamorphic rocks in the Xiaoqinling district of southern North China Craton and late Paleoproterozoic pegmatites derived from the former rocks, in an attempt to provide new insights into the gold sources for Early Cretaceous gold lodes genesis in this district. Pyrite from the metamorphic rocks typically occurs as inclusions in rock-forming minerals or disseminated grains roughly distributed along the foliation of the rocks, whereas pyrite from the pegmatites usually occurs as disseminations closely associated with quartz and magnetite. The textural data suggest that pyrite in the metamorphic rocks and pegmatites are of metamorphogenic and magmatogenic origins, respectively. LA-ICP-MS spot analyses show that pyrite both from the metamorphic rocks and pegmatites has Au contents mostly below the detection limit, with minor analyses revealing Au marginally higher than the detection limit. Considering that Au is moderately incompatible and highly siderophile, the very low gold contents in pyrite allow us to infer that the metamorphic rocks contain negligible gold. Pyrite grains from the metamorphic rocks and pegmatites have broadly consistent δ³⁴S values ranging from −2.7 to 31.5 (mean = 17.6) per mil and 6.3 to 17.9 (mean = 14.3) per mil, respectively. Similarly, they have comparable, highly radiogenic lead isotopes, which are 16.859–24.889 for ²⁰⁶Pb/²⁰⁴Pb, 15.355–15.694 for ²⁰⁷Pb/²⁰⁴Pb, and 37.480–43.848 for ²⁰⁸Pb/²⁰⁴Pb. The sulfur and lead isotopes of pyrites from the metamorphic rocks and pegmatites are distinct from those of Early Cretaceous gold deposits hosted by these rocks. Taken together, the pyrite trace element and S-Pb isotope data presented here preclude the Precambrian metamorphic basement rocks as an important gold source for the extensive Early Cretaceous gold mineralization in the Xiaoqinling district and, by inference, other major Early Cretaceous gold provinces across the North China Craton.
Low-temperature polymetallic melts can scavenge gold from aqueous fluids and may be instrumental in the formation of some hydrothermal lode gold deposits. However, this process is yet to be fully appreciated, because of the difficulty in recognizing textural evidence for preexisting melts and a lack of awareness that metallic melts can persist in hydrothermal systems down to very low temperature. The Xiaoqinling gold district, central China, belongs to the world-class East Qinling gold province in the North China Craton. Samples of pyrite from the S60 quartz vein at Xiaoqinling record evidence of multistage gold mineralization, with abundant Au-rich polymetallic droplets trapped as primary melt inclusions in pyrite. We examine this pyrite using a combination of nanoscale secondary ion mass spectrometry, electron probe microanalysis, and scanning electron microscopy. We present textural evidence left by migration of melt inclusions, which can be used to distinguish previously trapped polymetallic melt inclusions from mineral inclusions. We propose that polymetallic melt inclusions trapped early in the crystallization history of the host mineral could migrate to the crystal surface and enter into contact with aqueous fluids. The same effect can also be achieved by fracturing of the host mineral. In this way, relatively low volumes of polymetallic melts can continue to scavenge gold from the multiple pulses of ore fluids that are commonly involved in the formation of large gold deposits.
We present petrographic and microthermometric evidence for precipitation of Au-Ag-Te-rich melt directly from hydrothermal fluids and subsequent entrapment as primary melt inclusions within pyrite from quartz veins of the Xiaoqinling lode gold district, southern margin of the North China craton. We propose the formation of Au-Ag-Te-rich melt through adsorption-reduction mechanisms on pyrite and subsequent growth of the melt nuclei via direct scavenging of metals from fluids. Because neither initial formation nor later growth of the melt require saturation of the ore fluid with respect to the constituent metals, this mechanism offers a new understanding of the enrichment of low-abundance ore components, such as gold. Our model may thus partly explain the discrepancy between the high gold solubilities reported from experimental studies and the much lower gold concentrations usually measured in natural fluids. This study also implies that Au-Ag-Te-rich melt has probably gone unrecognized in other lode gold deposits in which Au-Ag tellurides are present.
The Linghu Au deposit is located within the northeastern part of the Xiaoqinling region in the southern margin of the North China Craton. Field investigations, cross-cutting relationships, and mineral paragenetic associations have identified three stages of hydrothermal activity. To determine the origin and evolution of ore-forming fluids, and better understand genesis of the Linghu Au deposit, we have undertaken a series of studies including fluid inclusion and He–Ar–H–O–S–Pb isotope systematics. Fluid inclusion study indicates that the early stage of gold mineralization was characterized by a high-temperature and low-salinity H2O–CO2–NaCl hydrothermal fluids that have δD values of – 82.0 to – 78.6‰ and δ18OH2O values of 5.3 to 6.4‰. The intermediate stage of gold mineralization involved moderate temperature H2O–CO2–NaCl hydrothermal fluids with δD and δ18OH2O values of – 92.7‰ to – 87.9‰ and – 1.4‰ to 0‰, respectively. Pyrite samples from this mineralization stage have 3He/4He and 40Ar/36Ar ratios of 0.26–0.31 Ra and 2834.7–4300.6, respectively. The last mineralization stage involved (low-temperature and low-salinity NaCl–H2O system of hydrothermal fluids with relatively lower δD values of – 93.1 to – 92.3‰ and δ18OH2O values of – 5.7 to – 5.2‰. Moreover, sulfides in ores yielded δ34S values of – 3.6 to 5.9‰, with an average of 2.65‰. The sulfides have 206Pb/204Pb ratios of 17.101–17.804, 207Pb/204Pb ratios of 15.438–15.554, and 208Pb/204Pb ratios of 37.438–38.654. The results of fluid inclusions and H–O, S–Pb, and He–Ar isotopes indicate that hydrothermal fluids associated with the early stage of mineralization originated from magmatic fluids, with sulfur and lead being derived from both units of the Taihua Group and a Late Triassic magmatic–hydrothermal system. All of these data indicate that the Linghu gold deposit formed as a result of magmatic–hydrothermal mineralizing processes.
Early Precambrian geological events in the Zhongtiao Mountain of China provide important clues for understanding Neoarchean to Paleoproterozoic crustal evolution in the southern segment of North China Craton (NCC). Based on analysis and compare of the component features, spatial and temporal distribution and geochemical features of the crystalline basements in the Zhongtiao Mountain with its surroundings, we identify five distinct episodes of the early Precambrian geological events in the Zhongtiao Mountain as: ca. 2.72–2.61 Ga, ca. 2.56–2.44 Ga, ca. 2.35–2.20 Ga, ca. 2.20–2.0 Ga and ca. 1.97–1.85 Ga. The ca. 2.72–2.61 Ga magmatism mainly involved a significant period of crustal growth with some crustal reworking. These ca. 2.72–2.70 Ga TTG gneisses were produced by partial melting of a subducted oceanic slab, and the ca. 2.62–2.61 Ga granitic rocks were originated from the partial melting of a protolith of juvenile origin (such as the pre-existing ca. 2.72–2.70 Ga TTG suite) together with its intermixing with mantle material. Together with other ca. 2.90–2.61 Ga old rocks in the southern segment of NCC, they made up the ‘Southern Ancient Terrane’. The ca. 2.56–2.44 Ga magmatism represented a major crustal reworking (melting) event with some juvenile addition in the Zhongtiao Mountain, and the formation of TTGs and K-rich granitic rocks during ca. 2.56–2.44 Ga marked a tectono-magmatic event resulting in stabilization of the NCC. The ca. 2.35–2.20 Ga magmatic activities reflected another stage of crustal extension and reworking of the basement rocks. The ca. 2.20–2.0 Ga volcanic-sedimentary rocks, A-type granites, and metamorphic basic volcanic rocks indicated that the stabilized blocks in the NCC still experienced the stage of extension. The ca. 1.97–1.85 Ga magmatic and metamorphic events formed in a phase of compressional deformation and led to the reworking of pre-existed old rocks.
The Fancha gold deposit is one of the representative “lode type” deposit in the Xiaoqinling goldfield. Four-stage mineralization process were identified, namely, I) the barren quartz stage; II) the pyrite-dominated stage; III) the quartz-polymetallic sulfides stage; and IV) the quartz-carbonate stage. Correspondingly, pyrite crystal can be divided into three generations, i.e. Py1, Py2 and Py3 according to their different textures and paragenesis during the first three mineralization stages. In order to better understand the ore genesis, an integrated analysis on Re-Os-He-Ar-S-Pb multi-isotopes was carried out for each mineralization stage to delineate the timing of the mineralization and the origins of the ore-forming materials in detail. Gold-bearing pyrite yields a Re-Os isochron age of 124.3 ± 2.6 Ma (MSWD = 1.9), overlapping with the previous hydrothermal mica ⁴⁰Ar/³⁹Ar ages, suggesting that gold mineralization occurred in the Early Cretaceous. The ³He/⁴He (R/Ra) and ⁴⁰Ar/³⁶Ar values of the Py2 are 0.68 to 1.17 and 656.55 to 7384.2, and those of the Py3 are 0.20 to 0.33 and 647.67 to 8913.55, respectively, which reveal a significant contribution of mantle component in the ore-forming fluids, and the content of crust fluid is increasing in the later evolution. In-situ δ³⁴S values of the sulfides and tellurides in the auriferous quartz veins, including the pyrite (Py1, Py2 and Py3), chalcopyrite, sphalerite, galena, bismuthinite, and tetradymite, display a relatively narrow range (−4.9 to 3.6‰) consistent with magmatic sulfur, which are quite different from those of the pyrite in surrounding rock (−7.8 to −9.3‰). In-situ Pb isotopic compositions of the galena and bismuthinite of stage III are homogeneous with values of ²⁰⁸Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁶Pb/²⁰⁴Pb being 37.482–37.508, 15.392–15.523, 16.995–17.006, and 39.279–39.287, 15.588–15.590, 18.283–18.288, respectively, indicating a mixed Pb sources with obvious proportions of mantle. Combined with previous data, we suggest that the ore-forming fluids and metals of the Fancha gold deposit stemmed directly from the regional mantle-derived magmatic hydrothermal system, which is coupled with the large-scale lithospheric extension and thinning in the eastern North China Craton during the Early Cretaceous.
The Fancha lode gold deposit is hosted in the Neoarchean Taihua Group metamorphic rocks in the Xiaoqinling gold field, on the southern margin of the North China Craton. Pyrite, as the predominant sulphide mineral and Au‐hosting mineral, was investigated using a combination of ore microscopy and in‐situ laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS). Three types of pyrite were identified during the ore‐forming process, that is, the coarse euhedral grains in milky quartz veins (Py1), the fine to medium, euhedral to subhedral grains in light grey quartz (Py2), and the fine grains intergrown with abundant sulphide minerals in light grey quartz (Py3). The trace elements exhibit systematic different concentrations among three types of pyrite, implying different crystallization processes. The Py1 grains have the lowest concentrations of Au and other accompanying elements such as Ag, Te, Bi, Cu, Pb, and Zn, and the trace elements of pyrite in wall rock are similar to those of Py1. The Py2 and Py3 grains show consistently high contents of Au, Ag, Te, Bi, Cu, Pb, and Zn. The uneven distribution of gold and positive correlation between Au, Ag, Te, and Bi within Py2 and Py3 grains, indicating that gold mainly occurs as submicroscopic inclusions of Au–Ag–Te–Bi assemblages in the pyrite. This interpretation is supported by the microscopic observation that large quantities of telluride and Bi‐sulfosalt minerals contact directly with gold. Observed Te–Bi minerals include petzite, sylvanite, hessite, calaverite, rucklidgeite, altaite, volynskite, tellurobismuthite, buckhornite, tetradymite, krupkaite, and bismuthinite, and native bismuth is also found. Bi (Te) melts, as an excellent gold scavenger, have played a certain role in governing gold distribution patterns and leading to high concentrations during the mineralization process in the Fancha gold deposit. The Te–Bi mineral assemblages also reveal that the gold was precipitated under variable redox conditions with log fTe2 ranged from <−11.0 to −6.4, and log fS2 ranged from <−11.8 to −8.6 at 300°C, vertically upward from the deep fluid source. Combined with available geochronological and geochemical data, enrichment of Te and Bi indicates that the ore‐forming fluids and metals might be stemed from a mantle‐derived magmatic system.
The Upper Taihua Complex in the Lushan area is one of the best preserved Paleoproterozoic metamorphic basements exposed in the southern North China Craton, which is mainly composed of Khondalite-dominated supracrustal rocks and associated meta-mafic intrusions (amphibolites) and granitic plutons. Detrital zircon U-Pb ages of four paragneisses from the supracrustal rocks can be divided into two groups: 2.39-2.10 Ga and 1.97-1.83 Ga. Concordant ²⁰⁷Pb/²⁰⁶Pb ages from the older group show typical magmatic features with a distinct peak around 2.31-2.23 Ga, whereas the metamorphic zircons define a remarkable age peak at ∼1.93 Ga. Magmatic zircons from the amphibolite sample have a weighted mean ²⁰⁷Pb/²⁰⁶Pb age of 2128 ± 29 Ma, representing the crystallization age of the protolith. Therefore, the depositional age of the supracrustal rocks in the Upper Taihua Complex can be well constrained at ∼2.23-2.13 Ga. Geochemically, the amphibolites are classified as subalkaline high-Fe tholeiitic basalts in compositions and characterized by slightly enrichment in LREE, flat HREE and weakly negative Eu anomalies, with depleted high field strength elements (e.g., Nb, Ta, and Ti), inconsistent with typical rocks derived from the asthenospheric mantle. The high FeOT (> 13.59 wt.%), CaO (> 6.67 wt.%), low Al2O3 (< 13.09 wt.%), Th (< 3.09 ppm), and lack of correlation between εNd (t) values and crustal contamination sensitive elements suggest that crustal assimilation was limited during magma evolution. The varied εNd (t) values (−2.99 to +0.44) and Nd model ages (2.65-2.98 Ga) suggest that they were likely originated from Archean subcontinental lithospheric mantle (SCLM) which have been refertilized by metasomatic processes. These geochronological and geochemical signatures indicate the meta-mafic rocks and associated supracrustal rocks of the Upper Taihua Complex in the Lushan area were most likely formed in an intra-continental rift setting, implying the extensional tectonic scenario rather than subduction-related regime occurred between ∼2.2 and 2.0 Ga at least in the southern margin of the NCC. Metamorphic ages suggest that the Taihua Complex in the Lushan area was involved in subduction-collision processes from 1.97 Ga to 1.83 Ga.
Recently, increasing lines of evidence for the 2.45–2.00 Ga magmatic rocks and Paleoproterozoic low-grade metasedimentary sequences have been identified, which can provide diagnostic constrains on the debate on the Paleoproterozoic (2.45–2.00 Ga) evolutional regime of the NCC. The widespread 2.45–2.20 Ga magmatisms occurred in the southern NCC mainly include TTG, dioritic-gabbroic gneiss, amphibolite, and high-K granites. The 2.45–2.20 Ga TTG or TTG-like gneisses show variable Mg# values, low Cr, Ni, and high Rb/Sr ratios, suggesting that they most likely derived from partial melting of basaltic lower crust with juvenile materials addition. The 2.45–2.20 Ga dioritic-gabbroic gneisses show the similar geochemical characteristics with adakitic rocks from thickened lower crust. Their ε
Hf(t) and ε
Nd(t) values are variable, and have weak Ta enrichment, and not obvious negative Nb anomalies, suggesting they were produced by partial melting of metasomatized lithospheric mantle. The 2.45–2.20 Ga amphibolites are consistent with magma derivation from MORB-like mantle wedge. The 2.45–2.20 Ga (high-K) calc-alkaline granites are representative of syn-collisional granites, and derived from older crust with variable mixing of a juvenile melt in a subduction-collision related setting. The 2.20–2.00 Ga magmatism reveals a major period of crustal reworking, rather than one of crustal addition. The 2.20–2.00 Ga monzonites have mixed IAB- and OIB-like geochemical signatures, possibly related to extension and thinning of the lithosphere and upwelling of asthenosphere. The 2.20–2.00 Ga potassic granites belong to highly fractionated aluminous A-type granite, and formed in an extensional-rift setting. As indicated by the zircon in situ Hf isotopic compositions, the injection of basaltic melt into the crust has been widely considered as an important mechanism to generate silicious melts. The 2.20–2.00 Ga tonalite would be derived from partial melting of delaminated lower crust. The temporal change from mostly 2.45–2.20 Ga low-K igneous rocks (TTG) to 2.20–2.0 Ga mostly high-K igneous rocks in the southern segment of the NCC indicates a tectonic transformation from accretionary orogenesis (ca. 2.30 Ga) to extensional regimes (ca. 2.10 Ga). On the other hand, provenances, depositional ages and tectonic settings of low-grade Paleoproterozoic metasedimentary units in the NCC can also provide rigorous constraints on the tectonic evolution in the period between 2.45 and 2.00 Ga. In the Henan-Shaanxi province on the southern NCC, the Paleoproterozoic sedimentary sequences include the Shangtaihua Group, the Songshan Group, the Yinyugou Group, and the Tietonggou Formation. The low-grade metasedimentary Songshan Group deposited after 2.35 Ga and before 1.78 Ga and sourced from felsic rocks including major 3.00–2.40 Ga TTG gneisses, 2.40–1.95 Ga granitoid plutons and meta-rhyolites of the Dengfeng, Zhongtiao and Taihua complexes in the southern NCC, and minor 3.70–3.00 Ga transported exotic Paleoarchean and Mesoarchean crustal materials because no lithologies or zircons with such age founded in study areas. The Tietonggou Formation deposited at 1.91–1.80 Ga, with detrital zircon age peak of ~2.10 Ga which possibly sourced from ~2.10 Ga lithologic units in the south of NCC. The depositional ages of the Paleoproterozoic low-grade metasedimentary units in the NCC are constrained at a certain period of 2.35–1.78 Ga, which overlaps with the stage of subduction-collision related 2.45–2.20 Ga magmatisms and rift setting related 2.20–2.00 Ga magmatisms. The detrital zircon Hf isotopes of the low-grade sediments varied mainly toward the reduction of the radiogenic Hf isotope and gradually show a similar trend of the isotope trajectories of crustal evolution. Like previous studies, all these groups were deposited in basin settings which were not simple long-lived foreland basins. Combining with 2.45–2.00 Ga igneous rocks, they may evolved from back-arc or intra-arc basins developing at the subduction-collision stage (from ∼2.45 Ga) to rift stage (from ∼2.20 Ga) and then to foreland basins at the collision stage (from ∼1.85 to ∼1.80 Ga).
This paper presents new geochemical, LA-ICPMS U-Pb zircon dating and LA-MC-ICPMS zircon Hf isotopic results for a biotite plagioclase gneiss from the Taihua Group at the South of Huashan pluton, Shaanxi Province. Geochemical results indicate that the piotolith is intermediate-acidic calc-alkaline granitic rock, with low REE content (ΣREE =83. 13 X10 ) and high Pb and LILE element contents (eg. Rb, Ba). The 176Hf/ 177 Hf ratio of zircons from this sample varies from 0. 281258 to 0. 281404 with obviously negative ε Hf(t) values ( -6. 86∼-11. 23). The Hf model ages vary from 2. 96 to 3. 24Ga, indicating that the original magma of the protolith derived from Mesoarchean crust. Comparisons show that the biotite plagioclase gneiss of Xiaoqinling area has similar source of Mesoarchean crust with the Taihua Group in Lushan area, but the timing of formation may be different. Structure of zircons, the Th/U ratio and age indicate that the Taihua Group in the Xiaoqinling area experienced an important thermal event at ∼ 1. 91Ga, which has relationship with the global collision event during convergence of Columbia Supercontinent The Taihua Group of Xiaoqinling area is part of the southern margin of North China craton, Out the Taihua Group in different area has distinction in composition timing of formation and metamorphic age. Therefore, the Taihua Group is the complex and may be at least separated into two units with Neoarchean and Paleoproterozoic ages, respectively.
Zircon U-Pb LA-ICPMS dating for the Xiaxie and Mulonggou granitoid plutons from the southern margin of the North China block yield 154 ±2Ma (2a, N = 16) and 151 ± IMa (2σ, N = 15), respectively. These granitoids are metaluminous or weakly peraluminous and high-K calc-alkaline or shoshonite series with A/CNK = 0. 75 ∼ 1. 04, Na2 O + K2 O = 6. 15 % ∼ 8. 42 %, K2 O/Na2 O = 0. 77 ∼2. 29. They are riched in LILE, e. g. LREE, Rb, Ba, K, Pb, Sr and depleted in HFSE, e. g. HREE, Zr, Hf, Ta, Nb, P, Ti with weak negative abnormal of Eu (δ5Eu = 0. 85 ∼ 0. 99). Whole rocks Sr-Nd compositions of the granitoids are characterized by ISr = 0. 708676 ∼0. 711480 and εNd(t) = -22 ∼ - 16. 1 with Nd model ages of 2. 37Ga to 2. 96Ga. The granitoids show a large variation in zircon Hf compositions with εHf(t) = -27. 8 ∼ - 18. 4 and two-stage model ages of 2. 37Ga to 2. 96Ga. Geochemistry and Sr-Nd-Hf isotopic compositions of the granitoids suggest that they are derived from an ancient continental crust such as the Archaean Taihua Group, but the zircon Hf compositions and the mafic magmatic enclaves in the granitoids may imply that juvenile component contribute to their formation. Acording to the petrography and regional geological features, the juvenile component are mainly mantle related material. Therefore, the formation of these granitoids could be interpreted as mixing/mingling of an underplated mantle-derived magma and its induced crustal-melted magma in a deep crust.
The Laoniushan granitoid complex is located in the southern margin of North China Block.Field work and LA-ICP-MS zircon dating suggest that this complex consists of Late Triassic (Indosinian) and Late Jurassic ( Yanshanian) granitoids. The rock types of the Indosinian granitoids are adamellite, quartz diorite and coarse-grained biotite monzogranite with ages of 223 ± IMa, 223 ± IMa and 214 ± IMa, respectively. The Yanshanian granitoids are mid-coarse-grained, mid-grained biotite monzogranite and finegrained biotite monzogranite with ages of 152 ±lMa and 146Ma, respectively. The Indosinian adamellite and quartz diorite are low in SiO 2 but rich in A1 2O 3 and Na 2O + K 2O, showing Shoshonite series and metaluminous I-type granite: coarse-grained biotite monzogranite are rich in SiO 2, A1 2O 3 and Na 2O + K 2O, but poor in MgO with the features of high-K calc-alkalic series and metaluminous to peraluminous I-type granite. The Yanshanian biotite monzogranite with high SiO 2, A1 2O 3 and Na 2O + K 2O also show the nature of high-K calc-alkalic series and metaluminous I-type granite. From Late Triassic to Late Jurassic SiO 2 content of these granitoids increase, but MgO, CaO and Na 2O decrease. The total REE contents of the granitoids are very high, especially LRRE, suggesting obvious LRRE and HRRE fractionation, and weakly negative Eu anomalies. The granitoids of Indosinian and Yanshanian are all rich in large ion lithophile elements (K, Rb, Ba, Sr) , and relative depleted in high-field strength elements (Nb, Ta, P). The Indosinian granitoids with ε/Nd (t) = -11.3- -14.87, tDM = 1.7 ∼ 1.9Ga, ε/Hf(t) = -9.57-25.11 ,t DM2 = 1863-2841Ma, and the Yanshanian ε/Nd (t) = -13.32- -16.83, tDM = 1.7-1.9Ga, ε/Hf(t) = -18.28- -24.79, t DM2 =2360 -2767 Ma, indicate that their sources are dominated by old crust component related to the Archaean Taihua Group and the sources of the Indosinian granitoids is with more juvenile component contributed.
Chronology research by SHRIMP II U-Pb dating on zircon from dikes of Xiaoqinling-Xiong' ershan area show that the zircons in dike magmas source mainly are inherited ones, which manifest chronologic characteristics of Southern edge of North China continental basement. The two dikes which have definite geological relation that invaded into granite of Mesozoic epoch may give the dating results of 1843 ± 10Ma and 768 ± 15Ma, and most zircon show the time of 1850Ma for a very large scale volcanic activity events of Xiong'er group in the region, only few of zircon show the reasonable time of 128Ma in Mesozoic epoch. To view the chronologic data as a whole, the zircons in dikes comprehensively record the regional history of tectonic evolution. The results of zircon dating reflected the tectonic and magmas events in North China craton as Fuping movement (2500-2400Ma), volcanic eruption activity of Xionger' group in Southern edge of North China craton (1850Ma), Paleo-Sinian tectonic movement (850-700Ma) and succession events of orogen process (∼200Ma) and dike magmas invading events(∼ 130Ma) with Yangtze plate subducted and matched to Southern edge of North China craton. Research on tracing of Sr, Nd, Pb of dikes reveal that the magmas source of dikes have much affinity to Yangtze Plate, the fact testified the dynamic process of Yangtze plate subduction to Southern edge of North China craton from Neo-Priterozoic to Pilo-Paleozoic time and delamination of continental low Crust of Qinling orogenic belt in Southern edge of North China in post of orogen in the late. The reason for most of dating results of zircon in dikes show the characteristics of inherited one possibly is that the zircon grain grow small in Mesozoic epoch, but the inherit zircons grain are bigger than the zircon in Mesozoic, so that most of inherit zircon were selected during mineral sorting but Mesozoic zircon were difficult to be selected out.
This paper reports the SHRIMP U-Pb dating of zircons from granite-pegmatite, granite-gneiss and gold-bearing quartz veins in the Xiaoqinling area, Henan. The zircons from granite-pegmatite veins are magmatic in origin and yield a weighted average 207 Pb/206 Pb age of 1955 ± 30Ma with MSWD = 1.4. The zircons from granite-gneiss are complex in origin and their "mantles" of metamorphic origin yield a 207 Pb/206 Pb weighted average age of 2462 ± 20Ma with MSWD = 2.0 and the upper intercept ages of their discordia trend lines due to Pb loss range from 2400 to 2600 Ma. The zircons in the gold-bearing quartz veins are relict ones and yield a weighted average 207 Pb/206 Pb age of 1995 ± 86 Ma with MSWD = 0.092. These age data provide more accurate age evidence for the tectonic evolution in the Xiaqinling area: 2400 - 2600 Ma and 1900 - 2000 Ma represent the ages of the first and second phases of metamorphism in the Xiaoqinling area respectively. The gold-bearing quartz veins were formed after 2000 Ma, and there is no hydrothermal zircons in the quartz veins.
Zircon U-Pb dating for three large granitoid batholiths, geochemical and Hf isotope analyses for two of them have been carried out in the different blocks of the Qinling. Zircon dating by LA-ICPMS for the Lantian granitoid in the southern margin of the North China Block gives an age of 133 ± IMa. The granitoids show whole-rock εNd(0 = -11.8 ∼ -18. 3, zircon εHf(t) = -37. 7 ∼ -5. 7. The Muhuguan and the Mangling granitoids in the North Qinling orogen yield zircon LA-ICPMS and SHRIMP age of 150 ± IMa and 149 ± 2Ma, respectively. The Muhuguan granitoids show whole-rock εNd (0 = - 7. 6 ∼ -11.4 and zircon εHf(t) = - 7. 3 ∼ - 17. 4. Combined with statistical analyses of 26 zircon ages and 3 Ar-Ar ages of granitoid plutons collected from the literature, the Late Mesozoic magmatism in the Qinling can be divided into two stages. The first-stage magmatism (160 ∼130 Ma) widely occurred in the southern margin of the North China Block, the North Qinling and occasionally in the South Qinling, and has features of I-type granitoids. The second-stage magmatism (120 ∼100 Ma) characterized by transition of I-to A-type and A-type granitoids took place in the North Qinling and the eastern part of the southern margin of the North China Block. The first-stage magmatism occurred in a transition from contractional to extensional settings, while the second-stage in the extension setting. The formation of the grantoids are interpreted as partial melting of old crust, mixed with juvenile mantle component. The second-stage granitoids contain more juvenile component than the first-stage. The isotope data of the granitoids show that juvenile compositions of the basement increas from the southern margin of the North China Block to the Shangdan suture.
The Taihua Group, exposed in the southernmost terminal Trans-North China Orogen (TNCO), is important for deciphering the mysterious evolution processes of the southern margin of the North China Craton during Proterozoic, and determination of the collision time of the eastern and western blocks of the North China Craton. Petrological study on three kinds of migmatites formed by anatexis from the Taihua Group in Xiaoqinling area, West Henan, indicates that the transformation of migmatites caused by anatexis is uneven, which is obviously limited by the composition of protolith, structure of rocks and other properties. LA-ICP-MS U-Pb dating of the anatexis zircons shows that the protolith crystallized in the Paleoproterozoic and the anatexis occurred at about 1.8 Ga. The migmatites and contemporaneous mafic dike swarms and A-type granite in the study area were generated in a post-orogenic, extensional environment following continent-continent collision at 1.85 Ga between the eastern and western blocks of the North China Craton.
The NW-SE-striking Taihua metamorphic complex crop out discretely along the southern margin of the Trans-North China Orogen (TNCO) , among which the Luoning metamorphic terrane is mainly composed of TTG-like gneisses, amphibolitic gneisses and metapelitic gneisses. Garnets in amphibolitic gneisses are commonly embayed and surrounded by amphibole + plagioclase + quartz symplectites. Three generations of mineral assemblages have been recognized in the amphibolites: the prograde assemblage (Ml) is represented by plagioclase + amphibole ± biotite ± epidote + quartz enclosed in garnet porphyroblasts, the peak metamorphic assemblage ( M2) is dominantly composed of garnet porphyroblasts and the matrix minerals plagioclase + amphibole + biotite + quartz, and the retrograde metamorphic assemblage ( M3 ) is represented by the symplectitic intergrowth of amphibole + plagioclase + quartz rimming garnet porphyroblasts. Thermodynamic computation shows that the metamorphic conditions of the plagioclase-amphibole gneisses are 600-680T: at 7. 0 ∼7. 6kbar for the M 1 stage, 680-790°C at 9. 5 ∼ 10. 7kbar for the metamorphic peak M 2 stage and 580-720°C at 6.5 ∼ 7. 6kbar for the retrograde M 3 stage, respectively. Two stages of metamorphic assemblages are preserved in the metapelitic gneisses, the prograde metamorphic assemblages ( M 1 ) and the peak metamorphic assemblages ( M 2) . Calculated metamorphic P-T conditions of these two stages are 620 ∼ 710°C at 4. 9 ∼ 5. 6kbar and 710 ∼ 760°C at 7. 3 ∼ 8. 3kbar, respectively. The Taihua metamorphic complex is deciphered to have undergone metamorphism characterized by clockwise P-T paths including the nearly isothermal decompression (ITD) segments, which are inferred to be related to the final amalgamation of North China Craton (NCC) along the TNCO. SIMS and ICP-MS U-Pb dating of metamorphic zircons extracted from amphibolitic gneisses yielded metamorphic ages ranging from 1938Ma to 1967Ma, ca. 100Ma earlier than the ubiquitous ∼ 1850Ma metamorphic event recorded in most of the metamorphic terrains in the TNCO. The amalgamation of NCC along TNCO was a long and somewhat different and complex process.
The Shibaogou granitoid pluton, consisting of porphyritic monzogranite and middle-fine-grained monzogranite as well as mafic magma enclaves, is located in the southern margin of the North China Craton. The zircon LA-ICPMS dating of the porphyritic monzogranite and mid-fine-grained monzogranite from this pluton yielded ages of 156±lMa (MSWD=0.34, N= 15) and 157±1Ma (MSWD=0.10, N=17), respectively. The rocks are of high K cale-alkaline series and belong to metaluminous to weak peraluminous I-type granite with A/CNK being 0.82-1.02, Na2O+K2O 7.61%-8.91% and K2O/Na2O 1.02-1.48. Their PvEE and trace elements are enriched in large ion lithophile elements (LPvEE, Rb, Ba, K and Pb), and depleted in high-field strength elements (HPvEE, P and Ti), with slighdy negative to positive anomalies of Eu (δ Eu=0.81∼1.12). Zircon Hf isotopic compositions of the porphyritic monzogranite and middle-fine-grained monzogranite are mainly characterized by ξ Hf (t) values of-22.6-8.3 and -26.9-12.4, and the two-stage model ages of 2.64 to 1.73 Ga and 2.91 to 1.99 Ga, respectively. Geochemistry and zircon Hf isotopic compositions show that they were derived from an ancient continental crust (probably Archean Taihua Group), with the addition of juvenile components.
Voluminous Late Mesozoic granitoids and the world’s largest Mo deposits occur in the East Qinling. This paper presents the results of Nd–Hf isotopic mapping for the Late Mesozoic granitoids (155–105 Ma) and demonstrates their constraint on the basements and distribution of the Mo deposits in the East Qinling. This isotopic map, made by 98 (21 new and 77 published) whole-rock Nd isotopic and 29 (7 new and 22 published) average zircon Hf isotopic data, shows large variations of whole-rock εNd(t) values from −22.1 to −1.5, and the correspondingly Nd model ages (TDM(Nd)) from 2.83 to 0.79 Ga, and zircon εHf(t) values from −26.3 to +0.1 and two-stage Hf model ages (TDM2(Hf)) from 2.86 to 0.96 Ga. Three regions of variations have been identified from north to south: (a) εNd(t) values range from −22.1 to −10.9 with TDM(Nd) of 2.82–1.47 Ga, and εHf(t) values 26.3 to −13.5 with TDM2(Hf) 2.86–2.04 Ga; (b) εNd(t) values −13.9 to −1.5 with TDM(Nd) 2.02–0.79 Ga, and εHf(t) values −16.2 to +0.1 with TDM2(Hf) 1.96–0.96 Ga; and (c) εNd(t) values −6.3 to −4.5 with TDM(Nd) 1.28–1.12 Ga, and εHf(t) values −1.0 to −0.3 with TDM2(Hf) 1.25–1.22 Ga, respectively. The three regions approximately correspond to the three different terranes, the southern margin of the North China Block (NCB), the North Qinling Belt (NQB) and the South Qinling Belt (SQB), respectively. These demonstrate that the granitoids in the different terranes have distinct sources and their sources change from old to more juvenile from the north (southern margin of the NCB) to the south (SQB). These also reveal the distinct basements for the terranes in Late Mesozoic. The southern margin of the NCB contains widespread Neoarchaean to Paleoproterozoic basement, the NQB comprises Archaean to Neoproterozic basement and the SQB Mesoproterozic to Neoproterozic basement. All these suggest that the three terranes underwent different tectonic evolution and the continental crust of the East Qinling were mainly formed during Archaean to Neoproterozic, different from a typical accretion orogen. The old sources of the granitoids and basements of the terranes constrain the distribution, scale and number of the Mo mineralization and deposits. Mo mineralization is closely related to the small granitic bodies with old continental component sources and Mo deposits are mainly hosted by the terranes with oldest basement. The scale and number of the Mo mineralization and deposits decreased from the southern margin of the NCB to SQB.
Precise age determination and source tracing of the granitic and pegmatitic gneisses of the Taihua Complex in the Xiaoqinling area are important to address the debates on the timing and processes of the amalgamation of the Western and Eastern Blocks along the Trans-North China Orogen. This paper conducted zircon dating of metamorphic rocks from the Xiaoqinling area. The results demonstrate that the collision between the Western and Eastern Blocks occurred in the Paleoproterozoic. Laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) zircon uranium–lead (U–Pb) analyses yielded consistent results. The Early Paleoproterozoic (the first period) age of 2346 ± 28 Ma was determined for granitic gneiss in the Taihua Complex and 2328 ± 14 Ma for the Xiaohe granite pluton that intruded into the granitic gneiss. The gneissose pegmatitic granite and granitic veins that intruded into the granitic gneiss yielded LA-ICP-MS zircon ages of 1881 ± 24 and 1866 ± 19 Ma, respectively. These Paleoproterozoic ages strongly indicate that the ocean between the Eastern and Western Blocks were completely subducted at ∼1.85 Ga. The ɛHf(t) values of the zircons from the granitic gneiss can be divided into a positive group (0.44 to 3.77) and a negative group (−3.11 to −1.27). The two-stage hafnium (Hf) model ages (TDM2(Hf)) corresponding to the positive values are between 2672 and 2887 Ma. The ɛHf(t) values of the zircons from the Xiaohe granite range from −2.49 to 2.58, with the Hf isotope model ages ranging from 2742 to 3022 Ma. Thus, the Xiaohe granite could have resulted from the partial melting of the Late Archean lower crust caused by subduction and the presence of juvenile mantle material. The primary magma of the granitic gneiss of the Paleoproterozoic Taihua Complex was derived from the differentiation of the depleted Late Archean mantle source with a small portion derived from the remelting of the subducted lower crust.
Late Paleoproterozoic rifting and accompanying magmatism and sedimentation, which occurred widely in the North China Craton, are interpreted to be related to the breakup of the supercontinent Columbia. The Ruyang Group, overlying the Xiong’er Group in the southern margin of the craton, is a typical fluvial-marine sedimentary sequence mainly composed of sandstone with minor shale and dolostone. Sandstones from the Ruyang Group exhibit high contents of SiO2 (86.8 - 98.7 wt.%) but relatively low contents of Al2O3, K2O, Na2O, TiO2 and MgO, typical of mature siliceous clastic rocks. Trace elements of these rocks indicate that the sequence was deposited in a passive continental margin environment and that the sedimentary detritus was derived from a Paleoproterozoic silicic-intermediate source, similar to other Paleo-Mesoproterozoic sedimentary sequences in the region.
Detrital zircons from three sandstone samples of the Ruyang Group yield 207Pb/206Pb ages ranging from 1.70 Ga to 2.70 Ga with two pronounced peaks at ca. 2.10 Ga and 1.86 Ga. A weighted mean age at 1744 ± 22 Ma from nine young zircon ages between 1.80 Ga and 1.70 Ga can constrain the maximum depositional age of the Ruyang Group. Most detrital zircons exhibit negative ɛHf(t) values ranging from -15.6 to 0 and old TDMC ages ranging from 2.50 Ga to 3.60 Ga, implying reworking of Archean crust. A close match between the U-Pb ages and TDMC(Hf) ages, as well as the positive ɛHf(t) values for some detrital zircons, indicate a contribution of juvenile materials. The detrital zircon grains have TDMC(Hf) ages clustering between 3.00 Ga and 2.60 Ga with a peak at around 2.80–2.70 Ga, indicating a major period of crustal growth at this time
The Yuchiling molybdenum deposit is one of the most significant porphyry molybdenum systems in the eastern Qinling of central China. The mineralization is mainly hosted by a porphyritic granite and associated cryptoexplosive breccia. Hydrothermal alteration minerals include K-feldspar, sericite, pyrite, chlorite, epidote, carbonate, kaolinite, fluorite, and gypsum. Ore minerals are dominated by molybdenite and pyrite, with lesser amounts of chalcopyrite, galena, scheelite, wolframite, ilmenite, leucoxene, native gold, sphalerite, and hematite. The δ34S compositions of sulfide minerals range from −6.0‰ to +4.0‰. The deposit is characterized by four hydrothermal stages: quartz–K-feldspar (stage I), molybdenite–quartz (stage II), pyrite–sericite-quartz (stage III), and quartz–carbonate (stage IV). Microthermometric studies of fluid inclusions show that the fluids evolved gradually during the ore-forming process. Homogenization temperatures, salinities, and minimum pressure estimates for the inclusions from each mineralization stage evolved as follows: (1) stage I: homogenization temperatures = 203.7–525.8 °C, salinities = 2.96–10.49 and 29.66 wt.% NaCl equiv., and minimum pressures = 101.9–196.2 MPa; (2) stage II: homogenization temperatures = 173.6–448.6 °C, salinities = 1.81–9.74 wt.% NaCl equiv., and minimum pressures = 93.1–172.0 MPa; (3) stage III: homogenization temperatures = 130.1–386.0 °C, salinities = 1.40–9.73 and 34.07 wt.% NaCl equiv., and minimum pressures = 95.5–142.5 MPa; (4) stage IV: homogenization temperatures = 170–230 °C and salinities = 0.18–5.71 wt.% NaCl equiv. Various fluid inclusions were observed to contain H2O, CO2, CH4, SO2, C2H2, C2H4, C2H6, and (or) H2S, as well as solids that include halite, sylvite, anhydrite, chalcopyrite, hematite, molybdenite, and jamesonite. The δ18O and δD of the hydrothermal fluids vary from −4.4‰ to +8.5‰ and −81‰ to −61‰, respectively. Microthermometric and stable isotope data indicate that the ore-forming fluids for the Yuchiling molybdenum deposit evolved from early magmatic, to a mixture of meteoric and magmatic water, and finally to a principally late stage meteoric water. A molybdenite Re–Os age of 131.2 ± 1.4 Ma coincides with the early part of the 131–112 Ma period of magmatic and related ore-forming events that are widely recognized in eastern Qinling.
The Taihua Complex in the Xiong'er area along the southern segment of the Trans-North China Orogen (TNCO) consists of gray gneisses with minor amphibolites. Zircon U-Pb dating of the gray gneisses reveals at least two episodes of Early Paleoproterozoic magmatism (2.30-2.32 Ga and 2.07-2.19 Ga), each with distinct geochemical features. The Tieluping TTG gneisses of the early suite have very low HREE (Yb-N = 0.58 -4.75) and Y contents (2.05-13.2 ppm) with moderate to high [La/Yb](N) (14.3-192.6) and Sr/Y ratios (38.5-220.1), pronounced negative Ta-Nb and Ti anomalies but positive Sr and Pb anomalies. The protoliths of these gneisses were most likely derived from partial melting of thickened lower crust with residual garnet and amphibole, and underwent garnet amphibole fractionation, plagioclase accumulation and/or fractionation. The Tieluping TTG gneisses have variable zircon Hf model ages (T-DM-Hf
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