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Geochronology, geochemical and isotopic constraints on petrogenesis of intrusive complex associated with Bianjiadayuan polymetallic deposit on the southern margin of the Greater Khingan, China
Abstract
The Early Paleozoic Bianjiadayuan complex of monzodiorite and biotite-bearing monzogranite is located in the southern part of the Huanggangliang–Ganzhuermiao metallogenic belt, southern Greater Khingan, China. The 206Pb/238U ages of zircons from the monzodiorite and biotite-bearing monzogranite are 129.67 ± 0.4 and 143.20 ± 1.2 Ma, respectively. The total REE contents of the rocks are very high, especially LREEs, suggesting obvious LREE and HREE fractionation; the monzodiorite has weak negative Eu anomalies, the biotite-bearing monzogranite highly negative anomalies. These rocks are all rich in large ion lithophile elements (Rb and U) and relatively depleted in high-field-strength elements (Nb and Ta). The monzodiorites and biotite-bearing monzogranites have ε
Hf(t) values of 1.39–5.69 and 0.86–2.46 and t
DM2 ages of 0.82–1.09 and 1.04–1.24 Ga, respectively. In the ε
Hf(t)–t diagram, the data plot between the chondrite and depleted mantle lines of Hf isotopic evolution, showing the rocks were derived mainly from new crustal material that had been derived by the differentiation of the mantle. We conclude that this area underwent an important episode of crustal growth in the Meso–Neoproterozoic. The relationship between the intrusive complex and the orebody was related to faulting; we infer that the Bianjiadayuan Pb–Zn polymetallic deposit is mainly related to Late Jurassic–Early Cretaceous (144–129 Ma) magmatic activity, and it represents large-scale mineralisation in the context of Paleo-Pacific plate subduction and regional extension.
... The well-preserved vein deposit allows for a systematic investigation of silver mineralogy, fluid origin, and deposition mechanisms. Previous studies on the Bianjiadayuan deposit, mostly published in Chinese, have addressed ore deposit geology (Wang et al. 2014d), mineralogy , whole rock geochemistry and Sr-Nd isotope compositions (Wang et al. , 2016Ruan et al. 2015), geochronology of intrusive rocks (Ruan et al. 2013(Ruan et al. , 2015Wang et al. 2013Wang et al. , 2014bWang et al. , 2016, stable isotope (S, C, H, O), Pb isotope geochemistry (Ruan et al. 2013(Ruan et al. , 2015Wang et al. 2014c), fluid inclusions (Ruan et al. 2015), and geotectonic settings (Wang et al. , 2016Ruan et al. 2015). In contrast, issues related to metal source, physicochemical conditions of ore formation, and precipitation mechanisms remain poorly constrained. ...
... The well-preserved vein deposit allows for a systematic investigation of silver mineralogy, fluid origin, and deposition mechanisms. Previous studies on the Bianjiadayuan deposit, mostly published in Chinese, have addressed ore deposit geology (Wang et al. 2014d), mineralogy , whole rock geochemistry and Sr-Nd isotope compositions (Wang et al. , 2016Ruan et al. 2015), geochronology of intrusive rocks (Ruan et al. 2013(Ruan et al. , 2015Wang et al. 2013Wang et al. , 2014bWang et al. , 2016, stable isotope (S, C, H, O), Pb isotope geochemistry (Ruan et al. 2013(Ruan et al. , 2015Wang et al. 2014c), fluid inclusions (Ruan et al. 2015), and geotectonic settings (Wang et al. , 2016Ruan et al. 2015). In contrast, issues related to metal source, physicochemical conditions of ore formation, and precipitation mechanisms remain poorly constrained. ...
... The well-preserved vein deposit allows for a systematic investigation of silver mineralogy, fluid origin, and deposition mechanisms. Previous studies on the Bianjiadayuan deposit, mostly published in Chinese, have addressed ore deposit geology (Wang et al. 2014d), mineralogy , whole rock geochemistry and Sr-Nd isotope compositions (Wang et al. , 2016Ruan et al. 2015), geochronology of intrusive rocks (Ruan et al. 2013(Ruan et al. , 2015Wang et al. 2013Wang et al. , 2014bWang et al. , 2016, stable isotope (S, C, H, O), Pb isotope geochemistry (Ruan et al. 2013(Ruan et al. , 2015Wang et al. 2014c), fluid inclusions (Ruan et al. 2015), and geotectonic settings (Wang et al. , 2016Ruan et al. 2015). In contrast, issues related to metal source, physicochemical conditions of ore formation, and precipitation mechanisms remain poorly constrained. ...
The Bianjiadayuan Ag-Pb-Zn deposit (4.81 Mt. @157.4 g/t Ag and 3.94% Pb + Zn) is located in the Great Hinggan Range Pb-Zn-Ag-Cu-Mo-Sn-Fe polymetallic metallogenic belt, NE China. Vein type Pb-Zn-Ag ore bodies are primarily hosted by slate, adjacent to a Sn ± Cu ± Mo mineralized porphyry intrusion. The deposit is characterized by silver-rich ores with Ag grades up to 3000 g/t. Four primary paragenetic sequences are recognized: (I) arsenopyrite + pyrite + quartz, (II) main sulfide + quartz, (III) silver-bearing sulfosalt + quartz, and (IV) boulangerite + calcite. A subsequent supergene oxidation stage has also been identified. Hydrothermal alteration consists of an early episode of silicification, two intermediate episodes (propylitic and phyllic), and a late argillic episode. Silver mineralization primarily belongs to the late paragenetic sequence III. Freibergite is the dominant and most important Ag-mineral in the deposit. Detailed ore mineralogy of Bianjiadayuan freibergite reveals evidence of chemical heterogeneity down to the microscale. Silver-rich sulfosalts in the late paragenetic sequence III are largely derived from a series of retrograde and solid-state reactions that redistribute Ag via decomposition and exsolution during cooling, illustrating that documentation of post-mineralization processes is essential for understanding silver ore formation. Sulfur and lead isotope compositions of sulfides, and comparison with those of local various geological units, indicate that the ore-forming fluids, lead, and other metals have a magmatic origin, suggesting a close genetic association between the studied Ag-Pb-Zn veins and the local granitic intrusion. Fluid cooling coupled with decreases in fO2 and fS2 are the factors inferred to have led to a decrease of silver solubility in the hydrothermal fluid, and successively promoted extensive Ag deposition.
... Two fresh quartz porphyry samples collected from the center and margin of the intrusion yielded indistinguishable mean 206 Pb/ 238 U ages of Notes: All uncertainties are reported at the 2σ scale; age was calculated using an 187 Re decay constant of 1.666 × 10 -11 y -1 with and without (bracketed value) an uncertainty of 0.31% (Smoliar et al., 1996;Selby et al., 2007) 140.8 ± 0.9 and 140.2 ± 0.6 Ma, which are consistent with a weighted mean Re-Os age of 140.0 ± 1.7 Ma for molybdenite associated with porphyry-type Sn ± Cu ± Mo veins/veinlets in the intrusion (Fig. 7A). These ages are also consistent with previously published zircon U-Pb ages for the porphyry intrusion at Bianjiadayuan, i.e., 143.2 ± 1.5 to 140.3 ± 0.3 Ma (Ruan et al., 2015;Wang et al., 2016;Gu et al., 2017). The breccia-type Sn-Pb-Zn mineralization at the top of the intrusion is considered to have occurred coevally with intrusion of the porphyry, based on the composition of the breccia and the ore mineral assemblage. ...
... The final magmatic event at Bianjiadayuan was the intrusion of diorite dikes that cut the gabbro intrusion and the Permian slate. The dikes, which cut both gabbro and slate, have zircon U-Pb ages from 130.5 ± 0.8 to 129.7 ± 0.4 Ma (data from this study Wang et al., 2016), respectively, suggesting that dike emplacement occurred during the same magmatic event (Fig. 7). The ages are consistent with field observations showing a slate-hosted diorite dike crosscutting Ag-Pb-Zn veins (Fig. 3A) dikes and Cu-Pb-Zn veins and their similar structural controls suggest that they could have formed coevally at about 130 Ma (Figs. 7B, 8D). ...
Many new discoveries of base and precious metal (Ag-Pb-Zn-Cu) veins in the Great Hinggan Range ore district have made this region the most important Ag-Pb-Zn metallogenic belt in northern China. The newly discovered Bianjiadayuan deposit, which is located in this district, is characterized by diverse mineralization types, including porphyry Sn ± Cu ± Mo, breccia Sn-Pb-Zn, and base metal veins. Geochronological studies have revealed two separate mineralization events. The earliest magmatic-hydrothermal event is recorded by two robust zircon U-Pb ages of 140.8 ± 0.9 and 140.2 ± 0.6 Ma for the quartz porphyry intrusion. These ages are indistinguishable , within error, from the mean Re-Os age of 140.0 ± 1.7 Ma for molybdenite veins/veinlets hosted by the porphyry. A slightly younger 40 Ar/ 39 Ar age of 138.7 ± 1.0 Ma was obtained for sericite in base and precious metal (Ag-Pb-Zn) veins hosted by slate adjacent to the porphyry. On the basis of the U-Pb, Re-Os, and 40 Ar/ 39 Ar data, we infer that the above mineralization occurred at ~140 Ma and was caused by fluids released from the magma that crystallized the quartz porphyry. A late hydrothermal event is evident from numerous Cu-Pb-Zn-mineral-ized veins hosted in a gabbro intrusion with zircon U-Pb ages of 133.2 ± 0.9 and 133.0 ± 0.8 Ma. The late base metal veins are interpreted to be coeval with or postdate diorite dikes that intruded both gabbro and slate; the diorite yielded a zircon U-Pb age of 130.0 ± 2.8 Ma. The discovery of separate but superimposed hydrothermal events has important implications for local and regional exploration.
... After the subduction of the Pacific plate during the Mesozoic, the central-eastern Inner Mongolia region underwent various significant episodes of faulting and volcanism. During this time, polymetallic mineralization occurred in the south-central part of the Great Xing'an Range [11,12]. In recent years, many large-sized deposits have been found in this area, including the Weilasituo and Bairendaba polymetallic deposits [13,14]. ...
The Jilinbaolige Pb–Zn–Ag polymetallic deposit is located in the eastern part of Inner Mongolia and in the central-southern part of the Great Xing’an Range, in which several large-sized Pb–Zn–Ag deposits have been found. The Jilinbaolige deposit, which occurs mainly at the contact zone between Yanshanian granite intrusion and sedimentary strata, shows strong NE-to-NNE structural control. The deposit includes three ore-forming stages: (1) the arsenopyrite–pyrite–chalcopyrite–sphalerite stage, (2) the galena–sphalerite–quartz stage, and (3) the pyrite–calcite–quartz stage. In this study, we present a systematic study on the mineralogical and geochemical characteristics (including major elements, S isotopes, and Pb isotopes) of the main sulfide ore minerals in the Jilinbaolige Pb–Zn–Ag deposit in order to evaluate the metallogenic environment, ore-forming material source, and genesis of this polymetallic deposit. The sulfide typomorphic characteristics, ore fabric, and thermometry suggest that the genesis of sulfides in the deposit is closely related to magmatic-hydrothermal activity. The early stage of mineralization might have evolved from a high-temperature hydrothermal environment. The sulfur isotopic results show that the δ34S values in the Jilinbaolige deposit range from 2.3‰ to 6.1‰, with an average value of 3.98‰, indicating that the sulfur originated from magmas with both mantle and crustal components. The Pb isotopic compositions (206Pb/204Pb =18.214-18.330, 207Pb/204Pb=15.478-15.615, 208Pb/204Pb =37.957-38.292, μ=9.24-9.50, ω=34.49-36.49) of the sulfide ores suggest that that the lead is of crust-mantle mixed origin. The comparison between the S and Pb isotopic compositions of the Jilinbaolige deposit and the polymetallic deposits from the central-southern parts of the Great Xing’an Range suggests that these deposits have a similar metallogenic source, which is closely related to the Yanshanian granite and medium-temperature hydrothermal fluids. These ore-bearing hydrothermal fluids that evolved from deep magmatic sources migrated along the contact and fracture zones and during the subsequent gradual decrease in temperature, and the metallogenic components were deposited in the relatively open fracture and fissure space. Our results provide insights for further mineral prospecting in the south-central part of the Great Xing’an Range.
... The Hf isotope systematics are widely used for investigating L. Wang, et al. Ore Geology Reviews 122 (2020) 103528 continental crust growth/recycling and evaluating the magmatic source characteristics (Amelin et al., 2000;Wang et al., 2016aWang et al., ,b, 2017Tang and Santosh, 2018;Santosh et al., 2020). The εHf ( Gu et al. (2017) proposed that the parental magma of syenogranite from Bianjiadayuan was mainly sourced from the reworked Mesoproterozoic crust based on the two-stage model ages of 1.6-1.3 ...
Quartz trace elements are extensively employed in studying magmatic evolution, fluid evolution, and metal enrichment. The Bianjiadayuan Ag-Pb-Zn-Sn deposit is a typical magmatic-hydrothermal system in northeastern China, however, studies on its complex magmatic-hydrothermal evolution are limited. This study investigates the quartz from the Bianjiadayuan deposit to gain insight into the physicochemical evolution of mineralization using cathodoluminescence (CL) textures and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) of quartz. Five types quartz (Q1 to Q5) were identified. From Q1 in quartz porphyry to Q5 in Ag-Pb-Zn veins, the CL intensity and Ti content gradually decreases, and Ge, Ge/Ti, and Al/Ti ratios increase, indicating a temperature decline from magmatic to hydrothermal stages. The Sb content shows an opposite trend to Ti content, correlating positively with Ge content in quartz, suggesting that Sb content could also be temperature-dependent. These trace elements in quartz indicate cooling is critical for Ag mineralization. Furthermore, quartz phenocryst (Q1) from the quartz porphyry shows low Al/Ti (mostly < 4) and Ge/Ti ratios (< 0.04), suggesting a low degree of magmatic evolution. The Sb content in Q5 from Ag-Pb-Zn-quartz veins (> 1 ppm, mostly tens of ppm) is notably higher compared to quartz in other lithologies including Sn-bearing quartz veins (< 1 ppm), suggesting that Sb contents can serve as an effective indicator of Ag mineralization.
The superlarge Huaaobaote Ag–Pb–Zn deposit is located on the western slope of the southern Great Xing’an Range (SGXR). The deposit includes four ore blocks, namely, ore blocks I, II, III, and V. Except for the no. I orebody of ore block I, which is hosted in the contact zone between the Carboniferous serpentinized harzburgite and the Permian siltstone, the other orebodies all occur as veins controlled by faults. The mineralization process at the deposit can be divided into four stages: cassiterite–arsenopyrite–pyrite–quartz stage (stage I), cassiterite–chalcopyrite–pyrite–freibergite–arsenopyrite–pyrrhotite–quartz stage (stage II), sphalerite–galena–jamesonite–stibnite–freibergite–silver mineral–quartz–calcite–chlorite stage (stage III), and argentite–pyrargyrite–pyrite–quartz–calcite (stage IV). Cassiterite U–Pb dating of the Huaaobaote deposit yielded ages of 136.3–134.3 Ma, indicating that the deposit formed in the Early Cretaceous period. Two types of fluid inclusions (FIs), including liquid-rich and gas-rich FIs, have been distinguished in the quartz vein and sphalerite. The homogenization temperature during the four stages gradually decreases, with temperatures of 302–340 °C for stage I, 267–304 °C for stage II, 186–273 °C for stage III, and 166–199 °C for stage IV, respectively. The salinity (wt% NaCl eqv.) at stages I, II, III, and IV is 3.7–6.6, 0.2–4.5, 0.2–5.0, and 0.4–1.6, respectively, indicating that the ore-forming fluid is characterized by low salinity. The δ18Owater and δD values of the ore-forming fluid range from −11.9‰ to 7.9‰ and −168‰ to −76‰, respectively, indicating that the ore-forming fluid was dominantly derived from a mixture of magmatic and meteoric water. The calculated δ34SH2S values range from −3.6‰ to 1.2‰, indicating that the sulfur mainly came from granitic magma. The 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios of sulfides are in the ranges of 18.195–18.317, 15.509–15.667, and 37.965–38.475, respectively, implying that the ore-forming material was mainly derived from felsic magma that may be formed by the partial melting of orogenic materials. Fluid mixing, cooling, and immiscibility were the three primary mechanisms for mineral precipitation in the Huaaobaote deposit.
The superlarge Baiyinchagan Sn–Ag–polymetallic deposit of Inner Mongolia is located in the west slope of the southern Great Xing'an Range, NE China. The vein orebodies of the deposit occur in the NEE-trending fault zones. The mineralization process at the deposit can be divided into four stages: quartz–fluorite–cassiterite–sphalerite stage (stage I), quartz–fluorite–cassiterite–sulfide stage (stage II), quartz–calcite–sulfide stage (stage III), and quartz–stibnite stage (stage IV). Cassiterite U–Pb dating indicates that the Baiyinchagan deposit formed approximately 140 Ma ago, and zircon U–Pb dating for granite porphyry in the Baiyinchagan deposit yielded an age of 140.8 Ma. Two types of fluid inclusions (FIs), including liquid-rich and gas-rich inclusions, have been distinguished in quartz and fluorite veins. The homogenization temperature of the FIs in the stage I ranges from 318 °C to 351 °C with salinities of 1.2–3.8 wt% NaCl eqv. The homogenization temperature of the FIs in the stage II is 262–276 °C with salinities of 1.8–3.4 wt% NaCl eqv. The homogenization temperature of the FIs in the stage III ranges from 174 °C to 233 °C with salinities of 1.8–3.0 wt% NaCl eqv. The homogenization temperature of the FIs in the stage IV is in the range of 136–168 °C, and the salinity is 0.8 wt% to 2.4 wt% NaCl eqv. The ore-forming fluid of the Baiyinchagan deposit is characterized by medium–high temperature and low salinity. The δ¹⁸Owater and δD values of ore-forming fluid range from −13.5‰ to 9.5‰ and −119‰ to −84‰, respectively, indicating that the ore-forming fluid was dominantly derived from magmatic fluid mixed with meteoric water. The calculated δ³⁴SH2S values range from −12.3 ‰ to −6.2 ‰, implying that the sulfur mainly came from granitic magma, but magmatic degassing occurred during mineralization. The ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁸Pb/²⁰⁴Pb values of the sulfides are in the ranges of 18.180–18.339, 15.525–15.643, and 38.005–38.477, respectively. The Pb isotopic compositions of sulfides indicate that the Pb mainly derived from granitic magma that may be formed by partial melting of orogenic materials. Fluid immiscibility and mixing were the two primary mechanisms for mineral precipitation.
New LA–ICP–MS zircon U–Pb geochronology, whole‐rock major and trace element geochemistry data, and petrographic observations are presented for three granitic dykes in the Changlingzi area of NE China. These data provide precise age and petrogenesis information with respect to the late Palaeozoic–Mesozoic intrusions in the area, which further constrain the geodynamic evolution of the southern Great Xing'an Range. Our zircon U–Pb data denote that the felsic dykes were emplaced during the Late Permian (~254 Ma) and Late Jurassic (143–142 Ma). Geochemically, the Late Permian monzonite porphyries are characterized by high Al2O3 (16.52–16.92 wt%) and Sr (490–579 ppm) contents and low Yb (0.52–0.57 ppm), Y (5.7–6.3 ppm), and heavy rare earth element (HREE) contents, which indicate an adakitic affinity. The Late Jurassic felsic dykes are characterized by high FeOt/MgO (8.2–11.9) and Ga/Al (3.3–3.8) ratios, high zircon saturation temperatures (888–929°C), and remarkable negative Eu (Eu/Eu* = 0.25–0.42) anomalies, indicating they are akin to A‐type granites. The Late Permian adakitic magma resulted from the partial melting of thickened lower crust, and was formed during collisional orogenesis related to subduction of Palaeo‐Asian Ocean crust. The Late Jurassic A‐type magmas were probably generated by the partial melting of amphibolite‐facies lower crustal materials. The melting occurred in response to the upwelling of asthenospheric material caused by collapse of thickened crust, due to gravitational instability during closure of the Mongol–Okhotsk Ocean. Subsequently, the latest stage of magmatic activity in this area and elsewhere in NE China was controlled mainly by subduction of Palaeo‐Pacific Ocean crust.
We describe the temporal-spatial distribution of the main Mesozoic metallogenic belts and regions in North China, comprising the Middle Lower Yangtze River valley, the Xiaoqinling-Xiong'ershan (eastern Qinling) and western Qinling, North margin of the North China craton, and southern part of the Daxing'anling as well as the eastern Shandong peninsular and Wulugetu-Jiawula (Manzhuli). After collecting and documenting the precise radiometric age data of the ore deposits there appear three metallogenic pulses, i. e. 190 ∼ 160 Ma, ca. 140 Ma, and ca. 120 Ma. Almost all the gold only depoists in eastern Shandong peninsular formed at time of ca. 120 Ma. It is obvious there are two pulses of mineralization at ca. 140 Ma and ca. 120 Ma in the Middle Lower Yangtze River valley, and Xiaoqinling-Xiong'ershan region, where the porphyry-skarn-manto Cu-Au-Mo-Fe and Mo-(W) deposits occurred at the age of ca. 140 Ma whereas the gold deposits and terrestrial volcanic rock related iron deposits appeared at age of ca. 120 Ma. The Mesozoic mineralization in the northern margin of the North China craton developed in three pulses and their ages are getting older from the eastern margin of the Euroasian continent inward. The gold deposits in the western Qinling are dated to be an age range of 190 ∼ 160 Ma. In southern part of the Daxing'anling the granite-related Cu-Ag and Pb-Zn-Cu deposits are ca. 160 ∼ 177 Ma, granite-related Sn-Cu-Pb-Zn and Sn deposits are ca. 140 Ma, and Nb-Y-Zr deposit is 127 Ma. Based on the study of Mesozoic tectonic evolution, we propose these three pulses of large-scale mineralization are the consequences of the postcollisional process of the Triassic convergence between the northern China craton and the Yangtze craton, late stage of the tectonic regime changing its main stress from NS-trending to EW-trending, and lithosphere thinning process, repectively. The gold deposits associated with S-type granite of 200 ∼ 160Ma develop in the extension setting of postcollisional stage. At ca. 140 Ma a great amount of I-type granite porphyry derived from the upper mantle and lower crust empleaced at the shllow crust and are accompanied by porphyry-skarn-(manto) Cu-Mo-Fe-Au and Mo-W mineralization. Due to lithosphere rapid thinning at ca. 120 Ma the asthenosphere got into the curst, which gave up to the mixed fluids from the mantle, metamorphic process, and crust to leach the metallic elements so as to form the gold ore-forming system as well as the iron deposit association related to terrestrial volcanic activity.
We describe the temporal-spatial distribution of the main Mesozoic metallogenic belts and regions in North China, comprising the Middle Lower Yangtze River valley, the Xiaoqinling-Xiong'ershan (eastern Qinling) and western Qinling, North margin of the North China craton, and southern part of the Daxing'anling as well as the eastern Shandong peninsular and Wulugetu-Jiawula (Manzhuli). After collecting and documenting the precise radiometric age data of the ore deposits there appear three metallogenic pulses, i. e. 190 ∼ 160 Ma, ca. 140 Ma, and ca. 120 Ma. Almost all the gold only depoists in eastern Shandong peninsular formed at time of ca. 120 Ma. It is obvious there are two pulses of mineralization at ca. 140 Ma and ca. 120 Ma in the Middle Lower Yangtze River valley, and Xiaoqinling-Xiong'ershan region, where the porphyry-skarn-manto Cu-Au-Mo-Fe and Mo-(W) deposits occurred at the age of ca. 140 Ma whereas the gold deposits and terrestrial volcanic rock related iron deposits appeared at age of ca. 120 Ma. The Mesozoic mineralization in the northern margin of the North China craton developed in three pulses and their ages are getting older from the eastern margin of the Euroasian continent inward. The gold deposits in the western Qinling are dated to be an age range of 190 ∼ 160 Ma. In southern part of the Daxing'anling the granite-related Cu-Ag and Pb-Zn-Cu deposits are ca. 160 ∼ 177 Ma, granite-related Sn-Cu-Pb-Zn and Sn deposits are ca. 140 Ma, and Nb-Y-Zr deposit is 127 Ma. Based on the study of Mesozoic tectonic evolution, we propose these three pulses of large-scale mineralization are the consequences of the postcollisional process of the Triassic convergence between the northern China craton and the Yangtze craton, late stage of the tectonic regime changing its main stress from NS-trending to EW-trending, and lithosphere thinning process, repectively. The gold deposits associated with S-type granite of 200 ∼ 160Ma develop in the extension setting of postcollisional stage. At ca. 140 Ma a great amount of I-type granite porphyry derived from the upper mantle and lower crust empleaced at the shllow crust and are accompanied by porphyry-skarn-(manto) Cu-Mo-Fe-Au and Mo-W mineralization. Due to lithosphere rapid thinning at ca. 120 Ma the asthenosphere got into the curst, which gave up to the mixed fluids from the mantle, metamorphic process, and crust to leach the metallic elements so as to form the gold ore-forming system as well as the iron deposit association related to terrestrial volcanic activity.
Two international zircon standards and one laboratory zircon standard were systematically measured using a Thermo Finngan Neptune MC-ICP-MS system and a New Wave UP213nm laser ablation system. The obtained 176Hf/177Hf ratios are 0.282700 ± 64 (2SD, N=22) for TEMORA, 0. 282008 ± 25 (2SD, N = 26) for GJ1 and 0. 282967 ± 44 (2SD, N = 27) for FM02. The results are in good agreement with the previously reported data within errors. Comparative measurements of the FM02 zircon standard using different ablation diameter show that the results are consistent within errors. Zircons GJ1 and FM02 show narrower variations in 176Hf/ 177Hf ratios than those of zircons TEMORA and thus are ideal standards for the Hf isotope analysis. The origin and material source of zircons from four different areas are also discussed based on the analysis of the Hf isotope compositions of zircons.
The Paleozoic granites in the Ergun block, exposed in the northeastern Da Hinggan Mts., northeastern China, are of I-type. Zircon U-Pb dating by LA-ICPMS technique indicates that the Shibazhan, Neihe and Baiyinna plutons were emplaced with ages of 499 ± 1,500 ± 1 and 460 ± 1Ma; whereas the Chalabanhe pluton was formed by several pulses with age between 465-481 Ma. Considering other previously reported age data, it is proposed that the granitic magmatism in the northeastern Da Hinggan Mts. during the Early Paleozoic took place at 460-50OMa. Zircon Hf analyses conducted by LA-MC-ICPMS show that these granites have εHf(t) values of +1.5 ∼ +3.8 with Hf modal ages of 1.1 ∼ 1.4Ga, indicating that the crust in the Ergun block was extracted from mantle during Meso-Neoproterozoic, which is much different from the Xing'an block to the south, in that it shows a characterized Phanerozoic crustal age.
Petrographically, the volcanic rocks in Manitu Formation from southern Manchuria are composed of andesite, trachyandesite and trachyte, but they are mainly trachyte with minor rhyolite based on chemical composition. Zircon U-Pb dating results show that they formed at Late Jurassic from 146 to 158Ma. These volcanic rocks are alkaline series in composition and rich in alkali and potassium; they are high in total rare earth elements ( ΣREE =328.2 × 10 -6 - 419.2 × 10 -6) , highly fractionated LREE from HREE ((La/Yb) N, = 12. 87 -23.10) and moderately negative Eu anomalies (δEu =0.41 -0.70). They contain high LILE (e. g. , Rb and K) and LREE, high ratios of Rb/Sr (0.34-1.88) and positive values of ε Hf,(t) (3.68-8.65), but low HFSE (e.g. , Nb, Ta, P and Ti). The initial 176Hf/ 177Hf ratios for magmatic zircons from these volcanic rocks vary in the range of 0. 282780 -0.282922, and the two-stage model ages of 652 ∼ 972Ma The data suggest that the magmas for these volcanic rocks derived from the newly accreted Neoproterozoic basic igneous crusts, and formed during the extensional setting of lithosphere after the closure of Mongol-Okhotsk Ocean.
The A-type granitoids can be divided into two chemical groups. The first group (A1) is characterized by element ratios similar to those observed for oceanic-island basalts. The second group (A2) is characterized by ratios that vary from those observed for continental crust to those observed for island-arc basalts. It is proposed that these two types have very different sources and tectonic settings. The A1 group represents differentiates of magmas derived from sources like those of oceanic-island basalts but emplaced in continental rifts or during intraplate magmatism. The A2 group represents magmas derived from continental crust or underplated crust that has been through a cycle of continent-continent collision or island-arc magmatism.
Trace-element data for mid-ocean ridge basalts (MORBs) and ocean island basalts (OIB) are used to formulate chemical systematics for oceanic basalts. The data suggest that the order of trace-element incompatibility in oceanic basalts is Cs ≃ Rb ≃ (≃ Tl) ≃ Ba(≃ W) > Th > U ≃ Nb = Ta ≃ K > La > Ce ≃ Pb > Pr(≃ Mo) ≃ Sr > P ≃ Nd (> F) > Zr = Hf ≃ Sm > Eu ≃ Sn (≃ Sb) ≃ Ti > Dy ≃ (Li) > Ho = Y > Yb. This rule works in general and suggests that the overall fractionation processes operating during magma generation and evolution are relatively simple, involving no significant change in the environment of formation for MORBs and OIBs. In detail, minor differences in element ratios correlate with the istopic characteristics of different types of OIB components (HIMU, EM, MORB). These systematics are interpreted in terms of partial-melting conditions, variations in residual mineralogy, involvement of subducted sediment, recycling of oceanic lithosphere and processes within the low velocity zone. -from Authors
Late Mesozoic volcanism is widespread throughout NE China. On the basis of lithological associations and spatial relationships, the volcanic rocks in the Lesser Hinggan Range can be divided into two formations, i.e., felsic-dominant Fuminghe Formation and overlying mafic-dominant Ganhe Formation. The Dong'an gold deposit, a typical adularia–sericite epithermal system, is spatially closely associated with rhyolitic porphyry, which is a subvolcanic intrusion of the Fuminghe Formation. Total measured, indicated, and inferred resources for the Dong'an deposit are 70 tonnes (2.25 Moz) of gold with the grade of 5.04 g/t Au, making it one of the largest epithermal gold deposits in China.
Lu-Hf is one of the isotopic dating and geochemical tracing techniques developed very rapidly during the past years. This paper presents a comprehensive review about the history, geochemical applications in petrology and remained problems surrounding the Lu-Hf isotope system. An overall introduction to the presently used sample digestion, mass spectrometric measurement and laser in-situ ablation techniques is also provided. The development of Hf isotopic systematics can be divided into 3 stages of TIMS, hot-SIMS and MC-ICP-MS, but the advent of MC-ICPMS accelerates their applications in petrology. After presenting the foundmantal geochemical behaviour and principles of the Lu-Hf isotope, this paper reviews its applications in petrology in details, including the isotopic dating of the garnet- and apatite-beraing rocks, early continental crustal formation and evolution, nature and petrogenesis of different mantle end-members, identification of various magmatic processes, regional geodynamic evolution and Hf isotopic variance during metamorphism. Finally, we discuss the uncertainties of 176Lu decay constant, Hf isotopic ratios of commonly used standards of solution JMC475 and zircon/baddeleyite, and closure temperature of Hf isotopic systems.
Exhalative mineralizations are frequently associated with various types of exhalites that often provide important evidence for ore genesis. The southern segment of the Da Hinggan Mountains is a well-known tin-polymetallic metallogenic belt of North China where Jurassic-Cretaceous volcanic-plutonic rocks are widespread. Based on this fact, most of the ore deposits were regarded as epigenetic hydrothermal deposits in genetic connection with the Mesozoic magmatism. However, nearly 90% of the deposits occur in Permian strata implying a close relation between mineralization and Permian strata. Case studies were made on the Huanggang Fe-Sn deposit and the Dajing Sn-polymetallic deposit. In combination with geochemical data, detailed geological, fabric, petrographical and mineralogical studies on the exhalites associated with ores demonstrated that subaqueous exhalative mineralization did occur during the basin evolution at the Permian time in the southern segment of the Da Hinggan Mountains, which is ignored and poorly understood, but might be as important as the hydrothermal mineralization connected with the Mesozoic magmatism. The stratiform skarns in the Huanggang deposit presents a peculiar example of exhalites. The siderite-sericite chert in the Dajing deposit, regarded as Mesozoic rhyolite porphyry before this study, is a new type exhalite formed in a lacustrine basin and closely associated with sulfide ore characteristic of complex metal assemblage of Sn-Ag-Cu-Pb-Zn. Exhalite is apparently one of the most important petrological evidences for exhalative mineralization.
The Huanggangliang deposit is a large Fe-Sn paragenic are deposit in northern China. The REE geochemistry of strata, altered rocks, ore-hosting skarn and garnet from various orebodies indicates that the comprehensive process of magma, magmatic water, wall rocks and especially meteoric water is responsible for metallization. The contribution of magmatism to metallization tends to increase toward intrusive, but the contribution of strata and meteoric water to metallization tends to increase away from intrusive. The effect of meteoric water on metallization tends to be intensified from barren ore to rich ore. In the late stage, magmatic hydrothermal process was superimposed on metallization. The various REE patterns symbolize the multi-source of fluid and multi-phase metallization. The REE patterns are the magmatic hydrothermal characteristics in Sumugou Cu-Pb-Zn deposit. The result of REE geochemistry primarily establishes the REE pattern model for the type of Huanggangliang skarn deposit.
The Dajing deposit is an important tin-polymetallic in Inner Mongolia, North China. The hypabyssal dikes, which are closely coexisting with ore veins in deposit, are extensively developed. The previous chronology studies show that both the dikes and ore veins were generated in Mid-Late Yanshanian Period in this study area, so the deposit was regarded to be magmatic hydrothermal type deposit, which related to the activities of the subvolcanic dike swarms in this area. We obtain the zircon LA-ICP-MS U-Pb ages of dacite porphyry and felsite dikes, which are widely distributed in the deposit and were considered to be closely connected with the genesis of the deposit. The zircon U-Pb ages are 240Ma and 239Ma for the dacite porphyry of DJ-7 and YX-20 respectively, and 162 ± 1 Ma for felsite dike of DJ-1. These results implicate that the dikes were formed in Early Indosinian and Middle Yanshanian in the deposit area. Combining with the previous regional research, these results indicate that the dacite porphyry was formed in syn-orogenic to post-orogenic setting, and felsite was formed in post-orogenic setting. Because of the 140Ma ore-forming age, we concluded that the dikes in the ore areas have no obvious relationship with the deposit genesis. However, it provided the advantageous space for the formation of the ore veins.
The Ganzhuermiao metamorphic core complex is found in the core of a quaquaversal anticalinoria in Da Hinngan Met., composed of three parts : the core of Early Permian low amphibolite facies - high greenschist facies rocks with ductile deformation, the intermediate layer of Middle Jurassic sandrock-slate with plasitic deformation and hornfelsing, and the overlying layer of Late Jurassic volcanic rocks, clastic rocks, and concurrent granite with brittle deformation but without metamorphism. Detachment surfaces exist between the above-mentioned parts. The extensional lineations in the flat slip planes and associated folds show that the layers abovethe detachment surfaces slipped downward NW and SE symmtrically and the underlying blocks detached continuously and rised to the superficial layer when the metamorphic core complex was upwelling, whereas the ultramafic-mafic rocks intruding into the core were exhumed. It is inferred from the difference between the respective metamorphism and deformation characterstics of the Middle and Late Jurassic formations that thermal metamorphism of the metamorphic core complex occurred at the end of the Middle Jurassic, and that its abrupt rising and the downward sliding of the overlaying layers happened at the end of the Late Jurassic or at the Early Creataceous. It is the thermal uplifting that caused extension but not on the contrary.
Located in eastern Inner Mongolia, the Dajing Cu-Ag-Sn polymetallic deposit is a large-scale deposit The ore bodies occur in Permian Linxi Formation as vein-like, and are controlled by the NW or NWW trending faults. The studies on geochronology and geochemistry of the main intrusive and volcanic rocks occurring in and around the Dajing Cu-Ag-Sn polymetallic ore district were conducted in this paper. In order to constrain the emplacement ages of the intrusive rocks and the eruption ages of the volcanic rocks, the zircons of ten samples from the intrusive and volcanic rocks were dated by using the LA-MC-ICP-MS method. Two reliable weighted mean 206Pb/ 238 U ages of 170.7 ±1.4Ma (MSWD = 1.9) and 170.7 ± 1.1Ma (MSWD = 1.3) were obtained from the altered felsile dyke close to the No.1 ore-vein in the Dajing ore district.The zircons from biolile-monzonitic granite in Maanzi, porphritic-like biotite-monzonilic granite in Dasiduan village and andesite porphyry near Tangjiayingzi yield three weighted mean 206Pb/ 238U ages of 279.7 ± 1.3Ma ( MSWD = 0.74), 252.0 ± 1.8Ma ( MSWD = 1.6) and 242.8 ± 1.7Ma ( MSWD = 1.7), respectively.The volcanic rocks of rhyolitic crystal ignimbrite, rhyolitic breccia lava and ciystal tuff from south Daba have the zircon U-Pb ages of 143.5 ±0.7Ma ( MSWD = 0.38), 144.3 ± 0.7Ma (MSWD = 1.2) and 145.3 ± 1.0Ma ( MSWD =2.5), respectively. The zircons from quartz porphyry dyke and andesite porphyry in south Xiaochengzi village give two U-Pb ages of 146.1 ± 0.9Ma ( MSWD = 1.7) and 133.2 ± 0.7Ma ( MSWD = 0.96), respectively. It indicates that there were four times of magmatic activities taking place in and around the Dajing Cu-Ag-Sn polymetallic ore district, i. e. Late Hercynian, Early Indosinian, Early Yanshanian and Middle Yanshanian, respectively. The geochemical analyses show that the all the intrusive and volcanic rocks are characterized by the high SiO 2, enriched alkali, meta-/ per-aluminum and calc-alkaline, and are all ploted in the "high K calc-alkaline series" in the diagram of SiO 2vs. K 2O. All the samples in this study have the leatures of LREE differentiation, and are enriched in LILE elements, characterized by relatively depleted Ba, Nb, Sr, P and Ti, and enriched Rb, Th, K, Ce, Nd, Hf, Sm, Y and Yb. Combined with the dating results ol the intrusive and volcanic rocks in this paper, the biotite-monzonilic granite in Maanzi and porphritic-like biotite-monzonilic granite in Dasiduan village were formed under collisional setting possibly related to the closure of the ancient Asian ocean. The Early Yanshanian magmatic activity was not developed in the study area, and its tectonic setting is not clear yet. It may be related to the consumption of the Okhotsk Ocean between Siberian Plate and Mongolia-North China Plate and post collision. The large-scale Middle Yanshanian magmatic intrusion and eruption may be caused by the lilhosphere thinning leading to the regional extention. Based on the studies on the intrusive and eruptive rocks occurring in or around the Dajing ore district, combined with ore deposit geology and the results of former studies, it is suggested that the ore-forming of the Dajing Cu-Ag-Sn polymetallic deposit was related to the Late Jurassic-Early Cretaceous ( 146 ∼ 133Ma ) magmatic activity, and was the product of the magmatism under the regional extension setting.
Huanggang large tin-iron skarn deposit, Inner Mongolia, is located in the Huanggangliang-Ulanhot tin-lead-zinc-copper polymetallic belt, South Daxinganling. In this paper, five molybdenite samples separated from the Huanggang skarn ore bodies are used for Re-Os dating and obtained the model ages ranging from 134.6 ± 2.0 to 136.5 ± 1.9Ma, averaging 135.31 ± 0.85Ma. High Re content of molybdenite indicates that mantle fluid is involved in mineralization process. The mineralization of the Da Hinggan Mts area is mainly in Mesozoic Yanshanian, there are two ore-forming eruptive periods, i. e. , ca. 140 - 130Ma and 180 - 160Ma, while the tin-lead-zinc- copper-silver polymetallic deposits related with the small intrusion in Yanshanian under lithospheric extensional and thinning environment mainly occurred in ca. 140-130Ma; the molybdenum-lead-zinc-copper-aurum polymetallic deposits related with the postcollision orogeny of Siberia plate and North China plate in Early Yanshanian mainly occurred in ca. 180-160Ma. Huanggang tin-iron deposit is the product of large-scale mineralization under the paleo-Pacific plate subduction environment.
Lu-Hf is one of the isotopic dating and geochemical tracing techniques developed very rapidly during the past years. This paper presents a comprehensive review about the history, geochemical applications in petrology and remained problems surrounding the Lu-Hf isotope system. An overall introduction to the presently used sample digestion, mass spectrometric measurement and laser in-situ ablation techniques is also provided. The development of Hf isotopic systematics can be divided into 3 stages of TIMS, hot-SIMS and MC-ICP-MS, but the advent of MC-ICPMS accelerates their applications in petrology. After presenting the foundmantal geochemical behaviour and principles of the Lu-Hf isotope, this paper reviews its applications in petrology in details, including the isotopic dating of the garnet- and apatite-beraing rocks, early continental crustal formation and evolution, nature and petrogenesis of different mantle end-members, identification of various magmatic processes, regional geodynamic evolution and Hf isotopic variance during metamorphism. Finally, we discuss the uncertainties of 176Lu decay constant, Hf isotopic ratios of commonly used standards of solution JMC475 and zircon/baddeleyite, and closure temperature of Hf isotopic systems.
The NE China is characterized by the widespread Phanerozoic granitic intrusions, most of them are of Mesozoic Indosinian-Yanshanian, which can be described as Large Granitic Province. The studies of petrology and geochemistry show that most of these granite are fractionated I- and A-type, but the S-type is rarely seen. According to the results of regional geology and isotopic dating, the Indosinian-Yanshanian granites in this area were formed after the closure of Paleo-Asian Ocean, we suggest a correlation between the formation of this huge area of granites with the deep mantle heat anomaly or mantle plume resulting from the subduction. Geochemically, a striking feature of these granites is their low value of I(Sr) (~ 0.705) and high value of ε(Nd)(t) (positive), which indicate a close relationship to the mantle. The young Nd model age ( < 1000Ma) suggests the Neoproterozoic-Phanerozoic is also one of the main stages in the continental growth, and the crust can also be greatly thickened that via vertical regime.
Located in the southern section of the Daxing'anling metallogenic belt, the Bianjiadayuan Pb-Zn-Ag deposit is a typical hydrothermal vein-type polymetallic deposit. In order to determine the diagenetic age of the deposit, LA-ICP-MS U-Pb age study was conducted on the zircons in the gabbro and diorite associated with the mineralization. The results suggest that the gabbro and diorite were crystallized in 133.19 Ma and 130.48 Ma, respectively. The gabbro and diorite are enriched in LILE, LREE and depleted in HFSE, which indicate that the magma were derived from lithospheric mantle and formed in extensional tectonic setting. Combined with the geological characteristics and the previous research in this region, the Yanshanian is considered to be a peak period of mineralization and magmatism of the southern Daxing'anling. The tectonic setting of the intrusive rocks was in the transition period from lithosphere compression to extension.
The Mesozoic granites in Da Hinggan Ling Ranges can be divided into high-Sr granite and low-Sr granite according to the geochemical characteristics of trace elements. The former is enriched in Ba, Sr and Ti elements, while the latter is intensely depleted in the above elements, but enriched in large-ion-lithophile elements and high field intensity elements. The high-Sr granites belong to I-type granite and include quartz diorite, tonalite and granodiorite. The low-Sr granites are composed of monzonitic granite, syenogranite, alkali-feldspar granite which are attributed to I-type granite and alkali granite which is attributed to A1-type granite. Both types of granites show positive εNd (t) value, low initial 87Sr/ 86Sr value and relatively low Nd-mode age. Such values may indicate that their source regions are related to mantle-source matters formed during Phanerozoic crustal accretion. The geochemical differences between high-Sr granites and low-Sr granites show that high-Sr granites were derived from differentiation of relatively DM-source magma and low-Sr granites were originated from partial melting of EM-source basic rocks. The geochemical similarity of the Mesozoic granites and rhyolites in Da Hinggan Ling Ranges and their relativity to basaltic rocks suggest that they resulted from a unitive tectonic-magma system. They are attributed to the crust-mantle interaction during closure of the Paleo-Asian Ocean and subsequent continental extension.
On the basis of investigation of the macroscopic and microscopic characteristics of deformation and kinematics of the Heilihe—Songsanjia and the Xilamulun near E—W—trending faults and the Xiaochengzi—Balihan NNE—trending fault in the Chifeng area，Inner Mongolia，this pape r perform ed biotite， K—feldspar，plagioc lase，and whole rock internal Rb—Sr isoc hron dating of mylonitic rocks．an d single—grain laser fusion Ar／ Ar dating of biotite from tllese faults．Deform ational features of the two E—W—trending faults have shown dextral shearing．whereas the Xiaochengzi—Balihan fault is characterized by sinistral shear on the horizontal plan and normal slip in the cross—section． According to the difference of feldspar porphyroclast an d ductile matrix in grain size，the mylonitic rock samples collected from the throe faults were broken to successively finer grains from which K—feldspar ，plagioclase，an d biotite were separated after removal of feldspar porphvroclasts． Mineral internal Rb—Sr isoc hron dating yielded reliable results． It shows that mylonitization has caused complete isotope resetting of the ductile matrix from the fault mylonitic rocks．Age of deform ation along the Heilihe—Songsanjia fault is dated at 232Ma．whereas the shearing and sliding of the Xilamulun fault is dated at 165Ma．The collisional suturing of tlle Mongolian Paleozoic magmatic arc with the North China block in the early Mesozoic．and far field effect of the collisional suturing of tlle combined North China—Mongol block with the Siberia plate from Late Jurassic to Early Cretaceous are responsible for the above two stages of deform ation．respectively．Ages of the sinistral shear an d norm al slip of tlle Xiaochengzi—Balihan fault are dated at about 125Ma an d l17Ma． Botll ages are concurrent with the rapid uplift of the Harkin metamorphic core complex．W e concluded that
the man tle—crust upwelling prompt ductility in the middle—low cru st and detachment of cover roc ks from the bas ement．Th ese conditions eventually resulted in tlle sinistral shear and normal slip along the NNE—trending faults
Sedimentary mineral assemblages commonly contain detrital zircon
crystals as part of the heavy-mineral fraction. Age spectra determined
by U-Pb isotopic analysis of single zircon crystals within a sample may
directly image the age composition—but not the chemical
composition—of the source region. Rare earth element (REE)
abundances have been measured for zircons from a range of common crustal
igneous rock types from different tectonic environments, as well as
kimberlite, carbonatite, and high-grade metamorphic rocks, to assess the
potential of using zircon REE characteristics to infer the rock types
present in sediment source regions. Except for zircon with probable
mantle affinities, zircon REE abundances and normalized patterns show
little intersample and intrasample variation. To evaluate the actual
variation in detrital zircon REE composition in a true sediment of known
mixed provenance, zircons from a sandstone sample from the Statfjord
Formation (North Sea) were analyzed. Despite a provenance including
high-grade metasediment and granitoids and a range in zircon age of 2.82
b.y., the zircon REEs exhibit a narrow abundance range with no
systematic differences in pattern shape. These evidences show zircon REE
patterns and abundances are generally not useful as indicators of
provenance.
Zircon megacrysts represent a late stage in the crystallisation of the magmas that produced the low-Cr megacryst suite (Ol+Opx+Cpx+Gnt+Ilm+Phl+Zir) found in many kimberlites, and may carry information on the sources of the parent magmas and the interaction of these magmas with the cratonic lithosphere. The isotopic composition of Hf has been measured in 124 mantle-derived zircon megacrysts from African, Siberian and Australian kimberlites, using a laser-ablation microprobe (LAM) and a multi-collector (MC) ICPMS. The zircons range in age from 90 Ma to ca 2500 Ma, allowing indirect analysis of mantle-derived Hf over a long time span. Most values of εHf fall between 0 and +10, but zircon suites from several kimberlites range down to εHf = −16. Combined with published Nd data on the silicate members of the low-Cr megacryst suite, these data indicate crystallisation of zircon from magmas lying well below the terrestrial εHf-εNd array. LAM-ICPMS analyses of garnets and clinopyroxenes from mantle-derived peridotite xenoliths suggest that cratonic lithospheric mantle has Hf/Nd (0.3–0.5) greater than estimated Bulk Silicate Earth. The depleted and metasomatised lherzolites and harzburgites that make up much of the Archean lithospheric mantle have Lu/Hf ratios (≤0.15) low enough to account for the lowest εHf observed in the zircons, over time spans of 1–3.5 Ga. We therefore suggest that the magmas from which the kimberlitic zircons crystallised were derived from Depleted Mantle or OIB-type sources, and developed negative εHf through reaction with the subcontinental lithospheric mantle.
Dajing is a large-scale tin polymetallic deposit that hosts the largest tin mine in North China. It is a hydrothermal vein-type deposit containing Sn, Cu, Pb, Zn, Ag, and minor components Co and In. The deposit consists of more than 690 veins hosted within Upper Permian sedimentary rocks. Three mineralization stages and six ore types are recognized with cassiterite constituting the dominant tin mineral. The SnO2 content of cassiterite increases in the sequence of mineralization stages shear-deformation-->cassiterite quartz-->cassiterite sulfide (or chalcopyrite pyrite) stage, while the content of FeO, TiO2, Nb2O5, Ta2O5, and In2O5 tends to decrease with increases in NiO and Ga2O5. It is considered that the negative correlation between SnO2 and FeO, Nb2O5, Ta2O5, and In2O5 results from elemental substitutions. The early stage cassiterite is much richer in Ta and the later stage cassiterite is much poorer in Ti and Fe than is usual in hydrothermal vein type tin deposits. This is interpreted to indicate that the component of early stage cassiterite reflects a granitic magma source while the composition of later stage cassiterite has a more obvious strata source. The compositional variation of cassiterite corresponds to decreasing crystallization temperatures within each stage and between sequential stages with time. The characteristics of REE in cassiterite from two stages are in accord with that of subvolcanic rocks and the Linxi formation. It suggests that tin transported during the cassiterite quartz stage may have originated from subvolcanic dikes (e.g., dacite porphyry), while in the cassiterite sulfide stage, tin may have been derived from wallrock (e.g. siltstone) of the Upper Permian-age Linxi Formation.
As a significant carrier of uranium, thorium and the rare earth elements (REEs) at ppm level, and hafnium at the percent level, zircon hosts a remarkable number of long-lived radioactive isotopes and their stable decay products. These include 238U, 235U and 232Th which decay via intermediate steps to 206Pb, 207Pb and 208Pb, respectively, 176Lu which decays to 176Hf, 147Sm which decays to 143Nd, and 138La which undergoes branched decay to 138Ce and 138Ba. This combination makes zircon one of the most versatile minerals available to the geochronologist. Whilst the majority of rock-dating studies involving zircon have utilized the U–Pb and Th–Pb decay schemes, as discussed in previous chapters, an increasing number of investigations are targeting the complementary age information available in the lesser known decay schemes. This chapter reviews the history of application of the Lu–Hf and Sm–Nd isotope systems in zircon and, in its conclusions, speculates on potential future use of the La–Ce system.
176Lu is an unstable radionuclide that undergoes spontaneous β− decay to stable 176Hf, with a half-life of approximately 35 billion years. Variations in the abundance of 176Hf are conventionally expressed with respect to 177Hf whose natural abundance is constant. Thus, the basic age equation for the Lu–Hf dating method, as applied to any closed system, is as follows:
\batchmode \[(^{176}Hf/^{177}Hf)\_{t}\ =\ (^{176}Hf/^{177}Hf)\_{initial}\ +\ (^{176}Lu/^{177}Hf)_{t}\ {\cdot}\ (e^{{\lambda}t}\ {-}\ 1)\]
where t is the elapsed time, and λ is the 176Lu β− decay constant. The exact value of the decay constant λ is currently under review. Most geological studies have either used the value 1.94 × 10−11 y−1, originally calculated from the slope of a Lu–Hf isochron for the 4.56 Ga eucrite achondrite meteorites (Patchett and Tatsumoto 1980a, Tatsumoto et al. 1981), or …
Zircon is the main mineral in the majority of igneous and metamorphic rocks with Zr as an essential structural constituent. It is a host for significant fractions of the whole-rock abundance of U, Th, Hf, and the REE (Sawka 1988, Bea 1996, O’Hara et al. 2001). These elements are important geochemically as process indicators or parent isotopes for age determination. The importance of zircon in crustal evolution studies is underscored by its predominant use in U-Th-Pb geochronology and investigations of the temporal evolution of both the crust and lithospheric mantle. In the past decade an increasing interest in the composition of zircon, trace-elements in particular, has been motivated by the effort to better constrain in situ microprobe-acquired isotopic ages. Electron-beam compositional imaging and isotope-ratio measurement by in situ beam techniques—and the micrometer-scale spatial resolution that is possible—has revealed in many cases that single zircon crystals contain a record of multiple geologic events. Such events can either be zircon-consuming, alteration, or zircon-forming and may be separated in time by millions or billions of years. In many cases, calculated zircon isotopic ages do not coincide with ages of geologic events determined from other minerals or from whole-rock analysis. To interpret the geologic validity and significance of multiple ages, and ages unsupported by independent analysis of other isotopic systems, has been the impetus for most past investigations of zircon composition. Some recent compositional investigations of zircon have not been directly related to geochronology, but to the ability of zircon to influence or record petrogenetic processes in igneous and metamorphic systems.
Sedimentary rocks may also contain a significant fraction of zircon. Although authigenic zircon has been reported (Saxena 1966, Baruah et al. 1995, Hower et al. 1999), it appears to be very rare and may in fact be related to …
The Gongshan block near the Eastern Himalayan Syntaxis is a fault-bounded block at the northern tip of the triangle-shaped Indochina continent (NIC). Exposed in this block are late Paleozoic (Carboniferous to Permian) strata and a north–south belt of intermediate to felsic batholiths (i.e., Gaoligongshan magmatic belt). The contact between the Gaoligongshan batholiths and Carboniferous/Permian strata is characterized by a series of high-grade metamorphic gneisses with leucosome granite veins (i.e., the so-called “Gaoligong Group”). U-Pb SHRIMP and LA-ICP-MS dating of zircons indicate that these gneisses are actually metamorphosed Paleogene sediments containing inherited Archean to Cretaceous detrital zircons (from 2690 to 64Ma) and have undergone medium- to high-pressure granulite-facies metamorphism at ~22Ma. Leucosome and S-type granite of 22–53Ma by anatexis are ubiquitous within high-grade metamorphic rocks in the southern part of the Gongshan block. An Early Paleozoic gneissic granite and granitoid intrusions of Jurassic, Cretaceous and Oligocene-Miocene ages are also recognized in NIC blocks. These ages suggest that the NIC differs distinctly from the Indian continent, the Greater and Lesser Himalaya zones, and the Yangtze Craton, but resembles the Lhasa Block in terms of Paleozoic to Mesozoic magmatism and detrital zircon ages. This offers an entirely new perspective on the tectonic evolution of the Gongshan block in particular and of the history of the Lhasa Block in the context of the India-Asia continental collision in general. Furthermore, the high-grade metamorphism in the NIC indicates a strong crustal thickening (vs. strike-slip shearing) event during much of the Eocene to the Oligocene (~53–22Ma) that has brought the Paleogene sediments to depths of greater than 25km. Continuous northward convergence/compression of the Indian Plate at the Eastern Himalayan Syntaxis may have led to the clockwise rotation, southeastward extrusion and extension of the southeastern part of the Indochina continent.
Granitoid rock compositions from a range of tectonic environments are plotted on a multicationic diagram devised by de la Roche and his coworkers. This shows that there is a systematic change through an orogenic cycle which leads progressively to the ultimate development of alkaline magmas. Possible source materials and mechanisms of magma generation are considered from analysis of mineral compositional vectors. These suggest that most granitoid series result from a two-stage process. First, fractional crystallisation of clinopyroxene, olivine and calcic plagioclase from a basic source with tholeiitic affinities produces a magma of intermediate composition. This magma then undergoes periodic mixing with a felsic magma followed by in situ fractionation to generate individual intrusions within granitoid series.
Voluminous granitic intrusions are distributed in the West Junggar, NW China, and they can be classified as the dioritic rocks, charnockite and alkali-feldspar granite groups. The dioritic rocks (SiO2 = 50.4–63.8 wt.%) are calc-alkaline and Mg enriched (average MgO = 4.54 wt.%, Mg# = 0.39–0.64), with high Sr/Y ratios (average = 21.2), weak negative Eu (average Eu⁎/Eu = 0.80) and pronounced negative Nb–Ta anomalies. Their Sr–Nd and zircon Hf isotopic compositions ((⁸⁷Sr/⁸⁶Sr)i = 0.7035–0.7042, εNd(t) = 4.5–7.9, εHf(t) = 14.1–14.5) show a depleted mantle-like signature. These features are compatible with adakites derived from partial melting of subducted oceanic crust that interacted with mantle materials. The charnockites (SiO2 = 60.0–65.3 wt.%) show transitional geochemical characteristics from calc-alkaline to alkaline, with weak negative Eu (average Eu⁎/Eu = 0.75) but pronounced negative Nb–Ta anomalies. Sr–Nd and zircon Hf isotopic compositions ((⁸⁷Sr/⁸⁶Sr)i = 0.7037–0.7039, εNd(t) = 5.2–8.0, εHf(t) = 13.9–14.7) also indicate a depleted source, suggesting melts from a hot, juvenile lower crust. Alkali-feldspar granites (SiO2 = 70.0–78.4 wt.%) are alkali and Fe-enriched, and have distinct negative Eu and Nb–Ta anomalies (average Eu⁎/Eu = 0.26), low Sr/Y ratios (average = 2.11), and depleted Sr–Nd and zircon Hf isotopic compositions ((⁸⁷Sr/⁸⁶Sr)i = 0.7024–0.7045, εNd(t) = 5.1–8.9, εHf(t) = 13.7–14.2). These characteristics are also comparable with those of rocks derived from juvenile lower crust. Despite of the differences in petrology, geochemistry and possibly different origins, zircon ages indicate that these three groups of rocks were coevally emplaced at ~ 305 Ma.
The southern segment of the Da Hinggan Mountains is a well‐known tin–polymetallic metallogenic belt of North China with Jurassic‐Cretaceous volcanic–plutonic rocks widespread. Principally because of this, most of the deposits are regarded as epigenetic hydrothermal deposits in genetic connection with the Mesozoic magmatism. But nearly 90 % of the deposits occur in Permian strata, and show concordant stratiform mineralization with a spatial distribution constrained by sedimentary facies of the Permian strata. A close association between mineralization and Permian strata is recognizable.
The Huanggang Fe‐Sn deposit was regarded as a standard skarn‐type deposit formed by magmatic hydrothermal solutions in connection with Mesozoic granites. But there are abundant fabrics indicating submarine hydrothermal exhalation both in magnetite ores and in skarns, including bedding/lamination, soft–deformation, synsedimentary brecciation, and collo‐form fabrics. The magnetite orebodies and skarn‐bodies are predominantly concordant stratiform, and extend nearly 20 km along certain stratigraphic horizon, that is, the upper section of the Lower‐Permian submarine volcanic rocks. The Mesozoic granitic rocks crosscut the magnetite and skarn zone. Instead of skarnization, they show strong greisenization associated with cassiterite‐quartz veins, distinct from the magnetite skarn‐ore with disseminated tin in the Permian rocks.
The Dajing Sn‐polymetallic deposit is generally regarded as subvolcanic‐hydrothermal origin, principally because of the close spatial association between ores and some of the Mesozoic subvolcanic dikes (called rhyolitic porphyry). Detailed geological, fabric, petrographical and mineralogical study demonstrates that this very kind of subvolcanic rocks is actually a new type of exhalites (called ‘siderite‐sericite chert’ according to its mineral assemblage), formed by hydrothermal sedimentation during the evolution of the Later‐Permian lacustrine basin. There are, however, indeed some rhyolitic porphyry dikes that crosscut orebod–ies. The orebodies and their associated exhalite predate, and thus have no genetic relation, to the Mesozoic magmatic process.
We thus conclude that subaqueous exhalative mineralization did occur during the basin evolution at the Permian time in the southern segment of the Da Hinggan Mountains, which is ignored and poorly understood, but might be as important as the hydrothermal mineralization connected with the Mesozoic magmatism.
Protolith zircon in high-grade metagranitoids from Queensland, Australia, partially recrystallized during granulite-grade metamorphism. We describe the zircon in detail using integrated cathodoluminescence, U–Pb isotope, trace element and electron backscatter diffraction pattern (EBSP) analyses. Primary igneous oscillatory zoning is partially modified or obliterated in areas within single crystals, but is well preserved in other areas. A variety of secondary internal structures are observed, with large areas of transgressive recrystallized zircon usually dominant. Associated with these areas are recrystallization margins, interpreted to be recrystallization fronts, that have conformable boundaries with transgressive recrystallized areas, but contrasting cathodoluminescence and trace element chemistry. Trace element analyses of primary and secondary structures provide compelling evidence for closed-system solid-state recrystallization. By this process, trace elements in the protolith zircon are purged during recrystallization and partitioned between the enriched recrystallization front and depleted recrystallized areas. However, recrystallization is not always efficient, often leaving a ‘memory’ of the protolith trace element and isotopic composition. This results in the measurement of ‘mixed’ U–Pb isotope ages. Nonetheless, the age of metamorphism has been determined. A correlation between apparent age and Th/U ratio is indicative of incomplete re-setting by partial recrystallization. Recrystallization is shown to probably not significantly affect Lu–Hf ages. Recrystallization has been determined by textural and trace element analysis and EBSP data not to have proceeded by sub-grain rotation or local dissolution/re-precipitation, but probably by grain-boundary migration and defect diffusion. The formation of metamorphic zircon by solid-state recrystallization is probably common to high-grade terranes worldwide. The recognition of this process of formation is essential for correct interpretation of zircon-derived U–Pb ages and subsequent tectonic models.
Various zircons of Proterozoic to Oligocene ages (1060-31 Ma) were analysed by laser ablation-inductively coupled plasma-mass spectrometry. Calibration was performed using Harvard reference zircon 91500 or Australian National University reference zircon TEMORA 1 as external calibrant. The results agree with those obtained by SIMS within 2s error. Twenty-four trace and rare earth elements (P, Ti, Cr, Y, Nb, fourteen REE, Hf, Ta, Pb, Th and U) were analysed on four fragments of zircon 91500. NIST SRM 610 was used as the reference material and ²⁹Si was used as internal calibrant. Based on determinations of four fragments, this zircon shows significant intra-and inter-fragment variations in the range from 10% to 85% on a scale of 120 μm, with the variation of REE concentrations up to 38.7%, although the chondrite-normalised REE distributions are very similar. In contrast, the determined age values for zircon 91500 agree with TIMS data and are homogeneous within 8.7 Ma (2s). A two-stage ablation strategy was developed for optimising U-Pb age determinations with satisfactory trace element and REE results. The first cycle of ablation was used to collect data for age determination only, which was followed by continuous ablation on the same spot to determine REE and trace element concentrations. Based on this procedure, it was possible to measure zircon ages as low as 30.37 0.39 Ma (MSWD = 1.4; 2s). Other examples for older zircons are also given.