Age and Origin of Paleogene Granitoids from Western Yunnan Province,China:Geochemistry,SHRIMP Zircon Ages,and Hf-in-Zircon Isotopic Compositions

We report geochemical data, SHRIMP zircon ages and Hf-in-zircon isotopic compositions for Cenozoic granitoids from major fault systems in the Tethyan belt in western Yunnan Province, southwestern China.Four magmatic pulses occurred in the Paleogene, namely at ca.57 Ma, ca.50 Ma, 45–40 Ma, and 38–34 Ma.Early magmatism of this episode（57–50 Ma） produced S-type granites whose zircons yielded εHf（t） values of-5.0 to-0.3.In contrast, late magmatism of this episode reflects heterogeneous sources.Zircons from a granite porphyry along the Ailaoshan-Red River fault system have slightly positive εHf（t） values suggesting derivation from relatively young crust and/or a juvenile source.However, zircons from a granite along the Gaoligong fault system have strongly negative εHf（t） values and suggest derivation from a Paleoproterozoic crustal source.The composition of the granitoids varies with age（from ca.57 Ma to ca.34 Ma） from peraluminous to metaluminous and also suggests a change from syn-collisional to late-orogenic tectonic setting.A new tectonic model, impacting lithospheric wedge（ILW） is shown for the origin of Paleogene granitoids in this paper.

Zircon U-Pb ages and Hf isotopic characteristics of the Dehe biotite monzonitic gneiss pluton in the North Qinling orogen and their geological significance

The Dehe granitic pluton intruded the Xiahe Group which is in the core complex of the North Qinling Orogenic Belt(NQOB).It shows gneissic bedding and possesses typical S-type granite minerals such as muscovite and garnet.LA-ICP-MS U-Pb isotopic dating of the Dehe granite yielded a weighted average age of 925±23 Ma which represents the emplacement age of the pluton.Most of the εHf(t) values are negative,and the two-stage model ages are consistent with the age of the Qinling Group.The isotope data show that the Dehe granite was formed in the following geological setting:in the syn-collision setting of the NQOB in the Neoproterozoic,crustal thickening induced partial melting of materials derived from the Qinling complex,and then the maga upwelled and intruded into the Xiahe Group.The formation of the Dehe S-type granite implied the occurrence of a convergent event in the QOB during the Neoproterozoic.

Zircon U-Pb age,geochemical and Nd isotopic data of Middle Jurassic high-Mg dioritic dike in Liaodong Peninsula,NE China

Zircon LA-ICP-MS U-Pb age, geochemical and Nd isotopic data are presented for a newly recognized high-Mg dioritic dike from Haicheng, Liaodong Peninsula, NE China, to constrain its petrogenesis. The zircons from the high-Mg diorite exhibit striped absorption and oscillatory growth zoning in the cathodoluminescence （CL） images, and have high Th/U ratios （0. 05-0.9）, indicating a magma origin. Zircon LA-ICP-MS U-Pb dating indicates that 206pb/238U ages of 12 spots of zircons are between 167 Ma and 178 Ma, yielding a weighted mean 206pb/238U age of 172 ＋ 2 Ma （MSWD =4. 1 ）, which represents the forming age of the high-Mg dioritic dike, i. e. Middle Jurassic. Geochemically, the samples have SiO2 =55.4-60. 6 wt. % , Na20 =2. 2-2.76 wt. % , K20 = 1.32-2. 02 wt. % and （Na2O ＋ K2O） =3.82--4. 47 wt. %, belonging to sub-alkaline series and displaying a calc-alkaline evolutionary trend. They are characterized by high MgO （4. 75-6.85 wt. % ）, Mg# （55-61）, Cr（130-262 ppm）, Ni（63-130 ppm）, Sr（568-857 ppm）, and Ba（484-1 130 ppm） contents, with geochemical features analogous to those of high-Mg adakites. They show variable end （t） values （ - 1.3 to - 3.9） , with a weighted value of - 2. 7, which plot intermediately between the field of the ancient continental crust and the depleted mantle source, indicating that both the lower crust and mantle source are necessary for the generation of the parent magma of the Haicheng high-Mg diorites. The Haicheng high-Mg dioritic dike in the Liaodong Peninsula and the Jurassic magmatism in the eastern North China Craton formed under a continental crustal thickening setting that may be related to subduction of the Paleo-Pacific oceanic plate.

K-Ar age, geochemical, and Sr-Pb Isotopic compositions of keban magmatics, elazig, EasternAnatolia, Turkey

Keban magmatics consist of plutonic rocks of acidic and intermediate compositions with diffe rent phases. They are the equivalent of surface rocks. In the current study on plutonic rocks, general petrographic features, disequilibrium textures such as skeletal formation in minerals, poikilitic texture, oscillatory zoning, and mineral fragmentation, and growth states are observed. Besides these microscopic properties, the existence of rounded mafic enclaves of various sizes, petrographic synplutonic dykes, and field data support the idea that mafic and felsic magmas are mixed. Keban magmatics have I-type, metaluminous-peraluminous characteristics. Diorites and quartz diorites have low-K tholeiitic features, whereas tonalites have low-K calcalkaline features. Compared with diorites, tonalites are richer in terms of LREE (Rock/ Chondrite);Rb, Sr, and Ba (LILE);and Hf, Zr, Th, and U (HFSE) elements. LILE enrichment, which signals the crustal contamination of mantle- originated magmas, is particularly observable in tonalites. In both rock groups, the negative anomaly of Nb is a sign of similarity of pluton to the subduction zone magma series. Based on the K-Ar geochronology dating of amphibole minerals, the ages of these rocks are found to be 75.65 ± 1.5 and 59.77 ± 1.2 Ma in tonalites and 84.76 ± 1.8 and 84.35 ± 1.7 Ma in diorite and quartz diorites. The 87Sr/86Sr isotope ratios in tonalites are 0.705405 and 0.706053, whereas these ratios are 0.704828 and 0.704754 in dioritic rocks. Pb isotope ratios are similar in both rock types.

Geochemistry, U-Pb, Hf isotopic characteristics and geological significance of Zhalaxiageyong trachydacite in Tuotuohe area, Qinghai

The Zhalaxiageyong lead-zinc-copper polymetallic deposit is a typical porphyry deposit of the Tuotuohe area. Whole-rock geochemical analyses,Zircon U-Pb dating and Hf isotope analysis are undertaken for the ore host trachydacite with the aim of constraining its petrogenesis,magma source and regional tectonic setting.LA-ICP-MS zircon U-Pb dating indicates that the trachydacite was formed in 32. 68 ± 0. 50 Ma( MSWD =1. 6),i. e.,Oligocene. The trachydacite is rich in potassium and poor in Mg#( 5. 10-9. 70),belonging to the peraluminous shoshonite series. The rocks are enriched in LILE( large ion lithophile elements) Rb,Ba,K and LREE,depleted in HFSE( high field strength elements) Nb,Ta,P,Ti,with high Sr and low Y and Yb,having the characteristics of the C type adakite. It is calculated that the initial εHf( t) of the zircons range from-0. 92 to 2. 07 and their two-stage Hf model ages T_(DM2) range from 978 Ma to 1 169 Ma. The magma source should be mainly the partially melt mafic rocks of the thickened Middle Neoproterozoic lower crust of the Northern Qiangtang massif with the addition of ancient aluminosilica material in the melting process. The rocks formed in the tectonic setting of delamination of lithosphere and extension of the thickened crust. During the period of 40-32 Ma,large-scale potassium rich alkaline magmatism occurred in this area. The porphyry metallogenesis is related to the magmatic activities in this period.

The Late Cretaceous Crustal Magmatism of the Geza Arc Metallogenic Belt in Yunnan Province,and Zircon Ages and Hf Isotopic Evidence of the Porphyry Cu-Mo Mineralization

Objective The Geza arc in Yunnan Province,located in the southern Yidun arc,is an important part of the Sanjiang tectonic-magmatic belts in southwestern China and is a newly discovered copper polymetallic ore-concentrating district.Recent studies show that the newly discovered Yanshanian porphyry Cu-Mo polymetallic mineralization superimposed in the Indosinian porphyry copper belt in this area.

LA-ICP-MS Zircon U-Pb Age and Hf Isotopic Composition of Late Carboniferous Granodiorite in the Southern East Junggar,Xinjiang:Genesis and Tectonic Implication

A large area of Late Paleozoic intrusions occursalong the Kalamaili fault in North Xinjiang,which is divided into I-type and A-type granite(Liu et al.,2013),and are the ideal objects for revealing the geological evolution of this region.However,the study of the granodioritic pluton in East Junggar is particularly weak.

New Ar-Ar Isotopic Ages of the Southern Tianshan Mountains, Kyrgyzstan and their Geological Implications

Objective The Late Paleozoic Southern Tianshan Ocean is usually considered to be the last-closed ocean in the Tianshan Orogeny. However, there is still no consensus if this is indeed the case. Blueschist, eclogite and ophiolite are present in the Atbashi Range, Kyrgyzstan, which are believed to be the relics of the Southern Tianshan Ocean. New data obtained through Ar-Ar isotopic analysis in this research provide reliable chronological restrictions for this problem.

Robust Timing Constraints for Granitic Magmatism and Hydrothermal Mineralization in the Tieshanlong W-Sn Ore Field,Eastern Nanling Range,South China

The Tieshanlong ore field is an important part of the Nanling Range,which is famous worldwide for its W-Sn mineralization.Notably,the mineralization age of the Tieshanlong ore field is not well constrained,and our field investigation reveals that granitic emplacement occurred at different stages.However,previous studies have not distinguished these multiple stages of magmatism.The Tieshanlong granite complex is closely related to the Huangsha quartz vein-type W-Sn deposit and Tongling skarn-type Cu-W-Sn deposit in this field.Through field investigations and isotopic age analyses,this work studies the relationship between multistage magmatic activity and mineralization in the Tieshanlong ore field.LA-ICP-MS zircon U-Pb isotope analyses revealed that the first-and second-staged granites formed at 154.2±0.6 Ma(MSDW=1.4)and 151.2±0.4 Ma(MSDW=1.5),with zirconε_(Hf)(t)values ranging from-13.1 to-10.5 and from-14.7 to-11.1,respectively.These data suggest that the Tieshanlong granite complex was derived from the partial melting of ancient crustal material.LA-ICP-MS U-Pb dating of wolframite and cassiterite reveals that W-Sn mineralization occurred at 160-150 Ma,which agrees well with the U-Pb dating results of the second-staged granite within analytical errors.The magmatic activity in this ore field can be divided into three stages:175-154 Ma,154-150 Ma and 150-145 Ma.The quartz vein-and skarn-type W-Sn mineralization is closely related to second-staged fine-grained twomica granite,and formed earlier than skarn-type Cu-mineralization.This study establishes a metallogenic model for the Tieshanlong ore field,and this model has important practical significance for identifying concealed W-Sn(-Cu)deposits around other granitic complexes in the Nanling Range.

Geology and mineralization of the Hongqiling large magmatic nickel-copper-cobalt deposit(22×10^(4)t)in Jilin Province,China:A review

The Hongqiling large nickel-copper-cobalt deposit(hereafter referred to as the Hongqiling deposit),a typical mafic-ultramafic copper-nickel deposit in China,boasts proven Ni(Ni)resources of approximately 22×10^(4)t,associated copper resources of 2×10^(4)t,and associated cobalt(Co)resources of 0.5×10^(4)t,with Ni reserves ranking 10th among China's magmatic nickel deposits.Geotectonically,the Hongqiling deposit is situated in the superimposed zone between the Xing'an-Mongolian orogenic belt and the circum-Western Pacific's active continental margin belt.Its ore-bearing plutons occur within the metamorphic rocks of the Ordovician Hulan Group,with the emplacement of plutons and the locations of orebodies governed by the deep-seated Huifahe fault and its secondary NW-trending Fujia-Hejiagou-Beixinglong-Changsheng fault zone.In the deposit,the rock assemblages of ore-bearing plutons predominantly encompass gabbro-pyroxenite-olivine pyroxenite-pyroxene peridotite(pluton No.1)and norite-orthopyroxenite-harzburgite(pluton No.7),with ore-bearing lithofacies consisting primarily of olivine pyroxenite and pyroxenite facies.The Hongqiling deposit hosts stratoid,overhanging lentoid,veined,and pure-sulfide veined orebodies.Its ores principally contain metallic minerals including pyrrhotite,pentlandite,chalcopyrite,violarite,and pyrite.Despite unidentified magma sources of ore-bearing mafic-ultramafic rocks,it is roughly accepted that the magmatic evolution in the Hongqiling deposit primarily involved fractional crystallization and crustal contamination.The ore-forming materials were primarily derived from the upper mantle,mixed with minor crustal materials.The ore-bearing mafic-ultramafic rocks in the deposit,primarily emplaced during the Indosinian(208-239 Ma),were formed in an intense extension setting followed by the collisional orogeny between the North China Plate and the Songnen-Zhangguangcai Range Block during the Middle-Late Triassic.From the perspective of the metallogenic geological setting,surrounding rocks,ore-controlling structures,and rock assemblages,this study identified one favorable condition and seven significant indicators for prospecting for Hongqiling-type nickel deposits and developed a prospecting model of the Hongqiling deposit.These serve as valuable references for exploring similar nickel deposits in the region,as well as the deep parts and margins of the Hongqiling deposit.

SHRIMP Age and Geochemistry of the Bikou Volcanic Terrane:Implications for Neoproterozoic Tectonics on the Northern Margin of the Yangtze Craton

The Bikou volcanic terrane is predominated by subalkaline tholeiitic lavas. Rock samples display lower initial ratios of Sr and Nd, 0.701248-0.704413 and 0.511080-0.512341 respectively. 207Pb and 208Pb are significantly enriched in the lavas. Most samples have positive εNd, which indicates that the magma was derived from EM-type mantle source, while a few samples with negative εNd indicate that there was contamination in the magma evolution. Magma differentiation is demonstrated by variations of LREE and LILE from depletion to enrichment. Additionally, normalized REE patterns and trace elements showed that lavas from the Bikou volcanic terrane have similar characteristics to those of basalts in arc settings caused by subduction and collision. Analyses showed that the Bikou volcanic terrane is a volcanic arc. New evidence proved that the Hengdan Group, north of the Bikou arc, is a turbidite terrane filling a forearc basin. Consequently, the Bikou volcanic terrane and the Hengdan turbidite terrane construct an arc-basin system. New SHRIMP ages showed that this arc-basin system developed on the northern margin of the Yangtze craton in the Neoproterozoic (846-776 Ma), and this arc-basin system is in agreement with the tectonic processes of Rodinia in the Neoproterzoic.

The Thermal History of the Huangmeijian Granite Intrusion in Anhui and Its Relation to Mineralization: Isotopic Evidence

Whole-rock Rb-Sr, zircon U-Pb and hornblende, biotite and K-feldspar K-Ar ages areused to reconstruct the cooling history of the Huangmeijian intrusion in the Anqing-Lujiangquartz-syenite belt in Anhui. Oxygen isotope geothermometry of mineral pairs demonstrates thatdiffusion is a dominant factor controlling the closure of isotopic systems. Assuming the coolingof the intrusion is synchronous with a dicrease in local geothermal gradients, an emplacementdepth of about 8 km and the magma crystallization temperature of 800±50℃ are estimated. TheHuangmeijian intrusion experienced a rapid cooling process and uplifted after its emplacementand crystallization at 133 Ma B.P. with a cooling rate of 34.5℃/Ma and an uplifting rate of 0.35mm/a. The intrusion was rising until it rested at a depth of 3km at a temperature of 300±50℃about 14 Ma later. Then the intrusion was in slow cooling and uplifting with a cooling rate of4.4℃/Ma and an uplifting rate of 0.04 mm/a. U-Pb dating of pitchblende is done for the hydrothermal uranium deposit formed in thecontact zone of the Huangmeijian intrusion. The result shows that the mineralization age is closeto the closing time of the K-Ar system in biotite. The fluid inclusion thermometry indicates thatthe mineralization temperature is in agreement with the closure temperature of the biotite K-Arsystem. This suggests a close relationship between the slow cooling of the intrusion and thehydrothermal uranium mineralization process.

U-Pb Age and Hf Isotope Study of Detrital Zircons from the Wanzi Supracrustals:Constraints on the Tectonic Setting and Evolution of the Fuping Complex,Trans-North China Orogen

Located in the middle segment of the Trans-North China Orogen, the Fuping Complex is considered as a critical area in understanding the evolution history of the North China Craton （NCC）. The complex is composed of various high-grade and multiply deformed rocks, including gray gneiss, basic granulite, amphibolite, fine-grained gneiss and marble, metamorphosed to upper amphibolite or granulite facies. It can be divided into four rock units： the Fuping TTG gneisses, Longquanguan augen gneisses, Wanzi supracrustals, and Nanying granitic gneisses. U-Pb age and Hf isotope compositions of about 200 detrital zircons from the Wanzi supracrustals of the Fuping Complex have been analyzed. The data on metamorphic zircon rims give ages of 1.82-1.84 Ga, corresponding to the final amalgamation event of the NCC, whereas the data for igneous zircon cores yield two age populations at -2.10 and -2.51 Ga, with some inherited ages scattering between 2.5 and 2.9 Ga. These results suggest that the Wanzi supracrustals were derived from the Fuping TTG gneisses （-2.5 Ga） and the Nanying granitic gneisses （2.0-2.1 Ga） and deposited between 2.10 and 1.84 Ga. All zircons with -2.51 Ga age have positive initial εHf values from ＋1.4 to ＋10.9, suggesting an important crustal growth event at -2.5 Ga through the addition of juvenile materials from the mantle. The Hf isotope data for the detrital zircons further imply that the 2.8 Ga rocks are important components in the lower crust, which is consistent with a suggestion from Nd isotope data for the Eastern Block. The zircons of 2.10 Ga population have initial εHf values of-4.9 to ＋6.1, interpreted as mixing of crustal re-melt with minor juvenile material contribution at 2.1 Ga. These results are distinct from that for the Western Block, supporting that the Fuping Complex was emplaced in a tectonic active environment at the western margin of the Eastern Block.

Re-Os isotopic data for molybdenum from Hejiangkou tungsten and tin polymetallic deposit in Chenzhou and its geological significance

Hejiangkou W-Sn-polymetallic deposit is a newly found deposit in Xitian ore field,one of the important and large scale W-Sn-polymetallic ore fields in the middle segment of Nanling metallogenic zone.Re-Os isotope dating was used on three molybdenite samples from Hejiangkou deposit to determine the ore forming period.The result is(224.9±2.6)Ma-(225±3.1)Ma and isochron age is(225.5±3.6)Ma.The field geological observations,geochronological data and optical petrography indicated that Hejiangkou deposit underwent multi-period of superimposed mineralization.It can be differentiated into three periods composed of six mineralization stages.The first period is the initial period for hydrothermal metasomatism and metal element enrichment during Indosinian Epoch.Further enrichment,strong brittle fracturing and hydrothermal metasomatism,remobilization and superimposition happened in the second period,during early Yanshanian.It is the major mineralization period of Hejiangkou deposit and can be subdivided into four mineralization stages,namely the skarn stage,oxide stage,high-temperature sulfide stage and low-temperature sulfide stage.And the third period is the mineralization period of a porphyry-skarn system related to the emplacement of the granite porphyry dyke.As minerogenic epoch of Hejiangkou deposit is similar with Hehuaping deposit,they show the possibility of Indosinian mineralization event in Nanling metallogenic zone.It can be an important perspective in any future mineral exploration in the same metallogenic zone.

New Insights into the Late Triassic Nadigangri Formation of Northern Qiangtang, Tibet, China： Constraints from U-Pb Ages and Hf Isotopes of Detrital and Magmatic Zircons

We report here U-Pb age and in situ Hf isotopic results for detrital and magmatic zircons from one conglomerate and four tuffite samples from the Late Triassic Nadigangri Formation across the North Qiangtang depression, Tibet. Coupled with previously published data in the region, this paper proposes new insights into the geochronological framework for the Nadigangri Formation. The deposition ages of tuffite from top to bottom in the Woruo Mountain, Quem Co and Dongqu River, are 203 Ma, 226 Ma, 221.5 Ma and 221.1 Ma, respectively. The detrital zircons yield a younger cluster of ages of 201.5-225 Ma from the conglomerate of the Quem Co Formation. The Late Triassic Nadigangri Formation defines a temporal range approximately between 201 and 225 Ma （Norian-Rhaetian）, including three predominant groups of 220-225 Ma, 210-217 Ma and 201-205 Ma, which correspond with the three main rifting episodes of initial rifting, further rifting and final rifting. Positive ~Hf（t） value and low model ages in younger detrital zircons suggests a juvenile character. However, the Hf isotopes of magmatic zircons display the presence of reworked ancient crust with 1.1-1.8 Ga. These results provide strong constraints not only on the temporal range of the Late Triassic Nadigangri Formation, but also on the onset of the Qiangtang Mesozoic rift basin.

Late Mesozoic Ore-forming Events in the Ningwu Ore District, Middle-Lower Yangtze River Polymetallic Ore Belt, East China: Evidence from Zircon U-Pb Geochronology and Hf Isotopic Compositions of the Granodioritic Stocks

Late Mesozoic volcanic-subvolcanic rocks and related iron deposits, known as porphyry iron deposits in China, are widespread in the Ningwu ore district （Cretaceous basin） of the middle-lower Yangtze River polymetallic ore belt, East China. Two types of Late Mesozoic magmatic rocks are exposed： one is dioritic rocks closely related to iron mineralization as the hosted rock, and the other one is granodioritic （-granitic） rocks that cut the ore bodies. To understand the age of the iron mineralization and the ore-forming event, detailed zircon U-Pb dating and Hf isotope measurement were performed on granodioritic stocks in the Washan, Gaocun-Nanshan, Dongshan and Heshangqiao iron deposits in the basin. Four emplacement and crystallization （typically for zircons） ages of granodioritic rocks were measured as 126.1±0.5 Ma, 126.8±0.5 Ma, 127.3±0.5 Ma and 126.3±0.4 Ma, respectively in these four deposits, with the LA-MC-ICP-MS zircon U-Pb method. Based on the above results combined with previous dating, it is inferred that the iron deposits in the Ningwu Cretaceous basin occurred in a very short period of 131-127 Ma. In situ zircon Hf compositions of εHf（t） of the granodiorite are mainly from -3 to -8 and their corresponding 176Hf/177Hf ratio are from 0.28245 to 0.28265, indicating similar characteristics of dioritic rocks in the basin. We infer that granodioritic rocks occurring in the Ningwu ore district have an original relationship with dioritic rocks. These new results provide significant evidence for further study of this ore district so as to understand the ore-forming event in the study area.

Zircon U-Pb age,trace element and Hf isotope composition of Sepon Au-Cu deposit, Laos:tectonic and metallogenic implications

The Truong Son Fold Belt,located at the northeastern margin of the Indochina Block,is considered to be tectonically linked to the subduction of the Paleotethys Ocean and subsequent collision.Sepon is one of the most important super large deposits of the Truong Son Fold Belt.Our LA-ICP-MS zircon U-Pb dating results show that granodiorite porphyry samples from the Sepon deposit have ages of 302.1-4-2.9 Ma, which is a crucial phase for magmatic-tectonical activities from the Late Carboniferous to Early Permian and has avital influence on the mineralization of copper and gold.Zircon from granodiorite porphyry yields εHf (t)values of 4.32 to 9.64,and TDM2 has an average age of 914 Ma,suggesting that the source of the granodiorite porphyry in the region were mainly mantle components but underwent mixing and contamination of crust materials.The Ce^4+/Ce^3+ value of zircon in the granodiorite porphyry varys greatly from 2.4 to 1438.29,which shows magma mixing might occur.Considering the characteristics of trace elements in the zircon and the whole rock geochemical characteristics of intrusion rocks as well as the characteristics of regional volcanic-sedimentary association,it is indicated that the tectonic setting may be the continental arc environment.The Sepon Au-Cu deposit is derived from emplacement of calc-alkaline intermediate-acid magma with coming from deep sources in the subduction process of the Paleotethys Ocean,forming porphyry Mo-Cu,skam Cu-Au mineralization and a hydrothermal sedimentary-hosted Au mineralization in the wall rocks.

Isotope systematics and metallogenetic age of Zhuanghe gold deposit, Liaoning province, China

Based on the metallogenetic geology conditions, the H, O, C and S isotopic compositions were measured by MAT-251 mass spectrometer, and Pb isotope and Rb-Sr dating were carried with MAT-261 multi-acceptor mass spectrometer. The results show that the δ^180 values of gold-bearing vein quartz from different levels are 1.19%-1.42%. The calculated δ^180 values of ore fluids are 0.55%-0.78%, and 319 values are from -8.64% to -6.66%. The calculated values of δ^34SH2s by the δ^34Spy values in quartz veins display sulfur isotope compositions from -0.053% to ＋0.413%. Carbon isotope compositions of carbonates are from -0.612% to 0.140%. The mole ratios of ^206Pb to ^204Pb, ^207Pb to ^204Pb and ^208Pb to ^204Pb in auriferous quartz vein are 16.987-17.545, 15.342-15.623, and 38.254-38.744, respectively. The age of the Zhuanghe gold deposit determined by Rb-Sr isochron of the fluid inclusions in quartzes is （143.0±5.8） Ma. These isotopic data suggest that the metallogenetic fluids are generated from magmatic hydrotherm and the origin of ore-forming matters is related to the deep-derived magmatic activities. Meanwhile, the metallogenetic epoch of the Zhuanghe gold deposit is in Yanshanian period.

Zircon U–Pb Ages and Lu–Hf Isotope of the Dongchuan Group in Central Yunnan, China, and their Geological Significance

On the southwestern margin of the Yangtze Block, the Dongchuan Group consists of slightly metamorphosed sedimentary rocks, including silty slate, argillaceous slate, clayey slate, arkose, dolomite, and minor volcanic rocks. To date, it is still a controversy over the depositional age and stratigraphic sequence of the Dongchuan Group. In this study, we analyzed five samples of meta-sedimentary rocks and one sample of meta-tuff from the Yinmin, Luoxue and Etouchang Formations of the Dongchuan Group in the Yuxi region for detrital zircon U-Pb ages and Lu-Hf isotope. The detrital zircon ages of the meta-sediments vary from 3073 to 1703 Ma, mainly clustered at three periods, from 1889 to 1840, 2490 to 2008 and 2878 to 2844 Ma. The youngest age peak of all the samples is ~1859 Ma, with the εHf(t) values of the zircons ranging from-20.3 to +4.3 and more than 90% being negative, indicating that the Paleoproterozoic crustal accretion on the southwestern margin of the Yangtze Block was dominated by reworking of the ancient crustal materials involved in the assembly and breakup of the Columbia supercontinent. Another important age range is between 2490 Ma and 2008 Ma, with εHf(t) values from-14.7 to +8.9 and 70% of them are negative, suggesting that the magmatism in the source area was also dominated by reworking and recycling of the ancient crustal materials, with minor juvenile mantle substances added. The detritus was probably derived from the Paleoproterozoic crystalline basement in the southern Yuxi region. The oldest peak age is ~2847 Ma and the εHf(t) values are from-7.7 to +7.0 with 50% of both positive and negative values, demonstrating a possible ~2.85 Ga ancient continental nucleus on the southwestern margin of the Yangtze Block and substantial growth in juvenile crust materials during this period. Besides, the weighted average age of the zircons from the meta-tuff of the Etouchang Formation is 1677 ± 14 Ma. Combining the previous research data and this study, we can constrain the depositional age of the Dongchuan Group in central Yunnan Province to the period from the late Paleoproterozoic to early Mesoproterozoic, slightly earlier than that of the Dongchuan Group in the Dongchuan area near to the southwestern Sichuan Province. The depositional age of the Dongchuan Group is older than that of the Kunyang Group.

Geochemistry and Zircon U–Pb–Hf Isotopic Systematics of the Sanchahe Quartz Monzonite Intrusion in the North Qinling Tectonic Zone, Central China: Implications for its Petrogenesis and Tectonic Setting

The Sanchahe quartz monzonite intrusion is situated in the middle segment of the North Qinling tectonic belt, Central China mainland, and consists chiefly of sanukitoid–like and granodioritic-monzogranitic rocks. The sanukitoid–like rocks are characterized by quartz monzonites, which display higher Mg#（55.0–59.0）, and enrichments in Na2 O＋K2 O（7.28–8.94 %）, Ni（21-2312 ppm）, Cr（56-4167 ppm）, Sr（553-923 ppm）, Ba（912-1355 ppm） and LREE（（La/Yb）N =9.47–15.3）, from negative to slightly positive Eu anomalies（δEu=＋0.61 to ＋1.10）, but also depletion in Nb, Ta and Ti. The granodioritic-monzogranitic rocks diaplay various Mg#of 6.00-53.0, high Na2 O＋K2 O（7.20– 8.30%）, Sr（455–1081 ppm） and（La/Yb）N（27.6–47.8）, with positive Eu anomalies（δEu=1.03–1.57） and depleted Nb, Ta and Ti. Laser ablation inductively coupled plasma mass spectrometry（LA-ICPMS） zircon U-Pb isotopic dating reveals that the sanukitoid-like rocks were emplaced at two episodes of magmatism at 457±3 Ma and 431±2 Ma, respectively. The monzogranites were emplaced at 445±7Ma. Sanukitoid–like rocks have their εHf（t） values ranging from ＋0.3 to ＋15.1 with Hf–depleted mantle model ages of 445 to 1056 Ma, and the monzogranite shows its εHf（t） values ranging from 21.6 to ＋10.8 with Hf–depleted mantle model ages of 635 to 3183 Ma. Petrological, geochemical and zircon Lu –Hf isotopic features indicate that the magmatic precursor of sanukitoid–like rocks was derived from partial melting of the depleted mantle wedge materials that were metasomatized by fluids and melts related to subduction of oceanic slab, subsequently the sanukitoid magma ascended to crust level. This emplaced mantle magma caused partial melting of crustally metamorphosed sedimentary rocks, and mixing with the crustal magma, and suffered fractional crystallization, which lead to formations of quartz monzonites. However, the magmatic precursor of the granodioritic-monzogranitic rocks were derived from partial melting of subducted oceanic slab basalts. Integrated previous investigation for the adackitic rocks in the south of the intrusion, the Sanchahe intrusion signed that the North Qinling tectonic zone was developed in an early Paleozoic transitionally tectonic background from an island arc to back–arc.