Single grain Rb-Sr dating of euhedral and cataclastic pyrite from the Qiyugou gold deposit in western Henan, central China

The Rb-Sr isotopic dating of pyrite mineral from ore deposits can directly provide mineralization age. However, many geological factors may affect the Rb-Sr isotopic system,which baffles application of this method. Employing ultra-low procedural blank Rb-Sr method,we have dated pyrites separated from the No. 4 breccia pipe of the Qiyugou gold deposit,western Henan Province. Single grains of euhedral pyrite crystal with few microcracks yield an isochron age of 126 ± 11 Ma, which represents time of the main mineralization stage of the deposit. Pyrite grains of cataclastic type show nevertheless scattered Rb-Sr isotopic composition and no reasonable isochron can be defined. Crystal morphology and mineral inclusion studies reveal that Rb and Sr of pyrite mineral probably are preserved mainly in biotite, K-feldspar, and sericite mineral inclusions. The dating results likely suggest that cataclastic pyrite is not suitable for the Rb-Sr dating due to modification of the Rb-Sr isotopic system by later hydrothermal activity of fluid.     

Sm-Nd and Rb-Sr isotopical ages of magnetite-chlorite formation gold deposit in the volcanic rock area of Late Paleozoic Era, East Tianshan

Through studying geo-geochemical characteristics and determining Sm-Nd and Rb-Sr isotopical ages in the Kanggur magnetite-chlorite formation gold deposit, some conclusions can be achieved: Sm-Nd isochron age is (290.4 ± 7)Ma, Rb-Sr isochron age is (282.3 ± 5)Ma, mineralization is Late Hercynian and the formation of this gold deposit is related to the macroscopic Huangshan-Qiugemingtashi ductile shear zone which is produced as a result of collision between the Tarim plate and the Junggar plate.     

Rb-Sr chronology and cooling history of the Renjiawan pyroxenite intrusion in North Dabie Terrane

A group of Rb-Sr ages, i.e. plagioclase-whole rock (WR) isochron age of (205 ± 7) Ma, hornblende-WR isochron age of (164 ± 10) Ma and biotite-WR isochron age of (123.4 ± 1.2) Ma, for one pyroxenite sample from Renjiawan in North Dabie Terrane (NDT) are reported. According to the closure temperature of 600℃ for plageoclase and 300℃ for biotite, the Renjiawan pyroxenite should intrude into the NDT before 205 Ma, and the younger Rb-Sr ages may reflect the cooling history of the intrusion or reset by the very strong Cretaceous thermal event in NDT.     

Mineralizing age of the Rushan lode gold deposit in the Jiaodong Peninsula：SHRIMP U-Pb dating on hydrothermal zircon

Knowledge of the mineralizing timing is fundamen-tal to understand the genesis of mineral deposits, and ex-act time spectrum of mineralization is essential to com-prehending the relationship among the genesis of en-dogenic hydrothermal deposits, regional tectonic-magma-tism event and the geodynamics of mineral deposits. The Jiaodong or eastern Shandong gold province islocated in the southeastern margin of the North Chinacraton, and belongs to the Mesozoic circum-Pacific oro-genic gold system…     

Re-Os dating of gold-bearing arsenopyrite of the Maoling gold deposit,Liaoning Province,Northeast China and its geological significance

The Maoling gold deposit, one of the large gold deposits in eastern Liaoning Province, NE China, is an arsenopyrite-disseminated gold deposit with a resource of approximately 25 t Au and an average Au grade of 3.2 g/t. Six arsenopyrites closely related to Au mineralization of the Maoling gold deposit are dated by Re-Os technique and define a Re-Os isochron with an age of 2316±140 Ma, which suggests that the deposit was formed in the Paleoproterozoic era rather than in the Indosinian period as some early researchers suggested. High initial ^187Os/^188Os ratio of 1.32±0.48 indicates a crustal derivation of the ore-forming material of the deposit, which may be derived from rocks of the Gaixian formation of the Liaohe Group. Furthermore,the result also implies that the age of the Gaixian Formation in the Maoling district is older than 2316±140 Ma.     

Re-Os dating of auriferous pyrite from the Zhenyuan super-large gold deposit in Ailaoshan gold belt, Yunnan Province, Southwestern China

Zhenyuan gold deposit is the largest super large gold deposit in the Ailaoshan gold belt,but its precise mineralization age is still lack.Re-Os isotopic age of the auriferous pyrite from the Zhenyuan gold deposit was determined by using a high-resolution inductively coupled plasma mass spectrometry(HR-ICP-MS).The pyrite samples were decomposed in carius tubes,Os was separated by distillation and Re was extracted by acetone,respectively.The results show that the Re-Os isochron age is 229±38 Ma(MSWD=2.0,confidence level is 95%),with an initial 187 Os/188 Os value of 0.68±0.24 and a corresponding Os value of 442±91.The Re/Os ratios of the pyrite vary from 40.8 to 100.5.The data suggest that at least one important ore-forming event was occurred during Indosinian epoch,and the ore-forming materials probably derived from mixed sources of crustal and mantle,while the later dominated.The Ailaoshan composite orogen experienced complicated evolutional processes,including formation of Precambrian-Early Paleozoic basement,subduction and orogenesis of Late Paleozoic era,collisional orogenesis of Late Hercynian-Indosinain epoch,and extensional or striking orogenesis of Yanshainan-Cenozoic epoch.The polycycle tectonic evolution and magmatism in this area caused multi-stage and superposition metallization characteristics of the Zhenyuan gold deposit:the mineralization probably occur mainly during the Indosinian collisional orogeny,while the minor gold ores of altered granite-porphyry and altered lamprophyre may be formed in the late superposition metallization.     

排山楼金矿床40Ar-39Ar年龄及其地质意义

采用Ar-Ar同位素测年法对辽宁排山楼金矿床矿化阶段形成的钾长石和似斑状花岗岩中的钾长石进行了测试,获得矿化阶段形成钾长石40Ar-39Ar坪年龄为(116.69±1.15)Ma,等时线年龄为(116.97±1.39)Ma,以及似斑状花岗岩中原生钾长石40Ar-39Ar坪年龄为(126.71±2.03)Ma,等时线年龄为(124.00±4.32)Ma的数据.前者代表了该矿床的形成年龄,即该矿床形成于早白垩世,后者表明金矿化不早于(126.71±2.03)Ma.这一成矿年龄与华北陆块北缘大部分金矿床的成矿年龄一致,表明华北陆块北缘绝大多数金矿床形成于中国东部中生代动力学体制发生转折的时期.     

Sm-Nd isotopic geochronology of the Yinachang Fe-Cu-REE deposit at Wuding, Yunnan Province and its genetic significance

Sm-Nd isotope systematics of ores and fluorites places precise time constraints on REE mineralization of the Yinachang Fe-Cu-REE deposit in Yunnan Province which occur in the Proterozoic Kunyan group. The ore-related fluorites contain high abundant REE, and show a strong enrichment of LREE and a positive Eu anomaly, which is in marked contrast to post-ore fluorites that are HREE enriched. The Sm-Nd isochron ages of the ores and fluorites are 1539±40 Ma and 1617±100 Ma, respectively, and calculated εNd（t） are -4.6 and -3.2. Accurate age determinations of the mineralization demonstrate that the REE mineralization took place during early Mesoproterozoic. Together with other geological evidence from the ore deposit, the primary REE-bearing ore-forming fluids are suggested to have been derived from the Enriched Mantle, and the Yinachang Fe-Cu-REE ore deposit is of volcanic exhalation- hydrothermal sedimentary origin. This study also imply that the sudden large-scale REE mineralization in the Mesoproterozoic epoch may have been induced by alkaline-rich anorogenic magmatism which occurred at marginal rifts of the continent in the Mesoproterozoic.     

Diagenetic-metallogenic ages of pyritic cherts and their implications in Mojiang nickel-gold deposit in Yunnan Province, China

Diagenetic-metallogenic ages of pyritic cherts formed by the syn-sedimentation of hydrothermal vent and ages of the Jinchang Rock Formation in the Mojiang large nickel-gold deposit in the Ailaoshan gold metallogenic belt have been discussed on the basis of chronology of isotopic geochemistry. Nickel-gold-bearing pyritic cherts in the mining were formed by syn-sedimentation of hydrothermal vent in the Late Devonian, i.e. age by Sm-Nd isochronal method (t) = (358±8.6) (2σ) Ma and age by Rb-Sr isochronal method (t) = (354.7±0.72) (2σ) Ma. On the other hand, deep-water cherts from the Jinchang Rock Formation of the Upper Devonian in the area were initiated at the same time; that is, age by Sm-Nd isochronal method (t) = (359±21) (2σ) Ma and age by Rb-Sr isochronal method (t) = (358.02±0.30) (2σ) Ma.     

On emplacement ages of lamproites in Zhenyuan County, Guizhou Province, China

Emplacement ages of lamproites that comprise lamproite and olivine lamproite in Zhenyuan County, Guizhou Province, China, have been constrained by the whole-rock Sm-Nd and Rb-Sr isochron methods and the whole rock K-Ar method. Intrusive activities of lamproites in the Sinantang area of Zhenyuan County, Guizhou Province, took place during the Late Cambrian, as indicated by the Sm-Nd isochron ages ( t ) = (503 ± 17) (2σ) Ma and by the Rb-Sr isochron ages ( t ) = (501.2 ± 4.6) (2σ) Ma. Intrusive activities of olivine lamproites at the Maping with Ⅱ-type diamond and Xitou in Zhenyuan County, Guizhou Province, took place from the Late Cambrian to the Early Ordovician, as evidenced by the Sm-Nd isochron ages ( t ) = (502 ± 27) (2σ) Ma and by the Rb-Sr isochron age ( t ) = (502 ± 27) (2σ) Ma. This suggests that the upwelling hot materials derived from the deep mantle were emplaced from the Late Cambrian to the Early Ordovician (503-497 Ma), while the time terminal of cooling of the geothermal event of magmatism-tectonism probably was at 442.64-435.54 Ma, as dated by the whole rock K-Ar method.     

山东焦家金矿田锶、铅同位素特征及其地质意义

焦家金矿田是胶西北地区重要的金矿产地,金矿类型以破碎带蚀变岩型为主,其成矿物质来源及成矿地质体尚存争议。采取了焦家金矿田深部样品,分析其同位素特征,研究成矿物质来源,探讨金矿成矿地质体。焦家金矿田金矿石黄铁矿⁸⁷Sr/⁸⁶Sr=0.711 653～0.732 45,按焦家金矿田平均成矿年龄120 Ma返算的(⁸⁷Sr/⁸⁶Sr)_i的值,其范围0.710 752～0.711 986,与郭家岭花岗岩较为接近。焦家金矿田金矿石黄铁矿²⁰⁸Pb/²⁰⁴Pb=37.683～38.103,²⁰⁷Pb/²⁰⁴Pb=15.43～15.547,²⁰⁶Pb/²⁰⁴Pb=17.04～17.44。焦家金矿田金矿体铅为地幔和下地壳的混合源。郭家岭型花岗岩与焦家金矿田金矿形成时间相近,分布空间相依,与金矿体同位素组成接近,成因上有密切联系,是金矿的成矿地质体。     

Dating of sediment－hosted disseminated－type gold deposit by using ^40Ar／^39Ar laser probe： A case study of Changkeng large－scale gold deposit, China

Hydrothermal clay minerals that formed in the main metallogenic stage of the Changkeng disseminated-type gold deposit in central Guangdong were analyzed by the 40Ar/39Ar laser probe. The results give Ar-Ar isochron ages of 109.9 1.4 to 110.1 1.3 Ma, which are 30 to 50 Ma older than the age of silver ore bodies in the deposit. Both gold and silver mineralizations were not related to hidden granite batholith in the mining district, but probably related to evo-lution of sedimentary basins. This study shows that the 40Ar/39Ar laser probe is a sound dating tool applicable to sediment-hosted disseminated-type gold deposit.     

Dating of sediment-hosted disseminated-type gold deposit by using ~(40)Ar/~(39)Ar laser probe: A case study of Changkeng large-scale gold deposit, China

Ore-forming age is one of the most important data in studying the genesis of mineral deposits. Dating of sedi-ment-hosted disseminated-type gold deposits, which areone of the most important types of gold deposits in theworld, is always a difficult task for ore geologists. Themajor reason is that most of the ores in this type deposit are of various siliceous and are composed of extremely fine-grained minerals, thus it will be very difficult to de-termine their ages by using conventional isotopi…     

Geochronolosic constraints on masmatic intrusions and mineralization of the Zhunuo porphyry copper deposit in Gansdese, Tibet

In situ zircon U-Pb ages for the recently discovered Zhunuo porphyry copper deposit in the western part of the Gangdese metallogenic belt in Tibet were determined by sensitive high-resolution ion microprobe （SHRIMP）. The ages can be divided into two separate groups, reflecting more than four major tectono-magmatic events in the area. The 62.5±2.5 Ma age of inherited zircons may be related to the volcanic eruption of the Linzizong Group formed shortly after the India-Asia continental collision. The 50.1±3.6 Ma age most likely corresponds to the time of underplating of mantle-derived mafic magma in Gangdese. The 15.6±0.6 Ma age obtained from magmatic zircons is interpreted as the age of crystallization of the Zhunuo ore-forming porphyry. Finally, a molybdenite Re-Os isochron age of 13.72±0.62 Ma is consistent with another zircon U-Pb age of 13.3±0.2 Ma, representing the time of copper mineralization. These ages, in combination with available literature data, indicate that magmatic crystallization and copper mineralization in the Gangdese metallogenic belt became gradually younger westward, and further suggest that the Zhunuo porphyry copper deposit was formed in the same tectonic stage as other porphyry copper deposits in the eastern and central Gangdese belt. This conclusion provides critical information for future exploration of porphyry copper deposits in western Gangdese.     

Indosinian isotope ages of plutons and deposits in southwestern Miaoershan-Yuechengling,northeastern Guangxi and implications on Indosinian mineralization in South China

The Miaoershan-Yuechengling complex pluton is the largest granitoid complex in the western Nanling metallogenic belt with a surface exposure of >3000 km2.The complex pluton is composed of an early stage granitoid batholith and late stage small intrusions.The early stage batholith contains mainly medium-grained porphyritic mica granite and porphyritic monzonite granite,whereas the late stage intrusions are composed of muscovite granite porphyry and muscovite monzonitic granite.There are many W-Sn-Mo-Pb-Zn-Cu ores in the contact zone between the batholith and strata,forming an ore-rich belt around the batholith.Based on zircon LA-ICP-MS U-Pb ages,the southwestern part of the early stage batholith formed at 228.7 ± 4.1 Ma(MSWD = 2.49),with slightly earlier magmatic activity at 243.0 ± 5.8 Ma(MSWD = 2.62).The Yuntoujie muscovite granite was associated with W-Mo mineralization and has a zircon LA-ICP-MS U-Pb age of 216.8 ± 4.9 Ma(MSWD = 1.44).The Re-Os isochron age of molybdenite from the Yuntoujie W-Mo ore was 216.8 ± 7.5 Ma(MSWD = 11.3).Our new isotope data suggest that the late stage intrusive stocks from the southwestern Miaoershan-Yuechengling batholith were closely associated with W-Mo mineralization from the Indosinian period.These new results together with previous isotope data,suggest that South China underwent not only the well-known Yanshanian mineralization event,but also a widespread Indosinian metallogenic event during the Mesozoic period.Therefore,South China has a greater potential for Indosinian mineralization than previously thought such that more attention should be given to the Indosinian ore prospecting in South China.     

黔西南贞丰水银洞基性岩锆石U-Pb测年及金矿成矿

基性岩与金矿成矿关系密切。而针对滇黔桂地区卡林型金矿成矿年龄一直缺乏年代学证据。测得黔西南贞丰水银洞基性岩锆石U-Pb年龄为218±3.2 Ma,与前人对水银洞卡林型金矿年龄的测定一致,说明该区金矿化与基性岩岩浆活动密切相关。该年龄对应印支晚期,并在此基础上提出一种印支期成矿的动力学模型:古特提斯洋封闭导致印支板块与扬子板块碰撞,强大的区域构造事件为矿化提供了动力,形成了贞丰地区218±3.2 Ma的基性岩。另外该地区可能存在一些埋藏的印支期花岗岩侵入体,这些入侵的岩体可作为热源,驱动主要为大气降水成因的流体浸出成矿元素,形成了贞丰水银洞地区卡林型金矿床。     

西藏邦布造山型金矿金的赋存状态研究

西藏邦布金矿为一处典型的碰撞造山型金矿,成矿主要与区域内巨厚石英脉密切相关.矿床主要发育四期成矿阶段:石英-粗粒硫化物阶段、金-细粒硫化物阶段、碳酸盐阶段和胶黄铁矿阶段,前两个阶段为主要金成矿阶段.通过手标本样品统计、显微镜观察、电子探针扫描等综合技术对金矿石中金的赋存状态进行了研究.结果表明,金主要以独立矿物相存在,自然金成色为750 ～931,Au/Ag为11.3～17.6.矿石中金的粒度以细粒金、微粒金为主.主要赋金矿物有石英、黄铁矿、黄铜矿、方铅矿和闪锌矿等,自然金主要呈裂隙金、包裹金形式嵌布在硫化物和石英中.     

Porphyry Cu-Mo deposits in the eastern Xing’an-Mongolian Orogenic Belt: Mineralization ages and their geodynamic implications

The eastern Xing’an-Mongolian (Xing-Meng) Orogenic Belt (XMOB) is one of the important areas of porphyry copper (Cu)-molybdenum (Mo) deposits in China. However, studies on the exact ages of mineralization and their geodynamic significance are very limited. In this study, granodioritic rocks from the Duobaoshan Cu deposit and Daheishan Mo deposit were selected to make zircon SHRIMP U-Pb analyses in order to constrain their mineralization ages. Geochronological data indicate that two episodes of mineralization took place in the Duobaoshan Cu deposits. The granodiorite related to the Duobaoshan porphyry Cu deposit was formed in the Early Paleozoic with zircon U-Pb age of 485±8 Ma, whereas the granodiorites related to the Sankuanggou skarn-type Cu deposit were emplaced in the Jurassic with zircon U-Pb ages of 176±3 and 177±3 Ma. In the Daheishan area of Jilin Province, the emplacement age of the granodiorite porphyry related to the porphyry Mo deposit was dated at 170±3 Ma, and the unmineralized monzogranite at 178±3 Ma. Therefore, two episodes of Cu-Mo mineralization were developed in the eastern XMOB, at ~485 Ma and ~175 Ma, respectively. Based on the geological history and spatial-temporal distribution of the granitoids in northeastern (NE) China, it is proposed that the Duobaoshan Cu deposit was related to the collision of the Xing’an and Erguna blocks in the Early Paleozoic, and the Sankuanggou Cu and Daheishan Mo deposits were related to subduction of the Paleo-Pacific plate during the Jurassic.     

Re-Os dating of pyrite from Giant Bayan Obo REE-Nb-Fe deposit

The giant Bayan Obo REE-Nb-Fe deposit is locatedat the northern margin of the North China Block, i.e. atlatitude 41.7° north and longitude 110.0° east. The depositis very special in the world because it is the largest LREEdeposit and the second largest Nb deposit in the world,and also a large iron deposit. Geological features, mineralassemblage and geochronology of the deposit have beenreported[1—6]. However, various dating methods gave dif-ferent mineralization ages, and discrepancie…     

广东长坑金银矿床矿石类型及矿物组合

长坑金银矿床中金和银分别构成独立的金矿体和银矿体.矿床的主要矿石类型包括原生矿石和次生氧化矿石.氧化矿石的矿物种类简单,主要是石英,其次是粘土矿物,少量的针铁矿、臭葱石,微量的磁铁矿、锆石、黄铁矿和其他硫化物,偶见自然金.原生金矿石包括硅质金矿石、钙硅质金矿石、铝硅质金矿石三种类型,原生银矿石主要是硅质银矿石.原生金矿矿石矿物包括黄铁矿、雄黄、雌黄、重晶石、辉锑矿,其次是白铁矿和极少量毒砂和自然金,为一套浅成低温矿物组合.原生银矿矿石矿物是方铅矿、闪锌矿、银黝铜矿、深红银矿、硫锑铜银矿、硫锑铅银矿、辉锑银矿、辉银矿,次要矿物有黄铁矿、黝铜矿、黄铜矿、脆硫锑银矿、淡红银矿,是一套中深成中温的含银单硫化物和含银硫盐矿物组合.反映金、银矿床分属浅成低温和中深成中温热液交代成因的两次不同成矿作用的产物,金矿成矿在先,银矿成矿在后并叠加改造了金矿.