LA-ICP-MS zircon U-Pb age of rhyolitic lithic-crystal tuffs in Erdaohezi lead-zinc deposit,Inner Mongolia

Erdaohezi lead-zinc deposit belongs to the Derbugan metallogenic belt lying on the northwestern Hailaer-Genhe Mesozoic volcanic basin,located on the western slope of the Da Hinggan Mountains. The deposit is considered as one of the hypabyssal low-temprature hydrothermal lead-zinc deposits associated with volcanism. In order to lay the foundation on studying its diagenesis and mineralization ages,the detailed studies were carried out by dating the host rocks( i. e. rhyolitic lithic-crystal tuffs) using zircon LA-ICP-MS U-Pb method.The dating results show three groups of ages. The first group is the captured zircons( the weighted mean ~(206)Pb /~(238) U age as 175. 6 ± 2. 3 Ma,MSWD = 0. 70,n = 3). The second group can be regarded as the rockforming age( the weighted mean ~(206)Pb /~(238) U age as 165. 3 ± 1. 9 Ma,MSWD = 2. 40,n = 14). The third group should represent the late stage of the magmatic evolution( the weighted mean ~(206)Pb /~(238) U age as 161. 0 ± 3. 1Ma,MSWD = 0. 86,n = 4). According to the ages and the crystal form or CL image characteristics of zircons,it is determined that the diagenesis occurred in the late Middle Jurassic. Based on the regional geology and geochronological research,the acidic pyroclastic rocks are space accompaniment and time connection with the Tamulangou Formation intermediate-mafic volcanic rocks. Both of them constitute the host rocks of the deposit together. The rock combination also provides favorable conditions for large-scale silver,lead and zinc mineralization in this area.     

Ore mineral characteristics and zircon U-Pb geochronology of Yuanjiacun iron deposit in Shanxi

In order to further understand the ore characteristics and metallogenic age of Yuanjiacun iron deposit in Shanxi, the mineral composition characteristics of iron ore were studied on the basis of field investigation and microscopic observation. Magnetite, hematite, goethite and pyrite of different stages were identified according to their texture and structure features. Two sets of ~(207)Pb/~(206)Pb ages have been obtained by ICPMS isotope dating of magnetite quartzite, of which the zircon age with metamorphic origin is 1 916±88 Ma, representing the main metamorphic age of iron deposit. Another group of magmatic zircons with rhythmic zones are of 2 280±30 Ma age, representing the diagenetic age of iron formation. In addition, scattered age records after metamorphism indicate frequent hydrothermal events after mineralization. Based on the mineral fabric characteristics and the age data of zircons of different origins, it is known that the deposit has undergone sedimentary mineralization period, metamorphic mineralization period, hydrothermal mineralization period and weathering mineralization period.     

松辽盆地大庆长垣南缘四方台组砂岩型铀矿碳氧同位素特征及铀成矿意义

为进一步探讨松辽盆地大庆长垣南缘四方台组砂岩型铀矿的成岩环境、铀沉淀机制及成矿机理,通过钻井岩心观察,岩石薄片,含铀砂岩碳酸盐胶结物碳、氧同位素分析,对研究区砂岩岩石类型、碳酸盐胶结物类型、成岩阶段以及碳、氧同位素特征进行了系统研究。结果表明:含铀砂岩岩石类型为长石岩屑砂岩、岩屑长石砂岩,碳酸盐胶结物可分为3个期次,以第一和第二期次为主,胶结物包括方解石、铁方解石,见极少量含铁白云石。δ13C_PDB值为-22.45‰~-13.65‰,平均值为-18.33‰,δ18O_PDB值为-17.56‰~-9.46‰,平均值为-13.52‰,揭示有一定有机质参与;古盐度Z值介于75.98~90.97之间,为淡水沉积;古温度介于67.31~94.92℃之间,结合以上岩石特征、胶结物类型及成岩作用判定成岩环境处于早成岩—中成岩阶段A期。综合分析认为:早成岩阶段砂岩的压实、胶结作用使含铀砂岩孔隙度减小,抑制含氧富铀流体运移;随着成岩作用进行,埋藏深度增加,有机质成熟度升高发生热脱羧基作用,与压实作用产生的吸附水形成酸性溶液对长石、碳酸盐胶结物等进行溶蚀形成次生孔隙,增大砂岩孔隙度,促进含氧富铀流体下渗运移,下伏油气由断裂向上逸散,为地层提供还原剂,使铀在四方台组底部大规模沉淀和富集。      

鲁西徂徕山南部花岗闪长斑岩锆石LA-ICP-MS U-Pb定年及其地质意义

出露于鲁西徂徕山南部的花岗闪长斑岩是鲁西中生代岩浆活动的重要记录,在野外地质工作的基础上,通过对其进行锆石LA-ICP-MS U-Pb同位素年代学研究,得到了花岗闪长斑岩的形成时代,并对鲁西地区中生代的岩浆活动进行了讨论。研究得到,谐和度90%的锆石中存在~2.5Ga的继承性岩浆锆石和125~130Ma的岩浆锆石。经分析,得到其加权平均年龄为(127.3±1.2)Ma(MSWD=1.3),认为这一年龄代表了花岗闪长斑岩的形成年龄,而~2.5Ga的继承性岩浆锆石的存在说明了花岗闪长斑岩的源区可能来自于华北古老基底或在岩浆侵位过程中遭受了古老基底的混染作用。     

东天山石灰窑钾长花岗岩体LA-ICP-MS锆石U-Pb年龄与地球化学特征

石灰窑花岗岩位于卡拉麦里蛇绿岩带的最东段,岩性为中粗粒钾长花岗岩。岩体具有高硅(74.13%～75.76%)、高钾(4.26%～5.59%)、低镁铁[w(MgO+Fe₂O₃+TiO₂)介于1.55%～3.37%之间]、高A/CNK(0.99～1.12)特征,刚玉标准分子略高(0.003%～1.46%),属高钾钙碱性过铝质S型花岗岩。岩体富钾(K₂O/Na₂O值介于1.12～2.06之间),高Rb、Cs,低CaO/Na₂O值(0.18～0.34之间),显示源区主体为富云母的变泥质岩区。岩石明显富集Rb、Th、U、K和Pb等大离子亲石元素,强烈亏损Ba、Sr、P、Ti、Eu等元素,并具有弱的Nb亏损,具有俯冲相关的火山弧和后碰撞伸展花岗岩类的地球化学特征。岩体侵位于下石炭统山梁砾石组地层,南界被蛇绿混杂岩的边界断裂切割,岩体LA-ICP-MS 锆石U-Pb年龄(282.9±3.6)Ma应代表了卡拉麦里蛇绿混杂岩带东段的闭合年龄。结合区域构造背景分析,石灰窑花岗岩形成于卡拉麦里俯冲碰撞向碰撞后伸展的过渡阶段,是局部减压和地幔热流异常导致上地壳物质发生部分熔融的产物。      

内蒙古克什克腾旗毛盖吐锡矿点LA-ICP-MS锡石U-Pb年龄及地质意义

毛盖吐锡矿点为北京矿产地质研究院在大兴安岭南段新发现的矿点, 位于内蒙古克什克腾旗境内。矿点地处大兴安岭中南段多金属成矿带, 矿化类型为锡石石英脉型。矿石矿物主要为锡石和少量闪锌矿、方铅矿、黄铜矿以及银的矿物, 脉石矿物主要为石英以及少量的萤石。该矿由于首次发现, 研究程度较低, 关于其矿床成因、成矿时代等规律尚不明确。大兴安岭中南段多金属成矿带上发育多个锡多金属矿床, 目前的研究表明这些锡多金属矿床的成矿年龄多集中在早白垩世, 成因与早白垩世花岗岩相关。为了研究毛盖吐锡矿与区域锡多金属成矿作用的联系, 开展了对毛盖吐锡矿点成矿时代的研究, 本研究选取1件石英脉型锡矿石样品进行LA-ICP-MS锡石U-Pb定年, 获得锡石的207Pb/206Pb-238U/206Pb谐和年龄为130.2±3.4 Ma(MSWD=2.9), 表明毛盖吐锡矿点形成于早白垩世, 这与区域上主要的锡多金属矿床成矿时代一致, 说明在大兴安岭中南段寻找锡多金属矿床拥有很好的前景。      

Geochemistry and zircon U-Pb chronology of quartz porphyry in Yuejinshan Fe-polymetallic deposit of Heilongjiang

Quartz porphyry in Yuejinshan Fe-polymetallic deposit is one of the rock masses, which formed the granite belt relating to the late Yanshanian skarn-type Fe-polymetallic deposits in the eastern Heilongjiang, and is also closely related to the metallogenic space of the Fe-polymetallic deposits. Quartz porphyry has the zircon U-Pb concordia age of 125.0±1.1 Ma, overall showing high Si(SiO_2=74.48%--75.00%), rich alkaline(Na_2O+K_2O=7.93%--8.17%, K_2O/Na_2O=1.39--1.46), and poor Mg(MgO=0.27%--0.31%), with the A/CNK value being 0.95--0.99, having the characteristics of obvious enrichment of LREE and medium Eu negative anomaly(0.69--0.74), indicating that the rock belongs to quasi-aluminous high potassium calc-alkaline series and has the same characteristics as those of the I-type granite. The rock is also characterized by the enrichment of LILE and active incompatible elements, and depletion of HFSE such as Nb, Ta, P and Ti, with the Mg~# value being 32--37, indicating that the rock originated from partial melting of crustal materials. It can be concluded from the above characteristics or data and from the distribution of contemporary magmatic rocks in the area, that quartz porphyry in Yuejinshan Fe-polymetallic deposit was formed in a tectonic background of the subduction of the paleo-Pacific plate in late Yanshanian.     

Petrogenesis of Paleoproterozoic diorite porphyries in Luojiazhuang,western Shandong:constraints from LA-ICP-MS zircon U-Pb geochronology and geochemistry

Based on the study of LA-ICP-MS zircon U-Pb geochronology and whole-rock geochemistry for the Luojiazhuang diorite porphyries in Menying,western Shandong,the analyzed zircons exhibit oscillatory growth zoning in the cathodoluminescence images and have high Th / U ratios( 0. 15--1. 53),indicating a magmatic origin. In addition,most of the zircons have narrow metamorphic edges,suggesting that late metamorphic events may exist. The youngest group of magmatic zircon207 Pb /206 Pb ages ranging from 2 384 Ma to 2234 Ma,yielding a weighted mean age of 2353 ± 14 Ma,which represents the forming age of the diorite porphyries,as the Early Paleoproterozoic. Geochemically,the samples are characterized by low SiO_2( 54. 54% and 55. 47%),high MgO( 5. 22% and 5. 49%) and Mg~#values( 58 and 59). Moreover,they show enrichment of light rare earth elements and large ion lithophile elements( Rb,Ba and K),depletion of heavy rare earth elements and high field strength elements( Nb,Ta,Zr and Hf),positive anomaly of Pb,and negative anomaly of Ti. The fact implies that the Luojiazhuang diorite porphyries might derive from partial melting of enriched lithospheric mantle and mixed with an amount of continental crust material. In summary,they may form in the compression tectonic setting that stretching along the east-west direction at the North China Craton in the Early Paleoproterozoic.     

鲁西徂徕山地区傲来山序列二长花岗岩锆石LA-ICP-MS U-Pb定年及其地质意义

出露于鲁西徂徕山地区的傲来山序列二长花岗岩是鲁西新太古代岩浆作用的重要记录,在野外地质工作的基础上,通过对其进行锆石LA-ICP-MS U-Pb同位素年代学研究,得到了二长花岗岩的形成时代,并对鲁西地区新太古代的岩浆活动进行了讨论。研究得到,谐和度90%的锆石中存在岩浆锆石~2 520Ma和继承性岩浆锆石2611Ma~2 766Ma两个年龄区间。岩浆锆石的加权平均年龄为(2 525±18)Ma,认为这一年龄代表了二长花岗岩的形成年龄。2 611Ma~2 766Ma继承性岩浆锆石的存在反映了鲁西地区至少经历了2次壳源物质的重熔和加入。     

Diagenesis tectonic setting and U-Pb dating for zircon from Tanjianshan Group in northern margin of Qaidam Basin

The shape,texture,content and REE characteristics of zircons from the O2tnd-1,O3tnd-2,O3tnd-3pyroclastic rock of Tanjianshan Group on the north margin of Qaidam Basin indicate that the O2-3tndis the product of volcanism during the transitional period from ocean-land interim crust to oceanic crust.The U-Pb surface ages obtained from O3tnd-2and O3tnd-3can be divided into 9 groups,every age group coincides with the period when significant tectonic-heat event took place at Oulongbuluke micro-continental base of northern Qaidam,suggesting that the base rocks have provided materials for the formation of sedimentary and volcanic rock in O2-3tnd.The volcanic rocks of O3tnd-3formed at 440 Ma,with time gap 46 Ma to those of O1tna-1and O3tnd-3may represent the minor period that Xitieshan back-arc extension have lasted,the scale of back-arc basin that formed in Xitieshan extension may approach to 1 400 km.Based on the test of ithochemistry data for major elements and analysis of Sr isotope geochemistry for the clastic sedimentary rock in O1tna-2and O3tnd-2,the authors get the conclusion that the O1tna-2and O3tnd-2of Tanjianshan Group may form in back-arc basin environment,while the lithology difference between these two formations may reflect the changes of geodynamic processes as the diagenesis tectonic environment transformed from continental margin depression to adjacent sea basin.