吉林二密铜矿区含矿次火山岩年代学及其形成环境探讨

吉林通化二密铜矿区次火山岩为其成矿的主要围岩。该次火山岩成岩时代未定,对其成岩及成矿机理等问题仍有很大的争论。本文即通过利用LA-MC-ICP-MS锆石U-Pb分析测定了该次火山岩的形成时代:二长闪长玢岩(JEM02)、石英二长闪长岩(JEM03-1)以及石英二长岩(JEM03-2)锆石的206Pb/238U加权平均年龄分别为(95.71±0.33)Ma(MSWD=1.6)、(97.18±0.46)Ma(MSWD=1.19)和(96.10±0.50)Ma(MSWD=2.0),与其相应的206Pb/238U-207Pb/235U谐和年龄一致。松顶山次火山岩侵位的先后顺序为:石英二长闪长岩、石英二长岩、二长闪长玢岩。通过主、微量元素分析,本文认为该次火山岩为碰撞后到晚造山或非造山环境下形成的花岗岩-A型花岗岩的系列。该次火山岩形成的过程为:在中国东部岩石圈减薄的过程中,地幔物质上涌与地壳发生强烈的相互作用形成富碱的钙碱性岩浆。该岩浆在岩浆房中进一步分异形成二长-闪长岩浆和花岗斑岩岩浆。两种岩浆先后沿火山喷发通道浅成侵入形成次火山岩。     

Geology,Geochemistry, and Geochronology of the Fenghuangshan Skarn‐type Copper Deposit in the Tongling Ore Cluster,Anhui Province,East China

The Fenghuangshan skarn-type Cu deposit, Tongling Ore Cluster, Anhui Province, is an important component in the Middle–Lower Yangtze River ore-forming belt. To better understand magmatism and its relationship to mineralization, we investigated geochemical features, ore-forming fluids, and geochronology of the Xinwuli intrusion and the related Fenghuangshan Cu deposit. Lithogeochemical characteristics show that the Xinwuli quartz monzodiorite is formed by mixing magma derived from upper mantle alkaline basalt that has been contaminated by crust materials. C, H and O isotopes indicate that ore-forming fluids mainly come from the magma, with minor amounts of meteoric fluids involved at the late stage. S and Pb isotopic components indicate that ore-forming materials are derived from the mantle. Molybdenite Re–Os isotopic dating yields Re–Os model ages ranging from 139.1±2.4 Ma to 142.0±2.2 Ma, with an isochronal age of 141.1±1.4 Ma, which is consistent with sensitive, high-resolution ion microprobe (SHRIMP) zircon U–Pb ages of quartz monzodiorite and granodiorite in the mining area. Dating analysis yields ages from 136.0±2.0 Ma to 143.0±2.4 Ma for the quartz monzodiorite (a weighted average of 139.4±1.2 Ma) and ages from 136.7±2.0 Ma to 145.3±2.4 Ma for granodiorite (a weighted average of 141.0±1.1 Ma).     

南极北维多利亚地难言岛侵入岩LA-ICP-MS锆石U-Pb年龄及其地质意义

对采自南极罗斯造山带中北维多利亚地难言岛的侵入岩进行了岩石学和锆石U-Pb同位素分析。难言岛的主要侵入岩类型为石英二长岩,并有少量石英二长闪长岩。采用LA-ICP-MS对石英二长岩和石英二长闪长岩样品进行锆石UTh-Pb同位素分析,获得石英二长岩的侵位年龄为482.4Ma±4.2Ma和484.3Ma±2.5Ma,石英二长闪长岩的侵位年龄为484.0Ma±3.0Ma,均为早奥陶世早期。难言岛石英二长岩和石英二长闪长岩岩浆应在伸展背景下侵位结晶,结合已有区域资料可以推测,在北维多利亚地罗斯造山运动应主要发生在寒武纪,并在早奥陶世早期之前趋于结束。     

西藏加多捕勒铁铜矿床晚白垩世岩浆活动成因

加多捕勒铁铜矿床位于冈底斯Pb-Zn-Ag-Cu-Fe成矿带西段。矿区出露的复式岩体由黑云二长花岗岩(50.9±1.8Ma)和石英二长闪长岩组成。本文以石英二长闪长岩为研究对象,分析了岩体地球化学特征、SHRIMP锆石U-Pb年龄以及原位锆石Hf同位素与稀土元素。分析结果显示石英二长闪长岩具岛弧岩浆活动特征,锆石U-Pb年龄84.3±1.4Ma,为晚白垩世岩浆活动产物,锆石Hf同位素与稀土元素指示岩浆源区具壳幔混源特征,且以古老地壳物质的部分熔融为主。综合分析已有研究成果及本文数据,笔者认为矿区晚白垩世岩浆活动可能与低缓角度俯冲的新特提斯洋壳有关。     

安徽铜陵狮子山矿田岩浆岩锆石SHRIMP定年及其成因意义

铜陵狮子山矿田发育大量岩浆岩,且与矿田中的铜金多金属成矿关系密切。锆石SHRIMP同位素精确定年表明,矿田中的岩浆侵位年龄在132.4～142.9Ma之间,即晚侏罗世—早白垩世,属燕山早期晚阶段。矿田岩浆岩体是在同期岩浆活动中多次侵位形成的,岩浆侵入活动可以划分为分别起始于140Ma前后和约136Ma的早晚两次。从岩浆上升侵位到冷却结晶的时间间隔均较短,但其中白芒山辉石二长闪长岩冷却史相对较长,且经历了早期深部岩浆房中的分离结晶作用和后期构造脉动、岩浆上升侵位、减压受热、早期晶体再熔蚀及冷却结晶的过程。结合主量元素和微量元素地球化学研究认为,狮子山矿田岩浆演化的后期,即起源于上地幔或下地壳的原生岩浆在同化了壳源物质并聚集到岩浆房中以后,在滞留的过程中发生了一定程度的分离结晶作用,但尚未固结,成分上显示了一定的带状分布,在区域构造应力松弛及构造事件诱发下,随机地沿发育的构造裂隙先后上升侵位,冷凝结晶。     

安徽铜陵凤凰山石英二长闪长岩和花岗闪长岩锆石SHRIMP U-Pb年龄及其地质意义

为建立矿区内岩浆演化序列、探讨成岩成矿关系,选取凤凰山石英二长闪长岩和花岗闪长岩进行锆石SHRIMP U-Pb精确定年。石英二长闪长岩样品测年获得年龄数据为（136.0±2.0）~（143.0±2.4）Ma,加权平均值为（139.4±1.2）Ma（n=15,MSWD=0.76）;花岗闪长岩样品测年获得年龄数据为（136.7±2.0）~（145.3±2.4）Ma,加权平均值为（141.0±1.1）Ma（n=17,MSWD=1.5）。岩体侵位年代为晚侏罗世、燕山晚期,与铜陵矿集区主要成矿岩体的形成时代一致。辉钼矿Re-Os等时线年龄与花岗闪长岩侵位年龄一致,老于石英二长闪长岩侵位年龄,说明花岗闪长岩为凤凰山矽卡岩型铜矿床的主成矿岩体,成岩成矿关系密切,它们为同期产物。同位素组成表明,幔源岩浆分异的深部流体参与了成矿作用。岩体侵位、岩石圈整体加厚产生的伸展作用和软流圈地幔、上覆地壳减压熔融产生玄武岩浆底侵作用有关。     

青海南山沟后岩浆杂岩体锆石U-Pb年代学、岩石成因及其地质意义

青海南山构造带是衔接宗务隆构造带、南祁连构造带和西秦岭造山带的重要结合带。沟后岩浆杂岩体位于青海南山构造带东段,主要由辉长岩、辉长闪长岩、石英闪长岩、花岗闪长岩组成。本文对沟后岩浆杂岩体进行了详细的岩石学、岩石地球化学和LA-ICP-MS锆石U-Pb同位素年代学研究。结果表明,辉长岩、辉长闪长岩、石英闪长岩、花岗闪长岩及暗色微粒包体的结晶年龄分别为248.8±2.6 Ma、243.2±2.1 Ma、243.1±0.9 Ma、244.0±2.1 Ma和249±3 Ma。辉长岩富铁、镁,贫碱;辉长闪长岩高铝、富钙和钠,二者均为钙碱性岩类。石英闪长岩和花岗闪长岩为准铝-弱过铝质高钾钙碱性岩,暗色微粒包体属钙碱性-碱性岩系列。不同岩石类型均表现为富集大离子亲石元素(Cs、Rb、K)和Pb,亏损高场强元素(Nb、Ta、Ti)和P、Ba负异常;稀土元素配分曲线均具有轻重稀土分异的右倾特征,具弱-中等负Eu异常。岩相学和岩石地球化学特征表明沟后岩浆杂岩体具壳幔岩浆混合特征,暗示其可能形成于由俯冲流体交代地幔楔部分熔融的幔源岩浆底侵作用下的构造环境。辉长岩为幔源岩浆经分离结晶的产物,辉长闪长岩为幔源岩浆经分异演化并混染少量壳源岩浆的产物;中基性岩浆与壳源中酸性岩浆发生混合并经历一定的分异演化过程形成了石英闪长岩和花岗闪长岩。结合区域地质资料分析认为,沟后岩浆杂岩体可能代表了研究区早三叠世晚期-中三叠世早期宗务隆洋向南消减作用相关的构造岩浆事件。     

Re–Os and U–Pb Geochronology of the Dawan Mo–Zn–Fe Deposit in Northern Taihang Mountains,China

The Dawan Mo–Zn–Fe deposit located in the Northern Taihang Mountains in the middle of the North China Craton (NCC) contains large Mo‐dominant deposits. The mineralization of the Dawan Mo–Zn–Fe deposit is associated with the Mesozoic Wanganzhen granitoid complex and is mainly hosted within Archean metamorphic rocks and Proterozoic–Paleozoic dolomites. Rhyolite porphyry and quartz monzonite both occur in the ore field and potassic alteration, strong silicic–phyllic alteration, and propylitic alteration occur from the center of the rhyolite porphyry outward. The Mo mineralization is spacially related to silicic and potassic alteration. The Fe orebody is mainly found in serpentinized skarn in the external contact zone between the quartz monzonite and dolomite. Six samples of molybdenite were collected for Re–Os dating. Results show that the Re–Os model ages range from 136.2 Ma to 138.1 Ma with an isochron age of 138 ± 2 Ma (MSWD = 1.2). U–Pb zircon ages determined by laser ablation inductively coupled plasma mass spectrometry yield crystallization ages of 141.2 ± 0.7 (MSWD = 0.38) and 130.7 ± 0.6 Ma (MSWD = 0.73) for the rhyolite porphyry and quartz monzonite, respectively. The ore‐bearing rhyolite porphyry shows higher K₂O/Na₂O ratios, ranging from 58.0 to 68.7 (wt%), than those of quartz monzonite. All of the rock samples are classified in the shoshonitic series and characterized by enrichment in large ion lithophile elements; depletion in Mg, Fe, Ta, Ni, P, and Y; enrichment in light rare earth elements with high (La/Yb)_n ratios. Geochronology results indicate that skarn‐type Fe mineralization associated with quartz monzonite (130.7 ± 0.6 Ma) formed eight million years later than Mo and Zn mineralization (138 ± 2 Ma) in the Dawan deposit. From Re concentrations in molybdenite and previously presented Pb and S isotope data, we conclude that the ore‐forming material of the deposit was derived from a crust‐mantle mixed source. The porphyry‐skarn type Cu–Mo–Zn mineralization around the Wanganzhen complex is related to the primary magmatic activity, and the skarn‐type Fe mineralization is formed at the late period magmatism. The Dawan Mo–Zn–Fe porphyry‐skarn ores are related to the magmatism that was associated with lithospheric thinning in the NCC.     

山东邹平火山岩盆地铜多金属矿SHRIMP 锆石U-Pb和辉钼矿Re-Os年龄

邹平火山岩盆地是山东省重要的铜多金属矿区之一,区内含有1套多旋回多期次的中生代火山-侵入杂岩,已发现的铜矿床、矿化点均与晚期侵入杂岩体及次火山岩有关。为了查明矿区的成岩成矿作用时代,采用SHRIMP同位素测定技术,对区内与铜多金属矿化有关的侵入岩中的锆石进行了U-Th-Pb同位素测定,获得王家庄铜矿床的赋矿围岩——石英二长闪长岩的侵位年龄为（128.8±0.8）Ma,盆地中部裂隙充填交代型铜金矿床的赋矿围岩环状二长岩岩墙的侵位年龄为（122.9±0.5）Ma;对王家庄铜矿中的5件辉钼矿样品进行了Re-Os同位素分析,获得的等时线年龄为（126.7±4）Ma及模式年龄加权平均值（128.2±0.8）Ma,代表了辉钼矿在流体中沉淀的时间。所获年龄数据准确地厘定了区内晚期岩浆活动及其矿化时限,表明王家庄杂岩体的侵位时间早于环状二长岩岩墙,其多金属矿化时间与成岩时间接近,岩体与矿化关系密切;而裂隙充填交代型铜矿的形成时间晚于环状二长岩岩墙,具有明显的构造控矿特征。所获得的年龄数据对于进一步研究区域成矿规律和指导找矿具有重要的意义。     

Early Cretaceous U–Pb zircon ages for the Copiapó plutonic complex and implications for the IOCG mineralization at Candelaria, Atacama Region, Chile

Four of the major plutons in the vicinity of the Candelaria mine (470 Mt at 0.95% Cu, 0.22 g/t Au, 3.1 g/t Ag) and a dike–sill system exposed in the Candelaria open pit have been dated with the U–Pb zircon method. The new geochronological data indicate that dacite magmatism around 123 Ma preceded the crystallization of hornblende diorite (Khd) at 118 ± 1 Ma, quartz–monzonite porphyry (Kqm) at 116.3 ± 0.4 Ma, monzodiorite (Kmd) at 115.5 ± 0.4 Ma, and tonalite (Kt) at 110.7 ± 0.4 Ma. The new ages of the plutons are consistent with field relationships regarding the relative timing of emplacement. Plutonism temporally overlaps with the iron oxide Cu–Au mineralization (Re–Os molybdenite ages at ∼115 Ma) and silicate alteration (ages mainly from 114 to 116 and 110 to 112 Ma) in the Candelaria–Punta del Cobre district. The dated dacite porphyry and hornblende diorite intrusions preceded the ore formation. A genetic link of the metallic mineralization with the quartz–monzonite porphyry and/or the monzodiorite is likely. Both of these metaluminous, shoshonitic (high-K) intrusions could have provided energy and contributed fluids, metals, and sulfur to the hydrothermal system that caused the iron oxide Cu–Au mineralization. The age of the tonalite at 110.7 Ma falls in the same range as the late alteration at 110 to 112 Ma. Tonalite emplacement may have sustained existing or driven newly developed hydrothermal cells that caused this late alteration or modified ⁴⁰Ar/³⁹Ar and K/Ar systematic in some areas.     

Geochemistry and Petrogenesis of Kunduru Betta Calc-Alkaline Ring Complex in the Dharwar Craton,Southern India

The Kunduru Betta Ring Complex (KRC), at the southern margin of Dharwar craton, South India, comprises metaluminous sub-solvus syenites and quartz monzonite with a concentric disposition younging towards the center. An outer mafic syenite (of lamprophyric affinity) is followed by porphyritic monzonite, quartz monzodiorite and finally a quartz monzonitic stock at the centre.SiO₂, Al₂O₃ and Na₂O increase from the primitive lamprophyric mafic syenite to the quartz monzonite through the intermediate members, while CaO, MgO, Fe₂O₃^T, TiO₂, P₂O₅ and MnO show an opposite trend suggesting fractionation of hornblende, clinopyroxene, biotite, apatite, sphene, and iron oxide minerals. Rb, Th and U increase with a complementary decrease in Sc, V, Cr, Co, Cu, Sr and Ba from the outer mafic syenite to the inner quartz monzonite. Y, Zr and Hf decrease from lamprophyric mafic syenite to quartz monzodiorite and the trend is reversed in the final quartz monzonite phase. However, the suite is characterised by a compositional gap between quartz monzodiorite and quartz monzonite. Total REE gradually decrease from the mafic syenite to quartz monzonite and the REE distribution patterns show LREE-enriched and HREE-depleted parallel distributions with negligible Eu anomalies.The geochemical data suggest that the rock types were formed as products of progressive differentiation by crystal fractionation of calc-alkaline lamprophyric parent magma which was derived by partial melting of metasomatically enriched mantle in the Kabini lineament. Although the quartz monzonites conform to the trend of differentiated Kunduru Betta suite, the compositional gap between them and the quartz monzodiorite precludes their origin by simple differentiation. It is suggested that convective liquid fractionation might have resulted in the discrete body of quartz monzonite.     

滇西莲花山富碱斑岩体LA ICP MS锆石U Pb年代学、地球化学特征及其地质意义

莲花山富碱斑岩体位于兰坪盆地东缘,是滇西富碱斑岩带的重要组成部分。该岩体主要由石英二长斑岩和角闪石英二长斑岩组成,对不同岩性中的锆石进行了LA ICP MS U Pb同位素测年,获得其形成年龄为(356±05)~(357±05) Ma,表明该岩体的形成时代为始新世。其K2O/Na2O比值为097~142、K2O+Na2O含量为886%~959%,显示高钾富碱的特征,属于钾玄岩系列岩石;岩体具有轻稀土元素富集、重稀土元素亏损的特征,显示弱的Eu负异常。利用锆石Ti温度计,获得岩体中岩浆锆石样品的结晶温度较低,介于594~788 ℃,说明该岩体岩浆源区的形成与俯冲－碰撞作用有关。样品中存在有少量年龄为1 177~68 Ma的继承锆石,Nb/U比值为131~473,表明莲花山岩体的源区是由洋壳俯冲作用形成的交代富集地幔,在其上侵过程中受到壳源物质不同程度的混染;岩体侵位于印度板块—欧亚板块陆－陆碰撞的挤压环境向后碰撞伸展环境转换的构造背景下。     

Early Mesozoic tectonic transition of the eastern South China Block: constraints from Late Triassic Dashuang complex in eastern Zhejiang Province

ABSTRACT

The Mesozoic tectonic transition from the Palaeo-Tethys tectonic regime to the Palaeo-Pacific tectonic regime in the eastern South China Block has long been debated. Geochemical and zircon U–Pb–Hf isotopic studies were conducted on the Dashuang complex in the eastern Zhejiang Province. The Dashuang complex consists mainly of quartz syenite in the northwestern part and quartz monzonite in the southeastern part. New laser ablation inductively coupled plasma mass spectrometry zircon U–Pb data show that the quartz syenite, the quartz monzonite, and its chilled margin (fine-grained granite) crystallized at 235 ± 4 Ma, 232 ± 3 Ma, and 230 ± 1 Ma, respectively. The Dashuang complex intrudes into the Chencai Group gneiss that postdated ~646 Ma and underwent anatexis at 443 ± 14 Ma. The quartz monzonite shows A-type granite affinity, characterized by high K₂O + Na₂O and Zr + Nb + Ce + Y, high FeO_T/(MgO + FeO_T) and Ga/Al ratios, an enrichment in light rare earth elements, and depletions in Ba, Sr, and Eu. The quartz monzonite has zircon ε_Hf(t) values of ?14.2 to –11.9 and two-stage model ages of 1788–1922 Ma. Zircon ε_Hf(t) values of the chilled margin (fine-grained granite) and wall rock (gneiss) are scattered (?18.2 to –6.3 and ?19.5 to 10.2). The corresponding two-stage model ages are 1482–2133 Ma and 1184–2471 Ma, respectively. The Dashuang complex was derived mainly from partial melting of Neoproterozoic clastic rocks in the Cathaysia Block. Geochemical data indicate that the quartz monzonite formed in a post-collision extensional environment. These results, considered with previous data, indicate that the transition from the Palaeo-Tethys to the Palaeo-Pacific tectonic regimes of the eastern South China Block occurred during the Late Triassic (225–215 Ma).     

鲁西临朐铁寨杂岩体锆石U-Pb年代学、地球化学特征及其地质意义

鲁西临朐铁寨杂岩体主要由石英二长玢岩和石英二长斑岩组成。为了精确厘定杂岩体的成岩时代和地球化学特征,对石英二长玢岩和石英二长斑岩进行了锆石U-Pb定年、全岩地球化学研究。结果表明,石英二长玢岩的锆石U-Pb年龄为(129.0±1.7) Ma,其含有的继承锆石年龄为(2 520±30) Ma;石英二长斑岩的锆石年龄为(125.0±1.6) Ma。两种侵入岩均具有富硅、富碱和低钙镁的特征,石英二长玢岩比石英二长斑岩的Mg^#值高;稀土总量较低,轻重稀土分馏明显,Eu基本无异常;Sr、Ba含量高,Nb、Ta和Ti等高场强元素负异常。岩石地球化学特征表明:鲁西铁寨杂岩体来源为富集地幔部分熔融、同化混染了部分古老的地壳物质,两种岩性的Mg^#值差异是磁铁矿分离结晶的结果。早白垩世滞留在地幔过渡带的太平洋板片脱水是岩石圈减薄的诱因,期间产生大量的岩浆岩,表明早白垩世是华北克拉通岩石圈减薄的峰期。     

蚌埠淮光“混合花岗闪长岩”的形成时代及源区：锆石SHRIMP U-Pb地质年代学证据

对蚌埠淮光花岗闪长岩的岩相学和锆石阴极发光图象研究表明,淮光"混合花岗闪长岩"为岩浆结晶作用的产物,岩石形成后受到了应力作用的改造.锆石SHRIMP U-Pb定年结果和岩浆锆石的SHRIMP U-Pb年龄显示淮光花岗闪长岩形成于130.0±2.0 Ma;大多数继承锆石的年龄集中在1 800～1 900 Ma、2 300～2 517 Ma和3 443 Ma,这意味着淮光花岗闪长岩的母岩浆起源于华北地块基底的部分熔融.早白垩世(130 Ma左右)的岩浆作用是引起继承锆石和碎屑锆石Pb丢失的重要原因,同时也是华北地块东部岩石圈减薄的最重要时期.130 Ma左右的岩浆作用和岩石圈减薄应与太平洋板块的俯冲相联系.     

Morphology, Chemistry and U-Pb Geochronology of Zircon Grains In Quartz Monzodiorite from the Sunzhuang Area, Fanshi County, Shanxi Province

The morphology, REE geochemistry and U-Pb geochronology of zircons from quartz monzodiorite in the Sunzhuang area, Fanshi County, Shanxi Province are presented in this study. The zircon crystals can be classified into four main types as: AB, L, S and P, and 24 subtypes such as AB4, AB5, L5, and S3. The maximum crystallization temperature of zircon was estimated as 850°C, with the minimum of 550°C. The peak temperatures of the zircon crystallization range from 650°C to 700°C. The abundances of Th and U in the zircon grains show large variation with the Th/U values 0.4. The Th and U values also show a positive correlation in most zircons. The REE abundance of zircon in the quartz monzodiorite ranges from 280.4 ppm to 2143 ppm with an average of 856.4 ppm. The chondrite normalized zircon REE patterns show two types, one is characterized by HREE enrichment and LREE depletion with positive Ce-anomaly and negative Eu-anomaly whereas the other is HREE enriched and LREE depleted with negative Eu-anomaly but without positive Ce-anomaly, and relatively flat patterns. The LA-ICP-MS U-Pb geochronology on the zircons yields a mean age of 133±0.87 Ma. Our data on zircon morphology, composition and U-Pb geochronology reveal that the parent magma of the quartz monzodiorite which was emplaced during late Yanshanian had a mixed crust-mantle source, with crustal components dominating. The magma is inferred to have been water rich and alkaline with initial high oxygen fugacity. Post-magmatic hydrothermal activity occurred under relatively reducing conditions which was conductive for gold precipitation in the Yixingzhai gold deposit.     

大兴安岭北部岔路口斑岩钼矿床岩浆岩锆石U Pb年龄及其地质意义

黑龙江省岔路口超大型斑岩钼矿床位于大兴安岭北部,是目前我国东北地区最大的钼矿床,矿体赋存于中酸性杂岩体及侏罗系火山-沉积岩内,其中花岗斑岩、石英斑岩、细粒花岗岩与钼矿化关系密切.本文采用LA-ICP-MS锆石U-Pb定年方法,获得了矿区内二长花岗岩、花岗斑岩、石英斑岩、细粒花岗岩、流纹斑岩、闪长玢岩及安山斑岩的结晶年龄分别为162±1.6 Ma、149±4.6 Ma、148±1.6 Ma、148±1.2 Ma、137±3.3 Ma、133±1.7Ma和132±1.6 Ma.岔路口矿区内至少存在3期岩浆活动,其顺序为侏罗纪火山-沉积岩、二长花岗岩→晚侏罗世花岗斑岩、石英斑岩、细粒花岗岩→早白垩世流纹斑岩、闪长玢岩、安山斑岩.岔路口矿床成矿时代为晚侏罗世,是东北亚大陆内部构造-岩浆活化的产物,形成于古太平洋板块俯冲作用引起的挤压向伸展构造体制转折背景,与我国东部大规模钼矿化爆发期相对应.     

安徽铜陵焦冲矿田侵入岩锆石U-Pb定年、Hf同位素特征及成因

安徽铜陵矿集区出露的侵入岩可划分为高钾钙碱性和橄榄安粗岩系列,作为铜陵7大矿田之一的焦冲地区是否也存在两个系列侵入岩?它们的时代及成因与整个铜陵地区的侵入岩是否相同?这些问题目前仍不清楚。本文选择铜陵焦冲矿田的侵入岩开展了岩相学、岩石地球化学、LA-ICPMS锆石U-Pb定年及原位Hf同位素地球化学研究。结果表明,焦冲矿田也存在高钾钙碱性系列和橄榄安粗岩系列侵入岩,前者的主要岩石类型为石英二长闪长岩、花岗闪长岩,后者为辉石二长闪长岩。LA-ICPMS锆石U-Pb定年结果显示,高钾钙碱性系列侵入岩年代与铜陵地区其他矿区同类岩石年代相同,约为142 Ma;而橄榄安粗岩系列侵入岩年代比铜陵地区其他矿区同类岩石年轻,约为136 Ma。总体上看,铜陵地区两个系列侵入岩具有多期次侵位的特征。焦冲高钾钙碱性系列侵入岩含有较多的老的继承性锆石,说明本区古老地壳卷入了岩浆形成过程。结合铜陵地区侵入岩的特征和焦冲矿田侵入岩岩石地球化学研究结果,笔者认为,焦冲矿田两个系列侵入岩成因与铜陵地区侵入岩相似,即橄榄安粗岩系列侵入岩是来自莫霍面附近深部位岩浆房富碱基性岩浆结晶分异后的产物,而高钾钙碱性系列侵入岩是深位岩浆房分异后的岩浆与浅位岩浆房长英质岩浆混合后的产物。     

青海东昆仑哈西亚图铁多金属矿区石英闪长岩LA-ICP-MS锆石U-Pb年龄和岩石地球化学特征

东昆仑地区是青海省重要的夕卡岩型铁多金属矿成矿带,哈西亚图铁多金属矿是近年来首例在东昆仑金水口岩群中发现的与中酸性岩体有关的夕卡岩型矿床,目前铁、金、锌矿已达中型。其成矿作用与矿区东北部石英闪长岩关系密切,矿体产于石英闪长岩的外接触带。采用LA-ICP-MS同位素测定技术,测得石英闪长岩锆石U-Pb年龄为246.8±1.8Ma(MSWD=0.074),形成于早三叠世,表明东昆仑地区早三叠世存在夕卡岩成矿作用。地球化学研究表明,石英闪长岩为高钾钙碱性系列,具有安第斯型活动大陆边缘火成岩的构造属性。研究认为,石英闪长岩是阿尼玛卿洋盆向北俯冲,致使壳幔岩浆发生混合,后经侵位、结晶分异形成的。     

Molybdenite Re-Os and Zircon SHRIMP U-Pb Dating at the Baishiding Deposit,Guposhan District: New Evidence for Silurian Mo Mineralization in South China

The Baishiding molybdenum deposit is located in the Central-Middle Guangxi depression zone of the South China Caledonian fold zone. Orebodies occur as quartz-molybdenite veins within the Guiling monzonite pluton and arkosic quartz sandstone of Zhengyuanling Group in the northeastern Guangxi. They are NEE-trending with a dip angle of 75–80°. Zircon SHRIMP U-Pb geochronologic analyses of the Guiling monzonite show age of 424.4 ± 5.6 Ma. It indicates that the Guiling monzonite was emplaced in Silurian. The ore minerals in quartz-molybdenite veins contain molybdenite, pyrite, chalcopyrite and scheelite. Six molybdenite samples yield Re-Os ages between 433.3 ± 6.3 Ma and 417.2 ± 5.7 Ma, with a weighted mean age of 424.6 ± 5.7 Ma, which agrees with the zircon age of the Guiling monzonite pluton. It suggests that the deposit was formed in the Silurian, not the Jurassic as previously thought. The Baishiding deposit is the only Silurian molybdenum deposit so far recognized in the South China. It was probably formed in a crustal shortening setting along the continental margin in the Silurian.