Geology,geochronology and geochemistry of large Duobaoshan Cu-Mo-Au orefield in NE China: Magma genesis and regional tectonic implications

Duobaoshan is the largest porphyry-related Cu-Mo-Au orefield in northeastern(NE)Asia,and hosts a number of large-medium porphyry Cu(PCDs),epithermal Au and Fe-Cu skarn deposits.Formation ages of these deposits,from the oldest(Ordovician)to youngest(Jurassic),have spanned across over 300 Ma.No similar orefields of such size and geological complexity are found in NE Asia,which reflects its metallogenic uniqueness in forming and preserving porphyry-related deposits.In this study,we explore the actual number and timing of magmatic/mineralization phases,their respective magma genesis,fertility,and regional tectonic connection,together with the preservation of PCDs.We present new data on the magmatic/mineralization ages(LA-ICP-MS zircon U-Pb,pyrite and molybdenite Re-Os dating),whole-rock geochemistry,and zircon trace element compositions on four representative deposits in the Duobaoshan orefield,i.e.,Duobaoshan PCD,Tongshan PCD,Sankuanggou Fe-Cu skarn,and Zhengguang epithermal Au deposits,and compiled published ones from these and other mineral occurrences in the orefield.In terms of geochronology,we have newly summarized seven magmatic phases in the orefield:(1)Middle-Late Cambrian(506-491 Ma),(2)Early and Middle Ordovician(485-471 Ma and~462 Ma),(3)Late Ordovician(450-447 Ma),(4)Early Carboniferous and Late-Carboniferous to Early Permian(351-345 and 323-291 Ma),(5)Middle-Late Triassic(244-223 Ma),(6)Early-Middle and Late Jurassic(178-168 Ma and~150 Ma),and(7)Early Cretaceous(~112 Ma).Three of these seven major magmatic phases were coeval with ore formation,including(1)Early Ordovician(485-473 Ma)porphyry-type Cu-Mo-(Au),(2)Early-Middle Triassic(246-229 Ma)porphyry-related epithermal Au-(Cu-Mo),and(3)Early Jurassic(177-173 Ma)Fe-Cu skarn mineralization.Some deposits in the orefield,notably Tongshan and Zhengguang,were likely formed by more than one mineralization events.In terms of geochemistry,ore-causative granitoids in the orefield exhibit adakite-like or adakite-normal arc transitional signatures,but those forming the porphyry-/epithermal-type Cu-Mo-Au mineralization are largely confined to the former.The varying but high Sr/Y,Sm/Yb and La/Yb ratios suggest that the ore-forming magmas were mainly crustal sourced and formed at different depths(clinopyroxene-/amphibole-/garnet-stability fields).The adakite-like suites may have formed by partial melting of the thickened lower crust at 35-40 km(for the Early Ordovician arc)and>40 km(for the Middle-Late Triassic arc)depths.The Early Jurassic Fe-Cu skarn orecausative granitoids show an adakitic-normal arc transitional geochemical affinity.These granitoids were likely formed by partial melting of the juvenile lower crust(35-40 km depth),and subsequently modified by assimilation and fractional crystallization(AFC)processes.In light of the geological,geochronological and geochemical information,we proposed the following tectonometallogenic model for the Duobaoshan orefield.The Ordovician Duobaoshan may have been in a continental arc setting during the subduction of the Paleo-Asian Ocean,and formed the porphyry-related deposits at Duobaoshan,Tongshan and Zhengguang.Subduction may have ceased in the latest Ordovician,and the regional tectonics passed into long subsidence and extension till the latest Carboniferous.This extensional tectonic regime and the Silurian terrestrial-shallow marine sedimentation had likely buried and preserved the Ordovician Duobaoshan magmatic-hydrothermal system.The south-dipping Mongol-Okhotsk Ocean subduction from north of the orefield had generated the Middle-Late Triassic continental arc magmatism and the associated Tongshan PCD and Zhengguang epithermal Au mineralization(which superimposed on the Ordovician PCD system).The Middle Jurassic closure of Mongol-Okhotsk Ocean in the northwestern Amuria block(Erguna terrane),and the accompanying Siberia-Amuria collision,may have placed the Paleo-Pacific subduction system in NE China(including the orefield)under compression,and formed the granodiorite-tonalite and Fe-Cu skarn deposits at Sankuanggou and Xiaoduobaoshan.From the Middle Jurassic,the consecutive accretion of Paleo-Pacific arc terranes(e.g.,Sikhote-Alin and Nadanhada)onto the NE Asian continental margin may have gradually distant the Duobaoshan orefield from the subduction front,and consequently arc-type magmatism and the related mineralization faded.The minor Late Jurassic and Cretaceous unmineralized magmatism in the orefield may have triggered mainly by the far-field extension led by the post-collisional(Siberia-Amuria)gravitational collapse and/or Paleo-Pacific backarc-basin opening.     

Zircon U–Pb and molybdenite Re–Os geochronology of copper–molybdenum deposits in southeast Liaoning Province,China

ABSTRACT

Liaoning Province in China is an area known for the occurrence of numerous copper and/or molybdenum deposits of variable size. However, the age of mineralization and tectonic setting in this region are still a subject of debate. In this study we describe the geology of these deposits and apply zircon U–Pb and molybdenite Re–Os isotopic dating to constrain their ages and define the metallogenic epochs of this province. The Huatong Cu–Mo deposit yields molybdenite Re–Os model ages of 127.6–126.3 Ma and an isochron age of 127.4 ± 0.7 Ma. The Dongbeigou Mo deposit yields molybdenite Re–Os model ages of 132.6–127.1 Ma, an isochron age of 128.1 ± 5.1 Ma, and a zircon U–Pb age of 129.4 ± 0.3 Ma for the associated monzogranite. The granodiorite associated with the Wanbaoyuan Cu–Mo deposit yields a zircon U–Pb age of 128.4 ± 1.1 Ma; the plagiogranite associated with the Yaojiagou Mo deposit yields an age of 167.5 ± 0.9 Ma; and the biotite–plagioclase gneiss from the Shujigou Cu deposit yields an age of 2549.4 ± 5.6 Ma. These results, together with previous geochronology data, show that intense Cu–Mo porphyry and skarn mineralization were coeval with Early–Middle Jurassic and Early Cretaceous granitic magmatism. The former was associated with the orogeny that followed the collision of the Siberian and North China plates and the resulting closure of the palaeo-Asian Ocean, and the latter with rifting that followed the subduction of the palaeo-Pacific Plate and associated lithospheric thinning. Volcanogenic massive sulfide Cu deposit. mineralization took place much earlier, in the late Archaean, and was related to continent–continent collision, palaeo-ocean closure, the formation of a united continental landmass, bimodal volcanism, magma emplacement, and subsequent metamorphism and deformation of syn-collisional granites.     

楚雄盆地砂岩型铜矿床构造-流体耦合成矿模型

砂岩型铜矿床是楚雄陆相红层盆地的典型矿床类型。在构造-流体-成矿体系的动力学演化中,该类矿床的形成经历了沉积-成岩成矿作用、改造成矿作用及后期断裂作用的演化过程:燕山中晚期形成煤-铜-盐"三色建造"和盆地流体;喜马拉雅早期构造-热演化形成褶皱圈闭盆地流体,来自基底的富铜流体沿同生断裂(隐伏断裂)上升将一些亲铜元素从深部带入煤层而被吸附,形成富铜的还原性流体(H2O-SO2-CO2-CH4(C3H8-C2H6)-HSO4-HCO3-型),还原性流体沿次级断裂、隐伏断裂和层间断裂及轴面变形带上升,与大气降水深循环淋滤膏盐层形成高盐度的氧化性流体(H2O-SO2-CO2-N2-CO-HSO4-型)在砂(页)岩相遇时发生水-岩相互作用,并封闭于高孔渗的砂(页)岩储层,在褶皱翼部或核部的中细粒砂岩和层间断裂带中形成层状、似层状矿体;喜马拉雅中期由于构造改造,在更次级断裂带中形成脉状矿(化)体。所以,该类矿床是褶皱构造圈闭盆地流体-含矿岩相和构造裂隙封闭成矿流体定位成矿的产物,是铜矿源、构造与流体三者耦合作用的结果,更好地解释了矿床既沿褶皱分布又沿含矿层定位及矿物、元素分带的主要原因。故建立了该类矿床的构造-流体耦合成矿模型。     

滇东磷块岩及工业磷矿床成因

滇东地区存在两套含磷岩系，十个磷块岩层位，可归纳为三类成因、四个工业磷矿层，进一步划分为四个沉积阶段、四个工业磷矿床成矿区。其中，研究较深的中谊村段磷矿，是由成矿地质背景和环境因素控制的八种主要成矿作用和四个成矿富集阶段多重反复叠加形成的生物沉积磷块岩矿床。     

滇东南微细浸染型金矿构造控矿型式

滇东南微细浸染型金矿的形成与该区构造关系密切,总体受右江裂谷系控制。主干断裂严格控制金矿的带状分布,次级断裂进一步控制成矿带内矿体的具体空间位置或定位。认为逆冲推覆构造为该区微细浸染型金矿的控矿构造型式,归纳出该区微细浸染型金矿在构造中的分布规律,并据此提出新的找矿思路与找矿方向。     

会理小青山铜(金)矿床地质特征及成因初探

四川省会理县小青山铜（金）矿床是以铜为主的多金属矿床,据矿体赋存层位,控矿构造,矿体产状、形态、规模,成矿物质来源等诸多因素分析,它是一种典型的火山沉积—热液富集型铜矿床。     

Magmatism and metallogenic mechanisms of the Baoshan Cu-polymetallic deposit from the Lesser Xing’an Range,NE China: Constraints from geology,geochronology, geochemistry,and Hf isotopes

The Baoshan Cu-polymetallic deposit is a recently discovered skarn deposit in the northern Lesser Xing’an Range, NE China. The orebodies are mainly hosted in the contact zone between granitic intrusions and Lower Cambrian dolomitic crystalline limestones or skarns. We present here zircon U–Pb and molybdenite Re–Os age data, whole-rock geochemistry, and zircon Hf isotopic data to constrain the geodynamic mechanisms of igneous activity and metallogenesis within the Baoshan Cu–polymetallic deposit. LA–ICP–MS zircon U–Pb dating suggests that a hornblende–quartz monzonite and porphyritic biotite granite were emplaced at 252.45 ± 0.70 Ma and 251.10 ± 0.98 Ma, respectively. Molybdenite separated from ore-bearing quartz veins or skarn-type ores yields a weighted mean model age of 250.3 ± 3.4 Ma, which coincide with the emplacement of the igneous rocks. These data suggest that the Late Permian-Early Triassic magmatic and mineralization event led to the formation of the Baoshan Cu–polymetallic deposit. Granitic intrusions are closely associated with this mineralization and have high contents of SiO₂ (60.90–68.98 wt.%), Al₂O₃ (15.15–16.98 wt.%) and K₂O (2.77–4.17 wt.%), with A/CNK ratios of 0.86–0.96. These granites are classified as metaluminous and high-K calc-alkaline I-type granites, and are enriched in Rb, Th, U, and K, and depleted in Nb, Ta, P, and Ti. Moreover, Moreover, the hornblende–quartz monzonite and porphyritic biotite granite have geochemical characteristics similar to adakites and island arc calc-alkaline rocks, respectively. In situ zircon Hf isotope data on the hornblende–quartz monzonite samples show ε_Hf(t) values from +0.1 to +3.1, and porphyritic biotite granite samples exhibit heterogeneous ε_Hf(t) values from −5.4 to +1.1. The geochemical and isotopic data for the Baoshan intrusions indicate that the Late Permian–Early Triassic continental–continental collision caused over thickening and delamination of the lower crust. Partial melting of delaminated lower crust formed the primary adakitic magmas, which may have reacted with surrounding mantle peridotite during ascent. Hornblende–quartz monzonite was formed by the emplacement of the adakitic magmas, whereas the formation of the porphyritic biotite granite was caused by the mixing of adakitic magmas with ancient crustal materials during ascent. Moreover, ore-forming materials were typically derived from the adakitic magmas with high oxygen fugacity, which incorporated significant amounts of ore-forming elements. Based on the regional geological history and the new geochemical and isotopic data from intrusions, we suggest that diagenesis and mineralization of the Baoshan Cu–polymetallic deposit took place in a transitional tectonic setting from collisional orogeny to extension, after collision of the North China Plate and Songnen Block, during the latter stages of the Xingmeng orogeny.     

AG MP-1阴离子交换树脂元素分离方法研究

在用多接收器等离子体质谱仪（MC—ICP—MS）测定过渡族元素同位素时,需要对待测样品进行分离纯化。目前,人们常用AGMP-1阴离子交换树脂在不同浓度的HCl和HNO,介质中依次分离出Cu,Fe和zn。为详细了解样品中基体元素与AGMP-1阴离子交换树脂的作用以及它们在该树脂中的淋洗过程,根据金属阳离子与Cl^-形成络合物的稳定性及它们与阴离子交换树脂的亲和力,对利用AGMP-1进行Cu和Fe分离过程中基质元素的行为进行了实验研究。结果表明,除Co外,在7mol／LHCl条件下,地质样品中基体元素（包括cr和Ni）能与Cu,Fe进行很好的分离。不同酸度下的实验研究表明,在6mol／LHCl条件下,可以将Cu和Co进行很好的分离。为此提出,对于基质元素含量较少的样品（如硫化物、氧化物、氢氧化物等）,可直接用6mol／LHCl进行样品分离。由于这类样品中K,Na,Ca,Mg,A1等元素含量较低,在Cu被洗脱前已被彻底淋洗,该方法可将Cu和包括Co在内的基质元素进行理想的分离。对于含Co较高的部分硅酸盐等样品,则应先用7mol／LHCl分离出Cu接收液,之后过二遍柱,以6mol／LHCl作淋洗液,去掉Co。建立的分离方法还可应用于Ca,Mg同位素的前期分离纯化     

浙江燕山期主要Cu（mo）矿化岩体的地球化学特征

本文系统研究了浙江省燕山期主要Ｃｕ（Ｍｏ）矿化岩体的稀土、微量元素和稳定同位素地球化学特征。Ｃｕ（Ｍｏ）矿化岩体多属轻稀土富集型，一类铕异常不明显，多为矽卡岩型等矿床的成矿母岩；另一类负铕异常强烈，多为直接含矿斑岩体。Ｃｕ（Ｍｏ）矿化岩体多为Ｉ型，属火山弧和同造山碰撞形成。     

新疆西天山莫斯早特石英钠长斑岩铜矿床——一个与埃达克质岩石有关的铜矿实例

与埃达克岩石有关,在环太平洋地区发现了大型、超大型斑岩型铜矿床.本文提供了一个产于中亚成矿域新疆西天山的莫斯早特铜矿床研究的实例.含矿岩体为石英钠长斑岩,岩体主量、微量元素地球化学特点与埃达克质岩石一致富Na、Al;高Sr,低Y;Sr/Y＞40,亏损HREE;La/Yb＞20;Eu为正异常(δEu/Eu*为～1.27).全岩40Ar/39Ar年龄268±5Ma,Rb-Sr年龄248±12Ma,K-Ar年龄254.5Ma,属中晚二叠世.矿体呈脉状、网脉状;围岩蚀变为绿帘石化、青盘岩化和黄铁矿化.铜品位1%～5%,主要工业矿物为辉铜矿、斑铜矿.矿石富含Ag(5.35～240μg/g)、Pb(0.01%～0.16%)、Zn(0.26%～2.40%)、Au(0.02～0.16μg/g).矿石矿物S同位素δ34S为-6.0‰～5.81‰,平均-0.28‰;辉铜矿、斑铜矿和孔雀石的207Pb/204Pb为15.46～15.77,206Pb/204Pb为18.01～18.42,属造山带与地幔Pb之间;矿石矿物包裹体的818O-2.54‰～-8.11‰,δDH2O-68.9‰～-98.8‰,属岩浆水与大气降水之混合.矿石矿物的(87Sr/86Sr)i为0.70596,(143Nd/146 Nd)i为0.512403,εNd(t)为+1.5,其Sr-Nd同位素组成及同位素年龄与合矿埃达克质石英钠长斑岩一致.含矿埃达克质石英钠长斑岩形成于后碰撞阶段,属由碰撞、挤压向伸展、拉张转变的构造动力学格架转折期.埃达克岩浆的较高温度、压力、富挥发分、较高氧逸度和岩浆快速上升,可能是其成矿的重要控制因素.