【作者】 陈辉；

【导师】 倪培；

【作者基本信息】 南京大学 ， 矿物学、岩石学、矿床学， 2014， 博士

【摘要】 平水铜矿和建德铜矿均位于钦杭成矿带北东段的浙西北地区。平水铜矿发育有铜矿体和金矿体。铜矿体赋矿地层为新元古代双溪坞群平水组火山岩;矿体直接产出于平水组细碧角斑岩系内,呈层状或似层状产出,与细碧角斑岩的关系为整合关系;矿石矿物主要有黄铜矿、黄铁矿、闪锌矿和磁铁矿,矿石构造主要为典型的块状构造和条带状构造,并存在特征性的喷流沉积岩:铁碧玉、重晶石和石膏等;平水铜矿体具有矿石矿物和特征性矿物分带现象。平水铜矿体形成之后,平水地区经历了后期的变质变形作用,在铜矿体的下盘普遍发育韧性剪切带。近期全国危机矿山找矿项目在该剪切带发现了金矿体。金矿体的产状严格受到韧性剪切带控制。锆石U-Pb定年表明,平水组细碧岩成岩年龄为952 Ma,平水组角斑岩成岩年龄为954 Ma,西裘石英闪长岩形成年龄为909 Ma,均形成于新元古代。平水组细碧角斑岩属于双峰式火山岩系列;富Na2O,贫K2O,轻稀土富集,富集大离子亲石元素和亏损高场强元素,显示火山岩形成于岛弧环境;相对亏损的εNd(t)(3.52～7.57)和εHF(t)值(0.72～9.00)说明火山岩主要来自于亏损地幔,并在上升过程中可能受到少量地壳物质的混染。西裘石英闪长岩可能是幔源玄武岩浆分离结晶的产物。平水铜矿体伴生石英中的流体包裹体类型比较简单,主要是气液两相包裹体,按照成因可以分为2类:Ⅰ类原生的流体包裹体,其均一温度217～328℃,盐度从3.2～5.7 wt%NaC1 eqv,Ⅱ类次生的流体包裹体,其均一温度从148～189℃,盐度从2.8～4.6 wt%NaCl eqv,拉曼测试表明流体包裹体的气相成分为水;流体包裹体的均一温度、盐度和气相成分表明成矿流体主要为海水。平水铜矿体的矿石硫同位素在频率图上零值附近呈比较明显的塔式分布,说明其来源单一,可能主要来自于平水组火山岩。铜矿体中硫化物的铅同位素组成与平水组火山岩中长石铅的同位素组成一致,均位于地幔铅附近,说明平水铜矿体的铅同位素主要来源于平水组火山岩。地质证据,结合成矿流体和同位素证据表明,平水矿铜矿体是新元古代平水组岛弧火山岩赋矿的的火山成因块状硫化物矿床(VMS),成矿类型属于双峰式-铁镁质岩石容矿的系列,类似于诺兰达型VMS矿床。平水金矿体中的流体包裹体可以划分为以下两类包裹体:Ⅰ型H2O-Co2包裹体,Ⅰ型包裹体在室温下呈两相或三相(LH2O+LCO2±VCO2);Ⅱ型H2O包裹体;Ⅰ型包裹体常和Ⅱ型包裹体在同一视域中共存,显示出流体不混溶的岩相学特征;Ⅰ型包裹体最终均一至气相,均一温度为225～282℃,盐度为1.2～6.0 wt.%NaC1 eqv,而Ⅱ型包裹体均一至液相,均一温度为214～2710C,盐度为2.7～8.7 wt.%NaCl eqv。Ⅰ型包裹体与共存的Ⅱ型包裹体有相近均一温度,较大差异的盐度,不同的均一方式,表明主成矿期发生了流体不混溶作用。流体不混溶导致了成矿流体在运移过程强烈的相分离作用,因此可能造成金的沉淀和金矿体的形成。石英Rb-Sr同位素定年研究表明金矿体的成矿年龄为450 Ma。平水金矿体是加里东期造山事件的产物,为典型的造山型金矿。建德铜矿矿体多呈层状-似层状产于石炭系黄龙组地层中,矿体产状与地层产状一致,矿体主要为块状矿体和矽卡岩化矿体,受石炭系灰岩和泥盆系砂岩之间“硅钙面”控制。矿区侵入岩广泛分布,呈不规则岩枝、岩脉产出,主要为中酸性浅成—超浅成侵入体,按其穿插关系可分为早期花岗闪长斑岩和晚期花岗斑岩。矿体与早期花岗闪长斑岩有密切关系,赋存于花岗闪长斑岩外接触带。锆石定年数据显示建德铜矿的花岗闪长斑岩形成于晚侏罗世(大约161Ma)。地球化学数据显示,花岗闪长斑岩以钙碱性为特征,同时具有埃达克质岩石的特征,如高 LaN/YbN(18.5～35.9)比值,以及低 Y(5.38～7.83 ppm)和Yb(0.45～0.62 ppm)含量等;此外,花岗闪长斑岩缺乏Eu负异常,具有低含量的MgO(0.22～1.0 wt.%)含量和相对高的207Pb/204Pb比值(15.518～15.608)。这指示着花岗闪长斑岩可能是形成于加厚下地壳的部分熔融。同时,花岗闪长斑岩具有类“弧”岩浆的地球化学特征,类整体地球的εNd(t)值,高的初始87Sr/86Sr值(0.7078～0.7105),相对亏损的εHf(t)值(-0.6～+2.8)和1.0～1.2 Ga的Hf模式年龄。因此,花岗闪长斑岩可为新元古代洋陆俯冲作用形成的新生地壳在晚侏罗世发生部分熔融的产物。建德铜矿的硫化物石英中发育三类包裹体:包括Ⅰ型的富液相气液两相包裹体,Ⅱ型的富气相气液两相包裹体,以及Ⅲ型的含子晶包裹体;Ⅰ类富液相包裹体加热后均一到液相,均一温度分布范围主要集中在280～340℃,流体包裹体盐度0.63～8wt.%NaC1 eqv,Ⅱ类富气相包裹体加热均一到气相,均一温度289～324℃,盐度1.22～2.00 wt.%NaC1 eqv的低盐度范围,Ⅲ类含子晶包裹体加热均一到液相,均一温度范围与Ⅱ类包裹体基本相同,290～336℃,盐度则较高,31.87～38.16 wt.%NaC1 eqv。Ⅱ类与共存的Ⅲ类包裹体的均一温度相似,盐度相差很大,表明强烈的流体沸腾作用发生。流体强烈沸腾作用是造成建德铜矿成矿物质沉淀富集的原因。氢氧同位素显示成矿流体主要为岩浆流体。硫化物硫同位素研究显示,δ34S值的总变化范围是0.93‰～4.77‰之间,并且总体分布在零值附近呈塔式分布。这暗示着建德铜矿硫化物的硫主要来自于岩浆。建德花岗闪长斑岩体长石铅与矿石硫化物铅具有一致的同位素组成,同时指示着建德铜矿体的铅也来自于花岗闪长斑岩体。地质地球化学证据均指示了,建德铜矿属于与岩浆热液有关的矽卡岩型铜矿。更多还原

【Abstract】 The Pingshui deposit and Jiande deposit are both located in the Northwestern Zhejiang province,Qin-Hang metallogenic belt.The Pingshui deposit has copper and gold ore bodies.Copper ore bodies in the Pingshui deposit are layered,layer-like and lenticular.The principal metallic minerals include pyrite,chalcopyrite,sphalerite,tennantite,tetrahedrite and magnetite,with minor galena.Gangue minerals are quartz,sericite,chlorite,calcite,gypsum,barite and jaspilite.Gold ore bodies in the Pingshui deposit are strictly hosted in the ductile shear zone which occurs beneath the massive sulfide copper orebodies.Quartz lenticles in the ductile shear zone display a ribbon structure and show undulatory extinction.Ore minerals are native gold and minor pyrite.Zircon U-Pb dating show that the Pingshui volcanic and intrusive rocks were produced during the Neoproterozoic(ca.954-908Ma).Host rocks are a suit of bimodal volcanic rocks of the Neoproterozoic Pingshui Formation.Na2O-rich,K2O-poor,and preciously obtained depleted epsilon Nd and Hf isotopes of host rocks show that they were generated by partial melting of depleted mantle in the subuction zone.Homogenization temperatures of primary fluid inclusions are 217 and 328℃,and salinities of them are 3.2 to 5.7 weight percent equivalent NaCl,suggesting ore fluids are deeply circulated seawater in origin.The δ34S values of ores are-3.6‰to+3.4‰,indicating that the ore-forming materials are mainly leached from the Pingshui Formation volcanic rocks.Lead isotopes of ores and plagioclase from host rocks share similar ranges,implying they have the same lead sources.Thus,the Pingshui copper orebodies belongs to typical Neoproterozoic volcanogenic massive sulfide deposits.Gold ore bodies in the Pingshui deposit contains H2O-CO2 inclusions(type I)and coexisting aqueous inclusions(type Ⅱ)in the ore veins.Homogenization temperatures of type I and II inclusions from gold orebodies in Pingshui deposit show similar homogenization temperature ranges(225 to 282℃),but contrasting salinity values(1.2 to 6.0%wt.%NaCl equivalent and 2.7 to 8.7%wt.%NaCl equivalent).Fluid inclusion petrological observations and microthermometric results showed that ore fluids are low-salinity and CO2-rich.Moreover,fluid immiscibility probably extensively occurred during the gold mineralization stage.Quartz fluid inclusion Rb-Sr ages(ca.450 Ma)of the gold mineralization at Pingshui,suggesting that regional gold orebodies were formed in the early Paleozoic period.Geological,fluid inclusion and dating results show that the Pingshui gold ore bodies are typical orogenic in origin.The Jiande copper deposit is dominated by layer massive sulfide and skarn orebodies,which is hosted in the dolomite of the Huanglong Formation.The principal metallic minerals include pyrite,chalcopyrite,sphalerite,bornite,tetrahedrite and chalcocite.Gangue minerals mainly are quartz,sericite,chlorite,calcite,and garnet.The major structure is the Songkenwu syncline.The Yanshanian granitoid intrusions widely distributed.It is mainly composed of stage-Ⅰ granodiorite porphyries,and stage-II granite porphyry.The stage-I granodiorite porphyries most closely relationship with mineralization.Our results show that the Jiande granodiorite porphyries were produced during the Late Jurassic(ca.161 Ma).Geochemically,granodiorite porphyries are characterized by calc-alkaline and show some adakitic affinities with high LaN/YbN ratios and low Y and Yb contents.The absence of a negative Eu anomaly,extreme depletion in Y and Yb,relatively low MgO contents(0.22 to 1.00 wt%),and relatively high 207Pb/204Pb ratio,indicate that granodiorite porphyries were likely derived from the partial melting of thickened lower continental crust.In addition,the granodiorite porphyries show similar element characteristics to arc-derived igneous rocks with bulk Earth-like εNd(t)values and initial 87Sr/86Sr(0.7078-0.7105),relatively depleted εHf(t)values(-0.6 to+2.8),and Hf model ages of 1.0-1.2 Ga.During late Jurassic,partial melting of Neoproterozoic juvenile crust caused the formation of adakitic rocks(granodiorite porphyries)in the Jiande deposit.The primary inclusions of Jiande deposit are three types:Two-phase liquid-rich(type Ⅰ),two-phase vapor-rich(type Ⅱ),and halite-bearing(type Ⅲ)fluid inclusions can be observed in the hydrothermal quartz-sulfides veins.Type Ⅰ inclusions widespread occur in the Jiande deposit,and show homogenization temperatures of 220-377℃ and salinities of 0.63～8 wt.%NaCl equivalent.Type Ⅱ and type Ⅲ inclusions primarily coexist in the ore veins.The statistics on the homogenization temperatures of type Ⅱ and type Ⅲ reveal peaks at 289-324℃ and 290-336℃ respectively,whereas those on the salinities of fluid inclusions peak at 1.22-2.00 wt%NaCl and 31.87-38.16 wt%NaCl respectively.It indicates that fluid boiling process took place.Raman analysis of the fluid inclusions indicates that,in the gaseous phase,water vapor is dominant with small amount of CO2 and N2.Hydrogen and Oxygen isotopic compositions are also within the range of magmatic water.δ34S of sulfides was positive value with narrow range,close to zero in average,which point to a magmatic source.Pb isotopic compositions of the sulfides and plagioclases from granodiorite porphyries were obtained to indicate the same origin of ore and granodiorite porphyries.Geological and geochemistry results show that the Jiande copper ore body is typical skam copper deposit in origin.更多还原