粤北棉花坑铀矿床热液蚀变与物质迁移研究

本文以粤北长江铀矿区棉花坑铀矿床的横向矿化蚀变剖面为研究对象,系统研究了代表性新鲜花岗岩、蚀变岩和矿石的主量、微量以及稀土元素地球化学特征,运用质量平衡计算方法探讨了各蚀变带组分的迁移规律,以期解决成矿物质来源、成矿流体来源及其性质等问题。结果表明,该矿化蚀变剖面具有明显的水平分带特征,可分为新鲜花岗岩带(Ⅴ带)、远矿碱交代蚀变带(Ⅳ带)、近矿绿泥石化蚀变带(Ⅲ带)、矿旁水云母化蚀变带(Ⅱ带)和矿化中心赤铁矿化蚀变带(Ⅰ带)。从侧缘碱交代带→矿化中心带,Si O2的带入率(0. 27%→0. 21%→0. 50%→0. 70%)整体上与U的带入率(4. 73%→8. 07%→39. 26%→98. 29%)呈正比,K+与Na+相互排斥呈现"钾钠不相容"现象,Mg O与Mn O呈现出"此消彼长"的迁移特征,是对流平衡迁移方式的表现。Th、Pb、Cs、Mo、As元素在矿化中心带的带入率最大,Ba、Sr、Co、V元素在矿化中心带迁出率最小,这对铀成矿(铀矿化)具有很好的指示作用。根据各蚀变带元素的含量、比值及迁移特征,结合前人的研究成果,认为矿床的成矿物质主要来源于赋矿围岩长江岩体,成矿流体在成分上富含挥发分和矿化剂(CO_2、F、H_2O等)、碱金属元素(K、Cs、Rb)和重稀土元素,性质上具相对高的氧逸度,其来源是地幔流体与经历了深循环大气降水的混合成因流体。挥发分和矿化剂(CO_2、F、H_2O等)的带入是矿床重要的矿质迁移机制,CO2的逸出伴随着氧化向还原过渡的环境是矿床重要的矿质沉淀机制。     

胶东谢家沟金矿热液蚀变作用过程的元素迁移规律

谢家沟金矿床位于胶西北焦家断裂带和招平断裂带之间。通过详细的野外地质观测与室内研究,查明了谢家沟金矿床的蚀变类型及空间分带,系统采集不同蚀变类型的岩石样品,进行岩石元素地球化学分析,运用Isocon方法分析探讨了热液蚀变过程中的元素迁移规律及其对成矿流体性质、矿质沉淀的制约。蚀变从中心到两侧分别为含陡立石英脉的黄铁绢英岩化、黄铁绢英岩化、钾长石化;从早到晚依次为钾长石化、黄铁绢英岩化、含陡立石英脉的黄铁绢英岩化。钾长石化蚀变表现为钾长石和黑云母分别交代玲珑黑云母花岗岩中的斜长石和角闪石,K明显的迁入,Si轻微迁入,Ca、Mg为迁出,Fe轻微迁出。黄铁绢英岩化蚀变叠加于钾长石化蚀变之上,主要表现为斜长石、钾长石、黑云母等矿物在含H+、HS-溶液中失稳,被绢云母、石英替代,Fe、Mg、Ca为迁入,K、Na、Si表现为元素迁出。从钾长石化阶段到黄铁绢英岩化阶段,流体从碱性转变为酸性; Au迁移形式也逐渐由氯的络合物转化为硫氢络合物。随着成矿流体的不断演化,成矿流体与围岩不断反应,含矿热液化学性质不断变化促进了金的沉淀。     

川西冕宁-德昌稀土矿带霓长岩的地球化学特征及地质意义

霓长岩化作用是指碳酸岩(或碱性岩)流体对围岩的交代蚀变,它是碳酸岩型稀土(REE)矿床常见的蚀变类型,其所形成的岩石即为霓长岩。对霓长岩的深入研究可以鉴别碳酸岩体的存在,厘定碳酸岩岩浆(或流体)的地球化学性质及源区特征,这对于找寻碳酸岩相关的矿产资源(尤其是REE)以及剖析矿床成因机制有着重要的地质意义。川西冕宁-德昌稀土矿带是中国最重要的轻稀土矿带之一,包括牦牛坪超大型、大陆槽大型、木落寨和里庄中小型REE矿床以及一系列矿点。REE矿化与碳酸岩-碱性岩杂岩体密切相关,受一系列新生代走滑断裂的控制。该矿带广泛发育霓长岩化蚀变带,尤以大陆槽及里庄矿床为显著。岩相学分析表明,大陆槽和里庄霓长岩中的矿物多呈他形粒状结构,主要由长石、黑云母、霓辉石以及少量副矿物组成;主微量元素分析表明,霓长岩的碱质(K_2O+Na_2O)、MgO、Fe_2O_3T含量较高,且富集REE、Sr、Ba等微量元素;电子探针分析表明,霓长岩中的霓辉石Fe OT含量较高,长石Na_2O及K_2O含量较高,Ca O含量极低。An-Ab-Or三角图解显示长石主要为透长石和钠长石,属碱性长石系列;黑云母的地球化学成分图解表明云母的成因类型为交代型且具有相对富镁、贫铁等特征,属镁质黑云母。霓长岩化作用的交代流体含有较高的CO_2组分,且富含碱质、Mg、Fe及REE、Sr、Ba等元素。对比霓长岩与原岩的主微量元素发现:相比于正长岩原岩,在主量元素中,霓长岩的Fe、Mg、Ca等元素含量增加,Si、Al等元素含量降低;微量元素中,霓长岩的REE及Sr、Ba等元素显著增加。这意味着交代流体含有的Fe_2O_3T、MgO、CaO等组分在霓长岩化过程中被带进了围岩,而SiO_2和Al_2O_3等从围岩中被逐出。大陆槽及里庄矿区发育的角砾岩指示了矿区曾经历过频繁的角砾岩化事件,这提高了霓长岩作用的强度,并且为矿脉的穿插及REE矿物的沉淀提供了空间。在霓长岩化过程中,流体-围岩的组分交换反复发生,这削弱了REE络合物的稳定性,伴随多期次的热液活动及构造事件,最终完成REE活化→迁移→沉淀的过程。     

与A型花岗岩有关锡矿的云英岩化蚀变矿化地球化学:以新疆卡姆斯特和干梁子矿床为例

新疆准噶尔盆地东部卡拉麦里地区发育我国典型的A型花岗岩型锡矿.通过对该区卡姆斯特和干梁子两个锡矿4个矿化蚀变带的岩相学及地球化学研究,发现矿体和致矿岩体是同源岩浆演化的结果,矿体是岩浆分异演化末期向流体演化过程中形成的.矿床的蚀变分带模式可分为两种:（1）（红色）细粒黑云母花岗岩→云英岩化细粒花岗岩→含锡石英脉;（2）细粒黑云母花岗岩→含锡云英岩→含锡石英脉.其蚀变带中岩石的地球化学组分总体迁移规律为:SiO₂迁入,Na₂O、K₂O迁出,Fe₂O₃总体表现为迁入,Th/U值不断降低,表明硅化和碱交代作用贯穿整个成矿过程,成矿环境由碱性向酸性变化,并伴随氧逸度的升高.F、Cl、W、Cu、Bi、In、Pb、Rb、Nb、Ta等元素与成矿元素Sn的迁移、富集和沉淀密切相关,其中F和Cl是迁移过程中最活跃的组分,是Sn元素最大的"搬运工",Sn元素的富集与W、Cu、Bi、In等元素迁移呈正相关,反映流体作用与Sn成矿密切相伴,而与Pb、Rb、Nb、Ta等元素的迁移呈负相关,反映致矿岩体自身元素的稀释和带出,Sn的富集和成矿是在岩浆向流体演化过程中完成的.      

安徽铜陵桂花冲斑岩铜矿围岩蚀变与矿化作用

桂花冲铜矿为安徽铜陵地区新发现的斑岩型铜矿,斑岩体为准铝质高钾钙碱性的花岗闪长斑岩。围岩蚀变与矿化作用是斑岩型矿床成矿过程研究的一项重要内容,对蚀变带岩石开展元素地球化学成分的迁移研究,是分析热液交代蚀变过程的基础。桂花冲铜矿区内围岩蚀变作用比较强烈,蚀变类型主要有钾化、绢云母化、硅化、绿泥石化和碳酸盐化等。蚀变分带比较明显,由内向外依次为钾化带、绢英岩化带和青磐岩化带,矿体主要产于绢英岩化带内。矿化蚀变自早至晚划分为钾长石、石英-绢云母、石英多金属硫化物和碳酸盐4个阶段。蚀变带物质组分迁移结果表明,在蚀变过程中,岩石的主量元素除TiO₂、MnO、MgO外,其他元素迁移量发生了明显改变;微量元素除Sr和Cu外,迁移量变化较小,稀土元素在矿化强的部位亏损,在矿化弱的地带富集。岩体及蚀变带岩石稀土元素球粒陨石标准化配分模式一致,说明岩体与蚀变岩石经历了相同来源流体的交代蚀变,是岩浆流体连续作用的结果。     

甘肃龙首山成矿带新水井铀(钍)矿床元素迁移规律及成矿作用过程研究

新水井铀(钍)矿床位于甘肃省龙首山成矿带,是碱交代型铀矿床的典型代表,其矿体完全产于钠交代蚀变花岗岩中,成矿过程可划分为钠交代蚀变、铀钍矿化和成矿后3个主要阶段。文章对该矿床花岗岩原岩、蚀变岩及矿石开展了系统主微量元素分析,采用Grant等浓度线法探讨了钠交代蚀变和铀钍矿化阶段的元素迁移规律,结果表明:钠交代蚀变阶段为富含Na、Ca、过渡族元素(Sc、V、Cr、Co、Ni)、U、Th及CO2、H2O等挥发分的复杂流体,钠交代过程中原岩中的大离子亲石元素(Rb、Ba)和部分轻稀土元素(LREE)不同程度带出;而铀钍成矿阶段成矿流体则富集重稀土元素(HREE)、U、Th、PO43-等成分,CO2等挥发分大量逸出。结合前人研究,认为新水井矿床成矿流体可能来自地幔流体和大气降水热液的混合;等挥发分CO2的逸出是新水井矿床最重要的矿质沉淀机制,导致了铀钍矿物和磷酸盐矿物(磷灰石)的共沉淀,而磷灰石的沉淀又促进了以磷酸盐形式搬运的Th元素的沉淀。     

赣南富城岩体黑云母及其蚀变产物绿泥石的矿物化学研究——对铀成矿的指示意义

富城花岗岩体位于赣南会昌盆地东侧,该岩体西部与橄榄玄粗岩系列火山岩接触,河草坑铀矿田就产于该花岗岩体的内外接触带中。在矿区外围花岗岩中发育大面积的蚀变带,其中的黑云母普遍蚀变为绿泥石。为了深入探讨蚀变与铀矿化的关系,文章运用电子探针技术对该蚀变带的黑云母及其蚀变产物绿泥石进行了矿物化学研究。结果表明,黑云母大部分属铁叶云母,估算出富城花岗岩岩浆的氧逸度lg(f O2)值约为-15.0~-14.3,氧逸度较低,源岩为还原性较强的岩石,有利于铀预富集于源区中;富城产铀花岗岩中黑云母的w(F)高达1.41%~2.01%,表明花岗质岩浆富F,而富F岩浆中U溶解度高,可能是富城岩体富铀的重要原因之一。黑云母被绿泥石交代后呈黑云母假象,绿泥石矿物化学分析结果表明,绿泥石以鲕绿泥石和蠕绿泥石为主,属于富铁的绿泥石,主要形成于还原环境;绿泥石的形成温度介于246~307℃之间,平均276℃。全岩U、Th含量分析结果表明,上部"红化"蚀变层中的w(U)(3.5×10-6~9.4×10-6,平均6.6×10-6)明显低于下部"绿色"蚀变层(7.7×10-6~23.1×10-6,平均13.9×10-6),而"红化"蚀变层与"绿色"蚀变层的Th含量相似,w(Th)平均值分别为35.7×10-6和36.5×10-6。矿前期的带状面型"绿色"蚀变层活化了矿物晶格中的结构铀,后期高氧逸度的流体萃取"绿色"蚀变层中已经活化了的铀而形成含铀热液,经迁移在还原带附近沉淀成矿。Th的价态(正四价)难以随这种氧化还原条件的改变而改变,因此未参与流体成矿过程。     

6122铀矿床蚀变岩中的物质迁移变化

应用水热蚀变过程中不活动元素确定蚀变岩质量变化的方法，对6122铀矿床不同标高蚀变岩的物质组分迁移变化进行了定量计算，探讨了围岩蚀变垂直分带性和成矿流体性质。研究表明，6122铀矿床矿化围岩蚀变过程中TiO2为不活动组分；围岩蚀变垂直分带上存在“土酸下碱”的特征；成矿流体为富含Na^ 、P的碱性流体。     

胶东焦家金矿床热液蚀变作用

胶东作为中国最重要的金矿集区,区内大型-超大型金矿床集中产出,已探明金矿资源量占全国近1/3。其中,破碎带蚀变岩型金矿床是最重要的金矿床类型,占胶东已探明金矿资源量的90%以上,焦家金矿床是著名的"焦家式"破碎带蚀变岩型金矿的命名地,内发育大规模的绢英岩化蚀变带(宽20~200m)和钾化蚀变带(50~300m),蚀变岩型金矿体主要发育在焦家断裂带下盘的绢英岩化蚀变带中。本文通过详细的野外地质观测,查清了焦家金矿床蚀变类型及矿物组合特征,系统采集了不同蚀变类型的岩石样品,进行了岩石元素地球化学分析,运用质量平衡方法讨论了热液蚀变过程中元素迁移规律,初步探讨了焦家金矿床热液蚀变机理。其中,钾化蚀变是成矿前蚀变,钾化花岗岩常以团块状或角砾状残留于黄铁绢英岩和绢英岩内;黄铁绢英岩化和绢英岩化蚀变受焦家断裂及其下盘的次级断裂控制,其规模大小受断裂的规模控制;其中焦家主断裂下盘的绢英岩化蚀变带规模最大,一般宽10~200m;而次级断裂控制的绢英岩化蚀变带规模相对较小,一般以0.1~1m宽的脉状发育在钾化花岗岩内,指示绢英岩化蚀变晚于钾化蚀变。相对于黑云母花岗岩,不同蚀变带岩石普遍表现出高K2O、低Al2O3、CaO和Na2O,而不同蚀变岩石Si、Fe、Mg等元素各表现出不同特征。钾化带岩石表现为K2O的富集,而绢英岩带和黄铁绢英岩带岩石表现为MgO、Fe2O3增加的趋势。黑云母花岗岩发生钾化蚀变过程中,SiO2、K2O表现为明显的带入,指示在钾长石化过程中,流体为富硅的碱性氧化流体。在钾化花岗岩→黄铁绢英岩过程中,Fe2O3表现为明显的带入,可能是由于黑云母等暗色矿物的分解造成的;此外,亲硫元素(Au、Ag、As、Pb、Zn)均表现为带入,特别是成矿元素Au表现为明显的带入。结合本区金的来源可能部分为玲珑黑云母花岗岩,本研究认为钾化过程中的富硅碱性氧化流体通过交代蚀变反应使金从围岩中释放、成为高价态离子活化进入成矿流体,即分散还原态的金(Au0)被活化为氧化态(Au+、Au3+)以AuH3SiO4形式随热液迁移。在绢英岩化过程中,热液中的SiO2等组分损失,引起热液中的AuH3SiO4稳定性降低,造成AuH3SiO4分解,Fe2+、Fe3+被消耗形成黄铁矿,导致金大量沉淀和聚集沉淀,此时完成了金由活化→迁移→沉淀富集成矿。     

豫西前河金矿热液蚀变地球化学研究

含矿热液在迁移过程中与围岩发生了广泛的流体-岩石反应而引起热液蚀变.前河金矿区内主要的热液蚀变有钾长石化、青磐岩化、绢云母化、硅化、黄铁矿化、碳酸盐化和萤石化等7种类型;划分了6个蚀变-成矿阶段,即黑云母-钾长石阶段→青磐岩阶段→绢英岩阶段→黄铁矿-石英阶段→石英-黄铁矿阶段→碳酸盐-卤化物阶段,以及外、中、内3个蚀变带.5种典型蚀变岩的常量和微量元素分析表明,绢英岩化蚀变中,Si、K大量迁入,Pb含量大大增加,在∑REE有所降低的情况下HREE有所富集:δ Eu和δ Ce在各蚀变阶段均呈现负异常:这些现象可能是导致金沉淀的元素地球化学响应.各阶段成矿流体-岩石的交代特点在绿泥石单矿物的矿物化学成分变化上也有所反映.     

新疆东天山小白石头钨(钼)矿辉钼矿Re-Os同位素年龄及成矿时代

小白石头钨(钼)矿床位于新疆东天山造山带中的中天山地块南缘,该矿床是一个由黑云母花岗岩和花岗闪长岩侵入中元古界卡瓦布拉格群形成的矽卡岩型钨(钼)矿床。辉钼矿作为其主要的矿石矿物之一,呈不同产出状态分布于花岗闪长岩、黑云母花岗岩、矽卡岩和石英脉中。目前,对于小白石头钨(钼)矿成矿时代尚有争议,特别是与花岗闪长岩有关的辉钼矿化形成时代缺乏精确的限定。本文选取与花岗闪长岩有关的不同产状辉钼矿进行Re-Os同位素定年,获得Re-Os加权平均模式年龄为245. 0±1. 7Ma,Re-Os等时线年龄为245. 5±4. 3Ma。准确的Re-Os同位素定年限定小白石头钨(钼)矿床的成矿年龄和花岗闪长岩的侵位年龄为245Ma左右,为矿床模型建立和找矿方向确定提供了关键依据,同时也为东天山区域成矿规律总结提供了重要的年代学证据,并指出新疆东天山—甘肃北山地区存在一条找矿潜力巨大的三叠纪钨钼成矿带。     

河北武安坦岭多斑斜长斑岩中基质矿物特征及其研究意义

河北武安坦岭斜长斑岩具有多斑斑状结构,基质为显微晶质结构。岩相学观察表明,斜长石斑晶有一个宽广的核部和一个宽度可变的条纹长石反应边,个别核部包含有角闪石、黑云母等矿物。基质矿物主要由蓝透闪石、条纹长石(An0Ab8.4Or91.5～An0.1Ab57.3Or42.6)、石英、钾长石(An0.3Ab5.9Or93.7～An0.3Ab4.7Or95.2)、钠长石(An0.2Ab98.3Or1.5～An0.1Ab99.2Or0.7)、磁铁矿、赤铁矿、钛铁矿、磷灰石、榍石和锆石等11种矿物组成。角闪石温压计计算结果得出,基质角闪石核部的结晶压力高于边部,核部为34.05 MPa,对应的结晶温度为660.35℃,结晶深度为1.29km;边部的结晶压力为24.32MPa,结晶温度为598.32℃,结晶深度为0.92km;而斜长石斑晶中的角闪石形成时压力为159.51～178.19MPa,温度为817.68～819.79℃,对应的形成深度为6.03～6.73km。基质角闪石在Al2O3-TiO2图上落在壳源区,而斑晶中的角闪石和黑云母都落在壳幔混合区。斜长石、条纹长石、磁铁矿和磷灰石的微量和稀土元素测试数据显示,其都具有相对富集LILE、亏损HFSE的特点,暗示了基质矿物的形成有流体参与。ICT三维扫描结果显示,斜长斑岩基质中的孔隙体积含量约为3.428%,铁质体积含量为4.371%,且铁氧化物和孔隙具弱连通性。通过讨论分析,笔者得出:(1)坦岭斜长斑岩中斜长石斑晶具有明显的交代结构,且晶体本身没有明显熔蚀现象,这些特征表明大量的斜长石斑晶快速上升,即"冻结岩浆房"的活化机制与流体密切相关;(2)斜长斑岩中基质矿物有十一种,且矿物类型复杂,不符合平衡系统矿物相律,应属于流体晶矿物组合;(3)坦岭斜长斑岩的基质"岩浆"可能是一种富Fe、K、P、Si、Na等元素的熔体-流体流;(4)多斑斜长斑岩的形成经历了(1)深度6～7km的深部岩浆房形成斜长石堆晶→(2)富Fe、K、P、Si、Na等元素的熔体-流体流加入深部岩浆房,冻结岩浆房活化→(3)由于流体超压,含大量斜长石斑晶的熔体-流体在地壳浅部(0.9～1.2km)呈小岩株状或岩脉状就位。多斑斜长斑岩为深部找矿提供了有力的线索。     

Mineralogy and Mineral Chemistry of the Cretaceous Duolong Gold‐Rich Porphyry Copper Deposit in the Bangongco Arc,Northern Tibet

The Early Cretaceous Duolong gold‐rich porphyry copper deposit is a newly discovered deposit with proven 5.38 Mt Cu resources of 0.72% Cu and 41 t gold of 0.23 g t^?1 in northern Tibet. Granodiorite porphyry and quartz diorite porphyrite are the main ore‐bearing porphyries. A wide range of hydrothermal alteration associated with these porphyries is divided into potassic, argillic and propylitic zones from the ore‐bearing porphyry center outward and upward. In the hydrothermal alteration zones, secondary albite (91.5–99.7% Ab) occurs along the rim of plagioclase phenocryst and fissures. Secondary K‐feldspar (75.1–96.9% Or) replaces plagioclase phenocryst and matrix or occurs in veinlets. Biotite occurs mainly as matrix and veinlet in addition to phenocryst in the potassic zone. The biotite are Mg‐rich and formed under a highly oxidized condition at temperatures ranging from 400°C to 430°C. All the biotites are absent in F, and have high Cl content (0.19–0.26%), with log (X_Cl/X_OH) values of ?2.74 to ?2.88 and IV (Cl) values of ?3.48 to ?3.35, suggesting a significant role of chloride complexes (CuCl₂^‐ and AuCl₂^‐) in transporting and precipitating copper and gold. Chlorites are present in all alteration zones and correspond mainly to pycnochlorite. They have similar Fe/(Fe+Mg), Mn/(Mn+Mg) ratios, and a formation temperature range of 280–360°C. However, the formation temperature of chlorite in the quartz‐gypsum‐carbonate‐chlorite vein is between 190°C and 220°C, indicating that it may have resulted from a later stage of hydrothermal activity. Fe³⁺/Fe²⁺ ratios of chlorites have negative correlation with Al^IV, suggesting oxygen fugacity of fluids increases with decreasing temperature. Apatite mineral inclusions in the biotite phenocrysts show high SO₃ content (0.44–0.82%) and high Cl content (1–1.37%), indicating the host magma had a high oxidation state and was enriched in S and Cl. The highest Cl content of apatite in the propylitic zone may have resulted from pressure decrease, and the lowest Cl content of apatite in the argillic zone may have been caused by a low Cl content in the fluids. The low concentration of SO₃ content in the hydrothermal apatite compared to the magmatic one may have resulted from the decrease of oxygen fugacity and S content in the hydrothermal fluid, which are caused by the abundant precipitation of magnetite.     

Formation Process of Zircon Associated with REE‐Fluorocarbonate and Niobium Minerals in the Nechalacho REE Deposit,Thor Lake,Canada

The two drill holes, which penetrated sub‐horizontal rare earth element (REE) ore units at the Nechalacho REE in the Proterozoic Thor Lake syenite, Canada, were studied in order to clarify the enrichment mechanism of the high‐field‐strength elements (HFSE: Zr, Nb and REE). The REE ore units occur in the albitized and potassic altered miaskitic syenite. Zircon is the most common REE mineral in the REE ore units, and is divided into five types as follows: Type‐1 zircon occurs as discrete grains in phlogopite, and has a chemical character similar to igneous zircon. Type‐2 zircon consists of a porous HREE‐rich core and LREE–Nb–F‐rich rim. Enrichment of F in the rim of type‐2 zircon suggests that F was related to the enrichment of HFSE. The core of type‐2 zircon is regarded to be magmatic and the rim to be hydrothermal in origin. Type‐3 zircon is characterized by euhedral to anhedral crystals, which occur in a complex intergrowth with REE fluorocarbonates. Type‐3 zircon has high REE, Nb and F contents. Type‐4 zircon consists of porous‐core and ‐rim, but their chemical compositions are similar to each other. This zircon is a subhedral crystal rimmed by fergusonite. Type‐5 zircon is characterized by smaller, porous and subhedral to anhedral crystals. The interstices between small zircon grains are filled by fergusonite. Type‐4 and type‐5 zircon grains have low REE, Nb and F contents. Type‐1 zircon is only included in one unit, which is less hydrothermally altered and mineralized. Type‐2 and type‐3 zircon grains mainly occur in the shallow units, while those of type‐4 and type‐5 are found in the deep units. The deep units have high HFSE contents and strongly altered mineral textures (type‐4 and type‐5) compared to the shallow units. Occurrences of these five types of zircon are different according to the depth and degree of the hydrothermal alteration by solutions rich in F and CO₃, which permit a model for the evolution of the zircon crystallization in the Nechalacho REE deposit as follows: (i) type‐1 (discrete magmatic zircon) is formed in miaskitic syenite. (ii) LREE–Nb–F‐rich hydrothermal zircon formed around HREE‐rich magmatic zircon (type‐2). (iii) type‐3 zircon crystallized through the F and CO₃‐rich hydrothermal alteration of type‐2 zircon which formed the complex intergrowth with REE fluorocarbonates; (iv) the CO₃‐rich hydrothermal fluid corroded type‐3, forming REE–Nb‐poor zircon (type‐4). Niobium and REE were no longer stable in the zircon structure and crystallized as fergusonite around the REE–Nb‐leached zircon (type‐4); (v) type‐5 zircon is formed by the more CO₃‐rich hydrothermal alteration of type‐4 zircon, suggested by the fact that type‐4 and type‐5 zircon grains are often included in ankerite. Type‐3 to type‐5 zircon grains at the Nechalacho REE deposit were continuously formed by leaching and/or dissolution of type‐2 zircon in the presence of F‐ and/or CO₃‐rich hydrothermal fluid. These mineral associations indicate that three representative hydrothermal stages were present and related to HFSE enrichment in the Nechalacho REE deposit: (i) F‐rich hydrothermal stage caused the crystallization of REE–Nb‐rich zircon (type‐2 rim and type‐3), with abundant formation of phlogopite and fluorite; (ii) F‐ and CO₃‐rich hydrothermal stage led to the replacement of a part of REE–Nb–F‐rich zircon by REE fluorocarbonate; and (iii) CO₃‐rich hydrothermal stage resulted in crystallization of the REE–Nb–F‐poor zircon and fergusonite, with ankerite. REE and Nb in hydrothermal fluid at the Nechalacho REE deposit were finally concentrated into fergusonite by way of REE–Nb–F‐rich zircon in the hydrothermally altered units.     

德兴铜厂斑岩铜(钼金)矿床蚀变-矿化系统流体演化:H-O同位素制约

江西铜厂斑岩铜(钼金)矿床是德兴斑岩矿集区最大的矿床.文章根据铜厂矿床发育的钾硅酸盐化、绢英岩化、青磐岩化蚀变组合特征,和已厘定的铜厂矿床脉体类型,选取代表不同蚀变矿化阶段的石英、黑云母、绢云母及绿泥石等,进行单矿物的H、O同位素测试.石英和黑云母单矿物O同位素,与石英、黑云母平衡流体的δ 18O 值和δD值联合示踪结果显示,铜厂矿床早期A脉(不规则疙瘩状A1脉、石英-黑云母A2脉和石英-磁铁矿A4脉)和中期B脉(矿物组合为石英-黄铁矿+黄铜矿±辉钼矿±斑铜矿)形成时,成矿热液均为岩浆流体来源,但B脉可能混入了少量大气降水;晚期低温D脉和碳酸岩脉(180～200℃)的成矿热液全部为大气降水来源.斑晶黑云母平衡水的δ 18O和δD值变化范围较大表明,黑云母形成时的热液系统主要为岩浆水,局部受区域变质水和大气降水的混染,也可能与少量黑云母斑晶受到后期绿泥石化、水云母化蚀变有关.绿泥石蚀变主要由岩浆流体作用形成,但混入了一些大气降水,导致其δ 18O值少量降低.绢云母平衡的水的δ18O值和δD值(4.6‰和-19.4‰)表明,绢云母是大气降水与千枚岩共同作用的结果.总体来说,铜厂矿床钾硅酸盐化、绿泥石化蚀变,以及钾硅酸盐化阶段形成的A脉和B脉,均由岩浆流体作用引起,大气降水在绿泥石化阶段进入蚀变-矿化系统,而绢云母化、晚期低温D脉和碳酸盐脉均是大气降水作用的产物.     

粤北石角围花岗岩型铀矿床沥青铀矿LA-ICP-MS原位U-Pb定年研究

石角围花岗岩型铀矿床位于粤北下庄铀矿田东部,沥青铀矿是矿床的主要矿石矿物,也是厘定成矿年龄的理想对象。前人采用同位素稀释法(ID-TIMS)和电子探针U-Th-totalPb化学定年法获得的成矿年龄为38～138Ma,但前人年龄变化范围大,可靠性有待考究,难以有效约束矿床的成矿时代。本文利用LA-ICP-MS原位微区分析技术,对石角围矿床矿石中沥青铀矿开展了原位U-Pb定年。研究表明:沥青铀矿的206Pb/238U年龄为52. 46～56. 89Ma,加权平均年龄为54. 68±0. 53Ma(MSWD=1. 19,n=18)。本次沥青铀矿原位U-Pb定年与前人相比更好地避免了矿物包裹体、后期次生变化、显微裂隙等因素的影响,获得的沥青铀矿原位U-Pb同位素年龄代表矿床的成矿年龄。本研究获得的石角围矿床成矿年龄(～55Ma)与华南花岗岩型铀矿床主成矿期(～50Ma)相一致,指示石角围矿床铀成矿作用与华南岩石圈局部伸展作用下的断裂构造活动密切相关。     

Hydrothermal alteration processes in the giant Dahutang tungsten deposit,South China: Implications from litho-geochemistry and mass balance calculation

The giant Dahutang tungsten (W) deposit has a total reserve of more than 1.31 Mt WO₃. Veinlet-disseminated scheelite and vein type wolframite mineralization are developed in this deposit, which are related to Late Mesozoic biotite granite. Four major types of alterations, which include albitization, potassic-alteration, and greisenization, and overprinted silicification developed in contact zone. The mass balance calculate of the four alteration types were used to further understanding of the mineralization process. The fresh porphyritic biotite granite has high Nb, Ta, and W, but low Ca and Sr while the Jiuling granodiorite has high Ca and Sr, but low Nb, Ta, and W concentrations. The altered porphyritic biotite granite indicated that the Nb, Ta, and W were leached out from the fresh porphyritic biotite granite, especially by sodic alteration. The low Ca and Sr contents of the altered Neoproterozoic Jiuling granodiorite indicate that Ca and Sr had been leached out from the fresh granodiorite by the fluid from Mesozoic porphyritic biotite granites. The metal W of the Dahutang deposit was mainly derived from the fluid exsolution from the melt and alteration of W-bearing granites. This study of alteration presents a new hydrothermal circulation model to understand tungsten mineralization in the Dahutang deposit.     

基于红外光谱技术研究内蒙古乌奴格吐山斑岩铜钼矿蚀变和矿化特征

近年来,红外光谱技术在矿物学研究、地质勘探与找矿等方面发挥了重要作用。本文通过测量与分析内蒙古乌奴格吐山斑岩铜钼矿Z661钻孔岩心短波红外和热红外波段的光谱,快速厘定了该矿床的蚀变矿物类型及组合特征。结果表明:乌奴格吐山斑岩铜钼矿床蚀变矿物主要有石英、钾长石、绢云母、伊利石、高岭石和蒙脱石等。蚀变矿物组合在空间上呈现出明显的分带性,其中石英+伊利石+绢云母+钾长石与矿化关系最为密切,可作为找矿的标型矿物组合;结合钻孔Cu、Mo矿化分布特征,发现绢(白云母)2200nm处吸收峰位置的波长偏移与成矿中心距离有关,波长变小,更趋向于成矿中心;且伊利石结晶度(IC)越大,结晶度较高,矿化程度强。因而,该技术方法通过蚀变矿物波谱,能够快速圈定斑岩铜钼矿蚀变矿物组合,进而提高勘查效率。     

汞同位素地球化学研究及其在矿床学中的应用进展

汞作为一种重要的成矿元素,广泛分布于不同地质体中,并参与成岩成矿作用。随着质谱技术的飞跃发展,汞同位素地球化学研究取得引人瞩目的进展。汞同位素被广泛地应用于示踪地球表生生物地球化学过程及汞污染等。近年来,汞同位素又被应用于揭示行星的演化过程、识别地质历史时期大火成岩省及示踪矿床成矿物质来源等方面。本文在前人研究的基础上,对不同地质储库汞同位素组成进行了系统总结。陨石、岩浆岩、变质岩、沉积岩、火山气体等地质储库汞同位素组成变化较大,部分样品还显示非质量分馏信息。本文着重阐述了低温热液矿床(现代热泉、汞矿床、铅锌矿床、锑矿床、金矿床)汞的赋存状态及同位素组成特征,构筑了汞同位素体系的基本格架。结合最新的研究成果,较全面地总结了矿床成矿过程中可能会发生的汞同位素分馏机制。热液矿床中汞同位素的质量分馏可能由流体挥发或者沸腾作用、冷凝作用、氧化还原反应、硫化物沉淀等引起。岩矿石中汞同位素的非质量分馏信息可能是地质历史时期汞光化学作用的产物,或者是继承某一特定的源岩信息所致。因此,未来汞同位素在示踪低温热液矿床的成矿物质来源、刻画成矿流体演化过程方面具有较大的应用潜力。     

Genesis of the Katugin rare-metal ore deposit: Magmatism versus metasomatism

Arguments in favor of magmatic or metasomatic genesis of the Katugin rare-metal ore deposit are discussed. The geological and mineralogical features of the deposit confirm its magmatic origin: (1) the shape of the ore-bearing massif and location of various types of granites (biotite, biotite–amphibole, amphibole, and amphibole–aegirine); (2) the geochemical properties of the massif rocks corresponding to A type granite (high alkali content (up to 12.3% Na₂O + K₂O), extremely high FeO/MgO ratio (f = 0.96–1.00), very high content of the most incoherent elements (Rb, Li, Y, Zr, Hf, Ta, Nb, Th, U, Zn, Ga, and REE) and F, and low concentrations of Ca, Mg, Al, P, Ba, and Sr); (3) Fe–F-rich rock-forming minerals; (4) no previously proposed metasomatic zoning and regular replacement of rock-forming minerals corresponding to infiltration fronts of metasomatism. The similar ages of the barren (2066 ± 6 Ma) and ore-bearing (2055 ± 7 Ma) granites along with the features of the ore mineralization speak in favor of the origin of the ore at the magmatic stage of the massif’s evolution. The nature of the ore occurrence and the relationships between the ore minerals support their crystallization from F-rich aluminosilicate melt and also under melt liquation into aluminosilicate and fluoride (and/or aluminofluoride) fractions.