胶东夏甸金矿床地球化学特征及其地质意义

为探讨夏甸金矿床不同元素的地球化学成矿行为,本次以夏甸金矿床外围花岗岩、构造碎裂岩和金矿石的主微量和稀土元素地球化学资料为依据,研究其化学成分、微量元素和稀土元素在不同岩矿石中丰减富集变化及成矿过程.在化学成分方面,招平断裂带碎裂岩中具有较高的SiO2、K2 O值,Fe2 O3、Na2 O、CaO降幅较多,反映了成矿阶段存在有普遍的硅化现象和钾化现象和铁质流失现象进入到热液成矿中;矿石化学成分中SiO2、Al2 O3和Fe2 O3具有较大幅度的增升和降低的双重变化特点,尤其是铁、钾、钙增加比例较高,指示与成矿过程中普遍发育的黄铁矿化相一致,矿石中K2 O含量比玲珑花岗岩平均含量高30％,则代表钾化的岩石更有利于金矿的沉淀.夏甸金矿区的围岩中Au元素含量普遍低于正常的玲珑花岗岩,但Ag、W等元素含量则普遍较高,是平均值的3～10倍,断裂带碎裂岩中亲硫(亲铜)元素Ag、Cu、Pb、Zn明显增高,尤其是Ag和Zn分别是玲珑花岗岩的2.79倍和2.09倍,说明亲硫(亲铜)元素与金矿成矿作用关系密切;亲铁元素Cr、Co、Ni、Mo、Au、Sn、W整体上呈递增状况,大离子亲石元素Li、Be、Rb、Zr、Nb、W、Sr、Ba、As大多呈亏损状态.矿石中Au、Ag、W、Cu等具有强烈的富集,其中Au富集了381.40倍,W富集了3961.23倍,Ag富集了254.16倍,Cu富集了116.19倍,而Bi、Mo、As、Pb、Zn等富集度相对稍低,在3～20倍之间.在围岩、破碎蚀变带和金矿石中,皆出现了非常高的W元素富集,展示了招平断裂带具有独特的成矿地球化学行为.夏甸矿区围岩、构造蚀变碎裂岩和金矿石中的ΣREE总量分别为78.82×10-6、27.15×10-6和102.43×10-6,LREE/HREE比值分别为19.3、8.46和12.66,金矿石中具有相对较高的ΣREE、LREE和HREE,说明在成矿过程中外来物质的加入改变了稀土元素的含量和比值,也是区分矿与非矿的重要地球化学标志.矿区围岩、构造蚀变碎裂岩和金矿石的δEu分别为1.88、1.49和0.83,Eu/Sm值分别为1.57、2.05和0.69,Ce/Yb值分别为25.15、5.33和12.86,轻重稀土内部分馏均较小,成矿环境为弱氧化环境,说明夏甸金矿在成矿过程中,稀土元素更多地是反映从流体体系中带入到成矿的过程,使矿石中稀土元素含量相对增加.结合光片鉴定结果,在金成矿过程中,先期形成的黄铁矿多呈碎粒状,裂纹十分发育,黄铜矿呈他形粒状充填于黄铁矿裂纹中与金共生,说明自然金是与黄铜矿是同期形成的,而晚于黄铁矿的形成时间.     

陕西凤县二里河铅锌矿床金属硫化物标型特征及地质意义

为寻找凤县二里河铅锌矿床成因类型证据,利用电子探针显微分析对二里河铅锌矿床金属硫化物进行分析,研究结果表明二里河铅锌矿床内黄铁矿含有两种不同类型:一种黄铁矿Co/Ni值为0.04～1.68,平均值为0.57,显示沉积成因(Co/Ni 1),矿物受后期热液熔蚀改造,形成时期较早;另一种黄铁矿Co/Ni值为0.98～7.67,平均值为2.46,显示热液成因(Co/Ni1),产于主矿体中,与铅锌成矿关系密切。闪锌矿中Fe的含量存在明显差异,划分为含铁闪锌矿(4%～8%)和闪锌矿(2%),推测可能是由于成矿过程的叠加改造所致,Zn/Cd比值为346～698,属中高温。矿物标型特征研究表明该矿床属于层控-岩浆热液型成因。     

金川超大型铜镍矿床钴的赋存状态与富集过程研究

金川矿床位于龙首山隆起带东段，是中国最大的岩浆镍钴（铂族元素）矿床。该矿床中最重要的金属硫化物组合是磁黄铁矿、镍黄铁矿和黄铜矿，仅局部含有微量的辉钴矿等独立钴矿物。全岩成矿元素分析显示：矿石中Co与S、Ni之间呈良好的正相关性，与As相关性较差，Co/Ni随硫化物含量的增加而降低。电子探针分析结果表明：镍黄铁矿中Co含量较高，其含量为0.32%～1.93%，平均为0.81%；磁黄铁矿和黄铜矿（方黄铜矿）中Co的含量较低，变化范围分别为0.02%～0.11%和0.01%～0.08%。元素面扫描结果表明：Co含量较高的部位与镍黄铁矿范围完全一致，说明Co主要赋存于镍黄铁矿中。金川矿床整体Co/Ni平均值为0.042，与全球典型橄榄岩相地幔Co/Ni值（0.055）相似，表明其岩浆源区主要为橄榄岩相。高程度的部分熔融可能是导致其母岩浆中Co绝对含量较高，但Co/Ni值相对较低的原因之一。硫化物熔离时，Co更倾向于进入硫化物；但相对于Ni，进入硫化物的Co较少，导致不同矿石类型之间S含量与Co/Ni值之间呈明显的负相关性。硫化物分离结晶作用进一步促使Co向镍黄铁矿中富集。     

贵州戈塘金矿含矿岩系元素地球化学特征

贵州戈塘金矿储量大、品位高、成矿环境特殊,具有“层位和岩溶不整合面”双重控矿的典型特征,含矿岩系中发育多种(硅化、构造)角砾岩、低温热液矿物(雄黄、雌黄、辉锑矿和萤石等)和围岩蚀变矿物组合,热液成矿期可分为主成矿期—黄铁矿阶段和成矿晚期—萤石阶段.通过对单矿物(黄铁矿和萤石)及含矿岩系各岩石(层位)微量元素含量、Co/Ni和Th/U值、稀土元素和硫同位素(黄铁矿、辉锑矿)组成特征的系统研究.初步认为戈塘金矿具有正常海水沉积特征,矿石层位形成于海相贫氧还原环境,初始成矿物质可能与峨眉山玄武岩浆活动有关,但后期深部物质为金的进—步富集成矿贡献也较为明显.     

拉拉铜矿黄铁矿微量元素地球化学特征及其成因意义

四川会理拉拉铜矿床是我国著名大型富铜矿床,针对该矿床中黄铁矿的微量元素、稀土元素地球化学分析表明:拉拉铜矿经历了早期火山喷发成岩成矿和晚期变质成岩成矿作用.条带状矿石中的黄铁矿Co/Ni比值集中于4.92～79.2之间,落入火山成因黄铁矿区,稀土元素分布具有Eu正异常和轻稀土富集的特征,反映矿床具有伴随河口群火山喷流沉积成岩过程的同生沉积成矿作用.脉状矿石中的黄铁矿Co/Ni比值集中于1.10～3.45,落在热液成因黄铁矿区,稀土元素较河口群岩石及其他典型块状硫化物矿床矿石稀土元素更加富集轻稀土元素,稀土含量变化范围更大,显著的负Eu异常,则又说明,矿床形成的主要成矿作用是伴随新元古代晋宁运动而发生的大规模的变质作用.     

玲珑金矿大开头矿区47号脉微量元素特征

选择胶东玲珑金矿典型矿体47号脉为研究对象,应用基岩地球化学方法,测试微量元素含量,研究微量元素与金的相关关系、计算微量元素的浓集系数并确定其轴向分带,探讨微量元素对深部金成矿的指示意义,期待能对玲珑金矿深部找矿提供一些参考.初步认识如下:矿区金矿体的最佳指示元素依次为Au、Ag、Bi、As、Cu、Co、Mo、Sb;金矿体的轴向分带序列从上到下依次为As、Pb、Ag、Cu、Hg、Sb、Mo、Ni、Th、V、U、Mn、Zn、Bi、Co、Au;矿体中Au、Bi、Ag、As富集系数大,Cu、Co富集系数中等,而Zn在矿体中相对亏损.研究结果表明,在深部47号矿体仍有较好的成矿前景.     

招远大尹格庄金矿床微量元素特征及其意义

该文以山东招远大尹格庄金矿床中微量元素为研究对象,通过对矿床围岩、矿石等微量元素的研究,表明大尹格庄金矿围岩中微量元素以富含 Bi,Au,Pb,W,Ag,Sn 为特点,矿体和矿化体中元素组合为 Au,Ag,As,Sb,Hg,B, Cu,Zn,Bi,Mo,Mn,Co,Ni,W。在5个成矿阶段中,第二阶段与第三阶段微量元素的富集程度较明显,表现为 Au, Ag,As,Co,Bi,Cu,Pb,Zn 等的富集,成矿元素可分为2个分带序列,主成矿元素为 Au Ag Cu Pb Zn Bi 组合、头晕元素 As Sb Hg 组合和尾晕元素 Co Ni 组合。     

胶东罗山金矿床成矿流体来源:蚀变岩型和石英脉型矿石载金黄铁矿稀土与微量元素特征约束

罗山金矿床是胶东玲珑金矿田最大的金矿床之一,同时发育蚀变岩型矿化和石英脉型矿化。本研究在系统的野外和镜下工作基础上,利用电感耦合等离子体质谱(ICP-MS)技术分析了载金黄铁矿的微量和稀土元素,对比了蚀变岩型和石英脉型矿石载金黄铁矿稀土和微量元素特征,探讨了成矿流体的性质与来源。黄铁矿稀土总含量较低,多呈较明显的"右倾"式稀土配分模式,总体表现出负Eu异常,基本无Ce异常; Hf/Sm、Th/La、Nb/La值均<1,推断成矿流体为富Cl的还原性流体。Co/Ni比值范围在0. 08～3. 77,平均值为1. 09; Co/Ni值以及Co、Ni、Bi、Cu和Zn含量均与变质热液型金矿平均含量相近; Y/Ho比值范围总体在21～32之间,与中国东部大陆地壳Y/Ho比值(20～35)基本重合;结合个别样品的弱正Eu异常以及前人的研究成果,推断成矿流体与变质热液类似,主要来源于古太平洋板块俯冲板片脱水和脱碳作用,且可能有长英质岩浆流体和地壳流体的混入。蚀变岩型和石英脉型矿石内的载金黄铁矿的稀土、微量元素组成没有明显区别,Y/Ho、Nb/Ta和Zr/Hf比值变化范围均很小,表明两类矿石的载金黄铁矿为同一期热液活动作用的产物。     

山东莱州曲家金矿黄铁矿微量元素对成矿过程的指示

曲家金矿位于我国重要的蚀变岩型金矿矿集区之焦家金矿带的中段，矿床赋存标高为-726～-1 334 m。为研究黄铁矿的演化及其对金成矿过程的指示，运用LA-ICP-MS分析黄铁矿原位微量元素含量，结合岩相学观察和点群分析对黄铁矿进行了分类。发现黄铁矿中Co、Ni、As等微量元素主要以类质同像形式赋存，而Au、Ag、Cu、Zn、Pb、Bi等元素主要以纳米级、微米级矿物包裹体形式赋存。黄铁矿主要分为5种类型：富Co型Py1,富Ni型Py2,富Au、As型Py3,富Au、Ag、Pb、Bi型Py4及“干净”型Py5。黄铁矿微量元素特征指示成矿物质可能主要来源于前寒武纪变质基底岩石和中生代岩浆岩，少量来源于地幔，成矿热液可能属变质热液、岩浆热液和浅部大气降水的混合成因。不同类型黄铁矿反映成矿热液由富Co、Ni经富As、Au向富Pb、Bi、Au、Ag演化。Py1和Py2形成后受构造活动影响发生强烈破碎，裂隙表面对热液中金络合物增强的吸附作用促使金在裂隙中沉淀，对金的富集成矿可能起重要作用。Co、Ni含量较低，同时Au、Ag、As、Pb、Bi等元素含量较高的黄铁矿与成矿作用有密切关系。另外，黄铁矿中C...     

南秦岭柞水-山阳矿集区王家坪金矿床地质特征及矿床成因探讨

王家坪矿床位于南秦岭柞水-山阳矿集区东部,金矿体主要产于上泥盆统星红铺组沉积地层中;金属矿物以黄铁矿为主,与金成矿关系密切的矿物为黄铁矿和雌黄.笔者利用LA-ICPMS和LA-MC-ICPMS对成矿期不同阶段硫化物进行微量元素及硫同位素研究,结果表明,该矿床成矿中阶段黄铁矿Co/Ni值为0.003～1.1,均小于1,暗...     

胶东西北部仓上金矿床上盘围岩蚀变和黄铁矿标型特征研究

上盘围岩是矿床钻探过程中首先遇到的围岩,研究其蚀变特征具有重要的找矿指导意义。对胶东西北部露天开采的仓上金矿床的详细研究表明,上盘围岩蚀变以绿泥石化为主,蚀变分带自远矿端到近矿端依次为方解石绿泥石化带、赤铁矿绿泥石化带、绿帘石化带和绢英岩化带。黄铁矿的形态、成分和热电性标型显示,成矿过程中上盘围岩提供了丰富的Ｆｅ、Ｃｏ、Ｎｉ、Ｃｕ、Ｐｂ、Ｚｎ和Ａｕ、Ｐｔ等。上盘围岩的近矿标志是绢英岩化增强,黄铁矿的｛１００｝＋｛２１０｝增多,Ｓ、Ｃｕ、Ｐｂ、Ｚｎ和Ａｕ、Ｐｔ增高,Ｓ／Ｆｅ离子比和ｗ（Ｃｏ＋Ｎｉ）／ｗ（Ａｓ＋Ｓｂ）降低,Ｐ型黄铁矿出现率增高,蚀变岩的金含量增高。     

山东昌邑莲花山铁矿矿床地质与矿石稀土、微量元素特征

莲花山铁矿位于昌邑-安丘铁成矿带的中部,铁矿体赋存于古元古代粉子山群小宋组中。本文通过矿石地球化学特征及其与矽卡岩矿物组合和赋矿围岩结构特征的对比研究,证明了莲花山铁矿与条带状铁矿相似。莲花山铁矿矿石稀土元素含量较低,经页岩标准化的稀土元素配分模式呈现轻稀土元素亏损、重稀土元素富集的特征,具有明显的Eu、Y、La异常,为无明显Ce异常,Y/Ho比值反映了在其沉积时受到海水作用的影响,表明莲花山铁矿的稀土元素来源于火山热液和海水的混合溶液。微量元素中Ti、V、Co、Ni、Mn、Sr、Ba等含量较低,原始地幔标准化的微量元素配分曲线显示,U、La、Hf呈正异常,Ba、Nb、Ta、Sr呈负异常,SiO2/Al2O3、Ti/V、Ni/Co、和Sr/Ba的比值指示了莲花山铁矿成矿物质来源于火山物质的沉积。研究结果表明,莲花山铁矿成矿作用源于火山热液与海水的混合,成矿物质来自火山沉积物,其地质与地球化学特征与五台山铁矿一致,为火山沉积变质型铁矿床。     

Alteration and mineralization styles of the orogenic disseminated Zhenyuan gold deposit,southeastern Tibet: Contrast with carlin gold deposit

Orogenic disseminated and Carlin gold deposits share much similarity in alteration and mineralization.The disseminated orogenic Zhenyuan Au deposit along the Ailaoshan shear zone,southeastern Tibet,was selected to clarify their difference.The alteration and mineralization from the different lithologies,including meta-quartz sandstone,carbonaceous slate,meta-(ultra)mafic rock,quartz porphyry and lamprophyre were researched.According to the mineral assemblage and replacement relationship in all types of host rocks,two reactions show general control on gold deposition:(1)replacement of earlier magnetite by pyrite and carbonaceous material;(2)alteration of biotite and phlogopite phenocrysts in quartz porphyry and lamprophyre into dolomite/ankerite and sericite.Despite the lamprophyre is volumetrically minor and much less fractured than other host rocks,it contains a large portion of Au reserve,indicating that the chemically active lithology has played a more important role in gold precipitation compared to structure.LA-ICP-MS analysis shows that Au mainly occurs as invisible gold in fine-grained pyrite disseminated in the host rocks,with Au content reaching to 258.95 ppm.The diagenetic core of pyrite in meta-quartz sandstone enriched in Co,Ni,Mo,Ag and Hg is wrapped by hydrothermal pyrite enriched in Cu,As,Sb,Au,Tl,Pb and Bi.Different host rock lithology has much impact on the alteration and mineralization features.Carbonate and sericite in altered lamprophyre show they have higher Mg than those developed in other of host rocks denoting that the carbonate and sericite incorporated Mg from phlogopite phenocrysts in the primary lamprophyre during alteration.The ore fluid activated the diagenetic pyrite in meta-quartz sandstone leading the hydrothermal pyrite enriched in Cu,Mo,Ag,Sb,Te,Hg,Tl,Pb and Bi,but the hydrothermal pyrite in meta-(ultra)mafic rock is enriched in Co and Ni as the meta-(ultra)mafic rock host rock contain high content of Co and Ni.However,Au and As shear similar range in both types of host rocks indicating that these two elements most likely come from the deep source fluid rather than the host rocks.It was shown in the disseminated orogenic gold deposit that similar hydrothermal alteration with mineral assemblage of carbonate(mainly dolomite and ankerite),sericite,pyrite and arsenopyrite develops in all types of host rocks.This is different from the Nevada Carlin type,in which alteration is mainly dissolution and silicification of carbonate host rock.On the other hand,Au mainly occur as invisible gold in both disseminated orogenic and Carlin gold deposits.     

南秦岭柞水—山阳矿集区夏家店金矿床黄铁矿微量元素和氢、氧、硫同位素对矿床成因的制约

为了研究柞水—山阳矿集区夏家店金矿床成因,采用LA-ICP-MS和LA-MC-ICP-MS技术分析夏家店金矿床矿体及围岩样品中黄铁矿原位微量元素及氢、氧、硫同位素组成特征。结果表明,该矿床黄铁矿的Co/Ni 比值为0.11~0.76,说明其与沉积作用有关。矿石中黄铁矿的δ³⁴S值(-9.40‰~7.16‰)与围岩碳质板岩的δ³⁴S值(-8.84‰~10.64‰)接近,黄铁矿的δ³⁴S均值(2.47‰)基本落在岩浆硫的范围内,指示矿石硫可能由地层硫和岩浆硫混合而成。氢、氧同位素测试结果表明,夏家店矿床成矿流体可能主要来自岩浆水,成矿后期有大气降水的加入。综合矿床地质特征、成矿温度、金赋存状态等特征和黄铁矿微量元素、硫同位素组成可知,夏家店金矿床属于卡林型金矿,其成矿流体主要来自岩浆水,成矿后期有大气降水加入;其成矿物质是由深部岩浆与地层混合而成。     

Cobalt as an exploration tool in the Outokumpu zone, Finland

The Outokumpu region in eastern Finland is an integral part of the Precambrian formations of the Karelidic orogeny. The copper-cobalt ore deposits discovered in the region are associated with a lithologic complex that consists of serpentinites, skarns, carbonate rocks and quartzites. The outer zone of this rock association adjacent to the surrounding mica schists is commonly occupied by black schists. The association constitutes the coherent stratigraphic sequence known as the Outokumpu zone, which is the environment in which the ore deposits of the Outokumpu type occur. The total length of the ribbon-like zone is about 240 km. Three Cu---Co ore deposits: Outokumpu, Vuonos and Luikonlahti are currently being exploited and four sub-economic ore showings have been found in the zone. All the deposits and ore showings are of the polymetallic sulphide type with copper, zinc, cobalt and nickel. There are also small amounts of silver, gold, tin and selenium in the orebodies. These stratabound ore deposits are submarine volcanic exhalative in origin. The immediate host rock of the ore is commonly quartzite, interpreted as a chemical silica precipitate.The Outokumpu copper-cobalt ore deposit was discovered in 1910. Owing to its economic potential, the Outokumpu zone is one of the most thoroughly studied parts of the Finnish Precambrian. More than 1000 holes have been drilled from the surface into the zone and provide a large source of material for lithogeochemical studies.The association does not lend itself easily to geophysical investigations because of its complex geology, characterized by black schists and other rocks giving a strong geophysical response. For this reason, and because of the extensive drilling, lithogeochemistry has become an important exploration tool in the region.The discovery of the blind Vuonos ore deposit in 1965 was the result of a comprehensive lithogeochemical study carried out in the early 1960's. Several old prospects were sampled in the Outokumpu zone and the sulphide phase was analyzed for Cu, Co, Ni and Zn.Clustering of the analytical data gives five groups of rock types: (1) quartzite-skarn-dolomite; (3) black schists; (4) mica schists; (5) copper-cobalt ore (Huhma and Huhma, 1970). The locations of these groups in Ni---Co and Cu---Co diagrams and in an Co---Cu---Ni triangular diagram are shown in Figs. 1, 2 and 3. The nickel content of serpentinites varies between 1500 and 2200 ppm and that of cobalt between 70 and 110 ppm. Thus the Ni/Co ratio averages 20:1. In the quartzite-skarn-dolomite-group the nickel content ranges from 900 to 3000 ppm and the cobalt content from 50 to 120 ppm. The Ni/Co 150 to 500 ppm and the cobalt content from 20 to 60 ppm. The Ni/Co ratio is about 10:1. Mica gneisses are poor in sulphides. Their nickel content averages from 40 to 90 ppm and the cobalt content from 15 to 30 ppm.The copper-cobalt ore occupies a discrete area in the Ni---Co diagram. Its nickel content varies between 1000 and 2000 ppm and the cobalt content between 1000 and 3000 ppm. The copper-cobalt diagram shows that the cobalt content of the serpentinites and the quartzite-skarn-dolomite group is fairly constant varying between 60 and 140 ppm. The copper content ranges from zero to 100 ppm in the former and from 10 to 100 ppm in the latter. In black schists the copper content varies from 100 to 300 ppm, the cobalt content being some tens of ppm. The mica gneisses are somewhat poorer in their Cu and Co contents. In this case too, the copper-cobalt ore has a Cu---Co content distinctly apart from those of the other groups.In the Cu---Co---Ni triangular diagram the serpentinite and the quartzite groups plot near the Ni apex of the triangle, the relative Ni content being 94–96% and that of Cu less than 1%. The black schists and mica gneisses have their own area near the centre of the Cu---Ni join with the Co content not exceeding 10%. There are several exceptions where points in the diagrams described above plot outside the normal field. Most of these anomalous points are located between the normal area of the rock type and that of the Cu---Co ore. The Ni---Co diagram in particular demonstrates that the deviations are due to the increase in the Co content.In summary, the anomalies of the Outokumpu type have: (1) a Ni/Co ratio lower than 15:1; and (2) a Cu percentage of the sum Cu+Co+Ni = 100 higher than 5. These anomaly units are applied to rank the analytical data of the Outokumpu zone. It is evident from the diagrams that the increase in cobalt content outside its normal field is the prime indication of the proximity of the ore. Being rather constant, the nickel content is used as a reference. Thus a decrease in the Ni/Co ratio indicates the presence of the ore. In some cases the decrease in the Ni/Co ratio may be due to a local decrease in the Ni content. The anomaly can be checked by the Cu/Cu+Ni+Co ratio. Except when testing the anomalies with Co, Cu and Ni as described above, the Co content alone can be used as an indicator of the proximity of a Cu---Co orebody. This was tested in one section of the Vuonos orebody (Fig. 4). The pyrite phase of the quartzites was selectively leached and its Co content analyzed. It was noted that the Co content of pyrite increased somewhat when the orebody was approached along strike.Before this method can be used more widely, the stratigraphic position and the structure of the potential ore horizon must be known fairly accurately. The proximity of an orebody can also be evaluated by means of the Co content of the black schists. As shown above, the Co content of the black schists is usually considerably under 100 ppm; it is usually over 100 ppm only adjacent to an orebody. Consequently, the extensive data on black schists in the Outokumpu zone can be sorted into potential and less potential ones.     

Decoupling of cobalt and nickel in high-temperature magmatic processes and its metallogenic indicationSCIEI北大核心CSCD

Cobalt ( Co) and nickel (Ni) have similar geochemical behaviors and commonly co -vary in nature, but they may undergo decoupling in certain geological processes, especially in ore -forming processes, and the decoupling mechanism is not yet clear. This paper analyzes the distribution characteristics and migration behaviors of Co and Ni in major rock -forming minerals in different types of mafic-ultramafic rocks. The Ni (2500 x 10(-6) 3400 x 10(-6)) and Co (110 x 10(-6) 160 x 10(-6)) contents of mantle olivine are both higher than those of the primitive mantle. The Ni content shows no obvious correlation with the Fo value, while the Co content has a strong negative correlation with both the Fo value and the Ni/Co ratio. This indicates that partial melting does not cause significant changes in Ni content of olivine, but can control the Co content and the Ni/Co ratio, mainly due to the differences in compatibility between the two elements in olivine. Melt-rock reactions can cause significant Co-Ni decoupling between minerals and within minerals, but the mechanisms differ. In the process of reacting with basaltic magma, olivine mainly absorbs Co and loses Ni, while being affected by coexisting spinet minerals. When reacting with carbonatite melt, olivine loses Co, but Ni remains almost unchanged. As mantle derived basaltic magma intrudes into the lower crust, the migration of Co and Ni in pyroxenes is controlled by concentration gradients and sulfide crystallization. The local enrichment of Co provides an important material basis for the formation of Co -rich melts in deep crustal melting. During the differentiation and evolution of mafic-ultramafic magma, the chromite fractional crystallization and sulfide segregation can cause Co-Ni decoupling at both rock and/or mineral scales. Meanwhile, the enriched hydrous fluids released during chromite aggregation and sulfide melt solidification can significantly promote the efficiency of element exchange in sub-solidus state, especially strengthening the activity of Co, thus causing negative correlations between Co and Ni in olivine and even in chromite. Comparative studies show that the trends of Co and Ni content changes in mineral assemblages are evidently different, or even opposite, between mineralized and barren bodies and between ore -bearing and ore -free rocks, which provides a basis for identifying mineralization in rock bodies and guiding prospecting.     

湖北嘉鱼县蛇屋山金矿硅质岩地球化学特征及成矿环境约束

湖北蛇屋山金矿是亚洲最大的红土型金矿,矿区内硅质岩发育,覆于含矿红土层之上,并与硅化灰岩呈渐变过渡。硅质岩主要由微晶和隐晶组成,其SiO2含量为96.87%～97.90%,w(Si)/w(Al)=92.84～287.66,平均值为173,处于纯硅质岩的范畴。硅质岩样品的w(Al)/w(Al+Fe+Mn)为0.189～0.388,平均值为0.303,具热液成因硅质岩的特征。根据Al、Fe、Mn三角图的投点,认为本研究区硅质岩为热液成因硅质岩。微量元素w(Ni)/w(Co)、w(Fe)/w(Ti)、w(Ti)/w(V)、w(U)/w(Th)也说明了硅质岩具有热水沉积成因。w(Ce)/w(Ce*)为1.05～1.27,平均值为1.12,(La/Ce)N为0.84～1.12,平均值为0.98,微量元素V的含量(3.02～4.26μg/g)以及常量元素w(MnO)/w(TiO2)(1.0～2.0)都显示此研究区硅质岩具有大陆边缘硅质岩的特征。结合宏观特征,确定硅质岩有可能形成于卡林型金矿去碳酸盐化阶段,属于热液活动的产物。     

Genesis of sediment-hosted stratiform copper–cobalt deposits, central African Copperbelt

The Neoproterozoic central African Copperbelt is one of the greatest sediment-hosted stratiform Cu–Co provinces in the world, totalling 140 Mt copper and 6 Mt cobalt and including several world-class deposits (10 Mt copper). The origin of Cu–Co mineralisation in this province remains speculative, with the debate centred around syngenetic–diagenetic and hydrothermal-diagenetic hypotheses.The regional distribution of metals indicates that most of the cobalt-rich copper deposits are hosted in dolomites and dolomitic shales forming allochthonous units exposed in Congo and known as Congolese facies of the Katangan sedimentary succession (average Co:Cu = 1:13). The highest Co:Cu ratio (up to 3:1) occurs in ore deposits located along the southern structural block of the Lufilian Arc. The predominantly siliciclastic Zambian facies, exposed in Zambia and in SE Congo, forms para-autochthonous sedimentary units hosting ore deposits characterized by lower a Co:Cu ratio (average 1:57). Transitional lithofacies in Zambia (e.g. Baluba, Mindola) and in Congo (e.g. Lubembe) indicate a gradual transition in the Katangan basin during the deposition of laterally correlative clastic and carbonate sedimentary rocks exposed in Zambia and in Congo, and are marked by Co:Cu ratios in the range 1:15.The main Cu–Co orebodies occur at the base of the Mines/Musoshi Subgroup, which is characterized by evaporitic intertidal–supratidal sedimentary rocks. All additional lenticular orebodies known in the upper part of the Mines/Musoshi Subgroup are hosted in similar sedimentary rocks, suggesting highly favourable conditions for the ore genesis in particular sedimentary environments. Pre-lithification sedimentary structures affecting disseminated sulphides indicate that metals were deposited before compaction and consolidation of the host sediment.The ore parageneses indicate several generations of sulphides marking syngenetic, early diagenetic and late diagenetic processes. Sulphur isotopic data on sulphides suggest the derivation of sulphur essentially from the bacterial reduction of seawater sulphates. The mineralizing brines were generated from sea water in sabkhas or hypersaline lagoons during the deposition of the host rocks. Changes of Eh–pH and salinity probably were critical for concentrating copper–cobalt and nickel mineralisation. Compressional tectonic and related metamorphic processes and supergene enrichment have played variable roles in the remobilisation and upgrading of the primary mineralisation.There is no evidence to support models assuming that metals originated from: (1) Katangan igneous rocks and related hydrothermal processes or; (2) leaching of red beds underlying the orebodies. The metal sources are pre-Katangan continental rocks, especially the Palaeoproterozoic low-grade porphyry copper deposits known in the Bangweulu block and subsidiary Cu–Co–Ni deposits/occurrences in the Archaean rocks of the Zimbabwe craton. These two sources contain low grade ore deposits portraying the peculiar metal association (Cu, Co, Ni, U, Cr, Au, Ag, PGE) recorded in the Katangan sediment-hosted ore deposits. Metals were transported into the basin dissolved in water.The stratiform deposits of Congo and Zambia display features indicating that syngenetic and early diagenetic processes controlled the formation of the Neoproterozoic Copperbelt of central Africa.     

黔西南泥堡金矿床大型隐伏金矿体地质特征研究

泥堡金矿区Ⅲ号金矿体是近年来发现的受断裂控制的大型隐伏矿体,是泥堡金矿区找矿勘探工作的重大突破。该矿体受F1断层控制,其容矿岩石为蚀变沉凝灰岩。蚀变沉凝灰岩普遍发育粘土化、碳酸盐化,而与金矿化密切关联的蚀变类型为黄铁矿化、硅化,次为毒砂化。对泥堡金矿床产出特征进行分析发现,Ⅲ号矿体明显受构造（F1断层）、地层（P3l2）和岩性（蚀变沉凝灰岩）控制。结合矿床赋矿岩石、矿物组合和控矿因素分析,认为泥堡金矿的形成与晚二叠世沉积火山凝灰质密切相关,F1断层活动及燕山期热水（液）作用是Ⅲ号金矿体成矿的关键。通过对比分析,认为区域上车榔—泥堡—三道沟—潘家庄一线是寻找类似金矿体（断控型）的重要区域,龙潭组二段及蚀变沉凝灰岩是重要的找矿标志。