【作者】 陈润生；

【导师】 李建威；

【作者基本信息】 中国地质大学 ， 矿产普查与勘探， 2013， 博士

【摘要】 论文以武夷山成矿带内新发现的建瓯上房大型钨矿床为研究对象,通过系统的野外地质调查、钻孔岩芯观察描述及室内综合分析测试,对上房钨矿床的成矿地质条件、矿化特征、成岩成矿时代、成矿流体性质及成矿物质来源等进行深入研究,在此基础上查明矿床成因和关键控矿因素,探讨武夷山成矿带晚中生代时期(主要为晚侏罗世)构造-岩浆活动与钨矿成矿作用的耦合关系,建立上房钨矿床的成矿模式和找矿预测模型,为闽北地区的钨矿勘查和找矿预测工作提供理论指导。上房钨矿床位于武夷山成矿带东缘的闽北建瓯地区,产于黑云母正长花岗岩和斜长角闪岩外接触带,主要赋矿围岩为古元古界大金山组。大金山组由斜长角闪岩及黑云斜长变粒岩组成,岩相学和岩石地球化学研究表明,变粒岩原岩为花岗闪长岩-二长花岗岩,A/CNK为1.08-1.95,属过铝质高钾钙碱性系列。岩石明显亏损Nb、Ta、P、Ti、Sr等,富集Rb、 K、Pb、Th等,具有S型花岗岩特征。斜长角闪岩的地球化学组成与闽北地区新元古代马面山群东岩组斜长角闪片岩相似,Ti、Nb、P、Zr、Th等含量低,Ta和Hf的含量高,(La/Yb)N=1.10～1.62,δEu=0.74～0.99,ISr=0.706452～0.708575,εNd(t)=0.15～1.09,其原岩可能为源自富集地幔的基性侵入岩(辉长岩?),形成于岛弧或活动陆缘环境。斜长角闪岩的LA-ICP-MS锆石U-Pb年龄为388±10Ma(MSWD=1.7),表明是加里东晚期区域变质事件的产物。内接触带为上房似斑状中细粒黑云母正长花岗岩体,岩石SiO2含量为71.11-75.39%,MgO、TiO2、P2O5含量低,K2O+Na2O含量为7.78%～8.94%,K2O/Na2O比值为1.39-2.07,A/CNK为1.01-1.11,属准铝质-弱过铝质高钾钙碱性系列。正长花岗岩样品的大离子亲石元素sr、Ba及高场强元素Ti、P强烈亏损；(La/Yb))N=2.20～13.47,δEu=0.11～0.43,ISr=0.711713～0.712804,εNd(t)=-10.10～-9.35,208Pb/204Pb为38.9450～39.0650,207Pb/204Pb为15.6544～15.6705,206Pb/204Pb为18.5630～18.5789,锆石的εHf(t)=-19.2～-14.7。以上地球化学特征表明上房黑云母正长花岗岩属准铝质—弱过铝质高分异I型花岗岩,是华夏地块古元古代地壳物质(古元古代侵入岩)部分熔融的产物。上房钨矿床的矿体呈层状、似层状、透镜状产于黑云母正长花岗岩外接触带的斜长角闪岩中,金属矿物以白钨矿、辉钼矿、磁黄铁矿、黄铁矿为主,另有少量黄铜矿、方铅矿和闪锌矿。非金属矿物有石榴子石、透辉石、钠长石、阳起石、透闪石、绿帘石、石英、绿泥石、绢云母、萤石、方解石,矿石类型以阳起石-磁黄铁矿型和透辉石-石英脉型为主。根据矿物组合及矿石结构特征,将上房钨矿床的成矿作用划分为四个阶段：干矽卡岩阶段(石榴子石-透辉石阶段)、湿矽卡岩-氧化物阶段(阳起石-白钨矿阶段)、石英-硫化物阶段、碳酸盐阶段。干矽卡岩阶段形成含石榴子石透辉石矽卡岩,湿矽卡岩阶段主要形成阳起石、透闪石、绿帘石、石英、绿泥石、绢云母等。白钨矿主要在湿矽卡岩-氧化物阶段和石英-硫化物阶段沉淀。白钨矿稀土元素含量变化范围581.22μg/g～3440.6μg/g, LREE/HRRR比值为1.09-8.75,属轻稀土弱富集型,可进一步分为高Eu低MREE和低Eu高MREE两类。当LREE/HREE>3.9时,属高Eu低MREE类,δEu=1.19-3.60；当LREE/HREE<3.6时,属低Eu高MREE类,δEu=0.14-0.80。正Eu异常低MREE和负Eu铕异常高MREE白钨矿暗示上房钨矿床的形成与两类含钙矿物的交代作用有关。成矿流体交代斜长角闪岩中的富铕钙长石形成具有正铕异常和低中稀土含量的白钨矿,交代低铕角闪石则形成具有负铕异常和富集中稀土的白钨矿。REE3+与Na-组合以化合价补偿形式有选择性地置换白钨矿晶格中的Ca2+,表明成矿流体为相对封闭富Na+的还原性热液体系。白钨矿、石英和方解石中含有丰富的流体包裹体,原生包裹体以富液两相包裹体为主(占总数90%以上)。从主成矿阶段到成矿晚阶段,成矿流体温度集中范围从190～240℃降低为150～180-C；而盐度则从4～6wt.%NaCl equiv.减小至1.2～3.2wt.%NaCl equiv.;密度从0.80～0.90g/cm3升高至0.88～0.94g/cm3。显然,上房钨矿床的成矿流体为中-低温、低盐度、低密度的热液,从主成矿阶段到成矿晚阶段,随着含矿热液温度的降低,其盐度逐渐降低,密度则逐渐上升。石英-硫化物阶段的石英中流体包裹体的氢同位素组成范围为-57.1‰～-76.3%。,石英矿物的氧同位素组成为11.3‰～12.3%。,与之平衡的流体δ18OH2O为0.60%。～1.60%。。硫化物的634S值介于0.78%。-5.29%o,辉铝矿、磁黄铁矿及黄铁矿的δ34S值依次降低(δ34SMo>δ34SCpy>δ34SPy),表明热液体系中硫同位素已达到平衡。氢-氧同位素和硫同位素组成表明,成矿热液体系中的硫主要来自岩浆,而水则为岩浆流体和循环大气降水的混合。。采自上房黑云母正长花岗岩两个新鲜样品的LA-ICP-MS锆石U-Pb年龄分别为157.6±1.4Ma (MSWD=1.3)和158.8±1.4Ma (MSWD=3.4),表明上房花岗岩体侵位于晚侏罗世早期。白钨矿的Sm-Nd等时线年龄为162士7Ma(n=5),与白钨矿共生的辉钼矿Re-Os等时线年龄158.1士5.4Ma(n=5)。白钨矿Sm-Nd等时线年龄与辉钼矿Re-Os等时线年龄在误差范围内完全一致,与上房黑云母正长花岗岩的锆石U-Pb年龄相近,表明矿区的成矿作用与岩浆活动具有同时性,进一步说明成矿流体和成矿物质主要来自岩浆。上房钨矿床与华南地区大多数钨矿床的形成时间一致,是同一区域成矿事件和相同成矿动力学背景的产物。本文的最新年代学数据表明,华南地区160-150Ma钨矿床的空间分布已从传统的南岭成矿带中东段湘南、粤北、赣南地区向东延伸至武夷山成矿带的闽西和闽北地区,因此这一成矿带不是如传统观点认为的那样呈近东西向分布,而是具有北东向或北东东向展布的特点,标志着晚侏罗世(160-150Ma)钨矿大规模成矿很可能不限于传统的南岭地区。这一新的认识有利于拓展华南钨矿尤其是武夷山地区钨矿的找矿思路和空间。综合成矿地质背景、赋矿地层、容矿岩石、矿化特征、矿物组合、围岩蚀变、成矿流体性质等方面特征分析,认为上房钨矿床属于还原型(磁黄铁矿型)矽卡岩型钨矿矿床,成矿元素w、Mo来源于晚侏罗世正长花岗岩岩浆。根据成矿要素的综合研究,首次建立了上房钨矿的成矿模式和闽西北地区钨矿床的区域成矿模式和找矿模型。在闽北建阳小松-建瓯玉山地区应用固体矿产矿床模型综合地质信息预测技术(MgeoM技术)圈定找矿远景区7个,找矿靶区10个,其中A级靶区2处,B级靶区4处,预测潜在W03资源量53万吨。更多还原

【Abstract】 The newly-discovered Shangfang large-scale scheelite deposit is located in Jian’ou County, Northwest Wuyishan metallogenic belt. Based on detailed field investigation and drilling-core logging, the author carried out a comprehensive study in order to reveal the ore-forming controls, composition and characteristics of of the ores, age and evolution of mineralization and ore-related magmatism, and source of mineralizing fluids and components in the fluids. The results provide, for the first time, significant insights into the genesis of the Shangfang tungsten deposit, enabling to build a metallogenic model for the deposit. When combined with existing geological and geochronological data, this study demonstrates a genetic association between the late Jurassic (160～150Ma) igneous magmatism and tungsten mineralization in the Shangfang mine and within the Wuyishan metallogenic belt, both formed under a continental-margin setting related to the westward subduction of the Paleo-pacific plate. The ultimate objective of this study is to build a predictive model as a guide for future prospecting and exploration of tungsten deposits in northern Fujian Province.Orebodies of the Shangfang scheelite deposit are localized along the contact zone between the biotite syenitic granite and the amphibolites of the Paleoproterozoic Dajinshan Formation. The Dajinshan Formation consists mainly of amphibolites and biotite-plagioclase granulite. Petrographic and geochemical analysis suggests that protoliths of the granulite are likely monzonite derived from reworking of Paleoproteroozic crustal components. Rocks of the monzonite are high K-calc-alkaline, and peraluminous with A/CNK ranging from1.08to1.95. These rocks are depleted in Mk Ta、P、Ti、Sr, but enriched in Rb、K、Pb、Th, and reselmbe S-type granites. The amphibolites have ISr=0.706452～0.708575and εNd(t)=0.15～1.09; and resulted likely from metamorphism of precursor gabbroic intrusions derived from an enriched mantle source. An amphibolite sample yielded a LA-ICP-MS zircon U-Pb age of388±10Ma (MSWD=1.7), which likely record the regional metamorphic event of the Late Caledonian.Rocks of the Shangfang biotite syenitic granite have71.11%to75.39%SiO2,7.78%to8.94%K20+Na20with K20/Na2O ratios from1.39to2.07and A/CNK of1.01and1.11, but low MgO、TiO2、P2O5contents. They belong to weak peraluminous to peraluminous and high-potassium calc-alkaline granite. They are depleted in LILE (e.g Sr、Ba) and HFSE (e.g. Ti、 P), and have (La/Yb)N=2.20～13.47and δEu=0.11～0.43. The bulk samples have ISr=0.712804～0.711713, εNd(t)=-10.10～-9.35,208Pb/204Pb=38.9450～39.0650,207Pb/204Pb=15.6544～15.6705, and206Pb/204Pb=18.5630～18.5789, which are consistent with zircon εHf(t) of-19.2～-14.7. It is suggested that the granites were formed by remelting of the Paleoproterozoic crustal material of Cathaysian Block.The orebodies are mostly layered, stratiform or lenticular and mostly confined within amphibolites that is intruded by the Shangfang syenitie granite. Metallic minerals are dominated by scheelite, molybdenite, pyrrhotite and pyrite with minor chalcopyrite, galena and sphalerite. Nonmetallic minerals are mainly composed of garnet, diopside, albite, actinolite, tremolite, epidote, quartz, chlorite, sericite, fluorite, and calcite. According to mineral assemblages, two types of ores can be recognized:actonolite-pyrrhotite-scheelite and diopside-quartz-scheelite veins.The paragenetic sequences of the ore and alteration minerals indicate four hydrothermal stages in the formation of the deposit, including garnet-diopside (skarn) stage, oxide (actinolite-scheelite stage) stage, quartz-sulfide stage and carbonate stage. Scheelite was mainly precipitated during the oxide stage and, less siginificantly, in the quartz-sulfide stage.The scheelite have rare earth elements (REE) ranging from581.22to3440.6μg/g with LREE/HREE ratios from1.09to8.75. They have two distinct chondrite-normalized REE pattern: low MREE with positive Eu anomalies and high MREE with negative Eu anomalies. Low MREE scheelite have LREE/HREE ratios higher than3.9and δEu from1.19to3.60, whereas the high MREE varieties have LREE/HREE lower than3.6and δEu from0.14to0.80. The author proposes that the Eu anomalies in scheelite were formed by metasomatism of ore-forming fluid with Eu enriched or depleted minerals in the country rocks. Scheelite with positive Eu anomalies were formed by fluids equilibrated with plagioclase, whereas the equivalents with negative Eu anomalies were precipitated from amphibole metasomatized fluids. REE3-and Na+can replaces Ca2+in scheelite lattice indicating ore-forming fluids are rich in Na-.Scheelite, quartz, and calcite contain abundant fluid inclusions. Primary fluid inclusions mostly have liquid phase with small vapor phase (L+V type)(more than90%). From the main metallogenic stage Ⅱ to the late metallogenic stage Ⅲ, homogenization temperatures decrease from190～240℃to150～180℃; the salinity of ore-forming fluid decrease from4～6wt.%NaCl equiv. to1.2～3.2wt.%NaCl equiv.; but fluid densities increase from0.80～0.90g/cm3to0.88～0.94g/cm3. Fluid inclusion extracted from quartz of stageⅢ have H isotope of-57.1‰to-76.3‰, and the quartz have δ18O from11.3%o to12.3%o, which are equilibrated with ore-forming fluid with δ18O of4.9%o to5.9‰. Sulfides have δ34S values between0.78%o and5.29‰; and the δ34S value of molybdenite, pyrrhotite and pyrite are decreased (δ34SMo>δ34SCpy>δ34Spy), indicating that sulfur isotopic equilibrium between the sulfides and ore-forming fluid. Results of the stable isotopes suggest that sulfur was dominantly derived from magmas, whereas ore-forming fluids have a mixing source of magmatic and meteoric fluids. Two samples collected from the Shangfang granites have identical LA-ICPMS zircon U-Pb ages, of157.6±1.4Ma (MSWD=1.3) and158.8±1.4Ma (MSWD=3.4), which represent the emplacement age of granite. The scheelite has a Sm-Nd isochron age of162±7Ma, which is within errors of molybdenite Re-Os isochorn age of158.1±5.4Ma. Both ages are in good agreement with zircon U-Pb ages suggesting that formation of the Shangfang scheelite deposit was synchronous with emplacement of granite intrusions and ore-forming fluids are derived from the intrusions. The ages are also contemporaneous with regional large-scale W mineralization in South China. Our newly obtained geochronological data have shown that the160～150Ma W mineralization in South China have extended from southern Hunan, northern Guangdong and southern Jiangxi (namly the Nanling metallogenic belt) to western and northern Fujian Province of the Wuyi Mountain. The distribution of the W deposits are nearly NE or NEE treading, rather than EW trending as previously thought. This indicates that the Late Jurassic (160～150Ma) large scale W deposites in South China were not limited in the well-known Nanling region, but in a much wider area.A combination of regional geology, ore-hosting rocks, mineralization styles, hydrothermal alteration, paragenetic sequences, fluid inclusions, stable isotopes, and geochronology support that the Shangfang scheelite deposit is of reduction skarn in origin (pyrrhotite type). Ore-forming-fluids and metals were derived from late Jurassic granites. A genetic model for the Shangfang W deposit is proposed, which is useful for future mineral exploration in the northwest Fujian Province.Using this model, combined with integrated geological information prediction technique (MgeoM technique), seven prospective zones and ten prospecting target areas have been delineated, among which two areas are level A prospecting targets, four areas are level B prospecting targets, and the predicted WO3resources are up to530000tons.更多还原