| 其他摘要 | 新疆西天山色勒特果勒斑岩-矽卡岩型铜钼矿位于新疆维吾尔自治区精河县城南偏东约60km处，所处大地构造位置属于伊犁板块东北的博罗霍洛古生代岛弧带。矿区内出露的岩体主要为黑云母花岗岩、石英闪长斑岩和闪长斑岩。黑云母花岗岩呈岩基状产出，大面积分布于矿区北部及其相邻地区。石英闪长斑岩及闪长斑岩相互渐变接触，并都呈脉状侵入黑云母花岗岩以及东图津河组之中，分别导致黑云母花岗岩的绢英岩化和东图津河组地层的矽卡岩化、角岩化和大理岩化。矿体主要赋存于石英闪长斑岩、闪长斑岩以及接触带矽卡岩之中。色勒特果勒矿区内的矿石矿物主要有黄铜矿、斑铜矿、辉铜矿、辉钼矿、磁黄铁矿和白钨矿；脉石矿物主要是石榴子石、透辉石、符山石、绿帘石、绿泥石、角闪石、石英、方解石、绢云母等。本论文利用电子探针、LA-ICP-MS、LA-MC-ICP-MS、激光拉曼光谱、MAT-253等现代分析技术对该矿床重点开展了成岩成矿年代学、矿物学、成矿流体演化、同位素示踪等方面的研究，主要取得了以下认识：色勒特果勒矿区内主要出露三种岩体；分别为黑云母花岗岩，石英闪长斑岩和闪长斑岩。黑云母花岗岩的锆石LA-ICPMS U-Pb加权平均年龄为307±3 Ma，时代较晚的矿化的闪长斑岩和石英闪长斑岩的锆石LA-ICPMS U-Pb加权平均年龄均为302±3 Ma。辉钼矿Re-Os加权平均年龄为301±2 Ma，辉钼矿和矿化斑岩体具有相近的年龄。色勒特果勒矿区花岗岩类岩体的地球化学特征显示它们均富集大离子亲石元素（LILE）而亏损高场强元素（HFSE），并且都具有Nb、Ti与P的负异常；富集轻稀土，亏损重稀土并具有弱的Eu负异常，说明其形成于岛弧环境。正的锆石εHf(t)值，低的Mg#值以及低的Cr （＜60ppm）和Ni（＜15ppm）含量说明它们的源区为新生的下地壳，而新生下地壳主要由大洋板片的俯冲消减作用而导致的地幔楔部分熔融形成的岛弧岩浆增生而成。受洋壳板片持续的俯冲消减作用的影响，新生地壳发生了部分熔融作用，形成的长英质熔体分别上侵形成了具有岛弧岩浆性质以及正的εHf(t)值的色勒特果勒黑云母花岗岩以及斑岩体。色勒特果勒三种岩体均具有高的Th以及轻稀土含量说明在俯冲过程中大洋沉积物的加入。相对于黑云母花岗岩，两种斑岩具有更高的Th/La比值以及较低的εHf(t)值，说明它们中加入了更多的大洋沉积物。通过对该矿床区域大地构造背景分析以及晚石炭世到早二叠世花岗岩的对比，我们认为西天山俯冲环境向伸展环境转变的时间大概为石炭纪末—二叠纪初（300Ma）。石榴子石是重要的矽卡岩矿物，具有明显的分带性，根据石榴子石位置和颜色可以将色勒特果勒的石榴子石分为三类：内矽卡岩及岩体周围的红色石榴子石、中间带矽卡岩中棕色石榴子石和靠近灰岩的灰绿色石榴子石。石榴子石电子探针分析数据表明三类石榴子石主要为钙铝榴石，少量为钙铁榴石，以及微量钛榴石、锰铝榴石、镁铝榴石和铁铝榴石。说明它们都是在酸性还原的条件下形成的。棕色石榴子石具有振荡环带并含有相对富Fe和富Al的环带，相对富Fe的环带可能是由岩浆活动间歇期流体中CH4的流失导致氧逸度升高而形成，而富Al的环带则由岩浆再次活动期间富CH4的还原性流体的叠加而形成。根据色勒特果勒铜钼矿床的流体包裹体特征，可将它们分为四类：超临界包裹体、富气相包裹体、含子晶的高盐度包裹体以及富液相的低盐度包裹体。超临界包裹体主要发育于斑岩体的石英斑晶以及早期矽卡岩矿物如石榴石和符山石之中。超临界包裹体的均一温度较高（378℃～454℃），一部分超临界包裹体在升温过程中见临界均一的现象。富气相包裹体较少见，最后均一到气相，均一温度为352℃～398℃。含子晶的高盐度包裹体均一温度范围一般在200℃～400℃之间，石盐子晶消失的温度可以高于气泡消失的温度，也会低于气泡消失的温度。富液相的低盐度包裹体在降温过程中，包裹体中气泡会突然缩小，降下温度在回温过程中，气泡慢慢变大同时会有笼合物出现，笼合物成絮状，一般在温度为3℃～7℃时笼合物消失，包裹体均一温度范围在185℃～276℃之间。超临界流体从岩浆中分异出来以后，向上运移，随着温度和压力的降低，会发生不混溶（沸腾）作用，形成富气相包裹体和含子晶的高盐度包裹体。流体进一步向上运移，可能与天水发生混合则会形成富液相的低盐度包裹体。流体包裹体激光拉曼数据表明色勒特果勒成矿流体中的气相成分以CH4为主。超临界流体包裹体盐度在2.1 wt.% 到6.4 wt.%之间，平均值为3.8 wt.%；矿化的石英脉中流体包裹体盐度在3.0 wt.% 到7.5 wt.%之间，平均值为5.4 wt.%。超临界流体包裹体中CH4的含量在3.8mol/kg到10.4mol/kg之间，所对应的氧逸度在FMQ-0.5到FMQ-1之间（假设该流体在地下5 km被捕获）。色勒特果勒矿床不同矿物组合中的金属硫化物具有比较均一的硫同位素组成。δ34S值的变化范围在-1.22‰～+2.52‰之间，平均值+1.402‰，显示出幔源硫同位素的特征。色勒特果勒流体包裹体中甲烷的碳同位素范围δ13CV-PDB（‰）在-29.2‰ 到 -19.1‰ 之间，平均值为-25.7‰；而甲烷氢同位素δDV-SMOW（‰）范围在-273.3‰到-234.9‰ 之间，平均值为-256.9‰。甲烷的碳、氢同位素结果加上富CH4的超临界包裹体的发现说明流体中的CH4可能是直接从岩浆中分异出来，而不是由热液作用导致而成的。色勒特果勒铜钼矿床在空间上和成因上都与含钛铁矿的还原性斑岩体有关；成矿流体为富CH4的还原性的流体，其氧逸度在FMQ-0.5到FMQ-1之间（假设富CH4的流体在地下5 km被捕获）；矿区发育大量代表低氧逸度的矿物如磁黄铁矿、钙铝榴石等而未发现磁铁矿、赤铁矿以及石膏等高氧逸度矿物，说明色勒特果勒是一个典型的还原性斑岩-矽卡岩型矿床。; The Seleteguole Cu–Mo deposit, which is located about 60 km southeast away from the Jinghe County Town, Xinjiang Uygur Autonomous Region, lies tectonically in the BoluHonu Paleozoic arc belt in northeastern side of the Yili plate. The outcropped intrusive bodies include biotite granite, quartz diorite porphyry and diorite porphyry in the deposit. The biotite granite occurs as batholith widely distributed in northern part of the deposit and the adjacent area. The quartz diorite porphyry and diorite porphyry occurred together and respectively intruded into biotite granite and sedimentary rocks of the Dongtujing Formation, resulting in the phyllic alteration of biotite granite, and the formation of skarn, hornfels and marble, respectively. Orebodies occur mainly in the quartz diorite porphyry, diorite porphyry, and skarns in the contact zone between carbonate and porphyries. Ore minerals mainly include chalcopyrite, bornite, chalcocite, molybdenite, pyrrhotite, and scheelite. Gangue minerals mainly include garnet, diopside, vesuvianite, epidote, chlorite, hornblende, quartz, calcite and sericite. In this paper, a series of modern analytical techniques including electron probe, LA-ICP-MS, LA-MC-ICP-MS, laser Raman spectroscopy and MAT-253 mass spectrometer have been applied to study the chronology, mineralogy, evolution of the ore-forming fluid and source of granitoids, and S and CH4 in the ore-forming fluid of the deposit. Following results are mainly obtained.Three kinds of intrusive bodies including biotite granite, diorite porphyry and quartz diorite porphyry have been identified in the Seleteguole deposit. The biotite granite has LA-ICP-MS zircon U-Pb weighted mean age of 307±3 Ma, while the relatively late intrusive bodies of diorite porphyry and quartz diorite porphyry have almost same zircon U-Pb weighted mean age of 302 ± 3 Ma. Molybdenite from the diorite porphyry has Re-Os weighted mean age of 301±2 Ma, which is similar to those of the porphyries.Geochemical characteristics of those granitoids in the Seleteguole deposit show that they are enriched in LILE and LREE, depleted in HFSE and HREE, with negative anomalies of Nb, Ti, and P in the spider diagram of trace elements and weakly negative Eu anomalies in the REE pattern, indicating that they were formed in the island arc environment. The positive εHf(t) values of zircons, low Mg# values (34–39), and low Cr (< 60 ppm) and Ni (< 15 ppm) contents of those granitoids suggest that they could be derived from juvenile lower crust which could be formed by the accretion of island arc magma which was derived from the partial melting of the mantle wedge due to the subduction of the oceanic plate. The felsic melts, which were respectively derived from the partial melting of the juvenile lower crust due to the influence of the continuous subduction of oceanic plate, emplaced respectively into the upper crust to have formed biotite granite and porphyries, which have properties of island arc magma and positive εHf(t) values of zircons. Those 3 kinds of granitoids in the Seleteguole area have relatively high Th and LREE contents, indicating the involvement of oceanic sediments during the subduction process. Comparing to the biotite granite, diorite porphyry and quartz diorite porphyry have higher Th/La ratios but lower zircon εHf(t) values, indicating that more subducted oceanic sediments were involved into the formation of porphyry magmas in the Seleteguole. Based on the study of the regional tectonic setting of the deposit and the analogical study of the Late Carboniferous and Early Permian granitoids in Northwestern Tianshan region, we suggest that the transition of the tectonic setting of the Northwestern Tianshan, from a subduction to an extension, could occur at the end of Carboniferous or the beginning of Permian (ca. 300 Ma).The garnet is an important skarn mineral in the Seleteguole. 3 kinds of garnets have been classified based on their occurring places and colours in the Seleteguole. The first one is red garnet which occurred in the endoskarn zone and the skarn around the porphyry bodies. The second one is brown garnet which mainly occurred in the middle zone between the porphyry bodies and the limestone. The third one is yellow-green garnet occurred close to the limestone or hornfels. EPMA analytical results of those three types of garnets show that they are major grossularite and minor andradite, with trace ivaarite, partschinite, pyrope, and almandite, indicating that these garnets were formed under acidic reduced conditions. The brown garnet has oscillating zones which are relatively enriched in Fe or Al. The Fe-rich zone could be formed due to the increase of the oxygen fugacity caused by the depletion of CH4 in the fluid during the intermittent period of magmatic activity, whereas the Al-rich zone could be formed due to the superposition of the CH4-rich reduced fluid during the next circle of magmatic activity.Based on properties of fluid inclusions in the Seleteguole Cu-Mo deposit, there are four types of fluid inclusions, including single-phase fluid inclusions, vapor-rich fluid inclusions, daughter mineral-bearing hypersaline liquid fluid inclusions, and aqueous low salinity fluid inclusions. The single-phase fluid inclusions are mainly observed in quartz phenocrysts of porphyries and the early stage skarn minerals such as garnet and vesuvianite. They have high homogenization temperatures ranging from 375o to 454oC. The critical homogenization behavior has been observed in some of the single-phase fluid inclusions. The vapor-rich fluid inclusions, which are relative rarely observed, are finally homogenized to the vapor phase with homogenization temperatures ranging from 352o to 398oC. The homogenization temperatures of the daughter mineral-bearing hypersaline liquid fluid inclusions vary generally from 200o to 400oC. The temperature for the disappearance of the daughter mineral halite can be either higher or lower than that of the disappearance of the bubble in the inclusions during heating process. The bubble in the aqueous low salinity fluid inclusions could be suddenly shrunk during freezing process. The flocculent clathrates can be observed when the bubble size is gradually increased with the increase of temperature during the reheating process of the frozen inclusions. Temperatures for the disappearance of clathrates generally vary from 3 oC to 7 oC. Homogenization temperatures of the aqueous low salinity fluid inclusions are ranging from 185o to 276oC. The supercritical fluid exsolved from the magma will migrate upward by the buoyancy. With the decrease of temperature and pressure, the un-mixing or boiling of the supercritical fluid will be initiated at the intersecting point on the V-L solvus. This will result in the formation of low salinity vapor-rich inclusions and daughter mineral-bearing hypersaline inclusions. The evolved fluid during the further upward migration process will possibly mix with meteoric water to form the low-salinity fluid inclusions.The laser Raman spectroscopy analyses of various kinds of fluid inclusions show that the vapor phase of the ore-forming fluid in the Seleteguole is mainly the CH4. Salinities of the single phase inclusion vary from 2.1 wt.% to 6.4 wt.%, with the mean of 3.8 wt.%. Salinities of fluid inclusions in ore-bearing quartz veins vary from 3.0 wt.% to 7.5 wt.%, with the mean of 5.4 wt.%. Contents of CH4 in the single phase fluid inclusions range from 3.8 mol/kg to 10.4 mol/kg, corresponding to FMQ values of the oxygen fugacity ranging from -0.5 to -1 under the assumption that the fluid was trapped at depth of 5 km. Sulfides of various mineral assemblages in the Seleteguole deposit have relatively consistent sulfur isotopic compositions, with δ34S values ranging from -1.22‰ to +2.52‰ and the mean of +1.402‰, showing the feature of the mantle sourced sulfur. Carbon isotopic compositions (δ13CV-PDB) of the CH4 in CH4-rich fluid inclusions vary from -29.2‰ to -19.1‰, with the mean of -25.7‰. Hydrogen isotopic compositions (δDV-SMOW) of the CH4 in CH4-rich fluid inclusions vary from -273.3‰ to -234.9‰, with the mean of -256.9‰. The carbon and hydrogen isotopic composition of the CH4 in CH4-rich fluid inclusions and the discovery of the CH4-rich single phase fluid inclusions indicate that the CH4 in the fluid could be derived directly from the magma rather than resulted from hydrothermal activity of the ore-forming fluid. The Seleteguole Cu-Mo deposit is spatially and genetically associated with the ilmenite-bearing reduced I-type granitoids. The ore-forming fluid is the CH4-rich reduced fluid, with calculated FMQ values of the oxygen fugacity ranging from -0.5 to -1.0 (Assuming the fluid was trapped at the depth of 5 km). Abundant minerals of low oxygen fugacity, such as pyrrhotite and grossularite, are developed in the deposit, whereas representative minerals of high oxygen fugacity, such as primary hematite, magnetite, and sulfate minerals (i.e., anhydrite), have not been observed. Therefore, we suggest that the Seleteguole is a typical reduced porphyry-skarn deposit. |
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