Combined investigations of fluid inclusions in opaque ore minerals by NIR/SWIR microscopy and microthermometry and synchrotron radiation X-ray fluorescence     

《Applied Geochemistry》2006,21(5):813-819

An alternative IR microscopy system in the NIR (near infrared, up to 10 μm) and SWIR (short wavelength infrared, up to 1.4 μm) ranges has been developed for the study of opaque ore minerals. The system uses either IR LED or IR light bulb sources depending on the degree of opacity of the investigated minerals. This paper presents the methodology and the promising results obtained in studies of opaque ore minerals such as Ag minerals (pyrargyrite) from epithermal deposits and Nb-tantalates (columbite) from pegmatites. It also presents results on the internal features of hematites from Fe ore banded formations and tungstates from granite–greenstone belt deposits. The data obtained on fluid inclusions from pyrargyrite and hematite crystals have been integrated by complementary information from X-ray fluorescence analysis using synchrotron radiation (μ-SXRF) under conditions specifically designed for the study of opaque ore minerals.  相似文献   

Significance of adakites in petrogenesis of early Silurian magmatism at the Yudai copper deposit in the Kalatag district,NW China     

《Ore Geology Reviews》2017

Yudai is a newly discovered copper deposit associated with a porphyritic quartz diorite, in the Kalatag district of the eastern Tianshan, China. SHRIMP U-Pb dating of zircons from the diorite yielded an age of 432 ± 3 Ma. The diorite is peraluminous (ASI = 0.98–1.10), calc-alkaline to tholeiitic with high Al₂O₃ of 16.6–17.7 wt% and Mg^# of 57.4–67.4. Trace element characteristics of the diorite show it is enriched in Ba, K and Sr, and depleted in Nb, Ta, Ti, with a positive Eu anomaly and high Sr/Y and La/Yb ratios. This diorite has positive ε_Nd(t) values ranging from 6.2 to 8.4 with low initial ⁸⁷Sr/⁸⁶Sr ratios of 0.704336 to 0.704450. These geochemical and isotopic characteristics indicate that the adakite-like diorite, associated with the copper mineralization, was emplaced in an island arc setting and resulted from partial melting of subducted oceanic plate in a mantle wedge.  相似文献   

胶西北大尹格金矿床成矿机理:载金黄铁矿标型及硫同位素地球化学约束   总被引：4，自引：3，他引：1  

张瑞忠  王中亮  王偲瑞  刘育  秦文凯 《岩石学报》2016,32(8):2451-2464

胶东是我国最重要的金矿集中区,破碎带蚀变岩型金矿床是区内最主要的金矿床类型,该类型金矿床已探明金资源量占全区的90%以上,其巨量金的来源是引人瞩目的关键科学问题。招平断裂带是该区内规模最大的断裂-成矿带,位于招平金矿带中段的大尹格庄金矿床是该金矿带最具代表性的破碎带蚀变岩型金矿床之一,已探明金金属量约283t。大尹格庄金矿床严格受沿胶东群与玲珑花岗岩接触带发育的NNE向招平断裂带控制,矿体赋存在招平断裂下盘黄铁绢英岩化和碎裂岩化玲珑花岗岩中,主要由Ⅰ号和Ⅱ号矿体组成,其具有相似的矿物组成,矿石主要矿物是绢云母、石英、黄铁矿,次要矿物是钾长石、斜长石、黑云母、方解石、黄铜矿、方铅矿、闪锌矿、磁黄铁矿、黝铜矿和自然金、自然银、金银矿、碲银矿等;其中黄铁矿是最主要的载金矿物。根据穿插关系和矿物共生组合,大尹格庄金矿床内成矿作用可划分为4个成矿阶段,分别是黄铁矿-石英-绢云母阶段(I)、石英-黄铁矿阶段(Ⅱ)、石英-多金属硫化物阶段(Ⅲ)和石英-方解石-多金属硫化物阶段(Ⅳ)。各个成矿阶段的黄铁矿的晶体形态标型研究表明,成矿Ⅰ阶段黄铁矿以粗粒自形立方体为主,含有少量五角十二面体;成矿Ⅱ和Ⅲ阶段黄铁矿以细粒五角十二面体为主,且具有更多五角十二面体、八面体和立方体形成的聚形;成矿Ⅳ阶段主要为细粒立方体晶形。不同矿体各个成矿阶段的硫化物的δ~(34)S值集中在4.58‰~7.54‰,具有一定的塔式效应,正向偏离陨石硫,与胶东地区胶东群变质岩、围岩花岗岩类δ~(34)S比较接近,指示大尹格庄金矿床各个成矿阶段的矿石硫源总体一致,与胶东群变质岩和中生代花岗岩间具有继承演化关系。此外,从成矿Ⅰ阶段→Ⅱ阶段→Ⅲ阶段→Ⅳ阶段,大尹格庄金矿床矿石硫化物δ~(34)S呈现出逐渐降低的趋势,反映了成矿过程中物理化学条件的演化趋势:Ⅰ阶段为较高温度(330~350℃)、快速冷却、低过饱和度、低氧逸度和硫逸度的成矿环境;Ⅱ和Ⅲ阶段黄铁矿形成于中-低温(200~300℃)、成矿流体过饱和度高、高氧逸度和硫逸度、缓慢冷却同时物质供应充分的成矿环境;Ⅳ阶段处于较低温度(200℃)、热液流体过饱和度较低、低氧逸度和硫逸度、同时物质供应不足的成矿环境。  相似文献   

焦家断裂渗透性结构与金矿床群聚机理:构造应力转移模拟   总被引：4，自引：3，他引：1  

王偲瑞  杨立强  孔鹏飞 《岩石学报》2016,32(8):2494-2508

焦家金矿带是焦家式金矿的命名地,也是我国第一个千吨级金矿田的发现地。其内构造破碎带蚀变岩型金矿床(体)受NE-NEE向焦家断裂及其下盘近平行的次级断裂控制,具有明显的空间群聚分布特征。然而,由于对这些金矿床成因机理的认识存在分歧,对其空间群聚分布的形成机制也有多种解释,对断裂带覆盖区及其深部成矿潜力更是缺乏科学评价。为此,针对这些难题,论文在详细控矿构造解析的基础上,通过建立焦家金矿带三维有限元模型,运用应力转移模拟计算成矿期的库仑破裂应力变化值(△CFS),标定了成矿期断层活动导致的应力转移情况及其形成的高渗透率区域,探讨它们对矿床空间分布的可能控制作用和金矿床群聚分布的形成机理及焦家式金矿的成因机理,并据此圈定了成矿远景区,估算了其深部资源潜力。应力转移模拟结果显示△CFS以焦家断裂为中心呈现玫瑰弧瓣图像分布,其中,应力减小(负值)区(-195bar≤△CFS≤-3bar)以新城-高家庄子为中心呈"十"字形分布(东西宽8km、南北长12km),为低渗透率区域,其内尚未发现金矿床产出;而应力增大(正值)区(3bar≤△CFS≤84bar)呈28个大小不等的弧瓣分布在断层走向转弯处或断层交汇处,为高渗透区域,已发现的金矿床均位于其中,且已探明的金金属量与其所处区域△CFS极值正相关(金金属量Q=4.526×△CFS-83.27)。这种金矿床与断层活动导致的△CFS在空间分布上的一致性,表明焦家式金矿床的形成和产出严格受焦家断裂及其次级断裂控制,区别于典型的"与侵入体有关的金矿"和"岩浆热液矿床",而与造山型金矿床类似。然而其独特的构造背景与成矿环境及蚀变-矿化组合,表明该类型金矿床不能被现有成矿模式所涵盖,而可能属于独特的"胶东型"金成矿系统。焦家金矿带上控矿断裂的形成受同震应力转移的制约,断裂带脆性变形过程中,地震破裂沿断层传播,在断层产状变化或多组断层交汇处,△CFS增大,造成反复余震活动破坏岩石,形成局部高渗透率结构,为金的沉淀提供有利场所,产生了金矿床的群聚现象。据此,圈定朱宋、徐家疃、西良、马埠庄子四个成矿远景区,预测金资源量分别为79t、66t、43t和16t;而寺庄、望儿山、河西、河东等金矿床深部仍有巨大找矿潜力。  相似文献   

Numerical modeling study of mineralization induced by methane cold seep at the sea bottom     

《Marine and Petroleum Geology》2016

In order to investigate the response of authigenic minerals to gas hydrate geo-systems, the biogeochemical processes and its induced mineralization were predicted by employing the comprehensive reactive transport modeling approach. Based on the available data extracted from the northern continental slope area of the South China Sea, a 1-D vertical column model was developed. Three cases with different upward methane flux rates and three cases with different mineral compositions, i.e., a total of six cases were designed to investigate the effects of variations in the depth of sulfate methane transition zone (SMTZ) and in the mineral composition on the formation of authigenic minerals. The simulation results indicate that the SMTZ depth influenced by both the upward methane flux rate and the initial composition played an important role in the formation of authigenic minerals. The AOM reaction is intensive at the interface, and the precipitation amount of calcite is large, which is mainly controlled by AOM. When the methane leakage rate is 20 times higher than the base case, aragonite starts to precipitate. During the simulation, oligoclase, k-feldspar, smectite-Na, smectite-Ca, chlorite dissolved. Our study specific to this area as a starting point may provide a quantitative approach for investigating carbonate and pyrite formation in hydrate-bearing sediments accounting for methane oxidation and sulfate reduction. The method presented here and the model built in this study can be used for other sites with similar conditions. In addition, this study may serve as an indication for the potential natural gas hydrate reservoir in depth, and is also significant for marine carbon and sulfur cycle.  相似文献   

Geodynamic regimes of thermochemical mantle plumes     

《Russian Geology and Geophysics》2016,57(6):858-867

Laboratory and numerical experiments simulating the heat transfer and flow structure of thermochemical mantle plumes provide insights into the mechanisms of plume eruption onto the surface depending on the relative thermal power of plumes Ka = N/N₁, where N and N₁ are the heat transferred from the plume base to the plume conduit and the heat transferred from the plume conduit to the surrounding mantle, respectively, under steady thermal conduction. There are three main types of plumes according to the Ka criterion: (i) plumes with low thermal power (Ka < 1.15), which fail to reach the surface, (ii) plumes with intermediate thermal power (1.15 < Ka < 1.9), which occur beneath cratons and transport melts from depths below 150 km, where diamond is stable (diamondiferous plumes), and (iii) plumes with a mushroom-shaped head (1.9 < Ka < 10), which are responsible for large intrusive bodies, including batholiths. The volume of erupted melt and the depth from which the melt is transported to the surface are estimated for plumes of types (ii) and (iii). The relationship between the plume head area (along with the plume head diameter) and the relative thermal power is obtained. The relationship between the thickness of the block above the plume head and the relative thermal power is derived. On the basis of the results obtained, the geodynamic-regime diagram of thermochemical mantle plumes, including the plumes with Ka > 10, has been constructed.  相似文献   

Carbonates and sources of fluids in ores and metasomatites of the Ermakovka fluorite-bertrandite-phenacite deposit (western Transbaikalia)     

《Russian Geology and Geophysics》2016,57(9):1288-1297

We present results of isotope-geochemical study of the Ermakovka F-Be deposit, including data on the oxygen and carbon isotope compositions in dolomite and calcite marbles and in carbonates accompanying skarns, of early and late stages of ore formation and of post-ore parageneses. To elucidate the sources of fluids participated in the ore formation, we calculated the oxygen isotope composition in water and the hydrogen isotope composition in hydroxyl-containing minerals. Phlogopite in marbleized dolomites, vesuvianite and amphibole in skarns, eudidimite and bertrandite in ore parageneses, and bavenite formed during post-ore processes are analyzed. Most of the ore-stage minerals are depleted in heavy oxygen. Their 5¹⁸O values are lower than 5-6%c (SMOW). Oxygen in carbonate minerals of the initial stage (dolomite and bastnaesite) is heavier (1.3-4.9%c) than that in calcite (+ 2 to -3.7%c). The 5¹⁸O values of water in equilibrium both with carbonate and with silicate minerals (-4 to -14%c) suggest the contribution of meteoric water to the mineral formation. A magmatic fluid (5¹⁸O from + 6 to + 9%c) participated in the skarn formation at the initial stage, and a meteoric fluid, at the final stage (5¹⁸O from -1 to -9%c). A meteoric source is confirmed by the depleted hydrogen isotope composition in minerals (5D from -119 to -192%c).  相似文献   

Early Cambrian palaeobiogeography of the Zhenba–Fangxian Block (South China): Independent terrane or part of the Yangtze Platform?     

《Gondwana Research》2016,29(4):1543-1565

Early Cambrian small skeletal fossils (SSFs) are studied and revised from the Zhenba–Fangxian Block of the transitional zone between the Yangtze Block and the South Qinling Terrane. The study reveals a diverse fauna with 47 species of various biological affinities, including the new species Gapparodus gapparites sp. nov. The SSFs are assigned to the newly defined Cambroclavus fangxianensis–Rhombocorniculum cancellatum Assemblage Zone. Based on the investigated SSF fauna from Zhenba County, Southeast Shaanxi of China and published data, a palaeobiogeographic study is carried out for the Cambrian Stage 3 (equivalent to the Atdabanian–Botoman of Siberia). A hierarchical Pearson similarity cluster analysis of 295 species from 32 regions of the world indicates a distinct palaeobiogeographic pattern with seven faunal provinces. The result is mostly consistent with existing palaeogeographic reconstructions for the early Cambrian. However, it is also shown that the SSF assemblages of the Zhenba–Fangxian Block have low similarity with those of the Yangtze Block. Instead, they share high similarity with those from Armorica, Tarim and the Karatau–Naryn terranes (South Kazakhstan/North Kyrgyzstan). The Yangtze Block has a unique SSF assemblage dissimilar to most of other regions. The Terreneuvian–Cambrian Stage 3 sedimentary sequence of the Zhenba–Fangxian Block is more consistent with that of the South Qinling Terrane. Besides, sedimentary Ediacaran manganese ore deposits and Cambrian barite/witherite deposits have unique distribution pattern on the Zhenba–Fangxian Block. Derived from the profound dissimilarities in faunal composition, sedimentary sequence and distribution of sedimentary ore deposits, we hypothesize that during the Neoproterozoic–Cambrian transition, the Zhenba–Fangxian Block might have been an independent terrane and more distant from the Yangtze Block. The palaeobiogeographic analysis of SSFs also indicates a closer alliance between Avalonia and Siberia. It corroborates the palaeogeographic reconstruction of North China at the margin of Gondwana, in the vicinity of Australia, Antarctica, and Armorica.  相似文献   

塔里木大火成岩省瓦吉里塔格霞石岩铂族元素地球化学特征     

刘秉翔  张招崇  张东阳  程志国 《岩石矿物学杂志》2018,37(5):799-810

作为塔里木大火成岩省形成最晚的火成岩,新疆巴楚瓦吉里塔格霞石岩的岩浆源区性质的确定对于揭示塔里木大火成岩省的深部地质过程具有重要的约束作用。对瓦吉里塔格霞石岩的铂族元素地球化学特征进行了研究,铂族元素(PGE)分析结果显示,原始地幔标准化的PGE呈正斜率型分布,且Pd/Ir值高于原始地幔比值,说明霞石岩的铂族元素发生了分异。霞石岩全岩的PGE与Mg O呈正相关,Pd/Ir、Cu/Pd与Mg O则呈负相关,说明PGE的分异主要受到橄榄石的结晶分异作用控制,也是其Cu/Pd值极高及岩浆S饱和的因素之一,同时Cu/Pd值说明霞石岩岩浆为硫饱和岩浆,但是没有因素导致岩浆S过饱和进而发生硫化物的熔离。与其他大火成岩省岩石相比,瓦吉里塔格霞石岩极度亏损PGE,SCSS(硫承载量)计算结果表明母岩浆在形成之初就发生S过饱和,主要是地幔低程度部分熔融造成的,据此认为地幔源区的部分熔融程度在塔里木大火成岩省Cu-Ni硫化物铂族元素矿床形成过程中起着至关重要的作用。  相似文献   

江南造山带黄金洞金矿床成矿机制:矿物形成环境与金成矿物理化学条件制约   总被引：4，自引：4，他引：0  

孙思辰  张良  吴圣刚  高磊  彭劲松  文亭 《岩石学报》2018,34(5):1469-1483

黄金洞超大型金矿床位于江南造山带中段,赋存于新元古界浅变质岩系中,受控于NNE-NE向长平断裂带,金资源储量达100吨。该矿床可由南至北分为金福、金塘、杨山庄和曲溪矿段,主要矿化类型有石英-硫化物脉型、构造角砾岩型和黄铁毒砂绢英岩型。金属矿物主要发育有自然金、毒砂、黄铁矿、黄铜矿、闪锌矿、方铅矿、磁黄铁矿等;非金属矿物有石英、绢云母、方解石和菱铁矿等,其中金主要以自然金与不可见金形式存在。根据野外与镜下观察,金成矿作用分为Ⅰ石英-金-毒砂-黄铁矿、Ⅱ石英-金-多金属硫化物-白钨矿和Ⅲ石英-辉锑矿-绿泥石3个阶段,前二者为主要成矿阶段。曲溪矿段Ⅱ阶段毒砂相对不发育、而磁黄铁矿和自然金显著发育,绿泥石主要发育于Ⅲ阶段中,与辉锑矿及闪锌矿共生。根据不同矿段各阶段毒砂与Ⅲ阶段绿泥石成分,计算其温度、lgf(S_2)与lgf(O_2),可见Ⅰ阶段成矿温度与硫逸度高于Ⅱ阶段:杨山庄矿段两阶段成矿温度分别为300～378℃、260～300℃,lgf(S_2)分别为-11～-7.2、-11.9～-10.1;金塘两阶段成矿温度为240～311℃、245～298℃;金福Ⅱ阶段成矿温度上限为297℃;曲溪矿段成矿温度为268～368℃,Ⅱ阶段毒砂lgf(S_2)与Ⅲ阶段绿泥石lgf(O_2)分别为-13.2～-8.7、-50.9～-40.1。根据不同阶段矿物之间的相互关系及成矿温度与硫逸度演化特征,推断Ⅰ、Ⅱ成矿阶段伴随强烈的硫化作用,金以类质同象方式进入毒砂和黄铁矿中,形成不可见金;其中Ⅱ阶段由于成矿流体压力骤降,含金流体发生相分离作用,H2S等气体大量逃逸,导致成矿流体中硫含量骤降,加以硫化作用持续消耗流体中的硫,促进了含金络合物分解与自然金的沉淀。  相似文献