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151.
The Niujuan breccia-type silver deposit forms part of the North Hebei metallogenic belt along the northern margin of the North China Craton. The Hercynian Baiyingou coarse-grained granite and the Yanshanian Er’daogou fine-grained granite are the major Mesozoic intrusions exposed in this region. Here we investigate the salient characteristics of the mineralization and evaluate its genesis through zircon U-Pb and fluorite Sm-Nd age data, and Pb, S, O, H, He and Ar isotope data. The orebodies of the Niujuan silver deposit are hosted in breccias, which contain angular fragments of the Baiyingou and Er’daogou granitoids. The δ34S values of pyrite from the silver mineralized veins range from 2.4‰ to 5.3‰. The 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios of the sulfide minerals show ranges of 16.837–16.932, 15.420–15.501 and 37.599–37.950, respectively. The 3He/4He and 40Ar/36Ar ratios of the fluids trapped in pyrite are 0.921–4.81Ra and 299.34–303.84, respectively. The δ18O and δ18Dw values of the ore-forming fluids range from 0.6‰ to −4.15‰ and from −119.4‰ to −98.7‰, respectively. Our isotopic data suggest that the ore-forming fluids were originally derived from the subvolcanic plutons and evolved into a mixture of magmatic and meteoric water during the main hydrothermal stage. The ore-forming materials were primarily derived from the lower crust with limited incorporation of mantle materials. The emplacement time of the Er’daogou granite is constrained by LA-ICP-MS zircon U-Pb geochronology at 145.5 ± 2.1 Ma. Five fluorite samples from the last hydrothermal stage yielded a Sm-Nd isochron age of 139.2 ± 3.8 Ma, indicating the upper age limit for the silver mineralization. These ages correlate with the formation of the Niujuan deposit in an extensional setting associated with the closure of the Mongol-Okhotsk Ocean and the subduction of the Paleo-Pacific oceanic plate beneath the North China Craton. 相似文献
153.
Zhang Shuai Carranza Emmanuel John M. Wei Hantao Xiao Keyan Yang Fan Xiang Jie Zhang Shihong Xu Yang 《Natural Resources Research》2021,30(2):1011-1031
Natural Resources Research - The excellent performance of convolutional neural network (CNN) and its variants in image classification makes it a potential perfect candidate for dealing with... 相似文献
154.
西藏雄梅铜矿区含矿斑岩与非含矿斑岩成因对比研究 总被引：1，自引：1，他引：0
西藏雄梅铜矿床是近年来在班公湖_怒江成矿带中段新发现的一处斑岩铜矿床,该矿床的发现使得班公湖_怒江成矿带真正具备了"带"的概念,大大地拓宽了找矿远景。文章通过对雄梅铜矿区斑岩体的LA_ICP_MS锆石U_Pb定年,发现矿区存在2套斑岩:一套是前人测定的年龄为106.7 Ma的含矿斑岩;另一套是本文测定的非含矿斑岩,3个年龄分别是(121.8±2.3)Ma(MSWD=0.32)、(122.8±2.1)Ma(MSWD=1.16)、(121.5±2.5)Ma(MSWD=0.54)。两套斑岩的岩性虽然都是花岗闪长斑岩,但非含矿斑岩比含矿斑岩含有更多的钾长石,矿化强度大大减弱。岩石地球化学分析结果表明,两套斑岩虽然都富集大离子亲石元素(LILE)Rb、Ba、Th、U、K、Pb,亏损高场强元素(HFSE)Nb、Ta、Ti,具有碰撞后岩浆作用的共同特征,但在岩浆源区和成因上显示出明显的差异。含矿斑岩和非含矿斑岩均属于强过铝质S型花岗岩,然而前者源区组成为杂砂岩,后者源区则以泥质岩为主。岩浆分异过程中,含矿斑岩受斜长石和钾长石的分离结晶控制,非含矿斑岩则受钾长石和黑云母的分离结晶控制。 相似文献
155.
The newly discovered large-scale Baiganhu W–Sn orefield, consisting of the Kekekaerde, Baiganhu, Bashierxi, and Awaer deposits, is located in Ruoqiang County, southeastern Xinjiang, China. These deposits comprise mainly three types of W–Sn mineralization: early-stage skarn-type, middle-stage greisen-type, and late-stage quartz-vein-type. In this study, we classified seven major vertical zones on the basis of petrographic characteristics, roughly from the bottom of the parental granitic intrusions upward, as (A) fresh syenogranite, (B) argillic alteration, (C) muscovite-dominated greisenization, (D) tourmaline-dominated greisenization, (E) marginal facies (including K-feldspar pegmatite and fine-grained granite), (F) aplitic apophysis, and (G1) skarn or (G2) infilled silification zones. According to the alteration–mineralization assemblages and cross-cutting relationships, five stages of mineralization are recognized in the orefield (I, skarn stage; II, greisen stage; III, quartz vein stage; IV, argillic alteration stage; and V, supergene stage), and reverse alteration zonation in the altered intrusion is also observed.The W–Sn deposits are spatially associated with syenogranite, which is part of the Caledonian Bashierxi magmatic series. Laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) zircon U–Pb dating of the syenogranite yields a weighted mean 206Pb/238U age of 413.6 ± 2.4 Ma (MSWD = 0.36, n = 30). Hydrothermal muscovite from three samples associated with W–Sn mineralization yields plateau 40Ar/39Ar ages of 411.7 ± 2.6 Ma (MSWD = 0.21), 412.8 ± 2.4 Ma (MSWD = 0.22), and 413.8 ± 2.6 Ma (MSWD = 0.22), which is consistent with the zircon U–Pb age, thus indicating a temporal link between the emplacement of the syenogranite and the W–Sn mineralization. Our age data and previously published ages, along with geochemical data, for the granitoids in the Bashierxi magmatic series show a nearly contemporaneous evolution of A- and S-type granites, which were emplaced in a post-orogenic setting at ca. 432–413 Ma. As compared with the A-type granites, the syenogranites with S-type affinities probably resulted from a lower degree of partial melting of metagreywackes, which was more likely to be enriched in the ore-forming elements W and Sn, as well as volatiles such as B and H2O. In addition, the syenogranites exhibit low oxidation states and underwent high degrees of factional crystallization, both of which favor post-magmatic W–Sn mineralization. We suggest that more attention should be given to buried syenogranites of S-type affinities during mineral exploration in this area, and that the proposed model of a vertical alteration zoning can act as a guide to the targeting of similar ore systems. 相似文献
156.
Zircon U–Pb and Molybdenite Re–Os Ages of the Lakange Porphyry Cu–Mo Deposit,Gangdese Porphyry Copper Belt,Southern Tibet,China 
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下载免费PDF全文 Qiu‐Feng Leng Ju‐Xing Tang Wen‐bao Zheng Bin Lin Pan Tang Hao Wang Hai‐Feng Li 《Resource Geology》2016,66(2):163-182
The Lakange porphyry Cu–Mo deposit within the Gangdese metallogenic belt of Tibet is located in the southern–central part of the eastern Lhasa block, in the Tibetan Tethyan tectonic domain. This deposit is one of the largest identified by a joint Qinghai–Tibetan Plateau geological survey project undertaken in recent years. Here, we present the results of the systematic logging of drillholes and provide new petrological, zircon U–Pb age, and molybdenite Re–Os age data for the deposit. The ore‐bearing porphyritic granodiorite contains elevated concentrations of silica and alkali elements but low concentrations of MgO and CaO. It is metaluminous to weakly peraluminous and has A/CNK values of 0.90–1.01. The samples contain low total REE concentrations and show light REE/heavy REE (LREE/HREE) ratios of 17.51–19.77 and (La/Yb)N values of 29.65–41.05. The intrusion is enriched in the large‐ion lithophile elements (LILE) and depleted in the HREE and high field‐strength elements (HFSE). The ore‐bearing porphyritic granodiorite yielded a Miocene zircon U–Pb crystallization age of 13.58 ± 0.42 Ma, whereas the mineralization within the Lakange deposit yielded Miocene molybdenite Re–Os ages of 13.20 ± 0.20 and 13.64 ± 0.21, with a weighted mean of 13.38 ± 0.15 Ma and an isochron age of 13.12 ± 0.44 Ma. This indicates that the crystallization and mineralization of the Lakange porphyry were contemporaneous. The ore‐bearing porphyritic granodiorite yielded zircon εHf(t) values between ?3.99 and 4.49 (mean, ?0.14) and two‐stage model ages between 1349 and 808 Myr (mean, 1103 Myr). The molybdenite within the deposit contains 343.6–835.7 ppm Re (mean, 557.8 ppm). These data indicate that the mineralized porphyritic granodiorite within the Lakange deposit is adakitic and formed from parental magmas derived mainly from juvenile crustal material that partly mixed with older continental crust during the evolution of the magmas. The Lakange porphyry Cu–Mo deposit and numerous associated porphyry–skarn deposits in the eastern Gangdese porphyry copper belt (17–13 Ma) formed in an extensional tectonic setting during the India–Asia continental collision. 相似文献
157.
Platinum-group element (PGE) and gold inclusions are usually present in peridotites and chromitite deposits associated with ophiolites. Here, we present the first detailed study of the mineralogy of precious metals in ultramafic rocks hosted in the Paleozoic Coastal Accretionary Complex of Central Chile. In these ultramafic rocks the mineralization of precious metals is associated with small meter-size pods and veins of massive chromitite hosted in serpentinite-filled shear zones. Crystallographic orientation maps of single chromite grains, obtained using the Electron-Backscattered Secondary Diffraction technique, allow us to identify two types of chromite in the precious-metal bearing chromitites: (1) Type A chromite, characterized by an average misorientation per grain of ≤ 2° and chemically homogeneous cores surrounded by a porous rim with abundant inclusions of chlorite, and (2) Type B chromite, which exhibits higher degrees of misorientation (2–8°) and porosity, and abundant silicate inclusions, but a relatively homogeneous chemical composition. In situ analyses using EMPA and LA-ICP-MS for major, minor and trace elements indicate that composition of the magmatic chromite is only preserved in the cores of Type A chromite grains. Core to rim chemical trends in these Type A chromites are characterized by a progressive increase of the Cr# with a decrease of the Mg#, loss of Al and addition of Fe2 + in the porous rim. The observed changes in the microstructure and chemistry of chromite are associated with the infiltration of external fluids through shear zones filled with antigorite (± talc) developed in partly serpentinized peridotites (i.e., olivine–lizardite dunites). Thermodynamic calculations using the phase equilibria relations in the system Cr2O3–MgO–FeO–Al2O3–SiO2–H2O (CrMFASH) indicate that Fe2 +-rich porous chromite + chlorite replaced the original assemblage chromite + olivine in the chromitite while prograde antigorite was formed. According to our results this transformation occurred at ~ 510–560 °C when external fluids penetrated the ultramafic/chromitite bodies through shear zones. These temperatures are slightly higher than estimated for the metamorphic peak in the host metapelitic rocks (i.e., ~ 420 °C at 9.3 kbar), suggesting that a hotter ultramafic body was captured by the metasediments of the accretionary prism during their exhumation through subduction channel. Chlorite geothermometry yielded a wide range of lower temperature from 430 to 188 °C, for chlorite present in the porous chromite rims. These results are in agreement with the retrograde overprint under greenchist-facies metamorphism conditions recorded by metapelitic host rocks and minor volcanogenic massive sulphide deposits in the area (300–400 °C, ~ 3–4 kbar). We suggest that although initially decoupled, the chromitite-bearing ultramafic rocks and their metasedimentary host undergone a common metamorphic PT pathway of exhumation during the formation and evolution of the subduction-related accretionary complex.The chromitites contain appreciable amounts of the platinum-group elements (up to 347 ppb total) and gold (up to 24 ppb), present as inclusions of platinum-group minerals (PGM) and alloys as well as native gold. The PGM identified include native osmium, laurite (RuS2), irarsite (IrAsS), osarsite (OsAsS), omeiite (OsAs2), Pt–Fe alloy (possibly isoferroplatinum) and a suite of inadequately identified phases such as PtSb (possibly stumpflite), PdHg (possibly potarite), RhS, Ir–Ni and Ir–Ni–Ru compounds. Only a few grains of osmium and laurite were identified in unaltered cores of chromite and therefore considered as magmatic in origin formed during the high-T event of chomite crystallisation in the upper mantle. The other PGM were located in the porous chromite associated with chlorite or base-metal minerals (BMM) that often fill the pores of this altered chromite or are intergrowth with antigorite in the host serpentinized ultramafic rock. The assemblage of BMM identified in the studied rocks include sulphides [millerite (NiS), polydymite (Ni3S4), violarite (FeNi2S4), galena (PbS), sphalerite (ZnS), chalcocite (CuS)], arsenides [(orcelite (Ni5 − xAs2) and maucherite (Ni11As8)], the sulpharsenide gersdorfitte (NiAsS), and native bismuth. The irregular shape of several PGM grains observed in porous chromite suggest disequilibrium, whereas others exhibit perfectly developed crystal faces with the associated secondary silicate or base-metal mineral suggesting neoformation of PGMs in situ from metamorphic fluids. We suggest that the origin of these PGM inclusions is magmatic, but some grains were reworked in situ when metalloid (i.e., As, Sb, Pb, Zn and Hg)-rich fluids released from metasediments penetrated the ultramafic rocks through active shear zones, once the ultramafic bodies became tectonically mixed with the host metasedimentary host rocks. During this event, gold sourced from the (meta)sediments was also precipitated within chromitites and serpentinites. 相似文献
158.
赣南园岭寨大型钼矿岩石地球化学、成岩成矿年代学及其地质意义 总被引：5，自引：0，他引：5
江西省安远县园岭寨钼矿是南岭地区新发现的大型独立斑岩型钼矿床,矿体主要产出在园岭寨花岗斑岩与寻乌组变质岩的内外接触带中。通过对园岭寨钼矿系统的岩石学、地球化学和成岩成矿时代研究,结果表明,园岭寨花岗斑岩化学成分具有富K2O(6.52%～8.33%)、P2O5(0.17%～0.21%)、过铝质(A/CNK=1.33～1.59),高Mg#(53～68)、贫CaO(0.37%～2.99%)、Na2O(0.27%～1.01%)和K2O/Na2O>1的特征;微量元素以富含Rb,亏损Ba、Sr等大离子亲石元素(LILE)和富含U、Pb、Nd、Zr、Hf等,亏损Nb、Ta、La、Ce、P、Ti等高场强元素(HFSE)为主要特征,Eu负异常不明显(δEu=0.80～0.90),(La/Yb)N=9.27～13.18,轻重稀土分馏明显。结合成因类型判别图解和矿物学特征,园岭寨斑岩为典型的S型花岗岩,以壳源物质的重熔为主,并受一定程度的幔源物质影响。利用LA-MC-ICP-MS锆石U-Pb年龄,获得了花岗斑岩的成岩年龄为165.49±0.59Ma(MSWD=1.4,n=19);利用辉钼矿Re-Os同位素测年法,获得园岭寨钼矿床辉钼矿的结晶年龄为160±1～162.7±1.1Ma,属赣南燕山期第二次钼成矿作用(150～162Ma)。结合区域年代学资料和已知的矿床(点),指出本区进一步找矿工作应集中在中-晚侏罗世-早白垩世Mo、Pb、Zn等矿床的查找上。 相似文献
159.
赣南加里东期阳埠(垇子下)岩体的锆石年龄、构造背景及含矿性评价 总被引：4，自引：3，他引：1
阳埠岩体是赣南著名的含稀土岩体之一,但研究程度低,缺乏精确的同位素年代学资料。文章对阳埠岩体风化壳的锆石样品进行了激光剥蚀-多接收器电感耦合等离子体质谱(LA-MC-ICPMS)U-Pb定年,获得206Pb/238U加权平均年龄为(461.1±1.3)Ma,说明该岩体形成于中奥陶世。区域上阳埠岩体与武功山山庄岩体(461 Ma)、赣南上犹岩体(464 Ma)、云开大山花岗岩(465～467 Ma)等为同时代岩体,属华南加里东晚期第一次岩浆活动峰期产物,暗示华南加里东期褶皱造山运动的开始。结合江西省加里东期花岗岩的地球化学资料,发现多数岩体的稀土总量较高,具备成矿母岩的首要条件。今后应对南岭地区加里东期花岗岩含矿性评价及找矿工作给予重视。 相似文献
160.
新疆可可托海近3号脉花岗岩成岩时代及地球化学特征研究 总被引：2，自引：2，他引：0
可可托海伟晶岩田内花岗岩类发育。本文研究的花岗岩体位于3号伟晶岩脉矿坑的东部,岩性为似斑状黑云母二长花岗岩,野外特征与矿区北部的阿拉尔花岗岩非常相似。花岗岩中锆石LA-MC-ICP-MS U-Pb测年结果表明,19个测点206Pb/238U年龄集中于399.6～409.0Ma,加权平均年龄为405.4±1.4Ma(MSDW=0.98),属于早泥盆世,比阿拉尔花岗岩的侵入时期早得多,与3号伟晶岩脉没有成因上的联系,应是区域上岩浆活动最为强烈时期的产物。岩石具有富硅(SiO2=70.69%～73.81%)、富铝(Al2O3=14.00%～15.74%)、总体髙钾(K2O/Na2O≥1),贫Fe、Mg、Ti、P特点,铝饱和指数较高(A/CNK≥1.1),属于髙钾钙碱性强过铝质花岗岩;微量元素表现出Sr、Ti、Ba、P、Nb、Ta明显的负异常和Th、U、La、Zr、Hf的正异常特征。稀土配分型式显示LREE的相对弱富集,HREE比较平坦以及Eu中等负异常。样品中87Sr/86Sr(0.72259～0.72810)、143Nd/144Nd(0.51235～0.51237)接近于陆源沉积物,Sr初始值(0.70155～0.70341)较低,f Sm/Nd(-0.32～-0.26)、Sm/Nd(0.222～0.240)比值显示分异小、较均一的Sm/Nd同位素体系;εNd(t)值变化于-3.07～-2.16,模式年龄t2DM集中在1.35Ga左右,属于中元古代。综合研究岩石中主量、微量和稀土元素、同位素特征,同时对比区域上同期岩浆活动特征,认为本文研究的花岗岩可能是在活动大陆边缘环境下,强烈的俯冲-碰撞作用导致的地壳加厚引发了深熔作用,使阿尔泰微古陆边缘内部中元古代基底部分熔融,同时有幔源物质参与;随后岩浆经过结晶分异,最终上升侵位,反映了陆缘弧花岗岩的特点。 相似文献