胶东金翅岭金矿构造控矿规律及找矿预测

金翅岭金矿是胶东招远北部的一个典型石英脉型金矿,构造是金矿最为重要的控矿因素。在前人资料的基础上,综合分析了矿区构造控矿特征,总结了构造控矿规律:矿脉分支复合,表现为NE向矿脉产生SN,NNE向次级矿脉,NNE向矿脉产生NE向次级矿脉;矿体厚度与金品位呈负相关,深部次级矿脉群在P4脉下盘出现;矿脉侧伏角和倾伏向变化处矿体富集,表现为SW向侧伏的P4矿脉,矿体富集于-240 m,侧伏角变大,同时倾伏向由SW向转变为NW向的部位。最后建立了平面和剖面P4矿脉的波形函数,并对深部进行了预测。     

柴达木盆地西北缘石英闪长岩的形成时代、岩石成因及地质意义

柴达木盆地西北缘石英闪长岩Al2O3含量较高,全碱(Alk)含量较低,Na2OK2O,铝饱和指数A/CNK为0.87~0.91,属钙碱性准铝质岩石系列。球粒陨石标准化的稀土元素配分曲线表现为轻稀土元素富集型,轻、重稀土元素分馏明显,Eu弱负异常;微量元素地球化学特征显示,岩石富集Rb、Th、U等大离子亲石元素,亏损Nb、Ta、P、Ti等高场强元素,Nb/La和Rb/Nb比值较低,具有I型花岗岩的特征。石英闪长岩Ca O/Na2O比值较高(2.32~2.64),结合源岩判别图解综合推断其源于变玄武岩的部分熔融。全岩Zr饱和温度计算结果显示初始岩浆温度768℃;岩石地球化学特征表明岩浆源区压力1.5 Ga,源岩部分熔融的残留相可能为石榴子石+角闪石+金红石。经过锆石阴极发光分析和MC-LA-ICP-MS锆石U-Pb测年,获得206Pb/238Pb加权平均年龄为252±1 Ma,代表了柴达木盆地西北缘石英闪长岩的成岩年龄。结合区域地质演化特征,认为该岩体形成于与板块俯冲有关的火山弧构造环境,是晚二叠世末期宗务隆洋壳向柴北缘欧龙布鲁克地块俯冲,变玄武岩在相对较高的温压条件下发生部分熔融形成的。     

大兴安岭扎兰屯地区晚奥陶世石英闪长岩体岩石地球化学特征及其地质意义

扎兰屯音河岩体被音河水系分为南、北两部分,研究发现南、北岩体形成年代不同,选取南部岩体(称为二村岩体)进行研究。二村岩体主要由石英闪长岩-英云闪长岩组成,石英闪长岩的LA-ICP-MS锆石U-Pb年龄为444.0±4.6Ma,时代为晚奥陶世。岩石化学组成相对富钠、贫钾,Na2O/K2O值大于1(1.73~3.17),属中钾钙碱性系列。岩石富含轻稀土元素、亏损重稀土元素,富集大离子亲石元素Rb、Ba、K,显著亏损Nb、Ta、P、Ti等高场强元素。矿物组成及岩石地球化学特征指示其为I型花岗岩。岩体的形成时代、构造背景与多宝山岛弧火成岩相似,为区域多宝山岛弧西南向延伸提供了新的制约。     

Fluid Inclusion Studies of Comb Quartz and Stibnite at the Hishikari Au–Ag Epithermal Deposit,Japan

Fluid inclusion microthermometry was conducted on late‐stage barren comb quartz and the latest stibnite at the Hishikari deposit to characterize the hydrothermal activity responsible for vein formation. Eight fluid inclusion assemblages (i.e. fluid inclusions trapped at the same time, ‘FIAs’) were studied to determine the formation fluid temperatures and salinities for the comb quartz in the Shosen No. 2 vein, Sanjin ore zone, and the stibnite in the Seisen No. 1–1 vein, Yamada ore zone. The average homogenization temperatures (the formation temperatures) of the seven FIAs from the comb quartz were between 207 and 230°C, while the average homogenization temperature (the formation temperature) of an FIA from the stibnite was 113°C. The measured fluid salinities of the seven FIAs from the comb quartz were low, ranging between 0.0 and 1.1 wt% NaCl equiv., indicating that dilute fluids were responsible for the comb quartz formation. By comparison with previous microthermometric data, the formation temperatures of the studied comb quartz were higher than those of columnar adularia and comb quartz at most other veins (generally around 200°C) but were similar to those of columnar adularia at Keisen veins (230°C) in the same ore zone. The higher formation temperatures both in the Shosen and the Keisen veins in the Sanjin ore zone indicate that the fractures corresponding to the vein system at the Sanjin ore zone were main conduits for hot ascending fluids. The low formation temperature of stibnite in the latest stage (113°C) indicates that stibnite precipitation occurred during a waning stage of hydrothermal activity. Combined with previous thermodynamic data on antimony solubilities, the large discrepancy between the formation temperature of the comb quartz (200–230°C) and that of the stibnite suggests that the stibnite may have precipitated as a result of a drastic cooling of the hydrothermal system.     

Ore-bearing fluids of the Eldorado gold deposit (Yenisei Ridge,Russia)

The Eldorado low-sulfide gold-quartz deposit, with gold reserves of more than 60 tons, is located in the damage zone of the Ishimba Fault in the Yenisei Ridge and is hosted by Riphean epidote-amphibolite metamorphic rocks (Sukhoi Pit Group). Orebodies occur in four roughly parallel heavily fractured zones where rocks were subject to metamorphism under stress and heat impacts. They consist of sulfide-bearing schists with veins of gray or milky-white quartz varieties. Gray quartz predominating in gold-bearing orebodies contains graphite and amorphous carbon identified by Raman spectroscopy; the contents of gold and amorphous carbon are in positive correlation. As inferred from thermobarometry, gas chromatography, gas chromatography-mass spectrometry, and Raman spectroscopy of fluid inclusions in sulfides, carbonates, and gray and white quartz, gold mineralization formed under the effect of reduced H₂O-CO₂-HC fluids with temperatures of 180 to 490 °C, salinity of 9 to 22 wt.% NaCl equiv, and pressures of 0.1 to 2.3 kbar. Judging by the presence of 11% mantle helium (³He) in fluid inclusions from quartz and the sulfur isotope composition (7.1-17.4‰ δ³⁴S) of sulfides, ore-bearing fluids ascended from a mantle source along shear zones, where they “boiled”. While the fluids were ascending, the metalliferous S- and N-bearing hydrocarbon (HC) compounds they carried broke down to produce crystalline sulfides, gold, and disseminated graphite and amorphous carbon (the latter imparts the gray color to quartz). Barren veins of milky-white quartz formed from oxidized mainly aqueous fluids with a salinity of < 15 wt.% NaCl equiv at 150-350 °C. Chloride brines (> 30 wt.% NaCl equiv) at 150-260 °C impregnated the gold-bearing quartz veins and produced the lower strata of the hydrothermal-granitoid section. The gold mineralization (795-710 Ma) was roughly coeval to local high-temperature stress metamorphism (836-745 Ma) and intrusion of the Kalama multiphase complex (880-752 Ma).     

Sugarloaf Mountain,central Arizona,USA: A small-scale example of Miocene basalt-rhyolite magma mixing to yield andesitic magmas

Sugarloaf Mountain is a 200-m high volcanic landform in central Arizona, USA, within the transition from the southern Basin and Range to the Colorado Plateau. It is composed of Miocene alkalic basalt (47.2–49.1?wt.% SiO₂; 6.7–7.7?wt.% MgO) and overlying andesite and dacite lavas (61.4–63.9?wt.% SiO₂; 3.5–4.7?wt.% MgO). Sugarloaf Mountain therefore offers an opportunity to evaluate the origin of andesite magmas with respect to coexisting basalt. Important for evaluating Sugarloaf basalt and andesite (plus dacite) is that the andesites contain basaltic minerals olivine (cores Fo_76-86) and clinopyroxene (～Fs_9-18Wo_35-44) coexisting with Na-plagioclase (An_48-28Or_1.4–7), quartz, amphibole, and minor orthopyroxene, biotite, and sanidine. Noteworthy is that andesite mineral textures include reaction and spongy zones and embayments in and on Na-plagioclase and quartz phenocrysts, where some reacted Na-plagioclases have higher-An mantles, plus some similarly reacted and embayed olivine, clinopyroxene, and amphibole phenocrysts.Fractional crystallization of Sugarloaf basaltic magmas cannot alone yield the andesites because their ～61 to 64?wt.% SiO₂ is attended by incompatible REE and HFSE abundances lower than in the basalts (e.g., Ce 77–105 in andesites vs 114–166?ppm in basalts; Zr 149–173 vs 183–237; Nb 21–25 vs 34–42). On the other hand, andesite mineral assemblages, textures, and compositions are consistent with basaltic magmas having mixed with rhyolitic magmas, provided the rhyolite(s) had relatively low REE and HFSE abundances. Linear binary mixing calculations yield good first approximation results for producing andesitic compositions from Sugarloaf basalt compositions and a central Arizona low-REE, low-HFSE rhyolite. For example, mixing proportions 52:48 of Sugarloaf basalt and low incompatible-element rhyolite yields a hybrid composition that matches Sugarloaf andesite well ? although we do not claim to have exact endmembers, but rather, viable proxies. Additionally, the observed mineral textures are all consistent with hot basalt magma mixing into rhyolite magma. Compositional differences among the phenocrysts of Na-plagioclase, clinopyroxene, and amphibole in the andesites suggest several mixing events, and amphibole thermobarometry calculates depths corresponding to 8–16?km and 850° to 980?°C. The amphibole P-T observed for a rather tight compositional range of andesite compositions is consistent with the gathering of several different basalt-rhyolite hybrids into a homogenizing ‘collection' zone prior to eruptions. We interpret Sugarloaf Mountain to represent basalt-rhyolite mixings on a relatively small scale as part of the large scale Miocene (～20 to 15 Ma) magmatism of central Arizona. A particular qualification for this example of hybridization, however, is that the rhyolite endmember have relatively low REE and HFSE abundances.     

粉色水晶内针状包裹体的成分与分布特征研究

粉色水晶内部的针状包裹体常被认为是三组呈三方对称的金红石或蓝线石,至今未有定论。本文选取含有针状包裹体的4颗星光粉晶,利用宝石学显微镜、激光拉曼光谱仪及紫外可见分光光度计对样品进行观察与测试,以确定包裹体的分布特征及矿物种类。无损拉曼测试发现包裹体的特征振动峰949 cm-1、999 cm-1与蓝线石标准峰相匹配,可确定针状包裹体为蓝线石或与其极为相近的矿物。放大检查发现,包裹体直径约0.5μm,长度可达毫米级,近定向分布,整体上呈汇聚状,在某些位置可粗略分为三组,同组针状包裹体近似平行分布。造成六射星光的三组蓝线石立体相交,未观察到明显的三方对称关系,与水晶的结晶习性无直接关系,故认为蓝线石为先成包裹体,在水晶的生长过程中被捕获。紫外可见分光光谱仅显示粉色蓝线石的特征吸收,表明大量的粉色蓝线石包裹体对粉色水晶的粉色有一定贡献。     

安徽茶亭铜金矿床赋矿石英闪长玢岩黑云母成分特征及成岩成矿指示意义

安徽宣城茶亭矿床位于长江中下游成矿带东南缘的南陵-宣城盆地内,是近年来该盆地内新发现的大型斑岩型Cu-Au矿床。石英闪长玢岩是茶亭矿床主要的赋矿岩石,文章从石英闪长玢岩的造岩矿物黑云母入手,利用EMPA及LA-ICP-MS等原位微区分析方法,对黑云母进行了详细的矿物化学分析,旨在查明赋矿石英闪长玢岩形成的物理化学条件,并探讨其成岩成矿意义。分析结果表明:茶亭赋矿石英闪长玢岩中黑云母具有高w(TiO_2)、低w(Al_2O_3)的特征,整体富Mg、贫Fe。黑云母温压计算结果表明,在不同深度上,石英闪长玢岩具有相似的结晶温度及压力,其结晶温度为746～773℃,压力为44～85 MPa,对应深度为1.7～3.3 km,平均为2.47 km,显示石英闪长玢岩侵位深度相对较浅。黑云母中高的氧化系数(0.613～0.864)、高Mg#(0.557～0.864),以及w(MgO)介于14.73%～15.86%,均显示石英闪长玢岩为壳幔混源,并且以幔源为主。黑云母成分显示石英闪长玢岩形成于较高氧逸度条件下。浅部岩体具有较高的X_(Mg)值,表明浅部岩体氧逸度较高,可能指示随着岩浆的不断演化,残余岩浆的氧逸度不断降低。同时,石英闪长玢岩黑云母相对一般斑岩型铜矿具有较高的w(Cu),并且高Cl、低F。这些特征均有利于茶亭Cu-Au矿床的形成。     

皖南东至兆吉口铅锌矿床成矿时代的厘定及其找矿指示意义

皖南东至兆吉口铅锌矿床是近年来在江南过渡带西段新发现的一个规模达中型的中-低温热液型矿床。目前揭露的铅锌矿体均赋存于东至断裂带及其西侧次级张(扭)性断裂及裂隙中。文章选取了该矿床主要矿石矿物闪锌矿以及与主成矿阶段金属硫化物紧密共生的石英,分别采用流体包裹体Rb-Sr法和40Ar-39Ar法进行同位素地质年龄测定。4件闪锌矿样品获得流体包裹体Rb-Sr等时线年龄为(128±1)Ma;2件石英样品获得流体包裹体40Ar-39Ar坪年龄分别为(128.74±3.02)Ma和(128.19±1.98)Ma,等时线年龄分别为(128.81±5.25)Ma和(128.30±3.47)Ma,反等时线年龄分别为(128.82±5.24)Ma和(128.31±3.47)Ma。同位素地质年龄测试结果基本一致,表明兆吉口铅锌矿床形成于128 Ma左右,成矿时代为早白垩世。该成矿年龄与赋矿闪长玢岩的形成时间((129.0±2.3)Ma~(128.4±2.7)Ma)一致,也与东至断裂燕山晚期的活动年龄((126.3±2.2)Ma)相近,表明该矿床成矿与燕山晚期的构造-岩浆活动密切相关,此时区域构造背景为强烈挤压后的伸展环境。这一矿化事件在成矿时代上明显晚于长江中下游成矿带中的断隆区(如铜陵、安庆-贵池等矿集区)的铜金多金属矿床和皖南成矿带中的钨钼多金属矿床(136 Ma),而与长江中下游成矿带断坳区的玢岩铁矿床的成矿时间(135~127 Ma)相近,指示长江中下游成矿带与皖南成矿带之间的江南过渡带中发育有燕山晚期较晚阶段(128 Ma左右)的铅锌矿化事件,为今后在该区开展铅锌多金属矿床找矿勘探提供了重要依据。     

西藏西北部浅变质石英砂岩岩石学特征及其构造意义

羌塘盆地中央隆起带主要由浅变质石英砂岩组成,由于化石匮乏、变形强烈,长期以来对这套浅变质石英砂岩成因的争议颇大,导致了对藏西北地区前中生代构造演化的认识长期模糊不清,其中,何处才是冈瓦纳大陆北界就是一个长期争论的议题。在西藏西北部,近东西走向的布尔嘎错断裂带将北部的查多岗日地块与南部的南羌塘地块分隔开,浅变质石英砂岩广泛出露于这两地块之内。沿近东西走向布尔嘎错断裂带断续产出的冈玛错蓝片岩、蛇绿岩等岩片大体呈南北向逆冲于浅变质石英砂岩之上,因此早期曾认为布尔嘎错断裂带是冈瓦纳大陆之北界。本文的调查与研究发现查多岗日和南羌塘地块内浅变质石英砂岩岩相学特征完全相同,均主要由石英组成,遭受了绿片岩相的变质作用,形成了钠长石+绿泥石+白云母组合,充填于早期石英颗粒之间,钠长石交代钾长石。这两地的浅变质石英砂岩均被未变质钙质胶结的钾长石石英砂岩平行不整合覆盖。碎屑锆石的阴极发光分析与U-Pb定年结果进一步证实了查多岗日与南羌塘地块内浅变质石英砂岩内的锆石来源完全相同。这些证据充分反映了查多岗日与南羌塘地块早期构造演化过程相似,源自同一大陆。碎屑锆石定年结果进一步表明浅变质石英砂岩的最大沉积年龄为520±8Ma,该岩石再被约480Ma的花岗岩脉侵入,因此其很可能形成于晚寒武世,而不整合面之上沉积岩的最大沉积年龄为460±8Ma,表明该不整合面上、下沉积岩之间存在明显的沉积间断,证实了该平行不整合面形成于奥陶纪。不整合面之下的浅变质石英砂岩因此与杨耀等(2014)报道的荣玛组相同,不整合面之上未变质长石石英砂岩则属于中上奥陶统塔石山组。查多岗日地块因此是西藏境内最北端的冈瓦纳大陆的碎块。在西藏西北部,冈瓦纳大陆北界为龙木错-帮达错-(83°40'E、35°N)-红脊山-荣玛乡。布尔嘎错断裂带不是冈瓦纳大陆之北界。