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

N.A. Gibsher  A.A. Tomilenko  A.M. Sazonov  T.A. Bul’bak  M.O. Khomenko  M.A. Ryabukha  E.O. Shaparenko  S.A. Sil’yanov  N.A. Nekrasova 《Russian Geology and Geophysics》2018,59(8):983-996

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).  相似文献   

Geodynamic setting,structure, and composition of continuous trachybasalt-trachyandesite-rhyolite series in the north of Altai-Sayan area: the role of crust-mantle interaction in continental magma formation     

A.A. Vorontsov  O.Yu. Perfilova  N.N. Kruk 《Russian Geology and Geophysics》2018,59(12):1640-1659

The geologic positions and geochemical and isotope parameters of the Ordovician-early Silurian and Early-Middle Devonian continuous volcanic series of the Minusa basin and its mountainous framing are compared. Both series are composed mostly of moderately alkaline rocks with variations in SiO₂ contents from 45 to 77 wt.%. The Ordovician-early Silurian series differs from the Early-Middle Devonian one in lower contents of TiO₂ (< 1.7 wt.%) and Fe₂O_3tot and higher contents of Al₂O₃ in all rock varieties and in the more fractionated REE patterns of trachybasalts. The compositions of both series reflect two simultaneous mechanisms of magma evolution. The main process was fractional crystallization leading to the formation of rocks from trachybasalts to trachyrhyodacites. The accessory mechanism was the contamination of fractionated melts by crustal material, anatectic melting of crust, and mixing of deep-seated magmas with crustal melts. These processes had specifics at each stage and were controlled by the composition of the sources of parental melts. Their geochemical and isotopic parameters (high alkalinity, high contents of lithophile elements, negative anomalies of Nb, Ta, and Ti, and enrichment in radiogenic Sr) point to the interaction of mantle plumes with the lithospheric mantle that was metasomatically transformed during the preceding Vendian-early Cambrian subduction processes.  相似文献   

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

《Resource Geology》2018,68(3):326-335

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.  相似文献   

Occurrence and Chemical Compositions of Amphiboles in Altered Dioritic Rocks of Laiwu Skarn‐Type Iron Deposit in West Shandong Area,China     

《Resource Geology》2018,68(4):425-445

The Laiwu Fe deposit is the largest skarn‐type deposit in West Shandong in China, with an estimated reserve of 290 Mt of iron ore. Here, we investigate the occurrence and chemical composition of amphiboles in altered dioritic rocks of this deposit. Three generations of amphibole group minerals were identified in these rocks. The first type (Type 1) is a hornblende with a generally euhedral crystal shape, 150–500 μm in size, and dominantly occurs in the host monzonite. The second type (Type 2) of hornblende occurs as fine grains (<100 μm) or concentric rims, less than 50 μm in thickness, around the Type 1 hornblende. The third type (Type 3) of amphibole is anhedral actinolite occurring along the boundary or the cracks of the Type 1 or 2 hornblende grains. The Type 1 hornblende has higher FeO (12.5–15.6 wt.%) and lower MgO contents (11.2–14.6 wt.%) than the Type 2 hornblende, which has an FeO content ranging from 8.8 to 10.5 wt.% and MgO content ranging from 14.2 to 17.1 wt.%. The Type 3 actinolite shows the lowest FeO (4.6–6.4 wt.%) and highest MgO (19.8–21.2 wt.%) contents. We infer that the Type 2 hornblende formed from Fe‐rich hydrothermal fluids released during rapid upwelling of the crystallizing magma. The fluids were relatively reduced and enriched in Fe. The Type 3 actinolite formed by coupled dissolution and reprecipitation, and its formation is one of the features denoting Fe‐enrichment events. Our study of these types of amphibole provides insights into the ore formation process.  相似文献   

滇西北卓玛Cu--Pb--Zn矿床成矿流体特征     

江海洋  马雪俐  高明波  王可勇  杨贺 《世界地质》2018,37(4):1058-1067

卓玛矿床位于云南香格里拉格咱弧东北部,属斑岩-热液脉型铜多金属矿床。矿体主要赋存于矿区石英二长斑岩内及附近,严格受NW向断裂控制。卓玛矿床的形成经历了黄铁矿-石英(Ⅰ)、黄铁矿±黄铜矿--石英(Ⅱ)、黄铁矿±黄铜矿±方铅矿±闪锌矿-石英(Ⅲ)及贫硫化物-石英-碳酸盐(Ⅳ)四个成矿阶段。通过对各成矿阶段研究样品石英颗粒中的原生流体包裹体进行岩相学、显微测温学及激光拉曼光谱研究,探讨卓玛铜多金属矿床成矿流体特征,结果表明:Ⅰ阶段石英中主要发育富CO_2及气液两相型包裹体;Ⅱ阶段石英中主要发育碳质、富CO_2、含CO_2及气液两相4种类型包裹体;Ⅲ阶段石英中主要发育含CO_2及气液两相型包裹体;Ⅳ阶段石英中主要发育富CO_2、含CO_2及气液两相3种类型包裹体。激光拉曼光谱显示碳质包裹体主要成分为CO_2和CH_4,而CO_2包裹体中除CO_2和CH_4气相成分外,还有部分H_2O。因此,综合研究结果显示卓玛铜多金属矿床成矿流体为中温、低盐度的CO_2--CH_4-Na Cl--H_2O体系热液。成矿过程中,流体温度和盐度数值略有降低趋势,成矿流体的不混溶作用是导致成矿物质大量卸载的关键因素。  相似文献   

甘肃省龙首山芨岭铀矿床成矿热液流体特征研究     

赵如意  王博  陈毓川  王刚  陈云杰  聂利  李涛 《地球学报》2018,39(3):282-294

芨岭铀矿是中国北方最典型的钠交代型铀矿床之一,文章通过对芨岭矿床ZKJ9-4钻孔深部所见含矿蚀变闪长岩、近矿蚀变闪长岩、远矿蚀变闪长岩、闪长岩原岩地球化学特征和组分迁移计算及矿体中心部位的淡粉红色方解石脉流体包裹体特征、均一温度、盐度和激光拉曼光谱研究,认为芨岭钠交代型铀矿床的成矿流体含有大量碳酸铀酰络合物[UO_2(CO_3)_2]~(2–)和[UO_2(CO_3)_2]~(4–)的同时还含有丰富的SiO_2、Na~+、Ca~(2+)、Mg~(2+)、Fe~(2+)、Mn~(2+)、∑REE、U、Th、Ga、Sr、Zr、Ba、Rb、Nb、Mo、Cd、Sn、Hf、Ti、Ta、CO_2、H_2S和CH_4等组分,成矿流体具有较强的还原性,并对MnO、K_2O、Cr和Co具有较强的交代溶蚀作用。成矿流体是起源于岩浆演化晚期的再平衡岩浆水,热液温度为(300±20)℃,盐度为2.99 wt%~4.57 wt%NaCl,密度为0.75~0.77 g/cm~3。流体沸腾是芨岭钠交代型铀矿成矿物质的早期卸载机制,晚期成矿流体中加入了大量的大气降水,流体混合作用进一步促进了成矿物质的卸载。  相似文献   

塔里木陆块西北缘萨热克砂岩型铜矿床构造-流体演化对成矿的制约     

王伟  李文渊  高满新  熊中乙  李天虎  宿晓虹  郭周平  孟勇  全守村  刘增仁  叶雷  陈传庆  唐小东 《地质通报》2018,37(7):1315-1324

塔里木陆块西北缘萨热克砂岩型铜矿床构造演化、流体演化与成矿之间具有密切关系,处于一个统一系统中。矿床成岩期方解石中包裹体水的δD值为-65.3‰~-99.2‰,改造成矿期石英包裹体水的δD值为-77.7‰~-96.3‰,成岩成矿期成矿流体δ~(18)OH_2O变化范围为-3.22‰~1.84‰,改造成矿期成矿流体δ~(18)OH_2O变化范围为-4.26‰~5.14‰,指示萨热克铜矿成岩期、改造期成矿流体主要为中生代大气降水及其经水岩作用而成的盆地卤水。矿石中辉铜矿δ~(34)S值为-24.7‰~-15.4‰,指示硫主要源自硫酸盐细菌与有机质还原,部分源于有机硫。构造与成矿流体演化对砂岩铜矿成矿起关键制约作用。盆地发展早期强烈的抬升运动使盆地周缘基底与古生界剥蚀,为富铜矿源层的形成提供了丰富物源,至晚侏罗世盆地发展晚期,长期演化积聚的巨量含矿流体在库孜贡苏组砾岩胶结物及裂隙中富集,在萨热克巴依盆地内形成具有经济意义的砂岩型铜矿床。  相似文献   

短期线状集中分布地磁日变化感应电流异常机理初步解释——以2012年唐山4.8级地震为例          下载免费PDF全文

姜楚峰  吴迎燕  冯志生  戴勇  孙君嵩  章鑫  冯丽丽  李军辉 《中国地震》2022,38(2):226-238

本文分析了2012年唐山4.8级地震前,震中附近出现的短期原地重现线状集中分布地磁日变化感应电流异常的时空变化特征,及其与地震、中-下地壳和上地幔高导层的关系,进一步证实了短期原地重现线状集中分布感应电流的走向与中-下地壳和上地幔高导层顶面界埋深走向一致,认为其机理可能是深部热流体的上涌导致壳幔高阻体出现带有上拱性质的拆离滑动,深部上涌的热流体和高导层内热流体侵入高导层内电阻相对较高的地区,高导层出现短时间高导电流通道,当地磁日变化感应电流扫描经过高导电流通道时,感应电流会呈线状集中分布于此,并基于趋肤效应分布于其顶面附近。由于重现异常是发生在震源下方中-下地壳和上地幔高导层的地震异常,且该异常不同于震源附近及其震源至地表的地震异常,因此对推进地震孕育与发生机理研究可能有一定作用。此外研究还发现,地震虽然主要位于重叠段的端部,但更有可能位于中-下地壳重叠段的端部,这一发现对日常震情跟踪中应用该异常确定未来地震位置有一定帮助。  相似文献   

西昆仑沃克金矿床地质特征、金的赋存状态及矿床成因探讨     

冯京  徐仕琪  邓军  何福保  薛小龙  尹得功  薛春纪  郝延海  李平  赵同阳 《矿床地质》2022,41(3):623-642

沃克金矿床是西昆仑西段金铜矿带近期发现的一处具有大型远景的金矿床。金矿体主要产于近东西向展布的韧-脆性剪切带中,赋矿岩石为穿切于绢云千枚岩中的石英脉。主要矿化类型为毒砂矿化、黄铁矿化、黄铜矿化,热液蚀变为绢云母化、硬绿泥石化和碳酸盐化。在野外地质勘查与研究的基础上,笔者结合镜下显微观察,将成矿阶段划分为早（S1）、主（S2）和晚（S3）阶段,主阶段形成大量硫化物及方解石石英脉。载金硫化物主要为毒砂,次为黄铜矿、方铅矿。利用电子探针（EPMA）对载金硫化物进行分析,结合单元素面扫描成像,笔者认为金矿石主要以细粒金和中粒金形式存在。流体包裹体显示温度变化范围230~493℃,w （NaCl） _eq为1.56%~18.19%,成矿流体具有中高温、中低盐度的特征,表现为NaCl-H₂O-CO₂体系。石英δ¹⁸O值为8.6‰~14.0‰,流体的δD值在-83.7‰~-103.6‰,显示出变质水和大气降水的混合流体来源特征;硫同位素组成显示成矿物质源自中浅变质岩。笔者认为,沃克金矿床为与韧-脆性剪切带有关的中成造山型金矿床。  相似文献   

福建李家坊金矿床磁铁矿成因及其对金矿化过程的指示     

陈娟  赵骏峰  刘文元  邢波  肖政  周小深  卢林 《矿床地质》2022,41(6):1142-1163

福建泰宁李家坊金矿床位于武夷山成矿带中段,为闽西北何宝山矿田内新发现的一个中型金矿床,成因类型尚未明确。磁铁矿是该矿床中常见的氧化物,文章应用磁铁矿微量元素特征对李家坊金矿床成矿过程与成因类型进行约束。基于野外地质踏勘和钻孔岩芯编录,结合室内详细的岩相学观察,依据磁铁矿的结构和矿物共生组合,文章将其分为4种类型（Mt1a、Mt1b、Mt2和Mt3）。其中,Mt1a位于铜金矿脉边缘,呈板柱状,与绿泥石共生; Mt1b位于铜金矿脉边缘,呈自形-半自形粒状,与绿泥石-赤铁矿共生; Mt2位于铜金矿脉中,呈脉状产出,穿插早阶段的石英-黄铁矿脉,与绿泥石-绿帘石共生; Mt3位于铜金矿脉中,呈半自形-他形粒状,与绿帘石-赤铁矿共生,被后阶段黄铜矿包裹、交代。金主要以自然金和银金矿的形式赋存于Mt3中。原位微区分析结果表明,李家坊金矿不同类型磁铁矿均属于热液型磁铁矿。此外,从Mt1a型到Mt3型磁铁矿,w（Ti）呈逐渐降低的趋势,指示热液流体逐渐向低温条件演化; w（V）表现出先降低后升高再降低的变化规律,暗示热液流体的氧逸度有明显波动,但总体呈升高趋势。磁铁矿的显微结构和化学组成具矽卡岩型矿化特征,是判断矿床成因类型的证据。其中,Mt3型磁铁矿与Au矿化密切相关,其矿物组合与微量元素特征可指示金在低温高氧逸度的环境下沉淀。  相似文献