山东省莱州市三山岛金矿床地质特征及成因探讨

莱州—招远地区是我国最重要的金矿资源基地,截止目前已发现的各类金矿床（点）200余处,其中大、中型金矿床20余处,已探明的储量占全国的1/4.三山岛金矿床是区内著名的“焦家式”金矿的典型代表之一.文章通过对三山岛金矿床地质特征研究表明,矿体地质特征与控矿断裂构造特征相一致,矿床成因属于重熔岩浆期后中温热液交代矿床.     

越南O Quy Ho钼矿床的成矿时代及成矿物质来源探讨

越南西北部O Quy Ho钼矿床为范士版成矿带的典型钼矿床之一,矿体以脉状形式就位于中生代花岗岩中,辉钼矿主要赋存于石英脉及长石石英脉中,与黄铁矿、黄铜矿、磁铁矿等共生。8件样品硫同位素分析结果表明,δ34S介于0.14‰～3.34‰之间,平均值为1.53‰,表明成矿物质具有深源特征。黄铁矿的206Pb/204Pb范围为18.583～22.355,207Pb/204Pb变化于15.632～15.812之间,208Pb/204Pb变化于38.989～39.199;辉钼矿的206Pb/204Pb、207Pb/204Pb、208Pb/204Pb分别为18.686～18.737、15.655～15.660和39.081～39.082,与范士版含角闪石花岗斑岩具有成因联系。辉钼矿Re-Os同位素等时线测年获得了(36±1)Ma的年龄,该年龄与金沙江-红河新生代斑岩铜钼矿成矿带岩浆-成矿活动的年龄一致,提出O Quy Ho钼矿床为金沙江-红河新生代斑岩铜钼矿带的一部分。     

后撤式逆冲推覆断层成因机制及物理模拟——以准噶尔盆地西北缘克-百断裂带为例

位于准噶尔盆地西北缘中段的克-百断裂带,晚二叠世以来发育了一系列后撤式逆冲断层。长期以来,关于克-百断裂带高角度逆冲断层的成因机制一直处于争论当中,后撤式逆冲断层的物理模拟在国内尚未见文献报道。论文通过地震解释研究了克-百断裂带的构造变形特征及其演化阶段;应用断层"活动性系数"理论,半定量地描述了挤压条件下断层"活动性系数"、摩擦系数与断层倾角之间的关系,证明了挤压条件下也能形成高角度逆断层;结合"造山楔"理论解释了后撤式逆冲断层的成因机制。研究认为,克-百断裂带后撤式逆冲断层是印支期、燕山期持续挤压和扎伊尔山隆升效应综合作用的产物:挤压过程中发生"泊松效应",随着断层倾角增大,断层面上的正压力迅速增大、"活动性系数"降低,当倾角增大到一个临界值后断层停止活动,形成高角度的逆断层;同时扎伊尔山隆升造成挤压应力上移,为断层的后撤奠定了基础。最后利用砂箱物理实验模拟了克-百断裂带后撤式逆冲断层的形成过程。     

准噶尔盆地结构及其圈闭类型

准噶尔盆地是复合叠加前陆盆地 ,其原型分别形成于板块俯冲、碰撞、造山带后期复活、拗拉槽回返和板内皱陷作用有关的大地构造环境。其古生代盆地的形成与相邻的阿尔泰山和东、西准噶尔山、天山及博格达山的造山作用相关。中新生代盆地的形成和改造与其南部特提斯域板块俯冲碰撞造山引起的盆地相邻造山带的复活有关。相邻造山带时空上不均一的造山作用对盆地的影响不同 ,形成了盆地独特的结构。各坳陷均由与其形成有关的造山带前缘冲断带、陡坡带、山前凹陷、缓坡带和前隆及前缘皱陷等构成 ,前隆之间的叠加构成了盆地的大型隆起 ,皱陷叠加构成了盆地的中央坳陷。不同类型的圈闭在坳陷中有规律地分布着     

西藏改则县多龙矿集区斑岩型铜金矿床的地质特征与成矿-找矿模型

多龙矿集区位于班公湖_怒江成矿带西段、羌塘地块南缘的岩浆弧中。过去十多年来,西藏地勘局第五地质大队在多龙矿集区内已发现和评价了多不杂、波龙、地堡那木岗、拿若、荣那等5处大型、超大型铜金多金属矿床,目前已探明的铜资源量近1000万吨,金300余吨。区内以斑岩型铜金矿床为主,兼有斑岩_浅成低温热液型和斑岩_角砾岩型矿化组合。研究发现,矿区黄铁矿的δ34S值变化于-2.2‰~2.3‰之间,平均为0.2‰,峰值在-1‰~1‰之间,塔式效应明显,接近幔源硫,显示成矿物质来源于深部岩浆;成矿温度介于250~420℃之间,成矿深度1~5 km,成矿流体为残余岩浆流体,大气降水在成矿过程中的作用不明显。作者根据多年的勘查实践,总结出多龙矿集区斑岩型铜金矿最有效的找矿勘查方法技术组合是:地质+化探(水系沉积物)+物探(高精度磁测、激电中梯)+钻探。     

塔里木板块东北部柳园粗面玄武岩带：软流圈地幔减压熔融的产物

在塔里木东北部,甘肃省西部敦煌市柳园镇南侧,有一条近东西向展布的粗面玄武岩带,长度约150km,宽度达10km,厚度为1900m。这条粗面石玄武岩带属下二叠统哲斯群,岩浆喷发方式以裂隙式溢流为主,枕状构造特别发育。在玄武岩层间夹有很薄的酸性凝灰岩和沉凝灰岩层,属典型的双峰式火山岩组合。按照岩石化学组成的 TAS 分类命名,主要岩石类型为玄武岩、夏威夷岩和橄榄粗安岩。主要造岩矿物为钠长石(Ab 91～100)和普通辉石。普通辉石斑晶、钠长石斑晶和部分基质中的钠长石具有中空结构,并被层状硅酸盐微晶充填。这些岩石基本属碱性玄武岩系列和过渡型系列,大部分属演化的岩浆。演化程度较低的样品具有轻稀土元素亏损型配分曲线,微量元素地球化学具有 MORB 亲和性,ε_(Nd)(t)= 10.14～10.89。玄武质岩浆与陆壳物质之间有较轻的同化混染作用。普通辉石、铁钛氧化物的分离结晶作用是岩浆演化的主要机制。玄武质岩浆源区属于软流圈地幔,部分熔融发生于尖晶石稳定域,是软流圈地幔减压(上涌)熔融的产物。     

Cobalt‐Bearing Grunerite in the Metamorphosed Banded Iron Formation in Orissa,India

Banded iron formation (BIF) comprising high grade iron ore are exposed in Gorumahisani‐Sulaipat‐Badampahar belt in the east of North Orissa Craton, India. The ores are multiply deformed and metamorphosed to amphibolite facies. The mineral assemblage in the BIF comprises grunerite, magnetite/martite/goethite and quartz. Relict carbonate phases are sometimes noticed within thick iron mesobands. Grunerite crystals exhibit needles to fibrous lamellae and platy form or often sheaf‐like aggregates in linear and radial arrangement. Accicular grunerite also occur within intergranular space of magnetite/martite. Grunerite needles/accicules show higher reflectivity in chert mesoband and matching reflectance with that of adjacent magnetite/martite in iron mesoband. Some grunerite lamellae sinter into micron size magnetite platelets. This grunerite has high ferrous oxide and cobalt oxide content but is low in Mg‐ and Mn‐oxide compared to the ones, reported from BIFs, of Western Australia, Nigeria, France, USA and Quebec. The protolith of this BIF is considered to be carbonate containing sediments, with high concentrations of Fe and Si but lower contents of cobalt and chromium ± Mg, Mn and Ni. During submarine weathering quartz, sheet silicate (greenalite) and Fe‐Co‐Cr (Mg‐Mn‐Ni)‐carbonate solid solution were formed. At the outset of the regional metamorphic episode grunerite, euhedral magnetite and recrystalized quartz were developed. Magnetite was grown at the expense of carbonate and later martitized under post‐metamorphic conditions. With the increasing grade of metamorphism greenalite transformed to grunerite.     

龙门山构造带南段向西南延伸的遥感影像证据及地震地质意义

在系统总结活动断裂遥感影像解译标志的基础上,利用Landsat ETM、Google Earth及ASTER GDEM等影像资料,结合前人研究成果,重点分析了龙门山构造带南段主要活动断裂的空间展布及几何学与运动学特征。研究结果表明,龙门山构造带在向南延伸过程中发生了明显的断裂分散现象,整个断裂带逐渐展宽,主要包括5条断裂带且其中包含多条次级断裂,至最南端被北西向鲜水河左旋走滑断裂带阻挡。其中活动性较为明显的断裂自西向东主要有4条:泸定断裂、天全断裂、芦山断裂和大邑-名山断裂,前两者是北川-映秀断裂的南延分支,而后两者是安县-灌县断裂的南延部分。由于龙门山构造带南段的构造变形被分解至多条次级断裂上,导致单条断裂错断地表的活动迹象明显变弱,因此单条断裂的潜在发震频率和强度也将相应变小,但潜在震源区会更为分散。结合已有的地震地质资料认为,未来应注意泸定和雅安2个地区的地壳稳定性及未来强震危险性问题。      

库车前陆褶皱-冲断带前缘盐构造分段差异变形特征

库车前陆褶皱-冲断带前缘秋里塔格构造带发育大量盐构造,其类型丰富多样。根据野外露头、钻井和地震资料识别出的盐构造样式主要有盐推覆、盐枕、盐墙、盐焊接、鱼尾构造、盐撤凹陷、突发构造、断层传播褶皱、断层转折褶皱和三角带构造等。秋里塔格构造带盐构造变形表现出明显的分段差异变形特征,其中西段却勒地区以古隆起(盐下)—盐枕(盐层)—逆冲推覆构造(盐上)为主;中段西秋地区以构造斜坡(盐下)—盐墙(盐层)—断层传播褶皱、向斜(盐上)为主;东段东秋地区则以断层转折褶皱(盐下)—盐推覆(盐层)—断层传播褶皱(盐上)为主。造成这种盐构造分段差异变形的主要控制因素包括基底断裂、含盐层系、构造转换带和变形空间等方面的差异性,其中基底构造和含盐层系的差异性起主导作用。     

The Lower Changjiang (Yangzi/Yangtze River) metallogenic belt, east central China: intrusion- and wall rock-hosted Cu–Fe–Au, Mo, Zn, Pb, Ag deposits

The lower valley of Changjiang, from Wuhan of the Hubei Province in the west to Zhenjiang of the Jiangsu Province in the east, contains more than 200 polymetallic (Cu–Fe–Au, Mo, Zn, Pb, Ag) deposits and is one of the most important metallogenic belts in China. This metallogenic belt, situated at the northern margin of the Yangzi craton and bordered by the Dabieshan ultrahigh pressure metamorphic belt to the north, consists mainly of Cambrian–Triassic marine clastic sedimentary rocks and carbonate and evaporite rocks, which overlay a Precambrian basement and are intruded by Yanshanian (205 to 64 Ma) granitoid intrusions and subvolcanic complexes. Repeated tectonism from Late Proterozoic to Triassic resulted in extensively developed networks of faults and folds involving the Cambrian–Triassic sedimentary strata and the Precambrian basement. The Yanshanian granitoid intrusions and subvolcanic complexes in the Lower Changjiang metallogenic belt are characterized by whole-rock δ¹⁸O of +8‰ to +10‰, initial ⁸⁷Sr/⁸⁶Sr of 0.704 to 0.708, and εNd^t from −10 to −17 and have been interpreted to have originated from mixing between juvenile mantle and old crustal materials. Also, the Yanshanian granitoids exhibit eastward younging and increase in alkalinity (i.e., from older calc–alkaline in the west to younger subalkaline–alkaline in the east), which are related to oblique collision between the Yangzi and Sino-Korean cratons and tectonic evolution from early compressional to late extensional or rifting regimes. Most polymetallic deposits in the Lower Changjiang metallogenic belt are clustered in seven districts where the Yanshanian magmatism is particularly extensive: from west to east, Edong, Jiurui, Anqing–Guichi, Luzhong, Tongling, Ningwu and Ningzhen. Mineralization is characterized by the occurrence of three distinct types of orebodies in individual deposits: orebodies in Yanshanian granitoid intrusions, skarn orebodies at the contact zones between the Yanshanian intrusions and Late Paleozoic–Early Mesozoic sedimentary rocks, and stratabound massive sulfide orebodies in the Late Paleozoic–Early Mesozoic sedimentary strata. The most important host sedimentary strata are the Middle Carboniferous Huanglong Formation, Lower Permian and Lower–Middle Triassic carbonate and evaporite rocks. The intrusion-hosted and skarn orebodies exhibit well-developed zonation in alteration assemblages, metal contents, and isotopic compositions within individual deposits, and apparently formed from hydrothermal activities related to the Yanshanian magmatism. The stratabound massive sulfide orebodies in the Late Paleozoic–Early Mesozoic sedimentary strata have long been suggested to have formed from sedimentary or volcano-sedimentary exhalative processes in shallow marine environments. However, extensive research over the last 40 years failed to produce unequivocal evidence for syngenetic mineralization. On the basis of geological relationships and isotope geochemical characteristics, we propose a carbonate-hosted replacement deposit model for the genesis of these stratabound massive sulfide orebodies and associated skarn orebodies. This model suggests that epigenetic mineralization resulted from interactions between magmatic fluids evolved from the Yanshanian intrusions with carbonate and evaporite wall rocks. Mineralization was an integral but distal part of the larger hydrothermal systems that formed the proximal skarn orebodies at the contact zones and the intrusion-hosted orebodies. The stratabound massive sulfide deposits of the Lower Changjiang metallogenic belt share many features with the well-studied, high-temperature, carbonate-hosted replacement deposits of northern Mexico and western United States, particularly with respect to association with small, shallow granitoid complexes, structural and stratigraphic controls on mineralization, alteration assemblages, geometry of orebodies, metal association, metal zonation and isotopic systematics.