共查询到20条相似文献，搜索用时 515 毫秒
1.
琼西抱板群变质沉积岩地球化学研究 总被引：15，自引：1，他引：15
琼西中元古代抱板群变质沉积岩可分为白云母石英片岩组和石英二云母片岩组，其原岩为砂岩质泥质沉积岩夹火山物质。白云母石英片岩组和石英二云母片岩组在地球化学成分上的差异是原始沉积化学分异作用的结果。对主元素、微量元素（含稀土元素）及Sm-Nd同位素的综合研究表明，海南岛存在古元古代或更早的古老基底，抱板群变质沉积岩一部分来源于成熟度较低的古老地壳物质，另一部分来源于含地幔火山物质较多的初生地壳，或与研究区大规模造山运动、构造－岩浆活动所伴生的地幔物质加入有关。初步研究显示，琼西抱板群变质沉积岩可能是造山带岛弧和活动大陆边缘区（扩张弧后或弧间盆地）大地构造环境下的沉积产物。 相似文献
2.
The Macraes orogenic gold deposit is hosted by a graphitic micaceous schist containing auriferous porphyroblastic sulphides. The host rock resembles zones of unmineralised micaceous graphitic pyritic schists, derived from argillaceous protoliths, that occur locally in background pelitic Otago Schist metasediments. This study was aimed at determining the relationship between these similar rock types, and whether the relationship had implications for ore formation. Argillites in the protolith turbidites of the Otago Schist metamorphic belt contain minor amounts of detrital organic matter (<0.1 wt.%) and diagenetic pyrite (<0.3 wt.% S). The detrital organic carbon was mobilised by metamorphic–hydrothermal fluids and redeposited as graphite in low-grade metaturbidites (pumpellyite–actinolite and greenschist facies). This carbon mobility occurred through >50 million years of evolution of the metamorphic belt, from development of sheared argillite in the Jurassic, to postmetamorphic ductile extension in the Cretaceous. Introduced graphite is structurally controlled and occurs with metamorphic muscovite and chlorite as veins and slicken-sided shears, with some veins having >50% noncarbonate carbon. Graphitic foliation seams in low-grade micaceous schist and metamorphic quartz veins contain equant graphite porphyroblasts up to 2 mm across that are composed of crystallographically homogeneous graphite crystals. Graphite reflectance is anisotropic and ranges from ~1% to ~8% (green light). Texturally similar porphyroblastic pyrite has grown in micaceous schist (up to 10 wt.% S), metamorphic quartz veins and associated muscovite-rich shears. These pyritic schists are weakly enriched in arsenic (up to 60 ppm). The low-grade metamorphic mobility and concentration of graphite in micaceous schists is interpreted to be a precursor process that structurally and geochemically prepared parts of the Otago Schist belt for later (more restricted) gold mineralisation. Economic amounts of gold, and associated arsenic, were subsequently introduced to carbonaceous sulphidic schists in the Macraes gold deposit by a separate metamorphic fluid derived from high-grade metaturbidites. Fluid flow at all stages in these processes occurred at metamorphic rates (mm/year), and fluids were broadly in equilibrium with the rocks through which they were passing. 相似文献
3.
The Whole‐Rock Geochemical Composition of the Wudaogou Group in Eastern Yanbian,NE China–New Clues to Its Relationship with the Gold and Tungsten Mineralization and the Evolution of the Paleo‐Asian Ocean 
下载免费PDF全文
下载免费PDF全文 The late Paleozoic Wudaogou Group, one of the oldest metamorphic units in the eastern Yanbian area, has important tectonic and metallogenic significance. Here, we provide new insights into their protoliths, tectonic setting of the metamorphic rocks and their relationships with the gold and tungsten mineralization, using new petrographic and whole‐rock geochemical data for various lithologies within the Wudaogou Group. The protolith of the metamorphic rocks of the Wudaogou Group was intermediate–basic volcanic rocks (e.g. basaltic andesite, trachyandesite, and basalt) and sedimentary rocks including argillaceous rocks, quartz sandstone, arkose and clayish greywacke, as well as pyroclastic sedimentary rock, covering tuffaceous sandstone. Before undergoing late Paleozoic epidote–amphibolite facies regional metamorphism, these protoliths were formed during the middle–late Permian in an island arc setting within a continental margin collage zone. Combined with the regional tectonic evolution, it can be speculated that the formation and the subsequent metamorphism of the protoliths of the metamorphic rocks from the Wudaogou Group were influenced by the change from subduction to collision of the Paleo‐Asian Ocean. Similarities of the rare earth element (REE) patterns and parameters among the metamorphic rocks within the Wudaogou Group, auriferous ores from the Xiaoxi'nancha gold (copper) deposit, and scheelites from the Yangjingou tungsten deposit, together with the favorable metallogenic element contents within the metamorphic rock series, imply that the Wudaogou Group could provide parts of metallic material for the gold and tungsten mineralization in the eastern Yanbian area, as exemplified by the Yangjingou deposit and Xiaoxi'nancha deposit, respectively. Further, the metamorphic sedimentary rocks, especially the metamorphic sandstones, quartz schists and quartz mica schists within the Wudaogou Group, have closer genetic relationships with the Yangjingou tungsten mineralization. However, the specific lithologies within this group which control the gold mineralization are still uncertain, and need further research. 相似文献
4.
下载免费PDF全文 老湾金矿带位于桐柏-大别造山带北缘,是一个由前寒武系绿帘角闪岩相、角闪岩相和麻粒岩相组成的中-低P/T变质带。通过对老湾金矿带变质岩产状、岩石组合特征、岩相学、岩石地球化学特征等进行综合研究,探讨了该区的变质岩原岩及其形成过程。研究结果表明：1）老湾金矿带龟山岩组斜长角闪岩类原岩为大陆拉斑玄武岩（玄武质熔岩）、火山碎屑岩及少量基性岩脉;云母石英片岩类原岩为中性泥质岩、砂岩等沉积岩;大理岩原岩为纯净的白云岩。2）龟山岩组形成于中-新元古代（920 Ma±）,经历了志留纪（410 Ma±）、石炭纪（314 Ma±）、白垩纪（130 Ma±）三期变质作用,龟山岩组变质岩是其先就位于地壳中的原岩后来发生陆壳俯冲再折返抬升退变质的产物。 相似文献
6.
At Dondo Mobi in the gold district of Eteke, south Gabon, gold mineralization was studied in a tropical forest setting. The mineralization occurs in quartz veins within amphibolites of an Archaean gneiss-amphibolite series. Gold distribution patterns were studied in the different horizons of the weathering profile and in the different grain-size fractions of the materials sampled from three pits sunk in the weathered zone: upslope (pit P1), directly overlying (pit P2) and downslope (pit P3) of the mineralization.The weathering profile consists of an upper, thick, loose sandy argillaceous horizon (H1), an irregular nodular horizon with laterite nodules or blocks (H2) and a saprolite layer (H3) up to 70 m thick. In each pit, the specific geochemical signature of the bedrock is recognized in the three horizons of the weathering profile. Some groups of elements, e.g., Cr-Ni or Ba-V-P2O3, characterize amphibolite or black shale, respectively. Signal attenuations in the upper horizon can be explained by a homogenization effect. That can be related to a mushroom supergene dispersion, simultaneously inducing vertical decrease and lateral enrichment in element contents. Gold also mushrooms extensively in the different horizons of the weathering profile. The dispersion pattern is somewhat anisotropic, a strong enlargement being observed in the upper (H1) and intermediate nodular (H2) horizons alike. However, the evolution of Au distribution is not the same for all grain-size fractions: (a) in the finest fraction, Au is regularly distributed in the weathering profile at the anomalous top and tends to preserve an equivalent level of concentration laterally; (b) in the coarsest fraction, the maximum Au content is found in the upper horizon just above the mineralized structure; it is rapidly decreases laterally, in the surface halo.The Au geochemical dispersion halo consists mainly of fine-grained gold developed from rather coarse-grained mineralization. Its characteristics suggest that Au dispersion was produced as a result of Au dissolution together with collapse of the weathering profile causing gold migration over short distances.The minimal volumetric reduction of saprolite in the upper horizon can be estimated to be in the range of 60%, on the basis of the content of the different grain-size fractions and the density variations in the various horizons.In exploration, geochemical techniques, even using wide sample spacing, are proving quite adequate to prospect for Au in tropical rainforest weathering environment. Indeed, significant, well-contrasted dispersion haloes facilitate detection of rather confined mineralization. 相似文献
7.
《Chemie der Erde / Geochemistry》2021,81(2):125739
The Natitingou area within the Atacora Structural Unit (ASU) of the Pan-African Dahomeyide orogenic belt, northwestern Bénin, is characterized by the monocyclic metasedimentary formations, amphibolites and orthogneisses which belong to the Internal zone of the belt. Representative samples of these different gold-bearing rocks have been analyzed geochemically to determine their petrogenesis, mode of emplacement, tectonic setting and role in the genesis of gold mineralization in the area. The orthogneisses are subalkaline, peraluminous and emplaced in a syn-collisional arc setting while the amphibolites are metaluminous, tholeiitic with an E-MORB affinity and emplaced in a rifted lithospheric setting. The metasedimentary rocks, comprising quartzites and mica schists are cross-cut by auriferous quartz veins. The metasedimentary rocks are recycled sediments varying from wackes to sublitharenite in composition and deposited in a passive margin setting. The quartz veins similar to the metasedimentary rocks are enriched in LREE, depleted in HREE and showed a negative Eu-anomaly (0.31–0.72). Their chondrite-normalised REE patterns deciphered them as Upper Continental Crustal materials which were probably derived from the reworking of their host metasedimentary rocks. Gold concentration in quartzites, amphibolites, mica schists, quartz veins and orthogneiss were 0.004–9.587, 0.26–1.76, 0.0005–0.464, 0.023–0.147 and 0.0−0.0005 ppm, respectively. Devolatilization process of the country-rocks, is the most probable mechanism for the ore-forming fluid, which could have been generated during the Pan-African Dahomeyide event. Remobilisation of gold and associated metal (As, W, Cu, Mo, Sb, and Sn) after the Pan-African Dahomeyide orogeny is suggested for enrichment of gold along shear and fault zones of the Natitingou area. 相似文献
8.
麻山群孔兹岩系地层新见 总被引：2，自引：0，他引：2
<正> 黑龙江省东部出露一个较为独特的地质构造单元,前人曾赋以“老爷岭台背斜”、“佳木斯隆起”及“佳木斯中间地块”等名称。地块总体呈南北向展布,向北向东分别越黑龙江和乌苏里江进入俄罗斯远东南部,周围均被加里东期及其后侵入的花岗岩所包围。地块内主要出露两套变质岩系,一为麻山群,构成该地块的主体,另一“黑龙江群”。张贻侠等认为,该地块是一个由异地的龙江地体和基本为原地的麻山地体在晚元古代末(600—750 相似文献
9.
K. Nicholson 《Mineralium Deposita》1990,25(2):126-131
A stratiform manganiferous horizon, up to 4 m thick but localised in aerial extent, occurs 10 km south-east of Inverness in north-east Scotland. It overlies Precambrian Grampian Group schists and is itself overlain by Middle Old Red Sandstone (Devonian) conglomerate, which elsewhere rests unconformably on the schists. The deposit was mined briefly in the early 1920s and is composed principally of fine-grained braunite with minor bustamite. Lower sections of the deposit contain cavities, infilled by late baryte, calcite and rhodochrosite, which resemble stromatactis. This horizon is underlain by a hematite-quartz layer, thought to represent a laterite formed by pre-MORS weathering of the underlying schists. The mineralogy and geochemistry of the manganese ore (enriched in Ag, As, Ba, Bi, Pb, Sb, Sr and Zn) are characteristic of a hydrothermal origin. Such an origin, when considered in conjunction with the outcrop, textures, mineralogy and stratigraphy of the deposit together with the palaeogeography of the region, can only be explained by deposition from hot-springs in a sublacustrine environment. Nearby baryte mineralisation may also have been deposited from the same geothermal system, which had the Caledonian 407 Ma Moy granitoid as heat source. The managanese ore is enriched in gold pathfinder elements and minor detrital gold has been found in the area. Gold mineralisation may therefore have also been deposited in the upper sections of this Devonian geothermal system. 相似文献
10.
11.
《International Geology Review》2012,54(10):1365-1375
A peculiar horizon of tourmaline-bearing quartzites has been identified in the study of basic intrusives of the South Urals. This horizon is quite consistent along the contacts of gabbro massifs, with the quartzites strongly metasomatized and altered in both structure and mineral composition. The tourmaline appears to be the result of an alkali metasomatism related to granitic intrusions. The principal sequence is albite, tourmaline and quartz. The quartzites appear to be of sedimentary origin, as they form a consistent horizon traceable for tens of kilometers and are intercalated with similarly consistent horizons of hornfels and schists. — F. E. Ingerson. 相似文献
12.
青海东昆仑哈西亚图铁多金属矿区石英闪长岩LA-ICP-MS锆石U-Pb年龄和岩石地球化学特征 总被引：2，自引：0，他引：2
东昆仑地区是青海省重要的夕卡岩型铁多金属矿成矿带,哈西亚图铁多金属矿是近年来首例在东昆仑金水口岩群中发现的与中酸性岩体有关的夕卡岩型矿床,目前铁、金、锌矿已达中型。其成矿作用与矿区东北部石英闪长岩关系密切,矿体产于石英闪长岩的外接触带。采用LA-ICP-MS同位素测定技术,测得石英闪长岩锆石U-Pb年龄为246.8±1.8Ma(MSWD=0.074),形成于早三叠世,表明东昆仑地区早三叠世存在夕卡岩成矿作用。地球化学研究表明,石英闪长岩为高钾钙碱性系列,具有安第斯型活动大陆边缘火成岩的构造属性。研究认为,石英闪长岩是阿尼玛卿洋盆向北俯冲,致使壳幔岩浆发生混合,后经侵位、结晶分异形成的。 相似文献
13.
Graphite‐schist blocks in the Franciscan Mélange,San Simeon,California: Evidence of high‐P metamorphism 下载免费PDF全文
下载免费PDF全文 The seacliff exposure at San Simeon, California, contains graphite‐schist blocks in a shale‐matrix, an undocumented lithology within the Franciscan mélange. Thirty graphite‐schist blocks were studied to discover all the varieties in this classic locality of mélange. Based on their mineralogical assemblage and composition, and textural characteristics the graphite‐schists in San Simeon are subdivided into two main types (Type I and II) with two subdivisions each (A and B). Type IA and IIA blocks are the most abundant. Type IA graphite‐schists are siltstone/fine greywacke‐like, preserve sedimentary textures, and lack lawsonite. Type IB graphite‐schists are mineralogical and texturally similar to Type IA schists, but are finer grained siltstone and shale. Type IIA graphite‐schists are compositionally layered and contain quartz‐ and albite‐rich layers and dark graphite‐ and intergrown mica/chlorite‐rich layers. Nine out of the 15 Type IIA blocks contain lawsonite. Two Type IIA blocks also contain aragonite (+calcite) in veins. Type IIB graphite‐schists are mostly composed of quartz and minor graphite, intergrown chlorite and white mica, and white mica pseudomorphs after lawsonite. The phengite content of mica in Type IIA blocks is higher than that of mica in Type IA graphite‐schists, confirming they were metamorphosed under high‐P/low‐T conditions. Type IA blocks were recrystallized between 200 and 250 °C at <~3 kbar; whereas, Type IIA blocks were metamorphosed under higher pressure conditions, probably at 250–300 °C and 3–5 kbar. Most likely both types of graphite‐schists were derived from a similar layered siltstone/fine greywacke/shale protolith. Organic matter‐rich sediments deposited in the trench axis were subducted along with oceanic crust during Franciscan subduction. Type I graphite‐schists were subducted to depths <10 km, whereas Type II graphite‐schists were subducted to depths ~15 km where they were underplated under high‐P conditions. The graphitic metasedimentary rocks were juxtaposed with mafic lithologies from the subducted oceanic crust that were metamorphosed to blueschist facies and retrograded to greenstone as they returned to the surface in the subduction channel shear zone. 相似文献
14.
浙北大银山金矿位于下扬子被动陆缘与江南古岛弧的接触带附近,为一矽卡岩相关的金矿床。文章对矿区内与矿化密切相关的石英闪长岩开展了主量与微量元素、锆石U-Pb 测年以及Lu-Hf 同位素地球化学研究。研究表明,该岩体为一套高钾钙碱性-钙碱性、准铝质向过铝质过渡的岩石系列,富集大离子亲石元素（Ba、Rb、K、Sr 等）、亏损高场强元素（Nb、Ta、Ti 等）,亏损重稀土元素,Eu 异常不明显,具有类似俯冲带岛弧岩石的特征。同时,该岩体具有较低的Sr/Y值,高Y和Yb含量,表明其岩浆源区的大陆地壳较薄。锆石U-Pb年龄表明,石英闪长岩的206Pb/238U加权平均年龄为144±1 Ma。锆石Lu-Hf 同位素数据表明,εHf(t)值为-5.0~-9.9,二阶段Hf 同位素模式年龄在1507~1815 Ma 之间,显示该岩体的源区物质以扬子板块下地壳为主,与长江中下游成矿带多数金矿成矿岩体具有相似的物质来源。大银山金矿与长江中下游地区的金矿化时间相近,其成矿可能受晚中生代古太平洋板块俯冲作用影响,是在陆内断裂坳陷带中不同构造环境下的响应。 相似文献
15.
安徽奥陶系石灰岩中含铁非骨架核形石的成因及其聚铁作用 总被引：7，自引：0，他引：7
安徽下扬子区下奥陶统顶部到中奥陶统的灰色生物屑微晶灰岩中,产出一种含铁的非骨架核形石。它形成于宁镇-皖南碳酸盐台地两侧边缘的浅水到潮坪环境中。这种核形石是由蓝绿藻以生物碎屑为核心,围绕核心以底部滚动和悬浮方式生长成同心圆状多层包壳的椭球体,有柱核形石和层柱核形石两种类型。蓝绿藻呈核形石生长过程中,吸附铁质形成含铁核形石,并能吸附铜、铅等金属元素。 相似文献
16.
Dr. A. K. Bhattacharya Mr. B. K. Chatterjee 《International Journal of Earth Sciences》1964,53(2):758-779
Pre-Cambrian Geology of an area of about 14 sq. miles has been investigated in this paper. The oldest rock is a very small patch of serpentinite, tentatively correlated with the huge ultrabasic body at Jojohatu, some 10 miles north. Granite and Newer dolerite are intrusive rocks of the area. Kolhan series, resting unconformably on Granite and showing facies variation from basal sandstone conglomerate to phyllitic shale through sandstone and impersistent limestone in a thickness of only a few tens of metres, is a shallow epicontinental deposit. Kolhan sandstone, rich in hematitic cement, is an argillaceous orthoquartzite practically devoid of feldspar and is very poor in heavy and accessory minerals. It is richly current bedded, immature, bimodal, fine grained, positively skewed and well sorted. Kolhan limestone is recrystallized micrite, its lower horizon is mostly high grade and contains pink calcite and quartz crystals in cavities. Its upper horizon is low grade, phyllitic and argillaceous and is partly metasomatic and exhibits contemporaneous deformation structures like hassock bedding and slickenside (slickolites?). Kolhan phyllitic shale exhibits effects of Singhbhum orogeny in development of cleavage and crumpling of foliation. Dirty green vug quartz contains abundant oriented microscopic chlorite inclusions. Non-metallic and metallic mineralization in Kolhans is represented by limestones, and local hematite-molybdenite and iron-rich manganese ore respectively. 相似文献
17.
The Bumo gold deposit is a low‐sulfide quartz vein type deposit, situated in the west of Hainan Island, approximately 25 km southeast of Dongfang City (termed Basuo in alias). Tectonically, the SW‐NE‐oriented Gezhen Ductile‐Shearing Zone was largely attenuated in Bumo. It is hosted by gneisses and schists of Proterozoic age (locally called the Baoban Group), but the radiometric age of ores mainly is Jurassic–Cretaceous, being coeval to the regional metallogenesis along the Eurasian margin. The affinity with the Phanerozoic orogenic gold deposits is indicated by low salinity (2.4 wt% NaCl–10.3 wt% NaCl), intermediate temperature (150–300°C) and appropriate δ18O value (approximately 7–11‰). The gold metal tonnage, proved previously, within an area smaller than 1.0 km2 in the gold belt II amounted to 11.59 t, with the average gold grades for the major Au quartz veins (7 and 8) in this belt of 52.7 and 71.1 g/t, respectively. This shows significant enrichment of gold and an unusual “nugget effect”. A ring structure, mainly represented by ridges, valleys, dikes, big bull quartz veins and lithological borders or pertinent faults, marks the gold field, and its origin was linked to a possible magmatic diapir. It was viewed as macroscopic evidence that the dip angles of strata tend to decline gradually from deeper ones in the center area to nearly horizontal in the outskirts, and certain intrusion‐affiliated elements such as Bi, As and W are considerably abundant in soil samples. Two areas, namely the area A (3.06 km2) in the outskirts of the ring structure or in northeastern Bumo and the area B (1.32 km2) in the field center or to the west of the gold belts I and II, were selected for the geochemical survey in a 50 × 50‐m sampling grid. The analytical results of the samples from horizon C and in a ?80 mesh size showed that the average contents of Bi, As and W amounted to 0.55, 19.3 and 3.67 ppm in the area A (1225 samples) and to 0.79, 68.3 and 4.14 ppm in the area B (529 samples), respectively. This geochemical exploration led to the discovery of several Au quartz veins in both areas A and B, which also manifested an Au nugget effect (the average Au grades between 50 and 100 g/t) in spite of their limited scales (from a couple of centimeters to 50 cm wide and from several meters to 15 m long). A mylonite zone in area A was also found by this study. An intimate spatial correlation between a lithological border (gneiss and schist or pegmatite) or the mylonite zone and Au anomalies indicates an important prospect for further gold exploration. 相似文献
18.
A.Bhaskara Rao 《Chemical Geology》1987,60(1-4):287-291
Geological studies made in the area of Mara Rosa in Goias State, Brazil, where small occurrences of gold are known in river placers, have revealed an interesting and extensive “lateritised gravel bed” overlying an inexpressive nodular lateritic crust horizon. The gravel has pebbles of vein quartz, quartzites and gneisses, which are interlocked and compacted by intense lateritisation with brown hydrous Fe-oxide (goethite). The underlying nodular crusts grade from deep brown to mottled, and occasionally have cavities. They possibly represent an interface between the bed rock and the gravel bed. The intensity of lateritisation is attributed to the existence of volcanogenic mafic sequences in the rock. The presence of pebbles of the same nature in the small placers with Au, suggest that Au has been dissolved and precipitated during the lateritisation process. Its abundance is mainly restricted to the lateritic gravel bed, which in turn has contributed Au to the stream placers. Thus, it is considered as a new guide horizon for lateritic Au. 相似文献
19.
昆嵛山花岗岩是牟平—乳山金矿成矿带的围岩，在其成因和定位时代上长期存在争议。本文对岩体地质和地球化学特征进行了系统研究，并就岩体成因及其与金矿的关系进行了讨论。作者认为，昆嵛山花岗岩是在中生代由岩浆缓慢冷凝结晶形成的大型复式岩基，并非交代成因。它由垛崮顶片麻状花岗闪长岩（１４７Ｍａ）、八门邹家斑状花岗闪长岩（１３５Ｍａ）、瓦善—水道弱片麻状二长花岗岩及五爪山片麻状含榴二长花岗岩（１２０Ｍａ）组成，成分具贫铝富碱的特点。岩浆来源于中下地壳中酸性变质火山岩系部分熔融形成的岩浆，其形成温度为６５０—７５０℃。岩体经历了韧性和脆性变形作用，不同方向的片麻状构造是岩浆结晶期韧性变形作用的结果。脆性变形形成的断裂和破碎带是本区主要的导矿和容矿构造。花岗岩定位、韧和脆性变形作用与金矿成矿作用有十分密切的关系 相似文献
20.
自然铁产于含金石英脉中,其外壳为磁铁矿。多数自然铁外壳被闪锌矿包裹,个别闪锌矿又被包裹在自然铁外壳中.按表面形态自然铁可分为两种类型:园滑状;不规则的港湾状.锯齿状。据穆斯堡尔谱峰面积法,外壳磁铁矿Fe~(+++)/Fe~(++)比值为1.4～1.7.电镜成分面扫描表明,随外壳厚度增加,氧浓度增高而硫浓度降低。不规则状自然铁外壳磁铁矿可能由黄铁矿氧化而来。 相似文献