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1.
新疆南天山查岗诺尔大型磁铁矿矿床地质特征及矿床成因 总被引：1，自引：0，他引：1
查岗诺尔铁矿床为新疆南天山近年来发现的大型磁铁矿床。该矿床产于南天山造山带下石炭统大哈拉军山组火山-碎屑-碳酸岩建造中,储量达到1.3亿吨。矿床由多个平行于地层层理的矿体组成,其主矿体位于隐爆角砾岩内。主要的矿物组合包括磁铁矿、磁赤铁矿、穆磁铁矿、赤铁矿、假象赤铁矿及极少量的镜铁矿等。通过对矿石的结构、构造以及矿石矿物化学成分的综合分析,表明该矿床的形成与火山通道附近的潜火山构造隐爆作用密切相关。该矿床的发现为区域上寻找同类矿床提供了广阔的找矿前景。 相似文献
2.
老挝万象省爬立山铁矿床位于长山褶皱带北西端,是长山成矿带内与岩浆作用有关的一个大型铁矿床.矿床类型以矽卡岩型为主,其次为热液型,成矿作用与花岗岩类侵入作用有关,矿区内发育致密块状磁铁矿、孔洞状赤铁矿、砂砾土状铁矿.该区地球物理工作研究程度较低,仅有部分航磁资料,难以准确控制矿化异常;老挝热带雨林气候植被覆盖严重,地表露头难寻,圈定矿体规模和划分地层界线难度较大.为了获得该区铁矿体地表规模及深部延展,笔者在该区开展了1∶10000地面高精度磁法测量,运用解析延拓、水平总梯度模、垂向导数、2.5D人机交互反演等方法有效克服了低纬度地区磁异常化极不稳定形成假异常的问题,解译了爬立山矿区磁异常特征,提高了磁异常的解译分辨率,更加准确的控制了爬立山铁矿区铁矿体的范围、深部延展.后期钻探验证结果表明,在老挝地质勘查程度低、覆盖严重的爬立山地区开展高精度磁法是控制该地区铁矿的有效地球物理方法. 相似文献
3.
行口铁矿位于沁阳市北部太行山山脚下,是上世纪80年代发现的一个中型贫磁铁矿床。矿体成群出现,延长900～1200m,宽度变化70～290m,厚度变化5～270m;呈似层状、透镜状,控制延深700m,有用矿物主要为磁铁矿和赤铁矿。矿体的品位在走向上和倾向上基本稳定,矿石化学成分和矿物组成简单,有害物质含量低,矿体群中夹层较多,属于火山沉积变质铁矿床。 相似文献
4.
Re-Os dating of magnetite from the Shaquanzi Fe-Cu deposit,eastern Tianshan,NW China 总被引：2，自引：0，他引：2
Magnetite separates from the Shaquanzi Fe-Cu deposit in the eastern Tianshan are used for Re-Os geochronological study.Re-Os data show that magnetite separates contain ca.0.7 to 50.9 ppb Re and ca.16 to 63 ppt Os.Eight samples yield a model 3isochron age of(303±12)Ma(2),which is within uncertainty consistent with of the Re-Os date(295±7 Ma)of associated pyrite.Tectonic evolution shows that the Late Carboniferous Aqishan-Yamansu belt was a back-arc rift.Therefore,the Re-Os age of ca.300 Ma indicates that the Shaquanzi Fe-Cu deposit may have formed in a back-arc extensional environment and was closely related to mantle-derived magmatism.The successful application of Re-Os magnetite geochronology in the Shaquanzi Fe-Cu deposit suggests that the purity of magnetite,relatively high Re and Os contents,and the closure of Re-Os systematic are base factors for a successful Re-Os geochronology.There would be a good prospect for Re-Os geochronology for magnetite. 相似文献
5.
Rock magnetic properties and ore microscopy of the iron ore deposit of Las Truchas, Michoacan, Mexico 总被引：1，自引：0，他引：1
Iron ore and host rocks have been sampled (90 oriented samples from 19 sites) from the Las Truchas mine, western Mexico. A broad range of magnetic parameters have been studied to characterize the samples: saturation magnetization, Curie temperature, density, susceptibility, remanence intensity, Koenigsberger ratio, and hysteresis parameters. Magnetic properties are controlled by variations in titanomagnetite content, deuteric oxidation, and hydrothermal alteration. Las Truchas deposit formed by contact metasomatism in a Mesozoic volcano-sedimentary sequence intruded by a batholith, and titanomagnetites underwent intermediate degrees of deuteric oxidation. Post-mineralization hydrothermal alteration, evidenced by pyrite, epidote, sericite, and kaolin, seems to be the major event that affected the minerals and magnetic properties. Magnetite grain sizes in iron ores range from 5 to >200 μm, which suggest dominance of multidomain (MD) states. Curie temperatures are 580±5°C, characteristic of magnetite. Hysteresis parameters indicate that most samples have MD magnetite, some samples pseudo-single domain (PSD), and just a few single domain (SD) particles. AF demagnetization and IRM acquisition indicate that NRM and laboratory remanences are carried by MD magnetite in iron ores and PSD–SD magnetite in host rocks. The Koenigsberger ratio falls in a narrow range between 0.1 and 10, indicating the significance of MD and PSD magnetites. 相似文献
6.
The Bayan Obo deposit in northern China is an ultra-large Fe–REE–Nb deposit.The occurrences,and geochemical characteristics of thorium in iron ores from the Bayan Obo Main Ore Body were examined using chemical analysis,field emission scanning electron microscopy,energy dispersive spectrometer,and automatic mineral analysis software.Results identified that 91.69%of ThO2 in the combined samples was mainly distributed in rare earth minerals(bastnaesite,huanghoite,monazite;56.43%abundance in the samples),iron minerals(magnetite,hematite,pyrite;20.97%),niobium minerals(aeschynite;14.29%),and gangue minerals(aegirine,riebeckite,mica,dolomite,apatite,fluorite;4.22%).An unidentified portion(4.09%)of ThO2 may occur in other niobium minerals(niobite,ilmenorutile,pyrochlore).Only a few independent minerals of thorium occur in the iron ore samples.Thorium mainly occurs in rare earth minerals in the form of isomorphic substitution.Analyses of the geochemical characteristics of the major elements indicate that thorium mineralization in the Main Ore Body was related to alkali metasomatism,which provided source material and favorable porosity for hydrothermal mineralization.Trace elements such as Sc,Nb,Zr,and Ta have higher correlation coefficients with thorium,which resulted from being related to the relevant minerals formed during thorium mineralization.In addition,correlation analysis of ThO2 and TFe,and REO and TFe in the six types of iron ore samples showed that ThO2 did not always account for the highest distribution rate in rare earth minerals,and the main occurrence minerals of ThO2 were closely related to iron ore types. 相似文献
7.
8.
Rock magnetic investigations of Permo-Carboniferous carbonate sediments from two areas on Spitsbergen are described, conducted to identify the carriers of the NRM in these rocks. Since microscopic and magnetic separation techniques could not profitably be applied, the nature of magnetic minerals was investigated by thermal demagnetization of the NRM and decay of saturation isothermal remanence (Irs) during heating to 600°C, as well as by the distribution of the median destructive fields of the NRM and observation of magnetic susceptibility after subsequent heatings. The results show that the NRM of these limestones resides mainly in magnetite, but creation of magnetic pyrrhotite and of fresh magnetite is observed during heating to 600°C. Presence of sulphides indicates that magnetite is an oxidation product of pyrite or of non-magnetic pyrrhotite. Examination of rock magnetic properties of limestones leads to the conclusion that most of the magnetite in the rocks of the Bellsund area is of detrital origin, whereas the rocks at Festningen contain magnetite derived from pyrite probably during an early stage of the diagenetic process. 相似文献
9.
In China, most Precambrian banded iron formations(BIFs) are situated in the North China Craton. The Yuanjiacun iron deposit, located in the Lüliang area, is arguably the most representative Superior-type BIF. This iron deposit is coherent with the sedimentary rock succession of the Yuanjiacun Formation in the lower Lüliang Group, and was interpreted to be deposited at 2.3–2.1 Ga, based on ages of overlying and underlying volcanic strata. This age overlaps with the time range of the Great Oxidation Event(GOE, 2.4–2.2 Ga). The Yuanjiacun BIF consists mainly of subhedral-xenomorphic magnetite and quartz and rarely other minerals with a lower degree of metamorphism, from greenschist to lower amphibolite facies. The geochemical characteristics of this BIF are similar to those of Superior-type BIFs. Prominent positive La, Y, and Eu anomalies normalized by the Post Archean Australian Shale(PAAS) indicate that the primary chemical precipitate is a result of solutions that represent mixtures of seawater and high-T hydrothermal fluids. The contamination from crustal detritus found is negligible based on low abundances of Al2O3 and TiO2(0.5%) and of trace elements such as Th, Hf, Zr, and Sc(1.5 ppm), as well as the lack of co-variations between Al2O3 and TiO2. In particular, the Yuanjiacun BIF samples do not display significant negative Ce anomalies like those of the Archean iron formations, but rather, the Yuanjiacun BIF samples exhibit prominent positive Ce anomalies, low Y/Ho ratios, and high light to heavy REE((Pr/Yb)SN) ratios, which are essentially consistent with the late Paleoproterozoic(2.0 Ga) BIFs around the world. These characteristics of the Yuanjiacun BIF samples imply that the ancient ocean(2.3–2.1 Ga) was redox-stratified from oxic shallow water to deeper anoxic water. The specific redox conditions of the ancient ocean may be related to the GOE, which gave rise to the oxidation of Ce and Mn in the upper water, and to the presence of a Mn oxide shuttle in the ocean, resulting in varying REE patterns due to the precipitation and dissolution of this Mn oxide shuttle under different redox states. Therefore, the Yuanjiacun BIF appears to have formed near the redoxcline and lower-level reduced marine water. 相似文献
10.
《Acta Geochimica》2017,(3)
Xianglushan-type iron deposits are one of the new types of iron deposits found in the Weining Area of Western Guizhou. The iron-bearing rock system is a paleo-weathered crustal sedimentary(or accumulating) stratum between the top of the Middle-Late Permian Emeishan basalt formation and the Late Permian Xuanwei formation. Iron ore is hosted in the Lower-Middle part of the rock system. In terms of the genesis of mineral deposit, this type of deposit should be a basalt paleo-weathering crustal redeposit type, very different from marine sedimentary iron deposits or continental weathering crust iron deposits. Based on field work and the analytical results of XRD Powder Diffraction, Electron Probe, Scanner Electron Microscope, etc., the geological setting of the ore-forming processes and the deposit features are illustrated in this paper. The ore-forming environment of the deposit and the Emeishan basalt weathering mineralization are also discussed in order to enhance the knowledge of the universality and diversity of mineralization of the Emeishan Large Igneous Province(ELIP), which may be a considerable reference to further research for ELIP metallogenic theories, and geological research for iron deposits in the paleo-weathering crust areas of the Emeishan basalt,Southwestern, China. 相似文献
11.
In order to establish the magnetic carriers and assess the reliability of previous paleomagnetic results obtained for Eocene marine marls from the south Pyrenean basin, we carried out a combined paleo- and rock-magnetic study of the Pamplona-Arguis Formation, which crops out in the western sector of the southern Pyrenees (N Spain). The unblocking temperatures suggest that the characteristic remanent magnetization (ChRM) is carried by magnetite and iron sulphides. The ChRM has both normal and reversed polarities regardless of whether it resides in magnetite or iron sulphides, and represents a primary Eocene magnetization acquired before folding. Rock magnetic results confirm the presence of magnetite and smaller amounts of magnetic iron sulphides, most likely pyrrhotite, in all the studied samples. Framboidal pyrite is ubiquitous in the marls and suggests that iron sulphides formed during early diagenesis under sulphate-reducing conditions. ChRM directions carried by magnetic iron sulphides are consistent with those recorded by magnetite. These observations suggest that magnetic iron sulphides carry a chemical remanent magnetization that coexists with a remanence residing in detrital magnetite. We suggest that the south Pyrenean Eocene marls are suitable for magnetostratigraphic and tectonic purposes but not for studies of polarity transitions, secular variations and geomagnetic excursions, because it is difficult to test for short time differences in remanence lock-in time for the two minerals. The presence of iron sulphide minerals contributing to the primary magnetization in Eocene marine marls reinforces the idea that these minerals can persist over long periods of time in the geological record. 相似文献
12.
D. M. Pechersky D. M. Gil’manova G. P. Markov I. O. Murdmaa D. K. Nurgaliev V. A. Tsel’movich Z. V. Sharonova 《Izvestiya Physics of the Solid Earth》2013,49(3):426-447
The thermomagnetic and microprobe analyses of sedimentary samples from DSDP 386, 387, 391A, and 391C boreholes in the northwestern Atlantic reveal the ubiquitous occurrence of particles of native iron. The concentrations of native iron are bimodal everywhere with the zero mode necessarily present. The nickel admixture in native iron forms two groups, one represented by pure iron and the comprising native iron with 5–6% Ni. The redeposition of iron particles manifests itself in the correlation between the concentrations of these particles and terrestrial minerals (magnetite), as well as in the equalization and reduction of the concentration of the iron particles. Pyrite and pyrrhotite are widespread in the studied sediments, and the distribution of native iron does not depend on the presence of pyrite (i.e., on redox conditions) in them. At the same time, the distributions of pyrite and particles of magnetite + titanomagnetite are inversely correlated, which can probably be accounted for by the partial dissolution of magnetite and titanomagnetite in the reducing conditions. The increased concentration of particles of volcanogenic homogeneous titanomagnetite is revealed in the volcanoclastic turbidites of the Oligocene and early and middle Miocene age at the base of the Bermuda Rise (borehole 386). The titanomagnetite composition is characteristic of the basalts of plume magmatism; it corresponds to the depth of the magmatic source in the interval of 50–25 km. 相似文献
13.
通过对西藏日土县材玛铁矿床的调查研究表明,南羌塘拗陷带的材玛铁矿床成矿地质条件较好.经地表槽探揭露和深部钻探工程控制,发现其矿体为似层状;矿体品位和厚度沿走向和倾向变化较小;容矿岩石主要为矽卡岩、矽卡岩化灰岩;矿石类型简单,主要为磁铁矿矿石.矿化富集与侵入于上三叠统地层的燕山晚期花岗闪长岩、二长花岗岩、花岗斑岩密切相关;矿体产出部位严格受碳酸盐岩层位及其层间破碎带的控制,属接触交代型矿床.其形成与燕山晚期岩浆活动关系密切,空间分布严格受岩浆岩和断裂的控制.花岗岩类岩体与上三叠统地层的接触带和层间破碎带是寻找铁矿的有利部位,外围地区具有寻找相同类型铁矿床的远景. 相似文献
14.
K.R. McClay 《Earth and Planetary Science Letters》1974,21(4):367-376
The feeder series gabbros of the Jimberlana Norite possess a large, stable NRM. Koenigsberger ratios of 20 or greater suggest that single-domain grains carry most of the NRM. Coercivity spectra extend up to 2000 Oe. Volumes of magnetite satisfying single-domain requirements occur principally as intergrowths of host magnetite between exsolution phases. Small discrete magnetite grains do occur in the Ca-rich pyroxenes but are thought to contribute only a minor fraction of the NRM. 相似文献
15.
Magnetic grains isolated from magnetococcoid bacterial cells were studied by means of transmission electron microscopy, electron diffraction and electron microprobe analysis. Observed in situ the magnetic grains are each surrounded by an organic membrane and are usually found in a random array although “chains” are also seen. Electron diffraction confirms the magnetite mineralogy and provides additional evidence in favor of vacancies in the structure. Electron microprobe analysis shows the magnetite to be slightly titaniferous. Electron microscopy indicates that the grains, rather than being flake shaped, are parallelepiped crystals with a mean length of99.3 ± 8.7nm, a mean width of62.3 ± 6.1nm yielding a width-to-length ratio of 0.63. These data support the contention that the magnetic bacterial grains are single-domain crystals capable of producing a natural remanent magnetization in sediments. 相似文献
16.
地震前异常的阶段性及其空间分布特征 总被引：21，自引：5，他引：21
将岩石变形曲线到达强度点以前比拟为地震前异常的中长期阶段，强度点至失稳点之间定义为短临阶段。在中长期阶段异常是由驱动力的增强或区域应力场的调整引起，前者引起的应力扰动场与原来的方向一致，强烈扰动区与原来的应力集中区一致，后者引起的应力扰动场应力方向可以发生变化，应力扰动对平均应力影响较大，强烈扰动区位于断层错列部位。二者的强烈扰动场均与未来的震源区无必然联系。在短临阶段异常是由局部断层扩展或弱化引起，与之相伴的是平均应力扰动场的四象限分布和最大剪应力扰动场的八瓣式分布 相似文献
17.
Richard Weaver Andrew P. Roberts Andrew J. Barker 《Earth and Planetary Science Letters》2002,200(3-4):371-386
Paleomagnetic, rock magnetic, and sedimentary micro-textural data from an early Miocene mudstone sequence exposed in Okhta River, Sakhalin, Russia, indicate the presence of pyrrhotite and magnetite at different stratigraphic levels. Sites that contain only magnetite have a reversed polarity characteristic remanent magnetization (ChRM) with a low-coercivity overprint, which coincides with the present-day geomagnetic field direction. Pyrrhotite-bearing sites have stable normal polarity ChRMs that are significantly different from the present-day field direction. After correction for bedding tilt, the ChRM data fail a reversals test. However, the normal polarity pyrrhotite ChRM directions become antipodal to the tilt-corrected magnetite ChRM directions and are consistent with the expected geocentric axial dipole field direction at the site latitude after 40% partial unfolding. These data suggest that the pyrrhotite magnetization was acquired during folding and after lock-in of the magnetite remanences. Electron microscope observations of polished sections indicate that fluid-associated halos surround iron sulphide nodules. Pyrrhotite is present in randomly oriented laths in and around the nodules, and the nodules do not appear to have been deformed by sediment compaction. This observation is consistent with a late diagenetic origin of pyrrhotite. Documentation of a late diagenetic magnetization in pyrrhotite-bearing sediments here, and in recent studies of greigite-bearing sediments, suggests that care should be taken to preclude a late origin of magnetic iron sulphides before using such sediments for geomagnetic studies where it is usually crucial to establish a syn-depositional magnetization. 相似文献
18.
Effect of citrate-bicarbonate-dithionite treatment on fine-grained magnetite and maghemite 总被引：8，自引：0，他引：8
Christopher P. Hunt Michael J. Singer Gunther Kletetschka Jeff TenPas Kenneth L. Verosub 《Earth and Planetary Science Letters》1995,130(1-4):87-94
Mineral magnetic properties of soils and parent materials have been interpreted in terms of paleoclimate and rates of soil formation but it is important to understand which minerals contribute to the mineral magnetic signal. Citrate-bicarbonate-dithionite (CBD) treatment has been used to determine the amounts of fine-grained, often pedogenic, ferrimagnetic minerals relative to coarse-grained, often inherited, magnetic minerals. However, questions have been raised about the effect of particle size on the efficacy of CBD in dissolving magnetite and maghemite grains. In this paper we use magnetic susceptibility and its frequency dependence, and the low-temperature behavior of a saturation isothermal remanent magnetization, to track the dissolution of carefully sized magnetite grains. We found that the standard CBD procedure dissolves fine magnetite particles (ca. < 1 μm) but leaves larger particles (ca. > 1 μm) essentially intact. Thin oxidized coatings, presumably maghemite, are also dissolved by the CBD procedure. These results support previous interpretations that the CBD procedure can be used to distinguish between pedogenic and lithogenic magnetic grains, assuming that most pedogenic magnetic grains are sufficiently small (ca. < 1 μm) and most lithogenic magnetic grains are sufficiently large (ca. > 1 μm). These results also show that the standard procedure is too harsh to differentiate between 1 μm grains of magnetite and maghemite. A modified CBD extraction that uses half as much dithionite reduces the magnetic susceptibility of 1 μm magnetite grains by only 10%. This method may be useful in distinguishing between magnetite and maghemite grains in this size range. 相似文献
19.
经资料整理与实地调研：老挝已发现铁矿床（点）42处。重要矿床为万象省（P．Vientiane）万荣（Vang—viang）铁矿、川圹省（P．Xiangkhouang）富诺安（Phou．Nhouan）铁矿、万象省（P．Vientiane）帕莱（PhaLek）铁矿、甘蒙省（P．Khammouan）班农洛（BanNonglao）铁矿。重要矿床的矿体呈似层状、脉状产出,矿石质量较好,矿床属接触交代矿床、热液矿床。据地层条件、岩浆岩条件、构造条件、铁矿床（点）的分布情况,老挝划分出琅勃拉邦（Louangphabang）、孟佩（MuangPek）、桑怒（Xam—Nua）3个成矿预测区。 相似文献
20.
Stable remanent directions encountered in three oriented lake-sediment cores, covering 6 m of gyttja deposits, reveal declination swings with amplitudes of the order of ± 50°. Anomalously low inclinations, scattered around the horizontal in the upper 2 m of core, is attributed to compressional disturbances of the alignment of magnetic grains during the coring procedure. Four 14C dates obtained (1250, 1940, 4600 and 6330 y B.P.) have enabled a correlation with features ‘c’–‘g’ of the British Geomagnetic Master Curve). For the older part of the curve, features ‘h’ and ‘i’, the correlation is questionable. Magneto-mineralogical parameters and qualitative chemical analysis of individual grains by secondary X-ray emission analysis reveal the presence of pure magnetite grains. Scanning electron micrographs show a dominant proportion of concoidal slightly elongated grains (10–80 μm). A few almost-perfect octahedral magnetite crystals can be related to outcrops of augen gneisses in the vicinity confirming a detrital origin of these grains. 相似文献