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1.
《Chemie der Erde / Geochemistry》2016,76(1):13-37
The Mombi bauxite deposit is located in 165 km northwest of Dehdasht city, southwestern Iran. The deposit is situated in the Zagros Simply Fold Belt and developed as discontinuous stratified layers in Upper Cretaceous carbonates (Sarvak Formation). Outcrops of the bauxitic horizons occur in NW-SE trending Bangestan anticline and are situated between the marine neritic limestones of the Ilam and Sarvak Formations. From the bottom to top, the deposit is generally consisting of brown, gray, pink, pisolitic, red, and yellow bauxite horizons. Boehmite, diaspore, kaolinite, and hematite are the major mineral components, while gibbsite, goethite, anatase, rutile, pyrite, chlorite, quartz, as well as feldspar occur to a lesser extent. The Eh–pH conditions during bauxitization in the Mombi bauxite deposit show oxidizing to reducing conditions during the Upper Cretaceous. This feature seems to be general and had a significant effect on the mineral composition of Cretaceous bauxite deposits in the Zagros fold belt. Geochemical data show that Al2O3, SiO2, Fe2O3 and TiO2 are the main components in the bauxite ores at Mombi and immobile elements like Al, Ti, Nb, Zr, Hf, Cr, Ta, Y, and Th were enriched while Rb, Ba, K, Sr, and P were depleted during the bauxitization process. Chondrite-normalized REE pattern in the bauxite ores indicate REE enrichment (ΣREE = 162.8–755.28 ppm, ave. ∼399.36 ppm) relative to argillic limestone (ΣREE = 76.26–84.03 ppm, ave. ∼80.145 ppm) and Sarvak Formation (ΣREE = 40.15 ppm). The REE patterns also reflect enrichment in LREE relative to HREE. Both positive and negative Ce anomalies (0.48–2.0) are observed in the Mombi bauxite horizons. These anomalies are related to the change of oxidation state of Ce (from Ce3+ to Ce4+), ionic potential, and complexation of Ce4+ with carbonate compounds in the studied horizons. It seems that the variations in the chemistry of ore-forming solutions (e.g., Eh and pH), function of carbonate host rock as a geochemical barrier, and leaching degree of lanthanide-bearing minerals are the most important controlling factors in the distribution and concentration of REEs. Several lines of evidences such as Zr/Hf and Nb/Ta ratios as well as similarity in REE patterns indicate that the underlying marly limestone (Sarvak Formation) could be considered as the source of bauxite horizons. Based on mineralogical and geochemical data, it could be inferred that the Mombi deposit has been formed in a karstic environment during karstification and weathering of the Sarvak limy Formation. 相似文献
2.
Sajid Ali Karl Stattegger Dieter Garbe-Schönberg Wolfgang Kuhnt Oliver Kluth Haddou Jabour 《International Journal of Earth Sciences》2014,103(1):265-280
The petrography, heavy mineral analysis, major element geochemical compositions and mineral chemistry of Early Cretaceous to Miocene–Pliocene rocks, and recent sediments of the Tarfaya basin, SW Morocco, have been studied to reveal their depositional tectonic setting, weathering history, and provenance. Bulk sediment compositional and mineral chemical data suggest that these rocks were derived from heterogeneous sources in the Reguibat Shield (West African Craton) including the Mauritanides and the western Anti-Atlas, which likely form the basement in this area. The Early Cretaceous sandstones are subarkosic in composition, while the Miocene–Pliocene sandstones and the recent sediments from Wadis are generally carbonate-rich feldspathic or lithic arenites, which is also reflected in their major element geochemical compositions. The studied samples are characterized by moderate SiO2 contents and variable abundances of Al2O3, K2O, Na2O, and ferromagnesian elements. Binary tectonic discrimination diagrams demonstrate that most samples can be characterized as passive continental marginal deposits. Al2O3/Na2O ratios indicate more intense chemical weathering during the Early Cretaceous and a variable intensity of weathering during the Late Cretaceous, Early Eocene, Oligocene–Early Miocene, Miocene–Pliocene and recent times. Moreover, weathered marls of the Late Cretaceous and Miocene–Pliocene horizons also exhibit relatively low but variable intensity of chemical weathering. Our results indicate that siliciclastics of the Early Cretaceous were primarily derived from the Reguibat Shield and the Mauritanides, in the SW of the basin, whereas those of the Miocene–Pliocene had varying sources that probably included western Anti-Atlas (NE part of the basin) in addition to the Reguibat Shield and the Mauritanides. 相似文献
3.
Fine grained sericite deposits occur at the interface between Archean Mewar Gneiss Complex and the Proterozoic Aravalli Supergroup
independent of shearing. They show a gradational contact with the basement granites and gneisses and a sharp contact with
the overlying quartz pebble conglomeratic quartzites. Rip-up clasts of these sericite schists are found in the overlying conglomerates.
The sericite schists are rich in sericite towards the top and contain chlorite towards the base. The sericite in these schists
was formed by metasomatic alteration of kyanite and not from the feldspars of the basement granitoids and gneisses. Uni-directional
variations of SiO2 and Al2O3, high Al2O3 content (>30%), positive correlation between Al2O3 and TiO2, Ti/Al and Ti/Zr ratios, high pre-metasomatic chemical indices of alteration (> 90), and enrichment of heavy rare earth elements
relative to the parent granites and gneisses—all these chemical characteristics combined with field evidence suggest that
the sericite schists are formed from a paleosol protolith, which developed on Archean basement between 2.5 and ~2.1 Ga in
the Precambrian of Rajasthan. The superimposed metasomatic alteration restricts the use of Fe2+/Ti and Fe3+/Ti ratios of these paleosols for interpretation of PO2 conditions in the atmosphere. 相似文献
4.
This study focuses on a late Cretaceous karst bauxite deposit in the Murge area of the Apulia district, southern Italy. The first analysis of the vertical distributions of a wide range of elements (including REEs and selected trace elements) throughout the deposit was shown in order to identify the processes determining element fractionation during the evolution of the bauxite.The studied karst bauxite deposit exhibits an ooidal texture, is mineralogically homogeneous, and contains higher abundances of boehmite than of hematite, kaolinite, and anatase. The major element composition of the bauxite is dominated by elevated concentrations of SiO2, TiO2, Al2O3, and Fe2O3, and analyses of element mobility within the bauxite indicate that all elements except for Nb and Ni, and to a lesser extent Cr, are depleted relative to the immobile element Ti. R-mode factor analysis revealed a number of key findings: (i) some low-solubility elements (e.g., Zr, Th, Ti, V, Ga) were concentrated in detrital zircon and monazite (Zr, Th), in anatase (Ti, V), and possibly in boehmite and hematite (Ga) during the later stages of bauxitisation; (ii) Fe and Cr were concentrated during wet conditions, whereas Al and Co accumulated during dry conditions; (iii) distributions of the light REEs (LREEs) and the heavy REEs (HREEs) are controlled by the same processes, suggesting that little LREE/HREE fractionation occurred during bauxite formation; and (iv) the behaviour of cerium is different from that of the other REEs, and highly variable cerium anomalies are observed across the deposit, with three characteristic Ce/Ce* maxima with values of > 2. Parisite was the only authigenic cerium mineral detected during this study. Thus, we propose a three-step model to explain the distribution of Ce: cerianite is dissolved by cerium reduction, is transported by downward-moving meteoric water (per descensum), and finally parisite is precipitated. This cycle was repeated several times in the Apulian karst bauxite in response to Eh decreases under alkaline conditions, promoted by fluctuations in the groundwater level. Finally, we used the value of the Eu anomaly to discuss the parental affinity or protolith of the bauxite. The value of the Eu anomaly (min. Eu/Eu* = 0.76, max. Eu/Eu* = 0.89) indicates that the bauxite was not derived from carbonates, but rather, that the majority of the bauxite was influenced by intermediate to mafic magmatic sources. Eu/Eu* vs Sm/Nd diagram suggests that the parental material for the bauxite was derived from a combination of a distant magmatic source and clastic material derived from a continental margin (northern Africa) to the south. 相似文献
5.
The Coniacian-Santonian high-phosphorus oolitic iron ore at Aswan area is one of the major iron ore deposits in Egypt. However, there are no reports on its geochemistry, which includes trace and rare earth elements evaluation. Texture, mineralogy and origin of phosphorus that represents the main impurity in these ore deposits have not been discussed in previous studies. In this investigation, iron ores from three localities were subjected to petrographic, mineralogical and geochemical analyses. The Aswan oolitic iron ores consist of uniform size ooids with snowball-like texture and tangentially arranged laminae of hematite and chamosite. The ores also possess detrital quartz, apatite and fine-grained ferruginous chamosite groundmass. In addition to Fe2O3, the studied iron ores show relatively high contents of SiO2 and Al2O3 due to the abundance of quartz and chamosite. P2O5 ranges from 0.3 to 3.4 wt.% showing strong positive correlation with CaO and suggesting the occurrence of P mainly as apatite. X-ray diffraction analysis confirmed the occurrence of this apatite as hydroxyapatite. Under the optical microscope and scanning electron microscope, hydroxyapatite occurred as massive and structureless grains of undefined outlines and variable size (5–150 μm) inside the ooids and/or in the ferruginous groundmass. Among trace elements, V, Ba, Sr, Co, Zr, Y, Ni, Zn, and Cu occurred in relatively high concentrations (62–240 ppm) in comparison to other trace elements. Most of these trace elements exhibit positive correlations with SiO2, Al2O3, and TiO2 suggesting their occurrence in the detrital fraction which includes the clay minerals. ΣREE ranges between 129.5 and 617 ppm with strong positive correlations with P2O5 indicating the occurrence of REE in the apatite. Chondrite-normalized REE patterns showed LREE enrichment over HREE ((La/Yb)N = 2.3–5.4) and negative Eu anomalies (Eu/Eu* = 0.75–0.89). The oolitic texture of the studied ores forms as direct precipitation of iron-rich minerals from sea water in open space near the sediment-water interface by accretion of FeO, SiO2, and Al2O3 around suspended solid particles such as quartz and parts of broken ooliths. The fairly uniform size of the ooids reflects sorting due to the current action. The geochemistry of major and trace elements in the ores reflects their hydrogenous origin. The oolitic iron ores of the Timsha Formation represent a transgressive phase of the Tethys into southern Egypt during the Coniacian-Santonian between the non-marine Turonian Abu Agag and Santonian-Campanian Um Barmil formations. The abundance of detrital quartz, positive correlations between trace elements and TiO2 and Al2O3, and the abundance mudstone intervals within the iron ores supports the detrital source of Fe. This prediction is due to the weathering of adjacent land masses from Cambrian to late Cretaceous. The texture of the apatite and the REE patterns, which occurs entirely in the apatite, exhibits a pattern similar to those in the granite, thus suggesting a detrital origin of the hydroxyapatite that was probably derived from the Precambrian igneous rocks. Determining the mode of occurrence and grain size of hydroxyapatite assists in the maximum utilization of both physical and biological separation of apatite from the Aswan iron ores, and hence encourages the use of these ores as raw materials in the iron making industry. 相似文献
6.
重庆市南川武隆铝土矿是黔中渝南铝土矿成矿带的重要组成部分。为初步查明重庆地区铝土矿稀土元素的地质意义,弥补重庆铝土矿成因研究的不足,笔者以重庆南川武隆铝土矿含矿岩系为研究对象,分析稀土元素(REE)的地球化学特征。通过研究发现,稀土元素总量较高,多数样品轻稀土富集,重稀土不同程度亏损。由于含矿岩系中的REE含量在沉积后只有极微弱的变化,因此利用稀土元素的特征及有关参数对铝土矿含矿岩系的形成环境及其物质来源进行了初步判断:Eu中等负异常,含矿岩系以陆相沉积为主,部分为海相沉积;从含矿岩系样品稀土元素总和、Ce异常、Eu 异常情况来看,含矿岩系形成的古水介质呈弱酸性,含矿岩系主要形成于氧化环境中,氧化能力增强时有利于铝土矿的形成;含矿岩系物质来源具有多样性,志留系韩家店组粉砂质页岩与石炭系黄龙组灰岩均可能为物质来源。 相似文献
7.
The Parnassos-Ghiona bauxite deposits of Greece are hosted within carbonate rocks and have been formed during different geological ages. The most economically important deposits occur in the B3 bauxite horizon, which is developed over long distance as a continuous layer of 1–10 m in thickness, within Cretaceous limestones. Due to intense tectonics, a significant (approximately 30 vol.%) bauxite ores along and near their contact with faults show a brittle deformation and change in the color from red to black-gray, in a distance of tens of meter. Commonly gray to whitish bauxites are aluminum-enriched (> 65 wt.% Al2O3) and iron depleted. 相似文献
8.
为了探讨青海软玉的成矿物质来源、成矿环境及成矿年代,对三岔口矿点、拖拉海沟矿点及大灶火矿点的样品进行了主量元素、微量元素、稀土元素及Ar-Ar法定年的测试。结果显示,软玉样品的主量元素变化不大,与透闪石的理论值相符;微量元素差异较大,说明不同矿点成矿环境不同;稀土元素总量较低(0.29×10-6~40.72×10-6),Eu中度负异常(0.49~0.84),除大灶火青玉样品具左倾的重稀土元素富集模式[(La/Yb)N=0.16~0.61]外,其他样品都具有右倾的轻稀土元素富集模式,(La/Yb)N=2.87~6.34。三岔口矿点、拖拉海沟矿点软玉样品的稀土元素分配曲线与纳赤台基性辉长岩相似,大灶火矿点黄玉的稀土元素分配模式与二长花岗岩相似,而青玉的分配模式与斜长花岗岩相似。样品的~TAl~(3+)、~CAl~(3+)和Ti含量变化表明,翠青玉的成矿温度最高、压力最大,黄玉成矿温度较高、压力较大;烟青玉和青玉成矿温度较高、压力较低;白玉、青白玉和糖玉成矿温度较低、压力较低。翠青玉和黄玉中明显较低的Zr/Hf、Nb/Ta和Sr/Ba值提示其成矿环境酸性明显加强。3个矿点样品的成矿年代301.38~237.28 Ma介于晚石炭世—中三叠世之间,属于印支-海西运动阶段。成矿年代均晚于侵入岩形成年代,说明矿体经历了多次热液交代过程。 相似文献
9.
The Mandan and Deh-now bauxite deposits are located 40 km northeast of the Dehdasht city in the Zagros simply fold belt. These deposits occur in eroded major NW–SE trending anticlines and occupy karst cavities near or at the boundary between the Sarvak and Ilam Formations. Local uplifts at the end of the Cenomanian and the mid-Turonian caused erosion and karstification of the Sarvak Formation. These unconformities in the Upper Cretaceous favoured the formation and enrichment of bauxite deposits in the Zagros fold belt. The bauxite sequence in the Mandan deposit consists of white, gray, black, pisolitic, red, and yellow bauxites. This sequence was repeated in the Deh-Now area, but without gray and black bauxites. The present mineralogical studies of the Sarvak Formation and the Mandan and Deh-now bauxite deposits indicate oxidizing to reducing conditions during the Upper Cretaceous in the Zagros fold belt, which had a significant effect on the compositions of the bauxites. At least two phases of bauxitization can be distinguished in the study area: (i) an oxidizing phase represented by boehmite, diaspore, hematite and kaolinite; and (ii) a reducing phase represented by pyrite and chlorite. Geochemical data show that trace elements, like Zr, Hf, Nb, Ta, Th, and U, were enriched during bauxitization. The bauxite deposits and carbonate rocks show similar REE patterns, namely they are enriched in REEs although the LREEs are more enriched than the HREEs. Mass change calculations demonstrate that Mg, Mn, Ca, K, and P2O5 were leached out of the weathered system whereas Al, Fe, and Si become concentrated in the residual system. This study indicates that the Mandan and Deh-now deposits are karst-type bauxites formed by karstification and weathering of the Sarvak Formation. 相似文献
10.
黔北务川瓦厂坪铝土矿床元素迁移规律研究 总被引：6，自引：0，他引：6
黔北务正道地区铝土矿矿床属古风化壳沉积型,成矿母岩具多源性,但主要来源于下覆的中下志留统韩家店组。本文依据Grant提出的质量平衡方程和图解法,对瓦厂坪矿床在成矿过程中元素迁移的富集、贫化（亏损）规律进行了定量研究。结果表明,主要成矿母岩韩家店组砂、页岩一中间产物铝土质页岩、粘土岩是主要元素A12O3、TiO2显著富集... 相似文献
11.
Sandstones and shales from the Upper Neoproterozoic (UN) succession in the Central Iberian Zone (CIZ) show parallel REE patterns and relatively restricted and similar ranges and average values of some element ratios such as Al2O3/TiO2, Ti/Nb, Eu/Eu*, (La/Yb)n, (Gd/Yb)n and Th/U. This remarkable geochemical homogeneity for related medium- and fine-grained rocks is unusual, and strongly suggests a recycled source area. However, the Lower Cambrian (LC) equivalent rocks are, in general terms, geochemically less mature, more heterogeneous and more fractionated. Their average REE patterns are practically coincident, probably as a consequence of REE redistribution related to the reworking of sediments during a stage of sea level fall in Lower Cambrian times. Ti and Zr abundances, chemical index of alteration (CIA) values and element ratios such as Al2O3/TiO2, K/Rb, Ti/Nb and Rb/Zr can be used for discriminating purposes between the UN and LC siliciclastic rocks. Detrital zircons from a UN and a LC sandstone display morphological differences. However, U-Pb data are discordant and cannot be interpreted in a straightforward manner. Nevertheless, age data are compatible with a model in which the continent of Gondwana would have supplied zircons, showing a bimodal age distribution, in variable proportions to the respective sandstone units. 相似文献
12.
为探讨南祁连喀克图蒙克山科克岩体的构造属性,对南祁连喀克图蒙克山中奥陶世科克岩体进行了详细的地球化学和定年研究。研究结果表明,该岩体主体岩性为正长花岗岩,具有高SiO_2(68.41%～73.10%)、高Al_2O_3(13.03%～14.35%)的特征,亏损高场强元素Nb、P、Ti和重稀土元素,发育明显的负Eu异常,反映岩石经历了强烈的分离结晶作用,其稀土元素配分曲线类型与壳源花岗岩相似;构造成因分类图解表明,这些花岗岩属同碰撞环境的产物。LA-ICP-MS锆石U-Pb测年结果表明,岩体形成于461±2.7Ma,时代为中奥陶世,表明该岩体的源岩为壳源或壳幔混合的产物。结合区域地质特征认为,该岩体为同碰撞作用的产物,佐证了南祁连地块在奥陶纪处于挤压状态,对进一步研究南祁连造山带的演化具有重要意义。 相似文献
13.
The Precambrian greywacke of Ribandar‐Chimbel belonging to the Sanvordem Formation of the Goa Group, India, has been studied for petrography and analyzed for major trace elements. The greywacke is characterized by angular to sub‐round grains of quartz, feldspar, biotite, chlorite and clay minerals. The abundance of clay in the matrix seems to have influenced the Al2O3 content and the K2O/Al2O3 ratio. The variation diagrams indicate a decreasing trend of TiO2, Al2O3, Fe2O3 and MgO; whereas Na2O and CaO exhibit a scatter which could be a result of the variable presence of feldspar within the sediments. The immobile elements, vanadium (25 to 144 ppm), nickel (up to 107 ppm) and chromium (up to 184 ppm), reflect abundance of clay minerals. The greywacke shows strongly fractionated REE patterns with LaN/YbN = 8 to 26 and with higher total REE abundances (up to 245 ppm). The low REE enrichment and depletion in heavier REE with prominent negative Eu anomaly (Eu/Eu*= 0.54 to 0.79) suggest a derivation of the greywacke from an old upper continental crust composed chiefly of felsic components. Petrological evidence and geochemical data suggest that the deposition of the greywacke largely took place in a deep to shallow basin that progressively changed from that of a continental island arc to an active continental setting. 相似文献
14.
Xuefei Liu Qingfei Wang Jun Deng Qizuan Zhang Silei Sun Jianyin Meng 《Journal of Geochemical Exploration》2010
The Dajia Salento-type bauxite deposit in western Guangxi is hosted within the Quaternary ferrallitic soil profile, and it formed via breaking up, weathering and oxidizing of Permian bauxite orebodies occurring as a semi-continuous layer in the upper Permian. Mineralogical analyses reveal that diaspore, hematite and kaolinite are the major minerals in bauxite ores with small amounts of anatase, chamosite, gibbsite, goethite, illite, zircon, quartz and pyrite. The ore texture and mineral assemblage reveal that the depositional/diagenetic environment of the Dajia bauxite was much close to phreatic environment. Both the ore texture and the morphology of zircon grains also indicate that most of the bauxitic soils were transported a short distance. Diaspore is suggested to be non-metamorphic in origin and mainly formed in a reducing condition of diagenetic environment, while kaolinite is the product of the in situ epigenetic replacement of alumina in diaspore by dissolved silica. Geochemical analyses indicate that Al2O3, Fe2O3, SiO2 and TiO2 are the main components of the bauxite ores and trace elements such as Zr, Hf, Nb, Ta, Th and U were enriched during the bauxitization process. Simultaneously, Zr vs. Hf and Nb vs. Ta show a high correlation. Geochemical indices such as Zr/Hf, Nb/Ta and Eu/Eu* (among others) denote that the magmatic rocks related to the Emeishan plume in western Guangxi and the carbonates in the underlying Maokou Formation provided the main sources of material for the bauxite ores. 相似文献
15.
北秦岭蟒岭岩体的锆石U-Pb年龄、地球化学及其演化 总被引：2，自引：1，他引：1
蟒岭岩体位于北秦岭构造带北部,岩石类型主要为似斑状黑云母二长花岗岩、中粗粒黑云母二长花岗岩、中细粒二长花岗岩、含辉石黑云角闪闪长岩和黑云母钾长花岗岩。依据LA-ICPMS锆石U-Pb定年结果,结合前人测试的年龄,将蟒岭岩体的岩浆演化划分为晚侏罗世早期、晚侏罗世晚期—早白垩世早期和早白垩世中期3期。第一期为含辉石黑云角闪闪长岩,其LA-ICPMS锆石U-Pb年龄为（157±1） Ma,该期岩石SiO2质量分数较低,富碱,属于准铝质,钾玄岩-高钾钙碱性系列;第二期二长花岗岩,侵位年龄为（148±1） Ma~（144±1） Ma,具有高硅、富碱的特征,属于准铝质-弱过铝质,钾玄岩-高钾钙碱性I-A过渡型花岗岩;第三期黑云母钾长花岗岩,侵位年龄为（124±2） Ma,具高硅、富碱、低镁、铝饱和指数偏高的特征,属过铝质,高钾钙碱性I-A过渡型花岗岩。组成蟒岭岩体的花岗岩从早到晚,SiO2质量分数逐渐升高,而Al2O3、TiO2、MgO、CaO、P2O5、TFe2O3质量分数逐渐降低;稀土元素总量具有由高到低的变化趋势,第一期和第二期岩石的稀土元素配分曲线为轻稀土元素相对富集的右倾型,而第三期的稀土元素配分曲线呈两边高中间低的不对称弧形,整体上负铕异常不明显或呈微弱正铕异常;微量元素上,这3期岩石均富集K、Rb、Ba、Sr等大离子亲石元素,而相对亏损P、Nb、Ta、Ti等高场强元素。与区域上同时代成矿花岗岩体对比,两者均具有高硅、富碱的特征,稀土元素球粒陨石标准化曲线呈轻稀土元素富集的右倾斜型,但蟒岭岩体中二长花岗岩没有明显的Eu异常,且Ba、P、Ti亏损及Ta、Nb富集没有含矿花岗岩明显。 相似文献
16.
Study of the concentration of major, trace, and rare earth elements (REE) in the Shahindezh karst bauxite deposit, northwestern Iran clarifies the relationship of the tetrad effect with geochemical parameters in the bauxite ores. The existence of irregular curves in the chondrite-normalized REE patterns as well as non-CHARAC behavior of geochemically isovalent pairs (Y/Ho) are related to the tetrad effect. The meaningful positive correlation between the sizes of the calculated T3 tetrad effect and some geochemical factors such as Y/Ho, ΣREE, La/Y, (La/Yb)N, and (LREE/HREE)N as well as some major oxides-based parameters like Al2O3 + LOI/SiO2 + Fe2O3, Al2O3/Fe2O3, Al2O3 + LOI, IOL, and SiO2 + Fe2O3 indicate that the studied bauxite horizon was likely deposited by different (acidic and/or alkalic) solutions at different stages. The lower part of the studied horizon with a thickness of ~4.7 m displays alkali characteristics whereas the upper parts of the horizon with a thickness of ~5.3 m are characterized by more acidic conditions. These results are fully supported by the co-occurrence of convex-concave tetrad effect curves in the chondrite-normalized REE patterns. Therefore, the tetrad effect phenomenon used in this study has proved to be a good and reliable geochemical proxy to assess the conditions of the depositional environment in the Shahindezh bauxite ores. 相似文献
17.
The San Rafael Massif is characterized by widespread fluorite and manganese epithermal ore deposits whose origin has been under debate to the present. Isotopic (Sm/Nd and K/Ar) and geochemical (trace elements and REE) data of fluorite and manganese ore allowed to establish the age and genesis of the deposits and to propose a regional genetic model. The fluorite deposits were formed during the Upper Triassic–Lower Jurassic as a result of the Triassic rifting that launched a hydrothermal activity at regional scale. The hydrothermal fluids had low T and high fO2 with fluorine probably derived from a mantle source and REE scavenged from the volcanics of the Gondwanan Choiyoi Magmatic Cycle upper section. The manganese deposits were formed by oxidizing hydrothermal fluids that collected Mn from deep sources and also leached REE from the upper section of the Choiyoi Magmatic Cycle during two mineralization episodes. One episode was linked to the rift tectonic setting that remained active up to the Upper Cretaceous and the other was related to an Early Miocene back-arc extensional geodynamic setting. Both manganese and fluorite deposits were formed in extensional tectonic settings within an epithermal environment near the surface, and can be ascribed to the general model of detachment-related deposits. 相似文献
18.
莲花山铁矿位于昌邑-安丘铁成矿带的中部,铁矿体赋存于古元古代粉子山群小宋组中。本文通过矿石地球化学特征及其与矽卡岩矿物组合和赋矿围岩结构特征的对比研究,证明了莲花山铁矿与条带状铁矿相似。莲花山铁矿矿石稀土元素含量较低,经页岩标准化的稀土元素配分模式呈现轻稀土元素亏损、重稀土元素富集的特征,具有明显的Eu、Y、La异常,为无明显Ce异常,Y/Ho比值反映了在其沉积时受到海水作用的影响,表明莲花山铁矿的稀土元素来源于火山热液和海水的混合溶液。微量元素中Ti、V、Co、Ni、Mn、Sr、Ba等含量较低,原始地幔标准化的微量元素配分曲线显示,U、La、Hf呈正异常,Ba、Nb、Ta、Sr呈负异常,SiO2/Al2O3、Ti/V、Ni/Co、和Sr/Ba的比值指示了莲花山铁矿成矿物质来源于火山物质的沉积。研究结果表明,莲花山铁矿成矿作用源于火山热液与海水的混合,成矿物质来自火山沉积物,其地质与地球化学特征与五台山铁矿一致,为火山沉积变质型铁矿床。 相似文献
19.
Takeru Moriyama Mruganka K. Panigrahi Dinesh Pandit Yasushi Watanabe 《Resource Geology》2008,58(4):402-413
The major, trace and rare earth element (REE) composition of Late Archean manganese, ferromanganese and iron ores from the Iron Ore Group (IOG) in Orissa, east India, was examined. Manganese deposits, occurring above the iron formations of the IOG, display massive, rhythmically laminated or botryoidal textures. The ores are composed primarily of iron and manganese, and are low in other major and trace elements such as SiO2, Al2O3, P2O5 and Zr. The total REE concentration is as high as 975 ppm in manganese ores, whereas concentrations as high as 345 ppm and 211 ppm are found in ferromanganese and iron ores, respectively. Heavy REE (HREE) enrichments, negative Ce anomalies and positive Eu anomalies were observed in post‐Archean average shale (PAAS)‐normalized REE patterns of the IOG manganese and ferromanganese ores. The stratiform or stratabound shapes of ore bodies within the shale horizon, and REE geochemistry, suggest that the manganese and ferromanganese ores of the IOG were formed by iron and/or manganese precipitation from a submarine, hydrothermal solution under oxic conditions that occurred as a result of mixing with oxic seawater. While HREE concentrations in the Late Archean manganese and ferromanganese ores in the IOG are slightly less than those of the Phanerozoic ferromanganese ores in Japan, HREE resources in the IOG manganese deposits appear to be two orders of magnitude higher because of the large size of the deposits. Although a reliable, economic concentration technique for HREE from manganese and ferromanganese ores has not yet been developed, those ores could be an important future source of HREE. 相似文献
20.
TAN Yuanlong QIAO Yansong ZHAO Zhizhong WANG Yan QI Lin FU Jianli LIU Zongxiu YAO Haitao WANG Shubing JIANG Fuchu 《《地质学报》英文版》2013,87(6):1712-1723
In this study Chengdu Red Earth （CRE） from the Chengdu Plain （CP）,Sichuan province,was analyzed for its elemental （major and trace elements） and isotopic （Sm-Nd） geochemistry and compared with Pleistocene loess and paleosol samples from the Chinese Loess Plateau （CLP） in Northern China.The geochemical composition of CRE is similar to north China loess,and also resembles the average UCC.This indicates that CRE,as loess deposits in Northern China,was derived from well-mixed sedimentary protoliths that have undergone numerous upper crustal recycling processes.However,obvious differences in the geochemical characteristics of CRE and the north China loess are also revealed in our results.For chemically stable elements,CRE has higher Ti,Zr,Hf and lower ΣREE,Ba contents in comparison with loess samples from the CLP.Further analysis shows that CRE has higher TiO2/Al2O3,SiO2/Al2O3,Ba/Rb and lower Ce/Yb,Eu/Yb,LaN/YbN and ΣLREE/ ΣHREE ratios.In Sm-Nd isotopic geochemistry,Sm and Nd content and the εNd（0） value in CRE are significantly higher than those in north China loess.The higher TiO2 content in CRE coincided with a high background concentration of Ti in the Sichuan Basin and the surrounding regions.The lower ΣREE and higher Sm,Nd,εNd（0） values are related to the wide distribution of basalt in the southwest Sichuan Basin.The elemental and isotopic geochemistry of CRE indicates that eolian materials in the CP predominantly come from the Sichuan Basin and the surrounding regions,which differs from loess deposits in the CLP. 相似文献