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1.
The Bitincke nickel laterite deposit, located in the south east of Albania, contains an estimated ore resource of 35.6?Mt of nickel ore with a grade of 1.2?% Ni. The deposit developed on peridotites within Late Jurassic ophiolites which were obducted in the Early Cretaceous and which form part of the Albanian Mirdita ophiolite zone. Limestones and conglomerates overlying the deposit delimit the minimum age of lateritization to the mid-Eocene. The laterite is composed of two distinct ore zones characterized by silicate nickel and iron oxide phases. Within the silicate zone, Ni concentrations reach a maximum of 1.5?wt% and although laterally and vertically variable this zone is typically characterized by olivine and serpentine at the base of the horizon which are gradually replaced by secondary silicates and iron oxides up section. The boundary between the silicate and the oxide zone above is normally sharp and characterized by an increase in Fe2O3 (from ~10 to 80?wt%), decreases in SiO2 (from ~30 to 5?wt%) and a dramatic reduction in MgO content (from ~10 to 0.1?wt%). The oxide horizon is dominated by goethite and displays relatively little variation in textural morphology or geochemistry. Nickel concentrations are greatest near the base of this zone, reaching a maximum of 2.3?wt%. Weathering profile formation and variation in the thickness of the deposit was controlled by the interaction between topography, faulting and protolith fracture density. The oxide zone formed on topographic highs was subject to increased rates of erosion, whereas the laterite profile within topographic lows, and in areas of relatively high fracture density, tends to be thicker due to increased permeability. The most substantive sections of the Ni laterite weathering profile developed in small fault controlled basins and were preserved by the deposition of a sequence of limestones and mudstones. 相似文献
2.
Geochemical and geochronological studies were conducted on basalts and laterites from the Bolaven Plateau in southern Laos in order to evaluate the mobility and mineralization of REE, Y and Sc during laterization. The basalts are classified into three categories: (i) small volumetric alkali basalt (eruption age: 15.7 Ma), large volumetric olivine tholeiite (1.2 Ma) and quartz tholeiite with olivine tholeiite (younger than 0.5 ± 0.2 Ma). Formation of REE minerals during laterization result in mobilization and fractionation of REE and Y in laterite profiles. Occurrence of florencite‐(Ce) in a laterite profile derived from alkali basalt immobilizes REE (particularly LREE) and this leads the laterites to be enriched in LREE relative to the parent basalt. Few positive Ce anomalies in this profile suggest that florencite‐(Ce) [(Ce)Al3(PO4)2(OH)2] formation was followed by CeO2 precipitation due to the change of redox condition. In tholeiite‐derived laterite profiles, florencite is not recognized and REE and Y tend to be depleted relative to the parent basalts with positive Ce anomalies. This is interpreted as scavenging REE3+ except for Ce4+ from the laterite profile in oxidizing conditions. Sc behaves similarly to Fe during laterization and it is more abundant in the tholeiitic laterite than that in the alkali basaltic laterite. Results of sequential extraction indicate that REE of the alkali basaltic laterite are contained in residual phase, which is dominantly florencite‐(Ce), but they are rarely present in ion‐adsorption phase. It is concluded that basaltic laterites have a low potential of REE resource in terms of low REE contents and a difficulty in REE extraction. 相似文献
3.
The Çalda? nickel laterite deposit located in the Aegean region of W. Turkey contains a reserve of 33 million tons of Ni ore with an average grade of 1.14% Ni. The deposit is developed on an ophiolitic serpentinite body which was obducted onto Triassic dolomites in the Late Cretaceous. The deposit weathering profile is both laterally and vertically variable. A limonite zone, which is the main ore horizon, is located at the base of the profile. A hematite horizon is located above the limonite, which in the south of the deposit is capped by Eocene freshwater limestones and in the north by a siliceous horizon. The deposit is unusual in lacking a significant saprolite zone with little development of Ni-silicates. The boundary between the limonite zone and serpentinite below is sharp with a marked decrease in concentrations of MgO from 13 to 1 wt.% over a distance of 2 mm representing the ‘Mg discontinuity’. Ni concentrations within goethite, the main ore mineral, reach a maximum of ~3 wt.% near the base of the limonite zone. Silica concentrations are high throughout most of the laterite with up to 80 wt.% silica in the upper portion of some profiles. The combination of a serpentinite protolith and a high water table at Çalda?, in association with an aggressive weathering environment in a tropical climate, resulted in the formation of an oxide-dominated deposit. The precipitation of silica may coincide with a change in climate with silica precipitation linked to an increase in seasonality. Additional variations within profile morphology are attributed to transportation during and after laterite development as a result of faulting, pocket type laterite formation and slumping, each of which produces a contrasting set of textural and geochemical features. 相似文献
4.
Geochemical and mineralogical investigations have been carried out on laterite profiles developed in the Lake Sonfon Au district of northern Sierra Leone. The area is underlain by Archean metavolcanics and constitutes part of the Sula Mountains greenstone belt, which is mineralized in Au. Extensive lateritization has affected the rocks of this region, resulting in a profile which from bottom to top consists typically of a decomposed bedrock zone, a pisolitic laterite layer and a duricrust layer. Both the pisolitic and duricrust layers of the laterite are sometimes punctuated by lenses of ironstones containing high amounts of Cu, Zn, Ni, Co and Ce. Gold occurs as small grains within the heavy mineral fraction recovered from the decomposed rock zones and pisolitic layers of the profiles and also in gravels of streams draining the area. The mineralogy of the duricrust and pisolitic layers is dominated by goethite, gibbsite and quartz, with minor amounts (<5% by volume) of ilmenite, magnetite, haematite, rutile and kaolinite. The kaolinite content increases towards the decomposed rock zone, where talc, vermiculite and other layer lattice silicates become abundant. The heavy-mineral fraction of stream sediments is composed essentially of ilmenite, magnetite, haematite, and traces of rutile, zircon, tourmaline and Au. The Au grains are often characterized by a 10–200-μm-wide rim having a much lower content of Ag (0.3 wt.% or lower) than the grain interior (about 5 wt.% on average). Dissolution effects are also observed on the grain surfaces. It is considered that Au derived from the amphibolite parent rock is dissolved, transported, and redeposited during laterization.The duricrust cover of the laterite profiles is characterized by high contents of Fe2O3 (ca. 60 wt.%) and Al2O3 (ca. 32wt.%) and low content of SiO2 (ca. 9 wt.%). In comparison, the pisolitic layer is higher in SiO2 (ca. 18 wt.%) as well as a slightly higher in Al2O3 (ca. 34 wt.%). Lateritic weathering has resulted in the removal of CaO, Na2O, MgO and SiO2, with relative enrichment of Fe2O3 and Al2O3. The geochemical distribution of the trace elements in the laterite profiles can be related to the occurrence of the auriferous mineralization. The significance of these observations is discussed in relation to the origin of the lateritic Au and the role of the associated trace elements as indicators of the mineralization. 相似文献
5.
Mineralogical and geochemical characterization of listwaenite from the Semail Ophiolite, Oman 总被引：2，自引：0，他引：2
Sobhi Nasir Abdul Razak Al Sayigh Abdulrahman Al Harthy Salah Al-Khirbash Omar Al-Jaaidi Abdullah Musllam Ali Al-Mishwat Salim Al-Bu'saidi 《Chemie der Erde / Geochemistry》2007,67(3):213-228
The late Cretaceous-lower Tertiary hydrothermal alteration of serpentinized peridotite in the Semail ophiolite has formed two distinct types of listwaenite. Type I is characterized by the presence of calcite (Type IA) or dolomite (Type IB)+fuchsite±spinel. Type II is dominated by silicate minerals (quartz, chlorite, fuchsite)±calcite+dolomite±magnetite±apatite±plagioclase. Most listwaenites occur as veins along thrust fault zones within the ophiolite mélange. High Cr and Ni contents, abundant occurrence of Cr-spinel within a matrix of red-brown ferruginous carbonates within a micro-vein network of goethite, and the relics of mesh texture indicate an ultramafic protolith. Type I and II listwaenites represent different stages of hydrothermal alteration. The mineralogical and chemical distinctions of both types are the response to the extent of the reactions between the protoliths and the solutions leading to different stages of metasomatic replacement. The hydrothermal fluids involved in the formation of Type I listwaenite were enriched in Ca, Mg, and CO2, whereas Type II listwaenite bodies were formed from a hydrothermal fluid enriched in SiO2. REE and trace elements in both listwaenite types were extracted in part from adjoining peridotite. No Au anomaly in the study areas has been detected. 相似文献
6.
Kolonodale矿床是东南亚红土镍矿带上一处典型矿床,位于印度尼西亚苏拉威西岛东部。矿床产自富镁超基性岩红土风化壳,矿化剖面自上而下出现红土层→腐岩层→基岩层垂向分带。红土镍矿石产在红土剖面上部,载镍矿物是铁质氧化物。硅镁镍矿石产在红土剖面中下部,载镍矿物为镍蛇纹石、镍滑石等含水层状硅酸盐矿物。地球化学分析显示,沿矿化剖面元素地球化学分异非常显著,Ni次生富集效应明显。超基性岩红土化过程的元素地球化学行为具有多样性,Fe、Al、Ti、Cr属残留富集组分,Si、Mg属淋滤缺失组分,Mn、Ca、Co、Ni属次生富集组分。通过典型矿床对比,Kolonodale矿床属原地自生硅酸盐型红土镍矿床,其发育受地质背景和地表环境条件的综合制约。富镁超基性岩、良好的构造组合、稳定的大地构造环境、湿热热带雨林气候、有利地形地貌等均是成矿有利条件。综合分析认为,Kolonodale矿床的成矿过程可划分为腐岩化、红土化和次生富集3个成矿阶段。 相似文献
7.
Kolonodale矿床是东南亚红土镍矿带上一处典型矿床,位于印度尼西亚苏拉威西岛东部。矿床产自富镁超基性岩红土风化壳,矿化剖面自上而下出现红土层→腐岩层→基岩层垂向分带。红土镍矿石产在红土剖面上部,载镍矿物是铁质氧化物。硅镁镍矿石产在红土剖面中下部,载镍矿物为镍蛇纹石、镍滑石等含水层状硅酸盐矿物。地球化学分析显示,沿矿化剖面元素地球化学分异非常显著,Ni次生富集效应明显。超基性岩红土化过程的元素地球化学行为具有多样性,Fe、Al、Ti、Cr属残留富集组分,Si、Mg属淋滤缺失组分,Mn、Ca、Co、Ni属次生富集组分。通过典型矿床对比,Kolonodale矿床属原地自生硅酸盐型红土镍矿床,其发育受地质背景和地表环境条件的综合制约。富镁超基性岩、良好的构造组合、稳定的大地构造环境、湿热热带雨林气候、有利地形地貌等均是成矿有利条件。综合分析认为,Kolonodale矿床的成矿过程可划分为腐岩化、红土化和次生富集3个成矿阶段。 相似文献
8.
选择印度尼西亚苏拉威西岛Kolonodale地区和中国云南省元江地区的2个超基性岩红土风化壳为研究对象,对比研究不同气候环境下超基性岩在红土风化过程中REE的地球化学特征及其演化机制.研究发现,印尼Kolonodale和中国元江剖面的REE分布型式具有一定的共性规律,都表现出显著的REE表生富集效应(相对于基岩的最大富集系数分别达44.21和236.19)、不均一的轻重稀土分异(分异程度随剖面深度加大而降低)以及剧烈的Ce异常正负转换现象(风化壳上部是正Ce异常,风化壳下部是负Ce异常).2个剖面中REE最大富集段的产出位置明显错位,表现在Kolonodale剖面中REE最大富集段出现在腐岩层,而在元江剖面中REE最大富集段出现在红土层.质量平衡计算指示,REE在超基性岩红土化过程中发生了显著的迁移和分异现象,其地球化学行为受红土剖面pH值环境与有机质(O.M.)含量的制约.案例对比分析表明,气候环境对超基性岩红土化过程中REE的地球化学演化具有重要影响.在热带雨林环境的印尼Kolonodale剖面中,风化壳中REE主要继承于基岩,在高强度的红土化作用下,REE经历了强烈的重新分配和垂向分异.而在亚热带季风气候环境的中国元江剖面中,风化壳中的REE具有更复杂的物源背景,除继承基岩外还可能叠加了风尘沉积物的影响.元江剖面的红土化程度偏弱,导致REE在表生演化中未发生强烈的淋滤和次生富集作用. 相似文献
9.
超大型红土型镍矿主要控矿因素,板块边界三联点构造控制的白垩纪、三叠纪、二叠纪蛇绿岩底部镁质超基性岩,基岩MgO/Fe0比值14～18,通过风化作用后,形成结构分带较好的风化壳,风化壳对数Mgo/全铁比值0.4～1,地貌20～400米标高、5～ 20度坡度角,中、低山面型地貌. 相似文献
10.
Platinum-group element (PGE) abundances in mantle rocks are generally considered to result from a late meteorite addition to the early Earth, post-dating the core separation event. As such, PGEs are key tracers for the Earth accretion history. For decades, the PGEs systematics of undepleted mantle peridotites has been used to constrain the composition of meteorite impactors involved in the late veneer material. Despite multiple evidence of considerable modifications by partial melting, harzburgites from the Sumail ophiolite (Oman) display a mean PGE composition very akin to recently refined estimates for the Primitive Upper Mantle (PUM) of the Earth. These rocks document a resetting of the PUM signature by percolating basaltic melts, which precipitated Pd-enriched Cu–Ni sulphides within a strongly Pd-depleted residual harzburgitic protolith. Such a resetting casts doubt on both the reliability of any PUM estimates and relevance of the PUM concept itself, at least for PGEs. 相似文献
11.
The Xigaze ophiolite is located in the middle section of the Yarlung Zangbo River ophiolite belt and includes a well-preserved sequence section of seven ophiolite blocks. The relatively complete ophiolitic sequence sections are represented by Jiding, Dejixiang, Baigang, and Dazhuqu ophiolites and consist of three–four units. The complete ophiolite sequence in order from the bottom to top consists of mantle peridotite, cumulates, sheeted sill dike swarms, and basic lavas±radiolarian chert. These cumulates are absent in the remaining blocks of Dejixiang and Luqu. The age of radiolaria in the radiolarian chert is Late Jurassic–Cretaceous. The basalt and ultramafic rock of the ophiolite also are overlaid by Tertiary Liuqu conglomerate, which contains numerous pebble components of ophiolite, indicating that the Tethys Ocean began to close at the end of Cretaceous Period. The isotopic data of gabbro, diabase, and albite granite in the Xigaze ophiolite are approximately 126–139 Ma, which indicates that the ophiolite formed in the Early Cretaceous. The K–Ar age of amphibole in garnet amphibolite in the ophiolite mélange is 81 Ma, indicating that tectonic ophiolite emplacement occurred at the end of Late Cretaceous. 相似文献
12.
The Batinah mélange which overlies the late Cretaceous Semail ophiolite in the northern Oman Mountains comprises mostly sedimentary rocks of deep-water facies, alkalic lavas and intrusives, all of continental margin affinities, together with smaller volumes of Semail ophiolitic and metamorphic rocks. Four intergradational textural types of mélange can be recognized. Sheet mélange has large (>1 km) intact sheets either with little intervening matrix or set in other mélange types, and with an organised sheet orientation fabric. Slab mélange is finer textured (>100 m) and more disrupted. Block mélange has smaller (> m) blocks with some matrix and a weak to random block fabric. Clast mélange is matrix-supported rudite with a weak depositional clast fabric. Structural relationships, particularly the absence of tectonic fabrics, the decreasing strength of fragment fabrics with increasing fragmentation, and the abundance of brittle fragmentation, suggest that these mélange types formed by either gravity-driven sedimentary processes or superficial sliding or thrusting of individual rock slabs.In the slab mélange, long sequences can be pieced together, passing up from Upper Triassic mafic sub-marine extrusives and sediments into radiolarian cherts, hemipelagic and redeposited limestones, and terminating in non-calcareous radiolarities with Mn-deposits of early Cretaceous age. Mafic sills are numerous. These sequences can be matched with sub-ophiolite rocks now exposed in fault corridors through the Semail. These sequences become progressively disrupted upwards in the corridors and can be traced continuously into overlying mélange, which then thins away from the corridors.We argue that, during late Cretaceous emplacement over the Arabian margin, active fault corridors split the Semail slab and acted as conduits up which sub-ophiolite rocks were supplied to the ophiolite surface. There the rocks were redisributed by superficial processes. 相似文献
13.
试论碳酸盐岩上覆红土的形成模式及演化趋势 总被引：14，自引：1，他引：14
据长期对岩溶及红土化作用等的研究成果,本文全面系统地分析了碳酸盐岩上覆红土的形成及演化规律,提出了一个新的碳酸盐岩上覆红土的形成模式,进而深入阐明了碳酸盐岩上覆红土的演化规律及其在现代气候条件下的演化趋势等,在解决岩溶及红土学术界存在的碳酸盐岩上覆红土的形成、碳酸盐岩与上覆红土之间的相互关系及其发展演化规律等一系列重大疑难问题上向前迈进了一步,对相关学科的发展将产生积极的推动作用. 相似文献
14.
Yousif Osman Mohammad 《Arabian Journal of Geosciences》2011,4(1-2):69-83
Two types of serpentinized peridotites are distinguished within the Northwest Zagros Thrust Zone (NW-ZTZ) in Kurdistan region of Iraq. One is found as lower members of ophiolite sequences, such as the Mawat and Penjwin ophiolites of the upper Cretaceous age. The other is represented by intraformational isolated serpentinite bodies in Betwat, Qaladeza, and Qalander areas within the Walash–Naopurdan volcano-sedimentary unit of the Paleocene to Eocene paleo-arc tectonic setting. Serpentinites within the NW-ZTZ consist mainly of lizardite and chrysotile, with subordinate amounts of syn-serpentinization magnetite, carbonates, chromium chlorite, tremolite, and talc as secondary minerals, and olivine, clinopyroxene, and chromian spinel as primary minerals. Minor antigorite is also found in the sheared serpentinites often found in ophiolite sequences. Petrological and geochemical studies of serpentinites from the NW-ZTZ show that, of the original protoliths of serpentinites, those associated with ophiolites are residual depleted harzburgite and dunite. The $ {\text{Cr}}\# \left( {{{ = {\text{ Cr}}} \mathord{\left/ {\vphantom {{ = {\text{ Cr}}} {\left( {{\text{Cr}} + {\text{Al}}} \right){\text{ atomic ratio}}}}} \right. \kern-0em} {\left( {{\text{Cr}} + {\text{Al}}} \right){\text{ atomic ratio}}}}} \right) $ of chromian spinel is more than 0.6, and the forsterite content of olivine is 91–92. On the other hand, the original protolith of isolated serpentinite bodies is less depleted harzburgite or depleted lherzolite, which has spinel with Cr# less than 0.6 and olivine with 90–91 forsterite contents. Whole rock chemistry of major, trace, and rare earth elements shows that the serpentinites of ophiolite sequences are depleted in CaO, Al2O3, and SiO2, Sr, and Zr, and are enriched in MgO, Ni, and Cr, in comparison with the isolated serpentinites. Cr# of the disseminated unaltered chromian spinels indicates that the serpentinites of both types had been originated from the supra-subduction zone tectonic setting; the serpentinites of ophiolite sequences obducted and thrusted over the continental margin during the obduction of the Tethyth oceanic crust onto the Arabian continental margin during the upper Cretaceous period. Isolated serpentinite bodies represent serpentinized forearc mantle wedge peridotites emplaced by diapiric upwelling into non-accretionary forearc tectonic settings during the Paleocene to Eocene age. 相似文献
15.
东昆仑东段东昆中构造混杂岩带长石山地区新发现一套蛇绿岩,主要由蛇纹岩、辉长岩、辉绿岩、玄武岩、含泥碳硅质岩组成。通过对蛇绿岩中辉长岩进行LA-ICP-MS锆石U-Pb同位素研究,获得年龄为(537.2±3.5)Ma,表明蛇绿岩形成于早寒武世。岩石地球化学研究显示,蛇纹岩的原岩为橄榄岩类,稀土元素配分曲线具开阔U型特征;辉长岩发育明显的堆晶结构,具不同程度的Eu正异常,轻稀土较重稀土富集,但稀土总量较低;玄武岩轻稀土相对重稀土富集,富集大离子亲石元素,高场强元素不分异,Nb轻微亏损,具E-MORB与IAB的双重特征。长石山蛇绿岩形成于弧后盆地环境,指示布青山—阿尼玛卿原特提斯洋在早寒武世((537.2±3.5)Ma)前已经开始向北俯冲,并在东昆中地区拉张形成弧后盆地。 相似文献
16.
Nickel geochemistry of a Philippine laterite examined by bulk and microprobe synchrotron analyses 总被引：1，自引：0，他引：1
Rong Fan 《Geochimica et cosmochimica acta》2011,75(21):6400-6415
The Ni geochemistry of limonite and saprolite laterite ores from Pujada in the Philippines has been investigated using a mixture of laboratory and synchrotron techniques. Nickel laterite profiles are typically composed of complicated mineral assemblages, with Ni being distributed heterogeneously at the micron scale, and thus a high degree of spatial resolution is required for analysis. This study represents the first such analysis of Philippine laterite ores. Synchrotron bulk and microprobe X-ray absorption spectroscopy (XAS), comprising both X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopies, together with synchrotron microprobe X-ray fluorescence microscopy (XFM) and diffraction (XRD) have been applied to provide quantitative analysis of the mineral components and Ni speciation.Synchrotron microprobe EXAFS spectroscopy suggests that the limonite Ni is associated with phyllomanganate via adsorption onto the Mn oxide layers and substitution for Mn within these layers. Laboratory scanning electron microscopy, coupled to electron dispersive spectroscopy analyses, indicates that Ni is also associated with concentrated Fe containing particles and this is further confirmed by synchrotron bulk and microprobe investigation. Linear combination fitting of the bulk EXAFS limonite data suggests 60 ± 15% of the Ni is associated with phyllomanganate, with the predominant fraction adsorbed above vacancies in the MnO6 layers with the remainder being substituted for Mn within these layers. The remaining 40 ± 10% of the Ni in the limonite ore is incorporated into goethite through replacement of the Fe. In the saprolite ore, 90 ± 23% of the Ni is associated with a serpentine mineral, most likely lizardite, as a replacement for Mg. The remaining Ni is found within phyllomanganate adsorbed above vacancies in the MnO6 layers. 相似文献
17.
对宣城第四纪红土剖面的研究表明,全氧化铁含量能够较好地指示中国南方第四纪气候的波动。与北方黄土古土壤序列相比,宣城剖面的全氧化铁明显较高,指示了南方地区更强的风化成壤作用。 相似文献
18.
菲律宾迪纳加特岛汇洋镍铬矿区发育板块碰撞成因的蛇绿岩,主要岩性为纯橄岩和方辉橄榄岩,与铬铁矿化关系密切,在纯橄岩和方辉橄榄岩的过渡带中铬铁矿化较为集中,铬铁矿多呈薄层块状或浸染状与围岩岩性条带呈"互层状"产出,块状、浸染状的铬铁矿重复出现;矿区内原生铬铁矿化非常普遍,虽然未构成原生铬铁矿体,但为次生红土型铬铁矿的成矿提供了丰富的物质来源。矿区内第四系中赋存有残坡积红土型铬铁砂矿,并与同类型镍矿共生;铁质红土层是最佳的含矿层位,松散状红土层次之;铬铁矿体呈层状、似层状,有3个铬铁砂矿化区,矿体厚度5~7m,铬铁矿品位w(Cr2O3)=2.0%~4.1%。 相似文献
19.
重点分析和总结了由显生宙增生复合体和造山带混杂岩重建的年轻造山带洋板块地层--太平洋洋板块地层,也简要介绍了东古印度洋(东新特提斯洋)和古亚洲洋洋板块地层的重建情况。通过对阿拉斯加南部中生代增生地体、俄罗斯远东和中国东北侏罗纪-早白垩世增生复合体、日本二叠纪-侏罗纪-白垩纪等不同时期的增生复合体、菲律宾侏罗纪增生复合体和美国加州海岸山脉中侏罗世-古新世弗朗西斯卡杂岩体等不同单元的岩石学特征、古生物地层学、年代地层学、因逆冲导致的构造叠置和混杂失序特征及演化阶段的分析,重建了太平洋洋板块地层。其中加州海岸山脉中侏罗世-古新世弗朗西斯卡杂岩体的研究比较深入,对该区俯冲带上叠蛇绿岩(大峡谷群弧前盆地蛇绿岩)和弗朗西斯卡北部马林海岬杂岩体(原岩为洋中脊玄武岩)进行了有效区分,不仅还原了太平洋板块的俯冲碰撞过程,还厘清了与之伴生的弧前盆地裂陷和扩张过程。另外,板块俯冲的滞留和幕式增生在活动时间较短的板块俯冲体系中可能不容易识别。 相似文献
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文章选取印尼苏拉威西岛Kolonodale红土型镍矿区为研究区,对201个浅井剖面共采取3 161件风化壳样品,进行了w(Ni)值的测试,以揭示超基性岩红土风化壳中Ni的表生富集规律及矿化结构特征。研究结果表明,在平面上,矿区内风化壳的w(Ni)平均值的高低与地形地貌关系密切。斜坡带、坡脚堆积带的风化壳为含镍高值区,其w(Ni)值为0.8%~1.8%;山顶平台区、山脊的风化壳为含镍低值区,其w(Ni)值为0.7%~1.4%。在垂向上,风化产物的w(Ni)值的高低与取样深度及样品属性密切相关。w(Ni)值随着红土带→腐岩带→基岩带的变化出现低值(0.85%~1.55%)→高值(1.15%~4.75%)→低值(≤0.55%)的波动变化规律。矿层的产状(分布、深度、厚度)与风化壳产状之间表现出明显的正相关关系。矿区内的低品位矿层〔1.5%≤w(Ni)≤2.0%〕和高品位矿层〔w(Ni)≥2.0%〕单独或组合发育,产出"正常型双层矿化"、"倒置型双层矿化"、"低品位单层矿化"、"高品位单层矿化"和"叠层矿化"等5种矿化结构类型。综合分析认为,富镁及中等程度蛇纹石化的超基性岩母岩、热带雨林气候环境是矿区内发育富镍红土风化壳的首要条件。吸附、离子交换以及次生沉淀等3种成矿作用的共同发育,导致了红土风化壳中Ni表生矿化的连续性、矿石类型的多样性及特高品位矿石的形成。矿床中矿化结构类型的多样化是区域构造背景、地形地貌、构造发育、水文条件等诸多因素耦合作用的结果。文章指出,在今后的红土型镍矿床的找矿勘查过程中,需要综合考虑各类内、外生控矿因素对矿床发育的影响,总结矿区尺度的矿化结构规律,可有效地指导矿床勘查工作。 相似文献