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1.
《Applied Geochemistry》2000,15(6):695-723
Ground and surface waters collected from two undisturbed Zn–Pb massive sulphide deposits (the Halfmile Lake and Restigouche deposits) and active mines in the Bathurst Mining Camp (BMC), NB, Canada were analysed for the rare earth elements (REE). REE contents are highly variable in waters of the BMC, with higher contents typical of waters with higher Fe and lower pH. There are significant differences between ground- and surface waters and between groundwaters from different deposits. The REE contents of surface waters are broadly similar within and between deposit areas, although there are spatial variations reflecting differences in pH and redox conditions. Surface waters are characterised by strong negative Ce anomalies ([Ce/Ce*]NASC as low as 0.08), produced by oxidation of Ce3+ to Ce4+ and preferential removal of Ce4+ from solution upon leaving the shallow groundwater environment. Groundwaters and seeps typically lack significant Ce anomalies reflecting generally more reducing conditions in the subsurface environment and indicating that Ce oxidation is a rapid process in the surface waters. Deeper groundwaters at the Halfmile Lake deposit are characterised by REE patterns that are similar to the host lithologies, whereas most groundwaters at the Restigouche deposit have LREE-depleted patterns compared to NASC. Halfmile Lake deposit groundwaters have generally lower pH values, whereas Restigouche deposit groundwaters show greater heavy REE-complexation by carbonate ions. Shallow waters at the Halfmile Lake and Stratmat Main Zone deposits have unusual patterns which reflect either the adsorption of light REE onto colloids and fracture-zone minerals and/or precipitation of REE–phosphate minerals. Middle REE-enrichment is typical for ground- and surface waters and is highest for neutral pH waters. The labile portion of stream sediments are generally more middle REE-enriched than total sediment and surface waters indicating that the REE are removed from solution by adsorption to Fe- and Mn-oxyhydroxides in the order middle REE≥light REE>heavy REE. 相似文献
2.
Matthew I. Leybourne Jan M. Peter John Volesky 《Geochimica et cosmochimica acta》2006,70(5):1097-1112
Primary massive sulfide gossans (MSG) in the Bathurst Mining Camp (BMC), New Brunswick, Canada, are characterized by relative enrichment of Au, Sb, and As, formation of jarosite group minerals (jarosite, plumbojarosite, and argentojarosite) and little or no fractionation in the rare earth elements (REE), including preservation of large positive Eu anomalies (average [Eu/Eu*]NASC = 4.14 in MSG; 6.61 in massive sulfide mineralization; 0.60 in host rocks). The chemical and mineralogical characteristics of MSG (e.g., Halfmile Lake deposit) imply low pH (<3) and relatively oxidizing conditions during gossan formation; oxidation of a volcanogenic massive sulfide body (comprising pyrite, pyrrhotite, sphalerite, galena, and chalcopyrite) with a falling water table. The lack of light REE or heavy REE fractionation and preservation of positive Eu anomalies characteristic of the original (465 Ma) hydrothermal fluid is consistent with relatively large water-rock ratios during massive sulfide mineralization oxidation, and removal of the REE predominantly as sulfate complexes (LnSO4+, Ln(SO4)2−). Low pH groundwaters recovered from past producing mines in the BMC display REE patterns reflecting those inferred to have occurred during gossan formation. Gossan at the Restigouche deposit, in contrast to the Halfmile Lake deposit, displays mineralogical and chemical evidence for having been chemically reworked since primary gossan formation. Evidence for chemical reworking includes loss of primary massive sulfide mineralization textures, replacement of plumbojarosite with anglesite, almost complete removal of jarosite minerals, loss of Au, Sb, and As and apparent preferential removal of Eu, resulting in loss of positive Eu anomalies for most samples (average [Eu/Eu*]NASC = 1.21 in the gossan, with many displaying strong negative anomalies; 3.65 in massive sulfide mineralization; 0.54 in host rocks). Based on geochemical modeling, conditions inferred for the chemical reworking of the Restigouche deposit include near neutral conditions and either relatively oxidizing conditions with Eu2+ hosted in a preferentially weathered mineral host (possibly through substitution for Pb in plumbojarosite and beudantite) or cycling between reduced and oxidized conditions during gossan reworking. 相似文献
3.
Stephen Roberts Martin R. Palmer Matthew J. Cooper Peter Buchaus Drew Sargent 《Mineralium Deposita》2009,44(8):881-891
Carbonate, largely in the form of dolomite, is found throughout the host rocks and ores of the Nchanga mine of the Zambian
Copperbelt. Dolomite samples from the hanging wall of the mineralization show low concentrations of rare-earth elements (REE)
and roof-shaped, upward convex, shale-normalized REE patterns, with positive Eu*SN anomalies (1.54 and 1.39) and marginally negative Ce anomalies (Ce*SN 0.98,0.93). In contrast, dolomite samples associated with copper and cobalt mineralization show a significant rotation of
the REE profile, with HREE enrichment, and La/LuSN ratios <1 (0.06–0.42). These samples also tend to show variable but predominantly negative Eu*SN and positive cerium anomalies and an upwardly concave MREE distribution (Gd-Er). Malachite samples from the Lower Orebody
show roof-tile-normalized REE patterns with negative europium anomalies (Eu*SN 0.65–0.80) and negative cerium anomalies (Ce*SN 0.86–0.9). The carbonate 87Sr/86Sr signature correlates with the associated REE values. The uppermost dolomite samples show Neoproterozoic seawater-like 87Sr/86Sr ratios ranging from 0.7111 to 0.7116, whereas carbonate from Cu–Co mineralized samples show relatively low concentrations
of strontium and more radiogenic 87Sr/86Sr, ranging between 0.7136–0.7469. The malachite samples show low concentrations of strontium, but give a highly radiogenic
87Sr/86Sr of 0.7735, the most radiogenic 87Sr/86Sr ratio. These new data suggest that the origin and timing of carbonate precipitation at Nchanga is reflected in the REE
and Sr isotope chemistry. The upper dolomite samples show a modified, but essentially seawater-like signature, whereas the
rotation of the REE profile, the MREE enrichment, the development of a negative Eu*SN anomaly and more radiogenic 87Sr/86Sr suggests the dolomite in the Cu–Co mineralized samples precipitated from basinal brines which had undergone significant
fluid–rock interaction. Petrographic, REE, and 87Sr/86Sr data for malachite are consistent with the original sulfide Lower Orebody being subject to a later oxidizing event. 相似文献
4.
Spectra of the REE distribution in the Quaternary–Recent peat bog ore of southern Karelia and Leningrad region are characterized by LaN/YbN < 1.0, presence of positive Eu and negative Ce anomalies, and higher Y enrichment (relative to Ho and Dy) because of the REE sorption by Fe-bearing minerals in acid boggy waters. The 87Sr/86Sr ratio is 0.7175 in iron oxyhydroxides of the Somino deposit (Leningrad region) and 0.7283 in the Polovinkino ore (southern Karelia). The 143Nd/144Nd ratio in them is 0.511844 and 0.511617, respectively. 相似文献
5.
We have collected ∼500 stream waters and associated bed-load sediments over an ∼400 km2 region of Eastern Canada and analyzed these samples for Fe, Mn, and the rare earth elements (REE + Y). In addition to analyzing the stream sediments by total digestion (multi-acid dissolution with metaborate fusion), we also leached the sediments with 0.25 M hydroxylamine hydrochloride (in 0.05 M HCl), to determine the REE + Y associated with amorphous Fe- and Mn-oxyhydroxide phases. We are thus able to partition the REE into “dissolved” (<0.45 μm), labile (hydroxylamine) and detrital sediment fractions to investigate REE fractionation, and in particular, with respect to the development of Ce and Eu anomalies in oxygenated surface environments. Surface waters are typically LREE depleted ([La/Sm]NASC ranges from 0.16 to 5.84, average = 0.604, n = 410; where the REE are normalized to the North America Shale Composite), have strongly negative Ce anomalies ([Ce/Ce∗]NASC ranges from 0.02 to 1.25, average = 0.277, n = 354), and commonly have positive Eu anomalies ([Eu/Eu∗]NASC ranges from 0.295 to 1.77, average = 0.764, n = 84). In contrast, the total sediment have flatter REE + Y patterns relative to NASC ([La/Sm]NASC ranges from 0.352 to 1.12, average = 0.778, n = 451) and are slightly middle REE enriched ([Gd/Yb]NASC ranges from 0.55 to 3.75, average = 1.42). Most total sediments have negative Ce and Eu anomalies ([Ce/Ce∗]NASC ranges from 0.097 to 2.12, average = 0.799 and [Eu/Eu∗]NASC ranges from 0.39 to 1.43, average = 0.802). The partial extraction sediments are commonly less LREE depleted than the total sediments ([La/Sm]NASC ranges from 0.24 to 3.31, average = 0.901, n = 4537), more MREE enriched ([Gd/Yb]NASC ranges from 0.765 to 6.28, average = 1.97) and Ce and Eu anomalies (negative and positive) are more pronounced.The partial extraction recovered, on average ∼20% of the Fe in the total sediment, ∼80% of the Mn, and 21-29% of the REEs (Ce = 19% and Y = 32%). Comparison between REEs in water, partial extraction and total sediment analyses indicates that REEs + Y in the stream sediments have two primary sources, the host lithologies (i.e., mechanical dispersion) and hydromorphically transported (the labile fraction). Furthermore, Eu appears to be more mobile than the other REE, whereas Ce is preferentially removed from solution and accumulates in the stream sediments in a less labile form than the other REEs + Y. Despite poor statistical correlations between the REEs + Y and Mn in either the total sediment or partial extractions, based on apparent distribution coefficients and the pH of the stream waters, we suggest that either sediment organic matter and/or possibly δ-MnO2/FeOOH are likely the predominant sinks for Ce, and to a lesser extent the other REE, in the stream sediments. 相似文献
6.
There is considerable debate about the mode and age of formation of large (up to ∼200 m long) hematite and goethite ironstone bodies within the 3.2 to 3.5 Ga Barberton greenstone belt. We examined oxygen and hydrogen isotopes and Rare Earth Element (REE) concentrations of goethite and hematite components of the ironstones to determine whether these deposits reflect formation from sea-floor vents in the Archean ocean or from recent surface and shallow subsurface spring systems. Goethite δ18O values range from −0.7 to +1.0‰ and δD from −125 to −146‰, which is consistent with formation from modern meteoric waters at 20 to 25 °C. Hematite δ18O values range from −0.7 to −2.0‰, which is consistent with formation at low to moderate temperatures (40-55 °C) from modern meteoric water. REE in the goethite and hematite are derived from the weathering of local sideritic ironstones, silicified ultramafic rocks, sideritic black cherts, and local felsic volcanic rocks, falling along a mixing line between the Eu/Eu* and shale-normalized HREEAvg/LREEAvg values for the associated silicified ultramafic rocks and felsic volcanic rocks. Contrasting positive Ce/Ce* of 1.3 to 3.5 in hematite and negative Ce/Ce* of 0.2 to 0.9 in goethite provides evidence of oxidative scavenging of Ce on hematite surfaces during mineral precipitation. These isotopic and REE data, taken together, suggest that hematite and goethite ironstone pods formed from relatively recent meteoric waters in shallow springs and/or subsurface warm springs. 相似文献
7.
辽宁本溪歪头山条带状铁矿的成因类型、形成时代及构造背景 总被引：12，自引：9，他引：3
辽宁鞍本地区位于华北克拉通东北缘,分布有诸多大型-特大型条带状铁矿床。本文对该区歪头山铁矿进行了岩石学、矿物学及年代学研究。歪头山铁建造以条带状铁矿石为主,兼含有少量的块状矿石,其顶底板围岩及矿体夹层主要为太古界鞍山群斜长角闪岩。元素地球化学分析表明,铁矿石富集重稀土[(La/Yb)PAAS=0.24~0.33],具La正异常(La/La*=1.43~1.61)、Eu正异常(Eu/Eu*=2.40~4.54)及Y正异常(Y/Y*=1.10~1.30),Y/Ho值平均30.59,Sr/Ba值平均17.62,Ti/V值平均19.45,反映成矿物质可能来源于由海底火山活动带来的高温热液与海水的混合溶液。铁矿石无明显Ce负异常(Ce/Ce*=0.92~1.06),暗示BIF沉积时海水处于缺氧环境。除Fe2O3T与SiO2外,铁矿石中其它氧化物含量均非常低,且贫Th、U、Zr等具有陆源性质的元素,表明大陆碎屑物质对BIF贡献极少。斜长角闪岩稀土元素配分型式近于平坦[(La/Yb)N=0.80~1.10],无明显Ce异常(Ce/Ce*=0.95~0.99)与Eu异常(Eu/Eu*=0.88~1.16);其大离子亲石元素富集,高场强元素无明显亏损。地球化学分析表明,斜长角闪岩原岩可能为产于弧后盆地的玄武质火山岩。锆石形态与微量元素分析显示,斜长角闪岩中的锆石均属岩浆成因。SIMS锆石U-Pb定年显示斜长角闪岩原岩形成于2533±11Ma,代表了歪头山BIF的成矿年龄;在玄武质岩浆喷发过程中,还捕获了一组年龄为2610±5Ma的锆石。电子探针分析显示磁铁矿成分纯净(FeOT=92.04%~93.05%),其标型组分特征暗示歪头山BIF属沉积变质型铁矿。综合分析认为,歪头山铁矿属Algoma型BIF,成矿与弧后盆地岩浆活动密切相关,指示了新太古代末华北克拉通普遍发育的一期BIF成矿事件。 相似文献
8.
Paul-Désiré Ndjigui Paul Bilong Dieudonné Bitom 《Journal of African Earth Sciences》2009,53(1-2):59-69
Strong negative cerium anomalies are developed in the saprolite zone of two serpentinite lateritic profiles in the Mada region of the Kongo–Nkamouma massif in the Lomié ultramafic complex (South-East Cameroon).The total lanthanide contents increase strongly from the parent rock (1.328 ppm) to the weathered materials (ranging from 74.32 to 742.18 ppm); the highest value is observed in the black nodules from the western weathering profile and the lowest one in the top of the clayey surface soil from the same profile. The lanthanide contents, except cerium, are highest in the saprolite and decrease along the profile. The light REE contents are very high compared to those of the heavy REE (LREE/HREE ranging from 3.21 to 44.37). The lanthanides normalized with respect to the parent rock reveal: (i) strong negative Ce anomalies with [Ce/Ce1] ranging from 0.006 to 0.680 in the saprolite zone; (ii) strong positive Ce anomalies with [Ce/Ce1] ranging from 1.23 to 23.96 from the top of the saprolite to the clayey surface horizon; (iii) positive Eu anomalies with [Eu/Eu1] ranging from 2.09 to 2.41 in all the weathered materials.Mass balance evaluation shows that, except cerium, lanthanides have been highly accumulated in the saprolite zone and moderately concentrated in the upper part of both profiles. Cerium has been highly accumulated in the nodules of the West Mada profile. The presence of negative Ce anomalies is confirmed by its low degree of accumulation whereas the positive ones are related to its high degree of accumulation. 相似文献
9.
This paper describes the occurrence of dolomite and the mechanism of dolomitization of the Upper Triassic-Lower Jurassic K?z?loren Formation in the autochthonous Bolkardag? unit of the middle Taurus Mountains in south western Turkey. Dolomites were analyzed for geochemical, isotopic and crystallographic variation. Dolomites occur as a replacement of precursor carbonate and cement. The dolomite crystals range from <10 to ~1000 μm existing as both replacements and cements. Sr concentrations range between 84 and 156 ppm, and the molar Sr/Ca ratios of dolomitizing fluids are estimated to range between 0.0066 to 0.013 ratios. Dolomites are Ca-rich (with average CaCO3 and MgCO3 equal to 56.43 and 43.57 mol%, respectively) and they are non-stoichiometric, with an average Sr=116 ppm, Na=286 ppm, Mn=81 ppm, Fe=1329 ppm, and δ18O and δ13C ranges from –0.6‰ to –6.1‰ Pee Dee Belemnite [PDB], and +1.2 to +3.9‰ PDB. The North American Shale Composition [NASC]-normalized rare earth element (REE) values of the both limestone and dolomite sample groups show very similar REE patterns characterized by small positive Eu (mean=1.32 and mean=1.42, respectively) and slightly or considerably negative Ce (mean=0.61 and mean=0.72, respectively) anomalies and a clear depletion in all REE species. The K?z?loren Formation dolomites have been formed as early diagenetic from mixing zone fluids at the tidal-subtidal environment and at the late diagenetic from basinal brines at the shallow-deep burial depths. 相似文献
10.
稀土的开发和广泛应用使得人们倍加关注其在环境中的分布及其环境地球化学行为。赣江作为鄱阳湖流域五大入湖河之一,发源于稀土资源富集的赣南地区,而其下游水体及周边地下水中稀土元素的含量和分异特征目前尚不完全清楚。以赣江北支水体及沉积物为研究对象,开展了稀土元素地球化学研究。结果表明,赣江北支水体中稀土元素总量在地表水中为230~1 146 ng/L(均值458.85 ng/L),地下水中为284~1 498 ng/L(均值634.94 ng/L),沉积物中稀土元素总量为177.9~270.7 mg/kg(均值226.99 mg/kg)。PHREEQC模拟计算表明,水体中的稀土元素主要以碳酸根络合物(REEC03+)的形式存在。地表水和地下水总体上均表现为重稀土元素相较于轻、中稀土元素富集,沉积物未表现出明显的富集特性;水体具有Ce、Eu负异常特点,而沉积物表现为Ce正异常和Eu负异常,指示氧化还原环境和水岩相互作用对稀土元素在水-沉积物系统中迁移转化的影响。地下水中稀土元素的含量沿流向具有上升趋势,而水体中重稀土元素的富集程度不断减弱,同时碳酸根络合物(REEC03+)的占比不断降低,反映水体中稀土元素的含量受到pH、胶体吸附、络合作用以及地下水-地表水相互作用的影响。水体中重稀土元素的富集受到碳酸根络合反应的影响,Ce、Eu负异常与Ce氧化沉淀和母岩特性相关。Gd异常值表明,研究区中下游水体中的Gd元素受到人为输入的影响。 相似文献
11.
The giant sediment-hosted Jinding zinc-lead deposit is located in the Lanping Basin, northwestern Yunnan Province, China. The genesis of the deposit has long been debated and the sources of the ore-forming fluids and metals are controversial. This study presents rare earth element (REE) and noble gas isotope data that constrain the origins of the ore fluids and the heat source driving the hydrothermal circulation. The early-stage sulfides are enriched in light REEs and have high ∑REE values (30.8–94.8 ppm) and weakly negative Eu (δEu 0.85–0.89) and Ce anomalies (δCe 0.84–0.95), suggesting that the fluids were likely derived from dissolution of Upper Triassic marine carbonates with input of REEs from aluminosilicate rocks in the basin. In contrast, the late-stage sulfides have irregular REE patterns, generally low ∑REE values (0.24–10.8 ppm) and positive Eu (δEu 1.22–10.9) and weakly negative Ce anomalies (δCe 0.53–0.90), which suggest that the ore-forming fluids interacted with evaporite minerals. The 3He/4He (0.01–0.04 Ra) and 40Ar/36Ar values (301–340) of the ore-forming fluids indicate crustal and atmospheric origins for these noble gases. These findings are in agreement with the published fluid inclusion microthermometry data and the results of H, O, C, S, Pb and Sr isotope studies. Our data, in combination with published results, support a two-stage hydrothermal mineralization model, involving early-stage basinal brines and late-stage meteoric water that acquired metals and heat from crustal sources. 相似文献
12.
P. Mo
ller P. Dulski H. Gerstenberger G. Morteani A. Fuganti 《Applied Geochemistry》1998,13(8):975-994
The sparkling waters from the area of Kyselka near Karlovy Vary at the western slope of the Doupovske hory, Bohemia (Czech Republic), and CO2-poor waters from two underground boreholes at Jachymov, Krusne hory, Bohemia, have been studied with the aim of characterizing the distribution of rare earth elements, yttrium, and H, O, C, Sr, Nd, Pb isotopes during the low-temperature alteration processes of the host rocks. Additionally, leaching experiments were performed at pH 3 on the granitic and basaltic host rocks from Kyselka and the granite of Jachymov. All REE patterns of the granite- and the basalt-derived waters from the Kyselka area are different from those of their source rocks and the leachates of the latter. This elucidates the inhomogeneous distribution of REE and Y among the solid phases in the altered magmatic rocks. The Eu and Ce anomalies in granite-derived waters are inherited, the Y anomaly is achieved by fluid migration. Yttrium is always preferentially leached by mineral waters, whereas Y/Ho ratios of rocks and their leachates are very similar. The REE abundances in waters from the wells in Jachymov are derived from rocks intensely leached and depleted in easily soluble REE-bearing minerals, whereas the granites and basalts from Kyselka still contain soluble, REE-bearing minerals. A comparison of REE/Ca patterns of the experimental leachates with those of the mineral waters elucidate the high retention of REE in rocks during water–rock interaction. In strongly altered rocks Sr isotope ratios of mineral waters and rocks differ widely, whereas the corresponding Nd isotope ratios are very similar. 207Pb/208Pb, 206Pb/208Pb and 206Pb/207Pb ratios in mineral waters are independent from U/Th ratios in the rocks. 206Pb/208Pb and 206Pb/207Pb are lower in mineral waters than in their source rocks and their leachates, which indicates that Pb is primarily derived from solid phases that do not contain significant contents of leachable U and Th. Thus, mineral waters, although CO2 rich, only interact with surface films on minerals and not with the bulk of the minerals as in the leaching experiments.Calculation of mixing ratios of waters from the granitic and basaltic sources of the waters from the Kyselka area yield about 40% of water from the underlying granite in water recovered from the basalt, whereas the granite-derived water is mixed with only about 5% of the water from the basalt. 相似文献
13.
The reservoir temperature and conceptual model of the Pasinler geothermal area, which is one of the most important geothermal areas in Eastern Anatolia, are determined by considering its hydrogeochemical and isotope properties. The geothermal waters have a temperature of 51 °C in the geothermal wells and are of Na–Cl–HCO3 type. The isotope contents of geothermal waters indicate that they are of meteoric origin and that they recharge on higher elevations than cold waters. The geothermal waters are of immature water class and their reservoir temperatures are calculated as 122–155 °C, and their cold water mixture rate is calculated as 32%. According to the δ13CVPDB values, the carbon in the geothermal waters originated from the dissolved carbon in the groundwaters and mantle-based CO2 gases. According to the δ34SCDT values, the sources of sulfur in the geothermal waters are volcanic sulfur, oil and coal, and limestones. The sources of the major ions (Na+, Ca2+, Mg2+, Cl?, and HCO3 ?) in the geothermal waters are ion exchange and plagioclase and silicate weathering. It is determined that the volcanic rocks in the area have effects on the water chemistry and elements like Zn, Rb, Sr, and Ba originated from the rhyolite, rhyolitic tuff, and basalts. The rare earth element (REE) content of the geothermal waters is low, and according to the normalized REE diagrams, the light REE are getting depleted and heavy REE are getting enriched. The positive Eu and negative Ce anomalies of waters indicate oxygen-rich environments. 相似文献
14.
Geochemical Characteristics of Cenozoic Basaltic High-K Volcanic Rocks from Maguan Area, Eastern Tibet 总被引：3，自引：0，他引：3
The major element, trace element and Nd-Sr isotopic composition of Cenozoic basaltic volcanic rocks from the Maguan area, eastern Tibet, indicates that the volcanic rocks are enriched in alkalis, especially K (K2O up to 3.81%) and depleted in Ti (TiO2 = 1.27%-2.00%). These rocks may be classified as two groups, based on their Mg# numbers: one may represent primary magma (Mg# numbers from 68 to 69), and the other, the evolved magma(Mg# numbers from 49 to 57). Their REE contents are very high (∑REE = 155.06-239.04μg/g). Their REE distribution patterns are of the right-inclined type, characterized by LREE enrichment [(La/Yb)N =12.0-19.2], no Ce anomaly (Ce/Ce*=1.0), and weak negative Eu anomaly (Eu/Eu*=0.9). The rocks are highly enriched in Rb, Sr and Ba (59.5-93.8μg/g, 732-999 μg/g, and 450-632 g/g, respectively), high in U and Th (1.59-2.31μg/g and 4.73-8.16 μg/g, respectively), and high in Nb, Ta, Zr and Hf (70-118 μg/g,3.72-5.93 μg/g, 215-381 μg/g, and 5.47-9.03 μg/g, respectively). In the primitive mantle-normalized incompatible element spidergram, Nb, Ta, Zr, Hf and P show positive anomalies, whereas Ba, Ti and Y show negative anomalies. The 87Sr/86Sr ratios range from 0. 704029 to 0.704761; 143Nd/144Nd from 0. 512769 to 0. 512949; and εNd from 2.6 to 6.1. These geochemical features might suggest that the potential source of the basaltic high-K volcanic rocks in the Maguan area is similar to the OIB-source mantle of Hawaii and Kergeulen volcanic rocks. 相似文献
15.
R. K. Bikramaditya Singh 《Journal of the Geological Society of India》2010,75(4):618-631
Low to medium grade crystalline rocks locally known as Bomdila Group extensively covers the Lesser Himalayan region in Western
Arunachal Himalaya. This Group consists dominantly of mylonitic gneisses of granitic composition of Palaeoproterozoic age,
named as Bomdila mylonitic gneiss (BMG) and a small body of hornblende bearing granite of Mesoproterozoic age known as Salari
granite (SG). The BMG is affinity to peraluminous (A/CNK > 1.1) with high content of SiO2, K2O/Na2O ratio, normative corundum, high ratio of FeOt/MgO in biotite (3.21–5.11) that shows characteristics of S-type granite whereas SG has granodiorite composition with high
Na2O, low K2O, presence of hornblende, normative diopside, low A/CNK ratio (<1.1) and low FeOt/MgO ratio in biotite (1.58–1.60) indicates metaluminous I-type granite affinity. The SG has more fractionated nature of REE
[(Ce/Yb)N = 9.06–18.53] and minor negative Eu anomalies [EuN/Eu* = 0.69–0.94] as compared to BMG which has less fractionation of REE [(Ce/Yb)N = 5.95–9.16] and strong negative Eu anomalies [EuN/Eu* = 0.37–0.43]. Geochemical and petrological studies suggest that the SG and BMG are not genetically related; SG appears
to have derived from igneous source whereas the BMG have been derived from sedimentary source, however these granitoids might
have produced during the same thermal event. 相似文献
16.
本文主要对沂水青龙峪出露的超镁铁质岩石和基性麻粒岩进行了锆石SHRIMP U-Pb定年研究。超镁铁质岩石以捕掳体形式存在于沂水杂岩中,不发育鬣刺结构,氧化物组成具有超镁铁质科马提岩的高MgO、富CaO、低SiO2、TiO2、K2O和Na2O含量特征;矿物组合以单斜辉石+橄榄石±斜方辉石+铬铁矿为主;变质矿物以角闪石+蛇纹石化为特征;该岩石以稀土元素总含量(∑REE)低、LREE/HREE=3.35～4.40及Ce和Eu负异常为特征。微量元素组成以Ba、Nb、Zr负异常和Nd、Sm正异常为特征。根据锆石SHRIMP U-Pb定年法对该超镁铁质岩石中捕获的早期岩浆结晶锆石和新生的变质锆石进行的研究,年龄值分别为2657～2702Ma和2551～2585Ma,表明该超镁铁质岩石形成年龄为2585～2657Ma。基性麻粒岩的氧化物组成特征表明其属高Mg的洋岛拉斑玄武岩,麻粒岩相——高角闪岩相变质作用与新太古代的深熔和岩浆侵入作用有关,矿物组合以紫苏辉石+单斜辉石±角闪石+斜长石±石榴子石为特征;晚期蚀变作用与辉长岩墙、辉绿岩脉及石英闪长岩买的侵入有关,矿物组合以滑石化+绢云母化+绿泥石化为特征;稀土元素组成以轻重稀土元素无分异和无Eu异常为特征;微量元素组成以Nb、Zr、P、Ti负异常和Sr、K正异常为特征;锆石SHRIMP U-Pb定年结果表明麻粒岩相——角闪岩相变质作用年龄为2498.4±7.6Ma,导致麻粒岩相——角闪岩相变质的深熔和岩浆结晶年龄为2551±24Ma,晚期蚀变作用的年龄分别为2231～2235Ma和1850±19Ma。 相似文献
17.
Shallow groundwater and hot springs were collected from northeastern Guangdong Province, Southeast China, to determine the concentrations and fractionation patterns of rare-earth elements(REE). The results show that the La, Ce and Nd of REEs are abundant in groundwater and rock samples, and the ∑REE contents in groundwater and rock samples range from 126.5 to 2875.3 ng/L, and 79.44 to 385.85 mg/L, respectively. The shallow groundwater has slightly HREE-enriched PAAS-normalized patterns. However, the granitic rocks PAAS-normalized patterns, with remarkable negative Eu anomalies, are different from that of shallow groundwater. The enrichment of HREE is considered to be controlled by REE complexation and readsorption for most groundwater has Ce and Eu positive anomalies. The Ce and Eu anomalies in groundwater are controlled by redox conditions. Moreover, the Fe-contain sediments dissolution and/or the reduction of Fe oxyhydroxides are another factor contributing to Ce anomalies. The Eu anomalies in groundwater are controlled by the preferential mobilization of Eu2+ during water-rock interaction compared to Eu3+. 相似文献
18.
The Jinshajiang–Red River alkaline igneous belt in the eastern Indian–Asian collision zone, of southwestern China, hosts abundant, economically important Cu–Mo–Au mineralization of Cenozoic age. Major- and trace-element compositions of titanites from representative Cu-mineralized intrusions determined by LA-ICP-MS show higher values for Fe2O3/Al2O3, ΣREE?+?Y, LREE/HREE, Ce/Ce*, (Ce/Ce*)/(Eu/Eu*), U, Th, Ta, Nb and Ga, and lower values for Al2O3, CaO, Eu/Eu*, Zr/Hf, Nb/Ta and Sr than those for titanites from barren intrusions. Different ΣREE?+?Y, LREE/HREE, U, Th, Ta and Nb values of titanites between Cu-mineralized and barren intrusions were controlled mainly by the coexisting melt compositions. However, different Sr concentrations and negative Eu anomalies of titanites between Cu-mineralized and barren intrusions were most probably caused by different degrees of crystallization of feldspar from melts. In addition, different Ga concentrations and positive Ce anomalies of titanites between Cu-mineralized and barren intrusions were most likely caused by different magmatic fO2 conditions. Pronounced compositional differences of titanites between Cu-mineralized and barren intrusions can provide a useful tool to help discriminate between ore-bearing and barren intrusions at an early stage of exploration, and, thus, have a potential application in exploration for porphyry Cu deposits in the Jinshajiang – Red River alkaline igneous belt, and to other areas. 相似文献
19.
《Journal of South American Earth Sciences》2007,24(4):271-289
The major and trace element characteristics of black shales from the Lower Cretaceous Paja Formation of Colombia are broadly comparable with those of the average upper continental crust. Among the exceptions are marked enrichments in V, Cr, and Ni. These enrichments are associated with high organic carbon contents. CaO and Na2O are strongly depleted, leading to high values for both the Chemical Index of Alteration (77–96) and the Plagioclase Index of Alteration (86–99), which indicates derivation from a stable, intensely weathered felsic source terrane. The REE abundances and patterns vary considerably but can be divided into three main groups according to their characteristics and stratigraphic position. Four samples from the lower part of the Paja Formation (Group 1) are characterized by LREE-enriched chondrite-normalized patterns (average LaN/YbN = 8.41) and significant negative Eu anomalies (average Eu/Eu1 = 0.63). A second group of five samples (Group 2), also from the lower part, have relatively flat REE patterns (average LaN/YbN = 1.84) and only slightly smaller Eu anomalies (average Eu/Eu1 = 0.69). Six samples from the middle and upper parts (Group 3) have highly fractionated patterns (average LaN/YbN = 15.35), resembling those of Group 1, and an identical average Eu/Eu1 of 0.63. The fractionated REE patterns and significant negative Eu anomalies in Groups 1 and 3 are consistent with derivation from an evolved felsic source. The flatter patterns of Group 2 shale and strongly concave MREE-depleted patterns in two additional shales likely were produced during diagenesis, rather than reflecting more mafic detrital inputs. An analysis of a single sandstone suggests diagenetic modification of the REE, because its REE pattern is identical to that of the upper continental crust except for the presence of a significant positive Eu anomaly (Eu/Eu1 = 1.15). Felsic provenance for all samples is suggested by the clustering on the Th/Sc–Zr/Sc and GdN/YbN–Eu/Eu1 diagrams. Averages of unmodified Groups 1 and 3 REE patterns compare well with cratonic sediments from the Roraima Formation in the Guyana Shield, suggesting derivation from a continental source of similar composition. In comparison with modern sediments, the geochemical parameters (K2O/Na2O, LaN/YbN, LaN/SmN, Eu/Eu1, La/Sc, La/Y, Ce/Sc) suggest the Paja Formation was deposited at a passive margin. The Paja shales thus represent highly mature sediments recycled from deeply weathered, older, sedimentary/metasedimentary rocks, possibly in the Guyana Shield, though Na-rich volcanic/granitic rocks may have contributed to some extent. 相似文献
20.
王剑锋 《中国地球化学学报》1991,10(3):277-287
Based on the data of 64 samples ,the REE geochemical characteristics of volcanic rocks in northern Zhejiang and eastern Jiangxi provinces are discussed in this paper.The REE distribution patterns in acid and intermediate-acid volcanic rocks in these areas display some similarities,as indicated by rightward-inclined V-shaped curves with negative Eu anomalies,which are parallel to earch other.In addi-tion,their REE parameters(ΣREE,ΣLREE/ΣHREE,δEu,Ce/Yb,La/Sm,La/Yb,etc)also va-ry over a narrow range with small deviations.HREE are particularly concentrated in the volcanic rocks as-sociated with uranium mineralization.The initial ^87Sr/^86Sr ratio in the volcanic rocks is about 0.7056-0.7139.All these features in conjunction with strontium isotopic data indicate that the rock-forming materials come from the sialic crust.The REE distribution patterns and REE geochemical parameters of the volcanic rocks ,as well as La/Sm-La and Ce/Yb-Eu/Yb diagrams may be applied to the sources of rock-forming and ore-forming materials. 相似文献