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1.
Summary The Shillong Plateau of northeastern India hosts four Early Cretaceous (105–107Ma) ultramafic-alkaline-carbonatite complexes (UACC), which have been associated with the Kerguelen plume igneous activity. Petrological and geochemical characteristics of one of these UACC, the Sung Valley, are presented. The Sung Valley UACC was emplaced in to the Proterozoic Shillong Group of rocks and consists of ultramafics (serpentinized peridotite, pyroxenite, and melilitolite), alkaline rocks (ijolite and nepheline syenite), and carbonatites. Serpentinized peridotite, pyroxenite, and ijolitic rocks form the major part of the complex, the others constitute less than 5% of the total volume. Ijolite and melilitolite intrude peridotite and pyroxenite, while nepheline syenite and carbonatite intrude the ultramafic rocks as well as ijolite. Mineralogically, the carbonatites are classified as calcite carbonatite with minor apatite, phlogopite, pyrochlore and ilmenite. The serpentinized peridotites are wehrlitic. Chemical compositions of the silicate rocks do not show a distinct co-genetic relationship amongst them, nor do they show any geochemical relationships with the carbonatites. No noticeable fractionation trend is observed on the chemical variation diagrams of these rocks. It is difficult to establish the genetic evolution of the Sung Valley UACC through fractional crystallization of nephelinitic magma or through immiscible liquids. On the basis of petrological and geochemical data and previously published isotopic results from these rocks, it is suggested that they have been derived from a primary carbonate magma generated by the low-degree melting of a metasomatized mantle peridotite. 相似文献
2.
The Siriwasan carbonatite-sill along with associated alkaline rocks and fenites is located about 10 km north of the well-known Amba Dongar carbonatite-alkaline rocks diatreme, in the Chhota Udaipur carbonatite-alkaline province. Carbonatite has intruded as a sill into the Bagh sandstone and overlying Deccan basalt. This resulted in the formation of carbonatite breccia with enclosed fragments of basement metamorphics, sandstone and fenites in the matrix of ankeritic carbonatite. The most significant are the plugs of sövite with varied mineralogy that include pyroxene, amphibole, apatite, pyrochlore, perovskite and sphene. REE in sövites is related to the content of pyrochlore, perovskite and apatite. The carbon and oxygen isotopic compositions of some sövite samples and an ankeritic carbonatite plot in the “mantle box” pointing to their mantle origin. However, there is also evidence for mixing of the erupting carbonatite magma with the overlying Bagh limestone. The carbonatites of Siriwasan and Amba Dongar have the same Sr and Nd isotopic ratios and radiometric age, suggesting the same magma source. On the basis of available chemical analyses this paper is aimed to give some details of the Siriwasan carbonatites. The carbonatite complex has good potential for an economic mineral deposit but this is the most neglected carbonatite of the Chhota Udaipur province. 相似文献
3.
I. L. Nedosekova 《Geology of Ore Deposits》2007,49(2):129-146
Carbonatites that are hosted in metamorphosed ultramafic massifs in the roof of miaskite intrusions of the Il’mensky-Vishnevogorsky alkaline complex are considered. Carbonatites have been revealed in the Buldym, Khaldikha, Spirikha, and Kagan massifs. The geological setting, structure of carbonatite bodies, distribution of accessory rare-metal mineralization, typomorphism of rock-forming minerals, geochemistry, and Sr and Nd isotopic compositions are discussed. Dolomite-calcite carbonatites hosted in ultramafic rocks contain tetraferriphlogopite, richterite, accessory zircon, apatite, magnetite, ilmenite, pyrrhotite, pyrite, and pyrochlore. According to geothermometric data and the composition of rock-forming minerals, the dolomite-calcite carbonatites were formed under K-feldspar-calcite, albite-calcite, and amphibole-dolomite-calcite facies conditions at 575–300°C. The Buldym pyrochlore deposit is related to carbonatites of these facies. In addition, dolomite carbonatites with accessory Nb and REE mineralization (monazite, aeschynite, allanite, REE-pyrochlore, and columbite) are hosted in ultramafic massifs. The dolomite carbonatites were formed under chlorite-sericite-ankerite facies conditions at 300–200°C. The Spirikha REE deposit is related to dolomite carbonatite and alkaline metasomatic rocks. It has been established that carbonatites hosted in ultramafic rocks are characterized by high Sr, Ba, and LREE contents and variable Nb, Zr, Ti, V, and Th contents similar to the geochemical attributes of calcio-and magnesiocarbonatites. The low initial 87Sr/86Sr = 0.7044?0.7045 and εNd ranging from 0.65 to ?3.3 testify to their derivation from a deep mantle source of EM1 type. 相似文献
4.
<正>Carbonatites are commonly related to the accumulation of economically valuable substances such as REE.Cu,and P.The debate over the origin of carbonatites and their relationship to associated silicate rocks has been ongoing for about 45 years.Worldwide,the rocks characteristically display more geochemical enrichments in Ba,Sr and REE than sedimentary carbonate rocks.However,carbonatite's geochemical features are disputed because of secondary mineral effects.Rock-forming carbonates from carbonatites at Qinling.Panxi region,and Bayan Obo in China show REE distribution patterns ranging from LREE enrichment to flat patterns.They are characterized by a Sr content more than 10 times higher than that of secondary carbonates.The coarse- and fine-grained dolomites from Bayan Obo H8 dolomite marbles also show similar high Sr abundance,indicating that they are of igneous origin.Some carbonates in Chinese carbonatites show REE(especially HREE) contents and distribution patterns similar to those of the whole rocks.These intrusive carbonatites display lower platinum group elements and stronger fractionation between Pt and Ir relative to high-Si extrusive carbonatite.This indicates that most intrusive carbonatites may be carbonate cumulates.Maoniuping and Daluxiang in Panxi region are large REE deposits.Hydrothermal fluorite ore veins occur outside of the carbonatite bodies and are emplaced in wallrock syenite.The fiuorite in Maoniuping has Sr and Nd isotopes similar to carbonatite.The Daluxiang fiuorite shows Sr and REE compositions different from those in Maoniuping.The difference is reflected by both the carbonatites and rock-forming carbonates,indicating that REE mineralization is related to carbonatites.The cumulate processes of carbonate minerals make fractionated fluids rich in volatiles and LREE as a result of low partition coefficients for REE between carbonate and carbonatite melt and an increase from LREE to HREE.The carbonatite-derived fluid has interacted with wallrock to form REE ore veins.The amount of carbonatite dykes occurring near the Bayan Obo orebodies may support the same mineralization model,i.e.that fluids evolved from the carbonatite dykes reacted with H8 dolomite marble,and thus the different REE and isotope compositions of coarse- and fine-grained dolomite may be related to reaction processes. 相似文献
5.
Recent exploration work in South Morocco revealed the occurrence of several carbonatite bodies, including the Paleoproterozoic Gleibat Lafhouda magnesiocarbonatite and its associated iron oxide mineralization, recognized here as iron-oxide-apatite (IOA) deposit type. The Gleibat Lafhouda intrusion is hosted by Archean gneiss and schist and not visibly associated with alkaline rocks. Metasomatized micaceous rocks occur locally at the margins of the carbonatite outcrop and were identified as glimmerite fenite type. Rare earth element (REE) and Nb mineralization is mainly linked to the associated IOA mineralization and is represented by monazite-(Ce) and columbite-(Fe) as major ore minerals. The IOA mineralization mainly consists of magnetite and hematite that usually contain large apatite crystals, quartz and some dolomite. Monazite-(Ce) is closely associated with fluorapatite and occurs as inclusions within the altered parts of apatite and along cracks or as separate phases near apatite. Monazite shows no zonation patterns and very low Th contents (<0.4 wt%), which would be beneficial for commercial extraction of the REE and which indicates monazite formation from apatite as a result of hydrothermal volatile-rich fluids. Similar monazite-apatite mineralization and chemistry also occurs at depth within the carbonatite, although the outcropping carbonatite is barren, suggesting an irregular REE ore distribution within the carbonatite body. The barren carbonatite contains some tiny unidentified secondary Nb-Ta-U phases, synchysite and monazite. Niobium mineralization is commonly represented by anhedral minerals of columbite-(Fe) which occur closely associated with magnetite-hematite and host up to 78 wt% Nb2O5, 7 wt% Ta2O5 and 1.6 wt% Sc2O3. This association may suggest that columbite-(Fe) precipitated by an interaction of Nb-rich fluids with pre-existing Fe-rich minerals or as pseudomorphs after pre-existing Nb minerals like pyrochlore. Our results most strongly suggest that the studied mineralization is economically important and warrants both, further research and exploration with the ultimate goal of mineral extraction. 相似文献
6.
Alkaline lamprophyre dykes from Taourirt (North Morocco) containnumerous xenoliths, ranging from alkaline pyroxenites, kaersutitites,gabbros and nepheline syenites to a calcite carbonatite. Thesilicate xenoliths and the host rocks consist of Al- and Ti-richdiopside–salite, mica or kaersutitite, ± nepheline,± plagioclase and K-feldspar, and ubiquitous apatite.Both the xenoliths and the lamprophyres are enriched in incompatibleelements. The chemical composition of the lamprophyres cannotbe accounted for by fractional crystallization alone. Moreover,the clinopyroxenes exhibit complex zoning, which requires repeatedmixing of pulses of more or less fractionated melts. The carbonatiteis a sövite cumulate with Sr-rich calcite, pyrochlore,fluorapatite, and rare salite. The Sr–Nd isotopic compositionsof the Taourirt rocks indicate a depleted mantle source, thecarbonatite having the most depleted composition, and definea linear trend similar to that of the East African carbonatites.The different rocks thus represent unrelated magmas, and thetrend is interpreted as mixing between two components with HIMUand EM1 mantle end-member signatures. An EM2 mantle componentcould also be involved for a few samples; it may correspondto hydrous metasomatized mantle of the PP–PKP (phlogopiteand phlogopite K-richterite peridotite) and MARID (mica, amphibole,rutile, ilmenite and diopside) type. KEY WORDS: alkaline magmatism; carbonatite; Morocco; REE; Sr–Nd isotopes 相似文献
7.
G.Nelson Eby 《Geochimica et cosmochimica acta》1975,39(5):597-620
are-earth (REE) and yttrium abundances were determined, by an ion-exchange-X-ray fluorescence procedure, for whole-rock (14) and mineral (87) samples from the Oka carbonatite complex. Whole-rock and mineral data indicate a trend of total REE + Y enrichment, and relative enrichment in light REE, in the order: ultrafenites < ijolites < okaites. The sövites may show wide variations in total REE + Y concentrations, but relative REE abundance patterns will be similar. The greatest REE and Y concentrations occur in apatite, niocalite, perovskite and pyrochlore. Many of the minerals show europium anomalies (both positive and negative), and these are believed to be the result of closed system competition between the various minerals for divalent Eu. The partition coefficients for mineral pairs are quite variable, indicating that the Oka rocks were emplaced through a wide-range of physicochemical and/or nonequilibrium conditions. A reasonable model for the origin of the complex involves a limited partial melting of mantle material, emplacement of the melt in a magma chamber, crystallization of mafic minerals resulting in a residual liquid which produced ijolite and subsequently okaite, and crystallization of the carbonatites from a volatile-rich, possibly immiscible, phase. 相似文献
8.
The early Cretaceous (Albian–Aptian) Sung Valley ultramafic–alkaline–carbonatite complex is one of several alkaline intrusions that occur in the Shillong Plateau, India. This complex comprises calcite carbonatite and closely associated ultramafic (serpentinized peridotite, pyroxenite and melilitolite) and alkaline rocks (ijolite and nepheline syenite). Field relationship and geochemical characteristics of these rocks do not support a genetic link between carbonatite and associated silicate rocks. There is geochemical evidence that pyroxenite, melilitolite and ijolite of the complex are genetically related. Stable (C and O) and radiogenic (Nd and Sr) isotope data clearly indicate a mantle origin for the carbonatite samples. The carbonatite Nd (+0.7 to +1.8) and Sr (+4.7 to +7.0) compositions overlap the field for Kerguelen ocean island basalts. One sample of ijolite has Nd and Sr isotopic compositions that also plot within the field for Kerguelen ocean island basalts, whereas the other silicate–carbonatite samples indicate involvement with an enriched component. These geochemical and isotopic data indicate that the rocks of the Sung Valley complex were derived from and interacted with an isotopically heterogeneous subcontinental mantle and is consistent with interaction of a mantle plume (e.g. Kerguelen plume) with lithosphere. A U–Pb perovskite age of 115.1±5.1 Ma obtained for a sample of Sung Valley ijolite also supports a temporal link to the Kerguelen plume. The observed geochemical characteristics of the carbonatite rocks indicate derivation by low-degree partial melting (0.1%) of carbonated mantle peridotite. This melt, containing a substantial amount of alkali elements, interacted with peridotite to form metasomatic clinopyroxene and olivine. This process could progressively metasomatize lherzolite to form alkaline wehrlite. 相似文献
9.
Mawpyut igneous suite in Jaintia Hills of Meghalaya plateau comprises differentiated suite of ultramafic–mafic rocks. The
complex differs from other ultramafic–alkaline–carbonatite igneous emplacements of Shillong plateau and Mikir Hills like Jesra,
Sung, Samchampi complexes, by the absence of alkaline–carbonatite rocks as major litho-units. Melanite garnet-bearing nepheline
syenite, occurs as late phase minor intrusion in Mawpyut igneous complex, posseses alkaline character and shows inubiquitous
relation with the host ultramafic–mafic rocks. On the other hand, this alkaline intrusive bodies of the Mawpyut igneous complex
shows chemico-mineralogical resemblance with garnet-bearing nepheline syenite, ijolite litho-members of Jesra, Sung, Samchampi
complexes of the region. It is interpreted that melanite garnet-bearing nepheline syenite intrusion in Mawpyut is contemporaneous
with Jesra, Sung, Samchampi ultramafic–alkaline–carbonatite complexes and the host rocks of Mawpyut complex is an earlier
magmatic activity possibly from a comparatively least enriched source. 相似文献
10.
《Journal of Asian Earth Sciences》2000,18(5):585-594
The results of a Sr isotopic study of coexisting alkaline silicate rocks and carbonatites of two Cretaceous alkaline complexes of India, Amba Dongar (Deccan Flood Basalt Province) and Sung Valley (Rajmahal–Bengal–Sylhet Flood Basalt Province) are reported. The overlapping nature of initial Sr isotopic ratios of alkaline rocks and carbonatites of both the complexes is consistent with a magmatic differentiation model. Modelling of initial 87Sr/86Sr variation in alkaline rocks of Amba Dongar is consistent with a process of crustal assimilation by the parent magma undergoing simultaneous fractional crystallization of silicate rocks and silicate–carbonate melt immiscibility. A maximum of ∼5% crustal contamination has been estimated for the parent magma of Amba Dongar, the effect of which is not seen in the Sr isotope ratio of carbonatites generated by liquid immiscibility. A two point Rb–Sr isochron of the Sung Valley carbonatites, pyoxenite and a phlogopite from a carbonatite yielded an age of 106±11 Ma, which is identical to the 40Ar–39Ar age of this complex. The same age for the carbonatites and the alkaline silicate rocks, similar initial Sr ratios and the higher Sr concentration in the former than the latter favour the hypothesis of liquid immiscibility for the generation of the Sung Valley. The higher initial 87Sr/86Sr ratio for these complexes than that of the Bulk Earth indicates their derivation from long-lived Rb/Sr-enriched sources. 相似文献
11.
《Journal of Asian Earth Sciences》2002,20(2):127-140
Carbonatites are often of economic importance, which raises the problem of distinguishing carbonatites from limestones when either are metamorphosed to high-grade marbles. They can be of similar appearance, particularly those from the Proterozoic and Archaean of the Indian Subcontinent. This study also contributes to solving the problem of determining the frequency of alkaline and carbonatitic magmatism during the early history of the Earth.The mineral assemblage of apatite–magnetite–phlogopite–calcite is common to marbles of both carbonatite and limestone origin. If pyrochlore is present that identifies the rock as carbonatite; if anorthite, fassaite, scapolite or spinel then it was formerly a limestone. If these minerals are absent, then trace element analysis can supply the critical Sr and REE data, which are both normally high in carbonatitic rocks and low in former limestones. These distinguishing factors are applied to the metamorphic carbonate, pyroxenite, calcite–apatite rock complex at Borra, Eastern Ghats, India, which has been variously interpreted as formerly a carbonatite and as a limestone. The evidence shows that the Borra rocks are meta-sedimentary. 相似文献
12.
The nature of the petrogenetic links between carbonatites and associated silicate rocks is still under discussion (i.e., [Gittins J., Harmer R.E., 2003. Myth and reality of the carbonatite–silicate rock “association”. Period di Mineral. 72, 19–26.]). In the Paleozoic Kola alkaline province (NW Russia), the carbonatites are spatially and temporally associated to ultramafic cumulates (clinopyroxenite, wehrlite and dunite) and alkaline silicate rocks of the ijolite–melteigite series [(Kogarko, 1987), (Kogarko et al., 1995), (Verhulst et al., 2000), (Dunworth and Bell, 2001) and (Woolley, 2003)]. In the small (≈ 20 km2) Vuoriyarvi massif, apatite is typically a liquidus phase during the magmatic evolution and so it can be used to test genetic relationships. Trace elements contents have been obtained for both whole rocks and apatite (by LA-ICP-MS). The apatites define a single continuous chemical evolution marked by an increase in REE and Na (belovite-type of substitution, i.e., 2Ca2+ = Na+ + REE3+). This evolution possibly reflects a fractional crystallisation process of a single batch of isotopically homogeneous, mantle-derived magma.The distribution of REE between apatite and their host carbonatite have been estimated from the apatite composition of a carbonatite vein, belonging to the Neskevara conical-ring-like vein system. This carbonatite vein is tentatively interpreted as a melt. So, the calculated distribution coefficients are close to partition coefficients. Rare earth elements are compatible in apatite (D > 1) with a higher compatibility for the middle REE (DSm : 6.1) than for the light (DLa : 4.1) and the heavy (DYb : 1) REE. 相似文献
13.
Geochemical constraints on the genesis of the Bayan Obo Fe-Nb-REE deposit in Inner Mongolia, China 总被引：2，自引：0，他引：2
Trace element and isotopic compositions of carbonate from ore bodies, country rock which hosts the ore bodies (H8 dolomite), a carbonatite dyke exposed in Dulahala near Bayan Obo, and rare earth element (REE)-rich dolomite in Bayan Obo have been determined to understand the genesis of the Bayan Obo Fe-Nb-REE ore deposit, the world’s largest resource of REE. The REE and trace element distribution patterns of samples from the REE-rich carbonatite dykes are identical to those of mineralized carbonate rocks, indicating a genetic linkage between the REE-rich carbonatite and mineralization in this region. By contrast, carbon and oxygen isotopes in the mineralized carbonate varied significantly, δ13C = −7.98‰ to −1.12‰, δ18O = 8.60-25.69‰, which are distinctively different from those in mantle-derived carbonatite. Abnormal isotopic fractionations between dolomite and calcite suggest that these two minerals are in disequilibrium in the carbonatite dyke, ore bodies, and H8 marble from Bayan Obo. This isotopic characteristic is also found in mineralized sedimentary marine micrite from Heinaobao, ∼25 km southeast of the Bayan Obo Fe-Nb-REE ore deposit. These facts imply that the carbonate minerals in the Bayan Obo deposit have resulted from sedimentary carbonate rocks being metasomatised by mantle-derived fluids, likely derived from a REE-enriched carbonatitic magma. The initial Nd isotope values of ore bodies and carbonatite dykes are identical, indicating that ore bodies, carbonatite dykes and veins may have a similar REE source. 相似文献
14.
The Purulia carbonatite, ‘carbonatite’-‘alkali-pyroxenite’-‘apatite-magnetite rock’ association, is located at Beldih area of Purulia district, West Bengal and falls within the 100 km long Northern Shear Zone (NSZ). Published literature suggests that the Purulia carbonatite was formed by the process of liquid immiscibility from under-saturated silicate parent magma. However, no silica under-saturated rocks like ijolite, nepheline-syenite etc. is known from the area. The trace element geochemistry (Ba/La, Nb/Th, Nb/Pb and Y/Ce ratios in the present study) also does not support this view. Present study indicates that the Purulia carbonatite is enriched in ΣREE and incompatible elements but the carbonatite is also poorer in Nb, Th and Pb compared to the world average of calicocarbonatites. The lower value of Nb is characteristics of carbo(hydro)thermal carbonatite where carbonatite is associated with alkali-pyroxenite and suggests probable origin of the carbonatite as carbothermal residua evolved from an unknown parentage. However, the field, petrographic and geochemical data indicate the genesis of this carbonatite from a primary carbonatitic magma of mantle decent. The 87Sr/86Sr ratio of the carbonatite and apatite separated from the carbonatite (～0.703) implies primary magmatic derivation of the Purulia carbonatite. Close similarity of the apatite of the apatite-magnetite rock with the mantle apatite (of type Apatite B) indicates that they are also of primary magmatic origin. The present work portrays a unique example where primary magmatic carbonatite is associated with the alkali-pyroxenite. 相似文献
15.
L. N. Kogarko 《Geochemistry International》2012,50(9):719-725
The study of radioactive element distribution in the rocks of the Guli Complex revealed an increase of uranium and thorium contents in the final products of magmatic differentiation. In the carbonatite complex, the radioactive elements are mainly accumulated in the early rocks—phoscorites, while their contents in the late phases, dolomitic carbonatites, decrease. The Th/U ratio increases from near-chondritic values in the weakly differentiated highly-magnesian primary magmas to the late rocks—phoscorites, calcitic carbonatites, and dolomitic carbonatites. The majority of radioactive elements are hosted in rare-metal accessory minerals: perovskite, pyrochlore, calzirtite, and apatite. Rock-forming minerals are characterized by extremely low contents of radioactive elements. 相似文献
16.
白云鄂博碳酸岩型REE-Nb-Fe矿床——一个罕见的中元古代破火山机构成岩成矿实例 总被引：16，自引：4，他引：16
白云鄂博碳酸岩型REE-Nb-Fe矿床是世界上最大的稀土矿床。稀土矿石产于整个白云石碳酸岩体和部分脉状碳酸岩中。对比世界上20余个火成碳酸岩地区的特征后发现,白云鄂博地区完全具备国外火成碳酸岩区的地质特征。在岩石、矿石组合上,本区也发育一套碳酸岩+超基性岩+碱性基性岩(含基性熔岩)+碱性岩+稀土矿石+铁矿石组合;在矿物组合上,以白云石为主,方解石次之,伴生一套碱性闪石、长石、霓石、磷灰石、萤石、磁铁矿、稀土矿物组合;在全岩化学成分、微量元素、稀土元素和Sr、Nd、Pb、C、O同位素上,这些岩石具有一定的亲缘关系,有着共同的来源;在岩体的形态与岩石组构上,它们以岩席、岩筒和脉岩的形式出现,并发育有强烈的熔离作用与流动构造;在区域构造上,发育隐伏穹窿构造、岩筒构造和巨型断裂汇聚构造。综合分析上述特征表明:白云鄂博地区具有中元古代破火山机构的痕迹,赋矿白云石碳酸岩体则是顺层侵入的火成碳酸岩体,东矿、主矿可能是一个火山颈构造控矿,而赋矿白云石碳酸岩体西南侧的苏木图矿床则是隐伏岩筒构造控矿。 相似文献
17.
L. G. Gwalani K. A. Rogers A. Demény D. I. Groves R. Ramsay A. Beard P. J. Downes A. Eves 《Mineralogy and Petrology》2010,98(1-4):123-141
The Yungul carbonatite dykes at Speewah in the Kimberley region of Western Australia were emplaced along a north-trending splay from the northeast-trending Greenvale Fault located at the western boundary of the Halls Creek Orogen. The Yungul carbonatite dykes intrude a thick composite sill of the Palaeoproterozoic Hart Dolerite (~1,790 Ma), consisting of tholeiitic dolerite and gabbro with its felsic differentiates that form the Yilingbun granophyres and associated granites. The carbonatite dykes consist of massive, calcite carbonatite that host very coarse, pegmatitic veins and pods of calcite, and have largely replaced (carbonatitized) and fenitized the country rock Hart Dolerite suite in a zone up to 150 m wide. Dykes of red-brown siliceous fluidized-breccia and epithermal-textured veins consisting of bladed quartz, adularia and fluorite are closely associated with the carbonatite dykes. The Yungul carbonatites are closely associated with fluorite occurrences with resources currently reported as 6.7 Mt at 24.6% CaF2. The precise age of the Yungul carbonatite is not known, although it is believed to be post early Cambrian. The total REE content of the Yungul carbonatite is low (174.0–492.8 ppm; La/Yb 2.28–10.74) and thus atypical for calciocarbonatite. Chondrite-normalized REE patterns for the carbonatite are relatively flat compared to average calciocarbonatite, and show small negative Eu anomalies. These unusual geochemical features may have been acquired from the Hart Dolerite suite during emplacement of the carbonatite, a process that involved extensive replacement and fenitization of country rocks. Carbon and oxygen isotope compositions of massive calcite carbonatite and the coarse calcite veins and pods from the carbonatite suggest a deep-seated origin. The C and O isotope compositions show an overall positive correlation that can be attributed to both magmatic and magmatic-hydrothermal processes in their evolution. The magmatic δ13C-δ18O trend is also indicative of crustal contamination and/or low-temperature water/rock exchange. The carbon isotopic compositions have δ13C values that range from about ?5.2‰ to ?6.3‰ that support a mantle-derived origin for the Yungul carbonatites and are consistent with earlier conclusions based on whole-rock geochemistry and radiogenic isotopes studies. 相似文献
18.
Altered rocks of the Onguren carbonatite complex in the Western Tansbaikal Region: Geochemistry and composition of accessory minerals 总被引：1，自引：0，他引：1
V. B. Savelyeva E. P. Bazarova V. V. Sharygin N. S. Karmanov S. V. Kanakin 《Geology of Ore Deposits》2017,59(4):315-340
The paper discusses the mineralogy and geochemistry of altered rocks associated with calcite and dolomite–ankerite carbonatites of the Onguren dyke–vein complex in the Western Transbaikal Region. The alteration processes in the Early Proterozoic metamorphic complex and synmetamorphic granite hosting carbonatite are areal microclinization and riebeckitization; carbonates, phlogopite, apatite, and aegirine occur in the near-contact zones of the dolomite–ankerite carbonatite veins; and silicification is displayed within separated zones adjacent to the veins. In aluminosilicate rocks, microclinization was accompanied by an increasing content of K, Fe3+, Ti, Nb (up to 460 ppm), Th, Cu, and REE; Na, Ti, Fe3+, Mg, Nb (up to 1500 ppm), Zr (up to 2800 ppm), Ta, Th, Hf, and REE accumulated in the inner zone of the riebeckitization column. High contents of Ln Ce (up to 11200 ppm), U (23 ppm), Sr (up to 7000 ppm), Li (up to 400 ppm), Zn (up to 600 ppm), and Th (up to 700 ppm) are typical of apatite–phlogopite–riebeckite altered rock; silicified rock contains up to (ppm): 2000 Th, 20 U, 13000 Ln Ce, and 5000 Ва. Ilmenite and later rutile are the major Nb carriers in alkali altered rocks. These minerals contain up to 2 and 7 wt % Nb2O5, respectively. In addition, ferrocolumbite and aeschynite-(Ce) occur in microcline and riebeckite altered rocks. Fluorapatite containing up to 2.7 wt % (Ln Ce)2O3, monazite-(Ce), cerite-(Ce), ferriallanite-(Ce), and aeschynite-(Ce) are the REE carriers in riebeckite altered rock. Bastnäsite-(Ce), rhabdophane-group minerals, and xenotime-(Y) are typical of silicified rock. Thorite, monazite-(Ce), and rhabdophane-group minerals are the Th carriers. 相似文献
19.
鲁中碳酸岩中磷灰石同位素地球化学研究 总被引：6，自引：0，他引：6
鲁中地区分布着100多个碳酸岩体，微量元素含量及稀土配分等均与世界典型碳酸岩相近。而碳酸岩的碳氧及斑晶磷灰石的锶、钛同位素组成与典型地幔物质有差异，与富集地幔颇为近似，从而证实在山东地区陆壳下存在富集地幔源区。 相似文献
20.
白云鄂博含矿碱性火山岩建造及其地球化学 总被引：3，自引：1，他引：2
白云鄂博矿床历经几十年的研究,主要集中在矿区H8岩性段矿化白云岩成因的认识,许多研究显示含矿白云岩是岩浆碳酸岩,本文主要从岩石学和地球化学方面进一步分析其属于火山喷发环境形成的火山碳酸熔岩。H8含矿白云岩段和H9板岩段作为一套含矿岩系主要由含矿白云岩、霓闪钠长岩、钾长板岩3类岩石组成,白云岩和霓闪钠长岩都具有的碎屑结构及角砾状构造、条带构造,显示为火山熔岩和火山碎屑岩特征,而钾长板岩则主要显示致密微晶火山熔岩特征。工业矿物主要是磁铁矿、赤铁矿、稀土矿物和铌铁矿物,其重要特征是出现大量原生赤铁矿,反映岩石氧化系数高,与火山喷发环境一致。霓闪钠长岩、钾长板岩岩石化学显示碱性特征,稀土元素与CaO、F相关系数在0.7以上,并与Fe2O3高氧化物相关,而与硅酸盐矿物组分反相关,表示碳酸岩与稀土成矿密切相关,并显示为表生氧化环境形成。稀土地球化学特征显示白云岩∑REE最高,钾长板岩∑REE最低,相应的岩脉∑REE低于喷发岩。各种岩石均表现为明显的轻重稀土分异,但是以白云岩LREE/HREE比值最大,霓闪钠长岩LREE/HREE比值最小,而纯钠长石岩脉和含稀土磁铁矿LREE/HREE明显高于其他岩石。白云岩和霓闪钠长岩均表现出不同的铕、铈负异常,但是碳酸岩脉和钾长板岩则显示弱正铈异常,霓闪钠长岩和钾长板岩铕异常不明显。矿化白云岩和碳酸岩脉的δ18O、δ13C值介于沉积灰岩与已知碳酸岩的δ18O、δ13C值之间,碳酸岩中白云石的δ18O低于方解石的δ18O,而δ13C高于方解石的δ13C,稀土矿物的δ13C、δ18O与碳酸岩脉δ13C、δ18O接近。归纳这些特征,含矿白云岩与霓闪钠长岩、钾长板岩是碱性火山岩组合,与一系列同期的碳酸岩、霓闪钠长岩碱性岩脉一起,构成一套完整碱性火山岩系。 相似文献