Carbonatite Plug Research Articles

SHRIMP U-Pb zircon geochronology of the carbonatite-hosted REE deposit of Kamthai, Late Cretaceous polychronous Sarnu Dandali alkaline complex, NW India: Links to plume-related metallogeny and CO2 outgassing at the K-Pg boundary

The carbonatite plug at Kamthai in the Late Cretaceous polychronous (66–89 Ma) Sarnu- Dandali alkaline complex (SDAC), NW India, is India’s only known carbonatite-hosted rare- earth-element deposit. The SDAC intrudes the Neoproterozoic (∼750 Ma) Malani silicic igneous suite in the Aravalli raton. The Kamthai carbonatite is a calcio-carbonatite dominated by calcite along with barite, strontianite, quartz, zircon and REE-bearing minerals. Textural features suggest an open-system exchange of the magma chamber at varying depths of crystallization. REE patterns are smooth and characterized by strong LREE enrichment, as typical of carbonatites. SHRIMP dating of 12 spots on three magmatic zircons from the carbonatite yielded a concordia age of 66.1 ± 1.4 Ma and an indistinguishable average 206Pb/238U mean age of 68.4 ± 1.8 Ma. The obtained U-Pb ages unambiguously link the carbonatite emplacement to the Deccan Large Igneous Province, i.e. the Réunion hotspot near the K-Pg (Cretaceous-Paleogene) boundary in the polychronous set-up of the SDAC. These ages are also indistinguishable from the 68.53 ± 0.16 Ma magmatic pulse recorded from the nearby Mundwara polychronous alkaline complex and the 69.7 ± 0.2 Ma alkaline sills from the Tethyan suture zone in Pakistan, which are regarded to be earliest manifestations of the Réunion hotspot in the Indian sub-continent. Our results in the context of REE mineralization in the Kamthai deposit have also implications with respect to CO2 outgassing, induced by at least four near-synchronous carbonatitic eruptions in NW India, and to triggering the mass extinction near the K-Pg boundary.

Lamprophyre-Carbonatite Magma Mingling and Subsolidus Processes as Key Controls on Critical Element Concentration in Carbonatites—The Bonga Complex (Angola)

The Bonga complex is composed of a central carbonatite plug (with a ferrocarbonatite core) surrounded by carbonatite cone sheets and igneous breccias of carbonatitic, fenitic, phoscoritic and lamprophyric xenoliths set in a carbonatitic, lamprophyric or mingled mesostase. To reconstruct the dynamics of the complex, the pyrochlore composition and distribution have been used as a proxy of magmatic-hydrothermal evolution of the complex. An early Na-, F-rich pyrochlore is disseminated throughout the carbonatite plug and in some concentric dykes. Crystal accumulation led to enrichment of pyrochlore crystals in the plug margins, phoscoritic units producing high-grade concentric dykes. Degassing of the carbonatite magma and fenitization reduced F and Na activity, leading to the crystallization of magmatic Na-, F- poor pyrochlore but progressively enriched in LILE and HFSE. Mingling of lamprophyric and carbonatite magmas produced explosive processes and the formation of carbonatite breccia. Pyrochlore is the main Nb carrier in mingled carbonatites and phoscorites, whereas Nb is concentrated in perovskite within mingled lamprophyres. During subsolidus processes, hydrothermal fluids produced dolomitization, ankeritization and silicification. At least three pyrochlore generations are associated with late processes, progressively enriched in HFSE, LILE and REE. In the lamprophyric units, perovskite is replaced by secondary Nb-rich perovskite and Nb-rich rutile. REE-bearing carbonates and phosphates formed only in subsolidus stages, along with late quartz; they may have been deposited due to the release of the REE from magmatic carbonates during the hydrothermal processes.

Ferrocarbonatites in the Amba Dongar Diatreme, Gujarat, India

In the Amba Dongar diatreme, “ferrocarbonatite” is not a single unit of late differentiate of calciocarbonatite magma but it is a family with variation on field occurrence, mineralogy and chemistry of each unit. The family includes dikes of ankeritic carbonatites (phase I and II), plugs of ankeritic carbonatite within sovite ring dike, dikes of sideritic carbonatite in ankeritic carbonatite plug and rodberg veins. Their intrusive relations are very clear in the field and each phase has characteristic mineralogy and trace and REE geochemistry. According to the nomenclature suggested by Harmer and Gittins (1997) majority of “ferrocarbonatites” of Amba Dongar plot in field of “ferruginous calciocarbonatite” and only siderite and rodberg plot in the field of “ferrocarbonatite”. Within these family members, their trace and REE show clear increase from early phase to last phase of sideritic carbonatite. The present short communication discusses various aspects of “ferrocarbonatites”.

The mineralogy and geochemistry of the Wicheeda Carbonatite Complex, British Columbia, Canada

The Wicheeda Carbonatite Complex, located 80km northeast of Prince George in British Columbia, Canada, has been historically explored for its REE potential but, until recently, there has been very little extensive exploration or scientific study. The Complex consists of a carbonatite plug with a series of carbonatite and potassic-syenite dykes and sills emplaced into the upper Cambrian and lower Ordovician Kechika Group. The carbonatite is classified as a calcio- to ferro-carbonatite. Sodic-fenitization is common around the carbonatite and the degree of alteration and frequency of syenite occurrences increase away from the carbonatite plug. The rare earth mineralogy of the Wicheeda carbonatite was defined through the use of petrography, scanning electron microscopy, electron probe microanalysis, and single-crystal X-ray diffraction. The REE mineralogy is complex, with multiple stages of primary, late-stage, rapidly cooling crystallization. The mineralogy consists of Ca-REE-fluorocarbonates [including bastnäsite-(Ce), parisite-(Ce), and synchysite-(Ce)], Ba-REE-fluorocarbonates [including cordylite-(Ce), kukharenkoite-(Ce), cebaite-(Ce), huangnoite-(Ce), and qaqarssukite-(Ce)], ancylite-(Ce), monazite-(Ce), euxenite-(Y) and allanite-(Ce); the majority of which are LREE-rich. The REE minerals typically form in anhedral aggregates with strontianite, calcite, dolomite, and ankerite. The aggregates range in size from a 1–2 mm but have been observed up to 7cm. The Ca-REE-fluorocarbonate minerals generally form as syntaxial intergrowths whereas the other REE minerals form individual crystals. The REE content varies throughout the carbonatite intervals with an average of 9663ppm. Evidence from the Wicheeda Carbonatite Complex and comparisons with other worldwide carbonatites suggest that the complex is derived from low-degree partial melts extracted from metasomatized lithospheric mantle.

First Carbonatite Hosted REE Deposit from India

Abstract Based on geological mapping and grid channel geochemical sampling, a carbonatite plug hosted REE deposit has been discovered at Kamthai, Barmer district, Rajasthan. The main REE minerals hosted by carbonatite plug are bastanesite (La), basnaesite (Ce), synchysite (Ce), carbocernaite (Ce), cerianite (Ce), ancylite and parisite. The highest value of LREE is 17.31%, whereas, mean works out 3.33% and weighted average is 2.97%. The carbonatite plug covers 19475 sq. meters and the resources have been estimated upto 84 m depth under Proved, Probable and Possible categories. The total resource estimation for carbonatite plug and other carbonate sills, dykes and veins is 4.91 million tons, making this as truly world class deposit. The TMC of individual LREO (lower rare earth oxide) calculated for carbonatite plug only are La=52196 tonnes, Ce =66026 tonnes, Nd = 13663 tonnes, Pr = 5415 tonnes, Sm = 920 tonnes and Eu = 207 tonnes. Besides these REE, the Kamthai resource will produce 551 tonnes of Ga, 44 tonnes of Ge and 1,12,830 tonnes of SrO during its mining life.

Analysis of airborne visible-infrared imaging spectrometer (AVIRIS) data of the Iron Hill, Colorado, carbonatite-alkalic igneous complex

The Iron Hill, Colorado, carbonatite-alkalic igneous rock complex consists mainly of pyroxenite, uncompahgrite, fenite and nepheline syenite, and carbonatite. The study area has been explored intermittently for several decades for thorium, niobium, rare earth elements, titanium, and vermiculite. Airborne visible-infrared imaging spectrometer (AVIRIS) data were acquired for the Iron Hill Complex on August 28, 1992, under clear sky conditions. The data were calibrated using a laboratory reflectance spectrum of a tuff-sagebrush mixture to represent the spectral response of a topographically flat, homogeneous image area within the ash-flow tuff. Analysis of the data was conducted using the spectral angle mapper (SAM) and linear spectral unmixing algorithms in the spectral image processing system (SIPS). Image spectra in the 2.1- to 2.45-mu m wavelength region were used in the SAM method to map dolomite in the Iron Hill carbonatite (rauhaugite) stock and in several smaller bodies, calcite in a small carbonatite (soevite) plug and in travertine spring deposits, illite mainly in sericitized felsite and granite, and kaolinite in hydrothermally altered ash-flow tuff. The general distribution of the main alkalic igneous rocks (pyroxenite, uncompahgrite, and ijolite) was mapped using a full AVIRIS wavelength range (0.40-2.45 mu m) image spectrum of pyroxenite, excluding channels affected by strong atmospheric absorption. However, some areas consisting of felsite and fenite were not spectrally distinguished from the alkalic rocks. Linear spectral unmixing, using full wavelength image spectra, was used to improve the compositional mapping achieved using the SAM algorithm. The fractional abundance images obtained for dolomite and calcite were similar to the SAM results, but the distinction between illite and kaolinite was significantly improved, especially where scattered coniferous trees are present. Hematite and goethite, which showed widely overlapping patterns in the SAM similarity images, were distinguished much better in the fractional abundance images. Biotite was used instead of pyroxenite as a reference end member in the unmixing analysis, and the results were better than those obtained in the SAM analysis...

The phlogopites from the Jacupiranga carbonatite intrusions

Electron microprobe analyses of phlogopites from five carbonatite intrusions (C1 oldest, to C5 youngest) constituting the carbonatite plug in the Jacupiranga complex support previous conclusions based on magnetite analyses that C2 to C5 represent a trend of differentiation, and that C1 has different chemical characteristics. All analyzed grains are zoned but no systematic zoning trends occur. The FeO/(FeO + MgO) ratio is very low (0.065 to 1.2), MgO is high (22.5 to 28.2%), TiO2 is very low (up to 0.44w%), BaO may be very high (up to 10.3 w%), and Na2O may be as high as 2.77 w%. With decreasing age from C2 to C5, MgO increases. Phlogopites from a banded reaction rock between carbonatite and jacupirangite are similar to, but not related to the phlogopites of the adjacent carbonatite. Compared with other carbonatite micas, the MgO-rich, TiO2-poor Jacupiranga phlogopites present one of the less evolved compositions, similar to those in mantle peridotites. Carbonatite micas are generally lower in TiO2 than BaO-rich micas from other rocks.

Petrographic and chemical characteristics of the Panda Hill carbonatite complex, Tanzania

The Panda Hill carbonatite complex, situated near the south-western flank of the Rukwa Trough in south-western Tanzania, comprises a carbonatite body, a fenite aureole and feldspathic agglomerate and breccia. Petrographic study, supported by some analyses of both rocks and minerals, indicates that the fenite zone and the agglomerate and breccia are very rich in potash. Fenites consist mainly of monomineralic orthoclase rock grading to basement gneiss away from the carbonate body. Fragments of agglomerates range from feldspathic fenites to altered basement gneiss with some fragments carbonatized. The central plug and most of the carbonatite body consist of sövite. Beforsite occurs as dyke-like bodies often cutting across flow-lines of sövite. Beforsite forms the outermost boundary of the carbonatite body on the south-east. Ferrocarbonatite forms the outermost boundary of the main body in the eastern foothills. A number of pseudo-phoscorite layers are associated with sövite often imparting a flow structure to the rock. Several mafic dykes intrude into the main carbonatite body. All these dykes are more or less carbonatized. Two types of mafic dykes are distinguished: carbonatized lamprophyre dykes; dolerite dykes. The primary magma from which the Panda Hill carbonatite and its associates originated appears to have had a potash-rich fraction. Explosiv eruption of alkali-rich magma and influx of alkali-rich solution led to extensive fenitization. The central plug indicates forceful injection of the body simultaneously with the explosive eruption. The distribution of tuffs and volcanic breccia around three hill-tops shows existence of volcanic vents. Intrusion of minor dykes of mafic and ultramafic rocks took place along with the intrusion of the carbonatite plug. During falling temperature, permeation of the country rocks surrounding the carbonatite body by carbonate fluids caused partial replacement of all the minerals by carbonates.

Sr and Nd Isotopic Composition of the Jacupiranga Carbonatite

Sr and Nd isotopic compositions are reported for minerals separated from the five distinct intrusions which comprise the central carbonatite body of the Jacupiranga alkaline complex. The calculated Rb-Sr age of is consistent with previously reported K-Ar ages. Calculated initial Sr and Nd isotopic ratios () plot near those estimated for the bulk earth at 130 m.y. ago. The carbonatite plug is isotopically heterogeneous with respect to initial ratios. Consequently the data do not lead to an unequivocal interpretation regarding source composition. We propose that the parental alkaline magma was isotopically similar to some Walvis Ridge basalts and that this parental magma was contaminated by continental crust during the differentiation process which culminated with the formation of the carbonatite.

Carbonatite tuffs and lava clasts of the Tinderet foothills, western Kenya: a study of calcified natrocarbonatites

Miocene 'limestones' around Tinderet, noted for their mammalian fossils, but recognized as in part carbonatitic, are now shown to be carbonatite tuffs and volcaniclastics. They contain ejectamenta of fenites, sövites and blocks and bombs of carbonatite lava which have quenched trachytoidal and flow-banded textures and consist largely (90%) of calcite, plus apatite and magnetite. The principal primary constituent is inferred to have been nyerereite (cf. the natrocarbonatite of Oldoinyo Lengai) now pseudomorphed by calcite, and accompanied by primary tabular calcite. Phase relations and other occurrences of such rocks are discussed. The tuffs comprise lithic and crystal lapilli, Pele's tear-drop and accretionary lapilli types. The silicate content of the tuffs and bombs is remarkably low ( c . 3%), and their eruption preceded major flows of nephelinitic agglomerates. We suggest this sequence followed simultaneous separation of immiscible silicate and natrocarbonatite magmas at depth, but the greater energy and mobility of the carbonatite enabled it to surface first. These pyroclastics (and one carbonatite plug) form an outpost of the Homa Bay petrographic province.

A new find of carbonatite in North Finland, the Sokli plug in Savukoski

A carbonatite plug discovered in the Savukoski district in North Finland covering an area of more than 20 km 2 and cutting through the pre-Karelian granite gneiss basement, consists mainly of sövite and is surrounded by a fenitized aureole. Considerable regolithic apatite concentrations are known and pyrochlore is common. Accessory minerals and elements are those typical of carbonatites. Radiometric datings give 350 m. y.

Additional data on the geology of the Mbeya carbonatite

Consists of an account of the geologic setting and age relations of the pyrochlore-bearing Mbeya carbonatite plug in southern Tanganyika (by van der Heyde) and discussion of the mode of emplacement of the plug, the character of associated dike and contact rocks, and the mineralogy of the carbonatite (by Fick). The main part of the intrusive mass is soevite, cut by numerous dolomitic, calcitic, and alvikitic dikes and surrounded by fenitized basement gneisses. Pyrochlore is most abundant in apatite-rich zones.

Isokite and triplite from Bohemia

SummaryIsokite (CaMgPO4F), a new mineral homologous with sphene, was described late in 1955 from a Rhodesian carbonatite plug. A fine-grained variety is now reported from Bohemia, where it occurs as a replacement of (probably a hydrothermal alteration product of) coarse medium brown ‘later’ triplites. It is intimately associated with fine-grained apatite that along with quartz formed post-isokite.

Isokite, CaMgPO4F, a new mineral from Northern Rhodesia

The mineral, for which the name isokite is now proposed, occurs in the carbonatite plug which forms Nkumbwa Hill Oat. 10° 10' S. long. 32° 51' E.), 15 miles east of Isoka (pronounced Iso̅ka) in Northern Rhodesia. A preliminary account of this interesting mineral locality has already been published (Reeve and Deans, 1954) and a more detailed account is now in preparation, so that only the main features of the occurrence need be mentioned here. The carbonatite plug or pipe, 0.6 by 1 mile across and rising to a height of 1000 feet above the surrounding country, pierces granitic and micaceous gneisses which are fenitized to a distance of 500 yards from the walls of the pipe, but, unlike the classic carbonatite complexes, no intrusive alkalic rocks are exposed.