Genesis of the Khaluta Alkaline-Basic Ba-Sr Carbonatite Complex (West Transbaikala, Russia)

See discussions, stats, and author proﬁles for this publication at: https://www.researchgate.net/publication/226169877

Genesis of the Khaluta alkaline-basic Ba-Sr carbonatite complex (West Transbaikala, Russia)

Article in Mineralogy and Petrology · March 2009 DOI: 10.1007/s00710-009-0063-4

CITATIONS READS 12 73

3 authors, including:

Anna Doroshkevich G. S. Ripp Sobolev Institute of Geology and Mineralogy Russian Academy of Sciences 52 PUBLICATIONS 239 CITATIONS 71 PUBLICATIONS 332 CITATIONS

SEE PROFILE SEE PROFILE

Some of the authors of this publication are also working on these related projects:

Petrological, geochemical, and physico-chemical factors of metal-bearing capacity of carbonate melts and magmatic ﬂuids as criteria of estimation of ore productivity (REE, Au, Pt) of alkaline massifs View project

All content following this page was uploaded by Anna Doroshkevich on 03 July 2016.

The user has requested enhancement of the downloaded ﬁle. Miner Petrol (2010) 98:245–268 DOI 10.1007/s00710-009-0063-4

ORIGINAL PAPER

Genesis of the Khaluta alkaline-basic Ba-Sr carbonatite complex (West Transbaikala, Russia)

Anna G. Doroshkevich & German S. Ripp & Kathryn R. Moore

Received: 18 November 2008 /Accepted: 11 June 2009 /Published online: 29 June 2009 # Springer-Verlag 2009

Abstract The Khaluta carbonatite complex comprizes Introduction fenites, alkaline syenites and shonkinites, and calcite and dolomite carbonatites. Textural and compositional criteria, One of the key questions regarding the petrogenesis of melt inclusions, geochemical and isotopic data, and carbonatite is whether they form directly by partial melting comparisons with relevant experimental systems show that of a carbonated peridotite mantle (e.g. Wallace and Green the complex formed by liquid immiscibility of a carbonate- 1988; Dalton and Wood 1993; Harmer and Gittins 1998), saturated parental silicate melt. Mineral and stable isotope by fractional crystallization (e.g. Otto and Wyllie 1993), or geothermometers and melt inclusion measurements for the by liquid immiscibility of a silicate parental melt (e.g. silicate rocks and carbonatite all give temperatures of Kjarsgaard and Hamilton 1989; Lee and Wyllie 1998). crystallization of 915–1,000°C and 890–470°C, respective- Both fractional crystallization and liquid immiscibility ly. Melt inclusions containing sulphate minerals, and may be important processes in carbonatite magma evolu- sulphate-rich minerals, most notably apatite and monazite, tion in subvolcanic and volcanic environments, and the occur in all of the lithologies in the Khaluta complex. All aim of this research is to define the most probable path lithologies, from fenites through shonkinites and syenites to from a source with identified characteristics to emplaced calcite and dolomite carbonatites, and to hydrothermal rock compositions for a particular occurrence (Khaluta) mineralisation are further characterized by high Ba and Sr based on integrated evidence from field, geochemical and activity, as well as that of SO3 with formation of the experimental studies. The hypothesis of liquid immisci- sulphate minerals baryte, celestine and baryte-celestine. bility has been favoured by many authors for alkali-rich as Thus, the characteristic features of the Khaluta parental well as alkali-poor carbonatites and is supported by field melt were elevated concentrations of SO3, Ba and Sr. In evidence, experimental data and melt inclusion studies addition to the presence of SO3, calculated fO2 for (e.g. Romanchev and Sokolov 1980; Panina 2005). Asso- magnetites indicate a high oxygen fugacity and that ciation with silicate rocks is one of the important criterion Fe+3>Fe+2 in the Khaluta parental melt. Our findings for the hypothesis of carbonatite formation by immiscible suggest that the mantle source for Khaluta carbonatite and separation. Carbonatites are often associated with alkaline associated rocks, as well as for other carbonatites of the igneous rocks such as ijolites and nepheline syenites, and

West Transbaikalia carbonatite province, were SO3-rich and only 10% of carbonatite occurrences have been found in characterized by high oxygen fugacity. association with mafic rocks (Woolley 2003). Examples of the latter are Mountain-Pass, USA (Olson et al. 1954), Mushugai-Khuduk, Mongolia (Samoilov and Kovalenko 1983), Kaiserstuhl, Germany (Hay and O’Neil 1983) and Editorial handling: L.G. Gwalani Khaluta, Russia (Yarmolyuk et al. 1997; Ripp et al. 2000). However, most of these occurrences do not have a well- * : : A. G. Doroshkevich ( ) G. S. Ripp K. R. Moore supported genetic model of formation. Some authors (e.g. Geological Institute SB RAS, Ulan Ude, Russia Yarmolyuk et al. 1997; Ripp et al. 2000; Mariano 1989) e-mail: [email protected] suggest that these carbonatites are magmatic, while others 246 A.G. Doroshkevich et al. regards these rocks as carbothermal residua (Mitchell 2005; carbonates. δ34S values were also measured in inclusions Rass et al. 2006). Therefore, the Khaluta carbonatite within minerals, where it had been shown that inclusions complex is now rigorously examined in order to also usually contain water-soluble K, Na sulphates, as found in establish the nature of the relationship between carbonatite previous investigations (Doroshkevich and Ripp 2004). The and associated mafic rocks. The petrogenetic association of samples of minerals containing the inclusions were crushed carbonatites with alkaline igneous rocks of the Khaluta to a powder and then processed using distilled water. K, Na complex has been previously ascertained on the grounds of sulphates from inclusions were dissolved during this geological, geochronological and petrographic data and the process, and then were precipitated by addition of BaCl2. 34 similarity of isotopic composition of carbonatites and the The resulting BaSO4 precipitate was analyzed for δ S carbonate component of alkaline rocks (Ripp et al. 1998, isotope values. 2000; Nikiforov et al. 1998, 2000; Bulnaev and Posokhov Inclusions were studied in polished wafers up to 0.3 mm 1995; Bulnaev 1996). In this paper, we present new results thick, using optical and thermometric methods. Primary and combined with previously reported mineralogical and secondary inclusions were distinguished using textural geochemical data on Khaluta carbonatites (Ripp et al. criteria formulated by Roedder (1983). Inclusions that 1998, 2000; Nikiforov et al. 1998, 2000). Specifically, the clustered along randomly orientated surfaces tracing healed results of melt inclusion studies, experimental phase microcracks were considered secondary. Random, solitary equilibrium studies, calculated trace element partition inclusions were considered to be primary. A heating stage coefficients between silicate and carbonate pairs, and for temperatures up to 400°C with a silicon carbide heating detailed mineralogical, geochemical and stable isotope element was used (Sobolev and Kostyuk 1975). Tempera- characteristics are examined, which collectively provide ture was measured using a Pt\Pt-Rh thermocouple (type S) important insights into the source characteristics of magmas calibrated against the melting points of S, NaNO3, and the petrogenesis of the Khaluta complex. K2Cr2O7, NaCl and two standard fluid inclusions synthe- sized at controlled temperature and pressure. The power- law best fit of these data yielded a standard error for Analytical methods temperature measurements of ± 5°C. Heating of inclusions under confining argon pressure was carried out using an Whole-rock chemistry was determined by atomic absorp- internally heated pressure vessel at the Institute of Exper- tion (Perkin-Elmer) and conventional chemical methods. imental Mineralogy (IEM RAS), Chernogolovka, for 24 h

CO2 was determined by titrametric chemical decomposi- at pressures up to 0.5 GPa and 1,000°C. tion. ICP-MS (Finnigan MAT, Bremen, Germany) was used Chemical analysis of daughter crystals was carried out for measuring trace and REE elements in a sample under using a MAR-3 WDS microprobe (accelerating voltage of standard operating conditions for these devices. All the 20 kV, a beam current of 40 nA, a beam size of 3–4 µm and above-mentioned investigations were carried out in the 20 s counting time) and scanning electron microscope Vinogradov Institute of Geochemistry and Analytical (LEO-1430) with energy-dispersive spectrometer (Inca Chemistry, SB RAS, Irkutsk, Russia. Energy-300) (SEM-EDS). Strontium isotope values in rubidium-free minerals were measured using an МI-1201 Т mass-spectrometer. The minerals were analyzed using electron probe micro-analysis Geology (EPMA): a MAR-3 WDS microprobe with an accelerating voltage of 20 kV, beam current of 40 nA, beam size of The Khaluta carbonatite complex is a part of a Late 3 μmto4μm and a 20 s counting time, and a LEO-1430 Mesozoic West Transbaikalia carbonatite province (Ripp scanning electron microscope with an IncaEnergy-300 et al. 2002) within an intracontinental rift (volcanic) zone energy-dispersive system (SEM-EDS) operated at 20 kV represented by a large (200–1,000 km) system of grabens and 0.5 nA. All the above analyses were carried out in the and associated fields of Late Mesozoic to Cenozoic laboratories of the Geological Institute SB RAS (Ulan-Ude, volcanic rocks (Yarmolyuk et al. 1995, 2001). The magmat- Russia). ic rocks (including carbonatites) have OIB—EM II mantle The δ13C, δ18O and δ34S values were analyzed in the source characteristics (Yarmolyuk et al. 1998) indicating isotope laboratory of the Analytical Center FESC RAS that their formation was related to mantle plume activity. (Vladivostok, Russia) using a Finnigan MAT 252 sensitive The Khaluta carbonatite complex located 25 km west of mass-spectrometer. The analytical errors for δ18O determi- Ulan-Ude (N 51°51′30.8″; E 107°08′36.8″), comprises nation were ± 0.05‰ or less for carbonates, ± 0.3‰ for calcite and dolomite carbonatites in association with silicates and oxides and ± 0.1‰ for sulphates. The alkaline syenites and shonkinites. Carbonatite outcrops analytical errors for δ13C determination were ± 0.1‰ for extend over an area of approximately 3 km2, with localities Genesis of the Khaluta alkaline-basic Ba-Sr carbonatite complex 247 at (1) Khalutinskii, (2) Verkhne-Khalutinskii, (3) Nizhne- formed as a result of alteration. New investigations Shalutaiskii, (4) Verkhne-Shalutaiskii and (5) Arshan- concur with previous investigations (Ripp et al. 1998, Khalutinskii (Fig. 1). The country rocks to the carbonatites 2000) that the Khaluta carbonatite complex formed by the are granites, quartz syenites and syenites, with outliers of following sequence of events: (1) fenitization of granites, crystalline slate and marble. Granites are fine- and (2) emplacement of alkaline shonkinites and syenites, (3) medium-grained rocks composed of feldspar, quartz, emplacement of carbonatites, with dolomite carbonatite biotite, amphibole with accessory titanite, apatite and post-dating calcite carbonatite, and (4) intense hydrother- muscovite. Sometimes the granites are preferentially mal processes. The hydrothermal processes were responsi- weathered close to carbonatite contacts, into granite gruss ble for the formation of related Sr (strontianite) ore deposit and sand ((1) Khalutinskii and (3) Verkhne-Shalutaiskii (Bulnaev 1997; Ripp et al. 1998). locations). The chemical composition of the host rocks Fenite comprises a network of veinlets that fills fracture was unchanged, but clay minerals (smectite group) zones within, and replaces, granites. Fenites have a variable

Fig. 1 Geology map and cross section of the Khaluta carbonatite complex. 1—conglomerates and sandstones; 2—marbles; 3—crystalline slates; 4—granites; 5—quartz syenites; 6—gabbro; 7—sheets of carbonatites; 8—dykes of carbonatites; 9—dolomite carbonatites; 10—dykes of shonkinites and syenites; 11—faults; 12—carbonatite locations: (1) Khalutin- skii, (2) Verkhne-Khalutinskii, (3) Nizhne-Shalutaiskii, (4) Verkhne-Shalutaiskii, (5) Arshan-Khalutinskii; 13—loca- tion of cross section; 14—drill-holes 248 A.G. Doroshkevich et al. texture from fine to coarse grained and sometimes contain 12, Fig. 2a). Dolomite carbonatites are light yellow rocks apatite-phlogopite rich zones. with massive texture composed of dolomite and calcite. Rb/ Dykes up to 3–5 m in thickness and over 160 m long Sr and U/Pb analysis of the carbonatite yielded ages of are shonkinites and alkaline syenites. The silicate rocks 127 Ma (Bulnaev and Posokhov 1995) and 130±1 Ma are fine- and medium-grained with taxitic texture, and are (Ripp et al. 2009) respectively. composed of K-feldspar, pyroxene, amphibole and biotite. Hydrothermal minerals related to carbonatites are stron- The rocks are characterized by the presence of schlieren, tianite, aragonite, calcite and baryte. In some places, the which are usually zoned and may contain a miarolitic hydrothermal mineralization occurs as diffuse replacements cavity in the core. Rb/Sr and U/Pb analysis of the of minerals in carbonatites and country rocks, but more shonkinites yielded ages of 127 Ma and 126 Ma often it occurs in the carbonatites as fracture fillings and respectively (Ripp et al. 2009). vugs up to a few centimeters in size. Late-stage silicifica- Carbonatite dykes that are associated with the dykes of tion of carbonatites and country rocks is widespread. The alkaline syenites and shonkinites are 1–80 m wide and over process was accompanied by leaching and re-crystallization 300–600 m long (localities 1, 3, 4 and 5) and the sheets of carbonate and sulphate minerals within carbonatites. (probably the remnants of carbonatite bodies after erosion) are up to 650×250 m in size. Sheet thickness is up to 60 m (localities 1, 2 and 5). The contacts of carbonatites with The mineralogy country rocks are sharp and marked by apatite-phlogopite contact zones. Calcite carbonatites are fine- and medium- Temporal relations among minerals in the rocks were grained and have massive, banded and lens-shaped textures documented by textural relationship and petrographic (Fig. 2a). Banded and lens-shaped textures are formed by observations. Below is a short summary of our previous common orientation of apatite-calcite and sulphate assemb- results and most recent findings. lages, and brown and light grey zones and lenses with sharp contacts. Brown zones consist of brown calcite, magnetite, Alkaline metasomatic rocks (fenites) apatite and phlogopite, and light grey zones consist of sulphates and light grey calcite. Sometimes, carbonatites Fine- and coarse-grained fenites are composed of albite, K- have brecciated textures, in which calcite carbonatite feldspar, quartz and amphiboles. Aegerine-diopside, phlog- xenoliths are cemented by dolomite. The xenoliths have opite and apatite are minor minerals. Zircon, titanite, angular shape and are from 0.5 cm to 5 cm in size. allanite, baryte and magnetite are accessory. Albite and Dolomite carbonatites form dykes up to 40 cm thick that aegerine are early minerals followed by K-feldspar and cut calcite carbonatites with sharp contacts (e.g., drill hole richterite. Phlogopite is the last primary mineral to

Fig. 2 Photographs of polished slabs illustrating: a banded textures of Khaluta carbonatites in drill hole 12, where baryte (Bar) occurs as bands and lenses in the calcite (Cal) matrix. The photograph illustrates the contact between dolomite carbonatite (Dol) and calcite carbonatite; b schlieres (Schl) in Khaluta shonkinites Genesis of the Khaluta alkaline-basic Ba-Sr carbonatite complex 249 crystallize. Quartz is a relic mineral from granite country rock. K-feldspar characteristically contains a variable amount of Ba (0 wt.% to 4.15 wt.% BaO). Amphiboles are richterite and hastingsite (Table 1), both of which contain significant K and little Ti. Phlogopite has low Al, Fe and Ti concentration and is rich in Mg (Table 2). Apatite is enriched in Sr, some Si, LREE, Na and Cl (Table 3). Allanite is Fe- and Ti-enriched, and has low Al content (Table 4). REE are dominated by the light elements and the Ce/La, Ce/Nd and La/Nd values are 1.85, 3.18, and 1.72, respectively. Zircon always has an admixture of Hf, up to

1.35 wt.% of HfO2. Magnetite and baryte contain no measurable impurities.

Alkaline syenites and shonkinites

Potash feldspar, aegerine-diopside and amphiboles domi- nate the mineral assemblage, which also contains phlogopite, apatite, titanite, albite, calcite, and celestine as minor minerals, and zircon and allanite as accessory minerals. Potash feldspar constitutes 40–60% of shonkinites and 85– 90% of syenites. The chemical composition of minerals in syenites is similar to that in shonkinites. Both syenites and shonkinites have schlieres (Fig. 2b), enriched in potash feldspar, phlogopite, calcite, celestine, and allanite, as a characteristic feature. The zoned schlieres have a calcite- celestine-allanite core assemblage and a potash feldspar- amphibole-titanite outer assemblage. The surface (boundary) of calcite-celestine is accompanied by a thin shell of phlogopite. Potash feldspar occurs as tabular grains (upto2–4 mm) filling interstices. It contains solid inclusions of pyroxene, phlogopite and titanite and is characteristically enriched in Ba (up to 2.5 wt.% BaO). Aegerine-diopside (Table 5) occurs as orthorhombic grains and contains melt inclusions (see description below). Amphiboles are hastingsite, richterite and riebeckite (Table 1), occurring as grains and also replacing the pyroxene. Hastingsite is magnesium hastingsite, containing up to 7.46 wt% FeO and up to 10.76 wt% Fe2O3. Richterite contains up to 9.31 wt.% FeO and up to 4.70 wt.% Fe2O3. The amphiboles are characteristically potassic and have low Ti concentration. Phlogopite comprises up to 4–6% by volume, disseminated throughout the rock as fine-grained plates and also replacing pyroxene and amphiboles. Phlogopite is poor in Al (Table 2). The average concentrations of FeO and TiO2 are 15.58 wt.% and 1.75 wt.%, respectively. Titanite occurs as fine (up to 0.6 mm) grains containing solid inclusions of apatite and calcite within melt inclusions (see description below). Titanite is enriched in REE (Table 4), of which the LREE are predominant. The 0.14 0.22.44 2.76 0.31 2.01 n.d. 0.75 n.d. 0.74 0.13 1.98 0.07 0.65 0.14 2.16 0.43 2.82 0.32 2.59 n.d. 0.51 0.08 1.56 0.07 1.23 0.47 11.31 12.13 n.d. 11.85 11.16 0.89 11.72 0.88 0.69 Chemical composition of amphibole from rocks of the Khaluta complex, West Transbaikalia RichteriteFenite1 2 Schlieren av from (29) silicate rocks 3 Silicate rocks Silicate rocks 4 Schlieren from silicate rocks Carbonatite (vein) Silicate rocks 5 6 Fenite av Riebeckite (7) 7 8 9 10 av (6) Hastingsite 11 12 av (9) 13 av (4) Ce/La, Ce/Nd and La/Nd values equal 1.92, 1.16, and 0.45, 51.71 51.41 52.29 55.16 55.75 52.51 55.13 51.96 51.21 50.81 56.47 53.51 53.95 40.94 41.22 40.19 40.87 41.87 3 2 2 O 3.79 4.65 4.28 3.84 3.85 4.31 3.44 4.17 6.05 6.3 6.73 5.64 5.89 2.88 2.91 2.91 2.91 2.93 respectively. Apatite is fluorapatite enriched in SO ,NaO, O

3 2 2 O 1.23 1.31 1.33 1.51 1.09 1.4 2.19 1.65 1.55 1.51 0.89 1.66 1.86 1.94 2.41 2.19 2.09 2.12 2 2 BaOF 0.15Total 0.18 99.2 2.24 0.12 99.8 2.01 n.d. - n.d. 97.9 n.d. n.d. 99.9 n.d. n.d. 96.1 - n.d. 96.3 n.d. n.d. n.d. - n.d. 96.2 n.d. 95.7 n.d. 99.8 2.11 n.d. 99.4 - 2.88 n.d. 2.98 n.d. n.d. 96 n.d. - 98 n.d. - 0.1 n.d. 98.4 - - Al FeOMnO 15.01 16MgO 0.52 14.41CaO 0.47 14.75 13.97Na 9.01 13.86 0.49 7.54 18.75 0.32 6.85 7.13 7.97 7.63 21.98 0.19 13.99 8.29 14.2 9.56 0.48 17.19 12.94 14.83 0.4 16.33 12.65 16.52 7.13 12.53 0.47 14.04 15.88 7.62 0.35 0.35 7.05 4.78 0.17 4.78 2.99 12.26 16.11 12.49 16.5 16.64 0.12 10.84 16.29 11.07 17.8 10.68 5.55 17.66 10.44 0.31 17.2 9.98 0.38 4.93 0.38 10.61 0.37 11.59 0.39 10.7 10.45 0.4 10.4 K Table 1 SiO SiO2 and LREE (Table 3), with Ce/La, Ce/Nd and La/Nd TiO 250 A.G. Doroshkevich et al.

values equal to 2.06, 1.03, and 0.43, respectively. Celestine fills interstices and occurs in the core of schlieres. It is characteristically enriched in Ba (up to 6 wt.%). Calcite is associated with celestine and likewise occurs filling interstices and in the core of schlieres, and it also occurs as solid inclusions in titanite. Calcite is rich in strontium and contains an admixture of FeO and MnO (Table 6). Allanite is depleted in iron and enriched in Al compared to the composition of the same mineral in fenites (Table 4). The Ce/La, Ce/Nd and La/Nd values equal 1.99, 3.34, and

av(15) 11 13 av (25) 1.68, respectively.

Carbonatites

The mineral assemblages and composition of minerals in calcite carbonatites, dolomite carbonatites and related hydrothermal mineralization are dissimilar. Calcite carbonatite consists of calcite, Ba-Sr sulphates, magnetite, phlogopite and apatite. Minor and accessory minerals are amphiboles, zircon, monazite, ilmenite, rutile and pyrochlore. In contrast, dolomite carbonatite consists of dolomite and apatite, with baryte, magnetite and calcite as

Silicate rock Schlieren from silicate rocks Fenite minor minerals. Hydrothermal mineralization occurs more intensively in calcite carbonatites than in dolomite carbonatites, and it is distributed from surface outcrop to a depth 6789 10 pf 187 m in drill-holes. The carbonatites contain 0.5–1cm wide hydrothermal veinlets plus disseminations and areas of hydrothermally altered rocks. Strontianite, aragonite, calcite, baryte and allanite are minerals of the hydrothermal assemblage. Formation of hydrothermal mineralization was accompanied by recrystallization of calcite, oxidation of magnetite and leaching of sulphates.

Calcite carbonatites

Calcite makes up 60–80% of carbonatite by volume. It occurs as white fine isometric grains (up to 2–3 mm) and is enriched in Sr, Fe and Mg (Table 6). Calcite is brown in areas that are hydrothermally altered, probably due to oxidation of Fe and Mn. The mineral was recrystallized by hydrothermal processes and became chemically depleted. Sr concentration is either below detection limits or up to 0.23 wt.% SrO. Mg and Fe concentrations (Table 6) were likewise lowered by alteration. Ba and Sr sulphates are baryte and baryte-celestine, which make up 10–15% by volume of rocks and form phenocrysts (1–5 cm). Crystals of the sulphate-rich assemblages are parallel to the banded rock textures (Fig. 2a) and have sharp contacts with the calcite mass. Baryte contains 5–10 wt.% SrO, and baryte- celestine contains equal amounts of the baryte and celestine 41.420.16 42.858.5 42.48 0.17 41.5 9.39 0.15 41.29 0.42 9.77 40.75 10.84 0.39 41.12 10.84 0.5 43.94 11.35 42.4 0.51 11.81 41.28 11.3 0.56 37.45 10.19 36.46 0.63 10.42 39.06 0.72 12.62 37.47 12.79 1.29 11.26 1.74 38.27 1.84 12.54 40.94 41.17 1.33 12.6 39.45 10.92 1.75 11.08 10.79 0.69 0.69 0.93 Carbonatite Sheet1 2 av (29) contact 3 4 Vein 3 4 av (11) contact 5 Chemical composition of mica from rocks of the Khaluta complex, West Transbaikalia end-members. Both minerals consistently occur within 3 2 2 O 0.25 0.44 0.18 0.17 0.14 0.2 0.22 0.16 0.2 0.19 0.21 0.22 0.14 0.16 0.16 0.15 0.11 0.14

O corroded crystal shells that retain their cleavage but that 2 O 9.71 6.31 9.57 10.14 10.01 9.89 10.04 9.96 10.15 10.35 9.84 9.9 9.64 9.72 10.16 10.14 10.12 10.1 2 2 BaOF n.d.Total 97.7 4.34 0.13 95.3 4.06 - - n.d. n.d. 3.32 99.3 3.6 n.d. 98.9 97.9 n.d. 3.79 98.6 3.74 - 3.71 n.d. 4.36 99 n.d. 4.34 98.5 0.33 2.61 96.7 0.58 2.27 0.34 2.33 97.1 97.1 0.71 1.82 96.9 0.29 1.76 0.13 3.34 n.d. 3.02 98.8 3.18 - 98.2 TiO Al FeOMnO 10.08MgO n.d.CaO 6.58 23.14Na n.d. 24.24 0.12 7.19 23.12 13.28 0.17 1.08 19.39 12.98 0.25 0.04 19.44 12.5 0.25 n.d. 18.82 11.23 0.13 19.77 n.d 12.67 18.79 0.12 11.45 n.d. 19.58 11.82 0.21 19.29 n.d. 15.57 0.07 16.56 17.89 14.95 0.1 - 16.05 16.1 16.87 0.22 n.d. 16.01 0.29 n.d. 15.58 0.33 16.22 0.05 12.15 0.32 19.96 11.92 0.04 19.72 11.49 n.d. 19.39 0.27 n.d. 0.27 0.27 - 0.36 0.11 0.06 0.08 K SiO Table 2 have clearly been leached. It is reasonable to assume that eei fteKauaakln-ai aS abntt ope 251 complex carbonatite Ba-Sr alkaline-basic Khaluta the of Genesis Table 3 Chemical composition of apatite and monazite from rocks of the Khaluta complex, West Transbaikalia

Apatite Monazite

Calcite carbonatite Dolomite carbonatites Silicate rocks Fenites Calcite carbonatites

Veins Sheet Veins Sheet

1234av(23) 5 6 av(5) 7 8 av(8) 9 10 av(22) 11 12 13 14 av(11)

SiO2 n.d. 0.09 n.d. 0.34 - 0.078 n.d. 0.13 0.15 0.35 0.66 0.47 0.4 0.57 0.37 0.92 n.d. 0.62 CaO 50.87 51.89 52.32 52.68 53.6 55.18 54.04 53.12 55.62 53.16 55.28 52.79 50.98 54.86 0.27 0.22 0.5 0.45 0.44

Na2O 0.73 0.59 0.43 0.73 0.65 0.59 0.55 0.57 0.23 0.66 0.42 n.d. 0.96 0.27 0.17 0.13 0.15 n.d. 0.14 SrO 1.05 0.86 1.05 0.02 0.51 0.85 0.97 1.01 0.6 n.d. 0.62 1.2 1.44 1.42 - - - - -

Ce2O3 0.28 0.52 0.49 0.49 0.61 0.69 0.7 0.68 0.45 1.26 0.64 0.53 0.61 0.57 34.86 37.23 36.63 36.45 34.52 La2O3 n.d. n.d. n.d. 0.19 0.23 0.22 0.23 0.22 0.23 0.55 0.31 n.d. n.d. - 21 20.33 19.08 21.57 19.76 Pr2O3 n.d. n.d. n.d. n.d. - n.d. n.d. - n.d. n.d. - n.d. n.d. - 2.56 2.73 3.96 3.58 3.68 Nd2O3 n.d. n.d. 0.14 0.5 0.5 0.55 0.51 0.42 0.43 0.89 0.58 0.6 0.56 0.24 7.33 8.94 12.6 11.58 10.91 P2O5 40.54 39.79 39.9 39.24 39.89 40.28 40.12 39.65 40.27 38.28 38.92 41.77 39.87 43.07 29.4 30.21 25.8 25.78 29.37 SO3 1.33 0.43 0.49 1.75 0.98 0.94 0.98 1.13 0.7 1.28 0.97 0.57 1.66 0.77 0.61 0.88 0.83 0.94 0.9 Cl n.d. n.d. n.d. n.d. - n.d. n.d. - n.d. n.d. - n.d. 0.16 0.06 0.24 0.22 n.d. n.d. - F 4.33 3.92 4.29 3.87 4.34 3 3.86 3.85 3.69 3.95 3.75 3.09 3.5 3.2 0.89 0.88 1.21 n.d. 0.99 Total 99.1 98.1 99.4 100 102.4 101.9 102.4 100.7 101.2 100.2 97.9 102.1 101.7 101.4

F=−O2 1.83 1.65 1.81 1.63 1.26 1.63 1.55 1.67 1.3 1.47 0.37 0.37 0.51 - 252 A.G. Doroshkevich et al.

Table 4 Chemical composition of allanite and titanite from rocks of the Khaluta complex, West Transbaikalia

Allanite Titanite

Silicate rocks Carbonatite (vein) Fenite Silicate rocks Fenite

1 2 av(6) 3 4 5 av(10) 6 7 av(16) 8 9 av(16)

SiO2 32.76 32.02 32.33 30.62 28.09 29.84 30.75 28.45 28.53 29.31 29.67 30.88 29.07

TiO2 0.15 0.27 0.39 1.03 1.13 2.17 1.33 34.1 33.19 33.61 33.62 33.14 32.19

Al2O3 17.8 16.81 16.38 10.04 7.37 8.61 7.8 1.42 1.75 2.21 1.84 3.38 1.31

Cr2O3 0.09 0.16 0.13 0.17 n.d. n.d. - n.d. n.d. - n.d. n.d. - FeO 12.41 13.33 13.67 18.09 21.32 19.74 18.26 2.78 2.85 2.61 2.24 1.35 2.28 MnO 0.59 0.54 0.49 0.67 0.5 0.97 0.42 n.d. n.d. 0.1 n.d. 0.38 - MgO 0.54 0.59 0.8 1.42 n.d. 1.18 0.71 n.d. 0.04 0.05 n.d. n.d. - CaO 11.12 10.04 11.53 9.59 9.51 8.97 10.63 26.23 25.84 26.68 26.77 27.18 27.68

Na2O 0.25 0.26 0.21 0.11 n.d. n.d. - 0.09 0.11 0.08 n.d. n.d. - SrO ------0.6 0.3 0.28 n.d. n.d. -

Ce2O3 10.48 11.28 10.61 12.83 13.19 13.39 13.56 1.21 1.1 0.84 n.d. n.d. -

La2O3 5.39 5.51 5.45 7.66 5.58 10.81 7.32 0.36 0.26 0.19 n.d. n.d. -

Pr2O3 1.16 1.16 1.15 1.7 2.21 0.98 1.24 0.22 0.25 0.26 n.d. n.d. -

Nd2O3 3.11 3.35 3.31 3.93 7.17 1.92 4.26 0.58 0.63 0.55 n.d. n.d. 0.13

Sm2O3 0.23 0.22 0.32 0.56 n.d. n.d. - 0.09 0.1 n.d. n.d. n.d. -

Y2O5 ------n.d. 2.12 0.78 Cl 0.06 0.06 0.05 n.d. n.d. n.d. n.d. 0.15 - n.d. n.d. - F 0.38 0.4 0.41 n.d. n.d. n.d. 1.15 1.2 1.29 1.81 1.26 0.68 Total 98.5 98 98.4 96.1 98.6 97.3 96.7 95.9 99.7

F=−O2 0.16 0.17 - - - 0.48 0.51 0.76 0.53 the leached minerals were intergrowths of baryte and/or margins of magnetite crystals. Apatite is fluorapatite, baryte-celestine with water-soluble K and Na sulphates, as enriched in Sr, Na and SO3, similar to apatite from fenites suggested by Doroshkevich et al. (2003) and Doroshkevich and silicate rocks (Table 3). The average total REE and Ripp (2004). Apatite forms as single crystals, making concentration is 1.34 wt.%, which is predominantly LREE. up 1–3% of the segregations that are parallel to the banded The Ce/La, Ce/Nd and La/Nd values equal 3.1, 1.74, and rock textures. There is a higher concentration of apatite 0.73, respectively. Phlogopite occurs as rare disseminations crystals at the contact of carbonatite with country rocks, in the rock, and as zones at the contact of carbonatites with and apatite also occurs as solid inclusions within the country rocks. It has a characteristically high F concentra-

Table 5 Chemical composition of pyroxene from rocks of the Pyroxene Khaluta complex, West Transbaikalia Fenite Silicate rocks Schlieren from silicate rocks

1 2 av(8) 345av(23) 6 7

SiO2 52.35 52.56 52.22 51.46 52.59 52.5 52.46 50.36 50.28

TiO2 0.13 0.45 0.32 0.08 0.07 0.14 0.11 0.2 0.15

Al2O3 0.77 0.83 0.77 0.51 0.8 2.75 2.04 2.08 1.82 FeO 15.1 16.07 16.15 20.76 17.99 12.36 13.61 15.57 15.41 MnO 0.25 0.2 0.2 0.25 0.46 0.31 0.37 0.44 0.43 MgO 8.99 8.15 8.5 5.93 6.85 9.38 9.02 8.27 8.26 CaO 17.2 16.31 17.32 12.9 15.67 18.5 18.27 18.38 18.45

Na2O 4.24 4.39 4.55 5.72 4.9 3.02 3.39 2.98 3.02 Total 99 99 97.6 99.3 98.9 98.3 97.8 eei fteKauaakln-ai aS abntt ope 253 complex carbonatite Ba-Sr alkaline-basic Khaluta the of Genesis Table 6 Chemical composition of carbonates from rocks of the Khaluta complex, West Transbaikalia

Calcite Dolomite

Carbonatite Silicate rock Fenite Carbonatite

Vein Sheet Recrystallized

1 2 av (8) 3 4 5 av (26) 6 7 av (30) 8 9 10 av (8) 10 11 12 13 av (18)

CaO 52.55 52.55 52.67 51.76 51.68 52.26 52.3 54.22 54.59 53.92 53.11 53.01 52.55 53.6 51.6 51.64 30.07 29.23 29.07 MgO 0.59 0.62 0.68 1.17 0.34 0.72 0.84 0.18 0.17 0.22 0.65 0.54 0.61 0.54 n.d. n.d. 17.69 18.69 18.4 FeO 0.93 1.01 0.72 2.62 0.81 0.97 1.03 0.09 n.d. 0.2 0.26 0.31 0.11 0.31 0.16 0.14 3.48 4.01 4.42 MnO 0.63 0.65 0.5 0.33 0.37 0.6 0.18 1.34 0.92 0.81 0.29 0.26 0.11 0.47 0.14 0.14 0.51 0.55 0.58 SrO 1.22 1.56 1.43 1.11 0.57 1.37 0.97 0.16 n.d. 0.12 1.35 1.46 1.65 1.16 1.56 1.75 0.59 0.68 0.42 BaO n.d. n.d. - n.d. n.d. n.d. - n.d. n.d. - n.d. n.d. n.d. - n.d. n.d. n.d. n.d. - Total 55.9 56.4 56.9 53.8 55.9 55.9 55.7 55.7 55.6 55 53.5 53.7 52.3 53.2 Molar %

CaCO3 93.54 93.54 92.13 91.99 93.02 96.51 97.17 94.53 94.36 93.54 91.85 91.92 53.52 52.03 MgCO3 1.23 1.3 2.45 0.71 1.5 0.38 0.36 1.36 1.13 1.27 - - 36.97 39.06 FeCO3 1.5 1.63 4.22 1.3 1.56 0.14 - 0.42 0.5 0.18 0.26 0.23 5.6 6.46 MnCO3 1.02 1.05 0.53 0.6 0.97 2.17 1.49 0.47 0.42 0.18 0.23 0.23 0.83 0.89 SrSO3 1.73 2.22 1.58 0.81 1.95 0.23 - 1.92 2.07 2.34 2.22 2.49 0.84 0.97 254 A.G. Doroshkevich et al.

tion (Table 2) and contains up to 3 wt.% Fe2O3,andupto and range in size from 4 µm to 55 µm. At room 3.49 wt.% of FeO. Average Al2O3 concentration is temperature, they contain up to 60–80 vol.% daughter 9.93 wt. %, although in some analyses it is lower (e.g. minerals and a gas bubble making up to 10 vol.%. The rest

8.50 wt% Al2O3). In this case, mineral composition is similar of the space is filled by liquid. Titanite contains not only to tetraferriphlogopite. Magnetite forms as octahedral crystals multiphase (crystallized melt) but also solid calcite inclusions. up to 5–7 cm that contain a solid inclusion assemblage of Calcite (with rounded shapes) contains Sr up to 1 wt.% SrO. phlogopite, apatite and zircon. Magnetite is low in titanium Melt inclusions in titanite are similar to those in pyroxene—

(up to 0.50 wt% TiO2) but contains fine ilmenite lamellae. they are isolated, no larger than 10–15 µm, and contain up to Sometimes rutile and hematite develop within metailmenite 10 vol.% gas phase at room temperature. The liquid phase lamellae as a result of oxidation. Ilmenite contains apprecia- amounts to no more than 5–7 vol.%. The rest (65–80 vol.%) is ble Mg (mean 3.22 wt.% MgO), Mn (mean 5.74 wt.% MnO) occupied by daughter minerals. Owing to the scarcity of large and Zn (up to 2 wt.% ZnO). Amphiboles are richterite and melt inclusions, only a few daughter phases were analyzed in riebeckite (Table 1) that occur as single grains. Richterite melt inclusions from pyroxene and titanite using EMPA and contains lower titanium and higher magnesium in carbona- SEM-EDS. These phases are potash feldspar, phlogopite, tites than in alkaline basic rocks and fenites. Monazite, zircon anhydrite, calcite, Ba-rich celestine and pectolithe (?) and pyrochlore are accessory minerals. Monazite occurs in (Table 8). The chemical composition of phlogopite is similar parts of the rocks that are enriched in apatite. It contains to that in shonkinites, although one analysis shows a higher appreciable SO3 (Table 3) and has Ce/La, Ce/Nd and La/Nd concentration of F (up to 4.5 wt.%) and the amount of F is values equal to 1.74, 3.16 and 1.81, respectively. Zircon similar to that in mica from carbonatites. The presence of contains solid inclusions of apatite that are also enriched in SO3 in the mineral is unusual and might be due to trapping SO3 (up to 1.2 wt.% SO3). of the element from other daughter minerals (anhydrite, celestine). Dolomite carbonatite On heating, the gas phase dissolved at 330–340°С in melt inclusions from pyroxene. One group of phases (probably Dolomite is the most abundant mineral (90–95%) and is Fe- salts) within the assemblage of daughter minerals began to and Sr-rich (Table 6). The composition of apatite in dissolve at 247°С, and the remaining phases were unaltered dolomite carbonatite is similar to that in calcite carbonatite up to 400°С. Some inclusions did not homogenize as they (Table 3). The Ce/La, Ce/Nd and La/Nd values equal 3.09, decrepitated at 400°C. For the remainder, inclusions were 1.62 and 0.52, respectively. heated at 1,000°С under 0.5 GPa confining pressure. On quenching, the partially (?) homogenized inclusions were Related hydrothermal mineralization composed of glass and a heterogeneous fluid phase (Fig. 3d). The fluid phase amounted to 10–20 vol.%, and was Strontianite, calcite, aragonite, baryte and celestine are heterogeneous due to the presence of microcrystalline hydrothermal minerals. Strontianite is Ca-rich (up to aggregates (salts ?). Some inclusions in pyroxene that were 16.34wt% CaO). Calcite contains up to 0.83 wt.% of MgO not modified to glass after heating and quenching comprised and up to 0.04 wt% of FeO, and Sr and Mn are below microcrystalline aggregates (salts ?) and a spherical or detection limits. Baryte contains no Sr, and celestine has low deformed fluid bubble. Melt inclusions in titanite were also Ba (up to 1.00 wt.% BaO). Both baryte and celestine occur heated at 1,000°С and 5 kbar confining pressure. After without having been subject to leaching, in contrast to quenching, these inclusions contained glass and a fluid carbonatite. bubble (Fig. 3c), which occupied up to 10 vol.%. These data and our previously published findings (Ripp The composition of glasses in inclusions from pyroxene et al. 1998, 2000) were used to construct a generalized and titanite was analyzed but the microcrystalline aggre- paragenetic table (Table 7), for crystallization of rock- gates were lost during polishing of the inclusions and their forming minerals throughout the history of the carbonatite compositions are not known. Glasses of melt inclusions in complex (e.g. phlogopite, calcite, sulphates, apatite, mag- pyroxene contain variable concentrations of Mg, Si, Ca and netite, amphiboles). Fe (Table 8). This may be due to the small size of the areas of glass (2–3 μm), such that the results reflect partial inclusion of host aegirine in the analyzed area. The

Melt inclusions omission of H2O and/or CO2 from the list of chemical components included in the analysis accounts for the low Melt inclusions have been found in pyroxene (aegerine- totals presented in Table 8. The silicate glass in pyroxene- diopside) and titanite from shonkinites (Fig. 3a, b). hosted inclusions is silica undersaturated (Table 8), and rich

Inclusions in pyroxene are solitary, multiphase inclusions in alkalis (Na2O>K2O, with Na2O/K2O ratios between 4.7 Genesis of the Khaluta alkaline-basic Ba-Sr carbonatite complex 255

Table 7 Simplified paragenetic sequence for the mineral assemblages in rocks of the Khaluta carbonatite complex

Minerals Fenites Shonkinites Syenites Calcite carbonatites Dolomite carbonatites Related hydrothermal mineralization Aegerine Albite Potash feldspar fldPhlogopite fld Calcite Ba, Sr sulphates Apatite Titanite Allanite Richterite Hastingsite Ribecite Magnetite Zircon Monazite Pyrochlore Dolomite Strontianite Aragonite

and 5.7), SO3 and Cl. The composition is analogous to Geochemistry and bulk rock chemistry melanephelinite, with nepheline, wollastonite, diopside, orthoclase and calcite as normative minerals. The compo- Fenites sition of titanite-hosted glass is similar to that of Khaluta alkaline syenite (Table 8). Comparison of glass composition Fenites are potassic (Na2O

Fig. 3 Photographs of melt inclusions from Khaluta silicate rocks at room temperature in a pyroxene and b titanite, and after homogenization and chill- ing in c titanite and d pyroxene. M: glass, G:gas bubble, L: liquid, S: solid phases (probably salts) 256 Table 8 Composition of daughter minerals and glasses from melt inclusions in minerals of shonkinites and syenites

Glass in pyroxene Glass in titanite Daughter minerals from inclusion in pyroxene Daughter minerals from inclusion in titanite

Micas Anhydrite Celestine Pectolite (?) Anhydrite Calcite Celestine Potash feldspar

SiO2 46.46 41.79 41.28 58.15 59.49 56.31 36.73 37.93 31.72 3.76 2.17 2.16 n.d. n.d. 58.2 0.37 1.34 0.92 n.d. 59.14 59.34 TiO2 0.46 0.51 0.55 3.27 2.04 3.25 n.a. n.a. n.a. n.a. n.a. n.a. n.d. n.d. n.d. 0.29 1.27 0.12 n.d. 0.67 1.27 Al2O3 5.37 5.61 5.56 16.35 17.08 16.05 12.61 12.92 10.9 0.65 0.29 0.29 n.d. n.d. n.d. n.d. 0.16 n.d. n.d. 16.65 21.26 FeO 10.22 9.40 9.03 3.77 4.07 3.98 12.89 13.59 13.41 1.27 0.76 0.75 n.d. n.d. n.d. 0.10 0.30 0.11 n.d. n.d. n.d. MnO 0.47 0.36 0.55 n.d. n.d. n.d. 0.32 0.28 0.28 n.d. 0.05 n.a. n.d. n.d. n.d. n.d. 0.26 0.11 n.d. n.d. n.d. MgO 3.31 1.14 1.25 0.67 0.63 0.56 16.37 16.89 14.86 1.00 0.62 0.62 n.d. n.d. n.d. n.d. 0.23 n.d. n.d. n.d. n.d. CaO 14.09 10.87 10.94 4.00 2.40 3.71 1.44 0.53 0.40 35.09 35.94 35.97 n.d. n.d. 23.82 42.45 54.35 52.55 n.d. n.d. 0.83

Na2O 11.69 11.87 11.48 3.98 4.25 4.04 0.26 0.15 0.18 0.012 0.14 0.14 n.d. n.d. 15.30 n.d. 0.22 0.27 n.d. 0.71 0.55 K2O 2.04 2.12 2.43 6.76 7.21 6.92 9.36 10.03 8.83 0.75 0.25 0.25 n.d. n.d. n.d. 0.05 0.09 n.d. n.d. 16.15 12.95 P2O5 n.d. n.d. n.d. n.d. n.d. n.d. n.a. n.a. n.a. n.a. n.a. n.a. n.d. n.d. n.d. 0.09 n.d. n.d. n.d. n.d. n.d. BaO 1.94 2.48 2.23 n.d. n.d. n.d. 0.47 0.09 0.61 n.d. 0.05 n.a. 20.04 20.38 n.d. n.d. n.d. n.d. 14.95 n.d. n.d. SrO 1.82 2.32 2.09 n.d. n.d. n.d. n.d. n.d. n.d. 3.33 2.99 2.97 33.04 32.74 n.d. n.d. n.d. 1.65 38.93 n.d. n.d. F n.d. n.d. n.d. n.d. n.d. n.d. 4.54 n.d. n.d. n.d. n.d. n.a. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d.

SO3 0.43 0.51 0.45 n.d. n.d. n.d. 0.54 0.17 1.29 52.28 54.54 56.48 39.74 39.14 n.d. 55.51 n.d. n.d. 44.39 n.d. n.d. Cl 0.42 0.73 0.69 n.d. 0.13 n.d. n.a. n.a. n.a. n.a. n.a. n.a. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. Total 98.7 89.7 88.5 96.9 97.3 94.8 95.5 92.6 82.5 98.1 97.8 99.6 92.8 92.3 97.3 98.8 58.22 55.73 98.3 93.3 96.2

The deficit of analytical totals of some analyses is probably due to exclusion of CO2,H2O from the analyses, and imperfect polishing of daughter minerals (as the inclusions are difficult to prepare) ..Drskvc tal. et Doroshkevich A.G. Genesis of the Khaluta alkaline-basic Ba-Sr carbonatite complex 257

Table 9 Representative chemical composition of rocks from the Khaluta carbonatite complex

Calcite carbonatite Dolomite carbonatite Fenite Silicate rocks

Sheet Vein

Weight percent

SiO2 1.12 8.05 7.6 1.2 1.25 59.9 67.43 56.76 48.37 63.20

TiO2 0.02 0.11 nd nd nd 0.59 0.46 0.64 1.36 0.43

Al2O3 0.1 1.5 0.1 nd nd 15.2 15.48 11.08 12.95 14.40

Fe2O3 4.6 0.34 0.42 1.47 2.14 3.93 2.43 7.28 2.61 1.16 FeO 0.32 1.92 2.7 1.28 1.2 1.13 1.8 1.41 MnO 0.26 0.16 0.49 0.47 nd 0.09 0.04 0.2 0.1 0.07 MgO 0.62 3.84 13.26 6.14 6.07 2.87 0.98 7.29 3.6 0.80 CaO 33.87 18.62 28 35.36 37.6 3.38 1.0 4.78 8.87 2.60

Na2O 0.06 0.13 0.04 0.09 0.07 3.63 4.25 2.82 3.05 4.34

K2O 0.03 1.7 0.02 0.02 0.02 7.64 7.1 6.94 6.56 8.27

P2O5 0.94 4.8 1.46 1.3 1.27 0.84 0.13 1.3 2.4 0.12 LOI 29.83 10.01 35.52 33.64 1.22 0.33 0.47 2.24 1.99 total 71.77 51.18 89.61 80.97 49.62 99.34 99.98 99.9 93.91 98.79 S 4.61 4.56 1.92 2.75 nd 0.74 0.12 F 0.09 1.23 0.16 0.14 0.24 0.38

CO2 23.52 9.46 34.51 30.03 30.59 0.22 1.20 1.32 ppm Be 0.4 0.8 0.2 <0.1 0.1 7.9 4.6 10.5 3.5 4.6 Sc 1.4 1.1 1.9 1.9 2.4 9.5 4.4 22.7 9.5 8.1 V 15.8 12.0 10.8 4.8 1.7 54.8 21.3 58.9 82.9 57.5 Co 2.0 3.0 1.7 3.7 3.3 7.0 3.3 12.8 16.3 9.6 Cu 9.2 17.5 8.9 60.5 18.6 Ga 0.8 5.2 1.2 0.9 1.7 15.1 13.1 15.5 20.2 18.5 Rb 76.4 166.6 148.6 168.2 46 160 Sr 78390 16788 31814 64542 65849 857 553 523 20650 1644.5 Y 14.3 51.2 18.1 14.9 14.9 33.0 19.9 26.2 28 32 Zr 23.6 5.5 1.2 7.2 14.8 366.9 221.8 324.0 760 556 Nb 1.1 9.9 0.047 <0.05 6.7 39.6 39.0 70.6 11 10 Mo 9.7 0.4 2.3 6.5 6.3 0.6 1.0 0.5 0.4 0.4 Ba 74713 109083 22240 34151 35385 6300 1820 2057 23020 5900 La 450.4 1058.3 250.9 298.1 304.8 163.6 73.3 139.9 146.9 113.9 Ce 571.4 1672.4 540.7 492.6 433.5 564.1 173.2 433.2 373.8 307.8 Pr 67.0 205.3 73.4 61.5 55.0 86.2 21.2 59.3 61.9 49.7 Nd 237.6 754.7 295.2 239.3 242.2 359.8 73.0 248.2 263.1 207.1 Sm 30.3 106.5 41.5 32.7 34.0 50.6 10.7 39.8 41.1 31.7 Eu 11.9 30.5 10.8 11.3 11.6 11.6 2.2 8.8 9.4 7.5 Gd 18.6 57.7 20.6 17.2 15.9 32.0 6.2 21.3 21.1 15.7 Tb 1.3 5.0 1.9 1.4 1.1 2.0 0.7 1.3 1.8 1.4 Dy 4.2 14.7 5.2 4.6 5.3 9.3 4.0 7.0 7.2 5.2 Ho 0.6 2.2 0.7 0.6 0.7 1.3 0.7 1.0 1.0 0.7 Er 1.1 3.9 1.3 1.1 1.2 3.1 1.9 2.5 2.0 1.6 Tm 0.1 0.5 0.1 0.1 0.1 0.4 0.3 0.3 0.2 0.2 Yb 0.9 2.0 0.4 0.6 0.6 2.4 1.8 1.9 1.6 1.2 Lu 0.1 0.2 0.1 0.1 0.1 0.3 0.3 0.3 0.2 0.1 Hf 0.4 0.3 0.1 0.2 0.4 9.2 5.9 8.4 9.35 6.98 Ta 0.1 0.3 0.039 0.014 0.6 0.9 1.7 1.5 0.23 0.16 258 A.G. Doroshkevich et al.

Table 9 (continued)

Calcite carbonatite Dolomite carbonatite Fenite Silicate rocks

Sheet Vein

W 53.9 0.6 1.5 1.2 0.7 0.2 0.3 0.3 0.7 0.15 Pb 45.2 265.6 24.9 30.8 35.7 26.6 35.0 23.3 70 26 Th 0.6 6.2 0.7 0.5 0.7 32.7 48.7 32.6 6.12 5.83 U 1.6 8.9 0.4 2.9 2.8 4.1 3.6 10.2 1.82 0.94 Ti nd nd nd nd nd 6817.0 2411.0 3511.0 nd nd Cr nd nd nd nd nd 74.5 4.8 41.3 nd nd Ni nd nd nd nd nd 49.9 8.5 40.2 nd nd Zn nd nd nd nd nd 112.8 42.5 222.4 nd nd Ge nd nd nd nd nd 1.2 0.9 1.5 nd nd Sn nd nd nd nd nd 1.8 2.0 1.6 nd nd Cs nd nd nd nd nd 2.0 2.4 3.4 nd nd Tl nd nd nd nd nd 0.9 0.6 1.0 nd nd

sulphate minerals. Fenites are characterized by a strong housed within potash feldspar, while Sr and SO3 are located enrichment in LREE (Fig. 5) with La/Yb=62. Average Nb/ within celestine. Average Nb/Ta, Y/Ho and Zr/Hf ratios in Ta, Y/Ho and Zr/Hf ratios are 50, 26 and 39, respectively. shonkinites and syenites are 47, 28, 81, and 62, 45, 80, respectively. The rocks have elevated REE content, which is Alkaline syenites and shonkinites housed in the minerals apatite, titanite and allanite. The LREE are more highly concentrated than the HREE with La/ Representative analyses of syenites and shonkinites are given Yb=92: the REE pattern, normalized to primitive mantle, is in Table 8. The rocks are alkali-rich, with potassium reasonably level from La to Pr and Er to Lu but decreases predominating (Na2O\K2O—0.3–0.7). Syenites contain less sharply from Nd to Ho (Fig. 5). The silicate rocks have a Mg, Ca, P, Fe, Ba and Sr, and more Si and Al than similar REE profile to fenites and, to a lesser degree, shonkinites (Table 9). However, both lithologies have carbonatites. elevated Ba, Sr, Th, Hf, Zr, Nb and Ta contents on the mantle-normalized trace element spiderdiagram (Fig. 4). Ba is Carbonatites

The carbonatites are characterized by low silica and alkali contents (Table 9), and strong enrichment in LREE with

Fig. 4 Primitive mantle-normalized patterns showing the abundance Fig. 5 Primitive mantle-normalized plot of the REE in the Khaluta of selected elements in the Khaluta carbonatites, associated silicate carbonatites, associated silicate rocks and fenites (whole-rock sam- rocks and fenites. Primitive mantle values are from McDonough and ples), (primitive mantle values from McDonough and Sun 1995). Sun (1995) Abbreviations are the same as in Fig. 4 Genesis of the Khaluta alkaline-basic Ba-Sr carbonatite complex 259 steep REE patterns (Fig. 5) that show negligible negative are consistent with those in silicate minerals from shonkin- Ce and Sm peaks relative to other LREE; average La/Yb= ites and carbonatites. One value for phlogopite from the 515 in calcite carbonatite, and 542 in dolomite carbonatites. contact of carbonatite with country rock is higher, which is These ratios are higher than those in silicate rocks and probably due to a late stage process (chloritisation) that 18 fenites. The characteristic Ba, Sr and SO3 enrichment of the involved some isotopic exchange. δ О values in magnetite carbonatites is reflected in the presence of Ba and Sr from shonkinites and carbonatites are comparable with sulphates. The concentration of SO3 is five times higher in those from the same mineral from carbonatites at Jacupir- Khaluta carbonatites than in average carbonatites (Woolley anga (Santos and Clayton 1995). δ18О VSMOW for apatite and Kempe 1989). The carbonatites are strongly enriched in is quite homogenous (5.4‰ to 5.8‰) and is also similar to LILE, particularly Sr, Ba, LREE, but not in HFSE=Ti, Zr, values reported for apatite from carbonatites at Jacupiranga Hf, relative to primitive mantle (Fig. 4). Compared to (Santos and Clayton 1995), Angola (Alberti et al. 1999), silicate rocks and fenites, the carbonatites have relatively Penchenga (Vrublevskii et al. 2003), Pogranichnoe and low concentrations of Hf, Zr, Th, Rb, Nb and Ta, and Veseloe (Doroshkevich et al. 2007), Precambrian carbona- higher Ba, Sr and LREE content, but nevertheless all tites from the Kola province (Tichomirowa et al. 2006), and Khaluta lithologies have similar relative enrichments and from the West Transbaikalia apatite-bearing basic rocks depletions of trace elements. Average Nb/Ta, Y/Ho and Zr/ (our unpublished data). Hf ratios in carbonatite are 21, 23 and 37, respectively, and Carbon and oxygen isotopic values for calcite from are similar to or below, the primitive mantle values of 18, syenite and shonkinite and samples of fresh calcite 29 and 37, respectively (McDonough and Sun 1995). carbonatite (Fig. 6) plot in the field of primary igneous carbonatites (Taylor et al. 1967; Keller and Hoefs 1995). The position of the values for dolomite indicates Rayleigh Carbon, oxygen, sulphur and strontium isotope isotope fractionation during magma crystallization. The composition hydrothermally altered carbonatites have an enrichment in δ18О (11.17 to 14.57) relative to the fresh carbonatites that The δ18О VSMOW and δ13C VPDB isotopic compositions is consistent with theoretical calculations and experimental were determined in calcite and dolomite from shonkinites data for isotope fractionation between vapour and melt and syenites, calcite and dolomite carbonatites, related (Appora et al. 2003; Chacko et al. 2001). Minerals from hydrothermal mineralization and marbles. Carbon and related hydrothermal rocks are more enriched in δ18О oxygen stable isotope analyses are given in Table 10 and (13.67 to 17.42) and slightly depleted in δ13C(−5.36 shown graphically in Fig. 8. δ34S CDT was obtained for to −9.54), which has probably been caused by a degassing sulphate minerals from shonkinites, carbonatites and related process, where the residual C was depleted in δ13C. hydrothermal mineralization. Initial 87Sr/86Sr ratios were According to Nikiforov et al. (1998), surface water determined in whole rocks and non-Rb-bearing minerals. containing organic carbon was most likely responsible for δ18О VSMOW values were obtained for phlogopite, the secondary alteration and isotopic composition shift of O richterite, aegerine, magnetite, potash feldspar and apatite. and C in carbonatites. But this explanation does not fit with δ34S CDT values and initial 87Sr/86Sr ratios are also listed the other isotopic data, as silicate and oxide minerals from in Table 10. New data is presented here, and compared to all Khaluta rocks would have to have undergone a similar that previously published in the literature (Nikiforov et al. change of Sr, S, O isotope values. 1998; Ripp et al. 1998). δ34S CDT values in sulphate minerals from shonkinites, Initial 87Sr\86Sr ratios in calcite, dolomite and baryte- carbonatites and related hydrothermal rocks are 9.5–13.0‰. celestine from carbonatites are 0.70548–0.70594. The ratios They are similar to sulphates from carbonatites of the West are similar to shonkinites and syenites of the Khaluta Transbaikalia (Ripp et al. 2000) and from many other complex (0.705706–0.705893; Nikiforov et al. 2000) and carbonatites worldwide (Deines 1989). δ34S CDT values in strontianite from related hydrothermal rocks, and all results sulphates from inclusions are also displayed in Table 10. fall within the range of values for the late Mesozoic The values are comparable with data from the same continental basalts of the West Transbaikalia obtained by minerals from shonkinites and carbonatites. Gordienko et al. (1999). δ18О values in phlogopite, richterite, aegerine, magnetite, potash feldspar and apatite from calcite carbonatites Temperature calculations and shonkinites are similar to mantle-derived silicate minerals, and their values correspond to oxygen isotope Mineral and isotopic thermometers, and thermometry of fractionation into crystallizing minerals (Chacko et. al. inclusions were used to calculate the temperature of 2001). δ18О values in phlogopite and richterite from fenites carbonatite and shonkinite formation. 260 A.G. Doroshkevich et al.

Table 10 Isotopic composition of О, С and Sr in minerals from Khaluta carbonatites, West Transbaikalia

Analyzed material δ13С‰VPDB δ18О‰VSMOW δ34S‰CDT 87Sr/86Sr

Shonkinites Silicate minerals (Nikiforov et al. 1998) 6.4 Silicate minerals (Nikiforov et al. 1998) 6.3 Silicate minerals (Nikiforov et al. 1998) 5.6 Aegerine 4.7 Phlogopite 5.6 Phlogopite 4.5 Potash feldspar 6.3 Calcite (Nikiforov et al. 1998) −4.5 9.61 Calcite (Nikiforov et al. 1998) −5.4 10 Calcite (Nikiforov et al. 1998) −5.5 10.3 Sulphates (Nikiforov et al. 1998) 10.7 Sulphates (Nikiforov et al. 1998) 12.6 Celestine 12.2 0.70607 Magnetite (Nikiforov et al. 1998)1 Magnetite (Nikiforov et al. 1998) −0.5 Alkaline syenites Silicate minerals (Nikiforov et al. 1998) 6.2 Calcite (Nikiforov et al. 1998) −5.8 9.9 Magnetite (Nikiforov et al. 1998) 0.5 Phlogopite 5.8 Potash feldspar 7.2 Fenite Richterite 5 Phlogopite 5.7 Calcite carbonatites Calcite −6.2 9 Calcite −5.9 8.3 Calcite −5.9 9.1 Calcite −5.5 5.4 0.70566 Calcite −5.9 8.4 0.70567 Calcite −5.9 8.3 Calcite −5.9 9.1 Phlogopite 6.2 Phlogopite 5.1 Phlogopite 5.3 Phlogopite 7.8 Apatite 5.8 Apatite 5.4 Recrystallised calcite carbonatite Calcite −5.37 12.89 0.70548 Calcite −5.3 12.41 Calcite −4.9 14.57 0.70583 Calcite −6.2 10.8 Calcite −6.5 12.1 Calcite (Nikiforov et al. 1998) −6 9.5 Calcite (Nikiforov et al. 1998) −5.5 10.7 Calcite (Nikiforov et al. 1998) −6 9.3 Sulphates 9.5 0.7059 Genesis of the Khaluta alkaline-basic Ba-Sr carbonatite complex 261

Table 10 (continued)

Analyzed material δ13С‰VPDB δ18О‰VSMOW δ34S‰CDT 87Sr/86Sr

Sulphates 12.3 0.70593 Sulphates (Nikiforov et al. 1998) 13 Sulphates (Nikiforov et al. 1998) 11.3 Sulphates (Nikiforov et al. 1998) 10.2 Magnetite 5.9 Magnetite 0.9 Magnetite 2.2 Magnetite 2.2 Apatite 6.4 Dolomite carbonatites Dolomite −4.33 8 Dolomite −4.61 7.71 Dolomite −4.3 10.24 Dolomite −4.3 11.17 Dolomite −4.6 10.37 Dolomite −4.2 11.37 Dolomite −4.6 9.3 Dolomite (Nikiforov et al. 1998) −4.7 9 Hydrothermal rocks Calcite −9.06 17.42 Calcite −9.54 17.06 Strontianite −8.05 13.67 0.70581 Strontianite −7.26 16.25 Strontianite −5.36 13.84 Strontianite −6.37 16.26 Strontianite −7.1 14.8 Barite 10.9 0.70594 Barite 11.2 Sulphates from inclusions 12.6 11.7

The clinopyroxene-melt geothermometer was used for temperature=657°C). Lower temperatures (448–616°C) the calculation of the temperature of shonkinite formation were calculated by Nikiforov et al. (1998), who obtained (Putirka et al. 1996). Given an aegirine composition and an δ18О values for recrystallised calcite in Khaluta cabonatites. average melt composition calculated from 12 bulk rock The calcite-dolomite thermometer (Anovitz and Essene analyses of shonkinite and four analyses of glass from 1987) yields temperatures of carbonatite formation from inclusions, the minimum temperature of formation corre- 474°C to 611°C: determination of the exact temperature sponds to 915–916°С. Partial (?) homogenization of melt was not possible because the dolomite and calcite were not inclusions in minerals from shonkinites occurred at co-existing minerals, with calcite as the early crystallizing 1,000°С, and corresponds to a minimum temperature of phase before dolomite. Calculations for calcite carbonatites formation for the host minerals. using the early crystallized apatite—phlogopite pair It is possible to estimate the crystallization temperature (Ludington 1993) gave temperatures of formation of of calcite carbonatites using the difference in δ18O between approximately 750°C. Apatite-magnetite and magnetite- magnetite (Table 10) and calcite (using the calcite- phlogopite isotopic thermometers (Chacko et al. 2001) magnetite formula of Chiba et al. 1989). δ18О values for gave temperatures of 782°С and 829–897°С, respectively, calcite from fresh carbonatites (8.3–9.1‰)andδ18О values for the early crystallized minerals (apatite, magnetite, for magnetite (0.9–2.2‰) have been used for calculation. phlogopite) from calcite carbonatite. The Fe-Ti oxide The difference varies from 6.1 to 8.2 (mean difference=6.8) geothermometer of Powell and Powell (1977), Spencer and corresponds to a temperature of 572–710°C (mean and Lindsley (1981) and Andersen and Lindsley (1985) 262 A.G. Doroshkevich et al.

fluid that was fractionated from a syenitic magma, and (2) immiscible liquid separation from a common parental magma. The formation of carbonatites by derivation from a carbothermal fluid has been investigated by Nielson and Veksler (2002), and Mitchell (2005). According to experimental investigations of fluid-melt partitioning behavior (Webster et al. 1989; Keppler and Wyllie 1991), fluid inclusion studies (Bühn and Rankin, 1999; Bühn et al. 2002, 2003) and empirical data (Chakhmouradian et al., 2008), carbothermal fluid should have Rb/Sr, Y/Ce, and Nb/Th ratios higher than those in the silicate melt, whereas their Y/Zr values should be comparable. Additional characteristic features of carbonatitic fluids are high-alkali and comparatively low-Ca contents (Na + K/Ca = 5.7), high Cl/F value and higher solubility of U than that of Th in the Fig. 6 Isotope composition of carbon and oxygen (in ‰ relative to V- fluids. The Khaluta carbonatites have enhanced U/Th but PDB and V-SMOW, respectively) in the Khaluta carbonatites. Calcite have many other geochemical characteristics that conflict — carbonatite* is recrystallised. The primary carbonatite box PIC with the established geochemical signature of a carbother- (Taylor et al. 1967, Deines 1989) is shown for reference mal fluid. Compared to silicate magmas, the carbonatite has extremely low Na+K/Ca (< 0.1); Rb/Sr, Y/Ce and Nb/Th ratios are also lower, and Y/Zr is higher. In addition, this was applied to the magnetite-ilmenite pair and yielded a scenario does not fit with isotopic evidence. Oxygen and temperature of between 496°C and 535°C. Oxygen fugacity carbon isotope fractionation between CO2 vapor and was estimated from the composition and temperature of silicate melt varies within 2–4‰; these large fractionations formation of the magnetite-ilmenite pair (QUILIF-95 and are the result of temperature-dependence (Appora et al. ILMAT-1.20 programs). The oxygen fugacity values varied 2003;Chackoetal.2001). The minerals from fresh from (−20.18) to (−23.22) and lie near HM buffer. carbonatites and silicate rocks of the Khaluta complex have similar primary magmatic δ13C and δ18O values and do not show vapour-melt fractionation. However, hydrothermally Discussion altered (recrystallized) carbonatites have a distinctly heavy- isotope enriched signature that is in good agreement with In summary, alkaline silica-undersaturated rocks and fractionation in fluid-carbonatite melt system (see Isotope carbonatites have similar ages and similar geochemical section). characteristics. The silicate rocks contain pyroxene Silicate-carbonate liquid immiscibility has been studied crystals that have melanephelinite composition melt in numerous experiments (e.g.: Kjarsgaard and Hamilton inclusions and schlieren that have a mineral assemblage 1989; Kjarsgaard 1998; Brooker 1998; Lee and Wyllie reminiscent of the carbonatites. The carbonatites contain 1998; Wyllie and Lee 1998) and it has effectively been segregations of sulphate-rich mineral assemblages and all demonstrated that there is a restricted range of liquid lithologies contain evidence that SO3 activity was high. compositions that are associated with carbonate-silicate Thus, field relations, mineralogical and geochemical data liquid immiscibility. Figure 7 shows liquid composition and age determinations imply that the Khaluta alkaline from the Khaluta complex (as represented by glass from silicate rocks, carbonatites and fenites are broadly coeval melt inclusions in titanite and aegerine of shonkinites, and and have a common magma source. To evaluate the the average composition of shonkinites and carbonatites) in petrogenesis of the Khaluta complex it is necessary to first comparison with the range of possible immiscible liquid unravel the evolution of the magma and its source compositions. The slopes of the silicate-carbonate tie-lines characteristics, testing alternative mechanisms of carbo- for the Khaluta Complex are similar to those for the natite formation. experimentally determined miscibility gap in the carbonated high-CaO nephelinite system at 0.5 GPa (Kjarsgaard 1998). Are carbonatites of the Khaluta complex a product of liquid The major element evidence therefore suggests that the immiscibility or carbothermal fluid? carbonatites of the Khaluta complex can be attributed to liquid immiscibility from a carbonate-saturated parental Two possible processes of formation are considered here for silicate (basic) melt with subsequent crystal differentiation the Khaluta carbonatite: (1) derivation from a carbothermal of the carbonatite melt after segregation. Liquid immisci- Genesis of the Khaluta alkaline-basic Ba-Sr carbonatite complex 263

Fig. 7 Compositions of average shonkinite (Sh), dykes of fresh et al. 1979). The silicate-carbonate miscibility gap for high-Ca calcite carbonatites (Sl), average calcite carbonatite (Ca), average nephelinite at 0.5 GPa (Kjarsgaard 1998) is shown. LS, silicate melt; glass from pyroxene inclusions (Pi), and average glass in inclusions LC, carbonate melt from titanite (Ti) plotted onto the Hamilton projection (after Hamilton

bility as a model for generation of the Khaluta complex is earth elements, against ionic potencials Z/r, (Fig. 9) further supported by the convergence of multiple and varied delineate a convex curve for the Khaluta complex with lines of evidence: a maximum at Sr, which is similar to curves for experimental data (Suk 2003) and for carbonate-silicate 1. The close spatial relationship and similar age (130 Ma partition coefficients in synthetic systems (Kjarsgaard and 126 Ma, respectively) of carbonatites and 1998; Veksler and Lentz 2006). schonkinite-syenite rocks. 7. The REE patterns of carbonatites are similar to those 2. Textural evidence: the presence of schlieren with calcite for the silicate rocks. The carbonatites have slightly and celestine in shonkinites, and solid inclusions of greater total REE enrichment and LREE/HREE frac- rounded calcite in minerals from silicate rocks. tionation than the silicate rocks, which is consistent 3. The composition of the minerals in shonkinites and with liquid immiscibility (e.g. Hamilton et al. 1989). carbonatites (phlogopite, calcite, apatite, sulphates, 8. A close genetic relationship between carbonatites and magnetite) is similar. For example, apatite in all of the silicate rocks of the Khaluta complex is also indicated Khaluta lithologies is enriched in Si, Na, Sr, SO , and 3 by their similar Sr, S, C and O isotopic composition. LREE; calcite is Sr-rich; phlogopite is Al-poor. 4. Melt inclusions in minerals from shonkinites and Separation of carbonatite from a carbonate-saturated syenites contain Sr-bearing calcite and Ca, Ba and Sr parental silicate melt was followed by crystal differentia- sulphates; their chemical composition is similar to that tion, such that the separated carbonatite melt evolved from in carbonatites. Homogenization of the inclusions a calcite to a dolomite melt, and subsequent hydrothermal appears to occur by a process that is similar to liquid processes. Textural features (lenses and layers with sharp immiscibility, though this hypothesis requires further contacts) and mineral associations for calcite carbonatites investigation. indicate that there was primary heterogeneity in the 5. The composition of the carbonate liquids produced in carbonatite liquid at Khaluta, due to the presence of two the experiments of Kjarsgaard (1998), shown in Fig. 7, phases, a phosphorus-rich and a sulphate-rich phase. was poor in alkalis but rich in P, F, Ba and Sr. These Sulphate-carbonate-silicate systems for the Khaluta com- characteristics are typical of Khaluta carbonatites. plex were experimentally studied (Suk 2003), and it was

6. Two-liquid trace element partitioning between silicate shown that Ba, Sr and SO3 accumulate in carbonate phases; rocks and carbonatites from Khaluta (Nb—0.5; Ta— their partition coefficients (D) are greater than one. 0.43; Zr—0.03; Hf—0.02; Nd—1.0) is similar to Moreover, the heterogeneity of carbonate and salt- published experimental data (Hamilton et al. 1989; carbonate (phosphate-, sulphate-carbonate) liquids that Veksler et al. 1998; Suk 2003). Although Sr and Ba was observed in these experimental products suggests the (Sr—3.27; Ba—4.75) are lower, and Sm (0.9), Tb possibility of a further evolution of a salt phase after its (0.85) and Y (0.57) are higher in the Khaluta separation from silicate melt. lithologies, the trace element patterns show identical slope (Fig. 8) to curves for carbonate-silicate immisci- Petrogenetic model and crystallization history ble melts from some experimental data (Veksler et al. 1998) and natural systems (Schultz et al. 2004). In A petrogenetic model for the formation of the Khaluta addition, calculated D values of the alkali and alkaline carbonatite complex as constrained by field, mineralogical, 264 A.G. Doroshkevich et al.

Fig. 8 Carbonate-silicate partitioning values for trace elements in rocks of the Khaluta complex (1) and comparison to data obtained for Cerro Sapo (Schultz et al. 2004) carbonatite complex (2), and experimental data (Veksler et al. 1998) with a REE-rich starting composition (3) and a HFSE-rich starting composition (4)

petrographical and published experimental studies, is the parental melt and subsequently evolved independently. illustrated in Fig. 10. There are multiple lines of evidence The immiscibly-separated silicate liquid evolved from for liquid immiscibility at Khaluta as well as the fact that shonkinites to syenites with separation of residual our data is consistent with experimental studies at 1,025°C sulphate-carbonate phases and formation of schlieres and 0.5 GPa (Fig. 7) that showed that carbonate liquid was (Fig. 2b). Emplacement of the silicate rocks was accompa- generated by liquid immiscibility from a high-Ca nephelin- nied by fenitisation of country rocks. Crystallization of the ite liquid (Kjarsgaard 1998). Glass inclusions suggest that earliest minerals (zircon, magnetite, phlogopite, apatite) in the parental carbonate-saturated silicate melt at Khaluta was the immiscibly-separated carbonate liquid occurred at 890– probably a melanephelinite that was enriched in Ba, Sr, 780°C. Crystallization of the carbonate liquid to calcite

REE, SO3 and F. Mineral and isotopic thermometers and carbonatite preceded crystallization to dolomite carbonatite, melt inclusions showed that crystallization of the first solid during cooling through the temperature interval 750–470° phases (pyroxene) in the carbonate-saturated parental C. Emplacement of carbonatites was accompanied by the silicate melt at Khaluta occurred above 915–1,000°C and ascent of fluids that resulted in the formation of phlogopite 5 kbar. Carbonate and silicate magmas then separated from zones. Formation of carbonatites was also accompanied by hydrothermal circulation of late stage subsolidus fluids which variously altered the C and O isotopic compositions of the affected carbonatites (Fig. 6) and formed veinlets of strontianite, aragonite, calcite and baryte. REE mineral (apatite, monazite, allanite) compositions and REE patterns for bulk rocks at Khaluta allow us to elucidate the REE distribution during the evolution of the complex. The data show that Ce/La and Ce/Nd ratios increase in REE minerals from fenite, through silicate rocks to carbonatites. La/Nd ratios are similar with a small decrease from calcite to dolomite carbonatites, which probably reflects an early- to late-stage evolution in the carbonatite-forming systems (Zaitsev et al. 1998;Fleischer1978; Doroshkevich et al. 2008). The REE patterns (Fig. 5) illustrate that silicate rocks and fenites are LREE-enriched but not as enriched as the carbonatites: chondrite-normalised plots are reasonably level from La to Nd and from Er to Lu. La/Yb ratios increase from Fig. 9 Carbonate-silicate liquid-liquid partition coefficients for alkali fenite, through silicate rocks, to carbonatites. It is consistent and alkaline earth elements in Khaluta natural system (average data), with REE partitioning between silicate and carbonate liquids where Z is the nominal charge of the metal cation, and r is the ionic in the experiment systems (e.g. Hamilton et al. 1989), where radius (after the method of Veksler and Lentz 2006). Synthetic systems are from Suk (2003), Veksler and Lentz (2006), and LREE are relatively more abundant in the carbonate melt Kjarsgaard (1998) than the HREE. Genesis of the Khaluta alkaline-basic Ba-Sr carbonatite complex 265

Fig. 10 Petrogenetic model for the Khaluta complex

The geometry of emplacement bodies and the fine- indicated by the presence of sulphates in melt inclusions grained texture of rocks suggest that the Khaluta complex in minerals from silicate rocks and by the presence of SO3 crystallized at shallow subvolcanic depths. The composi- in apatite and monazite from all Khaluta lithologies. tion of micas and amphiboles can be used as indicators of According to experiments by Barker and Rutherford (1996), the conditions of crystallization within a magma. For SO3-rich apatite can crystallize from SO3-enriched silicate +3 2+ example, tetraferriphlogopite crystallizes from melt with a melt. A high SO3 content, in addition to high Fe /Fe low aluminum content and total iron content dominated by ratios in the Khaluta parental melt and calculated fO2 in Fe+3, which testifies to a high oxygen fugacity (e.g. Santos magnetite indicates that formation conditions included a high and Clayton 1995). Micas of the Khaluta carbonatites are oxygen fugacity. This is in accordance with the experimental high-Mg (fm =0.85) tetraferriphlogopites and chemical and petrological data of Katsura and Nagashima (1974), analyses testify to the fact that micas, as well as Carroll and Rutherford (1987), and Luhr (1990), who amphiboles, have more ferrous than ferric iron. Total iron determined a high oxygen fugacity for sulphate-bearing is lower in mica from carbonatites than from fenites, which magmas. is lower again than in silicate rocks. A similar trend is Formation of West Transbaikalia carbonatite rock observed for titanium concentration, greatest in micas from associations (including the Khaluta complex) was con- silicate rocks, lower in fenite, to lowest in carbonatite. The trolled by the Lower Selenga mantle plume that was fed high magnesium content of micas from all the Khaluta from mantle of EM-II type (Yarmolyuk et al. 2001). lithologies attests to the relatively low total iron content of According to Nikiforov et al. (2002) the silicate rocks the parental melt. This is also supported by a low iron associated with the carbonatites of the Khaluta complex content in carbonatite (lower than in average carbonatite; have higher concentrations of Ba, Pb, LREE and Sr, and Woolley and Kempe 1989), dolomite and amphiboles much lower concentrations of Nb and Ta, than the basalts

(riebeckite and richterite with Fm =0.7). The fluorine that predominate in the volcanic area, with a distinctly content in mica increases from silicate rocks, to fenite, different Nd and Sr isotopic composition. Yarmolyuk and then to carbonatites. According to experimental data by (Yarmolyuk et al. 2001, 2002) and Nikiforov (Nikiforov Edgar and Arima (1985), the amount of fluorine increases et al. 2002) have concluded that these differences seem to in phlogopite with decreasing crystallization temperatures, have been produced by the mixing of two isotopically independent of pressure. heterogeneous (“tephritic” and “carbonatitic”)sources.In The carbonate-saturated parental silicate (basic) melt addition to this finding, we have concluded that the at Khaluta was enriched in SO3, Ba and Sr. The activity “carbonatitic” source was SO3-rich and characterized by a of the elements can be observed in all of the Khaluta high oxygen fugacity level. Other localities that may be lithologies (fenites, shonkinites and syenites, calcite and similar in this respect to West Transbaikalia SO3-rich dolomite carbonatites, and hydrothermal mineralization) carbonatite complexes are the Mountain Pass (USA), by the formation of sulphates (baryte, celestine and baryte- Mushugai-Khuduk and Bayan-Hoshuu (Mongolia) alkaline- celestine). SO3–enrichment in the parental melt is also basic carbonatite complexes. 266 A.G. Doroshkevich et al.

Conclusion Brooker RA (1998) The effect of CO2 saturation on immiscibility between silicate and carbonate liquids: an experimental study. J Petrol 39:1905–1915 Interpretation of geological and geochronological data, Bulnaev KB (1996) Strontianite carbonatites of Khaluta, West Trans- textural features of rocks, melt inclusion data, and miner- baikalia, Russia. Geol ore depos 38(5):437–448 alogical, geochemical and isotopic data of the Khaluta Bulnaev KB (1997) Possibility for find of abundant resources of – rocks has allowed us to draw the following conclusions strontianite ores in Buryatia. Expl Preserv Res 4:11 12 Bulnaev KB, Posokhov VF (1995) Isotopic and geochemical data concerning their origin. about nature and age of carbonate rocks of Transbaikalia. The alkaline-basic carbonatite Khaluta complex is the Geochem Int 2:189–196 product of liquid immiscibility from a carbonate-saturated Bühn B, Rankin AH (1999) Composition ofnatural, volatile-rich Na– – – parental silicate melt with crystallization beginning at 915– Ca REE Sr carbonatitic fluids trapped in fluid inclusions. Geo- chim Cosmochim Acta 63:3781–3797 1,000°C. Crystallization of the earliest minerals (apatite, Bühn B, Rankin AH, Schneider J, Dulski P (2002) The nature of magnetite, phlogopite) from the carbonate liquid occurred orthomagmatic, carbonatitic fluids precipitating REE, Sr-rich at 897–750°C. The parental carbonate-saturated silicate fluorite: fluid-inclusion evidence from the Okorusu fluorite – – melt was a melanephelinite that was enriched in Ba, Sr, deposit, Namibia. Chem Geol 186(1 2):75 98 Bühn B, Schneider J, Dulski P, Rankin AH (2003) Fluid–rock REE, F and significantly in SO3. The activity of these interaction during progressive migration of carbonatitic fluids, elements can be observed in all of the Khaluta lithologies: derived from small-scale trace-element and Sr, Pb isotope from fenites, through shonkinites and syenites, to calcite distribution in hydrothermal fluorite. Geochim Cosmochim Acta – and dolomite carbonatites, and to hydrothermal mineraliza- 67:4577 4595 Carroll MR, Rutherford MJ (1987) The stability of igneous anhydrite: tion. Formation conditions included a high oxygen fugacity. experimental results and implications for sulfur behavier in the Carbonate and silicate magmas were separated from the 1982 El Chichon trachyandesite and other evolved magmas. J parental melt and subsequently evolved independently. The Petrol 28:781–801 immiscibly-separated silicate liquid evolved from shonkin- Chacko T, Cole DR, Horita J (2001) Equilibrium oxygen, hydrogen and carbon isotope fractionation factors applicable to geological system, ites to syenites. The separated carbonatite melt evolved Stable isotope geochemistry. Rev Mineral Geochem 43:1–62 from a calcite to a dolomite melt, with subsequent Chakhmouradian AR, Mumin AH, Demeny A, Elliott B (2008) hydrothermal processes. There was primary heterogeneity Postorogenic carbonatites at Eden Lake, Trans-Hudson Orogen in the carbonatite melt at Khaluta, due to the presence of (northern Manitoba, Canada): Geological setting, mineralogy and geochemistry. Lithos 103(3–4):503–526 two phases, a phosphorus-rich and a sulphate-rich phase. Chiba H, Chacko T, Clayton RN, Goldsmidth JR (1989) Oxygen The alkaline-basic carbonatite Khaluta complex, and isotope fractionations involving diopside, forsterite and calcite: other carbonatites of the West Tranabaikalia carbonatite applications to geothermometry. Geochim Cosmochim Acta – province, represent a good and natural example of SO -rich 53:2985 2995 3 Dalton JD, Wood BJ (1993) The composition of primary carbonate subvolcanic carbonatites. melts and their evolution through wall rock reaction in the mantle. Earth Planet Sci Lett 119:511–525 Acknowledgements We are grateful to Ilya Veksler for his review Deines P (1989) Stable isotope varition in carbonatites. In: Bell K (ed) which led to significant improvement of manuscript and are indebted Carbonatites: genesis and evolution. Hyman, London, pp 301–359 to the anonymous referees for constructive reviews. Doroshkevich AG, Ripp GS (2004) Estimation of the conditions of The studies have been carried out with the support of the Integral formation of REE-carbonatites in Western Transbaikalia. Russ project of RAS (ОNZ 10.3), RFFR (grant 08-05-98028) and INTAS Geol Geophys 45(4):492–500 grant 05-1000008-7938. Doroshkevich AG, Kobylkina OV, Ripp GS (2003) The role of sulphates in formation of the West Transbaikalia carbonatites. Dokl Earth Sci 388(4):535–539 Doroshkevich AG, Wall F, Ripp GS (2007) Magmatic graphite in References dolomite carbonatite at pogranichnoe, North Transbaikalia, Russia. Contrib Mineral Petrol 153:339–353 Alberti A, Castorina F, Censi P, Comin-Chiaramonti P, Gomes CB Doroshkevich AG, Ripp GS, Viladkar SG, Vladykin NV (2008) The (1999) Geochemical characteristics of Cretaceous carbonatites Arshan REE carbonatites, southwestern Transbaikalia: mineralo- from Angola. J Afr Earth Sci 29:735–759 gy, paragenesis and evolution. Can Mineral 46:807–824 Andersen DJ, Lindsley DH (1985) New (and final) models for the Ti- Edgar AD, Arima M (1985) Fluorine and chlorine contents of magnetite/ilmenite geothermometer and oxygen barometer. Ab- phlogopites crystallized from ultrapotassic rock compositions in stract AGU 1985 Spring Meeting Eos Transactions. AGU 66 high pressure experiments: implication for halogen reservoirs in (18):416 source regions. Am Mineral 70:529–536 Anovitz LM, Essene EJ (1987) Phase equilibrium in the system Fleischer M (1978) Relative proportions of the lanthanides in minerals – CaCO3–MgCO3–FeCO3. J Petrol 28:389–414 of the basntasite group. Can Mineral 16:361 363 Appora I, Eiler JM, Matthews A, Stolper EM (2003) Experimental Gordienko IV, Bayanov VO, Klimuk VS, Ponomachuk BA, Travin determination of oxygen isotope fractionations between CO2 AV (1999) Composition and age of volcanic rocks of Chikoy- vapor and soda-melilite melt. Geochim Cosmochim Acta Hilokskoy rift depression in Transbaikalia. Russ Geol Geophys 67:459–471 40(4):583–591 Barker LL, Rutherford MJ (1996) Crystallisation of anhydrite-bearing Hamilton DL, Freestone IC, Dawson JB, Donaldson CH (1979) magmas. Trans R Soc Edinb Earth Sci 87:243–250 Origin of carbonatites by liquid immiscibility. Nature 279:52–54 Genesis of the Khaluta alkaline-basic Ba-Sr carbonatite complex 267

Hamilton DL, Bedson P, Esson J (1989) The behaviour of trace elements Putirka K, Johnson M, Kinzler R, Longhi J, Walker D (1996) in the evolution of carbonatites. In: Bell K (ed) Carbonatites: genesis Thermobarometry of mafic igneous rocks based on clinopyroxene- and evolution. Hyman, London, pp 405–427 liquid equilibrium, 0.3 kbar. Contrib Mineral Petrol 123:92–108 Harmer RE, Gittins J (1998) The case for primary, mantle-derived Rass IT, Abramov SS, Utenkov VA, Kozlovskiy VM, Korpechkov DI carbonatite magma. J Petrol 39:1895–1903 (2006) Role of fluid in the genesis of carbonatites and alkaline Hay RL, O’Neil JR (1983) Carbonatite tuffs in the Laetolil beds of rocks: geochemical evidence. Geochem Int 7:692–711 Tanzania and the Kaiserstuhl in Germany. Contrib Mineral Petrol Ripp GS, Khodanovich PYu, Smirnova OK, Kobylkina OV (1998) 82:403–406 Khaluta Ba-Sr carbonatites, BSC SB RAS, Ulan-Ude, 117 p. (in Katsura T, Nagashima S (1974) Solubility of sulfur in some magmas Russian) at 1 atm pressure. Geochim Cosmochim Acta 38:517–531 Ripp GS, Kobylkina OV, Doroshkevich AG, Sharakchinov AO (2000) Keller J, Hoefs J (1995) Stable isotope characteristics of natrocarbo- Late Mesozoic carbonatites of the West Transbaikalia, BSC SB natites from Oldoinyo Lengai. In: Bell K, Keller J (eds) RAS, Ulan-Ude, 224 p. (in Russian) Carbonatite volcanism: Oldoinyo Lengai and the petrogenesis Ripp GS, Platov VS, YuP G, Kobylkina OV, Doroshkevich AG (2002) of natrocarbonatites 113–123 A new alkali basic carbonatite complex in the West Trans- Keppler H, Wyllie PJ (1991) Partitioning of Cu, Sn, Mo, W, U, and Th baikalia. Otechestvennaya geologia 5–6:9–16 between melt and aqueous fluid in the systems haplogranite– Ripp GS, Doroshkevich AG, Posokhov VF (2009) Ages of Trans- H2O–HCl and haplogranite–H2O–HF. Contrib Mineral Petrol baikalia carbonatites. Petrology 17(6):79–96 109:139–150 Roedder E (1983) Fluid inclusions. Review in mineralogy, vol. 12. Kjarsgaard BA (1998) Phase relations of a carbonated high-Ca Miner. Soc. America nephelenite at 0, 2 and 0, 5 GPa. J Petrol 39:2061–2075 Romanchev BP, Sokolov SV (1980) Liquation in the production and Kjarsgaard BA, Hamilton BA (1989) The genesis of carbonatites by geochemistry of rocks in carbonatite complexes. Geochem Int immiscibility. In: Bell K (ed) Carbonatites: genesis and evolu- 16:125–135 tion. Hyman, London, pp 388–404 Samoilov VS, Kovalenko VI (1983) Alkaline silicate-carbonatite Lee W, Wyllie PJ (1998) Petrogenesis of carbonatite magmas from complexes of Mongolia Moscow-Nauka, 199 p. (In Russian) mantle to crust, constrained by the system CaO-(MgO + FeO)- Santos RV, Clayton RN (1995) Variations of oxygen and carbon (Na2O+K2O)-(SiO2 +Al2O3 +TiO2)-CO2. J Petrol 39:495–517 isotopes in carbonatites: a study of Brazilian alkaline complexes. Ludington S (1993) The biotite-apatite geothermometer revisited. Am Geochim Cosmochim Acta 59:1339–1352 Mineral 63:551–553 Schultz F, Lehmann B, Tawackoli S, Rössling R, Belyatsky B, Dulski P Luhr JF (1990) Experimental phase relations of water- and sulfur (2004) Carbonatite diversity in the Central Andes: the Ayopaya saturated are magmas and the 1982 eruptions of El Chichon alkaline province, Bolivia. Contrib Mineral Petrol 148(4):391–408 Volcano. J Petrol 31:1071–114 Sobolev VS, Kostyuk VP (1975) Data of melt inclusions study: Mariano AN (1989) Nature of economic mineralization in carbonatites application for magmatic crystallization Novosibirsk-Nauka, 232 and related rocks. In: Bell K (ed) Carbonatites: genesis and (in Russian) evolution. Chapman & Hall, London, pp 149–176 Spencer KJ, Lindsley DH (1981) A solution model for coexisting McDonough WF, Sun S (1995) The composition of the Earth. Chem iron-titanium oxides. Am Mineral 66(11–12):1189–1201 Geol 120:223–253 Suk NI (2003) Experimental investigation of fluid-magmatic differ- Mitchell RH (2005) Carbonatites and carbonatites and carbonatites. entiation of alkaline systems with the connection of carbonatite Can Mineral 43:2049–2068 genesis problem. In: Vladykin NV (ed) Plumes and problems of Nielson TFD, Veksler IV (2002) Is natrocarbonatite a cognate fluid deep sources of alkaline magmatism. Publishing House of the condensate? Contrib Mineral Petrol 142:425–435 Institute of Geography SB RAS, pp. 115–129 Nikiforov AV, Yarmolyuk VV, Pokrovskii BG, Kovalenko VI, Ivanov Taylor HP, Frechen J, Degens ET (1967) Oxygen and carbon isotope VG, Ripp GS (1998) Isotopic composition of oxygen, carbon, and studies of carbonatites from the Laacher See district, West sulfur in rocks from the Khalyuta volcanic carbonatite complex, the Germany and the Alno district, Sweden. Geochim Cosmochim Western Transbaikal Region. Dokl Earth Sci 363 A(9):1311–1314 Acta 31:407–430 Nikiforov AV, Yarmolyuk VV, Pokrovskii BG, Kovalenko VI, Ivanov Tichomirowa M, Grosche G, Gotze J, Belyatsky BV, Savva EV, Keller J, VG, Andreeva IA, Zhuravlev DZ, Ripp GS, Vladykin NV, Todt W (2006) The mineral isotope composition of two Precembrian Korshunov VV (2000) Late Mesozoic Carbonatites of Western carbonatite complexes from the Kola alkaline province—alteration Transbaikalia: Mineralogical, Chemical, and Isotopic (O, C, S, versus primary magmatic signatures. Lithos 91:229–249 and Sr) Characteristics and Relationships to Alkaline Magma- Veksler IV, Lentz D (2006) Melt inclusions in carbonate-rich magmas. tism. Petrology 8(3):278–302 In: Webster J (ed) Melt inclusions in plutonic rocks. Mineralog- Nikiforov AV, Yarmolyuk VV, Kovalenko VI, Ivanov VG, Zhuravlev ical Association of Canada 123–151 DZ (2002) Late Mesozoic carbonatites of Western Transbaikalia: Veksler IV, Petibon C, Jenner GA, Dorfman AM, Dingwell DB (1998) isotopic–geochemical characteristics and sources. Petrology 10 Trace element partitioning in immiscible silicate–carbonate liquid (2):146–164 systems: an initial experimental study using a centrifuge Olson JC, Shawe DR, Pray LC, Sharp WN (1954) Rare-earth mineral autoclave. J Petrol 39:2095–2104 deposits of the Mountain Pass district San Bernardino County, Vrublevskii VV, Pokrovskii BG, Zhuravlev DZ, Anoshin GN (2003) California, Washington, p. 74 Composition and age of the Penchenga linear carbonatite Otto JW, Wyllie PJ (1993) Relationships between silicate melts and complex, Yenisei range. Petrology 11:130–147 carbonate-precipitating melts in CaO–MgO–SiO2–CO2–H2O at Wallace ME, Green DH (1988) Experimental determination of 2 kbar. Mineral Petrol 48:343–365 primary carbonatite magma composition. Nature 335:343–346 Panina LI (2005) Multiphase carbonate–salt immiscibility in carbonate Webster JD, Holloway JR, Hervig RL (1989) Partitioning of lithophile melts: data on melt inclusions from the Krestovskiy massif trace elements between H2O+CO2 fluids and topaz rhyolite minerals (Polar Siberia). Contrib Mineral Petrol 150:19–36 melt. Econ Geol 84:116–134 Powell R, Powell M (1977) Geothermometry and oxygen barometry Woolley AR (2003) Igneous silicate rocks associated with carbona- using coexisting iron-titanium oxides. Mineral Mag 41 tites: their diversity, relative abundances and implications for (318):257–263 carbonatite genesis. Period Mineral 72:9–17 268 A.G. Doroshkevich et al.

Woolley AR, Kempe DRC (1989) Carbonatites: nomenclature, average Cenozoic (geochemical and isotope-geochemical data). Petrology chemical composition, and element distribution. In: Bell K (ed) 6(2):115–138 Carbonatites: genesis and evolution. Hyman, London, pp 1–14 Yarmolyuk VV, Nikiforov AV, Kovalenko VI, Ivanov VG, Zhuravlev Wyllie PJ, Lee W-J (1998) Model system controls on conditions for DZ (2001) Sources of the late mesozoic carbonatites of Western formation of magnesiocarbonatite and calciocarbonatite magmas Transbaikalia: trace-element and Sr–Nd isotopic data39. Geo- from the mantle. J Petrol 3:1885–1993 chem Int 39(Suppl 1):S60–S78 Yarmolyuk VV, Kovalenko VI, Ivanov VG (1995) Intraplate volcanic Yarmolyuk VV, Kovalenko VI, Sal’nikova EB, Budnikov SV, province of Asia (late MZ-KZ)—projection of mantle hot spot. Kovach VP, Kotov AB, Ponomarchuk VA (2002) Tectono- Geotectonics 5:41–67 magmatic zoning, magma sources, and geodynamics of the Yarmolyuk VV, Kovalenko VI, Ivanov VG, Vladykin NV, Nikiforov early mesozoic mongolia-transbaikal province. Geotectonics 36 AV, Ripp GS (1997) Late-Mesozoic volcanic carbonatites of (4):293–312 Transbaikalia. Dokl Earth Sci 355:659–663 Zaitsev AN, Wall F, Le Bas MJ (1998) REE-Sr-Ba minerals from the Yarmolyuk VV, Ivanov VG, Kovalenko VI (1998) Sources of Khibina carbonatites, Kola Peninsula, Russia: their mineralogy, intraplate magmatizm in West Transbaikalia in Late Mesozoic- paragenesis and evolution. Mineral Mag 62(2):225–250

View publication stats