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Article

Unusual Mineralogy of Kimberlites: Alkali Carbonates, Sulfates, and Chlorides Among Groundmass Minerals from Unserpentinized Coherent Kimberlite of the Udachnaya-East Pipe, Siberian Craton

by
Alexander V. Golovin
V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch Russian Academy of Sciences, 630090 Novosibirsk, Russia
Minerals 2025, 15(6), 586; https://doi.org/10.3390/min15060586
Submission received: 28 January 2025 / Revised: 11 May 2025 / Accepted: 14 May 2025 / Published: 30 May 2025
(This article belongs to the Section Mineral Geochemistry and Geochronology)
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Abstract

The paper reports the first findings of a series of alkali carbonate, chloride, and sulfate minerals among the usual groundmass kimberlite minerals, such as olivine, phlogopite, monticellite, calcite, spinel-group minerals, perovskite, ilmenite, rutile, and apatite. The sample was collected from an unserpentinized coherent kimberlite dyke that crosscuts earlier volcaniclastic kimberlite in the central part of the Udachnaya-East pipe. This rock can be described as primary/original kimberlite that did not interact with external/internal hydrothermal fluids either during its formation or after its crystallization. At least three alkali-rich carbonates have been found, a previously unknown (and perhaps, a new one) Na-, Ca-, K-, and S-rich carbonate with the calculated empirical formula (Na,K)6Ca4(CO3,SO4)7, shortite Na2Ca2(CO3)3, and nyerereite (Na,K)2Ca(CO3)2. Chlorides in this kimberlite are halite NaCl and sylvite KCl, and the sulfate is aphthitalite K3Na(SO4)2. The content of the Na-Ca-K-S-rich carbonate in the rock is ~15 vol %, that of shortite and halite is ≤5 vol % each, and those of sylvite and aphthitalite are ≤1 vol %. All alkali-rich minerals are of late magmatic origin. This follows from that (i) the studied kimberlite does not contain any secondary water-rich minerals of hydrothermal transformation of the rocks, such as serpentine, chlorite or iowaite; and (ii) crystalline inclusions of such usual kimberlite minerals as olivine, phlogopite, monticellite, calcite, spinel, perovskite, and apatite were found within Na-Ca-K-S-rich carbonate and halite. This publication expands the list of minerals of magmatic origin identified in the groundmass of worldwide kimberlites by at least three minerals: Na-Ca-K-S-rich (new?) carbonate, sylvite, and aphthitalite. It is important to note that all alkali carbonates, chlorides, and sulfates are unstable during secondary hydrothermal alterations of kimberlites, and hence, these minerals cannot be found in serpentinized rocks.

1. Introduction

Kimberlites are ultramafic rocks of igneous origin that are surrounded by a certain aura of mystery because they are the world’s main source of gem-quality diamonds. However, the diversity of kimberlite pheno/microphenocryst and matrix mineralogy appears to be quite limited. The dominant rock-forming minerals of more than 99% of kimberlites worldwide are silicates such as serpentine, olivine, monticellite, micas, as well as carbonates (calcite and dolomite). Kimberlites usually contain minor amounts (less than 10%) of such oxides as spinel-group minerals of various composition, perovskite, ilmenite, and rutile; and the phosphates are usually apatite (e.g., [1,2]). The accessory minerals (<1%) of kimberlites are such sulfides as pyrrhotite, pentlandite, chalcopyrite, and the quite exotic K- and Cl-rich sulfide djerfisherite (e.g., [1,3]). The dominant rock-forming mineral of kimberlites is serpentine/olivine, whose concentrations are typically ~25–50 vol % and sometimes even higher. Statistically, in many cases, kimberlites are fully serpentinized rocks. Even when kimberlites contain more olivine than serpentine, i.e., in so-called “fresh” hypabyssal kimberlite (e.g., [4,5,6]), the mineralogy of the matrix of these rocks is limited to the list of minerals mentioned above.
Studies of melt inclusions hosted in various minerals of kimberlites from three cratons (Siberian, North American, and Kaapvaal) have shown that these inclusions contain, in addition to such usual kimberlite minerals (e.g., olivine, micas, calcite, dolomite, oxides, and sulfides), also and assemblage of alkali-rich carbonates, sulfates, and chlorides. (e.g., [7,8,9,10,11,12,13]). The alkali carbonates of these inclusions are mostly nyerereite and shortite; the sulfates are aphthitalite and arcanite; and the halides are mostly halite and subordinate amounts of sylvive (see Table 3 in review [14]). Olivine in the mantle xenoliths of sheared peridotites from kimberlites (the Udachnaya-East and Komsomolskaya–Magnitnaya pipes in the Siberian craton and the Bultfontein pipe in the craton Kaapvaal) hosts secondary melt inclusions, which contain an assemblage of daughter minerals that is generally identical to that in melt inclusions in kimberlite minerals, i.e., the former inclusions host assemblages of both usual kimberlite minerals and alkali carbonates, sulfates, and chlorides [15,16,17,18]. This type of mantle xenoliths is deemed to represent the deepest-sitting mantle rocks, and the melt inclusions themselves are thought to present snapshots of primitive kimberlite melts. Olivine and spinel from a xenolith of granular garnet–spinel lherzolite from the V. Grib kimberlite pipe, East European craton, have been found to host secondary melt inclusions, whose daughter phases include alkali carbonates, sulfates, and chlorides [19]. Hence, it would have been reasonable to anticipate the assemblage of alkali-rich carbonates, sulfates, and chlorides in the kimberlite matrix, which is, however, not the case, and no such association has been found so far in the groundmass of any kimberlite, except only unserpentinized kimberlites from the Udachnaya-East pipe.
It should be mentioned that worldwide kimberlites are occasionally documented to contain alkali-rich carbonate, most of which were poorly identified, the origins of these carbonates are uncertain, and these minerals are so unusual in kimberlites that they have not attracted much attention from researchers who study kimberlites. For example, shortite Na2Ca2(CO3)3 was first found as a matrix mineral in serpentine-poor kimberlite dikes in the Upper Canada Gold Mine [20]. The other two finds of Na-bearing carbonate in insignificantly serpentinized kimberlite (from the Mir pipe) and unserpentinized one (from the Internationalnaya pipe) kimberlites did not yield stoichiometric analyses. Neither Raman spectroscopic studies of the minerals have been conducted, and the authors believe that this Na-bearing carbonate can be shortite [21,22]. Note that Na-rich carbonates were found in kimberlites in the Siberian craton only at deep levels of Borehole 56 (at depths of 760–810 m) drilled through the Mir pipe and at a depth of 1080 m in the Internationalnaya pipe.
Most individual finds of alkali carbonates or alkali carbonates in association with chlorides were performed in various kimberlites (both unserpentinized and poorly serpentinized) in the eastern body of the Udachnaya pipe. Shortite was first documented in 1981 as a mineral in the mesostasis of serpentine-poor kimberlite from the Udachnaya-East pipe, from a depth of 400–450 m [23]. After this find, a new mineral, so called zemkorite [24], a hexagonal-system mineral whose empirical formula is (Na1.8K0.29)Ca1.1(CO3)1.93, which is close in composition to nyerereite (Na1.64K0.36)(Ca0.95Sr0.05)(CO3)2, was found in 1988 at the same depths (400–450 m) in the Udachnaya-East pipe. Zemkorite is a fairly mysterious mineral, and many aspects of its structure and origin remain uncertain and will be discussed below. All early finds of alkali carbonates [23,24] in the Udachnaya-East pipe were performed in samples from the borehole core material. In the early 2000s, the opencast mine at the Udachnaya-East pipe exposed a block of unserpentinized volcaniclastic kimberlite at a depth of approximately 410 m. Its detailed descriptions can be found in, for example, [25,26]. Such rocks had been previously described as hypabyssal porphyritic kimberlite. The rocks of the block contain chloride–carbonate and chloride «nodules/segregations» [27,28], 5 to 30 cm across, which are unusual for any worldwide kimberlites.
No conventionally accepted name has been coined so far for such unusual segregations and mineral assemblages in kimberlites, or any other magmatic rocks, because they have been found and described only in the Udachnaya-East pipe. The carbonate–chloride nodules contain intergrowths of oriented halite sheets (with sylvite globules) and carbonates. The carbonate assemblages of the individual nodules may differ: these are an association of shortite, northupite, and calcite in some instances and a zoned aggregate of K-rich nyerereite and shortite in other instances [27,28]. In general, some alkali carbonates with halite were quite often found in the matrix of unserpentinized volcaniclastic kimberlite Udachnaya-East pipe (e.g., [25]), but neither their reliable XDR and elemental analyses nor their Raman spectroscopy study were performed and published.
Extensive factual data on another variety of fresh unserpentinized coherent kimberlite from a dyke/vein in the Udachnaya-East pipe are employed below to demonstrate that a series of alkali carbonates, sulfates, and chlorides occurs among the groundmass minerals of this phase of the coherent kimberlite, and a magmatic genesis of this assemblage will be proved. Moreover, one of the three alkali carbonates in these kimberlites is are rock-forming mineral, i.e., the rock contains more than 5 vol % of this mineral.

2. Geological Background and Sample Description

The Udachnaya pipe is located in the central part of the Siberian craton in the Daldyn kimberlite field (Figure 1, [29]). The pipe consists of two coupled bodies (eastern and western), which are made up of various kimberlite units (Figure 2). The western and eastern bodies (Figure 2) were produced by several pulses of kimberlite magmatism [30].
The SHRIMP U–Pb perovskite age constraints kimberlite emplacement age at 367 ± 5 Ma for the eastern body and 361 ± 4 and 353 ± 5 Ma for different samples from the western body [33]. However, not all events of kimberlite emplacement identified in [21] have been rigorously dated. All kimberlite units in the western body are fully serpentinized, while many varieties/units of kimberlites in the eastern body contain olivine. In general, there are at least four varieties of kimberlitic rocks with olivine within the depth range of 400 to 640 m (bottom of the quarry). In the central part of the Udachnaya-East pipe, a subvertical 30- to 50 m-wide body was located (in Figure 2, this is unit/phase 9) with ≤7 vol % sedimentary xenoliths from the rocks of the sedimentary cover of the Siberian craton that host the Udachnaya kimberlite pipe. In the quarry, a clear boundary between kimberlite varieties 8 and 9 (Figure 2) was found at depths of 400–640 m. Below depths of 400 m, dikes/veins of coherent kimberlite up to 30 cm thick (in Figure 2, this is unit/phase 10) were found in the unit/phase 9 volcaniclastic kimberlite. At the depth levels of 0–410 m and 500–640 m, kimberlite volcaniclastic rock unit 9 occurs (in Figure 2 this is unit/phase 9b), which is variably serpentinized, and dikes/veins of coherent poor serpentinized kimberlite (in Figure 2, this is unit/phase 10b) occur below depths of 400 m. Uniquely unaltered rocks for fundamental research were exposed in a quarry in the central part of the Udachnaya-East pipe, at depths of ~410–500 m (units 9a and 10a in Figure 2 and Figure 3).
These varieties are different from any kimberlites known worldwide in that they do not show even traces of any secondary alterations, that is, H2O-rich phases, such as serpentine, iowaite, and chlorite, and any other possible secondary minerals of the hydrothermal stage of kimberlite rocks transformation are completely absent (Figure 4a). Herein, the term primary/original kimberlite rock is used with reference to kimberlites anywhere worldwide that did not interact with external hydrothermal fluids either during their formation or after their crystallization. Unserpentinized sample 24-04-A (dike/vein of coherent kimberlite, unit/phase 10a) was found in 2004 in unserpentinized volcaniclastic kimberlite (unit/phase 9a) at a depth of ~480–500 m (Figure 3). This sample is unique in its kind, because no other such unserpentinized coherent kimberlites have ever been found. Based on the bulk composition of the rock, namely, its elevated contents of Na2O (3.4 wt%), Cl (0.9 wt%), and SO3 (0.7 wt%) [26,34], the presence of alkali-, Cl-, and S-rich mineral species should have been expected in this rock sample, and they were identified in it indeed. The mineral assemblage of this kimberlite consists of macro/microcrysts of olivine (~57 vol %), microphenocrysts of phlogopite, calcite, and Na-, Ca-, K-, and S-rich carbonate. The groundmass of this kimberlite consists of olivine, phlogopite, monticellite, calcite, spinel-group minerals, perovskite, ilmenite, rutile, apatite, a series of Na–Ca–K–S-rich and Na-Ca-rich (shortite) alkali carbonates, aphthitalite, halite, sylvite and the K-Cl-rich sulfide djerfisherite (Table 1, Figure 4a). Any secondary water-rich minerals of the hydrothermal stage of kimberlite transformation are completely absent from this rock (Figure 4a and Figure 4b, for comparison). The amount of sedimentary microxenoliths brought from rocks of the sedimentary cover of the Siberian craton, which host the Udachnaya kimberlite pipe, is ≤1 vol % in this rock sample.

3. Materials and Methods

The sample was sawed using WD-40 liquid, and the thin sections were polished on an anhydrous basis, using petroleum benzene. As our experience shows, when such rock samples are sawed with the use of water, alkali sulfates and chlorides are immediately destroyed. If thin sections are manufactured using any water-containing liquids, some alkali-rich carbonates can also be destroyed.
The mineral assemblage of sample UV-24-04-A was investigated under a scanning electron microscopy (SEM) coupled to an energy-dispersive X-ray spectroscopy (EDS) and was studied by Raman spectroscopy. A TESCAN MIRA 3 LMU scanning electron microscope (Tescan Orsay Holding, Brno, Czech Republic) combined with an EDS INCA Energy detector X-max 80 mm2 (Oxford Instruments Nanoanalysis, Abingdon, UK) was used to obtain the following data: (1) back-scattered electron (BSE) images of the kimberlite rock texture and individual minerals; (2) X-ray maps showing the distribution of minerals and elements in individual minerals; and (3) individual analyses of minerals. The EDS spectra were optimized for quantification using the standard XPP procedure incorporated into the INCA Energy 350 software. Chemical analyses of minerals were conducted at a 20 kV accelerating voltage.
Raman point measurements of individual minerals were carried out on a Horiba Jobin Yvon LabRAM HR800 confocal Raman spectrometer (Horiba, Kyoto, Japan) equipped with a 532 nm Nd:YAG laser and an Olympus BX41 microscope. A 100× objective lens with a numerical aperture of 0.9 was used. The instrument was calibrated using the first-order 520.6 cm−1 band of crystalline silicon. The wavenumbers were accurate to ±1 cm−1. The Raman signal was collected in the spectral range of 10–4000 cm−1. Raman spectra identification was carried out using the RRUFF database [35] and other spectra reports.

4. Results

4.1. Occurrences of Alkali-Rich Carbonates, Sulfates, and Chlorides

A series of alkali-rich carbonates, aphthitalite, halite, and sylvite, were identified among the groundmass minerals (≤0.25 mm in size) of the unserpentinized coherent kimberlite (Figure 4a).
A Na-, Ca-, K-, and S-rich carbonate (possibly a new mineral) was identified in the kimberlite matrix (Figure 5 and Figure 6), where it occurs as anhedral (Figure 5a–f and Figure 6) and, more rarely, tabular grains (Figure 5g). Sometimes, this carbonate occurs as microphenocrysts (grains 0.3–0.5 mm, Figure 5h,i). The Na-Ca-K-S-rich carbonate contains crystalline inclusions of olivine, phlogopite, monticellite, spinel-group minerals, perovskite, calcite, apatite, and aphthitalite (Figure 5f–h and Figure 6, Table 2). Shortite was often found at the margins of this Na–Ca–K–S-rich carbonate or at the boundary with this carbonate (Figure 5a,c–d,f–h and Figure 6b). It should be noted that shortite from this sample always contains abundant inclusions/lamellae of the sulfate aphthitalite (K3Na(SO4)2) (Figure 6b and Figure 7a–d). All shortite grains occur in close association with Na–Ca–K–S-rich carbonate were identified in this sample. It should be noted that, if the sample was sawn using water, aphthitalite on the sample surface was destroyed and removed during such production of the thin sections. If thin sections were manufactured in such a way, “pure” shortite with a spongy grain structure (with numerous holes on the surface) was sometimes found in the thin sections (Figure 5g and Figure 7e–g).
The aphthitalite forms individual anhedral grains in the rock matrix (Figure 8a) and is sometimes found as crystalline inclusions in the Na–Ca–K–S-rich carbonate (Figure 8b), but the volume of aphthitalite as inclusions/lamellae in shortite (Figure 7a–d) significantly exceeds the volume of aphthitalite from the rock matrix and inclusions in Na–Ca–K–S-rich carbonate.
The halite forms anhedral and sometimes subhedral grains (Figure 6a, Figure 9 and Figure 10) in the rock matrix. The halite hosts crystalline inclusions of olivine, phlogopite, spinel-group minerals, calcite, apatite, and sylvite (Figure 6a and Figure 9e–i, Table 2). Sylvite is much less common in the groundmass than halite and forms anhedral grains (Figure 9h,i and Figure 10).
The total content of alkali carbonates in this rock can be estimated at >15 vol % (approximately around 20 vol %), that of halite is ~3 vol %, and sylvite and aphthitalite are rarer accessory minerals (<1 vol %) in the matrix of this kimberlite. However, taken into account that ~40 vol % of the rock may be made up of xenogenic olivine from disintegrated mantle xenoliths, and this olivine “is subtracted” from the rock volume, the volume content of alkali carbonates and halite in the primary kimberlite rock will be significantly higher: ~30 and ~6 vol %, respectively.

4.2. Raman Spectroscopic Study of Alkali-Rich Carbonates and Sulfate

The Raman spectra of individual grains of Na–Ca–K–S-rich carbonate (in 22 grains) are characterized by two strong Raman bands at 1073–1074 and 1090–1091 cm−1 with a weak shoulder at 1099−1100 cm−1, a medium band at 705–707 cm−1 with wide shoulder between 708 and 742 cm−1, and medium/weak band at 1744–1745 cm−1, which reflect the different vibrations of the (CO3)2− anionic group. The Raman band at 1090–1091 cm−1 is the strongest in this Raman spectrum (Raman spectrum alkali carbonate type I, Figure 11a). There are additional Raman bands for this carbonate at 963–965 and 996–997 cm−1, which display the vibrations of the (PO4)2− and (SO4)2− anionic groups (Figure 11a).
The second type of the Raman spectra was obtained from 11 individual grains of the Na–Ca–K–S-rich carbonate. This type of Raman spectra exhibits two intense bands at 1074–1075 and 1090–1092 cm−1 with a shoulder at 1099−1101 cm−1 ((CO3)2− anionic group vibrations), but the Raman band at 1074–1075 cm−1 is stronger than that at 1090–1092 cm−1, in comparison with the spectrum of type-I alkali carbonate. The Raman spectra of alkali carbonate of type II also have three or four medium/weak bands that are assigned to the (CO3)2− anionic group vibrations within the range 690–740 cm−1, with peaks 699–700, 706–707, 726–727 and 737–738 cm−1, as well as a Raman band at 1746–1747 cm−1. The medium/weak Raman bands at 964–965 and 996–997 cm−1 are assigned to the (PO4)2− and (SO4)2− vibrations, these anionic groups (Figure 11b, Raman spectrum of alkali carbonate of type II).
It should be noted that the Raman spectra of the type-I and type II of the Na–Ca–K–S-rich carbonates (Figure 11a,b) do not correspond to the Raman spectra of any known synthesized and natural alkali-rich carbonates. These Raman spectra are not identical to the spectra of the hexagonal β- and γ-phases (the hypothetical spectra of “zemkorite” (Na1.8K0.29)Ca1.1(CO3)1.93)), or to the spectrum of the pure orthorhombic Na2Ca(CO3)2 α-phase, or to the reference spectra of nyerereite (Na,K)2Ca(CO3)2 or shortite Na2Ca2(CO3)3 (see Figure 11a,b and Figure 12 for comparison). However, it can be predicted from the position of the strong Raman bands that this Na–Ca–K–S-rich carbonate or carbonates (Figure 11a,b) are orthorhombic.
Two Raman spectra (Figure 11c) from many Raman analytical spots at the Na–Ca–K–S-rich carbonates correspond to the Raman spectra of the reference nyerereite (see Figure 12d for comparison and the Raman spectra of nyerereite of types I and III (Figure 5a,c) from [37]). Since the wide area of analysis of the Na–Ca–K–S-rich carbonates on BSE and MAP images was visually homogeneous, it can be concluded that nyerereite is present in these Na–Ca–K–S-rich carbonates as crystalline microinclusions or, perhaps, these are some kind of nyerereite domains (?) in the host Na–Ca–K–S-rich carbonates structure.
Two other Raman spectra (Figure 11d) from a set of Raman analytical spots of the Na–Ca–K–S-rich carbonate correspond to some microinclusions or domains of other alkali carbonates in the matrix of visually homogeneous grains of Na–Ca–K–S-rich carbonate. One Raman spectrum (black line in Figure 11d) with a strong band at 1083 cm−1 and a shoulder at 1072 cm−1 is identical in shape to the spectrum of nyerereite (see Figure 12d for comparison), but the strong band in this carbonate is shifted by ~3 cm−1 compared to nyerereite. Another Raman spectrum (red line in Figure 11d) with a strong band at 1076 cm−1 may correspond to, for example, gregoryite (Na,K,Cax)2−x(CO3) [37] or khanneshite (Na,Ca)3(Ba,Sr,Ce,Ca)3(CO3)5 [38], burbankite (Na,Ca)3(Sr,Ca,Ba,LREE)3(CO3)5 [39], or some similar alkali-rich carbonate.
The Raman spectra of shortite from the kimberlite matrix (Figure 13a) are fully consistent with the published reference spectra of shortite (see Figure 12e (RRUFF database R050248) for comparison or, e.g., [40]). Shortite is characterized by two major bands at 1071–1072 cm−1 and 1090–1091 cm−1 and a series of medium/weak bands at 695–696, 711, 717, and 866 cm−1 assigned to different (CO3)2− vibrations. Since shortite in this kimberlite sample always contains abundant aphthitalite inclusions/lamellae, aphthitalite Raman bands are always present in the Raman spectra of shortite (Figure 13a).
The Raman spectra of aphthitalite K3Na(SO4)2, inclusions/lamellae in shortite, inclusions in the Na–Ca–K–S-rich carbonate, and individual grains in the groundmass of the rock (Figure 13) are characterized by a major Raman band at 987–992 cm−1 and a series of medium/weak bands at 452–453, 620–621, 627–629 and 1080 cm−1, which are assigned to the vibrations of different (SO4)2− anionic group (RRUFF database R050651 or e.g., [41]).

4.3. Chemical Composition of the Alkali-Rich Minerals

The Na–Ca–K–S-rich carbonate with Raman spectra of type I is characterized by small variations in concentrations of the following components (in wt%): Na2O (21.2–21.8), CaO (29.1–29.7), K2O (5.0–5.6), SrO (up to 0.4), SO3 (5.2–5.9), and P2O5 (up to 0.3) (Table 3, Figure 14).
The composition of the Na–Ca–K–S-rich carbonate with Raman spectra of type II also varies insignificantly (in wt%): Na2O (21.4–22.3), CaO (29.0–29.9), K2O (5.2–5.6), SrO (up to 0.4), SO3 (5.3–5.7), and P2O5 (up to 0.5) (Table 3, Figure 14).
However, the average composition of the Na–Ca–K–S-rich carbonates with Raman spectra of both types is almost identical, within the analytical errors (3ϭ, Na2O ± 0.6, CaO ± 0.5, K2O ± 0.2, SO3 ± 0.4 wt%), and the Na–Ca–K–S-rich carbonates plot within the same narrow compositions field in co-variation diagrams (Figure 14).
The shortite shows minor composition variations (in wt%): Na2O (19.7–20.2), CaO (33.2–34.9) (Table 3). This shortite may contain some admixtures, K2O (up to 0.6 wt%) and SO3 (up to 0.6 wt%), if these are not aphthitalite K3Na(SO4)2 microinclusions (see Section 4.1).
The analysis of the composition of the aphthitalite is not stoichiometric (Table 3), due to the small size of its grains (up to 10 μm, Figure 8) and sodium loss during analysis, but confirms Raman spectroscopy data that this is a K-Na-rich sulfate (Figure 13).

4.4. Crystalline and Melt Inclusions in Calcite Microphenocryst

During the study of the rock, a calcite microphenocryst was found (Figure 15a) that contains crystalline and primary melt inclusions (Figure 15).
The crystalline inclusions (up to 30 μm across) are Na–Ca–K–S-rich carbonate, monticellite, and apatite (Figure 15). A crystalline inclusion of Na–Ca–K–S-rich carbonate near the core (Figure 15b) of the calcite microphenocryst is characterized by the following composition: Na2O—20.7, CaO—31.2, K2O—4.9, and SO3—3.4 wt% (Table 3). The Raman spectrum of this crystalline alkali-rich carbonate inclusion (Figure 16a) is identical to the Raman spectrum of the Na–Ca–K–S-rich groundmass carbonate of type I (see Figure 11a for comparison). A crystalline inclusion of the Na–Ca–K–S-rich carbonate in the calcite microphenocryst rim has the following composition (wt%): Na2O—22.6; CaO—29.1; K2O—5.0; and SO3—5.1 (Table 3).
In exposed primary melt inclusions (Figure 15c,e), the assemblage of daughter minerals consists of olivine (Figure 16b), phlogopite, apatite, Na–Ca–K–S-rich carbonate, and halite. The Raman spectrum of the daughter Na–Ca–K–S-rich carbonate (Figure 16a) is similar to the Raman spectrum of the Na–Ca–K–S-rich groundmass carbonate of type I. It should be noted that the daughter olivine from such primary melt inclusions is characterized by a very high Mg#, which varies from 96.5 to 98.7.

5. Discussion

5.1. What Were the Compositions of the Primitive Kimberlite Melts, and Why Kimberlites Should Have Been Dominated by a Carbonate Component of Mantle Origin?

As follows from the traditional paradigm, primitive kimberlite melts may have had an ultramafic composition similar to that of kimberlite rocks, with SiO2 and MgO dominating over other components, and with CaO concentrations much higher than the total concentration of alkalis (Na2O +K2O) (e.g., [42,43,44,45]). It is thought that these primitive kimberlite melts were enriched in H2O and CO2 (e.g., [2,43,44,46]). Therewith, it is commonly thought, within the frameworks of the traditional paradigm of the petrogenesis of kimberlites, that such components as Na2O and volatile Cl and S did not play any significant parts and are thus ignored. However, studies of melt inclusions hosted in minerals of kimberlites and mantle xenoliths in these rocks have shown that these inclusions contain various carbonates, including numerous alkali-bearing carbonates (mostly Na-rich) and carbonates with such additional anions as Cl−, SO42−, PO43−, and these carbonates always strongly quantitatively dominate over silicates (e.g., see the review [14]). The bulk compositions of these inclusions always contain less than 20 wt% SiO2, i.e., the melts whose relics are represented by the inclusions always fall within the fields of carbonate/carbonatite melts in the classification for igneous rocks [47]. Studies of these inclusions have also shown that Na, Cl, and S should have played an important part in the petrogenesis of kimberlites, whereas the role of H2O seems to have been previously unwarrantedly overestimated [14].
Another approach, namely, evaluations of the volumes of xenogenic olivine in kimberlite rocks (e.g., [48,49]) and those of the xenogenic mantle silicates dissolved during interactions with kimberlite melts (e.g., [50,51,52,53,54,55]), leads to the same conclusions that the primary or primitive kimberlite melts were of carbonate/carbonatite nature. For example, evaluations in [48] indicate that the amount of olivine produced during the magmatic crystallization of kimberlites was no higher than ≤5 vol % of ~50 vol % olivine in these rocks, i.e., ~45 vol % olivine in kimberlites is xenogenic, which predetermines the predominance of SiO2 and MgO over other components in kimberlite rocks. Hence, kimberlites should contain a diversity of primary magmatic carbonates, and the carbonate component of kimberlite is not calcite and/or dolomite alone.
Similar to the melt inclusions in minerals of mantle xenoliths and melt inclusions in kimberlite minerals themselves (see Introduction above), this sample of unaltered coherent kimberlite should have contained (as follows from the high bulk-rock concentrations of Na2O (3.4 wt%), Cl (0.9 wt%), and SO3 (0.7 wt%) [26,34]), magmatic mineral phases enriched in these exactly components, and these phases have indeed been identified as series of alkali carbonates, chlorides, and aphthitalite (see section Results). It will be demonstrated in the subsections below that all of these alkali-bearing phases are indeed of magmatic origin and are not secondary hydrothermal minerals.

5.2. Origin of Alkali Carbonates in Kimberlites: A Brief Review of Preexisting Data

As follows from the literature, alkali-rich carbonates in kimberlites were likely mentioned for the first time as a find of shortite as a groundmass mineral (about 8 vol %) in serpentine-poor kimberlite dikes in the Upper Canada Gold Mine [20]. Shortite in this kimberlite poikilitically encloses phlogopite, magnetite, apatite, and perovskite and is, according to [20], of late magmatic origin. However, according to experiments in the binary Na2CO3−CaCO3 system [56], shortite Na2Ca2(CO3)3 could not form on the liquidus at ambient conditions, but can be formed in igneous rocks by several subsolidus reactions at temperatures below 400 °C. Other experimental studies have shown that the liquidus minerals of the Na2CO3−CaCO3−MgCO3 system at 3 GPa and 700–950 °C are nyerereite, shortite, eitelite, and dolomite [57]. New experimental studies in various multicomponent systems at ambient conditions are thus needed to demonstrate that shortite can occur in kimberlites not only as a subsolidus mineral but also as a late magmatic one. According to [23], shortite in the serpentine-poor Udachnaya-East kimberlite also has a genetic link to kimberlite magma, and the “high concentration of Na in the deep zone of the kimberlite column promotes crystallization of shortite in kimberlite”.
The most mysterious alkali carbonate in kimberlites is zemkorite, a mineral whose calculated empirical formula is (Na1.8K0.29)Ca1.1(CO3)1.93, whose ideal formula is Na2Ca(CO3)2, and whose (Na + K)/Ca atomic ratio is 1.9. Very little information is available so far on zemkorite: only its composition and, perhaps, also its hexagonal space group P63/mmc or P63mc, or P 6 ¯ 2 c . Also, zemkorite is readily soluble in warm water. Zemkorite was found in core material from the Udachnaya-East pipe, from depths of 400−450 m, in kimberlite without any traces of serpentinization. Zemkorite is often found together with shortite and, more rarely, with halite. In the kimberlite, zemkorite locally occurs as interstitial material that poikilitically includes small grains from the groundmass of this rock. No euhedral crystals of the mineral were found [24]. The seemingly most controversial issue is the interpretation of the genesis of zemkorite. According to [24], zemkorite is a postmagmatic mineral and results from the reworking of kimberlite by highly mineralized sodic solutions derived by interaction of the Udachnaya pipe with subsurface brines from Lower Cambrian country rocks. However, a hydrothermal genesis of the zemkorite can hardly be consistent with the following facts: (i) zemkorite occurs only in unserpentinized kimberlites, i.e., rocks devoid of any hydrous minerals, and at the same time, zemkorite has never been found in any partly or completely serpentinized kimberlites in the Udachnaya pipe; and (ii) the “hydrothermal” zemkorite hosts inclusions of magmatic minerals of the rock groundmass. If the authors of [24] were mistaken, and the zemkorite is of late magmatic genesis, then a mineral of this composition cannot belong to the hexagonal system, because it is unstable under normal conditions (see review in [36]) and only orthorhombic nyerereite is stable at temperatures ≤ 360 °C [36].

5.3. Magmatic Origins of Alkali Carbonates, Chlorides, and Sulfates in the Coherent Kimberlite from the Udachnaya-East Pipe

The first issue discussed in this section is how many alkali carbonates (three or four, or five) occur in the kimberlite (Figure 11 and Figure 13). Na–Ca–K–S-rich carbonates show two types of intensities of strong Raman bands, and the Raman spectrum shapes are visually distinct for each of these types, although the positions of the peaks of the strong Raman bands are the same for types I and II (Figure 11a–b). Extensive factual material (a few hundred Raman analyses of individual grains) on orthorhombic alkali carbonates (pure synthetic (Na)2Ca(CO3)2 and nyerereite (Na,K)2Ca(CO3)2) was employed to demonstrated that, depending on the crystallographic orientations of individual grains, these minerals display three distinct end-member spectra in the region of the strongest Raman band ν1(CO3)2− vibration [37]. Inasmuch as the Raman spectra suggest that the Na–Ca–K–S-rich carbonate/carbonates also has (have) an orthorhombic symmetry, and the composition of this carbonate (or carbonates) with Raman spectra of type I and type II is identical (Figure 14, Table 3), the Na–Ca–K–S-rich carbonates with Raman spectra of type I and type II (Figure 11a,b) should be the same single alkali-rich carbonate but not two distinct ones. The composition of the Na–Ca–K–S-bearing carbonate in both inclusions in the calcite microphenocryst and the groundmass does not correspond to the composition of any known alkali-bearing carbonate (Figure 14, Table 3). The atomic (Na + K)/Ca ratio of this carbonate varies from 1.4 to 1.6 at an average of 1.5 in the Na–Ca–K–S-rich carbonate in the kimberlite matrix (Table 3, Figure 14), whereas this ratio of, for example, nyerereite (Na,K)2Ca(CO3)2 is 2, and that in shortite Na2Ca2(CO3)3 is 1. Moreover, this carbonate contains relatively much SO3 (up to 6 wt%). Such sulfur concentrations are atypical for nyerereite, and no shortite containing sulfur is known at all. The Raman spectra of this carbonate (Figure 11a,b) are remotely similar but far from identical to the spectra of reference [37] nyerereite (Figure 12d), gregoryite, and shortite (RRUFF database 050248, Figure 12e). Nevertheless, the position of the Raman spectral lines suggest that, similar to both nyerereite and shortite, this Na–Ca–K–S-rich carbonate belongs to the orthorhombic system. It is thus fairly probable that the new Na–Ca–K–S-bearing carbonate is of magmatic genesis.
The occurrence of shortite in this kimberlite is readily inferred from the Raman spectra (Figure 13a and Figure 12e for comparison) and chemical composition (Figure 14, Table 3). Moreover, two ideal [37]. Raman spectra have been obtained from crystalline inclusions of still another alkali-rich carbonate, nyerereite, in the Na–Ca–K–S-rich carbonate (Figure 11c). An issue remaining unresolved is which inclusions of alkali carbonates yielded the Raman spectra shown in Figure 11d. The Na–Ca–K–S-rich carbonate obviously hosts some other alkali carbonates, but their amounts are barely noticeable, and a few hundred to a few thousand Raman analyses should be additionally performed (perhaps, unsuccessfully) at various spots on the Na–Ca–K–S-rich carbonate to reach any progress in solving this issue.
The magmatic association of rock-forming alkali carbonate, nyerereite, and gregoryite, occurring together with sylvite, has been found at the world’s only occurrence of natrocarbonatites in Oldoinyo Lengai volcano [58,59,60,61,62]. This paper demonstrates (for the second time) that at least two alkali carbonates (a new? Na–Ca–K–S-rich carbonate and shortite) occur, together with chlorides, among magmatic minerals in the groundmass of kimberlites. The unusual mineral association consists of an even greater number of minerals than that of the Oldoinyo Lengai natrocarbonatites. The Na–Ca–K–S-rich carbonate in the kimberlite is a rock-forming mineral (~15 vol %), shortite and halite are minor minerals (≤5 vol %), and sylvite and aphthitalite are accessory minerals (≤1 vol %). There are no reasons to refer to this mineral association in the unserpentinized coherent kimberlite from the Udachnaya-East pipe as an association of late hydrothermal genesis, as was performed in [24] for the association “zemkorite” + shortite + halite from the same kimberlite body and from approximately same depths (see also Section 5.2 of this paper). Conversely, all data obtained on it (and presented above in this paper) indicate that the alkali carbonates, sulfates, and chlorides in the unaltered kimberlite from the Udachnaya-East pipe are of late magmatic kimberlite origin. Firstly, the studied rocks do not contain serpentine even in trace amounts (Figure 4a and for comparison Figure 4b), nor do they contain any H2O-rich secondary minerals, such as chlorite and iowaite, that are common in hydrothermally transformed kimberlites. Secondly, the Na–Ca–K–S-rich carbonate and halite host crystalline inclusions of such common kimberlite minerals as olivine, phlogopite, monticellite, calcite, spinel, perovskite, and apatite (Figure 5, Figure 6, Figure 9 and Figure 10). Thirdly, the Na–Ca–K–S-rich carbonate was found as a crystalline inclusion in a calcite microphenocryst (Figure 15). The calcite microphenocryst hosts both individual inclusions of the Na–Ca–K–S-rich carbonate (up to 40 μm across) (Figure 15b, Table 3 (Incl 1)) and polycrystalline inclusions of the Na–Ca–K–S-rich carbonate + phlogopite + apatite (Figure 15d, Table 3 (Incl 2)). Moreover, the same calcite microphenocryst was found out to host two crystallized melt inclusions, which contain, as daughter phases, at least olivine, phlogopite, apatite, Na–Ca–K–S-rich carbonate, and halite (Figure 15c,e). Thus, the occurrence of Na–Ca–K–S-rich carbonate and halite as daughter phases within primary melt inclusions provides unambiguous evidence of a magmatic origin of this mineral association in the kimberlite groundmass.
The only issue remaining unsettled is whether individual shortite grains with aphthitalite lamellas or rims of this association around Na–Ca–K–S-rich carbonate (Figure 5, Figure 6 and Figure 7) are liquidus or subsolidus minerals. As was mentioned above, according to experiments in the binary Na2CO3-CaCO3 system [56], shortite Na2Ca2(CO3)3 could not form as a liquidus mineral at ambient conditions but is a subsolidus mineral. However, other experimental studies show that shortite is a liquidus mineral in the Na2CO3−CaCO3−MgCO3 system at 3 GPa and 700–950 °C [57]. This calls for studies of the multicomponent systems at ambient conditions to resolve this problem. Right now, both scenarios of shortite origin in kimberlites (whether it is a liquidus or subsolidus mineral) seem to be equally plausible, and even with changes in the physicochemical parameters of magma during the formation of kimberlite bodies in surface conditions, the implementation of both scenarios cannot be ruled out.
I am generally more prone to believe, with reference to the kimberlite sample in which shortite always hosts abundant aphthitalite lamellas (if the thin sections were manufactured without using water-bearing liquids, Figure 7a–d), that the association of shortite with numerous aphthitatile lamellas is of subsolidus nature. I suggest that if roughly ≥8 wt% SO3 was accommodated in the structure of the Na–Ca–K–S-rich carbonate, this carbonate became unstable as the temperature decreased and exsolved by the reaction (in its simplified form):
(Na,K)6Ca4(CO3,SO4)7 → Na2Ca2(CO3)3(shortite) + K3Na(SO4)2(aphthitalite).
The shortite and aphthitalite assemblage has previously often been found in secondary melt inclusions in olivine from mantle xenoliths and kimberlites [17]. A similar subsolidus reaction was also proposed for this association, except that its right-hand part involved HT hexagonal carbonate (Na,K)2Ca(CO3,SO4)2 (high-temperature analog of nyerereite) rich in K and SO4, which crystallized at T > 500 °C and broke down into shortite Na2Ca2(CO3)3 and aphthitalite K3Na(SO4)2 during cooling, instead of Na–Ca–K–S-rich carbonate. This subsolidus reaction was written as
2(Na1.25K0.75)Ca(CO3)1.5(SO4)0.5 → Na2Ca2(CO3)3(shortite) + 0.5K3Na(SO4)2(aphthitalite).

6. Conclusions

This publication presents reliable data indicating that the sample of unserpentinized kimberlite from the Udachnaya-East pipe contains, in addition to carbonate, which is a quite common mineral in the matrix of kimberlites, at least three alkali-rich carbonates (Na–Ca–K–S-rich carbonate, shortite, and nyerereite). Raman spectroscopy data indicate that this kimberlite also contains a fourth alkali-rich carbonate, but its content is barely detectable, and I failed to reasonably accurately interpret its Raman spectrum. A Na–Ca–K–S-rich carbonate that has an unusual composition and Raman spectrum quantitatively dominates over the other alkali-rich carbonates (shortite and nyerereite), and its content (~15 vol %) is comparable to that of calcite in this rock. This carbonate was found as (i) a groundmass mineral of kimberlite; (ii) crystalline inclusions in calcite microphenocrysts; and (iii) among daughter phases within crystallized primary melt inclusions in calcite microphenocrysts. It is quite probable that this is a new orthorhombic carbonate, as follows from its Raman spectrum and its empirical formula (Na,K)6Ca4(CO3,SO4)7, but its structure has to be accurately interpreted, and the space group should be determined. In addition to alkali carbonates, the matrix of the kimberlite was found to contain chlorides (halite and sylvite) and the sulfate aphthitalite. This entire alkali-rich assemblage is of late magmatic origin. The only issue unsettled so far pertains to the shortite, which may be, strictly speaking, not a liquidus but a subsolidus mineral in this kimberlite, but nevertheless it has a genetic link with parental kimberlite magma.
The content of the sulfate component in the rock is very high for kimberlites (up to 0.7 wt% SO3 [26]), and it has not been known before which minerals concentrate the bulk of the sulfate component of the rocks. This study has proved that the sulfate component is concentrated in (i) Na–Ca–K–S-rich carbonate (Na,K)6Ca4(CO3,SO4)7 and (ii) its own individual phase—aphthitalite.
Literature data and materials presented above in this publication leave no doubts that alkali carbonates can be preserved only in unserpentinized or in very serpentine-poor (shortite) rocks. The same pertains to the late magmatic alkali chlorides and sulfates in the matrix of kimberlites: these phases can be preserved exclusively in unserpentinized rocks. My own experience with samples from the Udachnaya-East pipe indicates that even ~1 vol % serpentinization is sufficient to decompose all of the alkali sulfate and chlorides, as well as most of the alkali carbonates (Na–Ca–K–S-rich carbonate and nyerereite). The most resistant alkali carbonate in kimberlites seems to be shortite, but this mineral should also decompose in the presence of water at temperatures above 300 °C [1]. The rare occurrence of shortite in variably poorly serpentinized kimberlites worldwide apparently is directly related to both the degrees and the temperature of serpentinization of these rocks, but no conventionally acknowledged estimates/limits have been proposed so far for the term serpentine-poor kimberlite.

Funding

This work was supported by the Russian Science Foundation, project no 24-27-00287 (https://rscf.ru/project/24-27-00287/). The fieldwork and sampling were performed on a state assignment of IGM SB RAS (No. 122041400157-9).

Data Availability Statement

Data is contained within the article.

Acknowledgments

The author thanks A.A. Tarasov for help with the preparation of the Figures for this manuscript.

Conflicts of Interest

The author declares no conflicts of interest.

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Figure 1. Location map for the Udachnaya kimberlite pipe after [29] and references therein. The gray area in the Russia map inset shows the Siberian craton.
Figure 1. Location map for the Udachnaya kimberlite pipe after [29] and references therein. The gray area in the Russia map inset shows the Siberian craton.
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Figure 2. Geological cross-section of the Udachnaya kimberlite pipes according to Kryuchkov and Sviridov (modified by A.V. Golovin after Figure 47 from [21]). 1–4 = western body which contains volcaniclastic kimberlite (units 1–3) and veins/dykes of coherent kimberlite (4). Units 5–10 = eastern body, which consists of volcaniclastic kimberlite (units 5–9) and veins/dykes of coherent kimberlite (10). Kimberlite units 9 and 10 can be divided into two types (a) and (b). Although the textural and structural characteristics of these types are identical, there are various changes in groundmass mineralogy that occur at different depths. Volcaniclastic kimberlite unit 9: (a) green = unserpentinised “fresh” initial/pristine kimberlite (see, e.g., [15,25], depth interval at 410–500 m; (b) red = partially serpentinised kimberlite at 0–410 m and 500–640 m depth intervals. Veins/dykes of coherent kimberlite unit/units 10: (a) yellow = unserpentinised “fresh” initial/pristine kimberlite, depth interval at 410–500 m; black lines = partially serpentinised kimberlite. Host sediments are after [30]: limestones (1—clear; 2–silty; 3–sandy; 4–organogenic), dolomites (5), marls (6), calcareous conglomerates (7). Aquifer systems are after [31,32].
Figure 2. Geological cross-section of the Udachnaya kimberlite pipes according to Kryuchkov and Sviridov (modified by A.V. Golovin after Figure 47 from [21]). 1–4 = western body which contains volcaniclastic kimberlite (units 1–3) and veins/dykes of coherent kimberlite (4). Units 5–10 = eastern body, which consists of volcaniclastic kimberlite (units 5–9) and veins/dykes of coherent kimberlite (10). Kimberlite units 9 and 10 can be divided into two types (a) and (b). Although the textural and structural characteristics of these types are identical, there are various changes in groundmass mineralogy that occur at different depths. Volcaniclastic kimberlite unit 9: (a) green = unserpentinised “fresh” initial/pristine kimberlite (see, e.g., [15,25], depth interval at 410–500 m; (b) red = partially serpentinised kimberlite at 0–410 m and 500–640 m depth intervals. Veins/dykes of coherent kimberlite unit/units 10: (a) yellow = unserpentinised “fresh” initial/pristine kimberlite, depth interval at 410–500 m; black lines = partially serpentinised kimberlite. Host sediments are after [30]: limestones (1—clear; 2–silty; 3–sandy; 4–organogenic), dolomites (5), marls (6), calcareous conglomerates (7). Aquifer systems are after [31,32].
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Figure 3. Unique “fresh” unserpentinized kimberlite rocks from the Udachnaya-East pipe. A dyke of coherent kimberlite (CK, sample 24-04-A) in a volcanoclastic kimberlite (VK, sample 24-04-B). Within the dyke, near the boundaries, there are quenching zones (QZ) of coherent kimberlite. Photos of rocks (a–c) and reflected light photos of polishing thin sections (d) Ol—olivine.
Figure 3. Unique “fresh” unserpentinized kimberlite rocks from the Udachnaya-East pipe. A dyke of coherent kimberlite (CK, sample 24-04-A) in a volcanoclastic kimberlite (VK, sample 24-04-B). Within the dyke, near the boundaries, there are quenching zones (QZ) of coherent kimberlite. Photos of rocks (a–c) and reflected light photos of polishing thin sections (d) Ol—olivine.
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Figure 4. BSE images (a,b) and x-ray element maps of mineral assemblages of unserpentinized coherent kimberlite (a) (sample 24-04-A, unit/phase 10a in Figure 2) and for comparison partially (~20 vol %) serpentinized volcaniclastic kimberlite (b) (unit/phase 9b in Figure 2) from Udachnaya-East pipe. Na, K, and Cl element maps show the presence of alkali carbonates and chlorides among the groundmass mineral assemblage of unserpentinized kimberlites (a) and the absence of this mineral among the matrix of partially serpentinized kimberlites (b). Srp—serpentine, other mineral symbols are those defined in Table 1.
Figure 4. BSE images (a,b) and x-ray element maps of mineral assemblages of unserpentinized coherent kimberlite (a) (sample 24-04-A, unit/phase 10a in Figure 2) and for comparison partially (~20 vol %) serpentinized volcaniclastic kimberlite (b) (unit/phase 9b in Figure 2) from Udachnaya-East pipe. Na, K, and Cl element maps show the presence of alkali carbonates and chlorides among the groundmass mineral assemblage of unserpentinized kimberlites (a) and the absence of this mineral among the matrix of partially serpentinized kimberlites (b). Srp—serpentine, other mineral symbols are those defined in Table 1.
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Figure 5. BSE images of kimberlite groundmass alkali carbonates. Unidentified alkali carbonate (Alk.cb, (a–i) and intergrowth of shortite and aphthitalite (Sot + Att. (c,d,f,h). Figure (g) shows shortite without aphthitalite (the sample was prepared using water, and aphthitalite lamellae were destroyed/dissolved)). Mineral symbols are those defined in Table 1.
Figure 5. BSE images of kimberlite groundmass alkali carbonates. Unidentified alkali carbonate (Alk.cb, (a–i) and intergrowth of shortite and aphthitalite (Sot + Att. (c,d,f,h). Figure (g) shows shortite without aphthitalite (the sample was prepared using water, and aphthitalite lamellae were destroyed/dissolved)). Mineral symbols are those defined in Table 1.
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Figure 6. BSE images and x-ray element maps of kimberlite groundmass alkali carbonates (a,b). Mineral symbols are those defined in Table 1.
Figure 6. BSE images and x-ray element maps of kimberlite groundmass alkali carbonates (a,b). Mineral symbols are those defined in Table 1.
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Figure 7. BSE images (a–d) and x-ray element maps (d) of shortite-aphthitalite intergrowth and the same intergrowth where exposed aphthitalite was destroyed/dissolved during the preparation of a sample using water (e–g). Mineral symbols are those defined in Table 1.
Figure 7. BSE images (a–d) and x-ray element maps (d) of shortite-aphthitalite intergrowth and the same intergrowth where exposed aphthitalite was destroyed/dissolved during the preparation of a sample using water (e–g). Mineral symbols are those defined in Table 1.
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Figure 8. BSE images and x-ray element maps of kimberlite groundmass aphthitalite (a) and aphthitalite inclusions in alkali carbonate (b). Cavity—a cavity obtained by polishing the sample. Mineral symbols are those defined in Table 1.
Figure 8. BSE images and x-ray element maps of kimberlite groundmass aphthitalite (a) and aphthitalite inclusions in alkali carbonate (b). Cavity—a cavity obtained by polishing the sample. Mineral symbols are those defined in Table 1.
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Figure 9. BSE images of kimberlite groundmass chlorides—halite (a–i) and sylvite (h,i). Mineral symbols are those defined in Table 1.
Figure 9. BSE images of kimberlite groundmass chlorides—halite (a–i) and sylvite (h,i). Mineral symbols are those defined in Table 1.
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Figure 10. BSE images and X-ray element maps of kimberlite groundmass chlorides (a,b). Mineral symbols are those defined in Table 1.
Figure 10. BSE images and X-ray element maps of kimberlite groundmass chlorides (a,b). Mineral symbols are those defined in Table 1.
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Figure 11. Raman spectra of kimberlite alkali carbonates. Not-marked bands correspond to different vibration of (CO3)2− anionic group; ▲—medium/weak bands at 993–997 cm−1 assigned to the ν1(SO4)2− vibration; ■—weak bands at 963–965 cm−1 assigned to the ν1(PO4)3− vibration. Two types of Raman spectra of unknown Na-Ca-K-S-rich carbonate/carbonates are shown in Figures (a,b). The different colors of the Raman spectra correspond to two separate mineral grains.
Figure 11. Raman spectra of kimberlite alkali carbonates. Not-marked bands correspond to different vibration of (CO3)2− anionic group; ▲—medium/weak bands at 993–997 cm−1 assigned to the ν1(SO4)2− vibration; ■—weak bands at 963–965 cm−1 assigned to the ν1(PO4)3− vibration. Two types of Raman spectra of unknown Na-Ca-K-S-rich carbonate/carbonates are shown in Figures (a,b). The different colors of the Raman spectra correspond to two separate mineral grains.
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Figure 12. Ambient and high-temperature Raman spectra of natural and synthetic Na-Ca carbonates: (a) hexagonal γ-(Na,K)2Ca(CO3)2 at 500 °C and (b) hexagonal β-(Na,K)2Ca(CO3)2 at 400 °C [36]; (c) pure synthetic orthorhombic α-Na2Ca(CO3)2 and (d) nyerereite orthorhombic (Na,K)2Ca(CO3)2 [37]; (e) shortite orthorhombic Na2Ca2(CO3)3 (RRUFF database R050248, [35]).
Figure 12. Ambient and high-temperature Raman spectra of natural and synthetic Na-Ca carbonates: (a) hexagonal γ-(Na,K)2Ca(CO3)2 at 500 °C and (b) hexagonal β-(Na,K)2Ca(CO3)2 at 400 °C [36]; (c) pure synthetic orthorhombic α-Na2Ca(CO3)2 and (d) nyerereite orthorhombic (Na,K)2Ca(CO3)2 [37]; (e) shortite orthorhombic Na2Ca2(CO3)3 (RRUFF database R050248, [35]).
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Figure 13. Raman spectra of shortite-aphthitalite intergrowth (a), aphthitalite inclusions in kimberlite groundmass Na-Ca-K-S-rich carbonate (b), and kimberlite groundmass aphthitalite (c). Mineral symbols are those defined in Table 1. The different colors of the Raman spectra correspond to two separate mineral grains.
Figure 13. Raman spectra of shortite-aphthitalite intergrowth (a), aphthitalite inclusions in kimberlite groundmass Na-Ca-K-S-rich carbonate (b), and kimberlite groundmass aphthitalite (c). Mineral symbols are those defined in Table 1. The different colors of the Raman spectra correspond to two separate mineral grains.
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Figure 14. Variation diagrams of Na2O against CaO (a), K2O against Na2O (b), SO3 against K2O (c), and (Na+K)/Ca (at.%) against Na2O (d) in the composition of different alkali carbonates from Udachnaya-East unserpentinized coherent kimberlite. Blue cycles (Alk.cb1)—groundmass alkali carbonate with Raman spectra type I (Figure 11a); orange squares (Alk.cb2)—groundmass alkali carbonate with Raman spectra type II (Figure 11b); green rhombus (Sot + Att)—groundmass shortite-aphthitalite intergrowth (Figure 7a–d); red triangles (Sot)—groundmass shortite, in which exposed aphthitalite was dissolved during sample preparations (Figure 7e–g); yellow triangles (Incl 1)—alkali carbonate inclusions near the core of calcite microphenocryst (Figure 15b); pink triangles (Incl 2)—alkali carbonate inclusions in rim of calcite microphenocryst (Figure 15d); aquamarine triangles (Nye (G17))—nyerereite from Oldoinyo Lengai rocks [37]; violet squares (Zmk (Yeg88)) zemkorite from Udachnaya-East kimberlite [24]; red star (Na2Ca(CO3)2 (ideal))—calculated composition of pure carbonate with formula Na2Ca(CO3)2; aquamarine star (Na2Ca2(CO3)3 (ideal))—calculated composition of pure carbonate (shortite) with formula Na2Ca2(CO3)3. At panel (a), solid lines show compositions in which Na/Ca = 1 (at.%) and Na/Ca = 2 (at.%).
Figure 14. Variation diagrams of Na2O against CaO (a), K2O against Na2O (b), SO3 against K2O (c), and (Na+K)/Ca (at.%) against Na2O (d) in the composition of different alkali carbonates from Udachnaya-East unserpentinized coherent kimberlite. Blue cycles (Alk.cb1)—groundmass alkali carbonate with Raman spectra type I (Figure 11a); orange squares (Alk.cb2)—groundmass alkali carbonate with Raman spectra type II (Figure 11b); green rhombus (Sot + Att)—groundmass shortite-aphthitalite intergrowth (Figure 7a–d); red triangles (Sot)—groundmass shortite, in which exposed aphthitalite was dissolved during sample preparations (Figure 7e–g); yellow triangles (Incl 1)—alkali carbonate inclusions near the core of calcite microphenocryst (Figure 15b); pink triangles (Incl 2)—alkali carbonate inclusions in rim of calcite microphenocryst (Figure 15d); aquamarine triangles (Nye (G17))—nyerereite from Oldoinyo Lengai rocks [37]; violet squares (Zmk (Yeg88)) zemkorite from Udachnaya-East kimberlite [24]; red star (Na2Ca(CO3)2 (ideal))—calculated composition of pure carbonate with formula Na2Ca(CO3)2; aquamarine star (Na2Ca2(CO3)3 (ideal))—calculated composition of pure carbonate (shortite) with formula Na2Ca2(CO3)3. At panel (a), solid lines show compositions in which Na/Ca = 1 (at.%) and Na/Ca = 2 (at.%).
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Figure 15. BSE-images and x-ray element maps of calcite microphenocryst from coherent kimberlite (a) containing mineral (b,d) and primary melt (c,e) inclusions. Mineral symbols are those defined in Table 1.
Figure 15. BSE-images and x-ray element maps of calcite microphenocryst from coherent kimberlite (a) containing mineral (b,d) and primary melt (c,e) inclusions. Mineral symbols are those defined in Table 1.
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Figure 16. Raman spectra of alkali carbonate inclusions in calcite microphenocryst (a), shown in Figure 15b, and daughter olivine within melt inclusions in calcite microphenocryst (b), shown in Figure 15e. ▲—weak bands at 996 cm−1 assigned to the ν1(SO4)2− vibration. Mineral symbols are those defined in Table 1. The different colors of the Raman spectra correspond to two separate mineral grains.
Figure 16. Raman spectra of alkali carbonate inclusions in calcite microphenocryst (a), shown in Figure 15b, and daughter olivine within melt inclusions in calcite microphenocryst (b), shown in Figure 15e. ▲—weak bands at 996 cm−1 assigned to the ν1(SO4)2− vibration. Mineral symbols are those defined in Table 1. The different colors of the Raman spectra correspond to two separate mineral grains.
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Table 1. Groundmass mineral assemblage of unserpentinized Udachnaya-East kimberlite.
Table 1. Groundmass mineral assemblage of unserpentinized Udachnaya-East kimberlite.
MineralFormulaSymbol
Olivine(Mg,Fe)2SiO4Ol
MonticelliteCa(Mg,Fe)SiO4Mtc
PhlogopiteKMg3(AlSi3O10)(OH)2Phl
Spinel *(Fe,Mg)(Cr,Al,Fe,Ti)2O4Spl
PerovskiteCaTiO3Prv
ApatiteCa5(PO4)3(F,Cl,OH)Ap
CalciteCaCO3Cal
Unidentified alkaline carbonate(Na,K)6Ca4(CO3,SO4)7 **Alk.cb
Shortite ***Na2Ca2(CO3)3Sot
AphthitaliteK3Na(SO4)2Att
HaliteNaClHlt
SylviteKClSyl
*—spinel group minerals. **—proposed formula of unidentified alkaline carbonate was calculated from its chemical composition. ***—pure shortite was identified only in the samples/thin sections that were prepared using water; in initial samples, this mineral always forms a thin intergrowth with aphthitalite (Sot + Att).
Table 2. Assemblages of mineral inclusions in groundmass alkaline carbonates and halites from Udachnaya-East unserpentinized kimberlite.
Table 2. Assemblages of mineral inclusions in groundmass alkaline carbonates and halites from Udachnaya-East unserpentinized kimberlite.
Solid-Phase Mineral InclusionHost-Mineral
Alkaline carbonateHalite
Olivine++
Monticellite+-
Phlogopite++
Spinel *++
Perovskite+-
Apatite++
Calcite++
Aphthitalite+-
Sylvite-+
“+”—mineral was identified as solid-phase inclusions in the host-mineral. “-”—mineral is absent as mineral inclusions in the host mineral. *—spinel group minerals.
Table 3. Representative electron microprobe analyses (wt%) of groundmass alkali carbonates and sulfate from Udachnaya-East unserpentinized kimberlite and crystalline inclusions of alkali carbonates in calcite microphenocryst.
Table 3. Representative electron microprobe analyses (wt%) of groundmass alkali carbonates and sulfate from Udachnaya-East unserpentinized kimberlite and crystalline inclusions of alkali carbonates in calcite microphenocryst.
Na2OK2OCaOSrOSO3P2O5Total
Alk.cb 121.85.329.70.45.40.362.9
21.45.029.5b.d.l.5.5b.d.l.61.4
21.45.129.1b.d.l.5.2b.d.l.60.8
21.25.629.2b.d.l.5.9b.d.l.61.9
Alk.cb 222.35.629.90.35.70.564.3
21.85.329.00.45.70.362.5
21.85.229.60.35.70.362.9
21.45.329.40.35.60.362.3
Sot19.70.334.9b.d.l.0.4b.d.l.55.3
20.20.333.20.40.6b.d.l.54.9
Sot + Att*18.87.129.7b.d.l.8.30.264.6
Att9.038.7b.d.l.b.d.l.43.61.492.8
Incl 120.74.931.2b.d.l.3.4b.d.l.60.2
Incl 222.65.029.1b.d.l.5.1b.d.l.61.8
Alk.cb 1—groundmass alkali carbonates with Raman spectra type I (Figure 11a); Alk.cb 2—groundmass alkali carbonates with Raman spectra type II (Figure 11b). Sot—groundmass shortite-aphthitalite intergrowth where exposed aphthitalite was dissolved during sample preparations; Sot + Att*—groundmass shortite-aphthitalite intergrowth (average of five bulk analyses, see also Figure 14); Att—groundmass aphthitalite; Incl 1—alkali carbonate inclusion near the core of calcite microphenocryst; Incl 2—alkali carbonate inclusion in the rim of calcite microphenocryst (see details in Figure 15); b.d.l.—below the detection limit.
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Golovin, A.V. Unusual Mineralogy of Kimberlites: Alkali Carbonates, Sulfates, and Chlorides Among Groundmass Minerals from Unserpentinized Coherent Kimberlite of the Udachnaya-East Pipe, Siberian Craton. Minerals 2025, 15, 586. https://doi.org/10.3390/min15060586

AMA Style

Golovin AV. Unusual Mineralogy of Kimberlites: Alkali Carbonates, Sulfates, and Chlorides Among Groundmass Minerals from Unserpentinized Coherent Kimberlite of the Udachnaya-East Pipe, Siberian Craton. Minerals. 2025; 15(6):586. https://doi.org/10.3390/min15060586

Chicago/Turabian Style

Golovin, Alexander V. 2025. "Unusual Mineralogy of Kimberlites: Alkali Carbonates, Sulfates, and Chlorides Among Groundmass Minerals from Unserpentinized Coherent Kimberlite of the Udachnaya-East Pipe, Siberian Craton" Minerals 15, no. 6: 586. https://doi.org/10.3390/min15060586

APA Style

Golovin, A. V. (2025). Unusual Mineralogy of Kimberlites: Alkali Carbonates, Sulfates, and Chlorides Among Groundmass Minerals from Unserpentinized Coherent Kimberlite of the Udachnaya-East Pipe, Siberian Craton. Minerals, 15(6), 586. https://doi.org/10.3390/min15060586

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