The 20th century was noted for discovering the world's largest Yakutian Kimberlite Province (YaKP) within the Siberian craton, numbering more than 20 primary diamond deposits different in efficiency (Fig. 1). This discovery occurred due to works of Sobolev, 1941, Moor, 1940, Bobrievich et al., 1950, 1964. The first kimberlite pipe, Zarnitsa, was discovered by Larisa Popugaeva in 1955. Then, within several years, were discovered the major diamond pipes (Mir, Udachnaya, Aikhal, etc). In 1958, the Yakutalmaz industry (now PJSC "ALROSA") started quarry mining. Over 65 years, some of the deposits (Imeni XXIII S'ezda KPSU, Sytykanskaya, Dachnaya, Taezhnaya) had almost completed. Some of the deposits are continued open quarry mining (Komsomol'skaya, Yubileynaya, Zarnitsa) or quarry mining has turned into underground (Mir, Internatsional'naya, Udachnaya, Aikhal). Soon, water will fill the quarries, and, instead of the most primary deposits, deep-water lakes will emerge (at the Imeni XXIII S'ezda KPSU and Tayozhnaya pipes, they already exist), and many unique 'windows into the mantle' will be closed forever.
Despite a long mining history, the information on the pipe interior, and the kimberlite material composition has been insufficient in the literature. The first major monograph, Diamond Deposits of Yakutia was published in the late 1950s (Bobrievich et al., 1959). Kharkiv et al. (1991, 1997, 1998) provided a more detailed description of the pipe texture, chemical and mineral compositions of kimberlites, but only for a limited number of deposits. The isotope-geochemical characteristics of kimberlites were also provided only for the major fields in separate papers (Agashev et al., 2006; Bogatikov et al., 2004; Kononova et al., 2005; Kostrovitsky et al., 1999, 2007). The Atlas of primary deposits of diamonds in the YaKP (Kostrovitsky et al. 2015) presents volume models for pipe bodies, a description of deposit interior, graphic and tabular presentation for the composition of barophilic and groundmass minerals, as well as isotope-geochemical characteristics for kimberlites of all the 20 deposits in Western Yakutia. This book produced the basis for writing two papers: the present one provides general data on the deposits, describes their interior, and discusses the issues of interior multiphase structure, petrography, and mineralogy of kimberlites, while the other summarizes the results of studying the chemical composition, features of trace elements distribution, and Sr-Nd isotope systematics for the kimberlites composing the main deposits in Western Yakutia.
We use the following abbreviations for the minerals: olivine - Ol, monticellite - Mtc, serpentine - Srp, chlorite - Chl, Mg-Ilmenite - Ilm, garnet - Grt, spinel - Spl, chromite - Chr, calcite - Cal, dolomite - Dol, carbonate - Carb, phlogopite - Phl, apatite - Ap, magnetite - Mag, titanium-magnetite - TiMag, perovskite - Prv.
Issues Of Kimberlite Classification
Diamond deposits in Western Yakutia are composed of the kimberlites belonging, mainly, to Group I, the most widespread in all the kimberlite provinces worldwide (Smith, 1983; Mitchell, 1986). An exception is the Nakyn deposits composed of the kimberlites belonging to an intermediate type, between the Group I and Group II kimberlites (Bogatikov et al., 2004; Pokhilenko et al., 2000; Serov et al., 2001). The existence of regional distinctions among kimberlites (Group I) by FeOtot, TiO2, and K2O within the YaKP formed the basis to detect petrochemical types (Kostrovitsky et al., 2007). We differ kimberlites of 5 petrochemical types: 1) high-Magnesian low-potassium (high-Mg, low-К), 2) high-Magnesian high-potassium (high-Mg, high-К), 3) Magnesian-ferrous (Mg-Fe), 4) ferrous-titanous, low-potassium (Fe-Ti, low-К), 5) ferrous-titanous high-potassium (Fe-Ti, high-K). The kimberlites of the latter two types (4, 5) occur dominantly only in the YaKP northern fields. The kimberlites of the first three (1, 2, 3) petrochemical types prevail in the southern diamondiferous fields. Petrochemical heterogeneity is proven by different mineralogy. For example, high-Mg kimberlites contain Ol, where FeO is no more than 6–7 wt%; in the heavy-mineral concentrates, instead of Ilm, Grt, and Chr prevail (e.g., at the Aikhal, Internatsional'naya, Botuobinskaya, Nyurbinskaya, and Mayskaya). There is no Ilm in high-Mg kimberlites, or it is very rare. The Mg-Fe kimberlites contain Ol, in which FeO varies within 7–14 wt%; herewith, Ilm prevails in the heavy-mineral concentrates. The only exceptions are Mg-Fe kimberlites from the Upper Muna deposits, where perovskite (instead of Ilm) is widely developed.
Textural-genetic classification of kimberlites and kimberlite phases remains a debatable question. Kimberlite classification schemes with "volcanologic" terminology proposed over the last years (Cas et al., 2008; 2009; Scott Smith et al., 2013). There are basic textural-genetic subdivisions: coherent kimberlite - rock formed entirely from cooling and direct crystallization or solidification of Magma (or lava); and volcanoclastic kimberlite - rock related to a kimberlite volcano and including kimberlitic volcanic particles. The first is the hypabyssal kimberlites contain detritus, basically, of the lithospheric mantle rocks only, whereas detritus of frame directly containing pipe plays an Appreciable role in volcanoclastic kimberlite, along with xenogenic mantle material. The other distinction is in the texture and the composition of the kimberlite groundmass: a) massive and fluidal reflecting, mainly, the initial melt nature of the crystallizing kimberlite are characteristic of coherent kimberlites (formerly hypabyssal kimberlites); and b) breccia texture reflecting processes of fluidization, fragmentation, disintegration, segregation, etc (Smith et al., 2018), saturation by detritus of directly host rocks characterizes volcanoclastic kimberlites.
Nevertheless, despite our critical attitude, in this paper, while describing kimberlites, we use the terminology corresponding to the conventional (Smith et al, 2018): 1) coherent kimberlite (CK), 2) volcanoclastic kimberlite (VK), 3) pyroclastic kimberlite (PK), 4) re-sedimental volcanoclastic kimberlite (RVK).
General Information On Deposits
Primary diamond deposits in Western Yakutia (21 in total) are only in the YaKP southern half, within five kimberlite fields: Mirninsky, Daldyn, Alakit-Markha, Nakyn, and Upper Muna (Fig. 1). The deposits' age, judging from U-Pb by zircons and perovskites (Davis et al., 1980; Kinny et al., 1997; Agashev et al., 2004; Sun et al, 2014, 2018), is determined as D-C and varies within 350–370 mln years. All the pipe bodies of the deposits were intruded into a thick (2.0-2.5 km) sedimentary cover with the Cambrian-Silurian terrigenous-Carbonate composition (Kharkiv et al., 1998). This sedimentary cover, according to Brakhfogel (1984), Appeared to be eroded, by this time, about 300 m deep for the Mirninsky, 650 m for the Alakit-Markha, 950 m for the Daldyn, and 1300 m deep for the Upper Muna fields. However, judging by the preservation of kimberlite crater facies (at the Yubileynaya and Krasnopresnenskaya pipes within the Alakit-Markha field), judging by the difference (~ 100 m) in absolute marks of the territories for two adjacent Alakit-Markha and Daldyn fields, one may regard the specified erosive level thicknesses exaggerated. We assume that the eroded strata thickness for those fields does not exceed 300 m and 400 m, respectively.
The distribution of high diamond-grade pipes within separate fields of YaKP is extremely irregular. The following regularity was established empirically: the diamond grade of the kimberlite fields drops south-to-north of the YaKP (Fig. 1). At the southernmost deposits (Mirninsky and Nakyn), the dominating part of the known kimberlite deposits appeared with very high and high diamond content. At the Mirninsky field, five of nine pipes were related to deposits, herewith, the Internatsional'naya and the Imeni XXIII S'ezda KPSU are very high, and the Mir pipe is high diamond content deposits. The Nakyn field is represented by three kimberlite bodies, each of which is composed of a very high diamond content. The only five pipes, from more than 60 pipes within the Alakit-Markha field, belong to deposits with medium diamond content (Aikhal, Yubileynaya, Sytykanskaya, Komsomol'skaya, Krasnopresnenskaya). Further, northeastward, there is the Daldyn field, which comprises more than 60 pipes. There is only one pipe (Udachnaya) is a major deposit with a high diamond content, and two other pipes (Zarnitsa and Dal'nyaya) are deposits with a medium diamond content (Table 1) within the Daldyn field. The Upper Muna field is the most northern diamond area with 16 kimberlite bodies, where only three pipes are deposits with a medium diamond content.
Table 1
Characteristics of diamond mining in the deposits of Yakutia.
| Deposit | Total stock in carat, in mln | Content (reserves), ct/t | Diamond quality, USD/ct | Diamond quality, gradation |
| Mir | 453.00 | 4.038 | 108.7 | High |
| International’naya | 146.15 | 8.155 | 186 | High |
| Named XXIII Congress of the CPSU | 0.94 | 3.160 | 186 | High |
| Dachnaya | 0.70 | 1.780 | 109 | High |
| Zarnitsa | 43.71 | 0.266 | 143.9 | High |
| Udachnaya | 1025.99 | 2.045 | 80.7 | Average |
| Dal’nyaya | 9.71 | 0.540 | 37.7 | Low |
| Irelyakhskaya | 1.52 | 0.360 | 70 | Average |
| Krasnopresnenskaya | 35.12 | 0.912 | 25 | Low |
| Yubileinaya | 297.18 | 0.775 | 127 | High |
| Komsomolskaya | 7.36 | 0.385 | 217 | Unique |
| Aikhal | 163.50 | 5.074 | 39.5 | Low |
| Zarya | 7.11 | 0.179 | 200 | High |
| Sytykanskaya | 14.26 | 0.983 | 90 | Average |
| Zapolyarnaya | 21.70 | 0.671 | 107 | High |
| Deimos | 1.58 | 0.50 | 107 | High |
| Novinka | 10.54 | 0.692 | 107 | High |
| Komsomolskaya-Magnitnaya | 6.61 | 0.496 | 107 | High |
| Poiskovaya | 1.90 | 0.328 | 107 | High |
| Nyurbinskaya | 145.37 | 5.227 | 78.4 | Average |
| Botuobinskaya | 102.24 | 6.202 | 92.7 | Average |
| Maiskaya | 15.34 | 2.555 | 89.5 | Average |
Diamond deposits are represented by pipe bodies of different sizes and morphology, composed of different-composition kimberlites. Brief geological data on each of the deposits represented in this paper is a compilation of the information obtained both from our observations and from literature (Kharkiv et al., 1998; Kostrovitsky et al., 2015).
Economic Evaluation Of Diamond Deposits
All 21 primary diamond deposits of YaKP vary in size, diamond grade, and rough diamond quality (Table 1).
Each of the YaKP main diamondiferous fields has unique deposits by diamond resource weight (over 100 million carats). The Udachnaya deposit, which is represented by two ore bodies, contains more than one billion carats of diamonds, with total resources of over 1025 million carats. The deposit is the largest diamond deposit not only in Russia but also in the world. With the deposit open-pit mining, the annual production of diamonds in some years exceeded 20 million carats. Currently, about 5 million carats of diamonds are mined from the deposit annually. The second largest deposit is the Mir pipe. The total resources of the deposit are 453 million carats of diamonds. The Yubileynaya deposit contains 297 million carats of diamonds. Among the leaders of Yakutian deposits in terms of reserves, the following pipes should be also highlighted: Aikhal (163 million carats), Internatsional'naya (146 million carats), Nuyrbinskaya (145 million carats), and Botuobinskaya (102 million carats).
The rest of the deposits in terms of reserves may be classified as medium (10–25 million carats) and small (less than 10 million carats). There are Zarnitsa (43 million carats), Krasnopresnenskaya (35 million carats), and Zapolyarnaya (21 million carats) pipes.
The next main indicator for the estimation of diamond deposit economical potential and investment decisions is the average diamond content within the body. Among the deposits of Yakutia, the Internatsional'naya pipe stands out, there is an average diamond grade of more than 8.2 cts/t. Deposits with ultra-high grades of diamonds in the ore (more than 5 cts/t) also include the following pipes: Botuobinskaya (6.2 cts/t), Nuyrbinskaya (5.23 cts/t), Aikhal (5.07 cts/t). High diamond grades (2–5 cts/t) are identified in the Mir (4.04 cts/t), Imeni XXIII S'ezda KPSU (3.16 cts/t), Mayskaya (2.56 cts/t), Udachnaya (2.05 cts/t) deposits. The Dachnaya pipe has a higher diamond content (1.78 cts/t). The rest of the YaKP deposits are characterized by medium and low diamond grades (less than 1 cts/t).
The most important indicator for the decision on the deposit development is the level of "marketable production" or proceeds from the sale of diamonds contained in a ton of ore. This indicator determines the deposit's operating profitability. Currently, there are developing YaKP primary deposits with a level of marketable production higher than 30 US$/t. Deposits that do not meet this criterion remain in reserve (Dal'nyaya, Krasnopresnenskaya). The most marginal in terms of marketable output is the Internatsional'naya deposit, where one ton of ore contains diamonds worth US$ 1,516. High commercial production rates are observed mainly for the Mirninsky field (Imeni XXIII S'ezda KPSU – 587 US$/t, Mir − 438 US$/t, Dachnaya − 194 US$/t) and Nakyn field (Botuobinskaya − 574 US$/t, Nuyrbinskaya – 409 US$/t, Mayskaya – 228 US$/t) pipes. In the Alakit-Markha and Daldyn fields, the Aikhal (200 US$/t) and Udachnaya (165 US$/t) pipes are allocated. The rest of the pipes in the Yakutian province contain less than 100 US$/t of marketable output. However, it should be noted that the value of rough diamonds, despite the low grade, predetermines the efficiency of the development of deposits with a low grade, such as Komsomol'skaya, Zarnitsa, Zarya pipes, and others.
Currently, most of the primary diamond deposits in Yakutia are in the mining and development stage. Udachnaya, Aikhal, and Internatsional'naya pipes are mined by underground shafts. The Mir pipe underground mine is at the design stage and diamond production from the pipe is expected after 2030. Zarnitsa, Novinka, Zapolyarnaya, Deymos, Komsomol'skaya-Magnitnaya, Yubileynaya, Zarya, Botuobinskaya, Nuyrbinskaya, Mayskaya pipes are under operation by open pit mining. The extraction of diamonds from the Sytykanskaya, Komsomol'skaya, Imeni XXIII S'ezda KPSU, and Dachnaya pipes has been completed.
PJSC ALROSA carries out the production of diamonds from the primary YaKP deposits. The largest abundance of diamonds in 2020 was recovered from the Yubileynaya (7.0 million carats), Udachnaya (4.9 million carats), Aikhal (2.0 million carats), Internatsional'naya (1.9 million carats), Zapolyarnaya (1.8 million carats) pipes.
Brief Description For Deposits
The supplementary Table 1s provides information on the discoverers of the deposits and the size of the pipes.
Mirninsky Field
The Mir deposit is situated in the suburbs of the Mirny. Open-pit mining was started in 1959 and continued until 2001. The open mining depth was 525 m, the extracted ore volume was 67926 thousand tons, and the mean diamond grade was 4.07 carat/t; the marketed diamonds totaled 175 billion Dollars over that time. 2009 through 2017, there was underground mining at the deposit, but, after a major accident, it was temporarily stopped.
The Mir pipe (with the Sputnik pipe located 60 m NW) and three kimberlite veins form a common subvolcanic system (Fig. 2). The kimberlite veins are three sections of the common vein that is the feeder for the Mir and Sputnik and that was broken through by those pipes. Judging by the relations between the vein and pipe bodies, the following intrusion sequence was established: vein - Sputnik - Mir. Down to 300 m, the Mir is a diatreme, oval in the plan view, NW extended, funnel-shaped. Its surficial size was 340×225 m, turning into the conduit with sub-vertical walls with depth. The ratio between the long and short axes of the pipe's horizontal sections increases from 1.5 on the day surface to 2.4 at 600 m. Within 600–1000 m, the pipe horizontal section becomes an elongated oval, and, at 1000–1200 m, the mining body becomes dike-shaped.
The Sputnik surficial size was 106×51 m, its shape being oval with the NW-extended long axis. At a depth of 300 m, the quarry exposed a subhorizontal tubular body of kimberlite (~ 160 m long and 45x45 m wide) connecting the Sputnik and Mir pipes (Fig. 2). The Mir pipe breaks through terrigenous-carbonate and halogenous-Carbonate Cambrian rocks, as well as through two sills and a Late-Devonian dolerite dike at 500 m and 1100 m, respectively (Kharkiv et al., 1998). Starting with 550 m, evaporate strata with mineral salt play an essential role in the section.
There are different viewpoints on the Mir interior (Zolnikov et al., 1963, 1975; Francesson, 1962, 1968; Kharkiv et al., 1997, 1998; Shalaev, Vladimirov, et al., 1972). Unfortunately, most of the structure models were developed only for surficial levels of a pipe. According to Kharkiv et al. (1998), two VK phases and one CK phase participated in forming the Mir upper levels. The first and the second phases composed the NW and SE halves of the pipe, respectively. A dyke-like body 120x40 m in size, found in the southeastern part of the pipe, was attributed by the authors to the third phase. Botkunov and the geologist's team of the company "Yakutalmaz" (ALROSA's predecessor) detected six kimberlite types presumably relating to different intrusion phases (Vladimirov et al., 1981). What one may say reliably is that VKs and PKs with different detritus saturation of the host rocks, with different abundances of Ilm, Grt, Chr, and Ol, substituted by srp, dominate. At a pipe depth of more than 760 m, blocks of kimberlite rocks with unaltered olivine were found, which is assumed (Kostrovitsky and Yakovlev, 2018) to be associated with host rocks of evaporate salts. The relative volume of massive hypabyssal kimberlites increases with depth. The relative volume of hypabyssal massive-texture kimberlites increases with the depth. Also, a new species of fine-porphyry CK composing a dike is found (Zolnikov et al., 1981). A volume model for the Mir pipe (Fig. 2), where there are 4 kimberlite species relating to individual intrusion phases, is idealized.
By chemical composition, the kimberlites composing the Mir relate to the Mg-Fe type with a relatively high FeOtot, TiO2, and low CaCO3: on average, of 20 analyses, their compositions are 7.9, 1.86, and 16.7%, respectively (authors' data). In the heavy-mineral concentrates from kimberlite, Mg-Ilmenite dominates (Table 2).
Table 2
The content of indicator barophilic minerals from the heavy fraction of kimberlites in the pipes of the deposits (according to the data obtained by the geologists of NIGP AK ALROSA).
| | Content of minerals, in g/t |
| Pipe (Deposit) | grt | ilm | ol | prx | spl |
| Mir | 6700 | 12100 | 655 | 1259 | 28 |
| Internatsional’naya | 7176 | 203 | 991 | 55 | 200 |
| Named of the 23rd congress of the CPSU | 1151 | 470 | 0 | 0 | 300 |
| Dachnaya | 4000 | 700 | 0 | 0 | 110 |
| Tayozhnaya | 1500 | 16500 | 0 | 0 | 6 |
| Aikhal | 750 | 55 | 24 | 3.1 | 116 |
| Yubileynaya | 1050 | 2300 | 277 | 1.4 | 14 |
| Komsomol’skaya | 4326 | 9313 | 0 | 3.7 | 0.8 |
| Sytykanskaya | 1500 | 11000 | 0 | 0 | 6 |
| Krasnopresnenskaya | 1000 | 2000 | 0 | 0 | 300 |
| Zarya | 4817 | 18329 | 83 | 1.1 | 17 |
| Udachnaya-Eastern | 1990 | 3588 | 55275 | 11 | 6 |
| Udachnaya-Western | 2400 | 2268 | 240 | 2.3 | 2.4 |
| Zarnitsa | 3693 | 10638 | 159 | 5.6 | 7.3 |
| Botuobinskaya | 6487 | 25 | 2.0 | 13 | 42 |
| Nyurbinskaya | 1861 | 135 | 7.4 | 45 | 13 |
| Mayskoe | 388 | 30 | 0 | 0 | 1.3 |
| Zapolyarnaya | 2665 | 15 | 3135 | 27 | 3.4 |
| Deymos | 414 | 29 | 13612 | 10 | 6.4 |
| Komsomol’skaya-Magnitnaya | 2981 | 9.4 | 10867 | 19 | 1.4 |
| Novinka | 2079 | 54.0 | 11368 | 63 | 1.7 |
| Poiskovaya | 60 | 34.0 | 4620 | 2.3 | 4.8 |
The Imeni XXIII S'ezda KPSU deposit is located 14 km southwest of the Mirny. The single-phase pipe is composed of carbonized PK (Fig. 2) saturated irregularly with sediment rock fragments (10–60%). There are fluidal-structure kimberlite sites created by the subparallel orientation of Cal microlites. The kimberlite by its chemical composition refers to the high-Mg type with relatively low FeOtot, TiO2, and high CaCO3, the average of 6 analyses being 4.57, 0.66, and 38,1%, respectively (Kharkiv et al., 1998)). The garnet dominates in the heavy-mineral concentrates of kimberlites (Table 2).
The Internatsional'naya deposit is situated 16 km SW of the Mirny. The pipe breaks through terrigenous-carbonate Low-Paleozoic rocks and was overlain by 2-9-m low-Jurassic sediments. Until 1999, the deposit had been developed as a quarry, but now underground mining occurs. The quarry's total depth is 284 m.
The pipe is accompanied by a system of dikes oriented NE, NW, and sub meridionally. On the surface, the pipe Appeared as an irregular oval elongated NW (340°), its size being 152x112 m (Fig. 2). A sharp decrease in the cross-sectional area of the pipe to a depth of 120 m. Deeper, the pipe became sub-vertical, and, as deep as 1000 m, its horizontal section size does not decrease, although it varies depending on the host rock. The pipe cross-section change is established at -200 ÷-400 m. Here, at the low-Cambrian evaporate strata, one observes an appreciable expansion of the pipe body, where mineral salt layers intersect the latter, and its constrictions at the level of Dol interlayers (Fig. 2).
The Internatsional'naya pipe is composed of two VK phases and one phase of massive-texture CK, all being almost completely serpentinized. An exclusion is individual blocks of kimberlite rocks with unaltered Ol, which occurred at 650–750 m from the surface, where the pipe host rocks are Cambrian evaporate strata of essentially halite composition.
CK occurred in separate bulk massive blocks, in autholiths, as well as in dikes and veins. All the pipe-composing kimberlites by their chemical composition belong to the high-Mg type with a relatively low FeOtot and TiO2 (the average of 141 analyses being 5.81 and 0.43 wt%, respectively after Vasilenko et al., 1997). Garnet dominates in heavy-mineral concentrates (Table 2).
The Internatsional'naya deposit is the world leader in the diamond grade (7.82 carat/t). High-quality diamonds are, generally, octahedrons (63%), rhombic-dodecahedrons (9%), and combined shapes (27%). Approximately 70% of the diamonds are colorless. The inclusions of the ultramafic mineral assemblage are dominates (99%) in the diamonds (Kharkiv et al., 1997).
The Dachnaya deposit is located 7 km south of the Mirny. The quarry development of the deposit started in 2001 and was terminated in 2005. In the plan view, the Dachnaya has a rounded body. With depth, the kimberlite body narrows, persisting in the cross-section isometric outline; deeper, the cross-section obtains an oval shape with a long NE axis (Fig. 2).
This single-phase pipe is VK-composed. The host-rock xenolith abundances vary widely: from 15 to 50% in the pipe central part, reaching 70% near the host frame. High saturation with shallow fragmented material of sedimentary rocks (basically, with potassium feldspar), which one cannot dispose of, when preparing samples for analysis, affected the kimberlite composition, with a relatively high SiO2 and K2O (15.7–47.0% and 1–2%, respectively). By the FeOtot and TiO2 compositions (4.9–6.4% and 0.5–1.1%, respectively), the Dachnaya kimberlites refer to the high-Mg type. Garnet predominates in kimberlite heavy-mineral concentrates. (Table 2).
The Taezhnaya deposit is located 21 km southwest of the Mirny. The pipe is composed of VK and is a single-phase one (Fig. 2). According to variations in the compositions of FeOtot (3.9–5.3%) and TiO2 (0.85–2.7%), kimberlite belongs to the intermediate petrochemical type, between high-Mg (according to FeOtot) and Mg-Fe (according to TiO2). The kimberlites of the pipe are characterized by a high content of the Carbonate component, which is mainly secondary. Mg-Ilmenite dominates in heavy-mineral concentrates (Table 2).
Alakit-markha Field
The Aikhal deposit is situated within Aikhal city. Kharkiv et al (1997, 1998) provided a detailed description of the pipe geological structure. The pipe is an example of a multi-feeder kimberlite system with three hypabyssal separate feeder dykes, which merge into a common body within diatreme and crater zones (Fig. 3). At deep levels from + 374 to + 100 m (see Fig. 3) there are two ore bodies, divided by Carbonate host rocks and deeper (from − 100 m), the north-east body splits into 2 extra bodies. The morphology of feeder dykes changes with depth: sub-vertical walls dominate at the upper levels, but it becomes more variable and sometimes encounter subhorizontal step contacts with host rocks at the lower levels (Vladimirov et al., 1981).
There are different models of the Aikhal interior formation. According to Kharkiv et al. (1997), there are crater facies rocks that participated in the pipe formation: RVK and VK (3-phase intrusion). After Vladimirov et al (1981), massive-texture CK also participates in the pipe formation along with the above kimberlites. CK composes separate bodies in the form of lenses, apophyges, and autholiths in tuff species. It was established that CK intrusion in the Aikhal occurred repeatedly.
The Aikhal kimberlites are high magnesium and low TiO2, which allowed us to refer them to a high-Mg type. Garnet dominates in heavy-mineral concentrates, but there is practically no Ilm here (Table 2).
The Yubileynaya deposit is located 15 km NW of Aikhal city and is the largest within Yakutia. Several kimberlite dikes of the northwest orientation are adjacent to the pipe. Close to the pipe's southwest contact, there is another kimberlite body – the Ozyornaya pipe. On the north-west flank of the Yubileinaya pipe, a large block (more than 50 m long and about 10 m thick) of kimberlites were discovered in the host rocks, displaced by a later trap sill from the south-east part of the pipe. The quarry mining at the deposit started in 1989 and has proceeded until the present. The termination of the ore extraction is scheduled for 2030.
The Yubileynaya pipe was completely overlain by effusive-terrigenous Perm-Triassic deposits intruded Dolerite sills, whose total thickness averaged 66 m. The pipe (Fig. 3) breaks through sedimentary rocks lying subhorizontally (Cm, O1 + 2, and S1). The pipe persisted in a crater part 230 m deep. Deeper, the pipe obtains a steeper (70–85º) occurrence.
The pipe is composed of two phases of CK intrusion, forming (on the western and eastern flanks) large dike-like bodies, and one phase of PK, constituting (starting from the base of the crater part) the central body. Although the kimberlite rocks of the two initial phases are close by textural-structural features and by material composition, they differ in the diamond grade. The crater expansion is composed of RVK, volcanic-sedimentary formations, whose detailed description was done by many researchers (e.g., Kharkiv et al., 1998; Kurszlaukis et al., 2009). At the basement of the crater part, there was a zone saturated with major clumps of sedimentary host rocks, the so-called 'xenolithic belt'.
The kimberlites composing the Yubileynaya have a feature with relatively high FeOtot, TiO2, and dominant Ilm in the heavy mineral concentrates (Table 2), which indicates their belonging to the Mg-Fe type.
The Sytykanskaya deposit is located 27 km northeast of the Aikhal. It had been developed as a quarry from 1980 through 2001. A detailed description of its geological structure is in (Kharkiv et al 1997). About 85% of the pipe area was situated under traps and Permian deposits, and only its NE flank reached the surface. The trap sill thickness over the pipe varied from 5 to 72 m. The pipe host rocks are Carbonate deposits of the low, mid-Ordovician, and Low Silurian.
The deposit comprises two independent bodies: the northeast (main body) and the southwest (Fig. 3). Their size on the surface under traps is 735х160 m (northeast) and 205х62 m (southwest). The area of the ore bodies decreases dramatically through depth. The contacts between the kimberlites and the host rocks are sharp. The northeast body in the plan view is an irregular elongated shape. In essence, the Sytykanskaya north-east body is a two-feeder system at the hypabyssal levels. Within the northeast body, one detects two independent VK-composed conduits (central and northeast). Both conduits are linked between themselves through a transition zone of hybrid rocks, 5 to 40 m thick. This zone is saturated with the detritus of host carbonate rocks. The southwest body, being an elongated ellipse in the plan view, possesses a typical pipe shape with sub-vertical walls. This separate kimberlite body is also VK-composed.
According to A.D. Kharkiv et al. (1991) kimberlites of the north-east body is characterized by a low content of the carbonate component (the average content of CaO + CO2 over 132 samples is 14.5 wt%) and a high content of MgO (30.7 wt%). In the kimberlites of the southwest body, the average CaO + CO2 content for 35 samples is 29.3 wt. %, MgO − 21.9 wt.%. In terms of FeOtotal and TiO2 contents (> 8 wt.% and > 2 wt.%, respectively), the kimberlites of the Sytykanskaya pipe belong to the Mg-Fe petrochemical type. Mg-Ilmenite dominates in heavy mineral concentrates (Table 4).
The Komsomol'skaya deposit is situated 15 km northeast of the Aikhal. The Komsomol'skaya pipe is dike-shaped with a 650х250-m horizontal section. In the central part, it is complicated by a pillar-like expansion (representing the main volume of the deposit) with the 320x225 m horizontal section (Fig. 3). At the south-west and north-east flanks, the ore body narrows to 40–60 and 15–20 m, respectively. The pipe's upper part is funnel-shaped with a dip of the contacts with host rocks to the center at 50–70°. At 50–100 m down from the surface, the pipe contacts obtain sub-vertical occurrence (80–85°).
The pipe breaks through a sediment mantle represented by Ordovician and low-Silurian Carbonate and terrigenous-carbonate rocks, overlain (from the surface) by a trap sill and terrigenous deposits of Permian-Carboniferous. The pipe was intruded by tabular dolerite dykes that dismembered and displaced two large-size blocks from the main ore body.
The pipe is formed by two kimberlite phases: by massive-texture CK from dike-shaped bodies of the early intrusion phase at the northeast and south-west pipe flanks, and second-phase PK from the central body that cuts dike-shaped bodies. The pyroclastic kimberlite is saturated (5–25%) with host-rock detritus. The basement crystalline rock xenoliths in PK make an abundance of up to 3%.
By the FeOtot (7.0-11.5 wt.%) and TiO2 (2.0-3.2 wt.%) content, the Komsomol'skaya kimberlites refer to the Mg-Fe type, which also agrees with a relatively high Ilm content. Mg-Ilmenite dominates in the heavy-mineral concentrates. Ilm and Grt modal quantities are 0.96% and 0.2% in the CK, respectively, as well as 2.11% and 1,26% in PK (Kharkiv et al., 1998). PK, as compared with CK, has a considerably higher diamond grade.
The Krasnopresnenskaya deposit is situated at the Alakit river head, 32 km southwest of the Aikhal city. Kharkiv et al (1997) and Kryuchkov et al. (1989) provided a detailed description of the pipe geological structure. The pipe is overlain by thick C1 and C-P sedimentary deposits, as well as by Perm-Triassic tuffaceous formations (Fig. 3). The overlying rock thickness changes from 57 m at the north-east flank to 143 m in the south-east part of the deposit. In the plan view, under the overlying rocks, the pipe has an ellipse-like form shape. The pipe consists of two isolated cone-shaped bodies dividing from a depth of 160 m.
Krasnopresnenskaya pipe is broken through by a thick (90–118) flat-transverse Dolerite sill (Fig. 3). The sill intrusion caused a deep metasomatic transformation of both kimberlites, and Carbonate host rocks as well transform diamond shape. The thickness of the reaction zone over the sill varies from 20 to 120 m. A detailed description of the mineral composition of the reactionary metasomatic zone is provided in (Kharkiv, 1995).
The crater part of Krasnopresnenskaya pipe (80–100 m deep) is composed of RVK, a sedimentary-volcanogenic rock complex, comprising three sequentially occurring series (top-to-bottom): sedimentary, sedimentary-kimberlite, and tuff (of kimberlite material). Below the crater, the pipe's main volume is composed of pyroclastic kimberlite with a different abundance (2–3 to 20%) of the host rock xenogenous material.
By the FeOtot and TiO2 compositions ranging from low values to relatively high (≥ 8% and ≥ 1.0%, respectively), as well as by a varying Ilm/Grt ratio (the minerals dominate alternatively), the Krasnopresnenskaya kimberlites refer to the intermediate petrochemical type, between high-Mg and Mg-Fe.
The Zarya deposit is located 2 km south-east of Aikhal city (Fig. 3). The pipe is completely overlain by strata of trap-formation rocks (dolerites and tuffs) with large interlayers of terrigenous rocks belonging to the Aikhal'sky suite. The mean thickness of the overlying rock makes 103 m.
The Zarya is composed of two phases of kimberlites different in the diamond grade and the heavy-mineral concentrates content. The first intrusion phase localized, mainly, at the pipe periphery, is represented by massive-texture CK with a relatively low content of indicator minerals. The second phase is related to PK intrusion in the pipe central part. The PK diamond grade is almost 4 times higher than CK; PKs also feature a higher content of indicator minerals.
The Zarya kimberlites by their chemical composition refer to an intermediate petrochemical type (between high-Mg and Mg-Fe). They have wide variations in the FeOtot composition (4.4 through 8.6 wt.%) and relatively high TiO2 (1.5-2.0 wt.%). The heavy-mineral concentrates are represented by Grt and Ilm, the ratio between which, in different blocks, ranges from the dominance of one mineral to the dominance of the other.
Daldyn Field
The Udachnaya deposit is 2 km north of Udachny city. The pipe quarry mining started in 1971 and ended in 2015. Over the entire mining time, extracted were about 350 mln tons of ore containing rough diamonds for a total of $80 bln. Now, underground mining scheduled for more than 50 years has been in operation at the deposit deep levels.
The description of the interior and material composition of the Udachnaya is provided in several papers and monographs (Marshintsev, 1986; Kharkiv et al., 1998; Zinchuk et al., 2003; Kopylova et al., 2016).
On the surface, the deposit was represented by an 895×560 m single body that forked into two isolated cone-shaped pipes starting with the 270 m depth: the Udachnaya-Western (UW) and the Udachnaya-Eastern (UE) (Fig. 4). The body of Upper-Cambrian sedimentary rocks separating them in the diatremes' joint zone is strongly fragmented and crushed. The pipes are traced by drill holes as deep as 1400 m. Both pipes are bodies with steeply dipping sloping walls. There is no common view of both pipes' interiors. Various researchers (Gotovtsev, 1985; Marshintsev, 1986; Zinchuk et al., 1993; Kharkiv et al., 1998) detects up to five kimberlite phases in each pipe. Detailed observations of interrelations among the kimberlite species (Kostrovitsky, Egorov, 1982, 1983) corroborated the insights of mine geologists into a multiphase composition (5 phases) of both the UW and the UE.
The Udachnaya-Western morphological feature is the presence of a 100-150-m host-rock 'visor' in the pipe SW part. The visor reflects a partial overlying that existed by the pipe formation. Also, the so-called 'floating reefs' of the host rocks that were widespread at the UW upper levels circumstantially indicate this possibility. At the deep levels, the UW is assumed to split into two independent feeder dykes. In the UW structure, PK represented by different intrusion phases occupies the bulk of the volume. At the UW edges, established were major blocks of massive-texture CK representing the intrusion initial phase. CK separate clumps and debris are also encountered in the UW center.
The Udachnaya-Eastern pipe in the plan changes its shape from isometric to oval, elongated in the north-north-east direction. The ore body contacts with the host rocks, as well as it occurs in the western body, are, mainly, sharp, and distinct. Unlike the western, the eastern body persists the 295×200-m cross-sectional area almost invariable between 800 m and 1400 m deep (Kharkiv et al., 1998).
Like the UW, the UE pipe is predominantly folded in PK, and along the edges of the diatreme, segments folded in the CK of the phase of initial intrusion can be found. In PK, there are often single inclusions of CC (as a rule, rounded fragments). At deep levels of pipes (400–500 m from the surface), a large block of serpentine-free PK was found, injected with thin dikes composed of CK. The kimberlite of the block is distinguished by a high content of NaCl in composition and contains carbonate-sulfate Na-bearing mineralization (Kamenetsky et al., 2007). The block contains monticellite-bearing varieties of kimberlite (Kornilova et al., 1983).
By high FeOtot and TiO2 compositions, the UW and UE kimberlites refer to the Mg-Fe petrochemical type; in the heavy-mineral concentrates, Ilm dominates (Table 2).
The Zarnitsa deposit (the first pipe discovered within the YaKP) is 14 km east of the Udachny city, on the left bank of the Daldyn River. Quarry mining of the deposit started in 2000 and is scheduled to terminate after 30 years. By its size (554х534 m), the pipe is the second after the Yubileynaya. On the surface, the pipe had a horizontal section close to isometrically roundish (Fig. 4). With depth, the pipe area consistently decreases by 12–19% every 100 m.
The pipe breaks through carbonate and argillaceous-carbonate Ordovician and Cambrian rocks and features a simple structure. To a depth of 450 m, the pipe is composed of PK which contains 10–40% of the host-rock debris. The next type of PK with a groundmass massive texture is located from a depth of 450 m. This PK contains previous-intrusion-phase CK inclusions like small debris of mica fine-porphyry kimberlite, and larger debris, separate blocks of aphanitic kimberlite with massive and fluidal textures (Kharkiv et al., 1998).
By high FeOtot and TiO2 compositions, the Zarnitsa kimberlites refer to the Mg-Fe petrochemical type; Ilm dominates in the heavy-mineral concentrates (Table 2).
Upper Muna Field
The Zapolyarnaya-Deimos deposit is situated on the right bank of the Ulaakh-Muna River. The pipe comprises NW and SE bodies (Fig. 4). Both bodies become independent at the depth of 250 m; herewith, the SE body splits into two separate feeder conduits at the depth of 350 m. The neighboring Deimos pipe is located 110 m SE of the Zapolyarnaya pipe. Deimos is the fourth feeder conduit as part of the common Zapolyarnaya-Deimos kimberlite system. The deposit mining is scheduled for the 2020s.
According to Kornilova and Nikishov (1976), the Zapolyarnaya pipe is composed of two kimberlite species: CK and VK. CK composing the central parts of the NW and SE bodies participates in the pipe structure, and two types of VK, are located on the periphery of the bodies (after drill core data). The bulk of the SE body is performed by VK. VK is saturated with a considerable abundance of debris and separate CK blocks (up to 50 meters). The VK-to-CK ratio in the NW body makes 1:1, and, in the SE body, it is 3:1. There are many thick sub-vertical zones of kimberlite with secondary serpentinization, brutalization, and carbonatization alteration both in VK and in CK.
The Komsomol'skaya-Magnitnaya and Novinka deposits are located on the right slope of the Ulaakh-Muna River valley, close to each other in 100-m proximity. Both pipes in their plan views have dumbbell-like shapes north-west oriented (Fig. 4). The shape of both pipes indicates the existence of two independent bodies (for each pipe) with a common feeder conduit - a dike. The deposit mining operations are scheduled for the 2020s.
The Komsomol'skaya-Magnitnaya is VK-composed, with a high (20–40%) saturation of the host-rock debris, and by two CK species: without monticellite (in the eastern part of the pipe) and with monticellite (the main part of the pipe). There is an abundance of perovskite in CK groundmass. The Novinka pipe is composed of two kimberlite types: CK and VK after Kornilova and Nikishov (1976). Each of the pipes was formed as a result of a three-phase intrusion (after drill core data). VK localized at the periphery, and two CK varieties occupy the NW and SE parts, respectively. There is an abundance of monticellite (10–30%) and perovskite in CK groundmass.
The Poiskovaya deposit is situated on the right bank of the Ulaakh-Muna river. The pipe forms two oval bodies (SW and central) elongated in different directions and a third non-outcropping blind body at the east part (Fig. 4). The pipe is represented by two intrusion phases: 1) massive-texture CK, and 2) VK with abundances of monticellite and phlogopite. The Poiskovaya kimberlites, as compared with the other pipes within the Upper Muna field, are notably affected by the deuteric processes of serpentinization and carbonatization.
The Upper Muna kimberlites are characterized by increased FeOtot contents, relatively low TiO2 contents, and garnet prevalence in the heavy-mineral concentrates, which assumes their belonging to an intermediate petrochemical type, from high-Mg to Mg-Fe kimberlites.
Nakyn Field
The Nyurbinskaya deposit is located in the upper reaches of the Dyulyung-Otu Creek, the right confluent of the Nakyn River. The pipe was discovered by geologists of the Botuobinskaya expedition of ALROSA in 1996 while drilling a Magnetic anomaly for verification. The deposit exploitation started in 2002 and has proceeded until the present. The pipe breaks through terrigenous-Carbonate rocks (Cm3 and O1) and is overlain by a series of terrigenous Jurassic sediments. The pipe walls are sub-vertical. At 296–332 m deep, the pipe is broken through by sub-alkaline dolerites (Fig. 2). At the contact with dolerites, there emerged the zones of metasomatic modified kimberlites, 5–10 m thick. (Kharkiv et al., 1998).
According to the geologists of the Botuobinskaya expedition, the Nyurbinskaya is composed, mainly, of VK containing rare debris and blocks of hypabyssal kimberlite.
The Botuobinskaya deposit is located 3.3 km SW of the Nyurbinskaya and is timed back to the Dyakhtar fault controlling the localization of kimberlite bodies within the Nakyn field. The pipe overlain by strata of Jurassic sedimentary formations (78–110 m thick) breaks through terrigenous-carbonate O and Cm rocks. The kimberlite body area from the top to the depth of 400 m decreases by 85% (Fig. 2). The pipe horizontal section size under the overlying sediment mantle is 264х117 m.
By representations of the mine geologists, the Botuobinskaya pipe, similarly to the Nyurbinskaya pipe, is composed of two intrusion phases: 1) CK in the feeder dike, and 2) VK in the diatreme main body that contains debris and CK blocks. The CK groundmass contains Phl counting 25–50% of its volume. The VK contains the host-rock detritus ranging from 5–7 to 30%.
The Mayskaya deposit is dike-shaped, 15–40 m thick, and 430 m long. It is 3 km SW of the Botuobinskaya (Fig. 2). The Mayskaya was drilled to еру depth of 400 m. The contacts of the ore body with the host rocks are steep with a 90 − 80 ° angle throughout the pipe. The Mayskaya pipe breaks through terrigenous-carbonate O and Cm deposits; from the surface, the body is overlain by 65-100-m strata of Jurassic deposits.
The northeast part of the Mayskaya pipe is composed mainly of VK with magmaclasts; the southwest part is composed of PK without magmaclasts (after Botuobinskaya survey expedition reports). There are no clear contacts between them. The abundance of the host-rock debris in the kimberlites ranges widely: from 5–10–50%, and more.
Nakyn field kimberlites refer to the high-Mg type with a relatively low FeOtot and TiO2 content. In the mineral concentrates of minerals, Grt dominates and Ilm is practically absent. (Table 2).
Kimberlite groundmass comprises varying abundances of Cal, Srp, Phl, Chl, Ap, and ore minerals. Distinctive features of the kimberlites of the Nakyn field are a high content of diamonds, a low content of minerals of the heavy mineral concentrates with a high content of Grt of eclogite composition, Cr-spl diamond association, and a low content of Grt of dunite-harzburgite paragenesis. The isotope-geochemical systematization of Nakyn kimberlites is distinct from that of the other kimberlite fields of YaKP, specifically by intermediate Sr and Nd isotope values between the Group I and Group II kimberlites (Pokhilenko et al., 2000; Kornilova et al., 2001; Agashev et al., 2001; Lapin et al., 2007).
Petrography And Mineralogy Of Kimberlites
The upper levels (crater-facies) of all the deposits are mainly composed of VK or (and) PK with a higher diamond grade and are lesser composed of CK with a lower diamond grade (Kharkiv et al., 1997). Pyroclastic kimberlites are also dominated at the lower levels (hypabyssal-facies) of the prospected Udachnaya, Mir, and Aikhal pipes while the relative abundance of CK increases. An essentially Carbonate-serpentine matrix is a common feature for both pyroclastic and coherent kimberlites of the YaKP deposits. An exclusion is separate blocks of the kimberlites located deep at the Udachnaya-Eastern, Mir, and Internatsional'naya (Fig. S4 ÷ S6) that are composed of partially serpentinized or serpentine-free kimberlites (Marshintsev, 1976; Kornilova et al., 1981; Kostrovitsky, 1986; Egorov et al. 1988; Kharkiv et al., 1991; Kamenetsky et al., 2008, 2014; Kostrovitsky et al., 2015). Serpentine-poor kimberlites with a significant content of Ol are also found within Upper Muna kimberlites with Cal-Mtc-Phl-Srp groundmass (Yakovlev et al., 2009, 2021).
Macrocrysts in hypabyssal kimberlites Mg-Fe of the petrochemical type (pipes Mir, Taezhnaya) are mainly represented by Srp pseudomorphs (sometimes with a minor abundance of Cal) along Ol (Fig. S2, S3). The Srp to Cal ratio varies over a wide range, depending on the intensity of the corresponding secondary processes. Unaltered Ol is rare. In kimberlites of high-Mg petrochemical type (pipes Aikhal, Dachnaya, Botuobinskaya, etc.), calcite is more often formed in pseudomorphs. Serpentine-free kimberlites, which were found at deep horizons of the Udachnaya-Eastern, Mir, and Internatsional'naya pipes (Fig. S4 ÷ S6), differ from serpentinized kimberlites in the groundmass composition. Udachnaya-Eastern groundmass is composed of euhedral Ol (> 50%), abundant carbonates up to 30 vol% and chlorides (up to 10 vol %), halite, Na-Ca-carbonates (mainly, zemkorite and shortite) after Kamenetsky et al. (2007). Photo S5 shows a clear boundary between unaltered and serpentinized kimberlites, indicating the superimposed nature of the process of serpentinization by micro portions of aqueous fluid. The groundmass serpentine-free kimberlites from the Mir and Internatsional'naya pipes are composed mainly of Ol, Cal, Dol, halite, and shortite.
Kimberlites of different intrusion phases at all the deposits are altered by hydrothermal-metasomatic processes of serpentinization and carbonatization at different degrees of intensity (Bobrievich et al., 1964; Milashev, 1965; Podvysotsky et al., 1980, 1981; Kostrovitsky, 1986; Marshintsev, 1986). The three structural modifications of serpentine are detected in the kimberlites: lizardite, chrysotile, and serpophite that correspond to different serpentinization phases (Kornilova et al., 1981; Egorov et al., 1991). The early high-temperature phase is related to lizardite crystallization and is fixed by Ol macrocrysts, as well as in serpentinized peridotite xenoliths. The most abundant (among the Srp modifications) is chrysotile which is also detected both in Srp pseudomorphoses by Ol macro-/microcrysts and in cryptocrystalline mesostasis of kimberlites. The late low-temperature phase is represented by isotropic serpophite substituting chrysotile in Ol pseudomorphoses, more often like rims, and sometimes completely composing grains (Fig. S3). Frequently, Srp pseudomorphs are rimmed by a thin zone enriched in fine magnetite crystals. Sometimes, magnetite evolves over the kimberlite groundmass, forming separate small sites.
The kimberlite carbonate component is mainly represented by cryptocrystalline or microlite Cal in the groundmass. Cal and Srp are parts of pseudomorphs after the Ol macrocyst, forming sockets, veins, and hydrothermal mineralization phases (Fig. S7). Other carbonate minerals (dolomite, strontianite, aragonite, pyroaurite) are less abundant (Bobrievich et al., 1964; Marshintsev et al., 1980). The carbonatization intensity in kimberlites considerably increases from the center to the contact of the pipes with the host rocks (Kharkiv et al., 1991). As a rule, the VK is more affected by carbonatization than the CK. The carbonatization maximal degree is established for thin pre-eruptive kimberlite dykes accompanying most bodies at the deposits, in which not only the mesostasis composition, but also the Ol macrocryst pseudomorphoses become essentially calcite, and the total CaCO3 abundance varies within 60–90% (Zubarev, 1989, Table 15; Marshintsev, et al., 1989, Table 9). Carbonate (mainly calcite) plays a significant role in fluidization processes. This produces a peculiar type of kimberlite rock, which we have called splitting breccia (Fig. S7, S8, S9). In salt-enriched kimberlites, halite takes on the aggressive role of splitting massive kimberlite into small pieces. (Fig. S8).
The mineral composition of the kimberlite groundmass depends on the kimberlite belonging to different petrochemical types (high-Mg or Mg-Fe). On the other hand, it depends on whether they are of the hypabyssal or pyroclastic type. The mesostasis of high-Mg kimberlites (Aikhal, Internatsional'naya, Dachnaya, and all pipes of the Nakyn field) mainly involves Srp, Phl, Ap, Ol, Cal, and Spl, while minerals such as Mag, Ilm, and Prv are extremely rare (Table 2). The Mg-Fe kimberlite mesostasis (Mir, Udachnaya, Zarnitsa pipes) differs from the previous type in the predominance of Prv, Ilm, and Ti-Mag (Table 2) in its composition with a very low content of Phl and Ap. Although the indicator minerals abundance in each of the pipes ranges widely, the above regularity always persists.
The pyroclastic kimberlite mesostasis, as compared with hypabyssal species, differs in a greater abundance of carbonate components. Monticellite is one of the common groundmass minerals (along with Ol, Srp, and Cal) within some kimberlites of the Upper Muna field, herewith, in some kimberlite phases, it becomes the major groundmass mineral (Fig. S10, S11). The idiomorphic, sub-idiomorphic minerals (Ol phenocrysts or Srp pseudomorphs) are found mainly in CK (Fig. S4 ÷ S6).
