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19 December 2025

Geochemistry of Granites and Pegmatites of the North-Western Kalba (Eastern Kazakhstan): Implications for the Exploration of Rare-Metal Mineralization

and
1
Faculty of Earth Sciences, D. Serikbayev East Kazakhstan Technical University, 19, Serikbayev Street, Ust’-Kamenogorsk 070000, Kazakhstan
2
Geos LLP, 83, Protozanov Street, Ust’-Kamenogorsk 070000, Kazakhstan
3
V.S. Sobolev Institute of Geology and Mineralogy Siberian Branch of the Russian Academy of Sciences, 3 Koptyug Avenue, Novosibirsk 630090, Russia
*
Author to whom correspondence should be addressed.
Geosciences2026, 16(1), 4;https://doi.org/10.3390/geosciences16010004
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Abstract

The article presents the results of research conducted on several rare metal deposits and ore occurrences within the North-Western Kalba region (Eastern Kazakhstan). The high demand for rare metals such as Li, Ta, Cs, Be, and Sn, and the limited knowledge about this region are the driving factors behind the interest in this area. The article presents the results of geological and geochemical studies of granites and pegmatites within several ore occurrences. The granites of the 3rd phase of the Kalba complex are enriched with muscovite and show increased concentrations of Be, Nb, Ta, Mo, and W. The rare-metal pegmatites contain spodumene and are also characterized by increased concentrations of Be, Sn, Nb, Ta, and Mo in comparison to granites. Based on the evaluation of the obtained results, it is concluded that all the rare metal deposits in North-Western Kalba formed through a unified process of differentiation of the parental magmas of the Kalba granite complex. It is suggested that the North-Western Kalba region could be considered promising for the discovery of new rare metal deposits. Recommendations on approaches to the exploration of rare metal deposits in this area are proposed.

1. Introduction

Rare metals are now the basis of high-tech industry and in wide demand worldwide. One of the most popular rare metals is lithium, used in the production of power supplies for a variety of devices. The rare metals that are in demand include tantalum, tin, beryllium, and cesium, which are used to produce high-tech alloys with a variety of properties. These alloys are then employed in numerous industrial sectors. Given the high demand for these rare metals, the issue of replenishing their reserves is an urgent task, which raises interest in forecasting and searching for new rare-metal deposits.
Ore deposits bearing Li, Ta, Cs, Be, and Sn are traditionally associated with rare metal-magmatic systems related to the evolution of granites and associated pegmatite and hydrothermal deposits [1,2,3,4,5]. Despite significant progress in recent years in the study of the evolution of granite magmas and of the processes responsible for the formation of rare-metal ore-magmatic systems [2,4,6,7,8,9], there is still no definitive method of determining the ore-bearing potential of certain granite intrusions. Not all granite intrusions with high rare-metal potential are capable of producing rare-metal pegmatite or hydrothermal mineralization. In addition, there are known examples where rare-metal pegmatites form entire fields of dikes and veins far from any granite intrusions [10]. In that perspective, the investigation of granitoids and the evolution of related late- and post-magmatic systems is a significant step towards predicting new rare-metal deposits.
The territory of Eastern Kazakhstan is a well-known rare metal province, where large pegmatite Li, Cs, Ta, and Be deposits (Yubileynoye, Belogorskoye, and Ognevka) are known [11,12,13,14,15,16,17]. These deposits are associated with the granites of the Kalba complex [13,14], which occupy more than 80% of the large Kalba-Narym granite batholith [18]. Due to the emergence of interest in rare metals and new analytical possibilities for geological exploration, it is, therefore, timely to reassess the ore potential of rare metal deposits in East Kazakhstan.
The deposits mentioned earlier are concentrated in the central part of the Kalba-Narym terrane, while the peripheral (southeastern and northwestern) parts of the batholith have not been extensively explored for rare metal deposits. Nevertheless, during the preliminary geological exploration work in Northwestern Kalba, several manifestations of rare-metal pegmatites were identified, and the Kvartsevoye deposit was discovered. In the 1990s, the exploration ceased; therefore, the metallogenic potential of the North-Western Kalba is not yet well explored. A fundamental question also remains unresolved: is rare metal mineralization associated with the granites of the Kalba complex, as has been shown for the Central Kalba? To resolve this issue, we refined the geological position and studied the composition of granites and pegmatites that are common in the area. The focus of this article is to study the geochemistry of granites and pegmatites, establish their genetic relationships, and make a preliminary assessment of the metallogenic potential of the North-Western Kalba region.

2. Geological Background

The geological structure of East Kazakhstan was developed in the Late Paleozoic during the collision interaction of the Siberian and Kazakhstan continents and the closure of the Ob-Zaisan oceanic basin [19]. The formed geostructure consists of several belts from the northeast to the southwest, with each of these belts having a certain set of sedimentary and magmatic formations and corresponding metallogenic specifics. This facilitated the identification of metallogenic belts [11,20] (Figure 1, inset):
Figure 1. Scheme of the Kalba–Narym metallogenic belt structure [21]. The main ore districts are shown: Sh—Shulbinsk; NWK—North-Western Kalba; CK—Central Kalba; N—Narym. Rare metal deposits: 1—Mokhnatukha; 2—Malo-Kaindy; 3—Kvartsevoye; 4—Zelenoye; 5—Novo-Saryozek; 6—Kanaika; 7—Medvedka; 8—Ognevka; 9—Bakennoye; 10—Yubileinoye; 11—Belaya Gora; 12—Karagoin; 13—Komarovskoye; 14—Kozlovskoye; 15—Shebuntai; 16—Komsomolskoye; 17—Palatsy; 18—Kasatkinskoye; 19—Cherdoyak; 20—Burabai; 21—Karasu. The inset shows the position of the Kalba–Narym belt (red) on the metallogenic zoning scheme of the Eastern Kazakhstan according to [20].
(1)
The Rudny Altai polymetallic belt is composed mainly of volcanogenic rocks formed in the Devonian on the active margin of the Siberian continent;
(2)
The Kalba rare-metal belt, which was a fragment of a shallow perioceanic basin near the Siberian continent in the Early Carboniferous, within which many granite intrusions were formed in the early Permian;
(3)
The West Kalba gold ore belt, which is a fragment of the Devonian–Carboniferous island-arc system, in which numerous gold deposits were formed during the activity of small diorite and granite intrusions in the Late Carboniferous–Early Permian;
(4)
The Zharma-Saur copper-molybdenum belt, which is a fragment of the Silurian–Devonian margin of the Kazakhstan continent with a manifestation of Carboniferous–Permian granitoids.
The most interesting for Li mineralization is the Kalba-Narym rare metal belt, which extends from northwest to southeast for 400 km at a width of approximately 50 km. The main geological formation of this belt is the Kalba granitoid batholith, comprising two members: (1) the Kalba granodiorite-granite complex, formed at 297–287 million years, and (2) the Monastery leucogranite complex, formed at 283–276 million years [18]. The main Li, Cs, Be, Ta, Nb, Sn, and W deposits are concentrated within the Kalba-Narym rare metal belt; the vast majority of them are associated with granites of the Kalba complex. Four ore districts have been identified (Figure 1): Shulbinsk, North-Western Kalba, Central Kalba, and Narym. The Central Kalba ore district contains the majority of large, explored deposits and is extensively studied. The North-Western Kalba (NWK) district has been studied in less detail. Only the Kvartsevoe deposit has been discovered in this area [21]. Nevertheless, several rare-metal occurrences of pegmatite and hydrothermal origin are known but have not been explored to this day.
The NWK area is characterized by a slightly dissected relief and well-exposed outcrop. The geological structure is shown in Figure 2.
Figure 2. Schematic geological map of North-Western Kalba based on materials from [22]. Mineral deposits: Iz I—Izmailovskoe I; Iz II—Izmailovskoe II; Be—Belokamenskoye; Gr—Greisen; Al—Alypkel; Na—Nakhodka; Kv—Kvartsevoye; Ko—Kovalevskoe; T3—Point No. 3; Au—Aktube; Ch—Chudskoe; Zh—Zhamantas; Se—Severnoye; Ak—Aktobe; Ka—Kaindy; MK—Malo-Kaindy; KvI—Kvartsevoye I; KvII—Kvartsevoye II; Nd—Nadezhda; NK—Novo-Kaindy; Pr—Promezhutochnoye; NtK—North-Kaindy; T2—Point No. 2. The blue rectangles denote the location of the studied ore occurrences.
A significant part of the territory is covered by loose Quaternary deposits, which, nevertheless, have small thickness, thus making it possible to determine the contours of granitoid intrusions during geological surveys [22,23,24,25]. Most of the granite intrusions of the area belong to the Kalba complex (Figure 2). Biotite granites of the first phase of the Kalba complex are the most widespread, while biotite–muscovite granites of the second phase of the Kalba complex are less common. Biotite–muscovite leucogranites of the Dungaly intrusion of the Monastery complex are also located in the southeast of the district.
All identified mineralization points are associated with the granites of the Kalba complex. They are represented by manifestations of pegmatites with Li-Cs-Ta-Be mineralization, as well as hydrothermal veins with Sn-W mineralization. All mineralization manifestations are located in the near-contact or apical parts of granite intrusions, both within granites and among the host siltstones and shales of the Takyr formation. During the geological exploration carried out in the 1970s [22,26,27], rare metal occurrences were classified as microcline with beryl; albite with tantalite and beryl; and microcline–albite with spodumene (Figure 2).

3. Materials and Methods

The scientific study included field and analytical work. Samples from granite and rare-metal pegmatite outcrops (more than 50 samples) were collected for laboratory research. Analytical studies were performed in the VERITAS laboratory of the D. Serikbayev East-Kazakhstan Technical University (EKTU) (Ust-Kamenogorsk, Kazakhstan) and the V.S. Sobolev Institute of Geology and Mineralogy (IGM) of the Siberian Branch of the Russian Academy of Sciences (Novosibirsk, Russia). Petrographic studies on thin sections were performed at IGM using a Carl Zeiss AxioScope.A1 (ZEISS, Oberkochen, Germany) polarizing light microscope equipped with a Canon EOS 650D camera (Canon, Tokyo, Japan). Back-scattered electron images of ore minerals were taken by a scanning electron microscope (JEOL 100C, Tokyo, Japan) with an energy-dispersive attachment (Kevex Ray, Thermo Scientific, Waltham, MA, USA). For analyses, the beam current was 1 nA, the beam diameter was 5 μm, and the analysis was carried out by scanning an area of 20 × 20 μm. The live spectrum acquisition time was 60 s. The stability of the survey parameters was controlled by periodically measuring the intensity of the K-line of pure cobalt.
The content of major oxides was determined in IGM by the X-ray fluorescence (XRF) method using an Applied Research Laboratories ARL-9900-XP analyzer (Thermo Fisher Scientific (Ecublens) SARL, Switzerland), following the standard procedure. The content of trace elements and rare metals was determined in EKTU. The samples were dried at a temperature of 105 °C and then ground to a fraction of less than 71 μm. Before geochemical analyses, the samples were transferred into a solution using polyacid decomposition. Calibration solutions were prepared by diluting standard samples with nitric acid with a mass concentration of 2% or 5% and hydrochloric acid with a mass concentration of 10%. A solution of nitric acid with a mass concentration of 5% was used as a background solution. The analyses were performed at the VERITAS Laboratory of the EKTU. The analysis was performed by mass spectrometry with inductively coupled plasma (ICP-MS) on an Agilent 7500cx (Agilent Technologies, Santa Clara, CA, USA).

4. Results

4.1. Granites of North-Western Kalba

The granites of the Kalba complex are represented by three varieties within the studied area. The granites of the first phase of the Kalba complex are predominant. They are represented by medium- and fine-grained biotite granites. (Figure 3a). They contain about 40–50 vol.% plagioclase and potassium feldspar forming subidiomorphic grains. Potassium feldspar is usually predominant compared to plagioclase. Quartz occupies from 35 to 45 vol.%, forming xenomorphic grains. Biotite forms subidiomorphic flake grains (amount reaches 10–12 vol.%). Muscovite is scarce, mainly developed in interstitials between early minerals (amount does not exceed 2 vol.%). The sequence of mineral formation has been established as follows: Pl + Kfs + Bt → Otz → Ms.
Figure 3. Petrography of Kalba complex granites from the NWK district: (a) medium-grained biotite granites of the 1st phase, sample KV23-07 (crossed polars); (b) medium-grained biotite–muscovite granite of the 2nd phase, sample K23-04 (crossed polars); (c) fine-grained muscovite granite of the 3rd phase, sample AK23-06 (crossed polars); (d) fine-grained garnet-muscovite granite of the 3rd phase, sample AL23-05 (crossed and plain polars). Mineral abbreviations: Bt—biotite, Grt—garnet, Ms—muscovite, Kfs—K-feldspar, Pl—plagioclase, Q—quartz.
The second phase of the Kalba complex is represented by biotite–muscovite medium-grained granites (Figure 3b), which form small intrusive bodies between the granites of the first phase. Plagioclase and potassium feldspar predominate in these rocks, occupying a total of about 50 vol.%. Quartz occupies up to 40 vol.% and is represented by xenomorphic grains. Biotite forms small subidiomorphic flaky grains, and its presence does not exceed 5 vol.%. Muscovite is abundant and forms large, flaky grains in interstices between early minerals; its amount can reach 15 vol.%. The sequence of mineral formation has been established as follows: Pl + Kfs + Bt → Otz + Ms.
Granite veins belonging to the third phase cut the granites of both the first and second phases. They are represented mainly by fine-grained muscovite granites (Figure 3c). Plagioclase is the predominant mineral; its idiomorphic grains occupy up to 60 vol. %. Potassium feldspar occupies no more than 15 vol. %, and forms weakly idiomorphic grains. Quartz forms xenomorphic grains; its amount does not exceed 20 vol. %. Muscovite is abundant and found in the interstices as a late magmatic mineral, and its content varies from 1 to 2 vol. % to 10–12 vol. %. Biotite has not been found in any rock type of the third phase. Dark-colored minerals in some muscovite granite samples are represented by idiomorphic garnet grains (Figure 3d). In addition, single idiomorphic tourmaline grains are occasionally found. The sequence of mineral formation has been established as follows: (Turm) + Grt → Pl → Kfs + Otz → Ms.
The composition of the studied granite samples is given in Table 1. The studied granites have SiO2 content ranging from 68.8 to 75.4 wt%. The biotite granites of the 1st phase correspond to the magnesian type, and the granites of the 2nd and 3rd phases correspond to the ferroan type (Figure 4a). Almost all granites belong to the calcic or calc-alkaline series (Figure 4b). All granites are peraluminous (Figure 4c). These characteristics show their similarity to other granites of the Kalba complex from the Kalba batholith [18]. Granites of different phases exhibit different concentrations of major components. Granites of the 1st phase have increased concentrations of mafic components (Figure 4d–f) and calcium (Figure 4g), whereas granites of the 2nd phase show reduced concentrations of these components. The granites of the 3rd phase have the lowest concentrations of mafic components (excluding one sample of garnet-muscovite granite with a high Fe and Mn content) and the highest concentrations of Na2O and Al2O3 (Figure 4h,i).
Table 1. Composition of Kalba complex granites from the NWK district.
Figure 4. Composition of Kalba complex granites from the NWK district at binary diagrams: (a–c)—classification diagrams from [28]: (a)—SiO2 vs. FeOt/(FeOt + MgO), (b)—SiO2 vs. MALI (Na2O + K2O-CaO), (c)—A/NK (Al2O3/(Na2O + K2O) vs. ASI (Al/(Ca × 1.67P + Na + K, mol.%); (d–i)—Harker diagrams from [29]: (d)—SiO2 vs. TiO2, (e)—SiO2 vs. FeOt, (f)—SiO2 vs. MgO, (g)—SiO2 vs. CaO, (h)—SiO2 vs. Na2O, (i)—SiO2 vs. Al2O3. Concentrations are in wt %. All of the data sources can be found in Table 1.
All studied granites are characterized by the predominance of LREE over HREE, and this difference is best expressed in biotite granites of the 1st phase (Figure 5a). Biotite–muscovite granites of the second phase show reduced REE contents relative to the granites of the first phase. Muscovite granites of the third phase have wide variations in REE contents, but for most samples, they are lower than the granites of the first phase. On the spider diagram (Figure 5b), granites of all phases show increased concentrations of LILE (Cs, Rb) and HFSE (Hf, Zr), minima in Ba and Yb contents, and maxima in U, Ta, and Nb contents. For muscovite granites of the 3rd phase, the maximum in Ta content is clearly distinguished (Figure 5b).
Figure 5. Chondrite-normalized rare earth element patterns (a) and primitive mantle-normalized trace element diagram (b) for Kalba complex granites from the NWK district. Normalizing values are from [30].
The accessory cassiterite, galena, sphalerite, and wolframite were found in the Kalba granites using SEM. The mineral compositions are listed in Table 2.
Table 2. Composition of ore accessory minerals in granites, pegmatites, and Qtz veins from the NWK district.

4.2. Rare Metal Pegmatites of North-Western Kalba

The greatest exploration interest in the area is attracted by the rare-metal pegmatite occurrences discovered in the 1970–1980s [22,26,27]. The Kvartsevoye deposit is the most studied and was mined in the 1980–1990s. It is located in the endocontact of the Alypkel granite intrusion, composed of biotite granites of the 1st phase of the Kalba complex. The deposit consists of a series of pegmatite veins cutting granites. The largest pegmatite vein, called Glavnaya (the Main), contains most of the explored mineralization represented by spodumene, tantalite, and accessory cassiterite. The results of our study of the mineral assemblages and rock composition of the Kvartsevoye deposit have recently been published [21]. The following section will provide a description of some other ore occurrences in the NWK area.
The Alypkel ore occurrence is located 3.5 km northwest of the Kvartsevoye deposit and is located near the western edge of the Alypkel granite intrusion. Pegmatite veins cut both the granites of the 1st phase of the Kalba complex and the host siltstones of the Takyr formation (Figure 6). The veins have a NW or NE strike and are steeply dipping. Most of the veins comprise oligoclase–microcline and microcline–albite pegmatites.
Figure 6. Geological structure of the Alypkel ore occurrence. Based on the report [22].
The largest pegmatite vein (vein #3) dips to the southwest at 45–50° and has a thickness from 1 to 2 to 15 m. This vein has a zonal structure and contains the following mineral assemblages (from top to bottom): (a) quartz-microcline with large beryl crystals; (b) greisen zone, composed of large-flake muscovite; (c) quartz; (d) quartz-albite zone with tourmaline and garnet. Exploration wells within the Alypkel ore occurrence have discovered veins of quartz-albite-spodumene pegmatites containing up to 25–30% spodumene and are characterized by elevated concentrations of Li, Be, and Sn. In addition to beryl and cassiterite, accessory galena and sphalerite were found in Alypkel granites and pegmatites.
The Kovalevskoye ore occurrence is located 2.5 km northeast of the Kvartsevoye deposit and is situated above the northwestern part of the South-Kovalevskoye intrusion. It is represented by several subvertical veins of the northwestern strike that have a thickness of up to 10–15 m (Figure 7). Rare metal veins are composed of microcline–albite and albite-spodumene assemblages. Most veins have an uneven and irregular internal structure. Clearly defined zoning is observed only in a few veins. The albitization is observed in almost all veins, which is expressed in the formation of clusters of fine-grained albite. Also, the greisenization is observed in some veins, which is expressed in the formation of clusters of greenish muscovite. The vein called “Body 1” has spodumene content reaching up to 60–70% in the thickest sections and about 5–7% on average. The Li2O content in the body 1 vein varies from 0.6 to 0.9% to 1.3–1.5%.
Figure 7. Geological structure of the Kovalevskoye ore occurrence. Based on the report [22].
Exploration wells within the Kovalevsky occurrence showed that their thickness does not increase with depth, but in some places, elevated contents of Ta, Sn, and Be were found [22]. Exploration wells in this area also revealed, at a depth of about 200 m, in the contact zone of the granite intrusion, subvertical zones of quartz veins and greisenization zones, which revealed elevated tungsten concentrations (up to 0.6–1% WO3).
The Aktube ore occurrence is located 5 km southwest of the Kvartsevoye deposit and consists of a series of pegmatite veins cutting shales of the Takyr formation between the Nikolaevsky and Central granite intrusions (Figure 8). The veins exhibit a predominantly submeridional or north-western strike. Exploration wells have shown that most of the pegmatite veins are located above the apical part of the granite intrusion, which dips to the northeast (Figure 8b). A wide variety of pegmatite mineral assemblages have been identified here: (1) simple microcline pegmatites; (2) microcline–albite pegmatites without spodumene; (3) microcline–albite pegmatites with spodumene; (4) albite pegmatites without spodumene; and (5) albite pegmatites with spodumene. Veins of rare-metal pegmatites are localized in the central part of the site. The thickness of some veins reaches 50 m. The veins of rare-metal-bearing pegmatites do not exhibit pronounced zonation, and their structure is more consistent with aplite-pegmatites. With increasing thickness, coarser-grained rock structures appear in the veins, and the amount of spodumene and fine-flake muscovite also increases in the thickest sections of the veins.
Figure 8. Geological map (a) and cross-section (b) of the Aktube ore occurrence. Based on the report [22].
Albite-type pegmatites are of the greatest interest, in which spodumene is present in all areas. In the largest vein, “Moschnaya” (the Thick), the amount of spodumene can reach 50–60 vol.%, and the albite-spodumene mineral association is manifested here. The Moschnaya vein also contains iron-manganese phosphates in the form of 5–6 mm nests. The second largest vein is the Vetvistaya, which is composed of albite-microcline pegmatite with non-uniform albitization and greisenization. The weighted average content of Ta2O5 is 0.049%; BeO is 0.036%. The Kupolnaya vein exhibits a thickness ranging from 5 to 50 m and is composed of microcline–albite permatite with pronounced greisenization. It contains Fe-Mn phosphates as accessory mineralization. Exploration wells in the northwestern part of the Aktube occurrence have shown a series of veins of albite rare-metal pegmatites, characterized by elevated concentrations of Ta and Be. The accessory cassiterite, chalcopyrite, and galena were found in the greisenization zones of pegmatite veins using SEM. The mineral compositions are listed in Table 2.
The content of rare metals in the studied pegmatite samples is shown in Table 3. The rare metals content varies widely, likely due to the heterogeneity of pegmatite mineralogy and texture. Moreover, there are no significant differences between muscovite-dominated (greisens) zones and albite-dominated zones. Figure 9 shows a comparison of the rare metal contents in granites and pegmatites. Most pegmatite samples are characterized by high concentrations of Rb, Be, Sn, Nb, Ta, and Mo, similar to or higher than those of some samples of the 3rd phase muscovite granites. Li concentrations are high only in spodumene-containing varieties.
Table 3. Contents of rare metals in pegmatites of North-Western Kalba (ppm).
Figure 9. Rare metal contents (ppm) in Kalba granites and rare-metal pegmatites from the NWK.

4.3. Hydrothermal Occurrences of North-Western Kalba

Hydrothermal ore occurrences are widespread in the northern and eastern parts of the studied area (Figure 2). They are mostly located away from pegmatite deposits, but they are also associated with granite intrusions. The most promising of these is the Kaindy group, which is associated with the granites of the Kaindy intrusion.
Several large quartz veins have been identified in the Kaindy ore field, cutting the shales of the Takyr formation in the exocontact of the granite intrusion (Figure 10). Quartz veins have a north-west strike, stretch for hundreds of meters, and have a thickness of up to 2–3 m. The largest quartz veins contain tungsten and tin-tungsten mineralization. The mineralization is represented by wolframite, less often cassiterite, and scheelite (Figure 11). The accessory pyrite and rutile were also found in quartz veins using SEM. The mineral compositions are listed in Table 2.
Figure 10. Geological structure of the Kaindy ore occurrence. Based on the report [27].
Figure 11. Microinclusions of accessory minerals in the Kaindy quartz-vein rocks (BSE images): (a,b) cassiterite micrograins in orthoclase and albite; (c,d) wolframite micrograins in quartz.
The largest one is the Novo-Kaindy occurrence with concentrations of WO3—0.7%, Sn—0.3%, and an average ore body thickness of 1 m. According to the results of the preliminary geological exploration assessment [27], the projected resources of the Kaindy ore field may amount to 30.8 tons of WO3.

5. Discussion

Based on the patterns of deposits and occurrences in the North-Western Kalba region, as well as the relationship between different rock types within their boundaries, it can be suggested that rare metal deposits and occurrences are genetically linked to the granites of the Kalba complex. This hypothesis is supported by the following evidence.
Firstly, the geological observations prove that veins of rare-metal pegmatites are always located near Kalba granites, in endocontact or exocontact zones of intrusions.
The second piece of evidence is geochronological data. Although we did not perform any geochronological studies in this paper, we have data on the age of rare-metal pegmatites from the Kvartsevoye deposit (285–288 Ma, ref. [21]) and rare-metal deposits from the Asubulak ore region in Central Kalba (295–286 Ma, ref. [14]). These calculated ages are congruent with, or only slightly younger than, the age of the granite of the Kalba complex (297–287 Ma, ref. [18]). This suggests that the formation of granites and rare metal mineralization was the result of a single endogenous event.
The third piece of evidence for the genetic relation between Kalba granites and rare-metal pegmatites is mineralogical and geochemical. Based on the samples we studied, Kalba granites are represented by three intrusive phases: biotite granites of the first phase, which occupy the largest volume; biotite–muscovite granites of the second phase, which occupy a smaller volume; and muscovite granites of the third phase, represented by dikes; the volume of granites of the third phase is comparable to the volume of pegmatite veins.
Petrographic observations indicate that the proportion of muscovite increases from early to late granites, and the predominance of plagioclase over feldspar increases. This is evidence of the accumulation of sodium, alumina (increasing the albite proportion), and volatile components (increasing the muscovite proportion) during magmatic differentiation in the melt. Major element geochemistry also indicates a decrease in the content of mafic components and calcium from the 1st to the 2nd and 3rd phase granites (Figure 4d–g). This indicates fractionation of biotite, ilmenite, magnetite, and Ca-rich plagioclase. Granites of the 3rd phase are significantly enriched in Na and Al (Figure 4h,i). Such enrichment is common in the evolution of volatile peraluminous granite magmas, when a change in “normal” peraluminous melt composition to an Na-rich aqueous silica-bearing fluid occurs [31]. Both albite and muscovite can crystallize from this fluid. It has also been shown that aqueous silica-bearing fluid is enriched in F, Rb, Cs, Sn, Ta, Be, and Mn [31,32]. Accumulation of the Mn-enriched silica-fluid phase can lead to crystallization of spessartine-rich garnets [33,34]. This is precisely what we observe in some samples of 3rd phase granites with euhedral grains of Mn-rich garnet (Figure 3d) and containing 1.99 wt.% of MnO and 2.0 wt.% of FeOt (Table 1, sample Al-23-05).
The concentration of rare earth elements in most samples of muscovite granites of the 3rd phase is lower than in granites of the 1st and 2nd phases (Figure 5a). This is also a consequence of differentiation, since aqueous silica-bearing fluid has lower K, Fe, Nb, Ti, Y, and REE compared to the parent peraluminous silica melt [31,35,36,37]. Concurrently, muscovite granites of the 3rd phase exhibit elevated concentrations of Be, Nb, Ta, Mo, and W in comparison with granites of the 1st and 2nd phases (Figure 9), suggesting the accumulation of these elements in residual melts or aqueous silica-bearing fluid. Furthermore, the results of geochemical studies of granites show that the Nb/Ta and Zr/Hf ratios are a key indicator of magmatic fractionation [38]. The Nb/Ta value < 5 is an indicator of the interaction of magma with late magmatic fluids [39]. For the studied Kalba granites, the Nb/Ta ratio is 1.45–8.75 in Bt granites of the 1st phase, 2.88–5.05 in Bt-Ms granites of the 2nd phase, and 0.87–3.77 in Ms granites of the 3rd phase. The Nb/Ta vs. Zr/Hf diagram shows that the granites of northwestern Kalba depict fractional crystallization, and the muscovite granites of the 3rd phase correspond to rare metal-related granites with the Ta-Cs-Li-Nb-Be-Sn-W mineralization (Figure 12).
Figure 12. Kalba granites at the Nb/Ta vs. Zr/Hf diagram differentiating barren and ore-bearing peraluminous granites [39].
As shown in Figure 9, the pegmatites are characterized by increased contents of Be, Sn, Nb, Ta, and Mo in comparison to granites. This emphasizes the relation of pegmatites with 3rd phase muscovite granites and indicates pegmatite formation from an aqueous silica-bearing fluid phase. Based on these geochemical data, we can assume the sequential evolution of the original granite magma from biotite granites to biotite–muscovite and muscovite granites, and then to pegmatites. Similar models have been proposed previously for the Central Kalba ore region [13,14] as well as for rare metal pegmatite deposits in Thailand [40], Vietnam [41], and China [4,42].
At the later stages of evolution, albite and spodumene were crystallized, allowing the formation of albite-spodumene pegmatites, while the accumulation of volatiles led to the crystallization of greiseneized zones also enriched in Ta, Nb, Be, Sn, and Mo. As shown in Figure 9, pegmatites did not concentrate W; it can be assumed that W was mainly concentrated in the residual fluid. This fluid subsequently crystallized in the form of hydrothermal quartz W-bearing veins during the final stages.

6. Conclusions

It can be argued that all the rare metal deposits of North-Western Kalba were formed during a single process of differentiation of the parental magmas of Kalba granites, from pegmatites and to hydrothermal quartz veins with wolframite and cassiterite. The obtained geochemical data allow us to reasonably assume that rare metal mineralization is associated with the Kalba granites. The results of the previous exploration suggest the discovery of new rare metal deposits in the NWK region. In order to achieve this objective, it is necessary to study in more detail the contact zones of granite intrusions of the Kalba complex and conduct additional exploratory drilling. The internal structure of both exposed pegmatite veins and subsurface veins and greisenization zones should be carefully investigated. To assess the ore potential, it is necessary to take large-volume samples of potentially ore-bearing objects for geochemical study. It is important to note that geochemical data are not always reliable for coarse- and giant-granular pegmatites with a complex distribution of trace elements. Therefore, special attention should be paid to comprehensive mineralogical investigations. It is necessary to study the accessory mineralization of granites of all phases of the Kalba complex and to conduct a detailed study of the accessory and rare-metal mineralization of pegmatite and hydrothermal quartz veins.

Author Contributions

Conceptualization, T.A.O. and S.V.K.; methodology, S.V.K.; software, T.A.O.; validation, T.A.O. and S.V.K.; formal analysis, T.A.O. and S.V.K.; investigation, T.A.O.; resources, T.A.O.; data curation, T.A.O. and S.V.K.; writing—original draft preparation, S.V.K. and T.A.O.; writing—review and editing, S.V.K. and T.A.O.; visualization, T.A.O.; supervision, T.A.O.; project administration, T.A.O.; funding acquisition, T.A.O. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Science Committee of the Ministry of Science and Higher Education of the Republic of Kazakhstan (Grant No. AP19676805) and by the State Assignment of IGM SB RAS (Project No. 122041400044-2).

Data Availability Statement

The data presented in this study are available on request from the corresponding author.

Acknowledgments

We wish to thank the VERITAS Engineering Laboratory (EKTU) and the Analytical Center (IGM) for the analytical work. We are very thankful to reviewers whose comments helped us to revise the earlier version and sufficiently improve the manuscript. Our thanks are extended to Alexey Volosov for aid in the manuscript’s preparation.

Conflicts of Interest

The authors declare no conflicts of interest.

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