Aptian Li-F Granites of the Northern Verkhoyansk–Kolyma Orogenic Belt, Eastern Russia: Composition, Genesis, and Ore Potential

Abstract

This paper reports the results from an investigation on the geochemistry and petrogenesis of the Aptian Li-F granites from the Omchikandya, Burgali, and Arga Ynnakh Khaya ore fields in the northern Verkhoyansk–Kolyma orogenic belt in eastern Russia. Li-F microcline–albite granites intrude the Late Jurassic to Early Cretaceous syn-collisional granitoids. According to their geochemical composition, they are close to A-type granites and can be subdivided into low-P and high-P varieties, differing in their geochemistry and genesis. The low-P microcline–albite granites (Omchikandya massif) intrude syn-collisional biotite granites. It is assumed that the formation of their parent melt occurred at deep levels in the same magma chamber that produced biotite granites. The high-P granites (Verkhne–Burgali ethmolith and Kester harpolith) are supposed to have been derived from melts originated from a high-grade metamorphosed lower crustal protolith under the influence of deep-seated fluid flows related to diapirs of alkaline-ultrabasic or alkaline-basic composition. It is supposed that their formation was related to post-collisional extension during the early stages of the evolution of the Aptian–Late Cretaceous Indigirka belt of crust extension. All studied Li-F granites are enriched with rare metals and have associated Li deposits with accompanying Sn, W, Ta, and Nb mineralization. In the low-P Li-F Omchikandya massif, mineralization tends to occur within greisenized granites and greisens in their apical parts. In the high-P granite massifs, mineralization is found throughout their volume, and, therefore, the Verkhne–Burgali ethmolith and Kester harpolith can be considered as large ore bodies. There is a direct dependence of the content and reserves of Li₂O on the content of P₂O₅. Minimum Li₂O reserves are established in low-P Li-F microcline–albite granites of the Polyarnoe deposit of the Omchikandya ore field, whereas in the high-P granites of the Verkhne–Burgali and Kester deposits, the Li₂O reserves are significantly higher.

1. Introduction

Lithium is among the metals in great demand nowadays. Lithium and its compounds are widely used in the manufacture of batteries, in nuclear power engineering, radio electronics, etc. This led to more intensive studies on the geology of lithium deposits and the growing number of summarizing publications on the subject, e.g., [1,2,3].

Russia ranks among the first in the world in Li reserves (as of 1 January 2022, Li₂O reserves amounted to 2118.8 thousand tons [4]). About 60% of Li deposits are localized in Eastern Siberia and 37% on the Kola Peninsula [4]. The ores of the deposits are complex (Li, Ta, Nb, Be, and Cs). Most of the deposits are related to rare metal pegmatites; those associated with rare metal granites are fewer in number [4].

In the north of the Verkhoyansk–Kolyma orogenic belt, lithium mineralization is present as a by-product in most of the tin and tin–tungsten deposits associated with greisens (Deputatskoe, Kere-Yuryakh, Chalba, etc.). Lithium deposits, as such, are localized in Li-F granites [5,6], whose genesis remains debatable. Some of the researchers interpret them to be the latest differentiates of long-evolved crustal granitic melts [7,8,9,10], while others consider that they formed as a result of the liquid immiscibility of high-F granitic melts [11] or in consequence of the mixing of residual melts with deep-seated fluids [12]. There is an opinion about their mantle–crustal genesis and the generation of their parent melts after a crustal protolith under the influence of heat and fluids associated with diapirs of basaltic melts [13,14,15,16].

The lithium deposits Polyarnoe (Omchikandya ore field), Verkhne–Burgali (Burgali ore field), and Kester (Arga-Ynnakh-Khaya ore field) discussed in this article were previously assigned as tin ore deposits. The available publications describe in sufficient detail the petrography of their enclosing granites [5,12,17], but their mineralogy, geochemistry, composition, and structure of ore bodies remain little understood. The genesis of these deposits is yet under discussion. In our paper, the results of our studies are summarized, new data are presented on the composition of rocks and their essential and accessory minerals, characteristics of the ore bodies are given, and, in addition, an account of the petrogenesis of the host granitoids and their geodynamic setting is given.

2. Methods

During the field studies, the shape and internal structure of magmatic bodies, relationships between magmatic rocks of different compositions, and localization of mineralization were determined. The coordinates of the studied samples are shown in Table S1.

The petrography of the granitoids and ores was studied with the use of an Olympus optical microscope (Leica), enabling the determination of the crystallization and evolution paths of the melts. The compositions of the rock-forming and accessory minerals were analyzed using a Camebax-Micro X-ray microanalyzer (Cameca, Courbevoie, France). The analytical conditions were as follows: accelerating voltage, 20 kV; beam current, 1.08 nA; counting time, 10 s; detection limits, 0.01%; and reproducibility, 0.15–0.2.

All the analyses except ICP-MS were conducted at the Diamond and Precious Metal Geology Institute (DPMGI SB RAS), Yakutsk, Russia. Samples for analytical studies were prepared using standard crushing and grinding procedures. The mineral grains were separated by magnetic and density separation with final sorting under a binocular microscope to remove altered grains and other random minerals, and then they were crushed to 200 mesh. The chemical compositions of the rocks and the compositions of biotite and amphibole were determined using a conventional wet-chemistry analytical technique.

The REE content in the rocks was determined by ICP-MS analysis on a high-resolution ELEMENT 2 mass spectrometer (ThermoQuest Finnigann MAT) at the Geochemistry Institute, SB RAS (Irkutsk, Russia). Detection limits for the analyzed elements (ppm): La—0.72, Ce—0.19, Pr—0.029, Nd—0.035, Sm—0.044, Eu—0.017, Gd—0.039, Tb—0.0078, Dy—0.034, Ho—0.02, Er—0.032, Tm—0.016, Yb—0.033, Lu—0.016, Hf—0.037, Ta—0.027, Y—0.27, Zr—1.5, Be—0.22, Th—0.078, and U—0.061; reproducibility 0.1–0.3.

Trace elements were detected using a PGS-2 spectrograph equipped with a multi-channel atomic emission spectral analyzer (BMK Optoelectronics, Russia). The detection limits (ppm) were as follows: Ba—19, Sr—6, Cr—13, Ni—4, V—5, Co—1.3, Zr—23, Nb—8, Y—5, and Yb—0.5; reproducibility—0.1–0.2.

A complete whole-rock geochemical analysis and spectral analysis of REEs and trace elements in the ores were performed, followed by mathematical processing of the data using CGDkit and PetroExplorer software [18,19].

The calculation of the melt temperature was made following [20] and the pressure following [21]. The crystallization temperature of granitoids was calculated according to [18].

3. Regional Geology

The Verkhoyansk–Kolyma orogenic belt is the largest tectonic unit in Northeast Asia. It is believed to have formed as a result of the collision of the Verkhoyansk passive margin of the eastern Siberian Craton with the Kolyma–Omolon superterrane in the Late Jurassic–Early Cretaceous periods. The Kolyma–Omolon superterrane (or microcontinent) is a collage of terranes of various geodynamic affinities amalgamated at the end of the Middle Jurassic [22,23] and references therein. The studied Li-F granites are located within the rear part of the Verkhoyansk fold-and-thrust belt and the Kular–Nera terrane (deformed Verkhoyansk passive margin of Siberian Craton), in the south of the Polousnyi, and in the central part of the In’yali–Debin synclinoria of the Kolyma–Omolon superterrane [22,23] and references therein (Figure 1).

The rear part of the Verkhoyansk fold-and-thrust belt and Kular–Nera terrane are intruded by Cretaceous granitoids of transverse belts oriented across the strike of fold structures [22,23] and references therein (Figure 1).

The Jurassic rocks of the Polousnyi synclinorium are intruded by numerous Cretaceous-age large granodiorite–granite and smaller diorite–granite massifs of the Northern Batholith Belt (Figure 1).

The Jurassic rocks of the In’yali–Debin synclinorium are intruded by syn-collision Late Jurassic–Early Cretaceous granitoid plutons of the Main Batholith Belt [22,23,24,25] and references therein (Figure 1).

In the Aptian–Late Cretaceous in the east and north of the Verkhoyansk–Kolyma orogenic belt, large-scale extensions took place accompanied by volcanism and the intrusion of anorogenic granitoids (the Indigirka belt of crust extension), e.g., [22,23,25]. The reason for the formation of this belt is unclear. It is related either to an extension in the rear of the Okhotsk–Chukotka volcanic–plutonic belt located east of the Verkhoyansk–Kolyma orogenic belt or has resulted from a failed opening of the Eurasia basin and the breakup of Laurasia [22,23].

The Polyarnoe deposit belongs to the Omchikandya ore field and is localized in the granitoid massif of the same name in the south of the Polousnyi synclinorium. The Verkhne–Burgali deposit occurs within the Verkhne–Burgali granitoid massif of the Burgali ore field, on the border of the Kular–Nera terrane and the In’yali-Debin synclinorium. The Kester deposit belongs to the Arga Ynnakh Khaya ore field and is associated with the Western Arga Ynnakh Khaya massif. It is located in the north of the rear part of the Verkhoyansk fold-and-thrust belt (Figure 1).

4. Omchikandya Ore Field (Polyarnoe Deposit)

4.1. Geological Setting

The Polyarnoe Sn rare metal deposit (Omchikandya ore field) occurs in the south of the Polousnyi synclinorium within the Cretaceous Omchikandya granitoid massif with an area of 180 km² that intrudes the deformed clastic and volcaniclastic Jurassic rocks (Figure 2 and Figure S1a).

Biotite granites, which compose most of the Omchikandya massif, are intruded by stocks of microcline–albite rare metal granite (Figure 2). The Polyarnoe deposit is related to quartz–topaz–mica and quartz–mica greisens that developed after microcline–albite granite.

4.2. Age of the Studied Rocks

The ⁴⁰Ar–³⁹Ar isotopic age of biotite granites of the Omchikandya massif is 138–121 Ma [24]; the U-Pb zircon age is 134–131 Ma [25]; and the ⁴⁰Ar–³⁹Ar age of microcline–albite granites is 115 Ma [24]. The massif and host Jurassic rocks are intruded by numerous dykes of leucogranite, granite porphyry, and aplite. The ⁴⁰Ar–³⁹Ar age of granite porphyries is 121.2 ± 0.9 Ma [24].

4.3. Petrography and Mineralogy of Granitoids

The Omchikandya massif is composed of coarse-to-medium-grained biotite granites that grade, towards endocontact, into fine-grained porphyritic and pegmatoid leucogranites (Figure S2). The rocks are composed of unzoned or weakly zoned oligoclase (23%–15% an), orthoclase or microcline, and eastonite–siderophyllite [27] with (Fe/Fe + Mg) = 55%–72%. Biotite is similar in composition to that of S-type granites of granodiorite–granite and granite–leucogranite associations (

Table 1. Contents of major (wt.%) elements in micas of the microcline–albite granites in the Omchikandya, Burgali, and Arga Ynnakh Khaya ore fields.

Massif	Omchikandya (Polyarnoe Deposit)			Verkhne–Burgali Ethmolith				Kester Harpolith
Mineral	Eastonite–Siderophyllite		Trilithionite	Polylithionite				Li-Muscovite		Polylithionite
Sample	z1219	4/2 *	258/2	238	345	2544	327	2491	142 *	141	2403/2	106 *
SiO2	35.04	42.80	43.09	49.57	45.36	49.68	45.32	45.88	142 *	49.20	49.00	49.68
TiO2	4.24	0	0	0.03	0.04	0	0.15	0.29	49.20	0	0.06	0
Al2O3	11.89	24.12	23.45	22.09	36.75	23.50	21.27	30.89	0	25.60	24.54	23.50
Fe2O3	4.44	3.88	2.05	3.29	0.77	0	5.04	1.19	25.60	0.49	2.66	0
FeO	24.31	9.89	11.52	3.95	0	2.51	6.63	2.37	0.49	2.51	1.39	2.51
MnO	0.45	2.21	2.02	0.50	0.08	0.30	0.56	0.09	2.51	0.40	0.70	0.30
MgO	4.33	0.05	0.05	0	0	0.54	0.10	0.44	0.40	0.34	0.10	0.54
CaO	0	0.05	0.16	0.06	0.47	0.10	0	0.45	0.34	0	0.10	0.10
Na2O	0.56	0.16	0.25	0.47	0.44	0.54	0.56	0.52	0	0.60	0.35	0.54
K2O	8.35	9.50	9.40	10.10	10.73	9.46	9.74	10.50	0.60	9.42	9.60	9.46
H2O	3.49	1.51	1.56	0.95	3.48	1.68	1.03	3.67	9.42	2.32	1.67	1.68
F	2.41	3.51	3.78	4.09	1.68	7.00	5.45	2.73	2.32	7.00	5.11	7.00
Cl	-	0.05	0.05	-	1.11	-	0.80	-	7.00	-	-	-
Li2O	1.28	2.07	2.30	4.04	0.32	3.31	3.26	1.05	3.31	3.31	4.07	3.31
Rb2O	-	0.59	0.67	1.10	0.01	1.22	0.17	0.37	1.09	1.09	1.04	1.22
Total	99.51	100.39	100.36	100.21	101.24	99.84	100.08	100.96	102.28	102.28	100.64	99.84
O=F,Cl	1.02	2.07	2.74	1.72	0.96	2.87	2.48	1.15	2.95	2.87	2.15	2.95
f%	78.6	99.4	99.4	100	98.8	72.1	98.4	82.4	85.7	85.7	95.9	721
al,%	17.7	34.4	24.5	31.8	48.2	32.1	31.4	42.3	32.6	32.6	35.4	32.1

Notes: The analyses were performed at DPMGI SB RAS using the chemical analyses by V.S Gamyanina and N.A. Gomzyakova and the Camebax micro microanalyzer (z) by L.A. Pavlova and S.P. Roev. Li₂O and H₂O were calculated from the microanalyzer data published by the authors of [30]. *—analyses from [12]. f = FeO*/(FeO* + MgO), al = Al/(Al + Fe* + Mg + Si).

and Table S2; Figure 3) [28,29]. It crystallized at a temperature of 760–674 °C under reducing conditions (−log fO₂ = 15.2–17.2) typical of crustal Sn rare metal granites (Table 1 and Table S2).

Microcline–albite granites are fine-to-medium-grained (Figure S3a). They have a predominantly porphyritic texture, with rounded quartz grains, albite and K-feldspar plates, and mica flakes set in a fine-grained groundmass of albite composition. K-feldspar is represented by orthoclase and microcline. Porphyry quartz segregations are saturated with small albite prisms to form a snowball structure (Figure S3b,c). Microcline–albite granites are intensely greisenized with the formation of quartz-topaz-mica, quartz-mica, and kaolinite-mica greisens (Figure S3d).

Mica is represented by eastonite–siderophyllite and trilithionite with high contents of F (2.41%–3.78%) and Li₂O (1.25%–2.07%). It crystallized from a water-saturated melt (H₂O in melt = 5%–8%, calculated after [31]) at a higher F fugacity (Table 1) and is close in composition to A-type granite mica (Figure 3).

All microcline–albite granites contain Li-bearing tourmaline (3% Li₂O), topaz, fluorite, F-apatite with 0.4%–0.6% Ce, 0.4%–0.7% Y, and up to 0.93% La-, Ta- and Nb-enriched cassiterite (0.84%–0.94% Ta₂O₅ + Nb₂O₅), wolframite (0.46%–0.57% Ta₂O₅ + Nb₂O₅), manganese ilmenite, tin-bearing rutile (3%–4% SnO₂), Ta-niobates (3%–6% SnO₂ and up to 10% WO₃), and monazite. Titanomagnetite (4.5%–10% TiO₂) is also present. In cassiterite, wolframite, and protolithionite, an admixture of Sc is found (925, 4660, and 520 ppm, respectively).

4.4. Geochemistry of Granitoids

The chemical composition of the Omchikandya massif biotite granites (Table 1 and Table S3; Figure 4 and Figure S4a) corresponds to that of normally alkaline granites, with deviations towards moderately alkaline leucogranites [32], and according to the classification in [33]—to monzogranites and sienogranites (Figure 4a,b). They are peraluminous (Figure 4c) and high ferroan (Figure 4d, Table S3).

The rocks are corundum-normative, with close values of normative orthoclase and albite (avg. 23.7% and 26.7%, respectively) (Table 2). The contents of major element oxides in the granites correspond to those in S-type granitoids and continental collision-related granitoids (Figure 4c–f). The main geochemical features (Figure 5) indicate the generation of the parental melts by the partial melting of igneous rocks or metagraywacke. The maximum calculated temperatures of the parental melts for biotite granites are 916–911 °C at pressures up to 9.7–8.9 kbar. The crystallization temperature of the biotite granites is within 870–600 °C. The melts that formed leucogranite and aplite dykes were generated at T = 807–686 °C and P = 4.5–2.5 kbar.

Table 2. Average compositions of the magmatic rocks of the of the Omchikandya, Burgali, and Arga Ynnakh Khaya ore fields.

Sample	1	2	3	4	5	6	7	8	9	10	11	12	I	S	A	C g	C gr
n	14	6	11	4	18	13	6	16	4	24	12	4
SiO2	70.41	75.92	72.90	72.33	66.53	68.27	70.73	72.05	74.22	70.45	69.59	78.78	69.2	70.3	73.8
TiO2	0.37	0.05	0.03	0.04	0.43	0.38	0.20	0.39	0.02	0.01	0.01	0.01	0.43	0.48	0.26
Al2O3	14.70	12.92	15.5	17.5	15.68	15.63	15.20	14.33	14.32	17.14	17.02	12.50	14.3	14.1	12.4
Fe2O3	0.61	0.17	0.21	0,72	0.60	0.61	0.88	0.67	0.34	0.33	0.23	0.13	1.04	0.56	1.24
FeO	2.69	1.05	1.15	2.95	3.59	2.93	1.14	2.23	0.86	0.97	1.13	0.86	2.29	2.87	1.58
MnO	0.05	0.03	0.15	0.68	0.21	0.06	0.05	0.05	0.04	0.05	0.04	0.03	-	-	-
MgO	0.70	0.09	0.08	0.04	1.63	0.90	0.34	0.67	0.05	0.06	0.03	0.01	1.42	1.42	0.20
CaO	1.97	0.82	0.34	0.07	3.82	3.33	0.80	1.04	0.30	0.04	0.16	0.24	3.20	2.03	0.75
Na2O	3.19	2.59	4.04	0.26	3.38	3.33	4.17	3.17	4.29	4.74	4.33	1.11	3.13	2.41	4.07
K2O	4.00	5.09	3.97	3.61	2.93	3.10	4.93	4.54	4.39	3.38	3.84	1.90	3.40	3.96	4.65
H2O	0.12	0.06	0.09	1.32	0.10	0.08	0.27	0.22	0.30	1.76	1.10	2.35
P2O5	0.10	0.05	0.045	0.04	0.11	0.08	0.09	0.19	0.27	1.81	1.31	1.07
F	1.19	0.56	1.02	0.02	0.73	0.62	0.86	0.62	0.52	1.13	1.03	1.51
Cl	0.12	0.13	1.20	1.80	0.07	0.07	0.05	0.08	0.05
Total	100.22	99.53	100.82	101.38	99.81	99.39	99.62	100.25	99.97	101.87	99.92	100.50
B	12	31	47	40	13.4	19	24.6	74	60	26.5	195	420				37	26
Li	56	49	1213	952	42.9	40.1	61.1	88.6	65.3	1822	1708	1867	151	217	169	180	120
Rb	247	157	658	954	109	104	118	147	333	1260	1710	1795	247	120	48	150	440
Sr	220	75	40	25	600	506	300	230	213	111	346	437	538	468	352	650	560
Ba	510	150	36	23	873	860	560	640	543	99	235	220				21	20
Nb	23	35	63	45	12	11	24	12.1	12.4	148	226	200				3.6	2.8
Ta	4.3	4.8	112	78	1.7	1.1	1	1.9	2.5	27	33.3	22
Sc	8.4	6.2	44													3.0	1.9
Sn	6.5	9.8	37	170	2.4	3.2	2	6.3	7.8	79	41.5	6750				2.2	1.6
W	2.5	5.5	68	76	3.2	2.2	2.5	4.3	12.5	13.6	19	22				19	15
Pb	30	50	32	95	21.6	10	25	24.5	13	17	21	39.55				39	59
Zn	37	28	370	116	54.7	37	13	71.3	25	75	210	270				1.6	1.8
As	16.8	81.5	32	64.4	4.5	2.8	1.8	12.5	10.9	49	160	76.5				0.2	0.2
Sb	0.2	-	73	4.9	5.3	5.1	6.4	5.5	3.6	15	24.8	76				2.7	2.8
Au	5.7	3.6	25.5	7.7	8.5	4.9	4.9	16.6	13.6	7	6.5	25.6				180	140
Zr	108	220	107	118	210	206	527	235	117	89	130	90
Y	18	-	35	126	36.5	36.3	19.7	23	10.1	<1	3.5	20
Yb	0.8	-	3.1	12.3	3.8	3.4	18	2.2	1.3	<1	<1	1.6	187	151	229
K/Rb	223	247	50		223	247	346	256	132	22	19		-	-	2.1
Rb/Sr	0.18	0.21	16.4		0.18	0.21	0.39	0.64	1.56	11.35	4.94		0.61	1.81	3.52
Ba/Rb	8.0	8.3	0.05		8.0	8.3	4.70	4.4	1.63	0.08	0.02		0.42	0.52	0.43
K/(Na + K)	0.36	0.40	0.44		0.36	0.40	0.44	0.49	0.40	0.32	0.37		0.33	0.22	0.12
Ca/(Na + K)	0.40	0.34	0.06		0.40	0.34	0.06	0.09	0.05	0.003	0.013		0.62	0.58	0.95
(Na + K)/Al	0.56	0.57	0.80		0.56	0.57	0.80	0.71	0.82	0.67	0.66		0.96	1.18	0.95
Al/ (2Ca + Na + K)	1.00	1.05	1.11		1.00	1.05	1.11	1.20	1.15	1.48	1.47
Sample	13	14	15	16	17	18	19						I	S	A	C g	C gr
n	7	6	10	7	16	6	3
SiO2	66.53	70.72	72.68	73.18	71.91	71.21	81.63						69.2	70.3	73.8
TiO2	0.66	0.26	0.21	0.12	0.08	0.06	0.01						0.43	0.48	0.26
Al2O3	15.88	14.89	14.86	14.67	15.28	16.06	8.58						14.3	14.1	12.4
Fe2O3	0.68	0.48	0.36	0.07	0.19	0.17	0.04						1.04	0.56	1.24
FeO	3.23	2.28	1.46	1.15	0.61	0.66	1.5						2.29	2.87	1.58
MnO	0.04	0.03	0.02	0.03	0.07	0.06	0.12						-	-	-
MgO	1.43	0.70	0.33	0.13	0.04	0.07	1.13						1.42	1.42	0.20
CaO	2.90	1.58	0.67	0.71	0.34	0.38	0.01						3.20	2.03	0.75
Na2O	3.33	3.17	3.36	3.94	4.40	4.02	0.41						3.13	2.41	4.07
K2O	3.90	4.48	4.60	4.43	3.59	4.82	2.36						3.40	3.96	4.65
H2O	1.05	0.97	0.58	0.46	0.74	0.91	1.29
P2O5	0.23	0.24	0.35	0.43	1.42	0.76	0.24
F	2.8	0.08	0.28	0.20	0.94	0.99	2.7
Total	99.88	99.88	99.76	99.52	99.61	100.23	100.02
B	24.1	9.5	26	21	442	1031	120
Li	73.3	65.6	148	150	1822	1400	3040									37	26
Rb	185	192	294	310	1651	1140	1793						151	217	169	180	120
Sr	600	501	226	43	24	31	50						247	120	48	150	440
Ba	950	914	475	133	155	186	72						538	468	352	650	560
Nb	4.33	6.4	10	13	122	127	180									21	20
Ta	1.67	1.1	1.9	2.5	58	36	190									3.6	2.8
Sc
Sn	3	2.2	8.6	1.4	155	91	34									3.0	1.9
W	3	2.2	6.7	5	30.5	22.5	36.1									2.2	1.6
Pb	21.6	21.6	24.5	17	3.7	3.1	5									19	15
Zn	54.7	54.7	71.3	4	138	85	270									39	59
As	14.5	1.1	1.1	2.2	6.2	20.4	26.3									1.6	1.8
Sb	1.1	2.8	3.2	0.35	15	11.1	9.1									0.2	0.2
Au	13.4	66	11	10.4	7.6	10.8	5.4									2.7	2.8
Zr	214	153	61.2	29	35	83	19.5									180	140
Y		19	13	16	4.4	<1
Yb		2	1.5	1.6	0.7	<1
K/Rb	175	193	130	119	0.09	0.13							187	151	229
Rb/Sr	5.1	4.8	1.6	0.43	68.8	36.8							-	-	2.1
Ba/Rb	0.31	0.38	1.3	7.2	0.35	0.44							0.61	1.81	3.52
K/(Na + K)	0.44	0.48	0.47	0.43	0.03	0.03							0.42	0.52	0.43
Ca/(Na + K)	0.27	0.14	0.06	0.06	0.73	0.74							0.33	0.22	0.12
(Na + K)/Al	0.61	0.68	0.71	0.77	1.3	1.28							0.62	0.58	0.95
Al/ (2Ca + Na + K)	1.06	1.15	1.26	1.22	0.91	0.86							0.96	1.18	0.95

Notes: 1—granite, 2—leucogranite, 3—microcline–albite, 4—greisenized microcline–albite granite of the Omchikandya massif, 5—granodiorite, 6—andesine granite, 7—leucogranite of the Levo Dzolokag massif; 8—two-mica granite, 9—leucogranite of the Burgali massif, 10—microcline–albite granite of the Verkhne–Burgali ethmolith, 11—dykes of the microcline–albite granite, 12—gresenized granite;–topaz–mica greisen of the Verkhne–Burgali ethmolith, 13—granodiorite, 14—andesine granite of the Western Arga Ynnakh Khaya massif, 15—two-mica granite of the Eastern Arga Ynnakh Khaya massif, 16—leucogranite, 17—microcline–albite granite of the Kester harpolith, 18—the same, dykes, and 19–topaz–mica greisen. Oxides are in wt.%; elements in ppm; and Au is in ppb. The analyses were performed at DPMGI SB RAS by the analysts D. A. Kulagina, G. N. Okhlopkova, and S. E. Diakonova. H₂O⁻ is not included in the amount. I-, S-, and A-types of granitoids after [34]. n—number of samples. Cg—Clarke for granite, ppm. Cgr—Clarke for granodiorite, ppm [35].

Table 2. Average compositions of the magmatic rocks of the of the Omchikandya, Burgali, and Arga Ynnakh Khaya ore fields.

Sample	1	2	3	4	5	6	7	8	9	10	11	12	I	S	A	C g	C gr
n	14	6	11	4	18	13	6	16	4	24	12	4
SiO2	70.41	75.92	72.90	72.33	66.53	68.27	70.73	72.05	74.22	70.45	69.59	78.78	69.2	70.3	73.8
TiO2	0.37	0.05	0.03	0.04	0.43	0.38	0.20	0.39	0.02	0.01	0.01	0.01	0.43	0.48	0.26
Al2O3	14.70	12.92	15.5	17.5	15.68	15.63	15.20	14.33	14.32	17.14	17.02	12.50	14.3	14.1	12.4
Fe2O3	0.61	0.17	0.21	0,72	0.60	0.61	0.88	0.67	0.34	0.33	0.23	0.13	1.04	0.56	1.24
FeO	2.69	1.05	1.15	2.95	3.59	2.93	1.14	2.23	0.86	0.97	1.13	0.86	2.29	2.87	1.58
MnO	0.05	0.03	0.15	0.68	0.21	0.06	0.05	0.05	0.04	0.05	0.04	0.03	-	-	-
MgO	0.70	0.09	0.08	0.04	1.63	0.90	0.34	0.67	0.05	0.06	0.03	0.01	1.42	1.42	0.20
CaO	1.97	0.82	0.34	0.07	3.82	3.33	0.80	1.04	0.30	0.04	0.16	0.24	3.20	2.03	0.75
Na2O	3.19	2.59	4.04	0.26	3.38	3.33	4.17	3.17	4.29	4.74	4.33	1.11	3.13	2.41	4.07
K2O	4.00	5.09	3.97	3.61	2.93	3.10	4.93	4.54	4.39	3.38	3.84	1.90	3.40	3.96	4.65
H2O	0.12	0.06	0.09	1.32	0.10	0.08	0.27	0.22	0.30	1.76	1.10	2.35
P2O5	0.10	0.05	0.045	0.04	0.11	0.08	0.09	0.19	0.27	1.81	1.31	1.07
F	1.19	0.56	1.02	0.02	0.73	0.62	0.86	0.62	0.52	1.13	1.03	1.51
Cl	0.12	0.13	1.20	1.80	0.07	0.07	0.05	0.08	0.05
Total	100.22	99.53	100.82	101.38	99.81	99.39	99.62	100.25	99.97	101.87	99.92	100.50
B	12	31	47	40	13.4	19	24.6	74	60	26.5	195	420				37	26
Li	56	49	1213	952	42.9	40.1	61.1	88.6	65.3	1822	1708	1867	151	217	169	180	120
Rb	247	157	658	954	109	104	118	147	333	1260	1710	1795	247	120	48	150	440
Sr	220	75	40	25	600	506	300	230	213	111	346	437	538	468	352	650	560
Ba	510	150	36	23	873	860	560	640	543	99	235	220				21	20
Nb	23	35	63	45	12	11	24	12.1	12.4	148	226	200				3.6	2.8
Ta	4.3	4.8	112	78	1.7	1.1	1	1.9	2.5	27	33.3	22
Sc	8.4	6.2	44													3.0	1.9
Sn	6.5	9.8	37	170	2.4	3.2	2	6.3	7.8	79	41.5	6750				2.2	1.6
W	2.5	5.5	68	76	3.2	2.2	2.5	4.3	12.5	13.6	19	22				19	15
Pb	30	50	32	95	21.6	10	25	24.5	13	17	21	39.55				39	59
Zn	37	28	370	116	54.7	37	13	71.3	25	75	210	270				1.6	1.8
As	16.8	81.5	32	64.4	4.5	2.8	1.8	12.5	10.9	49	160	76.5				0.2	0.2
Sb	0.2	-	73	4.9	5.3	5.1	6.4	5.5	3.6	15	24.8	76				2.7	2.8
Au	5.7	3.6	25.5	7.7	8.5	4.9	4.9	16.6	13.6	7	6.5	25.6				180	140
Zr	108	220	107	118	210	206	527	235	117	89	130	90
Y	18	-	35	126	36.5	36.3	19.7	23	10.1	<1	3.5	20
Yb	0.8	-	3.1	12.3	3.8	3.4	18	2.2	1.3	<1	<1	1.6	187	151	229
K/Rb	223	247	50		223	247	346	256	132	22	19		-	-	2.1
Rb/Sr	0.18	0.21	16.4		0.18	0.21	0.39	0.64	1.56	11.35	4.94		0.61	1.81	3.52
Ba/Rb	8.0	8.3	0.05		8.0	8.3	4.70	4.4	1.63	0.08	0.02		0.42	0.52	0.43
K/(Na + K)	0.36	0.40	0.44		0.36	0.40	0.44	0.49	0.40	0.32	0.37		0.33	0.22	0.12
Ca/(Na + K)	0.40	0.34	0.06		0.40	0.34	0.06	0.09	0.05	0.003	0.013		0.62	0.58	0.95
(Na + K)/Al	0.56	0.57	0.80		0.56	0.57	0.80	0.71	0.82	0.67	0.66		0.96	1.18	0.95
Al/ (2Ca + Na + K)	1.00	1.05	1.11		1.00	1.05	1.11	1.20	1.15	1.48	1.47
Sample	13	14	15	16	17	18	19						I	S	A	C g	C gr
n	7	6	10	7	16	6	3
SiO2	66.53	70.72	72.68	73.18	71.91	71.21	81.63						69.2	70.3	73.8
TiO2	0.66	0.26	0.21	0.12	0.08	0.06	0.01						0.43	0.48	0.26
Al2O3	15.88	14.89	14.86	14.67	15.28	16.06	8.58						14.3	14.1	12.4
Fe2O3	0.68	0.48	0.36	0.07	0.19	0.17	0.04						1.04	0.56	1.24
FeO	3.23	2.28	1.46	1.15	0.61	0.66	1.5						2.29	2.87	1.58
MnO	0.04	0.03	0.02	0.03	0.07	0.06	0.12						-	-	-
MgO	1.43	0.70	0.33	0.13	0.04	0.07	1.13						1.42	1.42	0.20
CaO	2.90	1.58	0.67	0.71	0.34	0.38	0.01						3.20	2.03	0.75
Na2O	3.33	3.17	3.36	3.94	4.40	4.02	0.41						3.13	2.41	4.07
K2O	3.90	4.48	4.60	4.43	3.59	4.82	2.36						3.40	3.96	4.65
H2O	1.05	0.97	0.58	0.46	0.74	0.91	1.29
P2O5	0.23	0.24	0.35	0.43	1.42	0.76	0.24
F	2.8	0.08	0.28	0.20	0.94	0.99	2.7
Total	99.88	99.88	99.76	99.52	99.61	100.23	100.02
B	24.1	9.5	26	21	442	1031	120
Li	73.3	65.6	148	150	1822	1400	3040									37	26
Rb	185	192	294	310	1651	1140	1793						151	217	169	180	120
Sr	600	501	226	43	24	31	50						247	120	48	150	440
Ba	950	914	475	133	155	186	72						538	468	352	650	560
Nb	4.33	6.4	10	13	122	127	180									21	20
Ta	1.67	1.1	1.9	2.5	58	36	190									3.6	2.8
Sc
Sn	3	2.2	8.6	1.4	155	91	34									3.0	1.9
W	3	2.2	6.7	5	30.5	22.5	36.1									2.2	1.6
Pb	21.6	21.6	24.5	17	3.7	3.1	5									19	15
Zn	54.7	54.7	71.3	4	138	85	270									39	59
As	14.5	1.1	1.1	2.2	6.2	20.4	26.3									1.6	1.8
Sb	1.1	2.8	3.2	0.35	15	11.1	9.1									0.2	0.2
Au	13.4	66	11	10.4	7.6	10.8	5.4									2.7	2.8
Zr	214	153	61.2	29	35	83	19.5									180	140
Y		19	13	16	4.4	<1
Yb		2	1.5	1.6	0.7	<1
K/Rb	175	193	130	119	0.09	0.13							187	151	229
Rb/Sr	5.1	4.8	1.6	0.43	68.8	36.8							-	-	2.1
Ba/Rb	0.31	0.38	1.3	7.2	0.35	0.44							0.61	1.81	3.52
K/(Na + K)	0.44	0.48	0.47	0.43	0.03	0.03							0.42	0.52	0.43
Ca/(Na + K)	0.27	0.14	0.06	0.06	0.73	0.74							0.33	0.22	0.12
(Na + K)/Al	0.61	0.68	0.71	0.77	1.3	1.28							0.62	0.58	0.95
Al/ (2Ca + Na + K)	1.06	1.15	1.26	1.22	0.91	0.86							0.96	1.18	0.95

Notes: 1—granite, 2—leucogranite, 3—microcline–albite, 4—greisenized microcline–albite granite of the Omchikandya massif, 5—granodiorite, 6—andesine granite, 7—leucogranite of the Levo Dzolokag massif; 8—two-mica granite, 9—leucogranite of the Burgali massif, 10—microcline–albite granite of the Verkhne–Burgali ethmolith, 11—dykes of the microcline–albite granite, 12—gresenized granite;–topaz–mica greisen of the Verkhne–Burgali ethmolith, 13—granodiorite, 14—andesine granite of the Western Arga Ynnakh Khaya massif, 15—two-mica granite of the Eastern Arga Ynnakh Khaya massif, 16—leucogranite, 17—microcline–albite granite of the Kester harpolith, 18—the same, dykes, and 19–topaz–mica greisen. Oxides are in wt.%; elements in ppm; and Au is in ppb. The analyses were performed at DPMGI SB RAS by the analysts D. A. Kulagina, G. N. Okhlopkova, and S. E. Diakonova. H₂O⁻ is not included in the amount. I-, S-, and A-types of granitoids after [34]. n—number of samples. Cg—Clarke for granite, ppm. Cgr—Clarke for granodiorite, ppm [35].

Figure 4. Classification diagrams for biotite and microcline–albite granites of the Omchikandya massif based on the bulk geochemistry of the samples. (a) TAS. Diagram fields from [32]; (b) Q¹ vs. ANOR (after [33]); (c) Al₂O₃/(Na₂O + K₂O) vs. Al₂O₃/(CaO + Na₂O + K₂O). Diagram fields from [36]: IAG—island arcs; CAG—continental arcs; CCG—continental collision settings; POG—postorogenic; CEUG—continental epirogenic uplifts; and RRG—rift related; (d) FeO*/(FeO* + MgO) vs. SiO₂. Diagram fields from [37]; (e) (Na₂O + K₂O)/Al₂O₃ vs. Al₂O₃/(CaO + Na₂O + K₂O). Diagram fields from [38]. I, S, and A—types of granitoids; (f) Sr vs. Rb/Sr diagram. Differentiation trends of the type series include [39]: I—island arc tholeiitic; II—island arc calcareous-alkaline; III—active margin calcareous-alkaline; IV—continental rift zones; and I, S, and A—types of granitoids.

Figure 4. Classification diagrams for biotite and microcline–albite granites of the Omchikandya massif based on the bulk geochemistry of the samples. (a) TAS. Diagram fields from [32]; (b) Q¹ vs. ANOR (after [33]); (c) Al₂O₃/(Na₂O + K₂O) vs. Al₂O₃/(CaO + Na₂O + K₂O). Diagram fields from [36]: IAG—island arcs; CAG—continental arcs; CCG—continental collision settings; POG—postorogenic; CEUG—continental epirogenic uplifts; and RRG—rift related; (d) FeO*/(FeO* + MgO) vs. SiO₂. Diagram fields from [37]; (e) (Na₂O + K₂O)/Al₂O₃ vs. Al₂O₃/(CaO + Na₂O + K₂O). Diagram fields from [38]. I, S, and A—types of granitoids; (f) Sr vs. Rb/Sr diagram. Differentiation trends of the type series include [39]: I—island arc tholeiitic; II—island arc calcareous-alkaline; III—active margin calcareous-alkaline; IV—continental rift zones; and I, S, and A—types of granitoids.

Figure 5. Al/(Mg + Fe) vs. Ca/(Mg + Fe) diagram for the granitoids of the Omchikandya massif. The fields of magma-generating protolith were obtained from [40].

Figure 5. Al/(Mg + Fe) vs. Ca/(Mg + Fe) diagram for the granitoids of the Omchikandya massif. The fields of magma-generating protolith were obtained from [40].

In terms of chemical composition, the microcline–albite granites correspond to moderately alkaline-to-alkaline leucogranites [32] or alkaline feldspar granites and quartz alkaline feldspar syenites [33]. These are highly peraluminous, strongly ferroan rocks (Figure 4b,d). On an Al/(Mg + Fe) − Ca/(Mg + Fe) diagram, their data points define a trend intersecting the partial melting fields of various crustal protoliths (Figure 5) [40]. The contents of major element oxides in the microcline–albite granites almost completely coincide with those characteristic of A-type granites [38,39]. The parent melt temperature for microcline–albite granites does not exceed 798–759 °C. The maximum calculated depth of melt generation corresponds to a pressure of 8.6–8.3 kbar, and the crystallization temperature interval is 750–366 °C.

Biotite granites of the Omchikandya massif are characterized by Clarke values, which are the abundance of elements in the earth’s crust (average percentage of elements in the earth’s crust) [41] and the contents of most ore elements (Table 2) [34,35]. B, Sn, W, and Nb contents in leucogranites are 1.5–3 times higher than in biotite granites, while Li and Rb are lower. Microcline–albite granites exhibit a sharp increase in the amount of most ore elements, primarily Li, Ta, W, Zn, Sn, and Sc. The average rare metal index [42] is F*(Li + Rb + Cs)/(Ba + Sr) = 29,540 for microcline–albite granites, which is typical of high-ore-bearing rocks. For biotite granites, F*(Li + Rb + Cs)/(Ba + Sr) = 498.

The contents of REE in the biotite granites are close to the Clarke values (after [35]) and 1.5–2 times higher than in the upper and lower crustal rocks (after [43]). The REE distribution pattern of biotite granites is characterized by a sharp predominance of light lanthanides and a weak Eu negative anomaly (Table 3 and Figure 6): (La/Yb)_N = 7.5, (Ce/Yb)_N = 4.5, and Eu/Eu* = 0.134. Microcline–albite granites and their greisenized varieties show a similar REE pattern. However, they have a markedly lower LREE concentration and close-to-biotite granite HREE contents and show an enhanced Eu negative anomaly: (La/Yb)_N = 2.3, (Ce/Yb)_N = 2.5, and Eu/Eu* = 0.120.

Table 3. Contents of rare-earth elements in granitoids (ppm) of the Omchikandya, Burgali, and Arga Ynnakh Khaya ore fields according to data from ICP-MS analysis and parameters of tetrad effects.

Sample	15,896	12,192	3751	37,331	602/1	602/2	2005/1	2008/3	603/2	600/1
No.	1	2	3	4	5	6	7	8	9	10
Element
La	39	12	3.7	3.4	30	18	24	27	28	2.18
Ce	61	34	16	23	59.2	39.1	48.7	48	54	0.29
Pr	26	17	5.3	7.2	5.8	4.27	4.9	12	8.5	0.054
Nd	27	18	9.8	9	20.2	16.9	18.7	29	32	0.15
Sm	12	7.3	5.3	5	3.8	4.11	3.94	8	8	0.125
Eu	0.43	0.27	0.27	0.37	0.955	0.53	0.825	0.55	0.42	0.0126
Gd	6.7	6.1	5	6	3.77	4.83	4.28	7	5.8	0.12
Tb	1.2	0.68	0.8	0.87	0.51	0.81	0.6	0.96	0.87	0.02
Dy	6.2	4.6	4	3.7	2.9	5.08	3.7	6	5.9	0.165
Ho	1.3	1	0.89	0.96	0.62	0.99	0.74	0.98	0.97	0.026
Er	6	4.30	3.5	3.3	1.81	2.88	2.44	3	1	0.065
Tm	1.4	0.9	0.67	0.72	0.29	0.52	0.41	1.8	1.3	0.0086
Yb	3.7	3.9	1.5	2.2	1.94	2.95	2.31	3.6	2.7	0.077
Lu	-	-	-	-	0.33	0.49	0.36	-	-	0.0011
T1	1.73	2.3	2.16	3.29	1.3	1.24	1.04	1.24	1.03	0.2
T3	0.99	0.77	0.9	0.8	0.85	0.99	0.89	1.11	1.16	1.07
T4	-	-	-	-	0.84	0.91	0.91	-	-	1
Ti	1.3	1.33	1.39	1.62	0.98	1.04	0.94	1.17	1.09	0.6
Sample	601	K9	K19	K6	K13	K5	K17	K14	K10	K21
No.	11	12	13	14	15	16	17	18	19	20
Element
La	2.35	34	18	2.7	3.14	1.3	3.69	1.51	2.57	1.28
Ce	0.33	73.7	47.7	13.7	2.7	0.032	3	0.26	1.61	0.39
Pr	0.043	7.6	5.5	1.64	0.33	0.0067	0.34	0.024	0.25	0.077
Nd	0.14	28	21.5	6.9	1.4	0.073	1.5	0.14	1.32	0.225
Sm	0.14	5.2	5.04	1.6	0.4	0.038	0.36	0.06	0.44	0.15
Eu	0.0096	0.36	0.45	0.28	0.084	0.0038	0.14	0.02	0.08	0.012
Gd	0.115	5.1	4.09	1.28	0.53	0.057	0.42	0.066	0.54	0.104
Tb	0.029	0.78	0.45	0.165	0.097	0.0055	0.088	0.0075	0.07	0.021
Dy	0.14	4.51	1.88	0.68	0.68	0.034	0.63	0.11	0.4	0.19
Ho	0.024	0.93	0.34	0.15	0.16	0.0068	0.12	0.22	0.065	0.032
Er	0.084	3.1	0.96	0.35	0.44	0.016	0.4	0.083	0.18	0.063
Tm	0.0086	0.48	0.1	0.042	0.1	0.0057	0.065	0.011	0.024	0.0068
Yb	0.09	2.97	0.94	0.35	0.62	0.021	0.52	0.043	0.16	0.035
Lu	0.0017	0.48	0.11	0.032	0.09	0.0019	0.07	0.0048	0.02	0.0038
T1	0.29	1.08	1.15	1.55	0.72	0.06	0.61	0.33	0.74	0.46
T3	1.29	0.91	0.82	0.79	0.94	0.12	0.39	0.25	0.95	1.18
T4	0.82	0.86	0.83	1	1.08	1.85	0.97	0.97	0.94	0.85
Ti	0.67	0.95	0.92	1.07	0.9	0.24	0.61	0.43	0.87	0.77

Notes: 1–4—Omchikandya massif: 1—biotite granite, 2—microcline–albite granite, 3—greisenized granite, 4—greisen; 5–7—Levo–Dzholokag massif: 5 and 6—granodiorites, and 7—granite; 8—9—Burgali massif, granite; 10–11—Verkhne–Burgali ethmolith, microcline–albite granite; 12–15—Western Arga Ynnakh Khaya massif: 12—granodiorite, 13—granite, 14—granite porphyry, 15—leucogranite, and 16–20—Kester harpolith: 16–18—microcline–albite granite, 19—pegmatite, and 20—ongonite. T1, T3, and T4 are the tetrad effects that were calculated according to [44] for the 1st, 3rd, and 4th tetrads; Ti is the total tetrad effect.

Table 3. Contents of rare-earth elements in granitoids (ppm) of the Omchikandya, Burgali, and Arga Ynnakh Khaya ore fields according to data from ICP-MS analysis and parameters of tetrad effects.

Sample	15,896	12,192	3751	37,331	602/1	602/2	2005/1	2008/3	603/2	600/1
No.	1	2	3	4	5	6	7	8	9	10
Element
La	39	12	3.7	3.4	30	18	24	27	28	2.18
Ce	61	34	16	23	59.2	39.1	48.7	48	54	0.29
Pr	26	17	5.3	7.2	5.8	4.27	4.9	12	8.5	0.054
Nd	27	18	9.8	9	20.2	16.9	18.7	29	32	0.15
Sm	12	7.3	5.3	5	3.8	4.11	3.94	8	8	0.125
Eu	0.43	0.27	0.27	0.37	0.955	0.53	0.825	0.55	0.42	0.0126
Gd	6.7	6.1	5	6	3.77	4.83	4.28	7	5.8	0.12
Tb	1.2	0.68	0.8	0.87	0.51	0.81	0.6	0.96	0.87	0.02
Dy	6.2	4.6	4	3.7	2.9	5.08	3.7	6	5.9	0.165
Ho	1.3	1	0.89	0.96	0.62	0.99	0.74	0.98	0.97	0.026
Er	6	4.30	3.5	3.3	1.81	2.88	2.44	3	1	0.065
Tm	1.4	0.9	0.67	0.72	0.29	0.52	0.41	1.8	1.3	0.0086
Yb	3.7	3.9	1.5	2.2	1.94	2.95	2.31	3.6	2.7	0.077
Lu	-	-	-	-	0.33	0.49	0.36	-	-	0.0011
T1	1.73	2.3	2.16	3.29	1.3	1.24	1.04	1.24	1.03	0.2
T3	0.99	0.77	0.9	0.8	0.85	0.99	0.89	1.11	1.16	1.07
T4	-	-	-	-	0.84	0.91	0.91	-	-	1
Ti	1.3	1.33	1.39	1.62	0.98	1.04	0.94	1.17	1.09	0.6
Sample	601	K9	K19	K6	K13	K5	K17	K14	K10	K21
No.	11	12	13	14	15	16	17	18	19	20
Element
La	2.35	34	18	2.7	3.14	1.3	3.69	1.51	2.57	1.28
Ce	0.33	73.7	47.7	13.7	2.7	0.032	3	0.26	1.61	0.39
Pr	0.043	7.6	5.5	1.64	0.33	0.0067	0.34	0.024	0.25	0.077
Nd	0.14	28	21.5	6.9	1.4	0.073	1.5	0.14	1.32	0.225
Sm	0.14	5.2	5.04	1.6	0.4	0.038	0.36	0.06	0.44	0.15
Eu	0.0096	0.36	0.45	0.28	0.084	0.0038	0.14	0.02	0.08	0.012
Gd	0.115	5.1	4.09	1.28	0.53	0.057	0.42	0.066	0.54	0.104
Tb	0.029	0.78	0.45	0.165	0.097	0.0055	0.088	0.0075	0.07	0.021
Dy	0.14	4.51	1.88	0.68	0.68	0.034	0.63	0.11	0.4	0.19
Ho	0.024	0.93	0.34	0.15	0.16	0.0068	0.12	0.22	0.065	0.032
Er	0.084	3.1	0.96	0.35	0.44	0.016	0.4	0.083	0.18	0.063
Tm	0.0086	0.48	0.1	0.042	0.1	0.0057	0.065	0.011	0.024	0.0068
Yb	0.09	2.97	0.94	0.35	0.62	0.021	0.52	0.043	0.16	0.035
Lu	0.0017	0.48	0.11	0.032	0.09	0.0019	0.07	0.0048	0.02	0.0038
T1	0.29	1.08	1.15	1.55	0.72	0.06	0.61	0.33	0.74	0.46
T3	1.29	0.91	0.82	0.79	0.94	0.12	0.39	0.25	0.95	1.18
T4	0.82	0.86	0.83	1	1.08	1.85	0.97	0.97	0.94	0.85
Ti	0.67	0.95	0.92	1.07	0.9	0.24	0.61	0.43	0.87	0.77

Notes: 1–4—Omchikandya massif: 1—biotite granite, 2—microcline–albite granite, 3—greisenized granite, 4—greisen; 5–7—Levo–Dzholokag massif: 5 and 6—granodiorites, and 7—granite; 8—9—Burgali massif, granite; 10–11—Verkhne–Burgali ethmolith, microcline–albite granite; 12–15—Western Arga Ynnakh Khaya massif: 12—granodiorite, 13—granite, 14—granite porphyry, 15—leucogranite, and 16–20—Kester harpolith: 16–18—microcline–albite granite, 19—pegmatite, and 20—ongonite. T1, T3, and T4 are the tetrad effects that were calculated according to [44] for the 1st, 3rd, and 4th tetrads; Ti is the total tetrad effect.

Figure 6. Chondrite-normalized [45] REE distribution patterns for the granitoids and greisens of the Omchikandya massif.

Figure 6. Chondrite-normalized [45] REE distribution patterns for the granitoids and greisens of the Omchikandya massif.

4.5. Mineralization of the Polyarnoe Deposit

The bulk of the mineralization at the Polyarnoe deposit is localized in the apical part of the stock of intensely greisenized Li-bearing microcline–albite granite porphyry. The structure of the deposit is characterized by a quartz lens in the center and concentrically arranged quartz veins, lenses, and quartz–topaz–mica greisens [46].

Quartz veins and lenses have a flat dip; their thickness is up to 3 m, and their length is up to 250 m. Greisens form flat-lying or horizontal, isometric, or slightly elongated bodies up to 25–50 m thick [46]. They contain cassiterite, wolframite, lithium micas, topaz, fluorite, and columbite–tantalite minerals. The main Li-bearing mineral is protolithionite. Several boreholes drilled to a depth of 250 m revealed the absence of quartz veins and lenses at levels deeper than 100 m, where mineralization occurs as dissemination [46].

In addition to Sn and W, the ores of the Polyarnoe deposit contain Li, Ta, Nb, Sc, and Rb. Based on the results of prospecting and exploration work, the deposit is evaluated as medium-sized by inferred Sn and Ta reserves, as a large deposit with low-grade lithium ores [46], and as unique in Sc resources [47]. The predicted ore potential of the deposit is (in thousand tons): Sn—93.8, Li₂O—117.5, Ta₂O₅—2.3, and Nb₂O₅—6.1 [46].

5. Burgali Ore Field (Verkhne–Burgali Deposit)

5.1. Geological Setting

The Verkhne–Burgali deposit lies among the mica–amblygonite microcline–albite granites of the same named massif at the boundary of the In’yali–Debin synclinorium and the Kular–Nera terrane. This ore field includes two large Late Jurassic granitoid massifs, Levo–Dzholokag and Burgali, a small (2.2 km²) Early Cretaceous Verkhne–Burgali massif in between them, as well as dykes of granite porphyry, aplite, and leucogranite (Figure 7 and Figure S1b).

The Levo–Dzholokag massif is mainly composed of amphibole–biotite granodiorites and andesine granites. The prevailing hypidiomorphic granular texture of the rocks changes, on approaching the contact with the host rocks, to nevaditic. Orbicular granite is present in the most eroded horizons of the massif. Here, there are numerous ellipse-shaped quartz–diorite nodules.

The Burgali massif is composed of biotite and two-mica granites. Small Au-Bi and cassiterite–quartz occurrences are known in the exocontacts of the massif.

The Verkhne–Burgali massif of microcline–albite granites is an ethmolith up to 500 m thick. It intrudes Middle Jurassic sandstones, siltstones, and granodiorites similar to those of the Levo–Dzholokag massif. In the endocontacts and exocontacts of this massif, Sb occurrences are found confined to greisens and pegmatites.

5.2. Age of the Studied Rocks

The isotopic K-Ar age of the granodiorites of the Levo–Dzholokag, granites of the Burgali and Verkhne–Burgali massifs is 146–158 Ma, 152–159 Ma, and 115 Ma [48], respectively.

5.3. Petrography and Mineralogy of Granitoids

Amphibole–biotite granodiorites and andesine granites of the Levo–Dzholokag massif are composed of zoned andesine intergrown with short-prismatic hornblende grains, isometric grains of eastonite–siderophyllite, and xenomorphic grains of orthoclase and quartz. The average composition of amphibole–biotite granodiorites and andesine granites is as follows: quartz—33.4%, plagioclase—41.6%, orthoclase—15.1%, amphibole—2.3%, biotite—7.4%, and accessories—0.2%. Compositionally, biotite corresponds to that of I-type and S-type granitoids of the granodiorite–granite association (Figure 3 and Table S2). There are found corroded restite grains of magnesian gedrite and chermakite (FeO/(FeO + MgO) = 27.3–43.8, T = 790–792 °C, and P = 6.3–6.8 kbar), magnesioaugite and ferrosilite (Fe/(Fe + Mg = 39.4–59.9%, T = 1012–1118 °C, P = 12.4–15.5 kbar) [5,49,50] (Table S5), and single grains of pyrope–almandine with a pyrope content of 34–48%.

Accessory minerals include allanite, titanomagnetite, ilmenite, Cl- and F-apatite zircons of types D and J, and more rarely, type S according to classification in [51], pyrrhotite, and pyrite.

Biotite and two-mica granites of the Burgali massif are medium-grained. They are composed of zoned plagioclase (32–12% an), orthoclase, quartz, eastonite–siderophyllite, and muscovite. Compositionally, it corresponds to the biotites of S-type granites (Figure 3). Muscovite has elevated halogen contents of 2.03% F and 0.45% Cl. The following accessory minerals were identified: ilmenite, Cl- and F-apatite, zircons of the S type, pyrope–almandine (4–18% pyrope), allanite, monazite, xenotime, and cassiterite.

Dykes intruding both the granites and the sedimentary rocks are mostly composed of fine-grained tourmaline-bearing leucogranites, with fewer pegmatoid granites and aplite.

The Verkhne–Burgali ethmolith is composed (from bottom to top) of topaz–mica, amblygonite–mica, and mica–amblygonite microcline–albite granites. They only differ in their amblygonite content (1.2%, 2.1%, and 3%, respectively) [5]. The rocks are medium-grained with a hypidiomorphic granular texture; near the contacts with the Triassic sedimentary rocks, they are fine-grained and porphyritic, with a granitic or allotriomorphic-granular groundmass and black quartz phenocrysts with albite inclusions (Figures S6 and S7). The average mineral composition of topaz–mica granites is as follows: quartz—28.3%, albite—39.2%, K-feldspar—19%, mica—8.9%, and topaz—3.4%. They are composed of thin euhedral plates of polysynthetically twinned albite (3–6% an), sometimes in intergrowths with short-prismatic topaz grains, mica plates, isometric quartz grains, and xenomorphic grains of K-feldspar and amblygonite (montebrasite). On average, amblygonite contains 8.6% Li₂O and 2.85% F (Table 3).

Mica of the zinnwaldite series (polylithionite [27]) is the most widespread, while lithium muscovite is less abundant (Table 1). Their F content is up to 5.11% (corrected), while that of Li₂O is up to 4.07%. The intergrowths of mica with relatively large topaz crystals are also observed (Table 1).

The accessory minerals of microcline–albite granites include tourmaline, cassiterite, magnetite, Li and REE phosphates, tantalum–columbite, zircon, rare grains of F-apatite, and almost pure almandine (99% alm). Numerous grains of ferrosilite and subcalcic magnesioaugite, similar to those of the Levo–Dzholokag massif granitoids, as well as rare grains of gedrite and chermakite, are also found.

The Verkhne–Burgali ethmolith and Triassic sedimentary strata are intruded by rare 0.5–2.5 m-thick dykes of microcline–albite granite, similar in composition to the ethmolith rocks, and of fine-grained porphyritic and pegmatoid microcline–albite granite.

Amblygonite–muscovite–quartz greisens with disseminated topaz, pyrite, stibnite, and cassiterite aggregates compose veins that are 0.5 m thick and about 10 m long.

5.4. Geochemistry of Granitoids

According to geochemical data, the rocks of the Levo–Dzholokag massif are classified as granodiorites and granites of the calc-alkaline (Figure 8 and Figure S4b; Table 2 and Table S6), while the orbicules qualify as diorites. Metaluminous and weakly peraluminous varieties predominate (Figure 8c). The rocks, with the exception of diorites, have a high ferroan content (Figure 8d). According to their composition, they correspond to granitoids of the I or intermediate IS types (Figure 8c–f). The leucogranite dykes are slightly peraluminous. The Al/(Mg + Fe)–Ca/(Mg + Fe) ratios for the least evolved granitoids of the massif indicate melt generation at the boundary of dacite-tonalite and amphibolite protoliths [40] (Figure 9) at the calculated T = 985–1012 °C and P = 9–11 kbar. The crystallization temperature is within 949–660 °C.

The rocks of the Burgali massif correspond to normally alkaline granites with deviations to moderately alkaline leucogranites, and according to the classification in [33], they correspond to syenogranites and alkaline feldspar granites. These are high ferroan (Figure 8d) and highly peraluminous (Figure 8c) rocks. The calculated parameters of magma generation are: T = 1002–970 °C and P = 8.6–8.4 kbar. The crystallization temperature is within 849–602 °C. In terms of the composition, the granites of the massif are assigned to S-type granites of continental margin geodynamic setting and to continental arc granitoids (Table 2 and Figure 8e,f).

The microcline–albite granites of the Verkhne–Burgali ethmolith and dykes are mainly subalkaline and highly aluminous, with normative albite prevailing over orthoclase (avg. 40.5% and 20.2%, respectively) (Table 2). According to the classification in [33], they are categorized as alkali feldspar granites and quartz alkali feldspar syenites (Figure 8b). The maximum calculated pressure in the magma generation area is 11 kbar [52] at T = 730 °C. The crystallization temperature ranges between 663 and 563 °C. In general, these granites are incomparable, in most of their geochemical signatures, with granites from other massifs of the Burgali ore field. According to their composition, they are similar to A-type granites (Figure 8c–f).

The granitoids of the Levo–Dzholokag massif are only slightly richer in Li, F, W, Zr, and Ta as compared to Clarke values [35] but are significantly higher in Sb, Au, and As. In the granites of the Burgali massif, the contents of B, Au, and Sb are higher than their Clarke levels, while the Li, Sn, and W values are only two times higher. As compared to the granites of the massifs, B, Li, Au, and Sb concentrations in leucogranites of dykes are somewhat decreased, but the amounts of Rb and W are significantly higher, with Sn values showing a lower level of increase (Table 2 and

Table 4. The contents of the trace elements (ppm) in the granitoids of the Arga Ynnakh Khaya and Burgali ore fields according to the ICP-MS analysis.

Sample	2004/1	602/1	602/2	2005/1	603/2	600/1	K-9	K-13	K-19
No.	1	2	3	4	5	6	7	8	9
Elements, ppm
Li	25.2	39.7	64.4	35	10	467	112	107.3	74.7
Cs	20	10	14.3	36	23	200	-	-	-
F	500	800	1000	800	100	11,400	8500	3900	1200
P	459	561	408	408	51	2550	1530	2091	2240
Be	1.71	2.14	2.27	3.45	1.09	1.35	3.46	5.3	3.99
Ti	3005	2566	3282	2426	57	89	11,188	276	2368
V	32	22	40	19	2.17	0.61	5.2	0.88	18
Cr	41	11.3	25	29	4.98	4.73	7	11.2	170
Mn	654	552	751	534	115	626	255	109	338
Co	9.7	7.5	11.3	6.7	1.53	0.18	2.45	0.74	2.96
Ni	14.6	8.2	10.1	16	7	5.6	6.9	10.6	14.5
Cu	23	9.6	11.7	7.3	6.3	7.5	10.6	21	6.5
Zn	49	35	71	37	0.13	75	28	4.4	11.7
Ga	17	19	19	18	13.8	38	21	14.9	20
Ge	1.59	1.57	1.63	1.97	1.67	3.39	1.74	3.22	1.64
Rb	87	76	78	95	89	1629	201	412	215
Sr	145	169	127	139	78	29	72	43	83
Y	21	17	27	21	12.3	0.67	24	3.75	8.5
Zr	166	183	174	177	119	12	265	29	152
Nb	8.8	7.2	9.2	8.3	5.8	32	19	13.1	11.1
Mo	1	1.01	0.55	0.48	0.6	0.46	1.12	1.38	0.81
Sn	2.18	1.32	3.52	1.15	1.41	79	4.45	12.6	7
Sb	1.13	2.17	1.48	0.9	6.4	5.4	0.42	0.37	0.25
Ba	615	629	384	698	646	140	482	133	375
Hf	4.4	4.57	4.14	4.63	3.71	1.02	7.9	1.29	3.9
Ta	0.72	0.57	0.74	0.61	0.6	96.7	2.19	4.92	1.11
W	0.64	0.34	0.6	0.82	0.89	9.6	1.47	64	4.17
Pb	13.1	11.1	9	9.9	25	0.61	21	17	19
Th	8.1	9	6.1	10.3	18	0.21	20	0.92	14.7
U	2.53	1.74	2.48	1.75	3.21	8.9	4.06	15	4.62
Sample	K-6	K-10	K-1	K-2	K-14	K-8	K-21	K-5
No.	10	11	12	13	14	15	16	17
Element, ppm
Li	261.3	438.7	1139	2375	653.3	5376	840	4766
Cs	-	-	-	-	-	-	-	-
F	6000	4100	8200	8200	8000	16,400	6500	9200
P	1887	6222	8058	8058	6579	7089	1683	8823
Be	1.2	1.63	0.64	0.58	1.15	3.18	1.15	0.64
Ti	703	27	95	67	71	8029	124	112
V	-	-	-	-	-	177	1.16	-
Cr	531	70	284	66	110	358	115	303
Mn	226	274	499	497	284	605	459	411
Co	1.28	0.31	1.3	1.05	0.45	17	0.53	0.64
Ni	28	7.2	13	9.2	12.9	53	7.6	14.4
Cu	16	4.83	24	17	8.9	50	5.7	13.3
Zn	24	22	92	88	41	159	25	85
Ga	13.8	32	40	39	36	26	29	38
Ge	3.45	7.2	3.12	5.3	6	2.87	5.1	9.3
Rb	334	2935	1496	1689	1539	1408	985	1651
Sr	85	56	8.5	7	77	67	20	4.42
Y	2.89	1.76	0.06	-	0.52	23	0.58	0.054
Zr	54	10.2	27	24	18	214	21	19
Nb	10	19	75	113	30	37	57	70
Mo	2.35	0.6	0.49	0.41	1.02	2.03	1.22	1.27
Sn	92	35	948	568	14	90	93	352
Sb	0.15	0.12	1.11	0.21	0.35	5.9	0.44	0.5
Ba	302	8.5	6.6	62	26	399	71	1.43
Hf	1.8	0.4	2.95	3.12	1.31	5.45	1.78	2.23
Ta	2.62	4.09	61	102	30	6	43	51
W	15	10.6	24	36	17	7	11	18
Pb	4.99	3.13	4.21	1.54	2.5	10.8	4.15	1.67
Th	2.34	0.06	0.22	0.096	0.16	14.2	0.33	0.21
U	1.04	6.3	7.7	10.3	11.3	6.3	2.87	18

Notes: 1–6—Burgali ore field: 1–3—granodiorite of the Levo–Dzholokag massif; 4—granite of the Levo–Dzholokag massif; 5—granite of the Burgali massif; 6—microcline–albite granite of the Verkhne–Burgali ethmolith; and 7–17—Arga Ynnakh Khaya ore field: 7—granodiorite, 8—leucogranite, 9—granite of the Western Arga Ynnakh Khaya massif, 10—granite porphyry, 11—pegmatite, 12–15—microcline–albite granite of the Kester harpolith, 16—ongonite (dyke), and 17—microcline–albite granite (dyke). The analyses were performed at the Institute of Geochemistry SB RAS (Irkutsk) by O.I. Zarubina. Li, Cs, and F contents were calculated according to the silicate analysis at DPMGI SB RAS.

).

Microcline–albite granites of the Verkhne–Burgali ethmolith are an order of magnitude richer in Li, F, Rb, P, Sn, W, Au, Nb, As, and Sb relative to their Clarke values [35] (Table 2 and Table 4). The average value of the rare metal index [42] is F*(Li + Rb + Cs)/(Ba + Sr) = 167308. The most enriched components in Li are pegmatites and greisens, with up to 13% and 9% montebrasite, respectively.

The contents of LREE in the granodiorites of the Levo–Dzholokag massif are close to those in the upper crust or to the Clarke values, while the HREE amount is somewhat lower than the Clarkes. Overall, the REE distribution pattern is characterized by a sharp predominance of light lanthanides and a weak Eu negative anomaly (Table 3 and Figure 10): (La/Yb)_N = 10–5, (Ce/Yb)_N = 8–5, and Eu/Eu* = 0.76–0.61. In the Burgali massif granites, the total LREE amount is lower and that of HREE is higher than in the granitoids of the Levo–Dzholokag massif, and the negative Eu anomaly is, therefore, more pronounced: Eu/Eu* = 0.18–0.22.

Microcline–albite granites of the Verkhne–Burgali ethmolith differ from other granitoids of the Burgali ore field in very low REE concentrations (Figure 10 and Table 3), but their LREE content is much greater than that of HREE: (La/Yb)_N = 77–71, (Ce/Yb)_N = 3.8–1.7, and Eu/Eu* = 0.29–0.33.

5.5. Ore Mineralization of the Verkhne–Burgali Deposit

Ores of the Verkhne–Burgali deposit belong to the cassiterite–rare metal–quartz association, with their principal metal being lithium. Li mineralization is established in all rocks of the ethmolith and dykes. The average content of Li₂O is 0.5%, with close values recorded throughout the exposed part of the Verkhne–Burgali ethmolith. This allows us to classify the entire massif as an ore body with low-grade Li ores. In the pegmatoid granites of the dykes, the Li₂O content varies from 0.3 to 0.7%, and the richest Li mineralization is present in the greisens and pegmatites (2.28–6.28%) [46].

The main ore minerals are lithium mica and amblygonite. The former is present in the ethmolith rocks in an amount varying from 6% to 10%, while the latter ranges from 1% to 4%. In greisens and pegmatites, the amount of amblygonite is up to 9% and 13%, respectively. Spodumene is rare. Tantalum and niobium are found in columbite–tantalite, cassiterite, and mica [53]. The average contents of Sn, Nb, and Ta in the rocks are low (0.02% Sn, 0.003% Ta, and 0.018% Nb).

Inferred resources of the deposit (in thousand tons) are: Sn—15.3, Li₂O—386.3, Rb—116.3, Cs—283.1, Ta₂O₅—2.3, and Nb₂O₅—13.77 [46].

6. The Arga Ynnakh Khaya Ore Field (Kester Deposit)

6.1. Geological Setting

The Sn rare metal Kester deposit is localized within the Arga Ynnakh Khaya ore field. The latter includes two granitoid massifs, Western Arga Ynnakh Khaya and Eastern Arga Ynnakh Khaya, located in the northwestern Adycha anticlinorium of the Verkhoyansk fold-and-thrust belt (Figure 11) [5]. The ore field also comprises dykes of varying composition and numerous Sn and rare metal occurrences.

The Western massif is mainly composed of andesine granites grading, towards endocontacts, into fine-grained porphyritic granodiorites. The Eastern massif consists of two-mica granites, which contain granodiorite xenoliths similar to those of the Western massif. The granitoid massifs and dykes intrude strongly deformed Late and Middle Triassic clastic rocks. The dykes are composed of biotite–tourmaline leucogranite and aplite. The central part of the Western massif is intruded by Li-F microcline–albite granites of the Kester harpolith (Figure 11 and Figure S1c). The harpolith, both granitoid massifs, and the host sedimentary strata are intruded by numerous (more than 100) dykes of microcline–albite granite and ongonite. The harpolith is accompanied by a large rare metal deposit (Li, Sn, Nb, and Ta).

6.2. Age of Granitoids

The isotopic ⁴⁰Ar-³⁹Ar age of andesine granites of the Western massif determined on biotite is 128.1 ± 0.4 Ma, and that of the Eastern massif granites determined on muscovite is 120.9 ± 0.4 Ma [24]; the U-Pb zircon age of the Eastern massif granites is 131 ± 1.4 Ma [54,55]. According to Rb-Sr isotope dating, the age of Li-F microcline–albite granites in the Kester harpolith is ca. 115 Ma [5]; I₀ = 0.72877 ± 0.0977 Ma [56].

6.3. Petrography and Mineralogy of Granitoids

The medium-grained andesine granites of the Western Arga Ynnakh Khaya massif have a hypidiomorphic granular texture. The rocks are composed of zoned (52%–18% an), short prismatic magnesian hornblende and magnesiohastingsite, eastonite-siderophyllite, orthoclase, and quartz. First-generation eastonite–siderophyllite has FeO/(Fe + MgO) = 52.6%–63.2%, while xenomorphic grains of the second generation have FeO/(Fe + MgO) = 71.8%–73.8%. In terms of composition, the first generation is close to biotite from I-type granitoids, while the second generation corresponds to biotite from S-type granitoids (Figure 3; Table 1 and Table S2). The main accessory minerals of the granitoids of the Western Arga Ynnakh Khaya massif are titanomagnetite (4.1%–10.8% TiO₂ and 0.1%–0.25% Cr₂O₃), ilmenite, sphene, allanite, Cl- and F-apatite (0.85%–0.1% Cl and 1.5%–3.4% F), zircon, pyrrhotite, and single pyrope–almandine grains (21.5% pyrope). Solitary grains of ferrosilite and magnesioaugite are present with FeO/(FeO + MgO) = 13%–36.6%, crystallized at T = 1230%–1247 °C and P = 11.4%–14.1 kb [50] (Table S5).

The medium-grained two-mica granites of the Eastern Arga Ynnakh Khaya massif have a hypidiomorphic granular texture. The granites are composed of zoned oligoclase microcline, eastonite–siderophyllite (FeO/(FeO + MgO) = 71.2%–74.7%, F = 1.05%, and Li₂O = 0.16%), and light mica (phengite and muscovite with F = 1.04%–1.55% and Li₂O = 0.14%–0.25%). Accessory minerals include F-apatite, ilmenite, rutile, zircon, monazite, xenotime, magniotriplite, fluorite, and anatase.

The Kester harpolith is composed (from bottom to top) of Li-F muscovite–albite granites, lepidolite–amblygonite–albite granites, greisenized granites, and greisens [57]. Muscovite–albite granites consist of quartz, albite, microcline, or microcline–perthite, lithium micas, topaz, and montebrasite. The average rock composition is as follows: quartz—23.5%, albite—40.7%, microcline—23%, muscovite—8.6%, mica of the lepidolite series—0.8%, topaz—2%, montebrasite—1.1%, kaolinite—0.2%, tourmaline—0.1%, cassiterite—0.03%, and single grains of topaz [57]. The texture of the rocks is tabular granular, in places hypidiomorphic granular, with elongated euhedral albite plates, between which the interstices are filled with xenomorphic grains of quartz, microcline, mica, topaz, and montebrasite (Figure S7).

Mica is mainly represented by polylithionite, less often by trilithionite and lithim muscovite (Table 1 and Table S2). Their F and Li contents vary widely—from 2.73% to 7% F (corrected) and from 1.05% to 4.07% Li₂O. Their crystallization temperature is 578–668 °C [12]. Mica contains inclusions of tantalite–columbite and forms intergrowths with short-prismatic topaz grains.

Amblygonite has a composition of montebrasite, and it occurs as xenomorphic grains intergrown with K-feldspar. Ambligonite contains 8.1% Li₂O and 2.2% F.

In lepidolite–amblygonite–albite granites, the total contents of mica, montebrasite, and topaz increase, on average, to 15.8%, and that of quartz to 30.8%. The amount of mica in the lepidolite series increases, on average, to 11.7%, and that of amblygonite to 4%. Greisenized granites gradually change, from bottom to top, to topaz–mica greisens [57].

Dykes of medium-to-fine-grained microcline–albite granites are similar in their composition to the Kester harpolith rocks. There are subvolcanic analogues—ongonites averaging 6% lithium micas, 3% topaz, and 3% montebrasite [57]. They have a finely porphyritic texture with micropegmatitic, microallotriomorphic–granular, and less common felsic groundmass. The phenocrysts are composed of quartz, microcline, and albite.

Up to 140 accessory and postmagmatic minerals have been described from the Kester harpolith and its associated dykes [58]. The most abundant are cassiterite, spodumene, lithia phosphates, tantalite–columbite, monazite, xenotime, allanite, and kesterite; titanomagnetite (4%–11% TiO₂), zircons of types D and E, kyanite, and cordierite are common too. Also present are single grains of gedrite, tschermakite (Table S4), Cr-bearing native iron (3.89%–5.97% Cr₂O₃), and magnesioaugite.

6.4. Geochemistry of Granitoids

With regard to chemical composition, the Western massif rocks correspond to low-peraluminous granodiorites and granites, while those of the Eastern massif are close to highly peraluminous granites and leucogranites. Both are characterized by normal to moderate alkalinity, high Fe content, and metaluminous composition (Table 2, Figure 12 and Figure S4c). According to the classification in [33], the granites of the Western massif are ascribed to monzogranites and syenogranites, and those of the Eastern massif to syenogranites and alkaline feldspar granites. In terms of the major element oxide contents (Table 2), the granitoids of the Western massif fully correspond to I-type granitoids. The granites of the Eastern massif are close, in terms of these parameters, to S-type granites. On an Al₂O₃/(Na₂O + K₂O) vs. Al₂O₃/(CaO + Na₂O + K₂O) diagram (Figure 12d,f), the data points for the Western massif are mainly localized in the field of the continental arc granitoids, and those for the Eastern massif plot in the field of the continental collision-related rocks.

On an Al₂O₃/(MgO + FeO) vs. CaO/(MgO + FeO) diagram, the data points for the granitoids of the Western massif are localized in the field of partial melts of dacites–tonalites, and those for the Eastern massif granitoids plot in the field of partial melts of metapelites (Figure 13). The parental melts for the granitoids of the Western massif originated at T = 993–976 °C and P = 14–11 kbar, and those for the granites of the Eastern massif at T = 971–902 °C and P = 8.7–8.3 kbar. The crystallization temperature for the rocks of the Western massif is 899–786 °C, and for the Eastern massif it is 790–599 °C.

Microcline–albite granites of the Kester harpolith and dyke rocks chemically correspond to granites and leucogranites of normal to high alkalinity. According to the classification in [33], the granites of the Kester harpolith are assigned to alkaline feldspar granites, while the dyke rocks are similar to quartz alkaline feldspar syenites. All the rocks are peraluminous and have a high Fe content (Figure 12b,d), with extremely high P₂O₅ and F. According to their composition, they are similar to A-type granites (Figure 12b,e,f). The estimated T-P conditions of the parent melt formation are 842–824 °C and 10–12 kbar. Crystallization of the melt occurred at temperatures ranging from 793 °C to 532 °C.

Compared to the Clarke values [35], granodiorites of the Western massif are richer in Au, As, and Sb, and the granites of this massif are higher in As, Sb, and Au. In the granites of the Eastern massif, Li, B, Au, Sn, and W concentrations are higher than their Clarke levels. In its exocontacts, cassiterite–silicate–sulfide ore occurrences are found. As compared to the granites, the leucogranites of the dykes exhibit a decrease or preservation of the above elements, except for As and Au (Table 2).

The microcline–albite granites of the Kester harpolith exhibit, in comparison to other granitoids in the ore field, sharply increased contents of volatile and trace elements such as Sn, Li, B, Ta, Rb, W, F, and Nb. The average value of the rare metal index F*(Li + Rb + Cs)/(Ba + Sr) = 182,381 [42], which indicates their ultra-high ore potential.

The concentrations of most REEs in the granitoids of the Western and Eastern massifs are close to their Clarke levels. The exceptions are Eu, Gd, and Tb, whose contents slightly exceed their Clarke values, and Sm, which is below the Clarke level. In leucogranites of dykes, the decrease in REE contents is accompanied by the growing Eu negative anomaly. For the granitoids in this ore field, the prevalence of LREE over HREE is more sharply defined: (La/Yb)_N = 13–8, (Ce/Yb)_N = 13–6, and Eu/Eu* = 0.31–0.21. The microcline–albite granites of the Kester harpolith, like the analogous granites of the Verkhne–Burgali massif, have extremely low REE contents (Table 3 and Figure 14).

6.5. Ore Mineralization of the Kester Deposit

The Kester harpolith represents a large Sn rare metal deposit of the same name, with its highest-grade ores localized in topaz–mica–quartz and mica–quartz greisens containing cassiterite, amblygonite, Ta-niobates, and elbaite [46,59].

The deposit was discovered in 1937, with its Sn reserves evaluated as medium. It was recovered by a quarry, and boreholes were drilled to a depth of 200 m. The deposit was periodically exploited, beginning in the early 1940s and lasting until 1973. The richest tin ores have been extracted to date [46,59].

Currently, the deposit is assigned to a rare metal–topaz–mica mineral type of the cassiterite–quartz–rare metal association. Its principal ore element is lithium. The main ore minerals are amblygonite (montebrasite) and lithium mica. They are present in all rocks of the Kester harpolith as rock-forming minerals with average Li₂O contents varying from 0.2% to 0.5% [46,59]. A large number of microcline–albite granite dykes also contain increased Li concentrations, and this fact adds to the importance of the deposit.

In addition to lithium mica and amblygonite (montebrasite), the rocks of the harpolith and dykes contain tantalite–columbite and cassiterite. The average contents of Ta₂O₅ and Nb₂O₅ in the ores are 0.005% and 0.012%, respectively, while that of Sn is 0.2%. Noted are elevated Rb and Cs amounts averaging 0.123% and 0.009%, respectively. Ore minerals normally form scattered fine dissemination, but large (up to 12 cm) cassiterite crystals can also be found in greisens and pegmatites, though rarely [46,59].

The predicted reserves in the harpolith and dykes are (in thousand tons) as follows: Sn—11,277, Li₂O—2031, Nb—74.6, Rb—1037, Ta—19, and W—0.8 [46,59].

7. Discussion

7.1. Early Granitoids of the Studied ore Fields

Within the studied ore fields, the earliest are granitoids, with an age range from 158 to 121 Ma: biotite granites of the Omchikandya massif, granodiorite–granite of the Levo–Dzholokag massif, granite of the Burgali massif, amphibole–biotite granodiorites and granites of the Western massif, and two-mica granites of the Eastern massif.

Biotite granites of the Omchikandya massif belong, in terms of their petrochemical and geochemical signatures, to S-type crustal granites (Figure 4c,e,f, and Figure 15a,b). The average Nb/Ta value in biotite granites is 5.4; in leucogranites it is 7.3; and in microcline–albite granite, it is <1. This is much lower than is observed for igneous rocks of mantle genesis (Nb/Ta~17.5 [14]. The parental melt of biotite granites is assumed to have formed by partial melting of metagraywacke or dacite–tonalite substrata (Figure 5).

The earlier granitoids within the Burgali ore field are represented by the Levo–Dzholokag granodiorite–granite and Burgali granite massifs. Levo–Dzholokag granitoids of the massif are metaluminous, of the ilmenite–magnetite series. According to the composition parameters, they are defined as I- or intermediate IS-type granitoids (Figure 8e,f and Figure 15a,b). The parent melt was generated at the boundary of the dacite–tonalite and amphibolite horizons of the crust. The Burgali massif is composed of highly peraluminous biotite and two-mica granites of the ilmenite series. According to the composition parameters, they are defined as S-type granites (Figure 8e,f, and Figure 15a,b). The parent melt was generated by melting the metapelite protoliths. The granitoids of both massifs are close to continental arcs and continental collision granites (Figure 8c).

The earlier granitoids of the Arga Ynnakh Khaya ore field are represented by the Western massif of amphibole–biotite granodiorites and granites and the Eastern massif of two-mica granites. The Western massif rocks correspond to low-peraluminous granodiorites and granites, while those of the Eastern massif are close to highly peraluminous granites and leucogranites. Western massif granitoids belong to the ilmenite–magnetite series. The parent melt was generated in dacites–tonalites substrates. The Western massif corresponds to I-type granitoids (Figure 12e,f, and Figure 15a,b). The two-mica highly peraluminous granites of the Eastern massif with monazite–ilmenite association of accessory minerals are close to granites of S-type (Figure 12e,f, and Figure 15a,b). The parent melt was generated on metapelite substrates. Both massifs were formed in continental collision settings (Figure 12c).

7.2. Li-F Microcline–Albite Granites

The studied Li-F microcline–albite granites intrude earlier granitoids and have an age of 115 Ma (Aptian) (⁴⁰Ar–³⁹Ar, Rb–Sr). According to the geochemical composition [60,61], they correspond to A-type granites (Figure 4d, Figure 8d, Figure 12d, and Figure 15).

The genesis of Li-F microcline–albite granites remains debatable. Some authors consider them to be related to deep differentiation of crustal melts [8,9], or the initial basaltic/andesitic magma [61,62], while others believe they crystallized from independent mantle-crustal melts with mixing or mingling of mafic and silicic melts [13,14,15,37,63], or by metasomatic processing of magma-generating substrates [64].

Eby [60] distinguishes two genetic varieties of A-type granites: A₁-group granites formed from basalts of oceanic islands, continental rifts, and hot spots, and A₂-group granites, which are postcollisional, postorogenic, or anorogenic granites originated from basalts of island arcs and continental margins, or a crustal tonalite–granodiorite source, or by partial melting of the continental crust. In the Zr–Ga and Nb–Ga discrimination diagrams [34] (Figure 15a,b), a significant part of the data points for the studied granites are localized within the field of A-type granites. The Y–Nb–Ce and Y–Nb–3Ga ratios in the rocks are also inherent in the A₁-group granites (Figure 15c,d). The crustal origin of the protoliths is supported by a high (⁸⁷Sr/⁸⁶Sr)₀ value (0.7115–0.7122 and 0.71052–0.72877 for the microcline–albite granites of the Omchikandya massif [17] and the Kester harpolith [56], respectively) and the calculated depths of magma generation.

Taylor [65] distinguishes two fundamentally different types of Li-F granites of various genesis: low-P granites with P₂O₅ up to 0.1%, and high-P granites with more than 0.4% P₂O₅. The former are also characterized by low Al₂O₃ (14.5%) and high SiO₂ (over 73%) levels. The latter contain more than 14.5% Al₂O₃, less than 73% SiO₂, and are extremely low in REEs, Y, and Th. The Li-F granites we studied are represented by both types.

The first type includes Li-F microcline–albite granites of the Omchikandya massif. These granites are spatially coincident with biotite granites and break through them, and they have lower T (798–759 °C) and P (8.6–8.3 kbar) values of magma generation (Table S3). This suggests the formation of the parent melt for microcline–albite granites at deep levels in the same magma chamber that produced biotite granites. This is also confirmed by the similar trends of REE biotite and microcline–albite granites of the massif (Figure 6) and the presence of the lanthanide tetrad effect of REE fractionation M-type for the first and third tetrads (2.2 and 1.3, respectively) on trends of the Li-F microcline–albite granites of the Omchikandya massif (calculated according to the data from the ICP-MS analysis, Table 3), which is typical for the rocks formed by extended fractional crystallization of the parental melt [44,66]. Tauson [67] showed, on the example of rare metal deposits in Transbaikalia (Russia), the possibility of the formation of residual melts rich in volatile and ore elements at deep levels of granitoid chambers. So, a sharp increase in the contents of Li and F in microcline–albite granites suggests a possibility of supply into a deep granite chamber of ore-rich fluids from an “external”, probably mantle, source. The results of isotopic studies of He, Ar, H, and O from the Li-F granites of the Jiajika deposit (China), e.g., [16], similar in composition to the microcline–albite granites of the Omchikandya massif, indicate that hydrothermal fluids for such deposits can be a mixture of crust- and mantle-derived materials.

Microcline–albite granites of the Verkhne–Burgali ethmolith and Kester harpolith are high-P Li-F granites and have a sharply increased content of all rare metals with sharply reduced values of all REE (Table 2 and Table 3). On the discrimination diagrams, the points of the compositions of microcline–albite granites form trends or fields that do not coincide with those for earlier granitoids (Figure 8, Figure 9, Figure 12 and Figure 13). Thus, microcline–albite granites of the Verkhne–Burgali ethmolith and Kester harpolith mineralogically and geochemically differ greatly from earlier granitoids and cannot be considered as derivatives of their residual melts. Since the estimated depths of the parental melt generation of the Li-F microcline–albite granites and earlier granitoids are close, it can be assumed that the protoliths were significantly reworked after the formation of earlier granitoids.

Microcline–albite granites of the Kester harpolith and the Verkhne–Burgali ethmolith contain grains of magnesioaugite, similar in composition to clinopyroxene of mafic and ultramafic rocks [68], and zircon crystals of type D typical of rocks of mantle or crustal-mantle origin [51]. The Kester harpolith granites also contain grains of Cr-bearing native iron. Rare grains of gedrite and chermakite, characteristic minerals of the lower crustal metamorphic rocks, are found too. The crustal nature of the protoliths is also indicated by the results of Rb-Sr isotopic analyses of the microcline–albite granites of the Kester harpolith—I₀ = 0.71052–0.72877 [56]. These data led us to conclude that the Kester harpolith and Verkhne–Burgali ethmolith microcline–albite granites crystallized from melts generated in the lower crust.

Low temperatures of the microcline–albite granite melts are due to their saturation with Li and P, which, according to experimental studies, can reduce the melt temperature by 150–200 °C [69,70]. Since in the course of differentiation of the earlier granitoids the concentrations of these elements, in the direction from granodiorites to granites and leucogranites, were decreased or remained at the same level, it can be assumed that they are intensely supplied by deep mantle fluids, as is established for many areas where Li-F granites are developed [1,13].

Calculations made following [44] revealed total W-type tetrad effects for the microcline–albite granites of the Verkhne–Burgali ethmolith and Kester harpolith (T = 0.6–0.67 and T = 0.24–0.61, respectively) (Table 2). W-type tetrad effects indicate the crystallization of the rocks in the presence of aqueous fluids, which is associated with the redistribution of REEs between the melt and fluid [44,71,72]. The presence of aqueous fluids is also indicated by the values of geochemical coefficients for the studied granites: Zr/Hf = 7.7–13.8 (<38) and Sr/Eu = 739–3949 (Sr/Eu > 200 [73]).

7.3. Source of Volatiles for Studied Microcline–Albite Granites

The question of the source of volatiles for microcline–albite granites is widely debated. The enrichment of the melt in Li, Sn, Rb, and F and its depletion in REE could occur during magma generation due to the dehydroxylation of micas and amphiboles from the granulite facies rocks in the course of anatexis [73,74], as this could take place in the case of the microcline–albite granites we studied. According to our data, the input of volatiles, Li, and rare elements by transmagmatic fluids is more probable. The question of a source for high P contents is all the more debatable. As follows from the limited data available on the composition of high-grade metamorphosed Precambrian rocks of the lower horizons of the Verkhoyansk–Kolyma orogenic belt, their P₂O₅ content varies from 0.05 to 0.2% [53], and their Li content ranges from 18 to 89 ppm [75], which is comparable to their contents in granitoids, predating the crystallization of microcline–albite granites. High P₂O₅ values are only recorded in alkaline-basic and alkaline-ultrabasic rocks in the east of the study region—1.02%–2.42% in the Middle Paleozoic Tommot massif [76], 0.72%–1.02% in the latite and trachybasalt dykes from the Aptian–Late Cretaceous Dzhakhtardakh volcanic field [77], and 0.67%–1% in the trachybasalt dykes of the Takalkan ore field [78] (Figure 1). The dykes of the Dzhakhtardakh volcanic field and Takalkan ore field also have elevated F contents (up to 0.63% and 0.93%, respectively) and Li up to 420 ppm. For the studied high-P granites, a direct relationship is established between the P₂O₅ and Li contents and between P₂O₅ and the rare metal index (Figure 16). Thus, we can conclude that the parent melt for high-P Li-F granites was generated in the lower crustal protoliths under the influence of a flow of deep-seated F- and P-rich fluids associated with uprising diapirs of alkaline-basic—alkaline-ultrabasic compositions.

7.4. Ore Mineralization of the Studied Microcline–Albite Granites

All the studied Li-F microcline–albite granites contain lithium deposits with accompanying Ta, Nb, Sn, and W. In the Omchikandya ore field, mineralization is localized in the greisenized microcline–albite granites and greisens in the apical part of the massif. In the Verkhne–Burgali ethmolith and Kester harpolith, mineralization is widespread over the entire volume of magmatic bodies. There is a direct dependence of the content and reserves of Li₂O on the content of P₂O₅ (Figure 16). Minimum Li₂O reserves are established in low-P Li-F microcline–albite granites of the Polyarnoe deposit of the Omchikandya ore field (117.5 thousand tons), whereas in the high-P granites of the Verkhne–Burgali and Kester deposits, the Li₂O reserves are significantly higher (386.3 and 2031 thousand tons of Li₂O, respectively).

7.5. Tectonic Setting of the Studied Granitoids

The earliest syn-collisional granitoids, with an age of 158 to 121 Ma, were formed during the collision of the Siberian craton and Kolyma–Omolon superterrane during the Late Jurassic–Early Cretaceous periods, e.g., [22,23]. Li-F microcline–albite granites with an age of 115 Ma (Aptian) intrude these granitoids, and, as it was shown above, they are close to A-type granites in some petrochemical and geochemical parameters (Figure 4, Figure 8, and Figure 12) and could be formed in a postorogenic or riftogenic setting [22,56]. In the Aptian–Late Cretaceous period in the north and east of the Verkhoyansk–Kolyma orogenic belt, extensive extension occurred, which led to the formation of the Indigirka belt of crust extension. We assume that the studied Aptian Li-F microcline–albite granites could have formed during the early stages of this extension.

8. Conclusions

(1)

In the north of the Verkhoyansk–Kolyma orogenic belt, two types of Li-F granites are found: low P and high P. They differ in their chemical composition and have different forms of genesis. According to their geochemical composition, they correspond to A₁-type granites. These granites were formed during the Aptian period, probably at a post-collisional extension in the early stages of the formation of the Aptian–Late Cretaceous Indigirka belt of crust extension.

(2)

Low-P Li-F microcline–albite granites (Omchikandya massif, Polyarnoe deposit) are late derivatives of the melt that formed earlier S-type biotite granites. It is assumed that their parent melt originated at deep levels in the same magma chamber from which the biotite granites were produced.

(3)

High-P Li-F granites (Verkhne–Burgali ethmolith and Kester harpolith) crystallized from melts originated at a lower crustal level under the influence of a deep fluid flow related to ascending diapirs of alkaline-ultrabasic or alkaline-basic compositions, which were likely the main sources of Li, F, and P.

(4)

Low-P and high-P Li-F granites, which are enriched in rare metals, produce Li deposits in association with Sn, W, Ta, and Nb mineralization. The rare metal index for low-P granites corresponds to rocks of high ore potential, and that for high-P granites, to rocks of ultra-high ore potential [42]. In the low-P Li-F granites, mineralization is localized in the greisenized granites and greisens in the apical parts of the granite massifs. In the high-P Li-F granites, mineralization is distributed throughout the massifs.