Geodynamic Emplacement Setting of Late Jurassic Dikes of the Yana–Kolyma Gold Belt, NE Folded Framing of the Siberian Craton

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Article Geodynamic Emplacement Setting of Late Jurassic Dikes of the Yana–Kolyma Gold Belt, NE Folded Framing of the Siberian Craton: Geochemical, Petrologic, and U–Pb Zircon Data

Valery Yu. Fridovsky 1,*, Kyunney Yu. Yakovleva 1, Antonina E. Vernikovskaya 1,2,3, Valery A. Vernikovsky 2,3 , Nikolay Yu. Matushkin 2,3 , Pavel I. Kadilnikov 2,3 and Nickolay V. Rodionov 1,4

1 Diamond and Precious Metal Geology Institute, Siberian Branch, Russian Academy of Sciences, 677000 Yakutsk, Russia; [email protected] (K.Y.Y.); [email protected] (A.E.V.); [email protected] (N.V.R.) 2 A.A. Troﬁmuk Institute of Petroleum Geology and Geophysics, Siberian Branch, Russian Academy of Sciences, 630090 Novosibirsk, Russia; [email protected] (V.A.V.); [email protected] (N.Y.M.); [email protected] (P.I.K.) 3 Department of Geology and Geophysics, Novosibirsk State University, 630090 Novosibirsk, Russia 4 A.P. Karpinsky Russian Geological Research Institute, 199106 St. Petersburg, Russia * Correspondence: [email protected]; Tel.: +7-4112-33-58-72

Received: 30 September 2020; Accepted: 8 November 2020; Published: 11 November 2020

Abstract: We present the results of geostructural, mineralogic–petrographic, geochemical, and U–Pb geochronological investigations of maﬁc, intermediate, and felsic igneous rocks from dikes in the Yana–Kolyma gold belt of the Verkhoyansk–Kolyma folded area (northeastern Asia). The dikes of the Vyun deposit and the Shumniy occurrence intruding Mesozoic terrigenous rocks of the Kular–Nera and Polousniy–Debin terranes were examined in detail. The dikes had diverse mineralogical and petrographic compositions including trachybasalts, andesites, trachyandesites, dacites, and granodiorites. The rocks showed signiﬁcant similarities in distributions of REE, and their concentrations of most HFSEs were close to the intermediate ones between ocean islands basalts and enriched middle ocean ridge basalts. We propose that the subduction that was ongoing during the collision of the Kolyma–Omolon superterrane with Siberia led to melting in the asthenospheric wedge and in the lithosphere, which formed a mixed source for the dike systems from both an enriched and a depleted mantle source. The U–Pb SHRIMP-II dates obtained for the dikes corresponded to the Late Jurassic interval of 151–145 Ma. We present a geodynamic model for the northeastern margin of the Siberian Craton for the Tithonian age of the Late Jurassic.

Keywords: Siberian craton; Verkhoyansk–Kolyma folded area; dike magmatism; U–Pb zircon dating; SHRIMP II SIMS; geodynamics; Yana–Kolyma gold belt

1. Introduction Identifying the conditions and ages of magmatism in gold-bearing provinces is important for understanding the nature of mineralization systems and the metallogenic evolution of orogenic events [1–5]. TheYana–KolymagoldbeltisthelargestintheVerkhoyansk–Kolymametallogenicprovince.Itis ~1000 km long and ~200 km wide and is situated in the central part of the Verkhoyansk–Kolyma folded area. Past production of gold from the Yana–Kolyma gold belt since the 1930s was approximately 3200 tons, with current estimated resources of about 5000 tons of Au. The belt trends in parallel to

Minerals 2020, 10, 1000; doi:10.3390/min10111000 www.mdpi.com/journal/minerals Minerals 2020, 10, 1000 2 of 27 the northeastern margin of the Siberian craton [4,6,7]. This is comparable with the scale of major Paleozoic–Mesozoic gold provinces of the World (e.g., Jiaodong, China; Juneau gold belt, Alaska, USA; Lachlan fold belt, Australia; Baikal fold belt, Russia; Southern Tien Shan, Uzbekistan) [8,9]. The Yana–Kolyma gold belt is host to widespread Late Jurassic dike magmatism of the Nera–Bokhapcha complex [10–17]. The compositions of the dikes vary from maﬁc to felsic; they can reach 15 km in length and can be up to 160 m wide [16]. They occur in groups mainly NE or sometimes NW and WE strike and can also occur near granitoid plutons formed due to the collision between the Kolyma–Omolon superterrane and the Siberian Craton. The dikes cut weakly metamorphosed Mesozoic (T3–J2) terrigenous deposits that compose the continental margin terranes on the northeast of the Siberian craton. For the gold deposits that associate with the dikes, however, the genetic and age connections between the dikes and gold mineralization are not fully understood. For instance, it is not clear in what geodynamic settings the dikes of various compositions formed, what their magmatic sources were, or what is the relationship between the dike and collisional granitoid magmatism and the probable pre-collision island arc magmatism. Published geochronological data for the dikes show a wide range of ages, which prevents reliably correlating their formation with tectonic events in the region. The Rb–Sr isochron ages for the rocks of the dikes indicate the minimal time interval for their emplacement is 17 m.y. from 162 Ma to 145 Ma (Malo–Tarynskoye deposit) [12–14,18]. Published U–Pb ages of zircons (SHRIMP-RG method) from felsic dikes of the southeastern fragment of the Yana–Kolyma gold belt set a very brief interval of 153–150 Ma [19]. The dikes are a great tool for reconstructing geodynamic settings and for studying the mantle/crustal input in the generation of magmatic melts in the Late Jurassic on the margin of the Siberian craton. This age interval is important in the development of the northeastern margin of the craton, as it corresponds to the transition from the subduction to collision processes and to the formation of extensive volcanic–plutonic belts and deposits of Au, Sn, and W. Here, we discuss the results of geostructural, mineralogic–petrographic, geochemical, and U–Pb geochronological investigations of the maﬁc, intermediate, and felsic rocks from dikes of the Vyun gold deposit and the Shumniy occurrence (hereinafter, the Vyun and Shumniy sites) localized in the Mesozoic terrigenous rocks of the mid-western part of the Verkhoyansk–Kolyma folded area. This combination of a detailed geological characterization of the dikes and petrological and U–Pb zircon geochronology of the rocks enables us to establish their geodynamic emplacement setting and to propose a new tectonic model for the formation of the dikes and related gold deposits of the Yana–Kolyma gold belt.

2. Sample Description, Preparation, and Analytical Methods

2.1. Sample Description and Preparation The dikes were sampled in trenches and natural outcrops of creeks Vyun and Shumniy (right feeders of Burgandzha River, basin of Elgandzha River). The number, rock types, and coordinates are given in Table1. Preparation of the samples for analysis was done at the Diamond and Precious Metal Geology Institute, Siberian Branch of the Russian Academy of Sciences (Diamond and Precious Metal Geology Institute (DPMGI) SB RAS, Yakutsk, Russia) and included standard procedures for crushing and grinding. Minerals 2020, 10, 1000 3 of 27

Table 1. List of the studied samples from the Vyun and Shumniy sites with GPS coordinates.

Coordinates Number Sample No. Rock Type Order NE 1 V3-8 Trachyandesite 65.9640 138.2590 2 V3-9 Trachybasalt 65.9640 138.2589 3 V3-10 Dacite 65.9640 138.2589 4 VJ-108 Trachyandesite 65.9695 138.2795 5 V-20 Trachyandesite 65.9728 138.2481 6 V-21 Trachyandesite 65.9728 138.2481 7 V-22 Trachyandesite 65.9728 138.2481 8 V-43 Trachyandesite 65.9735 138.2513 9 V-47 Trachyandesite 65.9733 138.2506 10 VF-39 Trachyandesite 65.9733 138.2298 11 VK-8 Trachybasalt 65.9865 138.2801 12 VK-107 Dacite 65.9483 138.2969 13 VK-108 Dacite 65.9483 138.2969 14 VK-125 Trachyandesite 65.9760 138.2603 15 VK-127 Dacite 65.9759 138.2605 16 VK-128 Trachyandesite 65.9759 138.2605 17 Sh-6 Trachyandesite 66.0159 138.1491 18 Sh-7 Andesite 66.0159 138.1491 19 Sh-8 Andesite 66.0159 138.1491 20 Sh-12 Trachybasalt 66.0159 138.1491 21 Sh-25 Trachyandesite 66.0143 138.1393 22 Sh-26 Granodiorite 66.0143 138.1393 23 Sh-28 Trachybasalt 66.0143 138.1393 24 Sh-30 Andesite 66.0143 138.1393 25 Sh-38 Trachybasalt 66.0142 138.1412 26 Sh-39 Trachyandesite 66.0142 138.1412 27 Sh-40 Trachyandesite 66.0142 138.1412 28 Sh-41 Andesite 66.0142 138.1412 29 Sh-95 Trachyandesite 66.0215 138.1954 30 Sh-159 Trachybasalt 66.0123 138.1774 31 Sh-160 Trachyandesite 66.0123 138.1774 32 Sh-215 Andesite 66.0185 138.1636 33 Sh-217 Andesite 66.0185 138.1636 34 Sh-218 Andesite 66.0185 138.1636 35 K-4 Andesite 66.0166 138.1996 36 K-5 Andesite 66.0160 138.2006 37 K-8 Trachyandesite 66.0138 138.2059 38 K-9 Trachyandesite 66.0208 138.1797 39 K-11 Andesite 66.0207 138.1798 Minerals 2020, 10, 1000 4 of 27

Table 1. Cont.

Coordinates Number Sample No. Rock Type Order NE 40 K-13 Andesite 66.0207 138.1798 41 K-14 Trachyandesite 66.0205 138.1801 42 K-15 Trachyandesite 66.0204 138.1802

The handpicked zircons were cast in EpoKwick resin (Buehler Ltd., Lake Bluff, IL, USA) along with reference zircons Temora 2 [20] and 91500 [21] at the Centre of Isotopic Research of A.P. Karpinsky Russian Geological Research Institute (VSEGEI, Saint Petersburg, Russia). The zircons were then half-sectioned and polished. The epoxy disks with the zircons were covered with gold in a cathodic–vacuum atomization unit for one min at a current strength of 20 mA. Transmitted and reflected light images as well as Cathodoluminescence (CL) and Backscattered electrons (BSE) microphotographs reflecting the inner structure and zoning of the zircons were taken to help select analytical spots on the grains surface. The CL and BSE images were obtained on a CamScan MX2500 scanning electron microscope (Electron Optic Services, Inc., Ottawa, Canada); the operating distance was 30.5 mm, accelerating voltage 12 kV, and the current of the practically completely focused beam on the Faraday cylinder 7 nA.

2.2. Analytical Methods

2.2.1. Petrographic Analysis The petrographic composition of the rocks was studied on a P-211 POLAM polarizing microscope (AO LOMO, St. Petersburg, Russia) (DPMGI SB RAS, Laboratory of Geology and Mineralogy of Noble Metals). The mineralogical composition of the rocks was determined using a MIRA 3 LMU scanning electron microscope (Tescan Orsay, Brno, Czech Republic) at V.S. Sobolev Institute of Geology and Mineralogy SB RAS (Novosibirsk, Russia). Relative standard deviation during analysis of the main components (concentration >10–15 wt.% when recalculated for corresponding oxides) did not exceed 1.5%, and for components with concentrations 1–10 wt.%, no more than 2.0%. Studies of the secondary components with concentrations below 1 wt.% were qualitative. The major element concentrations in the rocks were determined in the section on physical–chemical analytical methods of the DPMGI SB RAS by combined use of an SF-56 (AO LOMO, St. Petersburg, Russia) spectrometer for SiO2, Al2O3, Fe2O3,P2O5, and TiO2, a METTLER TOLEDO (Greifensee, Switzerland) titrator for MgO and CaO, atomic emission spectrometry on an FPA-0102 photometer for Na2O and K2O, and an atomic absorption spectrometry of an AAS-30 spectrophotometer for MnO. Elements detection limits: spectral photometry was from 0.1%; volume complexometric method was from 0.1%; flame photometry—0.02%; atomic absorption were from 0.0002%; gravimetry was from 0.2%. The ICP-MS analyses were performed on an Agilent 7500ce (Agilent Technologies, Santa Clara, CA, USA) and an Element2 double-focusing sector field mass analyzer (Thermo Fisher Scientific, Waltham, MA, USA) at the A.P. Vinogradov Institute of Geochemistry SB RAS (Irkutsk, Russia) in accordance with the technique in [22]. The methodology is described in detail by A.E. Vernikovskaya et al. [23].

2.2.2. Zircon U–Pb Dating The U–Th–Pb isotope analyses of zircons were carried out on the SHRIMP-II SIMS (Australian Scientiﬁc Instruments, Canberra, Australia) at the Centre of Isotopic Research of VSEGEI (Saint Petersburg, Russia) using a secondary electron multiplier in the single collector mode following the procedure described in [24]. The current of the primary oxygen ion beam was 4 nA with analytical spots approximately 30 µm in diameter. The collected results were processed with the SQUID-1 Minerals 2020, 10, 1000 5 of 27 software v.1.12 (Berkeley, CA, USA) [25] and the Concordia diagrams were calculated using the ISOPLOT/Ex software v.3.22 (Berkeley, CA, USA) [26]. The U/Pb ratios were normalized to a 206Pb/238U ratio of 0.0668 for interspersed analyses of the TEMORA 2 reference zircon, which corresponded to 416.8 0.3 Ma [20] based on the power law relationship 206Pb/U = a(UO/U)2 [24]. The concentrations ± of U and Th in the studied zircons were obtained using the 91500-reference zircon with known concentrations of 81.2 U ppm [21]. Common lead was corrected for measured 204Pb/206Pb ratios. For comparison, the 206Pb/238U age corrected for common lead at 207Pb was also calculated for Mesozoic zircons. Individual zircon measurement errors (of ratios and ages) are given on the 1σ level, errors of calculated concordant ages (for total measurements) are given on the 2σ level.

3. Tectonic Setting

3.1. Regional Geology The Yana–Kolyma gold belt is defined in the central part of the late Mesozoic Verkhoyansk–Kolyma folded area, an accretionary-collisional structure of the northeastern margin of the Siberian Craton (Figure1). It is localized in the eastern part of the Verkhoyansk fold and thrust belt and mainly within the Kular–Nera and the Polousniy–Debin terranes [4,6,27,28]. The Verkhoyansk fold and thrust belt is composed of Mesoproterozoic–Devonian carbonate-clastic and carbonate rocks and Carboniferous–Middle Jurassic clastic rocks of the passive continental margin of the Siberian Craton. The entire complex was formed by material discharged from the Siberian paleocontinent and has distinct facies changes from west to east with deep-water marine sediments increasingly replacing continental ones [29]. The sedimentary formations of the fold belt include deltaic complexes, submarine fans, proximal shelf deposits, continental slope, and rise deposits [6,30,31]. Igneous rocks in the northern and central parts of the Verkhoyansk fold belt are nearly nonexistent except for individual plutons and dikes of the Kolyma (J3–K1) and Nera–Bokhapcha (J3) complexes. The Kular–Nera terrane extends for approximately 1100 km from the northwest to the southeast. It borders the Verkhoyansk fold and thrust belt along the large, regional-scale, and transcrustal Adycha–Taryn fault zone [6]. The latter is 40 km wide and over 1500 km long, including the Ten’ka fault to the south and the Baky–Bytantay fault to the north. Many large commercial gold deposits. such as Natalka, Pavlik, Degdekan, and Rodionovskoe, are localized along the Ten’ka fault [4]. The Kular–Nera terrane consists of sequences of upper Permian, Triassic and Lower Jurassic terrigenous sedimentary rocks corresponding to the deep-water part of the Siberian Craton passive continental margin (continental slope and rise). The northwestern part of the Kular–Nera terrane is composed of deformed carbonaceous and argillaceous Triassic–Lower Jurassic turbidites, and the southeastern part consists of upper Permian black shales turbidites [32]. These rocks are metamorphosed to the initial stages of the greenschist facies. The structural pattern is defined by linear folds and faults of northwestern strike manifesting several deformation stages [6,33]. Within the Kular–Nera terrane and in adjacent tectonic structures, the Adycha ore region of the Yana–Kolyma gold belt is defined. It contains a number of gold metallogenic zones (Inyali–Debin, Delakag–Nera, Adycha. etc.) [15,34]. The Vyun deposit and the Shumniy occurrence of the Vyun ore field that are considered in the present paper are located in the Delakag–Nera metallogenic zone. The Polousniy–Debin terrane is located to the northeast and east of the Kular–Nera terrane. They are separated by the Chakry–Indigirka and Chai–Yureya faults. The Polousniy–Debin terrane is mainly composed of Upper Triassic–Upper Jurassic turbidites. The lower parts of the section are composed of rhythmically alternating argillaceous rocks and sandstones with olistostrome horizons, transitioning up-section into turbidites with a gradual increase of shallow-marine and coarse-grained deposits and a decrease in the rounding degree [35]. In the northern part of the block, the Upper Jurassic rocks have an argillaceous composition with individual andesite, andesibasalt, and basalt flows. In the southern part of the terrane, the alternating siltstone–shale and sandstones also have layers of tuff sandstones and tuff siltstones. In the Debin River basin, a tectonic lens of gabbroids and serpentinites Minerals 2020, 10, 1000 6 of 27 was identified among Jurassic turbidites [36]. There is no consensus among researchers concerning the geodynamic nature of this terrane. Some consider it to be a tuffaceous–terrigenous complex of the back-arc basin (J2–3) of the Uyandina–Yasachnaya island arc [37,38]. Other assign these deposits to turbidites of the continental slope and rise of the Siberian paleocontinent [39]. Some researchers consider this rock association as a fragment of the accretionary wedge formed along the continental margin or the island arc [40,41]. The Polousniy–Debin terrane hosts the largest volume of the Kolyma complex granitoids and volcanic rocks and dikes of the Nera–Bokhapcha complex. Fragments of the Omulevka terrane are located to the east of the Polousniy–Debin terrane across the Polousniy–Kolyma suture zone represented mostly by thrusts and strike-slips. They also have tectonic contacts with blocks of the Uyandina–Yasachnaya paleo-island arc and ophiolites. The latter marks the axis of the collisional belt of the Chersky Range and construct packs of tectonic sheets [6,40,42]. The fullest ophiolite sections are represented by serpentinized metamorphosed peridotites, ultramafic cumulates, gabbro–amphibolites, and metabasalts. According to Oxman [42], these ophiolites represent relicts of back-arc or marginal sea basins, and their obduction took place ca. 174 Ma. Fragments of the Late Jurassic Uyandina–Yasachnaya island arc are composed of volcanogenic– sedimentary and volcanic rocks (andesites, basalts, rhyolites, typically large amounts of tuffs of various types and compositions) [49]. The age of this paleo-island arc corresponds to the Bajocian–Kimmeridgian interval (170–157 Ma) according to multiple ammonite and bivalve finds in the volcanogenic–sedimentary and terrigenous rocks [15,16,50]. There are different viewpoints about the subduction direction of the inferred slab [37,51]. Parfenov [6,51] argued for the formation of the Uyandina–Yasachnaya island arc due to the subduction zone dipping under the southwestern margin of the Kolyma–Omolon superterrane. Another group of researchers [16,37,38,45,52] argued that the slab plunged in the opposite direction—beneath the Siberian Craton. In this case, the Uyandina–Yasachnaya arc would occur in the continental margin setting and traces of the Oymyakon Ocean would be located to the northeast of the arc. This explanation agrees well with the location of the gold deposits of the Yana–Kolyma belt in the back-arc region, and they are consistent with the model of formation of orogenic deposits [53–55]. In the Omulevka terrane fragments, there are outcrops of upper Precambrian–lower Carboniferous carbonate and terrigenous–carbonate deposits with interbeds of gypsum, anhydrites, red-colored rocks, and conglomerates [42]. The upper Paleozoic rocks are represented by rather deep-water volcanogenic–siliceous–terrigenous rocks and Triassic–Middle Jurassic rocks consisting of siltstones and mudstones with interbeds of limestones, marls, siliceous rocks, andesites, and basalts. On different stratigraphic levels from the Precambrian to the upper Paleozoic, the sections contain volcanics of differentiated tholeiitic and alkaline series of continental rifts. Many researchers consider these fragments of the Omulevka terrane as part of the Kolyma–Omolon superterrane that was part of the Siberian paleocontinent in the early Paleozoic and separated from it in the Late Devonian (Famenian) due to the fact of continental rifting [6,40,56]. Paleomagnetic data support this idea [57]. The greatest discrepancy in latitudes for these terranes with Siberia is recorded for the Permian. In the Late Jurassic, they again drifted towards Siberia and became part of it after accretionary-collisional events. The magmatic complexes of the studied region are mainly represented by the granitoids of the Main Belt and intermediate-felsic intrusions and volcanics of the Tas–Kystabyt Belt belonging to the Kolyma complex, as well as by mafic–felsic dikes of the Nera–Bokhapcha complex. The Main Belt intrusions are mainly composed of granites and granodiorites formed due to the collision between the frontal structures of the Kolyma–Omolon superterrane and the Verkhoyansk margin of Siberia [6,38,58]. The granites of the Kolyma complex correspond to the S- and I-geochemical types of granites [59]. More recent data indicate that subduction processes were involved in their formation [19]. The U–Pb age of zircons from the granites of the Main Belt is 155–144 Ma [19]. In the southeastern part of the Tas–Kystabyt Belt, dacites of the Taryn subvolcano (149.9 1.2 Ma, U–Pb zircon, [44]) are exposed. ± Minerals 2020, 10, 1000 7 of 27

The granitoids were preceded by maﬁc dikes (162 4 Ma, whole rock, Rb–Sr, [12]) and diorites ± (161.8 Ma, amphibole, 40Ar–39Ar, [59]). Minerals 2020, 10, x FOR PEER REVIEW 6 of 26

Figure 1. Geology of the central part of the Verkhoyansk–Kolyma folded area with the main tectonic Figure 1. Geology of the central part of the Verkhoyansk–Kolyma folded area with the main units, Jurassic–Cretaceous magmatism, and sites of investigations. Compiled using [6,39,43]. Colored tectonic units, Jurassic–Cretaceous magmatism, and sites of investigations. Compiled using [6,39,43]. numbers show ages in Ma: red—U–Pb SHRIMP-II method, magenta—U–Pb SHRIMP-RG method; Colored numbers show ages in Ma: red—U–Pb SHRIMP-II method, magenta—U–Pb SHRIMP-RG blue—Ar–Ar method; black—Rb–Sr method (numbers in brackets come from the literature: (1)—[44]; method; blue—Ar–Ar method; black—Rb–Sr method (numbers in brackets come from the literature: (2)—[45]; (3)—[13]; (4)—[12]; (5)—[46]; (6)—[18]; (7)—[6]; (8)—[14]; (9)—[47]; (10)—[19]; (11)—[48]). (1)—[44]; (2)—[45]; (3)—[13]; (4)—[12]; (5)—[46]; (6)—[18]; (7)—[6]; (8)—[14]; (9)—[47]; (10)—[19]; Inset: VFTB––Verkhoyansk fold and thrust belt; OT—Okhotsk terrane; investigation sites are marked (11)—[48]). Inset: VFTB—-Verkhoyansk fold and thrust belt; OT—Okhotsk terrane; investigation as numbers in yellow circles: 1—Malo–Tarynskoye site; 2—Tin–Yuryuete site; 3—Vyun deposit and sitesShumniy are marked occurrence; as numbers sutures: inP—Polousniy-Kol yellow circles:yma; 1—Malo–Tarynskoye S—South Anyui; thrusts: site; 2—Tin–Yuryuete A—Adycha-Taryn; site; 3—VyunC—Chakry–Indigirka. deposit and Shumniy occurrence; sutures: P—Polousniy-Kolyma; S—South Anyui; thrusts: A—Adycha-Taryn; C—Chakry–Indigirka. Fragments of the Late Jurassic Uyandina–Yasachnaya island arc are composed of volcanogenic– The tectonic structures, magmatism, and ore deposits of the Verkhoyansk–Kolyma folded area are sedimentary and volcanic rocks (andesites, basalts, rhyolites, typically large amounts of tuffs of closely related to the Late Jurassic–earliest Early Cretaceous subduction–accretion and collision events various types and compositions) [49]. The age of this paleo-island arc corresponds to the Bajocian– at the eastern active continental margin of the Siberian Craton [6]. In the north of the Kular–Nera terrane Kimmeridgian interval (170–157 Ma) according to multiple ammonite and bivalve finds in the andvolcanogenic–sedimentary in adjacent tectonic structures, and terrigenous the Adycha rocks ore [15, region16,50]. isThere identiﬁed are different as part viewpoints of the Yana–Kolyma about the goldsubduction belt. This direction region contains, of the inferred among others,slab [37,51]. the Inyali-Debin, Parfenov [6,51] Adycha argued and forDelakag–Nera the formation metallogenic of the zonesUyandina–Yasachnaya[15,34] with the latter island including arc due the Vyunto the ore subduction ﬁeld with the zoneVyun dipping deposit andunder the theShumniy southwestern occurrence . margin of the Kolyma–Omolon superterrane. Another group of researchers [16,37,38,45,52] argued that the slab plunged in the opposite direction—beneath the Siberian Craton. In this case, the Uyandina–Yasachnaya arc would occur in the continental margin setting and traces of the Oymyakon

Minerals 2020, 10, 1000 8 of 27

3.2. Geology of the Vyun Ore Field

3.2.1. Structures and Host Rocks

The Vyun gold deposit (65◦97033.3” N, 138◦25006.1” E) and the Shumniy gold occurrence (66◦01058.7” N, 138◦14090.4” E) of the Vyun ore ﬁeld are located in the upper reaches of the Adycha River (east feeder of the Yana River) (Figure2). The general tectonic style of the Vyun ﬁeld is determined by NW-striking imbricated structures and cross-strike NE-trending faults (Figure2). The main thrust extends to ~400 km with a displacement of several tens of km [6]. In the footwall of the main—Charky–Indigirka—thrust, Upper Triassic deposits of the Kular–Nera terrane crop out, and the hanging wall consists of Middle Jurassic sandstones with siltstone and mudstone interbeds of the Polousniy–Debin terrane. The Charky–Indigirka thrust is manifested as a zone of intense folding and cataclasis of rocks, a tectonic mélange several tens of meters thick. The walls of the thrust are dominated by linear isoclinal and appressed asymmetric folds with a NW strike, SW vergence, and shallow hinges. Overprinting folds are characterized by steeply dipping hinges to the NE, N, and SE. Steep faults of NW strike are manifested as zones of cataclasis and folding several tens of meters wide. Vertical and horizontal displacements change in direction along the strike of the faults. The widely occurring NE-striking faults localize magmatic bodies. Minerals 2020, 10, x FOR PEER REVIEW 8 of 26

Figure 2. Geology of the region of the Vyun and Shumniy creeks, sampling sites locations and new Figure 2. Geology of the region of the Vyun and Shumniy creeks, sampling sites locations and new U–Pb ages. The approximate location of the area is shown on Figure 1. U–Pb ages. The approximate location of the area is shown on Figure1. 3.2.2. Magmatism and Mineralization 3.2.2. Magmatism and Mineralization Igneous rocks are widespread, and their age are estimated as Late Jurassic–Early Cretaceous Igneous[15,34]. The rocks dikes are widespread,consist of trachybasalts, and their age andesites, are estimated trachyandesites, as Late Jurassic–Early dacites, and Cretaceousgranodiorites. [15 ,34]. The dikesThere consistare also small of trachybasalts, granodiorite plutons andesites, (up trachyandesites,to 6 × 3 km) with hornfelsed dacites, and rims. granodiorites. Individual dikes There are are also smalltraced granodioritealong strike to plutonsseveral kilometers (up to 6 and3 km)have withthicknesses hornfelsed up to 30–40 rims. m. Individual Both the dikes dikes and are the traced × alongsmall strike plutons to several have a kilometers northeastern and strike have (Figure thicknesses 3). They up form to 30–40the Nitkan m. Both transverse the dikes belt 10–15 and the km small plutonswide have and a30–40 northeastern km long. The strike NE (Figure strike of3). the They dike forms dominates the Nitkan in both transverse walls of the belt Chakry–Indigirka 10–15 km wide and 30–40thrust, km long. and fewer The NEdikes strike have of sublatitudinal the dikes dominates and NW strikes. in both The walls dikes of theare boudinaged Chakry–Indigirka and bent, thrust, and fewerwhich is dikes manifested have sublatitudinal in different dip azimuths and NW along strikes. the strike. The dikes Most areof them boudinaged are cut by andsinistral bent, strike- which is slip faults, thrusts, and normal faults. The dikes have many cataclasis manifestations but no clear indications of plastic deformations, which possibly were overprinted by the abundant secondary alterations of the rocks, which include gold–quartz–sulfide mineralization. The ore bodies are veins, stockworks, and disseminations. On the Vyun deposit, the Shumniy occurrence and others, they are localized in dikes and fault zones (Figure 3). In veins and stockworks, the main minerals are quartz and carbonate with at most 1–3% of sulfides represented mostly by arsenopyrite. Rarer sulfides are pyrite, galena, sphalerite, chalcopyrite, tetrahedrite, freibergite, and argentotetrahedrite. There are insignificant quantities of bournonite and antimony. Gold in veins is free and characterized by high grades of up to several hundreds of g/t Au. The disseminated gold– sulfide mineralization is localized both in the fault zones up to several tens of meters thick and in dikes. The main ore minerals in them are auriferous pyrite and arsenopyrite. The host alteration is sericite–chlorite–quartz in composition. The structural control, ore mineralogy, and wall-rock alterations are typical of orogenic gold deposits [2,3].

Minerals 2020, 10, 1000 9 of 27 manifested in diﬀerent dip azimuths along the strike. Most of them are cut by sinistral strike-slip faults, thrusts, and normal faults. The dikes have many cataclasis manifestations but no clear indications of plastic deformations, which possibly were overprinted by the abundant secondary alterations of the rocks, which include gold–quartz–sulﬁde mineralization. Minerals 2020, 10, x FOR PEER REVIEW 9 of 26

Figure 3. Photographs of dated dikes and locations of samples: (A) Vyun deposit, (B) Shumniy ore Figure 3. A B occurrence.Photographs Attitude: of S0—bedding, dated dikes S—fault, and locations D—dike. of samples: ( ) Vyun deposit, ( ) Shumniy ore occurrence. Attitude: S0—bedding, S—fault, D—dike. 4. Results The ore bodies are veins, stockworks, and disseminations. On the Vyun deposit, the Shumniy occurrenceThe and studied others, igneous they are rocks localized underwent in dikes low andtemper faultature zones alterations (Figure due3). Into veinsthe hydrothermal– and stockworks, metasomatism and regional metamorphism processes (no higher than the greenschists facies) (Figure the main minerals are quartz and carbonate with at most 1–3% of sulfides represented mostly by 4). The intensity of the alterations increased from a moderate degree in intermediate and felsic rocks arsenopyrite.to a significant Rarer one sulfides in the mafic are rocks. pyrite, The galena, phenocry sphalerite,sts did not exceed chalcopyrite, 10% of the tetrahedrite, rock volumes. freibergite, Rock and argentotetrahedrite.names in the study as a Therewhole and are in insignificant this section are quantities given in accordance of bournonite with andtheir antimony.petrological and Gold in veinsmineralogical is free and characterized characteristics by (Table high 2, grades Figure 5). of up to several hundreds of g/t Au. The disseminated gold–sulfide mineralization is localized both in the fault zones up to several tens of meters thick and in dikes.4.1. Petrography The main oreand Mineralogy minerals in them are auriferous pyrite and arsenopyrite. The host alteration The trachybasalts had a fluidal structure (Figure 4A) and a hyalopilitic and fine-grained porphyritic texture. Olivine phenocrysts (up to 1 mm) were replaced by serpentine, iddingsite, and

Minerals 2020, 10, 1000 10 of 27 is sericite–chlorite–quartz in composition. The structural control, ore mineralogy, and wall-rock alterations are typical of orogenic gold deposits [2,3].

4. Results The studied igneous rocks underwent low temperature alterations due to the hydrothermal–metasomatism and regional metamorphism processes (no higher than the greenschists facies) (Figure4). The intensity of the alterations increased from a moderate degree in intermediate and felsic rocks to a signiﬁcant one in the maﬁc rocks. The phenocrysts did not exceed 10% of the rock volumes. Rock names in the study as a whole and in this section are given in accordance with their petrological and mineralogical characteristics (Table2, Figure5). Minerals 2020, 10, x FOR PEER REVIEW 11 of 26

Figure 4. Thin section photographs of rocks from dikes (crossed nicols): (A) sample V3-9, trachybasalt; Figure(B) 4.sampleThin Sh-215, section andesite; photographs (C) sample ofSh-25, rocks trachyandesite; from dikes (D (crossed) sample Sh-39, nicols): trachyandesite; (A) sample (E) V3-9, trachybasalt;sample VK-127, (B) sample dacite; Sh-215,(F) sample andesite; Sh-26, granodiorite. (C) sample Abbreviations Sh-25, trachyandesite; of minerals names (D) samplefrom [60]: Sh-39, trachyandesite;Ab—albite, Bt—biotite, (E) sample Cb—carbonate, VK-127, dacite; Chl—chlo (F) samplerite, Cpx—clinopyroxene, Sh-26, granodiorite. Ep—epidote, Abbreviations Hbl— of mineralshornblende, names fromIlm—ilmenite, [60]: Ab—albite, Kfs—potassium Bt—biotite, feldspar Cb—carbonate,, Mt—magnetite, Chl—chlorite, Ol—olivine, Pel—pelitization, Cpx—clinopyroxene, Ep—epidote,Pl—plagioclase, Hbl—hornblende, Qz—quartz, Rt—rutile, Ilm—ilmenite, Ser—sericite, Kfs—potassium Ttn—titanite, feldspar, and Zrn—zircon. Mt—magnetite, Ol—olivine, Pel—pelitization, Pl—plagioclase, Qz—quartz, Rt—rutile, Ser—sericite, Ttn—titanite, and Zrn—zircon. 4.2. Geochemistry The results of the chemical analyses of the major and trace elements for mafic, intermediate, and felsic rocks from dikes of the Vyun and Shumniy sites are shown in Tables 2 and 3. These rocks had highly variable contents of SiO2 (46.8–70.5 wt.%), K2O (0.55–4.06 wt.%), and Na2O (0.78–6.01 wt.%). The loss on ignition (LOI) in these rocks decreased from 9.54–12.74 wt.% in mafic varieties to 4.39– 11.85 wt.% and 2.52–5.43 wt.% in intermediate and felsic varieties, respectively. In the SiO2 versus Zr/TiO2 × 0.0001 diagram from [61], these volatile-enriched mafic and intermediate rocks were plotted in the fields for subalkaline and alkaline varieties (Figure 5). However, the lack of alkaline minerals in these rocks allowed us to assign them to trachybasalts and trachyandesites. On the other hand, the

Minerals 2020, 10, 1000 11 of 27

Table 2. Major element compositions of studied igneous rocks from the Vyun and Shumniy sites.

Sample VK- VK- VK- VK- VK-8 V3-9 V3-8 VJ-108 V-20 V-47 V-21 VK-128 V-22 V-43 VF-39 V3-10 Sh-12 Sh-38 Sh-159 Sh-28 Sh-40 Number 125 127 108 107 Number 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 Order Rock Type TB TB TA TA TA TA TA TA TA TA TA TA D D D D TB TB TB TB TA

SiO2 46.8 51.4 54.2 54.8 55.3 56.3 56.4 56.5 57.1 58.8 61.5 62.4 64.1 66.1 67.6 70.5 49.4 51.5 51.8 52.2 54.2

TiO2 1.06 0.46 0.47 0.54 0.65 0.53 0.53 0.58 0.57 0.52 0.39 0.37 0.35 0.4 0.3 0.19 0.63 0.57 0.54 0.57 0.6

Al2O3 14.7 16.4 16.5 16.8 16.5 16.4 15.8 15.7 17 16.9 15.6 15.3 16.9 15.3 15.3 14.8 17.5 15.6 14.2 15.2 16

Fe2O3 0.94 1.41 2.72 1.29 0.28 0.59 1.98 0.63 1.45 0.87 0.72 0.81 2.3 1.12 1.2 0.35 1.6 1.05 0.96 3.87 0.59 FeO 6.22 3.22 2.12 3.15 4.11 4.11 2.58 3.76 3.62 3.44 3 2.58 1.27 2.51 2.41 1.93 5.32 5.37 4.29 2.23 5.88 MnO 0.14 0.08 0.08 0.1 0.11 0.1 0.11 0.17 0.12 0.13 0.07 0.06 0.07 0.05 0.08 0.07 0.13 0.13 0.1 0.04 0.11 MgO 6.73 2.85 1.94 3.21 2.98 2.8 2.47 2.4 2.41 2.45 1.11 1.24 0.32 1.5 0.42 0.06 5.14 4.87 4.98 2.72 3.72 CaO 7.72 6.81 6.36 5.22 5.42 4.97 6.3 5.29 5.13 5.04 3.38 3.8 2.71 3.08 2.37 2.42 4.21 6.26 6.31 5.23 3.86

Components, wt.% Na2O 1.42 0.78 1.23 0.9 0.99 2.04 3.55 1.14 0.18 2.98 2.92 3.26 3.85 0.96 6.89 3.79 4.73 1.81 1.23 2.72 2.35

K2O 1.66 4.06 4.04 2.11 3.27 2.73 2.04 3.41 3.41 0.83 2.98 2.93 3.02 1.73 0.7 3.47 1.18 2.09 2.61 2.41 2.14

P2O5 0.17 0.09 0.11 0.12 0.12 0.11 0.12 0.11 0.12 0.12 0.1 0.11 0.1 0.1 0.1 0.09 0.12 0.11 0.11 1.38 0.17 LOI 11.8 11.82 10.07 11.85 9.93 8.93 8.37 9.5 8.57 7.95 7.88 7.12 5.43 6.64 2.73 2.52 9.54 9.94 12.74 11.41 9.48 Tot. 99.36 100 100 100 100 100 100 100 100 100.03 100 100 100 100 100 100 100 100 99.4 99.98 100 Minerals 2020, 10, 1000 12 of 27

Table 2. Cont.

Sample Sh- Sh- Sh- Sh- Sh- Sh- Sh- Sh- Sh- Sh- K-9 Sh-8 K-8 K-5 Sh-6 K-13 K-4 K-14 K-15 Sh-7 K-11 Number 39 160 25 41 215 95 218 217 30 26 Number 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 Order Rock Type TA TA TA A TA A TA A TA A A A TA TA A TA A A A A GD

SiO2 55.1 55.8 55.8 56 56.2 56.6 56.7 56.9 56.9 57 57.2 58 58.3 58.3 58.9 59.5 59.9 60.1 60.2 60.6 64.2

TiO2 0.42 0.53 0.57 0.75 0.59 0.65 0.57 0.65 0.59 0.59 0.63 0.6 0.65 0.66 0.63 0.47 0.52 0.58 0.55 0.59 0.5

Al2O3 13.6 14.5 15 18.3 16.5 16.4 14.9 15.2 15.9 14.9 16 15.4 14.6 15.6 15.8 16.04 15.7 15.5 15.5 16.1 16.4

Fe2O3 1.32 1.9 1.13 2.26 0.94 1.19 1.58 1.96 1.97 3.66 2.24 1.78 3.45 1.96 1.66 1.08 1.24 2.38 1.29 1.99 2.31 FeO 3.62 4.02 4.52 5.85 3.57 5.57 4.27 4.02 4.7 2.08 4.14 4.08 2.79 4.75 4.48 5.03 4.72 4.11 4.29 3.85 3.56 MnO 0.09 0.11 0.11 0.06 0.14 0.13 0.11 0.11 0.09 0.14 0.12 0.1 0.13 0.09 0.12 0.1 0.1 0.09 0.1 0.11 0.1 MgO 3.87 3.07 5.67 3.07 2.31 3.75 5.94 5.95 3.9 2.16 3.43 6.19 2.74 4.1 2.59 3.2 2.92 3.47 2.78 2.33 2.98 CaO 5.77 5.39 3.35 1.61 6.4 5.63 4.09 4.68 5.16 6.47 4.3 3.03 5.44 3.2 3.75 3.3 3.33 3.7 3.49 3.35 1.29

Components, wt.% Na2O 2.66 2.3 4.53 6.01 0.67 3.34 3.53 1.63 4.88 2.23 4.12 2.41 1.75 2.14 5.53 3.37 3.88 3.69 4.68 4.65 1.52

K2O 2.4 2.15 1.18 0.58 3.25 0.55 1.22 1.91 1.14 2.13 1.12 1.77 2.16 2.17 0.55 2.27 1.39 1.19 0.98 0.93 3.1

P2O5 0.11 0.19 0.11 0.19 0.11 0.12 0.12 0.11 0.17 0.17 0.16 0.11 0.17 0.18 0.19 0.15 0.11 0.15 0.16 0.16 0.15 LOI 11.19 10.03 8.14 5.15 8.64 5.68 6.75 7.08 4.79 8.45 6.06 6.61 7.74 6.56 5.9 4.39 6.31 5.29 6.01 4.56 3.44 Tot. 100 99.4 100 99.2 100 100 99.4 100 100 99.7 100 100 100 100 100 99.1 100 100 100 100 100 Here and in Tables3 and4: A—andesite, D—dacite, GD—granodiorite, TA—trachyandesite, TB—trachybasalt. Minerals 2020, 10, 1000 13 of 27

Table 3. Trace element compositions of the studied igneous rocks from the Vyun and Shumniy sites.

Rock Type A TA TA TB TA GD TB TA A TA Sample V-43 V-47 V-21 V3-9 VJ-108 Sh-26 Sh-28 Sh-6 Sh-215 Sh-160 Number Be 1.35 1.61 1.49 1.13 1.68 1.71 1.35 0.93 2.85 1.98 Ti 2873 3019 2994 2371 2692 2712 2676 3199 3234 2939 V 44 49 53 62 57 42 42 53 52 91 Cr 50 60 47 66 44 114 90 133 136 220 Mn 814 920 1059 710 806 787 817 837 899 758 Co 9.5 9.7 9.0 5.9 8.4 11.7 9.9 14.0 14.9 21 Ni 8.1 5.6 5.0 5.0 4.52 12.8 8.2 18 20 53 Cu 8.6 b.d.l. b.d.l. b.d.l. 48 20 2.77 8.7 94 63 Zn 54 69 49 41 59 116 55 87 102 68 Ga 18 17 17 17 19 19 20 18 18 17 Ge 1.33 1.43 1.54 1.17 1.36 1.56 1.43 1.38 1.70 1.32 As 9.9 7.2 16 18 12.0 3.51 16.714 0.93 4.98 47 Rb 80 64 89 115 85 33 103 14.7 30 18 Sr 386 358 431 549 503 303 294 408 409 692 Y 15 15 16 12.6 12.6 15 18 18 17 15 Zr 134 128 132 112 120 238 237 192 195 130 Nb 6.1 5.7 6.0 5.2 5.3 9.6 9.1 7.6 7.7 6.2 Mo 0.46 0.93 0.65 0.81 0.54 0.83 0.98 1.16 1.44 0.63 Sn 1.14 b.d.l. b.d.l. b.d.l. b.d.l. 0.90 1.31 1.22 1.44 0.86 Ba 561 580 550 839 644 1219 615 561 455 546

Components, ppm La 20 17 19 21 21 15 18 15 16 18 Ce 42 35 39 41 42 34 37 32 33 38 Pr 5.0 4.30 4.54 4.88 4.88 4.00 4.31 3.90 3.85 4.76 Nd 19 16 18 18 20 16 16 15 15 19 Sm 3.81 3.36 3.65 3.41 3.41 3.27 3.57 3.46 3.39 3.86 Eu 0.92 0.9 1.02 1.06 0.92 0.97 0.96 1.09 1.02 1.06 Gd 3.52 3.36 3.51 3.00 3.04 3.42 3.66 3.63 3.65 3.55 Tb 0.56 0.51 0.53 0.45 0.46 0.53 0.61 0.56 0.54 0.57 Dy 3.30 3.17 3.13 2.75 2.56 3.31 3.68 3.49 3.52 3.33 Ho 0.67 0.62 0.68 0.52 0.52 0.71 0.77 0.76 0.77 0.68 Er 2.04 1.95 2.07 1.59 1.66 2.17 2.40 2.21 2.27 1.98 Tm 0.31 0.27 0.29 0.24 0.25 0.35 0.36 0.35 0.34 0.29 Yb 2.03 1.93 2.00 1.68 1.66 2.36 2.53 2.25 2.36 1.83 Lu 0.32 0.30 0.30 0.25 0.26 0.37 0.41 0.37 0.37 0.28 Hf 3.98 3.86 3.74 3.30 3.60 6.4 6.5 5.4 5.6 3.89 Ta 0.50 0.43 0.47 0.39 0.38 0.58 0.56 0.45 0.47 0.43 Tl 0.52 0.54 0.55 0.65 0.60 0.38 0.63 0.34 0.22 0.29 Pb 7.5 3.43 5.6 7.8 5.7 7.8 9.2 5.5 8.8 6.5 Th 6.4 5.62 6.1 6.9 7.6 5.8 5.5 4.24 4.51 5.7 U 1.88 1.80 1.93 2.06 2.24 2.00 2.13 1.74 1.87 1.74 Minerals 2020, 10, 1000 14 of 27

Table 3. Cont.

Rock Type A TA TA TB TA GD TB TA A TA Eu/Eu* 0.95 0.98 1.01 1.11 1.02 0.99 0.98 1.03 0.99 1.02

(La/Yb)CN 6.69 5.98 6.45 8.49 8.59 4.32 4.30 4.53 4.61 6.68

(Tb/Lu)CN 1.19 1.16 1.20 1.23 1.21 0.98 1.01 1.031 0.99 1.39

b.d.l.—concentration below detection limit. Here and in Table4: Eu /Eu* = EuCN/(GdCN SmCN)0.5; CN—elements concentrations normalized for chondrite taken from [64]. · Table 4. Trace element compositions of trachybasalts from the Malo–Tarynskoye and Tin–Yuryuete sites.

Sample MTD-6 MTD-7 MTD-12 MTD-17 TYu-29 TYu-40 Number/Components Be, ppm 0.88 1.13 1.59 1.63 0.91 0.63 Ti 5602 5742 6120 5743 3323 3886 V 117 117 132 120 102 114 Cr 291 280 276 325 458 474 Mn 936 1001 1087 1036 1174 1064 Co 22 20 22 23 20 26 Ni 32 31 52 43 63 59 Cu 18 33 10.6 14.4 6.8 7.6 Zn 76 61 73 64 75 74 Ga 16 16 19 16 14.8 16 Ge 1.58 1.42 1.80 1.34 1.56 1.51 As 38 31 64 68 29 3.24 Rb 74 66 108 92 66 26 Sr 756 774 428 533 270 348 Y 20 18 25 20 14.0 18 Zr 142 133 174 136 91 103 Nb 11.0 11.0 12.8 11.1 3.97 4.50 Mo 1.37 0.61 0.39 0.37 0.35 0.30 Sn 0.73 0.51 1.49 1.14 0.69 0.30 Ba 302 318 539 446 531 843 La 23 19 29 23 12.7 15 Ce 46 41 60 48 23 29 Pr 5.7 5.1 7.3 5.8 2.84 3.49 Nd 23 20 27 24 10.5 14.4 Sm 4.37 4.15 5.8 4.62 2.17 3.06 Eu 1.43 1.26 1.46 1.32 0.86 1.11 Gd 4.32 3.93 5.3 4.40 2.50 3.40 Tb 0.62 0.59 0.73 0.65 0.37 0.55 Dy 3.77 3.47 4.63 3.91 2.61 3.41 Minerals 2020, 10, 1000 15 of 27

Table 4. Cont.

Sample MTD-6 MTD-7 MTD-12 MTD-17 TYu-29 TYu-40 Number/Components Ho 0.75 0.71 0.93 0.74 0.55 0.69 Er 2.24 2.20 2.98 2.42 1.72 2.10

Minerals 2020, 10, xTm FOR PEER REVIEW 0.34 0.32 0.41 0.32 0.24 0.31 12 of 26 Yb 2.13 1.92 2.61 2.23 1.71 1.95 less altered felsic rocks, in accordance with their mineralogical–petrographic features and position Lu 0.31 0.30 0.40 0.33 0.25 0.32 on this diagram, corresponded to dacites and granodiorites. These results agreed well with major and trace elements concentrationsHf for 3.95 mafic rocks 3.79 from the 4.81Malo–Tarynskoye 3.84 site 2.45 (Table 4 and 2.94 [12]) and for mafic and felsicTa rocks from 0.62the Tin–Yuryuete 0.54 site 0.67 (Table 4 and 0.55 [18]) (Figures 0.13 5). 0.18These rocks showed significantW similarities in 0.30 distributions 0.31 of REE 10.4and on spider 2.47 diagrams 1.56 (Figure 6). 2.97 They also showed similaritiesTl in distributions 0.37 of trace 0.32elements on 0.50 spider diagrams 0.38 with 0.30 the felsic 0.26rocks of the Ergelyakh pluton when compared using data from [13] (Figure 6). Samples from the Vyun and Pb 11.5 8.0 2.94 6.6 4.07 3.78 Shumniy sites had moderate (La/Yb)CN ratios (4.30–8.59) and either did not have or had small positive Th 4.41 4.04 6.3 4.45 2.69 3.25 or negative anomalies of Eu/Eu* (0.95–1.11) in which they were similar to rocks from the Malo– Tarynskoye andU Tin–Yuryuete sites 1.21 (La/Yb) 1.14CN (5.05–7.55) 1.85 and Eu/Eu* 1.20 (0.99–1.1). 0.78 All rocks 0.88 showed negative Nb andEu/Eu* Ta anomalies, 1.08which were 1.06 the lowest 0.99 of the rocks 1.03 of Tin–Yuryuete, 1.10 and 1.07 had flat

HREE distributions(La/Yb)CN ((Tb/Lu)CN = 7.340.98–1.39). 6.72In these rocks, 7.55 concen 7.01trations of 5.05most HFSEs 5.22 were close to intermediate ones, between ocean islands basalts (OIBs) and enriched middle ocean ridge basalts (Tb/Lu)CN 1.36 1.34 1.35 1.34 1.01 1.17 (E-MORBs), as was the case for the large ion lithophile element Sr, while for such LILEs, such as Rb, K, and Ba, and the HFSE, Th, they were above or close to OIB concentrations (Figure 6).

Figure 5. SiO2 versusversus Zr/TiO Zr/TiO2 × 0.00010.0001 diagram diagram from from [61] [61] for for the the st studiedudied igneous rocks. Samples from 2 2 × thethe Tin–YuryueteTin–Yuryuete site site included included samples samples from from [18]. Samples[18]. Samples from the from Malo–Tarynskoye the Malo–Tarynskoye deposit included deposit samplesincluded from samples [12]. from [12].

4.1. Petrography and Mineralogy The trachybasalts had a fluidal structure (Figure4A) and a hyalopilitic and fine-grained porphyritic texture. Olivine phenocrysts (up to 1 mm) were replaced by serpentine, iddingsite, and talc; some had kelyphite rims. Potassium feldspar and plagioclase phenocrysts (up to 0.4 mm) were replaced by albite, and idiomorphic clinopyroxene grains (up to 1 mm) were replaced by carbonate. The groundmass displayed pelitization, sericitization, chloritization, epidotization, and carbonatization. Accessory and opaque minerals included apatite, zircon, ilmenite, pyrite, and magnetite. The andesites had a fine-grained porphyritic texture (Figure4B) with plagioclase (up to 1 mm) and clinopyroxene (up to 0.5 mm) phenocrysts (up to 0.5 mm). The fine-grained groundmass had feldspars,

Figure 6. REE diagram (A) and spider diagram (B) for the studied igneous rocks. Chondrite and primitive mantle normalizing values were from [62]. Blue and grey fields—concentrations for Grenada Island (Lesser Antilles island arc) basalts with, respectively, a peridotite–pyroxenite source (5% mantle wedge melting) and a mainly peridotite source (25% Mg-enriched mantle wedge melting) [63]. Concentrations from the Ergelyakh pluton granite–porphyry and granodiorite–porphyry were from [13].

Minerals 2020, 10, 1000 16 of 27 clinopyroxenes, and quartz. Secondary minerals and aggregates included chlorite, sericite, albite, epidote, and pelite. Accessory and opaque minerals included apatite, zircon, magnetite, and pyrite. The trachyandesites had a ﬁne-grained porphyritic, hyalopilitic and intersertal texture (Figure4C,D). Phenocrysts (up to 1–3 mm) were represented by olivine, potassium feldspar (X Or up to 100), plagioclase (X An up to 37) with potassium feldspar rims, clinopyroxene (CaO = 19.4–20.0 wt.%; FeO = 3.92–9.01 wt.%; MgO = 16.2–18.7 wt.%; Al2O3 = 1.42–2.57 wt.%; small amounts of Cr2O3, MnO, Na2O), and hornblende (SiO2 = 46.7–47.9 wt.%; CaO = 9.55–10.87 wt.%; Na2O = 0.35–0.42 wt.%; K2O = 1.36–1.48 wt.%; Mg# = 0.43–0.61). The groundmass was dominated by plagioclase microlites. Secondary minerals and aggregates included talc, iddingsite, albite, actinolite, chlorite, epidote, carbonates, sericite, and pelite. Accessory and opaque minerals included apatite, zircon, rutile, titanite, magnetite, ilmenite, pyrrhotine, pentlandite, chalcopyrite, and cobaltine. The dacites (Figure4E) had a ﬁne-grained and porphyritic texture with hornblende, clinopyroxene, potassium feldspar, and plagioclase phenocrysts (up to 0.5–1 mm). The groundmass was dominated by quartz and feldspars. Secondary minerals and aggregates were chlorite, epidote, sericite, and pelite. Accessory minerals (up to 0.5 mm) were zircon and rutile. The granodiorite (Figure4F) had a medium-grained texture and contained mainly plagioclase (up to 4 mm), potassium feldspar, and quartz with lesser quantities of hornblende and biotite. Secondary minerals and aggregates were actinolite, chlorite, sericite, epidote, and pelite. Accessory and opaque minerals were apatite, ilmenite, and pyrite.

4.2. Geochemistry The results of the chemical analyses of the major and trace elements for mafic, intermediate, and felsic rocks from dikes of the Vyun and Shumniy sites are shown in Tables2 and3. These rocks had highly variable contents of SiO2 (46.8–70.5 wt.%), K2O (0.55–4.06 wt.%), and Na2O (0.78–6.01 wt.%). The loss on ignition (LOI) in these rocks decreased from 9.54–12.74 wt.% in mafic varieties to 4.39–11.85 wt.% and 2.52–5.43 wt.% in intermediate and felsic varieties, respectively. In the SiO versus Zr/TiO 2 2 × 0.0001 diagram from [61], these volatile-enriched mafic and intermediate rocks were plotted in the fields for subalkaline and alkaline varieties (Figure5). However, the lack of alkaline minerals in these rocks allowed us to assign them to trachybasalts and trachyandesites. On the other hand, the less altered felsic rocks, in accordance with their mineralogical–petrographic features and position on this diagram, corresponded to dacites and granodiorites. These results agreed well with major and trace elements concentrations for mafic rocks from the Malo–Tarynskoye site (Table4 and [ 12]) and for mafic and felsic rocks from the Tin–Yuryuete site (Table4 and [ 18]) (Figure5). These rocks showed significant similarities in distributions of REE and on spider diagrams (Figure6). They also showed similarities in distributions of trace elements on spider diagrams with the felsic rocks of the Ergelyakh pluton when compared using data from [13] (Figure6). Samples from the Vyun and Shumniy sites had moderate (La/Yb)CN ratios (4.30–8.59) and either did not have or had small positive or negative anomalies of Eu/Eu* (0.95–1.11) in which they were similar to rocks from the Malo–Tarynskoye and Tin–Yuryuete sites (La/Yb)CN (5.05–7.55) and Eu/Eu* (0.99–1.1). All rocks showed negative Nb and Ta anomalies, which were the lowest of the rocks of Tin–Yuryuete, and had flat HREE distributions ((Tb/Lu)CN = 0.98–1.39). In these rocks, concentrations of most HFSEs were close to intermediate ones, between ocean islands basalts (OIBs) and enriched middle ocean ridge basalts (E-MORBs), as was the case for the large ion lithophile element Sr, while for such LILEs, such as Rb, K, and Ba, and the HFSE, Th, they were above or close to OIB concentrations (Figure6). Minerals 2020, 10, x FOR PEER REVIEW 12 of 26 less altered felsic rocks, in accordance with their mineralogical–petrographic features and position on this diagram, corresponded to dacites and granodiorites. These results agreed well with major and trace elements concentrations for mafic rocks from the Malo–Tarynskoye site (Table 4 and [12]) and for mafic and felsic rocks from the Tin–Yuryuete site (Table 4 and [18]) (Figures 5). These rocks showed significant similarities in distributions of REE and on spider diagrams (Figure 6). They also showed similarities in distributions of trace elements on spider diagrams with the felsic rocks of the Ergelyakh pluton when compared using data from [13] (Figure 6). Samples from the Vyun and Shumniy sites had moderate (La/Yb)CN ratios (4.30–8.59) and either did not have or had small positive or negative anomalies of Eu/Eu* (0.95–1.11) in which they were similar to rocks from the Malo– Tarynskoye and Tin–Yuryuete sites (La/Yb)CN (5.05–7.55) and Eu/Eu* (0.99–1.1). All rocks showed negative Nb and Ta anomalies, which were the lowest of the rocks of Tin–Yuryuete, and had flat HREE distributions ((Tb/Lu)CN = 0.98–1.39). In these rocks, concentrations of most HFSEs were close to intermediate ones, between ocean islands basalts (OIBs) and enriched middle ocean ridge basalts (E-MORBs), as was the case for the large ion lithophile element Sr, while for such LILEs, such as Rb, K, and Ba, and the HFSE, Th, they were above or close to OIB concentrations (Figure 6).

Figure 5. SiO2 versus Zr/TiO2 × 0.0001 diagram from [61] for the studied igneous rocks. Samples from Mineralsthe2020 Tin–Yuryuete, 10, 1000 site included samples from [18]. Samples from the Malo–Tarynskoye deposit17 of 27 included samples from [12].

Figure 6. REE diagram ( A) and spider diagramdiagram ((B)) forfor thethe studiedstudied igneousigneous rocks.rocks. Chondrite and primitive mantlemantle normalizing normalizing values values were were from from [62]. [62]. Blue andBlue grey and fields—concentrations grey fields—concentrations for Grenada for IslandGrenada (Lesser Island Antilles(Lesser Antilles island arc)island basalts arc) basalt with,s respectively,with, respectively, a peridotite–pyroxenite a peridotite–pyroxenite source source (5% mantle(5% mantle wedge wedge melting) melting) and aand mainly a mainly peridotite peridotite source source (25% (25% Mg-enriched Mg-enriched mantle mantle wedge wedge melting) melting) [63]. Concentrations[63]. Concentrations from thefrom Ergelyakh the Ergelyakh pluton granite–porphyrypluton granite–porphyry and granodiorite–porphyry and granodiorite–porphyry were from were [13]. from [13]. 4.3. Zircon Morphology and U–Pb Geochronology The zircons from the dacite sample VK-127 (n = 8) were 150 to 300 µm long (elongation coefficient Kelong = 1–4), prismatic, brown semitransparent, and idiomorphic (Figure7A). In the CL images, they exhibited clear magmatic zoning. Measurements at spots 4.1 and 5.1 (dark zones in CL images) yielded higher values of U content relative to the other measurement spots (up to 1105 ppm, 680, on average; Th = 100–737 ppm; Th/U = 0.27–0.72). Their U–Pb ages (153.3 1.8 and 158.3 1.8 Ma, ± ± respectively) were apparently overestimated due to the matrix effect [65]. Measurements in the other spots (1.1, 1.2, 2.1, 2.2, 3.1, 3.2, 6.1, 7.1, and 8.1) yielded a Concordia age of 147.0 1.3 Ma (MSWD = 2.1, ± probability = 0.15) corresponding to the time of crystallization of the dacite (Figure7A, Table5). 206 The common lead ( Pbc) fraction was less than 0.3%. The zircons from the granodiorite sample Sh-26 (n = 9) were brown and reddish, transparent and semitransparent idiomorphic grains of prismatic appearance (Figure7B), varying in lengths from 150 to 400 µm. Most zircon grains were elongated along the (001) axis relative to the prism, with the elongation coefficient Kelong = 1.5–4. The predominant forms were prisms (110), while bipyramids (311) were less common. One grain (Figure7B, spot 7.1) had prisms (111) in addition to the mentioned simple forms (110) and (311). In the CL images (Figure7B), sub-idiomorphic grains demonstrated magmatic zoning and certain signs of a sectorial structure (spots 1.1, 2.1, and 5.1), while idiomorphic crystals and fragments showed magmatic zoning (spots 3.1/3.2, 4.1, 6.1/6.2, 7.1, 8.1, and 9.1). Based on the measurements, the zircons were divided into two age groups. The U content for the first group (spots 3.1/3.2, 4.1, 6.1/6.2, 7.1, 8.1, and 9.1) ranged from 236 to 1860 (634 on average), and the Th content 206 was 51–372 (Th/U = 0.13–0.39; 0.25 on average). The common lead fraction ( Pbc) was less than 0.61% and had not significantly corrected the calculations of the U/Pb systems. The Concordia age was 151.5 1.5 Ma (MSWD = 0.52, probability 0.47), corresponding to the time of rock crystallization ± (Figure7B). The second group (spots 1.1, 2.1, and 5.1) was represented by xenocrysts with the following U contents: 246 ppm, 228 ppm, and 597 ppm; and Th contents 105 ppm, 85 ppm, and 112 ppm, respectively. The value of the Th/U ratio ranged between 0.19 and 0.44. These grains yielded discordant ages (207Pb/206Pb) of 1865 21 Ma, 1829 16 Ma, and 1751 10 Ma. ± ± ± Minerals 2020, 10, 1000 18 of 27 Minerals 2020, 10, x FOR PEER REVIEW 18 of 26

Figure 7. Concordia diagrams and cathodoluminescence (CL) images of zircons from dacite sample Figure 7. Concordia diagrams and cathodoluminescence (CL) images of zircons from dacite sample VK-127 (A); granodiorite sample Sh-26 (B); and trachyandesite sample Sh-40 (C) from the Vyun and VK-127 (A); granodiorite sample Sh-26 (B); and trachyandesite sample Sh-40 (C) from the Vyun and Shumniy sites. Numbered circles on the grains denote analytical spots and correspond to the numbers Shumniy sites. Numbered circles on the grains denote analytical spots and correspond to the numbers in Table 5. in Table5.

Minerals 2020, 10, 1000 19 of 27

Table 5. Results of U–Th–Pb isotope investigations of zircons (SHRIMP-II SIMS) from dikes at the Vyun and Shumniy sites.

Content, ppm Isotope Ratios Age, Ma Spot Error (1) (1) (1) (1) %D 232Th/ % (1) (2) (1) (1) Number 206Pb* U Th 238U/206Pb* 207Pb*/206Pb* 207Pb*/235U 206Pb*/238U Correlation 238U 206Pb * 206Pb/238U 206Pb/238U 207Pb/235U 207Pb/206Pb c ( %) ( %) ( %) ( %) ± ± ± ± Dacite, Sample VK-127 1.1 8.18 413 213 0.53 0.22 43.4 1.4 0.0502 3.9 0.1592 4.1 0.02302 1.4 0.3 146.7 2 146.5 2 150.0 5.7 2 ± ± ± ± ± ± ± 1.2 6.86 347 163 0.49 0.27 43.6 1.4 0.0466 4.6 0.1473 4.8 0.02294 1.4 0.3 146.2 2.1 146.6 2.1 139.5 6.3 5 ± ± ± ± ± ± ± − 2.1 20.7 1058 714 0.70 0.19 44 1.2 0.0492 2.5 0.1543 2.8 0.02273 1.2 0.4 144.9 1.7 144.8 1.8 145.7 3.8 1 ± ± ± ± ± ± ± 2.2 21.4 1064 737 0.72 0.19 42.8 1.3 0.0478 2.7 0.1539 3 0.02336 1.3 0.4 148.9 1.8 149.1 1.9 145.4 4.0 2 ± ± ± ± ± ± ± − 3.1 22.3 1105 711 0.66 0.34 42.8 1.2 0.0472 3.1 0.1521 3.4 0.02337 1.2 0.4 148.9 1.8 149.2 1.8 143.8 4.5 3 ± ± ± ± ± ± ± − 3.2 20.2 1012 636 0.65 0.28 43.1 1.2 0.0486 3.1 0.1553 3.4 0.02318 1.2 0.4 147.8 1.8 147.8 1.8 146.6 4.6 1 ± ± ± ± ± ± ± − 4.1 51.7 2492 415 0.17 0.27 41.6 1.2 0.0473 2.2 0.1569 2.5 0.02406 1.2 0.5 153.3 1.8 153.6 1.8 148.0 3.4 3 ± ± ± ± ± ± ± − 5.1 63.9 2983 483 0.17 0.22 40.2 1.2 0.0469 1.7 0.1609 2.1 0.02486 1.2 0.6 158.3 1.8 158.8 1.8 151.5 2.9 4 ± ± ± ± ± ± ± − 6.1 7.99 404 105 0.27 0.28 43.6 1.4 0.0474 4.6 0.1501 4.8 0.02295 1.4 0.3 146.3 2 146.6 2.1 142.0 6.4 3 ± ± ± ± ± ± ± − 7.1 6.91 342 100 0.30 0.27 42.6 1.5 0.0488 4.5 0.1578 4.7 0.02347 1.5 0.3 149.6 2.2 149.6 2.2 148.8 6.5 0 ± ± ± ± ± ± ± 8.1 7.31 376 186 0.51 0.21 44.3 1.6 0.0469 4.2 0.1459 4.5 0.02257 1.6 0.4 143.8 2.2 144.2 2.3 138.3 5.8 4 ± ± ± ± ± ± ± − Granodiorite, Sample Sh-26 1.1 61.5 246 105 0.44 0.61 3.464 1.2 0.1141 1.1 4.541 1.7 0.2887 1.2 0.7 1635 18 1610 19 1738.4 14.1 1865 21 14 ± ± ± ± ± ± ± ± 2.1 61.6 228 85 0.38 0.12 3.1185 1.2 0.1118 0.9 4.839 1.5 0.3139 1.2 0.8 1760 19 1752 21 1791.7 12.7 1829 16 4 ± ± ± ± ± ± ± ± 3.1 6.54 319 51 0.16 0.00 41.86 1.6 0.049 3.5 0.1613 3.9 0.02389 1.6 0.4 152.2 2.4 152.2 2.4 151.8 5.4 0 ± ± ± ± ± ± ± 3.2 7.99 382 116 0.31 0.22 41.16 1.4 0.0486 3.9 0.1628 4.2 0.02429 1.4 0.3 154.7 2.2 154.8 2.2 153.2 5.9 1 ± ± ± ± ± ± ± − 4.1 4.84 236 75 0.33 0.00 41.98 1.6 0.0505 4.2 0.1659 4.5 0.02382 1.6 0.4 151.8 2.4 151.5 2.5 155.8 6.5 3 ± ± ± ± ± ± ± 5.1 138 597 112 0.19 0.01 3.722 1.2 0.10713 0.54 3.968 1.3 0.2687 1.2 0.9 1534 16 1514 17 1627.7 10.4 1751.2 10 14 ± ± ± ± ± ± ± ± 6.1 17.6 850 317 0.39 0.11 41.41 1.3 0.048 2.5 0.1599 2.8 0.02415 1.3 0.4 153.8 1.9 154 1.9 150.6 4.0 2 ± ± ± ± ± ± ± − 6.2 7.82 380 95 0.26 0.00 41.8 1.4 0.0476 3.4 0.1569 3.6 0.02392 1.4 0.4 152.4 2.2 152.7 2.2 148.0 5.0 3 ± ± ± ± ± ± ± − 7.1 15 747 95 0.13 0.30 42.79 1.3 0.048 3.4 0.1546 3.7 0.02337 1.3 0.3 148.9 1.9 149.1 1.9 146.0 5.0 2 ± ± ± ± ± ± ± − 8.1 6.15 300 70 0.24 0.41 42.01 1.5 0.0485 6.1 0.159 6.3 0.02381 1.5 0.2 151.7 2.3 151.8 2.3 150.0 8.8 1 ± ± ± ± ± ± ± − 9.1 37.4 1860 372 0.21 0.10 42.8 1.2 0.04922 1.8 0.1556 2.1 0.02336 1.2 0.6 148.9 1.7 148.8 1.7 149.4 2.9 0 ± ± ± ± ± ± ± Trachyandesite, Sample Sh-40 1.1 14.5 736 355 0.50 1.68 44.27 1.5 0.0512 6.1 0.159 6.3 0.02259 1.5 0.2 144 2.2 143.6 2.1 150.2 8.8 4 ± ± ± ± ± ± ± 2.1 12.7 662 163 0.25 0.35 45 1.5 0.0487 3.5 0.1491 3.8 0.02222 1.5 0.4 141.7 2.1 141.7 2.1 141.1 5.0 0 ± ± ± ± ± ± ± 3.1 30.3 1584 522 0.34 0.05 44.98 1.4 0.04838 1.6 0.1483 2.1 0.02223 1.4 0.7 141.8 2 141.8 2 140.4 2.8 1 ± ± ± ± ± ± ± − 4.1 17.1 890 490 0.57 0.09 44.87 1.5 0.0488 2.2 0.1498 2.7 0.02229 1.5 0.6 142.1 2.1 142.1 2.1 141.8 3.6 0 ± ± ± ± ± ± ± 5.1 8.75 432 252 0.60 0.00 42.35 1.6 0.0486 2.7 0.1581 3.2 0.02361 1.6 0.5 150.4 2.3 150.5 2.3 149.1 4.4 1 ± ± ± ± ± ± ± − 6.1 2.13 65 124 1.98 0.90 26.32 2.2 0.0563 9.7 0.295 10 0.038 2.2 0.2 240.4 5.2 238.8 5.1 262.3 23.1 9 ± ± ± ± ± ± ± 7.1 7.19 358 107 0.31 0.24 42.88 1.7 0.0522 3.7 0.1678 4 0.02332 1.7 0.4 148.6 2.5 148 2.5 157.5 5.9 6 ± ± ± ± ± ± ± Minerals 2020, 10, 1000 20 of 27

Table 5. Cont.

The zircons from the trachyandesite sample Sh-40 (n = 10) were colorless or light-yellow, clear, idiomorphic, and sub-idiomorphic (Figure7C) 30 to 120 µm long (elongation coefficient Kelong = 1–4). In the CL images, the zircons had a weak or moderate brightness with magmatic oscillatory zoning. The individual crystals (6.1) had mostly sectorial zoning. Measurements allowed defining a cluster (spots 1.1, 2.1, 3.1, 4.1, 5.1, 7.1, 8.1, 9.1, and 10.1/10.2), in which the U contents varied from 329 to 1584 ppm (647 ppm average), Th contents from 105 to 522 ppm, the Th/U ratio was in the range 0.25–0.6 206 (Table5). The common lead fraction ( Pbc) was between 0.05% and 1.68%. Excluding spots 6.1 and 11.1 the zircons yielded a Concordia age of 145.5 1.4 Ma (MSWD = 0.038, probability 0.85), which we ± accepted as the crystallization age for the andesite. One grain (spot 6.1) was clear and prismatic with smoothed out faces. This zircon had low U content (65 ppm), Th = 124 ppm, and a high Th/U ratio of 1.98%. The date obtained for this grain was 240.4 5.2 Ma. Another grain (spot 11.1) was elongated ± (150 µm) and mainly faced by prism (100). Like the second group zircons from the granite–porphyry sample, this grain was a xenocryst with U and Th contents 265 ppm and 29 ppm, and a Th/U ratio of 1.13. The 207Pb/206Pb age obtained for this zircon w 1875 18 Ma. ± 5. Discussion and Conclusions The results of our studies of the dikes of the Vyun deposit and the Shumniy occurrence of the Yana–Kolyma gold belt localized in Mesozoic (T3–J2) terrigenous deposits of the continental margin blocks of the western Verkhoyansk–Kolyma folded area have shown the wide petrographic diversity of the rocks composing them. The compositions include trachybasalts, trachyandesites, dacites, and granodiorites. The dikes on all studied sites and occurrences are dipping at mainly steep angles and associating with various faults. Both the intensely altered mafic and the weakly altered intermediate and felsic rocks of the dikes have close trace elements contents, which are also close to those of Late Jurassic mafic and felsic dikes and small intrusions in the vicinity of the Malo–Tarynskoye and Tin–Yuryuete gold deposits. These trace element concentrations correspond to rocks between the E-MORB and OIB with middle ocean ridge basalt (MORB)-like HREE content (Figure6). The rocks, including varieties with Kfs phenocrysts, are enriched in LILEs, such as Rb, Ba, K, and in HFSEs such as Th and U. The widest range in concentration among these incompatible elements was observed for K, which is slightly higher for the weakly altered intermediate and felsic rocks (K2O = 0.55–4.04 wt.%), unlike in the strongly altered mafic rocks (K2O = 1.18–4.06 wt.%). This is evidence in favor of a minor mobility of these components during the low temperature rock alteration processes. The rocks were depleted in HFSEs such has Nb, Ta, P, and Ti. The small range of contents of the latter two components in the rocks (P2O5 = 0.09–0.19 wt.%; TiO2 = 0.19–1.06 wt.%) also probably indicates their low mobility. These features also are agreeable with the input of a crustal component in their magmatic source and with fractional crystallization during the evolution of the melts. The mafic varieties were plotted in the fields of calk–alkaline and shoshonitic volcanic arc basalts on the Th/Yb versus Nb/Yb [66] and the Th/Yb versus Ta/Yb [67] tectonic discrimination diagrams (Figure8). The igneous rocks of the dikes could have formed from a mantle peridotite–pyroxenite source with a 5% input of mantle wedge melting according to the model in [63] (Figure6) and assimilation of a lower crustal component in a back-arc setting according to [68]. Minerals 2020, 10, x FOR PEER REVIEW 21 of 26 with the southwestward tectonic transport in the Late Jurassic due to the developing northeastern convergent margin of the Siberian craton. Since the dikes are welding the early fold and thrust structures [69], we can assume this deformation manifested in the latest Late Jurassic (Tithonian) at the youngest. This was preceded by greenschist facies regional metamorphism on the regressive phase in the sedimentary rocks of the Siberian passive continental margin terranes [4]. The observed alignment of deposits and areas of dike magmatism, their association with large regional faults as Mineralswell as2020 the, close10, 1000 ages of dikes and mineralization for some deposits indicate possible common22 deep of 27 sources of mineralization fluids and the Late Jurassic dike magmatism.

Figure 8. Tectonic setting discrimination diagrams for the mafic igneous rocks: (A) Th/Yb versus Figure 8. Tectonic setting discrimination diagrams for the maﬁc igneous rocks: (A) Th/Yb versus Nb/Yb from [66]; (B) Th/Yb versus Ta/Yb from [67]. All data points on this diagram are from this Nb/Yb from [66]; (B) Th/Yb versus Ta/Yb from [67]. All data points on this diagram are from thisstudy. study. Abbreviations Abbreviations are types are types of mafic of maﬁc volcanic volcanic rocks: rocks: MORBs—middle MORBs—middle ocean ocean ridge ridge basalts; basalts; N- N-MORBs—normalMORBs—normal middle middle ocean ocean ridge ridge basalts; basalts; E- E-MORBs—enrichedMORBs—enriched middle middle ocean ocean ridge ridge basalts; OIBs—ocean islands basalts;basalts; WPBs—within plates basalts;basalts; ALK—alkalic;ALK—alkalic; TH—oceanic tholeiitic; VABs—volcanicVABs—volcanic arcarc basalts; basalts; IAT—island IAT—island arc tholeiitic; arc tholeiitic; CABs—calk-alkaline CABs—calk-alkaline basalts; SHO—shoshonitic; basalts; SHO— TRs—transitionsshoshonitic; TRs—transitions between ALK between and TH. ALK and TH.

The paleogeodynamic setting for the formation of the Late Jurassic dikes of the Yana–Kolyma gold belt is shown on Figure9. The Middle–Late Jurassic stage was characterized by the Kolyma–Omolon superterrane and the Verkhoyansk passive margin of the Siberian craton drifting closer to each other. This process was accompanying the subduction of the lithosphere of the small Oimyakon oceanic basin under the Siberian craton and the formation of the Uyandina–Yasachnaya ensialic arc in the Bajocian–Kimmeridgian as was shown previously from paleontological data [15,16,50]. The drift of the Kolyma–Omolon superterrane towards Siberia caused the fragmentation and accretion of the Omulevka terrane, the Uyandina–Yasachnaya island arc, and ophiolites to the margin of the craton. This imbrication of oceanic and continental crust led to the generation of granite melts at the lower–upper crust boundary, and to the formation of the Main belt granitoids in the interval 154–144 Ma (U–Pb data for zircon [19]). This is in good agreement with tectonic models for the studied middle fragment of the Verkhoyansk–Kolyma folded area according to [40,45]. The ongoing subduction led to melting in the asthenospheric wedge and in the lithosphere, which formed a mixed source for the dike systems from both an enriched and a depleted mantle source. The formation of the mafic, intermediate, and felsic rocks of the dikes of the Nera–Bokhapcha complex took place prior to and synchronously with the collision: from the Oxfordian, at least 162 Ma, according to Rb–Sr geochronology [14] and up to the latest Tithonian, which is confirmed by our new U–Pb SHRIMP-II data for zircons from felsic rocks, 151–145 Ma. Available Ar–Ar dates (for amphibole) [45] and U–Pb SHRIMP-II zircon dates [44] for the intermediate and felsic dikes of the Tas–Kystabyt belt are also in the range of 162–145 Ma; however, assigning the igneous rocks of this belt to the same complex as the Nera–Bokhapcha rocks needs to be further verified. The volcanic belt was segmented by NE-striking faults of strike-slip and normal fault kinematics that are traced in the southwest in the structures of the Kular–Nera terrane and disappear in the inner zone of the Verkhoyansk margin of Siberia. The NE-striking faults localized the dike suites of the Nera-Bokhapcha complex and the small plutons of the transverse magmatic belts (Nitkan, Burgala, Burkat, etc.). The emplacement of the dikes in NE-striking faults (transverse ramps) is in agreement with the southwestward tectonic transport in the Late Jurassic due to the developing northeastern convergent margin of the Siberian craton. Since the dikes are welding the early fold and thrust structures [69], we can assume this deformation manifested in the latest Late Jurassic (Tithonian) at the Minerals 2020, 10, 1000 23 of 27 youngest. This was preceded by greenschist facies regional metamorphism on the regressive phase in the sedimentary rocks of the Siberian passive continental margin terranes [4]. The observed alignment of deposits and areas of dike magmatism, their association with large regional faults as well as the close ages of dikes and mineralization for some deposits indicate possible common deep sources of mineralization fluids and the Late Jurassic dike magmatism. Minerals 2020, 10, x FOR PEER REVIEW 22 of 26

Figure 9. ModelModel section section through through the the northeastern northeastern margin margin of of Siberia Siberia for for the the latest latest Jurassic Jurassic (Tithonian). (Tithonian). A—Adycha–Taryn thrust;thrust; C—Chakry–IndigirkaC—Chakry–Indigirka thrust;thrust; P—Polousniy–KolymaP—Polousniy–Kolyma suture.suture.

Author Contributions: Conceptualization, methodology, writing—original draft preparation, validation, Authorfunding Contributions:acquisition, V.Y.F.,Conceptualization, K.Y.Y., A.E.V., V.A.V.; methodology, investigation, writing—original writing—review draft and preparation, editing, V.Y.F., validation, K.Y.Y., A.E.V.,funding V.A.V., acquisition, N.Y.M., V.Y.F., P.I.K., K.Y.Y., N.V.R.; A.E.V., visualization, V.A.V.; investigation,K.Y.Y., N.Y.M., writing—review P.I.K., N.V.R.; Formal and editing, analysis, V.Y.F., N.V.R. K.Y.Y., All A.E.V., V.A.V., N.Y.M., P.I.K., N.V.R.; visualization, K.Y.Y., N.Y.M., P.I.K., N.V.R.; Formal analysis, N.V.R. All authors authors have read and agreed to the published version of the manuscript. have read and agreed to the published version of the manuscript. Funding: This research was supported by the Diamond and Precious Metals Ge Geologyology Institute, Siberian Branch of the Russian Academy of Sciences and was partially funded by the Russian Foundation for Basic Research (grant no. 18-45-140040 18-45-140040 r_a, 18-05-00854, 18-05-70035, and 20-05-00360). This This research research was was financially financially supported by the Russian Science Foundation (grant no. 19-17-00091). Acknowledgments: Larisa T. Galechnikova (Section on Physical–Chemical Analytical Methods of DPMGI SB Acknowledgments: Larisa T. Galechnikova (Section on Physical–Chemical Analytical Methods of DPMGI SB RAS) is thanked for helping with petrochemical studies. RAS) is thanked for helping with petrochemical studies. Conflicts of Interest: The authors declare no conflict of interest. The funders had no role in the design of the Conflictsstudy; in theof Interest: collection, The analyses, authors or declare interpretation no conflicts of data; of interest. in the writing The funders of the manuscript,had no role orin inthe the design decision of the to publishstudy; in the the results. collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results

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