Pyrochlore-Group Minerals in the Granite-Hosted Katugin Rare-Metal Deposit, Transbaikalia, Russia
by
, ,
Anastasia E. Starikova
1,2,*
,
Ekaterina P. Bazarova
3,
Valentina B. Savel’eva
3,
Eugene V. Sklyarov
3,4,
Elena A. Khromova
5 and
Sergei V. Kanakin
5 1
V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, 3 Akad. Koptyug av., 630090 Novosibirsk, Russia
2
Department of Geology and Geophysics, Novosibirsk State University, 2 Pirogov st., 630090 Novosibirsk, Russia
3
Institute of the Earth’s Crust, Siberian Branch of the Russian Academy of Sciences, 128 Lermontova st., 664033 Irkutsk, Russia
4
School of Engineering, Far East Federal University, 8 Sukhanov st., 690091 Vladivostok, Russia
5
Geological Institute, Siberian Branch of the Russian Academy of Sciences, 6a, Sakhjanova st., 670047 Ulan-Ude, Russia
*
Author to whom correspondence should be addressed.
Minerals 2019, 9(8), 490; https://doi.org/10.3390/min9080490
Submission received: 8 May 2019
/
Revised: 4 August 2019
/
Accepted: 13 August 2019
/
Published: 15 August 2019
(This article belongs to the Special Issue Accessory Minerals in Silicic Igneous Rocks)
Abstract
:Pyrochlore group minerals are the main raw phases in granitic rocks of the Katugin complex-ore deposit that stores Nb, Ta, Y, REE, U, Th, Zr, and cryolite. There are three main types: Primary magmatic, early postmagmatic (secondary-I), and late hydrothermal (secondary-II) pyrochlores. The primary magmatic phase is fluornatropyrochlore, which has high concentrations of Na2O (to 10.5 wt.%), F (to 5.4 wt.%), and REE2O3 (to 17.3 wt.%) but also low CaO (0.6–4.3 wt.%), UO2 (to 2.6 wt.%), ThO2 (to 1.8 wt.%), and PbO (to 1.4 wt.%). Pyrochlore of this type is very rare in nature and is limited to a few occurrences: Rare-metal deposits of Nechalacho in syenite and nepheline syenite (Canada) and Mariupol in nepheline syenite (Ukraine). It may have crystallized synchronously with or slightly later than melanocratic minerals (aegirine, biotite, and arfvedsonite) at the late magmatic stage when Fe from the melt became bound, which hindered the crystallization of columbite. Secondary-I pyrochlore follows cracks or replaces primary pyrochlore in grain rims and is compositionally similar to the early phase, except for lower Na2O concentrations (2.8 wt.%), relatively low F (4 wt.%), and less complete A- and Y-sites occupancy. Secondary-II pyrochlore is a product of late hydrothermal alteration, which postdated the formation of the Katugin deposit. It differs in large ranges of elements and contains minor K, Ba, Pb, Fe, and significant Si concentrations but also low Na and F. Its composition mostly falls within the field of hydro- and keno-pyrochlore.
1. Introduction
Pyrochlore-group minerals (part of the pyrochlore supergroup of minerals) are broadly occurring in nature and are of important economic interest due to their ability to host Ta, Nb, U, and REE. They are common accessory phases in carbonatite and are often found in such lithologies as nepheline syenite, alkaline gabbro and granitoids, pegmatite, and in albite and greisen granites [1,2,3,4,5,6,7,8]. Pyrochlore minerals have diverse compositions with the general formula A2−mB2O6−wY1−n, where A represents large cations (Na, Ca, U, Th, REE, Y, Sr, Ba, Pb, Sn, and H2O) and site vacancies, the B-site is occupied by smaller cations (Nb, Ti, and Ta), and Y is occupied by F, OH−, O2−, and H2O or site vacancies [9,10,11]. The symbols m, w, and n represent parameters indicating incomplete occupancy of the A, X, and Y.
The Ca/Na ratios vary considerably. Fluorcalciopyrochlore (Ca,Na)2Nb2O6F is the most widespread phase in the group [3,10,12]. Findings of pyrochlore with prominent Na enrichment over Ca and other cations at the A-site are very few and are limited to several rare-metal deposits hosted by the Nechalacho syenite and nepheline syenite (Canada) [13,14], the Mariupol nepheline syenite (Ukraine) [15], the Strange Lake granite (Canada) [16], and the Halzdan-Buregteg alkaline granite (West Mongolia) [17]. Fluornatropyrochlore (Na,Pb,Ca,REE,U)2Nb2O6F was reported as a mineral species from the Boziguoer granites (China) only in 2013 [18].
Pyrochlore is one of main ore phases in the exceptionally rich Ta-Nb-REE-Zr Katugin deposit. In spite of a long history of exploration and research at the Katugin field [19,20], the available knowledge on mineralogy of pyrochlore is insufficient to reveal its types and formation features at different stages of the ore formation process. Previous studies [19] and references therein] were restricted to pyrochlore monofractions identified according to color, habit, and other external characteristics and provided no constraints on mineral chemistry trends. Later publications on the Katugin deposit [20,21,22,23] did not give much attention to pyrochlore. This study bridges the gap by distinguishing several types of pyrochlore and tracing their crystallization sequences. Special focus is made on high-Na pyrochlore, which is of rare natural occurrence and thus remains poorly characterized.
2. Geological Setting
The Katugin deposit, extremely rich in REE, Nb, and Ta, is located in the Aldan shield, at the southern margin of the Chara-Olekma terrane near the border with terranes of the Central Asian Orogenic Belt marked by the Stanovik suture [24]. The ores are hosted by two relatively small (3 and 18 km2) A-type alkaline granite intrusions of the Katugin complex [21,22] (Figure 1a), which were earlier interpreted as alkaline metasomatites [19,25,26,27]. The Western intrusion is 80% buried under a moraine and remains quite poorly documented. The Eastern intrusion (Figure 1b) is composed of three types of granites corresponding to three phases of magmatism [21,22]: Phases I, II, and III, respectively, of biotite (Bt) and biotite-riebeckite (Bt-Rbk); biotite-arfvedsonite (Bt-Arf); and arfvedsonite, aegirine-arfvedsonite and aegirine (Arf, Aeg-Arf, and Aeg) granites. Phase III granites have diverse mineralogy and lack distinct boundaries. They are joined into one phase because the Aeg, Aeg-Arf, and Arf varieties sometimes grade from one to another in a single sample. All types are medium- and fine-grained, often gneissic, leucocratic and mesocratic quartz-albite-microcline granites with variable amounts of melanocratic minerals. At the same time, some arfvedsonite and aegirine granites appear as isolated pegmatitic veins.
Biotite and biotite-riebeckite granites (phase I) have moderate or high Al contents and relatively high CaO, but contain the smallest amount of F among all granites we sampled. Biotite-arfvedsonite granites (phase II) are supersaturated with respect to alkalis, rich in CaO and Y, but poor in Na2O and F. The ore-bearing granites of phase III are likewise supersaturated in alkalis; they have high concentrations of Na2O and F but very low CaO, and are mostly rich in Zr, Hf, Nb, and Ta [21].
The Katugin granites host Zr, Ta-Nb-REE, and F-Al mineralization [19,20]. Zircons are present either as sporadic grains or as large clusters (to 20 vol.%) in all rocks of the intrusion. Fluoraluminate minerals include abundant cryolite (a large body on the intrusion margin and ≤3 cm globules in Aeg granites) and smaller percentages of other phases (weberite, chiolite, prosopite, pachnolite, thomsenolite, and Ba-fluoraluminates). Ta-Nb-REE phases are mainly pyrochlore, columbite-(Fe), fluorides (fluocerite-(Ce), gagarinite-(Y), tveitite-(Y), yttrofluorite) and fluorcarbonates (bastnäsite-(Ce) and parisite-(Ce)) or less often monazite-(Ce). REE fluorides and fluorcarbonates often form aggregates unevenly distributed in the rocks [23,28,29]. Other minerals include ilmenite, magnetite, and sulfides (sphalerite, galena, pyrrhotite or pyrite). Ta-Nb-REE-Zr mineralization formed at 2055 ± 7 Ma, around the time of the Katugin granite emplacement (2066 ± 6 Ma), the difference being within the scope of analytical error [24,30].
3. Materials and Methods
The analytical work was performed at the Analytical Center for Multielement and Isotope Studies of the V.S. Sobolev Institute of Geology and Mineralogy (Novosibirsk, Russia) and at the Analytical Center for Mineralogical, Geochemical, and Isotope Studies of the Geological Institute (Ulan-Ude, Russia). We analyzed pyrochlore monofractions from different types of the Katugin granites: Biotite, biotite-riebeckite, biotite-arfvedsonite, arfvedsonite, aegirine-arfvedsonite, and aegirine granites, as well as aegirine granite enriched in zircon, pyrochlore, and REE phases (the ore-rich aegirine granite). The mineral phases were identified and analyzed using a Carl Zeiss LEO-1430VP scanning electron microscope equipped with an Oxford Instruments INCAEnergy 350 energy-dispersive microanalysis system (EDS method, Analysts E.A. Khromova and S.V. Kanakin, Geological Institute, Ulan-Ude). The electron beam was operated at an accelerating voltage of 20 kV, a beam current of >0.5 nA and a count time of 50 s. Element concentrations in pyrochlores were measured on a Jeol JXA-8100 electron-microprobe analyzer (WDS method) at the Institute of Geology and Mineralogy, Novosibirsk (analyst E.N. Nigmatulina). The operation conditions were: 2 μm beam diameter, 30 nA beam current, 20 kV accelerating voltage, and 10 s count time on peak per element. The results were calibrated using the following standards: albite (Na, Al, Si); diopside (Ca); F-phlogopite (F, K, and Mg); garnet (Fe, Mn); (LiNbO3 (Nb); rutile (Ti); Ta2O5 (Ta); zircon (Zr); UO2 (U); ThO2 (Th); SrSi glass (Sr); PbTe (Pb); BaSi glass (Ba); KLaMoO4 (La); LiCeWO4 (Ce); CsPrMoO4 (Pr); RbNdWO4 (Nd); LiSmMoO4 (Sm); LiGdMoO4 (Gd); LiDyWO4 (Dy); and Y3Al5O12 (Y). Detection limits were (3σ, in wt.%): 0.07 for Na, 0.06 for Al, 0.1 for Si, 0.02 for Ca, 0.09 for F, 0.02 for K, 0.04 for Mg, 0.01 for Fe, 0.02 for Mn, 0.08 for Nb, 0.04 for Ti, 0.16 for Ta, 0.15 for Zr, 0.09 for Th, 0.08 for U, 0.27 for Sr, 0.14 for Pb, 0.06 for Ba, 0.08 for La, 0.14 for Ce, 0.11 for Pr, 0.1 for Nd, 0.06 for Sm, 0.11 for Gd, 0.05 for Dy, and 0.18 for Y. The PAP program was applied for matrix correction. The error rate was less than 2 rel.% for major elements.
4. Results
Pyrochlore-group minerals are main ore phases of the Katugin rare-metal deposit common to different granitic rocks of the complex, except for Bt and Bt-Rbk granites of phase I which bear columbite-(Fe) as a predominant opaque mineral and low percentages of pyrochlore. Pyrochlore is especially abundant in phase III Aeg and Aeg-Arf granites where it occurs as round or rarely octahedral euhedral grains (≤5 mm) or as clusters and lenses, including in ore-rich zones. The pyrochlore grains are honey-yellow to almost black but most often brown (Figure 2). There are three main types of pyrochlore identified according to crystallization sequence and chemistry: Primary pyrochlore found as isolated crystals or aggregates; secondary-I pyrochlore looking darker-shaded in BSE images, which follows cracks, replaces earlier pyrochlore in grain rims, and is occasionally enclosed in zircon from Aeg-Arf granites; and the latest secondary-II in most strongly altered and deformed grain parts (Figure 2). Primary pyrochlore in Bt-Arf granites is rarely replaced by later phases but rather by aggregates of columbite, gagarinite-(Y), and bastnäsite-(Ce) (Figure 2a). Pyrochlore from Aeg, Aeg-Arf, and Arf (phase III) granites often encloses numerous veinlets or microcrystals (10 μm on average) of other minerals (bastnäsite-(Ce), gagarinite-(Y), yttrofluorite, and occasionally rutile) produced by alteration (Figure 2f). Columbite-(Fe) replaces pyrochlore in some grains. Some pyrochlores enclose cryolite, quartz, albite, feldspar, aegirine, zircon, and magnetite.
4.1. Primary Pyrochlore
The (#Nb) pyrochlore-group end-members predominate over those of microlite (#Ta) or betafite (#Ti) groups in all analyses of primary pyrochlore (Figure 3; Table 1, Table 2 and Table 3). The B-site is occupied by 1.54–1.84 apfu of Nb (#Nb—73–90 mol.%), 0.125–0.4 apfu of Ti (#Ti—7.5–23 mol.%), and up to 0.3 apfu of Ta (#Ta—0–15 mol.%). The A-site accommodates large cations of Na, REE + Y, and Ca (Figure 4), as well as U, Th and Pb (the total of the three elements in the A-site being no more than 6%). REE are mainly represented by Ce, while HREE and Y are low. This pyrochlore contains abundant F, which occupies the Y-site (Figure 5).
Primary pyrochlore from Bt-Arf granites differs from those in other granite types and contains as much as 6.4 to 10.7 wt.% Na2O (Figure 5; Table 1), which exceeds previously reported values from different occurrences worldwide (within 9.18 wt.% Na2O) [14]. It is also rich in niobium (up to 62 wt.% Nb2O5) but has low TiO2 of 2.4 to 3.8 wt.% (Figure 3). Some pyrochlore grains in these granites are zoned, possibly according to growth (Figure 2b), with Ta2O5-rich (to 15 wt.%) lighter-color zones. Ta enrichment may result from accumulation in evolving granitic melt [3]. The Bt-Arf granite-hosted pyrochlore shows the most complete cation occupancy of the A-site (1.55–2 apfu), with high REE (16.7 wt.% LREE2O3 and 1.6 wt.% HREE2O3) and 1.3 wt.% Y2O3 but low UO2 (0.3–0.9 wt.%) and PbO (to 0.21 wt.%). The contents of CaO vary from 1.4 to 3.5 wt.%, with the Na/Ca ratio from 3.7 to 13 (7.1 on average). Fluorine reaches 5.34 wt.% or 1.15 apfu. The LREE/HREE and Y/Ce ratios vary from 8 to 37 and 0.04 to 0.34, the averages of 18.2 and 0.16, respectively. The general formula of this pyrochlore can be expressed as (Na1.2Ca0.18LREE0.36HREE0.04Y0.03U0.02Th0.02)1.85(Nb1.8Ti0.15Ta0.05)2O5.94F1.06.
Primary pyrochlores from Bt, Bt-Rbk granites of phase I and Arf, Aeg-Arf and Aeg granites of phase III are compositionally similar (Table 2 and Table 3) and differ from that in the ore-rich Aeg granite. The latter hosts pyrochlore with low CaO (0.63–0.85 wt.%) but relatively high HREE2O3 (2.4 wt.%) and Y2O3 (4 wt.%) (Table 3), which has the highest ratios of Na/Ca (10.2–15.2) and Y/Ce (0.72–0.81) but lowest LREE/HREE (6.5–7.7) compared to the counterparts from other granite types (Figure 5e).
The betafite component (#Ti) with 3.75 to 8 wt.% TiO2 increases progressively from 9.8% in Bt and Bt-Rbk granites to 19.9% in Aeg granite, while pyrochlore component (#Nb) decreases correspondingly (Figure 3); the microlite component (#Ta) varies from 2 to 4.4 wt.% Ta2O5. The A occupancy in pyrochlores from Bt, Bt-Rbk, Arf, Aeg-Arf, and Aeg granites varies from 1 to 1.55 apfu while Na does not exceed 0.95 apfu (8.1 wt.% Na2O) being on average 0.83 apfu (6.5 wt.% Na2O). CaO in some pyrochlores from Bt, Bt-Rbk and Aeg-Arf granites has a large range, including within the same sample (2 to 5.5 wt.%; Na/Ca = 2–7.2), but is quite stable (2.3–2.8 wt.%; Na/Ca = 3.7–5) in pyrochlore from all aegirine granites (Figure 5). The latter pyrochlore also has high REE2O3: 15–16 wt.% (LREE/HREE = 16–21; Y/Ce = 0.08–0.23) against 10–14.5 wt.% REE2O3 (LREE/HREE = 10–19; Y/Ce = 0.1–0.25) in pyrochlores from other granite types. UO2, ThO2 and PbO do not exceed 2.6 wt.%, 1.8 wt.%, and 1.4 wt.%, respectively. F is 3.6 to 5.5 wt.% (4.6 wt.% on average).
4.2. Secondary-I Pyrochlore
Secondary-I pyrochlore differs from the primary variety in low contents of Na2O (1–4.5 wt.%, 2.8 wt.% on average), lower F (2–5 wt.%, 4 wt.% on average), and less complete occupancy of the A- and Y-sites (Table 1, Table 2 and Table 3; Figure 4 and Figure 5). Other cations have concentrations commensurate with those in early pyrochlore.
4.3. Secondary-II Pyrochlore
Secondary-II pyrochlore differs compositionally from the earlier pyrochlores. It has large ranges of both major and trace elements (Table 1, Table 2 and Table 3; Figure 3, Figure 4 and Figure 5) and analytical totals that are notably below 100%. Unlike the earlier counterparts, it contains minor amounts of K2O (up to 2.3 wt.%), BaO (to 3 wt.%), PbO (to 2.5 wt.%), and Fe2O3 (to 0.6 wt.%) and relatively high SiO2 (to 9.2 wt.%) (Figure 5f and Figure 6). The contents of ThO2 (to 2.1 wt.%) and UO2 (to 5.6 wt.%) are higher while REE2O3, CaO, Na2O, Nb2O5, Ta2O5, and F are markedly lower relative to those in primary and secondary-I pyrochlores. Most of secondary-II pyrochlore samples fall in the field of hydro- or kenopyrochlore (Figure 4).
5. Discussion
5.1. Comparison with Fluornatropyrochlore from Other Occurrences
Pyrochlores of three types from the Katugin granites differ notably in their chemistry and show quite large ranges of some element concentrations. Primary pyrochlore, with high Na and F concentrations and low Ca, is of special interest and can be classified as fluornatropyrochlore. The latter has been rarely found in natural occurrence [4,5,6,13,14,15,16,17] and became a registered mineral species as late as in 2013 [18]. In this respect, it is pertinent to compare the Katugin pyrochlore with its counterparts that are known from other places.
Fluornatropyrochlore from the Boziguoer rare-metal granites in China (the first finding of this mineral) differs from the samples we analyzed in higher concentrations of PbO (to 16.17 wt.%) and UO2 (5.8–7.5 wt.%) [18,33] and much lower Na2O (5.5–8.5 wt.%) (Figure 4 and Figure 5) at quite high Na/Ca ratios of 4.1–6.6. The F contents in the Boziguoer pyrochlore range within 4.6–7.1 wt.% or 1.25 to 1.63 apfu [33] exceeding the common value of 1 apfu at least by a factor of ~1.5 requires additional explanation, as overestimation may lead to notable structure distortion.
Fluornatropyrochlores with the highest Na contents were reported from the Nechalacho [13,14] and Mariupol [15] syenites and nepheline syenites but the pyrochlores from both occurrences have Na2O lower than in those from the Katugin Bt-Arf granites (7–9.18 wt.% Na2O against an average of 9.4 wt.%, respectively). On the other hand, they have UO2 (within 1.1 wt.%), ThO2 (≤1.6 wt.%) and PbO (≤0.5 wt.%) as low as in the Katugin pyrochlores.
All other published fluornatropyrochlore compositions with high Na/Ca ratios have predominant components with 0.78 to 0.93 #Nb (Figure 3), but their REE2O3 contents (mainly LREE) are much lower (to 13.4 wt.%) than in the Katugin pyrochlores (Figure 5d). Low Y/Ce ratios (0.04–0.32) in all Katugin pyrochlores we analyzed, except for those from ore-bearing Aeg granite (Y/Ce to 0.8), are similar to the ratios reported for their counterparts from other occurrences.
5.2. Isomorphism in the Katugin Pyrochlores
Judging by their chemistry, pyrochlore-group minerals are prone to extensive homo- and heterovalent isomorphic substitutions at all sites, which follow hardly decipherable scenarios. Incorporation of REE3+, U4+ and Th4+ in primary pyrochlore may balance the excess of Na with respect to the ideal neutral formula NaCaNb2O6F, at complete X occupancy. Therefore, the substitution in A-site is expected to proceed as 2Ca2+ → Na+ + REE3+; 3Ca2+ → 2Na+ + U4+(Th4+). However, Na in primary pyrochlore correlates neither with Ca nor with REE + Y (Figure 5a,d), but the latter shows distinct inverse correlation with Ca (Figure 5c). The substitution apparently followed the scenario 3ACa2+ → 2AREE3+ for the pyrochlores hosted by Bt-Arf granites and for some of those from Aeg-Arf granites, but 1 REE substituted for 1 Ca in the Bt-Rbk and Aeg granites. In the absence of other correlations with Ca, it remains unclear how the arising positive charge could be balanced. Most likely, several substitutions worked jointly.
Na correlates inversely with the A-site vacancy (r = −0.85 to −0.99) (Figure 5h), and its poor correlation with F (Figure 5g) is inconsistent with the ANa+ + YF− → A+Y substitution, where A and Y are the respective site vacancies. The high inverse Na-A correlation may result from incorporation of the (OH)-group in the X-site or H3O+ in the A-site by the ANa+ + XO2− → A + X(OH)− and Na+ → H3O+ or by some more intricate substitution. The contents of XOH−/AH3O+ in a charge-balanced formula should be 0.24 apfu on average for primary pyrochlore from Bt-Arf granite and as high as 0.78 apfu for primary pyrochlores from other granite types, as estimated proceeding from the total cation charge provided that all Y occupancy is by F−.
Secondary-I pyrochlore which differs from the early phase only in lower Na and F contents formed by alteration of primary fluornatropyrochlore mainly by the ANa+ + YF− → A + Y; ANa+ + XO2− → A + X(OH)− and ANa+ → AH3O+ substitutions. The ratio XOH−/AH3O+ in this pyrochlore is 1.09 apfu on average.
Secondary-II pyrochlore shows maximum Na, Ca and F leaching at incomplete A occupancy, with the Na+ + F− → A + Y or, possibly, also Ca2+ + 2F− → A + 2Y substitutions. The total cation charge is 0.7–2.1 less than that at complete X occupancy by oxygen. In addition to the ANa+ + XO2− → A + X(OH)− and Na+ → H3O+ substitutions inferred for two other types of pyrochlore, the substitution in the latest pyrochlore may be ACa2+ + XO2− → A + X (A and X are the respective vacancies).
Si in Secondary-II Pyrochlore
Silicon is a common component in pyrochlore-group minerals. Minor amounts of Si may incorporate in the B-site, as mentioned in a recent nomenclature paper [10]. However, there were reports of “silicified” pyrochlore with up to 9.31 wt.%, 11.51 wt.%, 13 wt.% and 15 wt.% SiO2 [15,34,35,36]. The Si mode of occurrence in the pyrochlore structure remains a subject of discussions, and several solutions have been suggested. The radius of Si4+ is much smaller than that of B-site cations and large amounts of Si4+ cannot incorporate without significantly distorting the mineral structure. The existence of “silicified” pyrochlore was attributed to the presence of Si-bearing mineral microinclusions [37], amorphous or dispersed Si [38], or submicronic intergrowths with komarovite (H,Ca,Na)2(Nb,Ti)2Si2O10(OH,F)2 [35]. On the other hand, M. Dumanska-Slowik et al. [15] showed metamictization to be the key factor that allows incorporation of Si as it causes damage to A- and B-sites. They [15] failed to detect Si at the B-site though, but Bonazzi et al. [34] confirmed the presence of Si and estimated that 30–50% of Si in “silicified” pyrochlore was incorporated in the B-site, where it replaced Nb and Ta, and partly in the structure portion damaged by radiation.
The Katugin secondary-II pyrochlore contains up to 9.24 wt.% SiO2 and apparently lacks Si-bearing mineral inclusions (all analyses were made for homogeneous grain portions). Furthermore, SiO2 shows significant inverse correlation with TiO2 (r = −0.85) and a weaker correlation with Nb2O5 (r = −0.65), which indicates that Si occupies the B-site (Figure 6). This pyrochlore contains more U, Th and Pb than both earlier phases and appears to be strongly metamictized. Thus, some amount of Si in the Katugin “silicified” pyrochlore may occupy the B-site and some Si may be incorporated in the α-damaged part, in the same way as suggested in reference [34].
5.3. Genesis of Different Pyrochlore Types in the Katugin Rare-Metal Deposit
It was previously found out that REE phases in the Katugin alkaline granites crystallized after main rock-forming minerals (feldspar and quartz) from residual melt rich in Fe, Na, Zr, Nb, Ta, Zn, Sn and volatiles (F, CO2, P, S, and H2O) [28]. Primary pyrochlore is the earliest REE phase. Crystallization of pyrochlore was synchronous with or slightly postdating the formation of melanocratic phases (aegirine, biotite, and arfvedsonite). Fe extracted from the melt became bound in the melanocratic minerals, which hindered the crystallization of columbite [2]. The unusual chemistry of primary pyrochlore with very high Na/Ca may be controlled by the composition of the host Katugin granites supersaturated with alkalis and F, rich in REE + Y, and depleted in Ca [21]. However, the chemical peculiarity of pyrochlore must be due more to high concentrations of REE than to high Na/Ca ratios, given that Na-richest pyrochlores occur in Bt-Arf granites containing more Ca than the Aeg, Aeg-Arf, and Arf granites. Rare earths are incorporated into the structure of pyrochlore (the earliest REE phase), while Na replaces Ca for charge balance.
Secondary-I pyrochlore likely formed at the early postmagmatic stage in the evolution of the Katugin complex, judging by its presence, along with primary pyrochlore, as inclusions in zircon which was previously interpreted as magmatic or early postmagmatic [24,39].
The presence of pyrochlores with almost leached Ca, Na, and F, as well as partial incorporation of K, Ba, and Sr, were attributed to weathering [1,40,41]. However, these pyrochlores show neither significant Si enrichment nor Nb depletion. The origin of “silicified” pyrochlore was explained in the context of high-temperature hydrothermal activity [15] and metasomatism [35]. The Katugin rocks are not much weathered, though they include widespread products of hydrothermal alteration of cryolite (weberite, pachnolite, etc.) and Ba-aluminosilicates [42]. Secondary-II pyrochlore was possibly formed by hydrothermal alteration at the late postmagmatic stage, judging by relatively high Ba contents. Yet, there is no evidence that it happened during the formation of the ore deposit.
6. Conclusions
Pyrochlore group minerals are the main raw phases in granitic rocks of the Katugin rare-metal deposit. They are of three main types: primary magmatic pyrochlore occurring as round or less often octahedral grains, early postmagmatic (secondary-I) pyrochlore following cracks or replacing primary pyrochlore in grain rims, and late hydrothermal (secondary-II) pyrochlore that replaces the two earlier types.
The primary magmatic phase is fluornatropyrochlore very rare in nature, with a Na/Ca ratio of 3.7 to 15.2. Some primary pyrochlores we discovered have exceptionally high Na2O contents (up to 10.7 wt.%), higher than those from any previously reported occurrences. The Katugin pyrochlores have greater REE2O3 enrichment (up to 17.3 wt.%) than high-Na pyrochlores from other known occurrences but similar low Y/Ce ratios (0.04–0.34). The total of other cations at the A-site (U, Th and Pb) does not exceed 6%. The Katugin fluornatropyrochlore is compositionally close to those from Nechalacho, Canada, and Mariupol (Ukraine) syenite and nepheline syenite. Primary pyrochlore owes its unusual chemistry more likely to high REE3+ activity during crystallization than to high alkalinity of the host granite. In this case, the arising positive charge became balanced by the 2ACa2+ → ANa+ + AREE3+ substitution. The substitutions in primary pyrochlore most often followed the ANa+ + XO2−→A + X(OH)−, ANa+ → AH3O+, and 3ACa2+ → 2AREE3+ scenarios.
Secondary-I pyrochlore may have replaced the primary phase during the cooling of the intrusion, at the postmagmatic stage. Compared to the primary pyrochlore, it has lower concentrations of Na2O (1 to 4.5 wt.%, 2.8 wt.% on average) and F (2 to 5 wt.%, 4 wt.% on average) and less complete occupancy of the A and Y sites, while the contents of other components are similar. Thus, secondary-I pyrochlore replaced that of primary by the ANa+ + YF- → A + Y; ANa+ + XO2−→A + X(OH)− or ANa+ → AH3O+ substitutions.
Secondary-II pyrochlore appears to be a product of late hydrothermal alteration of early fluoraluminate phases (mainly cryolite) and postdated the formation of two other pyrochlore types. It shows large ranges of major oxides (REE2O3, CaO, Na2O, Nb2O5, Ta2O5), contains minor amounts of K2O, BaO, PbO, and Fe2O3, and has totals notably below 100%. This pyrochlore type is remarkable because it has a relatively high enrichment in Si (up to 9.2 wt.% SiO2) which is partly incorporated in the B-site and partly in the α-damaged portion of the structure. The composition of secondary-II pyrochlore mostly falls within the field of hydro- and kenopyrochlore and results from the Na+ + F− → A + Y, Ca+ + 2F− → A + 2Y, ANa+ + XO2− → A + X(OH)−, Na+ → H3O+, and ACa2+ + XO2− → A + X substitutions (A, Y and X are vacancies at the respective sites).
Author Contributions
Conceptualization, A.E.S. and E.P.B.; formal analysis, A.E.S., E.A.K. and S.V.K.; investigation, A.E.S., E.P.B.; resources, A.E.S., E.P.B. and E.V.S.; writing—original draft preparation, A.E.S. and E.P.B; writing—review and editing, A.E.S., E.V.S. and V.B.S; visualization, A.E.S.
Funding
This research was funded by the Russian Foundation for Basic Research (Project 16-35-60054 mol_a_dk). Scanning Electron Microscopy was funded by the Russian Science Foundation (Project 14-17-00325). WDS was carried out as part of government assignment to the V.S. Sobolev Institute of Geology and Mineralogy.
Acknowledgments
We thank T. Perepelova and V.V. Sharygin for assistance in manuscript preparation. Thoughtful comments by four anonymous reviewers on this manuscript are gratefully acknowledged.
Conflicts of Interest
Authors declare no conflict of interest.
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Figure 1.
(a): Simplified geological map of the region of the Katugin granite complex, after [22,31]. 1 = Quaternary sediments; 2 = flood basalts (N2-Q); 3 = Jurassic coal-bearing clastic sediments; 4 = granite, granodiorite, granosyenite and monzonite of the Ingamakit complex (PZ3); 5 = nepheline syenite, granosyenite and monzonite of the Khanin complex (PZ3); 6 = Ordovician variegated sediments; 7 = Cambrian variegated sediments; 8 = Vendian variegated sediments; 9 = gabbro-dolerite, gabbro and dolerite porphyrite of the Doros complex; 10 = layered plutons of the Chinei complex; 11 = granite of the Kodar complex; 12 = rare-metal granite of the Katugin complex; 13–15 = carbonate and clastic sediments of the Udokan supergroup: Kemen group (13), Chinei group (14), and Kodar group (15); 16 = anorthosite of the Kalar complex; 17 = low-grade metamorphic volcanic-sedimentary rocks of the Subgan complex; 18 = tonalite-trondjemite orthogneis of the Olekma complex; 19 = Chara sequence (garnet-biotite and garnet-hypersthene-biotite plagiogneiss, mafic schists, quartzite and magnetite quartzite); 20 = Kalar sequence (garnet-biotite plagiogneiss with layers and lenses of two-pyroxene mafic granulite, clac-silicate rocks, quartzite, and magnetite quartzite; 21 = metamorphic and igneous complexes of the Selenga-Stanovik superterrane in the Central Asian orogenic belt; 22 = zones of widespread Precambrian granitic rocks; 23 = faults. (b): Simplified geology of the Katugin granite intrusion, after [21,32]. 1 = gneiss, migmatite, blastomylonite of the Kodar group, Udokan group; 2–6 = Katugin granites of different types: biotite (2), biotite-riebeckite (3), biotite-arfvedsonite (4), arfvedsonite (5), aegirine-arfvedsonite and aegirine (6); 7 = ore-bearing granite; 8 = faults; 9 = bedding elements.
Figure 1.
(a): Simplified geological map of the region of the Katugin granite complex, after [22,31]. 1 = Quaternary sediments; 2 = flood basalts (N2-Q); 3 = Jurassic coal-bearing clastic sediments; 4 = granite, granodiorite, granosyenite and monzonite of the Ingamakit complex (PZ3); 5 = nepheline syenite, granosyenite and monzonite of the Khanin complex (PZ3); 6 = Ordovician variegated sediments; 7 = Cambrian variegated sediments; 8 = Vendian variegated sediments; 9 = gabbro-dolerite, gabbro and dolerite porphyrite of the Doros complex; 10 = layered plutons of the Chinei complex; 11 = granite of the Kodar complex; 12 = rare-metal granite of the Katugin complex; 13–15 = carbonate and clastic sediments of the Udokan supergroup: Kemen group (13), Chinei group (14), and Kodar group (15); 16 = anorthosite of the Kalar complex; 17 = low-grade metamorphic volcanic-sedimentary rocks of the Subgan complex; 18 = tonalite-trondjemite orthogneis of the Olekma complex; 19 = Chara sequence (garnet-biotite and garnet-hypersthene-biotite plagiogneiss, mafic schists, quartzite and magnetite quartzite); 20 = Kalar sequence (garnet-biotite plagiogneiss with layers and lenses of two-pyroxene mafic granulite, clac-silicate rocks, quartzite, and magnetite quartzite; 21 = metamorphic and igneous complexes of the Selenga-Stanovik superterrane in the Central Asian orogenic belt; 22 = zones of widespread Precambrian granitic rocks; 23 = faults. (b): Simplified geology of the Katugin granite intrusion, after [21,32]. 1 = gneiss, migmatite, blastomylonite of the Kodar group, Udokan group; 2–6 = Katugin granites of different types: biotite (2), biotite-riebeckite (3), biotite-arfvedsonite (4), arfvedsonite (5), aegirine-arfvedsonite and aegirine (6); 7 = ore-bearing granite; 8 = faults; 9 = bedding elements.
Figure 2.
Pyrochlore-group minerals from the Katugin granites of different types (BSE image). (a,b): Bt-Arf granite; (c): Bt-Rbk granite; (d): Aeg-Arf granite; (e,f): Aeg granite. Mineral names are abbreviated as Bsn = bastnäsite, Clm = columbite, Fl = fluorite, Gg = gagarinite-(Y), Pcl1 = primary pyrochlore, Pcl2 = secondary-I pyrochlore, Pcl3 = secondary-II pyrochlore, Rt = rutile.
Figure 2.
Pyrochlore-group minerals from the Katugin granites of different types (BSE image). (a,b): Bt-Arf granite; (c): Bt-Rbk granite; (d): Aeg-Arf granite; (e,f): Aeg granite. Mineral names are abbreviated as Bsn = bastnäsite, Clm = columbite, Fl = fluorite, Gg = gagarinite-(Y), Pcl1 = primary pyrochlore, Pcl2 = secondary-I pyrochlore, Pcl3 = secondary-II pyrochlore, Rt = rutile.
Figure 3.
Ternary classification diagrams (B-site) for pyrochlore-group minerals from the Katugin granites. [14], [15], [33] = fields of fluornatropyrochlores from literature [14,15,33], respectively.
Figure 4.
Ternary classification diagrams (A-site) for pyrochlore-group minerals from the Katugin granites. In the Ca-Na + REE-H2O + □ diagrams, Ca stands also for other divalent cations (Mn, Pb, Sr, Ba); Na+REE stands also for Y, U, Th, and K; □ is vacancy.
Figure 4.
Ternary classification diagrams (A-site) for pyrochlore-group minerals from the Katugin granites. In the Ca-Na + REE-H2O + □ diagrams, Ca stands also for other divalent cations (Mn, Pb, Sr, Ba); Na+REE stands also for Y, U, Th, and K; □ is vacancy.
Figure 5.
Binary diagrams (apfu) for pyrochlore-group minerals from the Katugin granites. A = vacancy or H2O at the A-site. The HREE+Y/LREE diagram includes only WDS data.
Figure 5.
Binary diagrams (apfu) for pyrochlore-group minerals from the Katugin granites. A = vacancy or H2O at the A-site. The HREE+Y/LREE diagram includes only WDS data.
Figure 6.
SiO2 vs Nb2O5 + TiO2 diagram (wt.%) for secondary-II pyrochlore from the Katugin granites.
Figure 6.
SiO2 vs Nb2O5 + TiO2 diagram (wt.%) for secondary-II pyrochlore from the Katugin granites.
Table 1.
Chemistry (wt.%) of pyrochlore-group minerals from the Katugin biotite-arfvedsonite granite (WDS analyses).
Table 1.
Chemistry (wt.%) of pyrochlore-group minerals from the Katugin biotite-arfvedsonite granite (WDS analyses).
| Constituent | I | II | III | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | 2 | 3 | 4 | 5 | 6 | n = 12 | sd | n = 8 | min | max | |
| Na2O | 10.46 | 9.18 | 8.60 | 9.95 | 7.22 | 6.77 | 2.25 | 1.24 | 1.11 | 3.07 | 1.26 |
| K2O | bdl | bdl | bdl | bdl | bdl | bdl | bdl | 0.02 | 0.54 | 0.06 | 1.31 |
| CaO | 1.68 | 1.66 | 3.23 | 3.47 | 2.78 | 3.19 | 3.53 | 1.26 | 2.44 | 0.19 | 3.52 |
| SrO | bdl | bdl | bdl | bdl | bdl | bdl | 0.09 | 0.17 | 0.96 | 0.28 | 1.55 |
| BaO | bdl | bdl | bdl | bdl | bdl | bdl | 0.15 | 0.23 | 1.90 | bdl | 2.94 |
| PbO | bdl | bdl | bdl | bdl | 0.11 | 0.11 | 0.54 | 0.75 | 1.28 | bdl | 2.31 |
| La2O3 | 2.00 | 2.14 | 1.24 | 1.42 | 2.18 | 2.08 | 2.00 | 0.56 | 0.86 | 0.34 | 1.75 |
| Ce2O3 | 8.30 | 8.72 | 6.15 | 5.97 | 7.81 | 7.92 | 7.45 | 1.23 | 4.36 | 1.84 | 6.55 |
| Pr2O3 | 1.18 | 1.06 | 0.90 | 0.77 | 0.88 | 0.85 | 0.78 | 0.11 | 0.38 | bdl | 0.68 |
| Nd2O3 | 3.52 | 3.51 | 3.2 | 2.78 | 2.56 | 2.53 | 2.39 | 0.45 | 1.11 | 0.53 | 1.91 |
| Sm2O3 | 0.75 | 0.83 | 1.02 | 0.83 | 0.50 | 0.47 | 0.49 | 0.13 | 0.26 | bdl | 0.46 |
| Gd2O3 | 0.45 | 0.30 | 0.82 | 0.81 | 0.38 | 0.28 | 0.29 | 0.15 | 0.15 | bdl | 0.28 |
| Dy2O3 | 0.25 | 0.24 | 0.60 | 0.65 | 0.24 | 0.17 | 0.14 | 0.08 | bdl | bdl | bdl |
| Y2O3 | 0.49 | 0.53 | 0.90 | 1.29 | bdl | 0.56 | 0.19 | 0.24 | 0.09 | bdl | 0.30 |
| ThO2 | 1.30 | 1.51 | 0.84 | 0.69 | 0.81 | 0.82 | 1.35 | 0.69 | 1.26 | 0.73 | 1.63 |
| UO2 | 0.37 | 0.39 | 0.70 | 0.66 | 1.49 | 1.56 | 1.76 | 0.18 | 2.19 | 1.68 | 3.06 |
| Al2O3 | bdl | Bdl | bdl | bdl | bdl | bdl | bdl | - | 0.17 | bdl | 0.30 |
| SiO2 | bdl | Bdl | bdl | bdl | bdl | bdl | 0.02 | 0.06 | 4.47 | 1.49 | 7.40 |
| TiO2 | 2.84 | 2.79 | 3.05 | 2.67 | 2.85 | 3.05 | 4.20 | 1.19 | 3.66 | 2.64 | 4.56 |
| Nb2O5 | 59.75 | 61.24 | 62.21 | 61.86 | 49.32 | 52.87 | 55.71 | 1.67 | 50.06 | 46.13 | 55.38 |
| Ta2O5 | 2.64 | 2.06 | 2.20 | 2.27 | 15.23 | 11.51 | 4.54 | 1.42 | 5.03 | 4.39 | 6.13 |
| F | 4.83 | 4.94 | 4.89 | 4.91 | 4.52 | 4.81 | 4.26 | 0.46 | 2.28 | 0.63 | 3.91 |
| Total | 101.01 | 101.08 | 100.54 | 101.00 | 98.88 | 99.54 | 92.13 | 84.87 | |||
| O2=F | 2.03 | 2.08 | 2.06 | 2.07 | 1.90 | 2.02 | 1.79 | 0.96 | |||
| Total | 98.98 | 99.01 | 98.48 | 98.94 | 96.98 | 97.52 | 90.33 | 83.91* | |||
| ΣREE2O3 | 16.45 | 16.79 | 13.93 | 13.23 | 14.55 | 14.30 | 13.53 | 7.12 | |||
| Na | 1.354 | 1.174 | 1.075 | 1.261 | 0.979 | 0.895 | 0.295 | 0.136 | |||
| K | - | - | - | - | - | - | - | 0.044 | |||
| Ca | 0.120 | 0.117 | 0.223 | 0.243 | 0.208 | 0.233 | 0.256 | 0.165 | |||
| Sr | - | - | - | - | - | - | 0.003 | 0.035 | |||
| Ba | - | - | - | - | - | - | 0.004 | 0.047 | |||
| Pb | - | - | - | - | 0.002 | 0.002 | 0.010 | 0.022 | |||
| LREE | 0.382 | 0.389 | 0.292 | 0.279 | 0.355 | 0.344 | 0.323 | 0.161 | |||
| HREE | 0.015 | 0.012 | 0.030 | 0.031 | 0.014 | 0.010 | 0.009 | 0.003 | |||
| Y | 0.017 | 0.019 | 0.031 | 0.045 | - | 0.020 | 0.007 | 0.003 | |||
| Th | 0.020 | 0.023 | 0.012 | 0.010 | 0.013 | 0.013 | 0.021 | 0.018 | |||
| U | 0.006 | 0.006 | 0.010 | 0.010 | 0.023 | 0.024 | 0.027 | 0.031 | |||
| ΣA | 1.914 | 1.739 | 1.673 | 1.880 | 1.595 | 1.540 | 0.954 | 0.62 | |||
| Al | - | - | - | - | - | - | - | 0.013 | |||
| Si | - | - | - | - | - | - | 0.001 | 0.283 | |||
| Ti | 0.143 | 0.138 | 0.148 | 0.131 | 0.150 | 0.156 | 0.213 | 0.174 | |||
| Nb | 1.809 | 1.825 | 1.813 | 1.828 | 1.560 | 1.630 | 1.702 | 1.433 | |||
| Ta | 0.048 | 0.037 | 0.039 | 0.041 | 0.290 | 0.213 | 0.084 | 0.087 | |||
| ΣB | 2.000 | 2.000 | 2.000 | 2.000 | 2.000 | 2.000 | 2.000 | 2.000 | |||
| F | 1.018 | 1.028 | 0.996 | 1.016 | 1.001 | 1.037 | 0.911 | 0.456 | |||
| #Nb | 90.47 | 91.24 | 90.68 | 91.42 | 78.01 | 81.51 | 85.15 | 84.61 | |||
| #Ti | 7.13 | 6.91 | 7.39 | 6.56 | 7.50 | 7.82 | 10.67 | 10.27 | |||
| #Ta | 2.40 | 1.85 | 1.93 | 2.02 | 14.49 | 10.67 | 4.178 | 5.12 | |||
Note: 1–4 = pyrochlores without visible zoning; 5, 6 = rims in zoned pyrochlores. n is number of analyses; sd is standard deviation; numerals I, II, III correspond to primary, secondary-I and secondary-II pyrochlores, bdl is below detection limit. For compositionally variable secondary-II pyrochlore, minimum (min) and maximum (max) element contents are given instead of standard deviations. Formula is based on 2 cations at B-site. #Nb, #Ti, #Ta are pyrochlore, betafite, and microlite end-member components (mol.%), respectively. *The total also includes 0.07 wt.% Fe2O3 and 0.19 ZrO2.
Table 2.
Chemistry (wt.%) of pyrochlore-group minerals from the Katugin biotite and biotite-riebeckite granites (1) and arfvedsonite aegirine-arfvedsonite granites (2).
Table 2.
Chemistry (wt.%) of pyrochlore-group minerals from the Katugin biotite and biotite-riebeckite granites (1) and arfvedsonite aegirine-arfvedsonite granites (2).
| Constituent | 1 | 2 | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| I | II | I | II | III | |||||||
| n = 7 | sd | n = 3 | sd | n = 11 | sd | n = 21 | sd | n = 23 | min | max | |
| Na2O | 6.61 | 0.63 | 2.66 | 1.56 | 6.91 | 0.96 | 3.00 | 0.50 | 1.90 | 0.20 | 3.83 |
| K2O | bdl | - | bdl | - | bdl | - | bdl | 0.02 | 0.45 | 0.15 | 1.17 |
| CaO | 3.71 | 1.05 | 2.85 | 0.44 | 3.56 | 1.28 | 2.52 | 1.69 | 1.34 | 0.39 | 3.06 |
| SrO | bdl | - | bdl | - | 0.13 | 0.27 | 0.29 | 0.30 | 0.42 | bdl | 1.40 |
| BaO | bdl | - | bdl | - | bdl | - | 0.06 | 0.15 | 0.81 | bdl | 2.89 |
| PbO | bdl | - | bdl | - | 0.94 | 0.48 | 0.57 | 0.45 | 1.04 | 0.25 | 2.52 |
| La2O3 | 2.19 | 0.35 | 2.15 | 0.45 | 1.44 | 0.64 | 1.43 | 0.33 | 0.78 | 0.26 | 1.59 |
| Ce2O3 | 8.55 | 1.32 | 8.80 | 0.93 | 6.85 | 0.77 | 7.11 | 0.66 | 5.49 | 3.10 | 7.92 |
| Pr2O3 | 0.36 | 0.59 | bdl | - | 0.73 | 0.11 | 0.77 | 0.18 | 0.50 | 0.24 | 0.77 |
| Nd2O3 | 3.29 | 0.31 | 3.06 | 0.28 | 2.58 | 0.42 | 2.55 | 0.38 | 1.35 | 0.61 | 2.32 |
| Sm2O3 | bdl | - | bdl | - | 0.69 | 0.15 | 0.76 | 0.18 | 0.43 | 0.16 | 0.69 |
| Gd2O3 | bdl | - | bdl | - | 0.58 | 0.20 | 0.70 | 0.32 | 0.32 | bdl | 0.66 |
| Dy2O3 | bdl | - | bdl | - | 0.40 | 0.26 | 0.58 | 0.43 | 0.43 | bdl | 1.18 |
| Y2O3 | bdl | - | bdl | - | 1.10 | 0.93 | 1.81 | 1.52 | 0.71 | bdl | 1.99 |
| ThO2 | bdl | - | bdl | - | 1.00 | 0.43 | 1.03 | 0.45 | 1.05 | 0.20 | 2.06 |
| UO2 | 1.64 | 1.18 | 2.16 | 0.56 | 1.86 | 0.06 | 1.90 | 0.28 | 2.61 | 1.53 | 5.50 |
| Al2O3 | bdl | - | bdl | - | bdl | - | bdl | - | 0.23 | bdl | 0.64 |
| Fe2O3 | bdl | - | bdl | - | bdl | 0.01 | bdl | 0.01 | 0.17 | bdl | 2.05 |
| SiO2 | bdl | - | 1.51 | 0.23 | bdl | - | 0.02 | 0.07 | 5.47 | 2.34 | 9.24 |
| TiO2 | 4.33 | 0.87 | 4.3 | 0.97 | 5.92 | 0.91 | 6.27 | 0.82 | 5.04 | 2.81 | 6.54 |
| ZrO2 | bdl | - | bdl | - | 0.02 | 0.05 | 0.01 | 0.04 | 0.37 | bdl | 1.53 |
| Nb2O5 | 58.08 | 2.56 | 55.06 | 1.15 | 54.26 | 1.13 | 53.21 | 0.84 | 47.56 | 41.76 | 54.36 |
| Ta2O5 | 4.38 | 2.53 | 2.96 | 1.08 | 3.27 | 0.59 | 3.75 | 0.51 | 4.74 | 3.24 | 6.83 |
| F | 4.88 | 0.51 | 2.98 | 1.78 | 4.55 | 0.53 | 3.79 | 1.17 | 1.85 | bdl | 3.27 |
| Total | 98.10 | 88.51 | 96.79 | 92.13 | 85.05 | ||||||
| O2=F | 2.05 | 1.25 | 1.91 | 1.60 | 0.78 | ||||||
| Total | 96.05 | 87.25 | 94.88 | 90.53 | 84.27 | ||||||
| ΣREE2O3 | 14.43 | 14.02 | 13.28 | 13.90 | 9.23 | ||||||
| Na | 0.837 | 0.339 | 0.897 | 0.390 | 0.226 | ||||||
| K | - | - | - | - | 0.035 | ||||||
| Ca | 0.260 | 0.201 | 0.256 | 0.181 | 0.088 | ||||||
| Sr | - | - | 0.005 | 0.011 | 0.015 | ||||||
| Ba | - | - | - | 0.002 | 0.019 | ||||||
| Pb | - | - | 0.017 | 0.010 | 0.017 | ||||||
| LREE | 0.342 | 0.336 | 0.299 | 0.307 | 0.190 | ||||||
| HREE | - | - | 0.022 | 0.028 | 0.015 | ||||||
| Y | - | - | 0.039 | 0.065 | 0.023 | ||||||
| Th | - | - | 0.015 | 0.016 | 0.015 | ||||||
| U | 0.024 | 0.032 | 0.028 | 0.028 | 0.036 | ||||||
| ΣA | 1.463 | 0.907 | 1.577 | 1.038 | 0.679 | ||||||
| Al | - | - | - | - | 0.017 | ||||||
| Fe3+ | - | - | - | - | 0.008 | ||||||
| Si | - | 0.099 | - | 0.001 | 0.334 | ||||||
| Ti | 0.231 | 0.213 | 0.298 | 0.316 | 0.237 | ||||||
| Zr | - | - | 0.001 | - | 0.011 | ||||||
| Nb | 1.591 | 1.635 | 1.642 | 1.613 | 1.315 | ||||||
| Ta | 0.073 | 0.053 | 0.059 | 0.068 | 0.079 | ||||||
| ΣB | 2.000 | 2.000 | 2.000 | 2.000 | 2.000 | ||||||
| F | 1.005 | 0.619 | 0.963 | 0.804 | 0.357 | ||||||
| #Nb | 90.18 | 90.97 | 90.43 | 91.07 | 77.26 | 81.00 | 85.15 | 84.61 | |||
| #Nb | 85.49 | 86.02 | 82.13 | 80.75 | 80.65 | ||||||
| #Ti | 10.64 | 11.20 | 14.90 | 15.83 | 14.52 | ||||||
Note: 1 = EDS analyses; 2 = WDS analyses. Other symbols as in Table 1.
Table 3.
Chemistry (wt.%) of pyrochlore-group minerals from the Katugin aegirine granites (WDS analyses).
Table 3.
Chemistry (wt.%) of pyrochlore-group minerals from the Katugin aegirine granites (WDS analyses).
| Constituent | 1 | 2 | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| I | II | III | I | II | III | |||||
| n = 42 | sd | n = 46 | sd | n = 23 | min | max | n = 8 | n = 14 | n = 9 | |
| Na2O | 6.67 | 0.63 | 2.68 | 0.55 | 2.03 | 0.63 | 3.96 | 4.93 | 2.83 | 1.47 |
| K2O | bdl | - | bdl | - | 0.46 | bdl | 1.67 | bdl | bdl | 0.72 |
| CaO | 2.68 | 0.21 | 2.61 | 0.20 | 1.56 | bdl | 2.98 | 0.69 | 0.68 | 0.81 |
| MnO | bdl | - | bdl | - | 1.24 | bdl | 2.09 | bdl | bdl | bdl |
| SrO | 0.04 | 0.10 | 0.05 | 0.11 | 0.02 | bdl | 0.17 | bdl | 0.03 | 0.02 |
| PbO | 0.57 | 0.10 | 0.60 | 0.14 | 0.98 | bdl | 3.52 | 0.18 | 0.23 | 0.86 |
| La2O3 | 2.22 | 0.67 | 2.18 | 0.61 | 0.68 | bdl | 1.45 | 1.48 | 1.44 | 0.73 |
| Ce2O3 | 8.36 | 0.56 | 8.26 | 0.45 | 4.1 | bdl | 7.67 | 7.42 | 7.18 | 5.60 |
| Pr2O3 | 0.93 | 0.08 | 0.91 | 0.07 | 0.45 | 0.15 | 0.82 | 0.82 | 0.83 | 0.52 |
| Nd2O3 | 2.89 | 0.34 | 2.80 | 0.28 | 1.23 | 0.47 | 2.14 | 2.88 | 2.76 | 1.42 |
| Sm2O3 | 0.75 | 0.05 | 0.74 | 0.05 | 0.34 | 0.12 | 0.57 | 1.01 | 0.99 | 0.48 |
| Gd2O3 | 0.54 | 0.05 | 0.51 | 0.07 | 0.26 | bdl | 0.46 | 1.13 | 1.08 | 0.55 |
| Dy2O3 | 0.35 | 0.04 | 0.35 | 0.06 | 0.21 | bdl | 0.40 | 1.11 | 1.05 | 0.72 |
| Y2O3 | 0.88 | 0.18 | 0.82 | 0.12 | 0.06 | bdl | 0.50 | 3.84 | 3.70 | 0.96 |
| ThO2 | 1.12 | 0.11 | 1.13 | 0.10 | 1.39 | 0.80 | 1.91 | 0.75 | 0.70 | 0.93 |
| UO2 | 1.85 | 0.11 | 1.84 | 0.24 | 2.46 | bdl | 5.62 | 1.77 | 1.75 | 2.78 |
| Al2O3 | bdl | - | bdl | - | 0.18 | bdl | 0.38 | bdl | bdl | 0.35 |
| Fe2O3 | bdl | - | bdl | - | 1.18 | bdl | 2.89 | bdl | bdl | 0.05 |
| SiO2 | 0.04 | 0.19 | 0.08 | 0.27 | 5.07 | 1.23 | 9.05 | bdl | bdl | 5.50 |
| TiO2 | 7.57 | 0.87 | 7.49 | 0.73 | 6.47 | 4.52 | 10.01 | 7.76 | 7.51 | 5.94 |
| ZrO2 | bdl | - | bdl | - | bdl | bdl | bdl | bdl | bdl | 0.31 |
| Nb2O5 | 54.21 | 2.76 | 53.31 | 2.48 | 50.66 | 40.22 | 63.26 | 53.22 | 51.75 | 47.97 |
| Ta2O5 | 3.08 | 0.47 | 2.77 | 0.05 | 4.23 | bdl | 10.91 | 3.53 | 3.56 | 4.96 |
| F | 4.78 | 0.54 | 3.74 | 1.45 | 1.00 | 0.55 | 3.55 | 4.94 | 4.00 | 1.44 |
| Total | 99.54 | 92.88 | 85.86 | 97.45 | 92.06 | 85.10 | ||||
| O2=F | 2.01 | 1.58 | 0.42 | 2.08 | 1.69 | 0.61 | ||||
| Total | 97.53 | 91.30 | 84.51 | 95.37 | 90.37 | 84.49 | ||||
| ΣREE2O3 | 16.05 | 15.75 | 7.18 | 15.84 | 15.33 | 10.01 | ||||
| Na | 0.833 | 0.339 | 0.231 | 0.620 | 0.365 | 0.170 | ||||
| K | - | - | 0.034 | - | - | 0.055 | ||||
| Ca | 0.185 | 0.183 | 0.098 | 0.048 | 0.049 | 0.052 | ||||
| Mn | - | - | 0.122 | - | - | - | ||||
| Sr | 0.002 | 0.002 | 0.001 | - | 0.001 | 0.001 | ||||
| Pb | 0.010 | 0.011 | 0.015 | 0.003 | 0.004 | 0.014 | ||||
| LREE | 0.355 | 0.354 | 0.143 | 0.320 | 0.319 | 0.190 | ||||
| HREE | 0.019 | 0.018 | 0.009 | 0.047 | 0.046 | 0.025 | ||||
| Y | 0.030 | 0.028 | 0.002 | 0.132 | 0.131 | 0.031 | ||||
| Th | 0.016 | 0.017 | 0.019 | 0.011 | 0.011 | 0.013 | ||||
| U | 0.027 | 0.027 | 0.032 | 0.026 | 0.026 | 0.037 | ||||
| ΣA | 1.477 | 0.979 | 0.706 | 1.207 | 0.952 | 0.586 | ||||
| Al | - | - | 0.012 | - | - | 0.025 | ||||
| Fe3+ | - | - | 0.051 | - | - | 0.002 | ||||
| Si | 0.003 | 0.005 | 0.289 | - | - | 0.329 | ||||
| Ti | 0.366 | 0.369 | 0.277 | 0.378 | 0.376 | 0.268 | ||||
| Nb | 1.577 | 1.577 | 1.305 | 1.560 | 1.559 | 1.295 | ||||
| Ta | 0.054 | 0.049 | 0.066 | 0.062 | 0.065 | 0.082 | ||||
| ΣB | 2.000 | 2.000 | 2.000 | 2.000 | 2.000 | 2.000 | ||||
| F | 0.973 | 0.774 | 0.181 | 1.014 | 0.844 | 0.272 | ||||
| #Nb | 78.96 | 79.05 | 79.05 | 77.98 | 77.96 | 78.86 | ||||
| #Ti | 18.34 | 18.48 | 18.48 | 18.90 | 18.81 | 16.23 | ||||
| #Ta | 2.70 | 2.47 | 2.47 | 3.11 | 3.23 | 4.91 | ||||
Note: 1 = pyrochlore-group minerals from ordinary (1) and ore-rich (2) aegirine granites. Other symbols as in Table 1.
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Starikova, A.E.; Bazarova, E.P.; Savel’eva, V.B.; Sklyarov, E.V.; Khromova, E.A.; Kanakin, S.V. Pyrochlore-Group Minerals in the Granite-Hosted Katugin Rare-Metal Deposit, Transbaikalia, Russia. Minerals 2019, 9, 490. https://doi.org/10.3390/min9080490
AMA Style
Starikova AE, Bazarova EP, Savel’eva VB, Sklyarov EV, Khromova EA, Kanakin SV. Pyrochlore-Group Minerals in the Granite-Hosted Katugin Rare-Metal Deposit, Transbaikalia, Russia. Minerals. 2019; 9(8):490. https://doi.org/10.3390/min9080490
Chicago/Turabian StyleStarikova, Anastasia E., Ekaterina P. Bazarova, Valentina B. Savel’eva, Eugene V. Sklyarov, Elena A. Khromova, and Sergei V. Kanakin. 2019. "Pyrochlore-Group Minerals in the Granite-Hosted Katugin Rare-Metal Deposit, Transbaikalia, Russia" Minerals 9, no. 8: 490. https://doi.org/10.3390/min9080490
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