Geology of Ore Deposits

Zircon from granitoids of the multiphase Turga massif (Eastern Transbaikalia) shows various morphological features and compositions of trace elements. This granitoid massif of the Kukulbey complex is spatially associated with rocks of the Shakhtama monzonitoid complex, whose ages are about 133 and 158 Ma, respectively. Zircon from different granitoid phases of the Kukulbey complex demonstrates a decrease in Hf content and an increase in Th, U, Y, and REE concentrations. The trace element accumulation in zircon and rocks of the main phase of the Turga massif (Li-Li-siderophyllite granites) was accompanied by a significant rise of their crystallization temperature, relatively to the earlier phase. The indicative features of zircon in these granites—the intensive development of specific twinning (up to 30% of all grains) and the presence of contrasting growth zones—confirm the idea of increasing crystallization temperatures and alkalinity of the melt. These features of zircon, together with geochemical composition of rocks, indicate that amazonite granites of the Turga massif belong to the alkaline type of Li–F-bearing granites with a mixed geochemical specialization: on the one hand, Li, Ta, and Nb, which are typical for the ore-bearing (peraluminous rare-metal) Orlovka massif; and on the other hand, Zr, REE, Th, and U, which are more typical for alkaline granites.

The chemical composition of chlorites from the rocks that are conventionally classified as the residual weathering mantle of the Kolskii ophiolite massif was studied. The chlorites exhibit high Mg/ (Mg + Fe) atomic ratio values (Mg#) of 0.78–0.96 and elevated Si content (2.95–3.74 apfu), but are relatively poor in Al (1.28–2.66 apfu). In terms of octahedral occupancy (R^VI is 5.52–5.98 and [R³⁺]^VI is 0.87–2.04 apfu), they are classified as the trioctahedral subgroup. The NiO content in the chlorites varies from 0.2 to 21 wt %; in addition, the tabular low-Ni and high-Ni chlorite grains are often tightly intergrown. There is a pronounced negative correlation between NiO and MgO content. The crystallization temperature estimated using chlorite geothermometers varies widely. The crystallization temperature interval is 125–300°C or higher with a statistical maximum in the region of 175–300°C for the low-Ni chlorites and 50–250°С with a statistical maximum in the region of 75–125°С for the high-Ni chlorites. In addition, the high-Ni chlorites demonstrate a gradual decrease in temperature as the nickel content increases. This correlation indicates the important role of temperature as an ore generation factor during the formation of the oxide–silicate nickel deposits that are associated with the Kolskii massif. These tendencies support the conclusion that the hydrothermal processes not only preceded lateritization, but also played a significant part in the level of nickel concentration in phyllosilicates.

Dalnegorskite, a new pyroxenoid with the crystal chemical formula Ca₂Ca₂MnCa(Si₃O₉)₂ and simplified formula Ca₅Mn(Si₃O₉)₂, is a rock-forming mineral in the B-bearing calcic skarns in the Dalnegorsk borosilicate deposit (Dalnegorsk, Primorsky Krai, Russia). It belongs to the bustamite structural type and forms a continuous solid-solution series with isostructural ferrobustamite Ca₂Ca₂FeCa[Si₃O₉]₂. These pyroxenoids form beige, pinkish white and milky white radiated aggregates typically consisting of split thin acicular to fiber-like individuals and are associated with hedenbergite, datolite, andradite, galena, sphalerite, and pyrrhotite. D_meas. = 3.02(2), D_calc. = 3.035 g cm^–3. Dalnegorskite is biaxial negative, α = 1.640 (3), β = 1.647 (3), γ = 1.650 (3)°, 2V_meas. = 75(10)°. The average chemical composition of the holotype (electron microprobe data) is: 0.23 MgO, 40.02 CaO, 5.02 MnO, 3.64 FeO, 50.65 SiO₂, total 99.56 wt %. The empirical formula calculated for 18 O atoms is Ca_5.03Mn_0.51Fe_0.36Mg_0.04Si_6.01O₁₈. The crystal structure of the new mineral was obtained from X-ray diffraction data using the Rietveld method, R_p= 0.0345, R_wp = 0.0444, R₁ = 0.0790, and wR₂ = 0.0802. Dalnegorskite is triclinic, P-1, a = 7.2588(11), b = 7.8574(15), c = 7.8765(6) Å, α = 88.550(15), β = 62.582(15), γ = 76.621(6)°, V = 386.23(11) ų, and Z = 1. Dalnegorskite is distinct from the related mineral wollastonite in the infrared spectrum. The wave numbers of the maxima of strong bands in the Si–O stretching vibration region in the IR spectrum of dalnegorskite are (cm^–1): 905, 937, 1025, and 1070. The holotypic specimen of dalnegorskite is kept in the collection of the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow, Russia (no. 96201).

For the first time data on platinum group minerals (PGM) from the deluvial placer of the Veresovka River are given; their root source are dunites of the northern part of the Veresovoborsky massif. Among minerals typical of this type of placers, Pt–Fe minerals, Os–Ir–(Ru) intermetallic compounds, kashinite, bowieite, laurite, erlichmanite, and Ir–Rh thiospinels have been identified. Irarsite, hollingworthite, zvyagintsevite, potarite, cooperite, ferhodsite, and some unnamed Pb–Те minerals were also revealed, which rare for platinum placers associated with zonal clinopyroxenite–dunite massifs, but are widely distributed in the studied placer. Xingzhongite was detected there for the first time in placers of the Ural Platinum Belt. The morphological features of all these minerals are characterized in detail, together with their chemical composition, determined by electron microprobe analysis. Their genetic relationships are characterized taking into account the aggregate data obtained. This comprehensive study of PGM individuals and aggregates is used as a basis to distinguish the parageneses in their association.

The new data for the segregations, paragenetic assemblage, and composition of bismuthian jamesonite from gold–quartz mineralization at the Sredny Golgotai deposit located in the eastern part of the Mongolia–Okhotsk orogenic belt are reported. This mineral occurs as two varieties (I, II), which are slightly different in composition and chemically close to bismuthian jamesonite (“sakharovaite”) described from the Ustarasai deposit. In contrast to variety II, variety I is Cu- and Fe-free. The electron microprobe study has revealed that varieties I and II are close to jamesonite and tintinaite, respectively. The data obtained make it possible to conclude that individual sulfosalt species of the proper tintinaite and jamesonite series, which are close in composition, are probable members of the tintinaite–kobellite series. It is assumed that the Cu- and Fe-free variety of bismuthian jamesonite close in composition to “sakharovaite” is an individual mineral species.

A new Sc-bearing variety of tusionite has been found in the Eastern Pamirs, in the near-miarolitic Dorozhny granite pegmatite complex at the Kukurt pegmatite field (left bank of the Kukurt River, 45 km east of the settlement of Murghab, Gorno-Badakhshan Autonomous Oblast, Tajikistan). Miarolitic pegmatites are related to the alpine leucocratic granites of the Shatput intrusive complex and occur in rocks of the Sarydzhilga Formation (PR₃?) metamorphosed under amphibolite and epidote–amphibolite facies. Tusionite occurs in association with quartz, K-feldspar, albite, elbaite, Sc-bearing spessartine (up to 0.2 wt % Sc₂O₃) and accessory fluorapatite, Y-bearing fluorite, Sn-bearing titanite, magnetite, polycrase-(Y), B-rich gadolinite-(Y), ixiolite, manganocolumbite, pyrochlore, chernovite-(Y), cassiterite, varlamoffite, lepidolite, and Hf-rich zircon (up to 17.0 wt % HfO₂). Tusionite forms thin lamellae (0.05–0.25 mm) and fanlike aggregates. It is yellow and transparent with a vitreous luster. It has weak pleochroism, N_o (orange–yellow) > N_e (light yellow). It is a uniaxial negative mineral, n_o = 1.870(5), n_e = 1.760(3). The Raman spectrum has been reported for tusionite for the first time (laser excitation 532 nm); main bands: 228, 305, 379, 466, 661, 733, 750, 942, 1218, and 1458 cm^–1. Its X-ray diffraction pattern is similar to tusionite from the Southwestern Pamirs. Hexagonal unit cell parameters: a = 4.772(3), c = 15.28(3) Å. Chemical composition (electron microprobe, wt %, average of 14 analyses): 0.06 (0.00–0.31) Ta₂O₅; 50.28 (49.43–51.03) SnO₂; 0.02 (0.00–0.19) TiO₂; 1.02 (0.62–1.53) Sc₂O₃; 0.03 (0.00–0.19) CaO; 0.21 (0.16–0.46) FeO; 24.06 (23.59–24.34) MnO; 24.51 (calc. 23.90) B₂O₃; total 99.62 (99.08–100.79). The substitution mechanism involving Sc is not clear. Substitution of Sc⁺³ for Sn⁺⁴ with partial replacement of Mn⁺² by Mn⁺³ is possible; however, Sc negatively correlates not only with Sn, but also with (Fe + Mn), which may result from the location of Sc in both octahedral positions with Sn⁺⁴ and Mn⁺².

Compositional variations of the epidote-supergroup minerals from the different magmatic, metasomatic, and metamorphic formations of the Pelagonian Massif (Republic of North Macedonia), the Urals (Russia) and the Eifel Mountains (Germany) were studied. The new data on isomorphism in these minerals were obtained. Nine potentially new mineral species belonging to the epidote supergroup including the minerals, in which Cr, Ga, La, Ce, Nd, and Pb are the species-defining components, as well as a number of varieties with unusually high Zn and Cu contents, were identified. The relationship between the chemical composition of epidote-supergroup minerals and their Raman spectra is discussed.