Geological, geochemical and ground magnetic techniques are used to characterize the University alkaline-gabbroid pluton and crosscutting N-S trending alkaline dikes, located northeast of the Kuznetsk Alatau ridge, Siberia. Trace element concentrations and isotopic compositions of the igneous units were determined by XRF, ICP-MS and isotope analysis. The Sm-Nd age of subalkaline (melanogabbro, leucogabbro 494–491 Ma) intrusive phases and crosscutting alkaline dikes (plagioclase ijolite, analcime syenite 392–389 Ma) suggests two stages of activity, likely representing separate events. The subalkaline and alkaline rocks are characterized by low silicic acidity (SiO₂ = 41–49 wt %), wide variations in alkalinity (Na₂O + K₂O = 3–19 wt %; Na₂O/K₂O = 1.2–7.2 wt %), high alumina content (Al₂O₃ = 15–28 wt %) and low titanium content (TiO₂ = 0.07–1.59 wt %). The new trace element data for subalkaline rocks (∑REE 69–280 ppm; La/Yb 3.7–10.2) of the University pluton and also the crosscutting younger (390 Ma) alkaline dikes (∑REE 10–1567 ppm; La/Yb 0.7–17.8 ppm) both reflect an intermediate position between oceanic island basalts (OIBs) and island arc basalts (IABs). The presence of a negative Nb–Ta anomaly and the relative enrichment in Rb, Ba, Sr, and U indicate a probable interaction of mantle plume material with the lithospheric mantle beneath previously formed accretion complexes of subduction zones. The isotopic signatures of strontium (ε_Sr(T) +3.13–+28.31) and neodymium (ε_Nd(T) +3.2–+8.7) demonstrate the evolution of parental magmas from a plume source from moderately depleted PREMA mantle, whose derivatives underwent selective crustal contamination. Full article

The intermediate rocks classified as diorite-gneisses occur within the southern part of the Monchegorsk (2.5 Ga) layered mafic-ultramafic complex (Kola Peninsula, Russia). These diorite-gneisses belong to a block historically known as the diorite window (DW) block. The same rocks occur in a framing of the Monchegorsk complex. The DW block is predominantly composed of diorite-gneisses and, to a lesser degree, of amphibolites. Multi-ordinal banding, complex folding, boudinage and metamorphic transformations, garnet porphyroblasts, and tourmaline veinlets are typical of the diorite-gneisses. In accordance with the U-Pb isotope data, the age of the diorite-gneisses in the DW block is 2736.0 ± 4.6 Ma. The Sm-Nd mineral (garnet, biotite, and tourmaline) isochron for the DW rocks has yielded an age of 1806 ± 23 Ma (related to the processes of the Svecofennian orogeny). The DW diorite-gneisses are compared with the metadiorites of the Gabbro-10 massif. The latter is a part of the Monchegorsk complex, with U-Pb crystallization age of 2498 ± 6 Ma. On the basis of geological and isotope-geochemical data, it is shown that the DW rocks belong to the Archean basement while the Gabbro-10 metadiorites probably represent one of the late-magmatic phases of the Monchegorsk complex. Full article

In order to determine the U-Pb crystallization age of zircon from the tourmaline-muscovite granites of the Kolmozero–Voronya greenstone belt located in the northeastern Fennoscandian Shield (Kola Peninsula), an isotope-geochronological study of the zircon grains was performed using a SHRIMP-RG microprobe. The belt is represented by the Archaean volcano-sedimentary rocks (2.9–2.8 Ga). Deposits of rare-metal pegmatites (Li and Cs with associated Nb, Ta, and Be) occur within the belt and on its margins. The age of the pegmatites within the belt was estimated at 2.7–2.6 Ga. Until now, there has been no generally accepted view on the genetic relation of the pegmatites with granite. Various authors have suggested that the pegmatites could potentially be associated with many type of granitoids within the region, i.e., plagiogranites, tonalites, amphibole-biotite granodiorites, microcline granites, alkaline granites, or muscovite-tourmaline granites. Zircon crystals from the muscovite-tourmaline granites are heterogeneous; they have less altered cores and strongly altered rims. The zircon cores are slightly enriched in U at a value of 173–1030 ppm, Th/U = 0.1–0.4. The zircons’ rims are heavily enriched in U at a value of 700–3300 ppm, Th/U = 0.03–0.08, indicating metasomatic processes. Zircon characteristics show that it crystallized from a melt enriched in a fluid phase. Fluid activity lasted after zircon crystallization as reflected in the irregular composition of the mineral and its rare earth element (REE) patterns that are typical of a metasomatic zircon. The computed zircon crystallization temperature in the tourmaline-muscovite granites is in the range of 650–850 °C. The discordant age calculated for five analyzed points of the zircon crystal cores is 2802 ± 13 Ma. The discordant age for four analyzed points of the zircon crystal rims is found to be 2728 ± 14 Ma. On the basis of the obtained isotope-geochronological data, we conclude that the tourmaline-muscovite granites located in the immediate vicinity of rare-metal pegmatite veins are the most probable source of matter for the pegmatites. Full article

Carbonaceous material (CM) is common in meta-sediments and is generally interpreted to be intimately associated with gold mineralization. For the Bumo deposit in Hainan Province, South China, CM is mainly hosted by greenschist facies—to amphibolite-facies metamophic rocks of the Paleo—to the Mesoproterozoic Baoban Group, and by auriferous veins which could be used as an important gold prospecting indicator. However, the genesis of CM and its relationship with gold mineralization are still unclear. From the field work and thin section observations two types of CM occur, i.e., layered and veinlet. The layered CM occurred in CM-bearing black shales, up to meters thick, and prevails in the deposit. More importantly, Au-bearing sulfides are commonly distributed along the boundary between the quartz veins and layered CM. In contrast, the veinlet CM, co-precipitated with native gold and sulfides, has the thickness of micro- to centi-meters, and these thin veins occur in quartz veins and hydrothermally altered rocks. In addition, layered CM has a stringy shape and laminate structure, while veinlet CM occurs as isometric particles based on the Scanning Electron Microscope (SEM) analysis. The Raman carbonaceous material geothermometer indicates that layered CM with a high maturity is formed at elevated temperatures of 400–550 °C, consistent with X-ray diffraction (XRD) analysis. In contrast, veinlet CM with a low maturity is formed at 200–350 °C and generally consistent with gold mineralization. In addition, layered CM has ^δ13C values ranging from −30 to −20%, demonstrating a biogenic origin. Consequently, it is interpreted that layered CM is formed by a pre-ore metamorphic event during Caledonian, and its reducing nature promotes gold precipitation via destabilization of aqueous Au complexes or facilitating sulfidation. Veinlet CM is of hydrothermal origin, and its precipitation modified the chemical conditions of ore fluids, leading to the destabilization of Au complexes, which therefore are favorable for mineralization. Full article

The Kuergasheng Pb–Zn deposit is located in the Western Tianshan Orogen, Xinjiang Province, China. The ore bodies are mainly hosted in sandstone of the Tuosikuertawu Formation and are controlled by NW-trending faults. Three paragenetic stages were identified: early pyrite–chalcopyrite–quartz veins (stage 1), middle galena–sphalerite–quartz veins (stage 2), and late sulfide-poor calcite–quartz veins (stage 3). Fluid inclusions (FIs) include liquid-rich aqueous (LV-type), vapor-rich aqueous (VL-type), halite-bearing (S-type), and monophase liquid aqueous (L-type). Homogenization temperatures for FIs from stages 1–3 are 221–251, 173–220, and 145–172 °C, respectively. Stage 1 fluids in LV-, VL-, and S-type FIs yield salinities of 6.2–9.6, 1.7–3.1, and 32.7–34.9 wt % NaCl equiv., respectively. Stage 2 fluids in LV- and S-type FIs have salinities of 5.1–7.9 and 31.9–32.1 wt % NaCl equiv., respectively. Stage 3 fluids in LV- and L-type FIs have salinities of 3.4–5.9 wt % NaCl equiv. Oxygen, hydrogen, and carbon isotopic data (δ¹⁸O_H2O = −7.7 to 1.7‰, δD_H2O = −99.2 to −83.1‰, δ¹³C_H2O = −16.6 to 9.1‰) indicate that the ore-forming fluids have a hybrid origin —an initial magmatic source with input of meteoric water becoming dominant in the later stage. Sulfur and lead isotopic data for galena (δ34S = 5.6 to 6.9‰, ²⁰⁶Pb/²⁰⁴Pb = 18.002–18.273, ²⁰⁷Pb/²⁰⁴Pb = 15.598–15.643, ²⁰⁸Pb/²⁰⁴Pb = 38.097–38.209) reveal that the ore-forming materials were mainly derived from the Beidabate intrusive body and the Tuosikuertawu Formation. Full article

The historic Yinggelike nephrite jade deposit in the Altyn Tagh Mountains (Xinjiang, NW China) is renowned for its gem-quality nephrite with its characteristic light-yellow to greenish-yellow hue. Despite the extraordinary gemological quality and commercial significance of the Yinggelike nephrite, little work has been done on this nephrite deposit, due to its geographic remoteness and inaccessibility. This contribution presents the first systematic mineralogical and geochemical studies on the Yinggelike nephrite deposit. Electron probe microanalysis, X-ray fluorescence (XRF) spectrometry, inductively coupled plasma mass spectrometry (ICP-MS) and isotope ratio mass spectrometry were used to measure the mineralogy, bulk-rock chemistry and stable (O and H) isotopes characteristics of samples from Yinggelike. Field investigation shows that the Yinggelike nephrite orebody occurs in the dolomitic marble near the intruding granitoids. Petrographic studies and EMPA data indicate that the nephrite is mainly composed of fine-grained tremolite, with accessory pargasite, diopside, epidote, allanite, prehnite, andesine, titanite, zircon, and calcite. Geochemical studies show that all nephrite samples have low bulk-rock Fe/(Fe + Mg) values (0.02–0.05), as well as low Cr (0.81–34.68 ppm), Co (1.10–2.91 ppm), and Ni (0.52–20.15 ppm) contents. Chondrite-normalized REE patterns of most samples exhibit strong to moderate negative Eu anomalies (0.04–0.67), moderate LREE enrichments, nearly flat HREE patterns, and low ΣREE contents (2.16–11.25 ppm). The nephrite samples have δ¹⁸O and δD values of 5.3 to 7.4‰ and –74.9 to –86.7‰, respectively. The mineralogy, bulk-rock chemistry, and O–H isotope characteristics are consistent with the dolomite-related nephrite classification. Based on mineral paragenetic relationships, three possible mineral crystallization stages are recognized: (1) diopside formed by prograde metasomatism; (2) nephrite jade formed by retrograde metasomatism and replacement of Stage I anhydrous minerals; (3) hydrothermal alteration after the nephrite formation. Features of transition metal contents indicate that the color of the Yinggelike nephrite is likely to be controlled by the Fe²⁺, Fe³⁺, and Mn. Yellowish color is related to Mn and especially Fe³⁺, while greenish color is related to Fe²⁺. Our new mineralogical and geochemical results on the Yinggelike nephrite provide better constraints on the formation of other nephrite deposits in the Altyn Tagh Mountains, and can facilitate future nephrite prospecting and research in the region. Full article