Search Results (242)

Rare earth elements (REEs) have garnered significant global attention due to their essential role in advanced technologies. Sri Lanka is endowed with various REE-bearing minerals, including the apatite-rich deposit in the Eppawala area, commonly known as Eppawala rock phosphate (ERP). However, direct extraction of REEs from ERP is technically challenging and economically unfeasible. This study introduces a novel, integrated approach for recovering REEs from ERP as a by-product of nitrophosphate fertilizer production. The process involves nitric acid-based acidolysis of apatite, optimized at 10 M nitric acid for 2 h at 70 °C with a pulp density of 2.4 mL/g. During cooling crystallization, 42 wt% of calcium was removed as Ca(NO₃)₂.4H₂O while REEs remained in the solution. REEs were then selectively precipitated as REE phosphates via pH-controlled addition of ammonium hydroxide, minimizing the co-precipitation with calcium. Further separation was achieved through selective dissolution in a sulfuric–phosphoric acid mixture, followed by precipitation as sodium rare earth double sulfates. The process achieved over 90% total REE recovery with extraction efficiencies in the order of Pr > Nd > Ce > Gd > Sm > Y > Dy. Samples were characterized for their phase composition, elemental content, and morphology. The fertilizer results confirmed the successful production of a nutrient-rich nitrophosphate (NP) with 18.2% nitrogen and 13.9% phosphorus (as P₂O₅) with a low moisture content (0.6%) and minimal free acid (0.1%), indicating strong agronomic value and storage stability. This study represents one of the pioneering efforts to valorize Sri Lanka’s apatite through a novel, dual-purpose, and circular approach, recovering REEs while simultaneously producing high-quality fertilizer. Full article

The new mineral achyrophanite (K,Na)₃(Fe³⁺,Ti,Al,Mg)₅O₂(AsO₄)₅ was found in high-temperature sublimates of the Arsenatnaya fumarole at the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. It is associated with aphthitalite-group sulfates, hematite, alluaudite-group arsenates (badalovite, calciojohillerite, johillerite, nickenichite, hatertite, and khrenovite), ozerovaite, pansnerite, arsenatrotitanite, yurmarinite, svabite, tilasite, katiarsite, yurgensonite, As-bearing sanidine, anhydrite, rutile, cassiterite, and pseudobrookite. Achyrophanite occurs as long-prismatic to acicular or, rarer, tabular crystals up to 0.02 × 0.2 × 1.5 mm, which form parallel, radiating, bush-like, or chaotic aggregates up to 3 mm across. It is transparent, straw-yellow to golden yellow, with strong vitreous luster. The mineral is brittle, with (001) perfect cleavage. D_calc is 3.814 g cm^–3. Achyrophanite is optically biaxial (+), α = 1.823(7), β = 1.840(7), γ = 1.895(7) (589 nm), 2V (meas.) = 60(10)°. Chemical composition (wt.%, electron microprobe) is: Na₂O 3.68, K₂O 9.32, CaO 0.38, MgO 1.37, MnO 0.08, CuO 0.82, ZnO 0.48, Al₂O₃ 2.09, Fe₂O₃ 20.42, SiO₂ 0.12, TiO₂ 7.35, P₂O₅ 0.14, V₂O₅ 0.33, As₂O₅ 51.88, SO₃ 1.04, and total 99.40. The empirical formula calculated based on 22 O apfu is Na_1.29K_2.15Ca_0.07Mg_0.34Mn_0.01Cu_0.11Zn_0.06Al_0.44Fe³⁺_2.77Ti_1.00Si_0.02P_0.02S_0.14V_0.04As_4.90O₂₂. Achyrophanite is orthorhombic, space group P222₁, a = 6.5824(2), b = 13.2488(4), c = 10.7613(3) Å, V = 938.48(5) ų and Z = 2. The strongest reflections of the PXRD pattern [d,Å(I)(hkl)] are 5.615(59)(101), 4.174(42)(022), 3.669(31)(130), 3.148(33)(103), 2.852(43)(141), 2.814(100)(042, 202), 2.689(29)(004), and 2.237(28)(152). The crystal structure of achyrophanite (solved from single-crystal XRD data, R = 4.47%) is unique. It is based on the octahedral-tetrahedral M-T-O pseudo-framework (M = Fe³⁺ with admixed Ti, Al, Mg, Na; T = As⁵⁺). Large-cation A sites (A = K, Na) are located in the channels of the pseudo-framework. The achyrophanite structure can be described as stuffed, with the defect heteropolyhedral pseudo-framework derivative of the orthorhombic Fe³⁺AsO₄ archetype. The mineral is named from the Greek άχυρον, straw, and φαίνομαι, to appear, in allusion to its typical straw-yellow color and long prismatic habit of crystals. Full article

As a critical mineral, magnesite plays a vital role in industries such as steelmaking, construction, and advanced technologies due to its high thermal stability and chemical resistance. However, the beneficiation of low-grade magnesite ores (~38.36% MgO) remains challenging due to the presence of iron, silica, and calcium-bearing impurities. This study proposes an integrated beneficiation strategy combining medium-intensity magnetic separation and flotation techniques to upgrade a low-grade magnesite ore. After grinding to 75 µm (d₈₀), the sample was subjected to two-stage magnetic separation at 5000 Gauss to remove Fe-bearing minerals, reducing Fe₂O₃ below 0.5%. The non-magnetic fraction was then treated through a two-stage reverse flotation process using dodecylamine (350 g/t) and diesel oil (60 g/t) at pH 7 to reject silicate gangue. This was followed by a four-stage direct flotation using sodium oleate (250 g/t), sodium silicate (350 g/t), and SHMP (100 g/t) at pH 10 to selectively recover magnesite while suppressing Ca-bearing minerals. The optimized flowsheet achieved a final concentrate with MgO > 46.5%, SiO₂ ≈ 1.05%, Fe₂O₃ ≈ 0.44%, and CaO ≈ 0.73%, meeting the specifications for refractory-grade magnesite. These results highlight the effectiveness of a combined magnetic–flotation route in upgrading complex, low-grade magnesite deposits for commercial use. Full article

This study investigated the distribution and source of heavy metals and dispersed elements in the high-salinity brine of Qarhan Salt Lake. The brine with an average total dissolved solid content of 332.22 g/L, dominated by Cl⁻ (216.41 g/L) and Mg²⁺ (44.76 g/L), indicated strong evaporation and dolomite dissolution. As (6.57 ± 3.59 μg/L) and Hg (0.48 ± 0.14 μg/L) showed uniform distribution while Li (69.66 mg/L), B₂O₃ (317.80 mg/L), and Zn (5.69 mg/L) were highly enriched, highlighting the resource potential and geochemical complexity. Correlation analysis revealed that water–rock interaction played a key role in element differentiation, with Sr and Ca²⁺/Cl⁻ showing strong positive correlations (r = 0.693/0.768), reflecting isomorphic substitution and dissolution. Meanwhile, Na⁺ and Mg²⁺/Ca²⁺ showed negative correlations (r = −0.732/−0.889), suggesting cation exchange and gypsum precipitation. The self-organizing map yielded four clusters of elements and positive matrix factorization model identified four sources; the elements in the Salt Lake brine mainly came from the river water supply, weathering and leaching of minerals, and dissolution of salt-bearing layers and were locally influenced by human activities. The research provided valuable insights for future sustainable development and the environmental protection of the region. Full article

Spring waters (n = 103) from locations surrounding Great Salt Lake (GSL) were mapped, collected, and analyzed to determine their chemical compositions. A ternary Ca-SO₄-alkalinity plot was used to group these waters into compositional types based on the principle of chemical divides. Different spring water types were mixed with Bear, Jordan, and Weber River waters to determine the amount of spring inflow needed to reproduce the chemical composition of GSL. The Pitzer-based computer program EQL/EVP was used to simulate evaporation of spring-river water mixtures. The goal was to find spring-river water mixtures that, when evaporated, reproduced the chemical composition of modern GSL. This approach yielded GSL brine composition from a starting mixture of 12% spring inflow and 88% river water, by volume. The calculated spring inflow–river water mixture contains, on a molar percentage basis, greater than 50% of the B, K, Li, Na, and Cl supplied by springs and greater than 50% of the Ba, Ca, Sr, SO₄, and alkalinity derived from rivers. Understanding GSL spring inflow and brine evolution as lake elevation drops is critical to lake environments, ecosystems, and industrial brine shrimp harvesting and mineral extraction. Full article

This study investigates the impact of dynamically adjusting the potassium-to-calcium ratio (molar ratio) in nutrient solutions used on cherry tomatoes at different growth stages (seedling, flowering and fruit setting, and maturity) to enhance fruit appearance, nutritional quality, and mineral content. By focusing on the ‘Saopolo’ variety, 17 treatments were implemented, each involving a specific potassium-to-calcium ratio in the nutrient solutions applied during the seedling, flowering and fruit setting, and fruiting stages. The aim was to optimize the nutrient solution formula and enhance fruit quality. Fruit quality parameters were assessed at the initial maturity stage across various treatments, encompassing commodity quality (fruit stalk length, fruit shape index, and fruit hardness), taste quality (total soluble sugar, titratable acid content, and sugar-acid ratio), nutritional quality (vitamin C (Vc), soluble protein, and lycopene content), antioxidant quality (total phenol and flavonoid content), as well as comprehensive quality (soluble solids content). Principal component analysis was conducted on these parameters. Additionally, mineral element levels in fruits were analyzed at different developmental stages (white ripe, color transition, and mature stages). When tomato plants were treated with nutrient solutions containing varying potassium-to-calcium ratios at different growth stages, observations revealed distinct outcomes in the first fruit cluster. T15 (seedling stage (A): 0.5 times standard nutrient solution; flowering and fruit-setting stage (B): potassium-to-calcium = 1.6:1; fruiting stage (C): potassium-to-calcium = 2.1:1) exhibited the highest fruit firmness (1.54 kg·cm⁻²), while T14 (A; B (K:Ca = 1.6:1); C (K:Ca = 2.0:1)) elevated levels of total soluble sugars (6.59%), titratable acidity (0.74%), soluble proteins (2.79 mg·g⁻¹), and total phenolics (2.56 mg·g⁻¹). T13 (A; B (K:Ca = 1.6:1); C (K:Ca = 1.9:1)) demonstrated superior soluble solids (5.9%), lycopene (32.09 µg·g⁻¹), and flavonoid contents (0.77 mg·g⁻¹), whereas T12 (A; B (K:Ca = 1.6:1); C (K:Ca = 1.8:1)) showcased the highest sugar–acid ratio (12.63) and soluble solids content (5.9%). Notably, T8 (A; B (K:Ca = 1.5: 1); C (K:Ca = 1.9:1)) exhibited the highest Vc content (10.03 mg·100 g⁻¹). Mineral element analysis indicated that an increased potassium-to-calcium ratio in the nutrient solution during various growth stages enhanced phosphorus and potassium uptake by the fruits but hindered the absorption of nitrogen, calcium, magnesium, and iron. In summary, employing half the standard nutrient solution dosage during the seedling stage, utilizing a potassium-to-calcium ratio of 1.6:1 in the nutrient solution at the flowering and fruit setting stage, and applying nutrient solution T13 with a potassium-to-calcium ratio of 1.9:1 during the fruit-bearing phase, optimally coordinates fruit nutrient accrual and enhances flavor quality. These findings support the use of stage-specific nutrient modulation to improve cherry tomato quality in controlled-environment agriculture. Full article

Fluorite is commonly associated with calcite and other Ca-bearing gangue minerals in nature. Fluorite and its associated Ca-bearing gangue minerals share similar surface active sites involving Ca²⁺ ions and have comparable surface properties, making their flotation separation challenging. Traditional fatty acid collectors, such as oleic acid, suffer from poor selectivity. This study investigates the use of N-hydroxy-N-phenyloctanamide (HPOA) as a novel collector for fluorite, with the goal of improving its flotation separation from Ca-bearing gangue minerals. Flotation tests demonstrate that HPOA provides superior selectivity compared to oleic acid in separating fluorite from calcite. Research on the adsorption capacity of HPOA on mineral surfaces shows that, under equivalent testing conditions, HPOA shows greater adsorption amounts on fluorite than on calcite. As a result, HPOA has a superior collecting capacity in fluorite flotation. First-principles calculations reveal that HPOA adsorbs on the fluorite surface by forming chemical bonds with Ca²⁺ ions via its hydroxyl and carbonyl groups. Moreover, HPOA exhibits strong adsorption on fluorite surface, as indicated by more significant shifts in the binding energies of Ca²⁺ ions on fluorite compared to calcite after HPOA adsorption. This study highlights the potential of amide-based collectors to improve fluorite flotation and offers valuable insights into the development of more selective flotation reagents. Full article

In the Yuheng mining area (Jurassic coalfield, northern Shaanxi, China), the Yan’an Formation groundwater is characterized by elevated salinity, posing challenges for mine water pollution control and regional water resource management. However, the spatial distribution patterns and formation mechanisms of this high-salinity groundwater remain poorly studied. This study integrates hydrogeochemical data from 18 coal mines, analyzing the spatial salinity variations, major ion compositions and isotopic signatures. Combined with the evolution characteristics of ancient sedimentary environments and the composition analysis of rock salt minerals in the coal rock interlayers, the formation mechanism of high salinity water was explored. The results indicate that the groundwater mineralization degree of the Yan’an Formation in the Jurassic strata encountered in the Yuheng mining area is the highest, showing a decreasing trend upwards. On the plane, the western and northern regions are generally higher than the eastern and southern regions. The highest mineralization level of groundwater can reach 36.25g/L, and the high mineralization hydrochemical type is mainly SO₄-Na·Ca type, with occasional Cl-Na type in areas with extremely high mineralization level. The cause analysis shows that the highly mineralized groundwater in the Yuheng mining area comes from atmospheric precipitation, which infiltrates and dissolves salt rocks. In addition, the mining area is located in the arid area of northern Shaanxi, with insufficient water supply and no obvious structural faults, and has good sealing properties, thus exhibiting the characteristics of high mineralization. These mechanisms provide a formation model for the high-salinity groundwater in Jurassic coal-bearing strata, offering critical implications for predictive hydrogeochemical modeling and sustainable water management in arid mining regions. Full article

The Hammam–Zriba F–Ba (Zn–Pb) stratabound deposit is located within the Zaghouan Fluorite Province (ZFP), which is the most important mineral sub-province in NE Tunisia, with several CaF₂ deposits occurring mainly along the Zaghouan Fault and corresponding to an F-rich MVT mineral system developed along the unconformity surface between the uppermost Jurassic limestones and the late Cretaceous layers. Petrographic analysis, microthermometry, and Raman spectroscopy applied to fluid inclusions in fluorite revealed various types of inclusions containing brines, oil, CO₂, and CH₄ along with solid phases such as evenkite, graphite, kerogen and bitumen. Microthermometric data indicate homogenization temperatures ranging from 85 °C to 145 ± 5 °C and salinities of 13–22 wt.% NaCl equivalent. This study supports a model of heterogeneous trapping, where saline basinal brines, oil, and gases were simultaneously trapped within fluorite, which indicates fluid immiscibility. The Raman analysis identified previously undetected organic compounds, including the first documented occurrence of evenkite, a mineral hydrocarbon, co-genetically trapped with graphite. The identification of evenkite and graphite in fluid inclusions offers new insights into the composition of hydrocarbon-bearing fluids within the MVT deposits in Tunisia, contributing to an understanding of the mineralogical characteristics of these deposits. The identified hydrocarbons correspond to three oil families. Family I (aliphatic compounds) is attributed to the lower-Eocene Bou-Dabbous Formation, family II (aromatic compounds) is attributed to the Albian Fahdene Formation and the Cenomanian–Turonian Bahloul Formation, and family III is considered as a mixture of aliphatic and aromatic compounds generated by the three sources. The presence of graphite in fluid inclusions could suggest the involvement of a thermal effect from deep-seated sources through the reservoir to the site of fluorite precipitation. These findings suggest that the fluorite mineral system might have been linked with the interaction of multi-reservoir fluids, potentially linked to the neighboring petroleum system in northeastern Tunisia during the Miocene. This study aims to investigate the composition of fluid inclusions in fluorite from the Hammam–Zriba F–Ba (Zn–Pb) deposit, with a particular focus on the plausible sources of hydrocarbons and their implications for the genetic relationship between the mineralizing system and petroleum reservoirs. Full article

The Yidun island arc was formed in response to the Late Triassic westward subduction of the Ganzi–Litang oceanic plate, a branch of the Paleo-Tethys Ocean. The Zhongdian arc, located in the south of the Yidun island arc, has relatively large number of porphyry (skarn) type Cu–Mo ± Au polymetallic deposits, the largest of which is the Pulang Cu (–Mo–Au) deposit with proven Cu reserves of 5.11 Mt, Au reserves of 113 t, and 0.17 Mt of molybdenum. However, the relationship between mineralization and the potassic alteration zone, phyllic zone, and propylitic zone of the Pulang porphyry deposit is still controversial and needs further study. Titanite (CaTiSiO₅) is a common accessory mineral in acidic, intermediate, and alkaline igneous rocks. It is widely developed in various types of metamorphic rocks, hydrothermally altered rocks, and a few sedimentary rocks. It is a dominant Mo-bearing phase in igneous rocks and contains abundant rare earth elements and high-field-strength elements. As an effective geochronometer, thermobarometer, oxybarometer, and metallogenic potential indicator mineral, titanite is ideal to reveal the magmatic–hydrothermal evolution and the mechanism of metal enrichment and precipitation. In this paper, major and trace element contents of the titanite grains from different alteration zones were obtained using electron probe microanalysis (EPMA) and laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to define the changes in physicochemical conditions and the behavior of these elements during the process of hydrothermal alteration at Pulang. Titanite in the potassic alteration zone is usually shaped like an envelope. It occurs discretely or is enclosed by feldspar, with lower contents of CaO, Al, Sr, Zr and Hf; a low Nb/Ta ratio; high ∑REE + Y, U, Th, Ta, Nb, and Ga content; and high FeO/Al₂O₃ and LREE/HREE ratios. This is consistent with the characteristics of magmatic titanite from fresh quartz monzonite porphyry in Pulang and other porphyry Cu deposits. Titanite in the potassium silicate alteration zone has more negative Eu anomaly and a higher U content and Th/U ratio, indicating that the oxygen fugacity decreased during the transformation to phyllic alteration and propylitic alteration in Pulang. High oxygen fugacity is favorable for the enrichment of copper, gold, and other metallogenic elements. Therefore, the enrichment of copper is more closely related to the potassium silicate alteration. The molybdenum content of titanite in the potassium silicate alteration zone is 10²–10⁴ times that of the phyllic alteration zone and propylitic alteration zone, while the copper content is indistinctive, indicating that molybdenum was dissolved into the fluid or deposited in the form of sulfide before the medium- to low-temperature hydrothermal alteration, which may lead to the further separation and deposition of copper and molybdenum. Full article

Tungsten (W), a rare metal, is categorized as a Critical and Strategic Raw Material (CRM) by the European Union (EU), with the highest economic importance of all selected CRMs since 2014. Tungsten and its derivatives are extracted from their commercial raw materials, mainly wolframite [(Fe,Mn)WO₄] and scheelite (CaWO₄) ores. Subsequently to mining and mineral processing, the W ore is submitted to thermal treatment and hydrometallurgy under aggressive conditions (high pressure and temperature), which are usually applied for the extraction of tungsten compounds. This paper aims to investigate a thermal route for scheelite processing using various selected chemical agents, resulting in a W-bearing material that is capable of being leached under softer conditions. In this context, a thermodynamic study of the interaction between FeWO₄, MnWO₄ and CaWO₄ and various chemical reagents is described. The thermochemical calculations and data modeling show that, among other considerations, the reaction of CaWO₄ with magnesium chloride (MgCl₂) can lead to the formation of magnesium tungsten oxide (MgWO₄), which appears to be more easily leachable than CaWO₄. Experimental tests of the reaction of scheelite with MgCl₂ appear to validate the thermodynamic predictions with satisfactory process kinetics at temperatures from 725 to 775 °C. Full article

Recently, a variety of nephrite containing localized pink mineral aggregates has emerged on the market, which is sometimes referred to as “peach blossom jade” by some merchants. Currently, there is limited research on this type of nephrite containing pink minerals, and its detailed mineral composition characteristics and coloration mechanisms remain unclear. In this study, four samples of nephrite containing pink minerals were systematically investigated using conventional gemological tests, as well as modern analytical techniques such as X-ray powder diffraction (XRD), infrared spectroscopy (IR), laser Raman spectroscopy, ultraviolet–visible (UV-Vis) absorption spectroscopy, electron probe microanalysis (EPMA), and X-ray fluorescence spectroscopy (XRF). These techniques were employed to elucidate the mineral composition, chemical composition, spectroscopic features, and coloration origins of the samples. The results indicate that the primary mineral constituent of the samples is tremolite, with accessory minerals including zoisite, muscovite, orthoclase, andesine, diopside, and prehnite. The major chemical components of the samples are SiO₂, CaO, and MgO, along with minor amounts of Al₂O₃, K₂O, and FeO_T. The overall green hue of the samples is positively correlated with Fe content. The pink mineral present in the samples is predominantly Mn-bearing zoisite, and the pink coloration of zoisite is primarily attributed to the energy level transitions of Mn²⁺ at approximately 540 nm and 440 nm. Full article

Molybdenite Re–Os and zircon U–Pb isotopic data are first obtained from the stockwork and disseminated-style gold-bearing ores and the fine-grained granite hosting these ores in the Xiawolong gold mine, respectively, which is located within the Muping–Rushan gold metallogenic belt, eastern Jiaodong Peninsula, so as to illustrate the genesis of gold mineralization and its implication for exploration. Four molybdenite samples yield a well-defined Re–Os isochron age of 118.4 ± 2.5 Ma (2σ), which is identical to the weighted average Re–Os model age of 118 ± 1.7 Ma (2σ). Integration of the new geochronologic data with those reported recently from the other gold mines in the Muping–Rushan gold metallogenic belt suggests that a discrete gold event occurred in Xiawolong ca. 4 m.y. older than that for the other gold mineralization at ca. 114 Ma in eastern Jiaodong. In addition, two fine-grained granite samples, measured using the LA-ICP-MS zircon U–Pb method, produce the first precise ages of 118 ± 2 to 117 ± 2 Ma (2σ), identical to the molybdenite Re–Os ages, within the margin of error and obtained in this study. The fine-grained granite has a similar lithology and emplacement age as those of the medium-grained monzogranite consisting of the marginal facies of the Sanfoshan batholith, and is considered to be the crystallization products of Sanfoshan granitic magma in the late stage. Combined with the previous S-Pb-D-O isotope, fluid inclusion and geological studies, which suggest that the ore-forming fluid of Xiawolong gold mineralization is from magmatic water, and the identification that the magnetite coexists with the gold-bearing pyrite and molybdenite in the gold ores, which indicates a high oxygen fugacity (fO₂) of both the magma and resultant hydrothermal fluids, it is logical to infer that the Xiawolong gold deposit is genetically in relation to the Sanfoshan granitic magmatism, which is high in fO₂ and rich in Au at the magmatic–hydrothermal transition stage, and the change in fO₂ mostly likely makes a significant contribution to the precipitation of Au. This result reveals that the late-stage granitic magma with high fO₂, which is crystallized into the fine-grained granite, probably is also rich in Au, except the W–Mo–Cu–Zn–U–Be–Li–Nb–Ta–Sn–Bi-elements. Therefore, based on the extensional tectonic regime for the early Cretaceous Jiaodong gold deposits, we propose that gold exploration in the Jiaodong should not only focus on the fault-hosted Au but also on the fine-grained granite-hosted Au around the apical portions of the late Early Cretaceous small-granitic intrusions with high fO₂. This model could also be important for prospecting in other gold ore districts, which have a similar tectonic setting. Full article

The early Permian mafic–ultramafic intrusion-related Cu-Ni mineralization in Northern Tianshan offers valuable insights into the nature of the mantle beneath the Central Asian Orogenic Belt (CAOB) and enhances the understanding of magmatic sulfide mineralization processes in orogenic environments. The Yunhai intrusion, rich in Cu-Ni sulfides, marks a significant advancement for Cu-Ni exploration in the covered regions of the western Jueluotag orogenic belt in Northern Tianshan. This intrusion is well-differentiated, featuring a lithological assemblage of olivine pyroxenite, hornblende pyroxenite, gabbro, and diorite, and contains about 50 kilotons of sulfides with average grades of 0.44 wt% Ni and 0.62 wt% Cu. Sulfide mineralization occurs predominantly as concordant layers or lenses of sparsely and densely disseminated sulfides within the olivine pyroxenite and hornblende pyroxenite. In situ zircon U-Pb dating for the Yunhai intrusion indicates crystallization ages between 288 ± 1 and 284 ± 1 Ma, aligning with several Cu-Ni mineralization-associated mafic–ultramafic intrusions in Northern Tianshan. Samples from the Yunhai intrusion exhibit enrichment in light rare earth elements (LREE), distinct negative Nb and Ta anomalies, positive ε_Nd(t) values ranging from 2.75 to 6.56, low initial (⁸⁷Sr/⁸⁶Sr)_i ratios between 0.7034 and 0.7053, and positive ε_Hf(t) values from 9.27 to 15.9. These characteristics, coupled with low Ce/Pb (0.77–6.55) and Nb/U (5.47–12.0) ratios and high Ti/Zr values (38.7–102), suggest very restricted amounts (ca. 5%) of crustal assimilation. The high Rb/Y (0.35–4.27) and Th/Zr (0.01–0.03) ratios and low Sm/Yb (1.47–2.32) and La/Yb (3.10–7.52) ratios imply that the primary magma of the Yunhai intrusion likely originated from 2%–10% partial melting of weak slab fluids–metasomatized subcontinental lithospheric mantle (peridotite with 2% spinel and/or 1% garnet) in a post-collisional environment. The ΣPGE levels in the Yunhai rocks and sulfide-bearing ores range from 0.50 to 54.4 ppb, which are lower compared to PGE-undepleted Ni-Cu sulfide deposits. This PGE depletion in the Yunhai intrusion’s parental magma may have been caused by early sulfide segregation from the primary magma at depth due to the high Cu/Pd ratios (43.5 × 10³ to 2353 × 10³) of all samples. The fractional crystallization of minerals such as olivine and pyroxene might be a critical factor in provoking significant sulfide segregation at shallower levels, leading to the extensive disseminated Cu-Ni mineralization at Yunhai. These characteristics are similar to those of typical deposits in the eastern section of the Jueluotage orogenic belt (JLOB), which may indicate that the western and eastern sections of the belt have the same ore-forming potential. Full article

The Biggenden gold-bearing Fe skarn deposit in southeast Queensland, Australia, is a calcic magnetite skarn that has been mined for Fe and gold (from the upper portion of the deposit). Skarn has replaced volcanic and sedimentary rocks of the Early Permian Gympie Group, which formed in different tectonic settings, including island arc, back arc, and mid-ocean ridge. This group has experienced a hornblende-hornfels grade of contact metamorphism due to the intrusion of the Late Triassic Degilbo Granite. The intrusion is a mildly oxidized I-type monzogranite that has geochemical characteristics intermediate between those of granitoids typically associated with Fe-Cu-Au and Sn-W-Mo skarn deposits. The skarn mineralogy indicates that there was an evolution from prograde to various retrograde assemblages. Prograde garnet (Adr_11-99Grs_1-78Alm_0-8Sps_0-11), clinopyroxene (Di_30-92Hd_7-65Jo_0-9), magnetite, and scapolite formed initially. Epidote and Cl-bearing amphibole (mainly ferropargasite) were the early retrograde minerals, followed by chlorite, calcite, actinolite, quartz, and sulfides. Late-stage retrograde reactions are indicated by the development of nontronite, calcite, and quartz. Gold is mainly associated with sulfide minerals in the retrograde sulfide stage. The fluids in equilibrium with the ore-stage calcites had δ¹³C and δ¹⁸O values that indicate deposition from magmatically derived fluids. The calculated δ¹⁸O values of the fluids in equilibrium with the skarn magnetite also suggest a magmatic origin. However, the fluids in equilibrium with epidote were a mixture of magmatic and meteoric water, and the fluids that deposited chlorite were at least partly meteoric. δD values for the retrograde amphibole and epidote fall within the common range for magmatic water. Late-stage chlorite was deposited from metasomatic fluids depleted in deuterium (D), implying a meteoric water origin. Sulfur isotopic compositions of the Biggenden sulfides are similar to other skarn deposits worldwide and indicate that sulfur was most probably derived from a magmatic source. Based on the strontium (⁸⁷Sr/⁸⁶Sr) and lead (²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb) isotope ratios, the volcanic and sedimentary rocks of the Gympie Group may have contributed part of the metals to the hydrothermal fluids. Lead isotope data are also consistent with a close age relationship between the mineralization at Biggenden and the crystallization of the Degilbo Granite. Microthermometric analysis indicates that there is an overall decrease in fluid temperature and salinity from the prograde skarn to retrograde alterations. Fluid inclusions in prograde skarn calcite and garnet yield homogenization temperatures of 500 to 600 °C and have salinities up to 45 equivalent wt % NaCl. Fluid inclusions in quartz and calcite from the retrograde sulfide-stage homogenized between 280 and 360 °C and have lower salinities (5–15 equivalent wt % NaCl). In a favored genetic model, hydrothermal fluids originated from the Degilbo Granite at depth and migrated through the shear zone, intrusive contact, and permeable Gympie Group rocks and leached extra Fe and Ca and deposited magnetite upon reaction with the adjacent marble and basalt. Full article