Search Results (9)

Globally, most skarn deposits show a direct relationship with magmatic activity, indicating a genetic link between the geochemical composition of causative plutons and the metal content of associated skarns. Therefore, this study investigated the Early–Middle Eocene plutonic rocks and their relationship with Fe-Zn skarn deposits in the Esendemirtepe-Koçak and Horoz areas of south-central Türkiye. Despite the regional significance, previous studies have not adequately addressed the petrogenetic evolution of these intrusions and the geochemical characteristics of the related skarns. In particular, the fluid-aided mobility of elements at the contact between the causative plutons and the volcano-sedimentary country rocks remains poorly understood. Therefore, in this study, field studies, petrographic and mineralogical analysis, and whole-rock geochemical analysis were conducted to investigate the genetic link between the plutonic rocks and the skarn deposits. Field studies reveal that the skarn zones are within volcano-sedimentary sequences and marble-schist units intruded by four distinct plutonic bodies: (1) Esendemirtepe diorite, (2) Koçak diorite, (3) Horoz granodiorite, and (4) Çifteköy monzogabbro. These rocks exhibit calc-alkaline, I-type, and metaluminous signatures, except for the Çifteköy monzogabbro, which shows I-type, tholeiitic, and alkaline characteristics. All the plutonic rocks associated with the skarn formation display steep LREE-enriched REE patterns with minor positive Eu anomalies (Eu/Eu* = 0.98–1.35), suggesting a subduction-related volcanic arc setting similar to other granitoids in the Ulukışla Basin. The Horoz skarn exhibits both endoskarn and exoskarn features, while the Esendemirtepe-Koçak deposit is characterized by typical exoskarn features. Dominant ore minerals in both skarn deposits include magnetite, hematite, sphalerite, chalcopyrite, and pyrite, with minor arsenopyrite, galena, and cobaltite. The mineral composition of the skarn also shows the dominance of Na-rich and Mg-rich minerals in both locations. The geochemical compositions of the I-type, metaluminous Esendemirtepe-Koçak, and Horoz plutonic rocks are compatible with Fe-Zn skarn type deposits based on the moderate MgO (0.36–4.44 wt.%) and K₂O (1.38–7.99 wt.%), and Rb/Zr and Sr/Zr ratios. They also show typical volcanic arc features, and the variation in various trace element concentrations shows similarity with Fe-Zn skarn type granitoids. These findings support a strong genetic relationship between the mineralization and the geochemical and mineralogical characteristics of the associated plutonic rocks. Full article

A unique Li–Na metasomatic rock from Iwagi Islet in Southwest (SW) Japan is an episyenite that contains new Li-rich minerals, including sugilite, katayamalite, murakamiite, and ferro-ferri-holmquistite. We present petrographical, mineralogical, and geochronological data for the protoliths and episyenite. We classified the metasomatic rocks based on the mineral assemblages, from the protolith biotite granite to albitized granite, quartz albitite, hedenbergite albitite, aegirine albitite, sugilite albitite, and katayamalite albitite. The protolith of hedenbergite albitites may have been metasomatic granite that has been subjected to calcic skarnization. Albitites are formed related to fractures and shear zones that focused the fluid flow and metasomatism. Extensive albitization and formation of abundant Li minerals requires involvement of external Li-Na-Cl-rich fluids, which might be related to deep high-temperature Arima-like brines derived from dehydration of the subducted oceanic slab. Formation of the albitites began with quartz dissolution and vug formation, and record interface-coupled dissolution–reprecipitation processes in an open system. The ⁴⁰Ar/³⁹Ar age of 91.5 ± 0.3 Ma determined for the katayamalite is slightly younger than the protolith zircon U–Pb age of 93.5 ± 1.7 Ma (Turonian), reasonably explaining the timing of Li–Na metasomatism after the petrogenesis of host granites. Full article

The Fe skarn and vein-type Cu mineralization types are common in the Eastern Taurus Mountains. This study aims to determine the U-Pb geochronology of garnets of varying sizes within the skarn zone developed at the quartz diorite–marble contact zone in Ayazpınar, Pertek District, Tunceli Province, Turkey. Additionally, this study aims to determine the age of the skarnization and the types of inclusion minerals in the garnets. Faulting and magma emplacement along the thrust plane caused mineralization in the Eastern Taurus Mountains, especially at the marble and quartz diorite contact zone between the cities of Elazığ and Tunceli. The greenish garnets found in the Ayazpınar deposit are characteristic of distal skarns, while red or brown Pertek garnets are observed in the proximal skarns. The garnets typically feature a core–rim texture. The cores of the garnet crystals are large, reddish in color, and have a high REE (Ce, Pr) content. Moreover, the cores have higher Fe and lower Al ratios, alongside higher La, Ce, and Pr contents, than the rims. We propose that the compositional differences between the rims and the cores reflect the transition from oxidized REE- and Fe3+-rich liquids to liquids with lower REE and Fe3+ contents, producing the differences in the garnet colors. Green garnets show lower REE contents than brown garnets with Fe-rich cores. The skarn under study includes the following successively formed zones: diorite → epidote skarn → garnet–magnetite → pyrite–garnet–magnetite → calcite carbonate. Diopside, magnetite, and hematite, including small grains, are surrounded or enveloped by garnets. The U-Pb age of the mineralization is 74.1 ± 5 Ma, indicating that the mineralization occurred concurrently with the intrusion settlement. Full article

Demantoid is the green variety of andradite [Ca₃Fe₂(SiO₄)₃], an exceptionally rare and precious gemstone worldwide. In recent years, a small amount of gem-quality demantoid has been found in Pakistan. This research focuses on nine demantoids sourced from Muslim Bagh, Baluchistan, Pakistan, presenting a comprehensive analysis of the spectral characteristics and inclusions of Pakistani demantoid using classical gemological methods, energy dispersive X-ray fluorescence (EDXRF) chemical analyses, Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, and ultraviolet and visible (UV-vis) spectroscopy. The results show that the content of Cr and V in most samples is lower than the detection line of EDXRF, with only one sample containing a Cr₂O₃ content of 0.032%. The extremely low Cr content sets Pakistani demantoid apart from demantoid of the serpentinite type found in other regions. Notably, the UV-vis spectrum reveals characteristic absorption at 443 nm due to Fe³⁺, while a further contribution from Cr³⁺ would be highly likely, and weak absorption at 550 nm caused by Fe³⁺. This suggests that iron (Fe) is the primary chromogenic element of Pakistani demantoid, but the role of Cr³⁺ cannot be ignored. The FTIR spectrum of Pakistani demantoid displays the absorption peaks associated with [SiO₄]⁴⁻ groups at 937 cm⁻¹, 848 cm⁻¹, and 817 cm⁻¹, while the absorption peaks resulting from trivalent cations appear at 481 cm⁻¹ and 442 cm⁻¹, which are the characteristic FTIR spectra of demantoid. Raman spectroscopy further reveals absorption peaks are displayed near 994 cm⁻¹, 843 cm⁻¹, 818 cm⁻¹, associated with (Si–O)_Str vibrations (Si–O stretching vibration), and absorption peaks are displayed near 350 cm⁻¹ and 310 cm⁻¹, related to the rotation of SiO₄–R(SiO₄)⁴⁻, and the peaks near 514 cm⁻¹ and 494 cm⁻¹ are related to (Si–O)_bend vibrations (Si–O bending vibration). Additionally, related absorption peaks near 168 cm⁻¹ are attributed to the translation of SiO₄–T(SiO₄)⁴⁻, and absorption peaks near 234 cm⁻¹ are associated with the translation of X²⁺–T(X²⁺) (X²⁺ represents divalent ions). The common dark opaque inclusions found in Pakistani demantoid consist of a combination of magnetite and hematite. Additionally, some samples of Pakistani demantoid display inclusions of calcite. This unique combination of inclusions differentiates Pakistani demantoid from demantoids sourced from other regions. It signifies that Pakistani demantoid has a distinctive geological origin resulting from the interplay of serpentinization and skarnization processes. This geological formation distinguishes it from demantoids solely hosted in serpentinite or skarn environments in other origins. The identification of these characteristics holds significant importance for accurately determining the origin of Pakistani demantoid. Full article

The Caoziwa Pb–Zn deposit is one of the typical vein-type Pb–Zn deposits in the western part of the Tengchong block. Due to limited research, the genesis of these deposits is unknown. In this study, the sulfur isotopic and trace elemental compositions of sulfides from the Caoziwa Pb–Zn deposit were analyzed to trace the sources of ore-forming materials, and to reveal the genetic type of this deposit. The results show that abundant Co, Ni, As, and Se, and less Cu, Zn, Ag, Cd, Sn, Sb, Te, Pb, and Bi could enter pyrite by isomorphic substitution. Elemental Mn, Fe, Cd, Co, and Ni could substitute Zn to enter sphalerite, while the contents of Ag, Sn, and Sb are mainly controlled by the Pb-rich inclusions in sphalerite. Elemental Bi, Sb, Cd, Sn, Ag, and Tl mainly enter the galena grains via an isomorphic substitution mechanism of (Bi, Sb)³⁺ + (Cd, Sn)²⁺ + (Ag, Tl)⁺ ↔ 2Pb²⁺. Both sulfur isotopic compositions and trace elemental compositions indicate that the ore-forming materials and fluids of the Caoziwa Pb–Zn deposit mainly originate from magmatic hydrothermal fluid related to Paleocene granitic magmatism. Combined with the geological facts that some skarnizations developed in the northern part of the ore field near the Paleocene granite, the Caoziwa Pb–Zn deposit is suggested to be a magmatic hydrothermal vein-type deposit that probably belongs to a distal part of a skarn mineralization system developed by the intrusion of Paleocene granitic magmatism in the western part of the Tengchong block. Full article

The Changpo–Tongkeng tin polymetallic deposit in Dachang, Guangxi, is a world-class, superlarge, polymetallic tin deposit consisting of lower skarn zinc–copper ore bodies and upper tin polymetallic ore bodies. Garnet is the main gangue mineral in the skarn zinc–copper ore bodies and has a granular texture. Based on hand specimens and microscopic observations, the existing garnet can be divided into two generations: an early generation (Grt I) and a late generation (Grt II). The results of electron probe microanalysis (EPMA) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) in situ microanalysis show that the contents of SiO₂ and CaO in the garnets from the two generations present limited variations, while the FeO^T and Al₂O₃ contents vary significantly, indicating the grossular–andradite solid solution series (Gro_29–82And_12–69). Compared with Grt I (Gro₇₂And₂₅), Grt II (Gro₃₉And₅₉) is Fe-enriched and oscillatory zoning is developed. The total rare earth element (REE) contents in the two generations of garnet are relatively low, showing light rare earth element (LREE) depletion and heavy rare earth element (HREE) enrichment patterns. Grt II has higher REE content than Grt I and exhibits significant negative Eu anomalies (δEu = 0.18–0.44). The contents and variation characteristics of the major and trace elements in the two generations of garnet suggest that there were variable redox conditions and water/rock ratios in the hydrothermal system during the crystallization process of garnet. In the early stage, skarnization was in a relatively closed and low-oxygen fugacity system, with hydrothermal diffusion metasomatism being dominant, forming homogeneous Grt I lacking well-developed zoning. In the late stage of skarnization, the oxygen fugacity of the ore-forming fluids increased, with infiltration metasomatism being dominant, forming Grt II with well-developed oscillatory zoning. The contents of Sn, As, W, In, and Ge in the garnets are relatively high and increase with the proportion of andradite. Sn in zinc–copper ore bodies mainly exists in the form of isomorphic substitution in garnet, which may be the main reason for the lack of tin ore bodies during the skarn stage. This paper compares the trace element contents in garnets from domestic skarn deposits. The results indicate that the Sn content and δEu in garnet can be used to evaluate the tin-forming potential of skarn deposits. Full article

The Kamioka mine, located in Gifu Prefecture in Japan, is famous for the large water Cherenkov detector system, the Super-Kamiokande. The Kamioka skarn-type Pb–Zn deposits are formed in crystalline limestone and are replaced by skarn minerals within the Hida metamorphic rocks. The Kamioka deposits mainly consist of the Tochibora, Maruyama, and Mozumi deposits. The present study focuses on the ore-forming hydrothermal fluid activity in the Kamioka deposits and the peripheral exploration area based on the carbon and oxygen isotope ratios of calcite and rare earth element (REE) analyses. The carbon and oxygen isotope ratios of crystalline limestone (as the host rock) are not homogeneous, and depending on the degree of hydrothermal activity, they decreased to various degrees because of the reaction with the ore fluids. Thus, the carbon and oxygen isotope ratios of crystalline limestone can be used as an indicator of the influence of the hydrothermal fluids for the ore mineralization. The REE contents in the ores of igneous origin are one order of magnitude higher than the limestone origin. Further, depending on the formation temperatures, calcites precipitated during ore mineralization have a stable carbon isotope ratio and a widely varying oxygen isotope ratios. The Kamioka district fracture system is likely a major control factor on ore mineralization from hydrothermal activity. In addition, the skarnization-related ore-forming fluids are mostly meteoric in origin, confirming the conclusions from previous studies. Full article

The Hutouya polymetallic skarn deposit lies in the Qimantagh area of the East Kunlun Orogenic Belt, NW China. Skarnization and mineralization at the deposit are closely associated with contemporary felsic intrusions. In this paper, zircon U-Pb ages and zircon Hf isotope as well as whole-rock geochemical and whole-rock Sr-Nd isotope data are reported for intrusive rocks and crystal tuff of the Elashan Formation in the Hutouya area. Moreover, Re-Os ages and S-Pb isotopes are also reported for the ore minerals in the Hutouya deposit. The Zircon laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) U-Pb age of granodiorite and Re-Os isochron age of molybdenite suggest that mineralizations occurred at ca. 227 Ma and that the granodiorite and molybdenite are closely related petrogenetically. All the granitoids in the Hutouya deposit are high-K calc-alkaline and metaluminous to weakly peraluminous I-type granitoids. Among them, the ore-forming granitoids were derived by the mixing of crust-derived (either juvenile or ancient mature lower crust) and mantle-derived magmas, whereas the non-ore-related granite porphyry was generated by the partial melting of a single ancient mature lower crust. The magmas of all the granitoids underwent extensive fractionation–crystallization during the process of rising and emplacement. The sulfur of the analyzed samples from the northern and middle zone of Hutouya deposit (including No. II, III, IV, and VI ore belts) belongs to deep magmatic sulfur, while the sulfur of samples from the southern zone of Hutouya deposit (No. VII ore belt) includes not only deep magmatic sulfur but also a contribution of strata sulfur. All the ore mineral samples in the Hutouya deposit have similar Pb compositions that are consistently derived from a mixed source of upper crust and mantle. Tectonic discrimination diagrams indicate a post-collisional setting for all granitic rocks of the Hutouya skarn deposit, which is therefore considered a product of a the post-collision extensional system and is consistent with other porphyry-skarn deposits within the East Kunlun Orogenic Belt. Full article

Skarn Sn-polymetallic deposits, located in the southern Great Khingan Range, can be divided into Sn–Fe and Sn–Pb–Zn deposits. By systematically studying the geochemical characteristics of source granitoid and deposits, the ore-forming mechanisms were established, and the differences in ore-forming processes between Sn–Fe and Sn–Pb–Zn deposits are discussed. The main findings are as follows: (1) these two deposits were formed in the Late-Yanshanian period; (2) the source granitoid evolved at an early stage in a reducing environment, while the oxygen fugacity increased at a late stage through the influence of a deep-seated fault; (3) fine-grained syenogranite from Dashishan showed a higher degree of evolution than the syenogranite from Damogutu; (4) the Damogutu Sn–Fe and Dashishan Sn–Pb–Zn deposits shared a source of ore-forming fluid, and Fe, Sn, Pb, and Zn all derived from Late-Yanshanian granitoids; and (5) the ore-forming fluid experienced a continuous evolution process from the magmatic to hydrothermal stage, and the magmatic–hydrothermal transitional fluid played a very important role in skarnization and mineralization. Full article