Journal of Geochemical Exploration最新文献

{"title":"Growth history of garnet from the Dulong Sn-Zn-In polymetallic deposit: Geochemical and UPb age constraints and their metallogenic significance","authors":"Shiyu Liu ,&nbsp;Lin Ye ,&nbsp;Yuping Liu ,&nbsp;Hansheng Long ,&nbsp;Chen Wei ,&nbsp;Zhenzhong Xiang","doi":"10.1016/j.gexplo.2025.107699","DOIUrl":"10.1016/j.gexplo.2025.107699","url":null,"abstract":"<div><div>The Dulong skarn-type tin‑zinc‑indium (Sn-Zn-In) polymetallic deposit contains 5.5 million tonnes (Mt) Zn, 0.4 Mt. Sn, and 7 kt In. It is the third-largest cassiterite-sulfide deposit in China, and is located in the Laojunshan W<img>Sn polymetallic orefield on the southern margin of the Youjiang basin. While it is widely accepted that the Sn<img>Zn polymetallic mineralization is closely linked to the Yanshanian granites, the precise timing of skarn formation and its relationship to the granite magmatism has remained unclear due to a lack of reliable geochronological data. This has also hindered a comprehensive understanding of the ore-forming processes at Dulong. Garnet is a widely distributed major skarn mineral at Dulong. Field and laboratory studies have revealed two distinct garnet types (Grt I and II): Grt I is located near the main ore-controlling fault (F_M), while Grt II is found near a shallow granite porphyry in eastern Dulong. Both types of garnet exhibit a core-mantle-rim structure, indicating that they were formed by multistage fluid metasomatism. In this study, in situ LA-ICP-MS U<img>Pb dating was carried out on both types of garnet. Additionally, major and trace element analyses of the garnet and its coexisting pyroxene were conducted to examine the formation and evolution of the skarn. The results show that Grt I has generally higher ΣREE, Y, HFSE, and U concentrations, suggesting that it was formed under low W/R ratios in a relatively reducing environment. The garnet contains a grossular core (Grt Ia), andradite mantle (Grt Ib), and a grossular-andradite solid solution rim (Grt Ic), reflecting an initial increase and then decrease in the W/R ratio of the magmatic-hydrothermal system. During this process, the fluid pH was neutral-acidic, and the oxygen fugacity (<em>f</em>O₂) first decreased and then increased. In contrast, Grt II has lower ΣREE, Y, HFSE, and U concentrations, indicating its formation under higher W/R ratios in a more oxidizing environment. This garnet has also a grossular core (Grt IIa), andradite mantle (Grt IIb), and a grossular-andradite solid solution rim (Grt IIc). This reflects a system where the W/R ratio first increased and then decreased. The fluid pH shifted from neutral-acidic to acidic, and the <em>f</em>O₂ increased gradually. LA-ICP-MS U<img>Pb dating yielded 93 ± 2.4 Ma to 90.9 ± 0.7 Ma for Grt I and 80.4 ± 6.6 Ma for Grt II. Comparing these results with published data on the Cretaceous regional magmatism and Sn-polymetallic mineralization, we conclude that the magmatic-hydrothermal activity that formed Grt I and Grt II was associated with the concealed phase-II and phase-III Laojunshan granite, respectively. This study highlights the opportunities offered by garnet U<img>Pb dating for elucidating the formation age and ore genesis of Sn<img>Zn skarn systems.</div></div>","PeriodicalId":16336,"journal":{"name":"Journal of Geochemical Exploration","volume":"271 ","pages":"Article 107699"},"PeriodicalIF":3.4,"publicationDate":"2025-01-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143224580","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Multistage hydrothermal fluids evolution and precipitation mechanism of the Hongshi Cu deposit in Eastern Tianshan, NW China: Insights from cathodoluminescence, fluid inclusions, trace elements of quartz and in situ S isotopes of sulfides","authors":"Wen-Xin Gu,&nbsp;Yin-Hong Wang,&nbsp;Jian-Ping Wang,&nbsp;Kang Wang,&nbsp;Wei Zhang,&nbsp;Hui Zhang","doi":"10.1016/j.gexplo.2025.107700","DOIUrl":"10.1016/j.gexplo.2025.107700","url":null,"abstract":"<div><div>The Hongshi Cu deposit is located in the southeastern Kalatag district in Eastern Tianshan, northwest China. The Cu mineralization is mainly hosted by volcaniclastic rocks of the Daliugou Formation and structurally controlled by fracture zones. Comprehensive analyses of fluid inclusions, in situ sulfur isotopes, and trace elements in quartz were employed to unravel the evolution of ore fluids, identify the sources of ore-forming components, and refine the understanding of ore genesis. The ore formation at Hongshi could be divided into three hydrothermal stages, consisting of quartz-pyrite (stage I), quartz-sulfide (stage II), and quartz-calcite (stage III). Five hydrothermal quartz generations have been identified through cathodoluminescence (CL) imaging, including Q1–1 and Q1–2 from stage I, Q2–1 and Q2–2 from stage II, and Q3 from stage III. Aqueous fluid inclusions from stage I exhibit relatively high temperatures (208–313 °C) and moderate salinities (3.1–9.3 wt% NaCl equiv.). Microthermobarometry results confine the quartz−sulfide veins to temperatures ranging from 151 to 243 °C and salinities of 1.9–7.2 wt% NaCl equiv. Quartz−calcite veins formed from low−temperature and low−salinity fluids, with homogenization temperatures and salinities of 123–168 °C and 0.53–3.23 wt% NaCl equiv., respectively. Based on in situ trace element analysis of the five quartz generations, the Ti concentrations for the ore fluids are 33.20–129.00 ppm (mea<em>n</em> = 79.88 ppm), 5.12–27.30 ppm (mean = 16.54 ppm), 1.01–17.20 ppm (mea<em>n</em> = 6.96 ppm), 1.48–9.98 ppm (mea<em>n</em> = 5.15 ppm), and 14.70–52.70 ppm (mean = 24.19 ppm). The Al concentrations for the ore fluids are 2058–4889 ppm (mean = 3562 ppm), 150–1916 ppm (mea<em>n</em> = 1109 ppm), 133–2470 ppm (mean = 926 ppm), 32–174 ppm (mean = 82 ppm), and 686–2296 ppm (mean = 1555 ppm). The trace element data and trends across the five generations of quartz are optimally interpreted as indicative of magmatically derived ore fluids that were subsequently diluted by meteoric water, resulting in mineralization. Fluid mixing is regarded as the primary mechanism responsible for Cu precipitation at Hongshi. Sulfides of pyrite, chalcopyrite, and sphalerite yield δ³⁴S_V-CDT values from −0.21 to +6.21 ‰, with no discernible systematic variations among the various paragenetic stages. The data presented herein support a magmatic origin for the Hongshi deposit. This study clarifies the role of fluid dilution in initiating Cu deposition and offers insights into the genesis of Cu-polymetallic epithermal deposits within the Eastern Tianshan region.</div></div>","PeriodicalId":16336,"journal":{"name":"Journal of Geochemical Exploration","volume":"271 ","pages":"Article 107700"},"PeriodicalIF":3.4,"publicationDate":"2025-01-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143182831","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Geochemical and mineralogical characterization of weathered granite hosting secondary uranium mineralization: A case study from the eastern part of the Reguibat shield, Northern Mauritania","authors":"Brahim Salem-Vall ,&nbsp;Akinade Shadrach Olatunji ,&nbsp;Ahmed Hamoud","doi":"10.1016/j.gexplo.2025.107698","DOIUrl":"10.1016/j.gexplo.2025.107698","url":null,"abstract":"<div><div>The eastern part of the Reguibat shield hosts significant uranium deposits in Northern Mauritania. Weathered granite identified as the uranium host rock. The study area located at the extreme eastern part of the Requibat shield hosts uraniferous granites form part of neobirimian ensemble belonging to yetti complex. The present investigation concerns the petrographic, geochemical and mineralogical characterization and secondary uranium mineralization genesis. Analyses were conducted using EPMA-EDS and ICP-MS. The study area is made up of two uraniferous granites, coarse-grained porphyritic pink with a mylonitic texture and medium-grained grey granite. Paragenesis consists mainly of Qtz + K-F + Pl + Bt + Ap + Sph + Zr + Amp + Cal + Cls ± granet ± Barite ± Ilmenite. Both granites represent monzogranite weakly peraluminous and shoshonitic. REE signature illustrates a negative anomaly of Eu (Eu/Eu* = 0.1 and 0.18 average), and slight fractionation of LREE from HREE remarkable particularly for grey granite ((La/Yb)_<em>N</em> = 5.37–10.27). Multielement spectra show significant enrichments in U, Ta, and Pb, depletions in Ba, Nd, and Eu of pink granite. However, grey granite highlights significant enrichments in U, and Pb, while showing depletions in Nb, Eu, Zr, and Ba.</div><div>Geochemistry of the rocks highlights the emergence of the processes of fractional crystallization. Petrogenetic indicator K/Rb ratio suggests rock moderately evolved derived from fractionated magma with potential involvement of crustal material. Rock generated in deep sources of the lower crust or the upper mantle by partial melting. Grey granite similar to A-type however pink granite is S-I-type fractionated to nofractionated granite. Tectonic diagrams placed confirm <em>syn</em>-collisional pink granite and grey granite as within plate granite setting.</div><div>Both granites exhibit low CIA and PIA indicting low to moderate weathered rocks. Uranium bearing minerals (Carnotite and Tyuyamunite) occur as small grains size (∼ 10 μm) associated with weathering products filling voids and fractures of the granitoids. The presence of calcite, Celestine, fluorite are the indictors of uranium mineralization formation within evaporitic context in dry and low-temperature conditions.</div></div>","PeriodicalId":16336,"journal":{"name":"Journal of Geochemical Exploration","volume":"271 ","pages":"Article 107698"},"PeriodicalIF":3.4,"publicationDate":"2025-01-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143182835","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"OreGenes: An optimized neural network tool for ore deposits classification based on gold grain geochemistry","authors":"Angel A. Verbel ,&nbsp;Maria Emilia Schutesky ,&nbsp;Daniel D. Gregory ,&nbsp;Arturo Verbel","doi":"10.1016/j.gexplo.2025.107701","DOIUrl":"10.1016/j.gexplo.2025.107701","url":null,"abstract":"<div><div>Assessment of gold grains and their characterization in abundance and morphology can be used as a discriminatory tool for mineral deposits. However, the processes that lead to the formation of an ore deposit are multiscale and nonlinear. As a result, the elemental compositions recorded in gold grains during mineralization seem mostly irregular and unpredictable. Here, we took advantage of the capabilities of neural networks, computational models composed of layers of interconnected nodes. After training, it processed data through nonlinear transformations that approximate a complex natural function. It enabled the recognition of complex patterns and relationships in chemical variability observed in gold and relating it to the mineral system that formed the mineral, allowing for predictive modeling. This was achieved by using published trace element data in gold of four types of gold deposits (i.e., Orogenic, VMS, porphyry, and epithermal) from 47 different localities, obtained by laser ablation-inductively coupled plasma-mass spectrometry (LA- ICP-MS). The model was optimized by training five different architectures on the most influential elements, determined by principal component analysis (PCA). As a result, two hidden layers with ten neurons (series of nodes that process and transmit information) each were found to be the best architecture for using trace elements as predictors of the type of deposit that formed a natural gold grain. In order to encourage the use of the findings made in this paper, we introduce OreGenes, an app developed in Matlab2023b based on the best-obtained model. It allows any user who possesses compatible data the ability to import and process it to obtain a prediction with an average accuracy level of 88.9 % confidence to assess the mineral deposit type that an unknown gold grain came from, which grants the user the ability to have a powerful tool for exploration or research.</div></div>","PeriodicalId":16336,"journal":{"name":"Journal of Geochemical Exploration","volume":"271 ","pages":"Article 107701"},"PeriodicalIF":3.4,"publicationDate":"2025-01-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143182306","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Controls of Neoproterozoic magmatism on NiCu sulfide mineralization in the Jiangnan Orogenic Belt, South China: An example from the newly discovered Sibao NiCu sulfide deposit","authors":"Luqing Zhou ,&nbsp;Yonghua Cao ,&nbsp;Matthew J. Brzozowski ,&nbsp;Jianqing Lai ,&nbsp;Xiang-hua Liu ,&nbsp;Guiang Hu ,&nbsp;Zhongyu Zhang ,&nbsp;Joan Carles Melgarejo","doi":"10.1016/j.gexplo.2025.107694","DOIUrl":"10.1016/j.gexplo.2025.107694","url":null,"abstract":"<div><div>The newly discovered Sibao Ni<img>Cu sulfide deposit, situated in the western part of the Neoproterozoic Jiangnan Orogenic Belt (JOB), may be representative of Ni<img>Cu sulfide deposits that formed in convergent margins during the Neoproterozoic. The formation of this deposit may also have been influenced by activity of the mantle plume associated with the Neoproterozoic fragmentation of Rodinia. These characteristics make the Sibao deposit unique, because most convergent margin-related Ni<img>Cu sulfide deposits in China are of Paleozoic to early Mesozoic age and are typically not associated with mantle plume activity. Despite its geological significance, a paucity of research has been carried out on the Sibao deposit; the emplacement setting and mineralizing processes that operated to form this deposit, therefore, remain unclear. To address these ambiguities, we characterized the geochronological, geochemical, and isotopic characteristics of this deposit, focusing on zircon U<img>Pb dating, whole-rock trace-element chemistry and Sr<img>Nd isotopes, in situ S isotopes of sulfides, and trace-element chemistry of zircon and apatite. The host rocks to the Sibao deposit crystallized at ca. 837.7 ± 3.5 Ma, synchronous with ocean–continent subduction during formation of the JOB, but occurring prior to the mantle superplume event associated with the breakup of Rodinia (ca. 825–800 Ma). The systematically negative Nb<img>Ta anomalies and εNd(t) values (−5.6 to −2.2) suggest that the magma parental to the Sibao intrusion originated from metasomatized, enriched sub-continental lithospheric mantle (SCLM). This suggest that the Sibao deposit was emplaced in an Andean-style continental convergent margin, without any mantle plume contributions. Modeling of REE lambda values suggest that the mantle source of the Sibao parent magma contained a considerable amount of garnet-free pyroxenite, which formed through the reaction of mantle peridotite with fluids/melts derived from subducted oceanic crust. The <em>f</em>O₂ of the Sibao magma was estimated to be in the range of FMQ + 0.3 to FMQ + 1.2 based on the trace-element compositions of zircon and apatite. As demonstrated by the non-MORB δ³⁴S values of sulfides (+1.62 to +3.67 ‰), the Sibao parent magma required the addition of crustal sulfur to attain sulfide saturation. Thus, partial melting of metasomatized SCLM and incorporation of crustal sulfur were critical to the formation of the Sibao deposit. Overall, the Sibao deposit exhibits mantle source characteristics and sulfide saturation processes similar to other deposits emplaced along Andean-style continental convergent margins, such as the Xiarihamu, Erbutu, Kebu, and Aguablanca deposits. Together, these factors imply that Neoproterozoic convergent margins also have the potential to host economically significant Ni<img>Cu sulfide deposits.</div></div>","PeriodicalId":16336,"journal":{"name":"Journal of Geochemical Exploration","volume":"271 ","pages":"Article 107694"},"PeriodicalIF":3.4,"publicationDate":"2025-01-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143182836","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Geology and geochronology of the Xinqi WSn polymetallic deposit in the Tengchong block, western Yunnan, China","authors":"Meng-Fan Liu,&nbsp;Qing-He Yan","doi":"10.1016/j.gexplo.2025.107697","DOIUrl":"10.1016/j.gexplo.2025.107697","url":null,"abstract":"<div><div>Xinqi is one of the most significant tungsten‑tin polymetallic deposits in the Tengchong tin polymetallic metallogenic belt, Sanjiang area. However, the age of the mineralization and the potential parental granite for tungsten‑tin (W<img>Sn) deposits have not yet been constrained. In this study, the ore-forming process at Xinqi is categorized into five stages: potassic stage (Stage I), sodium stage (Stage II), greisen stage (Stage III), quartz-cassiterite-wolframite stage (Stage IV), and quartz-cassiterite-sulfide stage (Stage V). U<img>Pb dating of cassiterite and wolframite extracted from quartz vein ore in stages IV and V yields consistent ages of 65.4 ± 1 Ma and 64.65 ± 0.66 Ma, respectively, indicating that W<img>Sn mineralization occurred during the Late Cretaceous and is closely associated with the collision between the Indian and Eurasian plates. Integrating this data with previous findings on W<img>Sn mineralization ages in the Tengchong block suggests that tungsten‑tin mineralization in this area is closely linked to granite, predominantly occurring from the Early Cretaceous to the Paleogene. The ages of W<img>Sn mineralization at Xinqi align with the formation age of Guyong monzogranite (66.30 ± 0.23 Ma) but are approximately 15 Ma older than the Xinqi granite porphyry (51.66 ± 0.21 Ma). This correlation, along with the low oxygen fugacity of the monzogranite (the value of △FMQ from −2.54 to 1.50), indicates that the monzogranite plays a crucial role in tin enrichment and serves as the parental granite for W<img>Sn mineralization at Xinqi. The parental monzogranite exhibits low ε_Hf(t) values ranging from −10.94 to −19.54, suggesting that the ore-forming magma likely derived from ancient crust without mantle contamination. Furthermore, based on previous studies, we propose that a tin-rich continental crust exists in the Tengchong area, which has undergone a series of specific collisional orogenic events that led to the formation of granite and the associated tin mineralization in the Tengchong block.</div></div>","PeriodicalId":16336,"journal":{"name":"Journal of Geochemical Exploration","volume":"271 ","pages":"Article 107697"},"PeriodicalIF":3.4,"publicationDate":"2025-01-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143182837","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Machine learning-driven classification of PbZn ore deposits using pyrite trace elements and isotopic signatures: A case study of the Gunga deposit","authors":"Muhammad Amar Gul ,&nbsp;Huishan Zhang ,&nbsp;Yanguang Li ,&nbsp;Xiaoyong Yang ,&nbsp;Chao Sun ,&nbsp;Xiaojian Zhao ,&nbsp;Guangli Ren ,&nbsp;Asia Kanwal ,&nbsp;Muhammad Hafeez ,&nbsp;Yu Yang ,&nbsp;Rizwan Sarwar Awan ,&nbsp;Mohamed Faisal","doi":"10.1016/j.gexplo.2025.107693","DOIUrl":"10.1016/j.gexplo.2025.107693","url":null,"abstract":"<div><div>The mineral pyrite, commonly associated with Pb<img>Zn deposits, can contain a variety of trace elements and is influenced by factors such as temperature, fluid composition, and metal source. These trace elements have long been used to differentiate between various types of Pb<img>Zn deposits. However, traditional discriminant diagrams, which typically rely on two or three dimensions, fail to comprehensively capture the complex relationships between pyrite trace elements and deposit types. To address this limitation, this study employed four machine learning algorithms—random forest (RF), support vector machine (SVM), gradient boost (GB), and multilayer perceptron (MLP)—to develop classification models based on pyrite trace element compositions. The models were trained on a dataset of 5400 data points from 134 mineral deposits or stratigraphic units with trace element data from published sources. The performance of the classifiers was evaluated via cross-validation using a variant of the leave-one-group-out (LOGO) method. The study applied these machine learning models to newly obtained geochemical data from pyrite samples collected at the Gunga Pb<img>Zn deposit in the Lasbela-Khuzdar metallogenic belt. The results demonstrated that the classifiers could accurately identify the source of Pb<img>Zn deposits, producing reliable predictive outcomes. Specifically, the models indicated that the geochemical signature of pyrite from the Gunga deposit was derived from sedimentary-hydrothermal fluids enriched in Pb, Zn, Sb, Tl, As, and Ge, which is consistent with geological and geochemical evidence. The in-situ δ³⁴S values of pyrite ranged from −24 ‰ to +25 ‰, suggesting that the sulfur in the deposit originated primarily from coeval seawater sulfate. Additionally, Pb isotope compositions indicated crustal sources for Pb<img>Zn in the Gunga deposit. The combined predictions from the classifiers, along with isotopic analyses of sulfur and lead, suggest that the Gunga Pb<img>Zn deposit is a Clastic-Dominant (CD)-type deposit. These findings highlight the effectiveness of machine learning techniques in classifying ore deposits and provide new insights into the origin of the Gunga Pb<img>Zn deposit.</div></div>","PeriodicalId":16336,"journal":{"name":"Journal of Geochemical Exploration","volume":"272 ","pages":"Article 107693"},"PeriodicalIF":3.4,"publicationDate":"2025-01-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143403167","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"In-situ UPb geochronology, geochemistry, and spatial-temporal evolution of multi-generational garnet from the Muzuke FeCu polymetallic skarn deposit, Chinese Western Tianshan, NW China","authors":"Ying-Shuai Zhang ,&nbsp;Yong-Mei Zhang ,&nbsp;Xue-Xiang Gu ,&nbsp;Yi-Wei Peng ,&nbsp;Jia-Lin Wang ,&nbsp;Tao Wang ,&nbsp;Jia-Liang Xiao","doi":"10.1016/j.gexplo.2025.107686","DOIUrl":"10.1016/j.gexplo.2025.107686","url":null,"abstract":"<div><div>Spatial and temporal processes of variations in garnet composition and corresponding fluid evolution during the prograde skarn stage are matters of ongoing controversy. Here, we combine in situ U<img>Pb geochronology and major- and trace-element compositions of garnet (Grt) in the Muzuke Fe<img>Cu polymetallic skarn deposit to address the above debate. Three generations of garnets were identified concerning their locations in the contact zone, colors, textural and optical characteristics, and chemical compositions. They belong to the grossular-andradite solid solution and are characterized by a temporal and spatial chemistry zonation, which ranges greatly in composition from nearly pure grossular (Grs₉₈Adr_0.6) during early prograde stage in endoskarn and proximal exoskarn to almost pure andradite (Grs_1.7Adr₉₇) during late prograde stage in distal exoskarn. We observed a clear correspondence between the major-element compositions and optical characteristics of garnet from Muzuke, and the formation of the birefringent garnets is probably induced by the symmetry reduction due to trivalent cation ordering varieties at the Y site in the regular octahedron. From Grt-1 to Grt-3, the overall REE patterns shift from HREE enrichment to LREE enrichment, accompanied by negative to positive Eu anomalies, which can be attributed to the relative proportion of grossular and andradite end-members, while the chemical composition of fluid in the late prograde stage also has some effects on the REE patterns of garnet. The transitions of geochemical characteristics between three generations of garnets suggest that despite the existence of multiple pulses of fluid flux in the prograde stage, the overall trend of fluids evolution indicates that from the early to terminal prograde stage, from endoskarn to distal exoskarn, the formation mechanism of skarn transitions from diffusion metasomatism under a closed system to advective metasomatism under an open system, accompanied by a gradual decrease in temperature of hydrothermal fluids and an increase in <em>f</em>O₂ and W/R ratios. The above process inhibited premature sulfide precipitation and may be a precursor to the precipitation of magnetite in the later stage. In situ U<img>Pb dating on garnet yields an age of 364.9 ± 7.6 Ma for Grt-2 and of 363.2 ± 4.5 Ma to 363.0 ± 2.0 Ma for Grt-3 from the Muzuke deposit, suggesting a genetic connection between the polymetallic mineralization and the emplacement of the nearby granodioritic intrusion. The garnet spatial-temporal evolution model established in this study could assist in localizing and exploring regional skarn ore bodies with similar causative intrusions and wall rock properties.</div></div>","PeriodicalId":16336,"journal":{"name":"Journal of Geochemical Exploration","volume":"271 ","pages":"Article 107686"},"PeriodicalIF":3.4,"publicationDate":"2025-01-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143182308","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Provenance analysis signposts for sedimentary uranium exploration in aeolian sandstone systems: Insights from the Luohe Formation, Western Ordos Basin","authors":"Rui Tao ,&nbsp;Yang Song ,&nbsp;Liang Duan ,&nbsp;Mingtao Li","doi":"10.1016/j.gexplo.2025.107672","DOIUrl":"10.1016/j.gexplo.2025.107672","url":null,"abstract":"<div><div>The Lower Cretaceous Luohe Formation in the western Ordos Basin, North China, represents a rare aeolian sedimentary system with distinctive “uranium-bearing” characteristics. Sedimentary source of the uranium-bearing sandstones in this formation, which is crucial for advancing uranium exploration efforts, remains ambiguous. This study undertakes a comprehensive investigation encompassing petrology, geochemistry, and detrital zircon systematics (including zircon U–Pb ages, trace elements, and Hf isotopes) on the aeolian sandstones of the Luohe Formation within the western Ordos Basin. The objective is to provide crucial insights into conventional exploration for sedimentary uranium resources within aeolian sedimentary systems in intracontinental basins. Detrital zircon ages are categorized into a predominant age grouping within the Phanerozoic era (210–450 Ma), with notable peaks observed at 260 Ma and 420 Ma. Additionally, two minor age clusters are identified in the Early Paleoproterozoic (2240–2600 Ma), notably peaking at 2460 Ma, and the Late Paleoproterozoic (1600–2150 Ma), with a peak observed at 1850 Ma. Integrating the geochemical discrimination diagrams, it is suggested that the Alxa Block to the west of the Ordos Basin serves as the main provenance supplier of the hard detrital zircons. The uranium-bearing debris from the Alxa Block underwent sedimentary recycling and, therefore, were transported to the paleouplifts that formed on the western Ordos Basin during the Late Jurassic to Early Cretaceous. The paleoclimatic conditions characterized by prolonged arid periods interspersed with brief humid and warm episodes are crucial for the unique “uranium-bearing” nature of the sandstones. The sedimentary environment, dominated by aeolian deposition with localized fluvial deposition at basin-mountain interfaces, is identified as an ideal setting for uranium storage within aeolian sedimentary systems. We finally propose a generalized approach for exploring uranium reservoirs in aeolian sandstone systems at the basin level.</div></div>","PeriodicalId":16336,"journal":{"name":"Journal of Geochemical Exploration","volume":"271 ","pages":"Article 107672"},"PeriodicalIF":3.4,"publicationDate":"2025-01-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143182305","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Characteristics, water quality, health risks and sources of heavy metals of Qu River Basin","authors":"Dong Fu ,&nbsp;Yanchuan Gong ,&nbsp;Hua Liu ,&nbsp;Lvshan Zhou ,&nbsp;Wenjun Xiang ,&nbsp;Chenzheng Du","doi":"10.1016/j.gexplo.2025.107676","DOIUrl":"10.1016/j.gexplo.2025.107676","url":null,"abstract":"<div><div>With the continuous accumulation of heavy metals (HMs), the threat of HMs to the ecological environment has attracted high attention worldwide. The Qu River basin is located in the upper reaches of the Yangtze River, the largest river in China, but its water quality spatio-temporal distribution characteristics, pollution sources and health risks of HMs are still kept unclear. In this work, based on 2160 samples containing 8 HMs including Hg, Pb, Se, As, Cu, Cd, Zn and Cr from 36 sampling sites, the health risks, water quality variation characteristics and pollution sources in the Qu River Basin were studied. The mean HMs concentration varied in different seasons, with higher content of Zn, Cd, Cu, Pb and Cr in dry season, higher As value in wet season. The water quality distribution pattern of Qu River Basin shows that the upstream is superior to that in the middle and downstream. Health risks of Cd and Cr were most pronounced during the study period. Moreover, Cd poses a greater potential health risk in dry season while Cr in the rainy season, respectively. Positive matrix factorization (PMF) receptor model indicated that industrial pollution (26.2 %), soil erosion (24.3 %), natural source (22.4 %), atmospheric deposition (21.0 %) and agricultural activities (6.1 %) are identified as the potentially sources of HMs of the surface waters in Qu River Basin. Therefore, from the perspective of health risks, the treatment and discharge monitoring of industrial wastewater and the restoration of soil contaminated by HMs should be further strengthened in the Qu River basin. This work will provide basic data for water quality improvement and resource utilization of Qu River Basin.</div></div>","PeriodicalId":16336,"journal":{"name":"Journal of Geochemical Exploration","volume":"271 ","pages":"Article 107676"},"PeriodicalIF":3.4,"publicationDate":"2025-01-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143182838","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}