Acta Geochimica最新文献

{"title":"Mineralogical study and significance of the basalt-hosted Carlin-type Au deposits in southwestern Guizhou Province, China","authors":"Yuhong Yang,&nbsp;Shen Liu,&nbsp;Jianzhong Liu,&nbsp;Zepeng Wang,&nbsp;Bingqiang Zhang,&nbsp;Chengfu Yang","doi":"10.1007/s11631-024-00728-9","DOIUrl":"10.1007/s11631-024-00728-9","url":null,"abstract":"<div><p>The Jiadi and Damaidi gold deposits in southwest Guizhou Province are the largest basalt-hosted Carlin-type gold deposits recently discovered in China. This study uses the Tescan Integrated Mineral Analyzer, supported by detailed field investigations, regional geological data, and extensive sample collections, including mineralized ore, altered wall rock, and unaltered basalt samples, for ore-bearing and geochemical analyses. Comparative analysis between altered and unaltered basalt samples revealed a mineral assemblage of sericite, quartz, and pyrite. This mineral composition forms through the hydrothermal alteration of unaltered basalt, originally containing feldspar, pyroxene, and ilmenite. The wall rock primarily features sericite, quartz, and hematite. During the alteration process, major, trace, and rare earth elements notably migrate. In the Jiadi deposit, K₂O, Rb, Au, and REE significantly increase, while Na₂O, CaO, MgO, and MnO decrease. SiO₂, Al₂O₃, and Fe₂O₃ levels remain relatively stable. In the Damaidi deposit, K₂O, Rb, and Au enrich, contrasting with the depletion of Na₂O, CaO, MgO, and MnO, while SiO₂, Fe₂O₃, Al₂O₃, TiO₂, and REE show no significant changes. In the wall rock, TiO₂, Al₂O₃, K₂O, and REE increase, while Na₂O, CaO, MgO, and MnO decrease; SiO₂ and Fe₂O₃ content remains unchanged. The mineralization process likely originated from mid- to low-temperature, reductive magmatic hydrothermal fluids rich in CO₂, CH₄, N₂, H⁺, S²⁻, HS⁻, H₃AsO₃, and [Au(HS)₂]⁻. These fluids migrated to tectonically weak zones in the Lianhuashan area, where Emeishan basalts are present. They reacted with Fe-bearing minerals in the basalt, such as ferro-hornblende and ilmenite, forming pyrite, arsenic-bearing pyrite, and arsenopyrite, thus enriching Au in these minerals. Additionally, K⁺ and H⁺ in the fluid reacted with plagioclase in the basalt, forming sericite and quartz. As the fluid entered the wall rock from structural weak zones, its oxidation increased, leading to the complete or partial reaction of Fe-bearing minerals in the wall rock, resulting in the formation of hematite or magnetite. This mineralization process is similar to that observed in carbonate-hosted Carlin-type gold deposits in southwest Guizhou, with the primary distinction being the iron source. In carbonate deposits, iron originates from ferridolomite within the wall rock, while in basalt-hosted deposits, it derives from ferripyroxene and ilmenite.</p></div>","PeriodicalId":7151,"journal":{"name":"Acta Geochimica","volume":"43 6","pages":"1241 - 1254"},"PeriodicalIF":1.4,"publicationDate":"2024-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142664446","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Geochronology and geodynamic setting of the carbonate-hosted Pb-Zn deposits in world-class Sichuan-Yunnan-Guizhou triangle, South China","authors":"Zhongxi Xue,&nbsp;Wenxin Shi,&nbsp;Chen Wei,&nbsp;Tao Wu,&nbsp;Zhilong Huang","doi":"10.1007/s11631-024-00724-z","DOIUrl":"10.1007/s11631-024-00724-z","url":null,"abstract":"<div><p>Unraveling the precise mineralization age is vital to understand the geodynamic setting and ore-forming mechanism of the sediment-hosted Pb-Zn deposit; this has long been a challenge. The Sichuan-Yunnan-Guizhou (SYG) triangle in the southwestern margin of the Yangtze Block is a globally recognized carbonate-hosted Pb-Zn metallogenic province and also an essential part of the South China low-temperature metallogenic domain. This region has &gt; 30 million tons (Mt) Zn and Pb resources and shows the enrichment of dispersed metals, such as Ga, Ge, Cd, Se, and Tl. During the past 2 decades, abundant data on mineralization ages of Pb-Zn deposits within the SYG triangle have been documented based on various radioisotopic dating methods, resulting in significant progress in understanding the geodynamic background and ore formation of Pb-Zn deposits hosted in sedimentary rocks at SYG triangle. This paper provides a comprehensive summary of the geochronological results and Pb-Sr isotopic data regarding Pb-Zn deposits in the SYG triangle, which identified two distinct Pb-Zn mineralization periods influencing the dynamic processes associated with the expansion and closure of the Paleo-Tethys Ocean in the western margin of the Yangtze Block. The predominant phase of Pb-Zn mineralization at SYG triangle spanned from the Middle Triassic to Early Jurassic (226<b>–</b>191 Ma), which was intensely correlated with the large-scale basin fluid transport triggered by the closure of the Paleo-Tethys Ocean and Indosinian orogeny. The secondary Pb-Zn mineralization phase occurred during the Late Devonian to Late Carboniferous and was controlled by extensional structures associated with the expansion of the Paleo-Tethys Ocean. Further investigation is necessary to clarify the occurrence and potential factors involved in the Pb-Zn mineralization events during the Late Devonian to Late Carboniferous.</p></div>","PeriodicalId":7151,"journal":{"name":"Acta Geochimica","volume":"44 1","pages":"217 - 230"},"PeriodicalIF":1.4,"publicationDate":"2024-08-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143362217","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Precise and accurate Ga isotope ratio measurements of geological samples by multi-collector inductively coupled plasma mass spectrometry","authors":"Yuxu Zhang,&nbsp;Pan Qiao,&nbsp;Chuanwei Zhu,&nbsp;Haifeng Fan,&nbsp;Hanjie Wen","doi":"10.1007/s11631-024-00729-8","DOIUrl":"10.1007/s11631-024-00729-8","url":null,"abstract":"<div><p>Gallium isotope is a potential geochemical tool for understanding planetary processes, environmental pollution, and ore deposit formation. The reported Ga isotope compositions (δ⁷¹Ga_NIST994 values) of some international geological standards, such as BCR-2 and BHVO-2 basalts, exhibit inconsistencies between different laboratories. During mass spectrometry analysis, we found that δ⁷¹Ga_NIST994 values of geological standards with or without the correction of the interference of ¹³⁸Ba²⁺ (mass/charge ratio = 69) on ⁶⁹Ga show significant isotope offsets, and thus efficient separation of Ba and correcting the interference of ¹³⁸Ba²⁺ are both crucial to obtain accurate δ⁷¹Ga values. By comparing δ⁷¹Ga_NIST994 values (relative to NIST SRM 994 Ga) of the same geostandards from different laboratories, we suggest that the isotopic heterogeneity from NIST SRM 994 Ga is one of the key reasons for the inconsistencies in δ⁷¹Ga_NIST994 values of BCR-2 and BHVO-2. To facilitate inter-laboratory comparisons, we measured the Ga isotopic compositions of 11 geological reference materials (including Pb-Zn ore, bauxite, igneous rocks, and loess) and two Ga solution standards (NIST SRM 3119a and Alfa Aesar). The δ⁷¹Ga_NIST994 and δ⁷¹Ga_IPGP values of these reference materials vary from 1.12 ‰ to 2.63 ‰ and − 0.13 ‰ to 1.38 ‰, respectively, and can be used to evaluate the precision and accuracy of Ga isotope data from different laboratories.</p></div>","PeriodicalId":7151,"journal":{"name":"Acta Geochimica","volume":"43 6","pages":"1054 - 1064"},"PeriodicalIF":1.4,"publicationDate":"2024-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142664443","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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 S-Pb isotope geochemistry of the Hatu gold deposit in West Junggar, NW China: Insights into ore genesis and metal source","authors":"Shen Han,&nbsp;Zhenju Zhou,&nbsp;Xiaohua Deng,&nbsp;Yanshuang Wu,&nbsp;Xi Chen,&nbsp;Abulimiti Aibai,&nbsp;Yong Wang,&nbsp;Xiaoyu Jia,&nbsp;Yanjing Chen","doi":"10.1007/s11631-024-00727-w","DOIUrl":"10.1007/s11631-024-00727-w","url":null,"abstract":"<div><p>The Hatu gold deposit is the largest historical gold producer of the West Junggar, western China, with an Au reserve of about 62 t. The orebodies were controlled by NE-, EW-, and NW-trending subsidiary faults associated with the Anqi fault. This deposit exhibits characteristics typical of a fault-controlled lode system, and the orebodies consist of auriferous quartz veins and altered wall rocks within Early Carboniferous volcano-sedimentary rocks. Three stages of mineralization have been identified in the Hatu gold deposit: the early pyrite-albite-quartz stage, the middle polymetallic sulfides-ankerite-quartz stage, and late quartz-calcite stage. The sulfur isotopic values of pyrite and arsenopyrite vary in a narrow range from − 0.8‰ to 1.3‰ and an average of 0.4‰, the near-zero δ³⁴S values implicate the thorough homogenization of the sulfur isotopes during the metamorphic dehydration of the Early Carboniferous volcano-sedimentary rocks. Lead isotopic results of pyrite and arsenopyrite (²⁰⁶Pb/²⁰⁴Pb = 17.889–18.447, ²⁰⁷Pb/²⁰⁴Pb = 15.492–15.571, ²⁰⁸Pb/²⁰⁴Pb = 37.802–38.113) are clustered between orogenic and mantle/upper crust lines, indicating that the lead was mainly sourced from the hostrocks within the Early Carboniferous Tailegula Formation. The characteristics of S and Pb isotopes suggest that the ore-forming metals of the Hatu orogenic gold deposit are of metamorphogenic origin, associated with the continental collision between the Yili-Kazakhstan and Siberian plates during the Late Carboniferous.</p></div>","PeriodicalId":7151,"journal":{"name":"Acta Geochimica","volume":"43 6","pages":"1205 - 1222"},"PeriodicalIF":1.4,"publicationDate":"2024-08-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142664423","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Neoproterozoic tectonic evolution of the northwestern Yangtze Block: Constraints from the Bijigou intermediate-acid magmatism in the Hannan massif","authors":"Yan Luan,&nbsp;Yunxiu Ren,&nbsp;Ruiting Wang,&nbsp;Xiaohui Sun","doi":"10.1007/s11631-024-00731-0","DOIUrl":"10.1007/s11631-024-00731-0","url":null,"abstract":"<div><p>The Bijigou intrusion is one of the largest and most well-differentiated Fe–Ti oxide-bearing layered intrusions in the Hannan massif located in the northwestern margin of the Yangtze Block, South China. Besides the mineralization-related mafic-ultramafic rocks, the intermediate-acid intrusive rocks are also exposed in the mining area, which is of great significance for the understanding the Neoproterozoic tectonic evolution of the Yangtze Block, but studies on these intermediate-acid rocks are scarce. The Bijigou mafic-ultramafic layered intrusion is surrounded by granite and cut by syenite veins. Here, we report new zircon U-Pb ages, Lu-Hf isotope composition and bulk rock geochemical data of the Bijigou syenite vein and wall-rock granite in the northwestern margin of the Yangtze Block. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U-Pb dating results show that the Bijigou syenite vein and wall-rock granite formed at 770 ± 3.5 Ma (MSWD = 0.17, <i>n</i> = 28) and 810 ± 4 Ma (MSWD = 0.84, <i>n</i> = 26), respectively. The zircon εHf(t) values of the syenite veins range from + 1.52 to + 5.33 (average of + 3.05), combined with its high potassium contents, negative Nb–Ta anomalies and positive Pb anomalies, suggesting that they may have originated from mantle-derived basaltic magma, which was modified by materials from subducting oceanic slab. The zircon εHf(t) and T_DM2 ages of the wall-rock granite range from + 0.71 to + 5.71 (average + 3.06) and 1344 to 1659 Ma (average 1519 Ma), respectively, indicating that the granite was produced by partial melting of juvenile crust. The geochemical characteristics of the Bijigou syenite and granite indicate that they were formed in a continental margin arc setting. Thus, combined with previous studies, it suggests that there was a major subduction system along the northwestern margin of the Yangtze Block during 824–720 Ma, and the magmatism in the Hannan massif was divided into two episodes: (1) early magmatism (824–790 Ma), such as the Bijigou, Hongmiaozhen and Huangguanzhen granitoids, was derived from partial melting of the juvenile or pre-existing crust in a continental arc setting; (2) later magmatism (789–718 Ma), including Bijigou syenite, Wudumen, Erliba and Zushidian granitoids, formed in a subduction-related back-arc extensional environment. The long-term subduction system along the northwestern margin of the Yangtze Block during 824–720 Ma suggests that the Yangtze Block was previously located at the periphery of the Rodinia supercontinent.</p></div>","PeriodicalId":7151,"journal":{"name":"Acta Geochimica","volume":"44 2","pages":"404 - 419"},"PeriodicalIF":1.4,"publicationDate":"2024-08-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143749093","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Influence of igneous intrusions on maturation of the Cretaceous-Eocene source rocks of the offshore Tanzanian Basin","authors":"John William Gama,&nbsp;Emily Barnabas Kiswaka,&nbsp;Elisante Elisaimon Mshiu","doi":"10.1007/s11631-024-00730-1","DOIUrl":"10.1007/s11631-024-00730-1","url":null,"abstract":"<div><p>The offshore Tanzanian Basin contains numerous igneous intrusions emplaced at various stratigraphic levels. Previous studies indicate these intrusions have impacted petroleum systems, affecting key elements such as source rocks, reservoirs, seals, migration pathways, and trapping mechanisms. However, due to the limited number of wells drilled in the region, there have been few studies reporting the associated thermal effects on source rock maturation and their role in hydrocarbon generation. To gain a comprehensive understanding of the intricate relationship between intrusions and the petroleum system, particularly source rock, an integrated geochemical and resistivity log analysis was carried out. The geochemical results show that the Cretaceous-Cenozoic sediments of the study area have low total organic carbon contents (TOC &lt; 1 wt%), kerogen yield (&lt; 1 Mg HC/g), and Hydrogen Index (&lt; 100 Mg HC/g), primarily composed of Type III (gas-prone) to Type IV (inert) kerogens. These sediments have undergone varying levels of thermal maturity, ranging from post-mature (within Cretaceous), matured (in Paleocene) to immature (in Eocene) thermal states. The Cretaceous strata located proximal to the intrusions exhibit significant thermal alteration, resulting in a reduction of both organic matter (OM) content and source potential compared to the Eocene and Paleocene samples. This observation is consistent with the estimated paleotemperature (T) and resistivity log (ILD) along the depth profile, which have mapped local thermal alteration increasing from base Paleocene to Cretaceous. These findings have implications for source rock potential and thermal evolution history in the offshore Tanzanian Basin. This study highlights the necessity for thorough subsurface mapping in the area to identify both younger and older intrusive rocks. These intrusions pose a potential risk in petroleum exploration, especially when they intrude into matured source rock intervals.</p></div>","PeriodicalId":7151,"journal":{"name":"Acta Geochimica","volume":"44 2","pages":"387 - 403"},"PeriodicalIF":1.4,"publicationDate":"2024-08-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143749053","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Groundwater geochemical evolution, origin and quality in the Lower Pra Basin, Ghana: Insights from hydrogeochemistry, multivariate statistical analysis, mineral saturation indices, stable isotopes (δ2H and δ18O) and geostatistical analysis","authors":"Samuel Y. Ganyaglo,&nbsp;Joel Y. Binyiako,&nbsp;Emmanuel M. Teye,&nbsp;Abass Gibrilla,&nbsp;Dickson Abdul-Wahab,&nbsp;Samuel Edusei,&nbsp;Paulina Amponsah,&nbsp;Courage D. Egbi,&nbsp;Samuel B. Dampare,&nbsp;Ebenezer Aquisman Asare","doi":"10.1007/s11631-024-00725-y","DOIUrl":"10.1007/s11631-024-00725-y","url":null,"abstract":"<div><p>In many places across the globe, including the Wassa District of Ghana, groundwater provides a significant supply of water for various purposes. Understanding the groundwater origin and hydrogeochemical processes controlling the groundwater chemistry is a major step in the sustainable management of the aquifers. A total of 29 groundwater samples were collected and analysed. Ionic ratio graphs, multivariate statistical analysis, mineral saturation indices, stable isotopes, and geostatistics methods were used to examine the sources and the quality of the groundwater. The findings describe the water types in the district as Ca–Mg–HCO₃–Cl, Ca–Na–HCO₃, Na–Ca–HCO₃, Ca–Na–HCO₃–Cl, Na–Ca–HCO₃–Cl, mix water type, Na–HCO₃–Cl, with possible evolution to Ca–Na–Cl–HCO₃, and Na–Ca–Cl–HCO₃. According to the IEWQI for drinking water, around 53.6% of the samples have good quality, whereas 10.7% have very low-quality groundwater. Only 3.45% of the samples are suitable to use for irrigation without treatment, whereas 41.4% are somewhat safe with minimal treatment. Water-rock interactions, including the dissolution and weathering of silicate minerals, cation exchange processes, and human activities like mining and quarrying, are some of the main factors influencing groundwater chemistry. Principal component analysis revealed that groundwater chemistry is influenced by a combination of natural and anthropogenic sources. The APCs-MLR receptor model quantifies the factors that play important roles in groundwater salinization, including mineral dissolution and weathering (19.4%), localised Cd (16%), Ni (14.6%), Pb (12.8%), and Fe (11.4%) contamination from urbanisation while unidentified sources of pollution account for about 26.0%. The stable isotopes revealed groundwater is of meteoric origin and water-rock interaction the major mechanism for groundwater mineralization. The results of this research highlight the need of implementing an integrated strategy for managing and accessing groundwater quality.</p></div>","PeriodicalId":7151,"journal":{"name":"Acta Geochimica","volume":"44 2","pages":"348 - 372"},"PeriodicalIF":1.4,"publicationDate":"2024-08-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143749076","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Ore-forming mechanism of Huxu Au-dominated polymetallic deposit in the Dongxiang Basin, South China: Constraints from in-situ trace elements and S–Pb isotopes of pyrite","authors":"Hongze Gao,&nbsp;Jiajie Chen,&nbsp;Chengbiao Leng,&nbsp;Yuhui Hu,&nbsp;Huidan Xie,&nbsp;Zenghua Li","doi":"10.1007/s11631-024-00726-x","DOIUrl":"10.1007/s11631-024-00726-x","url":null,"abstract":"<div><p>The Huxu Au-dominated polymetallic deposit is a hydrothermal deposit located in the Dongxiang volcanic basin in the middle section of the Gan-Hang tectonic belt in South China. The orebodies primarily occur within the Jurassic-Cretaceous quartz diorite porphyry, while the genesis of this deposit is unclear. This study focused on geological and mineralogical characteristics, <i>in-situ</i> trace elements and S-Pb isotopes of three generations of pyrite of the Huxu deposit to clarify the distribution of trace elements in pyrite, ore-forming fluid and material sources, and genetic types of the deposit. The mineralization stage of the deposit can be divided into quartz-pyrite stage (S1), quartz-pyrite-hematite stage (S2), quartz-polymetallic sulfide stage (S3) and quartz-hematite stage (S4), with the corresponding pyrite being divided into three generations (Py1–Py3). <i>in-situ</i> trace element data of pyrite show that Au in pyrite mainly exists in the form of solid solution (Au⁺), and the content is relatively low at all stages (0.18 ppm for Py1, 0.32 ppm for Py2, 0.68 ppm for Py3), while Pb and Zn mainly exist as sulfide inclusions in the pyrite. S-Pb isotopes show that the sulfur and ore-forming material of this deposit are mainly sourced from magma. The mineral association, mineral textures and trace elements in different stages of pyrite indicate that fluid boiling and fluid mixing are the key factors of native gold precipitation in S2 and S4, respectively, while water-rock interaction controlled the precipitation of Pb-Zn sulfides. These integrating with geological characteristics suggests that the deposit should be an intermediate sulfidation epithermal deposit.</p></div>","PeriodicalId":7151,"journal":{"name":"Acta Geochimica","volume":"43 6","pages":"1223 - 1240"},"PeriodicalIF":1.4,"publicationDate":"2024-08-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142664464","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Geological studies and thermal treatment of some Paleogene deposits in east Beni Suef region, Egypt","authors":"Alaa T. A. Amin,&nbsp;Ahmed M. El-Mezayen,&nbsp;Darweesh M. Elkholy,&nbsp;Hossam A. Khamis,&nbsp;Hazem K. A. Sarhan","doi":"10.1007/s11631-024-00720-3","DOIUrl":"10.1007/s11631-024-00720-3","url":null,"abstract":"<div><p>Geological setting, facies characteristics, and geochemistry, including TGA (thermo-gravimetric analysis) of Paleogene deposits in east Beni Suef region (Egypt), were studied in the present work. Lithostratigraphically, the area consists of three rock units, arranged from oldest to youngest: Tarbul Member of Beni Suef Formation (Middle-Late Eocene), Maadi Formation (Late Eocene), and Gebel Ahmar Formation (Oligocene), this last formation registered for the first time in the east of Beni Suef area (Egypt). Seven microfacies types (F1–F7) were determined by the microscopic examination of the studied samples in low- to high-energy and shallow-subtidal marine conditions. The lithostratigraphic, petrological, and geochemical results revealed that the Eocene succession in the present area is composed mainly of carbonates as well as siliciclastics. The Oligocene Gebel Ahmar Formation consists mainly of silica and iron oxides. The enrichment of the rock units with iron oxides in the studied area, as well as the high proportions of trace elements such as Zr, Ba, V, and Sr, in particular in the Gebel Ahmar Formation, reflects the influence of the hydrothermal solutions during the Oligocene. TGA, which monitors weight changes during heating at a constant rate, was used to determine the thermal stability and volatile component content of the materials. The ferruginous sandstone of Gebel Ahmar Formation exhibits various decomposition phases when exposed to thermal influences, with TGA indicating an initial mass decrease starting at 61.8 °C. In contrast, the ferruginous limestone of the Maadi Formation shows a single-phase mass decrease between 650 and 875 °C.</p></div>","PeriodicalId":7151,"journal":{"name":"Acta Geochimica","volume":"44 2","pages":"278 - 296"},"PeriodicalIF":1.4,"publicationDate":"2024-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141807901","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Multiple-stage W mineralization in the Guanfang W deposit, southeastern Yunnan Province, China: Insights from scheelite in-situ trace elemental and Sr isotopic analyses","authors":"Bin Sun,&nbsp;Yi Liu,&nbsp;Zhigang Kong,&nbsp;Xuelong Liu,&nbsp;Xiaojun Jiang,&nbsp;Chao Li,&nbsp;Wenchang Li","doi":"10.1007/s11631-024-00722-1","DOIUrl":"10.1007/s11631-024-00722-1","url":null,"abstract":"<div><p>The Guanfang large-scale W deposit is located in the W polymetallic ore concentration area of Bozhushan in southeastern Yunnan, China. Despite extensive research, the fluid evolution process of the deposit remains ambiguous, leading to controversy regarding its genesis. This study conducted a detailed field geological survey, with systematic sampling of the KT6 orebody, to delineate mineralization stages. Fine mineralogy work, including the use of CL images of scheelite, <i>in-situ</i> LA-ICP-MS trace elements, and Sr isotopes, was carried out on different generations of scheelite formed in various stages. The findings identified the evolution of fluids in the mineralization process, shedding light on the genesis of the deposit. The study revealed four mineralization stages at the Guanfang W deposit: prograde skarn stage, retrograde skarn stage, quartz-sulfide stage, and carbonate-fluorite stage. Different generations of scheelite (Sch I, Sch II, Sch III) were observed in the first three stages, displaying distinct chondrite-normalized REE patterns. The REE of Sch I mainly substituted into the Ca site by REE³⁺  + □_Ca, and there may be a similar substitution of Nb for REE, whereas it is not the main substitution method. The REE of Sch II mainly enter the scheelite lattice in the form of REE³⁺  + Na⁺, and there may be a substitution of Nb for REE isomorphism. In the early stage, The REE of Sch III was mainly replaced by Nb for REE isomorphism, while in the later stage, the replacement mode of REE³⁺  +  □_Ca coexisted with it. The Mo content in scheelite, along with the corresponding Eu anomalies in both scheelite and garnet, collectively imply that the ore-forming fluids during various mineralization stages were predominantly oxidizing, with only slight reducibility observed in Sch II. The in-situ Sr isotope ratios of scheelite concentrates ranged from 0.7093 to 0.7153, resembling those of the Bozhushan granite, indicating a relationship between W mineralization and granite. In addition, the Y/Ho ratios of scheelite from various mineralization stages exhibit a narrow range (19–31), with a pronounced correlation between the contents of Y and Ho and a similar trend in their variation. This consistency suggests that the Guanfang deposit has undergone a uniform or comparable evolutionary process, implying a stable ore-forming fluid across different mineralization stages.</p></div>","PeriodicalId":7151,"journal":{"name":"Acta Geochimica","volume":"44 1","pages":"112 - 127"},"PeriodicalIF":1.4,"publicationDate":"2024-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141808792","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}