Pub Date : 2025-03-20DOI: 10.1016/j.chemer.2025.126285
Martin Vlieghe , Gaëtan Rochez , Stéphane Pire-Stevenne , Alexandre Felten , Marie Dechamps , Sébastien R. Mouchet , Francesca Cecchet , Olivier Bruguier , Jean-Louis Galéra , Gipsi Lima-Mendez , Marc Llirós Dupré , Johan Yans
Speleothems rarely exhibit stunning colors such as red, yellow, green, or blue. The colorations are often linked to elevated heavy metal ion concentration in the drip water and thus to a metal source/pollution in the catchment area. Here the blue-green speleothems coloration in Malaval Cave (Lozère, France) is characterized by a wide panel of optical, mineralogical and geochemical techniques. These techniques were applied on several small blue or white stalactites and a larger greenish stalactite. The speleothems are mostly composed of aragonite and contain variable amounts of Zn, Cu and Pb, which cause the colorations. Zn and Cu are mostly present in substitution in the aragonite and Cu2+ is the main cause of the blue coloration. Zn is also found in small amorphous gel particles, containing minor amounts of Mg, Cu and Si. These phases are responsible for microscopical scale variations in the blue coloration. Pb is present as Pb2+ ions in substitution within the aragonite, creating a saturated blue-to-greenish coloration. This coloration may depend on the Pb/Zn ratio due to metallic interaction. Pb, Zn and Cu ratios indicate that Pb likely deposited from distinct fluids and at a different timing than Cu and Zn. All three metals likely originate from the leaching of PbZn ores in the Jurassic formations surrounding the cave.
{"title":"Polymetallic interactions of Zn-Pb-Cu in blue/green-colored speleothems from Malaval Cave (France)","authors":"Martin Vlieghe , Gaëtan Rochez , Stéphane Pire-Stevenne , Alexandre Felten , Marie Dechamps , Sébastien R. Mouchet , Francesca Cecchet , Olivier Bruguier , Jean-Louis Galéra , Gipsi Lima-Mendez , Marc Llirós Dupré , Johan Yans","doi":"10.1016/j.chemer.2025.126285","DOIUrl":"10.1016/j.chemer.2025.126285","url":null,"abstract":"<div><div>Speleothems rarely exhibit stunning colors such as red, yellow, green, or blue. The colorations are often linked to elevated heavy metal ion concentration in the drip water and thus to a metal source/pollution in the catchment area. Here the blue-green speleothems coloration in Malaval Cave (Lozère, France) is characterized by a wide panel of optical, mineralogical and geochemical techniques. These techniques were applied on several small blue or white stalactites and a larger greenish stalactite. The speleothems are mostly composed of aragonite and contain variable amounts of Zn, Cu and Pb, which cause the colorations. Zn and Cu are mostly present in substitution in the aragonite and Cu<sup>2+</sup> is the main cause of the blue coloration. Zn is also found in small amorphous gel particles, containing minor amounts of Mg, Cu and Si. These phases are responsible for microscopical scale variations in the blue coloration. Pb is present as Pb<sup>2+</sup> ions in substitution within the aragonite, creating a saturated blue-to-greenish coloration. This coloration may depend on the Pb/Zn ratio due to metallic interaction. Pb, Zn and Cu ratios indicate that Pb likely deposited from distinct fluids and at a different timing than Cu and Zn. All three metals likely originate from the leaching of Pb<img>Zn ores in the Jurassic formations surrounding the cave.</div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 3","pages":"Article 126285"},"PeriodicalIF":2.6,"publicationDate":"2025-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143706136","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-03-07DOI: 10.1016/j.chemer.2025.126284
Yuanlin Chen , Huan Li , Wenting Jiang , Majid Ghaderi , Adi Maulana , Liming Ouyang , Kun Liu
The Langwashan Fe deposit, with 80 million tons of proven iron ore reserves, is located in the eastern portion of the Tianshan orogenic belt, NW China. Previous research carried out detailed geological, geochemical, and geophysical studies on the deposit, while there are still different views on the ore genesis. In this study, electron probe micro-analysis and laser ablation (multi-collector) inductively coupled plasma mass spectrometry analysis of variable minerals in ore samples were conducted. Based on ore texture, in-situ biotite RbSr dating, magnetite and pyrite composition, and mineral assemblage, the Langwashan Fe mineralization has been divided into two metallogenic periods: volcanic hydrothermal metallogenic period (∼344 Ma) and skarn metallogenic period (∼239 Ma). The Early Carboniferous mineralization is characterized by layered ore bodies, a narrow range of δ34S values (+1.37 to +2.77 ‰), and low Co/Ni ratio in early pyrite (Py I), and high Ti, V, Cr, Ni, and Co contents in early magnetite (Mag I), showing single and deep origin for the fluid. In contrast, the Early Triassic mineralization has irregular-shaped ore bodies, higher contents of Si, Al, Mn, Mg, and Ca in late magnetite (Mag II), higher Co, Ni, As, and Cu contents, and a wider range of δ34S values (−0.18 to +3.35 ‰) in late pyrite (Py II), indicating mixed origin for the fluid. Thus, we propose that the Langwashan Fe deposit is formed by the superposition of two types of mineralization. The Early Carboniferous Hongshishan inter-arc oceanic basin subducted beneath the southern Tarim plate, and the iron-bearing magma migrated along the volcanic channel and annular faults, forming the first period of layered Fe ore bodies together with the volcanic rock deposition. During the Early Triassic, a hidden intrusion was generated in an extensional environment in the region, interacting with surrounding rocks through metasomatism, forming superimposed skarn-type Fe ore bodies. The two periods of mineralization determined in Langwashan have great significance for further exploration and prospecting of Fe ore deposits in the Tianshan orogenic belt.
{"title":"Genesis of the Langwashan Fe deposit, NW China: Constraints from pyrite and magnetite geochemistry, and in-situ Rb-Sr dating","authors":"Yuanlin Chen , Huan Li , Wenting Jiang , Majid Ghaderi , Adi Maulana , Liming Ouyang , Kun Liu","doi":"10.1016/j.chemer.2025.126284","DOIUrl":"10.1016/j.chemer.2025.126284","url":null,"abstract":"<div><div>The Langwashan Fe deposit, with 80 million tons of proven iron ore reserves, is located in the eastern portion of the Tianshan orogenic belt, NW China. Previous research carried out detailed geological, geochemical, and geophysical studies on the deposit, while there are still different views on the ore genesis. In this study, electron probe micro-analysis and laser ablation (multi-collector) inductively coupled plasma mass spectrometry analysis of variable minerals in ore samples were conducted. Based on ore texture, in-situ biotite Rb<img>Sr dating, magnetite and pyrite composition, and mineral assemblage, the Langwashan Fe mineralization has been divided into two metallogenic periods: volcanic hydrothermal metallogenic period (∼344 Ma) and skarn metallogenic period (∼239 Ma). The Early Carboniferous mineralization is characterized by layered ore bodies, a narrow range of δ<sup>34</sup>S values (+1.37 to +2.77 ‰), and low Co/Ni ratio in early pyrite (Py I), and high Ti, V, Cr, Ni, and Co contents in early magnetite (Mag I), showing single and deep origin for the fluid. In contrast, the Early Triassic mineralization has irregular-shaped ore bodies, higher contents of Si, Al, Mn, Mg, and Ca in late magnetite (Mag II), higher Co, Ni, As, and Cu contents, and a wider range of δ<sup>34</sup>S values (−0.18 to +3.35 ‰) in late pyrite (Py II), indicating mixed origin for the fluid. Thus, we propose that the Langwashan Fe deposit is formed by the superposition of two types of mineralization. The Early Carboniferous Hongshishan inter-arc oceanic basin subducted beneath the southern Tarim plate, and the iron-bearing magma migrated along the volcanic channel and annular faults, forming the first period of layered Fe ore bodies together with the volcanic rock deposition. During the Early Triassic, a hidden intrusion was generated in an extensional environment in the region, interacting with surrounding rocks through metasomatism, forming superimposed skarn-type Fe ore bodies. The two periods of mineralization determined in Langwashan have great significance for further exploration and prospecting of Fe ore deposits in the Tianshan orogenic belt.</div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 3","pages":"Article 126284"},"PeriodicalIF":2.6,"publicationDate":"2025-03-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143601372","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We present mineralogic and elemental data on the Banded Iron Formations (BIFs) from the volcano-sedimentary greenstone belts of the Western Dharwar Craton to address redox conditions of Archean Oceans and origin of BIFs. The studied BIFs are restricted to the uppermost stratigraphic levels in the Sargur Group and Dharwar Supergroup greenstone belts. The BIFs of the older Sargur greenstone sequence are characterized by thick chert layers, which are interspersed with thin Fe-oxide and silicate layers. Iron-rich amphibole grunerite indicates that BIFs from the Sargur Group underwent lower-amphibolite facies metamorphism. In contrast, oxide-silicate‑carbonate-sulphide facies BIFs characterize younger Dharwar Supergroup greenstone belts. Rare silicate assemblages (e.g., stilpnomelane orreibeckite) in BIFs of Dharwar Supergroup reveal greenschist facies metamorphism. Field, mineralogic and elemental characteristics of studied samples show affinity to Algoma-type BIFs. The studied BIFs show significant variation in SiO2 (49.00–53.00 wt%) and Fe2O3 (27.00–51.5 wt%) content. The concentration of all other elements is typically <1 wt% except two samples of BIFs from the Chitradurga basin exhibit higher Al2O3 (5.42 wt%) and CaO (9.56 wt%) reflecting traces of terrigenous input. The low ΣREE content (<20 ppm) of studied BIFs from the Sargur Group Holenasirpur, Dharwar Supergroup Bababudan, and Chitradurga – Dharwar-Shimoga greenstone belts preclude continent derived terrigenous input whilst higher total REE (30–53 ppm) of two BIFs samples from the Chitradurga basin is in agreement with traces of terrigenous input. BIFs from the older Sargur Group and the younger Dharwar Supergroup exhibit positive Eu anomalies pointing to BIFs sourced from hydrothermal plumbing system. The trace element ratios (Y/Ho, Sm/Yb, and Eu/Sm) consistent with a dominant hydrothermal input in their origin. The mineralogical facies changes, combined with the redox-sensitive elemental signatures coupled with published redox sensitive isotope biomarkers suggest fluctuation in the redox conditions of ocean basins through Archean and oxygenation of ocean initiated at least two hundred million years before the Great Oxidation Event (GOE).
{"title":"Geochemistry and origin of the banded Iron formations (BIFs) from the Western Dharwar craton, southern India: Implications for evolving redox conditions of Archean oceans","authors":"Aindrila Mukherjee , Jayananda Mudlappa , Pritam Nasipuri , Aadhiseshan K.R. , Satyanarayanan M.","doi":"10.1016/j.chemer.2025.126268","DOIUrl":"10.1016/j.chemer.2025.126268","url":null,"abstract":"<div><div>We present mineralogic and elemental data on the Banded Iron Formations (BIFs) from the volcano-sedimentary greenstone belts of the Western Dharwar Craton to address redox conditions of Archean Oceans and origin of BIFs. The studied BIFs are restricted to the uppermost stratigraphic levels in the Sargur Group and Dharwar Supergroup greenstone belts. The BIFs of the older Sargur greenstone sequence are characterized by thick chert layers, which are interspersed with thin Fe-oxide and silicate layers. Iron-rich amphibole grunerite indicates that BIFs from the Sargur Group underwent lower-amphibolite facies metamorphism. In contrast, oxide-silicate‑carbonate-sulphide facies BIFs characterize younger Dharwar Supergroup greenstone belts. Rare silicate assemblages (e.g., stilpnomelane orreibeckite) in BIFs of Dharwar Supergroup reveal greenschist facies metamorphism. Field, mineralogic and elemental characteristics of studied samples show affinity to Algoma-type BIFs. The studied BIFs show significant variation in SiO<sub>2</sub> (49.00–53.00 wt%) and Fe<sub>2</sub>O<sub>3</sub> (27.00–51.5 wt%) content. The concentration of all other elements is typically <1 wt% except two samples of BIFs from the Chitradurga basin exhibit higher Al<sub>2</sub>O<sub>3</sub> (5.42 wt%) and CaO (9.56 wt%) reflecting traces of terrigenous input. The low ΣREE content (<20 ppm) of studied BIFs from the Sargur Group Holenasirpur, Dharwar Supergroup Bababudan, and Chitradurga – Dharwar-Shimoga greenstone belts preclude continent derived terrigenous input whilst higher total REE (30–53 ppm) of two BIFs samples from the Chitradurga basin is in agreement with traces of terrigenous input. BIFs from the older Sargur Group and the younger Dharwar Supergroup exhibit positive Eu anomalies pointing to BIFs sourced from hydrothermal plumbing system. The trace element ratios (Y/Ho, Sm/Yb, and Eu/Sm) consistent with a dominant hydrothermal input in their origin. The mineralogical facies changes, combined with the redox-sensitive elemental signatures coupled with published redox sensitive isotope biomarkers suggest fluctuation in the redox conditions of ocean basins through Archean and oxygenation of ocean initiated at least two hundred million years before the Great Oxidation Event (GOE).</div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 3","pages":"Article 126268"},"PeriodicalIF":2.6,"publicationDate":"2025-03-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143609226","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-23DOI: 10.1016/j.chemer.2025.126265
Rahul Nag , H. Hrushikesh , Nathan Cogné , Bivin G. George , Darius J.M. Thabah , N. Prabhakar
The widespread granite magmatism in the Assam-Meghalaya Gneissic Complex (AMGC) is crucial for understanding its tectono-magmatic evolution of NE India. This study presents geochemical and Sr-Nd isotopic data along with U-Pb zircon and U-Th-total Pb monazite ages of granites from western, central and eastern parts of the AMGC. Zircon U-Pb dating reveals two distinct episodes of granite magmatism during 1617–1603 Ma and 540–497 Ma. Geochemically, the ∼1.6 Ga and ∼ 0.5 Ga granites exhibit high SiO2, Na2O + K2O, and moderate to low CaO and MgO contents. These granites show high Ga/Al ratios and display enrichment in large-ion lithophile elements (LILEs) relative to high field strength elements (HFSE). The ∼1.6 Ga and ∼ 0.5 Ga granites are classified as A-type granites that were emplaced in post-collisional extensional tectonic setting. The ∼1.6 Ga granites show variable Nd composition [εNd(t) = 0.4 to −3.9] with Nd model ages (TDM) of 2.6–2.2 Ga, indicating that these granites were derived from the partial melting of juvenile underplated mafic lower crust. In contrast, the ∼0.5 Ga granites show uniform negative εNd(t) values of −10.8 to −12.1 and younger Nd model ages (TDM) of 2.2–1.7 Ga, suggesting that these granites were derived from the partial melting of the Paleoproterozoic to Mesoproterozoic continental crust beneath the AMGC. The two episodes of A-type granite magmatism in AMGC at ∼1.6 Ga and ∼ 0.5 Ga mark the collisional imprints of Columbia and East Gondwana assemblies, respectively.
阿萨姆-梅加拉亚片麻岩群（AMGC）中广泛存在的花岗岩岩浆活动对于了解印度东北部的构造-岩浆演化至关重要。本研究提供了来自阿萨姆-梅加拉亚片麻岩群西部、中部和东部地区花岗岩的地球化学和 Sr-Nd 同位素数据，以及 U-Pb 锆石和 U-Th 总铅独居石年龄。锆石U-Pb年代测定揭示了1617-1603Ma和540-497Ma两个截然不同的花岗岩岩浆期。从地球化学角度来看，1.6 Ga ∼ 和 0.5 Ga ∼ 花岗岩显示出较高的 SiO2、Na2O + K2O 含量，以及中等至较低的 CaO 和 MgO 含量。这些花岗岩显示出较高的镓/铝比率，并显示出大离子亲岩元素（LILEs）相对于高场强元素（HFSE）的富集。1.6Ga∼和0.5Ga∼花崗岩被分類為A型花崗岩，在碰撞後的伸展構造環境中噴出。1.6 Ga∼花崗岩呈現多變的釹成份﹝εNd(t) = 0.4至-3.9﹞，其釹模型年齡﹝TDM﹞為2.6至2.2 Ga，顯示這些花崗岩是由幼年的下plated岩漿下地殼局部熔融而成。与此相反，∼0.5 Ga花岗岩的εNd(t)值为-10.8至-12.1的均匀负值，钕模型年龄（TDM）为2.2-1.7 Ga，表明这些花岗岩是由AMGC下的古近纪至中新生代大陆地壳部分熔融而成。AMGC在1.6 Ga∼和0.5 Ga∼发生的两次A型花岗岩岩浆活动分别标志着哥伦比亚和东冈瓦纳集合的碰撞印记。
{"title":"Petrogenesis and tectonic significance of ∼1.6 Ga and ∼ 0.5 Ga A-type granite magmatism in the Assam-Meghalaya Gneissic Complex (NE India): Insights from geochronology, geochemistry and Sr-Nd isotopes","authors":"Rahul Nag , H. Hrushikesh , Nathan Cogné , Bivin G. George , Darius J.M. Thabah , N. Prabhakar","doi":"10.1016/j.chemer.2025.126265","DOIUrl":"10.1016/j.chemer.2025.126265","url":null,"abstract":"<div><div>The widespread granite magmatism in the Assam-Meghalaya Gneissic Complex (AMGC) is crucial for understanding its tectono-magmatic evolution of NE India. This study presents geochemical and Sr-Nd isotopic data along with U-Pb zircon and U-Th-total Pb monazite ages of granites from western, central and eastern parts of the AMGC. Zircon U-Pb dating reveals two distinct episodes of granite magmatism during 1617–1603 Ma and 540–497 Ma. Geochemically, the ∼1.6 Ga and ∼ 0.5 Ga granites exhibit high SiO<sub>2</sub>, Na<sub>2</sub>O + K<sub>2</sub>O, and moderate to low CaO and MgO contents. These granites show high Ga/Al ratios and display enrichment in large-ion lithophile elements (LILEs) relative to high field strength elements (HFSE). The ∼1.6 Ga and ∼ 0.5 Ga granites are classified as A-type granites that were emplaced in post-collisional extensional tectonic setting. The ∼1.6 Ga granites show variable Nd composition [εNd(t) = 0.4 to −3.9] with Nd model ages (T<sub>DM</sub>) of 2.6–2.2 Ga, indicating that these granites were derived from the partial melting of juvenile underplated mafic lower crust. In contrast, the ∼0.5 Ga granites show uniform negative εNd(t) values of −10.8 to −12.1 and younger Nd model ages (T<sub>DM</sub>) of 2.2–1.7 Ga, suggesting that these granites were derived from the partial melting of the Paleoproterozoic to Mesoproterozoic continental crust beneath the AMGC. The two episodes of A-type granite magmatism in AMGC at ∼1.6 Ga and ∼ 0.5 Ga mark the collisional imprints of Columbia and East Gondwana assemblies, respectively.</div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 3","pages":"Article 126265"},"PeriodicalIF":2.6,"publicationDate":"2025-02-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143632046","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-21DOI: 10.1016/j.chemer.2025.126264
Ashutosh Pandey , T. Pon Gayathri , K.-N. Pang , Irfan M. Bhat , H.K. Sachan
The Early Permian Panjal Traps in northwestern Himalaya are the by far largest continuous expression of the Panjal-Qiangtang large igneous province (LIP). The eruption of the Panjal Traps is connected with the rifting at the northern continental margin of Gondwana, leading to the formation of the ribbon-shaped continent ‘Cimmeria’ and the opening of the Neo-Tethys Ocean. This study presents geochemical investigations on the lava flows from the Sonmarg area in the Kashmir Valley, representing the northeastern extremity of the Panjal Traps, to understand the spatio-temporal variations in the compositions of the traps and to constrain their petrogenesis and tectonic implications. The upper and lower flows show distinct geochemical characteristics, with the lower flows (classified as Group I basalts) showing negative high-field strength elements (Nb, Ta, Ti) anomalies similar to arc-related basalts and melts derived from the sub-continental lithospheric mantle (SCLM), and the upper flows (classified as Group II basalts) having geochemical traits similar to enriched mid-ocean ridge basalts (E-MORB). The geochemical affinity of the Group I basalts with arc-related basalts is interpreted as a result of significant assimilation of continental crust during ascent of these melts while undergoing fractionation of a gabbroic assemblage. It is inferred that the Group I basalts erupted during continental extension when continental crust was thinned and available for the uprising magma for assimilation. In contrast, the petrogenesis of the upper Group II basalts is inferred to occur in an extended rift where hot convecting sub-lithospheric mantle underwent adiabatic decompression melting. The transition from the eruption of Group I basalts to Group II basalts reflects the progressive evolution of mantle sources from sub-continental lithospheric mantle to sub-lithospheric mantle melting regimes during the passive continental extension at the northern margin of Gondwana in the Early Permian.
{"title":"Geochemical insights into the origins of compositionally distinct Early Permian Panjal Traps basalts: Implications for the transition from continental lithospheric to sub-lithospheric mantle melting regimes","authors":"Ashutosh Pandey , T. Pon Gayathri , K.-N. Pang , Irfan M. Bhat , H.K. Sachan","doi":"10.1016/j.chemer.2025.126264","DOIUrl":"10.1016/j.chemer.2025.126264","url":null,"abstract":"<div><div>The Early Permian Panjal Traps in northwestern Himalaya are the by far largest continuous expression of the Panjal-Qiangtang large igneous province (LIP). The eruption of the Panjal Traps is connected with the rifting at the northern continental margin of Gondwana, leading to the formation of the ribbon-shaped continent ‘Cimmeria’ and the opening of the Neo-Tethys Ocean. This study presents geochemical investigations on the lava flows from the Sonmarg area in the Kashmir Valley, representing the northeastern extremity of the Panjal Traps, to understand the spatio-temporal variations in the compositions of the traps and to constrain their petrogenesis and tectonic implications. The upper and lower flows show distinct geochemical characteristics, with the lower flows (classified as Group I basalts) showing negative high-field strength elements (Nb, Ta, Ti) anomalies similar to arc-related basalts and melts derived from the sub-continental lithospheric mantle (SCLM), and the upper flows (classified as Group II basalts) having geochemical traits similar to enriched mid-ocean ridge basalts (E-MORB). The geochemical affinity of the Group I basalts with arc-related basalts is interpreted as a result of significant assimilation of continental crust during ascent of these melts while undergoing fractionation of a gabbroic assemblage. It is inferred that the Group I basalts erupted during continental extension when continental crust was thinned and available for the uprising magma for assimilation. In contrast, the petrogenesis of the upper Group II basalts is inferred to occur in an extended rift where hot convecting sub-lithospheric mantle underwent adiabatic decompression melting. The transition from the eruption of Group I basalts to Group II basalts reflects the progressive evolution of mantle sources from sub-continental lithospheric mantle to sub-lithospheric mantle melting regimes during the passive continental extension at the northern margin of Gondwana in the Early Permian.</div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 1","pages":"Article 126264"},"PeriodicalIF":2.6,"publicationDate":"2025-02-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143561901","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-19DOI: 10.1016/j.chemer.2025.126262
Adel A. Surour , Ahmed A. Madani , Mohamed A. El Sobky
The present research focuses on the application some remote sensing techniques, mostly ASD FeldSpec combined with principal component analysis (PCA) and fusion color composite (FCC), to discriminate different Neoproterozoic shield rocks at the Wadi Kalalat area, Egypt. In addition, geochemical characteristics are utilized for better understanding of geodynamic evolution of ophiolitic serpentinites in the area as the oldest rock unit. Also, the present research records two varieties of listwaenite (calcic and silicic) at a new locality in the Eastern Desert of Egypt. The ophiolitic serpentinites ± listwaenites, as well as the island-arc metagabbro-diorite complex, crop out at both flanks of the Wadi Kalalat main course while the arc-related fresh peridotite and olivine gabbro of the Gabal El-Motaghairat intrusion crop out at the northern flank of the wadi. Mineralogically, partially serpentinized peridotite relics contain ferroenstatite (12.49 wt% FeO, 28.6 wt% MgO), diopside, green transparent spinel (pleonsate) and Cr-spinel. Chemistry of Cr-spinel indicates freshness of a picotite composition (4.34–9.88 wt% MgO, 17.87–19 wt% Al2O3, 42.48–44.14 wt% FeO, 23.16–26.07 wt% Cr2O3). Trails of fine magnetite form at cores of chrysotile veinlets contemporaneous with the formation of mesh-textured massive serpentinite. Coarse magnetite disseminations and Cr-magnetite as the peripheral rim of zoned Cr-spinel are connected to antigorite formation at upper greenschist-lower amphibolite serpentinization condition. Feldspec reflectance bands in the range 0.45–2.5 μm, combined with results from PCA and FCC, discriminate serpentinites and their related listwaenites from other rock units in the area, and with perfect discrimination of El-Motaghairat mafic-ultramafic arc intrusion from the island arc rocks and the Batuga granite pluton. Magnetite content, serpentine mineralogy, contents of metal-OH, Mg2+, Fe2+, Fe3+, in addition to fresh phases such as olivine and clinopyroxene are the controlling factors for the lithological discrimination on the basis of reflectance spectroscopy. From the geodynamic point of view, and based on contents of SiO2, Al2O3, MgO, CaO and LILEs in the Wadi Kalalat serpentinites, the mantle peridotite was emplaced as a depleted wedge in a mid-ocean ridge (MOR) setting rather than in a supra-subduction zone (SSZ) setting. Our findings point out to the fact that listwaenitization is a hydrothermal process that lead to drastic depletion of transitional metals (Cr, Ni, V, Co) from the serpentinite precursor.
{"title":"Integration of mineralogical, geochemical and ASD reflectance spectra data for characterization and evolution of Neoproterozoic serpentinites and listwaenites at Wadi Kalalat area, South Eastern Desert of Egypt","authors":"Adel A. Surour , Ahmed A. Madani , Mohamed A. El Sobky","doi":"10.1016/j.chemer.2025.126262","DOIUrl":"10.1016/j.chemer.2025.126262","url":null,"abstract":"<div><div>The present research focuses on the application some remote sensing techniques, mostly ASD FeldSpec combined with principal component analysis (PCA) and fusion color composite (FCC), to discriminate different Neoproterozoic shield rocks at the Wadi Kalalat area, Egypt. In addition, geochemical characteristics are utilized for better understanding of geodynamic evolution of ophiolitic serpentinites in the area as the oldest rock unit. Also, the present research records two varieties of listwaenite (calcic and silicic) at a new locality in the Eastern Desert of Egypt. The ophiolitic serpentinites ± listwaenites, as well as the island-arc metagabbro-diorite complex, crop out at both flanks of the Wadi Kalalat main course while the arc-related fresh peridotite and olivine gabbro of the Gabal El-Motaghairat intrusion crop out at the northern flank of the wadi. Mineralogically, partially serpentinized peridotite relics contain ferroenstatite (12.49 wt% FeO, 28.6 wt% MgO), diopside, green transparent spinel (pleonsate) and Cr-spinel. Chemistry of Cr-spinel indicates freshness of a picotite composition (4.34–9.88 wt% MgO, 17.87–19 wt% Al<sub>2</sub>O<sub>3</sub>, 42.48–44.14 wt% FeO, 23.16–26.07 wt% Cr<sub>2</sub>O<sub>3</sub>). Trails of fine magnetite form at cores of chrysotile veinlets contemporaneous with the formation of mesh-textured massive serpentinite. Coarse magnetite disseminations and Cr-magnetite as the peripheral rim of zoned Cr-spinel are connected to antigorite formation at upper greenschist-lower amphibolite serpentinization condition. Feldspec reflectance bands in the range 0.45–2.5 μm, combined with results from PCA and FCC, discriminate serpentinites and their related listwaenites from other rock units in the area, and with perfect discrimination of El-Motaghairat mafic-ultramafic arc intrusion from the island arc rocks and the Batuga granite pluton. Magnetite content, serpentine mineralogy, contents of metal-OH, Mg<sup>2+</sup>, Fe<sup>2+</sup>, Fe<sup>3+</sup>, in addition to fresh phases such as olivine and clinopyroxene are the controlling factors for the lithological discrimination on the basis of reflectance spectroscopy. From the geodynamic point of view, and based on contents of SiO<sub>2</sub>, Al<sub>2</sub>O<sub>3</sub>, MgO, CaO and LILEs in the Wadi Kalalat serpentinites, the mantle peridotite was emplaced as a depleted wedge in a mid-ocean ridge (MOR) setting rather than in a supra-subduction zone (SSZ) setting. Our findings point out to the fact that listwaenitization is a hydrothermal process that lead to drastic depletion of transitional metals (Cr, Ni, V, Co) from the serpentinite precursor.</div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 1","pages":"Article 126262"},"PeriodicalIF":2.6,"publicationDate":"2025-02-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143561894","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-09DOI: 10.1016/j.chemer.2025.126255
FengChun Li , QingDong Zeng , HongRui Fan , KuiFeng Yang , Jolan Acke , Bing Yu , JinJian Wu , Anouk M. Borst
The Dashigou deposit is a carbonatite-hosted REE-Mo deposit within the Huanglonpu metallogenic district of the Qinling belt in central China. This work aims to study origin of heavy REE enrichment using the mineralogy, mineral chemistry and C-O-Sr-Nd isotope signatures of the carbonates. Two stages of REE mineralization are distinguished, along with two generations of calcite (Cal-I and Cal-II). Monazite, bastnäsite, and xenotime are the primary REE minerals at the early carbonatite stage, with Cal-I having a high REE content of 1257–1745 ppm. The late-stage veins are characterized by abundant REE minerals, sulfates, and sulfides, including monazite, allanite, betafite group minerals, celestine, baryte, molybdenite, pyrite and sphalerite. Early magmatic minerals show signs of secondary replacement and metasomatism, with particularly abundant hydrothermal calcite and allanite. This indicates that REEs were remobilized hydrothermally into a secondary REE-rich mineral assemblage, possibly in large part through the dissolution of early REE-rich calcite. This is also supported by Cal-II having lower REE contents compared to CalI. In situ trace element compositions display a flat REE pattern with HREE enrichment compared to bulk rock compositions. The Cal-I contains a higher HREE content of 768–1124 ppm with (La/Lu) N ratios of 0.84–1.37, making it the dominant mineral that controls the HREE budget in Dashigou. The CO isotopic compositions of calcite have a narrow range from −7.27 to −6.65 ‰, and from 9.10 to 9.28 ‰, respectively, falling within the primary igneous carbonatite field. This indicates it is mantle-derived. In situ Sr isotopic values of calcite vary between 0.70502 and 0.70572, which are comparable to bulk rock values for the Huanglongpu carbonatites. Monazite grains from the Dashigou carbonatites have 143Nd/144Nd ratios between 0.51190 and 0.51205, and their εNd (t) values vary from −10.0 to −7.1, with an average value of −8.5. Our data suggests that both enriched mantle and crustal components contributed to the formation of REE-Mo mineralization in the Dashigou carbonatites.
{"title":"The origin and evolution of REE enrichment in the Dashigou Mo-REE deposit, China: Insights from mineralogy, geochemistry and C-O-Sr-Nd isotope systematics","authors":"FengChun Li , QingDong Zeng , HongRui Fan , KuiFeng Yang , Jolan Acke , Bing Yu , JinJian Wu , Anouk M. Borst","doi":"10.1016/j.chemer.2025.126255","DOIUrl":"10.1016/j.chemer.2025.126255","url":null,"abstract":"<div><div>The Dashigou deposit is a carbonatite-hosted REE-Mo deposit within the Huanglonpu metallogenic district of the Qinling belt in central China. This work aims to study origin of heavy REE enrichment using the mineralogy, mineral chemistry and C-O-Sr-Nd isotope signatures of the carbonates. Two stages of REE mineralization are distinguished, along with two generations of calcite (Cal-I and Cal-II). Monazite, bastnäsite, and xenotime are the primary REE minerals at the early carbonatite stage, with Cal-I having a high REE content of 1257–1745 ppm. The late-stage veins are characterized by abundant REE minerals, sulfates, and sulfides, including monazite, allanite, betafite group minerals, celestine, baryte, molybdenite, pyrite and sphalerite. Early magmatic minerals show signs of secondary replacement and metasomatism, with particularly abundant hydrothermal calcite and allanite. This indicates that REEs were remobilized hydrothermally into a secondary REE-rich mineral assemblage, possibly in large part through the dissolution of early REE-rich calcite. This is also supported by Cal-II having lower REE contents compared to Cal<img>I. In situ trace element compositions display a flat REE pattern with HREE enrichment compared to bulk rock compositions. The Cal-I contains a higher HREE content of 768–1124 ppm with (La/Lu) N ratios of 0.84–1.37, making it the dominant mineral that controls the HREE budget in Dashigou. The C<img>O isotopic compositions of calcite have a narrow range from −7.27 to −6.65 ‰, and from 9.10 to 9.28 ‰, respectively, falling within the primary igneous carbonatite field. This indicates it is mantle-derived. In situ Sr isotopic values of calcite vary between 0.70502 and 0.70572, which are comparable to bulk rock values for the Huanglongpu carbonatites. Monazite grains from the Dashigou carbonatites have <sup>143</sup>Nd/<sup>144</sup>Nd ratios between 0.51190 and 0.51205, and their εNd (t) values vary from −10.0 to −7.1, with an average value of −8.5. Our data suggests that both enriched mantle and crustal components contributed to the formation of REE-Mo mineralization in the Dashigou carbonatites.</div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 1","pages":"Article 126255"},"PeriodicalIF":2.6,"publicationDate":"2025-02-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143561666","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-04DOI: 10.1016/j.chemer.2025.126258
Xuegen Chen , Shangguo Su , M. Santosh , Yanan Zhang , Xiaoman Wu , Jingyu Zhong , Xiaowei Li
Fluids play a critical role in the formation of porphyry copper (Cu)‑gold (Au) deposits, although the mechanism of metal transport remains enigmatic. The presence of phengite in the Oubulage porphyry Cu-Au deposit in Inner Mongolia provides a unique opportunity to evaluate this problem. In this study, we present results from texture, elemental and isotopic composition of phengite and calcite in the Oubulage quartz porphyry, with a view to understand the role of fluids in the ore genesis. The quartz phenocrysts from this deposit show shock-induced textures, substantial fragmentation, and deformation lamellae in quartz porphyry. The phenocrysts are frequently intersected by veins which consist of phengite, K-feldspar, rutile, ankerite, apatite, and sulfide. Phengite, with Si contents peaking at 3.40 apfu indicates a maximum pressure of approximately 14.4 Kbar. The quartz porphyry shows vesicular and amygdaloidal structures, with vesicular volumes reaching a maximum of 25 %. The elevated Nb + Ta contents and a Nb/Ta ratio exceeding 17.7 in phengite, suggest the important role of supercritical fluids for the origin of phengite. According to the Zr thermometer for rutile, the temperature of these supercritical fluids is approximately 788.3 °C. In-situ carbon‑oxygen isotopic measurements in calcite associated with the sulfide mineralization (δ13CPDB ranging from −6.54 ‰ to −4.26 ‰ and δ18OVSMOW between 8.24 ‰ and 9.13 ‰)， and the strontium isotope measurements in apatite (87Sr/86Sr = 0.7056–0.7060) associated with sulfide mineralization, suggest a mantle source for the fluids. We propose that the injection of supercritical fluids rich in Si, Ti, Al, K, Fe, C and F into sulfide melt might have caused fluid overpressure in the magma chamber. This resulted in the fracturing of the phenocryst minerals and formation of high-Si phengite, as well as propelling the upward movement of the ore-bearing melt-fluid towards the upper crust. Our findings also have implications for the exploration of porphyry ore deposits.
{"title":"The role of fluid overpressure in Cu-Au porphyry mineralization: Evidence from the Oubulage deposit, Inner Mongolia, China","authors":"Xuegen Chen , Shangguo Su , M. Santosh , Yanan Zhang , Xiaoman Wu , Jingyu Zhong , Xiaowei Li","doi":"10.1016/j.chemer.2025.126258","DOIUrl":"10.1016/j.chemer.2025.126258","url":null,"abstract":"<div><div>Fluids play a critical role in the formation of porphyry copper (Cu)‑gold (Au) deposits, although the mechanism of metal transport remains enigmatic. The presence of phengite in the Oubulage porphyry Cu-Au deposit in Inner Mongolia provides a unique opportunity to evaluate this problem. In this study, we present results from texture, elemental and isotopic composition of phengite and calcite in the Oubulage quartz porphyry, with a view to understand the role of fluids in the ore genesis. The quartz phenocrysts from this deposit show shock-induced textures, substantial fragmentation, and deformation lamellae in quartz porphyry. The phenocrysts are frequently intersected by veins which consist of phengite, K-feldspar, rutile, ankerite, apatite, and sulfide. Phengite, with Si contents peaking at 3.40 apfu indicates a maximum pressure of approximately 14.4 Kbar. The quartz porphyry shows vesicular and amygdaloidal structures, with vesicular volumes reaching a maximum of 25 %. The elevated Nb + Ta contents and a Nb/Ta ratio exceeding 17.7 in phengite, suggest the important role of supercritical fluids for the origin of phengite. According to the Zr thermometer for rutile, the temperature of these supercritical fluids is approximately 788.3 °C. In-situ carbon‑oxygen isotopic measurements in calcite associated with the sulfide mineralization (δ<sup>13</sup>C<sub>PDB</sub> ranging from −6.54 ‰ to −4.26 ‰ and δ<sup>18</sup>O<sub>VSMOW</sub> between 8.24 ‰ and 9.13 ‰)， and the strontium isotope measurements in apatite (<sup>87</sup>Sr/<sup>86</sup>Sr = 0.7056–0.7060) associated with sulfide mineralization, suggest a mantle source for the fluids. We propose that the injection of supercritical fluids rich in Si, Ti, Al, K, Fe, C and F into sulfide melt might have caused fluid overpressure in the magma chamber. This resulted in the fracturing of the phenocryst minerals and formation of high-Si phengite, as well as propelling the upward movement of the ore-bearing melt-fluid towards the upper crust. Our findings also have implications for the exploration of porphyry ore deposits.</div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 1","pages":"Article 126258"},"PeriodicalIF":2.6,"publicationDate":"2025-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143561816","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-03DOI: 10.1016/j.chemer.2025.126254
Hui Chen, Bin Li
The North China Craton (NCC) has undergone substantial thinning of its Paleozoic lithosphere. The original lithosphere was supplanted by a juvenile one during the Mesozoic era. Nevertheless, ongoing scholarly discourse exists concerning the precise age and mechanism of this lithospheric thinning. In this paper, we examined U-Pb dates on gold-related diabase-porphyry along with whole-rock elemental and Nd-Sr isotopes. Three categories of diabase-porphyry have been identified based on their petrographic features and titanium content. These are the low-Ti diabase-porphyry from Shangzhuang, the medium-Ti lamprophyres from Huangbuling, and the high-Ti diabase-porphyry from Qilishan. Their TiO2 content are <1.1, 1.1, and >1.1 wt% for the Shangzhuang, Huangbuling, and Qilishan, respectively. The Ti/Y ratio varies among them, with the highest value in the Qilishan diabase-porphyry, a lower value in the Shangzhuang diabase-porphyry (370), and medium values between 270 and 370 in the Huangbuling lamprophyres.
The geochemical nature of the low-Ti diabase-porphyry, which are LREE-rich and have a higher LILE/HFSE ratio, are evocative of volcanic arcs. The Nd-Sr isotopes of the low-Ti rocks closely resemble those of mafic dikes originating from a fertile mantle lithosphere in the Jiaodong Peninsula. Conversely, the high-Ti diabase-porphyry display OIB-like characteristics, featuring HFSE enrichment with no Nb-Ta depletion. Their Sr-Nd isotope compositions are similar to isotopic signatures from asthenosphere-derived rocks, suggesting that the high-Ti diabase-porphyry may have originated in an asthenospheric mantle. Lastly, the Sr-Nd compositions of the medium-Ti diabase-porphyry fall between those of the low and high titanium diabase-porphyry, and they show weak enrichments in LILE/HFSE and LREE. This implies that a mixed melt of lithosphere and asthenosphere may have generated the medium-Ti lamprophyres. Zircon U-Pb isotopes suggests that the medium-Ti lamprophyres record weak lithospheric thinning in response to the sinking and/or rollback of the subducting oceanic slab at 155 Ma. The coexistence of high-Ti and low-Ti diabase-porphyry signifies a rapid shift in the magma sources from those derived from the lithosphere to those derived from the asthenosphere. This suggests lithospheric detachment (at 75–85 km depth) just before 127 Ma beneath the Jiaodong Peninsula.
{"title":"Lithospheric thinning of the North China Craton: Constraints from Mesozoic mafic dikes in the Jiaodong Peninsula","authors":"Hui Chen, Bin Li","doi":"10.1016/j.chemer.2025.126254","DOIUrl":"10.1016/j.chemer.2025.126254","url":null,"abstract":"<div><div>The North China Craton (NCC) has undergone substantial thinning of its Paleozoic lithosphere. The original lithosphere was supplanted by a juvenile one during the Mesozoic era. Nevertheless, ongoing scholarly discourse exists concerning the precise age and mechanism of this lithospheric thinning. In this paper, we examined U-Pb dates on gold-related diabase-porphyry along with whole-rock elemental and Nd-Sr isotopes. Three categories of diabase-porphyry have been identified based on their petrographic features and titanium content. These are the low-Ti diabase-porphyry from Shangzhuang, the medium-Ti lamprophyres from Huangbuling, and the high-Ti diabase-porphyry from Qilishan. Their TiO<sub>2</sub> content are <1.1, 1.1, and >1.1 wt% for the Shangzhuang, Huangbuling, and Qilishan, respectively. The Ti/Y ratio varies among them, with the highest value in the Qilishan diabase-porphyry, a lower value in the Shangzhuang diabase-porphyry (370), and medium values between 270 and 370 in the Huangbuling lamprophyres.</div><div>The geochemical nature of the low-Ti diabase-porphyry, which are LREE-rich and have a higher LILE/HFSE ratio, are evocative of volcanic arcs. The Nd-Sr isotopes of the low-Ti rocks closely resemble those of mafic dikes originating from a fertile mantle lithosphere in the Jiaodong Peninsula. Conversely, the high-Ti diabase-porphyry display OIB-like characteristics, featuring HFSE enrichment with no Nb-Ta depletion. Their Sr-Nd isotope compositions are similar to isotopic signatures from asthenosphere-derived rocks, suggesting that the high-Ti diabase-porphyry may have originated in an asthenospheric mantle. Lastly, the Sr-Nd compositions of the medium-Ti diabase-porphyry fall between those of the low and high titanium diabase-porphyry, and they show weak enrichments in LILE/HFSE and LREE. This implies that a mixed melt of lithosphere and asthenosphere may have generated the medium-Ti lamprophyres. Zircon U-Pb isotopes suggests that the medium-Ti lamprophyres record weak lithospheric thinning in response to the sinking and/or rollback of the subducting oceanic slab at 155 Ma. The coexistence of high-Ti and low-Ti diabase-porphyry signifies a rapid shift in the magma sources from those derived from the lithosphere to those derived from the asthenosphere. This suggests lithospheric detachment (at 75–85 km depth) just before 127 Ma beneath the Jiaodong Peninsula.</div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 1","pages":"Article 126254"},"PeriodicalIF":2.6,"publicationDate":"2025-02-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143561896","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Intense alterations in the form of secondary carbonates, zeolites, and phyllosilicates characterize the volcanic rocks widespread in the Minusa Basin. A common feature of the studied Early Devonian sheet-like and Triassic dyke volcanics is the amygdules of solid bitumen, indicating a potential water-volcanic rocks-hydrocarbons interaction. This paper presents new data on petrography, mineralogy, and stable isotope geochemistry of carbonates and zeolites in Devonian and Triassic basaltic rocks of the Minusa Basin. Calcite and analcime are the main secondary minerals filling pores and fractures in the studied volcanic rocks. These rocks include basalts, trachybasalts, and trachyandesibasalts of the Early Devonian Byskar series, as well as altered olivine basalts of the Triassic Kopievo complex. Calcite was found in all studied samples, whereas analcime was identified only in altered olivine basalts. The carbon isotopic composition of calcite in the Devonian volcanic rocks indicates that the main carbon source was seawater, which could infiltrate into the basaltic bodies through numerous fractures after flooding the region. Atmospheric water and hydrothermal influence were present, as indicated by differences in the carbon isotopic composition of calcite from different locations. In Triassic altered olivine basalts, calcite is represented by two types differing in textural features, isotopic composition, and manganese content. Very low δ18O values indicate that calcite formation in Triassic volcanic rocks occurred through precipitation from high-temperature solutions. It is assumed that these solutions were of mixed origin and consisted of both meteoric waters from the surrounding rocks and deep hydrothermal fluids, the generation of which may have occurred due to the magma cooling. Analcime fills numerous primary pores, and its formation appears to result from the interaction between volcanic material and Na-enriched water. Secondary minerals in both Early Devonian and Triassic volcanics were formed in two stages. Filling of primary pores with calcite and analcime occurred during the early postmagmatic stage. In contrast, calcite veins formed later under the conditions of marine (Devonian rocks) or meteoric (Triassic rocks) water dominance, which was controlled by the fracture development.
{"title":"The carbonate and zeolite alterations in bitumen-containing volcanic rocks of the Minusa Basin, eastern Siberia","authors":"Alexey Ruban, Anastasiya Nikolaeva, Diana Molukpaeva, Evan Dasi, Marina Shaminova, Maxim Rudmin","doi":"10.1016/j.chemer.2025.126257","DOIUrl":"10.1016/j.chemer.2025.126257","url":null,"abstract":"<div><div>Intense alterations in the form of secondary carbonates, zeolites, and phyllosilicates characterize the volcanic rocks widespread in the Minusa Basin. A common feature of the studied Early Devonian sheet-like and Triassic dyke volcanics is the amygdules of solid bitumen, indicating a potential water-volcanic rocks-hydrocarbons interaction. This paper presents new data on petrography, mineralogy, and stable isotope geochemistry of carbonates and zeolites in Devonian and Triassic basaltic rocks of the Minusa Basin. Calcite and analcime are the main secondary minerals filling pores and fractures in the studied volcanic rocks. These rocks include basalts, trachybasalts, and trachyandesibasalts of the Early Devonian Byskar series, as well as altered olivine basalts of the Triassic Kopievo complex. Calcite was found in all studied samples, whereas analcime was identified only in altered olivine basalts. The carbon isotopic composition of calcite in the Devonian volcanic rocks indicates that the main carbon source was seawater, which could infiltrate into the basaltic bodies through numerous fractures after flooding the region. Atmospheric water and hydrothermal influence were present, as indicated by differences in the carbon isotopic composition of calcite from different locations. In Triassic altered olivine basalts, calcite is represented by two types differing in textural features, isotopic composition, and manganese content. Very low δ<sup>18</sup>O values indicate that calcite formation in Triassic volcanic rocks occurred through precipitation from high-temperature solutions. It is assumed that these solutions were of mixed origin and consisted of both meteoric waters from the surrounding rocks and deep hydrothermal fluids, the generation of which may have occurred due to the magma cooling. Analcime fills numerous primary pores, and its formation appears to result from the interaction between volcanic material and Na-enriched water. Secondary minerals in both Early Devonian and Triassic volcanics were formed in two stages. Filling of primary pores with calcite and analcime occurred during the early postmagmatic stage. In contrast, calcite veins formed later under the conditions of marine (Devonian rocks) or meteoric (Triassic rocks) water dominance, which was controlled by the fracture development.</div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 1","pages":"Article 126257"},"PeriodicalIF":2.6,"publicationDate":"2025-02-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143561902","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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