Sunit Mohanty, Divyareshmi Thottungal Ravy, Victor A. Zaitsev, Arundhuti Ghatak
Chemical variations in apatite in context to carbonatites and trace element partitioning between apatites and carbonatite-rich liquids are important in assessing the petrogenesis and evolution of the carbonatites as well as the associated carbonatitic breccia due to apatite's sensitivity to surrounding magma composition. Volcanic carbonatitic breccia is one of the constituent rock types found outside the ring structure of the Amba Dongar Carbonatite Complex (ADC) situated in western India. In the present work, we report the mineral chemistry of apatites from the carbonatitic breccias of the Mongra region (ADC outer core) and compare them to apatites from ADC carbonatites. Apatite chemistry from Mongra displays a larger concentration of rare earth elements, manganese, and chlorine when compared to those of ADC carbonatites. Morphology and distinct zoning of these apatites represent late-stage magmatic processes with high heavy rare earth element concentrations (high Lutetium), followed by interaction of fluids from the surrounding alkaline rocks. Variation in sulphur concentration in the apatites of this study indicates crystallisation under mildly reducing conditions. Integrated field observations, petrography, and apatite mineral chemistry from the Mongra region allow for an understanding of the genesis of apatites in the ADC outer core, with possible implications for late-stage mineral-melt interactions.
{"title":"Decoding Apatite in Volcanic Carbonatitic breccia from Mongra, Northwest of Amba Dongar Carbonatite Complex, Gujarat, India: Insights to Genesis & Rare Earth Element Budgets","authors":"Sunit Mohanty, Divyareshmi Thottungal Ravy, Victor A. Zaitsev, Arundhuti Ghatak","doi":"10.1144/sp551-2023-210","DOIUrl":"https://doi.org/10.1144/sp551-2023-210","url":null,"abstract":"Chemical variations in apatite in context to carbonatites and trace element partitioning between apatites and carbonatite-rich liquids are important in assessing the petrogenesis and evolution of the carbonatites as well as the associated carbonatitic breccia due to apatite's sensitivity to surrounding magma composition. Volcanic carbonatitic breccia is one of the constituent rock types found outside the ring structure of the Amba Dongar Carbonatite Complex (ADC) situated in western India. In the present work, we report the mineral chemistry of apatites from the carbonatitic breccias of the Mongra region (ADC outer core) and compare them to apatites from ADC carbonatites.\u0000 Apatite chemistry from Mongra displays a larger concentration of rare earth elements, manganese, and chlorine when compared to those of ADC carbonatites. Morphology and distinct zoning of these apatites represent late-stage magmatic processes with high heavy rare earth element concentrations (high Lutetium), followed by interaction of fluids from the surrounding alkaline rocks. Variation in sulphur concentration in the apatites of this study indicates crystallisation under mildly reducing conditions. Integrated field observations, petrography, and apatite mineral chemistry from the Mongra region allow for an understanding of the genesis of apatites in the ADC outer core, with possible implications for late-stage mineral-melt interactions.","PeriodicalId":281618,"journal":{"name":"Geological Society, London, Special Publications","volume":"58 2","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141923257","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Mafic magmatism has repeatedly taken place in Pakistan throughout its geologic history from the earliest Proterozoic to Recent. Much of it, however, does not have associated metallic mineralization. This paper concerns mineralization associated with mafic-ultramafic plutonic rock occurrences in the western- and northern suture zones of Pakistan, which demarcate the collision boundary between the northwestern Indian plate and Eurasian blocks. We discuss the petrology of the ophiolites and basaltic magma-related chromite deposits, showings of PGE and Ni minerals, and secondary mineral deposits (emerald and peridot gems, rodingite, and nephrite jade) associated with mafic-ultramafic complexes of the two suture zones. Chromite with high Cr#s (68 to 85) occurs in fair quantity and is mostly considered to be genetically related to basaltic magma of subduction-related environments. PGE and nickeliferous minerals are insignificant in quantity; PGE's are formed by a higher degree of partial melting and melt-rock reaction, whereas Ni-sulphides are the product of serpentinization of the ultramafic rocks. Emerald occurs in several localities in the ISZ, whereas the peridot has so far been reported from only one locality. Emerald is associated with Mg-carbonate ± quartz ± fuchsite ± talc ± serpentine, and peridot (Fo 89-92 ) is associated with chrysotile ± magnesite ± talc ± magnetite ± ludwigite. Both are formed via hydrothermal alteration of ultramafic rocks through the introduction of hydrous fluids incorporating CO 2 , Be, B, K, Al, and possibly Na. In view of the undeformed nature of the emerald and peridot and the 23 Ma age of emerald formation, the mineralization appears to post-date deformation and may be of Late Oligocene-Early Miocene age. The metasomatising fluids were either derived from the subducting Indian plate crust underneath the Kohistan arc or were related to 23-26 Ma silicic magmatism in this area of the NW Indian plate. The nephrite jade in the ophiolite mélange is hosted in serpentinites and has disseminated grains of chrome spinel with elevated Fe/(Mg + Fe) ratios (0.10–0.18), implying low-grade metamorphism of ultramafic rocks (protolith of serpentinite) with loss of Al and introduction of SiO 2 during accompanying metasomatism. The rodingite in Dargai ophiolite could have formed by the action of seawater channeled through fractures and cracks in rocks. However, their mineral assemblages indicate that they formed as a result of the influx of Ca, Al, and Na-bearing hydrothermal fluids related to the intrusion of gabbros/sheeted dykes in the serpentinized ultramafic rocks, resulting in Ca-metasomatism.
在巴基斯坦的地质历史上，从最早的原生代到近代，岩浆岩在巴基斯坦反复发生。然而，其中大部分并没有伴生金属矿化。本文涉及巴基斯坦西部和北部缝合带的黑云母-超黑云母浆岩矿点的相关矿化，这些矿点划分了印度西北板块和欧亚板块之间的碰撞边界。我们讨论了与这两个缝合带的黑云母-超基性岩复合体有关的蛇绿岩和玄武质岩浆相关铬铁矿床的岩石学、PGE 和 Ni 矿物的显示以及次生矿床（祖母绿和橄榄石宝石、罗定岩和软玉）。铬含量较高（68 至 85）的铬铁矿数量相当多，大多被认为与俯冲相关环境中的玄武质岩浆有遗传关系。PGE和含镍矿物的数量很少；PGE是通过较高程度的部分熔化和熔岩反应形成的，而镍硫化物则是超基性岩蛇纹石化的产物。祖母绿出现在 ISZ 的多个地点，而橄榄石迄今只在一个地点有所报道。绿宝石与镁碳酸盐±石英±辉石±滑石±蛇纹石伴生，而橄榄石（Fo 89-92）与温石棉±菱镁矿±滑石±磁铁矿±绿帘石伴生。两者都是通过超基性岩的热液蚀变形成的，其中引入了含有 CO 2、Be、B、K、Al 以及可能的 Na 的含水流体。鉴于祖母绿和橄榄石的未变形性质以及祖母绿形成的 23 Ma 年龄，矿化似乎发生在变形之后，可能属于晚渐新世-早中新世时期。变质流体要么来自科希斯坦弧下俯冲的印度板块地壳，要么与印度西北板块这一地区的23-26Ma硅质岩浆活动有关。蛇绿混杂岩中的软玉赋存于蛇纹岩中，并具有铬尖晶石的散粒，其铁/（镁+铁）比值较高（0.10-0.18），这意味着超基性岩（蛇纹岩的原岩）发生了低级变质作用，在伴随的变质作用过程中，铝流失，氧化硅加入。达尔盖蛇绿岩中的罗丁岩可能是海水通过岩石的裂缝作用形成的。然而，它们的矿物组合表明，它们是在蛇绿岩化超基性岩中的辉长岩/片状岩堤侵入过程中，与含钙、铝和镍的热液涌入有关，导致钙金属化作用而形成的。
{"title":"Magmatic (Cr-Ni-PGE) and secondary/hydrothermal (emerald-peridot-rodingite-nephrite jade) mineralization associated with mafic-ultramafic rock complexes of Pakistan","authors":"M. Q. Jan, Rahat Ullah, Muhammad Naveed Anjum","doi":"10.1144/sp552-2023-99","DOIUrl":"https://doi.org/10.1144/sp552-2023-99","url":null,"abstract":"\u0000 Mafic magmatism has repeatedly taken place in Pakistan throughout its geologic history from the earliest Proterozoic to Recent. Much of it, however, does not have associated metallic mineralization. This paper concerns mineralization associated with mafic-ultramafic plutonic rock occurrences in the western- and northern suture zones of Pakistan, which demarcate the collision boundary between the northwestern Indian plate and Eurasian blocks. We discuss the petrology of the ophiolites and basaltic magma-related chromite deposits, showings of PGE and Ni minerals, and secondary mineral deposits (emerald and peridot gems, rodingite, and nephrite jade) associated with mafic-ultramafic complexes of the two suture zones. Chromite with high Cr#s (68 to 85) occurs in fair quantity and is mostly considered to be genetically related to basaltic magma of subduction-related environments. PGE and nickeliferous minerals are insignificant in quantity; PGE's are formed by a higher degree of partial melting and melt-rock reaction, whereas Ni-sulphides are the product of serpentinization of the ultramafic rocks. Emerald occurs in several localities in the ISZ, whereas the peridot has so far been reported from only one locality. Emerald is associated with Mg-carbonate ± quartz ± fuchsite ± talc ± serpentine, and peridot (Fo\u0000 89-92\u0000 ) is associated with chrysotile ± magnesite ± talc ± magnetite ± ludwigite. Both are formed via hydrothermal alteration of ultramafic rocks through the introduction of hydrous fluids incorporating CO\u0000 2\u0000 , Be, B, K, Al, and possibly Na. In view of the undeformed nature of the emerald and peridot and the 23 Ma age of emerald formation, the mineralization appears to post-date deformation and may be of Late Oligocene-Early Miocene age. The metasomatising fluids were either derived from the subducting Indian plate crust underneath the Kohistan arc or were related to 23-26 Ma silicic magmatism in this area of the NW Indian plate. The nephrite jade in the ophiolite mélange is hosted in serpentinites and has disseminated grains of chrome spinel with elevated Fe/(Mg + Fe) ratios (0.10–0.18), implying low-grade metamorphism of ultramafic rocks (protolith of serpentinite) with loss of Al and introduction of SiO\u0000 2\u0000 during accompanying metasomatism. The rodingite in Dargai ophiolite could have formed by the action of seawater channeled through fractures and cracks in rocks. However, their mineral assemblages indicate that they formed as a result of the influx of Ca, Al, and Na-bearing hydrothermal fluids related to the intrusion of gabbros/sheeted dykes in the serpentinized ultramafic rocks, resulting in Ca-metasomatism.\u0000","PeriodicalId":281618,"journal":{"name":"Geological Society, London, Special Publications","volume":" 3","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141822718","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
W. D. Smith, B. Albrechtsen, W. Maier, J. E. Mungall
The Mount Ayliff Complex comprises five cognate mafic-ultramafic bodies emplaced along the southern margin of the Kaapvaal Craton. This study examines the Ingeli and Horseshoe lobes and assesses their magmatic sulphide prospectivity with respect to the Insizwa lobe, which hosts massive sulphides at its Waterfall Gorge occurrence. Ingeli consists of 465 m of olivine-chromite cumulates overlain by 340 m of (olivine-)gabbronorite, while Horseshoe consists of 45 m of olivine gabbronorite overlain by 5 m of gabbro. Ingeli possesses sparsely disseminated sulphides at its mafic-ultramafic transition, whereas disseminated sulphides are present throughout Horseshoe. A petrogenetic model is proposed, whereby magma accumulated and fractionated nickeliferous olivine and chromite in an upper-crustal staging chamber hosted by Proterozoic basement rocks. Magma then ascended and deposited olivine-chromite cumulates at the level of the complex. Prolonged magma flux in the staging chamber instigated the assimilation of basement rocks, triggering sulphide saturation and the crystallisation of Ni-poor olivine. Contaminated magma then ascended and intruded pre-existing cumulates, depositing sulphide melt that may have backflowed as magmatic activity waned. Basaltic magma then flowed over the ultramafic cumulates, depositing disseminated sulphides whilst undergoing closed-system fractionation. Basal depressions and underlying feeder structures are the most prospective locations for magmatic sulphide mineralisation.
{"title":"Petrogenesis and Ni-Cu-(PGE) prospectivity of the Mount Ayliff Complex in the Karoo Igneous Province: new insights from the Ingeli and Horseshoe lobes","authors":"W. D. Smith, B. Albrechtsen, W. Maier, J. E. Mungall","doi":"10.1144/sp552-2023-35","DOIUrl":"https://doi.org/10.1144/sp552-2023-35","url":null,"abstract":"The Mount Ayliff Complex comprises five cognate mafic-ultramafic bodies emplaced along the southern margin of the Kaapvaal Craton. This study examines the Ingeli and Horseshoe lobes and assesses their magmatic sulphide prospectivity with respect to the Insizwa lobe, which hosts massive sulphides at its Waterfall Gorge occurrence. Ingeli consists of 465 m of olivine-chromite cumulates overlain by 340 m of (olivine-)gabbronorite, while Horseshoe consists of 45 m of olivine gabbronorite overlain by 5 m of gabbro. Ingeli possesses sparsely disseminated sulphides at its mafic-ultramafic transition, whereas disseminated sulphides are present throughout Horseshoe. A petrogenetic model is proposed, whereby magma accumulated and fractionated nickeliferous olivine and chromite in an upper-crustal staging chamber hosted by Proterozoic basement rocks. Magma then ascended and deposited olivine-chromite cumulates at the level of the complex. Prolonged magma flux in the staging chamber instigated the assimilation of basement rocks, triggering sulphide saturation and the crystallisation of Ni-poor olivine. Contaminated magma then ascended and intruded pre-existing cumulates, depositing sulphide melt that may have backflowed as magmatic activity waned. Basaltic magma then flowed over the ultramafic cumulates, depositing disseminated sulphides whilst undergoing closed-system fractionation. Basal depressions and underlying feeder structures are the most prospective locations for magmatic sulphide mineralisation.","PeriodicalId":281618,"journal":{"name":"Geological Society, London, Special Publications","volume":"141 16","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141656107","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The chromatographic model for chromitite formation previously presented is updated to include sulphide as a possible participating phase. In the model, chromite is precipitated at an upward-moving reaction front as a Cr-bearing (gabbro)norite protolith reacts with a Cl-rich fluid that becomes progressively undersaturated in pyroxene as it rises into hotter parts of the crystal pile, leaving an anorthositic residue. The liberation of Fe during the dissolution of orthopyroxene can drive concurrent sulphide saturation. If the reaction front encounters an orthopyroxenite the model produces a first-order approximation for the Merensky Reef section of anorthosite – chromite – orthopyroxenite. In addition, MELTS modelling shows that the isothermal addition of Cr 2 O 3 alone to a nearly solid (gabbro)norite assemblage increases the amount of both chromite and liquid at the expense of other silicate minerals owing to the liberation of Ca, Na, and Si, the latter two acting as fluxing agents. A generalized constitutional zone refining model is presented in which a variety of spinel-silicate layering types (e.g, Bushveld magnetite layers and Skaergaard trough banding) in that they can develop over time.
对之前提出的铬铁矿形成的色谱模型进行了更新，将硫化物作为可能的参与相。在该模型中，铬铁矿是在一个向上移动的反应前沿析出的，因为含Cr的（辉长岩）诺雷石原岩与富含Cl的流体发生反应，当流体上升到晶体堆中温度较高的部分时，辉石的饱和度会逐渐降低，从而留下阳起石残留物。正辉石溶解过程中铁的释放会导致硫化物同时饱和。如果反应前沿遇到正长辉石，模型就会对梅伦斯基礁部分的正长辉石-铬铁矿-正长辉石产生一阶近似。此外，MELTS 模型还显示，在近乎固态的（辉长岩）诺拉岩集合体中单独等温添加 Cr 2 O 3 会增加铬铁矿和液体的数量，但由于 Ca、Na 和 Si 的释放，其他硅酸盐矿物的数量会减少，而后两者起到了助熔剂的作用。本文提出了一个广义的宪布区精炼模型，在该模型中，各种尖晶石-硅酸盐分层类型（如布什维尔德磁铁矿层和斯卡尔加德槽带状）都可能随着时间的推移而形成。
{"title":"Formation of PGE- and sulphide-bearing chromitites and associated anorthositic rocks in layered intrusion by infiltration of reactive, Cl-rich fluid","authors":"A. Boudreau","doi":"10.1144/sp552-2022-324","DOIUrl":"https://doi.org/10.1144/sp552-2022-324","url":null,"abstract":"\u0000 The chromatographic model for chromitite formation previously presented is updated to include sulphide as a possible participating phase. In the model, chromite is precipitated at an upward-moving reaction front as a Cr-bearing (gabbro)norite protolith reacts with a Cl-rich fluid that becomes progressively undersaturated in pyroxene as it rises into hotter parts of the crystal pile, leaving an anorthositic residue. The liberation of Fe during the dissolution of orthopyroxene can drive concurrent sulphide saturation. If the reaction front encounters an orthopyroxenite the model produces a first-order approximation for the Merensky Reef section of anorthosite – chromite – orthopyroxenite. In addition, MELTS modelling shows that the isothermal addition of Cr\u0000 2\u0000 O\u0000 3\u0000 alone to a nearly solid (gabbro)norite assemblage increases the amount of both chromite and liquid at the expense of other silicate minerals owing to the liberation of Ca, Na, and Si, the latter two acting as fluxing agents. A generalized constitutional zone refining model is presented in which a variety of spinel-silicate layering types (e.g, Bushveld magnetite layers and Skaergaard trough banding) in that they can develop over time.\u0000","PeriodicalId":281618,"journal":{"name":"Geological Society, London, Special Publications","volume":"99 2","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141657262","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Fractal dimensions characterise the spatial distribution pattern of mineral deposits, allowing the mineralization processes to be grasped beneath and at the surface. This study considered the mineralized vein along the fracture/shear zone near Dona temple, Jonnagiri gold deposit and borehole data from Sangli block, Gadag gold deposit. The above mentioned zones are considered using fractal dimensional analysis to constrain the fluid flow pathways. The box-counting technique is used to measure the fractal dimension of the mineralized vein along the surface from a detailed to regional scale. The fractal correlation integral method is used to provide the fractal dimension values from the gold assay (in g/t). The obtained box-counting fractal dimension values vary from 1.07 to 1.36, whilst fractal dimensions obtained from the fractal correlation integral method range from 0.03 to 1.97. Higher fractal values signify a fully matured interlinked fracture/fault network with steep fluid flow pathways, while lower values indicate the converse condition. Further, the study shows that the fractal analysis of the mineralized vein along fracture/shear zone appears to correlate with the fault system rather than the litho-contact. Economic gold deposition is mainly along the structure with steep fractal gradient, which is the target area for economic gold exploration.
{"title":"Fractal dimension and its implication to Mineral Exploration: A case study from Jonnagiri and Gadag gold deposits in India","authors":"S. Swain, P. N. S. Roy","doi":"10.1144/sp552-2023-33","DOIUrl":"https://doi.org/10.1144/sp552-2023-33","url":null,"abstract":"Fractal dimensions characterise the spatial distribution pattern of mineral deposits, allowing the mineralization processes to be grasped beneath and at the surface. This study considered the mineralized vein along the fracture/shear zone near Dona temple, Jonnagiri gold deposit and borehole data from Sangli block, Gadag gold deposit. The above mentioned zones are considered using fractal dimensional analysis to constrain the fluid flow pathways. The box-counting technique is used to measure the fractal dimension of the mineralized vein along the surface from a detailed to regional scale. The fractal correlation integral method is used to provide the fractal dimension values from the gold assay (in g/t). The obtained box-counting fractal dimension values vary from 1.07 to 1.36, whilst fractal dimensions obtained from the fractal correlation integral method range from 0.03 to 1.97. Higher fractal values signify a fully matured interlinked fracture/fault network with steep fluid flow pathways, while lower values indicate the converse condition. Further, the study shows that the fractal analysis of the mineralized vein along fracture/shear zone appears to correlate with the fault system rather than the litho-contact. Economic gold deposition is mainly along the structure with steep fractal gradient, which is the target area for economic gold exploration.","PeriodicalId":281618,"journal":{"name":"Geological Society, London, Special Publications","volume":"99 7","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141657257","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The climate action plan to limit global warming to 1.5–2°C has substantially enhanced the demand for metals. This has significant implications both for mineral-rich developing countries and for countries with actively exploited deposits. This book will broaden our understanding of existing deposits of PGE–Ni–Cu–Co–Ti–V–Cr and of new prospects for these metals.
{"title":"About this title - Mineral Resources Related to Ultramafic–Mafic Magmas, from Archean to Present: Old Deposits and New Prospects of Chromite, Ti–V–Magnetite and Ni–Cu–(PGE) Sulfides","authors":"S.K. Mondal, L.C. Reisberg, J.M. González-Jiménez, H.S.R. Hughes","doi":"10.1144/sp552-000","DOIUrl":"https://doi.org/10.1144/sp552-000","url":null,"abstract":"The climate action plan to limit global warming to 1.5–2°C has substantially enhanced the demand for metals. This has significant implications both for mineral-rich developing countries and for countries with actively exploited deposits. This book will broaden our understanding of existing deposits of PGE–Ni–Cu–Co–Ti–V–Cr and of new prospects for these metals.","PeriodicalId":281618,"journal":{"name":"Geological Society, London, Special Publications","volume":"23 23","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141660438","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The common spatial and temporal association of calk alkaline lamprophyres with orogenic gold deposits has been recognized for more than a century, although interpretations regarding the significance of this association have varied greatly. A persistent lack of consensus on Archean geodynamics and the deposits themselves presented a challenge to the use of a Mineral Systems approach, given that models should strive to encompass a source to sink understanding of deposit generation. Lamprophyres helped to resolve these issues because the compositions of the most primitive examples establish firm constraints on deep crustal and upper mantle regimes at the time of deposit formation, despite not being directly related to mineralization. Following the initial contribution of lamprophyres toward a coherent model of mineralization, numerous workers provided the important observations and refinements that have resulted in a robust Mineral Systems model for the deposit type. The discovery of diamonds in gold-associated lamprophyres, and circumstantial evidence that this association has been long-lived and widespread, presents opportunities to further refine orogenic gold models.
{"title":"Lamprophyres, Gold and Orogenies: A Mineral Systems Perspective","authors":"Derek A. Wyman","doi":"10.1144/sp551-2024-53","DOIUrl":"https://doi.org/10.1144/sp551-2024-53","url":null,"abstract":"The common spatial and temporal association of calk alkaline lamprophyres with orogenic gold deposits has been recognized for more than a century, although interpretations regarding the significance of this association have varied greatly. A persistent lack of consensus on Archean geodynamics and the deposits themselves presented a challenge to the use of a Mineral Systems approach, given that models should strive to encompass a source to sink understanding of deposit generation. Lamprophyres helped to resolve these issues because the compositions of the most primitive examples establish firm constraints on deep crustal and upper mantle regimes at the time of deposit formation, despite not being directly related to mineralization. Following the initial contribution of lamprophyres toward a coherent model of mineralization, numerous workers provided the important observations and refinements that have resulted in a robust Mineral Systems model for the deposit type. The discovery of diamonds in gold-associated lamprophyres, and circumstantial evidence that this association has been long-lived and widespread, presents opportunities to further refine orogenic gold models.","PeriodicalId":281618,"journal":{"name":"Geological Society, London, Special Publications","volume":" 12","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141676801","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Meteorites provide a wealth of information about the origin of the Earth and the Solar system. Systematic searches have proved successful in cold and hot desert areas. Meteorite finds are favoured in areas with light-coloured surfaces stable over tens of thousands of years and in hyper-arid climates. The deserts of Arabia are well suited for the search for meteorites. Following the first finds by explorers in the 1930s' and during oil exploration in the 1950s', a significant number of finds have been recorded from Oman since 1999 with >4000 meteorites currently recorded. Exploratory searches in Saudi Arabia have also shown significant potential for meteorite discoveries. A collaborative Omani-Swiss search project was initiated in 2001 and 23 search campaigns since have yielded more than 7300 samples, including meteorites from the Moon and Mars and,37 strewn fields. Arabia has the potential to become one of the key regions for meteorite recovery and future research. Only three confirmed (Wabar, Saqqar, Jebel Waqf as Suwwan), several suspected and some dubious impact structures have been reported. The Wabar impact locality in Saudi Arabia features impact craters in dune sands, shocked and melted sand and finds of several large meteorites.
{"title":"The meteoritic record of Arabia","authors":"Beda A. Hofmann, E. Gnos","doi":"10.1144/sp550-2024-8","DOIUrl":"https://doi.org/10.1144/sp550-2024-8","url":null,"abstract":"Meteorites provide a wealth of information about the origin of the Earth and the Solar system. Systematic searches have proved successful in cold and hot desert areas. Meteorite finds are favoured in areas with light-coloured surfaces stable over tens of thousands of years and in hyper-arid climates. The deserts of Arabia are well suited for the search for meteorites. Following the first finds by explorers in the 1930s' and during oil exploration in the 1950s', a significant number of finds have been recorded from Oman since 1999 with >4000 meteorites currently recorded. Exploratory searches in Saudi Arabia have also shown significant potential for meteorite discoveries. A collaborative Omani-Swiss search project was initiated in 2001 and 23 search campaigns since have yielded more than 7300 samples, including meteorites from the Moon and Mars and,37 strewn fields. Arabia has the potential to become one of the key regions for meteorite recovery and future research. Only three confirmed (Wabar, Saqqar, Jebel Waqf as Suwwan), several suspected and some dubious impact structures have been reported. The Wabar impact locality in Saudi Arabia features impact craters in dune sands, shocked and melted sand and finds of several large meteorites.","PeriodicalId":281618,"journal":{"name":"Geological Society, London, Special Publications","volume":" 2","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141673814","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
P. Callapez, F. Barroso-Barcenilla, Mélani Berrocal-Casero, Pedro P. Cunha, P. Dinis, Fernando C. Lopes, Senay Ozkaya de Juanas, Mário M. Mendes, R. Pimentel, Vanda F. dos Santos, M. Segura
The thick post-rift series that cover the Triassic to Lower Cretaceous sedimentary succession of the Lusitanian Basin, in West Central Portugal, are crucial to understand the Mesozoic evolution of the West Iberian Margin, motivating a long history of studies, including those by Daniel Sharpe (1806–1856). They record platform carbonates interbedded with marginal marine and alluvial facies. The post-rift infill was deposited above a late Aptian breakup unconformity and is organised in three unconformity bounded sequences: ‘UBS-4A’ (upper Aptian-upper Cenomanian), ‘UBS-4B’ (lower Turonian-lower Campanian), and ‘UBS-5B’ (lower Campanian-Maastrichtian). The first comprises alluvial siliciclastics and shallow-marine, carbonate sequences rich in Tethyan faunas with ammonites and rudists. During the late Cenomanian, the carbonate platform entirely covered the onshore sectors of the Lusitanian Basin. Several diapiric axes controlled the differentiation of inner platform areas with corals and rudists. The infill of ‘UBS-4B’ occurred after the tectonic uplift and emersion of the sectors located to the south of first order Nazaré Fault Zone. The platform carbonate facies were overlain by regressive micaceous and alluvial coarse siliciclastics. The sequence ‘UBS-5’ overlies a lower Campanian unconformity and has a Campanian-Maastrichtian thick record of alluvial to lagoonal, reddish pelites, rich in vertebrate assemblages.
{"title":"The Cretaceous post-rift series from the Portuguese onshore ranges of the West Iberian Margin and their history of research","authors":"P. Callapez, F. Barroso-Barcenilla, Mélani Berrocal-Casero, Pedro P. Cunha, P. Dinis, Fernando C. Lopes, Senay Ozkaya de Juanas, Mário M. Mendes, R. Pimentel, Vanda F. dos Santos, M. Segura","doi":"10.1144/sp545-2023-183","DOIUrl":"https://doi.org/10.1144/sp545-2023-183","url":null,"abstract":"The thick post-rift series that cover the Triassic to Lower Cretaceous sedimentary succession of the Lusitanian Basin, in West Central Portugal, are crucial to understand the Mesozoic evolution of the West Iberian Margin, motivating a long history of studies, including those by Daniel Sharpe (1806–1856). They record platform carbonates interbedded with marginal marine and alluvial facies. The post-rift infill was deposited above a late Aptian breakup unconformity and is organised in three unconformity bounded sequences: ‘UBS-4A’ (upper Aptian-upper Cenomanian), ‘UBS-4B’ (lower Turonian-lower Campanian), and ‘UBS-5B’ (lower Campanian-Maastrichtian). The first comprises alluvial siliciclastics and shallow-marine, carbonate sequences rich in Tethyan faunas with ammonites and rudists. During the late Cenomanian, the carbonate platform entirely covered the onshore sectors of the Lusitanian Basin. Several diapiric axes controlled the differentiation of inner platform areas with corals and rudists. The infill of ‘UBS-4B’ occurred after the tectonic uplift and emersion of the sectors located to the south of first order Nazaré Fault Zone. The platform carbonate facies were overlain by regressive micaceous and alluvial coarse siliciclastics. The sequence ‘UBS-5’ overlies a lower Campanian unconformity and has a Campanian-Maastrichtian thick record of alluvial to lagoonal, reddish pelites, rich in vertebrate assemblages.","PeriodicalId":281618,"journal":{"name":"Geological Society, London, Special Publications","volume":"92 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141686977","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
B. Bomou, E. De Kaenel, Nicolas Thibault, J. E. Spangenberg, B. Gertsch, G. Frijia, T. Adatte
The mechanisms and palaeoenvironmental conditions leading to and occurring through the Coniacian-Santonian Ocean Anoxic Event 3 (OAE3) are poorly known, particularly with regard to the marine phosphorus cycle and the climatic conditions in general. To explore further these issues, two famous locations have been studied: Olazagutia (Spain) and Ten Mile Creek-Arbor Park (Texas, USA), located in different palaeogeographic areas and deposited at different palaeodepths. Their study is based on mineralogy (bulk and clay), geochemistry (stable isotopes, organic matter, phosphorus and major element), and high-resolution biostratigraphy (nannofossils) to infer changes in climate and primary productivity across OAE3. The investigated sections were both previously proposed as candidates for the base Santonian global boundary stratotype section and point (GSSP). The Olazagutia section was ratified in 2013, where the base of the Santonian was defined by the first appearance datum (FAD) of the inoceramid Platyceramus undulatoplicatus . Both sections, deposited in oxygenated conditions, record the δ 13 C patterns which characterised the Coniacian-Santonian OAE3 interval, in particular the positive carbon-isotope excursions comprising the K2, Michel Dean and Bedwell events. New nannofossil biostratigraphy for both sections is presented including new occurrences. Significant diachronism of marker taxa is observed between the Spanish and Texan sections. Based on a weathering index and mineralogy, similar climate changes are observed in all sections. The climate shifted synchronously from relatively drier to warmer and wetter conditions above the Coniacian-Santonian boundary (C-S boundary) from the Michel Dean event to above the Bedwell event during the early Santonian. Fluctuations in total phosphorus contents appear mainly to have been driven by changes in detrital input and consequently by climate change in Spain and Texas. Several bentonite layers were observed in Texas close to the Coniacian-Santonian boundary, but only one located 7m above the C-S boundary provided sufficient well-preserved zircon minerals, and gives an age of 86.24 ± 0.12 Ma based on U-Pb geochronology, consistent with an early Santonian age. Supplementary material at https://doi.org/10.6084/m9.figshare.c.7268133
{"title":"Palaeoenvironmental and palaeoclimatic study of the Olazagutia (Spain) and Ten Mile Creek-Arbor Park (USA) sections during the Coniacian-Santonian interval","authors":"B. Bomou, E. De Kaenel, Nicolas Thibault, J. E. Spangenberg, B. Gertsch, G. Frijia, T. Adatte","doi":"10.1144/sp545-2023-178","DOIUrl":"https://doi.org/10.1144/sp545-2023-178","url":null,"abstract":"\u0000 \u0000 The mechanisms and palaeoenvironmental conditions leading to and occurring through the Coniacian-Santonian Ocean Anoxic Event 3 (OAE3) are poorly known, particularly with regard to the marine phosphorus cycle and the climatic conditions in general. To explore further these issues, two famous locations have been studied: Olazagutia (Spain) and Ten Mile Creek-Arbor Park (Texas, USA), located in different palaeogeographic areas and deposited at different palaeodepths. Their study is based on mineralogy (bulk and clay), geochemistry (stable isotopes, organic matter, phosphorus and major element), and high-resolution biostratigraphy (nannofossils) to infer changes in climate and primary productivity across OAE3. The investigated sections were both previously proposed as candidates for the base Santonian global boundary stratotype section and point (GSSP). The Olazagutia section was ratified in 2013, where the base of the Santonian was defined by the first appearance datum (FAD) of the inoceramid\u0000 Platyceramus undulatoplicatus\u0000 . Both sections, deposited in oxygenated conditions, record the δ\u0000 13\u0000 C patterns which characterised the Coniacian-Santonian OAE3 interval, in particular the positive carbon-isotope excursions comprising the K2, Michel Dean and Bedwell events. New nannofossil biostratigraphy for both sections is presented including new occurrences. Significant diachronism of marker taxa is observed between the Spanish and Texan sections. Based on a weathering index and mineralogy, similar climate changes are observed in all sections. The climate shifted synchronously from relatively drier to warmer and wetter conditions above the Coniacian-Santonian boundary (C-S boundary) from the Michel Dean event to above the Bedwell event during the early Santonian. Fluctuations in total phosphorus contents appear mainly to have been driven by changes in detrital input and consequently by climate change in Spain and Texas. Several bentonite layers were observed in Texas close to the Coniacian-Santonian boundary, but only one located 7m above the C-S boundary provided sufficient well-preserved zircon minerals, and gives an age of 86.24 ± 0.12 Ma based on U-Pb geochronology, consistent with an early Santonian age.\u0000 \u0000 \u0000 Supplementary material at\u0000 https://doi.org/10.6084/m9.figshare.c.7268133\u0000","PeriodicalId":281618,"journal":{"name":"Geological Society, London, Special Publications","volume":"24 27","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141379064","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：