S. Lohmeier, B. Lottermoser, T. Schirmer, W. Fuchsloch
Historic tin mining and mineral processing of the Uis pegmatite deposit (Namibia) has resulted in a series of tailings impoundments. In this study, Uis tailings were characterised to establish their suitability for brick manufacturing and reprocessing potential for rare metals (Be, Li, Nb, Ta). Tailings occur on-site as two distinct types (a) fine- to medium-grained sand (d50 = 120 to 420 μm) in dune-like spoil dumps; and (b) fine- to medium-grained sand (Fraction A: d50 = 120 to 410 μm; ~25% of tailings type) and fine-grained silt (Fraction B: d50 = 18 to 83 μm; ~75% of tailings type) in four low-lying dried-out waste impoundment cells. The two tailings types have a similar and homogeneous mineralogical composition, comprising quartz, plagioclase, K-feldspar and mica as well as minor cassiterite, columbite-tantalite and petalite, reflecting the micaceous quartzo-feldspathic composition of the source rocks. The main clay mineral is illite with minor (ferroan) clinochlore, cookeite and kaolinite. Such a mineralogical composition allows contemporary brick fabrication due to illite as the main clay mineral, a large proportion of quartz as a stabilizer and only trace amounts of minerals that could have a detrimental effect (e.g. Fe oxides and pyrite). Consequently, the consistent particle size distribution and homogeneous mineralogical composition allow present-day production of high-quality fired bricks from tailings. To date, the use of Uis tailings for brick manufacturing supports the local economy, aids building development and removes silica-rich mine wastes prone to dust dispersion in a remote part of Namibia. In addition, geochemical analysis of the tailings reveals strongly elevated mean concentrations of rare metals (~2 760 mg/kg Li, ~140 mg/kg Be, ~41 mg/kg Ta, ~55 mg/kg Sn, ~74 mg/kg Nb). Resource estimates suggest the presence of ~25 200 t Li2O, ~1 600 t BeO and significant Nb-Ta-Sn in impoundment cell material and a total resource of ~365 000 t Li2O and ~27 900 t BeO in bulk tailings. Thus, Uis tailings also offer the opportunity for reprocessing and extraction of rare metals.
Uis伟晶岩矿床（纳米比亚）历史悠久的锡矿开采和矿物加工导致了一系列尾矿库。在本研究中，对Uis尾矿进行了表征，以确定其适用于砖块制造和稀有金属（Be、Li、Nb、Ta）的再加工潜力。尾矿以两种不同的类型出现在现场：（a）沙丘状弃土场中的细粒至中粒砂（d50=120-420μm）；以及（b）四个低洼干燥废物蓄水池中的细至中粒砂（馏分A:d50=120-410μm；约25%为尾矿类型）和细粒粉土（馏分b:d50=18-83μm；75%为尾矿类型。这两种尾矿的矿物成分相似且均匀，包括石英、斜长石、钾长石和云母，以及少量锡石、铌钽铁矿和花瓣岩，反映了源岩的云母-石英-长石成分。主要粘土矿物为伊利石，含少量（铁）斜绿石、库克石和高岭石。由于伊利石是主要的粘土矿物，大量的石英是稳定剂，而且只有微量的矿物（如氧化铁和黄铁矿）可能会产生有害影响，因此这种矿物成分允许现代砖的制造。因此，一致的粒度分布和均匀的矿物成分使当今能够从尾矿中生产出高质量的烧结砖。迄今为止，在纳米比亚偏远地区，使用Uis尾矿制造砖块支持了当地经济，有助于建筑发展，并清除了易粉尘扩散的富含二氧化硅的矿山废物。此外，尾矿的地球化学分析显示，稀有金属的平均浓度显著升高（~2760 mg/kg Li，~140 mg/kg Be，~41 mg/kg Ta，~55 mg/kg Sn，~74 mg/kg Nb）。资源量估计表明，蓄水池材料中存在约25 200 t Li2O、约1 600 t BeO和大量Nb-Ta-Sn，散装尾矿中的总资源量为约365 000 t Li2O和约27 900 t BeO。因此，Uis尾矿也为稀有金属的再加工和提取提供了机会。
{"title":"Reprocessing potential of pegmatite tailings for rare metal extraction and brick fabrication, Uis, Namibia","authors":"S. Lohmeier, B. Lottermoser, T. Schirmer, W. Fuchsloch","doi":"10.25131/SAJG.124.0015","DOIUrl":"https://doi.org/10.25131/SAJG.124.0015","url":null,"abstract":"Historic tin mining and mineral processing of the Uis pegmatite deposit (Namibia) has resulted in a series of tailings impoundments. In this study, Uis tailings were characterised to establish their suitability for brick manufacturing and reprocessing potential for rare metals (Be, Li, Nb, Ta). Tailings occur on-site as two distinct types (a) fine- to medium-grained sand (d50 = 120 to 420 μm) in dune-like spoil dumps; and (b) fine- to medium-grained sand (Fraction A: d50 = 120 to 410 μm; ~25% of tailings type) and fine-grained silt (Fraction B: d50 = 18 to 83 μm; ~75% of tailings type) in four low-lying dried-out waste impoundment cells. The two tailings types have a similar and homogeneous mineralogical composition, comprising quartz, plagioclase, K-feldspar and mica as well as minor cassiterite, columbite-tantalite and petalite, reflecting the micaceous quartzo-feldspathic composition of the source rocks. The main clay mineral is illite with minor (ferroan) clinochlore, cookeite and kaolinite. Such a mineralogical composition allows contemporary brick fabrication due to illite as the main clay mineral, a large proportion of quartz as a stabilizer and only trace amounts of minerals that could have a detrimental effect (e.g. Fe oxides and pyrite). Consequently, the consistent particle size distribution and homogeneous mineralogical composition allow present-day production of high-quality fired bricks from tailings. To date, the use of Uis tailings for brick manufacturing supports the local economy, aids building development and removes silica-rich mine wastes prone to dust dispersion in a remote part of Namibia. In addition, geochemical analysis of the tailings reveals strongly elevated mean concentrations of rare metals (~2 760 mg/kg Li, ~140 mg/kg Be, ~41 mg/kg Ta, ~55 mg/kg Sn, ~74 mg/kg Nb). Resource estimates suggest the presence of ~25 200 t Li2O, ~1 600 t BeO and significant Nb-Ta-Sn in impoundment cell material and a total resource of ~365 000 t Li2O and ~27 900 t BeO in bulk tailings. Thus, Uis tailings also offer the opportunity for reprocessing and extraction of rare metals.","PeriodicalId":49494,"journal":{"name":"South African Journal of Geology","volume":" ","pages":""},"PeriodicalIF":1.8,"publicationDate":"2021-05-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49304971","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
T. Owen-Smith, R. Trumbull, K. Bauer, J. Keiding, T. Will
The geochemical discrimination of different magma types in Large Igneous Provinces is conventionally based on a few, pre-selected variables that are regarded to have petrological meaning. An alternative approach explored in this study is to apply the neural network technique of self-organising maps (SOM) to identify inherent groupings in data without knowledge or assumptions (unsupervised learning). The dataset used in this study comprises whole-rock analyses from extrusive (lava) and intrusive (dykes, sills) mafic suites in the Etendeka province, Namibia, taken from published sources and augmented by 103 new chemical analyses of dykes. Six SOM-classified groups are identified, which are unevenly distributed among the extrusive and the intrusive rock suites. The lava samples are dominated by just three of the six SOM groups (95% of all samples) and one group is absent entirely, whereas all six groups are present in the intrusive suite and five of them each comprise more than 5% of the samples. The geographic distribution of SOM-grouped dykes is heterogeneous and groups that are under-represented in the lava suite occur preferentially in a region of the pre-Etendeka basement where few lavas are preserved. Thus, the difference in magma diversity between intrusive and extrusive suites may be partly an artefact of erosion, which implies that a proper assessment of magma diversity in this and other LIPs must include the intrusive components. The correspondence of our SOM groupings with magma types in the Etendeka province that were established from petrologically defined variables is reasonably good for most trace-element abundances and ratios. However, some of the SOM groups have a wide range of initial Sr–Nd isotope ratios and a poor correspondence with the established magma types. We conclude that the SOM approach is useful for sorting out large and complex geochemical datasets but the method gives all input variables equal weight, which may be problematic if they have different responses to processes in the system under study (e.g., partial melting, fractional crystallisation, degassing, alteration). It is no substitute for expert petrological knowledge in discriminating genetically distinct magma types in an application like the present one.
{"title":"A neural network application to assess magma diversity in the Etendeka igneous province, Namibia","authors":"T. Owen-Smith, R. Trumbull, K. Bauer, J. Keiding, T. Will","doi":"10.25131/SAJG.124.0034","DOIUrl":"https://doi.org/10.25131/SAJG.124.0034","url":null,"abstract":"\u0000 The geochemical discrimination of different magma types in Large Igneous Provinces is conventionally based on a few, pre-selected variables that are regarded to have petrological meaning. An alternative approach explored in this study is to apply the neural network technique of self-organising maps (SOM) to identify inherent groupings in data without knowledge or assumptions (unsupervised learning). The dataset used in this study comprises whole-rock analyses from extrusive (lava) and intrusive (dykes, sills) mafic suites in the Etendeka province, Namibia, taken from published sources and augmented by 103 new chemical analyses of dykes. Six SOM-classified groups are identified, which are unevenly distributed among the extrusive and the intrusive rock suites. The lava samples are dominated by just three of the six SOM groups (95% of all samples) and one group is absent entirely, whereas all six groups are present in the intrusive suite and five of them each comprise more than 5% of the samples. The geographic distribution of SOM-grouped dykes is heterogeneous and groups that are under-represented in the lava suite occur preferentially in a region of the pre-Etendeka basement where few lavas are preserved. Thus, the difference in magma diversity between intrusive and extrusive suites may be partly an artefact of erosion, which implies that a proper assessment of magma diversity in this and other LIPs must include the intrusive components.\u0000 The correspondence of our SOM groupings with magma types in the Etendeka province that were established from petrologically defined variables is reasonably good for most trace-element abundances and ratios. However, some of the SOM groups have a wide range of initial Sr–Nd isotope ratios and a poor correspondence with the established magma types. We conclude that the SOM approach is useful for sorting out large and complex geochemical datasets but the method gives all input variables equal weight, which may be problematic if they have different responses to processes in the system under study (e.g., partial melting, fractional crystallisation, degassing, alteration). It is no substitute for expert petrological knowledge in discriminating genetically distinct magma types in an application like the present one.","PeriodicalId":49494,"journal":{"name":"South African Journal of Geology","volume":" ","pages":""},"PeriodicalIF":1.8,"publicationDate":"2021-05-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46110748","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Kasai alluvial field in southern Democratic Republic of Congo (DRC) is part of central Africa’s largest diamond placer that has produced more than 200 million carats, mainly derived from Quaternary deposits. A small part of these deposits, along and within the Longatshimo River, is the subject of this study providing a glimpse into the alluvial history of the Kasai diamond placer. This work documents their sedimentological and diamond mineralization attributes, as well as their emplacement processes, which can inform future exploration models. The key controls of this placer formation, notably Quaternary climatic variations, fluvial landscape evolution and bedrock conditions are also evaluated. A consequence of the interplay among these processes is that diamond supply (from Cretaceous alluvial sources), recycling and concentration were most pronounced and consistent, in the Late Quaternary. Alluvial diamond mineralization in this central African region thus evolved differently to those in southern Africa. Based on exploration results in the Longatshimo Valley, diamond concentration improves but diamond size diminishes with decreasing deposit age, and thus the modern river sediments contain the highest abundance but smallest diamonds. This is opposite to the grade and diamond size trend that characterises southern African fluvial diamond placers. The Longatshimo River study offers insight into the Kasai alluvial field, and its placer model is expected to be applicable to the exploration of other central African diamond placers.
{"title":"Diamondiferous alluvial deposits of the Longatshimo Valley, Kasai Province, southern DRC: a sedimentary and economic model of a central African diamond placer","authors":"R. Spaggiari, M. Wit","doi":"10.25131/SAJG.124.0033","DOIUrl":"https://doi.org/10.25131/SAJG.124.0033","url":null,"abstract":"\u0000 The Kasai alluvial field in southern Democratic Republic of Congo (DRC) is part of central Africa’s largest diamond placer that has produced more than 200 million carats, mainly derived from Quaternary deposits. A small part of these deposits, along and within the Longatshimo River, is the subject of this study providing a glimpse into the alluvial history of the Kasai diamond placer. This work documents their sedimentological and diamond mineralization attributes, as well as their emplacement processes, which can inform future exploration models. The key controls of this placer formation, notably Quaternary climatic variations, fluvial landscape evolution and bedrock conditions are also evaluated. A consequence of the interplay among these processes is that diamond supply (from Cretaceous alluvial sources), recycling and concentration were most pronounced and consistent, in the Late Quaternary. Alluvial diamond mineralization in this central African region thus evolved differently to those in southern Africa. Based on exploration results in the Longatshimo Valley, diamond concentration improves but diamond size diminishes with decreasing deposit age, and thus the modern river sediments contain the highest abundance but smallest diamonds. This is opposite to the grade and diamond size trend that characterises southern African fluvial diamond placers. The Longatshimo River study offers insight into the Kasai alluvial field, and its placer model is expected to be applicable to the exploration of other central African diamond placers.","PeriodicalId":49494,"journal":{"name":"South African Journal of Geology","volume":" ","pages":""},"PeriodicalIF":1.8,"publicationDate":"2021-05-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43728051","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The narrow, short-lived Taconic-Grampian Orogen occurs along the north-western margin of the Appalachian-Caledonian Belt from, at least, Alabama to Scotland, a result of the collision of a series of early Ordovician oceanic island arcs with the rifted margin of Laurentia. The present distribution of Taconian-Grampian ophiolites is unlikely to represent a single fore-arc from Alabama to Scotland colliding at the same time with the continental margin along its whole length; more likely is that there were several Ordovician arcs with separate ophiolites. The collision suture is at the thrust base of obducted fore-arc ophiolite complexes, and obduction distance was about two hundred kilometres. Footwalls to the ophiolites are, sequentially towards the continent, continental margin rift sediments and volcanics and overlying rise sediments, continental shelf slope carbonates, and sediments of foreland flexural basins. The regionally-flat obduction thrust complex between the ophiolite and the rifted Laurentian margin is the collision suture between arc and continent. A particular problem in drawing tectonic profiles across the Taconic-Grampian Zone is several orogen-parallel major strike-slip faults, both sinistral and dextral, of unknown displacements, which may juxtapose portions of different segments. In western Newfoundland, most of the Grenville basement beneath the Fleur-de-Lys metamorphic complex (Neoproterozoic to early Ordovician meta-sediments) was eclogitised during the Taconic Orogeny and separated by a massive shear zone from the overlying Fleur-de-Lys, which was metamorphosed at the same time but in the amphibolite facies. The shear zone continued either to a distal intracontinental “subduction zone” or to the main, sub-fore-arc, subduction zone beneath which the basement slipped down to depths of up to seventy kilometres at the same time as the ophiolite sheet and its previously-subcreted metamorphic sole were being obducted above. Subsequently, the eclogitised basement was returned to contact with the amphibolite-facies cover by extensional detachment eduction, possibly enhanced by subduction channel flow, which may have been caused by slab break-off and extension during subduction polarity flip. Although the basal ophiolite obduction thrust complex and the Fleur-de-Lys-basement subduction-eduction surfaces must have been initially gently-dipping to sub-horizontal, they were folded and broken by thrusts during late Taconian, late Ordovician Salinic-Mayoian, and Acadian shortening.
狭窄、短命的Taconic Grampian造山带发生在阿巴拉契亚-喀里多尼亚带的西北边缘，至少从阿拉巴马州到苏格兰，这是一系列早奥陶世洋岛弧与劳伦蒂亚裂谷边缘碰撞的结果。Taconian Grampian蛇绿岩的目前分布不太可能代表从阿拉巴马州到苏格兰的单一前弧沿其整个长度同时与大陆边缘碰撞；更有可能的是，有几个奥陶纪弧带独立的蛇绿岩。碰撞缝合线位于逆冲弧前蛇绿岩杂岩的逆冲基底，逆冲距离约200公里。蛇绿岩的下盘依次朝向大陆、大陆边缘裂谷沉积物和火山岩以及上覆隆起沉积物、大陆架斜坡碳酸盐岩和前陆弯曲盆地的沉积物。蛇绿岩与断陷劳伦期边缘之间的区域性平坦的倒冲-逆冲杂岩是弧与大陆的碰撞缝合线。绘制Taconic Grampian带构造剖面的一个特殊问题是，几个造山带平行的主要走滑断层，包括左旋和右旋断层，具有未知的位移，这些断层可能将不同区段的部分并置。在纽芬兰西部，Fleur de Lys变质杂岩（新元古代至早奥陶世变质沉积物）下方的大部分Grenville基底在Taconic造山运动期间被榴辉岩化，并被与上覆Fleur de Lys的巨大剪切带分隔开，Fleurr de Lys在同一时间变质，但处于角闪岩相。剪切带继续延伸至远端陆内“俯冲带”或主要的亚弧前俯冲带，在该俯冲带之下，基底滑至70公里深处，同时蛇绿岩片及其先前的亚网状变质基底在上方被挤压。随后，榴辉岩基底通过伸展脱离-喷出作用与角闪岩相覆盖层重新接触，这可能是由于俯冲极性翻转过程中板块断裂和伸展引起的俯冲通道流而增强的。尽管基底蛇绿岩冲断-逆冲杂岩和Fleur de Lys基底俯冲-抛射表面最初一定是平缓地倾斜到亚水平的，但它们在晚塔科尼阶、晚奥陶世Salinic Mayoian和阿卡迪亚缩短期间被逆冲褶皱和破碎。
{"title":"Mid-Ordovician subduction, obduction, and eduction in western Newfoundland; an eclogite problem","authors":"J. Dewey, John F. Casey","doi":"10.25131/SAJG.124.0029","DOIUrl":"https://doi.org/10.25131/SAJG.124.0029","url":null,"abstract":"\u0000 The narrow, short-lived Taconic-Grampian Orogen occurs along the north-western margin of the Appalachian-Caledonian Belt from, at least, Alabama to Scotland, a result of the collision of a series of early Ordovician oceanic island arcs with the rifted margin of Laurentia. The present distribution of Taconian-Grampian ophiolites is unlikely to represent a single fore-arc from Alabama to Scotland colliding at the same time with the continental margin along its whole length; more likely is that there were several Ordovician arcs with separate ophiolites. The collision suture is at the thrust base of obducted fore-arc ophiolite complexes, and obduction distance was about two hundred kilometres. Footwalls to the ophiolites are, sequentially towards the continent, continental margin rift sediments and volcanics and overlying rise sediments, continental shelf slope carbonates, and sediments of foreland flexural basins. The regionally-flat obduction thrust complex between the ophiolite and the rifted Laurentian margin is the collision suture between arc and continent. A particular problem in drawing tectonic profiles across the Taconic-Grampian Zone is several orogen-parallel major strike-slip faults, both sinistral and dextral, of unknown displacements, which may juxtapose portions of different segments. In western Newfoundland, most of the Grenville basement beneath the Fleur-de-Lys metamorphic complex (Neoproterozoic to early Ordovician meta-sediments) was eclogitised during the Taconic Orogeny and separated by a massive shear zone from the overlying Fleur-de-Lys, which was metamorphosed at the same time but in the amphibolite facies. The shear zone continued either to a distal intracontinental “subduction zone” or to the main, sub-fore-arc, subduction zone beneath which the basement slipped down to depths of up to seventy kilometres at the same time as the ophiolite sheet and its previously-subcreted metamorphic sole were being obducted above. Subsequently, the eclogitised basement was returned to contact with the amphibolite-facies cover by extensional detachment eduction, possibly enhanced by subduction channel flow, which may have been caused by slab break-off and extension during subduction polarity flip. Although the basal ophiolite obduction thrust complex and the Fleur-de-Lys-basement subduction-eduction surfaces must have been initially gently-dipping to sub-horizontal, they were folded and broken by thrusts during late Taconian, late Ordovician Salinic-Mayoian, and Acadian shortening.","PeriodicalId":49494,"journal":{"name":"South African Journal of Geology","volume":" ","pages":""},"PeriodicalIF":1.8,"publicationDate":"2021-04-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41851707","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Recurring progression from S- to I- to A-type granites has been proposed for a subset of granitic rocks in eastern Australia. The wider applicability and the validity of this idea is explored using the Cape Granite Suite (CGS) of South Africa and the granitic and silicic volcanic rocks of central Victoria, in southeastern Australia. Within the CGS there is presently little justification for the notion that there is a clear temporal progression from early S-type, through I-type to late A-type magmatism. The I- and S-type rocks are certainly spatially separated. However, apart from a single slightly older pluton (the Hoedjiespunt Granite) there is no indication that the S- and I-type granites are temporally distinct. One dated A-type granitic sample and a syenite have poorly constrained dates that overlap with those of the youngest S-type granites. In central Victoria, the granitic magma types display neither a spatial separation nor a temporal progression from one type to another. All magma varieties are present together and were emplaced within a far narrower time window than in the CGS. Thus, a progression may or may not exist in a particular region, and the occurrence of such a progression does not hold true even in a part of southeastern Australia, which afforded the type example. Thus, the idea that, globally, there should be a progression from S- to I- to A-type magmatism is unjustified. The critical factor in determining the temporal relationship between granitic magmas of different types is probably the compositional structure of the deep crust in a particular region, a reflection of how the individual orogen was assembled. In turn, this must reflect significant differences in the tectonic settings.
{"title":"S- to I- to A-type magmatic cycles in granitic terranes are not globally recurring progressions. The cases of the Cape Granite Suite of Southern Africa and central Victoria in southeastern Australia","authors":"J. Clemens, G. Stevens","doi":"10.25131/SAJG.124.0007","DOIUrl":"https://doi.org/10.25131/SAJG.124.0007","url":null,"abstract":"\u0000 Recurring progression from S- to I- to A-type granites has been proposed for a subset of granitic rocks in eastern Australia. The wider applicability and the validity of this idea is explored using the Cape Granite Suite (CGS) of South Africa and the granitic and silicic volcanic rocks of central Victoria, in southeastern Australia. Within the CGS there is presently little justification for the notion that there is a clear temporal progression from early S-type, through I-type to late A-type magmatism. The I- and S-type rocks are certainly spatially separated. However, apart from a single slightly older pluton (the Hoedjiespunt Granite) there is no indication that the S- and I-type granites are temporally distinct. One dated A-type granitic sample and a syenite have poorly constrained dates that overlap with those of the youngest S-type granites. In central Victoria, the granitic magma types display neither a spatial separation nor a temporal progression from one type to another. All magma varieties are present together and were emplaced within a far narrower time window than in the CGS. Thus, a progression may or may not exist in a particular region, and the occurrence of such a progression does not hold true even in a part of southeastern Australia, which afforded the type example. Thus, the idea that, globally, there should be a progression from S- to I- to A-type magmatism is unjustified. The critical factor in determining the temporal relationship between granitic magmas of different types is probably the compositional structure of the deep crust in a particular region, a reflection of how the individual orogen was assembled. In turn, this must reflect significant differences in the tectonic settings.","PeriodicalId":49494,"journal":{"name":"South African Journal of Geology","volume":" ","pages":""},"PeriodicalIF":1.8,"publicationDate":"2021-04-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42695320","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Volcanological maps of the sub-Antarctic Prince Edward Islands were first published in 1968, with a revised surface geology map of Marion Island produced in 2006. These maps have been widely used in terrestrial studies on the Prince Edward Islands but they have limitations in spatial accuracy and detail. Using high-resolution satellite imagery and digital elevation data, more spatially accurate data for both Prince Edward and Marion Island’s surface geology are presented here. In particular, Marion Island’s volcanology on the western coast, including the 1980s lava flow, and the newly exposed Central Highland following the disappearance of extensive ice and snow cover is mapped with greater detail and verified through field observations. The spatial data are downloadable as ESRI layer packages, which can assist in future investigations of island biotic-abiotic processes and interactions and enable improvements in spatial modelling. In addition, this paper highlights geological features and specimens from the Prince Edward Islands as unique examples of geodiversity in a South African context. An overview of these features are provided in terms of their geoheritage value to enable a more comprehensive geoconservation strategy be incorporated into the Prince Edward Islands Management Plan.
{"title":"The surface geology of the Prince Edward Islands: refined spatial data and call for geoconservation","authors":"E. Rudolph, D. Hedding, W. Nel","doi":"10.25131/SAJG.124.0014","DOIUrl":"https://doi.org/10.25131/SAJG.124.0014","url":null,"abstract":"\u0000 Volcanological maps of the sub-Antarctic Prince Edward Islands were first published in 1968, with a revised surface geology map of Marion Island produced in 2006. These maps have been widely used in terrestrial studies on the Prince Edward Islands but they have limitations in spatial accuracy and detail. Using high-resolution satellite imagery and digital elevation data, more spatially accurate data for both Prince Edward and Marion Island’s surface geology are presented here. In particular, Marion Island’s volcanology on the western coast, including the 1980s lava flow, and the newly exposed Central Highland following the disappearance of extensive ice and snow cover is mapped with greater detail and verified through field observations. The spatial data are downloadable as ESRI layer packages, which can assist in future investigations of island biotic-abiotic processes and interactions and enable improvements in spatial modelling. In addition, this paper highlights geological features and specimens from the Prince Edward Islands as unique examples of geodiversity in a South African context. An overview of these features are provided in terms of their geoheritage value to enable a more comprehensive geoconservation strategy be incorporated into the Prince Edward Islands Management Plan.","PeriodicalId":49494,"journal":{"name":"South African Journal of Geology","volume":" ","pages":""},"PeriodicalIF":1.8,"publicationDate":"2021-04-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45111007","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
S. Reimann, C. Heubeck, P. Fugmann, D. V. Rensburg, A. Zametzer, S. Serre, T. Thomsen
The ~3.22 Ga Moodies Group, Barberton Greenstone Belt (BGB), South Africa, provides a unique window into Archaean sedimentary, magmatic and ecological processes. In the central BGB, a regional mafic complex, consisting of a genetically related major mafic sill, a peperitic dyke stockwork, and extensive basaltic lava flows affected thick quartzose sandstones of the Moodies Group. We argue that epithermal hydrothermalism associated with this magmatic event occurred, at least in part, syndepositionally and in places destroyed, in other places preserved the abundant benthic microbial mats in terrestrial- and coastal-facies sandstone of this unit. We differentiate four principal types of hydrothermal alteration: (1) Sericitization resulted from ubiquitous feldspar breakdown; (2) iron-oxide alteration replaced the original matrix by fine-grained iron oxide; (3) silicification replaced matrix and most non-silica grains by microcrystalline silica and locally preserved kerogenous microbial mats; and (4) hydraulic fracturing at shallow depth brecciated consolidated Moodies Group sandstone and created closely spaced, randomly oriented fractures and quartz-filled veins. Because stockwork intrusion locally interacted with unconsolidated water-saturated sediment and because the dykes connect the sill with the mafic lava but also follow zones of structural weakness, we suggest that hydrothermalism associated with this magmatic event occurred syndepositionally but was also – within the resolution of radiometric age data – contemporaneous with tight regional folding. We conclude that microbial organisms in Paleoarchaean coastal (tidal, estuarine) environments may have been formerly widespread, possibly even abundant, but are nearly nowhere preserved because they were easily degradable. Preservation of Early Archaean microbial mats in a thermal aureole in the central BGB was controlled by the “just right” degree of heating and very early hydrothermal silicification.
南非Barberton Greenstone Belt（BGB）的~3.22 Ga Moodies群为了解太古宙沉积、岩浆和生态过程提供了一个独特的窗口。在BGB中部，一个区域性镁铁质杂岩，由一个成因相关的主要镁铁质岩床、一个泥质脉网和广泛的玄武岩熔岩流组成，影响了穆迪群的厚石英砂岩。我们认为，与这一岩浆事件相关的浅成热液热液作用至少部分发生在同沉积和被破坏的地方，在其他地方，该单元的陆地和海岸相砂岩中保留了丰富的海底微生物垫。我们区分了四种主要的热液蚀变类型：（1）绢云母化是由普遍存在的长石分解引起的；（2） 氧化铁蚀变用细粒氧化铁取代了原始基质；（3） 硅化作用用微晶二氧化硅和局部保存的干酪根微生物垫取代了基质和大多数非二氧化硅颗粒；和（4）浅层水力压裂使固结穆迪组砂岩角砾化，并形成紧密间隔、随机定向的裂缝和石英填充的矿脉。由于网状侵入体与松散的水饱和沉积物局部相互作用，并且堤坝将岩床与镁铁质熔岩连接起来，我们认为，与这一岩浆事件相关的热液作用是同沉积发生的，但在辐射年龄数据的分辨率范围内，也与紧密的区域褶皱同时发生。我们得出的结论是，古太古代沿海（潮汐、河口）环境中的微生物以前可能分布广泛，甚至可能数量丰富，但由于易于降解，几乎没有保存下来。BGB中部热晕中早期太古宙微生物垫的保存受到“恰到好处”的加热程度和非常早期的热液硅化作用的控制。
{"title":"Syndepositional hydrothermalism selectively preserves records of one of the earliest benthic ecosystems, Moodies Group (3.22 Ga), Barberton Greenstone Belt, South Africa","authors":"S. Reimann, C. Heubeck, P. Fugmann, D. V. Rensburg, A. Zametzer, S. Serre, T. Thomsen","doi":"10.25131/SAJG.124.0012","DOIUrl":"https://doi.org/10.25131/SAJG.124.0012","url":null,"abstract":"\u0000 The ~3.22 Ga Moodies Group, Barberton Greenstone Belt (BGB), South Africa, provides a unique window into Archaean sedimentary, magmatic and ecological processes. In the central BGB, a regional mafic complex, consisting of a genetically related major mafic sill, a peperitic dyke stockwork, and extensive basaltic lava flows affected thick quartzose sandstones of the Moodies Group. We argue that epithermal hydrothermalism associated with this magmatic event occurred, at least in part, syndepositionally and in places destroyed, in other places preserved the abundant benthic microbial mats in terrestrial- and coastal-facies sandstone of this unit. We differentiate four principal types of hydrothermal alteration: (1) Sericitization resulted from ubiquitous feldspar breakdown; (2) iron-oxide alteration replaced the original matrix by fine-grained iron oxide; (3) silicification replaced matrix and most non-silica grains by microcrystalline silica and locally preserved kerogenous microbial mats; and (4) hydraulic fracturing at shallow depth brecciated consolidated Moodies Group sandstone and created closely spaced, randomly oriented fractures and quartz-filled veins. Because stockwork intrusion locally interacted with unconsolidated water-saturated sediment and because the dykes connect the sill with the mafic lava but also follow zones of structural weakness, we suggest that hydrothermalism associated with this magmatic event occurred syndepositionally but was also – within the resolution of radiometric age data – contemporaneous with tight regional folding. We conclude that microbial organisms in Paleoarchaean coastal (tidal, estuarine) environments may have been formerly widespread, possibly even abundant, but are nearly nowhere preserved because they were easily degradable. Preservation of Early Archaean microbial mats in a thermal aureole in the central BGB was controlled by the “just right” degree of heating and very early hydrothermal silicification.","PeriodicalId":49494,"journal":{"name":"South African Journal of Geology","volume":"124 1","pages":"253-278"},"PeriodicalIF":1.8,"publicationDate":"2021-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44141677","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Barberton region of South Africa is characterized by a broad variety of granite types that range in age from ca. 3.5 Ga to 2.7 Ga and reflect the processes involved in the formation of Archaean continental crust on the Kaapvaal Craton. These granites are subdivided into three groups, as follows: A tonalite-trondhjemite-granodiorite (TTG) suite diapirically emplaced at 3 450 Ma and 3 250 Ma into pre-existing metamorphosed greenstone belt material. TTG melts were derived from melting amphibolite in the lower crust, with individual plutons being emplaced at various crustal levels. The dome-and-keel geometry that characterizes the TTG-greenstone dominated crust at this time is inconsistent with a plate tectonic domain and reworking was likely controlled by gravity inversion or ‘sagduction’; Regionally extensive potassic batholiths (the GMS suite) were emplaced at 3 110 Ma during a period of crustal thickening and melting of a TTG-dominated lower crust. Subsequent to emplacement of the voluminous GMS granites, the thickened continental crust had stabilized sufficiently for large sedimentary basins to form; Late granite plutons were emplaced along two distinct linear and sub-parallel arrays close to what might have been the edge of a Kaapvaal continent at 2 800 to 2 700 Ma. They are subdivided into high-Ca and low-Ca granites that resemble the I- and S-type granites of younger orogenic episodes. The high-Ca granites are consistent with derivation from older granitoids in the lower crust, whereas the low-Ca granites may have been derived by melting metasedimentary precursors in the lower-mid crust. Granites with similar characteristics are associated with a subduction zone in younger terranes, although the recognition of such a feature at Barberton remains unclear. The petrogenesis of granites in the Barberton region between 3.5 Ga and 2.7 Ga provides a record of the processes of Archaean crustal evolution and contributes to discussions related to the onset of plate tectonics.
{"title":"Petrogenesis of Archaean granites in the Barberton region of South Africa as a guide to early crustal evolution","authors":"L. Robb, F. Meyer, C. Hawkesworth, N. Gardiner","doi":"10.25131/SAJG.124.0021","DOIUrl":"https://doi.org/10.25131/SAJG.124.0021","url":null,"abstract":"\u0000 The Barberton region of South Africa is characterized by a broad variety of granite types that range in age from ca. 3.5 Ga to 2.7 Ga and reflect the processes involved in the formation of Archaean continental crust on the Kaapvaal Craton. These granites are subdivided into three groups, as follows:\u0000 A tonalite-trondhjemite-granodiorite (TTG) suite diapirically emplaced at 3 450 Ma and 3 250 Ma into pre-existing metamorphosed greenstone belt material. TTG melts were derived from melting amphibolite in the lower crust, with individual plutons being emplaced at various crustal levels. The dome-and-keel geometry that characterizes the TTG-greenstone dominated crust at this time is inconsistent with a plate tectonic domain and reworking was likely controlled by gravity inversion or ‘sagduction’;\u0000 Regionally extensive potassic batholiths (the GMS suite) were emplaced at 3 110 Ma during a period of crustal thickening and melting of a TTG-dominated lower crust. Subsequent to emplacement of the voluminous GMS granites, the thickened continental crust had stabilized sufficiently for large sedimentary basins to form;\u0000 Late granite plutons were emplaced along two distinct linear and sub-parallel arrays close to what might have been the edge of a Kaapvaal continent at 2 800 to 2 700 Ma. They are subdivided into high-Ca and low-Ca granites that resemble the I- and S-type granites of younger orogenic episodes. The high-Ca granites are consistent with derivation from older granitoids in the lower crust, whereas the low-Ca granites may have been derived by melting metasedimentary precursors in the lower-mid crust. Granites with similar characteristics are associated with a subduction zone in younger terranes, although the recognition of such a feature at Barberton remains unclear.\u0000 The petrogenesis of granites in the Barberton region between 3.5 Ga and 2.7 Ga provides a record of the processes of Archaean crustal evolution and contributes to discussions related to the onset of plate tectonics.","PeriodicalId":49494,"journal":{"name":"South African Journal of Geology","volume":"124 1","pages":"111-140"},"PeriodicalIF":1.8,"publicationDate":"2021-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43218149","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Poujol, J. Jaguin, J. Moyen, P. Boulvais, J. Paquette
S-type granites correspond to reworking of pre-existing continental material and form by partial melting of (meta)sediments. Early-to-mid Archaean S-type granites are rare and are more frequently found, usually as relatively small intrusions, during the Neoarchaean and the Archaean-Proterozoic transition. In the context of Archaean geology, their paucity is therefore significant, in that it matches the uncommon nature of processes during this period. In this study, we focus on the Late Mesoarchaean Willie pluton and Neoarchaean Lekkersmaak pluton, which crop out to the south of the Murchison Greenstone Belt in the Northern Kaapvaal Craton, South Africa. These intrusions represent the oldest S-type plutons known so far in the region. We constrain their petrogenesis by documenting their petrology, mineralogy (mineral composition), geochemistry (major and trace elements, Sr, Nd and O isotopes) and zircon U-Pb geochronology. The large Lekkersmaak and smaller Willie plutons represent two granites sharing many geochemical characteristics; they are both peraluminous, Ms-bearing S-type granites although they are more sodic and less potassic than typical S-type granites. The Willie granite was emplaced 2 816 ± 9 Ma ago while the Lekkersmaak yielded an emplacement age of 2 771 ± 2 Ma. Therefore, S-Type magmatism in the area occurred twice at 2.82 Ga and then 40 Myr later at 2.77 Ga, involving comparable immature metasedimentary sources and conditions of partial melting. Finally, a sample from the Lekkersmaak pluton devoid of S-type features as it is muscovite-free and aluminum poor was emplaced 2 734 ± 11 Ma ago. This confirms the episodic nature of magmatic activity south of the Murchison Greenstone Belt.
{"title":"Archaean S-Type granites: petrology, geochemistry and geochronology of the Lekkersmaak and Willie plutons, Kaapvaal Craton, South Africa","authors":"M. Poujol, J. Jaguin, J. Moyen, P. Boulvais, J. Paquette","doi":"10.25131/SAJG.124.0004","DOIUrl":"https://doi.org/10.25131/SAJG.124.0004","url":null,"abstract":"\u0000 S-type granites correspond to reworking of pre-existing continental material and form by partial melting of (meta)sediments. Early-to-mid Archaean S-type granites are rare and are more frequently found, usually as relatively small intrusions, during the Neoarchaean and the Archaean-Proterozoic transition. In the context of Archaean geology, their paucity is therefore significant, in that it matches the uncommon nature of processes during this period. In this study, we focus on the Late Mesoarchaean Willie pluton and Neoarchaean Lekkersmaak pluton, which crop out to the south of the Murchison Greenstone Belt in the Northern Kaapvaal Craton, South Africa. These intrusions represent the oldest S-type plutons known so far in the region. We constrain their petrogenesis by documenting their petrology, mineralogy (mineral composition), geochemistry (major and trace elements, Sr, Nd and O isotopes) and zircon U-Pb geochronology. The large Lekkersmaak and smaller Willie plutons represent two granites sharing many geochemical characteristics; they are both peraluminous, Ms-bearing S-type granites although they are more sodic and less potassic than typical S-type granites. The Willie granite was emplaced 2 816 ± 9 Ma ago while the Lekkersmaak yielded an emplacement age of 2 771 ± 2 Ma. Therefore, S-Type magmatism in the area occurred twice at 2.82 Ga and then 40 Myr later at 2.77 Ga, involving comparable immature metasedimentary sources and conditions of partial melting. Finally, a sample from the Lekkersmaak pluton devoid of S-type features as it is muscovite-free and aluminum poor was emplaced 2 734 ± 11 Ma ago. This confirms the episodic nature of magmatic activity south of the Murchison Greenstone Belt.","PeriodicalId":49494,"journal":{"name":"South African Journal of Geology","volume":" ","pages":""},"PeriodicalIF":1.8,"publicationDate":"2021-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47593757","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
N. Gardiner, J. Mulder, C. Kirkland, T. Johnson, O. Nebel
The continental crust that dominates Earth’s oldest cratons comprises Eoarchaean to Palaeoarchaean (4.0 to 3.2 Ga) felsic intrusive rocks of the tonalite-trondhjemite-granodiorite (TTG) series. These are found either within high-grade gneiss terranes, which represent Archaean mid-continental crust, or low-grade granite-greenstone belts, which represent relic Archaean upper continental crust. The Palaeoarchaean East Pilbara Terrane (EPT), Pilbara Craton, Western Australia, and the Barberton Granite-Greenstone Belt (BGGB), Kaapvaal Craton, southern Africa, are two of the best exposed granite-greenstone belts. Their striking geological similarities has led to the postulated existence of Vaalbara, a Neoarchaean-Palaeoproterozoic supercraton. Although their respective TTG domes have been compared in terms of a common petrogenetic origin reflecting a volcanic plateau setting, there are important differences in their age, geochemistry, and isotopic profiles. We present new zircon Hf isotope data from five granite domes of the EPT and compare the geochemical and isotopic record of the Palaeoarchaean TTGs from both cratons. Rare >3.5 Ga EPT evolved rocks have juvenile εHf(t) requiring a chondritic source. In contrast, younger TTG domes developed via 3.5 to 3.4 and 3.3 to 3.2 Ga magmatic supersuites with a greater range of εHf(t) towards more depleted and enriched values, trace element signatures requiring an enriched source, and xenocrystic zircons that reflects a mixed source to the TTGs, which variously assimilates packages of older felsic crust and a more juvenile mafic source. EPT TTG domes are composite and record multiple pulses of magmatism. In comparison, BGGB TTGs are less geochemically enriched than those of the EPT and have different age profiles, hosting coeval magmatic units. Hafnium isotopes suggest a predominantly juvenile source to 3.2 Ga northern Barberton TTGs, limited assimilation of older evolved crust in 3.4 Ga southern Barberton TTGs, but significant assimilation of older (Hadean-Eoarchaean) crust in the ca. 3.6 Ga TTGs of the Ancient Gneiss Complex. The foundation of the EPT is younger than that for the oldest components of the Eastern Kaapvaal. Although the broader prevailing Palaeoarchaean geologic framework in which these two cratons formed may reflect similar a geodynamic regime, the superficial similarities in dome structures and stratigraphy of both cratonic terranes is not reflected in their geochemical and age profiles. Both the similarities and the differences between the crustal histories of the two cratons highlights that they are formed from distinct terranes with different ages and individual evolutionary histories. Vaalbara sensu lato represents typical Palaeoarchaean cratonic crust, not in the sense of a single homogeneous craton, but one as diverse as the continents are today.
{"title":"Palaeoarchaean TTGs of the Pilbara and Kaapvaal cratons compared; an early Vaalbara supercraton evaluated","authors":"N. Gardiner, J. Mulder, C. Kirkland, T. Johnson, O. Nebel","doi":"10.25131/SAJG.124.0010","DOIUrl":"https://doi.org/10.25131/SAJG.124.0010","url":null,"abstract":"\u0000 The continental crust that dominates Earth’s oldest cratons comprises Eoarchaean to Palaeoarchaean (4.0 to 3.2 Ga) felsic intrusive rocks of the tonalite-trondhjemite-granodiorite (TTG) series. These are found either within high-grade gneiss terranes, which represent Archaean mid-continental crust, or low-grade granite-greenstone belts, which represent relic Archaean upper continental crust. The Palaeoarchaean East Pilbara Terrane (EPT), Pilbara Craton, Western Australia, and the Barberton Granite-Greenstone Belt (BGGB), Kaapvaal Craton, southern Africa, are two of the best exposed granite-greenstone belts. Their striking geological similarities has led to the postulated existence of Vaalbara, a Neoarchaean-Palaeoproterozoic supercraton. Although their respective TTG domes have been compared in terms of a common petrogenetic origin reflecting a volcanic plateau setting, there are important differences in their age, geochemistry, and isotopic profiles. We present new zircon Hf isotope data from five granite domes of the EPT and compare the geochemical and isotopic record of the Palaeoarchaean TTGs from both cratons. Rare >3.5 Ga EPT evolved rocks have juvenile εHf(t) requiring a chondritic source. In contrast, younger TTG domes developed via 3.5 to 3.4 and 3.3 to 3.2 Ga magmatic supersuites with a greater range of εHf(t) towards more depleted and enriched values, trace element signatures requiring an enriched source, and xenocrystic zircons that reflects a mixed source to the TTGs, which variously assimilates packages of older felsic crust and a more juvenile mafic source. EPT TTG domes are composite and record multiple pulses of magmatism. In comparison, BGGB TTGs are less geochemically enriched than those of the EPT and have different age profiles, hosting coeval magmatic units. Hafnium isotopes suggest a predominantly juvenile source to 3.2 Ga northern Barberton TTGs, limited assimilation of older evolved crust in 3.4 Ga southern Barberton TTGs, but significant assimilation of older (Hadean-Eoarchaean) crust in the ca. 3.6 Ga TTGs of the Ancient Gneiss Complex. The foundation of the EPT is younger than that for the oldest components of the Eastern Kaapvaal. Although the broader prevailing Palaeoarchaean geologic framework in which these two cratons formed may reflect similar a geodynamic regime, the superficial similarities in dome structures and stratigraphy of both cratonic terranes is not reflected in their geochemical and age profiles. Both the similarities and the differences between the crustal histories of the two cratons highlights that they are formed from distinct terranes with different ages and individual evolutionary histories. Vaalbara sensu lato represents typical Palaeoarchaean cratonic crust, not in the sense of a single homogeneous craton, but one as diverse as the continents are today.","PeriodicalId":49494,"journal":{"name":"South African Journal of Geology","volume":"124 1","pages":"37-52"},"PeriodicalIF":1.8,"publicationDate":"2021-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41861474","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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