Pub Date : 2023-06-22DOI: 10.1080/08120099.2023.2210201
Y. Zhen, I. Percival, P. Smith
Abstract This study documents Middle to Late Ordovician conodont faunas primarily from the Billabong Creek Formation exposed in the Gunningbland area located west of Parkes and northwest of Forbes in central New South Wales. Forty-four identifiable conodont species recovered from 105 limestone samples in this area form the basis of the most complete biostratigraphic succession in shallow-water facies known through this interval from Australia. Four conodont biozones are recognised, extending from the middle Darriwilian Histiodella holodentata–Eoplacognathus pseudoplanus and Eoplacognathus suecicus biozones, through the upper Darriwilian Pygodus serra Biozone, to the Pygodus anserinus Biozone spanning the uppermost Darriwilian to basal Sandbian interval. A lower to middle Sandbian carbonate gap coincides with an unzoned interval, followed by the successively younger Belodina compressa, Phragmodus undatus and Taoqupognathus blandus conodont biozones in the upper Sandbian to lower Katian. The T. blandus Biozone directly correlates with the detailed conodont biozonation established in Katian limestones of the Molong Volcanic Belt further east. These age determinations provide much improved precision for correlation within Phases 2 and 3 in the mineral-rich Macquarie Volcanic Province. Analysis of conodont biofacies data supports an enhanced understanding of the geological evolution of the Macquarie Volcanic Province by interpreting the interplay between volcanic activity and carbonate deposition. KEY POINTS Conodont studies in the Billabong Creek Formation of the Gunningbland area reveal the only known biostratigraphic succession in Australia that extends continuously from the middle Darriwilian to basal Sandbian. Three Late Ordovician (late Sandbian to early Katian) conodont biozones in the upper Billabong Creek Formation correlate precisely with carbonates of the Molong Volcanic Belt to the east. Revised stratigraphic definitions of the Billabong Creek and Gunningbland formations are provided.
{"title":"Middle–Upper Ordovician conodonts from the Gunningbland area in central New South Wales with implications for regional correlations","authors":"Y. Zhen, I. Percival, P. Smith","doi":"10.1080/08120099.2023.2210201","DOIUrl":"https://doi.org/10.1080/08120099.2023.2210201","url":null,"abstract":"Abstract This study documents Middle to Late Ordovician conodont faunas primarily from the Billabong Creek Formation exposed in the Gunningbland area located west of Parkes and northwest of Forbes in central New South Wales. Forty-four identifiable conodont species recovered from 105 limestone samples in this area form the basis of the most complete biostratigraphic succession in shallow-water facies known through this interval from Australia. Four conodont biozones are recognised, extending from the middle Darriwilian Histiodella holodentata–Eoplacognathus pseudoplanus and Eoplacognathus suecicus biozones, through the upper Darriwilian Pygodus serra Biozone, to the Pygodus anserinus Biozone spanning the uppermost Darriwilian to basal Sandbian interval. A lower to middle Sandbian carbonate gap coincides with an unzoned interval, followed by the successively younger Belodina compressa, Phragmodus undatus and Taoqupognathus blandus conodont biozones in the upper Sandbian to lower Katian. The T. blandus Biozone directly correlates with the detailed conodont biozonation established in Katian limestones of the Molong Volcanic Belt further east. These age determinations provide much improved precision for correlation within Phases 2 and 3 in the mineral-rich Macquarie Volcanic Province. Analysis of conodont biofacies data supports an enhanced understanding of the geological evolution of the Macquarie Volcanic Province by interpreting the interplay between volcanic activity and carbonate deposition. KEY POINTS Conodont studies in the Billabong Creek Formation of the Gunningbland area reveal the only known biostratigraphic succession in Australia that extends continuously from the middle Darriwilian to basal Sandbian. Three Late Ordovician (late Sandbian to early Katian) conodont biozones in the upper Billabong Creek Formation correlate precisely with carbonates of the Molong Volcanic Belt to the east. Revised stratigraphic definitions of the Billabong Creek and Gunningbland formations are provided.","PeriodicalId":8601,"journal":{"name":"Australian Journal of Earth Sciences","volume":"70 1","pages":"815 - 839"},"PeriodicalIF":1.2,"publicationDate":"2023-06-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48703477","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}
Pub Date : 2023-06-19DOI: 10.1080/08120099.2023.2217882
R. J. Reid, E. Cowan
Abstract Mineral Resource downgrades can be prevented by integrating better structural geological interpretations into project evaluations. Geological modelling for Mineral Resource estimation is presented as a systematic process of structural geological analysis at the deposit-scale using drill-sampled grade data. The initial step in this process is to use Maximum Intensity Projection (MIP) rendering to interpret axial symmetry and its orientation from the grade interval mid-points at the deposit-scale, thus reducing the modelling process’s degrees of freedom to only three—estimating the prolateness of the grade or lithological distribution. This approach contrasts with the brute-force methods for assessing modelling uncertainty because the axial direction is fixed to the down-plunge orientation, thus eliminating from the outset, structurally implausible geometric configurations and unrealistic geological scenarios common in brute-force methods. Adopting this new approach of creating geological models means moving away from conventional mining industry methods that prioritise operational considerations in constructing resource estimates but fail to explain the geometric complexities of mineral deposits. We use experiments and a practical case study of a historical gold mine in Western Australia to highlight the significance of analysing the structural control of a gold deposit at the deposit-scale using raw grade data. Our research is based on anecdotal evidence suggesting that erroneous geological modelling leads to unforeseen Mineral Resource downgrades. However, we cannot confirm this hypothesis because there have been few, if any, independent public inquiries into Mineral Resource downgrades. To establish the underlying reasons for significant resource downgrades with certainty, impartial investigations (modelled on accident investigations in the aviation industry) are imperative. KEY POINTS There is a general lack of incorporating structural geological knowledge in creating resource models, which can lead to poor outcomes such as Mineral Resource downgrades. Structural geological analysis of drill-sampled raw grade data allows the structural controls on a deposit to be better understood. We offer a simple workflow for understanding and modelling these patterns.
{"title":"Towards quantifying uncertainties in geological models for mineral resource estimation through outside-in deposit-scale structural geological analysis","authors":"R. J. Reid, E. Cowan","doi":"10.1080/08120099.2023.2217882","DOIUrl":"https://doi.org/10.1080/08120099.2023.2217882","url":null,"abstract":"Abstract Mineral Resource downgrades can be prevented by integrating better structural geological interpretations into project evaluations. Geological modelling for Mineral Resource estimation is presented as a systematic process of structural geological analysis at the deposit-scale using drill-sampled grade data. The initial step in this process is to use Maximum Intensity Projection (MIP) rendering to interpret axial symmetry and its orientation from the grade interval mid-points at the deposit-scale, thus reducing the modelling process’s degrees of freedom to only three—estimating the prolateness of the grade or lithological distribution. This approach contrasts with the brute-force methods for assessing modelling uncertainty because the axial direction is fixed to the down-plunge orientation, thus eliminating from the outset, structurally implausible geometric configurations and unrealistic geological scenarios common in brute-force methods. Adopting this new approach of creating geological models means moving away from conventional mining industry methods that prioritise operational considerations in constructing resource estimates but fail to explain the geometric complexities of mineral deposits. We use experiments and a practical case study of a historical gold mine in Western Australia to highlight the significance of analysing the structural control of a gold deposit at the deposit-scale using raw grade data. Our research is based on anecdotal evidence suggesting that erroneous geological modelling leads to unforeseen Mineral Resource downgrades. However, we cannot confirm this hypothesis because there have been few, if any, independent public inquiries into Mineral Resource downgrades. To establish the underlying reasons for significant resource downgrades with certainty, impartial investigations (modelled on accident investigations in the aviation industry) are imperative. KEY POINTS There is a general lack of incorporating structural geological knowledge in creating resource models, which can lead to poor outcomes such as Mineral Resource downgrades. Structural geological analysis of drill-sampled raw grade data allows the structural controls on a deposit to be better understood. We offer a simple workflow for understanding and modelling these patterns.","PeriodicalId":8601,"journal":{"name":"Australian Journal of Earth Sciences","volume":"70 1","pages":"990 - 1009"},"PeriodicalIF":1.2,"publicationDate":"2023-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48079378","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}
Pub Date : 2023-06-12DOI: 10.1080/08120099.2023.2214928
J. Vearncombe, T. Blenkinsop
Abstract Basic, nuts and bolts structural geology is the unheralded success story central to brownfields exploration that in Australia, and globally, has grown manyfold mineral deposits beyond the start-of-mine Reserve. Since the last (2012) meeting on applied structural geology and Resources, the topic has changed dramatically. Now, structural geology is practised daily and in house by most exploration and mining companies. KEY POINTS A diversity of settings, host rocks, control and geometry make it critical to document precisely the rocks in front of the geologist as distinct to what is in a preconceived conceptual model. It is detail that makes for new discoveries and deposit extensions. Three-dimensional computer visualisation helps with volumetric thinking, but there remains no computer alternative to the 3D cognitive geologist. Now essential structural data are integrated with other data, but the product is a hypothesis to be tested, not a silver bullet. Lineations matter and inform. The primary deliverable is images, be they hand-drawn or computer-generated showing the inter-relationships of structure, lithology, mineralisation and mine-site infrastructure/design. With their important embedded knowledge, the geologist, who took the readings, should also be entering, plotting data, synthesising, modelling and presenting to management and Directors.
{"title":"Function and status of structural geology in the Resource industry","authors":"J. Vearncombe, T. Blenkinsop","doi":"10.1080/08120099.2023.2214928","DOIUrl":"https://doi.org/10.1080/08120099.2023.2214928","url":null,"abstract":"Abstract Basic, nuts and bolts structural geology is the unheralded success story central to brownfields exploration that in Australia, and globally, has grown manyfold mineral deposits beyond the start-of-mine Reserve. Since the last (2012) meeting on applied structural geology and Resources, the topic has changed dramatically. Now, structural geology is practised daily and in house by most exploration and mining companies. KEY POINTS A diversity of settings, host rocks, control and geometry make it critical to document precisely the rocks in front of the geologist as distinct to what is in a preconceived conceptual model. It is detail that makes for new discoveries and deposit extensions. Three-dimensional computer visualisation helps with volumetric thinking, but there remains no computer alternative to the 3D cognitive geologist. Now essential structural data are integrated with other data, but the product is a hypothesis to be tested, not a silver bullet. Lineations matter and inform. The primary deliverable is images, be they hand-drawn or computer-generated showing the inter-relationships of structure, lithology, mineralisation and mine-site infrastructure/design. With their important embedded knowledge, the geologist, who took the readings, should also be entering, plotting data, synthesising, modelling and presenting to management and Directors.","PeriodicalId":8601,"journal":{"name":"Australian Journal of Earth Sciences","volume":"70 1","pages":"908 - 931"},"PeriodicalIF":1.2,"publicationDate":"2023-06-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47612322","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}
Pub Date : 2023-05-31DOI: 10.1080/08120099.2023.2212026
G. Retallack, B. Jones
Abstract The paleosol record of the Early Cretaceous Wonthaggi and Eumeralla formations of Victoria reveals a suite of non-calcareous Histosols and Ultisols, as well as stump casts, indicative of humid temperate ecosystems. At some stratigraphic levels, frigid temperatures are indicated by clastic dykes (ice wedges), load casts of mud (periglacial convolutions), and coal-mantled stone rolls (aapamires). The largest tree stumps and thickest paleosols correspond to known Early Cretaceous greenhouse spikes, as revealed by stomatal index of fossil ginkgo leaves, by black shales of oceanic anoxic events, and both marine and non-marine carbon isotopic anomalies. Temperature and CO2 spikes coincide with appearance of broadleaf deciduous forests, including Ginkgo australis, with dinosaurs, monotremes, placentals, early birds and angiosperms. In contrast, permafrost paleosols represent fern-lycopsid tundra and coniferous taiga vegetation. Early Cretaceous CO2 greenhouse spikes allowed southward migration of tree lines and polar biomes several times during the Cretaceous, which was not continuously a hothouse period. The same greenhouse spikes are recorded by maximal marine transgressions in the Great Artesian Basin of Queensland, and the frigid intervals by dropped pebbles and glendonites in South Australia, New South Wales and Arctic regions. KEY POINTS Victorian Cretaceous Wonthaggi and Eumeralla formations have Histosol and Ultisol paleosols. Hauterivian and Barremian ice wedges, convolutions and aapamires were frigid. Temperature and CO2 spikes were times of polar invasion by taiga and broadleaf trees. Greenhouse spikes are also recorded by maximal marine transgressions in Queensland. Dropped pebbles and glendonites in Central Australia also represent frigid intervals.
{"title":"Dinosaur and tree-line invasion of southeastern Australia during Cretaceous greenhouse spikes","authors":"G. Retallack, B. Jones","doi":"10.1080/08120099.2023.2212026","DOIUrl":"https://doi.org/10.1080/08120099.2023.2212026","url":null,"abstract":"Abstract The paleosol record of the Early Cretaceous Wonthaggi and Eumeralla formations of Victoria reveals a suite of non-calcareous Histosols and Ultisols, as well as stump casts, indicative of humid temperate ecosystems. At some stratigraphic levels, frigid temperatures are indicated by clastic dykes (ice wedges), load casts of mud (periglacial convolutions), and coal-mantled stone rolls (aapamires). The largest tree stumps and thickest paleosols correspond to known Early Cretaceous greenhouse spikes, as revealed by stomatal index of fossil ginkgo leaves, by black shales of oceanic anoxic events, and both marine and non-marine carbon isotopic anomalies. Temperature and CO2 spikes coincide with appearance of broadleaf deciduous forests, including Ginkgo australis, with dinosaurs, monotremes, placentals, early birds and angiosperms. In contrast, permafrost paleosols represent fern-lycopsid tundra and coniferous taiga vegetation. Early Cretaceous CO2 greenhouse spikes allowed southward migration of tree lines and polar biomes several times during the Cretaceous, which was not continuously a hothouse period. The same greenhouse spikes are recorded by maximal marine transgressions in the Great Artesian Basin of Queensland, and the frigid intervals by dropped pebbles and glendonites in South Australia, New South Wales and Arctic regions. KEY POINTS Victorian Cretaceous Wonthaggi and Eumeralla formations have Histosol and Ultisol paleosols. Hauterivian and Barremian ice wedges, convolutions and aapamires were frigid. Temperature and CO2 spikes were times of polar invasion by taiga and broadleaf trees. Greenhouse spikes are also recorded by maximal marine transgressions in Queensland. Dropped pebbles and glendonites in Central Australia also represent frigid intervals.","PeriodicalId":8601,"journal":{"name":"Australian Journal of Earth Sciences","volume":"70 1","pages":"840 - 858"},"PeriodicalIF":1.2,"publicationDate":"2023-05-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44952587","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}
Pub Date : 2023-05-25DOI: 10.1080/08120099.2023.2210197
G. Carr, G. Denton, M. Korsch, J. Parr, L. Wyborn, S. Sun
{"title":"A Pb isotope model for the Proterozoic of northern Australia with a focus on the McArthur Basin","authors":"G. Carr, G. Denton, M. Korsch, J. Parr, L. Wyborn, S. Sun","doi":"10.1080/08120099.2023.2210197","DOIUrl":"https://doi.org/10.1080/08120099.2023.2210197","url":null,"abstract":"","PeriodicalId":8601,"journal":{"name":"Australian Journal of Earth Sciences","volume":"1 1","pages":""},"PeriodicalIF":1.2,"publicationDate":"2023-05-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"59577183","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}
Pub Date : 2023-05-25DOI: 10.1080/08120099.2023.2210635
B. Yang, A. Collins, M. Blades, F. Jourdan
{"title":"Orogens and detritus: unravelling the Mesoproterozoic tectonic geography of northern Australia through coupled detrital thermo- and geo-chronometers","authors":"B. Yang, A. Collins, M. Blades, F. Jourdan","doi":"10.1080/08120099.2023.2210635","DOIUrl":"https://doi.org/10.1080/08120099.2023.2210635","url":null,"abstract":"","PeriodicalId":8601,"journal":{"name":"Australian Journal of Earth Sciences","volume":" ","pages":""},"PeriodicalIF":1.2,"publicationDate":"2023-05-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44702732","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}
Pub Date : 2023-05-25DOI: 10.1080/08120099.2023.2210637
T. Blenkinsop
Abstract Rock mechanics experiments show that the magnitude of the intermediate principal stress significantly affects rock failure. Since triaxial stress states (no principal stress is zero) are ubiquitous in the crust, and polyaxial axial states (all three principal stresses are different) are general, the magnitude of the intermediate principal stress should have an important effect on hydrothermal mineralisation. For example, extensional veins or dykes in vein-hosted gold or porphyry deposits may have multiple orientations when the intermediate and least principal stresses have similar magnitudes, or single orientations when the intermediate and maximum principal stresses are similar. The Griffith-Murrell triaxial fracture criterion with a tensile cutoff can be used to illustrate the effects of the intermediate principal stress on failure. At the lowest values of mean stress, the criterion suggests that only extensional failure can occur. At low–intermediate values of mean stress, either extensional or shear failure may occur: extensional failure is favoured when the intermediate and maximum principal stresses have similar magnitudes. At higher mean stresses, shear failure will occur at lower values of pore fluid pressure and differential stress when the magnitudes of the intermediate and minimum principal stresses are similar. KEY POINTS The intermediate principal stress has significant effects on rock strength, which should be considered for understanding failure in hydrothermal mineralising systems, because stress states in the Earth are generally triaxial and polyaxial. The magnitude of intermediate principal stress relative to those of the other principal stresses affects the range of orientations of extensional fractures, for example in stockworks and sheeted veins. At low values of mean stress, only extensional failure occurs. At low to intermediate values of mean stress, extension is favoured over shear failure when the magnitudes of intermediate and maximum principal stresses are similar. At high values of mean stress, shear failure will occur at lower values of pore fluid pressure and differential stress when the magnitudes of the intermediate and minimum principal stresses are similar.
{"title":"Triaxial stress and failure modes in hydrothermal mineral systems","authors":"T. Blenkinsop","doi":"10.1080/08120099.2023.2210637","DOIUrl":"https://doi.org/10.1080/08120099.2023.2210637","url":null,"abstract":"Abstract Rock mechanics experiments show that the magnitude of the intermediate principal stress significantly affects rock failure. Since triaxial stress states (no principal stress is zero) are ubiquitous in the crust, and polyaxial axial states (all three principal stresses are different) are general, the magnitude of the intermediate principal stress should have an important effect on hydrothermal mineralisation. For example, extensional veins or dykes in vein-hosted gold or porphyry deposits may have multiple orientations when the intermediate and least principal stresses have similar magnitudes, or single orientations when the intermediate and maximum principal stresses are similar. The Griffith-Murrell triaxial fracture criterion with a tensile cutoff can be used to illustrate the effects of the intermediate principal stress on failure. At the lowest values of mean stress, the criterion suggests that only extensional failure can occur. At low–intermediate values of mean stress, either extensional or shear failure may occur: extensional failure is favoured when the intermediate and maximum principal stresses have similar magnitudes. At higher mean stresses, shear failure will occur at lower values of pore fluid pressure and differential stress when the magnitudes of the intermediate and minimum principal stresses are similar. KEY POINTS The intermediate principal stress has significant effects on rock strength, which should be considered for understanding failure in hydrothermal mineralising systems, because stress states in the Earth are generally triaxial and polyaxial. The magnitude of intermediate principal stress relative to those of the other principal stresses affects the range of orientations of extensional fractures, for example in stockworks and sheeted veins. At low values of mean stress, only extensional failure occurs. At low to intermediate values of mean stress, extension is favoured over shear failure when the magnitudes of intermediate and maximum principal stresses are similar. At high values of mean stress, shear failure will occur at lower values of pore fluid pressure and differential stress when the magnitudes of the intermediate and minimum principal stresses are similar.","PeriodicalId":8601,"journal":{"name":"Australian Journal of Earth Sciences","volume":"70 1","pages":"947 - 957"},"PeriodicalIF":1.2,"publicationDate":"2023-05-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48904011","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}
Pub Date : 2023-05-25DOI: 10.1080/08120099.2023.2209649
B. Hines, D. Turnbull, L. Ashworth, S. McKnight, C. Fergusson
Abstract The Dorchap Dyke Swarm hosts the first recorded occurrence of lithium–caesium–tantalum (LCT) pegmatites in Victoria, Australia. Syn-orogenic emplacement of pegmatite dykes occurred along a northwest-trending shear system during the Benambran Orogeny. Pegmatites are derived from fractionated melt associated with the Mount Wills Granite, which is an S-type, peraluminous granite originating from supracrustal melting of Ordovician sedimentary sequences. A distinct, eastward-oriented fractionation trend across the Dorchap Dyke Swarm has highlighted a 20 × 8 km highly fractionated zone in the northeastern Dorchap Range, which includes spodumene- and petalite-bearing pegmatites. A distinct pattern of elemental enrichment (P > Cs > Be > Nb ≥ Ta > Li > Sn) is observed across the strongly fractionated zone of the Dorchap Dyke Swarm. Subsequent metasomatic fluid movements and hydrothermal overprinting have resulted in redistribution of mobile elements in the Dorchap Range, either as hydrothermal alteration species or in some instances as the development of exomorphic halos. Additionally, a regional alteration overprint, likely associated with subsequent metamorphism of pegmatite dykes has resulted in alteration of primary petalite to spodumene plus quartz, and primary spodumene to cookeite. Bulk rock geochemical data from the Dorchap Dyke Swarm suggest a syn-collisional setting for dyke intrusion, consistent with the inferred tectonic setting of the central Lachlan Fold Belt at the time of pegmatite emplacement. Pegmatite dykes locally contain an overprinted structural foliation, which is consistent with the primary structural trend of deformed metasediments and may indicate that dyke emplacement was syngenetic with regional folding and compression of the surrounding Omeo Metamorphic Complex during the Benambran Orogeny. Subsequent hydrothermal alteration of some dykes likely occurred immediately following the Bindian Orogeny. KEY POINTS Dorchap Dyke Swarm are the first recorded Li–Cs–Ta pegmatites in Victoria, Australia. Pegmatites were emplaced synchronous with or immediately following the Benambran Orogeny. Dorchap Dyke Swarm pegmatites are geochemically correlated with the Mount Wills Granite.
摘要Dorchap Dyke Swarm是澳大利亚维多利亚州首次记录到的锂-铯-钽（LCT）伟晶岩。贝南布拉造山运动期间，伟晶岩脉沿西北走向的剪切系统发生同造山侵位。伟晶岩来源于与Wills山花岗岩相关的分馏熔融，Wills山是一种S型过铝质花岗岩，起源于奥陶系沉积序列的表壳熔融。多尔恰普堤坝群中明显的、向东的分馏趋势突出了20 × 8. 位于多尔恰普山脉东北部的km高度分馏区，包括含锂辉石和花瓣岩的伟晶岩。元素富集的明显模式（P > Cs > 是 > Nb ≥ Ta > 李 > Sn）在多尔恰普·戴克群的强分馏区中被观察到。随后的交代流体运动和热液叠加导致多尔恰普山脉中可移动元素的重新分布，要么作为热液蚀变物种，要么在某些情况下作为变质晕的发育。此外，区域蚀变叠加，可能与伟晶岩脉的后续变质作用有关，导致原生绿柱石蚀变为锂辉石加石英，原生锂辉石蚀变为库克辉石。Dorchap堤坝群的大块岩石地球化学数据表明，堤坝侵入的同碰撞环境与伟晶岩侵位时拉克伦褶皱带中部的推断构造环境一致。伟晶岩岩脉局部含有叠加的结构叶理，这与变形变质沉积物的主要结构趋势一致，并可能表明岩脉侵位与Benambran造山运动期间周围Omeo变质杂岩的区域折叠和挤压是同生的。随后的一些岩脉的热液蚀变可能发生在宾甸造山运动之后。要点Dorchap Dyke Swarm是澳大利亚维多利亚州第一个有记录的Li–Cs–Ta伟晶岩。伟晶岩与本南布拉造山运动同步或紧接着侵位。多尔查普戴克群伟晶岩与威尔斯山花岗岩具有地球化学相关性。
{"title":"Geochemical characteristics and structural setting of lithium–caesium–tantalum pegmatites of the Dorchap Dyke Swarm, northeast Victoria, Australia","authors":"B. Hines, D. Turnbull, L. Ashworth, S. McKnight, C. Fergusson","doi":"10.1080/08120099.2023.2209649","DOIUrl":"https://doi.org/10.1080/08120099.2023.2209649","url":null,"abstract":"Abstract The Dorchap Dyke Swarm hosts the first recorded occurrence of lithium–caesium–tantalum (LCT) pegmatites in Victoria, Australia. Syn-orogenic emplacement of pegmatite dykes occurred along a northwest-trending shear system during the Benambran Orogeny. Pegmatites are derived from fractionated melt associated with the Mount Wills Granite, which is an S-type, peraluminous granite originating from supracrustal melting of Ordovician sedimentary sequences. A distinct, eastward-oriented fractionation trend across the Dorchap Dyke Swarm has highlighted a 20 × 8 km highly fractionated zone in the northeastern Dorchap Range, which includes spodumene- and petalite-bearing pegmatites. A distinct pattern of elemental enrichment (P > Cs > Be > Nb ≥ Ta > Li > Sn) is observed across the strongly fractionated zone of the Dorchap Dyke Swarm. Subsequent metasomatic fluid movements and hydrothermal overprinting have resulted in redistribution of mobile elements in the Dorchap Range, either as hydrothermal alteration species or in some instances as the development of exomorphic halos. Additionally, a regional alteration overprint, likely associated with subsequent metamorphism of pegmatite dykes has resulted in alteration of primary petalite to spodumene plus quartz, and primary spodumene to cookeite. Bulk rock geochemical data from the Dorchap Dyke Swarm suggest a syn-collisional setting for dyke intrusion, consistent with the inferred tectonic setting of the central Lachlan Fold Belt at the time of pegmatite emplacement. Pegmatite dykes locally contain an overprinted structural foliation, which is consistent with the primary structural trend of deformed metasediments and may indicate that dyke emplacement was syngenetic with regional folding and compression of the surrounding Omeo Metamorphic Complex during the Benambran Orogeny. Subsequent hydrothermal alteration of some dykes likely occurred immediately following the Bindian Orogeny. KEY POINTS Dorchap Dyke Swarm are the first recorded Li–Cs–Ta pegmatites in Victoria, Australia. Pegmatites were emplaced synchronous with or immediately following the Benambran Orogeny. Dorchap Dyke Swarm pegmatites are geochemically correlated with the Mount Wills Granite.","PeriodicalId":8601,"journal":{"name":"Australian Journal of Earth Sciences","volume":"70 1","pages":"763 - 800"},"PeriodicalIF":1.2,"publicationDate":"2023-05-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44132369","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}
Pub Date : 2023-05-25DOI: 10.1080/08120099.2023.2213297
B. Jones, B. Sainsbury
Abstract Through this research, we measure the direct tensile strength of three important southeast Australian heritage dimension stones and compare the results with published values. The three stones are Sydney Sandstone, Victorian Bluestone and South Australian Black Granite. This information is crucial for stone masons when they are selecting and cutting stone for construction projects, as they need to ensure that the stone they use and the repair will be strong enough to withstand the loads and stresses it will be subjected to in its final location. Results show that direct methods of testing provide tensile strengths that are 30–63% of the indirect methods. When the direct tension to compressive strength ratio is considered, results of 2–7% are calculated for these stones. This is significantly less than the typically assumed 10% for intact rock. Three masonry bonding agents have been selected to determine their capacity to re-bond the dimension stone. Highly variable results were achieved, with re-bonded tensile strengths ranging from 6% to 104% of the intact strength. This variability is most likely related to the heterogeneity of the stones and the surface preparations. Based on these outcomes, it is recommended that stone masons carefully consider the product that is used for restoration works and that test samples be prepared to confirm capacities. KEY POINTS Direct tension testing has been completed on Sydney Sandstone, Victorian Bluestone and South Australian Black Granite dimension stones. Direct tension results have not been previously published for these stones. Direct methods of testing provide tensile strengths that are 30–63% of the indirect methods on these stone types. When the direct tension to unconfined compressive strength ratio is considered, results of 2–7% are returned for these stones. This is significantly less than the typically assumed 10%. The performance of bonding agents on each of the stones provides variable results suggesting that careful selection of products is required and, if possible, test samples be prepared to confirm bond capacities.
{"title":"Characterisation of the tensile performance of bonding agents for the restoration of heritage dimension stone from southeast Australia","authors":"B. Jones, B. Sainsbury","doi":"10.1080/08120099.2023.2213297","DOIUrl":"https://doi.org/10.1080/08120099.2023.2213297","url":null,"abstract":"Abstract Through this research, we measure the direct tensile strength of three important southeast Australian heritage dimension stones and compare the results with published values. The three stones are Sydney Sandstone, Victorian Bluestone and South Australian Black Granite. This information is crucial for stone masons when they are selecting and cutting stone for construction projects, as they need to ensure that the stone they use and the repair will be strong enough to withstand the loads and stresses it will be subjected to in its final location. Results show that direct methods of testing provide tensile strengths that are 30–63% of the indirect methods. When the direct tension to compressive strength ratio is considered, results of 2–7% are calculated for these stones. This is significantly less than the typically assumed 10% for intact rock. Three masonry bonding agents have been selected to determine their capacity to re-bond the dimension stone. Highly variable results were achieved, with re-bonded tensile strengths ranging from 6% to 104% of the intact strength. This variability is most likely related to the heterogeneity of the stones and the surface preparations. Based on these outcomes, it is recommended that stone masons carefully consider the product that is used for restoration works and that test samples be prepared to confirm capacities. KEY POINTS Direct tension testing has been completed on Sydney Sandstone, Victorian Bluestone and South Australian Black Granite dimension stones. Direct tension results have not been previously published for these stones. Direct methods of testing provide tensile strengths that are 30–63% of the indirect methods on these stone types. When the direct tension to unconfined compressive strength ratio is considered, results of 2–7% are returned for these stones. This is significantly less than the typically assumed 10%. The performance of bonding agents on each of the stones provides variable results suggesting that careful selection of products is required and, if possible, test samples be prepared to confirm bond capacities.","PeriodicalId":8601,"journal":{"name":"Australian Journal of Earth Sciences","volume":"70 1","pages":"731 - 740"},"PeriodicalIF":1.2,"publicationDate":"2023-05-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45464578","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}
Pub Date : 2023-05-17DOI: 10.1080/08120099.2023.2207628
A. Ord, B. Hobbs, J. Vearncombe
Abstract Every nonlinear system grows by increments, and the final probability distributions for components of that system emerge from an amalgamation of these increments. The resulting probability distribution depends on the constraints imposed on each increment by the physical and chemical processes that produce the system. Hence there is the potential that the observed probability distribution can reveal information on these processes. Complex systems that grow by competition between the supply and consumption of energy and mass have growth laws that are cumulative probability distributions for their component parts that reflect such competition. We show that the type of probability distribution is characteristic of the endowment of orogenic gold deposits with the sequence: Weibull → Fréchet → gamma → log normal representative of increasing endowment. Further, the differential entropy of the probability distribution is indicative of the quality of the deposit, with low-quality deposits represented by high entropy and high-quality deposits represented by low or negative entropy. The type of probability distribution gives an indication of the processes that operated to produce the deposit. These conclusions hold for mineralisation as well as for the associated alteration assemblages. We suggest that the probability distribution for the mineralisation or the alteration assemblage gives a good indication of the endowment and quality of a deposit from a single drill hole. KEY POINTS A single drill hole from a deposit can provide information on endowment and organisation. Weibull → Fréchet → gamma → log normal probability distributions are representative of increasing gold endowment. The differential entropies of these distributions characterise the organisation of the system.
{"title":"The growth and size of orogenic gold systems: probability and dynamical behaviour","authors":"A. Ord, B. Hobbs, J. Vearncombe","doi":"10.1080/08120099.2023.2207628","DOIUrl":"https://doi.org/10.1080/08120099.2023.2207628","url":null,"abstract":"Abstract Every nonlinear system grows by increments, and the final probability distributions for components of that system emerge from an amalgamation of these increments. The resulting probability distribution depends on the constraints imposed on each increment by the physical and chemical processes that produce the system. Hence there is the potential that the observed probability distribution can reveal information on these processes. Complex systems that grow by competition between the supply and consumption of energy and mass have growth laws that are cumulative probability distributions for their component parts that reflect such competition. We show that the type of probability distribution is characteristic of the endowment of orogenic gold deposits with the sequence: Weibull → Fréchet → gamma → log normal representative of increasing endowment. Further, the differential entropy of the probability distribution is indicative of the quality of the deposit, with low-quality deposits represented by high entropy and high-quality deposits represented by low or negative entropy. The type of probability distribution gives an indication of the processes that operated to produce the deposit. These conclusions hold for mineralisation as well as for the associated alteration assemblages. We suggest that the probability distribution for the mineralisation or the alteration assemblage gives a good indication of the endowment and quality of a deposit from a single drill hole. KEY POINTS A single drill hole from a deposit can provide information on endowment and organisation. Weibull → Fréchet → gamma → log normal probability distributions are representative of increasing gold endowment. The differential entropies of these distributions characterise the organisation of the system.","PeriodicalId":8601,"journal":{"name":"Australian Journal of Earth Sciences","volume":"70 1","pages":"932 - 946"},"PeriodicalIF":1.2,"publicationDate":"2023-05-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41787488","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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