{"title":"Ngubevu金矿和贱金属矿(南非Tugela Terrane Natal冲断层前缘)的微观断裂:它们与宏观尺度的变形一致吗?它们告诉我们什么?","authors":"N. S. Busakwe, E. Carranza, O. Chagi, L. Hoyer","doi":"10.25131/sajg.125.0008","DOIUrl":null,"url":null,"abstract":"\n In the Natal Thrust Front (NTF) of the Tugela Terrane, there is a lack of multi-scale characterisation of structural controls on shear-zone hosted precious and base metal mineralisation. This paper contributes to the current understanding of the structural controls on shear-zone-hosted precious and base metal mineralisation in the NTF with insight derived from the analyses of micro-fractures at and around the known shear-zone-hosted lode gold and base metal mineralisation in the Ngubevu area of the NTF. Based on the notion that the spatial distribution of stresses that control geological structures is fractal (i.e., possessing scale-invariance or self-similarity properties) across a range of geographic scales, this study (a) determines whether the stresses inferred from micro-fractures in the gold mines in Ngubevu are consistent with the stresses associated with regional- to local-scale geological structures in the NTF, and (b) interprets the mineralisation controls implied by these inferred and known stresses. From rose diagrams showing trends of micro-fractures in oriented vein material samples from Ngubevu, the relative micro-scale stress field per sample based on the maximum horizontal stress (SHmax) and the minimum horizontal stress (SHmin) were inferred. These were then compared to the local- to regional-scale stress field orientations derived from existing studies in the NTF.\n The north-northeast–south-southwest orientations of SHmax of micro-fractures in samples from Ngubevu are consistent with the north-northwest–south-southeast orientations of SHmax of regional- to district-scale thrust faults in the NTF of the Tugela Terrane. Likewise, the west-northwest–east-southeast orientations of micro-fractures in samples from the eastern part of Ngubevu are consistent with the general east–west orientations of local-scale S1 foliation. These orientations are associated with a D1 thrusting event, which was due to north to north-northeast-directed regional thrust tectonics. The clockwise change from the north-northwest–south-southeast orientations of SHmax of regional- to district-scale thrust faults to the north-northeast–south-southwest orientations of SHmax of micro-fractures in vein material attests to an earlier posited notion of clockwise rotation of regional- to district-scale thrust vergence. These suggest that V1 veins in Ngubevu were likely formed late in the D1 event. The orientations of micro-fractures in samples, mostly from the western part of Ngubevu, depict a strike-slip regime, which is consistent with D2 sinistral transpression that affected the earlier-formed east–west-trending structures. This suggests that some V1 veins in Ngubevu, particularly those in its western part, were affected by the D2 sinistral transpression (e.g., by remobilisation of gold in some of the V1 veins). The novel findings in this study are crucial to geological mapping, recognition of mineralisation controls and mineral prospecting in poorly-explored regions where the geology is permissive (i.e., represents processes that are favourable) for the formation of certain type(s) of mineralisation.","PeriodicalId":49494,"journal":{"name":"South African Journal of Geology","volume":" ","pages":""},"PeriodicalIF":1.2000,"publicationDate":"2022-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Micro-fractures in the Ngubevu Gold and Base Metal Mines (Natal Thrust Front, Tugela Terrane, South Africa): Are they consistent with macro-scale deformation, and what do they tell us?\",\"authors\":\"N. S. Busakwe, E. Carranza, O. Chagi, L. Hoyer\",\"doi\":\"10.25131/sajg.125.0008\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"\\n In the Natal Thrust Front (NTF) of the Tugela Terrane, there is a lack of multi-scale characterisation of structural controls on shear-zone hosted precious and base metal mineralisation. This paper contributes to the current understanding of the structural controls on shear-zone-hosted precious and base metal mineralisation in the NTF with insight derived from the analyses of micro-fractures at and around the known shear-zone-hosted lode gold and base metal mineralisation in the Ngubevu area of the NTF. Based on the notion that the spatial distribution of stresses that control geological structures is fractal (i.e., possessing scale-invariance or self-similarity properties) across a range of geographic scales, this study (a) determines whether the stresses inferred from micro-fractures in the gold mines in Ngubevu are consistent with the stresses associated with regional- to local-scale geological structures in the NTF, and (b) interprets the mineralisation controls implied by these inferred and known stresses. From rose diagrams showing trends of micro-fractures in oriented vein material samples from Ngubevu, the relative micro-scale stress field per sample based on the maximum horizontal stress (SHmax) and the minimum horizontal stress (SHmin) were inferred. These were then compared to the local- to regional-scale stress field orientations derived from existing studies in the NTF.\\n The north-northeast–south-southwest orientations of SHmax of micro-fractures in samples from Ngubevu are consistent with the north-northwest–south-southeast orientations of SHmax of regional- to district-scale thrust faults in the NTF of the Tugela Terrane. Likewise, the west-northwest–east-southeast orientations of micro-fractures in samples from the eastern part of Ngubevu are consistent with the general east–west orientations of local-scale S1 foliation. These orientations are associated with a D1 thrusting event, which was due to north to north-northeast-directed regional thrust tectonics. The clockwise change from the north-northwest–south-southeast orientations of SHmax of regional- to district-scale thrust faults to the north-northeast–south-southwest orientations of SHmax of micro-fractures in vein material attests to an earlier posited notion of clockwise rotation of regional- to district-scale thrust vergence. These suggest that V1 veins in Ngubevu were likely formed late in the D1 event. The orientations of micro-fractures in samples, mostly from the western part of Ngubevu, depict a strike-slip regime, which is consistent with D2 sinistral transpression that affected the earlier-formed east–west-trending structures. This suggests that some V1 veins in Ngubevu, particularly those in its western part, were affected by the D2 sinistral transpression (e.g., by remobilisation of gold in some of the V1 veins). The novel findings in this study are crucial to geological mapping, recognition of mineralisation controls and mineral prospecting in poorly-explored regions where the geology is permissive (i.e., represents processes that are favourable) for the formation of certain type(s) of mineralisation.\",\"PeriodicalId\":49494,\"journal\":{\"name\":\"South African Journal of Geology\",\"volume\":\" \",\"pages\":\"\"},\"PeriodicalIF\":1.2000,\"publicationDate\":\"2022-03-01\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"South African Journal of Geology\",\"FirstCategoryId\":\"93\",\"ListUrlMain\":\"https://doi.org/10.25131/sajg.125.0008\",\"RegionNum\":4,\"RegionCategory\":\"地球科学\",\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q2\",\"JCRName\":\"GEOLOGY\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"South African Journal of Geology","FirstCategoryId":"93","ListUrlMain":"https://doi.org/10.25131/sajg.125.0008","RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"GEOLOGY","Score":null,"Total":0}
Micro-fractures in the Ngubevu Gold and Base Metal Mines (Natal Thrust Front, Tugela Terrane, South Africa): Are they consistent with macro-scale deformation, and what do they tell us?
In the Natal Thrust Front (NTF) of the Tugela Terrane, there is a lack of multi-scale characterisation of structural controls on shear-zone hosted precious and base metal mineralisation. This paper contributes to the current understanding of the structural controls on shear-zone-hosted precious and base metal mineralisation in the NTF with insight derived from the analyses of micro-fractures at and around the known shear-zone-hosted lode gold and base metal mineralisation in the Ngubevu area of the NTF. Based on the notion that the spatial distribution of stresses that control geological structures is fractal (i.e., possessing scale-invariance or self-similarity properties) across a range of geographic scales, this study (a) determines whether the stresses inferred from micro-fractures in the gold mines in Ngubevu are consistent with the stresses associated with regional- to local-scale geological structures in the NTF, and (b) interprets the mineralisation controls implied by these inferred and known stresses. From rose diagrams showing trends of micro-fractures in oriented vein material samples from Ngubevu, the relative micro-scale stress field per sample based on the maximum horizontal stress (SHmax) and the minimum horizontal stress (SHmin) were inferred. These were then compared to the local- to regional-scale stress field orientations derived from existing studies in the NTF.
The north-northeast–south-southwest orientations of SHmax of micro-fractures in samples from Ngubevu are consistent with the north-northwest–south-southeast orientations of SHmax of regional- to district-scale thrust faults in the NTF of the Tugela Terrane. Likewise, the west-northwest–east-southeast orientations of micro-fractures in samples from the eastern part of Ngubevu are consistent with the general east–west orientations of local-scale S1 foliation. These orientations are associated with a D1 thrusting event, which was due to north to north-northeast-directed regional thrust tectonics. The clockwise change from the north-northwest–south-southeast orientations of SHmax of regional- to district-scale thrust faults to the north-northeast–south-southwest orientations of SHmax of micro-fractures in vein material attests to an earlier posited notion of clockwise rotation of regional- to district-scale thrust vergence. These suggest that V1 veins in Ngubevu were likely formed late in the D1 event. The orientations of micro-fractures in samples, mostly from the western part of Ngubevu, depict a strike-slip regime, which is consistent with D2 sinistral transpression that affected the earlier-formed east–west-trending structures. This suggests that some V1 veins in Ngubevu, particularly those in its western part, were affected by the D2 sinistral transpression (e.g., by remobilisation of gold in some of the V1 veins). The novel findings in this study are crucial to geological mapping, recognition of mineralisation controls and mineral prospecting in poorly-explored regions where the geology is permissive (i.e., represents processes that are favourable) for the formation of certain type(s) of mineralisation.
期刊介绍:
The South African Journal of Geology publishes scientific papers, notes, stratigraphic descriptions and discussions in the broadly defined fields of geoscience that are related directly or indirectly to the geology of Africa. Contributions relevant to former supercontinental entities such as Gondwana and Rodinia are also welcome as are topical studies on any geoscience-related discipline. Review papers are welcome as long as they represent original, new syntheses. Special issues are also encouraged but terms for these must be negotiated with the Editors.