The Marwar Supergroup(NW Peninsular India)is thought to be of Ediacaran-Cambrian age,based on previous paleontological and geochronological studies.However,direct constraints on the onset of sedimentation within the M...The Marwar Supergroup(NW Peninsular India)is thought to be of Ediacaran-Cambrian age,based on previous paleontological and geochronological studies.However,direct constraints on the onset of sedimentation within the Marwar basin are still scarce.In this study,we report U–Pb zircon,LA-ICP-MS,and SIMS ages from the Chhoti Khatu felsic volcanic rocks,interlayered with the Jodhpur Group sandstones(Lower Marwar Supergroup).The cathodoluminescence images of the zircons indicate complex morphologies,and core-rim textures coupled with the wide range of ages indicate that they are likely inherited or in the case of thin poorly indurated ash-beds,detrital in origin.The age spectra of 68 zircon analyses from our sampling display a dominant 800–900 Ma age peak corresponding to the age of basement"Erinpura granite"rocks in the region.The youngest inherited zircon from a felsic ash layer yielded a U–Pb age of651 Ma±18 Ma that,together with previous studies and paleontological evidence,indicates a postCryogenian age for the initiation of Marwar sedimentation following a~125 Ma hiatus between the end of Malani magmatism and Marwar deposition.展开更多
The noncarbonaceous Ediacaran discs of variable morphologies from the Jodhpur Sandstone Formation of the Marwar Supergroup, western Rajasthan, suggest different biologic affinities of plant and animal kingdom. These d...The noncarbonaceous Ediacaran discs of variable morphologies from the Jodhpur Sandstone Formation of the Marwar Supergroup, western Rajasthan, suggest different biologic affinities of plant and animal kingdom. These discs are commonly preserved on the bedding surfaces of siliciclastic sandstone and shale in strong positive relief and appear to possess a flexible to rigid body. Discs assignable to Aspidella, Cyclomedusa, Nimbia and Heimalora;all possibly inclining towards cnidarian affinity are being reported from the sandstone beds in Sursagar area. Variable morphologies among discs preserved in siliciclastic shale beds from the Artiya Kalan area support scyphozoan affinity (earlier named Marsonia from the same locality) and cnidarian affinity for small discs comparable with Funisia (considered being the first animals having sexual reproduction). Disc’s morphologies also suggest ephyra stage of Aurilia (a cnidarian form) or budding stages of some fungi, like Germinosphaera (multicellular benthic fungal fossils) and noncarbonaceous discs with well preserved wrinkles and folds like in Chuaria. Discs from the Jodhpur Sandstone, may at times display taphonomic interplay, but consistency and repetition in morphology support variable biological affinities representing diverse assemblage and advance ecosystem prevailing during Ediacaran period. A degree of genetic variability can be expected within any taxa, and this may be compounded by preservation factors affecting the Jodhpur Ediacaran discs. Sudden increase in size or gigantism is a common feature of Ediacaran life, which is evident in case of Jodhpur discs also. On the basis of fossil assemblage, the Jodhpur Group (the Marwar Supergroup) is regionally correlated with the Bhander Group of the Vindhyan Supergroup and Krol Group of Lesser Himalaya. Globally, the assemblage is comparable with the Long Mynd Group, Shropshire, UK, Fermuse Formation Newfoundland, South Australia, Russia and Norway.展开更多
Ediacaran discs from the Jodhpur Sandstone of the Marwar Supergroup, Rajasthan, exhibit a wide size ranging from a few millimetres to 75 cm in diameter. Exceptionally large size of the discs in these rocks represent t...Ediacaran discs from the Jodhpur Sandstone of the Marwar Supergroup, Rajasthan, exhibit a wide size ranging from a few millimetres to 75 cm in diameter. Exceptionally large size of the discs in these rocks represent the largest reported so far from any Ediacaran assemblage. Although, larger medu-soid discs have been reported from USA, they are from the middle Cambrian and even younger rocks. Presence of microbial mats and weed-like structures with well preserved hold fasts and horizontal rhizome-like structures in association with some of these large-sized discs support their animal affinity, which probably feed on this weed-like vegetations. This association also supports their benthic habitat. Unlike the general trend of sudden increase in size of organisms in Ediacaran period and further decrease in size during Cambrian, these discs continued increasing in size in Cambrian also.展开更多
The Paleoproterozoic Aravalli Supregroup of rocks, hosted in Aravalli Craton of NW shield, is deposited in shallow and deep water conditions. The major lithologies are phyllites and quartzites with significant compone...The Paleoproterozoic Aravalli Supregroup of rocks, hosted in Aravalli Craton of NW shield, is deposited in shallow and deep water conditions. The major lithologies are phyllites and quartzites with significant components of greywacks and dolomite. Geochemical indices in particular, CIA (Chemical Index of Alteration) values (avg. phyllites: 51.6 - 81.5, avg. quartzites: 57.4 - 95.5) calculated from the data of clastic rocks of ASG suggest minimum to highly intense weathering in the source region. Other indices including PIA, CIW and ICV along with plot patterns on the A-CN-K diagram also nearly endorse CIA based interpretation. These rocks possess relatively high Th/U ratios compared to that found in fresh igneous rocks or their high grade metamorphic equivalents. This high Th/U ratio is neither a source inheritance nor a result of oxidation state rather a manifestation of Th hosting mineral accumulation through sorting. Viewed in the context of present stratigraphic succession, the weathering history adduced from geochemistry does not seem compatible but matches well with earlier classification scheme wherein the evolution of Aravalli Supergroup was considered episodic.展开更多
Ghana is the largest producer of gold in West Africa,a region with over 2,500 years of history with regards to gold production and trade.Modern exploration for and mining of gold in Ghana dates from 1874 with the esta...Ghana is the largest producer of gold in West Africa,a region with over 2,500 years of history with regards to gold production and trade.Modern exploration for and mining of gold in Ghana dates from 1874 with the establishment of the British Gold Coast Colony,which was followed in 1957 by the independence of Ghana and increased gold production since the early 1980s through Ghana’s Economic Recovery Plan.At the time of writing,gold production(108.2 tonnes or 3.48 million ounces[Moz]in 2014)accounted for approximately one-third of Ghana’s export revenues,with 36%of gold production coming from small-scale mining.展开更多
The Marwar Basin in western Rajasthan is one among the many Proterozoic sedimentary basins developed in Peninsular India that preserve rich records of the geological history and is traditionally considered as Trans-Vi...The Marwar Basin in western Rajasthan is one among the many Proterozoic sedimentary basins developed in Peninsular India that preserve rich records of the geological history and is traditionally considered as Trans-Vindhyan basin developed across Delhi and Aravalli orogens.It contains sedimentary package classified under Marwar Supergroup thought to be equivalent to the Vindhyan Supergroup.However,recently acquired radiometric dates suggest that the Marwar Supergroup is distinctively younger than the Vindhyan Supergroup,and the two basins were independently developed although they shared some of their provenance regions(Malone et al.,2008;McKenzie et al.,2011;Davis et al.,2014;Turner et al.,2014).展开更多
Banded iron formation-hosted high-grade(>60 weight percent(wt%)iron(Fe))hematite ore deposits make up the bulk of the world’s iron ore production and reserves.They developed mainly through supergene and/or hydroth...Banded iron formation-hosted high-grade(>60 weight percent(wt%)iron(Fe))hematite ore deposits make up the bulk of the world’s iron ore production and reserves.They developed mainly through supergene and/or hydrothermal leaching of silica from the iron formation host rock under oxidizing conditions.Early Palaeoproterozoic iron formations of the Transvaal Supergroup host several such high-grade hematite ore deposits.The largest ones are developed in the Asbesheuwels Subgroup iron formation on the Maremane Dome,between Sishen and Postmasburg in the Northern Cape Province of South Africa.These deposits currently produce virtually all of South Africa’s annual supply of about 78 million tonnes(Mt)of high-grade hematite ore.展开更多
The Upper Kaimur Group of the Vindhyan Supergroup in Central India,primarily consists of three rock types-DhandraulSandstone,Scarp Sandstone and Bijaigarh Shale.Mineralogically and geochemically,they are quartz arenit...The Upper Kaimur Group of the Vindhyan Supergroup in Central India,primarily consists of three rock types-DhandraulSandstone,Scarp Sandstone and Bijaigarh Shale.Mineralogically and geochemically,they are quartz arenite,sublitharenite to litharenite and litharenite to shale in composition,respectively.The A-CN-K ternary plot and CIA and ICV values suggest that the similar source rocks suffered severe chemical weathering,under a hot-humid climate in an acidic environment with higher PCO2,which facilitated high sediment influx in the absence of land plants.Various geochemical discriminants,elemental ratios like K2O/Na2O,Al2O3/TiO2,SiO2/MgO,La/Sc,Th/Sc,Th/Cr,GdN/YbN and pronounced negative Eu anomalies indicate the rocks to be of post-Archean Proterozoic granitic source,with a minor contribution of granodioritic input,in a passive margin setting.The sediments of the Upper Kaimur Group were probably deposited in the interglacial period in between the Paleoproterozoic and Neoproterozoic glacial epochs.展开更多
The dependence of groundwater quality on borehole depth is usually debatable in groundwater studies, especially in complex geological formations where aquifer characteristics vary spatially with depth. This study ther...The dependence of groundwater quality on borehole depth is usually debatable in groundwater studies, especially in complex geological formations where aquifer characteristics vary spatially with depth. This study therefore seeks to investigate the relationship between borehole depth and groundwater quality across the granitoid aquifers within the Birimian Supergroup in the Ashanti Region. Physicochemical analysis records of groundwater quality data were collected from 23 boreholes of public and private institutions in the Ashanti Region of Ghana, and the parametric values of iron, fluoride, total hardness, pH, nitrate, and nitrite were used to study the groundwater quality-depth relationship. The results showed that the depth-to-groundwater quality indicated a marginal increase in water quality in the range of 30 to 50 m, which is mathematically represented by the low-value correlation coefficient (r<sup>2</sup> = 0.026). A relatively significant increase occurs in the depth range of 50 to 80 m, which is given by a correlation coefficient of r<sup>2</sup> = 0.298. The mean percent parameter compatibility was 74%, 82%, 89%, and 97% at 50, 60, 70, and 80 m depths, respectively. The variations in groundwater quality per depth ratio ranged from 1.48, 1.37, 1.27, and 1.21 for 50, 60, 70, and 80 m depth, respectively. The recommended minimum borehole depth for excellent groundwater quality is suggested with a compatibility per meter depth ratio of 1.37. This results in a range between 50 and 70 m as the most desirable drilling depth for excellent groundwater quality within the granitoids of the Birimian Supergroup of the Ashanti Region in Ghana.展开更多
Hydroxycalciopyrochlore,ideally （Ca,Na,U,□）2（Nb,Ti）2O6（OH）,cubic,is a new mineral species （IMA2011-026） within the pyrochlore supergroup that was found occurring at the Maoniuping mine,Mianning County,Xichang...Hydroxycalciopyrochlore,ideally （Ca,Na,U,□）2（Nb,Ti）2O6（OH）,cubic,is a new mineral species （IMA2011-026） within the pyrochlore supergroup that was found occurring at the Maoniuping mine,Mianning County,Xichang prefecture,Sichuan Province,southwest China.The mineral is found in an alkali feldspar granite rare-earth ore deposit （26-27 Ma）.Associated minerals include calcite,barite,celestine,albite,aegirine,aegirine-augite,fluorite,parasite-（Ce）,thorite,thorianite,zircon,galena,sphalerite,magnetite,and pyrite.Crystals occur mostly as octahedra,and less often as dodecahedra and tetrahexahedra or combinations thereof.Some occur with an allotriomorphic habit with a thick triangular tabular form.Crystals generally range from 0.1 to 1 mm in size.The mineral is brownishblack,greenish-black and black on fresh sections with a brown streak.The crystal is translucent,and has a greasy lustre on fresh sections.It is metamict without any observed parting or cleavage and with a conchoidal fracture.The Vickers microhardness is 572 kg/mm2 （5-6 on the Mohs hardness scale）.The density measured by hydrostatic weighing is 5.10（3） g/cm3.The strongest four reflections in the X-ray powder-diffraction pattern [d in（A） （Ⅰ） hkl] are：2.9657 （100） 2 2 2,1.8142 （34） 0 4 4,1.5463 （21） 2 2 6,2.5688 （18） 0 0 4.The unit-cell parameters are a =10.381（4） （A）,V=1118.7（7）（A）3,Z =8.The structure was solved and refined in the space group Fd3m with R =0.09.The empirical formula is （Ca0.74Na0.5sU0.40Ce0.05Fe0.02□0.21）2.00（Nb1.15Ti0.s0Ta0.03Al0.01Mg0.01）2.00O6.02 [（OH）1.01F0.09]1.10,on the basis of 2 atoms of B pfu; the simplified formula is （Ca,Na,U,□）2（Nb,Ti）2O6（OH）.Type material is deposited in the Geological Museum of China,Beijing,People＇s Republic of China,catalogue number M11800.展开更多
The Balfour Formation has a pronounced lithological variation that is characterized by alternating sandstone- and mudstone-dominated members. The sandstone-dominated Oudeberg and Barberskrans Members are composed of l...The Balfour Formation has a pronounced lithological variation that is characterized by alternating sandstone- and mudstone-dominated members. The sandstone-dominated Oudeberg and Barberskrans Members are composed of lithofacies that range from intraformationai conglomerates to fine-grained sediments, whereas the mudstone-dominated members （Daggaboersnek, Elandsberg, and Palingkloof） are dominated by the facies Fm and FI. Petrography, geochemistry, and a paleocurrent analysis indicated that the source rock of the Balfour Formation was to south east and the rocks had a transitional/dissected magmatic arc signature. The sandstones-rich members were deposited by seasonal and ephemeral high-energy, low-sinuous streams, and the fine-grained-rich members were formed by ephemeral meandering streams. The paleoclimates have been equated to present temperate climates; they were semiarid becoming arid towards the top of the Balfour Formation. This has been determined by reconstructing the paleolatitude of the Karoo Basin, geochemistry, paleontology, sedimentary structures, and other rock properties, like color.展开更多
The subsidence history of the Soutpansberg Basin was reconstructed by a tectonic subsidence analysis coupled with backstripping calculations based on data of newly interpreted sequence boundaries. Furthermore, burial ...The subsidence history of the Soutpansberg Basin was reconstructed by a tectonic subsidence analysis coupled with backstripping calculations based on data of newly interpreted sequence boundaries. Furthermore, burial and time plots were constructed in order to understand the burial and thermal history of the basin. Input data were based on facies, lithostratigraphic models and tectonic interpretations. The studied succession is up to 1000 m and is underlain by the Achaean Limpopo Mobile Belt. The subsidence within the basin supports the primary graben system which must have been centred within the present basins, and later became a region of faulting. The subsidence and burial history curves suggests two phases of rapid subsidence during the Early-Late Permian （300–230 Ma） and Middle Triassic （215–230 Ma）. The areas of greater extension subsided more rapidly during these intervals. Two slow subsidence phases are observed during the Late Triassic （215–198 Ma） and Early Jurassic （198–100 Ma）. These intervals represent the post-rift thermal subsidence and are interpreted as slow flexural subsidence. Based on these observations on the subsidence curves, it is possible to infer that the first stage of positive inflexion （300 Ma） is therefore recognised as the first stage of the Soutpansberg Basin formation.展开更多
The Balfour Formation was subdivided into five members based on lithological variation that is characterized by alternating sandstone-and mudstone -dominated members.The sandstone dominated Oudeberg and Barberskrans m...The Balfour Formation was subdivided into five members based on lithological variation that is characterized by alternating sandstone-and mudstone -dominated members.The sandstone dominated Oudeberg and Barberskrans members are composed of lithofacies that range from intraformational conglomerates to fine-grained sediments,whereas the mudstone dominated members(Daggaboersnek, Elandsberg and Palingkloof) are dominated by the fine-grained facies(Fm and F1).Petrography,geochemistry and palaeocurrent analysis indicated that the source rock of the Balfour Formation was to展开更多
基金JGM by the US National Science Foundation Grant EAR09-10888HRX by the National Natural Science Foundation of China Grant 41974078。
文摘The Marwar Supergroup(NW Peninsular India)is thought to be of Ediacaran-Cambrian age,based on previous paleontological and geochronological studies.However,direct constraints on the onset of sedimentation within the Marwar basin are still scarce.In this study,we report U–Pb zircon,LA-ICP-MS,and SIMS ages from the Chhoti Khatu felsic volcanic rocks,interlayered with the Jodhpur Group sandstones(Lower Marwar Supergroup).The cathodoluminescence images of the zircons indicate complex morphologies,and core-rim textures coupled with the wide range of ages indicate that they are likely inherited or in the case of thin poorly indurated ash-beds,detrital in origin.The age spectra of 68 zircon analyses from our sampling display a dominant 800–900 Ma age peak corresponding to the age of basement"Erinpura granite"rocks in the region.The youngest inherited zircon from a felsic ash layer yielded a U–Pb age of651 Ma±18 Ma that,together with previous studies and paleontological evidence,indicates a postCryogenian age for the initiation of Marwar sedimentation following a~125 Ma hiatus between the end of Malani magmatism and Marwar deposition.
文摘The noncarbonaceous Ediacaran discs of variable morphologies from the Jodhpur Sandstone Formation of the Marwar Supergroup, western Rajasthan, suggest different biologic affinities of plant and animal kingdom. These discs are commonly preserved on the bedding surfaces of siliciclastic sandstone and shale in strong positive relief and appear to possess a flexible to rigid body. Discs assignable to Aspidella, Cyclomedusa, Nimbia and Heimalora;all possibly inclining towards cnidarian affinity are being reported from the sandstone beds in Sursagar area. Variable morphologies among discs preserved in siliciclastic shale beds from the Artiya Kalan area support scyphozoan affinity (earlier named Marsonia from the same locality) and cnidarian affinity for small discs comparable with Funisia (considered being the first animals having sexual reproduction). Disc’s morphologies also suggest ephyra stage of Aurilia (a cnidarian form) or budding stages of some fungi, like Germinosphaera (multicellular benthic fungal fossils) and noncarbonaceous discs with well preserved wrinkles and folds like in Chuaria. Discs from the Jodhpur Sandstone, may at times display taphonomic interplay, but consistency and repetition in morphology support variable biological affinities representing diverse assemblage and advance ecosystem prevailing during Ediacaran period. A degree of genetic variability can be expected within any taxa, and this may be compounded by preservation factors affecting the Jodhpur Ediacaran discs. Sudden increase in size or gigantism is a common feature of Ediacaran life, which is evident in case of Jodhpur discs also. On the basis of fossil assemblage, the Jodhpur Group (the Marwar Supergroup) is regionally correlated with the Bhander Group of the Vindhyan Supergroup and Krol Group of Lesser Himalaya. Globally, the assemblage is comparable with the Long Mynd Group, Shropshire, UK, Fermuse Formation Newfoundland, South Australia, Russia and Norway.
基金Financial assistance from DST, New Delhi in form of a WOS-A project No. SR/OY/WOS-A/ES-20/ 2008
文摘Ediacaran discs from the Jodhpur Sandstone of the Marwar Supergroup, Rajasthan, exhibit a wide size ranging from a few millimetres to 75 cm in diameter. Exceptionally large size of the discs in these rocks represent the largest reported so far from any Ediacaran assemblage. Although, larger medu-soid discs have been reported from USA, they are from the middle Cambrian and even younger rocks. Presence of microbial mats and weed-like structures with well preserved hold fasts and horizontal rhizome-like structures in association with some of these large-sized discs support their animal affinity, which probably feed on this weed-like vegetations. This association also supports their benthic habitat. Unlike the general trend of sudden increase in size of organisms in Ediacaran period and further decrease in size during Cambrian, these discs continued increasing in size in Cambrian also.
文摘The Paleoproterozoic Aravalli Supregroup of rocks, hosted in Aravalli Craton of NW shield, is deposited in shallow and deep water conditions. The major lithologies are phyllites and quartzites with significant components of greywacks and dolomite. Geochemical indices in particular, CIA (Chemical Index of Alteration) values (avg. phyllites: 51.6 - 81.5, avg. quartzites: 57.4 - 95.5) calculated from the data of clastic rocks of ASG suggest minimum to highly intense weathering in the source region. Other indices including PIA, CIW and ICV along with plot patterns on the A-CN-K diagram also nearly endorse CIA based interpretation. These rocks possess relatively high Th/U ratios compared to that found in fresh igneous rocks or their high grade metamorphic equivalents. This high Th/U ratio is neither a source inheritance nor a result of oxidation state rather a manifestation of Th hosting mineral accumulation through sorting. Viewed in the context of present stratigraphic succession, the weathering history adduced from geochemistry does not seem compatible but matches well with earlier classification scheme wherein the evolution of Aravalli Supergroup was considered episodic.
文摘Ghana is the largest producer of gold in West Africa,a region with over 2,500 years of history with regards to gold production and trade.Modern exploration for and mining of gold in Ghana dates from 1874 with the establishment of the British Gold Coast Colony,which was followed in 1957 by the independence of Ghana and increased gold production since the early 1980s through Ghana’s Economic Recovery Plan.At the time of writing,gold production(108.2 tonnes or 3.48 million ounces[Moz]in 2014)accounted for approximately one-third of Ghana’s export revenues,with 36%of gold production coming from small-scale mining.
文摘The Marwar Basin in western Rajasthan is one among the many Proterozoic sedimentary basins developed in Peninsular India that preserve rich records of the geological history and is traditionally considered as Trans-Vindhyan basin developed across Delhi and Aravalli orogens.It contains sedimentary package classified under Marwar Supergroup thought to be equivalent to the Vindhyan Supergroup.However,recently acquired radiometric dates suggest that the Marwar Supergroup is distinctively younger than the Vindhyan Supergroup,and the two basins were independently developed although they shared some of their provenance regions(Malone et al.,2008;McKenzie et al.,2011;Davis et al.,2014;Turner et al.,2014).
文摘Banded iron formation-hosted high-grade(>60 weight percent(wt%)iron(Fe))hematite ore deposits make up the bulk of the world’s iron ore production and reserves.They developed mainly through supergene and/or hydrothermal leaching of silica from the iron formation host rock under oxidizing conditions.Early Palaeoproterozoic iron formations of the Transvaal Supergroup host several such high-grade hematite ore deposits.The largest ones are developed in the Asbesheuwels Subgroup iron formation on the Maremane Dome,between Sishen and Postmasburg in the Northern Cape Province of South Africa.These deposits currently produce virtually all of South Africa’s annual supply of about 78 million tonnes(Mt)of high-grade hematite ore.
基金The financial assistance from University Grants Commission,New Delhi under grant No. F. 31-196/2005 (SR) is thankfully acknowledged by one of the authors (MM)
文摘The Upper Kaimur Group of the Vindhyan Supergroup in Central India,primarily consists of three rock types-DhandraulSandstone,Scarp Sandstone and Bijaigarh Shale.Mineralogically and geochemically,they are quartz arenite,sublitharenite to litharenite and litharenite to shale in composition,respectively.The A-CN-K ternary plot and CIA and ICV values suggest that the similar source rocks suffered severe chemical weathering,under a hot-humid climate in an acidic environment with higher PCO2,which facilitated high sediment influx in the absence of land plants.Various geochemical discriminants,elemental ratios like K2O/Na2O,Al2O3/TiO2,SiO2/MgO,La/Sc,Th/Sc,Th/Cr,GdN/YbN and pronounced negative Eu anomalies indicate the rocks to be of post-Archean Proterozoic granitic source,with a minor contribution of granodioritic input,in a passive margin setting.The sediments of the Upper Kaimur Group were probably deposited in the interglacial period in between the Paleoproterozoic and Neoproterozoic glacial epochs.
文摘The dependence of groundwater quality on borehole depth is usually debatable in groundwater studies, especially in complex geological formations where aquifer characteristics vary spatially with depth. This study therefore seeks to investigate the relationship between borehole depth and groundwater quality across the granitoid aquifers within the Birimian Supergroup in the Ashanti Region. Physicochemical analysis records of groundwater quality data were collected from 23 boreholes of public and private institutions in the Ashanti Region of Ghana, and the parametric values of iron, fluoride, total hardness, pH, nitrate, and nitrite were used to study the groundwater quality-depth relationship. The results showed that the depth-to-groundwater quality indicated a marginal increase in water quality in the range of 30 to 50 m, which is mathematically represented by the low-value correlation coefficient (r<sup>2</sup> = 0.026). A relatively significant increase occurs in the depth range of 50 to 80 m, which is given by a correlation coefficient of r<sup>2</sup> = 0.298. The mean percent parameter compatibility was 74%, 82%, 89%, and 97% at 50, 60, 70, and 80 m depths, respectively. The variations in groundwater quality per depth ratio ranged from 1.48, 1.37, 1.27, and 1.21 for 50, 60, 70, and 80 m depth, respectively. The recommended minimum borehole depth for excellent groundwater quality is suggested with a compatibility per meter depth ratio of 1.37. This results in a range between 50 and 70 m as the most desirable drilling depth for excellent groundwater quality within the granitoids of the Birimian Supergroup of the Ashanti Region in Ghana.
基金supported by the National Natural Science Foundation of China (grant #41172052)
文摘Hydroxycalciopyrochlore,ideally （Ca,Na,U,□）2（Nb,Ti）2O6（OH）,cubic,is a new mineral species （IMA2011-026） within the pyrochlore supergroup that was found occurring at the Maoniuping mine,Mianning County,Xichang prefecture,Sichuan Province,southwest China.The mineral is found in an alkali feldspar granite rare-earth ore deposit （26-27 Ma）.Associated minerals include calcite,barite,celestine,albite,aegirine,aegirine-augite,fluorite,parasite-（Ce）,thorite,thorianite,zircon,galena,sphalerite,magnetite,and pyrite.Crystals occur mostly as octahedra,and less often as dodecahedra and tetrahexahedra or combinations thereof.Some occur with an allotriomorphic habit with a thick triangular tabular form.Crystals generally range from 0.1 to 1 mm in size.The mineral is brownishblack,greenish-black and black on fresh sections with a brown streak.The crystal is translucent,and has a greasy lustre on fresh sections.It is metamict without any observed parting or cleavage and with a conchoidal fracture.The Vickers microhardness is 572 kg/mm2 （5-6 on the Mohs hardness scale）.The density measured by hydrostatic weighing is 5.10（3） g/cm3.The strongest four reflections in the X-ray powder-diffraction pattern [d in（A） （Ⅰ） hkl] are：2.9657 （100） 2 2 2,1.8142 （34） 0 4 4,1.5463 （21） 2 2 6,2.5688 （18） 0 0 4.The unit-cell parameters are a =10.381（4） （A）,V=1118.7（7）（A）3,Z =8.The structure was solved and refined in the space group Fd3m with R =0.09.The empirical formula is （Ca0.74Na0.5sU0.40Ce0.05Fe0.02□0.21）2.00（Nb1.15Ti0.s0Ta0.03Al0.01Mg0.01）2.00O6.02 [（OH）1.01F0.09]1.10,on the basis of 2 atoms of B pfu; the simplified formula is （Ca,Na,U,□）2（Nb,Ti）2O6（OH）.Type material is deposited in the Geological Museum of China,Beijing,People＇s Republic of China,catalogue number M11800.
基金supported by the Govan Mbeki Research Centre(GMRC) at the University of Fort Hare and by the Council for Geoscience
文摘The Balfour Formation has a pronounced lithological variation that is characterized by alternating sandstone- and mudstone-dominated members. The sandstone-dominated Oudeberg and Barberskrans Members are composed of lithofacies that range from intraformationai conglomerates to fine-grained sediments, whereas the mudstone-dominated members （Daggaboersnek, Elandsberg, and Palingkloof） are dominated by the facies Fm and FI. Petrography, geochemistry, and a paleocurrent analysis indicated that the source rock of the Balfour Formation was to south east and the rocks had a transitional/dissected magmatic arc signature. The sandstones-rich members were deposited by seasonal and ephemeral high-energy, low-sinuous streams, and the fine-grained-rich members were formed by ephemeral meandering streams. The paleoclimates have been equated to present temperate climates; they were semiarid becoming arid towards the top of the Balfour Formation. This has been determined by reconstructing the paleolatitude of the Karoo Basin, geochemistry, paleontology, sedimentary structures, and other rock properties, like color.
基金financially supported by the Coaltech Research Association and the University of Fort Hare
文摘The subsidence history of the Soutpansberg Basin was reconstructed by a tectonic subsidence analysis coupled with backstripping calculations based on data of newly interpreted sequence boundaries. Furthermore, burial and time plots were constructed in order to understand the burial and thermal history of the basin. Input data were based on facies, lithostratigraphic models and tectonic interpretations. The studied succession is up to 1000 m and is underlain by the Achaean Limpopo Mobile Belt. The subsidence within the basin supports the primary graben system which must have been centred within the present basins, and later became a region of faulting. The subsidence and burial history curves suggests two phases of rapid subsidence during the Early-Late Permian （300–230 Ma） and Middle Triassic （215–230 Ma）. The areas of greater extension subsided more rapidly during these intervals. Two slow subsidence phases are observed during the Late Triassic （215–198 Ma） and Early Jurassic （198–100 Ma）. These intervals represent the post-rift thermal subsidence and are interpreted as slow flexural subsidence. Based on these observations on the subsidence curves, it is possible to infer that the first stage of positive inflexion （300 Ma） is therefore recognised as the first stage of the Soutpansberg Basin formation.
文摘The Balfour Formation was subdivided into five members based on lithological variation that is characterized by alternating sandstone-and mudstone -dominated members.The sandstone dominated Oudeberg and Barberskrans members are composed of lithofacies that range from intraformational conglomerates to fine-grained sediments,whereas the mudstone dominated members(Daggaboersnek, Elandsberg and Palingkloof) are dominated by the fine-grained facies(Fm and F1).Petrography,geochemistry and palaeocurrent analysis indicated that the source rock of the Balfour Formation was to
