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Jingwen Mao - One of the best experts on this subject based on the ideXlab platform.
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early Cambrian black shale hosted mo ni and v mineralization on the rifted margin of the yangtze platform china reconnaissance chromium isotope data and a refined metallogenic model
Economic Geology, 2016Co-Authors: Bernd Lehmann, Robert Frei, Jingwen MaoAbstract:The transgressive basal unit of the Early Cambrian black-shale sequence along the rifted margin of the southeastern Yangtze platform hosts a wide spectrum of marine sedimentary Rocks distributed over more than a length of 1,000 km. A few-centimeter-thick sulfide-rich black shale units have spectacular metal tenors (Mo and Ni in the percent range, PGE + Au around 1 ppm) and consist of submillimeter-scale laminated sulfide and carbonaceous material and centimeter-sized pebble-like rip-up clasts of Mo-S-C compounds, pyrite, and Ni-rich polymetallic sulfides in carbonaceous and phosphate-rich matrix. The δ 53/52 Cr authigenic values of Mo-Ni sulfide-rich black shale samples from the Zunyi mining district (Guizhou province), as well as from the Sancha district (Hunan province), 400 km northeast, have a mean of 0.96 ± 0.22‰ ( n = 8), while V-rich black shale from both districts has a mean of 1.34 ± 0.46‰ ( n = 5). These data indicate significantly positively fractionated values compared to igneous silicate Earth. The Cr isotope values of the studied shales compare with recent findings of positively fractionated δ 53/52 Cr values in Late Neoproterozoic-Phanerozoic marine carbonates and shale/mudstones and attest for the operation of an intensified oxidative surface Cr cycle from at least around ~0.75 Gyr ago. We propose that the major change in Cr cycling around the PreCambrian-Cambrian boundary was caused by a significant rise of atmospheric oxygen levels. The Cr isotope data confirm earlier conclusions from Mo and Os isotopes, which indicate a seawater metal source with ultimate metal supply by oxidative weathering of continental crust. In particular, covariation trends of Re-Os and of platinum-group elements display a distinct seawater signature, and a degree of metal enrichment which is an extension of the normal black shale pattern. The Mo-Ni sulfide-rich black shale units are probably produced by winnowing of subaquatic hardground deposited under euxinic conditions. The same stratigraphic level also hosts anoxic/suboxic V-rich black shale (V in illite) and huge phosphorite deposits in oxic/suboxic settings, bedded barite, as well as 10s of meter-thick sapropelic alginite (combustible shale). We show that the extreme metal enrichment of the Mo-Ni sulfide-rich black shale can be understood as a combination of redox cycling and bottom-water/sediment-interface scavenging under euxinic conditions (Mo, noble metals), and of oxidation (remineralization) of organic matter settling from the photic zone, with sulfide fixation of Ni and other biophile elements under denitrifying and sulfate-reducing conditions. High biological activity (as in coastal upwelling settings with high nutrient supply), very low clastic accumulation rate (as in protected basins), and low organic matter deposition (high rate of remineralization) in stratified oxic-suboxic-euxinic basins are requirements for advanced metal enrichment in black shales. A special bathymetric condition of slope deposition with intrabasinal olistostrome-like mass movement and gravitational winnowing explains both the peculiar ore textures and the further metal enrichment to ore grade in the Early Cambrian Rock units on the Yangtze platform. The Mo-Ni sulfide-rich sediments can be regarded as the euxinic variant of the marine hydrogenous ore deposit spectrum, where ferromanganese nodules/crusts represent the oxic variant of extreme fractionation from seawater.
Bernd Lehmann - One of the best experts on this subject based on the ideXlab platform.
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early Cambrian black shale hosted mo ni and v mineralization on the rifted margin of the yangtze platform china reconnaissance chromium isotope data and a refined metallogenic model
Economic Geology, 2016Co-Authors: Bernd Lehmann, Robert Frei, Jingwen MaoAbstract:The transgressive basal unit of the Early Cambrian black-shale sequence along the rifted margin of the southeastern Yangtze platform hosts a wide spectrum of marine sedimentary Rocks distributed over more than a length of 1,000 km. A few-centimeter-thick sulfide-rich black shale units have spectacular metal tenors (Mo and Ni in the percent range, PGE + Au around 1 ppm) and consist of submillimeter-scale laminated sulfide and carbonaceous material and centimeter-sized pebble-like rip-up clasts of Mo-S-C compounds, pyrite, and Ni-rich polymetallic sulfides in carbonaceous and phosphate-rich matrix. The δ 53/52 Cr authigenic values of Mo-Ni sulfide-rich black shale samples from the Zunyi mining district (Guizhou province), as well as from the Sancha district (Hunan province), 400 km northeast, have a mean of 0.96 ± 0.22‰ ( n = 8), while V-rich black shale from both districts has a mean of 1.34 ± 0.46‰ ( n = 5). These data indicate significantly positively fractionated values compared to igneous silicate Earth. The Cr isotope values of the studied shales compare with recent findings of positively fractionated δ 53/52 Cr values in Late Neoproterozoic-Phanerozoic marine carbonates and shale/mudstones and attest for the operation of an intensified oxidative surface Cr cycle from at least around ~0.75 Gyr ago. We propose that the major change in Cr cycling around the PreCambrian-Cambrian boundary was caused by a significant rise of atmospheric oxygen levels. The Cr isotope data confirm earlier conclusions from Mo and Os isotopes, which indicate a seawater metal source with ultimate metal supply by oxidative weathering of continental crust. In particular, covariation trends of Re-Os and of platinum-group elements display a distinct seawater signature, and a degree of metal enrichment which is an extension of the normal black shale pattern. The Mo-Ni sulfide-rich black shale units are probably produced by winnowing of subaquatic hardground deposited under euxinic conditions. The same stratigraphic level also hosts anoxic/suboxic V-rich black shale (V in illite) and huge phosphorite deposits in oxic/suboxic settings, bedded barite, as well as 10s of meter-thick sapropelic alginite (combustible shale). We show that the extreme metal enrichment of the Mo-Ni sulfide-rich black shale can be understood as a combination of redox cycling and bottom-water/sediment-interface scavenging under euxinic conditions (Mo, noble metals), and of oxidation (remineralization) of organic matter settling from the photic zone, with sulfide fixation of Ni and other biophile elements under denitrifying and sulfate-reducing conditions. High biological activity (as in coastal upwelling settings with high nutrient supply), very low clastic accumulation rate (as in protected basins), and low organic matter deposition (high rate of remineralization) in stratified oxic-suboxic-euxinic basins are requirements for advanced metal enrichment in black shales. A special bathymetric condition of slope deposition with intrabasinal olistostrome-like mass movement and gravitational winnowing explains both the peculiar ore textures and the further metal enrichment to ore grade in the Early Cambrian Rock units on the Yangtze platform. The Mo-Ni sulfide-rich sediments can be regarded as the euxinic variant of the marine hydrogenous ore deposit spectrum, where ferromanganese nodules/crusts represent the oxic variant of extreme fractionation from seawater.
Fanwei Meng - One of the best experts on this subject based on the ideXlab platform.
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clay minerals from Rock salt of salt range formation late neoproterozoic early Cambrian pakistan
Carbonates and Evaporites, 2017Co-Authors: Iaroslava Iaremchuk, Mohammad Tariq, Sofiya P Hryniv, Serhiy Vovnyuk, Fanwei MengAbstract:The clay minerals of Late Neoproterozoic–Early Cambrian Rock salt of Salt Range Formation of Pakistan have been studied by means of X-ray diffraction, scanning electron microscopy and dispersive X-ray spectrometry, complex thermal and chemical analyses. The clay minerals association of pelitic fraction of water-insoluble residue of these deposits consists of corrensite, chlorite and illite with the admixture of unordered mixed-layered chlorite–corrensite and chlorite–smectite; in some samples, the admixture of smectite occurs. The expandable layers in corrensite are determined as smectite. In studied samples the chlorite, corrensite and mixed-layered species are presented by trioctahedral Mg-rich type and illite is dioctahedral and enriched by Fe; this association of clay minerals is typical for evaporite deposits. Transformation of clay minerals proceeded under the impact of several factors of different direction and intensity. In evaporite basin, the elevated salinity of brines reinforces the processes of clay minerals structure ordering causing disappearance of mixed-layered minerals and thus decreasing the number of clay mineral species; in the brines originated from SO4-rich seawater, the clay mineral associations are richer comparing to Ca-rich brines. Local factors—volcanic ash input, elevated content of organic matter slow down the transformation processes thus also increasing the number of clay mineral species. We explain the unexpectedly rich clay mineral association (as for the halite stage of evaporation) in studied Rocks by the strong effect of local factors.
Robert Frei - One of the best experts on this subject based on the ideXlab platform.
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early Cambrian black shale hosted mo ni and v mineralization on the rifted margin of the yangtze platform china reconnaissance chromium isotope data and a refined metallogenic model
Economic Geology, 2016Co-Authors: Bernd Lehmann, Robert Frei, Jingwen MaoAbstract:The transgressive basal unit of the Early Cambrian black-shale sequence along the rifted margin of the southeastern Yangtze platform hosts a wide spectrum of marine sedimentary Rocks distributed over more than a length of 1,000 km. A few-centimeter-thick sulfide-rich black shale units have spectacular metal tenors (Mo and Ni in the percent range, PGE + Au around 1 ppm) and consist of submillimeter-scale laminated sulfide and carbonaceous material and centimeter-sized pebble-like rip-up clasts of Mo-S-C compounds, pyrite, and Ni-rich polymetallic sulfides in carbonaceous and phosphate-rich matrix. The δ 53/52 Cr authigenic values of Mo-Ni sulfide-rich black shale samples from the Zunyi mining district (Guizhou province), as well as from the Sancha district (Hunan province), 400 km northeast, have a mean of 0.96 ± 0.22‰ ( n = 8), while V-rich black shale from both districts has a mean of 1.34 ± 0.46‰ ( n = 5). These data indicate significantly positively fractionated values compared to igneous silicate Earth. The Cr isotope values of the studied shales compare with recent findings of positively fractionated δ 53/52 Cr values in Late Neoproterozoic-Phanerozoic marine carbonates and shale/mudstones and attest for the operation of an intensified oxidative surface Cr cycle from at least around ~0.75 Gyr ago. We propose that the major change in Cr cycling around the PreCambrian-Cambrian boundary was caused by a significant rise of atmospheric oxygen levels. The Cr isotope data confirm earlier conclusions from Mo and Os isotopes, which indicate a seawater metal source with ultimate metal supply by oxidative weathering of continental crust. In particular, covariation trends of Re-Os and of platinum-group elements display a distinct seawater signature, and a degree of metal enrichment which is an extension of the normal black shale pattern. The Mo-Ni sulfide-rich black shale units are probably produced by winnowing of subaquatic hardground deposited under euxinic conditions. The same stratigraphic level also hosts anoxic/suboxic V-rich black shale (V in illite) and huge phosphorite deposits in oxic/suboxic settings, bedded barite, as well as 10s of meter-thick sapropelic alginite (combustible shale). We show that the extreme metal enrichment of the Mo-Ni sulfide-rich black shale can be understood as a combination of redox cycling and bottom-water/sediment-interface scavenging under euxinic conditions (Mo, noble metals), and of oxidation (remineralization) of organic matter settling from the photic zone, with sulfide fixation of Ni and other biophile elements under denitrifying and sulfate-reducing conditions. High biological activity (as in coastal upwelling settings with high nutrient supply), very low clastic accumulation rate (as in protected basins), and low organic matter deposition (high rate of remineralization) in stratified oxic-suboxic-euxinic basins are requirements for advanced metal enrichment in black shales. A special bathymetric condition of slope deposition with intrabasinal olistostrome-like mass movement and gravitational winnowing explains both the peculiar ore textures and the further metal enrichment to ore grade in the Early Cambrian Rock units on the Yangtze platform. The Mo-Ni sulfide-rich sediments can be regarded as the euxinic variant of the marine hydrogenous ore deposit spectrum, where ferromanganese nodules/crusts represent the oxic variant of extreme fractionation from seawater.
Iaroslava Iaremchuk - One of the best experts on this subject based on the ideXlab platform.
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clay minerals from Rock salt of salt range formation late neoproterozoic early Cambrian pakistan
Carbonates and Evaporites, 2017Co-Authors: Iaroslava Iaremchuk, Mohammad Tariq, Sofiya P Hryniv, Serhiy Vovnyuk, Fanwei MengAbstract:The clay minerals of Late Neoproterozoic–Early Cambrian Rock salt of Salt Range Formation of Pakistan have been studied by means of X-ray diffraction, scanning electron microscopy and dispersive X-ray spectrometry, complex thermal and chemical analyses. The clay minerals association of pelitic fraction of water-insoluble residue of these deposits consists of corrensite, chlorite and illite with the admixture of unordered mixed-layered chlorite–corrensite and chlorite–smectite; in some samples, the admixture of smectite occurs. The expandable layers in corrensite are determined as smectite. In studied samples the chlorite, corrensite and mixed-layered species are presented by trioctahedral Mg-rich type and illite is dioctahedral and enriched by Fe; this association of clay minerals is typical for evaporite deposits. Transformation of clay minerals proceeded under the impact of several factors of different direction and intensity. In evaporite basin, the elevated salinity of brines reinforces the processes of clay minerals structure ordering causing disappearance of mixed-layered minerals and thus decreasing the number of clay mineral species; in the brines originated from SO4-rich seawater, the clay mineral associations are richer comparing to Ca-rich brines. Local factors—volcanic ash input, elevated content of organic matter slow down the transformation processes thus also increasing the number of clay mineral species. We explain the unexpectedly rich clay mineral association (as for the halite stage of evaporation) in studied Rocks by the strong effect of local factors.
