We review petrologic observations of reaction textures from high-grade rocks that suggest the passage of fluids with variable alkali activities. Development of these reaction textures is accompanied by regular composi...We review petrologic observations of reaction textures from high-grade rocks that suggest the passage of fluids with variable alkali activities. Development of these reaction textures is accompanied by regular compositional variations in plagioclase, pyroxenes, biotite, amphibole and garnet. The textures are interpreted in terms of exchange and net-transfer reactions controlled by the K and Na activities in the fluids. On the regional scale, these reactions operate in granitized, charnockitized, syenitized etc. shear zones within high-grade complexes. Thermodynamic calculations in simple chemical systems show that changes in mineral assemblages, including the transition from the hydrous to the anhydrous ones, may occur at constant pressure and temperature due only to variations in the H2O and the alkali activities. A simple procedure for estimating the activity of the two major alkali oxides, K2O and Na2O, is imple- mented in the TWQ software. Examples of calculations are presented for well-documented dehydration zones from South Africa, southern India, and Sri Lanka. The calculations have revealed two end-member regimes of alkalis during specific metamorphic processes： rock buffered, which is characteristic for the precursor rocks containing two feldspars, and fluid-buffered for the precursor rocks without K-feldspar. The observed reaction textures and the results of thermodynamic modeling are compared with the results of available experimental studies on the interaction of the alkali chloride and carbonate-bearing fluids with metamorphic rocks at mid-crustal conditions. The experiments show the complex effect of alkali activities in the fluid phase on the mineral assemblages. Both thermodynamic calculations and experiments closely reproduce paragenetic relations theoretically predicted by D.S. Korzhinskii in the 1940s.展开更多
A problem of evolution of high-grade polymeta- morphic terrain appeared in last decades:in worldwide complexes the identification of true stages of polymetamorphism encounters a problem of zircon zoning(or garnet etc....A problem of evolution of high-grade polymeta- morphic terrain appeared in last decades:in worldwide complexes the identification of true stages of polymetamorphism encounters a problem of zircon zoning(or garnet etc.)that is the function of fluid activity and therefore the newly formed zone can not always be recorded.Structural geology allows discriminating between different stages of metamor-展开更多
We conducted a geochemical study of the major elements of 29 clay samples from 10 mining fronts, which are used for ceramic coatings at Santa Gertrudes Ceramic Pole, São Paulo, Brazil. This region is consider...We conducted a geochemical study of the major elements of 29 clay samples from 10 mining fronts, which are used for ceramic coatings at Santa Gertrudes Ceramic Pole, São Paulo, Brazil. This region is considered as the biggest ceramic pole in Latin America. The mines are located in Corumbataí Formation (Paraná Sedimentary Basin) and are mined in bench system. The samples were analyzed as a whole and along each profile to evaluate the variation of the concentration of major elements and weathering effects. The results show a differentiation into three groups: 1) carbonate clays;2) lower portion samples;3) upper portion samples, and properties that allow obtaining useful information about the use and selection of raw materials to the formulation of ceramic masses and for quality control of raw materials in order to achieve products of similar quality.展开更多
The Gelmandeh Massive is located in the Central part of Iranian Microcontinent. Amphibolitic rocks occupy the main portion of Gelmandeh complex, which consists of hornblendite, garnet amphibolites, and gneiss. Geochem...The Gelmandeh Massive is located in the Central part of Iranian Microcontinent. Amphibolitic rocks occupy the main portion of Gelmandeh complex, which consists of hornblendite, garnet amphibolites, and gneiss. Geochemical investigations indicate that the ratio of Eu/Eu* separates samples into two categories: first category with ratio of Eu/Eu* > 1 and the second with ratio of Eu/Eu* < 1, which the former indicates an enriched mantle origin while the latter points to crustal contamination. Generally, amphibolites can be differentiated into two separate series. First series is characterized with calc-alkaline to alkaline composition with enriched mantle origin, and the second one has calc-alkaline to tholeiitic nature and it is of continental type that underwent crustal contamination within subduction zone. The microprobe electron analysis shows that the amphiboles were a member of the calcic group and hastingsite-tschermakite series. Geo-barometric studied and mineral paragenesis show that the metamorphism is of Barovian type with PT condition upto 7 K bar and 580°C.展开更多
Mercury pollution from small-scale gold mining poses a serious threat to the global and local environment. Recycling of mercury for small-scale miners has been introduced over decades in Tanzania with little success. ...Mercury pollution from small-scale gold mining poses a serious threat to the global and local environment. Recycling of mercury for small-scale miners has been introduced over decades in Tanzania with little success. The environmentally benign borax gold extraction method invented more than thirty years ago in the Philippines and presently used by more than thirty thousand Philippine miners has proved to work on the gold ores in Chunya and Singida gold districts of Tanzania. By using borax instead of mercury the miners reduce the risk of polluting the environment and spoil their health for generations. The most convincing argument for the miners to change to borax is that they can increase their gold recovery up to fifty percent without need for investing in new equipment and without much more work on processing.展开更多
基金supported by Russian Foundation for Basic Research(project 10-05-00040 to OGS)Russian President Grants for Young Scientists(MD-222.2012.5 to OGS)+1 种基金grant from the National Science Foundation of South Africa(GUN:20531 92 to DDvR)University of Johannesburg as a part of the Russian South African scientific collaboration
基金supported by Russian Foundation for Basic Research (projects 13-05-00353a to OGS,12-05-00303a to LYA)Federal Task Program 3586by grants from the National Science Foundation of South Africa(GUN:2053192)University of Johannesburg as part of the Russian-South African scientific collaboration
文摘We review petrologic observations of reaction textures from high-grade rocks that suggest the passage of fluids with variable alkali activities. Development of these reaction textures is accompanied by regular compositional variations in plagioclase, pyroxenes, biotite, amphibole and garnet. The textures are interpreted in terms of exchange and net-transfer reactions controlled by the K and Na activities in the fluids. On the regional scale, these reactions operate in granitized, charnockitized, syenitized etc. shear zones within high-grade complexes. Thermodynamic calculations in simple chemical systems show that changes in mineral assemblages, including the transition from the hydrous to the anhydrous ones, may occur at constant pressure and temperature due only to variations in the H2O and the alkali activities. A simple procedure for estimating the activity of the two major alkali oxides, K2O and Na2O, is imple- mented in the TWQ software. Examples of calculations are presented for well-documented dehydration zones from South Africa, southern India, and Sri Lanka. The calculations have revealed two end-member regimes of alkalis during specific metamorphic processes： rock buffered, which is characteristic for the precursor rocks containing two feldspars, and fluid-buffered for the precursor rocks without K-feldspar. The observed reaction textures and the results of thermodynamic modeling are compared with the results of available experimental studies on the interaction of the alkali chloride and carbonate-bearing fluids with metamorphic rocks at mid-crustal conditions. The experiments show the complex effect of alkali activities in the fluid phase on the mineral assemblages. Both thermodynamic calculations and experiments closely reproduce paragenetic relations theoretically predicted by D.S. Korzhinskii in the 1940s.
文摘A problem of evolution of high-grade polymeta- morphic terrain appeared in last decades:in worldwide complexes the identification of true stages of polymetamorphism encounters a problem of zircon zoning(or garnet etc.)that is the function of fluid activity and therefore the newly formed zone can not always be recorded.Structural geology allows discriminating between different stages of metamor-
文摘We conducted a geochemical study of the major elements of 29 clay samples from 10 mining fronts, which are used for ceramic coatings at Santa Gertrudes Ceramic Pole, São Paulo, Brazil. This region is considered as the biggest ceramic pole in Latin America. The mines are located in Corumbataí Formation (Paraná Sedimentary Basin) and are mined in bench system. The samples were analyzed as a whole and along each profile to evaluate the variation of the concentration of major elements and weathering effects. The results show a differentiation into three groups: 1) carbonate clays;2) lower portion samples;3) upper portion samples, and properties that allow obtaining useful information about the use and selection of raw materials to the formulation of ceramic masses and for quality control of raw materials in order to achieve products of similar quality.
文摘The Gelmandeh Massive is located in the Central part of Iranian Microcontinent. Amphibolitic rocks occupy the main portion of Gelmandeh complex, which consists of hornblendite, garnet amphibolites, and gneiss. Geochemical investigations indicate that the ratio of Eu/Eu* separates samples into two categories: first category with ratio of Eu/Eu* > 1 and the second with ratio of Eu/Eu* < 1, which the former indicates an enriched mantle origin while the latter points to crustal contamination. Generally, amphibolites can be differentiated into two separate series. First series is characterized with calc-alkaline to alkaline composition with enriched mantle origin, and the second one has calc-alkaline to tholeiitic nature and it is of continental type that underwent crustal contamination within subduction zone. The microprobe electron analysis shows that the amphiboles were a member of the calcic group and hastingsite-tschermakite series. Geo-barometric studied and mineral paragenesis show that the metamorphism is of Barovian type with PT condition upto 7 K bar and 580°C.
文摘Mercury pollution from small-scale gold mining poses a serious threat to the global and local environment. Recycling of mercury for small-scale miners has been introduced over decades in Tanzania with little success. The environmentally benign borax gold extraction method invented more than thirty years ago in the Philippines and presently used by more than thirty thousand Philippine miners has proved to work on the gold ores in Chunya and Singida gold districts of Tanzania. By using borax instead of mercury the miners reduce the risk of polluting the environment and spoil their health for generations. The most convincing argument for the miners to change to borax is that they can increase their gold recovery up to fifty percent without need for investing in new equipment and without much more work on processing.
