The Chertovo Koryto gold deposit（80 t Au at 1.84 g/t） in the Lena world-class province,Siberia,is hosted in a metamorphosed sequence of the Paleoproterozoic Mikhailovsk Formation that comprises the oldest black shal...The Chertovo Koryto gold deposit（80 t Au at 1.84 g/t） in the Lena world-class province,Siberia,is hosted in a metamorphosed sequence of the Paleoproterozoic Mikhailovsk Formation that comprises the oldest black shale strata of the Baikal-Patom region.The mineralisation is confined to the thrust zone complicated with a conjugate anticline fold,zones of shearing and dislocation.The struaural position of the mineralisation is similar to that at the giant Sukhoi Log deposit in the neighbouring Mama-Bodaibo zone.In the latter,the isotope age data suggest that Khomolkho black shales,hosts to Sukhoi Log mineralisation,are of Ediacaran age and underwent prograde metamorphism during early Paleozoic.The geochemical composition of the terrigenous rocks that host Sukhoi Log,Chertovo Koryto,and a number of other deposits at the various stratigraphic levels throughout the Proterozoic sequence have much in common.They do not show elevated metal contents above the common black shale abundances,except for Au and As,which is at variance with the accepted view on diagenetic enrichment of black shales in the Lena province.The occurrence of sagenitic rutile in quartz and chlorite pseudomorphs after biotite and other petrographic observations provide evidence on a retrograde nature of the metamorphic mineral assemblages in the Mikhailovsk rocks.The sulphides are pyrrhotite and arsenopyrite with very minor pyrite at Chertovo Koryto,whereas pyrite is the predominant sulphide in the Sukhoi Log ore.Fluid inclusion data on both deposits emphasise a high-temperature nature of the mineralisation albeit revealing great contrast in the fluid composition.Sukhoi Log mineralisation was formed at mixing between low-salinity aqueous solutions and dense gaseous carbonic fluids,which facilitated effective gold scavenging and precipitation,as demonstrated by thermodynamic simulation.The precursory devolatilisation of the Mikhailovsk sediments at the prograde stage results in the paucity of gaseous carbonic fluid during retrograde metamorphism and mineralisation.The similarity in the styles and chemical parameters of mineralisation,and the predominant structural control of ore localisation within the same Precambrian regional tectonic unit support an idea that orogenic gold mineralisation in the Lena province was produced during a single early Paleozoic event.展开更多
Tin has been mined in Nigeria since the 9th century with the famous Benin Bronzes dating from the 13th century.Significant African tin production began at the beginning of the 20th century and maximum output was reach...Tin has been mined in Nigeria since the 9th century with the famous Benin Bronzes dating from the 13th century.Significant African tin production began at the beginning of the 20th century and maximum output was reached in the 1970s.Since then production has declined to less than 2%of world output.展开更多
We examine the energy function with respect to the zeros of exceptional Hermite polynomials. The localization of the eigenvalues of the Hessian is given in the general case.In some special arrangements we have a more ...We examine the energy function with respect to the zeros of exceptional Hermite polynomials. The localization of the eigenvalues of the Hessian is given in the general case.In some special arrangements we have a more precise result on the behavior of the energy function. Finally we investigate the energy function with respect to the regular zeros of the exceptional Hermite polynomials.展开更多
Africa has been a significant world producer of uranium since 1945 when it was discovered in the DRC(then the Belgian Congo).There are four major types of deposits that produce the majority of the uranium in Africa:th...Africa has been a significant world producer of uranium since 1945 when it was discovered in the DRC(then the Belgian Congo).There are four major types of deposits that produce the majority of the uranium in Africa:the Archaean quartz-conglomerate hosted golduranium deposits of South Africa;the Neoproterozoic end-orogeny sheeted leucogranites and small stocks of Namibia;the Mesozoic sandstone-hosted roll-front deposits of Niger and Malawi;and the recent channelhosted calcrete and alluvial deposits in Namibia.Primary deposits are regarded in this text as those where mines extract uranium as the main,or sole commodity,whereas secondary deposits such as the Witwatersrand Basin,produce another commodity as the prime metal with uranium as a by-product.展开更多
基金partly supported by the Russian Scientific Foundation(Grant 14-17-00693)
文摘The Chertovo Koryto gold deposit（80 t Au at 1.84 g/t） in the Lena world-class province,Siberia,is hosted in a metamorphosed sequence of the Paleoproterozoic Mikhailovsk Formation that comprises the oldest black shale strata of the Baikal-Patom region.The mineralisation is confined to the thrust zone complicated with a conjugate anticline fold,zones of shearing and dislocation.The struaural position of the mineralisation is similar to that at the giant Sukhoi Log deposit in the neighbouring Mama-Bodaibo zone.In the latter,the isotope age data suggest that Khomolkho black shales,hosts to Sukhoi Log mineralisation,are of Ediacaran age and underwent prograde metamorphism during early Paleozoic.The geochemical composition of the terrigenous rocks that host Sukhoi Log,Chertovo Koryto,and a number of other deposits at the various stratigraphic levels throughout the Proterozoic sequence have much in common.They do not show elevated metal contents above the common black shale abundances,except for Au and As,which is at variance with the accepted view on diagenetic enrichment of black shales in the Lena province.The occurrence of sagenitic rutile in quartz and chlorite pseudomorphs after biotite and other petrographic observations provide evidence on a retrograde nature of the metamorphic mineral assemblages in the Mikhailovsk rocks.The sulphides are pyrrhotite and arsenopyrite with very minor pyrite at Chertovo Koryto,whereas pyrite is the predominant sulphide in the Sukhoi Log ore.Fluid inclusion data on both deposits emphasise a high-temperature nature of the mineralisation albeit revealing great contrast in the fluid composition.Sukhoi Log mineralisation was formed at mixing between low-salinity aqueous solutions and dense gaseous carbonic fluids,which facilitated effective gold scavenging and precipitation,as demonstrated by thermodynamic simulation.The precursory devolatilisation of the Mikhailovsk sediments at the prograde stage results in the paucity of gaseous carbonic fluid during retrograde metamorphism and mineralisation.The similarity in the styles and chemical parameters of mineralisation,and the predominant structural control of ore localisation within the same Precambrian regional tectonic unit support an idea that orogenic gold mineralisation in the Lena province was produced during a single early Paleozoic event.
基金The NRF-DST Centre of Excellence,CIMERA,is acknowledged for financial support.
文摘Tin has been mined in Nigeria since the 9th century with the famous Benin Bronzes dating from the 13th century.Significant African tin production began at the beginning of the 20th century and maximum output was reached in the 1970s.Since then production has declined to less than 2%of world output.
基金Supported by Hungarian National Foundation for Scientific Research,Grant No.K-100461
文摘We examine the energy function with respect to the zeros of exceptional Hermite polynomials. The localization of the eigenvalues of the Hessian is given in the general case.In some special arrangements we have a more precise result on the behavior of the energy function. Finally we investigate the energy function with respect to the regular zeros of the exceptional Hermite polynomials.
文摘Africa has been a significant world producer of uranium since 1945 when it was discovered in the DRC(then the Belgian Congo).There are four major types of deposits that produce the majority of the uranium in Africa:the Archaean quartz-conglomerate hosted golduranium deposits of South Africa;the Neoproterozoic end-orogeny sheeted leucogranites and small stocks of Namibia;the Mesozoic sandstone-hosted roll-front deposits of Niger and Malawi;and the recent channelhosted calcrete and alluvial deposits in Namibia.Primary deposits are regarded in this text as those where mines extract uranium as the main,or sole commodity,whereas secondary deposits such as the Witwatersrand Basin,produce another commodity as the prime metal with uranium as a by-product.
