Field observation of the macromorphology and analyses of micromorphology and geochemistry were conducted to the worm-shaped veins (WSVs) in the red earth of South China. The WSVs exhibit outward features of root trace...Field observation of the macromorphology and analyses of micromorphology and geochemistry were conducted to the worm-shaped veins (WSVs) in the red earth of South China. The WSVs exhibit outward features of root traces and contain the traces of stele that can be used as the definite evidence of root traces. Surrounding the worm-shaped veins there are some micro-features pressed by past root growth. Geochemical analyses indicate that the white part in the WSV was depleted in Fe content. These lines of evidence suggest the WSVs in the red earth of South China are the root traces of past forest.展开更多
Veined gold deposit is product of crustal evolution in special space and special time.It has close relations between the product of veined gold deposit and the formation mechanism (process of mineralization geodynamic...Veined gold deposit is product of crustal evolution in special space and special time.It has close relations between the product of veined gold deposit and the formation mechanism (process of mineralization geodynamics),It has special geological significance in the aspect of source of metallogenic material and metallogenic fluid,migration and precipitation, especially in vein gold deposit of structure boundary.This pater discusses four aspects,i.e. The geodynamic background,source of metallogenic fluid,fluid migration mechanism and structural position of deposits.The concluding remarks are given as follows. 1\ The Pre Cambrian metamorphic complexes emerged extensively in the Wutaishan Hengshan area, more than 60% of those are granitic rock, as the oldest continential crust of crystalline basement they all have the characteristics of deformation and gneiss, and many of them were formed in 2500～2700 Ma, in them some high rank deformed super crust inclusions, or relicts of different rock facies showing 2800～2900 Ma or earlier ages. Through the comphrehensive analysis of large rock chemical data on the relevant diagram about their characteristics, it reflects that not only the granitic rock has two different characteristics of rock series and regionalization but also shows several distinct source tendencies. Itsuggests that the large emergence of granitic rock in Archean era in the area is related to certain collision mechanism, thus resulted in the connection of the landmass, north to Hengshan and the landmass of Bupin,and so completed the cratonization of North China platform. The formation of granitic rock in early Proterozoic era is relevant to rifting which belongs to the genetic series of later orogenic to postorogenic period. 2\ The zonal super crust rock series that stretches in NEE direction on the Archaeozoic crystalline basement in Wutaishan and its vicinity area is called Wutai Group and Hutuo Group. The Wutai Group is mainly consisted of mafic volcanic rock, and uncomformably was under laid the Hutuo Group of thick littoral shallow sea facies deposit. They formed at 2600～2000 Ma and underwent two foldings, riftings, metamorphisms and granitic intrusions, So it has the complicated inner structure. The analysis of geometry and dynamics shows that they were formed under NW SE horizontal compression. The characteristics of rock,stratum, metamorphism and deformation show that the geodynamics pattern fo the orogenic belt belongs to inner sialic orogenic process and it can be divided into 5 devloping stages:① basin riftings stage(2500～2600 Ma);② basin spreading stage(2500 Ma±);③ local rift stage(2400 Ma±);④ rift southern migration stage(2000～2400 Ma)⑤ under crust detachment stage(1800～2000 Ma). 3\ The formation and migration of metallogenic fluid is the important part of the metallogenic geodynamics process. In the area of Wutaishan and Hengshan the formation and migration process of vein gold deposit metallogenic fluid underwent two tectonic systems early Per Cambrian collision orogenics period or interior sialic orogenics and Mesozoic intracontinental orogenics in the light of the character of typical gold deposit fluid inclusion, gas liquid composition, hydroxide isotopic component and their formation conditions of physics and chemistry. The formation and migration of metallogenic fluid is not only controlled by genetic mechanism of vein gold deposit but also correlated with the formation tectonic background of gold deposit.So the greenstone type vein gold deposit is mainly primary fluid, but the epigenetic hydrothermal vein gold deposit is the secondary fluid. The surface water distinctly takes part in the mineralization, but its migration mechanism is another different type of tectonic deformations. 4 Greenstone type gold deposit and epigenetic hydrothermal vein gold deposit are the most important vein gold deposits of Wutaishan area. Basin on the study of the source bed (rock) and S, Pb isotopic compositions, their metallogenic material sources show that the greenstone vein gold展开更多
文摘Field observation of the macromorphology and analyses of micromorphology and geochemistry were conducted to the worm-shaped veins (WSVs) in the red earth of South China. The WSVs exhibit outward features of root traces and contain the traces of stele that can be used as the definite evidence of root traces. Surrounding the worm-shaped veins there are some micro-features pressed by past root growth. Geochemical analyses indicate that the white part in the WSV was depleted in Fe content. These lines of evidence suggest the WSVs in the red earth of South China are the root traces of past forest.
文摘Veined gold deposit is product of crustal evolution in special space and special time.It has close relations between the product of veined gold deposit and the formation mechanism (process of mineralization geodynamics),It has special geological significance in the aspect of source of metallogenic material and metallogenic fluid,migration and precipitation, especially in vein gold deposit of structure boundary.This pater discusses four aspects,i.e. The geodynamic background,source of metallogenic fluid,fluid migration mechanism and structural position of deposits.The concluding remarks are given as follows. 1\ The Pre Cambrian metamorphic complexes emerged extensively in the Wutaishan Hengshan area, more than 60% of those are granitic rock, as the oldest continential crust of crystalline basement they all have the characteristics of deformation and gneiss, and many of them were formed in 2500～2700 Ma, in them some high rank deformed super crust inclusions, or relicts of different rock facies showing 2800～2900 Ma or earlier ages. Through the comphrehensive analysis of large rock chemical data on the relevant diagram about their characteristics, it reflects that not only the granitic rock has two different characteristics of rock series and regionalization but also shows several distinct source tendencies. Itsuggests that the large emergence of granitic rock in Archean era in the area is related to certain collision mechanism, thus resulted in the connection of the landmass, north to Hengshan and the landmass of Bupin,and so completed the cratonization of North China platform. The formation of granitic rock in early Proterozoic era is relevant to rifting which belongs to the genetic series of later orogenic to postorogenic period. 2\ The zonal super crust rock series that stretches in NEE direction on the Archaeozoic crystalline basement in Wutaishan and its vicinity area is called Wutai Group and Hutuo Group. The Wutai Group is mainly consisted of mafic volcanic rock, and uncomformably was under laid the Hutuo Group of thick littoral shallow sea facies deposit. They formed at 2600～2000 Ma and underwent two foldings, riftings, metamorphisms and granitic intrusions, So it has the complicated inner structure. The analysis of geometry and dynamics shows that they were formed under NW SE horizontal compression. The characteristics of rock,stratum, metamorphism and deformation show that the geodynamics pattern fo the orogenic belt belongs to inner sialic orogenic process and it can be divided into 5 devloping stages:① basin riftings stage(2500～2600 Ma);② basin spreading stage(2500 Ma±);③ local rift stage(2400 Ma±);④ rift southern migration stage(2000～2400 Ma)⑤ under crust detachment stage(1800～2000 Ma). 3\ The formation and migration of metallogenic fluid is the important part of the metallogenic geodynamics process. In the area of Wutaishan and Hengshan the formation and migration process of vein gold deposit metallogenic fluid underwent two tectonic systems early Per Cambrian collision orogenics period or interior sialic orogenics and Mesozoic intracontinental orogenics in the light of the character of typical gold deposit fluid inclusion, gas liquid composition, hydroxide isotopic component and their formation conditions of physics and chemistry. The formation and migration of metallogenic fluid is not only controlled by genetic mechanism of vein gold deposit but also correlated with the formation tectonic background of gold deposit.So the greenstone type vein gold deposit is mainly primary fluid, but the epigenetic hydrothermal vein gold deposit is the secondary fluid. The surface water distinctly takes part in the mineralization, but its migration mechanism is another different type of tectonic deformations. 4 Greenstone type gold deposit and epigenetic hydrothermal vein gold deposit are the most important vein gold deposits of Wutaishan area. Basin on the study of the source bed (rock) and S, Pb isotopic compositions, their metallogenic material sources show that the greenstone vein gold
