Altered Mineral Petrologic Characteristics Andgenetic Analysis Of Saccharoidal Compresso-crushed Zone In Dam Site Of Yebatan Hydropower Station

Under the effect of regional tectonism,saccharoidal compresso-crushed zone is extensively developed in nu-lanchang-jinsha river tectonic belt,which lies between the Eurasian plate and Indian plate.Saccharoidal compresso-crushed zone has become a significant engineering geological problem for largehydropower project construction.The special geological phenomenon is analyzed to provide a scientific basis for a comprehensive analysis on rock mass quality and availability evaluation.The subject combines particular field survey,scanning electron microscopy(SEM),x-ray diffraction(XRD)and geochemical testing,reveals macro-geological characteristics and altered mineral petrology characteristics of saccharoidal compresso-crushed zone,classifies alteration types,explores controlling factors and evolutionary process of saccharoidal compresso-crushed zone.The consequences of the study includes six aspects.(1)The development space of saccharoidal compresso-crushed zone mainly is between the bank slop elevation of 2790 ~ 2850 m,which has not good correlation with the process of abutment slope.Saccharoidal compresso-crushed zone is wide distribution in left bank.On the contrary,horizontal and vertical distribution range of saccharoidal compresso-crushed zone is narrow in right bank.The horizontal depth of saccharoidal compresso-crushed zone has positive correlationwiththe slopecutting depth and slope-shape twist degree.(2)Saccharoidal compresso-crushed zonemostly inherits early structural joints and exhibits evident shear.Additionally,saccharoidal compresso-crushed zone has weak water permeability.The permeability increases in the position where structure and fissuringdense develop.The permeability gradually reduces along with the increase of buried depth.(3)Quartz morphology structure includes shell-like structure,subconchoidal structure,orange peel shape structure,lichen amyloidosis structure and insect columnar structure.Quartzparticles' dissolution time and structure is positively correlation with the elevation of slope in left bank.There is slimy stress trace in quartzparticles' surface in the deep rock mass.Saccharoidal compresso-crushed zone has violent activity between middle Pleistocene and late Pleistocene.(4)Rock mass has experienced alternation many times.Alteration products formed in different stage,the amplitude of temperature changed heavily.thehydrotherm invades surrounding rock is rich magnesium iron oxide fluid.Saccharoidal compresso-crushed zone is rich aluminumpoor alkali.It is connected with the decomposition of plagioclase and the formation oflight colormica.The same adit changes show that the main elements in fracture of the main elements of redistribution has obvious control effect.(5)Combined with superposition of the role of alteration,according to the alteration temperature,fracture zone width,fracture zone of the color,weathering status and effect of groundwater,will be saccharoidal compresso-crushed zone is divided into slight corrosion forms,medium corrosion forms,strong erosion forms;Different alteration type is the different combination of dynamic structural alteration and secondary weathering alteration.(6)The special lithology,geological structure and rock mass structure conditionsprovidethe material and structure of the foundationfor saccharoidal compresso-crushed zone.Along with the rapid incised valley,internal high strain energy release,strong rock mass slope rock mass deforming toward unloading rebound direction,form saccharoidal compresso-crushed zoneand produce tectonic dynamic alteration.According to the temperature change of dynamic heat flow,divide to slight corrosion forms and medium corrosion forms;By the late reformation of groundwater,in-band overlay form secondary weathering alteration,generate strong erosion forms.