The Ancient Karst Of Majiagou Formation And Its Influence On The Al-bearing Rock Series In Yanlong Area,Western Henan

Taking bauxite as the research object in Yanlong area,with nearly 300 coring drilling and large open bauxite pits as the research focus,and refering to the latest research results of bauxite at home and abroad and the exploration practice of bauxite in Western Henan in recent years,we conducted the systematic geological observation of core and land surface.Conducting research about the ancient karst of Majiagou Formation and its influence on the Al-bearing rock series by experiments of thin section,SEM,EDS,X-Ray Diffraction,differential thermal,infrared spectrum and rock geochemical analysis and so on.The development condition of ancient karst been analyzed in Yanlong area,we found the development conditions in different periods of ancient karst are different.There have been better ancient karst conditions from the process of the transgression beginning of Southern North China in Late Carboniferous to the deposition process of Benxi Formation.Ancient karst has different individual patterns of karren,channelling,clint,solution crack,karst funnel,karst depression,karst plain,karst cave,dissolution windows and dissolution niche,and they form different combinations of karren-channelling-karst funnel,karst funnel(channelling)-dissolution windows(dissolution niche),karst funnel-horizental karst cave,horizental karst cave-channelling and karst funnel-karst funnel(karst depression),with karst collapse in Yanlong area.The ancient karst collapse mainly developed in the karst funnel and its internal lateral sides that were strongly dissoluted,and the main features are strong deformation in Benxi Formation and Taiyuan Formation.The ancient karst type is covered karst,and exists in three different periods of Late Ordovician to Lower Carboniferous,Late Carboniferous to Middle Triassic and Meso-Cenozoic.The Al-bearing rock series can be divided into four different lithologic sequences in general: bauxitic mudstone sequence;bauxitic mudstone-pisolitic-oolitic(clastic)bauxite-bauxitic mudstone sequence;bauxitic mudstone-pisolitic-oolitic(clastic)bauxite with interlayes-bauxitic mudstone sequence and thick laminated bauxitic mudstone-lamellar pisolitic-oolitic(clastic)bauxite-bauxitic mudstone sequence.Mineralogical rules of all the Al-bearing rock series are that the main clay mineral in the lower part is illite,the content of illite decreases gradually upward,gradually transformes to kaolinite maily,and the diaspore with high content and good crystallinity mainly occurres in the pisolitic-oolitic(clastic)bauxite.The reason about mineralogical change of different lithologic sequence is related to the enrichment degree of iron and aluminum in different physical and chemical conditions of original rocks in the Al-bearing rock series,and the fundamental reason of the phenomenon is related to the sea level change and the intensity of ancient karst.The different lithologic sequence all have the character of original sediments forming in sudden transgression period,original sediments hydrolysing during regression period.And the regression increases from lower part to middle-upper part;the sea suddenly transgresses on the Al-bearing rock series;but then the sea level drops by a lesser extent,and transforms into a gradual transgression process.The bauxitic mudstone-pisolitic-oolitic(clastic)bauxite-bauxitic mudstone sequence and the bauxitic mudstone-pisolitic-oolitic(clastic)bauxite with interlayes bauxitic-bauxitic mudstone sequence mainly developed in the karst funnel and its strongly karsted lateral sides in Majiagou Formation limestone.Bauxitic mudstone sequence mainly developed away from the karst funnel.Thick laminated bauxitic mudstone-lamellar pisolitic-oolitic(clastic)bauxite-bauxitic mudstone sequence mainly developed in the karst depression accordance with the distribution of karst funnel near the sea level of epicontinental sea.