Study On The Provenance Of Aluminiferous Rocks In Benxi Formation At Yanlong Area,Western Henan

The aluminous rock series of Benxi Formation is well-known for its enrichment of high-grade bauxite,but similar to karst bauxite in other parts of the world,there is controversy in its minerogenetic source material.In this paper,to determine its source material,the aluminous rock series of Benxi Formation of Carboniferous Series in the Yanlong area is taken as the research object;a multitude of open pit and all coring drilling are observed,and theories such as sedimentology,mineralogy,geochemistry,mineralogy and soil science as guide;representative aluminiferous rock series is selected to conduct field profile and drilling,and the samples are systematically collected;measurement methods such as rock thin section,X-ray diffraction,scanning electron microscopy with energy spectrum,LA-ICP-MS U-Pb dating and Hf isotope determination are adopted;composition and its horizontal as well as vertical changes of detrital material of the original rock of the aluminous rock series are paid full attention;and the carrying way of detrital particles of Benxi Formation in depositional stage is taken as the link connecting the provenance and sedimentary area.The results showed that the obvious peak of detrital zircon~445Ma of the aluminous rock series of Benxi Formation in Yanlong area accounts for 79% of all zircon,and there is also an unobvious peak,311 Ma,which accounts for only 2% of all zircon.The remaining 21% is mainly the Precambrian zircon.In addition to the obvious peak of 981 Ma,there are also less significant peaks yet.The original rock of aluminiferous rock series is mainly rock debris with compositions of extremely low maturity(including magmatite debris),which is caused by rapid transgression and rapid deposition;Hercynian detrital zircon(peak ~311Ma)similar to stratigraphic age mainly originates from the uplift of Inner Mongolia in the northern part of North China plate,which is carried by waves and rapidly carried to the research area;the Caledonian magmatic zircon(peak ~445Ma)and Precambrian zircon mainly originate from North Qinling orogenic belt in the southern part of the North China plate,and the Caledonian-acidic granitic intrusive rocks and the main metamorphic strata invaded in this area--the Kuanping Group,Erlangping Group and Qinling Group,are rapidly carried to the research area by the backflow of the sea water reaching the piedmont area of North Qinling orogenic belt.