松辽盆地西南部含铀岩系沉积时的古气候演变及其与铀成矿关系
摘要
Although, the paleoclimate plays an important role in controlling uranium mineralization during the deposition of uranium-bearing rocks, it has not attracted enough attention of uranium geologists for a long time.The lower member of Yaojia formation is the ore bearing target layer in the southwest of Songliao basin.Taking the lower member of Yaojia formation as the research object, the contents of the main and trace elements and total organic carbon of mudstone samples from representative boreholes were tested.A number of chemical weathering indexes, such as K/Na ratio, a Al Na, chemical proxy of alteration (CPA), modified chemical index of alteration (CIX), plagioclase index of alteration (PIA), chemical index of weathering (CIW), chemical index of alteration (CIA), are used to judge the intensity of chemical weathering of the samples, and reconstruct the paleoclimate conditions during the depositional period.At the same time, combined with the contents of U and TOC and the ratio of Fe 2+ / Fe 3+ , the constraints of paleoclimate conditions on uranium mineralization during the deposition of uranium-bearing rock series in the study area are discussed.The results show that the clastic rocks in the study area have experienced the change of chemical weathering intensity from weak to strong to weak, indicating that the evolution law of paleoclimate from relative cold and drought to relative warm and humidity to relative cold and drought.This paleoclimate change leads to low TOC content in uranium reservoir sand bodies (average value 0.05%) and large-scale development of interlayer oxidation zone, so uranium ore bodies are mainly located in the hinterland of the basin far away from the erosion source area.Dark mudstone formed in humid climate has higher TOC (average 0.61%) and U content (up to 885×10 -6 ).It has become one of the important sources of uranium due to its strong preconcentration during deposition.The discharge of reducing pore water during diagenesis may be