胡力海洼陷主含矿层层间还原流体地球化学特征及其对铀矿化的控制作用OA

To clarify the geochemical characteristics of interlayer reducing fluids in Qingshankou Formation and the lower member of Yaojia Formation in Huliha sag and their control on uranium mineralization,the ore host sand bodies in gray sandstone of the target layer were studied by testing the acidic hydrocarbon decomposition and vitrinite reflectance(Ro),and a comprehensive analysis was conducted in combination with the previous zircon U-Pb dating results of diabase and the current measured borehole geothermal data.The study area is a fault-depression type double-faulted asymmetric sag,developed with multiple sets of high-quality source rocks.The NE-trending normal faults penetrating the basement controlled the uranium orebodies which present the characteristics of"zonal distribution,lateral development,multi-layer occurrence,and superimposed location",and the reducing fluids supplied by the underlying source rocks served as the key driving force for uranium mineralization.Geochemical analysis of acidic hydrocarbons in the ore hosting sandstones reveals that their components are dominated by methane with low heavy hydrocarbon content and a dryness coefficient ranging from 0.59 to 0.99(mainly wet gas),which confirms that the interlayer reducing fluids originate from the hydrocarbon expulsion generated from deep source rocks.Ro values was used to quantitatively calculating the paleotemperature,and the paleotemperature of the target layer was estimated from 58.1 to 136.6℃by the Ro values from 0.36%to 1.11%,which indicate that the source rocks are mainly in the stage of low-maturity-maturity hydrocarbon generation and have sufficient hydrocarbon generation potential.Diabase dating and geothermal data were combine to analyze the driving mechanism of fluid activity,and interlayer reducing fluids was found driven by tectonic thermal events related to the intrusion of diabase in the Paleogene Eocene(39 Ma,47 Ma),which generally show a heat transfer and fluid migration pattern from deep to shallow.The interlayer reducing fluids control the unique distribution pattern of uranium metallization through the dual effects of creating a reducing environment to form a reduction barrier and constructing a temperature-increasing hydrothermal system to accelerate the activation and enrichment of uranium elements.This study clarifies the genesis,driving mechanism and ore-controlling effect of interlayer reducing fluids in Qingshankou Formation and the lower member of Yaojia Formation in Hulihai sag,providing an important geological basis for the uranium prospecting and exploration in Hulihai sag and the similar fault-depression area.