GEOCHEMICAL CHARACTERISTICS OF THE SANDSTONE FROM HOUSHIGOU FORMATION IN SOUTHERN SANJIANG BASIN: Geological Implication

The Cretaceous Houshigou Formation in Sanjiang Basin is the main ore-bearing layer of uranium deposit, developed with a large area of grey and light yellow gravel fine-medium sandstone. Taking the sandstone of Houshigou Formation in Songmuhe sag as the study object, the paper discusses the provenance composition, weathering intensity and tectonic setting of Houshigou Formation on the basis of detailed petrological and geochemical characteristics. The results show that the formation is mainly feldspar and lithic sandstone, with the major element SiO₂ content of 58.91%-71.51%, total alkali content of 4.59%-10.05%, and Al content of 12.87%-16.12%. The total content of rare earth element (∑REE) is 100.72×10^-6-171.34×10^-6, averagely 134.532×10^-6, with obvious negative Eu anomaly (δEu=0.27-0.84), indicating that the rock originates from the upper crust. The element geochemical characteristics reveal that CIA is 13.13-45.25, ICV 0.74-1.02 and PIA 53.08-67.90, indicating that the sedimentary period of Houshigou Formation was in arid-semi arid environment, and the source area experienced weak weathering. The Sr/Ba ratio is mostly less than 1, the equivalent B content mostly less than 200×10^-6 and the SiO₂/Al₂O₃ ratio averagely 4.35, indicating that the sedimentary period of Houshigou Formation was in low salinity environment. The sandstone has the geochemical properties of active continental margin. Combined with the regional evolution history, it is believed that the source area should be the felsic rock developed in Jiamusi uplift.