ZHANG Lan, XIE Hong*, YANG Xu, WANG Zhi-gang, LU Zheng-hao

(College of Resource and Environmental Engineering, Guizhou University, Guiyang 550000, China)

Abstract: There is a lot of powdery, flocculent, and hairy white mineral occurred in form of aggregate in surfaces, joints, fissures of the Niutitang uranium-containing phosphorus rocks in the Bahuang area, Tongren, Guizhou. It is verified as sasaite by using the X-Ray Diffraction (XRD) and scanning electron microscopy energy spectrum analysis (SED). It has commonly euhedral rhomboid laminated crystal with sizes varying from 1.55-1.85 mm, a set of complete cleavage with {001}, and relatively strong hygroscopicity. Its calculated chemical formula and crystal cell parameters are (Al8.75Fe0.75)(PO4)3.26(SO4)1.24(OH)16.24·55.67H2O, and a≈10.8150 nm, b≈15.0956 nm, c≈22.6058 nm, respectively. Comparing to sasaites in other areas, the sasaite in U-bearing phosphorus rocks in the Bahuang area has relatively high contents of Al2O3, Fe2O3, SO3, and OH-, but relatively low contents of P2O5 and H2O. This could be caused by the isomorphouse substitution of Al3+ by Fe3+ and PO43- by OH- and SO42- in the crystal lattice of sasaite during the strong supergene weathering and leaching process. The sasaite in the Bahuang area is closely related to the supergene weathering. It is a secondary oxide mineral. It should be formed by the long-term supergene weathering of the phosphorus sediments. Therefore, it is indicated that the phosphorus rock in the Bahuang area had been reworked and superimposed by the supergene weathering after its sedimentary diagenesis and the secondary weathering may result in the migration and loss of protogenetic phosphorus in the sedimentary rock.

Keywords: Sasaite; uranium-containing phosphorus rock; secondary oxide mineral; mineralogical properties

ACTA MINERALOGICA SINICA Vol. 40, No.3, 2020, page 305-312