FAN Guang, GE Xiang-kun, YU A-peng
(Beijing Research Institute of Uranium Geology, Beijing 100029, China)

Abstract: Tristramite is one of the main industrial uranium minerals from No. 2082 sand-stone type uranium deposit located in Erlian basin of Inner Mongolia, China. It was discovered for the first time in China. This mineral is co-existence with black charcoal and sulfide such as pyrite, marcasite and so on. The optical properties of tristramite are gray black to black and non-transparent in transmitted light, but gray to dark gray, homogeneous, and without internal reflection in reflected light. The average chemical concentraitons of of UO2, CaO, P2O5, SO3, and FeO from tristramite by 13 points analysis with EPMA are 41.60%, 14.50%, 22.71%, 1.33%, and 0.81%, respectively. Based on the total cation number for 1 except that of phosphorus, the calculated empirical formula is ((Ca0.589U0.351Fe0.026Na0.016Al0.009Y0.007)0.998[(PO4)0.729(CO3)0.225(SO4)0.038(SiO4)0.008]1.00•1.75H2O, which can be simplified as (Ca,U4+,Fe)[(PO4)(CO3)]•2H2O. According to the X-ray diffraction data, the lattice parameter refinement result refined by SHELXTL PC indicates that tristramite belongs to hexagonal crystal system with the lattice parameters of a=b=0.69030±0.00129 nm and c=0.63300±0.00083 nm.

Key words: tristramite; uranium deposit; chemical composition; EPMA; X-ray diffraction

E-mail: fanguang2008@163.com

ACTA MINERALOGICA SINICA Vol. 33, No. 3, 2013, Page 265-270