Magmatic evolution characteristics of two types of rhyolite dacite in Xiangshan uranium ore field——Evidence from chemical composition of feldspar and biotite

This paper is the result of mineral exploration engineering.

Objective Minerals formed by magmatic differentiation, such as feldspar and biotite, can be used as indicators of magmatic evolution of host rocks.There are disputes between rhyodacite and rhyodacite porphyry from Xiangshan, in the aspects of formation age, origin, material source and mantle material participation.

Methods In this paper, the electron probe technology is used to quantitatively analyze the feldspar and biotite in two types of rhyodacites in Xiangshan, and the composition, material source, formation temperature, oxygen fugacity and rock properties of the two types of rhyodacites are analyzed and studied.

Results The results show that the rhyodacite of Xiangshan Daguding Formation can be divided into two types, one is the effusive rhyodacite (K₁d^2a) and the other is the intrusive rhyodacite porphyry (K₁d^2b). The types of feldspar from rhyodacite are more than those of rhyodacite porphyry. The feldspar types of rhyodacite include albite, potassium feldspar, potassium sanidine, feldspar and andesine. The main feldspar types of rhyodacite porphyry are albite, potassium feldspar and potassium-sanidine. The biotite formation temperature of rhyodacite and rhyodacite porphyry is basically the same (750±20℃). Rhyodacite and rhyodacite porphyry both have high oxygen fugacity and belong to calc-alkaline rocks, indicating the same magma material source with part from mantle material.

Conclusions The chemical composition is basically the same, together with the same feldspar type, the same material source, the same crystallization temperature, the sameoxygen fugacity, and the same rock properties, indicating that the two have homology.