Li, Z., G. Jianhua, Z. Wang, and Z. Wang. “Exploration Potential of the Yanxi Formation in Middle Ordovician of Hunan Province”. Journal of Mines, Metals and Fuels, vol. 67, no. 5, Oct. 2022, pp. 279-84, http://www.informaticsjournals.com/index.php/jmmf/article/view/31555.