QIU Hong-xin1, ZHANG Gui-shan1,2*, WEN Han-jie1,3, PENG Ren1, MENG Qian-kun1, LI Shi-lei4
(1. School of Earth Science and Resources, Chang’an University, Xi’an 710065, China;
2. Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits, Ministry of Natural Resources, Xi’an 710065，China;
3.State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China;
4.Mining Corporation of Chuanwei Group, Chengdu 610059, China)
Abstract: The Baicao deposit in the Huili area of the Panzhihua-Xichang Rift is famous for its V-Ti magnetite mineralization. However, it has a certain amount of the cobalt-rich sulfide ore whose formation mechanism was not deeply studied yet. In this paper, the pyrrhotite from disseminated, dense massive, stockwork veining, and spotted cobalt-rich sulfide ores in the deposit is taken as the research object. On the basis of field geological survey, the compositions and crystal types of pyrrhotites have been studied by using means of mineralography and electron microprobe. Based on the principle that magnetic colloid can be used to identify crystal types of pyrrhotites, it is determined that there are two crystal types of pyrrhotites, including monoclinic pyrrhotite (Mpo) and hexagonal pyrrhotite (Hpo) which were intergrown with each other in forms of veinlet, leaf and irregular shape. The formation temperature, sulfur fugacity and M/S value of pyrrhotites were calculated based on the study of characteristics of major elements in pyrrhotites. The formation of pyrrhotite can be divided into the magmatic metallogenic period (sulfide segregation stage, contact metasomatic stage) and hydrothermal metallogenic period. The sequence of four types of pyrrhotites is preliminarily determined in following order form the first of disseminated pyrrhotite and massive pyrrhotite, to the second of variegated pyrrhotite, and to the last of stockwork veining pyrrhotite.
Keywords: pyrrhotite; mineralogical characteristics; ore genesis; Baicao deposit
ACTA MINERALOGICA SINICA Vol. 41, No.3, 2021, page 245-257