Mineral characteristics of Sayak large-scale Cu ore-field in Kazakhstan and their geological significance
Li Jing1,2, Xu Yingxia1, Shen Ping2, Pan Hongdi3, Zhong Shihua2,4, Eleonora Seitmuratova5
1. Hebei United University, Tangshan, Hebei 063000;
2. Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029;
3. College of Earth Sciences, Chang'an University, Xi'an 710054;
4. University of Chinese Academy of Sciences, Beijing 100049;
5. Laboratory of Geological Formations, Satpaev Institute of Geological Sciences, Almaty 050010
The ore body of skarn type deposit in Sayak is located in the contact zone between Carboniferous limestone and granite, surrounded by skarn. The skarn minerals in Sayak mainly include garnet, pyroxene, epidote and chlorite. Metallic minerals are mainly chalcopyrite, bornite, pyrite, pyrrhotite, cobaltite. The mineralization of Sayak deposit can be divided into five metallogenic stages: Diopside-garnet skarn stage, garnet skarn stage, epidote-magnetite stage, quartz-sulfide stage and carbonate stage. Electron microprobe analyses show that skarns in Sayak belong to typical calcic skarns. There are three types of garnet in skarn, and they all belong to andradite-grossularite solid solution series. The garnet shifted from andradite towards andradite-grossularite with time, and the andradite-grossularite is most relevant to the mineralization besides. The content is changing with the zone rhythmically, which means that its growth is discontinuity indicating multi-stages of fluid. The pyroxenes are mainly composed by diopside with a small amount of hedenbergite. The epidote is almost epidote with a little clinozoisite. The magnetite is composed by a high TFeO content with a negative correlation with other oxide. Chalcopyrite-pyrite-pyrrhotite-marcasite and chalcopyrite-cobaltite are developed in early quartz-sulfide stage, while compact massive chalcopyrite formed in the later main stages. The chalcopyrite and pyrite are both lean sulfur and rich metallic element, and pyrrhotite is lean cobalt but rich nickel. The mineralogical features such as paragenetic association of skarn minerals and the composition evolution of garnet indicated that the ore-forming hydrothermal evolved from alkalescence to acidity as the decrease in temperature and oxygen fugacity. Meanwhile the chalcopyrite-based metal sulfides occurred enrichment and precipitation with the neutralization in the contact zone.