LI Hong-liang1,2, LI Guang-ming2*, LI Ying-xu2, DONG Sui-liang2, QING Cheng-shi2, Fu Jian-gang2,3, LIU Hong2, HUANG Han-xiao2
(1. College of Earth Science, Chengdu University of Technology, Chengdu, Sichuan Province 610059, China;
2. Chengdu Centre,China Geological Survey, Chengdu, Sichuan Province 610081, China;
3.College of Earth Science and Resources, China University of Geosciences (Beijing), Beijing 100083, China)
Abstract: Jienagepu gold deposit, a newly discovered gold deposit in Zhaxikang Ore Concentration District in recent years, is located in the eastern part of Southern Tibetan gold-antimony metallogenic belt. Jienagepu gold deposit is hosted in altered diabase. The ore bodies are mainly controlled by ductile-brittle faults and interlayer fracture zones with northwest-southeast stretch. Two different kinds of ore types are identified as altered rock type and quartz vein type, characterized by mesh-vein, brecciated and oriented structure, amorphous, crystal, cataclastic and mylonitic texture. Ore minerals are dominantly comprised of pyrite, arsenopyrite, stibnite, galena, sphalerite and native gold, while the gangue minerals are mainly quartz, sericite and chlorite. Wall rock alterations mainly include beresitization and chloritization. According to the intercalation relationships of different veins and paragenetic associations of minerals, primary hydrothermal ore-forming period can be divided into 3 stages, namely, quartz-pyrite stage (early), quartz-gold-base metal sulfides stage (middle) and quartz-carbonate minerals (late). Primarily study on the fluid inclusions of quartz in ore shows that the main fluid inclusions of Jienagepu gold deposit in main metallogenic (middle) stage are pure CO2, aqueous and rich CO2-aqueous fluid inclusions, which constitute a fluid inclusion association (F.I.A) trapped in non-homogenized condition. The homogenization temperatures, salinities and densities of fluid inclusions range from 221.7 to 279.4 °C, 1.57% to 6.74%, and 0.58 to 0.88 g/cm3, respectively, belonging to the H2O-NaCl-CO2±CH4±N2 system, and are characterized by the medium-low temperature, low salinity, low density and rich CO2. There are always many different types of inclusions and same types of inclusions with different gas/liquid ratios in a vision in middle stage, and the homogenization temperatures of those inclusions are similar, which shows that the ore-forming fluid is immiscible. The metallogenic temperature and pressure can be estimated to be 218.6－280.4 °C and 73－93 MPa，respectively. Based on the metallogenic pressure, metallogenic depth and geothermal gradient during the mineralization can be estimated to be 5.8－7.9 km and 35－45 °C/km, respectively. These results show that Jianagepu gold deposit is an orogenic gold deposit, which is closely related to the magmatic or magmatic hydrothermal activity, and has been interpreted to form in Miocene transformation stage from intracontinental orogeny to extension between the India plate and Eurasian plate.
Keywords: ore geology; fluid inclusion; orogenic-type gold deposit; Zhaxikang Ore Concentration District; southern Tibet
ACTA MINERALOGICA SINICA Vol. 37, No. 6, 2017, Page 684-696