Ore-Forming Fluid Geochemistry and Metallogenic Mechanism from Mazhala Gold-Antimony Deposit in Southern Tibet, China
详细信息
- 责任者：Mo Ruwei (Department of Earth Sciences ; Sun Yat-Sen University ; Guangzhou 510275 ; China) ; Sun Xiaoming
- 刊名：Acta Petrologica Sinica
- 出版年：2013
- 卷期：29(4)
- 关键词：金矿 ; gold ores ; 锑矿 ; antimony ores ; 西藏 ; Tibet
- 页码：p.1427-1438
- 图表：illus., 3 tables, 36 refs.
- 分类号：1001
- issnNo：ISSN1000-0569
- isbnNo：CN11-1922/P
摘要
The Mazhala Deposit is the most representative gold-antimony deposit in the gold-antimony ore-forming belt in southern Tibet, China. Microscopic observation and microthermometric study were performed on fluid inclusions hosted in gold-bearing mineral (stibnite and quartz), in order to directly characterize the physicochemical conditions of ore-forming fluid and investigate the genetic type of the deposit, source of ore-forming fluids and metallogenic mechanism of Mazhala antimony-gold Deposit. The results of microscopic observation show that the fluid inclusions hosted in stibnite and quartz are nearly the same and can be divided into four types: i.e. two-phase aqueous, three-phase CO2-H2O, pure CO2 and pure H2O inclusions, respectively. Infrared microthermometric study show that the homogenization temperature (Th) values of the fluid inclusions hosted in stibnite peak at 180～210℃, the salinity values peak at 2.5～3.4%NaCleqv, and density values peak at 0.895～0.915g/cm3, and that the Th, salinity and density of the fluid inclusions hosted in quartz show triple peaks at 270～300℃, 225～255℃ and 180～210℃, 4.3%～4.9%NaCleqv, 3.4%～4.0%NaCleqv and 2.8%～3.4%NaCleqv, and the 0.895～0.915g/cm3, 0.835～0.855g/cm3 and 0.775～0.795g/cm3, respectively. Comparison of the microthermometric measurements shows that the Th, salinity and density of the fluid inclusions hosted in stibnite match with the lower Th and salinity and higher density values of inclusion hosted in the late stage of quartz, indicating that quartz was deposited from the ore-forming fluid before stibnite, also suggesting the input of low temperature and low salinity while high density fluids during stibnite precipitation. The δDH2O of the fluid inclusions hosted in stibnite and quartz is -68.1‰～-108‰, and their δ18OH2O is -2.2‰～12.2‰, projected near metamorphic fields in the δD-δ18O diagram, occasionally near meteoric line, indicating that ore-forming fluid is the mixture of metamorphic and meteoric waters. The δ13C of fluid inclusion hosted in quartz is -2.9‰～-3.5‰, with an average of -3.1‰, which falls within the range of mantle-derived carbon(δ13C=-5‰～-2‰), indicating CO2 is probably mantle-derived. Moreover, the δ13C of fluid inclusion hosted in stibnite is -12.6‰, which is significantly smaller than the mantle-derived carbon, suggesting a considerable amount of organic carbon was involved in ore-forming fluid during stibnite deposited. The ore-forming fluids of the Mazhala gold deposit is characteristics by high content of CO2, low salinity, low to moderate Th and low density, which are similar to those of typical orogenic gold deposits. Geologic and geochemical features show that the Mazhala gold-antimony deposit may be a Cenozoic orogenic gold-antimony deposit formed under continental collisional background.