Application of the Removing Carbonate Method to Study the Origin of Silica in ‘Bainitangceng’ of Yunnan-Guizhou Area

Abstract

Bainitangceng in the Yunnan and Guizhou area has a close relationship with manganese deposits. Previous geochemical studies focused on the whole rock of siliceous limestones rather than siliceous components. The question of whether or not whole rocks can really reflect the source of siliceous components needs further study. In this study, Bainitangceng' siliceous limestone in Yunnan and Guizhou area was selected and HCl was used to remove the carbonate minerals in siliceous limestone to acquire simple composition siliceous components. Trace elements in siliceous components were determined by ICP-MS/OES. The origin of siliceous components is discussed by comparing the trace elemental composition of the whole rock of siliceous limestone and siliceous components after removing carbonate. Results show that Th/U ratios (0.02-0.05) in siliceous components are lower than those (0.08-0.2) of the whole rock of siliceous limestone. Siliceous components after removing the carbonate minerals have Eu/Eu* values of 0.86 to 1.54 with positive Eu anomaly, different from Eu/Eu* values (0.87-0.93) of the whole rock of siliceous limestone with negative Eu anomaly. Both whole rock of siliceous limestone and siliceous components are characterized by enriching the light rare earth elements, but the proportion of light rare earth elements in siliceous components is larger than that in whole rock. The above characteristics indicate that the siliceous component of ‘Bainitangceng’ may have been derived from hydrothermal fluid, which is important for explaining the formation of Permian manganese deposits.

Keywords

• ‘bainitangceng’
• silica component
• carbonate minerals
• hydrothermal fluid origin
• inductively coupled plasma-mass spectrometry/optical emission spectrometry