Distribution of soluble salts and sulfur isotope in the Yungang Grottoes,Datong

The Yungang Grottoes in northern China,which are primarily made of sandstone,are suffering from deterioration due to salt weathering.In order to elucidate the distribution and sources of salts,samples of water,rock debris,salts,soil from different locations in and around the Yungang Grottoes,together with dust and coal,were analyzed for water chemistry and sulfur isotope.X-ray diffraction quantitative analyses show that the main deposit salts are sulphate,with main composition of epsomsalt and gypsum.Carbonate is the second deposit,in which calcite and magnesium carbonate are the main component.Knowledge of source of sulfur and its cycling behavior is the basis to understand salt movement and assembling discipline.Sulfur content of sandstone is only 13~35mg /100g,while it reaches 720mg /100g for dust in Grotto 3.Coal mine around the Yungang Grottoes has high quantity of pyrite.Sulfur isotope indicates that δ34S of coal is the lowest,secondly the rainwater,and thirdly the drip water and groundwater.δ34S value for salt is a little lower than that of the soil.δ34S value for soil is the highest.Pyrite in sandstone has almost changed to limonite,which is not the main source of sulfur.Sulfur element in the Yungang Grottoes mostly comes from products of coal mine burning and atmosphere contamination due to production and transportation of mine.