| Nitrate mineral is an important industrial raw material, widely used in agriculture, chemical industry, metallurgy, building materials, and light industry, medicine and food products. In recent years, with the development of national economy, the China demands larger amount of nitrate products, and depend on more imports. Xinjiang is the unique area in the China because of their large nitrate distribution. Recently, a large nitrate ore field in this basin was found recently. It is estimated there are about 250 million tons resources of nitrate and the amount is as much as Atacama Desert super-scale nitrate deposit in Chile.But the study in this area is in low degree and studies in this area mainly on geology,and there is no rearch in isotopic geochemistry as yet.We researched geological character of the Kumutage, Xiaocaohu, Wuzongbulak, Dawadi,T uyugou and Shaer nitrate deposits,collected various ore, soil and water samples from different location and different type mineral deposits. The concentration of nitrate in samples were measured. We measured the age of the deposite by OSL. We draw the following creative conclusion:(1) The program of purification and separation for nitrate and sulfate was established. Methods of δ17O,δ18O and δ15N analysis of nitrate was set up,and the technology has already arrived at an international advanced leval.(2) The 15N in nitrate minerals from Tulufan-Hami nitrate ore fields was enriched with 15N values ranging from 0.65%o-27.63‰, but almost spanned in 2‰-4‰ which is similar to air-source nitrate.Different types ore deposits have different15N values.The 15N values of potassium nitrate deposit is more higher than sodium nitrate deposit. The 15N values in the north is higher than the south.It indicated that the nitrate in Turpan-Hami area comes from atomosphere.The process of potassium nitrate forming process,there must be affacted by denitrification of bacteria. The 15N values in the north is higher than the south which is the result of higher amount of bacteria in the north than south.(3) δ18O values of in nitrate minerals from Turpan-Hami nitrate ore fields vary from 35.4-47.9‰, which is deifferent from other resourses nitrate. This result provided evidence for atomospheric origin of urpan-Hami nitrate deposits. The δ18O value (44.9‰-46.0‰) of Dawadi potassium nitrate deposit was similar to sodium nitrat deposits.The δ18O value (30.2‰-36.3‰) of Wuzongbulak potassium nitrate deposit was lower than others.The low δ18O value would be the result of dentrification of microorganism in the process of ore-forming process.(4) The 17O values of sodium nitrate deposits vary from 12.2~27.9‰. It indicated that there is obviously mass-independent fractionation. The 17O values (14.3‰-18.4‰)of Dawadi potassium nitrate deposit was lower slightly than sodium nitrat deposits.The 17O values(3.9‰-12.4‰) of Wuzongbulak potassium nitrat deposit was the lowest in this area.A little mass-independent fractionation phenomenon was also found in sulfate As far as we know,photochemically reaction in the atomophere was the only reason that caused mass-independent fractionation According to the nitrogen, Oxygen isotopes Chracters,we could concluded that long term atmospheric deposition is the source of super large nitrate deposit. Based on the photochemical box model for NO3-atm 17O production,we caculated that at least 75% of the NO3- in the Turpan-Hami nitrate ore deposits was the direct result of atomospheric deposition of photochemically produced NO3-.(5)The was a week correlation between δ18O and δ15N values,but obviously negtive correlation between 17O and δ15N values in a 1:2 ratio. It showed that the potassium nitrate deposits and sodium nitrate deposits have the same material resource.All changed by dentrification of microorganism.Not only sodium nitrate deposits compliant with this law but also potassium deposits.(6) The OSL age of the sodium nitrate ore-bearing horizons is about 350Ka,it indicated that the sodium nitrate deposit was evaporated after 350Ka,in late Middle Pleistocene.(7)We set up a mineralzation model of the Tulufan-Hami area based on δ18Ov-SMOW, △17O values and 15N values. The long accumulation of NO3- produced by phtotchemical reactions in the tropsphere and stratosphere was removed by dry deposition.When the NO3- particals accumulated in the earth’s surface, they transferred by rain and wind in a short distance. In the late Middle Pleistocene, the brine started to evaporated.Then, in the environment of exactly arid, they gradually evaporated and formed sodium nitrate in the fissures in gravels. By long time and long-distance trasferred, atomosperic nitrate accumulated in the salt lake.Potassium nitrate deposit was formed by evaporated in the enclosed salt lake. |
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