The Geological Characteristics And Genesis Of The Da’nanhu Nitrate Deposits In Hami, Xinjiang

Turpan-hami basin is being found as the only super large nitrate deposit metallogenic province in Xinjiang, China. On the basis of previous research, this paper study on the geological characteristics, geochemistry and stable isotope of Hami Da’nanhu nitrate deposit, in addition to the metallogenic geological background, ore-controlling conditions and so on.In order to mainly discuss the ore-forming material source of giant accumulation nitrate deposition in Hami Da’nanhu, further deepening the study on ore-forming mechanism of nitrate deposits in the region. Main conclusions as following:(1) Da’nanhu mining area’s nitrate deposit mainly occurrence at residual terraces or slopes zone in the middle and lower part of alluvial and diluvial fan. Ore types based on gravel-bearing sandstone-type halite matrix nitratite-ore, in some areas appears "dual structure", The upper part is gravel-bearing sandstone-type halite matrix nitratite, The lower part is breccia type halite matrix nitratite. Nitrate-ore have a mineral association of halite, nitratine, darapskite, thenardite and so on, and its chemical composition belongs to NaCl-NaNO3-Na2SO4 combination.(2) The major elements geochemistry characteristics of Da’ nanhu nitrate deposits show that they have depleted sulfate, chloride-rich features, and its has a more obviously relationship between the components. NaCl and NaN03 is generally a positive correlation; NaN03 and CaSO4 is a positive correlation.(3) Nitrate nitrogen and oxygen stable isotope’s analysis showed that Da’ nanhu mine’s nitratite mainly from atmospheric deposition (contribution reached at 82.3%), which has a consistent settlement with the Chilean Atacama nitrate deposits in the atmosphere deposition. Specific sources of metallogenetic mechanism may be:the ore-forming fluid of the Da’nanhu nitrate deposit derived from meteoric water, nitrate mainly through atmospheric deposition then settlement to the ground, meanwhile certain micro-organisms can take advantage of the N2 and NH3, which is eruption materials of volcanic activity, or Jurassic coal-bearing strata of organic matter degradation and ultimately form the nitrate. Microbial growth is limited in the extremely arid climate conditions in the process, atmospheric sources of nitrate accounted for the major parts; Nitrate is easily soluble in water, and thus enriched with surface dive to migrate ultimately mineralization.(4) Da’nanhu nitrate deposit genesis belong to polygenic, hypergenic, pore bittern evopration deposition. The stages of mineralization is mainly contain the product of atmospheric photochemical reactions transformed into the surface phase of the continental crust, phreatic evaporation deposition stage and late tectonic destruction combined with the leaching transformation stage.