Abstract:The Wucheng trona deposit, one of the rare ancient trona deposits in the world, is genetically of typical terrestrial facies carbonate sediments of brine lake. Contained in an Eogene block basin composed of terrigenous clastic-evaporite rocks some 2400 m in thickness, it occurs 650 to over 900 m beneath the earth's surface in the form of multilayers, the lower part being pure trona beds while the upper part consisting of trona beds interbedded with halite streaks. Saline minerals are trona and to a much less amount, halite and nahcalite, associated with such minerals as shortite and northupite. Mirabilite, a rather common mineral in the carbonate salt lake, has not yet been found here. The unusually developed sedimentary cyclothem of the host rock, predo-minantly argillaceous dolomite- kuchersite- (halite-bearing) trona, makes up a most striking feature of this deposit, and the trona bed lies invariably on the kuchersite-dolomite facies. Although belonging to one of the minerogenetic series of saline deposit, the trona deposit, instead of being simply a product of the evaporation of brine, has its specific mineral-forming conditions and sedimentation mechanism. Trona is a typical product of the terrestrial facies carbonate lake. lts formation, therefore, requires the persistent supply of large quantities of Na-rich carbonate type water which, being actually surface water or ground water circulating through the metamorphic and igneous rocks at the periphery of the basin, constitutes an indispensable factor in the sedimentation of trona by its concentration and evaporation. Besides, the coicentration of CO8<.sub>-2 and HCO8- in the solution is related to the partial pressure of CO2. Only when sufficient CO2 is unceasingly supplied can nahcalite and trona be precipitated. CO2, in turn, depends on the presence of large amounts of organism for its formation. These factors are prerequisites for the precipitation of the trona deposit, making it distinctly different from other saline deposits. Other formation conditions of the Wucheng trona deposit, such as the existence of a closed basin controlled by tectonics, the alternate arid and semiarid climates, are quite analogous to those of other saline deposits. Some controversial problems concerning this kind of deposit are also put for ward in this paper for further investigation, including the feasibility of taking the abundance of sulfate minerals as a criterion of distinguishing ancient tronas from recent ones, the influence of material resources and climate conditions upon the variation of ore types, and the origin of the highly-concentrated sodium brine in areas adjacent to the Wucheng deposit.
文章编号：
中图分类号：
文献标志码：
引用文本：
张幼勋.1983.河南吴城天然碱矿床地质特征及戍因探讨[J].矿床地质,2(3):69~71.1983.A preliminary study on the geologic characteristics and genesis of the Wucheng Trona deposit in Henan Province[J].Mineral Deposits2(3):69~71
图/表
