Sedimentary Facies Of Manganese-bearing Falang Formation And Genesis Of Manganese Ore Deposits, Southeast Yunnan

Southeastern Yunnan is a high-quality manganese areas in southern China region, the distribution of manganese ore bed along the south-east of Jianshui-Qiubei. The manganese deposit of Ladinian Falang Formation of the Middle Triassic ,to a marine mudstone and siltstone, sandstone sedimentary interbeded carbonate. Manganese-bearing Sequences of Falang Formation overlying formation is Upper Triassic clastic rocks Niaoge-Formation, underlying formation is Middle Triassic limestone Gejiu Formation, between the two Formation there is a cessation of deposition. Falang Formation manganese paragraph two, the next paragraph manganese group located in the lower part of the Falang Formation, the other is located above the upper part of the Falang Formation. Only Dounan manganese deposit from top to bottom layer of manganese have two paragraphs.Yanzijiao has the lower section of manganese layer, the upper strata pinch out, Laowu has the upper section of the manganese layer, the lower strata pinch out. Manganese ore in the ore-bearing strata is mainly braunite, containing a small amount of calcium ropperite. Calcite cement is dominant, dolomite, quartz sand and authigenic albite take second place.Although previous the study on the source of manganese and their sedimentary environments is extensive. However, there has not been noted in the oolitic and pisolitic structures in manganese ores, as well as the construction of these structures - the blue green algae micro-organisms on manganese concentration may be of great significance. The manganese deposit of Ladinian Falang-Formation of the Middle Triassic lies in the Southeast Yunnan.Concentric rings structure are obviously observed in oolitic and pisolitic manganese ores. The thin sections from manganese ore samples are systematically observated from typical deposits in Dounan,Yanzijiao and Laowu. The microstructures of oolitic and pisolitic ores are detailed described on the observation of microscope. The cathodeluminescence and SEM(scanning electron microscope) are firstly used to distinguish micro-texture changes in mm-μm scale laminar. It is suggested that these concentric laminar structures in manganese deposits are origin of blue-green algae micro-organism and similar to common oncolitic structures. They have nucleus and encrustation fabric that can be compared with present Fe-Mn nodule in modern deep ocean environment. The preliminary study results show that Mn enrichment in this region probably relative to micro-organism activity.In this paper, according to our fieldwork and study on measured section of Manganese-bearing Sequences of Falang Formation in Baixian, Tangde, Yanzijiao, Laowu, Dounan of southeastern Yunnan. Combined with previous data, the manganese deposit( points) of the survey area is obviously subject to the same period but not same facie controlling, through the trace elements and rare earth elements (REE) data, the relevance of the element and distribution patterns ,the application of a reasonable model for the study area.In this ara there are manganese oxide and manganese carbonate mixed together,it's sedimentary manganese , metamorphic phenomena is not clear. Ore generally contains biological debris, it can determine the formation of manganese nearby redox interface. Flunctuation of the sea level , manganese oxide also dissolved continuous precipitation, and ultimately make the poor oxygen layer pore water concentrations of manganese ions to achieve the best value, the formation of manganese carbonate. As a result of incomplete oxidation of dissolved manganese to form manganese oxide and the existence of the phenomenon of mixed manganese carbonate. At the same time, the formation of manganese deposit in Southeast Yunnan region, clearly influenced by the spatial distribution of its strata (petrostratigraphy), facies (lithofacies), bit (construction site) control, was "three-in-one".In brief, the key issues of study on the sedimentary formation, mineralize environment, basin distribution of manganese in the Southeast Yunnan; Be conducive to find and identify new manganese deposit in sedimentary basin, predict the occurrence of high-quality manganese ore location.It is of great significancein theory and practice on the establishment of a new, rational and effective model for exploration sedimentary manganese and high-quality manganese ore.