A PRELIMINARY APPROACH ON THE CHARACTERISTICS AND GENESIS OF XIAOTIANJING MANGANESE DEPOSIT, HEQING COUNTY, WESTERN YUNNAN

Xiaotianjing manganese deposit,Heqing in west Yunnan occurs in the transitional zone of limestone ( T₃Sn^2-2 ) and mudstone (T₃S.n^2-1) of the Upper Triassic Sungkuei group. Its surface is pyrolusite which is gradually substituted by rhodoch-rosite along with the depth. The Mining area is a synclinal folding. Mineralizatin intermittently appears in the northeastern limb. Its distribution is not very homogeneous. The orebody is rich and thick, comparatively concentratted and better continuous in the southwestern limb. It is obviously controlled by the paleogeogreaphic environment. The orebody of forms presents the stratified mangnese deposit, lenticular pyrolusite, belt-shaped py rolusite. But only the stratified manganese 4eposit has the industrial value. The mineral composition is comparatively simple, ore minerals are mainly pyrolusite,rhodochrosite and psilomelane,next are manganite, braunite and a little manganese-calcite. Gangue minerals are calcite, chlorite quartz and clay minerals, etc. and associated with a small quantity of pyrite and magnetite. The content of pyrolusite is high (64.12-82.5% ), harmful components are very few, so it is a rich ore for chemical industry. On the average, rhodochrosite is therichest ( 39.39% ) , therefore it is a rich ore for metallurgical manganese. At present, manganese orebody extends along the trend or the strike the thickness of its tenor and its ore quality are comparatively stable. The long axis direction of oredody is NW55°-60°, its form is like a narrow basin. There are three zones from outside to inside, they are pyrolusite zone-rhodochrosite zone-non-orebody zone ( Figure 1 ). With regard to the gneesis of deposit, there are two different views. The first is based on the fact that the manganese orebody is held in the fissure, it is related to wall-rock alteration, and considered as hydrothermal deposit. The second is based on the control of the orebody strata, it is considered as a sedimentary deposit. The author agrees to the latter. He has proposed eight proxves. The division of sedimentary rocky phase, analysis of orebody zonality and investigation of rock and mineral identification indicate that after the deposition,the deposit was slightly metamorphic. This view is comparatively accord with the objective reality of this area. And the view of hydrothermal genesis is very difficult to explain satisfactorily a series of ore-forming features of manganese deposit. Moreover, it is also a controversial issue that pyrolusite is an orignal sediment or comes from rhodochrosite with secondary oxidation. The autthor agreed to the former and has proposed 4 proxves to demonstrate that most pyrolusite may be of original sedimentation, and not the secondary oxidation from rhodochrosite. To sum up, Xiaotianjing deposit is rich orebody with a little impurity, its quality is good, it is a rich ore for chemical industry and metallurgical industry. Its industrial value is comparatively high. It is of great realistic significance for expanding the regional search of orebody to understand clearly the genesis of deposit and the condition of enrichment.