| The manganese ore in Guangxi takes the first place in China. It has many series manganese-bearing rock and a lot of types manganese ore.The Southwest Guangxi is one of the most important prospecting area. The manganese deposit of study area is mostly congregated in Tiandeng, Debao and Jingxi. Manganese ore in this place has spatial distribution imbalance, but layer of manganese ore shows a certain distribution, such as manganese-bearing rock series in the Upper Devonian are Liujiang Formation and Wuzhishan Formation, and manganese-bearing rock series in the Lower Triassic is Beisi Formation.We made the outdoor survey and indoor research of manganese-bearing rock series which is existing in the lower Triassic of Debao Fuwan, Southwestern Guangxi. Combining with the previous data and using sedimentary facies analysis, lithofacies paleogeography and ore-controlling factor,we study the sedimentary characteristics of manganese-bearing rock in the researched area. The main work, knowledge and results summarized as follows:1.Selecting four drilling core of Debao Fuwan manganese ore and taking their magnetic susceptibility, including 297 of the seam and 5207 of the surrounding rock. Result of the analysis shows that the susceptibility of seam in manganese-bearing rock series exists obvious abnormality compared with surrounding rocks. Generally, the susceptibility value of manganese carbonate ore is overtopping 1-2 order of magnitude compared with surrounding rocks, and there is no significant difference between the susceptibility value of siliceous and mudstone. This paper points out that susceptibility can be used as a substitutive index to rapidly distinguish manganese-bearing rock series in field.2.By collecting the regional geological data, integrating the surveyed stratigraphic profile data and microscopic analysis, and using the characteristics of rocks, sedimentary structure, paleontology category, etc. we can analyze the sedimentary facies. The result of analysis shows that there are four types of sedimentary environment in the study area, including restricted platform, open platform, fore-platform slope and deep water basin. Based on the lithology, restricted platform mainly deposits dolomitic lime and limy dolomite, open platform mainly deposits muddy limestone, fore-platform slope is marked by appears of breccia limestone, deep water basin mainly deposits siliceous rock and mudstone.3. Mapping early Triassic paleogeographic map of study area, we consider that the lower Triassic formation mainly deposited in platform facies and basin facies, and the secondary deposit environment is platform margin facies. From west to east, it has a gradually transition from the carbonate platform to deep-water basin through the narrow platform margin facies.4. Based on the lithofacies paleographic map and distribution map of manganese deposits, it shows that there are manganese ore deposits, including middle to large scale ones and more small scale ones, which distributed in the platform basin facies, and only a little manganese ore deposits distributed in the platform facies and the platform margin facies. In order to get a further study for knowing the relationship between origin of manganese ore deposits and those elements, such as the lithofacies, the stratum thickness and the metallogenic essential factor, this paper analysised ore-controlling factors and chosed the Debao Fuwan manganese ore deposits as a case study. By comprehensive analysis, we consider that the distribution of manganese ore has the same direction with deposition center, synsedimentary faulting and volcanic rocks, it shows that the sources and position of manganese may be related to seafloor hydrothermal jet. |
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