| The study area is located in the south of Daba East, the eastern margin of the Sichuan Basin, the tectonic unit belonging to the concave fold bundle of Wuxi which in the overthrust belt of Yangze block Micang-Dabashan base. It has been found with multiple sandstone-type copper mineral occurrences and mineralized spot, ore-bearing strata is the middle Triassic Badong Formation, the Badong formation is nearly EW distributed in the are of Tongfong-Lingjiao and Zhuyuan-Shanghuang.This article based on the data of field geological investigation and measured stratigraphic section, Through the study of Rock characteristics, sedimentary structure, Sedimentary environment of Badong Formation,conducted the stratigraphic division and correlation, sedimentary facies analysis; meanwhile, the characteristics of copper, metallogenic geological conditions and the misneralization genesis which producted in the Sec of Badong Formation were discussed, we made the following understanding:1. The lithology of Badong Formation are mainly purple folder with gray-green-the thin layer of shale, calcareous mudstone, silty mudstone, marl and argillaceous siltstone folder, Central sandwiched thin gray- in the thick laminated argillaceous limestone, dolomitic limestone, dolomite, marl and a small amount of calcium. Overall barrier, the sedimentary environment of Badong Formation belongs to barrier coast. According to its lithologic characteristics can be subdivided into four lithologic.2. The rock combination of the first period of Badong Formation is dolomitic mudstone, silty mudstone and calcareous mudstone. It belongs to the barrier coast phase clastic tidal flat environmental sedimentary. The second period of Badong Formation is mainly about purple thick layer-block containing calcareous tuberculosis silty mudstone, purple middle- thin layer of silty mudstone, calcareous mudstone and with celadon middle fine sandstone. It belongs to barrier island off the coast of tidal flat facies. The basic sequence of the third period of Badong Formation is: micritemarl- calcareous mudstone- dolomite- bioclastic limestone, and it belongs to carbonate tidal flat environmental sedimentary. The basic sequence of the forth period of Badong Formation is calcareous mudstone- dolomicrite and which belongs to lagoon subfacies deposition.3. Six copper or mineralized points have been found in the study area. The tectonic positions are all in the southern flank of the Qinglongbao-Lengjiao syncline or the southern flank of anticline structure which nearly east-west and in the area of Zhaibao-Changliangzi. The ore-hosting horizons of the second period of Badong Formation developed in the interlayer of celadon siltstone and argillaceous siltstone. The mineralized bodies intermittent outputted with the shape of like-layered, irregular pulse shape, lenticular and nest shape. The mineralization is mainly about copper and accompanied by the enrichment of silver and molybdenum etc. The ore body is 0.35~4.10 meters thick. The grade of the copper is 0.94~5.08%. The content of Ag is mainly between(2.5~7.9) ×10-6 and the highest is to 6500 ×10-6. The content of Mo is between(0.32~1.8×10-6) and the highest is to(400×10-6). The ore minerals discontinuous distributed along the crack and showed thin film shape and fine vein. The natural types of the copper ore are: ①Shallow celadon middle-thick layered fine-grained sandstone type which mineral composition is mainly about malachite and a bit of chalcocite. ②Gray-green silty mudstone copper ore, the contents of the mineral are malachite and a small amount of covellite, chalcocite and azurite. ③Light gray-green siltstone type which gives give priority to malachite and secondary to covellite, chalcocite, bornite, tetrahedrite chalcopyrite. The mineral composition distributed uneven. The gangue minerals are mainly quartz, feldspar, calcite, etc.4. The main controlling factors of enrichment of the sandstone type copper mine in the second period of Badong Formation are stratigraphic and sedimentary environment which has obviously horizon characteristics. Secondly is related to rock properties and the development of structural fissure. It specific showed in the thickness, the scope, the organic matter content and the development degree of structural fissure of the sage green powder- fine sand layers. It is a typical stratabound type-hydrothermal superimposed transformation type of copper. |
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