Sedimentary Characteristics And Metallogenic Prospect Of Upper Triassic Maichuqing Formation In Nanjian,yunnan Province

There is a detailed study on the lithological association, sedimentary structure, fossils, sedimentary facies and analysis of the metallogenic conditions and prospect of Upper Triassic Maichuqing Formation in research area through the base of stratigraphic section measuring, field geological surveying and sampling, rock and minerals identification, SEM and EDS component analysis, isotopic analysis, element geochemistry etc. on this article.As the main strata of Triassic, Upper Triassic Maichuqing Formation is widely distributed in the research area, outcrops in the northern and southwest corner of Mengpuma village and extends to the northern of Gonglang, and is a conformable contact with the overlying strata of Lower Jurassic Yangjiang Formation.It is not outcropped in study area that the bottom of Upper Triassic Maichuqing Formation. So there do not have a complete sequence. The clastic rocks of what we see is mainly the upper or middle upper of Maichuqing Formation, mainly consists of a set of a yellow-green mudstone, gray green argillaceous siltstone, gray siltstone, gray white fine grain quartz sandstone, lithic quartz sandstone, etc.. The carbonate rock is the middle upper strata of Maichuqing Formation, or the same layer’s lateral phase-change, mainly consists of a set of dark gray limestone, marl and their interbed, sandwiches khaki calcareous mudstone, gray and black calcareous feldspar quartz sandstone, quartz sandstone of carbonate rocks in the local, and its color, lithology, lithofacies and sedimentary characteristics are more complex, especially in the lateral variation. There are not easy to grasp that the overall appearance and longitudinal changes and lateral changes due to the lack of complete sequence.There is a whole sand mudstone sandwiched coal line sedimentary combination of Upper Triassic Maichuqing Formation, developed in parallel to the bedding of sand, the large oblique bedding, and rippled bedding, visible ripples in the siltstone surface. Local visible gray and black thick-bedded limestone and dark gray thin- the layered sandwich shelly limestone. Carbonate rock is a very thin layer of limestone, marl and a fine-grained clastic combination of sedimentary rock, visible horizontal bedding and ripple marks impression on limestone levels. According to the outcropped and measured sections, also combined with the sedimentary structures, fossils and the basic sequence, we think that the upper or top of Maichuqing Formation are maily sedimentary cycle of sandstone and mudstone. According to the sedimentary and sequence characteristics, we inferred that the sedimentary facies of Maichuqing Formation is mainly littoral neritic facies and delta facies. Additionally, we also inferred that the sedimentary facies of Maichuqing Formation are mainly continental shelf facies because the Maichuqing Formation is a fossil rich limestone, marl and clastic rock.Combined with abundant fossils in the Upper Triassic Maichuqing Formation, conodont and pollen samples, we can see it belongs to the Late Triassic Norian. In the pale yellow sandstone to extract detrital zircon U-Pb isotopic dating in the profile of the near Ake Village of Leqiu Township, Nanjian County, Yunnan Province. Get the relevant data show age of detrital zircons from 560 ±120Ma to 2246 ±85Ma peak, the new age is obtained for 245.8Ma(effective measuring point12). Therefore, it showed that the formation should be later in the Early Triassic.In ore spot inspection, there are the gray green, gray black siltstone, fine sandstone and mudstone occurring to sandstone copper, copper silver ore, magmatic hydrothermal copper of Upper Triassic Maichuqing Formation. In Mengpuma village sheet, Nanjian Dafoshan copper and copper lead mine, Mali copper silver ore spot are mainly occurrence in Maichuqing Formation. The Lamaju copper(molybdenum) ore spot of Gonglang sheet, mineralized bodies mainly occurs in the exocontact site of rock mass, essentially free of mineral rock. Thus, we speculated that the ore-forming material mainly comes from Maichuqing Formation.There are showed that the distribution area of Upper Triassic Maichuqing Formation have a higher Cu background values, and been found Dafoshan copper and copper lead point of Nanjian, copper silver of Mali and the copper(Mo) deposits point of Lamaju, and is for the period of construction or acidic magmatism Himalayan region and has a good prospect for copper polymetallic ore through the stream sediment geochemical survey in 1: 50000.