Lead-zinc Deposits ¢ñ No. Ore Group Alteration - Mineralization Zoning Mode. Northeast Yunnan Maoping Study

Maoping in the Zhaotong area is a potentially large scale ore deposit in the Pb-Zn polymetallic metallogenic belt in northeast Yunnan. In the past, researches are weak on its ore deposit, especially on the field of mineralogy. This project is based on the Maoping Pb-Zn ore deposit (situated in the Upper Devonian dolomite in Maomaoshan). Alteration zonation mapping and petrology was studied, with emphasis on the metallogenesis and alteration of the numberⅠgroup. As a result, alteration zonation pattern was established. Causes of the metallogenesis were also discussed based on the combination of fluid inclusion and isotope studies. The main conclusions are listed as follows:(1) According to the occurrence of the ore, crosscutting relationship of the veins and ore mineral textures, the metallogenesis can be divided to different stages, including diagenesis of ore-forming process, gas phase, hydrothermal mineralization and supergene oxidation of the period. Mineralization-alternation exist in five stages:Ⅰ,Ⅱ,Ⅲ,ⅣandⅤ.Ⅱ,Ⅲstage is the major lead-zinc mineralization stage. Altered wall rock in the ore body and the discovery of a large number of solid bitumen, both direct and hydrothermal diagenesis period of the decomposition of organic matter occurred before the signs, and also reflect the existence of hydrothermal mineralization process of organic matter mixed.(2) The results indicate that the alternation zonation from the center of ore bodies outward is silicification zone, carbonation+silicification+argillation zone and carbonation zone. As a result, the mineralization zonation changes from massive high grade ore to massive pyrite shell, disseminated-vein-patchy low-grade ore and star-shaped pyrite shell, the mineral composition zonation can be divided into Py +Mrc+(Cpy)+Apy,Py+Gn+Sp+Dol+Ank+Cal+Q+Ill zone, Py+Dol+Ank+Cal +Q+Sd zone and Dol+Cal zone.; Sphalerite has color zonal structure which contain dark red, reddish orange, saffron, buff and light green. From center to edges of the ore bodies and the upper the zoning increased more significant, but that are always occurrence in the form of darker stain. (3) Horizontal band, with the northeastern end of the galena-rich ore bodies pinch out instructions. Elements bring vertical points, pb in the lower part, zn front, indicates the presence of fluid superimposed. Banded ore is another evidence of fluid overlay.Ⅱ,Ⅲstage of mineralization elements in the 670～784m near the superposition of more than 784m to the main mineralization stageⅡ.(4) Py shell is an early product of the fluid. Rich ores are compact blocks of yellow iron shell of the package, low-grade ores are star-shaped yellow iron shell of the package, the ore body in the lens and the upper side, dense block will appear in the high-grade ore shell Py inside the body, and pyrite mine pentagonal dodecahedron crystal form part of the more high-grade ore. Sulfide minerals change from the ore body center to the sides and top of gradually less structural types of ore from the bottom up easier.(5) Q, Dol, Ank, Py structure of the ring occur only in high-grade ore body and the upper edge, does not appear in the lower part is a sign of fluid forward,(6) Fluid occurs with multiple centers, and along faults, fractures from south to northeast with access to the upward migration, fracture and formation is a key factor in controlling mineralization. Evolution of ore-forming fluid, there is significantly lower temperature and pressure, salinity and density of the trend (not significant). The same stage of the fluid in the vertical, since the bottom-up salinity, density decreased, but the pressure and temperature increase. Which,Ⅱstage in-high temperature and high salt, low-density fluid;Ⅲstage in the temperature and low pressure low-salt, low-density fluid. With pyrite, dolomite of the special crystal, indicating that the exothermic effect of precipitation on the crystal properties of the fluid cannot be ignored. Quartz crystal distortion and also showed the supply of fluid in the local one-way circulation occurred.(7) Mineralization occurred during the Yanshanian (Mesozoic) period. Forming materials were derived from the construction of the basement, there is also the Devonian carbonate strata of the contribution of rock salt. Ore-forming fluid of meteoric water and hot brine, the organic mixture of water and deterioration of water flow, indicating the involvement of organic matter and fluid leaching cycle has a definite effect on the mineralization, and the eruption of the Emeishan basalt forming meaningful activities.(8) The established pattern ofalteration and mineralization zoning of Sichuan-Yunnan-Guizhou Pb-Zn ore field can be of universal significance, and can contribute to the genesis of fluid migration and accumulation of ore deposit researches. Under the current reviewed Mining Area No.Ⅰsituation, there is still much space of deeper prospects.