Metallogenic Model And Prospecting Model In Longtoushan Ag-Pb-Zn Polymetallic Ore Deposit, Inner Mongolia

The recent years research indicated that middle-south section of Da Hinggan Mountains metallogenic belt has two periods(Hercynian and Yanshanian) characteristics of metallogenesis, as well as the most of ore deposits in the area closely relate to Permian strata. Longtoushan ore deposit discovered in 2004 is an Ag-Pb-Zn polymetallic ore deposit born in Permian and located in the east hillside of the metallogenic belt, which has considerable resources potentials. It has important research value for its good metallogenic location and blank research history. Base on the detail field geology studies, the geology characteristics of"two stages and three kinds of metallogensis"has established. According to further work through geochemistry research including trace element,REE, S, Pb and Sr isotope,as well as petrography, microtemperature measurement, Laser Raman analysis and thermodynamics calculation of fluid inclusion, origin and characteristic of the ore-forming material and fluid has been discussed. And a new technology of single pellet Rb-Sr isochrones has been tried for dating its born time. Base on above work, study of ore deposit comparison has been carried out, and metallogensis controlling factor and geological prospecting symbol have been summarized. Finally, metallogenic model and prospecting model have been established. According to above, the next step work direction has been proposed. Main achievement of the paper are listed as follow:1,Longtoushan ore deposit has experienced two metallogenic periods including hot-water sedimentation period and hydrothermal reformation period. There are three kinds of metallizing phase: bedded(or near-bedded) phase, vein-shaped phase and pipe-shaped phase. The main metallogenic period is hot-water sedimentation period.2,Ore deposit geochemistry research indicated that the metal sulfides have characteristic of hot-water sedimentation metallogensis, but generally suffered later hydrothermal transformation. The barite mineral isotopic content is homogeneous, showing the seabed hot-water sedimentation origin characteristic. Wall rock, such as limestone and tuff are one of metallogenic material origins. Both of Pb model age and Rb-Sr isochrone research obtained older age value than that of strata, possibly for been influenced by hydrothermal transformation, and interfusion of ancient basis material.3,There are two kinds of main metallogenic fluid inclusion in barite of the Longtoushan ore deposit, which are rich gas phase(C type) and liquid phase (D type) . Their size is 2~7 um, and principal components is H2O. Both kinds fluid inclusion have freezing point temperature -7.1℃～-2.4℃and -5.5℃～-0.3℃, salinity 4.0~10.6wt% and 0.5~8.5wt%, homogeneous temperature 176.8℃～361.6℃and 101.4℃～279.9℃,which peak value around 270℃and 170℃, respectively. Density of the ore-forming fluid is 0.73～0.97g/cm3, and metallogenic pressure is 62.3×105～377.9×105Pa. Above characteristic of the fluid inclusion are well geared to that of ore deposit originated in seabed hot-water sedimentation.4,Through the comparison research, that Longtoushan ore deposit has main characteristics of hot-water sedimentation ore deposit has been indicated. Ore-forming control factor and prospecting symbol of it has been summarized, as well as metallogenic model and prospecting model. Next step work direction about prospecting has also been proposed finally.