Study Of The Geological Characteristic, Ore-controlling Conditions And Genesis For The Jiaochong Au-S Ore Deposition In Tongling Areas, Anhui Province

This article, guided by modern theories of mineralization and metallogenic prognosis, makes a comprehensive analysis on the information about the stratum, structure, magmatic rocks and characteristics of fluorite mineralization fluid of the the Jiaochong Au-S ore deposit area. Combined with field investigation and the results of work on metallogenic regularity and metallogenic prognosis of the Jiaochong Au-S ore deposit, it enloses a prospect forecast area and provides guidance for the arrangement of the exploration in this area.Studies on the metallogenic regularity of the Jiaochong Au-s ore deposit show that Au-s ore deposit has a lot to do with Yanshanian orogenic movement. Obviously controlled by fault structure, the ore-bearing faults in this area run in E-W and N-S direction. The Jiaochong Au-S ore deposit mineralization liquid comes from the magmatic thermal fluid, extracting mineralizing substance from the rocks, and eventually produces the deposit. Research on the mineral fluid inclusions indicate that the temperature is divided by 3 ranges: 410℃～440℃,320℃～350℃和260℃～320℃,showing a decreasing trend of the temperature from the Quartz-sulfide stage earlier to calcite thermal fluid stage. The depth of the mineralization of Jiaochong Au-S ore deposit is 1.5 Km, and the mineralization pressure is 0.4 Gpa. The S-containing minerals including in the Jiaochong Au-S ore deposit are mostly sulfide. The averagement value of theδ³⁴S of the sulfide which equates the sum value of theδ³⁴S of the thermal fluid is 4.16‰, The value indicates that the sulfur of the ores has the characteristics of the deep-resource sulfur, which means that the sulfur mostly comes from the deep magma and little may come from the marine sulfate in the stratum. Theμvalue of the lead in the ores never shows the wave in big scales, indicating their crustal characteristics and the close association with the magmatic activity. The value also shows this kind of lead comes from the lower crust or the upper mantle, lead isotope basically evolved in the enclosed system and hasn't been contaminated by the crustal substance.The intrusive pyroxene monzodiorite and granodiorite porphyry have the characteristics of granite deriving from the crustal sedimentary rocks remelting. Combing with the ore-geological function background and ore-forming chronological study, it's considered that in the mid-late stage of the Yanshan the continental crust in the East China thinned, causing the up-raising of deep mantle-derived magma and directly intrude beneath the crustal sedimentary rocks which makes the crustal sedimentary rocks partly melting and derives to the mid-acid granodiorite porphyry magma. Meanwhile, mantle-derived magma differentiates to the alkaline direction, producing the pyroxene monzodiorite magma in this section. According to the analysis and interpreter of the LA-ICP-MS zircon U-Pb dating of the intrusive rocks, the 206Pb/238U average age of the pyroxene monzodiorite's crystalization is 122±1Ma, which is latter than that of the granodiorite porphyry, exactly 128±2 Ma.This dating is controversial to the primitive petrogenetic age in this district. The sequence of the magmatic rocks'crystaliztion should be granodiorite poryphyry-pyroxene monzodiorite.After the comprehensive study, it's considered that Jiaochong Au-S ore deposit is the moderate-to-high temperature thermal filled-alteration ore deposit affected by both Qinggshan anticline and the magma activity. The ore-forming depth is mesogenetic, and the type of the ores are filled primarily and alteration secondarily.