The Mississippivalley type (MVT) PbZn deposits, south China, occur in the Devonian platform sandstonecarbonate rocks, are associated with the basin brine in Cretaceous. Two types were recognized, one is middlelow temperature hydrothermal type such as Fankou, and the other is low temperature type such as Siding and Beishan deposits. The studies on geologic setting, fluid inclusion microthermometry, and δ34S values indicate that sulfur mainly came from reduced fluid, minor reduced from ΣSO42- in oxidized brine, and a few from wall rocks in the deposits. In the middlelow temperature type hydrothermal deposits, δ34S ranges from 12‰ to 22‰, and thermochemical fractionation of sulfur isotope is the principal for metal precipitation, without obvious bacteria fractionation observed. In low temperature type deposits, δ34S value of the ore is lower and in a wide range, bacteria fractionation is the principal, the thermochemical fractionation only in the forming of the coarsegrain ore. The ore lead isotope composition of the deposits shows a linear array, indicating the mixing sources for lead. The old lead came from the eroded Paleozoic continent, young lead represents the common lead mainly from the Devonian sediments. The proportion of two sources of leads is related to the content of the debris in the Devonian sedimentary rocks. The lead directly precipitated from the oxidized basin brines, ultimately from the Devonian sediments (especially clastic rocks at the Transgression) that fluid flows through, further more ultimately from the Paleozoic continent and marine sediments. It is suggested that the mineralization mechanism is given as follows: The mixing of the two types of fluid leads to the precipitation of sulfide rapidly. The oxidized brines rich in metal richbasin, and contains a small amount of sulfur of ΣSO42-, migrated along the red sandstone of Lower Devonian. The reduced fluid is rich in sulfur of ΣH2S. Fluid mixing function is limited to within the scope of a deposits or ore field, but not the regional.