| Abstract:Orebodies of the Baiyinnuo ore deposit occur mainly in magannocalcic garnet along the contact zone between Late Triassic granodiorite porphyry or quartz syenite porphyry and Lower Permian marble. Obvious alteration and mineralization zoning exists both longitudinally and laterally in the ore deposit. From southwest to northeast, garnet content of skarn gradually decreases whereas pyroxene content progressively increases Di component in pyroxene gradually decreases while Hd and Jo progressively increase. Jo in pyroxene of skarn at the northeastern end is by 20～28 mol％higher than that in pyroxene at the southwesteln end, whereas Di is by 70 mol％lower. Correspondingly, minerals of degeneration alteration in skarn roughly vary in order of epidote (amphibole, ilvaite), quartz, chlorite and calcite. According to difference in ore type, within a distance of some 3 km from southwest to northeast in the ore deposit, there exists primary metallic zoning of Fe(Cu)-Zn(Sn)-Cu, Zn-Zn(Pb)-Pb, Zn, Ag, along which regular variations can be observed not only in Zn/(Zn+Pb), Cu/(Cu+Pb+Zn)and Fe/(Fe+Mn) ratios of ores and minor components Bi, Sn, F, Sb and C1 but also in Bi/(Bi+Ag+Sb)and Sb/(Bi+Ag+Sb)ratios of galena as well as Zn/Cd and Ga/In ratios of sphalerite. In addition, minor sulfate minerals in ores change progressively from Bi-bearing ones to Sb-bearing ones. From southwest to northeast in the ore deposit, the temperature gradient vaIues are 26-40℃/km)in profile, the horizontal temperature gradient(1.4℃/m) is by far larger than the vertical temperature gradient (0.16℃/m). Longitudinally, salinity, fO2, pH and fS2 of ore fluid vary regularly. All this implies that the evolution of ore fluid is an important factor causing the skarn and mineralization zoning. Ore fluid flowed gradually from the depth in the southwest of the ore deposit to the shallow place in the northeast. Quite a few high-value areas that appear in the Zn/Pb isopleth map suggest that ore fluids diffused and permeated from the center of the ore vein to both sides. When the ore fluid migrated, its frontal part constantly reacted with the wall rocks to form different types of skarn, accompanied by the evolution of its properties, and the follow-up fluid carried on the reaction with the skarn, forming different types of alterations and ore accumulations. |
