Study On The Sources Of Ore-forming Materials In The Major Gold-silver-polymetal Doposits In Tongbai County, Henan Province, China

Located in the central part of the Qinling-Dabie orogenic belt and the east of the Nanyang basin, Tongbai county in Henan province is one of major gold-silver-metallogenic provinces in China. The regional geologic background and mineral deposit geology of the Poshan silver deposit, Yindongpo gold deposit , Liushanyan copper-zinc deposit and Laowan gold deposit were concluded in this thesis. Meanwhile, the sulphur and lead isotopic data, both from the former analysis and this study, of the strata, intrusives and ore bodies in the study area were systematically analyzed and discussed in order to identify the sources of the ore-forming materials.Situated at the northern part of the Weishancheng gold-silver metallogenic belt in the study area ,the Posan silver deposit and Yindongpo gold deposit are both controlled by the strata and structures. The ore bodies in Posan silver deposit occur in the monoclinal strata which constitute the southwest wing of the Heqianzhuang anticline, and the host rocks are composed of carboniferrous sericite-quartz schist of the second segment of the upper part of the NeoproterozoicWaitoushan Formation. The ore bodies of the Yindongpo gold deposit occur in the axis of the Heqianzhuang anticline and the bedding-plane shear belt, and the host rocks consist of carboniferrous sericite-quartz schist of the third segment of the middle of the Neoproterozoic Waitoushan Formation.Theδ³⁴S(‰) values in these two deposits range from 1.0 to 6.8, and are characterized by the tower effect. It indicates that the sulphur was derived from the deep earth. Meanwhile, the lead isotope composition of the ore in these two deposits is similar to their host rocks, which is typical of epimetamorphic rocks relatively rich in Th. Therefore, it is suggested that the sources of ore-forming materials were mainly derived from the wall rocks of the Neoproterozoic Waitoushan Formation.The Liushanyan copper-zinc deposit lies in the compresso-crushed zone between the Heqianzhuang anticline and the Aoziling inverted syncline. Its country rocks are composed of spillite-keratophyre, metamorphic tuff and breccia of the LiushanyanFormation. Theδ³⁴S values of the sulfides from the Liushanyan deposit range from -1.40‰to 13.3‰, with the average of 3.87‰. whileδ³⁴S values of two barite samples are similar with that of seawater. The homogeneous lead isotope composition are plotted along the mantle evolution line. It indicates that the sources of ore-forming materials are from the country rocks of the Liushanyan Formation and seawater.The ore bodies of the Laowan gold dopisit occur in the NW-trending Laowan ductile shear zone between the Songba fault and the Laowan fault. Their host rocks consit of plagioclase-amphibole schist, quartz schist and granulite of the Mesoproterozoic Guishan Formation. The sulphur isotope composition of the ore and host rocks is similar, which mainly varies from 3‰to 5‰. So the sulphur of the ore may be derived from the host rocks of the Mesoproterozoic Guishan Formation. In the lead-tectono model, the dots of the ores are located between those of host rocks the Laowan granite,which implies that the sources of ore-forming materials are both from strata and granite.