| Abstract:The Xianghualing orefield, a well-known rare and nonferrous metals orefield in South China, is noted for its very typical metallogenic zoning in the depressed area of Nanling region. In the orefield, the intrusion of three granite stocks into Cambrian sandstone and Devonian carbonate rocks along the intersections of NE-trending and NW-trending faults resulted in the formation of three corresponding mineralization districts. Around the ore-bearing granite bodies, different types of ore deposits are in regular zoned distribution as follows: Nb-, Ta-deposits of magmatic type in the upper part of the granite bodies and W, Sn(Be)deposits of greisen type at the top of the granite bodies→Sn, W, Be deposits of metasomatic type near the contact zone→Sn, W deposits of metasomatic-hydrothermal type at the exocontat zone→Pb, Zn deposits of hydro- thermal type far away from the contact zone, with the correponding zonation of metallogenic elements being REE, Nb, Ta, Sn, W(Be)-Sn, W, Be-Sh, W(Pb, Zn)-Pb, Zn-Pb, Zn, Sb(Ag). In the same ore deposit, the differences in ore-controlling structures and lithologic characters of the wall rocks have led to the regular upward variation of the orebody shapes from stratoid through pipe-like to veinlike. In addition to the lateral zoning of metallogenic elements within an ore deposit, such as the zoning of Sn(W) →Sn, Be(W) →Sn, Pb, Zn→Pb, Zn, Sb in the Xianghuajing tin polymetallic deposit, the concentration position and extent of the major elemerits also show regular variation with the change in ore-controlling structures and the distance from the granite body. The ore-forming processes of the tin-polymetallic ore deposits might be divided into four main stages which gave birth to eight sorts of mineral asselublages. During the mineralization, the metallic minerals were precipitated approximately in order of oxides-sulfides-sulfosalts. The early stage mineral assemblages are distributed near the granite contact zone, while the late stage ones occur somewhat away from the contact zone or are superimposed on the early ones. In ore minerals, the cassiterite magnetite, sphalerite and galena, which were formed at different stages, also display certain regular variation in their major element contents. The authors consider that the repeated structuraj and magmatic activities must have been the major factor leading to the metallogenic zoning in the area in that these activities not only caused the formation of vertical and horizotntal zoning for structural elements and their combinations, but also stimulated the repeated pulsating diffusion of ore fluids towards the fatflts and fissures. The evolution of the properties of ore fluids seems to be another factor causing the formation of metallogenic zoning. From the early ore-forming stage to late, the temperature and salinity of the ore fluids decreased gradually, accompanied by corresponding variation in acidity and chemical potential of the volatiles. Ore fluids with differnt properties precipitated corresponding distinct mineralassemblages. These assemblages are arranged in order of time and space and thus make up the metallogenic zoning that we see today. |
