REGIONAL GEOLOGICAL SETTINGS OF THE SOUTH CHINA AND SANJIANG-SOUTHEAST ASIA TUNGSTEN-TIN METALLOGENIC BELTS AND COMPARISON OF THEIR ORE-FORMING PROCESSES

The South China and Sanjiang（the Lancang,Jincha and Nujiang Rivers region）-Southeast Asia tungsten-tin metallogenic belts are both located in a Sinian-Paleozoic or Paleozoic depression belt sandwiched between two oldlands. The South China metallogenic belt was a miogeosynchie in the duration between Sinian and Early poleozoic,which underwent strong Caleclonian movement, indicated by a distinctive angular unconformity between the Devonian to Middle Triassic platform-type sedimentary cover and the underlying folded basement. The Sanjiang-Southeast China tungsten-tin metallogenic belt was mainly represented by geosynclinal sediments from the early Paleozoic to Late Carboniferous,while in the Early Permian it was mainly marked by the platform-type carbonate formations.It and the underlying strata exhibit a successive transitional relation,that is,the geosyncline“passed peacefully to”a platform.This is quite different from the case in the South China metallogenic belt.The end of the mesozoic was an epoch of the culmination of the activity of granitoids as well as the Main epoch of tungsten and tin mineralization of the two belts. it has been proved that in the South China metallogenic belt the granites of the crustal anatectic type and the mixed （mainly mantle-derived）anatectic type are both associated with tungsten and tin mineralizations,with the former predominating.The Tungsten and tin mineralizations are of equal important significance.Tin deposits consist mainly of tin-sulfide deposits,and skarn-type tin-bearing magnetite deposits are also well developed.In the deposits the principal tin mineral is cassiderite,but in some deposits the manner of tin occurrence is rather complex.The mineralizations of the Sanjiang-South China metallogen- ic belt are mainly associated with the crustal anatectic granite,with tin mineralization predominating.The overwhelming majority of the tin deposits are the tin-quartz deposits,while the tin-sulfide deposits are not developed. The principal tin mineral is cassiderite.The intensity and scope of the tungsten and tin mineralizations in the two metallogenic belts are proportional to those of the metasomatism and alteration of the cations of alkali metals and anions （groups）such as F.（B0₃）and（OH）.The differences in mineralization between the two metallogenic belts are mainly due to the heterogeneity of the continental crust:i.e.the difference in the regional geological settings in which the belts are located.