Abstract:1. Kaolinite deposits of Xuyong type in Xuyong area of southern Sichuan are distributed mostly in Xuyong syneclise, lying on the top of the limestone of the Lower Permian Yangsin series or on the discontinuous surface between the Upper and Lower Permian strata. The ore bed seems to occur discontinuously but consistently at the fixed stratigraphic position and is complicated in shape. lts top is flat whereas its bottom is zigzag but closely sutured with the underlying strata. The individual ore bodies look like nests, wormwood or crumpled paper. The ores are quite simple in mineralogic composition, consisting mainly of halloysite associated with gibbsite, hydromica, allophane and, to a much less amount, fragmental quartz, calcite, rutile, limonite, organic matter etc. Among them, calcite fragments increase in the lower part of the ore bed. The ores are also rather stable in chemical composition and are of good quality, containing generally less than l% Fe2O3. They possess a variety of colors: white, black, yellow and red. Their textures range from argillaceous, andy-silty-argillaceous to encrustation-like, often fine at the top and going Jarser toward the bottom because of the presence of relict calcite. They have massive, loose, porous, striped and brecciated structures, the last one appearing mostly in the upper ore bed and bearing the mark of washing out and corrosion. The ores fall into three types according to their colors, textures, structures and composition: 1) red brecciated halloysite; 2) xvhite massive halloysite; 3) black stripecl halloysite. At a typical section from the top downward the three types occur as layers in sequence. The zoning structures of the ore-bearing cross section can be roughly divided into four types on the basis of the degree of their development and the perfection of their preservation. Type I has fully-developed zoning while Type II and III have only incomplete one. As to Type IV, zoning is mostly lacking or could hardly be seen. These types have a lot to do with the thickness of the ore bed, which can reach around Im for the best developed and preserved zoning but is only tens of centimeters or even completely missing for the incomplete one. 2. The limestone immediately beneath the deposit contains insoluble clay and organic matter. Its surface has suffered intense karst corrosion, The ore bed has a stable spatial position with its clay content and chemical composition changing progressively towards the bottom. The underlying rocks have strictly controlled the shape and thickness of the ore bed whereas the overlying rocks have often found their way into the ore bed. At the top of the ore bed, there are brecciated detritus accumulations formed by washing out and corrosion. The ore bed shows zoning and has a transitional relationship with the underlying rocks. From all this one may have the impression that it is unreasonable to ascribe the origin of the deposit to deposition, weathering plus infiltration or so-called eluviation or downhill creep. 3. In consideration of the fact that l) the underlying Maokou limestone bears genetic connection with the deposit, 2) kaolinization develops in direct proportion to the dissolution relict of calcite; 3) there remains in the deposit the pseudomorphism of fossils pertaining to the underlying strata, the author holds the opinion that the deposit seems to be a residual deposit in a fossil crust of weathering on the interface between Upper and Lower Permizm period, but it has been made complicate by the washing out, corrosion and then the hypergene action following the main ore-forming phase and displays the characters of a strata-bound deposit with multiorigins. 4. It is necessary to investigate the effect of fossil crust of weathering and the karst erosion in the distribution of the deposit.
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关铁麟.1982.叙永式高岭土矿床地质特征及其成因的探讨[J].矿床地质,1(2):69~79.1982.A discussion on the geological features and the origin of the Kaolinite deposits of Xuyong type[J].Mineral Deposits1(2):69~79
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