Abstract：Nodular，striped and lump-shaped siliceous rocks of the Permian are primarily distributed in the Maokou and Wujiaping Formations in Xuanhan region， Sichuan Province. The origins of the siliceous rocks have been researched systematically based on their lithological and geochemical characteristics. Field observations about the siliceous rocks suggest that the shape of siliceous rocks is diversified， and they contact with surrounding rocks in line shape. They are controlled by certain position in the section，and the lump-shaped siliceous rocks contain limestone nodules. Thin section analyses suggest the relic texture of calcite and dolomite rhombus pseudomorphic crystal could be found in the siliceous rocks. Field observations and thin section analyses suggest the origin of siliceous rocks is metasomatosis. The major element analysis indicates SiO2 is the main chemical composition(69.61％—99.21％)， others are extremely lower(0.01％—16.07％)， some major element ratios of Fe/Ti，(Fe+Mn)/Ti， Al/(Al+Fe+Mn)reflect the formation of siliceous rocks is associated with the hydrotherm activities， and the samples are projected in the unit where Fe being rich in the Al-Fe-Mn diagram; Some trace element ratios including Co/Ni， V， Ti/V， Th/U， Rb/Sr are relatively lower， and the samples are projected in the unit where Fe being rich in the(Cu+Co+Ni)-Fe-Mn diagram too; The REE(<10×10-6)is lower， Ce is remarkable negative anomalies， Eu is negative anomalies slightly， LREE/HREE is lower and the Eu/Eu* is relatively high. All these features above suggest that there may be hydrotherm participating in during the sedimentary process，and siliceous rocks are formed by metasomasis during the diagenetic process.
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