Abstract: The Cambrian silicalite formation,composed of bedded chert and slate, is the host rock of Laerma and Qiongmo gold deposits in western Qinling. The presence of the typical chert offers an important evidence to evaluate the possible submarine exhalative system and its controls over the formation of gold deposits. The ore bearing chert is characterized by massive, banded, laminated, porous spherulitic and pseudobrecciated structures which changes regularly in space. The thickness of a chert bed generally varies from 30 to 200 meters. It contains principally SiO2 (95.30% on average), with FeO, Fe2O3 and organic carbon greater than 1.0%. The ratios of Al/(Al+ Fe+Mn) in all chert samples are lower than 0.3 (0.153 on average). The chert is enriched in most trace elements, which is characterized by not only the basic and ultrabasic elements group (e.g. Ag, Pt, Pd, Cu, Cr)but also the acid elements group ( e.g. W, Mo, U ). Rare-earth are characterized by a low total contents (ranging between 3.29× 10^-6 and 100×10^-6), negative Ce anormaly and a gradually increasing NASC-normalized value with increasing atomic number δ18O Values of chert mainly vary from l7.6O‰ to 23.24‰ (19.17‰ On average), suggesting that the tempreature for deposition was from 70℃ to 118℃, δ30Si values of the chert in the area range mainly from +0.4‰ to +0.8‰. All the geological and geochemical characteristics show that the chert is a product of submarine exhalative sedimentation. During the submarine exhalative sedimentary period, the silicalite formation and mineralization of some elements were all formed.