The silicalites dealt with in this paper are a kind of silica-rich rock which occur in the middle Devonian lead-zinc deposits in the Qinling Mountains. They take the form of layer which are conformable with the underlying and overlying rocks. As they are controlled by a syndepositional fault system, the silicalites are distributed in the form of lines. The geochemical properties of Fe, Ti, Al, Mn and other elements are coincident with or similar to those of Iecent and fossil hot water sediments.Moreover, the silicalites are also characterized by lower REE contents,LREE>HREE, apparently negative Ce anomaly and weakly positive Eu anomaly. The hydrogen and oxygen isotope data of the inclusions suggest that the metallogenic fluids forming the silicalites mostly came from the hydrothermal solutions in deep-seated rocks. According to the Doe method, the lead single-stage model ages calculated are mainly between 390--552Ma,older than those of the middle Devonian strata thus also implying that lead was derived possibly from the basement rocks. As main ore-bearing rocks, the silicalites are neither the product of volcanic exhalation, nor the product of marine deposition, but their features are similar to those of the sea-floor exhalogene deposit.