Sedimentary Environmental Analyses Of The Lower Cambrian Shuigoukou Formation Black Rock Series In Xichuan, Henan

The black rock series is an enriching layer of important polymetallic elements aswell as significant ore-bearing formation of large-superlarge scale deposits. Xichuan islocated in a significant silver-antimomy-vanadium polymetallic ore zone on the eastpart of Qinling orogenic zone of the northern margin of Yangtze Plate. Black rock seriesis well developed in the Lower Cambrian Shuigoukou Formation in Xichuan, which isthe major ore-bearing stata of large scale vanadium-molybedenum deposits. Theanalyzing of sedimentary environments of black rock series of Shuigoukou Formation isof obvious significance in both the metallogenetic research and prospecting practice.Combined means of geochemistry and sedimentology is implemented in black rockseries studies in Shuigoukou Formation. Primary analyses of Sedimentary environmentsand metallogenic responses are conducted on the basis of the above achievements.Geochemistory analyses of major elements and trace elements of34samples in6sections of Shuigoukou Formantion in Xichuan show that trace elements V、Cu、Zn、Sr、Ag、Ba et al. are highly concentrated. Negative anomalies of Ce and Eu occur inREE diagrams. These, together with some element ratios, have showed that thesedimentary provenence includes amount of hydrothermal deposition besides contenitalsources. The sedimentary environments include the transitional regions from thecontinental margin to the pelagic deep sea. Ore deposits in black rock series aremulti-sourced with the synchronous deposition of hydrothermal and normal sediments.Besides, organisms and ocean currents provided vital condition for the organic matterconcentration.Based on the previous combined geochemical results and sedimentologicalanalyses, we suggest the tectonic position of Xichuan in Cambrian should be thetransitional regions from the northern margin of Yangtze Plate to the Qinling troughwith a sedimentary system of a continental margin sea. Sedimentary facies are furtherdivided into three types according to the depositional assemblages and lithologicalfeatures-confined basin facies, marginal sea slope facies and neritic shelf facies.Sedimentary environments evolved in the early Early Cambrian from the neritic shelf tothe confined basin, and then to the marginal sea solpe when the Shuigoukou Formation has formed. The black rock series formation can be considered as a moderate cycle fromtransgression to regression. Metal-bearing black rock series occur at the beginning ofevery small transgression-regression cycle. On the one hand, reducing and oxygen-poorbathyal environments which the study area were right in in early Cambrian constitudethe basic conditions for the formation of black rock series; on the other hand, kinds ofmetal element, SiO2colloform and nutrient salts carried by transgression and oceancurrents nourished organisms, which then give birth to abundant metarials. All of themcomposed vital basement to the enrichment of large scale of deposit in black rock series.