Geology and geochemistry of Lower Paleozoic albitite in the Xunyang basin, South Qinling

Abstract：Hydrothermal sedimentary albitite in the Upper Paleozoic in the South Qinling is closely related to many large-superlarge lead-zinc deposits in the south Qinling orogenic belt． Recently, a nearly E-W-striking, over 10 km long albitite zone has been recognized for the first time in the Lower Silurian Meiziya Formation in a Lower Paleozoic lead-zinc ore deposit concentration area of the Xunyang basin, South Qinling. It shows a conformable contact and gradational relationships with the country rocks and has thick-bedded and massive, banded, brecciated structures and fine and very fine equigranular and intraclastic textures． It is chemically characterized by enrichment in SiO2, Al2O3 and Na2O and is rich in the trace elements Fe and Mn and poor in the trace elements Co, Ni and Cu. Its ∑REE, LREE and HREE are lower than those of the country rocks and exhibit pronounced Eu depletion. The chondrite-normalized REE distribution patterns are inclined to the right. In comparison with the petrography and petrochemistry of hydrothermal sedimentary albitite in the Devonian of the Qinling, combined with the fact that its Lower Paleozoic belongs to a passive continental-margin rift environment on the northern margin of the Yangtze plate，the authors think that the Lower Paleozoic albitite in question is probably of hydrothermal sedimentary origin.