The Geochemistry,and Geochronology Of The Chagangnuoer Deposit Towards A Genetic Model For Submarine Volcanic Rocks-Hosted Skarn Iron Deposit,XinJiang,NW China

The Chagangnuoer iron deposit is a typical submarine volcanic rocks-hosted skarn deposit,where orebodies occur mainly in andesitic rocks of the Dahalajunshan Formation with skarns well developed around orebodies.This study suggests:(1)Dahalunshan Formation(DF)is a marine volcanic succession and has been identified ranging in composition from basalt to rhyolite.This volcanic succession displays calc-alkaline characteristics.In the Chagangnuoer iron deposits,ore bodies occur mainly in andesitic rocks of the DF.The ore-bearing andesitic rocks have high 87Sr/86Sr(i)(0.7047-0.7117)and ?Nd(320Ma)(0.26-5.09).They probably formed through mixing of basaltic melts and the induced crustal melts.(2)LA-ICP-MS U-Pb zircon ages of 250Ma and 305Ma are obtained for granite and granodiorite in the Chagangnuoer deposit,respectively.These age data indicate that the granitoids have no contribution to skarn alteration and associated iron mineralization.(3)We propose a new genetic model for skarn iron deposits occurred in marine volcanic rocks.It stress that during ascent through the crust,the basaltic magma not only assimilate/contaminate the silicate rocks,but also assimilate the limestones.The limestone would melt directly when basaltic magma intrude into,even if with low CO2/(CO2+H2O).The generated carbonate melts continue to react with basaltic magma and form Fe(?)carbonate complex.Percolation and migration of the FeCO3-fluids toward surface will lead to magnetite precipitation due to decreasing pressure and temperature.