Petrogenesis of the Chagangnuoer deposit, NW China: a general model for submarine volcanic-hosted skarn iron deposits

The Chagangnuoer deposit is a typical submarine volcanic rock-hosted skarn iron deposit, where orebodies mainly occur in andesitic rocks of the Dahalajunshan Formation (DF) with skarns well developed around orebodies. The volcanic rocks of the DF in the Chagangnuoer deposit display calc-alkaline characteristics. The ore-bearing andesitic rocks have high 87Sr/86Sr(i) (0.7058-0.7117) and low εNd(t) (−3.51 to 1.67). They probably formed through mixing of basaltic melts and the induced crustal melts. LA-ICP-MS U-Pb zircon ages of 250 and 305 Ma are obtained for the granite and granodiorite in the Chagangnuoer deposit, respectively, which are significantly younger than the timing of the skarn formation (316 Ma). These age data indicate that the granitoids have no contribution to the skarn and associated iron mineralization. This paper proposes a new genetic model for submarine volcanic rock-hosted skarn iron deposits, in which the iron mineralization, skarn formation and volcanic magmatism are necessary aspects of the same system; the iron separates and concentrates from the silicate magma in the form of Fe(II) carbonate complex. While this conceptual model is largely based on observations on the Chagangnuoer deposit, it may have general significance for skarn-type iron deposits associated with submarine volcanic rock sequences and warrants further testing and improvement.