Ar-40-Ar-39 dating of phologopite from the Xishimen skarn iron deposit in the Handan-Xingtai area, southern Hebei, and its implications

The Xishimen iron deposit is the largest skarn iron deposit in the Handan-Xingtai area, southern Heibei. The principal ore mineral is magnetite. Ar-40-Ar-39 dating of phlogopite associated with magnetite in ores yields a plateau age of 133.1 +/- 1.3 Ma and an isochron age of 133.6 +/- 2.5 Ma, suggesting an Early Cretaceous age for the formation of the Xishimen iron deposit, which is conssitent with or close to the ages of the porphyrite iron deposit in the Ning-Wu area and skarn iron deposits in Laiwu and Jinling, Shandong. The deposit formed in a tectonic setting of substantial lithospheric thinning.