The Main Characteristics and Age of Xiaozhangjiakou Ultrabasic Rocks in Chicheng County, Hebei Province
河北省赤城县小张家口超基性岩体主要特征和时代

Xiaozhangjiakou ultrabasic rocks is the host rock of gold deposit, mainly consisting of pyroxenide rocks, including pyroxenite, pyroxene-peridotite, hornblende- pyroxenite and diopsidite, etc. Their petrochemistry is charaterized by the richness of FeO and CaO and the poorness of MgO (m/f=2. 21), belonging to the ferruginous ultrabasic rocks. They are of LREE-enriched REE distribution pattern, They are rich in incompatible elements such as Rb, Ti, Sr, V and poor in compatible elements such as Cr, Ni, Co etc. Petrological, geochemical and isotope geochemical evidences indicate that the rocks are the products of differentiation and crystallization of magma which was derived from the partial melting of the depleted mantle. Sm-Nd isochron analysis shows that the age of the ultrabasic intrusive rocks is 1837 Ma, the mid-Proterozoic.