The Shuangxiwu volcanic socks near Xiqiu belong to spilite-keratophyre series, which is chemically rich in Na2O and poor in K20, CaO and contains a lot of albite. Based upon original rock texture, presence of primary albite and evolution patterns of elements, it is shown that the spilite-keratophyre near Xiqiu might be crystalized directly from a kind of spilitic magma. The Xiqiu quartz-diorite is closely associated with the Shuangxiwu volca- nic rocks and intruded into the latter. The age of Xiqiu quartz-diorite given by Rb-Sr isotopes is about 853Ma, initial 87Sr/86Sr in whole rock is about 0.7024. Comparison of major elements, trace elements and isotope compositions, reveals a serial evolutionary trend between the Xiqiu quartz-diorite and Shu- angqiwu spilite-keratophyre. So it is believed that they are comagmatic in origin. The Xiqiu quaitz-diorite, differing from other genetic types in geologic, petrographic and chemical aspects, is surely of mantle-derived granitoid.