小寺沟位于燕山台褶带张家口-平泉-北票断裂带南侧及其派生的共轭断裂之间。断裂带北盘为太古界迁西群片麻岩,南盘为中上元古界和古生界碳酸盐及中、新生界火山沉积建造。斑岩体呈小岩株侵位于蓟县统雾迷山灰岩中,岩体走向310°—330°、倾向南西倾角60°—80°,出露长5公里、宽1—1.5公里(图1)。岩石 Xiaosigou is located between the Yanshan platform fold Zhangjiakou-Pingquan-Beipiao fault south and its derived conjugate faults. The north plate of the fault zone is the Qianxi Group gneiss in the Archean. The south plate is built in the middle-upper Proterozoic and Paleozoic carbonates and Meso-Cenozoic volcano deposits. The porphyry body was intruded in the small fog rock magma in Jixian. The rock mass is 310 ° -330 ° with a dip of 60 ° -80 ° to the south and west, with a length of 5 km and a width of 1-1.5 km (Figure 1) . rock