The Origin of the "Changcheng Type" Gold Deposits in East Hebei
冀东“长城式”金矿的成因探讨

Based on geologic characteristics, ore forming material sources and modes of occurrence of "Changcheng type" gold deposits, this paper deals mainly with the genetic mechanism of such deposits. Studies of regional geological and metallogenic features show that North China region entered the stage of mantle branch structure activity in Yanshanian period, and strong activation occurred along EW striking Maoshan Jinchangyu Xiaoyingzi ductile shear zone and NNE striking Qianan qinglong ductile shear zone in East Hebei. Large scale magmatic intrusion took place at the intersection of the two ductile shear zones, forming Xiaoyingzi porphyritic granite as well as a series of big and small intrusive bodies. At the same time, intensive uplifting of this area resulted in the outcropping of the magmatic metamorphic complex along the axis and the detachment of Mid-Upper Proterozoic covers. The activity of Lengkou fault or reversed listric faults formed fault step and caused the Lengkou Qingheyan fault block to remain as the Mid Upper Proterozoic remnant block over magmatic metamorphic complexes. The main and second detachment belts as well as interformational faults were formed during the gliding of rock masses, and became well developed structural expanding space. Therefore, the ore bearing fluids migrated up, injected and aggregated along these structural expanding belts during the main metallogenic stage, forming a series of structural altered type and vein type deposits. This recognition has been confirmed by deep drill holes in the Xinfangzi gold field. The widening and enrichment phenomena at the top of the orebody is the shallow expression resulting from collapse and leaching during the upward migration. Thus, special attention should be paid to the search for deep orebodies.