Analysis of ore-controlling structure in the Qifengcha-Detiangou gold deposit, Huairou County, Beijing

The Qifengcha-Detiangou gold deposit is a medium-sized deposit recently fou nd in Huairou County, Beijing. It belongs to the altered mylonite type with superimposed quartz vein type and is related to the early Yanshanian magma tic activity. Characterized by multiperiodic activity, the NE-trending Qife ngcha fault is a regional ore-controlling structure in the area, and gold m ineralization develops only in its southeastern part. Meanwhile, gold miner alization is controlled by the Yunmengshan metamorphic core complex. The ne arly N-S- and E-W-trending low-angle detachment faults, reformed by the Qif engcha fault in the northwestern part of the core complex, are the main ore -bearing faults. All discovered gold deposits are located within an area 1. 5-4.0 km away from the boundary of the upwelling centre. The N-S- (NNE-) an d E-W-trending ore-bearing faults are ductile-brittle structural zones deve loping in shallow positions and subjected mainly to compressive deformation . The structural ore-controlling effects are as follows. (1) The attitude, shape, and distribution of gold orebodies are controlled by faults. (2) The re is a negative correlation between the gold abundance and the magnetic an isotropy CP) of the altered mylonite samples from the deposit, which shows that the gold mineralization is later than the structural deformation. (3) Quartz vein type mineralization is superimposed on altered mylonite type mi neralization. (4) In mineralized mylonite, the stronger the ductile shear d eformation, the easier the late-stage gold mineralization to occur and the higher the gold abundance. The richest gold mineralization occurs only arou nd the centre of the fault subjected to the strongest deformation.