Structural Networks Constraints on Alteration and Mineralization Processes in the Jiaojia Gold Deposit, Jiaodong Peninsula, China

Abstract

Structural network studies could give appropriate opportunities to understanding structural/hydrothermal events, transportation of ore-forming fluids and water/rock interaction process. Four structural deformation/hydrothermal events have been identified in the Jiaojia fault zone according to microtexture and deformation of quartz and feldspars. Plagioclase experienced ductile deformation period with bended polysynthetic twin stripes (>450 °C) in the early stage, followed by K-feldspar alteration period with ductile-brittle deformation and subgrain rotation recrystallization of quartz (380–450 °C). Then, sericitization period occurred extensive ductile-brittle deformation (350–420 °C) and extensive subgrain rotation recrystallization with a little bulging recrystallization in quartz. In the last, gold precipitation-related pyrite-sericite-quartz alteration was dominated by brittle deformation (300–380 °C) and total bulging recrystallization of quartz. From the K-feldspar alteration zone and sericitization zone to pyrite-sericitequartz alteration zone, fractal dimension values of dynamically recrystallized quartz grains increase from 1.07 and 1.24 to 1.32, the calculated paleo strain rate values of dynamically recrystallized quartz range from 10−10.7 (380 °C)−10−96 (450 °C) and 10−9.3 (350 °C)−10−82 (420 °C) to 10−9.5 (300 °C)−10−80 (380 °C), and the paleo differential stress values increase from 36.9 and 39.3, to 121.3 MPa. The increase of fractal dimension values and decrease of grain size from pyrite-sericite-quartz alteration zone and sericitization zone to K-feldspar alteration zone decreased average water/rock ratio values, which could lead to different acidity and redox conditions of ore-forming fluids and mineralization differences. Two kinds of orecontrolling fractures have been distinguished which include the gentle dip types (18°–50°) with NW (315°–355°) and SW (180°–235°) dip hosting No. I orebodies and the steep dip types (74°–90°) with NE (45°–85°) and SE (95°–165°) dip hosting No. III orebodies. These faults/fractures crosscut altered Linglong granite of footwall of the Jiaojia fault zone as rhombohedrons that promoted the connection between fractures in the K-feldspar alteration zone and fluid flow passages near the main fault face. Research results indicate No. I and No. III orebodies should be derived from the same mineralization event and belong to different orebody types in different mineralization sites under the same structural networks.