Two episodes of orogenic gold mineralization at Chaihulanzi, NE China, in response to superimposed orogeny associated with subduction of the Paleo-Asian and Paleo-Pacific Ocean plates

Abstract Detailed structural studies and dating of mineralization define two discrete gold mineralization events during formation of the Chaihulanzi gold deposit. This complexity in gold mineralization resulted from overlap of two distinct orogenic events on the northern margin of the North China Craton. The earlier gold lodes are hosted by NW-SE–trending thrusts and ENE-WSW–trending extensional faults that formed under far-field sub-horizontal NE-SW–trending compression. These lodes comprise pyrite, pyrrhotite, chalcopyrite, sphalerite, tellurides, and native gold associated with quartz-sericite alteration. The later gold veins are controlled by steeply dipping NW-SE– and NE-SW–trending faults that formed under far-field sub-horizontal E-W–trending compression. These veins comprise pyrite, pyrrhotite, and native gold associated with quartz-carbonate or quartz-sericite alteration. The quartz in the earlier and later veins has c-axes with preferred orientations that are sub-parallel and sub-perpendicular to the ore-controlling fault plane, respectively. U-Pb ages of magmatic zircons from the diorite and granite that host later gold ores are dated at ca. 265 Ma. In situ U-Pb dating of hydrothermal rutile and monazite intergrown with gold-bearing pyrite in both earlier and later auriferous quartz veins indicates that the two gold events were at ca. 290 Ma and ca. 170 Ma. These two discrete gold events are related to crustal shortening during subduction of the Paleo-Asian oceanic plate and crustal rotation during subduction of the Paleo-Pacific oceanic plate. The recognition of two gold mineralization events that occurred more than 100 m.y. apart in the Chaihulanzi deposit has implications for district-scale gold exploration in tectonically complex terranes.