Metamorphic rock-hosted orogenic gold deposit style at Lakhshak deposit: Their key features and significances for gold exploration in Sistan suture zone

This paper focuses on metamorphic rock-hosted gold mineralization in Lakhshak gold-antimony deposit, lies along the southwestern margin of the Sistan suture zone. The area is occupied by metamorphosed Eocene volcano-sedimentary rocks, Oligocene granitoid intrusion, dikes, and quartz veins/veinlets. At Lakhshak, gold-bearing quartz-veins are hosted by the Eocene metamorphic complex. At least two generations of quartz veins are identified in Lakhshak deposit. The first is parallel to the foliation of the host rock, the second crosscuts the first generation of veins as well as the foliation. Gold grades in the first-stage veins are on average higher than that in the second veins. Ore mineral comprises pyrite, stibnite, arsenopyrite, chalcopyrite, pyrrhotite, sphalerite, native gold, and electrum. The mineralized- alteration zone controlled by NE-SW-trending ductile-brittle shear zone. Fluid inclusions in parallel quartz vein types consist of 4 phases including V-rich, L-rich, L-V-rich and L1-L2-V (CO2)-rich phases. Homogenization temperatures and salinities vary from 200 to 330 ºC and 8 to 13 wt. % NaCl eq., respectively. Microthermometric and Laser Raman Spectroscopy studies of fluid inclusions indicate abundant N2, CH4 ± CO2 fluids. Crush-leach analysis of fluid inclusions suggests that the halogen fluid chemistry is not identical to sea water, magmatic or epithermal related fluids, but tends to be similar to fluids in orogenic-type gold deposits. Based on those key features, gold mineralization in Lakhshak deposit tends to meet the characteristics of orogenic, mesothermal types of gold deposit. Metamorphic rock-hosted gold deposits could represent the new targets for gold exploration particularly in Sistan suture zone.