Structural Evolution And Gold Mineralization Of The Katebasu Gold Deposit In The Western Tianshan,China

The western Tianshan orogen is one of the world's most important gold provinces and hosts numerous world-class gold deposits along the southern and northern margins of the Middle Tianshan.Most gold deposits occur within large-scale fault zones and/or ductile-brittle deformation zones that were formed during the Paleozoic evolution of the Paleo-Asian Ocean,thereby indicating a correlation between orogenic tectonics and gold mineralization.However,the correlation is of great concern and the following questions remain obscure:what kind of deformation controlled gold mineralization and what is the effect of post-mineralization tectonic episode on gold mineralization?The Katebasu gold deposit?89 t@3.84 g/t?in Xinjiang,China,is a large,newly-found gold deposit that is located on the northern margin of Middle Tianshan and is hosted by secondary fault zones to the south of the North Nalati Fault.The main period of gold mineralization is suggested to be the Late Carboniferous,which is broadly coeval with the late Paleozoic collisional orogeny of the western Tianshan.Therefore,the Katebasu gold deposit provides an excellent opportunity to search for possible correlations between deposit structural evolution and regional orogenic processes to better understand the tectonic controls on large-scale gold mineralization in the western Tianshan.In this paper,we report detailed structural mapping and field investigations on the fault geometries and kinematics of the Katebasu gold deposit that permit the inversion of the tectonic stress field.Our structural data,combined with geochronological data and results of previous studies of the regional tectonics,allow us to reconstruct the structural evolution of the Katebasu gold deposit.The first stage of deformation?D₁?was top-to-the-north thrusting that was likely related to the final closure of the South Tianshan Ocean and the resulting collision between the Tarim craton and Middle Tianshan–Yili block during the Late Carboniferous.A roughly N–S compression led to the formation of the secondary ENE–WSW-striking fault–fracture system to control the gold mineralization.The second stage of deformation?D₂?was dextral strike-slip motion along the ENE–WSW-striking faults and conjugate NNW–SSE-striking sinistral faults that were caused by the WNW–ESE stress field.D₂ deformation corresponded to Permian dextral wrenching in the western Tianshan orogen.The third deformation event?D₃?was characterized by the NW–SE-striking reverse faults and NNE–SSW-striking dextral faults by a roughly NE–SW compression,and it was suggested to be a distal response to the Cenozoic India–Eurasia collision.Thermochronological study in this paper and previous geochronological data allow us to perform the inverse modelling of the thermal history and to reveal the post-mineralization tectonic exhumation in the Katebasu gold deposit.The first phase of exhumation was the Late Carboniferous–Early Permian rapid exhumation that was affected by the regional collisional orogeny in the Middle Tianshan.The second and third phases of exhumation was related to the surface erosion.The deposit experienced long-term and extremely slow exhumation from²90.2 Ma to 114.4 Ma and¹14.4 Ma to present-day,respectively.The structural model of the Katebasu gold deposit can be summarized as follows.The Late Carboniferous closure of the South Tianshan Ocean and subsequent collisional orogeny led to the regional N–S shortening and D₁-stage top-to-the-north thrusting took place in the Katebasu gold deposit.It made the North Nalati Fault reactivated to be the first-order structure as passageways to control the gold mineralization and the ENE–WSW-striking fault–fracture system to the south of the North Nalati Fault?hanging wall?became the second-order host structure.The large-scale thrusting allowed the gold-bearing hydrothermal fluids to ascend and migrate,and the ENE–WSW-striking fault–fracture system provided space for the deposition and enrichment of the ore-forming materials,thereby controlling the gold mineralization of the Katebasu gold deposit.