金川铜镍硫化物矿床F1断裂系统演化及其意义

金川铜镍硫化物矿区构造活动频繁且复杂,查明矿区构造规律,是实现深部找矿突破的必经途径之一.文章在充分挖掘区域及以往勘查资料的基础上,通过野外实地调查,对矿区内成矿后断裂系统——F1断裂系统分析研究,发现F1断层角砾岩呈棱角状,深部产状北倾,断层发育在龙首山岩群一侧,无法仅靠现今的叠置关系解释F1的演化.结合潮水盆地研究...

Evolution of F_1 Fracture System in Jinchuan Cu-Ni Sulfide Deposit and its Significance

The Jinchuan deposit is the third largest Cu-Ni sulfide deposit in the world.With the continuous consumption of the proven reserves,the deep resource exploration become crucial for the sustainable development and utilization.The mining area experienced multiphase and complicated tectonic activities,which leads to the highly controversial interpretations of the evolution of the largest F₁ fault in the mining area.Some researchers believe that F₁ is a rock-and ore-controlling fault,which was formed in the Lüliang period,while the others argue that F₁ is a nappe structure,which is a SW-dipped listric fault in the upper crust.Therefore,delineating the structural controls on the ore mineralization is an essential step to realize a breakthrough of deep prospecting.On the basis of fully mining of the previous exploration data and geophysical exploration achievements,combined with the development and evolution of regional structures,the post-metallogenic F₁ fracture system in the mining area is systematically analyzed and studied through field investigation.It is found that the structural breccia of the F₁ fault zone is angular to subangular,with argillaceous cementation,and comes mainly from the Longshoushan Rock Group along with the Quaternary sandy gravel and Neogene sandstone and conglomerate.Two-dimensional seismic profile and other geophysical results show that the occurrence of the F₁fault is steep in the deep part,so it is difficult to explain this phenomenon reasonably and reveal its internal genetic relationship even though it is clear that the F₁fault is a reverse fault according to the superposition relationship.Combined with the research results of the Chaoshui Basin,the authors firstly proposed a possible mechanism for the formation and evolution of the F₁fracture system and its genetic relationship with the Chaoshui Basin evolution.1)The F₁fault and the Chaoshui Basin evolved synchronously,and a series of contemporaneous normal faults were formed in the basin during the early and middle Jurassic rift basin period.During the depression period of the late Jurassic,the basin scale was further expanded,and during the uplift and contraction period from the end of the late Jurassic to Cretaceous,the stress in the mining area changed from tension to compression.Finally,during the Cenozoic extinction period,the stress was transmitted to the Chaoshui Basin through the Yongchang uplift,and the F₁fault was strongly reversed and transformed into a left-lateral reverse fault by the SSW horizontal compression caused by the strong uplift of the Qinghai Tibet Plateau.2)The other fault structures originated(secondary)from the F₁fault were formed under the influence of the unified stress field.F₈ fault is a branch of F₁fracture system,showing‘入’-type structure.3)F₈ has left-lateral translation,which dislocated the tail of the ore body in theⅢmining area.Due to the inversion of F₁and secondary faults in the shallow part,the strata and rock/ore bodies in theⅠ,ⅡandⅣmining areas displaced from SSW to NNE,and as a consequence damaged the rock integrity.The deep part of the ultrabasic rock body is less affected and basically keeps its original emplacement form,which indicates that the deep continuous extension section of the rock orebody is a favorable prospecting area.