Protolith reconstruction and its significance in the search for the ore-hosting metamorphic rock series in Hekou Group, the Lala copper orefield, Sichuan Province

The Lala copper deposit in Sichuan is one of the large copper-rich deposits in China.The ore bodies occur in the metamorphic rock series of the Hekou Group, and have typical stratabound characteristics.Therefore, the protolith reconstruction of this metamorphic rock can better define the genesis of the deposit and also provide directions for the next ore prospecting in this area.A series of geological and geochemical studies of its ore-bearing metamorphic rocks indicate that the original rocks are a set of argillaceous siltstone-spilite rock associations which were formed in an intracontinental rift of passive continental margin.The protoliths of biotite quartz schist, muscovite quartz schist and two-mica quartz schist are pelitic siltstone, while the original rocks of quartz albite, metavolcanic breccia and metavolcanic tuff are spilite.Based on the stratabound characteristics of stratiform as well as lenticular orebodies and diagenetic-metallogenic ages available, it is concluded that the deposit exhibits early VMS copper mineralization.Compared with the rock types of host rocks of different types of VMS deposits, Besshi type is considered to be of the early copper mineralization type.At last, the interface between mafic volcanic rocks and siliceous clastics in this region should be the direction of further prospecting work.