ORE-CONTROL FEATURES OF ARC STRUCTURES AT BOTH ENDS OF THE BAILONGJIANG ANTICLINORIUM OF THE WESTERN QINLING

The hydrothermal gold,uranium,arsenic and antimony deposits in the Bailongjiang anticlinorium of the western Qinling orogen are controlled by fault structures and closely related to magmatism and sub-volcanism in the Mesozoic.Two sets of en echelon arranged arc structures occur respectively at both ends of the Bailongjiang anticlinorium,controlling two highly mineralized areas (HMA) in the south-western Qinling.The Dashui-type gold deposits with gold-bearing jasperoid ores (an oxidation type),and the Lar'erma-type Au-U-Cu deposits with gold and uranium siliceous mudstone ores enriched in organic carbon (a reduction type) in the Maqu-Ruo'ergai Au-U(Cu) HMA in the west,are controlled by the Dashui arc structure and the Langmusi arc structure respectively.The Manaoke-type As-Au deposits,Xiaojinchang-type Fe-Cu-Au deposits,and the Xinguan-type hydrothermal gold deposits in the Zhouqu-Wenxian Au(Cu) HMA in the east,are controlled by the Wudu arc stucture and Wenxian arc structure respectively.As the major ore-control structures,the subsidiary fractures at the apices of the arcs have exerted some important effect on the formation of the two huge gold deposits,the Dashui super-large gold deposit and the Xinguan Lianhecun large gold deposit,as well as on the hypabyssal alkaline intermediate-acid magmatic and continental volcanic rocks which are genetically associated with the mineralization of the gold and uranium deposits.