Geological Characteristics And Metallogenic Regularities Of The Zhaishang Gold Deposit In Gansu Province

The Zhaishang gold deposit is located in the western part of Min-Li gold metallogenic belt and is an important gold deposit found recently in the western Qinling area.The ore body occurred in the Guoying-Niuchang anticline is divided into the northern and southern ore belt.The northern ore body is in the northern wing of the anticline and the southern ore body is in the core of the anticline.All of the veins associated with mineralization were produced within faults and interlayer fracture zones.There is no large amount of magmatic rocks in the mining area along with the data and results in literature,the mineral deposit might be directly related to the sillite veins.Through this research for mining faults and interlayer fracture zones,it's clear that the ore body of the south mine belt mainly lies in the interface between sandstone(sandy slate)and limestone(calcareous slate),but the north mine belt is located between calcareous slate(carbonaceous slate)and sandstone.The mineralization fracture(interlayer fracture zone)is unique in physics and chemistry,summarized as:(1)the lithological interface was filled with broken rocks and then formed a closed system blocking the transition of ore-forming elements,which led to the formation of enrichment mineral elements-physical interface.(2)Between the siliceous rock and calcareous rock interface,due to the physical and chemical barrier effect,ore-forming elements in fluid were easily deposited.This interface is also known as silicon calcium.Through this research for the allgovite veins,it can be concluded that:(1)microscopic identification and major-trace elements results of the rock type are consistent with field observation;(2)the U-Pb ages of zircon grains from the veins consists 200~350 Ma,400~650 Ma,700~1200 Ma,1800~2050 Ma,and 2300~2600Ma age peaks,coeval with the evolution of continental crust.The youngest age peak of 200~230 Ma represents the formation period of the allgovite veins.Along with the research on the formation mechanism of this deposit and the study of the allgovite veins,we can conclude that the allgovite veins should be formedduring the late Indosinian,approximately at ca.200~230 Ma.In combination with previous studies on the formation period of scheelite and muscovite in ores(220 Ma and 212 Ma),we can basically infer that the intrusion of allgovite veins was accompanied by the first phase of mineralization of Au and W.The age of 125 Ma from dated muscovite in ores was coeval with the large-scale active tectonic period in the Western Qinling area.With the atmospheric precipitation,surface underwater infiltration,and the heat source generated during those tectonic processes,the early formed veins were migrated to the interlayer fracture zone and formed the distribution of Zhaishang gold deposit nowadays.