The Primary Halo Characteristics And Metallogenic Prediction Of The Zhaishang Gold Deposit,Gansu

Located in the western part of the Min-Li metallogenetic belt, western Qinling Mountains, the Zhaishang gold deposit is a ultra-large Carlin-like type disseminated gold deposit. The deposit occurred in the Middle Devonian and Lower Permian. The veins mainly distributed in core and wings of Zhuo-Zha anticline had traditionally been divided into the north and the south metallogenic belt, where gold mineralization was controlled by faults, and the ore(halo)-forming processes were characteristic with several metallogenic stages superimposed. On the basis of field geological work, we used the methods of geo-mathematic and geochemical theories to study the geology, elements distribution and the primary halo in the Zhaishang gold deposit, and got conclusions as follows:1 With the methods of geo-mathematic analysis and the calculation of the background values of the elements of Zhaishang gold deposit, we concluded that the anomalies of Au, As, Sb could be related to ore-forming process of gold, and were the obvious, direct and effective prospecting criteria for gold deposit. The data ascertained from the factor models of 10 th ore vein and 32 nd ore vein suggested that superposition of Au came from two main hydrothermal stage, and the associated elements, like As, Sb, Ag, Pb, Zn, etc, were precipitated in different positions at the same time.2 According to the calculation of zonality index, the primary halo axial zoning sequence of 10 th ore vein was Zn-As-Pb-Au-Ag-Sb-Mo-W, and the primary halo axial zoning sequence of 32 nd ore vein was Zn-Ag-Sb-As-Mo-Au-Pb-W. The results showed that the front halo elements were Sb, As, the near-ore hole elements were Au, Ag, Pb, Zn, and the rear halo elements were W, Mo. In ore veins, there were two ore bodies with different types of superpositions in different exploration lines and altitudes. It was speculated that upper ore body was formed in arsenian pyrite-arsenopyrite-quartz stage and lower ore body was formed in polymetallic sulphides-scheelite-quartz-carbonate stage since As element abnormity mainly showed at the first middle, but Ag, Sb, Pb, Zn element abnormities were found at all middles.3 Combined with the change rule of geochemical parameter, we built the ideal models of the primary halos superposition zone of the 10 th and 32 nd ore veins. Three prospecting target areas were pointed out, including the areas of 10 th ore vein below the altitudes of 2350 m in the 100 th exploration line and 2300 m in the 108 th exploration line, and the area of 32 nd ore vein at altitude of 2550~2300m in 79 th exploration line.