| Dashui deposit,a typical superlarge gold ore with rich hematite in the western Qinling belt,is hosted in Triassic shallow marine carbonate rocks and strongly controlled by the fault belt.Hydrothermal alteration is mainly characterized by silicification,hematite(and / or limonite)and carbonation,which are associated with gold mineralization,especially the extent of mineralization increasing with intensity of the silica-hematite alteration.There is a close space-time relationship between the gold deposit and granodiorite dikes,some of which can be mineralized directly into the orebody.As we all know,Primary Halo method is one of the most effect ways to explore the blind or deeply-buried ore in the world.In order to discuss deep prospecting potential of Dashui deposit in Gansu Province,based on the understanding of the geological charateristics of this ore deposit,the targeted research of Primary Halos of Au2 orebody in the deposit has been carried out in this paper.Statistical analysis shows that the content of Au,Sb,Ag,As,Hg,U and other elements in the mining area is relatively high,and as a whole the average element content of the Geerkuohe stock is higher than that of the limestone.Geochemical data are typically considered as compositions,which have closure effect.It is necessary to use the log-ratio transform to eliminate this effect of compositional data in order to meet the requirements of statistical analysis of data.And then PCA applied to original geochemical data and log-transformed data,which shows by comparing the results that Au,Ag,As,Sb,Hg,W,Te(Mo,Se)can be regarded as association of ore-forming elements.As a whole,the features of the primary halo concentration zoning of the Au2 orebody show that the anomaly intensity of the front halo elements are more obvious than that of the tail halo elements.The inner,middle and outer concentration anomalies of Au,Ag,Hg,As,Sb,Te,W are obvious and complete,and they also have multiple concentration centers,which indicate that the gold deposit has the feature of superimposed mineralization.In the upper part of Au2 orebody(about 3800 m elevation),superposition or coexistence of the front halo(such as As and Sb)and the tail halo(such as W,Ni,Co and V)in the deposit indicates that upper orebody has been denuded.Significantly,the front halo elements of the gold deposit,such as Hg,Te,As,Sb,developed strong anomalies at the tail(about 3500 m elevation)of the orebody again,resulting from the blind orebody in the depth of the Au2 ore deposit.There is a downward trend for the intensity of Au element concentration centers in Au2 orebody,especially in the elevation of 3500m-3600 m.The axial zoning sequence of Au2 orebody of Dashui gold deposit which has been studied is characterized by zoning in opposite direction,and the ratios of the front halo to the tail halo continue to rise at about 3490 m elevation,which may imply that there could be a good exploration potential in depth below the Au2 orebody.Based on the characteristics of geological and primary halo of Dashui deposit,an ideal model of primary superimposed halo is established to predict the blind orebody,and also the primary halo indicators of prospecting blind orebody are summarized. |
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