Study On Mechanisms Of Ore Formation And Primary Dispersion In Grassland-capped Area, And Their Prospecting Application

The middle-southern part of Da Hinggan Mountains is typical grassland-capped area and has good metallogenetic conditions, which is as known as the Nanling of the grasslands. Through the comparison and analysis of the geochemical features of primary halos of three typical magmatic hydrothermal Pb-Zn-Ag polymetallic deposits(Bianjiadayuan,Bairendaba and Huaaobaote), Halo-Forming and metallogenic Mechanism at the grassland-capped area are discussed in this study. The main achievements are listed as following:1. Comparative analysis of ore-forming and halo-forming shows :(1)Ore-hosting structure,hydrothermal fluid property and hydrothermal activities in stages are the main factors for Scale and shape of primary halos. The shape and scale of ore body and primary halos show that the original concentration of Ore-forming materials is higher and the intensity of forming ore and halo is larger in Bairendaba and Huaaobaote. The Bianjiadayuan deposit shows that the ore-forming and halo-forming are weaker relatively. Be restricted by attitude characteristics of structure, Primary halo mainly developed in the hanging wall of ore bodies in Bairendaba and Bianjiadayuan, While it is usually the same in hanging wall and footwall of ore bodies in Huaaobaote. Periodic sedimentation process of ore forming fluids is the main reason that front halo(tail halo) elements appears anti-zoning phenomenon.(2)Characteristic of ore-forming element(Pb, Zn, Ag)content in wall rock, Comparative studies on Pb isotope ratios of wall rock and ore, and structure constraints on the ore forming suggest that metallogenic material weren’t derived from wall rock.(3)With the change in temperature, pressure and other physical and chemical conditions in the process of mineralization, the reason for the variation of correlation coefficients should be the different host minerals for Ag, Sn and other trace elements.(4)Concentration zoning diagram from the exploration line of B-B′ in the Bianjiadayuan deposit and the exploration line 16 th in the Bairendaba western deposit, reflecting the transformation of the late rock(veins) in the preservation process of primary halo.2. Geochemical features of primary halo show that the southeast area adjacent to exploration line of A-A′ may have some buried ores and quartz porphyry body enriched Pb, Zn, Ag, Cu, Sn, Mo and other elements that constrained by exploration line of B-B′ in Bianjiadayuan deposit; the northwest area adjacent to exploration line of 16 in the Bairendaba western deposit may be the center of the ore-forming hydrothermal system, with potential an enrichment to a high temperature element(W, Mo, Sn, etc.) minerals in the deep.3. On the basis of the regional geological characteristics in Bianjiadayuan, Bairendaba and Huaaobaote deposits, combination with the regional geochemical features and deposits(points) distribution, establishing a comprehensive exploration guide of Linxi region(Huanggangliang-Dajing), Bairendaba region and Huaaobaote region.