The Primary Halo Characteristics And Deep Prospecting Of Dashui Gold Deposit In Maqu, Gansu Province, China

The national industrial economic development is closely related with the mineralresources, but the ensuing situation of resources shortage will also become more andmore serious. As a result, strengthen the mineral resource exploration and makebreakthroughs is of great significance. Because it has become more and more difficultto prospect by the macroscopic signs directly, how to use the deep microscopicinformation to look for concealed ore is a key consideration in future geological work.The lithogeochemical prospecting, that is, the primary halo method, is a means ofprospecting by extracting the microscopic information of elements. A number of goldexplorations demonstrate that studying the zonation of primary halo is an effective wayof assessing anomaly distribution, geochemistry, denudation degree; searchingconcealed ore body, evaluating potential at deep and making ore prediction.Dashui Gold Deposit in Maqu, Gansu Province is of very high economic valueowing to its unique mineralization characteristics and high grade during the past20years’ mining. As the grade has sharply declined, the whole mine is requested toachieve results in searching concealed ore bodies. The primary halo work carried out inNo.77exploration line before has been proved that it can get the information ofanomaly distribution, primary halo geochemistry and ore-bearing potential at depth ofthe research profile. While there is few application example of primary halo method inthe mining area, carrying out the research and application of primary halo in DashuiGold Deposit, are of great significances in identifying the element associationcharacteristics, the relationship between element anomaly and ore forming process,searching new ore bodies, assessing mineral resource at depth and developing thewhole mine. It can also provide the scientific proof and theoretical support for further exploration.On the basis of lithogeochemical prospecting theory, Grigorian Zoning IndexMethod was used to calculate the axial zoning sequence of primary halo of No.70exploration line profile. Combining with the anomaly distribution of trace elements andthe element association characteristics, characteristics of the hangingwall and footwall,the geochemical parameters had been studied. Then a preliminary prediction was doneon the denudation and extending degree of the ore body. Finally the prediction modelhad been established to perform the mineral resource assessment at depth.Basing on the most suitable indicating element association for gold depositprimary halo summarized by predecessors’ work, and combining with the traceelements correlation analysis results of ores and wall rocks of Dashui Gold Deposit, Au,As, Hg, Sb, Bi, W, Mo, Co, Cu, Pb, Zn, Ag, Mn was finally selected as the generalindicating elements for content Analysis in the research area.The the axial zoning sequence of primary halo of No.70exploration line profile,from top to bottom, had been calculated by the improved Grigorian Zoning IndexMethod. The result is: Mn-Pb-Cu-Co-Bi-W-Ag-Au-Mo-Hg-Sb-Zn-As.According to the results of correlation analysis, R type cluster analysis, factoranalysis, the ore forming of Au has relative independence, and it appears obviouslinear relationship with As, Sb, Hg. Because Sb is closely related to Au, the anomalydistribution of it can be used as the main evidence of the hanging wall development toestimate the enrichment range of Au.Through the element anomaly contour map it can be indicated that the highanomaly area of Au concentrate near3645m middle section. The anomalydistributions of typical hanging wall elements have broad ranges from top to bottom;and most footwall elements’ anomalies are well developed except Co. The near-orehalo elements Pb and Zn have a broad anomaly distribution while Ag rarely appearsan anomaly.The geochemical parameters of No.70exploration line profile demonstrate thatthe best developed location of ore body concentrates in the range of3605-3645mmiddle section. Below3605m middle section, the denudation degree enhanced withan obvious development of footwall characteristics meanwhile some parametersincrease slightly. So it can be estimated that there might be concealed ore body with asmall range at depth.After the establishment of primary halo axial zoning anomaly model of No.70exploration line profile, it can be concluded that there is superposition of at least two ore bodies; the best developed location of the ore body is near3605-3645m middlesection, and the footwall is still extending downwards with a small range of hangingwall developing in the bottom level. Along the dip of the ore body there is a smallrange of potential at depth.