Elemental Features Of Geogas Over Polymetallic Deposits And Its Significance For Mineral Exploration In Qilian Basin, Qinghai

Geogas survey, which emerged at the end of the 20th century, is a new geochemistry method and technique for concealed mineral deposits in geochemistry.Many Exploration geochemistrists has paid much attention to this new method because of its possibility of being widely used in the future. This paper mainly organizes and analyzes geogas observation data in Black River Basin in Qilian, Qinghai province in recent years (Bailiugou in 2004, binggou in 2005, fuomisi in 2006). In order to provide theoretical bases for anomaly interpretation and to raise anomaly interpretation level, this paper tries to find the relationship between geogas anomaly and different geologic body especially deep orebodies by making comparisons between the elements' characteristics of VMS deposits' anomaly area and the elements' characteristics of background area.It can be concluded:1. After the long-term bid in recent years,obversational accuracy has been improved, especially in the area such as the blank control, the capacity to catch metals, and reproductivity of geogas observation.2. According to the suvey data inBlack River Basin, the writer discovered the regularity of multi-element geochemical anomaly and the similarities between element association and known orebodies. This implies that there is the possibility of large-scale polymetallic mineralization of in this area.3. According to the consequences of factorial analysis, the elements in geogas are obviously related to one another. Polymetal factpr and gold factor and ore-enchiching element are consistent with each other, and it demonstrate that the two has causal relation.4. Ore and wall rock are obviously different from each other and ore contains less proportion of REE. But in geogas anomaly area and in background area, the geogas' distribution model of REE is similar. This distribution model belongs to light REE enrichment model and most of it has Eu loss. However it is strange that in anomaly area geogas' REE content is higher and changes in a large scale. The reason is that it may be relevant to the geogas genetic types.5. According to the survey in wall rock, ore, and geogas trace elements spider, in the survey area geogas anomaly area and geogas background area 's distribution model is similar, so it is difficult to differentiate anomaly area's sample and background area's sample. But from the proportion of elements point of view, element content in anomaly area is higher than background area, which is just contrary to the content of wall rock and its reason is still under study.6 According to wall rock, ore, geogas mineralized element spider, the distribution model of geogas anomaly area and geogas background area has large disparity. Geogas anomaly element content is high and is near ore's distribution model, especially Cu, Zn , Ag, Pb is rich. All this proves that geogas anomaly element may come from deep orebodies.7. In guomisi geogas, Zn ans Cd has notable positive correlation. According to Zn/Pb-Cu/Pb ratio chart, the samples in anomaly area and background area can be clealy divided. Thus geogas element assemblage ratio can be used in anomaly interpretation.