| Prospecting geochemistry is an exploration method to find and evaluate thegeochemical anomaly and delineate the perspectives and prospecting target area byinvestigating the element distribution of elements in geologic bodies. Thedetermination of anomaly threshold is not only the basic research contents but also thecritical issue in e×ploration geochemistry. The thesis, on the basis of the data ofstream sediment surveying in Helong from East Jilin province, presents thecomparisons of anomaly thresholds determined by traditional method, fractalconcentration-area method and fractal concentration-number method, followed bycomparisons of plural anomalies delineated by the factor score method andsuperposed with individual anomalies, so as to get some simple, fast and accurate dataprocessing methods of regional geochemistry, and provide scientific support forreasonable delineation of anomaly and selection of ore exploration perspectives.The research area is located in Helong from the eastern part of Jilin province.The natural landscape of this area is of alpine forest one. The climate of this area is ofthe temperate continental monsoon one, the seasons are distinct. The geologicalsetting of the area is located in the intersected zones between the east section of NorthChina platform and the Jihei orogenic belt, and also in superposed zones between thePal-Asian tectonic domain and the Pacific ocean tectonic domain. The strata occurredin the area dated from the earlier to the later are Neo-Archaen, Neoproterozoic,Permian, late Triassic, early Jurassic, intermediate Jurassic, Cretaceous, and Cenozoic,respecticely. Magmatic rocks within the area are Hercynian-Yanshanian granitic rocks.Metamorphic rocks in the area are mainly Archaen Jinan lithologic unit composed ofbiotite plagioclase gneiss magnetite amphibolites, magnetite quartzite, andNeoproterozoic xindongcun lithologic group composed of Changren marbles, meta-siltstone, phyllite, schist, etc.2021stream sediment samples are collected in research area, Cu、Pb、Zn、Au、Ag、W、Mo、Co、Ni、As、Sb、Bi、Hg in each sample are tested, and26273concentration data are obtained. The distribution of elements in stream sediments andthe correlations among elements are investigated with SPSS16.0. It is shown that theaverage content of elements from least to most areZn>Pb>Ni>Cu>Co>As>Mo>W>Sb>Bi>Ag>Hg>Au; the element concentrationcoefficients are Sb>As>Mo>Bi>Pb>W>Au>Zn>Co>Cu>Hg>Ni>Ag；the elementvariation coefficient are Ni>Hg>Zn>As>Mo>Cu>Co>W>Au>Pb>Bi>Pb>Sb>Ag。The correlation coefficient between Co and Ni is the biggest, up to0.769, thatbetween Co and Cu ranks second, up to0.737, and that between Co and Zn ranks third,up to0.705. Mo has the negative correlations with Ni、Co、Pb、Au, and correlationsbetween Mo and Sb、Zn、Hg, Bi and As、Hg, and Au and Ag、W、Pb、Bi、Hg、As are lower.Factor analysis are performed with SPSS16.0, getting5factors with initialeigenvalue of more than or equal to1.0, and their cumulatives is65.901%, so thesefive factors can be used to evaluate the formation of rocks and ore mineralization. F1factor has the variance of29.519%, and its element associations are Co、Ni、Cu、Zn,the factor may be the representative of intermediate-mafic igneous process; F2factorwith variance of12.005%has the element associations of Sb、As、W、Hg，which isthe representative of W mineralization. The F3factor with variance of9.016%, F3factor has variance of9.016%, with the element associations of Mo、Bi，which is therepresentative of Mo mineralization. F4factor has variance of7.727%, the elementwith loadings more than0.5is Ag only; F5factor has variance of7.634%, the elementwith loadings more than0.5is Au only.Using MapGIS6.7as platform to determine the element thresholds with differentmethods, then the individual element anomalies such as anomalous area and strengthare compared.The anomalous thresholds of Co,Ni,Cu,Zn,Mo,Ag,Sb,W,Pb,Bi,As，Hg,Au determined by the traditional method are as follows:31×10-654×10-630×10-698×10-62.4×10-60.074×10-61.38×10-63.2×10-626×10-60.42×10-615.1×10-631×10-9,1×10-9,respectively.The anomalous thresholds ofCo,Ni,Cu,Zn,Mo,Ag,Sb,W,Pb,Bi,As，Hg,Au determined by fractal concentration-area method are15×10-634×10-620×10-6 50×10-63.2×10-60.087×10-61.88×10-61.29×10-618×10-60.66×10-611.6×10-636×10-9,1.02×10-9,respectively. The anomalous thresholds of Co, Ni, Cu, Zn, Mo, Ag, Sb, W,Pb,Bi,As，Hg,Au determined by fractal concentration-number method are24×10-638×10-630×10-683×10-61.9×10-60.073×10-61.48×10-63.4×10-626×10-60.45×10-69.8×10-633×10-9,1.44×10-9,respectively. The results mentionedabove and the process to get element thresholds show that fractalconcentration-number method is superior to the fractal content-area method and thetraditional method. Among the methods fractal content-number method is simple,without normal inspection of element content distribution, with the moderatedelineated range of anomaly.On basis of element correlations, individual element anomalies are superposedtogether to form plural element anomaly, and at the same time using factor loadingmethods to delineate plural element anomaly.When compared the two plural elementanomalies, it would find that the numbers of plural anomalies delineated with factorloading methods are more than those superposed with individual element anomaly,but the locations and ranges of plural anomalies delineated by both methods arecoincident, suggesting that using factor loading methods to delineate plural anomaliesis available. |
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