The separation of anomalies from backgrounds is a critical step in geochemical prospecting. However, the determination of stream sediment geochemical anomalies is always affected by lithologic backgrounds in areas with variable lithologies. If this influence is not eliminated prior to anomaly determination, some serious errors may occur. In fact, a problem of lithologic background is essentially a problem of multiple population, which can be effectively solved by the clustering method based on the Expectation-Maximization (EM) algorithm. In this study, the authors applied the EM clustering method to a geochemical data set from a 1∶200,000 scale stream sediment survey, and then discussed the influence of separating multiple populations on anomaly determination. A practical example demonstrates that geochemical anomalies of stream sediments in lithologically complex regions can be determined in a more reasonable way by using the EM clustering method. This is mainly reflected in two aspects: on the one hand, strong but false anomalies can be eliminated, and on the other hand, weak but important anomalies can be uncovered.
孙尧尧, 郝立波, 赵新运, 陆继龙, 马成有, 魏俏巧. EM聚类方法在岩性复杂区水系沉积物地球化学异常圈定中的应用[J]. 物探与化探, 2020, 44(6): 1306-1312.
SUN Yao-Yao, HAO Li-Bo, ZHAO Xin-Yun, LU Ji-Long, MA Cheng-You, WEI Qiao-Qiao. The application of EM clustering method to the determination of stream sediment geochemical anomalies in areas with variable lithologies. Geophysical and Geochemical Exploration, 2020, 44(6): 1306-1312.
Cheng Z Z, Xie X J. Influence of variation in element background values in rocks on metallogenic prognosis in geochemical maps[J]. Geology in China, 2006,33(2):411-417.
Hao L B, Li W, Lu J L. Method for determining the geochemical background and anomalies in areas with complex lithology[J]. Geological Bulletin of China, 2007,26(12):1531-1535.
[4]
Hao L B, Zhao X Y, Zhao Y Y, et al. Determination of the geochemical background and anomalies in areas with variable lithologies[J]. Journal of Geochemical Exploration, 2014,139:177-182.
[5]
Zhao X Y, Hao L B, Lu J L, et al. Origin of skewed frequency distribution of regional geochemical data from stream sediments and a data processing method[J]. Journal of Geochemical Exploration, 2018,194:1-8.
Zhou D. Unit-wise adjustment of geochemiacl background data and its significance in geochemical anomaly delineation[J]. Geophysical and Geochemical Exploration, 1986,10(4):263-273.
[7]
Vistelius A B. The skew frequency distributions and the fundamental law of the geochemical processes[J]. The Journal of Geology, 1960,68:1-22.
[8]
Govett G J S, Goodfellow W D, Chapman R P, et al. Exploration geochemistry—Distribution of elements and recognition of anomalies[J]. Mathematical Geology, 1975,7:415-446.
Hao L B, Ma L, Zhao H B. Elemental homogenization during weathering and pedogenesis of volcanic rocks from North Da Hinggan Ling[J]. Geochimica, 2004,33(2):131-138.
Hao L B, Lu J L, Ma L. Relation between the chemical compositions of residual soils and bedrocks in shallow overburden areas and its significance:A case study of the northern Da Hinggan Mountains[J]. Geology in China, 2005,32(3):477-482.
[11]
Reimann C, Filzmoser P, Garrett R. Background and threshold: critical comparison of methods of determination[J]. Science of the Total Environment, 2005,346:1-16.
[12]
Ahrens L H. A fundamental law of geochemistry[J]. Nature, 1953,172:1148.
[13]
Miesch A T, Chapman R P. Log transformation in geochemistry[J]. Mathematical Geology, 1977,9:191-198.
[14]
Hoyle M H. Transformations: An introduction and a bibliography[J]. International Statistical Reviews, 1973,41:203-223.
[15]
Box G E P, Cox D R. An analysis of transformations[J]. Journal of the Royal Statistical Society:Series B, 1964,26:211-252.
[16]
Stanley C. Numerical transformation of geochemical data: 1. Maximizing geochemical contrast to facilitate information extraction and improve data presentation[J]. Geochemistry: Exploration, Environment, Analysis, 2006,6:69-78.
[17]
Cheng Q M, Xu Y G, Grunsky E. Integrated spatial and spectrum method for geochemical anomaly separation[J]. Natural Resources Research, 2000,9:43-51.
[18]
Cheng Q M. A new model for quantifying anisotropic scale invariance and for decomposition of mixing patterns[J]. Mathematical Geology, 2004,36:345-360.
Xie S Y, Bao Z Y. Continuous multifractal model of geochemical fields[J]. Geochimica, 2002,31(2):191-200.
[20]
Whitehead R E S, Govett G J S. Exploration rock geochemistry—detection of trace element halos at heath steele mines (N.B., Canada) by discriminant analysis[J]. Journal of Geochemical Exploration, 1974,3:371-386.
[21]
Sinclair A J. Selection of threshold values in geochemical data using probability graphs[J]. Journal of Geochemical Exploration, 1974,3:129-149.
[22]
Dempster A P, Laird N M, Rubin D B. Maximum likelihood from incomplete data via the EM Algorithm[J]. Journal of the Royal Statistical Society:Series B, 1977,39:1-38.
[23]
Akaike H. Statistical predictor identification[J]. Annals of the Institute of Statistical Mathematics, 1970,22:203-217.