International Geologiical Congress - Oslo 2008

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MAG-05 New frontiers of mathematical geology for resources exploration

 

Application of multi-fractal filtering to extract Cu, Ni, AuaAnomalies of the East Tianshan Ore-forming Belt, North-western China

 

Jingning Huang, China University of Geosciences (China)
Hongguang Liu, China Library of Geosciences (China)
Pengda Zhao, China University of Geosciences (China)
 

 

The geochemical pattern related to ore-forming process commonly represents high frequency feature, and the geochemical pattern associated with tectonic-intrusive process commonly represent intermediate frequency feature. The S-A method developed by Cheng et al (2000) can be used to identify local anomalies from regional anomalies by constructing fractal filters on the basis of distinct power-laws, which determined by fitting different relations A(>S)=S. The threshold yielded from the Log A- Log S plot can be used to construct different types of filters to separate local anomalies from regional anomalies. By means of the Inverse Fourier Transformation, these anomalies obtained through filters mentioned above in frequency domain can be transformed back into the corresponding components in spatial domain. The east Tianshan Mountain ore-forming belt, located at the joined belt between the Siberian plate and Tarim plate, is of complicated geological background. The collision of the two plates cause tectonic-magmatic activities and mineralization of Cu, Ni, Au in the study area. The multi-periods of tectonic-magmatic activities and ore-forming processes write complicated geochemical records. It is difficult to decompose geochemical data from stream sediment into different hierarchical anomaly. In case study, Multi-fractal filtering is adopted to separate local Cu, Ni, Au anomalies from their regional anomalies based on Cu, Ni, Au concentration data from stream sediment survey. Their thresholds of Cu(S0=10.83 and S1=9.28), Ni(S0=11.2 and S1=8.52), Au(S0=9.24 and S1=8.02) are obtained from the Log-Log plots respectively. Based on these thresholds, for each element, two types of filters can be constructed respectively as the local and regional anomaly filter. Conclusions are as follows: (a) The multi-fractal filtering can effectively separate the local Cu, Ni, Au anomalies associated with mineralization from their regional anomalies caused by tectonic-magmatic activities.(b) The regional anomalies of Cu, Ni, Au associated with mineralization are obviously controlled by tectonic-magmatic activities and regional faults of EW trend. The local anomalies of Cu, Ni, Au are more associated with intermediate-acidic intrusions of the Mesozoic, and most related to mineralization for some known Cu, Ni, Au deposits occurred in the local anomaly area.(3) However, not all local anomalies appear in the study area with known Cu, Ni, Au deposits occurred. So, those local anomaly area may be the potential place to mineralization and need to be interpreted carefully within the local geological environment.

 

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