Page 86 - Geochemical Anomaly and Mineral Prospectivity Mapping in GIS

Geochemical Anomaly and Mineral Prospectivity Mapping in GIS
by E.J.M. Carranza
Handbook of Exploration and Environmental Geochemistry, Vol. 11 (M. Hale, Editor)
© 2009 Elsevier B.V. All rights reserved. 85

Chapter 4

FRACTAL ANALYSIS OF GEOCHEMICAL ANOMALIES

INTRODUCTION
The exploratory analysis of geochemical anomalies presented in the preceding
chapter considers mainly the empirical density distributions of data. This may be
inadequate in modeling geochemical anomalies because exploration data sets are
incomplete samples of the geochemical landscape of a study area. It is possible to
improve models of geochemical anomalies by considering also (a) the spatial correlation
and variability of geochemical data and (b) the geometry and scale-independent
properties of geochemical landscapes.
On the one hand, the consideration of spatial correlation and variability of
geochemical data aims to accurately portray background and anomaly patterns (i.e.,
geochemical landscapes) that reflect controls by geological processes and thus facilitate
recognition of significant geochemical anomalies. This objective can be achieved by
application of a variety of techniques that employ weighted moving average of point
data within a zone of influence, which is usually but not always circular, in order to
interpolate and portray spatial distributions of a whole set of point data (e.g., uni-
element concentrations geochemical samples). The applications of weighted moving
average techniques, especially geostatistical techniques that rest on variogram analysis,
to model geochemical landscapes have been discussed extensively in the literature (e.g.,
Wackernagel and Butenuth, 1989; Goovaerts, 1992; Bellehumeur et al., 1994; Jimenez-
Espinosa and Chica-Olmo, 1999; Reis et al., 2003; Pardo-Igúzquiza and Chica-Olmo,
2005) are therefore not discussed in this chapter.
On the other hand, the consideration of geometry and scale-independent properties of
geochemical landscapes aims to accurately separate background and anomalies in such
landscapes. This has been demonstrated in the seminal works of Cheng et al. (1994) and
Cheng (1999b) dealing with the fractal geometry of geochemical landscapes. This
chapter reviews briefly the concept that geochemical landscapes have fractal properties
and then demonstrates GIS-based applications of the concentration-area method for
fractal analysis of geochemical anomalies.