Constraints on interpretation of geochemical data for gold exploration in multiply deformed and metamorphosed areas: an example from Legadembi gold deposit, southern Ethiopia

The Legadembi Au deposit, situated in southern Ethiopia, is hosted in shear ed metamorphic rocks of Pan-African age. The ore minerals and country rocks were subjected to multiple phases of deformation, metamorphism and mineral isation. Correlation studies and factor analysis are applied to test whethe r geostatistical studies can identify factors responsible for element relat ionships and pathfinder elements for Au. The results are compared with mine ral paragenetic studies to decipher the temporal relationships between mine rals and to further constrain possible pathfinder elements for Au. Spearman correlation coefficients identify Ni-Cu-Pb-Au, Ag-Au-Pb, Ba-Zn-Ti- Pb and Cd-Zn-Yb-Ti-V-Sr-Sc-Ni-Cu-Cr-Y correlations at 95 and 99% confidence levels. A four-factor model explains 99% of the data variability. Factor 1 (Ba-Cd-Sc-Sr-Ti-V-Y-Zr) is a lithological factor. Factor 2 (Au-Cu-Zn-Pb-Cd -Ni-Co) is an overlap of mineralisation factor. Factor 3 (Cr-Ni-Pb-Ag-Sr-V) and Factor 4 (Cd-Cr-Cu-V-Yb) are due to the overlap of lithological and mi neralisation factors. Even though the data are not normally distributed, ge ostatistical data processing using factor analysis gives geologically meani ngful results. Mineral paragenetic studies show two main phases of mineralisation. The ear ly phase is represented by chalcopyrite, pyrite, pyrrhotite and sphalerite. The later phase includes Au, galena and electrum. Based on geochemical fac tors and mineral paragenetic studies, Ag and Pb are potential pathfinder el ements for Au for Legadembi-type Au deposits. The correlation of other elem ents with Au is due to the spatial overlap of mineralisation events with di fferent metal associations. (C) 1999 Elsevier Science Limited. All rights r eserved.