A molar element ratio analysis based on whole-rock, multi-element geochemical data for regional lag talus composite samples is evaluated as an exploratory method for iron oxide–copper–gold mineralization (IOCG) in hyperarid settings. This study is focused in the now hyperarid Mantoverde area, III Región of northern Chile (latitude 26°01′ to 26°53′S), and comprises the Andean Coastal Cordillera and Central Valley. The area contains numerous structurally controlled iron oxide-Cu-(Au) prospects and deposits hosted by calc-alkaline volcanic and plutonic rocks of Jurassic–Cretaceous age. Comparison with data for outcrop samples indicates that lag talus composite samples reflect the composition of bedrock in terms of major and selected trace elements. As with outcrop samples, zirconium is the most conserved element in the talus samples, and is therefore used as common denominator in different molar ratios.
A molar element ratio analysis using geochemical data from talus composite samples indicates that rocks associated with mineralization have been K-enriched and Na-depleted. Consequently, gradients in the K/Al and Na/Al molar ratios are useful targeting parameters. Similarly, a lithogeochemical alteration index, recently defined by the authors, quantifies the degree of hydrothermal alteration of host rocks and can be used to both target potential anomalous sectors (strongly altered rocks) and delimit barren areas. It is evident that lag talus composite samples constitute a reliable and effective sampling medium in regional exploration programmes for IOCG deposits in hyperarid settings.
- Central Andes
- northern Chile
- hyperarid settings
- IOCG-type deposits
- lithogeochemical analysis
- lag talus composite samples
- © 2008 AAG/The Geological Society of London