Exploration targeting in porphyry Cu systems using propylitic mineral chemistry: a case study of the El Teniente deposit, Chile

The mineral chemistry of epidote and chlorite from the propylitic halo at El Teniente, in samples collected at distances up to 6.6 km from the deposit centre, was determined by microprobe and LA-ICP-MS analysis. Results show that both minerals incorporate a range of trace elements in a systematic way that define a much larger footprint to the system than is easily recognised using conventional means. In chlorite, geothermometry temperatures, Ti and V are high proximal and Li, As, Co, Sr, Ca and Y are low proximal (high distal); ratios of these elements define gradients towards ore varying over 3-5 orders of magnitude. In epidote, As defines a broad proximal low and is generally elevated at distances of at least 3 km from the edge of the ore shell. Zn, La, Yb, Y and Zr amongst others appear to define a geochemical shoulder that surrounds the deposit. These patterns are broadly similar to those observed in previous work at Batu Hijau and in the Baguio District suggesting that these minerals behave consistently and can therefore provide useful exploration tools within propylitic “green rocks”.