Use of porphyry indicator zircons (PIZs) in the sedimentary record as an exploration tool for covered porphyry copper deposits in the Atacama Desert, Chile
Résumé
This work explores the potential of geochemical and petrographic characteristics of detrital
zircons coming from the sedimentary record of the Centinela District in Northern Chile to identify
the presence of buried porphyry copper deposits under a transported gravel cover. The sampled
sedimentary section was recovered from the pit of the exotic copper deposit of El Tesoro, located
approximately 2 and 4 km west of the Esperanza and Mirador porphyries, respectively. The
sedimentary cover comprises four units, Tesoro II, Tesoro III, Arrieros and Recent gravels,
deposited since the late Cenozoic in an arid continental environment dominated by alluvial fans.
Except for the Tesoro III gravels, all other units contain exotic-Cu mineralisation. In order to
interpret the geochemical footprint of the investigated zircons, the Porphyry Indicator Zircon (PIZ)
concept (Pizarro et al., 2020) is used. A PIZ need to comply with each of the following geochemical
values: Hf >8,750 (ppm), Ce/Nd >1, Eu/Eu* >0.4, 10,000×(Eu/Eu*)/Y >1, (Ce/Nd)/Y >0.01,
Dy/Yb <0.3 and 0.1 < Th/U < 1. These zircons also have Ti <9 ppm and Ce/Ce* <100 and usually
show euhedral morphologies characterised by prismatic forms of type {110}. The geochemical and
petrographic characteristics of the PIZs collected in the gravels are similar to zircons from the
nearby Mirador and Esperanza porphyries. The highest PIZ concentration coincides with the gravel
horizons with exotic-Cu mineralisation. Therefore, the PIZs found in the sedimentary record are a
potential tracer of adjacent copper porphyries and represent a promising exploration tool for this
type of hidden ore deposits in challenging sediment-covered areas.
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