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Iodargyrite (AgI) in supergene zones of argentiferous Cu deposits in the Atacama Desert, Chile: Involvement of I-rich waters?

Alvear, M., Reich, M., Palacios, C., Cameron, E.M., Leybourne, M.I. and Deditius, A. (2009) Iodargyrite (AgI) in supergene zones of argentiferous Cu deposits in the Atacama Desert, Chile: Involvement of I-rich waters? In: Goldschmidt Conference 2009, 21 - 26 June 2009, Davos, Switzerland


We document the occurrence of inclusions of a (Ag,I)-rich mineral in supergene chalcocite from the Mantos de la Luna argentiferous stratabound Cu depos it in the Coastal Range of northern Chile. In this deposit, located 30 km south of Tocopilla, Cu mineralization occurs preferentially in the lower levels of amygdaloidal and porphyritic horizons. Mineral paragenesis is simple and composed exclusively of Ag-bearing supergene chalcocite (digenite), atacamite, and chrysocolla.

EMPA observations reveal the presence of discrete, micron-sized (1-10 μm) inclusions of a Ag iodide mineral in supergene chalcocite. The inclusions were identified as iodargyrite by means of EDS and WDS elemental mapping. The Ag concentrations in the inclusions vary from 1.0-67.6 wt% and they are contaminated by Cu and S from chalcocite. The small size and the beam-sensitivity of the Ag-I inclusions precluded the precise descript ion of its chemical formula. However, the Ag and I elementa l maps strongly correlate with the inclusions, whereas the WD S maps of Cu and S correlate well with the chalcocite sulfide host.

The occurrence of iodargyrite inclusions in supergene chalcocite suggests the involvement of iodine-rich waters during supergene enrichment at the Mantos de la Luna Cu deposit. Considering the fact that the occurrence of iodargyrite is restricted to extremely arid environments [1], our observations strongly suggest the prevalence of hyperarid conditions during the latest stag es of supergene enrichment of the Mantos de la Luna argentiferous Cu deposit in northern Chile. This suggests that supergene enrichment processes of Cu deposits in the hyperarid Atacama Desert are dynamic in nature and do not exclusively require the presence of meteoric water. Further studies are needed not only to address the isotopic signature (and age) of iodine-rich waters involved in supergene enrichment of these deposits (e.g. deep formation waters), but also to constrain the origin of iodine in the extensive nitrate deposits occurr ing in the eastern flank of the Coastal Range.

Publication Type: Conference Paper
Murdoch Affiliation: School of Information Technology
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