Surface geochemical anomalies in northern Chile

Surface geochemical anomalies in northern Chile product of the extended metallogenesis of buried copper deposits 

Eion M. Cameron Matthew I. Leybourne Martin Reich , Carlos Palacios  

KEYWORDS Chile, copper, atacamite, anomalies. Pleistocene 

Supergene enrichment piayed a criticai roie in making northern Chiie the worid s prime copper-producing province. For copper porphyry deposits in the centrai 

Reich et al. (2008) measured CI in atacamite from Mantos Blancos, Spence and three other deposits. These show low CI-to-CI ratios (11xi0 to 28x10 ), comparable to previously reported ratios of deep formation waters. Further, CI-to-Cl ratios in atacamite correlate with U and Th concentrations in host rocks. This suggests that subsurface production of fissiogenic CI was in secular equilibrium with waters involved in atacamite formation. Because atacamite does not contain U or Th, production of CI is not continued once chlorine has entered the crystal structure from that time the CI-to-Cl ratio decreases with age. The fact that measurable Cl is present indicates that atacamite formation occurred less than 1.5 Ma ago (five times half-life of CI). 

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