Upon arrival in Chile in 1965, the only available radiometric ages for rocks in the central Andes were from intrusions in northern and central Chile, with most of the determinations carried out using the lead-alpha zircon method, first by the US Geological Survey in Washington, DC and then by Francisco Munizaga at IIG’s in-house facility in Santiago (Ruiz et al., 1961, 1965). The ages, including one for a porphyry intrusion in the Chuquicamata porphyry copper deposit (41 ± 10 million years ago [Ma]) and others for unspecified intrusions at the El Salvador and Potrerillos deposits, all have...

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