Test of a Model for Formation and Preservation of an Ancient Late Stage Epithermal Precious Metal Deposit

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9909359Hall/KeslerThis project tests a model for the formation and preservation of an unusual epithermal precious metal deposit in the Greater Antilles. Features which make the Camaguey District on the island of Cuba distinct include: 1) the deposits formed late in the history of the host island arc; 2) mineralization took place on a deeply eroded arc batholith; 3) the deposits are relatively old (late Cretaceous) indicating that they were preserved early in their history and left undisturbed since. Central to the model we propose are the ages of such features as the Camaguey Batholith, the rhyolites of the associated La Sierra Formation, and the age of mineralization itself. Existing geochronological constraints are poor, with the exception of adularia-sericite related mineralization at the Jacinto deposit. We address this issue by proposing to date all of the relevant units. Specifically, laser 40Ar/39Ar will be used to date hornblendes and biotites of the Camaguey batholith, feldspars from La Sierra Formation rhyolites, plus adularia and alunite from precious metal deposits. In addition, we will use vacuum encapsulated irradiation to date sericite samples from both adularia-sericite and acid sulfate deposits. The project addresses important issues, both for economic geology and for the history of the Caribbean. In particular, if the model for formation of the Camaguey District can be confirmed, it opens up new exploration strategies for epithermal deposits in what would normally be considered unpromising terranes. In addition, we will be able to constrain the petrological evolution of this island arc, as well as estimate the rate of erosion between the emplacement of the Camaguey Batholith and formation of the gold and silver deposits.