THE ROLE OF EXHUMATION IN THE TEMPORAL DISTRIBUTION OF ORE DEPOSITS

We show here that the temporal (age-frequency) distribution of ore deposits is controlled largely by exhumation, the combination of burial, uplift, and erosion that exposes subsurface rocks and ore deposits. Exhumation rates calculated from modal ages and emplacement depths for epithermal, porphyry copper, and orogenic gold deposits of Phanerozoic age are 167, 158, and 63 m/m.y., respectively. These rates agree with rates estimated for continent-scale terranes by numerous independent methods. Thus, the scarcity of Precambrian epithermal and porphyry copper deposits is probably due to their removal by exhumation. Archean and Pale-oproterozoic orogenic gold deposits are more abundant than indicated by the exhumation record of their Phanerozoic counterparts, suggesting that the Precambrian deposits formed in greater numbers. Recognition of the pivotal role of exhumation requires that the temporal distribution of ore deposits be corrected for this effect before it can be used as an indicator of large-scale changes in Earth history.