THE GLOBAL AGE DISTRIBUTION OF GRANITIC PEGMATITES AND RARE-METAL PEGMATITES

A global compilation of 312 pegmatite ages indicates that granitic pegmatites range in age from Mesoarchean to Neogene and have a semi-periodic age distribution. Granitic pegmatites show nine age maxima: ca. 2925, 2650, 1800, 1400, 1175, 1000, 525, 350, and 100 Ma. These peaks correspond broadly with various proxy records of supercontinent assembly, including the global time trends of granites, detrital zircon ages, and passive margin abundance. Pegmatite ages are generally offset a few tens of millions of years following the corresponding peak in the granite age record. Lithium-cesium-tantalum (LCT) type pegmatites have a similar age distribution to the granitic pegmatites, with maxima at ca. 2640, 1790, 960, 530, 375, and 275 Ma. While the ages of these rare-metal pegmatites correspond to the record of pegmatite formation in general, the development of ore deposits, which require sufficient grade and tonnage of economic mineralization, are characterized by a bimodal trend, with concentrations in the Archean and Phanerozoic. While there are some lithium resources from the Proterozoic, the dominantly bimodal distribution of resources is particularly evident in the tantalum record. This distribution is similar to that of orogenic gold deposits, and reflects the preservation potential of the orogenic belts where these deposits are formed. Niobium-yttrium-fluorine (NYF) type pegmatites show similar age distributions to LCT pegmatites but with a strong maximum at ca. 1000 Ma.