Application of Thermochronology to Hydrothermal Ore Deposits

Abstract

Thermochronology finds many applications in economic geology. Utilizing temperature-sensitive radiometric dating techniques to reveal low-temperature, upper crustal processes can elucidate many aspects of deposit genesis, including timing and duration of mineralization processes, rate of exhumation and erosion of intrusive ore deposits and comparative preservation potential. The tools are utilized to best advantage when combined with other thermochronometry techniques that provide complementary information. In addition, when thermochronometers are combined with geochronometers (e.g., zircon U/Pb), over 800 °C of thermal history is revealed from emplacement to erosion (Fig. 1⇓). With the advent of computational algorithms that provide more accurate and detailed models of thermochronology results, the economic geologist has a powerful tool to use when assessing economic favorability of a region or prospect. This chapter summarizes the various ways that low-temperature thermochronometers have been utilized in studies of economic mineralization and primarily focuses on studies of porphyry ore deposits. These deposits are well characterized and provide a good platform from which to demonstrate the extended understanding of ore formation processes that is provided by thermochronology studies. In this section we review the fundamental application of (U-Th)/He, fission track and 40Ar/39Ar thermochronometry methods to mineralized systems. We then present a synopsis of how these techniques can be used in thermal history analysis, either alone or in combination with other chronometers, in order to provide more information on deposit genesis. The discussion is presented from low through to higher temperature thermochronometers, corresponding to their presentation on Figure 1⇓. ### (U-Th)/He thermochronology As documented earlier in the volume, (U-Th)/He thermochronology is based on measuring the accumulation of radiogenic 4He produced from U and Th decay. The daughter helium is retained until the mineral is heated to a temperature at which its structure and helium retentivity change. This “closure temperature” varies from …