GEOCHRONOLOGY OF ORE DEPOSITS: NEW TRENDS ABOUT AGE AND LIFETIME OF THE HYDROTHERMAL SYSTEMS
COLOMBO C.G. TASSINARI
Centro de Pesquisas Geocronológicas, Universidade de São Paulo, São Paulo, Brazil
Presented by ALCIDES N. SIAL
Over the last decade we have been able to produce accurate and highly precise ages of ore-forming episodes due to the recent geochronologic techniques that allow for direct dating of ore and gangue minerals using Re-Os, Ar-Ar and stepwise leached Pb-Pb and Rb-Sr methods. The use of integrated geochronologic approaches have led us to characterize the age and thermochronological history of dynamic geologic events associated with hydrothermal and mineralizing episodes, as well as the duration and episodic nature of ore-forming events. Many authors have demonstrated that while the geological episodes take many millions of years, the hydrothermal circulation and mineralizing processes take about 10,000 to 200,000 years. Dating hydrothermal fluid circulation, mineralizations and relationships between ore-forming processes and termochronological history of igneous and metamorphic episodes will be focused. Dating ore deposits is a very complicated process, because many factors (e.g. post-mineralization geological events) may reset the isotopic systems, and measured age not necessarily indicate the true age and, many times, yield ages of no geological significance. Nevertheless, the use of multi-isotopic systems in different types of minerals may minimize this problem. Determination of precise ages by different isotopic systems, coupled with computer modeling of how long an igneous episode can sustain geothermal activity, can improve establishing the length of ore-forming episodes. ( May 18, 2001 )
Publication Dates
-
Publication in this collection
05 Oct 2001 -
Date of issue
Sept 2001
