A NEW WHOLE-ROCK MAJOR-OXIDE AND TRACE-ELEMENT GEOCHEMICAL DATABASE FOR INTRUSIVE ROCKS OF NORTHERN NEVADA: IMPLICATIONS FOR PETROGENESIS AND METALLOGENY

Earth scientists working in northern Nevada have long recognized that regional to local intrusive activity has played a critical role in the geologic evolution of the region and has been key to the genesis of many ore deposits located therein. Although these rocks have been the focus of much research, most studies have focused on limited numbers of intrusive centers. Compilation and interpretation of whole-rock major-oxide, trace-element, mineralogic, and geochronologic data are essential to an understanding of regional magmatism and how various magmatic episodes contribute to the genesis of numerous, large ore deposits, particularly gold deposits.

Previous work in northern Nevada has documented major magmatic pulses in the Jurassic, Cretaceous, and middle Tertiary. By establishing compositional characteristics of intrusive rocks associated with these time increments, particularly their relative trace-element abundances, the tectonic setting in which associated magmas were generated can be inferred. For example, region-scale genetic links and postulated continuity between magmatism represented by the Sierra Nevada and Idaho batholiths are ambiguous. Northern Nevada bridges these two classically arc-related magmatic systems. Consequently, defining the tectonic setting of northern Nevada intrusive rocks using trace element abundances may help determine whether arc magmatism was spatially and temporally continuous across this region. Similarly, the intrusive rock geochemical database may define empirical geochemical associations between some intrusive centers and ore deposits, thereby helping focus the search for ore deposits through refinement of exploration methodologies. A specific goal related to compilation and synthesis of this database is to determine whether descriptive geochemical indices can be developed to identify intrusive centers that are associated with ore deposits, particularly gold deposits. Defining geochemical indices that identify barren plutons is equally important. The northern Nevada intrusive rock geochemical database is a work in progress. Ultimately, data contained therein can be used to characterize the geochemical attributes of northern Nevada intrusive rocks and interpret their petrogenetic evolution and metallogenic associations.