ZIRCON TEXTURE AND COMPOSITION DEFINE COPPER DEPOSIT POTENTIAL IN METALLOGENIC BELTS; CASE STUDIES FROM THE WESTERN TETHYAN AND NORTH AMERICAN CORDILLERAN OROGENIC BELTS

Metallogenic belts occur along convergent margins where deep structural plumbing allows melts to ascend through the crust culminating in systems that may include copper and other critical mineral deposits. The physicochemical cause determining whether a district will form a mineral deposit can depend on numerous factors, including composition and oxidation state. Mineral exploration in a large-scale orogenic belt focuses on understanding regional settings using multiple geophysical and geochemical techniques. However, analyzing intrusive bodies to determine if they could produce an ore deposit would significantly improve exploration success.

Studies on zircon composition have identified features that define magma fertility and potential for ore deposition. These studies often focus on a specific district to describe the temporal genesis of the magmas that hosted and formed mineralizing fluids. We present results from over a hundred samples and thousands of analyses covering districts in the Western Tethyan and the North American Cordillera that describe how to best assess the fertility potential of magmatic-hydrothermal mineralized systems across an orogenic belt.

The Western Tethyan belt extends from the Balkans to the Lesser Caucasus, with numerous ore deposits forming during the Jurassic, Cretaceous, Paleogene and Neogene. The rocks sampled vary in type, but regardless of age, composition and location, the samples directly related to mineralization have elevated Hf, Eu/Eu_N*, Ce/Ce_C*, and REE ratios. Calculated zircon temperatures for the mineralized samples tend to be less than 730°C. Zircon from the barren arc rocks and older basement rocks statistically have lower compositional values, while calculated zircon temperatures are typically higher than the fertile ones.

In the North American Cordillera, zircon from mineralized districts in southern British Columbia to the Yukon Territory also show significant chemical anomalies related to the magmatic fluid and oxidation state. Further evaluation of zircon textures from the samples related to mineralization show potential as a method to discriminate grains during analysis. Growth zoning and inclusions differ in mineralized systems, highlighting the magma change over time.

The composition of zircon provides age control and understanding of the tectonic setting, which improves mineral exploration in a regional program. Applying the zircon method to a few samples per site can indicate the fertility of the district, helping to improve the chances of discovery.