TRACKING THE EXHUMATION OF LARAMIDE-RELATED PORPHYRY COPPER DEPOSITS IN SE ARIZONA USING A MULTI-THERMOCHRONOMETER APPROACH

Arizona is host to world-class porphyry copper deposits that formed during arc magmatism related to the Laramide orogeny and were subsequently exhumed during Basin and Range extension. This study focuses on constraining the timing of exhumation for the Sierrita-Esperanza and Copper Creek porphyry copper deposits, which formed in southeastern Arizona between 58-63 Ma. This study uses a multi-thermochronometer approach to constrain the thermal history of the intrusions associated with these ore deposits as a proxy for exhumation. Samples were collected along a ~10 km paleo-vertical transect from the Ruby Star pluton associated with the Sierrita-Esperanza deposit, while drill core samples from 1800m depth and surface samples in the hanging wall and footwall of an inferred Laramide thrust fault were collected from the Copper Creek granodiorite. We use zircon U-Th/He, apatite fission track, and apatite U-Th/He dating techniques to constrain the plutons’ passage through these systems’ closing temperatures of ~140-200˚ C, ~90-150˚ C, and ~45-90˚ C, which correspond to 5-8 km, 4-6 km, and 1.5-3.5 km depth using our modelled geotherm. Preliminary results for the two locations yielded similar ZrHe ages of 30-32 Ma but contrasting ApHe ages. The Ruby Star Pluton yielded ApHe ages that young with paleo-depth and range from 21 to 27 Ma, correlating with the formation of the Catalina metamorphic core complex. In contrast, ApHe data from 1800m depth in the Copper Creek granodiorite yield significantly younger ages of 3 Ma. These results indicate a clear difference in exhumation history between the two mining districts. These ages show that the Copper Creek deposit was exhumed much more recently, which provides context for the lack of a supergene enrichment zone within this district. When more data is received, these exhumation histories will be related to regional tectonic processes, including the onset of core complex formation and Basin and Range extension. We plan to quantitatively model the exhumation of porphyry copper deposits in SE Arizona in order to evaluate the preservation potential of these deposits which contain critical minerals necessary for the green energy transition.