GEOCHRONOLOGIC AND MINERALOGIC CONSTRAINTS CONNECTING THE DIAMOND JOE PORPHYRY ROOT TO THE BIG SANDY PORPHYRY COPPER PROSPECT, NORTHWESTERN ARIZONA, USA

The ore-bearing Diamond Joe composite pluton is located along the eastern flank of the central Hualapai Mountains and ~13 km west-southwest from the concealed Big Sandy porphyry copper prospect in the Big Sandy Valley. The pluton is a concentrically zoned pluton (~7 km in diameter) with three major intrusive phases and cut by aplitic and lamprophyre dikes. In addition, deep forms of high-temperature alteration and Cu-Mo mineralization are observed in the Leviathan vein area. While Diamond Joe has been proposed as the roots of a porphyry Cu-Mo system, Bell Copper’s Big Sandy porphyry copper prospect being drilled out potentially corresponds to the top of the same porphyry system and displaced to the ENE along the largely covered Hualapai low-angle normal fault.

The Diamond Joe magmatic system has a maximum duration of ~4 million years, with new LA-ICP-MS U-Pb zircon ages for the outer equigranular granodiorite (74.0 ± 1.6 Ma), intermediate porphyritic quartz monzonite (74.4 ± 1.4 Ma), inner quartz monzonite porphyry (72.9 ± 1.1 Ma), quartz porphyry (72.4 ± 1.0 Ma), and aplitic dikes (73.3 ± 0.7 Ma). A U-Pb zircon age of 74.1 ± 1.0 Ma was obtained on altered quartz porphyry from hole BS-3 at the Big Sandy prospect overlapping with a reported age of 74.1 ± 1.0 Ma on granodiorite in hole BS-1. Previously unreported Re-Os molybdenite ages from the Leviathan lode and Big Sandy prospect are respectively 72.6 ± 0.3 Ma and 74.2 ± 0.3 Ma. The Diamond Joe lamprophyre dikes yielded a younger U-Pb zircon age of 22.4 ± 0.3 Ma.

Main hydrothermal features observed in the Leviathan area include greisen veins together with qz-mo and qz-py-cp(-fh-cc) veinlets and veins associated with transitional potassic and sericitic alteration. At Big Sandy, the ore is confined to qz-mo and qz-py-cp-gn-fh-cc(-sl) veinlets associated with pervasive sericitic alteration and minor chlorite alteration.

Collectively, the geochronology of the igneous phases between the two locales overlaps within error. This suggests that they are part of the same protracted magmatic system, however, the Re-Os molybdenite ages do not overlap and may represent distinct ore-forming pulses. The ore and alteration mineralogy could suggest that Leviathan mineralization represent deeper parts of a porphyry system relative to that of Big Sandy. This supports the hypothesis that Big Sandy is the offset upper portion of the Diamond Joe porphyry system.