Integrating Geochronology and Ore Mineralogy Constraints to Correlate the Formation of the Diamond Joe Pluton and Big Sandy Porphyry Copper Prospect, NW Arizona, USA

Abstract

This study compares the Laramide (Late Cretaceous to Early Paleogene) Diamond Joe pluton, located along the eastern flank of the central Hualapai Mountains, with the subsurface Big Sandy porphyry Prospect, situated approximately 13 km east-northeast of Diamond Joe in the Big Sandy Valley. The Diamond Joe pluton is a concentrically zoned intrusion (~7 km in diameter) consisting of three major intrusive phases, which are intersected by aplitic and lamprophyre dikes. High-temperature alteration (transitional potassic-phyllic, phyllic) and Cu- Mo mineralization are observed in the Leviathan Vein area, while lower-temperature alteration (phyllic) and base-metal mineralization are found at the Silvertrails Vein. These features, along with the presence of abundant greisen veins, suggest that Diamond Joe represents the deepest part of a porphyry Cu-Mo system. The Big Sandy porphyry Prospect has been proposed as potentially representing the upper part of the same porphyry Cu-Mo system, with Bell Copper’s exploration model suggesting it was transported northeast by the Hualapai low-angle normal fault. To explore the potential connection between the Diamond Joe pluton and the Big Sandy Prospect, this study integrates geochronology with ore mineral petrography and chemistry. The Diamond Joe magmatic system is defined by four primary units and aplitic dikes, emplaced over a maximum duration of ~4 million years, including the outer equigranular granodiorite (74.0 ± 1.6 Ma), intermediate porphyritic quartz monzonite (74.4 ± 1.3 Ma), inner quartz monzonite porphyry (72.9 ± 1.1 Ma), central quartz porphyry (72.4 ± 1.0 Ma), and aplitic dikes (73.3 ± 0.7 Ma). Lamprophyre dikes (22.4 ± 0.3 Ma) within the Diamond Joe pluton post- date the magmatic system. The altered quartz porphyry host rock from drill-hole BS-3 at the Big Sandy Prospect (74.1 ± 1.0 Ma) overlaps with the oldest intrusions at Diamond Joe. Previously unreported molybdenite Re-Os ages from Bell Copper for the Leviathan Vein (72.6 ± 0.3 Ma) and the Big Sandy Prospect (74.2 ± 0.3 Ma) suggest temporal overlap with igneous activity, although the timing of magmatic hydrothermal pulses in the two locations di\ers. The primary hydrothermal features at Diamond Joe include non-mineralized greisen veins, and the mineralized Leviathan and Silvertrails Veins. The Leviathan Vein is a quartz lode with stockwork veinlets mineralized with quartz-molybdenite(-rutile), quartz-pyritechalcopyrite- tennantite, and quartz-molybdenite-pyrite-chalcopyrite-tennantite, associated with transitional potassic-phyllic and phyllic alteration. In contrast, the Silvertrails Vein is a quartz lode mineralized with galena-sphalerite-tetrahedrite-covellite, associated with phyllic alteration. This study suggests that the ore and hydrothermal alteration features observed in the Leviathan and Silvertrails Veins may have originally been continuous. Assuming an idealized model of zonation in porphyry copper systems, the Leviathan Vein, dominated by Cu and Mo, would represent the innermost zone of the hydrothermal system, directly above the porphyry stock, while the Silvertrails Vein, rich in base metals, would correspond to a more distal zone. Mineralization at the Big Sandy Prospect is characterized by quartz-molybdenite(- chalcopyrite), quartz-molybdenite-pyrite, and quartz-pyrite-chalcopyrite-galenasphalerite- fahlore-digenite-chalcocite-bornite stockwork veinlets, with pervasive phyllic and minor propylitic alteration. If the mineralization at Big Sandy is genetically related to that at Diamond Joe, it can be interpreted as a transition zone between the Cu-Mo-rich inner zone (represented by the Leviathan Vein) and the base-metal-rich distal zone (represented by the Silvertrails Vein), which contains minor copper-iron sulfides. This hypothesis is further supported by the tennantite-tetrahedrite chemistry at the Big Sandy Prospect, which exhibits a compositional continuum with respect to those formed in the Leviathan and Silvertrails veins. Based on geochronology and ore-alteration mineralogy, the Diamond Joe pluton and Big Sandy Prospect are likely components of a single porphyry Cu-Mo system formed between 74.1 and 72.4 Ma, later dismembered by the Hualapai low-angle normal fault. However, the lack of clear exposures and intersections of the Hualapai low-angle normal fault prevents definitive constraints on potential models. Alternative interpretations of the relationship between the two sites include the possibility of two distinct magmatichydrothermal systems sourced from spatially separate magmatic complexes formed concurrently in the Hualapai-Big Sandy basin region.