Paper No. 9-14
Presentation Time: 8:30 AM-6:00 PM
PUMPKIN HOLLOW DEPOSIT, YERINGTON DISTRICT, NV: INSIGHTS ON MINERALIZATION BASED ON ASSOCIATED ALTERATION AND COMPOSITION OF EPIDOTE GROUP MINERALS
The Yerington district, western Nevada, hosts a variety of copper systems, many of which are magmatic-hydrothermal products of the Jurassic Yerington batholith. Porphyry copper deposits in the district formed within the Yerington batholith, adjacent to porphyry dike swarms, and the Fe oxide-rich Pumpkin Hollow deposit formed distal to porphyry dike swarms. Previous work documented multiple styles of alteration (e.g., sodic-calcic, calcic, and potentially potassic-calcic) and at least two generations of chalcopyrite and Fe oxide-rich mineralization in the Pumpkin Hollow deposit. The amount and timing of discrete alteration and mineralization events remain unclear. Epidote-group minerals are present in many of the alteration types at Pumpkin Hollow. This study documented multiple generations of epidote-group minerals in different types of alteration through petrographic investigation and electron probe microanalyses. Epidote-group minerals were analyzed from sodic-calcic alteration of quartz monzodiorite and epidote-pyroxene hornfels clasts supported by epidote-magnetite-pyrite breccia matrix. Results show epidote-group minerals have variable SiO2, Al2O3, CaO, and Fe2O3 + FeO (based on charge balance through normalization of microprobe data) contents. Rare earth element (REE) contents are represented by analyses of La, Ce, Y, Nd, Pr, Gd, and Sm. The REE contents indicate at least two distinct epidote group compositions in the samples, a low REE (< 1 wt% total REE oxide of analyzed REEs) and a high REE (> 1 wt% total REE oxide of analyzed REEs) group. Back-scattered electron images document that epidote from sodic-calcic alteration of quartz monzodiorite and epidote-magnetite-pyrite breccia matrix. Further evaluation of mineral assemblages with this epidote-group mineral composition data will better inform our understanding of the hydrothermal evolution of the Pumpkin Hollow deposit.