Gold mineralization associated with alkaline intrusives at the Carache Canyon breccia pipe prospect, Ortiz Mountains, New Mexico

The Carache Canyon hypabyssal breccia pipe developed along the Tijeras–Cañoncito fault system near the eastern Rio Grande rift margin. Upper Cretaceous clastic strata were intruded by several stacked 34± 2.2 Ma calc-alkaline sills and subsequently brecciated during early phases of a 28-30 Ma alkaline intrusive event. Breccia fragments collapsed 400-800 ft into the pipe, retaining a well-defined relict stratigraphy. Coinciding with a late alkaline dike swarm, hydrothermal fluids exploited open-spaced fractures and voids preserved in competent sill and sandstone lithologies outside and inside the southwest pipe margin. Early fluids were hot (275–>400°C), saline (25-46 wt% eNaCl), CO₂-rich, and apparently of magmatic origin. The fluids deposited quartz, adularia, calcite, sericite, additional gangue, tungsten minerals and base-metal sulfides. Late stage gold-bearing fluids were cooler (160-250°C), less-saline (10.4-12.1 wt% eNaCl), CO₂-rich and of meteoric and/or magmatic origin. Late fluids deposited iron sulfides, iron oxides, coarse native gold and carbonate gangue. The Carache Canyon adularia- sericite epithermal system contains a 1,169,000 troy oz gold resource averaging 0.070 oz/short ton. The coarse native gold occurrence and irregular fracture distribution induced a significant nugget effect, providing uncertainty in the average deposit grade. Consequently, a decline was designed to collect statistically accurate bulk samples and evaluate fracture pattern predictability.