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

Abstract:

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.


Citation:

  1. Schutz, J. Leroy, 1995, Gold mineralization associated with alkaline intrusives at the Carache Canyon breccia pipe prospect, Ortiz Mountains, New Mexico, in: Geology of the Santa Fe Region, Bauer, Paul W.; Kues, Barry S.; Dunbar, Nelia W.; Karlstrom, K. E.; Harrison, Bruce, New Mexico Geological Society, Guidebook, 46th Field Conference, pp. 167-173.

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