2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 83-10
Presentation Time: 10:40 AM


BAIN, Wyatt, Geoscience, University of Nevada, Las Vegas, 4505 S. Maryland Pkwy, Las Vegas, NV 89154-4010, CLINE, Jean S., Department of Geoscience, University of Nevada Las Vegas, 4505 Maryland Parkway, Las Vegas, NV 89154-4010 and MARSH, Timothy M., 9420 E. Placita Oaxaca, Tucson, AZ 85749, bain@email.arizona.edu

The Kabba porphyry Cu prospect in NW Arizona contains two zones of porphyry style mineralization and alteration, spatially separated by a NS trending normal fault. These two zones are referred to as the Kabba footwall (FW) and hanging wall (HW) and are hypothesized to represent root and intermediate depths, respectively, of a single porphyry system. If this hypothesis is correct, fluid inclusions in the FW and HW at Kabba should be distributed similarly to fluid inclusions in known porphyry deposits.

Vein and alteration petrography, fluid inclusion petrography and microthermometry, and Raman and LA-ICP-MS analyses of individual fluid inclusions produced the following observations: 1) the textures and paragenetic sequence of alteration and mineralization in the HW and FW are almost identical, 2) the mineralization and alteration are consistent with the FW and HW having formed in the deep roots and intermediate zones, respectively, of a porphyry system, 3) the distribution of fluid inclusions in the FW and HW wall broadly match the distribution of inclusions in the deep roots and intermediate zones, respectively, of studied porphyries, 4) the chemical and physical conditions indicated by fluid inclusions at Kabba are very similar to conditions indicated by fluid inclusions in the Butte porphyry system, and 5) Cu is in greatest concentrations in vapor-rich fluid inclusions. These observations strongly suggest that the mineralization and alteration at Kabba formed at significant depth in a porphyry system similar to Butte, and that the FW and HW represent the root and intermediate depth levels of a single porphyry system, respectively. Based on microthermometry of fluid inclusions from the HW and FW: 1) the mineralization and alteration at Kabba formed in response to flux of five distinct hydrothermal fluids through the footwall and hanging wall, 2) aqueous fluid immiscibility contributed to mineralization in the hanging wall, 3) fluids evolved over time from being metal-bearing, aqueous fluids to metal-poor, CO2-rich, fluids, 4) the Kabba FW and HW formed at pressures of ~2500-3000 bars (10-12 km) and ~1500-2000 bars (6-8 km), respectively, and 6) fluids in the FW and HW were trapped between approximately <300-545°C and <300-525°C, respectively.