New Mexico Geological Society Annual Spring Meeting — Abstracts

The Copper Flat Hydrothermal System is located in Hillsboro, New Mexico, USA is a copper porphyry system mostly hosted by a coarsely phaneritic quartz monzonite intrusive body. The mineralization itself is dominantly hosted within an enigmatic breccia. Although the breccia is dominated by quartz monzonite, locally fragments include clasts of rock having a latitic composition and strongly porphyritic texture. Additionally latite dikes are present, but generally not strongly mineralized in most of the system. Because of the low copper concentrations, the latite was not previously considered to be important in the genesis of the deposit. The role of the latite magma relative to brecciation and mineralization has not been considered in prior models of the genesis of the deposit. This is compounded by the fact that not all prior workers differentiated the latite intercepts from the breccia or quartz monzonite. In order to resolve what role the latite played in the formation of the breccia and mineralized system, drill core from the deposit was relogged with the goal to identify latite intercepts and carefully document contact effects due to the latite dikes, including variation in intensity of alteration and mineralization. Drill core relogging was supplemented by thin section petrographic analysis. Assays of the drill core proximal to and including the latite intercepts were examined for evidence of metal gradients away from the latite since any such relationship could imply that the latites brought in at least some of the mineralization in the system. Petrography of the latites sampled demonstrates a commonly present quenched texture that indicates that a fluid was exsolved. The exsolution of a fluid from the latite provides evidence to support a model where the latites produced fluid for alteration and mineralization, and may have been responsible for the generation of the breccia due to volume expansion. The assay review indicates an increase in mineralization near most of the latite contacts studied, also suggesting that the latites brought in mineralization. Based on the combination of observations made in this study, a new genetic model involving the latite dikes in the generation of the breccia body and associated mineralization should be considered.