OBSERVATONS AT 10-5, APPLICATONS TO 10+3: NANO-SCALE FEATURES OF INTRUSIVE BRECCIAS IN THE RED CONE PEAK COMPLEX, COLORADO

Core drilling of the Red Cone Peak complex in northern Park County, Colorado, penetrated bodies of intrusive breccia that offer a rare opportunity for study. Intrusive breccias often occur as pipe-like intrusions (“breccia pipes”) that may be hundreds of meters in diameter and extend to 1000’s of meters depth. They often carry sulfide mineralization, and may be oxidized for 100’s of meters depth. By contrast, the Red Cone breccias are quite small and were sampled below the zone of oxidation. We have studied samples in thin sections and polished surfaces, and most recently with electron optics.

A TEM sample was prepared from a polished surface of breccia material using a FocusedIon Beam (FIB) instrument in the Campus Electron Optics Facility at OSU. Scanning Transmission Electron Microscope (STEM) study indicated that: (1) fragments exist down to <10 nanometers; and (2) these fragments are set within a glass phase of uncertain origin. “Feathering” of the minerals in the breccias, coupled with the nano-scale size of fragments suggest that they were “sucked” off the walls in micro-rock bursts as fractures opened and propagated. We believe further that the glassy matrix around the fragments originated as a mixture of water vapor and silicate material from the heated country rocks that were host to the dilational fractures.

This first look at the initiation of brecciation is significant insofar as it helps us understand how breccia pipes begin to form, ultimately producing bodies that have long been known to contain significant mineralization. Igneous-hydrothermal pressure from below builds to the point where it can no longer be contained, at which point it begins to escape through the fractures described above, enlarging them and depositing mineral matter as pressures and temperatures evolve – completely obliterating the evidence we were able to examine in the Red Cone samples.