New Mexico Geological Society Annual Spring Meeting — Abstracts

Clay mineral analysis by x-ray diffraction and near-IR spectroscopy for the Questa mine rock piles and nearby natural alteration scars indicate the presence of four different secondary phyllosilicate minerals: kaolinite, smectite, illite (mica) and chlorite. The abundance of these clay minerals varies significantly from the different sample localities. Kaolinite is most abundant in samples where the host rock is feldspar-rich lithology (e.g. Amalia tuff) that has not been propylitically altered and is a minor component on samples from within the rock piles (predominantly andesite). Chlorite is common to the volumetrically most abundant propylitically altered andesites.

Analysis of materials from the alteration scars indicate illite, smectite, chlorite as the major clay minerals, with mixed layer illite/smectite and kaolinite as minor components. Veinlets of halloysite clay have been identified in some zones within alteration scars.

Within the rock piles, yellow-orange brown oxidized zones (most common on the outer edges) contain more abundant illite and smectite. Chlorite is of greater abundance within darker brown to gray units more common to the center of the rock piles, removed from the oxidized zones. The distribution of clay materials within the rock piles and alteration scars suggest the formation of illite and smectite in zones that are the weathered. Chlorite is most abundant away from the oxidizing/weathering surface of the rock piles and may represent a less oxidized type of weathering within the piles or a clay phase inherent to premined propylitically altered andesite.