New Mexico Geological Society Annual Spring Meeting — Abstracts

Conodont elements, which are microscopic toothlike hardparts of an unknown organism, irreversibly change in color in response to increasing temperature and time, and, therefore, these elements should record thermal events related to are deposition. Three ore deposits representing different thermal environments were studied to test this concept; the Carthage Mississippi-Valley -Type deposit (70-120°C), the Hansonburg Mississippi-Valley-Type deposit (140-210°C), and the Continental Cu-skarn deposit (250-450°C). Samples of carbonate country rock were collected away from these deposits over vertical and horizontal intervals. Conodont elements, which are composed of francolite (a carbonate apatite), were extracted by dissolving the carbonate hosts in a 15% formic acid solution. Conodont colors were defined by comparing the
conodonts collected in the field to a set of conodont standards, as well as, the published conad.ont color alterati.on index established by Epstein et al. (1977). Conodonts from the Carthage, Tennessee deposit do not demonstrate any alteration, indicating either that the temperature of the deposit was insufficient to change conodont colors, or that the mineralizing event was too short-lived to imprint any thermal effects upon the conodont elements. The Hansonburg conodonts do show a progressive change in the color index away from the deposit, recording a thermal anomaly up to .4 kilometers away from the deposit. The Continental Cu-skarn is located against a granodiorite intrusive stock. Conodonts extracted from the surrounding Paleozoic carbonates decrease in color away from the stock, and the conodont colors reflect the thermal anomaly associated with the intrusion rather than the later mineralizing event. From this study I have concluded that conodont color alteration may be used as a directional indicator towards sediment.-hosted ore deposits which are ≥140°C and spatially isolated from other heating sources.