New Mexico volcanogenic massive-sulfide occurrences, which typically contain pyrite and pyrrhotite accompanied by variable amounts of base-metal sulfides and precious metals, are found within mainly subaqueous, compositionally bimodal metavolcanic successions of Early to Middle Proterozoic age that are exposed primarily in the north-central part of the state. Host rocks include both mafic and felsic volcanic rocks or their volcaniclastic equivalents, silica-rich chemical sediments, and locally developed carbonate horizons. Some host rocks display variably preserved relict volcanic and (or) sedimentary textures, but the majority are metamorphic rocks having original textures and mineralogies substantially changed. In addition, many host rocks experienced significant premetamorphic chemical alteration that further obscures their origins. For these reasons, the "Host rock lithology" column in table 1 first lists a metamorphic rock description and them, in parentheses, suggests a possible volcanic or chemical-sediment protolith.

With the exception of the Pecos mine and a subsurface deposit partially outlined by recent drilling at Jones Hill, New Mexico occurrences shown on this map do not exhibit enough of the classic features of volcanogenic massive-sulfide deposits to make their classification (or origins) unequivocal. Nonetheless, these occurrences are included because they might be genetically, spatially, chronologically, or in some combination of ways related to volcamogenic massive-sulfide-forming systems and are therefore deserving of further study.

The following two sections 1) outline the general geologic setting and character of New Mexico’s Proterozoic volcanic terranes, which host volcamogemic massive-sulfide occurrences, and 2) describe the general features of two occurrences--the Pecos mine and Jones Hill--which display the most complete and convincing collection of "classic" volcanogenic massive-sulfide features of any of the New Mexico examples.