The Mogollon Mountains form the heart of the enormous Mogollon-Datil volcanic field of southwestern New Mexico. The Mogollons trend north-northwest and stretch from the Gila River northward to Lost Lake Mountain, a distance of about 35 miles. They are extremely rugged and cut by many deep canyons.
The Mogollons are comprised exclusively of volcanic rocks. They range in composition from basaltic andesite to andesite to rhyolite and include lava flows and ash-flow tuffs. The oldest rocks exposed in the Mogollon district are found at the bottom of Whitewater Canyon, where the creek has cut the deepest. Here, the Whitewater Creek Rhyolite crops out for a short distance along the creek bed. The Whitewater Creek Rhyolite is overlain by the Cooney Quartz Latite, named for the old mining town founded by James C. Cooney. It consists of alternating layers of latite lava flows
and ash-flow tuff. The Cooney Quartz Latite is overlain by the Mineral Creek Andesite which is, in turn, overlain by the Fanney Rhyolite. The Fanney Rhyolite is one of the major units that comprise the ring-fracture flows of the famous Bursum cauldron and is distinguished by the presence of spherulites. The Fanney Rhyolite is overlain by the Last Chance Andesite. This unit alters readily and serves as a host rock for much of the mineralization in the Mogollon district. The Last Chance Andesite is topped by the Deadwood Gulch Rhyolite Tuff which is, in turn, overlain by the Mogollon Andesite, the youngest volcanic unit in the district.
Faults are important controls and loci for mineralization in the Mogollon district. Virtually every ore deposit in the district is emplaced along a fault or fracture zone.
The Fanney Rhyolite is one of the major volcanic units that comprise the ring-fracture flows of the immense Bursum cauldron of southwestern New Mexico. The Fanney Rhyolite is sandwiched top and bottom by the Last Chance Andesite and the Mineral Creek Andesite, respectively. These andesite flows alter quite readily and serve as a host rock for much of the mineralization in the Mogollon district.
Faults are important controls and loci for mineralization in the Mogollon district. In the famous Eberle Mine, the gold, silver, and copper-bearing ores were emplaced along a normal fault separating the Fanney Rhyolite from the Mineral Creek Andesite. In the southern part of the Mogollon district, near Dripping Gold Spring, a similar situation occurs. In this case, a number of small gold and silver-bearing bodies occur along a southern extension of the Queen Fault. Again, the ore bodies were emplaced within the cavities and open spaces of the fault, which in this area forms the boundary between the Fanney Rhyolite and the Last Chance Andesite.
Prospectors may want to concentrate on the streams and canyons that drain the western flank of the Mogollon Mountains, including the drainages of Sycamore Creek, Mineral Creek, and Silver Creek. The entire western edge of the Mogollons extending from Deep Creek in the north to Big Dry Creek in the south appears to be the most promising country for the prospector. Prospectors may want to focus on the various fault zones that cut the range along its western edge. The andesites that underlie and cap the Fanney Rhyolite would also be worthy of attention, especially where they are highly faulted.