The La Plata Mountains (and adjacent Ohwiler Range) are an uplifted, southwestern outlier of the main San Juan massif. Averaging 12,000 feet in elevation, the La Plata Mountains are the remnant of a highly dissected, elliptical dome consisting of folded upper Paleozoic and Mesozoic sedimentary rocks intruded by Laramide sills, dikes, laccoliths, and stocks. The sedimentary rocks consist mostly of Pennsylvanian and Permian red beds in the eastern and central part of the range and younger Cretaceous sediments along the western edge. Two pulses of magmatism during Laramide times produced the small intrusive bodies found in the La Platas. These were emplaced 60 to 70 million years ago. The igneous bodies intrude the surrounding Pennsylvanian-Permian red beds which make up most of the country rock in the La Plata Mountains. Indeed, most mineral deposits in the La Platas are hosted in sedimentary rocks.
An extremely diverse array of mineral deposits occurs in the La Plata Mountains. Four major types of deposits are recognized:
the unique Copper Hill stockworks which contain chalcopyrite, native platinum, native palladium, and native gold;
gold-bearing sulfide veins containing pyrite, chalcopyrite, and arsenopyrite;
distinctive ruby silver veins which contain proustite, pyrargyrite, stephanite, argentite, and native gold;
The central part of the La Plata dome consists of highly altered sedimentary rocks cut by monzonite and diorite dikes, sills, and stocks. Skarn deposits of garnet, epidote, specular hematite, hornblende, and magnetite occur in some of the limestones within this sequence of altered sedimentary rocks. Economic ore deposits occur in the form of replacement bodies, stockworks, and mineralized faults and fractures. Veins of gold and silver tellurides make up the vast majority of precious metal deposits in the La Plata Mountains. These telluride deposits are especially abundant in the Baker Peak/Lewis Mountain/Snowstorm Peak area and in the region south of Madden Peak and Deadwood Mountain. A zone of proustite-bearing veins stretches from Fassbinder Gulch to the Cumberland basin. Massive replacement deposits of gold and silver-bearing tellurides occur in cavities in the Pony Express Limestone member of the Wanakah Formation. Metasomatic deposits of pyrite, chalcopyrite, and native gold have been worked near Jackson Ridge. These unique deposits consist of large metallic masses made up of a core of native gold surrounded by shells of pyrite and chalcopyrite.
The La Plata Mountains of southwestern Colorado present the modern-day prospector with bright and promising ground to explore. Several factors combine to make the La Platas extremely attractive to prospectors. First of all, the history of the area suggests that hidden lodes still exist. The last big strike took place as late as the 1930's. This occurred after nearly 200 years of sporadic and sometimes heavy prospecting! Secondly, the Geology of the Area is quite favorable for the emplacement of rich mineral deposits. Indeed, many types of mineral assemblages and modes of emplacement occur in the La Platas. The presence of small Laramide intrusions throughout the range with proven mineral deposits associated with them makes the district attractive to prospectors.
The western flank of Parrott Mountain is especially appealing to modern-day gold-seekers. It also has proven mineral deposits and is the site of the last big strike in the La Platas - the famous Red Arrow Mine. Lone Wolf's hidden vein is one of the better documented tales of lost La Plata mines. It is supported by assay records and reputable witnesses. One such witness was the mining engineer sent by Horace Tabor to assess the gold vein. The mining engineer thought enough of the vein to return to the La Platas 34 years later to search for it.
Prospectors may want to concentrate their search on the ravines and draws that slice the western flanks of Parrott Mountain. Particular attention should be paid to the lower slopes of the mountain, especially near its base. The ravines and dry washes that feed into the East Mancos River should be carefully checked. Prospectors should remember that most mineral deposits in the La Plata Mountains are hosted in sedimentary rocks. Prospectors must not be deterred from searching an area just because there are no Laramide intrusives in the immediate vicinity. Lone Wolf's vein has been hidden for over a hundred years. A metal detector may prove to be useful in locating buried gold-bearing float.