The La Plata Mountains, located 10 miles northwest of Durango, are an isolated branch of the San Juan range. The La Platas are separated from the San Juan massif by a terrane of upper Paleozoic and early Mesozoic sedimentary rocks. The La Plata Mountains themselves consist of a domed and uplifted sequence of sedimentary rocks intruded by younger, Laramide igneous rocks.
Two pulses of magmatism are recognized in the igneous rocks of the La Plata Mountains. The first pulse produced an assortment of laccoliths and sills ranging in composition from syenite to diorite. The second pulse produced much more alkaline magmas. These occur as small discordant stocks which have intruded and altered the surrounding country rock. Alteration is most intense near the syenite stocks. Pennsylvanian and Permian red beds make up most of the country rock in the La Plata Mountains. Indeed, most mineral deposits in the La Platas are hosted in these sedimentary rocks.
An extremely diverse array of mineral deposits occurs in the La Plata Mountains. Four major types are recognized:
fracture fillings of chalcopyrite, native platinum, palladium, and gold in syenite near Copper Hill;
gold-bearing sulfide veins hosted in Triassic-Jurassic limestones and marbles;
veins of proustite, pyrargyrite, stephanite, argentite, and native gold hosted in Permian red beds;
veins and replacement bodies of sylvanite, calaverite, krennerite, petzite, and coloradoite hosted in Pennsylvanian and Jurassic sediments.
The central part of the La Plata dome consists of highly altered sedimentary rocks cut by monzonite and diorite dikes, sills, and plutons. Skarn deposits of garnet, epidote, hornblende, specular hematite, 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 and highly mineralized fractures and fault zones. Ore-bearing faults and fractures containing gold and silver-bearing 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. Chalcocite-bearing veins occur in the basal part of the Dolores Formation near the contacts of monzonite porphyry dikes. Massive replacement bodies 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 consisted of a core of native gold surrounded by sheaths of pyrite and chalcopyrite.
The La Plata Mountains of southwestern Colorado present the modern-day prospector with a number of exciting possibilities. The La Platas are well-endowed mineralogically and contain a vast array of distinctive precious metal deposits. These include rich fracture fillings of chalcopyrite, gold, platinum, and palladium, gold-bearing sulfide deposits, veins of ruby silver, and gold-silver telluride deposits. The mountains are extremely rugged and heavily wooded. It is quite conceivable that a small hidden deposit of precious metal has eluded discovery for all these years. After all, the fabulous Red Arrow ore body was not discovered until the 1930's.
Prospectors may want to concentrate on the rugged upper slopes of Parrott Mountain in their search for the Lost Clubfoot Mine. Most accounts of the story place the hidden mine somewhere near treeline, just below Sunset Pass. Most mineral deposits in the La Platas are hosted in sedimentary rocks, so a detailed search of the surrounding country rock may prove to be rewarding. Prospectors may want to comb the slopes of the peak for gold-bearing float. A metal-detector may prove to be useful in the search for rich float hidden in the leaf litter and vegetation that cloaks the flanks of Parrott Mountain.