Free ResourcesFree Membership
Bookmark and Share


COLORADO

The Lost Tenderfoot Mine

GEOLOGY OF THE AREA

Located in the heart of the Colorado Rockies, the famous Breckenridge Mining District straddles the scenic Blue River near its source. The headwaters of the stream are nestled between the lofty Tenmile Range to the west and the towering chain of mountains that form the Continental Divide to the east. The Blue River is fed by a number of tributaries that drain the mountains on both sides of the valley.

The Tenmile Range on the west side of the Blue River valley consists of an uplifted core of ancient Precambrian metamorphic and igneous rocks. These Precambrian basement rocks are bounded on the east by folded and tilted Pennsylvanian-Permian red beds and younger Jurassic-Cretaceous sandstones and shales. The chain of mountains that form the eastern wall of the Blue River valley are likewise composed of Precambrian metamorphics but in many places along the Divide the Precambrian country rock is covered by Pennsylvanian-Permian red beds and Jurassic-Cretaceous sandstones and shales. In addition, this side of the Blue River valley is dominated by Laramide-age rhyodacite and quartz monzonite intrusions. These Laramide intrusions extend for nearly 20 miles in a northwest-trending direction just east of Breckenridge. The mining history and economy of Breckenridge revolves around these Laramide intrusions.

Laramide-age rhyodacites, quartz monzonites, and the adjacent altered and brecciated country rock are the source rocks and host rocks for most of the


click for larger image

precious metal deposits at Breckenridge. The famous "Wire Patch" was a locus of mineralization in which the brecciated portions of the rhyodacite porphyry and the surrounding shales were impregnated with gold-bearing ore. The apex of this amazing deposit cropped out near the top of Farncomb Hill, just 5 miles east of Breckenridge.

Mineralization in the Breckenridge area consists of both placer deposits and primary lode deposits. The placer deposits near Breckenridge were some of the richest in Colorado. Virtually every creek bed and dry gulch in the area contained gold. A few of them (like French Gulch, Illinois Gulch, and Georgia Gulch) were legendary producers.

Lode deposits consisting of gold and silver-bearing polymetallic sulfide veins are also found in the Breckenridge District. By far, the most important of these occur on Farncomb Hill. On the western side of the hill, veins containing native gold, pyrite, chalcopyrite, and galena are hosted within a Laramide quartz monzonite intrusion. On the southern side of the hill, the same ore minerals occur in a shattered and brecciated portion of the intrusion and in the surrounding Cretaceous shales. Other lode deposits occur on Gibson Hill, Humbug Hill, and Mineral Hill.

PROSPECTING POTENTIAL

The rugged chain of mountains that form the Continental Divide just east of Breckenridge is wonderfully mineralized. And no wonder - the area lies in the heart of the famous Colorado Mineral Belt. Its mining history is therefore long and protracted. Of course, this means the area has been heavily prospected, and yet the potential for new strikes is fairly good. Recent geochemical testing has borne this out.

The Breckenridge area has yielded extraordinarily rich deposits in the past. The famous blow-out deposits at the "Wire Patch" on Farncomb Hill are indeed legendary, but many smaller deposits were also discovered in the area. The renowned Rocky Mountain preacher John L. Dyer discovered a rich silver lode while traveling from the Tarryall mines in South Park to Breckenridge. After crossing the range at Boreas Pass, Father Dyer entered the beautiful Blue River watershed where he promptly discovered a rich lode deposit.

 


click for larger image

This strike occurred in the area between Red Mountain and Bald Mountain. The surface ore from Father Dyer's mine assayed out at 6000 ounces to the ton!

Red Mountain in particular seems to fit the description given by the young tenderfoot prospector back in 1880, but Bald Mountain and Mount Argentine are also possible sites. The focus of any prospecting venture should probably be the numerous Laramide quartz monzonites and rhyodacites that dominate the eastern part of the Breckenridge Mining District. Particular attention should be paid to the altered and brecciated margins of the intrusions and especially to the surrounding country rock. A metal-detector may prove useful in the search for gold-bearing veins.