Missouri Girl Claim
Mesa County, Colorado
Copper and Silver
LODE, 20.66 acres
$5,000
History
The Missouri Girl mine was discovered by a cowboy named Joseph Bieser sometime in 1887 while rounding up his herd in McKenzie Canyon, 30 miles southwest of Grand Junction high on the Uncompahgre Plateau. Bieser never forgot about the rich copper float he saw on the creek and in May 1890 he and a fellow cattleman, J.T. Selby, began investigating the site. The pair quietly started shipping small lots of hand-sorted ore to outside reduction works. At first, they collected all the rich float at surface and then sunk a shaft on the most promising spot to hunt for a suspected fissure vein. Selby was originally a native of Chilicothe, Missouri and the men decided to name their new prospect the Missouri Girl Mine.
The first shipments of ore were exceedingly rich and contained up to 60 wt% copper and 30 ounces of silver to the ton. Their payments from the smelters more than covered the cost of the shaft sinking, so the pair hired five men to continue the work. At a depth of 45 feet in the shaft a streak of high-grade ore eighteen inches thick consisting of nearly solid chalcocite (copper sulfide) with some native silver was found. Selby brought large samples of this ore into Grand Junction, which created a sensation and triggered a rush to the region.
Throughout 1890, the Missouri Girl made regular shipments of ore to the smelter in Pueblo, Colorado. Due to the excessive freight charges associated with hauling the ore to the railroad, only the highest grade ores could be shipped profitably. In August 1890, ten tons of ore yielded 50 wt% Cu and 30 oz/ton silver. In November, a further two carloads returned 64.5 wt% copper and 35 oz/ton silver.
At a depth of 55 feet in the shaft, a crosscut was extended to the level of the canyon floor and drifts were started north and southward along the fissure vein. Some of the ore encountered in this drift was rich in wire silver. The last shipments in 1890 averaged up to 100 oz/ton silver. Experienced mining engineers and wealthy mining men of the rich silver camps at Leadville and Aspen were regular visitors to the mine. In the fall of 1890, Selby and Bieser refused an offer of $50,000 for the mine or the modern equivalent of $1.58 million USD! From 1891 to 1892 the shaft was extended to a depth of 100 feet and the fissure vein was five feet wide and ran 24 wt% Cu and 145 oz/ton Ag.
Although the ore was very high grade, its remote location greatly hampered its development. Proposals to build a copper smelter in Grand Junction and survey new bridges across the Colorado River never materialized. In a final attempt to capitalize the mine, the Missouri Girl Mining Company was organized in 1906, and funds were raised to continue sinking the shaft down to 180 feet. At this depth the fissure passed out of the Triassic sedimentary rocks and into Precambrian granite. Here the vein was much stronger and was up to ten feet wide. Hundreds of assays collected from the fissure while sinking to 180 feet ranged from 8 to 68 wt% copper, 10 to 30 oz/ton silver and importantly, small pockets containing up to 0.3 oz/ton gold. Despite an average copper value of around 20 wt% copper on the 180-ft level, this ore could not be profitably shipped. The mine was abandoned in 1909.
Geological Potential
The Missouri Girl was the first significant copper mine discovered on the Colorado Plateau and predated the discovery of the important Big Indian Mines in Lisbon Valley, Utah in 1892 and the Cashin Mine on La Sal Creek, Colorado in 1896. Both have since gone on to be fabulous producers. The Missouri Girl has many similarities with the Cashin Mine.
Intermittent mining at Cashin between 1896 and 1946 produced a total of 1.8 million lbs of copper and 425,000 ounces of silver at an average ore grade of 4 wt% Cu and 18.5 oz/ton Ag. Some ore ran up to 11 wt% Cu and 136 oz/ton Ag. Mineralization occurs along faults cutting the Wingate Sandstone and Chinle Formation. In the Chinle (like the Missouri Girl), the fissure was seldom more than a few feet wide but was famous for producing the mine’s highest-grade ores, up to >70 wt% copper and up to 500 oz/ton silver. Large nuggets and sheets of native copper alloyed with native silver were found in the Chinle that weighed up to 500 pounds! Sometimes copper was coated with a layer of native silver, producing hybrid copper-silver nuggets that are prized by mineral collectors to this day.
The mineralization at the Missouri Girl also occurs in a high-grade fissure in the Chinle Formation and produced similarly high-grade copper-silver ores as well significant native silver. Around 100 feet of vertical erosion has occurred on the Missouri Girl fissure below the Wingate-Chinle contact. This horizon is where the richest copper-silver masses were discovered at Cashin. Metal detecting in McKenzie Canyon on the Missouri Girl claim may prove interesting as it is possible that some important amounts of native copper-silver ore was eroded in recent times!
A casual search of the Missouri Girl dump produced many fine specimens of copper sulfide ores running up to 25 wt% Cu and 30 oz/ton Ag. A small amount of native silver was panned from dump fines.
