San Francisco Mining District, Beaver County, Utah, USAi

Regional Level Types
San Francisco Mining District	Mining District
Beaver County	County
Utah	State
USA	Country

The San Francisco (Preuss, Newhouse, Frisco) mining district is in the southern San Francisco Mountains about 16 mi west- northwest of Milford in north-central Beaver County. The district was organized in 1871 and was a sporadic metal producer into the early 1950s. The San Francisco district is about the ninth most productive metal mining district in Utah. Total district metal production at modern metal prices is estimated at $907 million. The history of the district is dominated by the Horn Silver Pb-Ag underground mine and Cactus Cu-Au-Ag open pit/underground mine (Wray, 2006).
The district lies on the Wah Wah–Tushar mineral belt in the eastern Basin and Range Province. The district is centered on the 9-sq-mi, Oligocene (~31 Ma) Cactus granodiorite stock which intrudes a section of Neoproterozoic clastic sedimentary rocks that have been thrust over lower Paleozoic sedimentary rocks. The stock is medium- to coarse-grained, dark-gray, mafic-rich, and strongly magnetic. The San Francisco district is zoned from Cu ±Au ±Mo at the Cactus and Imperial mines outward to Pb-Zn-Ag zones as at the Horn Silver mine (Wray, 2006).
The Cactus Cu mine is a magmatic-hydrothermal tourmaline breccia pipe hosted on the north flank of the Cactus granodiorite stock. The Cactus pipe is about 820 ft by 200 ft in plan view, elongated to the northwest, and plunges steeply to the north to a depth of at least 900 ft. Past production from the Cactus mine is estimated at about 1.4 million tons averaging recovered grades of 1.23% Cu, 0.34 ppm Au, and 6.8 ppm Ag and reportedly still contains a similar subeconomic inferred resource (Wray, 2006). A zone of weak porphyry Cu-Mo stockwork mineralization has been intersected by a few scattered, moderately deep drill holes as a series of chalcopyrite-bearing veins adjacent to and beneath the Cactus breccia pipe. The Imperial Cu skarn adjoins the south flank of the Cactus stock.
Much of the rest of the metal production from the San Francisco district is attributable to the 1.1 million tons of high-grade, supergene-enriched Horn Silver replacement ore running over 18% Pb and 592 ppm Ag, recovered (Perry and McCarthy, 1977). Mineralization at the Horn Silver mine is developed in a very steeply east-dipping normal fault, that juxtaposes moderately northwest-dipping Cambrian-Ordovician carbonate rocks on the west and gently east-dipping, altered Oligocene Horn Silver andesitic volcanic rocks on the east. Throw on the fault is over 4600 ft. Mineralization occurs in a crudely arrowhead-shaped orebody over 700 ft long at the surface, 100 ft thick, and reaching a point at a depth of about 1030 ft. The deposit resulted from a combination of breccia filling and replacement, mostly of the hanging wall volcanic rocks, although mineralization is also known in the footwall carbonates. The Beaver Carbonate mine lies about 3 mi northeast of the Horn Silver and has been a modestly productive Pb-Ag mine (Wray, 2006).

From 1870 to 1976, the San Francisco district produced 2.36 million tons of ore that yielded 44,900 ounces of gold, 19.6 million ounces of silver, 44.1 million pounds of copper, 405 million pounds of lead, 46.8 million pounds of zinc, and 892 pounds of tungsten.

In 1870, the Cactus ore body was the first metallic mineral deposit discovered here, and the district was formally organized in 1871. Four years later, the Horn Silver ore body (the largest lead-silver ore body ever found in Utah) was discovered by James Ryan and Samuel Hawkes. These two prospectors sunk a shaft 30 feet and encountered chlorargyrite or horn silver (a rich silver ore), hence the name, Horn Silver mine. Fearing that the ore deposit would be small, they decided to sell the claim five months later, in 1876, to A.G. Campbell, Matthew Cullen, Dennis Ryan, and A. Byram for $25,000. These new owners proceeded to develop the ore body, erect a smelter, and process and sell the ore. During the three-year period from 1876 to 1879, the total value of mine production was $2.54 million, which included almost 50 percent paid out as dividends. In 1879, they sold the greater part of their interest to the newly incorporated company, Horn Silver Mining, for $5 million. The town of Frisco was established and by 1880 had about 800 inhabitants. Drinking water was brought to the town via the railroad from Black Rock, Utah about 30 miles to the east, or hauled by wagon for 10 miles from springs in the Wah Wah Mountains to the west.

From 1880 to February 12, 1885, the mine was a constant producer until the upper 800 feet of the original shaft caved in. The desire for high production possibly caused disregard for good mining practice; miners reported the mine creaking and shifting prior to the cave-in. Luckily, the mine collapsed during a shift change and no one was hurt. The cave-in was so violent that windows shattered 15 miles away in the town of Milford. This was the beginning of the end for the Horn Silver mine, town, and district. Mining ceased while the underground workings were improved and a new 1600-foot-deep shaft (Horn No. 1) was constructed east of the old shaft. Mining resumed in 1886 and continued until 1952 with a brief period of inactivity from 1932 to 1937. From 1875 to 1952, the Horn Silver mine produced 834,000 tons of ore yielding 196,000 tons of lead, 17.9 million ounces of silver, 25,700 ounces of gold, 9,650 pounds of copper, and 23,300 pounds of zinc.

Other mines that produced ore in the district include the Beaver Carbonate group, Cactus, King David, Cupric, and the Frisco Contact. Of these, the Beaver Carbonate group (including the Carbonate, Rattler, and Quadmetals mines) was the largest silver producer. From 1879 to 1942, this group produced an estimated 92,900 tons of ore generating 12 million pounds of lead and 1.18 million ounces of silver. The Cactus mine was the most productive for gold and copper. From 1870 to 1957, the Cactus mine produced 1.40 million tons of ore yielding 13,500 ounces of gold, 34.5 million pounds of copper, and 301,000 ounces of silver.