The Independent Mining District lies about two miles up Gamble Gulch in northern Gilpin County, south of Rollinsville. The Central Mining District is located over the hill just east of the Independent District at the head of Lump Gulch. The Deadwood Diggings, the first placer gold discovery made in the Snowy Range mountains in January of 1859, is located downstream where Gamble and Lump Gulches join, adjacent to South Boulder Creek.

The Independent Mining district was founded during the summer of 1860 with the discovery of the Gold Dirt Mine. The Perigo mine was soon discovered about one half a mile further west along the same set of roughly east-west trending veins. The early placer workings in Gamble Gulch were fabulously rich and at first appeared to rival Central City. A town of log houses named Perigo soon sprung up in Gamble Gulch. One sluice took out $2,227 (112 ounces of gold) in 17 days. By the end of 1860 six stamp mills were operating in the gulch.

The placer gold was worked out of the gulch by the summer of 1861 and the focus of mining switched to the weathered quartz veins in the upper portions of the Gold Dirt and Perigo mines. The weathered or oxidized vein material from the upper 140 feet of the Gold Dirt mine was very rich. In 1860, Sweet and Hollister, owners of the Eagle Gold Mining Company, made $150,000 (7,500 ounces of gold) from the mine. Between June and November of 1861, two other men cleared $35,000 (1,750 ounces of gold) from the Gold Dirt mine.

John Quincy Adams Rollins owned the Perigo mine and much of the land along Gamble Gulch west of the Gold Dirt mine. The Perigo mine is the largest mine in the district. The total production of the mine is unknown, but during the fall of 1861 he recovered $3,000 (150 ounces of gold) from 90 tons of ore. J. Q. A. Rollins laid out the town of South Boulder, now known as Rollinsville, in 1861 as a site for the milling and processing of ore from the Perigo mine. The lower grade ore was treated at a 100 ton per day stamp mill at Perigo and the concentrates were shipped from South Boulder (Rollinsville).

Processing technology of that era incorporated wet crushing, gravity separation, and mercury amalgamation of free-milling gold ore from the weathered and degraded upper portions of the vein. Below depths of about 150-250 feet the unweathered and unoxidized sulfide (mostly pyrite) bearing vein material needed to be sent to a smelter for the gold to be recovered. Prior to 1869, this high-grade direct smelting ore had to be sent across the ocean to Swansea, Wales, for smelting at a considerable expense. From 1859 to 1869, these primitive stamp-mills were only recovering something like 15 to 40 percent of the gold from the unoxidized sulfide bearing vein material found in the deeper portions of the mines, and none of the silver or copper. The miners did recover enough of the gold to make a profit without having to ship the ore across the ocean. At this recovery rate, nothing less than $100 per ton (5 ounces per ton) gold ore could be mined at a profit.

By the end of 1861 the upper weathered portions of most mines were mined out and rendered unsafe from careless mining practices. The Gold Dirt mine, which was paying $1,500 to $2,000 a week from the work of 60 men, could only recover $1.40 from 18 hours of work once the unweathered vein material was reached below a depth of about 140 feet.

The mine owners soon realized that there was an easier way to make money other than digging gold out of the ground. “The inclination to neglect mining and trade, speculate, do anything but mine, is also an evil as old as the country, and doubtless destined to outlast it (Hollister, 1867).”

Starting close to the end of 1863 cash-rich eastern investors from New York and Boston began to purchase Colorado mining properties at fabulously high prices, even though it was generally known that many of the large 50 stamp mills built in 1862 were unable to turn a profit. The eastern companies would hire mill men fresh out of school in the east who were new to the business, only to discover that few of them could actually operate a mill at a profit.

The new owners of the Gold Dirt mine built a brand new 50-stamp mill in South Boulder (Rollinsville) at the mouth of Gamble Gulch in 1861, but the mill could not be made to pay and was rendered useless by June of 1865. In 1868, Perigo was mostly abandoned.

All this changed when Professor Nathanial P. Hill established the Colorado Smelting Works in Black Hawk in 1868, and recoveries were improved to 50-70% of the value in the unoxidized sulfide ore, so ore paying $15 to $20 per ton (0.75-1.0 ounces per ton gold) could be mined with success. Many of the abandoned mines were reopened in 1869, and the mining districts of Colorado reached their highest production during the 1870s.

The mines of Perigo reopened and large mills built at the mouth of the Gold Dirt mine and the Perigo mine. As it turned out, the mines were unable to properly overcome inexperienced mill men and the high cost of building such large milling operations, equipped with expensive brand new equipment. A vast amount of labor was required to run these mills and run they would, pay or no pay, to keep up appearances.

The last gasp of Perigo occurred in the early part of the 20th century when a large mill was built about one half a mile down Gamble Gulch from the Gold Dirt mine. The mill was built at the mouth of the Penobscot Tunnel. The Penobscot Tunnel was a development tunnel driven under Tip Top Hill, intended to mine the veins of the Perigo mine. By the time the tunnel reached the Perigo vein, the company had run out of money and they were never able to mine any of the vein.

References

Bastin, E.S., and Hill, J.M., 1917, Economic geology of Gilpin County and adjacent parts of Clear Creek and Boulder Counties, Colorado: U.S. Geological Survey Professional Paper 94, 379 p.

Fossett, F., 1876, Colorado, Its Gold and Silver Mines, Farms and Stock Ranges and Health and Pleasure Resorts: 1st ed., Crawford, N.Y.

Hollister, O.J., 1867, The Mines of Colorado, Samuel Bowles and Co., Springfield Mass., 45 p.

Lovering, T.S., and Goddard, E.N., 1950, Geology and ore deposits of Front Range, Colorado: U.S. Geological Survey Professional Paper 223, 319p.