During their tenure on the site, the San Francisco Copper Mine and Reduction Works Co. sank shafts and drifts to a depth of roughly 150 feet in depth, and, after the cave-in of 1880, excavated an open cut mine 300 feet long, 70 feet wide, and 75 feet deep. They produced more than 150,000 tons of ore, averaging about 5% copper. The cement copper - averaging about 80 to 83% Cu - was bagged and shipped to Boston, MA for final refining (Aubury, 1902).
In 1888, with the higher quality ore available on site depleted and copper prices sorely depressed, the San Francisco Copper Mine and Reduction Works terminated their mining activities on the site. They sold the property to the Imperial Paint Company and Copper Works.
There is no evidence that the Imperial Paint Company actively mined on the site. Instead, they reworked the tailings left behind by their predecessor, recovering additional cement copper by leaching, and also used the iron oxides left as a residuum from the roasting/leaching process for a Venetian red paint pigment.
Irelan (1892) describes the dump being reworked by the Imperial Paint Co. as "a very large one. It is over 200 feet long, 80 feet high, and 100 feet throuh... about 2 per cent of copper, or a little over, was left on the dump."
The leaching of the copper, and recovery of cement copper, by the Imperial Paint Co. appears to have generally followed the same plan as implemented by the San Francisco Copper Mine and Reduction Works:
Water is sprayed upon the top of the dump in various places, which, working its way through, is collected at the bottom and run into a large trough; this solution is heavily charged with sulphates of iron and copper. The copper in solution is precipitated upon scrap iron placed in the trough, which is 2 feet wide and 1 foot deep. A deep riffle is put in every 40 feet to settle the cement; the scrap is placed near the riffle, leaving the lower portion of each space free for the perfect precipitation and settling of the cement. The scrap is turned and brushed off twice each day. The cement settles and is cleaned up twice a month, when the scrap is thrown out and washed off. The cement is then worked through a 30-mesh screen into settling vats, dried and shipped. It could be melted into bars if desired. The cement contains 80 per cent copper, the resulting bars being .998 fine, and equal to the best lake copper. The sluice run is 1,000 feet in length. The lower portion of the sluice is only cleaned up occasionally, and yields a 60 per cent cement. In summer, when water fails, which is about three months during the year, water is hoisted in buckets from the open pit and run through the sluice. The mine water is nearly as heavily charged [with copper in solution - DER] as the water from the dump. (Irelan, 1892)
The spent leachate was then processed to recover suspended, fine grained iron oxide for paint pigment. After being washed in vats with stirrers, and any coarse particulates removed, the iron oxide was dried, roasted in a reverberatory furnace, and ground in a paint mill. Irelan gives the following analysis of the pigment:
SiO2 / Insoluble...............14.65
Moisture (combined).......... 4.40
CaO, MgO, and loss........... 0.15
Irelan pronounced the resultant paint as being of "an excellent color and is far superior in quality, composition, and preservative effects to any of the metallic paints imported from the East. Its composition is as follows: For rough work this paint can be put on with a mixture of three fourths water and one fourth oil; when put on with this small proportion of oil it will not rub in the least. The entire dump is available for the manufacture of paint after the copper has been leached." However, his optimism was premature. "The paint, enormously popular to begin with (Gold Medal in SF 1894 Winter Exposition) ended in infamy sometime around 1896/97 when it was discovered that the paint corroded structural nails and barns were beginning to collapse." (Wanket et alia, 2002).
The mine was purchased in 1897 by the Spence Mineral Company, who used the remaining low-grade sulfide ores for the production of sulfuric acid. After the mine was dewatered, they resumed mining the low grade pyrite which they shipped to sulfuric acid manufacturers in San Francisco as raw feed. Charles W. Howard was the general manager and superintendent. After the acid factories had desulfurized the ores by roasting, the remaining "clinker" was returned to the Spence Mineral Co (apparently not to the Spenceville site, but rather to a new treatment works in the San Francisco Bay area) to be treated to recover copper along with small percentages of gold and silver. According to Aubrey (1902) "The copper contained in these cinders, amounting to from 3 to 3.5 per cent, together with the gold and silver, and the iron which has a value as a flux, netted the company from $2 to $3 per ton when subsequently sold to smelters."
The facilities were destroyed by fire sometime between 1915 and 1917, and about 1918 all mining on site ceased.
In the 1960's, the land surrounding the Spenceville Copper Mine became the Spenceville Wildlife Area, under the jurisdiction of the California Department of Fish & Game. In the late 1990's, the mine site was determined to pose an environmental risk, and a survey determined that the open pit mine contained 5 million gallons of copper-laced water with a pH of 2.5, as well as 60,000 cubic yards of metalliferous mine waste. A site remediation was executed during the period 2000-2002.
As part of the planning of the remediative action, a Cultural Resources Assessment was required which identified some archaeological remains dating from the copper mine. The discoveries included:
....a 126 foot by 30 foot concrete platform, which apparently was used to dry copper cement with associated strap rail system to move the material, and a subterranean tar and felt covered wooden containment tank, 24 feet long by 12 feet wide, with canvas gaskets designed to be placed between wallboards and uprights. The most striking finds were made during mine waste excavation. A wooden conduit was discovered beneath tailings exceeding 25 feet in depth. The conduit was 134 feet long on a 10 percent grade with an internal channel that narrowed from 6 inches wide to 4 inches wide. Also, a tar covered brick settling tank and a tar-coated canvas covered wooden tank were discovered beneath tailings of 14 to 16 feet in depth. The mine pit proper revealed an incline on the southwest wall with only strap rails missing, and a partially timbered vertical shaft was discovered in the west wall. Two ore buckets were recovered both with wooden trap doors in the base and one bucket has remnants of tar lining the inside. Overseas Chinese porcelain and stoneware shards were found near some refractory ovens. (Wanket et alia 2002)
Working Copper Ores At Spenceville
Scientific American Supplement Vol. XIV No. 363
New York, December 16, 1882
Aubury, Lewis E.
The Copper Resources Of California
Bulletin No, 23, California State Mining Bureau San Francisco, April, 1902,
Sacramento, CA 1905
Irelan, William Jr
Eleventh Report of the State Mineralogist, (First Biennial) Two Years Ending September 15, 1892. Sacramento CA (1893)
Raymond, Rossiter W (1875)
Statistics Of Mines And Mining In The States And Territories West Of The Rocky Mountains; Being ÃÂ¢hÃÂµ Seventh Annual Report United States Commissioner Of Mining Statistics, Government Printing Office 1875
Robert, E. W. (1867) Historical Sketch Of Rough & Ready Township.
In: Bean, E. F. - Bean's History and directory of Nevada county, California With sketches of the various towns and mining camps Also full statistics of mining and all other industrial resources. Nevada, CA Printed at the Daily Gazette Book and Job Office 1867
Wanket, Daniel; Pujol, Alberto; Walker, William J.; Reynolds, Stephen (2002)
Spenceville Mine Closure https://fs.ogm.utah.gov/pub/MINES/AM...MD1/Wanket.pdf
Completed 13 May 2008
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