Also Known As:	Advance, Colorado, Tarshish
Commodity:	Gold, Silver
Span of Operation:	1857 - ?
County:	Alpine
Property Ownership:	Unknown
Location:	Sec. 31 T. 10 N. R. 21 E.

Show Mine on Map (Experimental)

Clark, William B., 1977
Mines and Mineral Resources of Alpine County, California; p. 22-26

Zaca (Advance, Colorado, Tarshish) mine, by James R. Evans

History. This famous and productive mine was one of the first to be located in Alpine County. It is a consolidation of two adjacent mines once known as the Advance and the Colorado. L. L. Hawkins, rancher and mining engineer, claimed to have made the discovery of silver ore along Monitor Creek on Colorado Hill at or very near the site of the present mine workings in 1857. The discovery was originally known as the Tarshish mine. By 1866 the mine was purchased (from Hawkins?) by the Schenectady Gold and Silver Mining Company, New York. At that time an indefinite amount of tunnel work was done. In 1867 news of a rich strike at the Tarshish mine was recorded by the Silver Mountain Bulletin (April 1867):

"We saw a piece of the ore, of about a pound in weight, on Thursday evening, which was nearly all a mass of antimonal silver. We understand that an assay by Mr. Graff, gave $150 in gold, and over $800 in silver to the ton."

Unfortunately, high-grade ore like this came only in local areas, and the owners also had trouble in milling and processing the complex sulfide ore. These very high assays, however, kept alive hope of finding another bonanza such as that at the Comstock Lode near Virginia City, Nevada. In fact, another strike of rich ore in the late summer of 1870 by the Schenectady Company prompted the following statement from the Alpine Miner (September 1870):

"Well the county is safe now without a doubt, for this soft ore, without further reduction works than a simple system of concentration, is convertible into sack sulphurets worth 75 cents to $1 per pound. Above, below, and on all sides the Tarshish is proving to be a great and continuous mine, and anybody who doubts the future prosperty of Monitor would see cause to doubt that of the United States of America."

Monitor was a mining town established in 1863 in Monitor Canyon just east of the discovery at the Tarshish mine. It was named in honor of the famous ironclad ship of the Civil War. Monitor thrived because of British investors who controlled many of the mines in Alpine County until about 1880.

A 20-stamp mill and chlorination processing plant, which cost an estimated $70,000, was built in 1871 or 1872 by the Schenectady Company at Monitor. Apparently the Washoe process was used for silver recovery, but unfortunately, less than half of the assay value of the ore was recovered. This inefficient process plus the additional panic created when the United States discontinued coinage of silver dollars and demonetized silver resulted in a mine shut-down by the end of 1873. In November 1876 the Tarshish or Schenectady mill was sold by the sheriff on a judgment for B. E. Hunter of Monitor for $6,544 plus costs (Alpine Chronicle, November 1876).

Logan (1921, p. 402) reported that Peter Curtz opened the mine in 1879 and operated it for one year. Chlorination processes were used on the ore, and bullion recovered was 91 to 95 percent of the assay value of the concentrates. Concentrates ranged in value from $20 to $900 a ton and averaged $585, of which 38 to 43 percent was gold and the remainder silver. Ore, however, averaged only $12 a ton.

The record of mine activity from 1876 to 1920 is sketchy. It was reported inactive in 1888 (Irelan, p, 38) and 1914 (Eakle, 1919, p. 23 and 25), but some "recent" mining activity was reported by Eakle. Logan (1921, p. 401) writes that Mr. DuBoise held a lease and option on the property about 1912, and took out several thousand dollars worth of ore from the DuBoise stope in the Advance tunnel in one year. High-grade ore was shipped to an unnamed refinery, and low-grade was processed at the Colorado mill (same as the Schenectady mill?). The ore occurred in bunches and was associated with pink and black manganese minerals. A. M. Dahl, J. H. Pearson, and A. L. Stewart of Markleeville and G. P. Merrill of Woodfords were the owners in 1920. They "ran" a 40-foot raise on a 1-inch stringer of sulfide ore adjacent to the DuBoise stope. Small shipments were made in the summers of 1920 and 1921 and are reported in table 4. The mill was removed in 1921.

The name "Zaca" may have been taken from the large yacht Zaca that belonged to Templeton Crocker, a noted San Francisco financier, who apparently had an interest in the mine during the 1930s (Francis Frederick, personal communication, 1965).

Continuous production was reported from the mine from 1931 to 1941 although ownership is not known. By 1960, the Siskon Corporation, Box 889, Reno. Nevada, owned the property and had leased it to the present (1973) operator Claude Lovestedt, who began exploration and development work.

Under option, the W. S. Moore Company of Reno, Nevada, trenched and drilled a few hundred feet on the top of Colorado Hill over the underground workings in 1963 and 1964. They hoped to block out sufficient ore of mining grade to develop the area by open cut and bench quarry methods but have since removed all equipment. Underground mining continued in the Colorado tunnel under the direction of Claude Lovestedt. From 1962 to 1966, high-grade silver-gold ore assaying from about $40 to as much as $300 per ton was mined from overhand stopes in the tunnel, sacked, and shipped to the American Smelting and Refining Company's smelter at Selby, California. Assays from drill cores adjacent to the stopes showed values that ranged from $0.10 to $100 a ton.

From 1967 through 1969, on an intermittent basis, Bruce Wachter, a graduate student at Stanford University, worked in the Monitor district. His dissertation -- Rapid fresh and altered rock-analysis for exploration reconnaissance: Infrared absorption applications in the Monitor district, California--was completed in 1971. Part of his study was a cooperative venture with the U.S. Bureau of Mines. The Bureau drilled one 500-foot core hole (inclined 40° N 30° W) by the portal of the Lower Advance tunnel.

From 1970 through 1972, the Parnasse Company, Scottsdale, Arizona, did extensive exploration work around the Zaca mine area. Five vertical core holes were drilled, four just over 2,000 feet and one about 1,600 feet. Surface geochemical sampling was done prior to drilling. The Parnasse Company has since removed all equipment and released all interest in the property.

Tunnels B and C and an extension of the Upper Advance tunnel were done from 1968 to 1973 by Claude Lovestedt. In October of 1973, a drift was being driven in a southwest direction off the main workings of the C tunnel about 190 feet from the portal. The drift is on a sheared mineralized zone about 12 feet thick that dips about 75° to the southeast.

Geology and Mineralogy. The Colorado Hill area is composed of dark gray to green andesitic flows, tuff breccia, volcanic breccia, lapilli-tuff, and agglomerate of Late Tertiary age, which are intruded by light colored and prominently flow banded rhyolite wall rocks that have been intensely altered and silicified. Outcrops of rhyolite are striking in appearance and locally mineralized. Lindgren (1911, p. 191) described them as: "white, yellow, and red outcrops consisting of jaspery and chalcedonic rocks as well as kaolin. In places the rocks are rich in sulphides, principally pyrite, but also argentite, and various rich silver antimonites. Zinc-blende, chalcopyrite, pyrargyrite, enargite, and galena also occur. No well defined veins could be seen."

Eakle (1919, p. 9-14) also discussed the vividly colored mineralized rocks and noted several other minerals in the Monitor-Mogul area not mentioned by Lindgren: gold, polybasite, stephanite, stromeyerite, and tetrahedrite. He mentioned the occurrence of rhodochrosite as a gangue mineral, typically with silver-rich minerals, and that it weathered readily to form black stains on outcrops. Eakle also noted the absence of definite veins and walls within the mineralized rocks.

Gianella (1938, p. 341, 345-347) described minute acicular crystals of hübnerite (MnO, 23.6%; FeO, 2.38%; WO₃, 73.97%) in specimens from the Zaca mine. It was found encrusting ore minerals, drusy quartz crystals, and on quartz crystals filling vugs. Mill superintendent (1937) O. J. Benstron felt that hubnerite was an indicator of high-grade ore and at times was so abundant as to form a brownish band on the concentrating table. Quartz and rhodochrosite were described as gangue minerals by Gianella (1938, p. 342-343). Locally, the rhodochrosite contained cavities lined with clear quartz crystals.

Three main rock types are exposed in the immediate area of the Zaca mine: dark gray finely porphyritic andesitic basalt, white and yellow to reddish-brown rhyolite locally showing abundant thin ribbons of gray quartz and some blocks of whitish-gray lapilli-tuff breccia, which apparently have been caught up in the rhyolite during its intrusion. The intrusive contact between andesitic basalt and rhyolite is well exposed at the portal of the Colorado adit and in parts of the Colorado, Advance, and Upper Advance adits. Locally, contacts between these rocks are sheared.

Colorado Hill is largely covered with talus and slope wash, but on the south slope prominent "ribs" of rhyolite and rhyolite-breccia are exposed and are readily visible from the Monitor Pass road. "Ribs" trend north and are as much as 50 feet in outcrop width, a few tens of feet in maximum height, and from a few to several hundred feet long.

Bright colors of the silicified rocks are a result of oxidation of sulfide grains and the formation of sulfuric acid. The acid has attacked the rock, leaving iron and manganese stains along seams and fracture planes. Cube- and prismatic-shaped cavities that contained pyrite and other sulfide minerals are common, and some are partially filled with a residue of hydrous iron oxide. In places, as much as 50 percent of the rhyolite is composed of gray quartz bands ranging in thickness from a fraction of an inch to as much as 1 inch and occasionally more. Material between the bands of gray chert is white and locally shows phenocrysts of sanidine (?) locally altered to clay.

Rhyolite in the underground workings is gray to white and contains fresh disseminated sulfide minerals. Locally, areas are strongly mineralized with pyrite, silver-rich tetrahedrite, galena, and polybasite with minor free gold and silver. Argentite, chalcopyrite, arsenopyrite, sphalerite, and enargite may be present. Mineralized areas occur in soft clay pockets a few inches to several feet in longest dimension parallel to and crosscutting quartz banded zones and in soft friable cores of anticlinal structures. Since 1960, the bulk of high-grade ore has come from the cores of these anticlinal structures, and lower grade ore from the flanks. Many cavities occur in the rhyolite and are filled with gray euhedral quartz crystals as much as three-quarters of an inch long. Most crystals, however, are much smaller. Crystals of rhodochrosite, hilbrierite, pyrite, and silver-bearing sulfide minerals have been deposited upon the vuggy quartz, testifying to the late stage development of mineralization.

Mining Operations and Water Use. Ore is trammed from the workings to surge piles near the portals of each tunnel and transported by a 10-ton truck to the mill on the south side of Monitor Creek adjacent to the Monitor Pass highway. The mill flow-sheet is shown in figure 7. Concentrate from the complex ore is shipped after milling to the American Smelting and Refining Company smelter at East Helena, Montana.

Waste discharge requirements for the Zaca mining and milling operation were adopted by the Lahontan Regional Water Quality Control Board in 1962 and revised in 1968. After the valuable metals have been recovered in the mill, a slurry of ground rock and water is discharged into two ponds operated in a series for the settling of waste solids. The water from the second or lower pond filters slowly into the ground. No water is discharged into Monitor Creek.