New Mexico Mineral Symposium — Abstracts

Unlike gold, silver occurs in more than 100 silver-bearing minerals. However, only 12 are common enough to be found in the true silver-only deposits in the western United States. Most collectors have well-crystallized specimens of many of the silver minerals in their collections, probably from the classic European localities or from Central and South America. Most likely the dominant silver mineral represented is native silver. But how many collectors have the "bonanza" silver minerals from the classic silver deposits of the western United States, especially from the localities listed in this paper? Don't feel bad, most state museums don't have them either. If they do, they are buried in the basement listed as "study" or "research" specimens and are probably the massive, noncrystallized "ugly ores" taken from these deposits after the main production years have long since passed.

The twelve silver minerals, which made up the bonanza deposits of silver in the western United States, are:

These minerals occur as the only ores of silver in the following silver deposits:

New Mexico
Silver City - Chloride Flats - argentite, chlorargyrite
Lake Valley - Bridal Chamber -chlorargyrite, bromargyrite
Utah
Silver Reef district - argentite, chlorargyrite
Colorado
Gold Brick district - Courtland mine - argentite, stephanite, pyrargyrite
Aspen - Mollie Gibson, Smuggler - argentite, polybasite, pearceite, pyrargyrite
Arizona
Chloride district - Distaff mine -argentite, chlorargyrite, proustite, pearceite
Tombstone district - Santa Ana mine - chlorargyrite, bromargyrite
Nevada
Comstock - argentite, stephanite, pyrargyrite, chlorargyrite, sternbergite
Tonopah - chlorargyrite, bromargyrite, argentite, stephanite, pyrargyrite, polybasite
Idaho
Silver City - naumannite, chlorargyrite, pyrargyrite, proustite, polybasite, miargyrite,
argentite
Delamar - argentite, chlorargyrite, miargyrite, polybasite, pyrargyrite
California
Calico district - chlorargyrite, bromargyrite

A review of the literature written when these deposits were being mined at their peak production revealed that these minerals often occurred as well-developed crystals and clusters. Unfortunately, very few, if any, of these well-crystallized specimens ever found their way into a collection, private or public. 

The most attractive group of silver minerals are the ruby silvers: proustite, pyrargyrite, and miargyrite. Even so, most of these are either massive or are poorly formed crystals. In fact, you have to look hard to detect any ruby-red color. This is probably because the ruby silvers, like the silver haloids, are light sensitive and darken with exposure to light. Yes, most of the important ore minerals of silver you see today from the United States are black, poorly crystallized, and ugly. But it wasn't always that way. 

A few of the silver deposits deserve some discussion:
Lake Valley, NM—The Bridal Chamber was one of the few true bonanza occurrences of silver in the United States. In a space of 20 ft high by 70 ft wide, 2.5 million ounces of silver were extracted. Most of this came from a 4-ft-thick seam of nearly pure chlorargyrite, much of it well crystallized. Chloride Flat (Silver City), NM—This is another bonanza-type deposit in New Mexico. Over three million ounces of silver were taken from this area over a period of 5 yrs.
Silver City and Delamar, ID—These two districts produced over $35 million in silver. When you consider that they are only 5 mi apart, this area becomes one of the major silver deposits in the United States. The chlorargyrite from both Delamar and Silver City occurred as fine-crystallized masses. Miargyrite was also an abundant ore mineral and occurred as excellent crystals in vugs. Naumannite, with properties similar to argentite, was the most common silver mineral in the district, commonly occurring as cubic and octahedral crystals. Most of the minerals previously identified as argentite were in reality naumannite. Proustite was also a very common ore mineral, especially in the Silver City district. A 500-pound mass of crystallized proustite from the Poorman mine was exhibited at the Paris Exposition in 1967. Two other silver minerals, polybasite and pyrargyrite, were also widely distributed in the ore from this area. Both occurred as well-developed crystals in vugs and on other minerals. 

The most productive district was the Comstock Lode with a recorded production of $150 million of silver. Tonopah, Nevada was second with a $125 million silver output. Thus, Nevada's title as the "Silver State". Probably the silver district that produced the least attractive silver ores is the Silver Reef of Utah. Although more than seven million ounces of silver were produced from argentite and chlorargyrite ore, these silver minerals occurred disseminated in sandstone. 

A modern (but mined out) silver deposit in Tombstone, Arizona deserves the final discussion. The Santa Ana mine consists of high-grade chlorargyrite and bromargyrite ore with native gold. I am
familiar with this mine as I was fortunate to do some work for the owners while it was still in the development state in 1963. An article in Newsweek, published in March 1964, described the mine as being so rich that "canvas was spread on the tunnel floor to catch almost pure silver dust". As mentioned before, the silver minerals were only the silver haloids, no native silver. I offered to sell and trade some of the higher-grade specimens with visible chlorargyrite and bromargyrite to collectors and clubs in Boston and New York City. The assays on these specimens were typically 1.5 ounces of Au and 1,500 ounces of Ag per ton. Guess what? — I still have all the specimens.