The Source of Silver – Its Minerals and Silver-Containing Minerals

Silver has been at more than $10 an ounce for the better part of a year, causing some people to be curious about where silver came from. Silver is mined from a variety of rock-like minerals, commonly in combination with gold. In some minerals gold predominates, but in others it is silver, while in a third class these two precious metals may be mixed with various common metals, such as lead, copper, zinc and iron. Few silver ores are absolutely free of gold, and vice versa, so a separate consideration of the two is more or less a tall order. For those minerals where the most valuable element is silver, silver is normally found in minerals that have a gray to black appearance. These minerals range from those with a metallic sheen to others with an earthy, sooty appearance. Black sooty minerals are common in many very rich silver ore samples. Most of these sooty black deposits consist of acanthite or various complex silver-containing sulfides (a sulfide is a mineral that contains sulfur in combination with one or more metals).

The most common valuable minerals that can constitute rich silver ores include native silver; acanthite (silver sulfide); pyargyrite (dark ruby ​​silver or silver antimony sulfide); Proustite (light ruby ​​silver or silver arsenic sulfide); Stephanite (brittle silver, also a silver antimony sulfide); Polybasite (also a silver antimony sulfide); cerargyrite (silver chloride); Bromyrite (silver bromide) and Iodirite (silver iodide). Bonanza grade silver ore can also contain various silver telluride minerals including Calaverite, Sylvanite and Hessite. To a lesser extent, base metal sulfides, including galena, sphalerite, pyrite, chalcopyrite, and chalcocite, can and often do contain silver, but in most silver ore deposits, silver it is more concentrated in the minerals of the group mentioned above. Of the base metal ores, the most common primaries are silver galena, sphalerite, and pyrite, while native silver and sulfides and arsenides are less common.

Standard types of silver ores:

There are two general classes of silver ore that have been mined: 1) lead-silver and 2) high-grade silver ores. Both almost always have varying amounts of gold. Lead and silver mines also supply, as noted above, by far the majority of the lead produced in the United States. High-grade silver ores typically have considerably lower base metal content and often contain a significant amount of gold.

1. Dry or siliceous minerals. These include: (a) Gold and silver ores proper, including bonanza epithermal silver ores; (b) flux minerals containing considerable amounts of iron and manganese oxides with small contents of gold and silver; (c) minerals containing precious metals with copper, lead and zinc in small amounts; and (d) scattered low-grade silver deposits. The states of Colorado, California, Nevada, South Dakota and Alaska have been the largest producers of this category of silver ore. The siliceous ores are partly free grinding; partly just concentrating, like parts of Colorado and Arizona; partly increasing slimming and cyanidating; and partly foundry. Much of the silver in siliceous gold and silver ores is obtained from the gold by cyanidation, with the silver being recovered by refining mill ingots. The rest is obtained by smelting rich ores and refining the copper or lead ingots produced. Siliceous silver minerals have variable ages, but most epithermal minerals are young, typically post-Miocene in age. Those found primarily in Colorado, Nevada, and Montana are associated with Tertiary lavas and are characterized by rich Bonanza-grade minerals. Some of the most productive may carry fluorite and usually also tellurides. In some, the value of gold may predominate; in others, silver.

2. Copper ores, generally with more than 1 percent copper, but with less in the case of Western Disseminated Minerals and Lake Superior. The largest gold producers are those in Utah, Arizona, Nevada and Montana. Silver production comes from the electrolytic refining of blister copper produced by smelting. Large scattered deposits from Utah, Arizona, Nevada and New Mexico are producing increasing amounts, while vein deposits from places like Butte, Mont., have also been important. Gold- and silver-bearing copper ores exhibit large differences in shape and age; not all occurrences yield much gold or silver, and, moreover, they are of greater importance as gold producers, silver being less associated with copper.

3. Lead-bearing silver ores: These are silver ores that contain 4 percent or more lead. The silver comes primarily from the lead and silver ores of Coeur d’Alene, Idaho, Utah (mainly Park City and Tintic), Colorado (Leadville and Aspen). Most of the production is obtained by desilverizing lead ingots using molten zinc. The silver and lead ores form a large class, with a fairly wide distribution, and although the two metals that characterize the group are the most prominent, there may also be, and often are, a variable amount of other metals such as gold, zinc, and copper. Silver contents, although sometimes high, are not necessarily visible and may be contained within the galena as Ag2S which partially replaces lead sulfide in the crystal. Ore deposits as a whole come in a variety of forms, the ore having been deposited either by fill or replacement of the fissure vein cavity, or both. Most of the major occurrences appear to have formed at intermediate depths. Oxidation zones frequently overlie ore bodies, and in many cases downstream secondary enrichment has probably occurred. Silver and lead ores form a widely distributed class in the Cordilleran region of the United States and supply most of the lead mined in this country. Prominent deposits have been mined in Colorado, Idaho, and Utah, but are also known from New Mexico, Montana, Wyoming, Nevada, Arizona, California, and South Dakota. Canada provides a small but steady output from British Columbia, while in other foreign countries, districts noteworthy for their commercial or historical importance are Broken Hill, New South Wales, Australia; Clausthal and Freiberg, Germany; Przibram, Bohemia; Hall, Sweden; Laurium, Greece; Mexico etc

4. Copper-lead or copper-lead-zinc ores. These are not important compared to the others. The gold they supply is small and the main silver production came from mines in Colorado and Nevada. Historically, the Eureka district of Nevada produced significant amounts of copper, lead, and zinc ore with large amounts of gold and silver. They are often designated as polymetallic minerals in modern classification systems.

5. Zinc minerals, containing at least 25 percent zinc. These produce little gold, and silver which is obtained primarily as a byproduct of smelting zinc concentrates and in the United States has been obtained primarily from deposits in Nevada, Montana, and Arizona.