Native silver

Silver is widely distributed in sulfide ores of which silver glance (argentite), Ag2S, is the most important. Native silver is sometimes associated with these ores as a result of their chemical reduction, while the action of salt water is probably responsible for their conversion into hom silver , AgCl, which is found in Chile and New South Wales. The Spanish Americas provided most of the world s silver for the three centuries after about 1520, to be succeeded in the nineteenth century by Russia. Appreciable quantities are now obtained as a byproduct in the production of other metals such as copper. 

Native silver is found in bornite-rich black ore (Matsukuma and Yui, 1979 Matsukuma, 1985) and it is thought to be secondary mineral. 

Electrum is abundant, compared with Type 1-B deposits. Native silver is poor in amounts. 

Abundance of electrum is small, although native silver is abundant in some deposits (e.g., Toyoha, Ikuno). 

Koryu aguilarite, pearceite, polybasite, proustite, pyrargyrite electrum, miargyrite, native silver, chalcopyrite, fahore, hematite, magnetite, pyrite, galena, sphalerite quartz, adularia, johannsenite, chlorite, kaolinite, vermiculite, Mn-calcite... 

Main opaque minerals are chalcopyrite, pyrite, pyrrhotite, sphalerite and bornite (Table 2.22). These minerals commonly occur in massive, banded and disseminated ores and are usually metamorphosed. Hematite occurs in red chert which is composed of fine grained hematite and aluminosilicates (chlorite, stilpnomelane, amphibole, quartz) and carbonates. The massive sulfide ore bodies are overlain by a thin layer of red ferruginous rock in the Okuki (Watanabe et al., 1970). Minor opaque minerals are cobalt minerals (cobaltite, cobalt pentlandite, cobalt mackinawite, carrollite), tetrahedrite-tennantite, native gold, native silver, chalcocite, acanthite, hessite, silver-rich electrum, cubanite, valleriite , and mawsonite or stannoidite (Table 2.22). 

Galena, tetrahedrite-tennantite, mawsonite and native silver occur in the copper rich ores but not in ordinary pyritic ores and copper rich ores most commonly occur as offshoots, tongues and veins in the deformed deposits. This suggests that these minor minerals formed during the metamorphic deformation stage accompanied by recrystallization. 

Native silver is rarely found in the form of nuggets, and it is probably for this reason that silver was recognized and came into widespread use at later times than did gold. Much native silver occurs as minute grains dispersed in small concentration in argentiferous (silver-rich) sands. Now, when silver is mixed with mercury, it forms amalgams (see below) the amalgamation... 

Man has used this metal for centuries. It sometimes is found in native silver, but is more commonly foimd combined with sulfur as argentenite. Most of the World s supply of silver is obtained as a by-product when other metals such as lead, zinc, and copper are processed. Silver is used in photography, in medicines, and in coins. 

Native silver and argentenite are not luminescent in their natural form, but as in the case of gold, it is possible to induce the artificial emission (Fig. 8.19). 

Nickel in Meteorites. Centuries before the discovery of nickel, primitive peoples shaped meteoric iron into implements and swords and appreciated the superiority of this Heaven-sent metal (125). In 1777 J. K. F. Meyer of Stettin noticed that when he added sulfuric acid to some native iron which P. S. Pallas had found in Siberia, he obtained a green solution which became blue when it was treated with ammonium hydroxide. In 1799 Joseph-Louis Proust detected nickel in meteoric iron from Peru (126). This grayish white native iron had been observed by Rubin de Celis. Since it did not rust, it was sometimes mistaken for native silver. 

The native silver in serpentine in which Vauquelin discovered iodine had been obtained from Joseph Tabary, a dealer in Mexican and South American minerals (137). In an attempt to ascertain the exact locality from which this mineral had been obtained, D.-F. Arago questioned some young Mexican army officers who had been sent by their government to study in Paris. To his surprise, one of them, Captain Yniestra, was able to give the following clear and definite reply ... 

This mineral, eays Phillips, which was formerly eupposod to bo of rare occurrence, constitutes one of the richest and most abundant ores of Chili, where it is frequently associated with native silver, apparently resulting from its decomposition. It also occurs in massive amorphous fragments in connection with sulphide of silver, but still more frequently in small cubical crystals disseminated in the ferruginous rock known in Chili and Peru under the names of paeoe and colloradoe. Specimens of this mineral, although of comparatively rare occurrence in the European mines, have bean obtained from Norway, Siberia, Saxony, the Harts, and Cornwell. ... 

Metallurgy. As is true for any metal, the procedure employed in the metallurgy of silver must be adapted to the particular form in which the metal exists in its ores. Native silver may be separated by the process of amalgamation. The crude ore containing metallic silver is treated with mercury to form an amalgam, which is then separated from the undesired earthy components of the ore. The amalgam is heated in a retort, and the silver remains behind as a residue, while the mercury is distilled from the retort, condensed, and used again. This... 

ICP-MS has also been used to measure trace elements in archaeological native silver artifacts [345] in order to identify their geographical origins. The low detection limits provided by ICP-MS allowed analysis of trace elements on 3 to 15 mg of sample. The passivation of alloy steels using acid solutions has been studied by XPS measurements of the solid in combination of ICP-MS analysis of the passivation solutions [346,347]. When bullets are crushed on impact, striations cannot be used for identification. The percentage of antimony, trace element composition, and lead isotope ratios in bullets was measured for forensic evidence [348]. The lead isotope ratios were found to be the most useful evidence. 

Silver is another native metal found in museum collections in a variety of forms. Chemically, silver differs gready from gold in that it is highly reactive. Silver occurs in its native state, but is more stable in compounds with other elements. The black tarnish so common on silver items is silver sulfide. Silver objects that have been buried for any length of time may be completely altered, particularly if water is present. When the alteration that begins as tarnish is complete, and all native silver has been combined with other elements, a worked piece will usually lose its integrity and disintegrate. If silver is subjected to moisture in the presence of the element chlorine, as it would in seawater or brackish water, horn silver or silver chloride may develop. 

Silver ores are also leached by the cyanide process. For native silver the reaction is similar to that for gold ... 

The amalgamation process is used for native silver. The ore is treated with mercury, which dissolves the silver. The liquid amalgam is then separated from the gangue and distilled, the mercury collecting in the receiver and the silver remaining in the retort. 

Ores of silver native silver, argentite, cerargyrite (horn silver). Metallurgy of silver cyanide process, amalgamation process, Parkes process. O mpoimds of silver silver oxide, silver chloride, silver bromide, silver iodide, silver ammonia complex, silver cyanide complex, silver thiosulfate complex, silver nitrate. 

What chemical reaction is used to convert native silver to a soluble silver salt in the cyanide process ... 

Mexico, the leading silver producer, obtains about half of its output from mines in which silver is the principal ore metal. Many of the mines are epithermal fissure veins, and most host a polymetallic assemblage whose exploitation is economically dependent on the high silver values. Although acanthite [Ag2S] and native silver predominate in some veins, in others much of the silver occurs in silver sulfosalts and as silver substitutions in tetrahedrite [(Cu,Fe,Ag)i2Sb4Si3] and other minerals. 

Derivation By-product of operations on copper, zinc, lead, or gold ores, but some smelters still operate on native silver. The recovery ranges from 166 ounces to a few thousandths of an ounce per ton. 

Source Chief silver ores are native silver, argentite (silver sulfide), and cerargyrite (silver chloride). 

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