Silver

silver

bornite

zeolite

chalcocite

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Formula: Ag
Native element, transition metal

Varieties

Küstelite is a variety of silver containing 10% - 30% of gold
Antimonial silver is a variety of silver containing less than 5% of antimony
Native amalgam is a mercury-bearing variety of silver

Properties of Silver

Crystal System: Isometric
Specific gravity: 10.1.to 11.1 measured, 10.497 calculated
Hardness: 2½ to 3
Streak: Silver white
Colour: Silver white
Solubility: Insoluble in hydrochloric acid; slightly soluble in sulphuric acid; moderately soluble in nitric acid
Melting point: 961.95oC
Boiling point: 2155V
Abundance: 75 parts per billion by mass, 20 parts per billion by moles in the Earth's crust, 1 part per billion by mass, 10 parts per trillion by moles in the Solar System (ChC)
Common impurities: Au,Hg,Cu,Sb,Bi
Environments:

Plutonic igneous environments
Placers
Hydrothermal environments

Native silver is found in the enriched zone of hypothermal (high temperature) hydrothermal veins, and sometimes also as a primary mineral, either in epithermal (low temperature) veins associated with sulphides, zeolites, calcite, baryte, fluorite and quartz, or in hypothermal (high temperature) veins associated with uraninite, arsenides and sulphides of cobalt, nickel and silver and native bismuth.

Localities

At the Mount Kelly deposit, Gunpowder District, Queensland, Australia, the deposit has been mined for oxide and supergene copper ores, predominantly malachite, azurite and chrysocolla. The ores overlie primary zone mineralisation consisting of quartz-dolomite-sulphide veins hosted in dolomite-bearing siltstone and graphitic schist.
Filaments of native silver to 2 mm long were observed with goethite and brochantite on one specimen (AJM 22.1.20).

At Cobalt, Ontario, Canada, skutterudite has been found as pseudomorphs after silver (KL p133).

At the Langis mine, Cobalt, Ontario, Canada, safflorite has been found as pseudomorphs after silver (KL p134).

At the Lin Ma Hang mine, North District, New Territories, Hong Kong, China, the lead-zinc deposit is a hydrothermal deposit which lies along a fault zone within altered acid volcanic rocks, consisting mainly of chlorite, biotite, sericite and actinolite, with scattered quartz. (Hong Kong Minerals (1991). Peng, C J. Hong Kong Urban Council)
The mineralisation consists of a series of fissure vein deposits varying from a few mm to several metres on width. The initial vein filling was coarse milky quartz. this was followed by an intrusion of fine-grained quartz carrying the metallic minerals, galena, pyrite, sphalerite and chalcopyrite, in order of abundance (Geological Society of Hong Kong Newsletter, 9.4.3-27).
Silver-bearing galena occurs as cleaveable granular masses (Hong Kong Minerals (1991). Peng, C J. Hong Kong Urban Council).

At Chuen Lung, Tsuen Wan District, New Territories, Hong Kong, China, in fissure veins in granite rocks in a small stream near Chuen Lung, silver-bearing galena occurs associated with massive granular amber coloured sphalerite, chalcopyrite, pyrite and pyrrhotite (Hong Kong Minerals (1991). Peng, C J. Hong Kong Urban Council)

The Lin Fa Shan deposit, Tsuen Wan District, New Territories, Hong Kong, China, is located in a remote area of the Tai Mo Shan Country Park, on a steep west facing slope of Lin Fa Shan, just above the abandoned village of Sheung Tong. The surrounding hillsides are covered with shallow excavations, representing past searches for wolframite, the natural ore of tungsten. The abandoned workings are extremely dangerous with unsupported tunnels, open shafts and no maintenance since their closures in 1957; the workings should not be entered (http://industrialhistoryhk.org/lin-shan).
Silver-bearing galena occurs here (Hong Kong Minerals (1991). Peng, C J. Hong Kong Urban Council).

At the Příbram District, Central Bohemian Region, Czech Republic, silver has been found as pseudomorphs after dyscrasite (KL p117).

At Zacatecas, Mexico, silver has been found as pseudomorphs after pyrargyrite (KL p118).

At Tsumeb, Namibia, native silver has been found associated with chalcocite, and as cementation on native copper (R&M 93.6.548).

At the Clargillhead vein, Garrigill, Alston Moor, Eden, Cumbria, England, UK, native silver occurs both as 1 to 2 micron diameter ‘droplets’ within banded limonite which locally forms alteration crusts on chalcopyrite and rarely as discrete grains up 8 microns within the quartz-fluorite gangue (JRS 23.51).

At the New Cliffe Hill quarry, Stanton under Bardon, Leicestershire, England, UK, native silver has been found with azurite and cuprite on diorite (RES p198).

At the Magma mine, Pioneer District, Pinal county, Arizona, USA, silver has been found as veinlets and sheets within solid bornite (R&M 95.1.87).

At Keweenaw county, Michigan, USA, some fine silver specimens have been found. They include crystallised silver 9.4 cm wide on a little prehnite matrix from near the North Cliff mine, a lone 1.9 mm wide twinned silver crystal on a crystallised pumpellyite substrate from the Franklin mine, and a striking specimen of ropy copper partially encrusted with blobs of silver from the Isle Royale mine (R&M 97.4.354-363).

The Central Mine, Central, Keweenaw county, Michigan, USA, initially targeted a series of sub-parallel mineralised fissure veins where the most copper-rich portion of the vein was close to the base of the main greenstone flow.
The Central mine has produced some outstanding examples of crystallised silver, typically showing branching arborescent crystallisation, composed of complexly twinned tetrahexahedral and spinel-twinned forms. Specimens showing native silver on native copper, and rarely the reverse, are known from the Central mine as well. Crystallised silver specimens are sometimes associated with prehnite, quartz, epidote and other minerals (MinRec 54.1.81).

At the Copper Falls Mine, Copper Falls, Keweenaw county, Michigan, USA, mineralisation occurs primarily in hydrothermal veins cutting preexisting lavas and as amygdules in the Ashbed flow.
Despite records of significant amounts of silver being recovered, mostly from the veins, very few silver specimens from the mine survive. Most of the known silver specimens were discovered in 1980 in a small surface-exposed vein which had never been mined. Silver specimens from this find consist of delicately branching groups of hoppered crystals, mostly cubes. Most of the crystals are quite small, few exceeding 5 mm, yet the specimens are exquisite and highly sought after (MinRec 54.1.112-113).

The Cliff Mine, Phoenix, Keweenaw county, Michigan, USA, is situated at the base of a roughly 70-metre basalt cliff. A curious feature of the impressive thickness of the greenstone flow here is that it contains zones of “pegmatoid”: areas where slow cooling in the core of the lava flow allowed for large feldspar crystals exceeding 1 cm to grow. Such features are normally only observed in intrusive igneous rocks and are almost unheard of in basalt flows.
The Cliff mine primarily exploited rich copper mineralisation in the Cliff fissure (vein). Although mineralised with copper to some extent along its entire length, the part of the vein just below the greenstone flow carried the richest copper mineralisation by far. A significant amount of the copper recovered at the Cliff mine came from amygdaloids in the tops of 13 basalt flows which were cut by the Cliff vein. The discovery and mining of this vein proved that the veins were the source of the large masses of float copper that were already well known, and proved that the primary ore mineral in the district was native copper, not sulphides, as had been suspected earlier.
The Cliff vein is widely regarded as one of the most silver-rich in the Lake Superior District. Cliff mine silver specimens are typically made up of complex twinned crystals, often severely distorted. Wires and sheets of silver have also been found in the Cliff mine (MinRec 54.1.25-49).

Alteration

Oxidation of pyrite forms ferrous (divalent) sulphate and sulphuric acid:
pyrite + oxygen + H2O → ferric sulphate + sulphuric acid
FeS2 + 7O + H2O → FeSO4 + H2SO4

The ferrous (divalent) sulphate readily oxidizes to ferric (trivalent) sulphate and ferric hydroxide:
ferrous sulphate + oxygen + H2O → ferric sulphate + ferric hydroxide
6FeSO4 + 3O + 3H2O → 2Fe2(SO4)3 + 2Fe(OH)3

Ferric sulphate is a strong oxidizing agent; it attacks silver according to the reaction:

silver + ferric sulphate → silver sulphate + ferrous sulphate
2Ag + Fe2(SO4)3 → Ag2SO4 + 2FeSO4
(AMU b3-3.7)

Silver-bearing minerals include:

Antimonides
allargentum
dyscrasite

Arsenides
kutinaite
novakite

Sulphides
acanthite
aguilarite
argentite
argentopentlandite
argentopyrite
arsenopyrite
canfieldite
kravtsovite
mckinstryite
panskyite
petrovskaite
pirquitasite
sternbergite
stromeyerite
uytenbogaardtite

Tellurides
hessite
krennerite
petzite
sopcheite
sylvanite
volynskite

Sulphosalts
argentotennantite
baumstarkite
benjaminite
cupropavonite
écrinsite
ferrofettelite
fizelyite
freieslebenite
gustavite
hatchite
jasrouxite
kenoargentotetrahedrite-(Fe)
makovickyite
miargyrite
ourayite
owyheeite
pearceite
polybasite
proustite
pyradoketosite
pyrargyrite
sicherite
stephanite
thunderbayite
trechmannite
vikingite
xanthoconite

Halides
bideauxite
bromargyrite
chlorargyrite
iodargyrite

Sulphates
argentojarosite

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