Galena

sulphide

anglesite

Formula: PbS sulphide
Specific gravity: 7.2 to 7.6
Hardness: 2½
Streak: Lead-grey
Colour: Lead-grey
Solubility: Slightly soluble in hydrochloric and nitric acids
Environments:

Carbonatites
Metamorphic environments
Hydrothermal environments

Galena is a common primary mineral, found in hypothermal (high temperature) and mesothermal (moderate temperature) veins and in contact metamorphic deposits.
In hydrothermal veins it is often associated with anglesite, baryte, bornite, calcite, cerussite, chalcopyrite, dolomite, fluorite, marcasite, pyrite, quartz and sphalerite.

At Tsumeb, Namibia, galena has been found associated with enargite (R&M 93.6.544).

At Alderley Edge, Cheshire, England, UK, copper mineralised solutions percolated through porous sandstones and deposited barium, cobalt, copper, lead, vanadium and zinc minerals between the sand grains. Anhydrite formed as cement in permeable rocks, then baryte was deposited, followed by pyrite, chalcopyrite, sphalerite and galena. Subsequently a second generation of baryte and iron-rich calcite followed. These minerals crystallised from highly saline, sulphate-rich brines, at a temperature of 50 to 60o C. About 65 million years ago the deposit was uplifted, and oxygenated ground water oxidised original sulphide minerals. Galena was oxidised to cerussite, anglesite and pyromorphite (RES pps 49-50). A sample of galena has been found associated with copper and pyromorphite (RES p54).

At the Gregory mine, Ashover, Derbyshire, England, UK, galena is associated with fluorite (RES p102).

At the Odin mine, Castleton, Derbyshire, England, UK, galena occurs in limestone (RES p102).

At Wakebridge mine, Crich, Derbyshire, England, UK, galena is associated with baryte and calcite (RES p129).

At the Millclose mine, Daley Dale, Derbyshire, England, UK, galena is associated with calcite, sphalerite, fluorite, pyrite and baryte, on limestone (RES p92, 94).

At Eyam, Derbyshire, England, UK, galena is associated with fluorite, calcite and sphalerite (RES p117, 118).

At the Whitwell quarry, Whitwell, Derbyshire, England, UK, galena is associated with baryte (RES p138).

At the Breedon quarry, Breedon on the Hill, Leicestershire, England, UK, galena is associated with cerussite, baryte and wulfenite (RES p202, 203).

At Cloud Hill quarry, Breedon on the Hill, Leicestershire, England, UK, galena is associated with dolomite and calcite (RES p204).

At the Ticklow Lane mine, Shepshed, Leicestershire, England, UK, galena is associated with cerussite (RES p225).

At Earl Ferrers mine, Staunton Harold, Leicestershire, England, UK, galena is associated with calcite, dolomite, sphalerite, chalcopyrite and baryte, in dolomitised limestone (RES p217-222).

At the Bog mine, Callow Hill-Bog district, Shropshire, England, UK, galena is associated with fluorite, sphalerite and calcite (RES p279).

At Snailbeach mine, Callow Hill-Bog district, Shropshire, England, UK, galena is associated with quartz and calcite (RES p272, 275).

At the Callow Hill quarry, Pontesbury, Callow Hill-Bog district, Shropshire, England, UK, galena is associated with pyrite (RES p290).

At the Tankerville mine, Hope-Shelve district, Shropshire, England, UK, galena is associated with calcite (RES p281).

At the Shadwell quarry, Much Wenlock, Shropshire, England, UK, galena is associated with calcite in limestone (RES p296).

At the Ecton mine, Staffordshire, England, UK, galena is associated with chalcopyrite, sphalerite and calcite (RES p306).

At Cookes Peak mining district, Luna county, New Mexico, USA, galena is the primary lead sulphide mineral present, but most of the galena occurs in replacement pods hosted by limestone, where oxidation has not occurred. Some specimens have been found where the galena has been partially altered to cerussite and coated with microcrystalline wulfenite (R&M 94.3.232-233).

Alteration

In the oxidation zone of epithermal (low temperature) veins initially pyrite is oxidised to ferric sulphate, which is itself a strong oxidising agent. The ferric sulphate then reacts with galena to form anglesite.
Oxidation of pyrite:
pyrite + oxygen + H2O → ferrous sulphate + sulphuric acid
FeS2 + 7O + H2O → Fe2+SO4 + H2SO4
The ferrous (divalent) sulphate readily oxidises to ferric (trivalent) sulphate and ferric hydroxide
ferrous sulphate + oxygen + H2O → ferric sulphate + ferric hydroxide
6Fe2+SO4 + 3O + 3H2O → 2Fe3+2(SO4)3 + 2Fe3+(OH)3

galena, ferric sulphate, water and oxygen to anglesite, ferrous sulphate and sulphuric acid
PbS + Fe3+2(SO4)3 + H2O + 3O → PbSO4 + 2Fe2+SO4 + H2SO4
Galena is oxidised to anglesite and ferric iron is reduced to ferrous iron (AMU b3-3.7).

Galena may also dissolve in carbonic acid from percolating rainwater to form hydrogen sulphide, which is then oxidised to form anglesite (KB).
galena and carbonic acid to Pb2+, hydrogen sulphide and HCO3-
PbS + 2H2CO3 → Pb2+ + H2S + 2HCO3-
(KB)
then hydrogen sulphide, oxygen, Pb2+ and HCO3- to anglesite and carbonic acid
H2S + 2O2 + Pb2+ + 2HCO3- → PbSO4 + 2H2CO3
(KB)

galena and oxygen to anglesite
In air, at outcrops of galena,
PbS + 2O2 → PbSO4
At ordinary temperatures the equilibrium is displaced far to the right, and the apparent stability of galena is a result of the slowness of the oxidation (KB).

In the oxidation zone of epithermal veins galena alters to anglesite or cerussite depending on the acidity. Cerussite forms in more basic (alkaline) environments than anglesite.

During the progressive weathering of assemblages of supergene lead minerals anglesite disappears first, then cerussite, and finally only pyromorphite, mimetite and vanadinite persist (AM 100:1584-1594).

Common impurities: Ag,Cu,Fe,Bi

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