Galena

galena

sphalerite

cerussite

anglesite

Images

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
Common impurities: Ag,Cu,Fe,Bi
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.

Localities

The Two Mile and Three Mile deposits, Paddy's River, Paddys River District, Australian Capital Territory, Australia, are skarn deposits at the contact between granodiorite and volcanic rocks. Galena is a primary sulphide that occurs with chalcopyrite in chlorite-rich material, and intergrown with sphalerite in the magnetite skarn at the Two Mile deposit. It also occurs associated with aikinite (AJM 22.1.37).

At Kwun Yum Shan, Yuen Long District, New Territories, Hong Kong, China, the deposit is a hydrothermal deposit which lies along a fault zone withi 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).
There are several “hot pots” near the top of the hill. These hot pots were thought to be outlets of warm and moist air, which is heated below the ground and ejected through fissures and cracks in the rocks. The rocks here, however, are more likely to be pyroclastic in nature. Mineral veins of quartz, pyrite and galena can be identified, and large crystals of quartz are present in the rock. The Hong Kong Geological Survey has now re-interpreted the rock as an altered intrusive rhyolitic hyaloclastite. It is possible that the outcrop marks a vent feeder of volcanic rocks (Geological Society of Hong Kong newsletter 14.1).

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).

The Ma On Shan Mine, Ma On Shan, Sha Tin District, New Territories, Hong Kong, China, is an abandoned iron mine, with both underground and open cast workings. The iron ores contain magnetite as the ore mineral and occur predominantly as masses of all sizes enclosed in a large skarn body formed by contact metasomatism of dolomitic limestone at the margins of a granite intrusion. In parts of the underground workings magnetite is also found in marble in contact with the granite. The skarn rocks consist mainly of tremolite, actinolite, diopside and garnet. Galena has been reported to occur in quartz veins cutting the skarn (Hong Kong Minerals (1991). Peng, C J. Hong Kong Urban Council)

The Needle Hill Mine, Needle Hill, Sha Tin District, New Territories, Hong Kong, China, is a tungsten mine, abandoned in 1967. The principal ore is wolframite, and the principal gangue mineral is quartz. Molybdenum also occurs. The mineralisation consists of a series of parallel fissure veins that cut through granite. Wolframite and quartz are the main minerals, but galena, sphalerite, pyrite, molybdenite and fluorite have also been found here (Geological Society of Hong Kong Newsletter 9.3.29-40). The quartz-wolframite veins are of high-temperature hydrothermal formation, and grade into wolframite-bearing pegmatites (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 Shijiang Shan-Shalonggou mining area, Inner Mongolia, China, the mineral deposits occur predominantly in veins of hydrothermal origin in skarn. Galena is rarely found in association with borate specimens as small grains. One specimen shows an unusual cuboidal crystal of galena, 2 cm long, with roweite and minor olshanskyite. This crystal is probably of secondary origin (R&M 96.5.401).

At Poullaouen, France, galena has been found as alteration pseudomorphs after pyromorphite (KL p129).

At the Old Hope of God pit, Freiberg, Saxony, Germany, acanthite has been found as pseudomorphs after galena (KL p126).

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

At Berg Aukas, Grootfontein, Otjozondjupa Region, Namibia, galena occurs most commonly as intergrowths with sphalerite. It is found in veins with smithsonite, willemite and cerussite. Galena from this locality contains traces of antimony and manganese (R&M 96.2.131-132). The paragenetic sequence for the sulphides is proposed to be pyrite (oldest) - bornite - chalcopyrite - tennantite - sphalerite - galena - enargite - germanite - renierite - tetrahedrite - jordanite (youngest) (R&M 96.2.131-132).

At the Witwatersrand goldfield, South Africa, attractive specimens of galena have been found at several gold mines in the Carletonville and Welkom goldfiends (R&M 96.4.326).

At the Geduld Mine, Welkom, Lejweleputswa District, Free State, South Africa, well-formed cubic, cuboctahedral and distorted cubic galena crystals, some associated with sphalerite and/or pyrrhotite were found (R&M 96.4.326).

At the Kusasalethu Mine, Carletonville, Western Sector, Far West Rand, West Rand District Municipality, Gauteng, South Africa, crystallographically more complex galena specimens were collected. Some galena displays highly distorted forms with elongated and/or flattened shapes caused by constricted growth. With a few exceptions, the lustre is rather dull with crystal surfaces being finely pitted. Associated minerals include quartz, baryte and pyrobitumen (R&M 96.4.326).

At Alderley Edge, Cheshire, England, UK, copper mineralised solutions percolated through porous sandstone 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 Force Crag Mine, Coledale, Above Derwent, Allerdale, Cumbria, England, UK, a specimen has been found of galena with a dense coating of cerussite formed into ingrown crystals in a vug (AESS)

At Old Brandley Mine, Catbells, Keswick, Allerdale, Cumbria, England, UK, a specimen has been found of a crystalline quartz matrix with a dense coverage of galena crystals showing advanced stages of alteration to cerussite (AESS)

At the Clargillhead vein, Garrigill, Alston Moor, Eden, Cumbria, England, UK, galena is the dominant opaque phase and mainly forms euhedral and subhedral crystals up to a few millimetres in diameter. Whereas some of the galena is inclusion-free, some carries inclusions of other sulphide and sulphosalt minerals. The most abundant of these is bournonite. Inclusions of chalcopyrite, pyrite, ullmannite and sphalerite are common inclusions in the galena, with much rarer grains of gersdorffite and boulangerite. Galena is locally intergrown with chalcopyrite (JRS 23.49).

At Nenthead, Alston Moor, Eden, Cumbria, England, UK, galena is associated with sphalerite and ankerite (SY p161).

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 Croft Quarry, Croft, Blaby, Leicestershire, England, UK, galena occurs as dull grey cubes to 2 mm on edge with analcime, marcasite, calcite and, occasionally, cerussite. It also occurs as groups of cubo-octahedral crystals to 2 mm that may be associated with chalcopyrite, analcime and calcite (JRS 20.17).

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 Barrasford Quarry, Chollerton, Northumberland, England, UK, small masses of galena up to 20 mm across, accompanied by sphalerite, have been found in quartzcalcite veins; small amounts of pyrite, pyrrhotite and traces of chalcopyrite have also been seen in these veins (JRS 21.9).

At Divethill Quarry, Little Bavington, Northumberland, England, UK, galena crystals up to 10 mm across have been seen in a narrow vein of calcite (JRS 21.9).

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 Roar Hill, Ballater, Buchan Grampian, Scotland, UK, lead-bearing vein mineralisation was exposed during recent work carried out on an unmetalled vehicle track. A small temporary quarry exposed fluorite-bearing quartz veins and minor wulfenite in light-coloured granite. At a second site, a little further to the west, an oxidised galena-bearing quartz vein was exposed.
Galena occurs as altered crystals in vein quartz at the track exposure, commonly overgrown by cerussite and possibly anglesite and may be associated with lime-green crustose pyromorphite, brown spheroidal mimetite and drusy orange wulfenite (JRS 22.33).

At the Sweetwater mine, Missouri, USA, chalcopyrite pseudomorphs after galena have been found (KL p131).

At the PC Mine, Cataract Mining District, Jefferson county, Montana, USA, galena was found as cubes and octahedra to 12 cm coated with a thin grey layer of anglesite and containing trace amounts of silver. Sulphides are not common in the deposit, but a few pockets near the level of the creek did have sulphides of surprising size (R&M 96.6.494).

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).

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