Vein Style Deposits

Vein Style Deposits
Loca
tio n:
Base m etal- tin association. Nigadoo River, New
Brunswick, Canada
Major Minerals:
Pyrrhotite, pyrite, sphalerite, arsenopyrite, galena
Minor Minerals:
Stannite group minerals, marcasite, chalcopyrite, cassiterite,
argentite, tetrahedrite
Trace Minerals:
Include rutile, dyscrasite, pyrargyrite, native bismuth, native
antimony, boulangerite, jamesonite, mackinawite, bournonite
Textures:
Prismatic and acicular cassiterite is unzoned and untwinned.
Euhedral arsenopyrite is replaced by pyrrhotite, chalcopyrite,
galena and sphalerite. Chalcopyrite encloses mackinawite and
exsolved sphalerite stars.Sphal erite has a number of
generations and encloses stannite and tetrahedrite inclusions
and has suffered from chalcopyrite disease. It is rimmed by
stannite g roup minerals, especially at sphalerite- chalcopyrite
junctions. Galena enclose s native bismuth and silver
sulphosalt inclusions. Pyrrhotite is extensively alter ed to
Pyrite and marcasite giving bird's-eye textures and lathshaped intergrowths parallel to (0001) planes of pyrrhotite
Reference:
Suensilpong and Stumpfl, 1971
Pyrrhotite, pyrite and galena. Nigadoo River, New Brunswick,
Canada
250µm
A small galena crystal (blue-white, centre) lies at the junction of a
number of pyrrhotite (brown, centre) grains, which show faint differences
in reflectance and surface colour due to the presence of monoclinic
(darker brown) and hexagonal (lighter brown) pyrrhotite (centre).
Euhedral pyrite crystals (pale yellow, high reflectance, right) carry
pyrrhotite inclusions (top right). Pyrrhotite is extensively altered to finegrained pyrite and marcasite which are not distinguishable from each
other at this magnification. The alteration is to lath-shape d pyrite,
marcasite aggregates (bottom centre) oriented along the (0001) plane of
the pyrrhotite and to areas of very fine-grained pyrite-marcasite (top left);
these appear brown due to the fine grain size of the sulphides. Probably
all the pyrite in this section was originally pyrrhotite. The gangue
minerals are dark grey.
Polished block, plane polarized light, x 80, air
Sphalerite, pyrite, chalc opyrite and arsenopyrite. Nigadoo River,
New Brunswick, Canada
500µm
Sphalerite (grey, top right) has chalcopyrite (yellow) inclusions and an
incomplete chalcopyrite rim (bottom right). Two euhedral rhombs of
arsenopyrite (white, centre, bottom right) have higher reflectance than
coarse-grained pyrite (light yellow, bottom left). Fine-grained pyrite and
marcasite have totally replaced pyrrhotite and appear brown-yellow due
to their fine grain size. Successive 'shells' of pyrite-marcasite with
different grain sizes can be seen and form a poorly defined bird's-eye
texture (bottom left) growing out from coarse-grained pyrite. Gangue
phases are dark grey (centre).
Polished block, plane polarized light, x 40, air
Chalcopyrite, sphalerite, pyrite and mackinawite. Nigadoo River,
New Brunswick, Canada
110µm
Sphalerite (grey, bottom left) contains submicroscopi c chalcopyrite
inclusions (yellow-grey areas) and is intergrown with chalcopyrite
(yellow, right) which carries sphalerite exsolution stars (top right). Pyrite
(light yellow-white, top right) is euhedral or has been replaced by
chalcopyrite (centre). Mackinawite (brown, centre) is intergrown with
chalcopyrite and shows polysynthetic twins (oriented north-south), some
of which have a colour and reflectance that is very similar to the host
chalcopyrite. Black areas are polishing pits.
Polished block, plane polarized light, x 180, air
Loca
tio
n:
Copper- silver polymetallic veins. Ballycummisk,
County Cork, Ireland
Small polymetallic sulphide-oxide quartz veins of
Hercynian age cut Upper Palaeozoic sediments
within the Munster Basin. The ores of Ballycummisk
were mined in the nineteenth century and are
associated with a quartz,c hlorite and siderite
gangue.
Major Minerals:
Haematite, chalcopyrite, silver-bearing tetrahedrite
Minor Minerals:
Molybdenite, pyrite
Trace Minerals:
Include magnetite, bornite, chalcocite, galena, native
gold, native bismuth, bismuthinite, bismuth
sulphosalts
Textures:
Lath-shaped haematite is enclosed within
chalcopyrite. Chalcopyrite and tetrahedrite form
coarse-grained symplectite-like intergrowths
References:
Reilly, 1986; Ixer, 1987
Chalcopyrite, tetrahedrite and pyrite. Ballycummisk, County Cork,
Ireland
250µm
Chalcopyrite (yellow, centre) is intergrown with silver-bearing
tetrahedrite (light grey-green, bottom centre). A single crystal of pyrite
(light yellow-white, top centre) is enclosed within chalcopyrite. Dolomite
rhombs (medium grey, top right), euhedral quartz (centre left) and
chlorite (bottom right) are the gangue phases.
Polished block, plane polarized light, x 80, air
Stromeyerite, bornite, tetrahedrite group mineral and pyrite.
Unknown Provenance
250µm
Euhedral pyrite (light yellow-white, top left) and subhedral tetrahedrite
(green-grey, centre) are harder than bornite (brown, top) and stromeyerite
(pink-grey to blue-grey, bottom right). Stromeyerite shows faint
bireflectance and reflection pleochroism from pink-grey (centre right) to
blue grey (bottom right). Black areas are polishing pits.
Polished block, plane polarized light, x 80, air
Pyrite, stromey erite, bornite and tetrahedrite group mineral.
Unknown Provenance
250µm
Euhedral to subhedral pyrite (light yellow-white, bottom left) is replaced
by copper-silver sulphides and is associated with tetrahedrite (green-grey,
centre top). Bornite (brown, centre top) is intergrown with stromeyerite
which shows strong reflection pleochroism from blue-lilac (top left) to
light purple (centre right). Black areas are polishing pits. Pyrite is
scratched (centre left), showing the effect of incomplete polishing at
coarser grades leaving relict scratches not removed by later polishing
with finer grades of polishing paste .
Polished block, plane polarized light, x 80, air
Stromeyerite, bornite, gale na, chalcocite and tetrahedrite group
mineral and pyrite. Unknown Provenance
250µm
Inclusion-free galena (white, centre right) is intergrown with bornite
(brown, top) and stromeyerite, showing purple-grey (left centre) to bluegrey (bottom centre) reflection pleochroism. Stromeyerite occurs in a
symplectite-like intergrowth with chalcocite (light blue, centre, bottom
right) which is accentuated in the section by relief differences. Subhedral
tetrahedrite (green-grey, moderate reflectance, centre left, extreme bottom
right) is pitted and is associated with euhedral quartz (dark grey, centre
left). Pyrite (light yellow-white, high reflectance, centre) is subhedral to
euhedral.
Polished block, plane polarized light, x 80, air
Chalcopyrite, tetrahedrite, pyrargyrite and pyrite. Sark's Hope
Mine, Sark, Channel Islands, Britain
110µm
Altered euhedral tetrahedrite (light grey, left) is rimmed by chalcopyrite
(yellow, centre). Chalcopyrite is zoned with inclusion-rich growth bands
(lower reflectance) alternating with inclusion-free bands (centre).
Pyrargyrite (blue, centre) has infilled a void betw
ee n chalcopyrite
crystals. Minor amounts of pyrite (pale yellow-white, high reflectance,
bottom centre) have altered to limonite (grey) or form small framboids
(bottom right, centre top) associated with tetrahedrite. Limonite (grey, top
right) pseudomorphs after pyrite occur in chalcopyrite. Quartz is black.
Polished block, plane polarized light, x 180, oil
Galen a, chalcopyrite, argentian tetrahedrite, bournonite and native
antimony. Le Pulec, Jersey, Channel Islands,Britain
50µm
Galena (white, top) is intergrown with chalcopyrite (yellow, bottom)
which carries bournonite inclusions (blue-grey, bottom centre). Argentian
tetrahedrite (brown, centre) is rimmed by bournonite (blue-grey, centre
right) and chalcopyrite. Small grains of native antimony (white, high
reflectance, bottom right) are enclosed within bournonite. Black areas are
polishing pits.
Polished block, plane polarized light, x 400, oil
Loca
tio
n:
Copper-be aring arsenopyrite veins. Wanthwaite
Vein, English Lake District, Britain
Copper-bearing quartz-chlorite veins are associated
with the faulted contact between the Skiddaw Slates
and Borrowdale Volcanic s.
Major Minerals:
Pyrite, arsenopyrite, sphalerite, chalcopyrite
Minor Minerals:
Galena, rutile
Trace Minerals:
Include pyrrhotite, graphite
Textures:
Arsenopyrite is euhedral and optically zoned.
Sphale rite shows extensively developed chalcopyrite
disease
References:
Stanley and Vaughan, 1980, 1982
Arsenopyrite and covelline. Cligga Head, Cornwall, Britain
250µm
Characteristic rhombic crystals of arsenopyrite (white, high reflectance,
centre) occur within quartz (low reflectance, bottom centre) and the main
gangue phase, tourmaline, which shows bireflectance (greys, centre).
Banded covelline (deep blue, top left) has extensively replaced a large
arsenopyrite crystal. Black areas are vugs and polishing pits.
Polished block, plane polarized light, x 80, air
Arsenopyrite, covelline, altered sphalerite, stannit e and chalcocite.
Cligga Head, Cornwall, Britain
250µm
Coarse-grained subhedral to euhedral arsenopyrite (white, high
reflectance, right) has been replaced by banded covelline (deep blue,
bottom left). Altered sphalerite (bottom centre) shows an anomalous, but
characteristic, brown-grey surface colour associated with its replacement
by copper-rich minerals. Chalcocite (light blue, centre) has replaced
sphalerite about its grain edges and along veinlets. Chalcocite has altered
to covelline (deep blue, centre). Minor amounts of stannite (brownyellow, centre right) surround the altered sphalerite. Quartz (light grey,
centre) is the main gangue material.
Polished block, plane polarized light, x 80, air
Chalcopyrite, arsenopy rite, pyrite, sphale rite and native gold. Clogau
Mine, Wales, Britain
250µm
Arsenopyrite (white, centre) is highly fractured and these fractures are
infilled by sphalerite (light grey, centre left), native gold (yellow-white,
high reflectance, poorly polished, centre) and chalcopyrite (yellow).
Chalcopyrite also encloses much of the arsenopyrite. A euhedral cube of
pyrite (light yellow-white, right centre) has lower reflectance than
arsenopyrite. Dark grey area is quartz (bottom). The native gold is 950
fine, and to the eye has a higher reflectance than the photomicrograph
would suggest.
Polished block, plane polarized light, x 80, air
Pyrite, arsenopy rite, sphale rite and chalcopyrite. English Lake
District, Britain
500µm
Euhedral rhombic arsenopyrite (white, right) has higher reflectance than
pyrite (light yellow, bottom left). Sphalerite (light grey) occurs as rare
inclusions in arsenopyrite (top right) but mainly as large aggregates
(bottom) with abundant crystallographically oriented chalcopyrite
inclusions (chalcopyrite disease). Dark grey areas are chlorite-rich
gangue.
Polished block, plane polarized light, x 40, air
Loca
tio
n:
Lower temperature copper-bearing assemblages.
Wood-tin. Devon and Cornwall, Britain
Major Minerals:
Chalcopyrite, bornite, pyrite, chalcocite, covelline,
haematite, cassite rite (as wood-tin)
Minor Minerals:
Galena, sphalerite, arsenopyrite
Trace Minerals:
Include tetrahedrite group minerals, lead sulphosalts,
silver sulphosalts
Textures:
Rhythmical and botryoidal haematite or cassiterite
(known as wood-tin) are common. Bornitechalcocite form symplectite-like intergrowths and
have sulphosalt inclusions. Sphalerite and
chalcopyrite are intergrown with tetrahedrite group
minerals. Galena carries silver sulphosalt inclusions.
Alteration of primary sulphides to secondary copper
sulphides is widespread
Reference:
Hosking, 1969
Chalcopyrite, pyrite, stannite group mineral, arsenopy rite and
covelli ne. Wheal Jane, Cornwall, Britain
250µm
A single euhedral pyrite (light yellow-white, centre) and subhedral to
anhedral arsenopyrite grains (white, higher reflectance than pyrite,
bottom centre) are enclosed within chalcopyrite (yellow, left).
Chalcopyrite is rimmed by a stannite group mineral (pink-brown, centre),
which is inclusion-free, but is also altered to covelline (deep blue, centre
right). Quartz is dark grey and well polished (bottom right); chlorite is
poorly polished and has lower reflectance than quartz (right centre).
Black areas are polishing pits.
Polished block, plane polarized light, x 80, air
Chalcocite, bornite and pyrite. Levant Mine, Cornwall, Britain
250µm
Chalcocite (blue) has a symplectite-like intergrowth with bornite (brown,
centre right). Euhedral to subhedral pyrite (light yellow-white, centre
bottom) shows relief against chalcocite and its irregular shape suggests
that it has been partially replaced by chalcocite.
Polished block, plane polarized light, x 80, air
Bornite, covelline and sulphosalt. Levant Mine, Cornwall, Britain
250µm
Bornite (brown, bottom right) is intergrown with covelline (blues) which
shows good cleavage, bireflectance and reflection pleochroism. Trace
amounts of an uncharacterized sulphosalt (cream-white, bottom right) are
intergrown with bornite. Black areas are polishing pits.
Polished block, plane polarized light, x 80, air
Cassiterite. Botallack Mine, Cornwall, Britain
110µm
Radiating botryoidal cassiter ite, known as wood-tin (light grey-brown), is
intergrown with quartz (dark grey, top right). Variations in colour of the
cassiterit e are related to grain size and abundance of fine-grained silica
inclusions.
Polished block, plane polarized light, x 180, air
Cassiterite. Botallack Mine, Cornwall, Britain
110µm
This is the same field of view as 32e but with crossed polars. Radiating
wood-tin showing very strong internal reflections from white (bottom) to
dark brown (top) which mask the anisotropy of the cassiter ite.
Polished block, plane polarized light, x 180, air
Loca
tio
n:
Stibnite ores. Bo Thong,T hailand
Major Minerals:
Stibnite, stibiconite, cervantite
Minor Minerals:
Pyrite
Trace Minerals:
Include chalcopyrite, carbonaceous matter, enargite
group minerals
Textures:
Bladed crystals of stibnite are extensively alter ed to
antimony ochres. Deformation textures in stibnite are
complex and common
Stibnite. Bo Thong, Thailand
250µm
Stibnite crystals, showing bireflectance and reflection pleochroism
(brown-grey to light brown-grey), have altered to stibiconite (dark grey,
centre top) along a fracture. Black areas are polishing pits.
Polished thin section, plane polarized light, x 80, air
Stibnite. Unknown Provenance
250µm
This is the same field of view as the previous section but with crossed
polars. Stibnite showing strong anisotropy along complex deformation
twins and 'pressure lamellae'.
Polished block, crossed polars, x 80, air
Cinnabar. Mount Amiata, Italy
110µm
Bladed aggregates of fine-grained cinnabar crystals show characteristic
deep red internal reflections. Light coloured internal reflections belong to
quartz and carbonates (top right).
Polished block, crossed polars, x 180, oil
Cinnabar (and pyrite). Mount Amiata, Italy
250µm
This is the same field of view as 41e but with partially crossed polars.
Pyrite is no longer visible. Cinnabar crystals show strong anisotropy
(bottom left), but the anisotropy colours are largely masked by st rong red
internal reflections (centre bottom). The grain size difference betw
ee n
single crystals and aggregates of cinnabar is clearly seen.
Polished block, partially crossed polars, x 80, air
Loca
tio
n:
Uranium-rich ores. Port Radium, Northwest Territories,
Canada
Uranium ores with by-product radium and silver were mined
until 1960. The ores occur as veins within faults and shear zones
cutting cherry sediments of the Lower Echo Group, close to
biotite granite and granodiorite. The mineraliza tion is multistage
and comprises e arly haematite and quartz followed by
pitchblende, haematite and quartz; by quartz, cobalt-nickel
arsenides and sulphides; by copper sulphides with chlorite and
carbonates; and a final silver, bismuth, chalcopyrite-rich stage
associated with carbonates. Argillization, chloritization,
haematitization and carbonatiz ation of the wallrocks are
associated with the mineraliz ation. The assemblage is very
complex, with over forty recorded ore minerals and is essentially
the same as that of the Camsell Rive r area.
Major
Uraninite (Pitchblende), haema tite, chalcopyrite, niccolite,
Min
er als:
rammelsbergite, skutterudite, native silver
Minor and
Include lollingite, tetrahedrite, bornite, chal cocite, sphalerite,
Trace
galena, marcasite,a canthite, magnetite,coffin ite, native bismuth
Min
er als:
Textures:
Pitchblende is collomorphic, dendritic and botryoidal, forming
'blasenblende' within quartz and carbonates. It forms rims around
wallrock clasts but is fractured and cemented by later sulphides
References:
Campbell, 1957; Robinson and Morton, 1971; Robinson and
Ohmoto, 1973; Miller, 1982
Uraninite and chalcopyrite. Port Radium, Northwest Territories,
Canada
500µm
Coarse botryoidal uraninite (light grey, bottom) is accompanied by
smaller botryoidal uraninite, 'blasenblende' (top). Chalcopyrite (yellow,
centre bottom) lies along fractures and shrinkage cracks of the uraninite.
The carbonate gangue shows bireflectance (top left).
Polished block, plane polarized light, x 40, air
Uraninite and chalcopyrite. Port Radium, Northwest Territorie s,
Canada
500µm
Botryoidal, collomorphic uraninite (light grey, centre) encloses a rhombic
carbonate (dark grey, centre). Fine-grained chalcopyrite (yellow, centre
bottom) is abundant within uraninite. The carbonate gangue shows
bireflectance (light and darker grey, top). Grey area (bottom) is resin.
Polished block, plane polarized light, x 40, air
Uraninite, carbonaceous matter and chalcopyrite. Port Radium,
Northwest Territories, Canada
500µm
Uraninite (light grey, left) forms coarse botryoidal aggregates and smaller
'blasenblende' (bottom centre) and contains chalcopyrite (yellow, top
centre), often along shrinkage cracks. Coarse carbonaceous matter
(brown-grey, top right) shows faint bireflectance and reflection
pleochroism (brown-grey to grey, right centre). The carbonate gangue
(dark greys) shows cleavage, polysynthetic twinning (centre top) and
bireflectance.
Polished block, plane polarized light, x 40, air
Loca
tio
n:
Zinc-lead-silver ore. Le Pulec, Jersey, Channel
Islands
Zinc-lead-silver dolomite veins cut Brioverian
sediments close to an exposed granite in northwest
Jersey. They were unsuccessfully mined in the
nineteenth century.
Major Minerals:
Sphale rite
Minor Minerals:
Chalcopyrite, galena
Trace Minerals :
Include argentian tetrahedrite (freibergite ),
bournonite, stibnite, plagionite, native antimony,
cubanite, bornite and pyrite
Textures:
Coarse-grained sphalerite has chalcopyrite disease
and small crystallographically oriented tetrahedrite
inclusions. Chalcopyrite, with cubanite lamella e
within it, and galena form rims about sphalerite.
Galena carries intergrowths of tetrahedritebournonite-native antimony. Tetrahedrite has colourzoning, is argentian and has replaceme nt rims of
bournonite with minor chalcopyrite. Discrete lathshaped crystals of stibnite are present in dolomite
References:
Ixer and Stanley, 1980; Stanley and Ixer, 1982