9. Copper shale

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					SEDIMENT-HOSTED Cu +/-Ag +/-Co

SYNONYMS: Sediment-hosted stratiform copper, shale-hosted
copper, Kupferschiefer-type, redbed Cu, Cu-shale, sandstone

COMMODITIES (BYPRODUCTS): Cu, Ag (Co, Pb, Zn, rarely
PGE, Au, U, Va).

Redstone (Northwest Territories, Canada), Kennicott (Alaska,
USA), Spar Lake (Troy), Rock Creek and Montanore (Montana,
USA), White Pine (Michigan, USA), Creta (Oklahoma, USA),
Corocoro (Bolivia),
Mansfield-Sangerhausen and Spremberg, Kupferschiefer
district (Germany), Konrad and Lubin (Poland),
Dzherkazgan (Kazakhstan),
Copper Claim (Australia),
Kamoto and Shaba, Zambia-Zaire copperbelt.
Black carbonaceous shale-hosted copper deposits
These stratiform deposits account for a significant proportion of the
world's copper reserves. Two main copper provinces: the Upper
Proterozoic Zambian Copper Belt and the Lower Permian
Kupferschiefer of central and northwest Europe have been
studied intensively. Both provinces have huge, essentially
syngenetic/diagenetic ores found in shallow marine sediments
associated with major transgressions. Anoxic conditions and
bacterial reduction of sea water sulphate were important controls
on mineralization. The ores have both lateral and vertical
mineralogical zonation related to palaeogeographical conditions. In
the Kupferschiefer, this zoning is copper- and silver-rich passing
upward into lead- and zinc-rich ores, whereas in the Zambian
Copper Belt, it is chalcocite passing basinwards into bornite,
then chalcopyrite and finally pyrite. In unmetamorphosed examples
the sulphides are fine-grained and their distribution reflects primary
sedimentary features of the host sediments. Associated volcanicity is
minor in extent or absent.
The main sulphides of the unmetamorphosed Kupferschiefer
are fine-grained pyrite, chalcocite, galena, sphalerite,
digenite, djurleite, bornite, chalcopyrite and covelline.

Minor minerals include anilite, tennantite, luzonite,
mooihoekite, haycockite together with trace amounts of
cobaltite-gersdorffite, smaltite-chloanthite, clausthalite,
molybdenite, native gold, native silver and platinum group

                        Feldspar                  Galena

Sedimentary-hosted copper deposits. Galena (white, bottom right)
cements quartz (dark grey, well polished, right) and feldspar (dark grey,
less well polished, centre). An aggregate of small pyrite (yellow-white,
centre top) crystals occurs between two feldspars. The larger feldspar
(centre left) is euhedral and is partially authigenic in origin. Black areas
are polishing pits. Polished block, plane polarized light, x 80, air
Red bed copper deposits. Chalcopyrite (yellow, centre top) is the
main cement and is altered along its edges to covelline (deep blue,
centre left) and limonite (medium grey, centre top). Sphalerite (light
grey, centre top, centre left) occurs as small inclusions within
chalcopyrite. Quartz (dark grey) and feldspar (dark grey with
cleavage, bottom left, bottom right) show faint light-coloured internal
reflections. Black areas are polishing pits. Polished block, plane
polarized light, x 80, air

DESCRIPTION: Stratabound disseminations of native copper,
chalcocite, bornite and chalcopyrite in a variety of
continental sedimentary rocks including black shale,
sandstone and limestone. These sequences are typically
underlain by, or interbedded with, redbed sandstones with
evaporite sequences. Sulphides are typically hosted by grey,
green or white strata.

TECTONIC SETTINGS: Predominantly rift environments
located in both intracontinental and continental-margin settings;
they can also occur in continental-arc and back- arc settings.
The characteristic presence of redbed and evaporite
sequences points to deposition of sediments in a hot, arid to
semi-arid paleoclimate near the paleoequator. The host rocks
are produced in a variety of local anoxic depositional
environments, including deltaic sediments, Sabkha-type
lagoonal carbonate basins or high intertidal mudflats, and shallow
“coal basins”.

AGE OF MINERALIZATION: Proterozoic or younger; Middle
Proterozoic, Permian and early Mesozoic most favourable
Sediment-hosted Cu deposits

                 Zaire, Zambia
                 900 Ma

   Germany, Poland
   260 Ma
Redbed Cu deposits

               Zaire, Zambia
               900 Ma

    45 Ma

Most deposits are hosted by pale gray to black shale, but some are
found in sandstone, siltstone, limestone, silty dolomite, laminated
carbonate units (sabkha origin) and quartzites. Favourable horizons
contain reactive organic matter or sulphur. Algal mats, mudcracks
and scour-and-fill structures indicative of shallow-water deposition are
common. Local channel- conglomerate beds sometimes contain
wood fragments. The associated sequence includes redbed
sediments, evaporites and sometimes volcanics. In many cases
the rift-related layered rocks rest unconformably on older basement

Orebodies are generally conformable with the bedding,
although in detail ore may transgress bedding at low angles
and is typically more transgressive near the margins of the
deposit. Mineralized horizons are from tens of
centimetres to several metres thick (rarely more than 5 m);
they are often contained within broader zones of
anomalous copper values. Tabular ore zones extend
laterally for kilometres to tens of kilometres. Less
commonly the deposits are elongate lobes. Some deposits
have a C-shaped, “roll front” configuration in cross-section.
Common lateral and/or vertical zoning is from hematite
(barren) > chalcocite > bornite > chalcopyrite > pyrite, or
from a chalcocite/bornite core grading to chalcopyrite
with peripheral galena and sphalerite.

Sulphides are fine grained and occur as disseminations,
concentrated along bedding, particularly the coarser
grained fractions, or as intergranular cement. Sharp-walled
cracks or veinlets (< 1 cm thick, < than a metre in length) of
chalcopyrite, bornite, chalcocite, galena, sphalerite or barite
with calcite occur in some deposits, but are not an important
component of the ore. Pyrite can be framboidal or colloform.
Cu minerals often replace pyrite grains, framboids and
nodules; less commonly they form pseudomorphs of
sulphate nodules or blade-shaped gypsum/anhydrite grains.
They also cluster around carbonaceous clots or fragments.
ORE MINERALOGY (Principal and subordinate):
Chalcocite, bornite and chalcopyrite; native copper in
some deposits. Pyrite is abundant in rocks outside the ore
zones. Enargite, digenite, djurleite, sphalerite, galena,
tennantite, native silver with minor Co-pyrite and Ge minerals.
In many deposits carrollite (CuCo2S4) is a rare mineral,
however, it is common in the Central African Copperbelt.

GANGUE MINERALOGY (Principal and subordinate):
Not well documented; in several deposits carbonate, quartz
and feldspar formed synchronously with the ore minerals
and exhibit zonal patterns that are sympathetic with the ore
minerals. They infill, replace or overgrow detrital or earlier
authigenic phases.
Lateral or underlying reduced zones of green, white or grey
colour in redbed successions. In the Montana deposits these
zones contain chlorite, magnetite and/or pyrite. Barren,
hematite-rich, red zones grade into ore in the Kupferschiefer.
Kupferschiefer ore hosts also show elevated vitrinite
reflectances compared to equivalent stratigraphic units.

Surface exposures may be totally leached or have malachite
and azurite staining. Near surface secondary chalcocite
enrichment is common.
Most sediment-hosted Cu deposits are associated with the sag
phase of continental rifts characterized by deposition of shallow-
water sediments represented by redbed sequences and
evaporites. These formed in hot, arid to semi-arid paleoclimates
which normally occur within 20-30o of the paleoequator. Host
rocks are typically black, grey or green reduced sediments with
disseminated pyrite or organics. The main control on fluid flow from
the source to redoxcline is primary permeability within specific rock
units, commonly coarse-grained sandstones. In some districts
deposits are located within coarser grained sediments on the flanks
of basement highs. Growth faults provide local controls in some
deposits (e.g., Spar Lake).

Sandstone U, volcanic redbed Cu, Kipushi Cu-Pb-Zn, evaporite
halite, sylvite, gypsum and anhydrite; natural gas (mainly CH4) in
GENETIC MODELS: Traditionally these deposits have been
regarded as syngenetic, analogous to sedex deposits or late
hydrothermal epigenetic deposits. Currently most researchers
emphasize a two-stage diagenetic model. Carbonaceous shales,
sandstones and limestones deposited in reducing, shallow
subaqeuous environments undergo diagenesis which converts
the sulphur in these sediments to pyrite. At a later stage during
diagenesis, saline low-temperature brines carrying copper from
a distant source follow permeable units, such as oxidized redbed
sandstones, until they encounter a reducing unit. At this point a
redoxcline is established with a cuperiferous zone extending
“downstream” until it gradually fades into the unmineralized, often
pyritic, reducing unit. The source of the metals is unresolved, with
possible choices including underlying volcanic rocks, labile (easily
decomposed) sediments, basement rocks or intrusions.

COMMENTS: Sediment-hosted Cu includes Sabkha Cu deposits
which are hosted by thin-bedded carbonate-evaporite-redbed
„sabkha‟ sequences.

GEOCHEMICAL SIGNATURE: Elevated values of Cu, Ag, Pb,
Zn and Cd are found in host rocks, sometimes with weaker
Hg, Mo, V, U, Co and Ge anomalies. Dark streaks and specks
in suitable rocks should be analysed as they may be sulphides,
such as chalcocite.

GEOPHYSICAL SIGNATURE: Weak radioactivity in some

OTHER EXPLORATION GUIDES: Deposits often occur near
the transition from redbeds to other units which is marked by
the distinctive change in colour from red or purple to grey,
green or black. The basal reduced unit within the stratigraphy
overlying the redbeds will most often carry the highest grade

contains 22 Mt grading 2.1 % Cu and 23 g/t Ag (Mosier et al.,
1986). Approximately 20% of these deposits average 0.24 % Co.
The Lubin deposit contains 2600 Mt of >2.0% Cu and ~ 30-80
g/t Ag. Spar Lake pre-production reserves were 58 Mt grading
0.76% Cu and 54 g/t Ag. Montanore contains 134.5 Mt grading
0.74% Cu and 60 g/t Ag, while Rock Creek has reserves of
143.7 Mt containing 0.68 % Cu and 51 g/t Ag.

ECONOMIC LIMITATIONS: These relatively thin horizons
require higher grades because they are typically mined by
underground methods. The polymetallic nature and broad
lateral extent of sediment-hosted Cu deposits make them

These deposits are the second most important source of
copper world wide after porphyry Cu deposits. They are an
interesting potential exploration target in British Columbia,
although there has been no production from sediment-hosted
Cu deposits in the province. The stratigraphy that hosts the
Spar Lake, Montanore and Rock Creek deposits in Montana
extends into British Columbia where it contains numerous small
sediment-hosted Cu-Ag deposits.
Origin of the copper-cobalt deposits of the Zambian
Copperbelt: An epigenetic view from Nchanga

The Zambian Copperbelt is arguably the most significantly
mineralized Neoproterozoic basin on Earth, preserving a truly
spectacular scale of mineralization: in excess of 1 x 10e+9 t of
ore at 2.7% copper has been extracted to date, and there are
also major cobalt accumulations. The origin of these
deposits has been hotly debated for more than six decades,
yet the driving forces that generated this system are poorly
understood, in particular the relationships between tectonics,
paleo–fluid circulation, and ore deposition. In the Nchanga
deposits, the bulk of the mineralization is hosted by shale-
capped feldspathic arenites and arkoses that have undergone
recrystallization and hydrothermal alteration within a host-rock
package controlled by low-angle thrust faults.
15. Nchanga
17   18
By using in situ laser combustion, range of δ34S for copper-
cobalt ore sulfides (–1 to +18) cannot have the same source
as diagenetic pyrite (–1 to –17). A new epigenetic model for
the formation of these spectacular Nchanga orebodies
involves the introduction of metal- and sulfate-bearing
hydrothermal fluids into quartzofeldspathic units during
basin inversion, with sulfide derived from thermochemical
reduction of the sulfate near the site of deposition.
Origin of the Kupferschiefer polymetallic mineralization in

The Kupferschiefer ore series, between the Lower Permian
(Rotliegendes) terrestrial redbeds/volcanics and the Upper
Permian (Zechstein) marine sequence, is developed as dark-
grey organic matter-rich and metal sulphide-containing deposits
(reduced zone) and as red-stained organic matter-depleted and
iron oxide-bearing sediments (oxidized zone = Rote Fäule). The
transition zone from oxidized to reduced rocks occurs both
vertically and horizontally. This zone is characterized by sparsely
disseminated remnant copper sulphides within hematite-
bearing sediments, replacements of copper sulphides by iron
oxides and covellite, and oxide pseudomorphs after framboidal
          Cu mineralization

Cu ores
These textural features and copper sulphide replacements
after pyrite in reduced sediments imply that the main
oxide/sulphide mineralization postdated formation of an
early-diagenetic pyrite. Hematite-dominated sediments
locally contain enrichments of gold and PGE. The
Kupferschiefer mineralization resulted from upward and
laterally flowing fluids which oxidized originally pyritiferous
organic matter-rich sediments to form hematitic Rote Fäule
areas, and which emplaced base and noble metals into
reduced sediments. It is argued that long-lived and large-
scale lateral fluid flow caused the cross-cutting relationships,
expansion of the hematitic alteration front, redistribution of
noble metals at the outer parts of oxidized areas, and the
location of copper orebodies directly above and around
oxidized and gold-bearing areas. The Rote Fäule may be a
guide to favourable areas for both the Cu-Ag and new Au-
Pt-Pd Kupferschiefer-type deposits.
The Kupferschiefer: Lithology, stratigraphy, facies and metallogeny
of a black-shale.

Author: Paul, Josef
Source: Zeitschrift der Deutschen Gesellschaft für
Geowissenschaften, Volume 157, Number 1, January 2006, pp.
The Kupferschiefer Fm. is a well-known stratigraphic marker horizon
throughout central Europe. It is a typical black shale, representing the
lowermost unit of the marine Upper Permian Zechstein Group of the
Central European Basin. It is missing only in peripheral subbasins and
bights, like the South German Bight. Thickness and facies depend on
the palaeogeography and hydrography of the Zechstein Sea.

Generally, the Kupferschiefer is less than one metre thick and
consists of laminated black mudstones, marls and carbonates. A
thin basinal, a thicker marginal and a swell facies rich in carbonates can
be distinguished. There is a fossiliferous carbonate bed, called
Mutterflöz, on swells and marginal areas below the typical black shale
facies. Other names of this bed are Border Dolomite, Border Limestone,
or Productus Limestone. It is time equivalent with the lower part of the
Kupferschiefer in basinal sites and therefore a subformation of the
Kupferschiefer. The typical Kupferschiefer was deposited under
anoxic conditions in a stratified sea. Three cycles consisting of
varying carbonate and TOC contents can be traced all over the basin.
Most likely, these cycles were caused by a fluctuating redox
discontinuity layer (RDL) which corresponds to Milancovitch cycles.
Benthic fauna is missing in the Kupferschiefer Sea because of
the H2S containing water.

The lacking oxygen protected the dead and at the bottom lying
nekton against decay. The benthos occurring in the schwellen facies
was transported to the black shale facies from shallow water areas
above the RDL. Brachiopods, bryozoa, pelecypods, gastropods,
cephalopods, crinoids, and corals, nearly all organisms found in the
overlying Zechstein Limestone also occurred in the Kupferschiefer
Sea. But only pollen and spores facilitate the biostratigraphic
classification of the Kupferschiefer to subzone Ia of the
Lueckisporites virkkiae assemblage Zone which corresponds to the
Abadeh Stage (early Dzulfian).
The main components of the organic matter in the
Kupferschiefer are kerogenes. Under the light microscope,
only structureless particles are to be seen, whereas under
the fluorescence microscope algal or bacterial cysts can be
recognized. The analysis of the biomarkers, e.g. hopane,
sterane, and porphyrines, proved that photosynthetic
micro-organisms are producers of the organic matter.
In terms of sequence stratigraphy, the Kupferschiefer is
deposited in the Transgressive Systems Tract (TST) of the
first Zechstein Sequence. The position of the maximum
flooding surface (mfs) of this first sequence is in the lower
part of the Zechstein Limestone.
The Kupferschiefer hosts a large quantity and variety of heavy
metals like copper, lead, zinc, silver and other precious metals.
High concentrations of these metals are restricted to small
regions of the depositional area. Ascending epigenetic
solutions leached these metals from Rotliegend sediments and
volcanics. The metal-containing areas are situated at the
margins of the Zechstein basin or above deep-reaching faults.
In the other areas, the synsedimentary contents of heavy
metals do not exceed values which are normal for black shales.
The epigenetic flux of metals containing solutions took
place in several phases starting from the Triassic up to the
Tertiary. High concentration areas are in Lower Silesia in
Poland, east of the Harz Mountains, and in the Richelsdorf area.
In Germany, mining of the Kupferschiefer stopped 1990,
whereas in Lubin, Silesia, a large quantity of copper, silver,
and other precious metals is produced. It is one of the largest
copper mines in the world.
Two-brine model of the genesis of strata-bound Zechstein deposits
(Kupferschiefer type), Poland

The Kupferschiefer deposits were probably formed as a result of a
mixing of two brines. The upper cold brine (UCB) is an unmineralized
brine rich in Na, Ca, Cl and SO4, with a pH>7 and originating from
evaporites overlying the metal-bearing Zechstein rocks. The lower hot
brine (LHB) rich in Mg, K, Cl, SO4 and CO3 with a pH<=7 formed in
sediments in the central part of the Zechstein basin at a depth of 7,000
m. This brine was subjected to heating and upward convection
toward the Fore-Sudetic monocline along the bottom of the Z1
carbonates. During its migration, it caused albitization, serpentinization
and leaching of the primary metal deposits in rocks underlying the
Zechstein becoming enriched in heavy metals. The mineralization
process, being a result of the mixing of the two brines (UCB and
LHB), and catalytic oxidation of the organic matter of the black
shale were initiated at shallow depths in the area of the Fore-
Sudetic monocline. The boundary of the two brines generally
overlapped the strike of the black shale.
Parts of the deposit with shale-free host rock suggest that the
action of two brines alone was capable of producing
economic concentrations of Cu, Pb and Zn. Where the
boundary of the two brines overlaps the autooxidation zone (the
black shale bottom) and also coincides with radiation of
thucholite, concentrations of noble metals result.
The characteristic vertical distribution of the triplet CuPbZn from
the bottom upward is universal in the Kupferschiefer
“Background” δ34S values of Kupferschiefer sulphides in
Poland: pyrite-marcasite nodules

Regional background 34S values of pyrite-(marcasite) nodules
throughout the Zechstein basin in Poland have been measured to
help estimate the proportion of externally derived sulphur in the
Kupferschiefer Cu-Ag ores. The 34S values of the 17 FeS2 nodules
measured range widely, from -25.2 to -51.9%o, similar to the
previously published -28 to -43%o range in disseminated pyrite in the
Kupferschiefer. The wide variation cannot be attributed to pyrite
versus marcasite mineralogy, amount of contained chalcopyrite or
sphalerite, carbonate versus shale host rock, early versus late
formation, percent of included calcite, or to size, shape, or texture.
There is also no relation with proximity to the centres of copper
mineralization in southwestern Poland where sulphides are
typically isotopically heavier. The 34S values do, however, vary
directly with percent of host-rock fragments included in the nodules.
Repeat samples that were washed with acid or hot water show the
same wide variation, indicating that contamination by sulphate
sulphur in the host rock is not a factor. Neither is organic sulphur
because of its small volume. Instead, the sulphur composition may
be fundamentally controlled by the formation mechanism of the
nodule, whereby 34S-rich sulphide is preferentially concentrated,
possibly replacing anhydrite lenses. Alternatively, a network of
host rock inclusions might act as a more accessible conduit for
later, 34S-rich fluids to infiltrate the nodule and add to earlier, 34S-
poor pyrite.
In the ore deposits, higher 34S values of ore nodules suggest less
indigenous sulphur in limestone than shale lithologies. An
isotopic temperature of 61 °C from a chalcopyrite-galena pair
agrees with other estimates of <105°C. Higher values in ore
nodules/veinlets than in adjacent disseminations, and the
calculated 34Spy value from a pyrite-bornite mixture support the
idea that metal-bearing 34S-rich fluids penetrated the Kupfer-
schiefer through a network of fractures.
Kupferschiefer: Supplement

   Copper slate fossils
Kupferschiefer is a clay/tone and more kalkhaltiger, by
organic substance blackened clay stone, which
schwefelhaltige Kupfererze different in fine distribution as well
as a multiplicity at metals, among other things silver, zinc and
lead contains.
Kupferschiefer was formed for the last section of the earth
antiquity in the Permian. It marked after long mainland time a
sea raid in the today's Central Europe at the beginning of the
carousing unity and is one of the most salient geological
horizon flight directors in Germany and Europe. The term
“Zechstein” is used only in Europe. The carousing A SEa was
enough thereby from northeast England over Belgium and
parts of Denmark, Germany over Poland until Lithuania.
Kupferschiefer resulted from deposit and following
solidification of sediments. It formed only in the deeper part of
the sea basin in completely Europe, whose Bodenwasser was
oxygne-free. This explains the sulfur content as well as the
good preservation of the fossils received therein. The material
was only easily compressed with the solidification, why the
individual layers of a copper slate block can be divided well
into thin disks. As origin of the metals both a hydrothermale
genesis and the a washing from the demolition debris of the
Variszi mountains of the red-lying are occupied.
The name the Kupferschiefer of the production of copper (and
other metals) has, which as sulfides finely distributed in the rock
present is, more rarely than thin volumes or bohnenförmige
inclusions occur. The copper slate seam is far common in
Central Germany. Dismantling gave it since the Middle Ages
among other things in one fields the country (dismantling with
Hettstedt, one field, Helbra, ice life, Niederröblingen,
Sangerhausen until 1990), at the south and edge of west resin
(new one field close Seesen), in the Richelsdorfer to mountains
(with Sontra, to the middle Saale (Rothenburg) and with Bieber
in the Spessart (there from equivalent “Kupferletten” until 1925).
Today from the Kupferschiefer still copper in Niederschlesien
(Poland) is won.
Despite its name Kupferschiefer is a sedimentary rock and not
metamorphic rock.
    Polish Kupferschiefer Ores

Covellite (strongly pleochroic from dark to light bluish gray) cementing
quartz (dark gray) sand grains in the upper 2-3 inches of the
sandstone beneath the copper shale (Kupferschiefer) in the Rudna
copper mine, Poland. Part of the lighter blue is chalcocite that
appears very similar to covellite in it lighter blue position. Reflected
light ore microscopy, plane polarized light, low magnification.
Same view as above but under crossed polars. Covellite (orange)
cementing quartz (black) sand grains in the upper 2-3 inches of the
sandstone beneath the copper shale (Kupferschiefer) in the Rudna copper
mine, Poland. Reflected light ore microscopy, crossed polars, low
Covellite (dark to light bluish gray) cementing and filling fractures in a
clastic quartz (dark gray) sand grain that exhibits mosaic (pieces could
be put back together again) brecciation. Upper 2-3 inches of the
sandstone beneath the copper shale (Kupferschiefer) in the Rudna
copper mine, Poland. Reflected light ore microscopy, plane polarized
light, low magnification.
Single clastic quartz grain (dark gray) brecciated and cemented by
covellite (dark to light bluish gray). Quartz breccia fragments have
been moved farther apart than in the above photomicrograph. Upper
2-3 inches of the sandstone beneath the copper shale (Kupferschiefer)
in the Rudna copper mine, Poland. Reflected light ore microscopy,
plane polarized light, low magnification.
Local vertical bornite-digenite vein traversing disseminated copper
ores in the Kupferschiefer at the Rudna copper mine, Poland. Bornite
(Bo; purple) and digenite (Di; bluish gray) are traversed by a single
galena (Gn; white) vein and by later thin carrollite (Car) veins. Quartz
(Qz; black) has selectively replaced galena. Reflected light ore
microscopy, plane polarized light, moderate magnification, oil
Local bornite vein traversing disseminated copper ores in the
Kupferschiefer at the Rudna copper mine, Poland. Chalcopyrite (Cp;
yellow) has coated and veined the bornite (Bo; purple) vein and
disseminated bornite grains in the host shale (black).

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