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

1. SEDIMENT-HOSTED Cu +/-Ag +/-Co SYNONYMS: Sediment-hosted stratiform copper, shale-hosted copper, Kupferschiefer-type, redbed Cu, Cu-shale, sandstone Cu. COMMODITIES (BYPRODUCTS): Cu, Ag (Co, Pb, Zn, rarely PGE, Au, U, Va). EXAMPLES: 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.

3. Black carbonaceous shale-hosted copper deposits These stratiform deposits account for a significant proportion of the world's copper reserves. Twomain 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.

4. 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 minerals.

5. Quartz Galena Feldspar 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

6. 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

7. GEOLOGICAL CHARACTERISTICS 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.

8. DEPOSITIONAL ENVIRONMENT / GEOLOGICAL SETTING: 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 ages.

9. Sediment-hosted Cu deposits Copperbelt, Zaire, Zambia 900 Ma Zechstein, Germany, Poland 260 Ma

10. Redbed Cu deposits Copperbelt, Zaire, Zambia 900 Ma Bolivia, 45 Ma

11. HOST/ASSOCIATED ROCK TYPES: 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 rocks.

12. DEPOSIT FORM: 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.

13. TEXTURE/STRUCTURE: 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.

14. 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.

15. ALTERATION MINERALOGY: 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. WEATHERING: Surface exposures may be totally leached or have malachite and azurite staining. Near surface secondary chalcocite enrichment is common.

16. ORE CONTROLS: 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). ASSOCIATED DEPOSIT TYPES: Sandstone U, volcanic redbed Cu, Kipushi Cu-Pb-Zn, evaporite halite, sylvite, gypsum and anhydrite; natural gas (mainly CH4) in Poland.

17. 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.

18. EXPLORATION GUIDES 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 deposits. 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 mineralization.

19. ECONOMIC FACTORS TYPICAL GRADE AND TONNAGE: Average deposit in US 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 attractive.

20. IMPORTANCE: 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.

22. 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 tof 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.

23. 15. Nchanga

24. 14 18 17

25. 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.

27. Origin of the Kupferschiefer polymetallic mineralization in Poland 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 pyrite.

28. Cu mineralization Cu ores

29. 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.

30. 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. 57-76(20)

31. 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.

32. 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).

33. 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.

34. 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.

35. Two-brine modelof 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.

36. 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 environment.

37. “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.

38. 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.

40. Kupferschiefer: Supplement Copper slate fossils

41. 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.

42. 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.

43. 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.

44. 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.

45. 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 magnification.

46. 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.

47. 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.

48. 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 immersion.

49. 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).