Sediment-hosted Stratiform Copper Research Articles

Biomarker signatures and depositional environment of ore-bearing black shale in the Luishia Cu–Co deposit, Democratic Republic of Congo: Implications for regional copper mineralization

The Central African Copperbelt is a globally important sediment-hosted stratiform copper cluster, with regional Cu–Co deposits controlled by Neoproterozoic rift basin. Ore formation in the Copperbelt involves multiple stages of mineralization during diagenesis, basin inversion, and collisional orogeny. Understanding the depositional environment of ore-hosting rocks is crucial for revealing the geological settings and pre-orogenic ore genesis. This paper presents a biomarker study focusing on the ore-bearing black shale in the Luishia Cu–Co deposit, Democratic Republic of Congo. The research investigates thermal maturity, source, and depositional environment of organic matter through rock organic carbon and pyrolysis analysis, chloroform bitumen “A” group component analysis, as well as saturated hydrocarbon gas chromatography-mass spectrometry (GC-MS) analysis. The results indicate significant thermal maturation of organic matter in Luishia black shale. Bacteria are identified as the primary source of organic matter followed by red algae and green algae. The sedimentary environment is characterized by a restricted rift basin under shallow marine conditions with a stratified water column. The processes of bacterial sulphate reduction (BSR) and thermochemical sulphate reduction (TSR) significantly influence the mineralization during diagenesis and basin inversion, respectively. Enhanced thermal maturity promotes methane generation which plays a role in reducing anhydrite and subsequently precipitating ore minerals. The findings have important implications for regional exploration strategies.

Fluid Flow, Alteration, and Timing of Cu-Ag Mineralization at the White Pine Sediment-Hosted Copper Deposit, Michigan, USA

Abstract White Pine, located in Michigan’s Upper Peninsula, is an archetypal sediment-hosted stratiform copper deposit. The Midcontinent rift system is one of only seven basins globally that host a giant sediment-hosted stratiform copper deposit. Despite many similarities with other deposits of this type, White Pine displays some important differences, including the late Mesoproterozoic age, a thick basalt sequence, an apparent lack of evaporites, and a lacustrine depositional setting. This study analyzes paleofluid flow related to the formation of White Pine and places a particular emphasis on structural and diagenetic fluid pathways. Most of the ore is located in a 30-m-wide zone spanning the Copper Harbor Formation red beds and the overlying Nonesuch Formation shales. Sedimentation of these units was accompanied by subtle synsedimentary faulting. Premineralization phases include calcite concretions and nodules, illite and hematite grain coatings, isopachous chlorite rims, emplacement of liquid petroleum (now pyrobitumen), and bleaching. Mineralization introduced native copper into the footwall sandstones and a zoned suite of native copper and sulfur-poor copper sulfide minerals across a migrating redox front in the overlying shales where copper minerals nucleated on authigenic and detrital chlorite grains. Postmineralization phases include quartz cement, calcite cement, and calcite veins that partially overlapped inversion of synsedimentary faults. Contrary to previous studies, we identified evidence for only one phase of mineralization. An Re-Os chalcocite age of 1067 ± 11 Ma places mineralization 11 to 17 m.y. after host-rock deposition. Sulfide δ34S values of –14.0 to 29.9‰ suggest an important contribution from sour gas and thermochemical sulfate reduction of seawater. Carbon (δ13C) and oxygen (δ18O) isotope compositions of five calcite generations range from –15.1 to –1.3‰ and 10.4 to 41.3‰, respectively, and record early meteoric pore water displaced by later seawater. White Pine is both a sediment-hosted stratiform copper deposit and a paleo-oil field. Synsedimentary faults controlled the sedimentological character of the upper Copper Harbor Formation, and together these imparted a strong control on fluid flow and later diagenetic processes. Early oxidized meteoric fluids were displaced by liquid petroleum and sour gas, which were in turn succeeded by metal-rich but sulfate-poor oxidized seawater. Burial compaction during deposition of the overlying Freda Formation drove fluids through White Pine due to its situation on a paleotopographic high near the basin margin. Mineralization occurred at ~125°C at depths of ~2.0 km and spanned incipient basin inversion related to the distal effects of Grenvillian orogenesis. The hightenor copper mineral assemblage is the product of an abundant supply of metal from basaltic volcanic detritus in the Copper Harbor Formation and low seawater sulfate concentrations in late Mesoproterozoic oceans. This demonstrates that viable sediment-hosted stratiform copper systems can form when a readily leachable metal source rock is present, even if hypersaline and sulfate-rich brines are not.

Comparison of main and accompanying metals distribution patterns in newly documented deposits of the Northern Copper Belt in Poland

Three new world-class sediment-hosted stratiform copper deposits have recently been documented in SW Poland, in the deep parts of the Fore-Sudetic Monocline: Nowa Sól, Sulmierzyce North and Mozów. Along with the adjacent prognostic areas, these deposits form an extensive west–east-trending belt, distant from the well-known deposits of the Sieroszowice–Lubin area and referred to as the Northern Copper Belt. This major discovery was a result of an exploration program performed by the Canadian Miedzi Copper Corporation, which involved studies of archival data and the company's own drilling program. Investigation of the core material included microscopic observations of thin sections and chemical analyses using inductively coupled plasma (ICP) mass spectrometry and/or ICP optical emission spectrometry. The aim of this study was to compare available geochemical data from the documented deposits and determine the distribution patterns of the main and accompanying metals. Particular attention was paid to Cu, Ag, Pb, Zn, Co, Ni, Mo, V and Au. Each of the studied deposits is characterized by a different position of the ore mineralization in the lithological profile. Average concentrations of the analysed elements and their distribution in the ore series, both vertically and laterally, indicate that distinct mineralizing systems were responsible for the formation of each orebody. Among the main factors influencing metal distribution in the analysed deposits are: the spatial range of the epigenetic, oxidized Rote Fäule facies; composition and thickness of the source rocks for the mineralizing brines; and tectonics.

Textures, in situ trace element and sulfur isotope of pyrite from the sediment-hosted Cu–Co deposits in the Zhongtiao Mountains, Trans-North China Orogen: Implications for ore genesis

Sediment-hosted Cu–Co deposits in the Zhongtiao Mountains are hosted by the metasedimentary rocks of the Paleoproterozoic Zhongtiao Group in the southern part of the trans-North China orogen, North China Craton. The ore genesis is still disputed with proposed genetic models including metamorphosed sedimentary exhalative (M−SEDEX), metamorphosed sediment-hosted stratiform copper (M−SSC) and metamorphogenic mineralization type. Pyrite occurs as a ubiquitous mineral throughout all ore-forming stages and is ideal for clarifying this issue via the integration of in situ (LA–ICP–MS and EPMA) elemental and LA–MC-ICP–MS sulfur isotope composition analyses. Two main types of pyrite are identified based on petrographic and SEM observations: fine- to medium-grained, variably deformed and inclusion-rich Py1 (including Py1a and Py1b subtypes) in the disseminated–veinlet mineralization stage (S1), and coarse-grained, fractured Py2 (including Py2a and Py2b subtypes) in the fracture-controlled vein-type mineralization stage (S2, main ore stage). Deformed and inclusion-rich Py1a is overgrown by inclusion-poor Py1b, and nonporous Py2a is rimed by porous Py2b. Geochemical results show that the studied pyrite samples have considerable contents of Co (mean > 1000 ppm) and Ni (mean > 100 ppm). These features could be related to both the Co and Ni-rich sedimentary environment (e.g., a volcaniclastic-rich sulfidic marine) and metamorphic enrichment. The content of Se (mean > 200 ppm) in Py2 is significantly higher than that in Py1, indicating the extensive interaction of mineralizing fluids with Se-bearing graphite schist. LA–ICP–MS mapping and textural studies indicate the presence of coupled dissolution-reprecipitation (CDR) reactions that could lead to trace metal compositions (e.g., Co, Ni, Se, Pb, Bi) in the product phases (Py1b, Py2b) that differ from those of their parent phases (Py1a, Py2a). These variations were most likely controlled by fluid temperature and precipitation of specific minerals. The grain-scale chemical zoning of Py2a revealed by elemental mapping indicates fluctuating fluid parameters (e.g., temperature, fS2, and/or parent fluid compositions). The bimodal distributions in Py1 (10–14 ‰ and 18–24 ‰) are consistent with the inheritance of sulfur from sedimentary pyrite and the input of thermochemical sulfate reduction (TSR) -related sulfur from reworked evaporite sulfates in an increasingly open system. The relatively lighter and wider variation in δ34S values (3.2–22.4 ‰, mean = 15.1 ‰) of Py2 implies that the evolution of the ore fluid in S2 was far more complicated, probably as a result of fluid–rock interactions and fluid cooling. During this process, hydrothermal rims with lighter δ34S values (8.4 ‰) grew on older metamorphic pyrite cores with relatively heavier δ34S values (17.4–18.2 ‰). Chalcopyrite displays overlapping S isotopic compositions with pyrite from different mineralization stages, suggesting that copper sulfides inherited reduced sulfur from earlier formed pyrite. Cooling and fluid–rock interactions serve as the critical controls triggering Cu precipitation from the fluid. The combined textural and compositional data of pyrite and chalcopyrite are suggestive of a syn-orogenic copper deposit model, in which all the ore-grade copper was introduced during the Zhongtiao orogeny.

Co–Mn Mineralisations in the Ni Laterite Deposits of Loma Caribe (Dominican Republic) and Loma de Hierro (Venezuela)

Cobalt demand is increasing due to its key role in the transition to clean energies. Although the main Co ores are the sediment-hosted stratiform copper deposits of the Democratic Republic of the Congo, Co is also a by-product of Ni–Co laterite deposits, where Co extraction efficiency depends, among other factors, on the correct identification of Co-bearing minerals. In this paper, we reported a detailed study of the Co mineralisation in the Ni–Co laterite profiles of Loma Caribe (Dominican Republic) and Loma de Hierro (Venezuela). Cobalt is mainly associated with Mn-oxyhydroxide minerals, with a composition between Ni asbolane and lithiophorite, although a Co association with phyllosilicates has also been recorded in a Loma de Hierro deposit. In Loma Caribe, Co-bearing Mn-oxyhydroxide minerals mainly developed colloform aggregates, and globular to spherulitic grains, while in Loma de Hierro, they displayed banded colloform, fibrous or tabular textures. Most of the compositional analyses of Mn-oxyhydroxides yielded 20 and 40 wt.% Mn, with Ni and Co up to 16 and 10 wt.%, respectively. In both profiles, Mn-bearing minerals were mainly found in the transition from the oxide horizon to the saprolite, as observed in other laterite profiles in the world, where the precipitation of Mn-bearing minerals is enhanced because of the pore solution saturation and pH increase.

Geometallurgy of Cobalt Black Ores in the Katanga Copperbelt (Ruashi Cu-Co Deposit): A New Proposal for Enhancing Cobalt Recovery

Copper-cobalt deposits in the Central African Copperbelt belong to the Sediment-Hosted Stratiform Copper (SHSC) type and are situated in the Neoproterozoic Katanga Supergroup. This paper describes in detail the geology, geochemistry and hydrometallurgy of cobalt, with a special focus on the Black Ore Mineralised Zone (BOMZ) unit from the Ruashi Cu-Co deposit as a case study. Based on results from fieldwork and laboratory testing, it was concluded that the BOMZ consists of a succession of massive and stratified dolostones, which are weathered into carbonaceous clay dolostones and clays. The Lower “Calcaire à Minéreaux Noirs Formation” (Lower CMN Formation) consists of stratified and finely laminated dolostones, which are weathered at the surface into clayey to siliceous dolostones. The cobalt concentration in the weathering zone is due to supergene enrichment, a process that is linked to the formation of a cobalt cap. The ore consists of heterogenite associated with minor amounts of chrysocolla and malachite. Minor carrollite, chalcopyrite, chalcocite and bornite are present in unweathered fragments. The cobalt grade in both the BOMZ and Lower CMN decreases within depth while the copper grade increases. These grade changes reflect the variation in mineralogy with depth from heterogenite with minor amounts of malachite and chrysocolla to malachite, chrysocolla with traces of heterogenite, spherocobaltite, chalcocite, chalcopyrite, carrollite and bornite. Based on the Cu (100xAS Cu/TCu) and Co ratio (100 xAS Co/TCo), which is related to the ore mineralogy, oxide ores (Cu ratio ≥ 75%) and oxide dominant mixed ores (Cu ratio < 75%, containing the copper sulphide chalcocite) can be differentiated in both the BOMZ and Lower CMN. The absence of talc and the low concentration of Ni, Mn and Fe, on the one hand, and the high-grade Cu in the BOMZ, on the other hand, facilitate the hydrometallurgy of cobalt but require a specific processing. Consequently, the recovery of Co from the BOMZ requires the application of a processing method that is based on sulphuric acid (30 g/L) leaching under reducing conditions (300–350 mV) and the removal of impurities (Cu > 95% and Mn ≈ 99%) from the pregnant leach solution (PLS) by solvent extraction (SX) prior to the precipitation of cobalt as a high-grade hydroxide (40.5%). The sulphuric acid leaching of the BOMZ enabled achieving, after 8 h of magnetic stirring (500 rpm), a highest yield of 93% Co, with other major elements Mn (84%) and Cu (40%). The latter forms a main co-product of the Co exploitation. In contrast, the highest leaching yield for Fe remained smaller than 5%.

New perspective on trace element (Re, Ge, Ag) hosts in the Cu-Ag Kupferschiefer deposit, Poland: Insight from a LA-ICP-MS trace element study

The Kupferschiefer deposit in SW Poland provides an opportunity to study an ore system where besides factors such as temperature, salinity and pH, redox conditions play a major role in controlling trace element incorporation in sulphides. Chalcocite, djurleite, bornite, chalcopyrite, sphalerite, covellite and pyrite from the Cu-Ag deposit in the Lubin-Sieroszowice district were analysed with laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to study the distribution of trace elements and to identify the main carriers of by-products such as silver and rhenium. Trace element anomalies are not only associated with certain minerals but also linked to specific mineralization styles. Chalcopyrite in epigenetic veins has significantly higher content of Ge, As and Sb while sulphides adjacent to hematitic “red spots” are enriched in redox sensitive elements: djurleite is enriched in V, Se, Re, Au, Hg and Tl, chalcopyrite in V, Se, Hg and Tl, and pyrite in Tl in comparison with bulk Cu-Ag mineralization. Elevated and substantially more variable data for V, Mn, Ni, Co, Ga, Mo, Sn in shale hosted sulphides can be attributed to submicron inclusions of Kupferschiefer silicate matrix which might skew low concentration values even if careful petrographic observations and precise spot selection are applied. Silver concentrations form a linear pattern from chalcocite/djurleite > bornite > chalcopyrite > sphalerite. Silver distribution in the deposit on a broad scale could be linked to the general Fe3+-Cu-Pb-Zn-Fe2+ zonation as well as mineral sequence (hematite-chalcocite-bornite-chalcopyrite-galena-sphalerite-pyrite) observed in the majority of sediment hosted stratiform copper deposits. Epigenetic sulphide-calcite veins associated with local faults and tectonic zones contain chalcopyrite exceptionally rich in germanium (up to 4806 μg/g of Ge) suggesting that the potential of Kupferschiefer Cu-Ag ores in terms of Ge grades and resources could be underestimated. The majority of analysed sulphides do not contain rhenium above detection limits (0.1 μg/g Re) with measurable quantities found almost exclusively in djurleite (up to 3.9 μg/g Re). This indicates that copper sulphides, in particular djurleite, could be a preferred host and an important carrier of rhenium in the deposit.

Geologic observations in the San Marcos area, Coahuila, Mexico: the case for sediment-hosted stratiform copper–silver mineralization in the Sabinas basin during the Laramide orogeny

The sediment-hosted stratiform copper–silver mineralization in the San Marcos area of Coahuila, northeastern Mexico occurs predominantly at an Early Cretaceous redox boundary between footwall siliciclastic red beds of the San Marcos Formation and hanging-wall carbonate strata of the Cupido Formation in the Sabinas basin. The hypogene mineralization is mainly present as chalcocite-group minerals, with additional bornite and chalcopyrite, and everywhere occurs in both disseminated and vein/veinlet forms. Supergene copper-bearing oxides (malachite, chalcanthite, azurite, chrysocolla) are, however, the dominant surface expression of the mineralization. Additional sediment-hosted stratiform copper–silver mineralization also occurs, albeit erratically, in lower strata of the Sabinas basin as well as in veins in basement granitoids, thus spanning ~3000 m of basin stratigraphy. Where best developed, the stratiform mineralization displays intense structural control proximal to the regional San Marcos fault system. This major bounding fault, regional in nature and with numerous periods of activity, controlled the evolution of the Sabinas basin. Structural controls on mineralization include stacked, shallow-angle, bedding-parallel, northeast-vergent thrust faults and associated drag folds, in addition to numerous, steeply-dipping, northeast-trending copper-bearing veins and veinlets. The mineralized veins and veinlets, and the bedding-parallel thrusts display mutually crosscutting relationships. These elements are all consistent and in harmony with a regional northeast-trending direction of horizontal shortening accompanying reverse motion of the San Marcos fault system. Inversion along the San Marcos fault system, and the entire Sabinas basin in the Paleogene from ~60 to 40 Ma, resulted from wholesale contractional deformation during the Laramide (Mexican) orogeny. Hence, emplacement of the sediment-hosted stratiform copper–silver mineralization at San Marcos, and elsewhere in the larger Coahuila region, is interpreted as a natural corollary of large-scale, metal-bearing fluid expulsion, migration, and precipitation resulting from orogenic shortening, lithostatic loading, and squeezing of the Sabinas basin during Mexican orogen construction. Although sedimentation of the host strata in the Sabinas basin took place in a pericratonic setting associated with the opening of the Gulf of Mexico, sediment-hosted stratiform copper-silver mineralization occurred during orogenic uplift and conversion of the original basin into an orogen-foreland pair, with similarities to some of the world´s largest sediment-hosted stratiform copper provinces.

Ore Minerals and Metal Distribution in Tailings of Sediment-Hosted Stratiform Copper Deposits from Poland and Kazakhstan

This study, carried out in tailings from two sediment-hosted stratiform copper deposits in the Lublin-Głogów Copper District in Poland (Kupferschiefer-type deposit) and Zhezkazgan (cupriferous sandstone-type deposit) in Kazakhstan, analysed the mineralogy of copper, zinc, and lead minerals as related to metal accumulation in sediments. Microscopic study in reflected light and SEM–EDS (Scanning Electron Microscope—Energy Dispersive Spectrometer) analysis, as well as chemical diversity in the used INAA (Instrumental Neutron Activation Analysis), ICP (Inductively Coupled Plasma), and AAS (Atomic Absorption Spectroscopy) methods in 35 samples from Kazakhstan and 35 from Poland were examined due to their diversity. In both tailing deposits in Kazakhstan and Poland, heavy fractions were dominated by copper sulphides: chalcopyrite (CuFeS2), bornite (Cu5FeS4). and chalcocite (Cu2S). Moreover, sphalerite, galena, and cerussite have been recognized as a carriers of Zn and Pb. Their geochemistry was dominated by Cu, showing a mean content of 2500 ppm, in both Poland and Kazakhstan. Zinc and lead also occurred, showing a content of approximately 200 ppm and 500 ppm in Poland, and 1500 ppm Zn and 2500 ppm Pb in Kazakhstan, respectively. Grain size analysis indicated that the dominant grain size in both districts corresponded to the silt and fine sands fractions. Copper, zinc and lead sulphides accumulated in fine fractions in tailings from Kazakhstan (in sandstones and quartz grains), and mainly in coarse fractions in Poland (within carbonates, sandstones, and black shales). Mineralogical and geochemical features should be taken into consideration when assessing potential metal sources of technogenic materials.

The prospecting strategy for a deep Cu-Ag ore deposit in Poland – An anatomy of success

The article presents the prospecting strategy implemented by Miedzi Copper Corporation in search for new Cu-Ag ore deposits of the Kupferschiefer type. Sediment-hosted stratiform copper deposits in Poland occur mostly in the Fore-Sudetic Monocline, in the contact zone between the continental red beds (Rotliegend) and Zechstein marine sediments. The ore-bearing series consists of white sandstone (Weissliegend), copper-bearing shale (Kupferschiefer) and carbonates (Zechstein Limestone). The southern-central part of the Fore-Sudetic Monocline is a well-known Lubin-Sieroszowice mining area, where mining operations are conducted at the depths up to 1300 m below surface. However, due to significant depletion of shallower reserves, deep Cu-Ag mineralisation have recently become a subject of interest. Several basic problems had to be resolved in order to reach for such deposits: finding indicators suggesting the presence of rich mineralisation; more precise identification of the current geothermal field in the area of the Fore-Sudetic Monocline; and the availability of modern technologies which would allow safe and economic operation of a deep underground mine. In 2011, Miedzi Copper Corporation initiated its exploration programme focused on deep Cu-Ag ore deposits, based on known prognostic areas in the vicinity of palaeorises and contacts between oxidised and reduced facies, as copper mineralization occurs at the rims of oxidised areas, on the reduced side of the redox boundary. Exploration programme has led to the documentation of three new deep deposits: Nowa Sól, Sulmierzyce North and Mozów, two of which were identified in areas previously described as prospective by the Polish Geological Institute.

On the timing and metallogenic implications of the sediment-hosted stratiform copper–silver mineralization in the Creston Formation (Belt-Purcell Supergroup), British Columbia, Canada

Sediment-hosted stratiform copper–silver mineralization is common in Middle Creston strata of southeastern British Columbia, a correlative lithostratigraphic unit of the Ravalli Group of western Montana. The Ravalli Group hosts the largest sediment-hosted stratiform copper–silver deposits of the Belt-Purcell Supergroup. Strata of the Belt-Purcell Supergroup accumulated between ~1540 and 1300 Ma in a pericratonic rift basin (Belt-Purcell basin) constructed over Archean and Paleoproterozoic blocks of Laurentia. The basin underwent several events of deformation and metamorphism at ~1380–1325 Ma (East Kootenay orogeny), ~1200–1000 Ma (Grenvillian), and 900–800 Ma (Goat River orogeny) prior to Meso-Cenozoic Cordilleran tectonism. U–Pb geochronology of detrital zircons from Middle Creston rocks define a maximum age of deposition of ~1470 Ma, in agreement with the established age range for the Belt-Purcell Supergroup in southeastern British Columbia. Molybdenite is locally part of the sediment-hosted stratiform copper–silver mineralization in the region, either as isolated grains within mineralized strata or in paragenetic sequence with the cupriferous sulfides. Re–Os geochronology on molybdenite reveals repetitive episodes of fluid flow through Middle Creston strata in the study area, with principal events at 1170–1140 and 1043–990 Ma. Paragenetically constrained molybdenite, in growth sequence with bornite and chalcocite, yields an age of 1043 ± 6 Ma. Hence, the fluid responsible for the sediment-hosted stratiform copper–silver mineralization in southeastern British Columbia permeated the host sequence ~440 m.yr. after its deposition, coincident with the Grenville-age metamorphic event at ~1200–1000 Ma. Such tectono-thermal activity extended along the western margin of Laurentia beyond the limits of the Belt-Purcell basin, and was a far-field response to orogen-scale collisions taking place off Laurentia during Rodinia assembly.

The Kupferschiefer Deposits and Prospects in SW Poland: Past, Present and Future

Polish sediment-hosted stratiform copper deposits associated with Zechstein sediments are one of the country’s most valuable natural resources and the basis for its copper industry. The paper presents the history of their research and current exploration. Although documented deposits and their identified resources are described and characterized, much attention is paid to areas located outside of them, including those where geological exploration is currently underway. The gradual depletion of shallow Cu–Ag reserves in the Lubin-Sieroszowice district and elsewhere in the world requires exploration for deeper-seated deposits. To expand resources, time span and scale of copper production in Poland, exploration and definition of new prospects is of great importance. Thirty-five prospective areas with hypothetical and speculative resources have been delineated in SW Poland, including the most prospective areas adjacent to the Cu–Ag Lubin-Sieroszowice deposit. The paper also focuses on those parts of the Fore-Sudetic Monocline where new copper deposits were recently identified. Their resources are described along with the methodology of establishing their boundaries, which differs from recommended Polish threshold parameters not taking into account the depths exceeding 1500 m. Intelligent modern mining and ore processing technologies are considered as a prerequisite for future profitable development of deposits at deeper levels.

Sediment Hosted Stratiform Copper (SSC) Mineralization in Bhudoli-Basari Area, North Delhi Fold Belt, Mesoproterozoic Delhi Supergroup, Rajasthan

The rocks of the Kushalgarh Formation of the Delhi Supergroup in northeast Rajasthan, host low-temperature prospect generally known as sediment hosted stratiform copper (SSC) mineralization in Bhudoli-Basari area, district Sikar, Rajasthan. Mineralization is about 3km in length with variable width of up to 600m and sulphides occur mainly as fine dissemination as well as veinlets within the steeply dipping carbonate rocks, which were remobilized along the quartz-calcite veins during compaction and subsequent deformation. The prospect is product of low-temperature aqueous brines. The brines leached, transported, and deposited copper (and associated metals) as per physical and chemical stabilities. The mineralization in the Bhudoli-Basari SSC consists mainly of bedding-parallel disseminations of fine-grained sulphides, typically zoned. Copper is leached from poorly sorted first-cycle clastic sediments of footwall redbeds, associated meta/volcanics of the Raialo Group and basement rocks during their progressive diagenetic alteration by moderate-temperature oxygen rich brines. Ore mineral zoning from chalcocite to pyrite in the Bhudoli-Basari area is archetypal to other SSC deposits viz. the Kupferschiefer of Poland-Germany and the Central African Copper belt of Zambia.

Stable isotope and fluid inclusion study of sediment-hosted stratiform copper deposits from the Neuquén Basin, Argentina

The Los Chihuidos and El Porvenir deposits of the Neuquen Basin are examples of sediment-hosted stratiform Cu deposits generated by interaction of hydrocarbons and formation water with host red beds and metal-charged basinal brines. During early diagenesis of red beds precipitated hematite, kaolinite at 60 °C from meteoric water followed by calcite 1 (δ13C − 8 to − 3.3‰) and barite (δ34S + 4.1‰) with increasing temperature (75–85 °C) from an evolved surface fluid (δ18Ofluids + 0.9 to + 2.7‰). During the Tertiary Andean orogeny, hydrocarbons and formation water migrated and reacted with the red beds resulting in bleaching of the sandstone. Smectite (fluid δ18O − 2.2‰ and δD − 73.7‰), chlorite-smectite mixed-layer minerals (fluid δ18O − 6.9‰ and δD − 84‰), pyrite (δ34S + 10.2‰), and calcite 2 (δ13C − 12.9 to − 6.8‰) formed as by-product of the redox reactions. Calcite 2 formed from low-salinity fluids (0.4 to 5.9 wt% NaCl equiv.) at slightly higher temperatures (125–145 °C) at El Porvenir and at Los Chihuidos deposit (80–105 °C). During subsequent uplift, metal-charged basinal brines flowed into the bleached sandstone and precipitated chalcopyrite-bornite (δ34S + 12.3‰) followed by chalcocite-spionkopite (δ34S − 64 to + 4.1‰). Calcites 3a (δ13C − 19 to − 10.1‰) and 3b (δ13C − 31.4 to − 9.5‰) that accompanied Fe-Cu and Cu sulfides, respectively, formed from saline fluids (up to 21.3 wt% NaCl equiv.) at temperatures of 159–70 °C. The δ18O values (+ 5.6 to + 11.4‰) of fluids in equilibrium with calcite 3a are similar to oilfield and basinal brines. Fluids in equilibrium with calcite 3 in Los Chihuidos and calcite 3b in El Porvenir show much lighter δ18O values (− 7.3 to − 4.6‰ and − 0.6 to + 2.3‰, respectively), which suggests the involvement of methane as the main reductant and possibly meteoric water interaction.

Physiochemical Restrictions of Mineral Zoning of Sediment-Hosted Stratiform Copper Deposit in SW China

The Chuxiong basin, located in southwest China, is well known as a mineralization area of red-bed type copper deposits in China. These deposits are characterized by mineral zoning, which is especially true for the Dayao deposits. The mineral zoning is consistent for both horizontal and vertical zoning; from the base (center) of the ore body to the top (outermost), the mineral zones are from hematite, chalcocite, chalcocite + bornite, and bornite + chalcopyrite to pyrite. We studied the mineral zoning in detail using a thermodynamic phase diagram method, such as log⁡fO2-log⁡fS2, pH-log⁡fO2, and pH-Eh, and discussed the constraints on the order of the minerals precipitation under different physiochemical conditions. It is indicated that changes in temperature have little effect on pH and Eh in the formation of minerals. S2− is stable only below 473 K, and the forming temperature of chalcocite must be below 473 K. In this paper, we also explain the mineral zoning formation mechanism and propose that the main controlling factor of mineral zoning is pH. Because this mineral zoning is widespread in sediment-hosted deposits, studies on this mechanism can considerably promote better understanding of the genesis of ore deposits in order to guide the exploration.

Latent volcanic heat and further unique aspects of early diagenetic stratiform copper mineralization in the White Pine-Presque Isle District, northern Michigan

The curious occurrence of copper-rich early diagenetic sediment-hosted stratiform copper mineralization in the finest-grained facies of Nonesuch greybeds in northern Michigan has been previously attributed to the warming of cupriferous brines in the footwall Copper Harbor Conglomerate by latent volcanic heat from the subjacent Porcupine Volcanics shield volcano. That anomalous footwall warming is employed here to explain other unique aspects of the White Pine-Presque Isle mineralization: the abrupt downward sulfide zoning from disseminated pyrite to chalcocite across the top of the cupriferous zone; the absence of bornite and chalcopyrite in the cupriferous zone proper; and the essential absence of pseudomorphs after pyrite euhedra and framboidal aggregates within the cupriferous zone proper, as well as the relatively coarse-grained character of disseminated chalcocite in the cupriferous zone.

In Situ Monazite Dating of Sediment-Hosted Stratiform Copper Mineralization in the Redstone Copper Belt, Northwest Territories, Canada: Cupriferous Fluid Flow Late in the Evolution of a Neoproterozoic Sedimentary Basin

AbstractThe 300-km-long Redstone copper belt in the Mackenzie Mountains, Northwest Territories, Canada, is composed of a series of sediment-hosted stratiform copper (SSC) deposits hosted in Neoproterozoic fault-bounded intracontinental rift basins. Mineralization at Coates Lake, the largest of these deposits, is concentrated within microbial laminite layers in the transition zone between underlying continental red beds of the Redstone River Formation and overlying marine carbonates of the Coppercap Formation. Disseminated cupriferous sulfides (chalcopyrite, bornite, and chalcocite) form part of a late diagenetic mineral association with dolomite, K-feldspar, albite, quartz, monazite, apatite, and pyrite that partially replaced detrital and early diagenetic minerals, including calcite cements, sulfate, and earlier generations of pyrite. Bornite (± minor chalcopyrite), calcite, dolomite, quartz, K-feldspar, and albite were also deposited in rare bedding-parallel veins adjacent to the lowermost mineralized microbial laminite layer in the transition zone.The absolute timing of mineralization was constrained by in situ U-Th-Pb chemical dating of monazite from four samples hosting disseminated SSC-type mineralization. The monazite have rounded, Th-U-heavy rare earth element-rich, detrital cores surrounded by Th-U-poor, light rare earth element-S-Sr-rich rims. The rim stage of monazite growth is intergrown with and enveloped by cupriferous sulfide and is paragenetically constrained as being part of the disseminated SSC-type mineralizing event. Eleven detrital cores yielded dates between 1843 and 1025 Ma, older than the depositional age of transition zone strata previously constrained to be between 775 and 732 Ma. Ten monazite rims yielded dates between 661 and 607 Ma. A weighted average date of 635 ± 13 Ma provides a maximum estimate, and is our preferred interpretation, for the absolute age of all copper mineralization at the Coates Lake deposit. Mineralization formed approximately 100 m.y. after deposition of the host rocks, during the thermal sag phase of continental rifting.Stratigraphic reconstructions, coupled with estimates of sediment compaction, indicate that at 635 Ma the transition zone was buried by ~4 km of sediments and overlaid another ~1.7 km of sediments that formed the Redstone River and Thundercloud Formations. Mudstone and carbonate-rich units above the transition zone acted as low permeability caps that led to suprahydrostatic fluid pressures in the underlying sediments. The bedding-parallel veins indicate transient supralithostatic fluid pressures. Free convection of pore fluids began within the transition zone and underlying units once they became hydrologically isolated from overlying strata. Mineralization formed as oxidized saline pore fluids circulated through the red beds (± underlying basaltic flows and basal sedimentary detritus), stripping copper and carrying it up into the transition zone. The salinity of the pore fluids may have, at least in part, originated from cryogenic brines generated by the Sturtian (717–662 Ma) global glaciation event.

Constraints on Conceptual and Quantitative Modeling of Early Diagenetic Sediment-Hosted Stratiform Copper Mineralization

Early diagenetic sediment-hosted stratiform copper (eSSC) mineralization results from low-temperature cuprous chloride complexes carried by saline aqueous solution circulating through footwall aquifers. Favorable copper solubilities are attained in moderately oxidizing, near-neutral pH solutions. That specific oxidation level is not determined by co-existence with hematite, with its near-indiscriminant control over Eh. Instead, redbed footwall aquifers are signatures of diagenetic oxidation. Relentless in-situ oxidation of ferrous minerals in redbeds produces pore waters too reduced to transport copper, thus eliminating compaction waters as ore solutions. Continuous early influxes of descending oxygen-rich meteoric waters which have assimilated evaporitic salts may redden aquifers and still retain oxidation levels capable of carrying copper to form downstream eSSCs.

Geology and geochemistry of the sediment-hosted Cheshmeh-Konan redbed-type copper deposit, NW Iran

The several-hundred-m-thick Miocene Upper Red Formation in northwestern Iran hosts stratiform and fault-controlled copper mineralization. Copper enrichment in the percent range occurs in dm-thick carbonaceous sandstone and shale units within the clastic redbed sequence and consists of fine-grained disseminated copper sulfides (chalcopyrite, bornite, chalcocite) and supergene alteration minerals (covellite, malachite and azurite). The copper mineralization formed after calcite cementation of the primary rock permeability. Copper sulfides occur mainly as replacement of diagenetic pyrite, which, in turn, replaced organic matter. Electron microprobe analysis on bornite, chalcocite and covellite identifies elevated silver contents in these minerals (up to 0.12, 0.72 and 1.21wt%, respectively), whereas chalcopyrite and pyrite have only trace amounts of silver (<0.26 and 0.06wt%, respectively). Microthermometric data on fluid inclusions in authigenic quartz and calcite indicate that the Cu mineralization is related to a diagenetic fluid of moderate-to low temperature (Th=96–160°C) but high salinity (25–38wt% CaCl2 equiv.). The range of δ34S in pyrite is −41.9 to −16.4‰ (average −31.4‰), where framboidal pyrite shows the most negative values between −41.9 and −31.8‰, and fine-grained pyrite has relatively heavier δ34S values (−29.2 to −16.4‰), consistent with a bacteriogenic derivation of the sulfur. The Cu-sulfides (chalcopyrite, bornite and chalcocite) show slightly heavier values from −14.6 to −9.0‰, and their sulfur sources may be both the precursor pyrite-S and the bacterial reduction of sulfate-bearing basinal brines. Carbonates related to the ore stage show isotopically light values of δ13CV-PDB from −8.2 to −5.1‰ and δ18OV-PDB from −10.3 to −7.2‰, indicating a mixed source of oxidation of organic carbon (ca. −20‰) and HCO3− from seawater/porewater (ca. 0‰). The copper mineralization is mainly controlled by organic matter content and paleopermeability (intragranular space to large fracture patterns), enhanced by feldspar and calcite dissolution. The Cheshmeh-Konan deposit can be classified as a redbed-type sediment-hosted stratiform copper (SSC) deposit.

Two Ages of Copper Mineralization in the Mwombezhi Dome, Northwestern Zambia: Metallogenic Implications for the Central African Copperbelt

Approximately 10% of copper resources in the Central African Copperbelt, the world’s largest, sediment-hosted stratiform copper province, occur in the Domes region of northwestern Zambia. The copper deposits and prospects are commonly hosted by amphibolite-facies metamorphic rocks and lie within or adjacent to several basement inliers. Minor molybdenite accompanies the copper-iron sulfide minerals in two deposits and four prospects within the Mwombezhi dome as well as in deposits elsewhere in the Domes region. The results of Re-Os dating of 11 molybdenite samples reveal the existence of two discrete copper-mineralizing epochs, separated by >500 m.y. Most of the mineralization, including that in the Chimiwungu orebody at Lumwana, the largest deposit in the Mwombezhi dome, formed within a maximum interval of ~42 m.y. (538.9–497.1 Ma), which spans the peak of the Lufilian collisional orogeny. In contrast, three samples (four determinations) from the Nyungu prospect returned Mesoproterozoic ages of 1084 to 1059 ± 5 Ma, coincident with the Irumide collisional orogeny. Although several investigators have speculated that the copper in the Central African Copperbelt deposits was extracted from the basement, this is the first unambiguous evidence for an appreciable copper concentration of pre-Katangan (pre-Neoproterozoic) age. Based on this evidence, additional Mesoproterozoic and possibly even older copper concentrations seem likely to exist elsewhere beneath and/or alongside the Copperbelt in both Zambia and the Democratic Republic of Congo. Such preenrichment of the basement in copper may have contributed to the enormous metal endowment of the Central African Copperbelt.