CONTENT, DATES and DESCRIPTIONS OF ORE DEPOSITS
Porter GeoConsultancy, continued its International Study Tour series of professional development courses during May 2014 by visiting a representative selection of the different styles, and the most important examples, of sediment hosted deposits of the great copperbelts of Southern and Central Africa, and Europe in Botswana, Zambia, Democratic Republic of Congo and Poland.
Cu-Ag, Kalahari Copperbelt, northern Botswana.
Lumwana Cu-U, Domes Region, Zambia.
Kansanshi Cu-Au, Domes Region, Zambia.
Nchanga-Konkola Cu-Co, Kafue Anticline, Zambia.
Mufulira Cu-Co, Kafue Anticline, Zambia.
Nkana-Mindola, Cu-Co, Kafue Anticline, Zambia.
Kinsevere Cu-Co, Southern Congolese Copperbelt, DRC.
Tenke-Fungurume Cu-Co, Northeastern Congolese Copperbelt, DRC.
Kolwezi - Kamoto (KTO), T17 and KOV Cu-Co, Northern Congolese Copperbelt, DRC.
Kamoa Cu-Ag, Northern Congolese Copperbelt, DRC
Mutanda Cu-Co, Northern Congolese Copperbelt, DRC.
Overview Workshop & Rudna Kupferschiefer Cu-Ag mine, Poland.
The date for each visit or workshop is shown alongside the heading of the respective description below.
The mine and project visits were complemented by field & classroom workshops presented by experts from academia, government geological surveys and industry.
The full tour commenced in Johannesburg, South Africa on the evening of Wednesday 31 April, 2014 and ended in Wroclaw, Poland, on the evening of Tuesday 20 May.
Participants were able to take any 3 or more days, up to the full tour, as suited their interests or availability, with participants joining and leaving the tour at appropriate locations along the route.
The main components of the planned itinerary were:
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Travelling from Johannesburg South Africa, to Maun, Northern Botswana ...................... Thursday 1 May, 2013.
Boseto - Kalahari Copperbelt, Northern Botswana - Discovery Metals ...................... Friday 2 May, 2014.
The Boseto project represents a group of Neoproterozoic, stratabound, sediment-hosted, copper-silver deposits, which are part of the ~800 km long Kalahari Copperbelt of Namibia and Botswana. The Kalahari Copperbelt is located on the southeastern margin of the Damaran-Katangan rift basin, in rocks of broadly comparable age to those that host the Central African Copperbelt of Zambia and the DRC in the Lufilian structural arc that defines the northeastern extremity of the same rift basin.
Geological Summaries of deposits visited and Scheduled Dates of visits and travel
In Botswana, significant deposits are found within a zone of deformed bimodal metavolcanic and metasedimentary rocks. The ~5500 m thick host succession commences with rhyolites and sub-alkaline basalts, overlain by immature wackes, sandstones, sometimes including red-beds, and lesser shale, followed by a sequence dominated by reduced, pyritic facies, mainly laminated grey-green to black siltstones and mudstones, with interbedded fine-grained sandstones and lesser limestones. These are, in turn, overlain by by fine to medium-grained arkosic sandstone, interbedded with siltstone, mudstone and limestone.
The Boseto deposits, occur within the lower sections of the reduced mudstones and siltstones, immediately above the contact with the underlying oxidised arkoses and sandstones. Copper-silver mineralisation typically occurs as: i). Disseminated sulphides in porous sandstones; ii). Cleavage related, fine grained sulphides, in non-porous finer sedimentary rocks; and iii). Vein related mineralisation, comprising coarse grained sulphides in quartz and quartz-carbonate veins and veinlets. The total mineral resource at the end of 2012 for all Boseto deposits was 177.1 Mt @ 1.3% Cu, 15 g/t Ag. .... MORE
Travelling from Maun, Northern Botswana to Solwezi, NW Zambia, via Johannesburg ...................... Sat. 3 and Sun. 4 May, 2014.
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Lumwana - Domes Region, Zambia - Barrick Gold ...................... Monday 5 May, 2014.
The extensive, tabular, stratabound, Malundwe and Chimiwungo copper deposits of the Lumwana Project are located in the North West province of Zambia, ~220 km west to northwest of the main Zambian Copper Belt mines. These deposits are hosted by overturned, highly sheared amphibolite facies schists to gneisses within the north-eastern lobe of the Mwombezhi Dome. This north-east trending, ~20 x 70 km, basement dome occurs in the western arm of the 900 km long, arcuate (northeast to southeast trending, convex to the north) Pan-African fold-thrust belt, known as the Neoproterozoic Lufilian Arc.
In the Domes Region of Zambia, the Lufilian Arc is characterised by broadly north-directed thrust structures and antiformal basement inliers/domes, surrounded by Neoproterozoic Katangan Supergroup metasedimentary rocks that host the 'classic' Central African Copper Belt deposits. The Lumwana deposits are variously interpreted to represent metasomatic alteration and mineralisation of foliated pre-Katangan basement (Bernau, 2007), or alternatively, sheared and structurally interleaved, mineralised Katangan Roan Group sedimentary rocks (Nisbett, 2005; Barrick, 2013).
The orebodies almost entirely comprise high-grade metamorphosed, intensely mylonitised, schists with disseminated sulphides (typically <5%), dominated by chalcopyrite and bornite. Weak Cu, Au, Co and U mineralisation is also found in the intervening gneiss units between stacked orebodies. The total mineral resource at Lumwana at the end of 2012 for all deposits was 954 Mt @ 0.47% Cu. .... MORE
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Kansanshi - Domes Region, Zambia - First Quantum Minerals ...................... Tuesday 6 May, 2014.
The Kansanshi sediment hosted copper-gold deposit is located in the 'Domes Region' of the Lufilian Arc, ~12 km north of the basement Solwezi Dome, ~70 km ENE of Lumwana, and ~180 km to the NW of the Copperbelt town of Chingola.
The stratigraphic sequence at Kansanshi is composed of dolomitic and calcareous schists, marbles, pebble schist, biotite schists and phyllites. The distribution of facies in the succession is interpreted to be a symmetrically repeated sequence representing a recumbent isoclinal fold (with an almost flat lying axial plane) that has subsequently been gently folded to form the Kansanshi Antiform that has a series of parasitic domal structures along its crest. The host rocks have been subjected to upper-greenschist to upper-amphibolite facies metamorphism and are equated with the Neoproterozoic Mwashya Subgroup rocks of the uppermost Roan Group and the overlying Nguba Group, both of which belong to the Katangan Supergroup. These sequences are cut by numerous ~750 Ma gabbro bodies.
The main Kansanshi deposit are developed within parasitic domal structures along the crest of the Kansanshi Antiform. Mineralisation occurs as swarms of quartz-carbonate-sulphide veins, fringed by selvages of bedding replacement ore, and in breccia zones, hosted within a suite of interbedded graphitic shale, knotted schist, quartzite and lesser limestone. The total mineral resource at Kansanshi at the end of 2012, for all deposits was 1092 Mt @ 0.81% Cu, 0.13 g/t Au. .... MORE
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Nchanga-Chingola and Konkola, Zambian Copperbelt, Zambia - Konkola Copper Mines .......... Wednesday 7 May, 2014.
Nchanga-Chingola and Konkola are the first of the 'classic' Zambian Copperbelt copper-cobalt deposits of the itinerary. The Zambian Copperbelt is hosted by the (~880 to ~600 Ma) Neoproterozoic Katangan Supergroup, and is part of the larger Central African Copperbelt, that extends north into the neighbouring Democratic Republic of Congo (DRC), to continue as the Congolese Copperbelt. The deposits of the Zambian Copperbelt flank the NW-SE trending Kafue Anticline, which coincides with the southeastern Domes Region of the complex, arcuate structural zone, the Lufilian Arc, that in turn, defines the northeastern extremity of the trans-continental Damaran-Katangan rift basin. .... MORE
The Nchanga-Chingola stratabound, sediment-hosted copper-cobalt deposits are located on the northern section of the western margin of the Kafue Anticline in Zambia. Mineralisation is hosted by the Neoproterozoic Lower Roan Subgroup, where its lower members lap onto a palaeo-basement high that corresponds to the core of the current Kafue Anticline. Primary copper mineralisation is found at five overlapping levels over a total stratigraphic interval of 150 m, occurring as 'Footwall ore' in the Mindola Clastics Formation, the lowermost unit of the Lower Roan Subgroup, in the Lower Banded Shale (equivalent to the regional Copperbelt Orebody Member) at the base of the overlying Kitwe Formation, and in succeeding members of the latter formation. Mineralisation, which is generally found at progressively higher stratigraphic positions from south to north, is hosted by a variety of lithologies, including micaceous and dolomitic feldspathic quartzite, coarse grained arkose and greywacke, and, to a lesser extent, by siltstones and shales which cap these arenite units. Primary sulphides, which include chalcopyrite, bornite, chalcocite and pyrite, occur mainly as disseminations within the arenitic units and as disseminations orientated along bedding or cleavage planes, and in quartz veins, within the finer facies. Much of the sulphides have been oxidised to depths of over 300 m, with malachite and secondary chalcocite being ubiquitous. Total production + resources at the Nchanga-Chingola cluster is 1080 Mt @ 2.16% Cu. .... MORE
The Konkola-Kirila Bombwe and Konkola Deep stratabound, sediment-hosted, copper-cobalt deposits, which are ~15 km to the north of Nchanga on the northwestern extremity of the Kafue Anticline in Zambia, are part of the Konkola Copper Mines operation which also includes Nchanga-Chingola. The Konkola mineralisation continues north at depth, becoming the neighbouring Lubambe (previously Konkola North) mine that emerges on the eastern margin of the Konkola Dome to the NW, following the rim of dome northwestward into the DRC, as the Musoshi deposit. The ore is predominantly hosted by banded siltstones and sandy shales of the up to 60 m thick Lower Roan Subgroup Copperbelt Orebody Member, equivalent to the Lower Banded Shale facies that hosts some of the ore at Nchanga. Total production + resources from Kirila Bombwe to Musoshi is estimated to total >1000 Mt @ ~3% Cu. ..... MORE
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Mufulira, Zambian Copperbelt, Zambia - Mopani Mines ...................... Thursday 8 May, 2014.
The Mufulira stratabound, sediment-hosted, copper-cobalt deposit is located 30 km north of the town of Kitwe, in the Zambian Copper Belt of central Zambia. It is also one of the 'classic' Zambian Copperbelt deposits, located on the eastern margin of the Kafue Anticline, hosted by the Lower Roan Subgroup of the Neoproterozoic Katangan Supergroup. Copper sulphides occur at 21 distinct stratigraphic positions within the Mufulira mine, of which only three are economically exploited, termed the 'A', 'B' and 'C', within the 30 to 80 m thick "Ore Formation". The Ore Formation overlies the westward thinning "Footwall Formation", which is equivalent to the Mindola Clastics Formation on the western flank of the Kafue Anticline. The 'C' Orebody is the lowest and most extensive, having lateral dimensions of 5800 m, continuous down dip for >1300 m, to at least the 1500 m level, and is up 23 m thick, averaging ~14 m.
The ore at Mufulira is almost exclusively within 'arenites' and not in the intervening and overlying finer sedimentary rocks. Copper sulphides occur as discontinuous bands of 'fly speck' disseminations following bedding planes and as irregular angular clots of weak to dense interstitial disseminations of sulphides whose elongation is influenced by bedding, but may also be markedly transgressive. Chalcopyrite dominates in the 'C' Orebody (although in sections this grades to bornite dominant), whilst in the 'B' Orebody, the predominant ore mineral is bornite. The uppermost 'A' Orebody is also the highest grade, with bornite and chalcocite. Total production + resources were estimated in 1988 as 335 Mt @ 3.3% Cu. ..... MORE
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Nkana-Mindola, Zambian Copperbelt, Zambia - Mopani Mines ...................... Friday 9 May, 2014.
The Nkana-Mindola stratabound, sediment-hosted, copper-cobalt deposits are exploited from four open pit and four underground mines, from north to south, the North Mindola, Mindola, Nkana Central and Nkana SOB (Southern Ore Body). Mineralisation, is more or less continuous over a strike length of 14 km, with narrow 'barren gaps', on the SW margin of the Kafue Anticline, immediately to the east of the town of Kitwe and is hosted within the 21 to 23 m thick Copperbelt Orebody Member, or 'Ore Shale'. The Copperbelt Orebody Member is the basal unit of the Kitwe Formation, predominantly composed of dark grey dolomitic argillite, overlain by quartzites and dolomitic argillites of the main bulk of the Kitwe Formation. It overlies an eastward thinning sequence of oxidised sandstones and conglomerates that comprise the Mindola Clastics Formation, which rest on basement gneisses.
Orebodies are distributed throughout the Copperbelt Orebody Member. Overall, the best grades of primary mineralisation (~4% Cu) are found to the NE in the Mindola orebody, dropping off to nearer 2.2% Cu at depth to the south in the SOB (South Orebody), where the host then passes into black carbonaceous shale, with only low grade chalcopyrite, carrollite and pyrite, then to pyrite with scattered chalcopyrite. To the north and up-dip of this facies gradation, the primary ore is chalcopyrite dominant, passing into a bornite-chalcopyrite in the Mindola deposit. At Mindola, bornite accompanies chalcopyrite at the base of the ore zone, decreasing upwards. Total production + resource were estimated in 1988 as 690 Mt @ 2.5% Cu. ..... MORE
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Travelling from Ndola, Zambia, to Lubumbashi, DRC ...................... Saturday 10 May, 2014.
Rest, study and discussion day - Lubumbashi, DRC ...................... Sunday 11 May, 2014.
A day was set aside for the group to rest, update notes from the previous week, and to study to prepare for the visits in the DRC. This culminated with a presentation and discussion session in the mid- and late-afternoon by Professor Louis Kipata Mwabanwa, Head of Department of Geology, University of Lubumbashi on the tectonic, structural and geological setting of the Congolese Copperbelt in Katanga. Professor Kipata is known for his detailed studies of the tectonics and geology of the Lufilian Arc in the DRC. He also brought a collection of specimens illustrating the various lithologies that comprise the host Mines Sub-group succession of the ore-bearing Roan Group in Katanga.
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Kinsevere, Congolese Copperbelt, DRC - MMG Limited ...................... Monday 12 May, 2014.
Kinsevere is the first of the Congolese Copperbelt deposits on the itinerary. The Congolese (or Katangan) Copperbelt (CCB), extends over an arcuate interval of ~350 km in Katanga Province of the DRC, part of the larger, >500 km long Central African Copperbelt, that continues south as the Zambian Copperbelt. As in Zambia, mineralisation is hosted by Neoproterozoic metasedimentary rocks of the Katangan Supergroup, but in different stratigraphic positions, structural setting and facies suite, occurring within the External Fold and Thrust Belt of the Lufilian Arc, external to the Domes Region in which the Zambian deposits are found. ...... MORE
The Kinsevere sediment hosted copper-cobalt deposit is located ~35 km NNE of Lubumbashi in Katanga Province. Primary mineralisation is hosted by reduced carbonate rich rocks of the Mines Subgroup, which overlie the oxidised, predominantly coarse-grained clastic sequence of the R.A.T. Subgroup. These are the lowest two units of the Neoproterozoic Roan Group in the CCB. The host rocks occur as a series of jumbled tabular tectonic blocks within a Roan Group megabreccia, characteristic of many deposits within the CCB. At Kinsevere, this megabreccia has been diapirically injected into the overlying Nguba Group rocks forming a ~2.5 x 1 km window of Roan Group rocks. Within this window, three steeply dipping Roan Group slabs are juxtaposed, resulting in primary mineralisation over a thickness of >200 m.
This mineralisation is largely composed of chalcocite, bornite and chalcopyrite, hosted by finely laminated silty dolostone to dolomitic shales, occurring in stratabound nodules and bedding parallel veins, and in dolomite/calcite veins in joints and fractures. The regolith profile at Kinsevere includes a near-surface veneer of bleached clays, underlain by a zone in which the country rocks are progressively less oxidised downward. The bulk of the economic ore is supergene, forming a well defined horizontal layer from just below the surface to the base of oxidation at 60 to 100 m depth, cross-cutting the steeply dipping primary orebodies at a high angle. The oxide ore mineral assemblage is predominantly composed of malachite and pseudomalachite, with minor chrysocolla and rare intergrown heterogenite. These are found as disseminations and/or in veins and veinlets, and sometimes coalesce into prominent 'clots'. Total measured + indicated + inferred resources in June 2012 were 52.2 Mt @ 3.0% Cu Total, 1.8% Cu Acid Sol.. ..... MORE
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Tenke-Fungurume, Northeastern CCB, DRC - Tenke Fungurume Mining ...................... Tuesday 13 May, 2014.
The Tenke-Fungurume cluster of sediment-hosted copper-cobalt deposits occupies the northeastern apex of the Lufilian Arc, straddling a change in structural grain, from a north-south directed high compressional regime in the west, which has an east-west trend, to moderate, NW-SE trending folds in the east. The ore deposits of the district, lie within the >500 km2 Tenke-Fungurume tectonic window of allochthonous Roan Group megabreccias (the Roan window), both overlain and underlain across thrusts by younger Nguba and Kundelungu lithotectonic assemblages. This is the largest such window in the Central African Copperbelt. The megabreccia is composed of a chaotic matrix of rock flour through silt and gravel sized talc, dolomite, quartz and Mg-rich chlorite, as well as larger blocks of clastic and carbonate rocks, encasing scrambled slabs (locally known as écailles) of the Mines Subgroup that are tens metres to 1.8 km in strike length and down-dip extent, and from 20 to >200 m thick.
The bulk of the ore at Tenke-Fungurume occurs within écailles of the Mines Subgroup in the southern half of the Roan window, and is present in the lower part of the subgroup, immediately above the regional oxidation-reduction lithogeochemical contact between the underlying, red, hematitic, oxidised RAT Lilas, and the reduced lower units of the overlying Mines Subgroup. There is ~120 km strike length of the potentially mineralised intervals within écailles in the southern part of the Roan window, not all of which are economically mineralised. Ore occurs in the stratabound Upper and Lower orebody units, each generally 5 to 15 m thick, sandwiching a 15 to 30 m thick, largely barren layer of strongly silicified, cavernous and porous, stromatolitic dolostone, the RSC. The host rocks of the two orebody beds are composed of laminated and silicified dolostones and dolomitic shales.
Below the supergene-oxide zone, primary chalcocite, bornite and carrollite are the most common ore minerals in the lower orebody, while chalcopyrite is the most common sulphide ore mineral in the upper orebody. The zone of supergene-oxide ore normally extends to depths of 80 to 150 m below surface, comprising copper and cobalt carbonates, phosphates, silicates and oxides, with copper predominantly occurring as malachite (91%), pseudomalachite (9%) and trace libethenite, while oxide cobalt is mainly dark brown heterogenite. Mineralisation is similar to the deposits of the Kolwezi Klippe (see below), but with a different geometry. Total historic production + reserves/resources to 2012 are estimated to be 547 Mt @ 3.5% Cu, 0.27% Co. ..... MORE
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Kolwezi - Kamoto (KTO), T17 and KOV Mines, Northern CCB, DRC - Katanga Copper Company ...................... Wednesday 14 May, 2014.
Kamoto, T17 and KOV are 3 of more than 20 sediment hosted, stratabound copper-cobalt deposits hosted by jumbled slabs (écailles) of Mines Subgroup (Roan Group) rocks within a megabreccia (similar to that described at Tenke-Fungurume, above) that forms the allochthonous Kolwezi Klippe near the northern margin of the Congolese Copper Belt (CCB). The Klippe overlies a gently folded detachment, which closely parallels the stratigraphy of the immediately underlying, younger Kundelungu and Nguba group rocks at depths of 0 to 1400 m below the surface. Individual écailles are up to 250 m thick, and range from tens of metres to several kilometres in length.
The Kolwezi Klippe covers an ENE-WSW elongated elliptical area of some 23 x 8 km, centred on the town of Kolwezi, ~55 km west of Tenke-Fungurume. The immediate host sequence within the écailles comprises the stratabound Upper and Lower orebody units of fine-grained, laminated, argillaceous, chloritic and siliceous dolostones and chloritic-dolomitic siltstones, each from ~5 to 15 m thick. These two units sandwich a generally barren, 10 to 30 m thick band consisting almost exclusively of strongly altered cellular dolomite and secondary quartz, the RSC. Mineralised écailles are juxtaposed across faults and bands of breccia. Mineralisation preceded the halokinetic brecciation of the evaporite-bearing host sequence that formed the megabreccia.
Primary copper and cobalt occur as fine disseminations, layers and nodules of sulphide minerals, dominantly chalcocite and carrollite in both orebodies, with lesser bornite, accompanied by minor chalcopyrite on the upper margins of the Upper orebody. The distribution of these sulphides is largely controlled by sedimentary features, following bedding planes in the finely bedded host rocks. Late crosscutting fractures and veinlets contain dolomite, silica and chalcocite-digenite-hematite mineralisation.
The bulk of the copper and cobalt mined from the Kolwezi Klippe has been from supergene oxide and sulphide ore. Supergene mineralisation is generally associated with the oxidation of both the Upper and Lower orebodies, sometimes to >100 m below surface, occurring as supergene carbonates, silicates and phosphates. The most common secondary copper mineral is malachite, with lesser cuprite, cornetite, libethenite and pseudomalachite. Heterogenite and kolwezite are the principal secondary cobalt minerals, with some goethite. The supergene copper-cobalt oxide assemblage is underlain by secondary chalcocite, overprinting the primary chalcocite and bornite. Total production + resources estimated in the Kolwezi District in 2012 were 726 Mt @ 4.48% Cu, 0.33% Co, with additional resources of >300 Mt @ ~1.5% Cu. ..... MORE
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Kamoa, Northern CCB, DRC - Ivanhoe Mines ...................... Thursday 15 May, 2014.
The Kamoa sediment hosted copper deposit lies on the northwestern margin of the Central African Copperbelt, ~25 km west of Kolwezi, in the DRC. The deposit is hosted within carbonaceous shales and diamictites of the Grand Conglomérat, at the base of the Neoproterozoic Nguba Group, immediately above the redox boundary at the contact with the underlying oxidised Mwashya Subgroup arenites, which, in turn, lap onto, and directly overlie, the Mesoproterozoic Nzilo basement block. As such, the Mines Subgroup that hosts the ore at Kolwezi is absent below the Kamoa deposit, and the Nguba Group is the first reduced unit overlying the oxidised footwall sequence.
The copper sulphide mineralisation is capped by the hanging wall Kamoa Pyritic Siltstone-Sandstone unit. Sulphide mineralisation at Kamoa was precipitated in two main stages: i). an early stage, during diagenesis, which formed abundant fine framboidal and coarse secondary cubic pyrite that overgrows pyrite framboids, and may be either uniformly distributed within individual beds, or mimic sedimentary structures; ii). a later period of dominantly hydrothermal copper sulphide mineralisation, which affected the uppermost Mwashya Subgroup rocks, the lower diamictite/siltstone package, and, locally, the Kamoa Pyritic Siltstone-Sandstone. Copper sulphides both overgrow, and replace diagenetic framboidal and secondary cubic pyrite. The principal sulphide minerals are chalcocite, bornite, chalcopyrite and pyrite, which share common bedding and replacement textures, ranging from semi-massive accumulations, to disseminations, to very coarse blebs, and occasionally occur as veins. Sulphides commonly mantle and or partially replace clasts in the diamictite.
Copper sulphides are zoned, relative to the Mwashya Subgroup-Grand Conglomérat contact, upward, from chalcocite, through bornite to chalcopyrite, then pyrite and, finally, minor sphalerite and/or galena. The deposit covers an area of ~22 x 12 km, and varies from 2 to 15 m in thickness. At a 1% Cu cutoff, indicated resources are 739 Mt @ 2.67% Cu + inferred resources of 227 Mt @ 1.96% Cu. ..... MORE
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Mutanda, Northern CCB, DRC - Mutanda Mining ...................... Friday 16 May, 2014.
Mutanda is one of a string of sediment hosted copper-cobalt deposits that define a generally east-west trending, 30 km long, mineralised corridor to the south and east of the Kolwezi Klippe, distributed along two parallel fault zones that are 3 to 5 km apart. This corridor contains combined resources in excess of 1 Gt @ 1.4 to 2.6% Cu.
Mineralisation at Mutanda is hosted within generally shallow-dipping, structurally inverted imbrications of the upper Dipeta Subgroup Kansuki Formation, and partly in the basal Nguba Group, rather than by the stratigraphically lower Mines Subgroup écailles within megabreccia as at Kolwezi and Tenke-Fungurume.
The succession within the deposit area at Mutanda includes rocks of the lower to middle Dipeta Subgroup, deposited below the Kansuki Formation, mainly comprising argillites, but also some green pyroclastic rocks. The stratigraphically younger Kansuki Formation itself is largely composed of recrystallised stromatolitic dolostone, with intercalated, finely bedded, dolomitic argillites in its lower sections, and a characteristic suite that includes a specular haematite layer, often in close proximity to a thin jaspilite bed, and an oolitic dolomite band, in the upper sections. The Nguba Group is represented by green diamictites of the Grand Conglomérat, and by argillaceous siltstones of the overlying Kakontwe Formation.
Within the deposit area, the stratigraphy is overturned, and contacts between the main units are tectonic, and in places occupied by breccias, representing north vergent D1 thrusting. The tectonically imbricated sequence strikes east-west, dips shallowly to the south (<5 to 30°S), but is bounded by steep, east-west trending D2 strike-slip faults to the north and south to form an ~3 km long, lensoid sliver of Roan Group rocks in-faulted into the younger Nguba and Kundelungu Group rocks.
Mineralisation occurs as veinlets and disseminations of chalcocite and carrollite, and more rarely bornite with minor chalcopyrite, in the lower Kansuki Formation recrystallised dolostone, whilst in the upper sections of the same formation, finely bedded dolomitic argillites contain fine disseminations and veinlets of copper and cobalt sulphides (carrollite, chalcocite and bornite with minor chalcopyrite) along bedding planes, with coarser disseminations of the same minerals, particularly euhedral carrollite, dispersed throughout.
The bulk of the mineralisation in the open pit resource has been oxidised, composed mainly of malachite, pseudomalachite and heterogenite, although portions retain sulphides. Total measured + indicated + inferred resources at the end of 2011 were 299.5 Mt @ 1.48% Cu, 0.59% Co. ..... MORE
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Travelling from Kolwezi, DRC, via Lubumbashi, Nairobi, Zurich and Frankfurt to Wroclaw and Lubin, Poland ...................... Sat. 17 and Sun. 18 May, 2014.
Kupferschiefer Mines - SW Poland - KGHM ...................... Monday 19 and Tuesday 20 May, 2014.
The program in Poland comprised an overview workshop on Monday 19 May led by Dr Sławomir Oszczepalski of the Geological Institute of Poland who is a recognised expert of long standing on the Polish Kupferschiefer. It included:
i). classroom presentations on the tectonics/structure, geology, distribution, characteristics and styles of mineralisation and associated alteration, and prospectivity of the Kupferschiefer mineralisation in south-west Poland;
ii). inspection of drill core through the ore and host section, and
iii). a field component comprising inspection of exposures of the host sequence in the historic mines of the North Sudetic Trough.
This was followed on Tuesday 20 May by an underground visit to the Rudna mine to study the geology of the host sequence, ore and alteration.
The Permian Polish Kupferschiefer mineralisation is developed on the south-western margin of the Polish Trough, a basin that forms the south-eastern section of the Southern Permian Basin, which extends across northern Europe, from the North Sea, through northern Germany, to Poland.
The sequence within the Polish Trough rests on a basement of crystalline Proterozoic rocks, and lesser Palaeozoic, mainly Carboniferous extrusive and intrusive magmatic rocks and overlying coal measures. The Lower Permian sequence includes a basal, red-brown, coarse clastic succession, overlain by a suite of 285 to 270 Ma bimodal volcanic rocks (from 0 to 1500 m thick), followed in turn by the up to 500 m thick Rotliegendes Clastic Rocks sequence, composed mainly of red sandstones and conglomerates. The uppermost Rotliegendes has been bleached and chemically reduced to a white or grey colour, referred to as the Weissliegendes and Grauliegendes respectively, over a thickness generally of up to several metres, but locally as much as 65 m. The uppermost Rotliegendes clastic rocks are overlain by the Upper Permian Zechstein succession, which varies from 250 to 1500 m in thickness. It is composed of four evaporitic cyclothems. The first of these cyclothems commences with a basal 0 to 0.3 m thick limestone to dolomite, overlain by the 0 to 0.7 m thick Kupferschiefer, the ~1 to 120 m thick Zechstein Limestone, and the up to >200 m thick halites and anhydrites of the PZ-1 Evaporites. The other three cyclothems, each varying from <10 to 60 m in thickness, are variably distributed, with not all represented in any particular section of the basin.
The Kupferschiefer (sensu stricto) covers an area of ~600 000 km2 within northern Europe. The base frequently comprises tectonically crumpled, pitchy, shales, overlain by an up to 10 cm thick layer of laminated, black, organic rich, clayey-shale, then by up to 40 cm of laminated clayey-dolomitic shale, followed by an upper band, up to 40 cm thick, of more dolomitic clayey-shale with an upward increasing calcareous component.
Significant 'Kupferschiefer' deposits in Poland and Germany appear to be localised where the reduced Zechstein carbonaceous shale-carbonate-evaporite sequence overlies the Rotliegendes sequence of oxidised clastic and bimodal volcanic rocks and overlaps the Devono-Carboniferous Variscan Orogen, characterised by upper Palaeozoic magmatism. They are also restricted to the irregular southern margin of the Southern Permian/Polish Basin where the underlying Rotliegendes was developed within a series of fault controlled elongate basins on the flanks of the Rhenish and Bohemian Massifs.
Copper mineralisation is strata bound, occurring in three main ore types, reflecting host rocks and stratigraphic position. These are i). Sandstone-ore, hosted by coarse clastic footwall sedimentary rocks of the Weissliegendes and Grauliegendes of the uppermost Rotliegendes; ii). Shale-ore, hosted by Kupferschiefer sensu stricto black shale, which is characterised by abundant organic carbon; and iii). Carbonate ore, within hanging-wall marl and limestone, locally even extending into the overlying evaporites. Mineralisation gradually transgresses the immediate host sequence, passing upwards from a reduced and bleached sandstone, more commonly to the SE, to a thin (<1 m thick) carbonaceous shale (the Kupferschiefer sensu stricto) and into overlying dolostones to the NW, capped by the thick Zechstein evaporites.
The principal copper minerals in all types of ore are chalcocite and digenite, which generally occur together in concentrations of up to 6 wt.%. Bornite (up to 3.5 wt.%), chalcopyrite (up to 1 wt.%), covellite (up to 1 wt.%) are also abundant, as are locally, minerals from the tetrahedrite group. Within the sandstone ore, sulphides occur as fine grains and aggregates disseminated as interstitial pore fillings, clouds and clots, and as replacement of pre-existing carbonate and clay cements, diagenetic pyrite and other minerals. In the shale ore, they are found as fine disseminations (~80% of the sulphides), typically concentrated in the organic-rich dark matrix; as coarser grained aggregates and lenses parallel to shale laminae; and as thin veinlets of massive sulphide that are both concordant and transgressive to the laminae. Within the carbonate ore, sulphides occur as very fine, irregular disseminations, spotted carbonate-replacements, nodules and as veinlets. Pre-mining (1963) reserve + inferred resources to 1250 m depth in the 175 km2 of the Fore-Sudetic copper district of Poland was ~2.70 Gt @ 1.92% Cu, 52 g/t Ag. ..... MORE
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The summaries above were prepared by T M (Mike) Porter from a wide range of sources, both published and un-published. Most of these sources are listed on the "Tour Literature Collection", available from the CopperBelts 2014 Tour options page, and as listed on the linked detailed description pages.
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T M (Mike) Porter, of Porter GeoConsultancy
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