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Kainantu - Kora, Kora North, Eutompi, Judd, Irumafimpa, Maniape, Arakompa, Blue Lake |
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Papua New Guinea |
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Au Ag Cu
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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All papers now Open Access.
Available as Full Text for direct download or on request. |
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The Kainantu Gold Project is located ~20 km north of the town of Kainantu at between 800 and 1900 m elevation on the north eastern fall of the Eastern Highlands, overlooking the Markham Valley. It lies between Yandera to the northwest and Wafi to the southeast. The deposits that constitute the project extend over an interval of 7 km northward as a series of individual lode systems, including Kora, Kora North, Eutompi, Judd and Irumafimpa on the same continuous, >5 km long mineralised structure, and Maniape and Arakompa, 3 km to the NE.
(#Location: 6° 6’ 36"S, 145° 53’ 8"E).
The Blue Lake low grade porphyry Cu-Au deposit is located ~4 km southwest of the Kainantu Mine - see description below.
Gold was discovered in the Kainantu area in 1928 on a small creek draining into Abinakenu Creek. Between 1948 and 1952 copper was discovered at Yonki Creek. The southern end of the Irumafimpa lodes was discovered some time prior to 1967. In 1967, small scale mining was started on Prospect Claim 6 for copper and gold. The workings, known as the Kora mine, produced about 1000 tonnes of gold and copper ore between 1967 and 1970. Highlands Gold undertook work in the area between 1989 and 1994 and delineated targets at Irumafimpa, Maniape and Arakompa. Exploration was focused on Irumafimpa where diamond drilling was conducted in 1992 and 1993. Highlands Pacific Limited commenced underground development of the Irumafimpa deposit in 2004, but the mine struggled to achieve
planned mined grades, through a combination of geological complexity and unplanned dilution. After the discovery of the Irumafimpa deposit, Highlands Pacific had focused on high grade Au‐telluride mineralisation. The Kainantu gold project and surrounding tenements was sold to Barrick Gold by Highlands Pacific during 2007 and in 2008 the mine was put on care and maintenance. Barrick concentrated on increasing resources at Irumafimpa‐Kora and discovering economic porphyry Cu‐Au mineralisation and carried out exploration from 2008 to August 2012. K92 Mining acquired the project from Barrick Gold in 2014 and restarted operations in late 2016, ramping up to commercial production in January 2018.
The Kainantu deposits are located within the New Guinea Thrust Belt, adjacent to its northern contact with the Finisterre Terrane which is juxtaposed across the northwest trending Ramu‐Markham Fault, a major suture zone that defines the northern margin of the Australian Craton. The New Guinea Thrust Belt produced an Early Miocene or older tight, ductile, folding event that was followed by middle Miocene intrusions. This was followed by Late Miocene regional scale low‐angle thrust faulting, associated with the collision of the Finisterre Terrane. The belt is characterised by a number of NNE trending fault zones that commonly host ore deposits (Williamson and Hancock. 2005).
The basement host rocks in the area comprise the Triassic Bena Bena Formation pelite, psammite, conglomerate and marl beds that have been metamorphosed to greenschist to amphibolite grade facies and are intruded by the syntectonic gniessic quartzo-feldspathic Karmantina Granite. These are unconformably overlain by the Oligocene Omaura Formation tuffaceous shale and siltstone, greywacke, pebbly conglomerate and lithic sandstone with minor lava and pyroclastics, and limestone lenses. All of these units are intruded by the 17 to 13 Ma mid-Miocene Akuna Intrusive Complex which is well exposed and ranges from olivine gabbros, dolerites, hornblende gabbros and biotite diorites to granodiorites. Parts of the Akuna Intrusive Complex may be equivalent to the Morobe Granodiorite. The hornblende-biotite porphyry of the 9 to 7 Ma Late Miocene Elandora Porphyry forms small high level crowded feldspar dykes and diatreme breccias associated with mineralisation, and intrudes the Akuna Intrusive Complex and occurs as fragments in diatreme breccias at Irumafimpa and Maniape. A NNE trending transfer structure transects the area, with associated mineralization, alteration and porphyry complexes aligned along it.
The mineralisation at Irumafimpa and Kora is of a quartz-sulphide, low-sulphidation type and occurs within a corridor of steeply dipping northwest-trending structures, parallel to the Ramu-Markham Fault. Eutompi is a mineralized lode between Kora and Irumafimpa. These structures display a protracted pre-, syn-, and post-mineral history of activity, as suggested by the observation that the host Bena Bena Formation changes to a crenulation cleavage in the vicinity of these structures, suggesting they have been formed at depths in the order of 5 km, and exhumed prior to reactivation and mineralisation. The mineralised corridor consists of several parallel, northwest-trending, steeply dipping structures with slickensided fault faces, puggy fault gouge and breccia with a vertical exposure of more than 800m. At lower topographic levels, the structures contain minor breccias of phreatomagmatic affinities exhibiting epidote-altered Elandora Porphyry fragments and specular haematite. Geological mapping suggests that ore shoots are localised at the intersection with north-south structures, possibly in association with dextral strike-slip movement on the northwest-trending host structures. Individual lodes range from a few cm to several metres in width and occur within a 300 m wide zone as remarkably continuous features. The western lode is more copper rich while the eastern lode is more gold rich. Veins anastomose slightly and are locally cut by post-mineral faults. Mineralogical and textural variations of vein assemblages within the lodes suggest a progression from early mesothermal to a more epithermal style of mineralisation. Structures exhibit protracted pre-, syn- and post-mineral activity, and occur in the vicinity of porphyry Cu-Au alteration and mineralisation. Sulphides occur as massive chalcopyrite lodes at Kora, but elsewhere the lodes are typically an assemblage of coarse crystalline pyrite with minor sphalerite, galena, chalcopyrite and tennantite. Coarse, bright green fuchsite and mariposite (chromium micas) occur in the selvages of the lodes. High fineness (834-922) gold is found as inclusions in chalcopyrite and coarse pyrite or associated with ferberite, although the bonanza gold occurs within tellurides associated with late stage banded and comb quartz, and is commonly associated with bismuth minerals. Irumafimpa, in particular is an epithermal Au-Te deposits with 0.5 to 2 m wide quartz veins intruding chlorite‐sericite schist over strike length of ~1 km. The composite Kora deposit, which incorporates the Kora, Eutompi and Kora North lodes hosted by discontinuous quartz veins intruding chlorite‐sericite schist ove a strike length of >2.5 km strike and width of up to 60m.
The Judd vein system is a narrow, low sulphidation epithermal vein located generally east of and parallel to Kora. This sporadic drill testing on the Judd lodes by Barrick returned a maximum intersection of 3 m @ 278 g/t Au. Two types of Judd vein mineralisation are recognised, a quartz dominant, Au‐rich component and a
sulphide dominant, Cu‐rich vein style. Surface mapping and sampling has indicated a mineralized strike length of >2.5 km.
A set of NE trending fractures, normal to the northwest structures, hosts veins at Maniape and Arakompa.
At Arakompa, northeast-trending steep-dipping structures host quartz-sulphide lodes within the Akuna Intrusive Complex granodiorite distributed over a strike length of ~3 km. The individual lodes can be traced for several hundred metres adjacent to polished or puggy faults, and vary in width from a few cm to a maximum of 3 m. These lodes lie a few hundred metres north of the outcropping Taneka porphyry Cu-Au alteration-mineralisation zone and pebble dykes, exploiting pre-existing structures, represent a manifestation of a porphyry system at depth. The pebble dykes host fragments of quartz-veined Akuna Intrusive Complex and shale fragments derived from deeper crustal levels. The pebble dykes are in turn cut by veins of quartz with associated pyrite-sericite-magnetite-epidote-carbonate. Most of the gold mineralisation is found as inclusions within the coarse cubic pyrite associated with chalcopyrite, bornite, sphalerite and galena, while higher grade gold occurs with a range of Bi-Ag-Pb telluride and sulphide minerals.
Maniape, which is 1.5 km to the southwest of Arakompa, occurs within a regionally significant north-northeasttrending structure. This structure, which cuts the Akuna Intrusive Complex granodiorite and Bena Bena Metamorphics, is intruded by andesitic porphyry of the Elandora Porphyry and breaks into a series of imbricate puggy faults over an 800 m strike length. Quartz-sulphide lodes occur within the imbricate structures, and also as intervening, northeast-trending lodes interpreted to have developed in response to dextral strikeslip movement on the imbricate faults. These are developed over a width of up to 34 m. Mineralisation commenced with quartz-pyrite lodes with associated sericite alteration, followed by Fe-poor sphalerite, galena and minor chalcopyrite associated with quartz-chloriteillite- carbonate wall rock alteration. Massive to banded carbonate fills open spaces with minor interbanded base metal sulphides. The carbonates have a vertical zonation from shallow Mn-Fe rhodochrosite-siderite, through Mn- Mg kutnahorite and Mg-calcite with increasing depth, to calcite and low-Mg calcite at depth. Geochemical evidence suggest that the Maniape mineralisation was also derived from the Taneka porphyry.
The Kora-Irumafimpa and Maniape-Arakompa mineralised systems have been interpreted to be respectively related to the separate Oro and Taneka porphyry intrusions/ alteration systems. The Taneka porphyry system is refl ected by fracture-controlled secondary biotite-magnetitesilica- pyrite imposed upon the Akuna Intrusive Complex granodiorite. The Oro porphyry system is part of a much larger porphyry Cu-Au manifestation, including pervasive barren silica-alunite grading to silica-sericite-dickite alteration, which crops out at several hundred metres higher elevation and contains enargite-bearing vughy silica breccia within a fault (the Headwaters Prospect). These two low grade porphyry Cu-Au porphyry systems at Taneka and Oro, which are associated with partially exposed intrusions, are reflected by magnetic data as an intense high and a diffuse low, respectively, as the former contains secondary biotite-magnetite, and some parts of the latter have been overprinted by intense magnetitedestructive sericite-clay alteration.
Further evidence of an intrusive association is provided by clay-altered diatreme breccias with vughy or residual silica and associated Elandora-style porphyry intrusions near Yar Tree Hill where alluvial gold is worked in the vicinity of the poorly exposed diatreme. No details are generally available on the testing that has been carried out on the Oro and Taneka porphyry systems.
Highlands Pacific Ltd had estimated a resource for the Kora-Irumafimpa system of 1.7 Mt at 22 g/t Au for 37.5 t of gold at a 5 g/t Au cut off.
Ore Reserves and Mineral Resources as quoted on the K92 Mining Website viewed July, 2023 were:
Proved + Probable Ore Reserves
Kora - 5.81 Mt @ 6.5 g/t Au, 18 g/t Ag, 0.9% Cu;
Judd - o.34 Mt @ 8.6 g/t Au, 14 g/t Ag, 0.6% Cu;
TOTAL - 6.15 Mt @ 6.7 g/t Au, 18 g/t Ag, 0.9% Cu.
Measured+Indicated Mineral Resources
Kora - 7.2 Mt @ 7.6 g/t Au, 18 g/t Ag, 0.9% Cu;
Judd - 0.38 Mt @ 9.7 g/t Au, 18 g/t Ag, 0.7% Cu;
Irumafimpa - 0.56 Mt @ 12.8 g/t Au, 9 g/t Ag, 0.3% Cu;
TOTAL - 8.13 Mt @ 7.84 g/t Au, 17 g/t Ag, 0.9% Cu.
Inferred Mineral Resources
Kora - 8.1 Mt @ 7.12 g/t Au, 27 g/t Ag, 1.4% Cu;
Judd - 1.01 Mt @ 4.24 g/t Au, 11 g/t Ag, 0.9% Cu;
Irumafimpa - 0.53 Mt @ 10.7 g/t Au, 9 g/t Ag, 0.3% Cu;
TOTAL - 9.64 Mt @ 7.02 g/t Au, 25 g/t Ag, 1.3% Cu.
TOTAL MINERAL RESOURCE - 17.77 Mt @ 7.40 g/t Au, 21 g/t Ag, 1.12% Cu, for 131 tonnes of gold and 380 t of silver.
NOTE: Kora = the combined Kora, Kora North and Eutompi segments of the deposit. Resources are inclusive of Reserves.
This summary is in part drawn from "Woodward, A., Tear, S., Desoe, C. and Park, L.J., 2020 - Revised independent technical report, mineral resource estimate update and preliminary economic assessment for expansion of the Kainantu Mine to treat 1 Mtpa from the Kora Gold Deposit, Kainantu Project, Papua New Guinea; Prepared by Nolidan Mineral Consultants, H and S Consultants, Australian Mine Design and Development and Mincore for K92 Mining Inc., 245p."
The Blue Lake Porphyry Project at Kotampa is approximately 4 km SW of the producing high-grade Kora and Judd low sulphidation epithermal gold deposits at the Kainantu Gold Mine. To the end of 2022, a large composite tonalite porphyry stock had been defined within the mid-Miocene Akuna Intrusive Complex granodiorite. This complex comprises multiple overprinting intrusives, that are variably mineralised with gold and copper. The Akuna Intrusive Complex consists of multiple phases ranging from olivine gabbros, dolerites, hornblende gabbros and biotite diorites to granodiorites.
A prominent silica-clay lithocap was recognised near surface, overlying mineralised propylitic epidote-chlorite alteration, with encompassing higher grade potassic alteration. The mineralised porphyry is concentrically zoned, with regard to both alteration and metal sulphide distribution, and has been tilted towards the NW. The zonation comprises a gradation from bornite grading, passing outward into chalcopyrite with a molybdenum periphery, and an outer pyrite zone. The alteration assemblage is similarly zoned, from an inner biotite-K feldspar core, passing out, through a transitional actinolite zone, into a peripheral epidote-albite annulus. The prograde assemblages have been largely overprinted by intense sericite-pyrite phyllic alteration. There is a prominent silica-clay cap, characterised by dominant pyrophyllite, with alunite feeder zones. The highest grades correspond to the potassic core, characterised by biotite, K feldspar and chalcopyrite/bornite mineralisation, within a quartz stockwork vein system. Copper/Gold mineralisation is 1:1 ratio in Cu%:Au g/t, and open to the south-west.
A preliminary Inferred Mineral Resource at a 0.4 g/t AuEquiv. cut-off has been estimated (K92 Technical Report, July, 2023) as:
549 Mt @ 0.21 g/t Au, 2.42 g/t Ag, 0.23% Cu, (0.61 g/t Au Equiv. or 0.38% Cu Equiv.)
At a 0.6 g/t Au Equiv. cut-off , this becomes:
233 Mt @ 0.3 g/t Au, 2.43 g/t Ag, 0.28% Cu, (0.77 g/t Au Equiv. or 0.49% Cu Equiv.).
This brief resume has been drawn from: "Tear, S. and Woodward, A., 2022 - Independent technical report, mineral resource estimate, Blue Lake porphyry deposit, Kainantu, Papua New Guinea; Prepared for K92 Mining Inc., 95p."
The most recent source geological information used to prepare this decription was dated: 2020.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
Kainantu mill
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Blenkinsop, T., Tripp, G. and Gillen, D., 2017 - The relationship between mineralization and tectonics at the Kainantu gold-copper deposit, Papua New Guinea: in Geological Society, London, Special Publications, v.453, pp. 269-288. https://doi.org/10.1144/SP453.11.
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Williamson, A. and Hancock, G., 2005 - The Geology and Mineral Potential of Papua New Guinea,: in Papua New Guinea Department of Mining, Port Moresby, 152p.
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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