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Frieda River, Nena |
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Papua New Guinea |
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Cu Au
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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 Frieda River copper and gold project is located in north-western Papua New Guinea, some 120 km NE of Ok Tedi and comprises a number of porphyry type deposits, including Horse Ivaal and Koki, and the high grade, gold rich Nena high sulphidation breccia deposit. Nena is 6 km north of Horse and Ivaal. The deposits of the project contain over 7.5 Mt of copper and 445 tonnes of gold. (Location: 4° 41' 48"S, 141° 46' 7"E).
All of the Frieda project deposits are hosted within the Miocene (17 to 13 Ma) Frieda River Igneous Complex (FRIC), which lies towards the southern margin of the New Guinea Thrust Belt, within the New Guinea Orogen, in the transition zone from the stable Australian plate to the south and oceanic crust and island arcs of the Pacific plate in the north. It is separated from the Papuan Fold Belt (and the Ok Tedi deposits) to the south by the shallowly north dipping New Guinea Thrust. Deformation in the Orogen is characterised by thrusting and faulting which has been active since middle Miocene time. Intrusive and extrusive complexes of Miocene age, such as the FRIC, are distributed at intervals along the Orogen.
The basement in the vicinity of the FRIC comprises the metamorphosed Upper Cretaceous to Eocene Ok Binai phyllite to pelitic schist and greenschist with a 27 to 25 Ma (Oligocene) metamorphic age, fault controlled ophiolites and unconformably overlying middle Miocene Wogamush Formation micaceous sandstone and sub-greywacke with intermediate to basic volcanics at the base. At intrusive contacts, these sequences are hornfelsed, brecciated, and in places host skarn and porphyry mineralisation.
Within the FRIC the mid sections of this sequence comprise a 1400 m thick unit of andesitic lavas, pyroclastics and volcaniclastics, the Debom volcanics, representing the extrusive phase of the FRIC. The FRIC is the 15 x 7 km erosional remnant/root zone of an original 20 x 15 km andesitic stratovolcano. Mineral deposits accompany intrusive/extrusive centres, mainly in its southern sections, represented by the five main Frieda Complex porphyries, all cutting the Debon volcanics. The Frieda Complex porphyries include, from oldest to youngest: i). the 10 x 1 km Koki Diorite porphyry, ii). the widespread Frieda Diorite porphyry which is an important host to porphyry mineralisation, iii). the Horse Microdiorite porphyry which is considered to be the progenitor of porphyry copper mineralisation, iv). the Knob Diorite occurring as unaltered plugs and dykes of andesite to diorite, and v). the post mineralisation Flimtem Trachyandesite dykes.
Three dominant sets of structures are recognised: i). post-mineral NNE-NE structures which dissect all the porphyries, and displace mineralisation; at the Horse, Koki and Ekwai prospects, these structures are often intruded by Flimtem Trachyandesite; ii). steeply north dipping syn-mineral WNW faults which are recognised within the high-grade part of the main mineralised zones and often have hydrothermal and tectonic breccia roots and iii). E–W structures,
Porphyry copper-gold mineralisation, including the Horse Ivaal and Koki deposits, is found in the more deeply eroded south-eastern parts of the FRIC where it occurs in the cupola zone of Horse microdiorite intrusions. Associated alteration, which covers an area of 32 sq. km, has been dated at between 13.6 and 11.5 Ma. Five distinct alteration assemblages have been recognised in association with the porphyry mineralisation, which are from earliest to youngest:
i). Potassic (biotite-magnetite) or POK - which is variably developed and widespread, characterised by secondary biotite, magnetite, quartz and rutile. Mineralisation associated with this phase is relatively widespread within the Horse Microdiorite, typically occurring as fine-grained and fracture-fill chalcopyrite-bornite, granular quartz-biotite-magnetite-anhydrite veins, and less commonly as extremely fine-grained chalcopyrite-bornite intermixed with biotite–magnetite grains pseudomorphing hornblende. Grades typically range between 0.3 and 0.4% Cu, and exceptionally 0.5% Cu.v
ii). Propylitic alteration which is transitional and peripheral to the early potassic phase, with an assemblage of sericite, chlorite and epidote, with lesser, variable quartz, carbonate, clay (usually smectite) and hematite. No significant mineralisation accompanies this style of alteration.
iii). Potassic (K-feldspar-quartz; K-feldspar) or POB, which overprints the earlier POK style and its propylitic halo. This phase is characterised by K-feldspar, quartz, muscovite, anhydrite and magnetite, and is more restricted, being confined to the WNW-structures or to hydrothermal breccias where the highest grades are generally associated with veining. While the POB rarely occurs in isolation, it has been estimated that it contributes around an additional 0.3 to 0.5% Cu to the grade. The associated mineral assemblage comprises chalcopyrite, bornite, molybdenite, pyrite and gold which are typically associated with granular and seamed quartz veins, with a gangue of K-feldspar, anhydrite, and haematite-magnetite.
iv). Sericite-clay-chlorite±carbonate-rutile-quartz, or SCC - which overprints both potassic alteration assemblages. Associated copper mineralisation is primarily chalcopyrite with comb quartz veins and chlorite-pyrite. The veins and fractures typically have wide sericite-chlorite-clay-carbonate-rutile-quartz selvages. This phase often contributes 0.5% Cu or more to the overall tenor of the porphyry mineralisation to produce grades that are typically >0.80%.
v). Phyllic-argillic, which is poorly developed due to the composition of the hosts. Where present, it comprises an assemblage of illite-kaolinite-anhydrite-carbonate, and has no associated hypogene mineralisation.
All of the previous assemblages are overprinted by an advanced argillic alteration (AAA) assemblage, unrelated to the porphyry intrusion, and which strips copper, and to a lesser extent gold from the system.
Porphyry mineralisation is generally centred on an irregular core zone of secondary biotite and overprinting quartz-K feldspar-sericite-anhydrite-chlorite veining which grades out into pervasive sericite or chlorite, and an outer propylitic halo. Advanced argillic alteration is found at higher levels in the Horse-Ivaal deposit. Copper is present predominantly as veins and disseminations of chalcopyrite with less common bornite and molybdenite. A 35 m thick supergene chalcocite-covellite blanket in the north-western segment of Horse Ivaal and a 30 m thick oxide zone with malachite, rare azurite and secondary chalcocite at Koki both occur within the pyritic sericite alteration zone.
The Nena high sulphidation copper-gold deposit is located on the prominent NW-SE-striking Nena structure, and is preferentially hosted by a 300 m section of permeable andesitic lapilli tuffs within the Debom volcanics, capped by impermeable andesitic lavas. It lies within an extensive advanced argillic-altered zone covering an area of around 13 x 4 km, where intense pervasive acid leaching and clay alteration of the immediate host rocks has obliterated all textures and characteristics of the protoliths. The ore occurs as a sub-horizontal cigar shaped body approximately 1200 m long by 300 m in diameter at the intersection of an inferred sub-vertical structure within the permeable pyroclastics. Alteration is symmetrical about the NW-striking Nena structure and occurs as three zones: i). an inner, highly leached, porous, silica core to a maximum of 250 m in diameter, ii). an intermediate broad silica ±alunite zone up to 450 m in diameter surrounding the silica core, and iii). an outer zone of clays ±weak silicification 20 to 30 m wide with gradational margins. All three zones are sometimes brecciated or stockworked by later sulphide veining with broad alunite halos. A major pyrite ±marcasite event preceded the hypogene copper which is largely confined to the silica core, commonly as coarse crystalline matrix to open spaced breccias.
The primary mineralisation at Nena has been variously described as complex intergrowths of covellite, stibnoluzonite and polymorphic luzonite-enargite (Bainbridge, et al., 1998) or as polymorphs of luzonite and enargite and less commonly chalcocite, which frequently occur in fractures accompanied by barite, and are less commonly found as small isolated grains filling interstitial sites between pyrite, quartz and alunite (Williamson and Hancock, 2005). The chalcocite zone is hypogene and contains less arsenic and silver than the luzonite/enargite zone. Gold accompanies the copper mineralisation.
Intense weathering and surface leaching produced a supergene profile that is erratically developed and extends to a maximum depth of 130m. It has formed an oxide gold cap containing cuprite, malachite, azurite and scorodite and an underlying supergene blanket of black sooty (and locally grey steely) chalcocite and lesser digenite and covellite which averages 40 m in thickness. Secondary copper sulphides are nucleated on the earlier pyrite.
Indicated + inferred Resources in 2007 were:
Horse Ivaal & Trukai - 1005 Mt @ 0.5% Cu, 0.3 g/t Au,
Koki - 274 Mt @ 0.4% Cu, 0.3 g/t Au,
Ok Nerenere & Ekwai - 60 Mt @ 0.4% Cu, 0.3 g/t Au,
Nena copper - 71.8 Mt @ 2.0% Cu, 0.5 g/t Au,
Nena oxide gold - 18 Mt @ 0.1% Cu, 1.4 g/t Au.
Measured + indicated + inferred resources in January 2010 were (XStrata news release):
Horse Ivaal & Trukai - 1060 Mt @ 0.53% Cu, 0.29 g/t Au, o.8 g/t Ag (0.3 g/t Cu cutoff)
The most recent source geological information used to prepare this decription was dated: 1995.
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.
Frieda River
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Bainbridge A L, Hitchman S P, DeRoss G J 1998 - Nena copper-gold deposit: in Berkman D A, Mackenzie D H (Ed.s), 1998 Geology of Australian & Papua New Guinean Mineral Deposits The AusIMM, Melbourne Mono 22 pp 855-862
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Hall R J, Britten R M, Henry DD 1990 - Frieda River copper-gold deposits: in Hughes F E (Ed.), 1990 Geology of the Mineral Deposits of Australia & Papua New Guinea The AusIMM, Melbourne Mono 14, v2 pp 1709-1715
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Hall R J, Simpson P G 1975 - Frieda porphyry copper prospect, Papua New Guinea: in Knight C L, (Ed.), 1975 Economic Geology of Australia & Papua New Guinea The AusIMM, Melbourne Mono 5 pp 836-845
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Holzberger I, Bainbridge T, Hitchman S and Wilkes M, 1996 - The Frieda River - Nena copper and gold deposits, discovery and assessment, a case example: in Porphyry Related Copper and Gold Deposits of the Asia Pacific Region, Conf Proc, Cairns, 12-13 Aug, 1996, AMF, Adelaide pp 11.1 - 11.12
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Whalen J B, Britten R M 1982 - Geochronology and geochemistry of the Frieda River prospect area, Papua New Guinea: in Econ. Geol. v77 pp 592-616
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White, N.C., Leake, M.J., McCaughey, S.N. andd Parris, B.W., 1995 - Epithermal gold deposits of the southwest Pacific: in J. of Geochemical Exploration v.54, pp. 87-136.
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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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