Papua New Guinea
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The Ramu lateritic Ni-Co deposit is located on the Kurumbukari plateau, in the foothills of the Bismarck Ranges, 600 to 800 m above sea level and 75 km SW of the provincial capital of Madang on the north coast of Papua New Guinea and 5° south of the equator.
The Ramu deposit was discovered in 1962 by the Australian Bureau of Mineral Resources. Highlands Gold Properties Pty Limited (HGP) first undertook work in the area in 1989/90. An intensive period of geological exploration and engineering led to a prefeasibility study and in 1996 the Ramu Nickel Joint Venture was established to prepare a bankable feasibility study. Highlands Pacific Limited purchased HGP's interest in April 1997 and prepared the 1998 feasibility study but project development did not progress. In 2000 the project was granted a Special Mining Lease and in 2005 Metallurgical Corporation of China Limited (MCC) joined the joint venture taking a 61% interest with Highlands share reducing to 8.56% and the PNG Government and landowners (through the holding company MRDC) 6.44%, with the remaining 39% held by a number of other Chinese entities. MCC prepared a feasibility study in 2007 for the Ramu project and commenced construction in 2008, financed by MCC. In 2009 MCC increased its stake in the project to 67%. The mine and refinery began commissioning and ramp up in 2012, eventually reaching a nominal capacity of 31 150 tpa of nickel and 3300 tpa of cobalt. In 2018 MCC Ramu announced plans for an expansion to double the existing production capacity. In 2018 production from the refinery was 35 355 t of contained Ni and 3275 t of contained Co. Beneficiated ore is pumped from the mine via a 135 km slurry pipeline to the Basamuk refinery on the coast, 55km southeast of Madang. This plant
produces a mixed nickel-cobalt hydroxide product.
The Ramu deposit is located on the northern margin of the New Guinea Thrust Zone in the Central New Guinea Orogenic Belt. The outcropping rocks in this zone consist of the NW-SE trending, ~10 to 14 km wide, Tertiary Marum Basic Belt mafic and ultramafic intrusive rocks. It lies just to the SW of the major, terrane boundary Ramu-Markhan Fault.
Intrusives within the Marum Basic Belt include two main rock types, i). mafic hypersthene-augite gabbro, intercalated with lesser norite, anorthosite and gabbro pegmatite dykes which are distributed in the NW and SE of the Ramu deposit area; and ii). ultramafic rocks mostly comprising dunite with minor harzburgite and pyroxenite,which are distributed in the Ramu deposit area. The latter form the central section of the Marum Basic Belt and are the main source for the lateritic nickel-cobalt mineralisation at Ramu.
The Marum Basic Belt is truncated by the NW-trending Bundi fault zone to the SW, and the Ramu-Markham fault zone in the NE, respectively. The vertical displacement along the latter is ~400m. In the Ramu deposit area, a series of horst-like plateaus bounded by faults have been developed parallel to this fault.
The area to the NE of the Ramu deposit is covered by Pleistocene and Holocene river sediments.
The deposit has been divided into three contiguous resource blocks, i). Kurumbukari (KBK); ii). Ramu West; and iii). Greater Ramu, which together cover a drilled resource that extends over an area of ~25 km2. However, the mineral potential is much larger based on the distribution of surrounding underlying dunite that has been mapped.
The lateritic mineralisation is related to the weathering and leaching of the ultramafic intrusives in a tropical environment. The lateritic profile is as follows from the surface to bedrock:
• Overburden which is 0.7 to 48 m thick, averaging 4.5 m, including the upper humic layer which is black, dark brown or greyish-brown colour, primarily composed of clays, colloidal goethite, olivine fragments and sandy chromite. Goethite occurs locally in bands. This overlies and the lower red limonite overburden which is brownish red to maroon in colour, and is primarily composed of clays, goethite, olivine fragments, chromite, talc, gibbsite and some minor amounts of other minerals. It has a gradual transitional boundary with both the overlying humic layer to the underlying yellow limonite. It
contains low nickel (<0.5% Ni) and cobalt grades and is to be stripped as waste before mining the lower ore layers.
• Limonite which is 0.3 to 19 m thick, averaging 4.6 m - Yellow limonite ore; hosts the bulk of the nickel-cobalt resource. This zone is greyish yellow, brownish yellow to brown in colour and is primarily comprised of clays, limonite, goethite and gibbsite, talc, chalcedonite, asbolan (cobaltiferous manganese wad) and chromite. Characteristic asbolan and manganese striations or dendrites and fracture coatings occur throughout the zone.
Chromite grains are also found throughout the zone, and are not necessarily restricted to planar surfaces. This layer has gradual lower transition int the underlying saprolite. Its nickel grade is generally above the resource cutoff of 0.5% Ni.
• Saprolite which is 0.4 to 13 m thick, averaging 3.9 m and contains enriched in Ni and Co. The top of the saprolite marks the boundary between
acidic and alkaline weathering conditions in the profile. It has a light greyish green and brown colour, and is primarily composed of clays, goethite, chromite, talc, gibbsite, iddingsite, asbolan, serpentine (including garnierite), chalcedonite and quartz. This zone generally contains no bedrock boulders and occasionally outcrops over small areas. The original texture of the protolith and crystal structure of the original minerals is well preserved. This layer is one of the main ore-bearing horizons in the deposit area. It is significantly enriched both in Ni, Co and Mg compared with the yellow limonite above.
• Rocky Saprolite R1 which is 0.4 to 21 m thick, averaging 2.8 m - which contains <30% (averaging 17 vol.%) dunite boulders in a saprolite
host, and is enriched in Ni but not in Co. It contains some serpentinised dunite in a saprolite matrix similar to the overlying saprolite layer. The top of the rocky saprolite is defined by the first >150 mm of dunite rock intercepted.
• Rocky Saprolite R2 which is 0.4 to 21 m thick, averaging 2.8 m - which is similar to the R11 saprolite, but contains >30% (averaging 51 vol.%) dunite boulders in a saprolite host. It is also enriched in Ni but not in Co. The lower boundary is determined by either the first 1.5 m boulder intersected or a 3 m intersection with >50% of the volume of the intersection being rock.
• Bedrock, typically dunite with minor harzburgite and pyroxenite.
Cobalt is generally depleted in the overburden layer, is enriched in the saprolite layer and is usually not enriched in the rocky saprolite. Magnesium has mostly been leached out in the humic layer and the limonite layers where it is <10%, but only partially leached out in the saprolite layers. It is ~18% in the R1 layer and in the R2 layer is ~20.4%. Aluminium is strongly enriched in the humic layer and the red limonite layer, slightly enriched in the yellow limonite layer, and not enriched in the saprolite layers. Chromium occurring as residual chromite is generally enriched in the limonite layers and slightly enriched in the saprolite layers. Iron is generally enriched in the limonite layers and slightly enriched in the saprolite layers.
• Goethite occurs as ochre-coloured, porous, cryptocrystalline, needle-like matrix in the limonite and saprolite zones of the laterite. The highest concentrations are in the yellow limonite. Goethite-silica, goethite-smectite and other goethite-clay mixtures dominate the matrix of these zones. The goethite structure has an average nickel grade of 1.6% Ni in the limonite zone and 2.9% Ni in the saprolite zone.
• Asbolan ((Ni,Co)2-xMn4+(O,OH)4•nH2O) is recognised as bluish black dendrites and fracture coatings throughout the laterite profile. It has a range of compositions due to elemental mixtures of cobalt, nickel, manganese and aluminium. In the limonite zone, asbolan contains 8.4% Co and 5.2% Ni, and in the saprolite zone, 5.6%
Co and 15.1% Ni.
• Garnierite, which is nickeliferous serpentine, is an apple green coloured mineral found at deeper levels in the deposit in the alkaline weathering zone, generally at the base of the limonite horizon and in the saprolite and rock saprolite zones. It most commonly occurs as one to ten cm wide veins, as fracture infillings and in the weathered rind of bedrock boulders. It may also occur as infill with serpentine in calcic magnesite breccia, and has a range of compositions depending upon the proportions of serpentine, talc and lizardite minerals. Lizardite samples contain an average of 1.2% Ni.
The distribution of the laterite layers is generally affected by topography and erosions. The laterite layers dip at 10 to 35°, consistent with the topographic dip angles.
Mineral Resources estimated at 31 December, 2017 were (Cobalt 27 Capital Corp., 2018) at a cut-off of 0.5% Ni:
Measured Resource - 34 Mt @ 0.9% Ni, 0.1% Co;
Indicated Resource - 42 Mt @ 0.9% Ni, 0.1% Co;
Inferred Resource - 60 Mt @ 1% Ni, 0.1% Co.
Mineral Resources do not include the >2 mm rock fragments in the rocky saprolite layers.
This summary is drawn from Behre Dolbear Australia, 2019 - Ramu Nickel Cobalt Project; an NI 43-101 Technical Report prepared by Behre Dolbear Australia for Cobalt 27 Capital Corp., 98p.
The most recent source geological information used to prepare this summary was dated: 2017.
This description is a summary from published sources, the chief of which are listed below.
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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 takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.
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