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Ban Phuc |
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Vietnam |
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Ni Cu Co
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Super Porphyry Cu and Au
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The Ban Phuc magmatic sulphide nickel-copper deposit is located approximately 160 km WNW of Hanoi in northern Vietnam, just south of the NW-SE trending major Red River Lineament between the South China and Indochina plates (#Location: 21° 11', 22"N, 104° 19', 22"E).
The mineralisation is hosted by the Ban Phuc intrusion, a 940 x 420 m, north-westerly trending ultramafic body, one of the larger in the region. The intrusion is exposed in the Ta Khoa window where it cuts a basement metamorphic complex of Devonian meta-sedimentary and metavolcanic rocks which include phyllite, meta-quartzite, sericite schist, muscovite-biotite schist and intercalated crystalline marble, overlain by a thin unit of limestone.
In addition to the Ban Phuc ultramafic body, the Devonian metamorphic complex in the same window are cut by more than 70 smaller intrusive bodies, 28 of which are of ultramafic to gabbroic (werhlite) composition, the remainder being granite and granite-pegmatite. These intrusions are lensoid and up to as much as 3.5 km in length, generally paralleling bedding in the host metasediments. Both the meta-sediments and the intrusives have undergone tilting and folding, possibly during the Triassic orogeny. The overlying Permian-Triassic komatiite-basalt complex, which includes komatiites, komatiitic basalts and olivine basalts are interpreted to at least in part, be extrusive equivalents of the subvolcanic ultramafic to mafic intrusions of dunite and plagioclase-bearing wehrlite that host the Ni-Cu-PGE sulphide ores. The ultramafic-mafic intrusives are believed to be Triassic in age. However, some of the basalts may be lower to mid-Palaeozoic in age.
The Ban Phuc ultramafic body is elongated parallel to the strike of the Devonian meta-sedimentary host rocks and was intruded along the trend of a discontinuous unit of crystalline limestone. To the north-west, only its flat lying base is preserved, while to the south-east the intrusion narrows and deepens to where it has an oval shaped cross-section and dips steeply northeast, generally concordant with the enclosing metasediments. Locally discordant contacts with sediments to the south confirm the body is intrusive and not an extrusive komatiite.
Low-grade nickel-rich sulphide layers define a concave layering within the intrusion, conformable with the base and walls of the body. To the northwest end where the intrusion and sulphide banding is flat lying flat lying, with minor convexity. However in the south-eastern section the layering is tightly compressed and strongly concave. Structural studies suggest the strongly concave layering may reflect a synformal structure and folding, with the ultramafic originally having been a thinner sill which now occupies a fold axis. Cumulate sulphides found along the base and walls of the intrusion indicate suggest it is upright, and that folding is isoclinal and the hanging wall is overturned.
A range of mineralisation styles are represented in the deposit, as follows:
i). A structure containing massive nickel and copper sulphides within Devonian hornfels-schist and tremolite altered dykes in the southern contact aureole of the Ban Phuc ultramafic body. The massive sulphide comprises pyrrhotite (70%), pentlandite (10%), chalcopyrite (5%), magnetite (4%), pyrite (3%), violarite (2.5%), siderite, ilmenite, sphalerite, galena (<1%), non-Opaques (5%). The pyrrhotite occurs as 1 to 3 mm grains with fine exsolutions of pentlandite. The pentlandite is found in granular masses with a grain size of 0.06 to 2 mm, and as fine inclusions in pyrrhotite, while chalcopyrite forms irregular grain aggregates up to 3 mm in diameter and as inclusions in pyrrhotite.
ii). Disseminated copper-nickel sulphide in hornfels-schist and tremolite altered dykes abutting the massive sulphides. This style of mineralisation forms a halo around the massive sulphide veins and can vary from a width of zero to several metres. Sulphides occur as veinlets, stringers, and disseminations of pyrrhotite (25%); chalcopyrite (30%); violarite and pentlandite (15%); pyrite (10%); ilmenite, niccolite, galena, sphalerite, valerite (20). The massive and disseminated sulphide accumulations are considerably different, particularly with regard to the amount of pyrrhotite.
iii). Low grade disseminated nickel sulphides in dunite near the base and walls of the Ban Phuc ultramafic intrusive. Grades in the range 0.5 to 1.0% are common, while significant widths of higher grades (ie., 2 to 15 m at >2% Ni) appear to be localised. Minor chalcopyrite is also present in this type of mineralisation. Nickel is present in both sulphide and silicate forms with the sulphide type being dominant.
iv). Nickel silicate as garnierite in serpentine at the base of the lateritic weathering profile, vertically above the nickel bearing Ban Phuc dunite intrusives. Oxidation of both massive and disseminated sulphides has typically taken place to depths of 10 to 40 m below the surface, with nickel being dissolved and leached while copper has been altered to malachite and other oxides.
The massive sulphide mineralisation occupies a major shear controlled vein structure in hornfelsed host rock along the southern margin of the main intrusion, occurring as an 280 to 310° striking, steeply NE dipping, vein which is approximately 730 m long has been traced to a depth of 450 metres below surface by drilling. Although broadly conformable in section, the vein cuts across the sedimentary lithological layering at a low angle. There are only minor offshoots and bifurcations and the vein is predominantly a single structure with evidence of local structural thickening.
The massive Ni-Cu sulphide veins in the meta-sedimentary wall rocks and their envelopes of disseminated sulphides are interpreted to have been derived from an immiscible sulphide melt expelled from a crystalline ultramafic magma body into a shear zone and as such are believed to be similar in origin to the Thompson deposit in Manitoba, Canada.
Current published reserves and resources (Asian Mineral Resources website, 2007) include:
Proved + probable reserves - 1.01 Mt @ 2.4% Ni, 1.0% Cu,
Measured + indicated + inferred resource - 1.23 Mt @ 2.77% Ni, 1.13% Cu, 0.09% Co.
Sub-economic open pit resources of nickel silicate (garnierite) mineralisation, totals: 1.14 Mt @ 1.08% Ni.
Ore reserves and mineral resources at 7 September, 2012 (CSA technical report to Asian Mineral Resources, 2013) were:
Massive sulphide vein ore
Measured + indicated resources - 1.69 Mt @ 2.68% Ni, 1.19% Cu, 0.06% Co, 13.20% S, 3.06% MgO, 25.48% Fe;
Inferred resources - 0.17 Mt @ 1.94% Ni, 0.80% Cu, 0.03% Co, 10.04% S, 6.76% MgO, 20.27% Fe.
Disseminated ore
Measured + indicated resources - 0.9 Mt @ 1.19% Ni, 0.14% Cu, 0.02% Co, 0.67% S, 20.37% MgO, 5.17% Fe;
Inferred resources - 0.4 Mt @ 1.14% Ni, 0.04% Cu, 0.00% Co, 0.09% S, 5.93% MgO, 1.66% Fe.
Ore reserves (included within resources)
Proven reserves - 0.71 Mt @ 2.4% Ni, 1.0% Cu, 0.06% Co;
Probable reserves - 0.90 Mt @ 2.1% Ni, 1.0% Cu, 0.04% Co;
Total reserves - 1.61Mt @ 2.21% Ni, 1.01% Cu, 0.05% Co.
The mine operated from 2013 to 2016 and mined 0.975 Mt @ 2.4% Ni, 1.0% Cu for 20.7 kt of Ni and 10.1 kt Cu (Blackstone Minerals investor site visit presentation, August 2019);
The most recent source geological information used to prepare this decription was dated: 2007.
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.
Ban Phuc
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Selected References:
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Glotov, A.I., Polyakov, G.V., Hoa, T.T., Balykin, P.A, Akimtsev, V.A, Krivenko, A.P., Tolstykh, N.D., Phuong, N.T., Thanh, H.H., Hung, T.Q. and Petrova, T.E., 2001 - The Ban Phuc Ni-Cu-PGE deposit related to the Phanerozoic komatiite-basalt association in the Song Da Rift, Northwestern Vietnam: in The Canadian Mineralogist v.39, pp. 573-589.
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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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