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Nui Phao


Regional Geology

The Nui Phao project is located within an area of Palaeozoic to Cainozoic rocks within the South China tectonic plate, northeast of the Da River mobile zone. The region has been subject to several episodes of rifting and periods of compression from the collision of the South China and Indochina plates. The country rocks are intruded by Triassic and Cretaceous granites that are typically associated with tin mineralization, but, locally, tungsten and base metals are also found in economic concentrations. The adjacent region of southern China hosts some of the largest hard rock tin and tungsten mines in the world. However, to date, no similar large deposits have been found in northern Vietnam. This likely reflects a paucity of exploration in this part of the country, since the area shares similar complex tectonics and a close spatial relationship with other districts in southern China.

Local Setting

 The rocks in the Nui Phao region range in age from lower Palaeozoic to Cainozoic. The Ordovician-Silurian shales, sandstones, siltstones and marbles form the principal hosts to the Nui Phao mineralization. The sequence has been intruded, first by the Triassic Nui Phao granite, which outcrops to the south of the deposit and underlies much of the mineralization, and then by the Cretaceous Da Lien granite, which outcrops to the north of the deposit and is generally considered the source of the mineralization. The intrusion of the Nui Phao biotite granite resulted in the formation of an intercalated assemblage of magnetite, garnet, pyroxene and amphibole-rich skarns, as well as granitic and pegmatitic dykes and sills. The later intrusion of the relatively coarse grained two-mica muscovite-biotite Da Lien granite resulted in greisenisation, massive pyrrhotite-fluorite-albite overprinting and tungsten mineralization.

In the Nui Phao region, the sedimentary sequence strikes east-west and dips shallowly to the north. The Nui Phao granite cuts off the mineralization to the south; the contact with the Nui Phao granite dips shallowly to the north, forming a base to the mineralization. The granite forms a ‘high’ between the Central and Western zones. The northern limit of mineralization is formed by a fairly steep, southerly-dipping contact with the Da Lien granite.

Northwest-southeast high angle strike slip faults have been interpreted as forming the contacts between many of the rock units in the region. An east-west fault is interpreted as forming the locus for magma intrusions between the Nui Phao and Da Lien granites. Magnetic data indicates the presence of two northerly-trending structures, which appear to define the limits of the known mineralization. However, field evidence for major structural displacements within the mineralized area remains scant