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Sin Quyen

Vietnam

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The Sin Quyen magnetite-copper-gold deposits is located ~300 km NW of Hanoi and 1 km from the bank of the Red River which marks the boundary between Vietnam and China in this area.

Setting

The Sin Quyen deposits are within the Lao Cai district, in northern Vietnam and neighbouring southern China, broadly following the northwest-trending Red River (Song Hong) fault zone. The Red River fault zone is a major structural complex accommodating lateral strain associated with the Himalayan collision between the Indo-Australian and Eurasian plates. It lies within, and close to the northeastern margin of the similarly northwest-trending, ~200 km wide, Song Da mobile belt, which was developed over the southwestern edge of the South China plate/Yangtze craton, immediately adjacent to the suture with the Indochina plate to the south (Metcalfe, 1995).

The southern margin of the Song Da mobile belt is defined by the major northwest-trending Song Ma fault, and by the Cambrian to Devonian greenschist facies oceanic sediments (metagreywackes, greenschists, amphibolites, and marbles) and calc-alkaline to mafic volcanics (including ophiolites) of the "anticlinorial" Song Ma terrane immediately to its north. This terrane also includes low to high-grade unfossiliferous schists intruded by Devonian and Triassic granitoids and is characterised by large scale folding, thrusting and nappe formation, interpreted to indicate continent-continent collision in the early to middle Carboniferous (Metcalfe, 1995).

The Song Da rift zone occupies much of the interval between the Song Ma terrane and the Red River fault zone. It developed during the Permo-Triassic and was filled by marine volcanic and sedimentary rocks, deposited in an extensional basin on continental crust. The volcanic rocks include spilites, tholeiitic to calc-alkaline porphyritic basalts and komatiites. Basin inversion followed in the Jurassic, as evidenced by a period of folding and thrusting, and deposition of red-beds. During the Cretaceous to Miocene, calc-alkaline to alkaline felsic volcanism, with associated alkaline granitoids (144 to 89 Ma) and lesser gabbroids, commenced within the core of the earlier rift basin, to define the Tu Le terrane (Khuong, 2010; McLean 2001, and sources cited therein). The northern edge of the Song Da mobile belt is occupied by the Phan Si Pan-Song Hong terrane, a broad band of Proterozoic metamorphic basement rocks, largely gneisses and schists, representing mafic volcanic and volcano-sedimentary rocks that have undergone multiple deformation and are locally migmatised. The principal regional metamorphism and deformation has been constrained between 2.36 and 1.96 Ga, although Permo- Triassic ages of 245 to 220 Ma (Carter et al., 2001) are also recorded, all of which are overprinted by a diachronously partitioned Cenozoic mylonitisation with ages variably dated between 60 and 12 Ma (Burchfiel et al., 2008).

Intrusive pulses within the Phan Si Pan-Song Hong terrane include late Palaeo- to Mesoproterozoic mafic and felsic rocks (as described below from the Sin Quyen deposit area); late Neoproterozoic (750 to 760 Ma) Po Sen complex diorite-granodiorite-granites; Devonian to Carboniferous Song Chay complex; Cretaceous (75 Ma) alkaline granitoids (granosyenite and granite) of the Muong Hum complex; and extensive Paleogene (~35 Ma) I- and A-type ganitoids (Khuong, 2010; and numerous sources cited therein). Sin Quyen and the other related iron oxide-alkali altered deposits of the Lao Cai district are hosted by the basement metamorphics of the Phan Si Pan-Song Hong terrane. The Red River fault zone is predominantly restricted to the Phan Si Pan-Song Hong terrane. It represents a series of late brittle, dextral faults, which dislocated what may have originally been a single continental-scale mylonitic shear zone with sinistral, transpressive shear kinematic indicators. This mylonite zone is interpreted to have dipped northeast, underlain by a thrust that flattened into the middle crust, and overlain by a normal fault. The late brittle fault dislocation produced an en echelon, overlapping complex of at least three broad (up to 30 km wide) zones of intensely mylonitised rocks, represented in Vietnam by the Day Nui Con Voi, Middle Belt and Ailao Shan zones (Burchfiel et al., 2008). The Day Nui Con Voi is bounded to the northeast and southwest respectively by the brittle Song Chay and Red River faults. The Middle Belt is developed to the southwest of the Red River fault zone, while the southeastern extremity of the Ailao Shan zone occurs to the south of that again, tapering to the southeast and bounded by brittle faults (Burchfiel et al., 2008).
Sin Quyen setting
Burchfiel et al. (2008) conclude that the metamorphosed and mylonitised lithologies on the northeastern margin of the Song Da mobile belt are largely metamorphosed Proterozoic rocks, but may also include mylonitised Palaeozoic and Mesozoic protoliths. Triassic and younger rocks locally separate the mylonite zones across brittle faults. During the early Cenozoic, all were metamorphosed to mid-amphibolite facies within the middle crust, and subsequently extruded within the mylonite zones, largely between 40 and 28 Ma (Burchfiel et al., 2008 and sources cited therein).

Sin Quyen

The Sin Quyen deposit, which is located 300 km northwest of Hanoi, is hosted within strongly deformed, steeply dipping, amphibolite facies, migmatised gneiss and schist of the 800 m thick, Proterozoic Sin Quyen Formation. This formation, is divided into a lower, predominantly graphitic (~15 to 20%) quartz-feldspar-biotite-muscovite interleaved schist and gneiss unit, and an upper plagioclasequartz- biotite gneiss. The lower Sin Quyen Formation, which is intruded by extensive 'granito-gneiss', granite, pegmatite and amphibolite, is host to the bulk of the Sin Quyen alteration and mineralisation.

Sin Quyen section The Sin Quyen Formation conformably overlies metasediments of the Proterozoic Lung Po Formation, and at the surface, is overlain, across a faulted contact, by dolostones and shales of the Cambrian Cam Duong Formation. At depth, the upper Sin Quyen Formation is in faulted contact with limestones and marbles of the Neoproterozoic to Lower Cambrian Sa Pa suite (McLean, 2001).

The oldest intrusives within the deposit area are small, irregular, lensoidal, banded 5 to 50 x 10 to 100 m Proterozoic gabbros and amphibolites and albitised gabbrodolerites (1777 Ma, Rb-Sr; 1036, Ar-Ar; Khuong 2010). These rocks are intimately associated with mineralisation, particularly where altered, and may contain up to 70% of the ore, and include all of the high grade zones (McLean, 2001).

Strongly deformed, gneissic and migmatised Proterozoic felsic intrusive rocks occur as 2 to 200 x 10 to 300 m lenses and dykes, overprinted by mylonitic fabrics. These "granito-gneisses" enclose enclaves of both amphibolite and biotite gneiss country rock (McLean, 2001). Small, generally lensoid, younger granitoids, many being plagio-granites, are found intruding along faults, commonly occurring in close association with mineralisation. They are seen to cut the Neoproterozoic to Cambrian Sa Pa Suite. Ta Viet Dung et al. (1975) recorded these intrusives to be mineralised, and preceding sulphide development, and further, that magnetite accumulations only contained sulphide where they were present. McLean (2001) however, logged the same intrusives as post-mineralisation as they separate mineralised intervals and are themselves barren. Other young intrusives include plagioclase-quartz pegmatites and minor gabbro-dolerites.

The Sin Quyen area is characterised by early widespread sodic alteration (albitisation), overprinted by more localised sodic-calcic and potassic-iron assemblages. The latter has completely altered amphibolites and biotite gneisses at Sin Quyen to form a hastingsite-biotite-quartz rock with accessory apatite, calcite, chlorite and epidote, that hosts virtually all of the magnetite and orthite mineralisation and the bulk of the sulphides (McLean, 2001).

Alteration and mineralisation is interpreted to have taken place in two stages, an early metasomatic phase, characterised by early albite, followed by biotite and hastingsite, and lesser hedenbergite, epidote and garnet, with late stage magnetite and orthite, with lesser uraninite. This was followed by a hydrothermal phase accompanied by chalcopyrite, pyrrhotite and lesser pyrite (Ta Viet Dung et al., 1975).

Magnetite occurs as disseminations and veins and is strongly developed as bands along foliations and as massive accumulations, generally in metasomatite, but also in adjacent biotite gneiss. It is generally closely associated with biotite and hastingsite, but is also found as mono-minerallic bands. Orthite is commonly associated with magnetite within the metasomatite, occurring as disseminations, but also in magnetite- and sulphide-poor hedenbergite-garnet skarn assemblages (McLean, 2001). Sulphides are dominantly present as disseminations and foliation parallel bands and fracture fillings, also occurring as breccia cement within fractured magnetite bands. Two main generations of sulphide are recognised. The older is an early, minor, commonly deformed, phase of chalcopyritepyrrhotite- pyrite associated with quartz, forming veins cutting the magnetite and metasomatites. The second, dominant variety, which has not been deformed, comprises chalcopyrite and pyrrhotite with lesser pyrite. A number of sub-stages of the latter are also recognised, representing deposition at progressively declining temperatures (McLean, 2001). Gold is recognised both within the sulphides (both chalcopyrite and pyrrhotite-pyrite) and in the native form (~15%) (McLean, 2001).

Numerous occurrences of magnetite, from high to low grade, and variable associated copper mineralisation are found over an interval of several hundred kilometres along the Red River fault zone in Vietnam and China (McLean, 2001). Ta Viet Dung et al. (1975) favoured a Proterozoic age for the metasomatic alteration and associated magnetite, orthite and uranninite (due to the close association of this assemblage with Proterozoic lithologies), and a Permo-Triassic emplacement, of sulphides on the basis of their lack of deformation, and interpreted association with Permo-Triassic plagio-granites. McLean (2001) suggested all of the mineralised phases are of Proterozoic origin, based on his observation that the younger plagio-granites post-dated mineralisation. However, the coincidence with the Red River fault zone would seem fortuitous, unless it represents a reactivated Proterozoic structure. Similarly the lack of infl uence by the Cenozoic mylonitisation would seem anomalous. Further work is required to resolve these relationships.

Mineralisation at Sin Quyen is concentrated adjacent to major faults that parallel and are interpreted to be splays of the Red River fault zone. The deposit is reported to be hosted by extensive fault zones adjacent to the Sin Quyen reverse fault, which was described as a 50 m wide zone of "crushed, sheared and folded rock" (Ta Viet Dung et al., 1975). Ore occurs as steeply northeast-dipping, anastomosing lenses, within a NW-trending, 100 to 200 x 2500 m zone, that persists to depths of generally <500 m. Although northeast dipping, these lenses are stacked in a steeply southwest dipping envelope. In plan the mineralised zone has a gentle "S" shape, with the best grades concentrated in the central limb, consistent with sinistral dilation (McLean, 2001).

The main ore zone represents the largest of four discontinuous "broken zones" within banded, upper Sin Quyen formation quartz-feldspar gneiss, interpreted to be splays of the Sin Quyen fault. These zones are characterised by strong fracturing and dislocation of the gneissic fabric and the development clay-matrix tectonic breccias. Sulphide mineralisation appears to post-date deformation (McLean, 2001).

This summary is an extract from Porter (2010) in "Hydrothermal Iron Oxide Copper-Gold and Related Deposits: A Global Perspective, v.3, Advances in the Understanding of IOCG Deposits", available from PGC Publishing, Adelaide.

The most recent source geological information used to prepare this summary was dated: 2002.    
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.


  References & Additional Information
   Selected References:
Li, X.-C. and Zhou, M.-F.,  2018 - The Nature and Origin of Hydrothermal REE Mineralization in the Sin Quyen Deposit, Northwestern Vietnam: in    Econ. Geol.   v.113, pp. 645-673.
Li, X.-C., Zhou, M.-F., Chen, W.T., Zhao, X.-F. and Tran, M.D.,   2018 - Uranium-lead dating of hydrothermal zircon and monazite from the Sin Quyen Fe-Cu-REE-Au-(U) deposit, northwestern Vietnam: in    Mineralium Deposita   v.53, pp. 399-416.
McLean R N,  2002 - The Sin Quyen Iron Oxide-Copper-Gold-Rare Earth Oxide Mineralisation of North Vietnam: in Porter T M (Ed.), 2002 Hydrothermal Iron Oxide Copper-Gold and Related Deposits: A Global Perspective, PGC Publishing, Adelaide   v.2 pp. 293-301
Porter T M,  2010 - Current Understanding of Iron Oxide Associated-Alkali Altered Mineralised Systems: Part II, A Review: in Porter T M, (Ed),  2010 Hydrothermal Iron Oxide Copper-Gold and Related Deposits: A Global Perspective, PGC Publishing, Adelaide   v.3 pp. 33-106

   References in PGC Publishing Books: Want any of our books ? Pricelist
McLean R N, 2002 - The Sin Quyen Iron Oxide-Copper-Gold-Rare Earth Oxide Mineralisation of North Vietnam,   in  Porter T M, (Ed.),  Hydrothermal Iron Oxide Copper-Gold & Related Deposits: A Global Perspective,  v2  pp 293-301
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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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