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Seligdar |
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Siberia - Sakha-Yakutia, Russia |
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P REE
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Super Porphyry Cu and Au
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The Seligdar apatite-Rare Earth Element (REE) deposit is located ~30 km southwest of the town of Aldan in the Central Aldan region of Yakutia, Sakha Republic, East Siberia, Russia (#Location: 58° 24' 19"N, 125° 18' 29"E).
The Seligdar deposit is located in the Central Aldan Shield, and lies within a major, broad, ENE-trending lineament zone that crosses the terrain, localised at its intersection with a transverse NW-trending fault zone. It is hosted by a suite of Archaean metamorphic rocks which comprise diopside-hypersthene, hypersthene-amphibole, diopside, diopside-amphibole, biotite-amphibole, biotite-garnet crystalline schists and gneisses, that enclose lenses of marble and forsterite-carbonate-apatite rocks on a district-wide scale. The marbles have undergone intense replacement by diopside, diopside-phlogopite and rarely wollastonite skarns. In the deposit area, these skarns almost always contain ~10 to 15 vol.% apatite and locally up to 10 to 15 vol.% magnetite.
The deposit overprints the Archaean metamorphic suite, essentially occurring as a mass of metasomatic carbonate-apatite or carbonate-quartz-apatite rocks. These metasomatites contain 60 to 65 vol.% dolomite, 1 to 30 vol.% apatite, 5 to 20 vol.% quartz and variable amounts of calcite, hematite, feldspars, forsterite, phlogopite, diopside, tremolite, talc, barite, scapolite and anhydrite. Relicts of the Archaean metamorphic country rocks are common in the mineralised zones, while on its margins, the mineralisation passes outward into a series of disconnected veins.
The deposit has no defined geological margins, being delineated by the P2O5 cut-off grade. It occurs as a steeply-plunging, downward tapering, 'funnel-shaped' mineralised zone, with a NW-SE elongated ovoid surface exposure that has dimensions of 2.2 x 1.3 km. Mineralisation has been traced by drilling to a depth of 1660 m, where its plan dimensions have contracted to only a few hundred metres across. Magnetic data suggests it persists to as deep as 3 km below the surface, while gravity indicates it continues to even greater depths (Roganov and Karsakov, 1991). Beyond the main, most heavily mineralised and altered central deposit, there are a series of adjoining and disconnected satellite lenses, both concordant and discordant to the host Archaean metamorphic rocks, often with gradational contacts. Some of these lenses are tens to hundreds of metres thick and up to 1 km in length.
According to Roganov and Karsakov (1991), the deposit was formed in three main phases, namely:
• An early stage, including orthoclase-plagioclase-quartz, carbonate-apatite, sulphate and carbonate-hematite assemblages;
• An intermediate stage that includes microcline-albite-quartz and chlorite-epidote-serpentine assemblages, and
• A late stage, comprising calcite-apatite and chlorite-epidote-serpentine assemblages.
The carbonate-apatite assemblage of the early stage forms the bulk of the apatite mineralisation. Martite (hematite pseudomorphed after magnetite) forms 10 to 50 vol.% of the metasomatites. The apatite occurs as hydroxide-fluorapatite (Bulakh et al., 1990; Roganov and Karsakov, 1991). REE are also concentrated in allanite and monazite. The deposit is characterised by the extensive occurrence of various breccias. According to Bulakh et al. (1990), breccias are abundant in association with the dolomite-apatite and carbonate-quartz-martite-apatite ores in particular, while the ores themselves have also been brecciated. These breccias comprise 20 to 25 and locally up to 50 vol.%, ore fragments and lesser gneisses, with smaller fragments composed of broken apatite, microcline and quartz crystals, serpentine aggregates and fine-grained anhydrite. The breccia is cemented by a fine-grained mylonite-like matrix composed of dolomite, hematite and apatite, with the latter forming 35 to 75 vol.% of the rock. Another style of breccia is represented by dense, finely dispersed mylonites, containing 1 to 70 mm fragments of cataclastic apatite (70 to 80 vol.% of the total fragments) and quartz crystals, with minor chlorite, serpentine, feldspars, dolomite, hematite, etc., cemented by a matrix of fine-grained hematite-dolomite and hematite-quartz.
Dating of the early apatite-carbonate ores include Pb-U-Th isochron ages of 1990 to 1870 Ma, and a Pb-Pb isochron age of 1840±90 Ma. Pb-U-Th and U-Pb ages of apatite were 1850±15 Ma and 1800 Ma, respectively (Bulakh et al., 1990), indicating a Palaeoproterozoic age. The late hydrothermal event may be Mesozoic, as thin apatite-calcite rims are observed along the contacts of some Mesozoic syenite and shonkinite dykes. With the exception of these younger (Mesozoic) dykes, no igneous rocks have been confidently identified in association with the deposit. Two alternate origins have been suggested: i). A metamorphic origin, resulting from the metamorphism of phosphatic dolomites, supported by the regional distribution of apatite-carbonate lenses in the host Archaean metamorphic rocks; ii). a variety of low-alkaline carbonatite. Most authors suggest a metasomatic origin for the early apatite-carbonate ores resulting from fluid flow in zones of deep-seated faults and their intersections (Bulakh et al., 1990; Roganov and Karsakov, 1991).
The deposit has measured + indicated resources of 117 Mt @ 5.8 to 9.8 wt.% P2O5 to a depth of 350 to 400 m, with additional inferred resources (Russian P1 category) of 116 Mt (Bulakh et al., 1990; Roganov and Karsakov, 1991). It is also one of the largest REE deposits in Russia containing (in 2010) 15% of the Federation's REE resources. The REE is found within the apatite which occurs as hydroxide-fluorapatite and contains 0.4 to 0.6 wt.% REE, mostly La, Ce and Nd (Bulakh et al., 1990; Roganov and Karsakov, 1991). The apatite ore contains 5 to 10% hematite, with ~10% of the resource represented by apatite-hematite mineralisation averaging 15% FeTotal (e.g., Belousov et al., 1983).
This summary is largely drawn from Soloviev (2010) and Prokopyev et al., 2017).
The most recent source geological information used to prepare this decription was dated: 2017.
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.
Seligdar
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Selected References:
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Prokopyev, I.R., Doroshkevicha, A.G., Ponomarchuk, A.V. and Sergeev, S.A., 2017 - Mineralogy, age and genesis of apatite-dolomite ores at the Seligdar apatite deposit (Central Aldan, Russia): in Ore Geology Reviews v.81, pp. 296-308.
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Soloviev, S.G., 2010 - Iron Oxide Copper-Gold and Related Mineralisation of Siberian Craton, Russia 2 - Iron Oxide, Copper, Gold and Uranium Deposits of the Aldan Shield, South-Eastern Siberia: in Porter, T.M., (Ed.), 2010 Hydrothermal Iron Oxide Copper-Gold and Related Deposits: A Global Perspective PGC Publishing, Adelaide v.4, pp. 515-534.
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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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