By Sergey M. Rodionov1, Alexander A. Obolenskiy2
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Nimnyr Metallogenic Belt ofApatite Carbonatite Deposits(Belt NM) (Russia, Aldan-Stanovoy Shield)This Paleoproterozoic metallogenic belt is related to carbonatite plutons in the Nimnyr orthogneiss and granite gneiss terrane in the Central Aldan superterrane. The age of the belt is interpreted as late Paleoproterozoic and has isotopic ages of 1800 to 1900 Ma. The main deposit is the Seligdar apatite carbonatite mineral deposit. The metallogenic belt extends longitudinally for 400 km in the northern Aldan-Stanovoy shield and is 40 km wide in the central part. The belt contains eleven deposits and occurrences related to carbonatite plutons. Seligdar Apatite Carbonatite DepositThis deposit (Smirnov, 1978; Entin and others, 1991) consists of apatite in an asymmetric carbonatite stock with dimensions of 2 by 1.02 km. At a depth of 1.6 km, the stock narrows to a few hundred square meters. The stock contains carbonatite composed of: apatite and carbonate; apatite, quartz, and carbonate; martite, apatite, quartz, and carbonate; martite, apatite, and carbonate; and quartz. Occurring in the periphery are apatite-quartz-feldspar metasomatite and tourmaline-K-feldspar-quartz metasomatite. Both early and late stage carbonatite occur. The early carbonatite occurs in veins, vein zones, and stockworks in a mafic complex and in crystalline basement of the Aldan-Stanovoy shield. Thickness of the veins varies from a few centimeters to 30 to 40 m and the length varies from a few meters to 500 m and rarely up to 1.5 km. The early carbonatite is mainly calcite rich with lesser feldspar, magnetite, serpentine, phlogopite, and apatite. The late carbonatite occur in dikes and stocks that intrude the early carbonatite, and consists of dolomite, anhydrite, apatite, quartz, chlorite, and lesser barite. Martite also occurs along with rare tourmaline, fluorite, sulfates, and apatite. A typical lithology consists of apatite-silicified rock with hematite that resembles jaspilite. The deposit is large with reserves of 1,616 million tonnes averaging 6.72% P2O5. Origin and Tectonic Controls forNimnyr Metallogenic BeltThe metallogenic belt is related to carbonatite that is interpreted as forming during interplate rifting. Deposits consist of apatite-carbonate, apatite-quartz-carbonate, martite-apatite-quartz-carbonate, and martite-apatite-carbonate and apatite-carbonate-quartz that is related to and hosted in asymmetrical carbonatite stocks. REFERENCES: Smirnov, 1978; Entin and others, 1991; Parfenov and others, 1999, 2001. Dyos-Leglier Metallogenic Belt ofFe Skarn Deposits(Belt DL) (Russia, Aldan-Stanovoy Shield)This Paleoproterozoic(?) metallogenic belt is related to Nimnyr orthogneiss and granite gneiss terrane and Timpton-Uchur granulite-paragneisss terrane in the in Central Aldan granulite-orthogneiss superterrane. The isotopic age of the belt is interpreted as 1.9 Ga. The major Fe skarn deposits are at Tayozhnoe, Dyosovskoe, and Emeldzhak. The metallogenic belt extends 400 km in southwest-northeast accross the Nimnyr and Timpton-Uchur terranes. The major deposits are in the South Aldan and Emeldzhak districts. The South Aldan Fe district occurs in the central part of the Aldan-Stanovoy shield, about 80 to 130 km north of the Berkakit railway station, and contains the Leglier, Dyos, and Sivagli groups of deposits that comprise 32 Fe skarn deposits and occurrences. The largest are at Tayozhnoe and Dyosovskoe. The Emeldzhak district occurs in the northeastern part of the Dyos-Leglier metallogenic belt, extends over an area of 100 by 25 sq. km, and contains several phlogopite-magnetite deposits and occurrences in Paleoproterozoic amphibole-diopside gneiss, coarse-grained marble, and biotite gneiss. These deposits are genetically related to magnesian skarn. Dyosovskoe Fe Skarn DepositThis deposit (Biryul'kin and others, 1990) consists of Fe skarn that extend sublatitudinally for 20 km and range from 1-3 km wide. The Fe ore horizon occurs in three parallel synforms overturned to the N that dip at 30-70° and are complicated by larger folds and zones of longitudinal thrust and strike-slip faults. Structures causes sharp variations in thickness of ore horizon both along strike and downdip. Thickness of Fe ore bodies varies from 1 to 40 m. Diopside-magnetite and serpentine-magnetite are predominate. Deposit is metamorphosed to amphibolite facies. Deposit and host rock contain irregularly distributed pyrite, pyrrhotite, and chalcopyrite in disseminations. The deposit is large with resources of 700 million tonnes ore, with concentrate grading 66.7% Fe and Mn, and 0.43% Cu and Co. Impurities are 1.11% S, 0.12% P, 0.02% Zn. Tayozhnoe 2 Fe Skarn DepositThis deposit (Bilanenko and others, 1986; Biryul'kin and others, 1990; Kovach and others, 1995a, 1995b) is 200 m thick and consists of magnetite skarn, magnesian skarn, amphibole-diopside rock, coarse-grained marble, and biotite gneiss of Paleoproterozoic age with an isotopic age of 2.3 to 2.1 Ga. Subjacent rocks are amphibole gneiss and schist, and the overlying rocks are high-alumina and quartz gneiss. Metamorphic rocks are intruded by metamorphosed ultramafic rock and metagabbro, and diorite. Host rocks are metamorphosed to granulite facies. In plan the deposit is horseshoe shaped, curved to the northwestern, and in section forms a recumbent synform that dips steeply southwest. Concordant and en-echelon deposits are 2 km long and range from 10 to 100 km thick. The major sulfides are pyrite, pyrrhotite, and chalcopyrite. Some layers contain ludwigite and ascharite. Gangue minerals are diopside, olivine, chinohumite, salite, hornblende, and phlogopite in various combinations. The deposit is large with resources of 1.2 billion tonnes grading 20-60% Fe with an average grade of 39.8% Fe, 2.12% S, and 0.1% P2O5. Origin and Tectonic Controls forDyos-Leglier Metallogenic BeltThe belt is interpreted as forming during a late-stage or post-collisional tectonic event. Deposits consist of magnetite skarn, magnesian skarn, amphibole-diopside rock, calciphyre, and biotite gneiss that are metamorphosed to amphibolite facies. Host rocks are amphibole gneiss and schist and high-alumina gneiss and quartzite-gneiss that are intruded by metamorphosed ultramafic rock, gabbro, and diorite that are metamorphosed to granulite facies. Deposits range from concordant to en-echelon. REFERENCES: Arkhipov, 1979; Bilanenko and others, 1986; Kovach and others, 1995a, 1995b; Parfenov and others, 1999, 2001. |