By Sergey M. Rodionov1, Alexander A. Obolenskiy2
|
|  Yüklə 2.21 Mb.
|
Timpton Metallogenic Belt ofPhlogopite Skarn Deposits(Belt TM) (Russia, Aldan-Stanovoy Shield)This Paleoproterozoic metallogenic belt is related to replacements in Nimnyr orthogneiss and granite gneiss terrane in Central Aldan superterrane and in the eastern Amga tectonic melange zone. The age of the belt is interpreted as Paleoproterozoic (about 2000 Ma). The metallogenic belt extends for 250 km and ranges from 250 km wide to the south and to 50 km to the north. The phlogopite deposits and occurrences occur mainly in Paleoproterozoic diopside and phlogopite-diopside schist, marble, and coarse-grained marble that are metasomatized into coarse-grained phlogopite-diopside skarn with isotopic ages of 1.9 to 1.8 Ga. Some deposits and occurrences are in synforms along fold hinges and centroclinals, and the cores of superposed transverse folds. Several dozen phlogopite deposits and prospects occur in the belt. The length of the deposits ranges from 0.7 to 2.5 km and the width from 0.2 to 0.5 km. The deposits contain several parts, each consisting with two or more phlogopite zones with thicknesses from a few meters to several tens of meters, and lengths from 10 to 20 m to several hundreds of meters. The main deposit is at Nadyozhnoe. Nadyozhnoe Phlogopite Skarn DepositThis deposit (Biryul’kin and others, 1990; Kovach and others, 1995a, 1995b) consists of phlogopite occurring in Paleoproterozoic diopside and phlogopite-diopside schist, marble, and coarse-grained marble that are metasomatized into coarse-grained phlogopite-diopside skarn with isotopic ages of 1.9 to 1.8 Ga. The deposit occurs on the northern limb of a latitudinal synform, extends for 5 km, and ranges from 100 to 150 km wide. Twenty mica-bearing zones occur that are concordant with host rocks. The zones vary from 20 to 200 m long and 3 to 12 m thick, and consist of skarn with phlogopite, diopside, hornblende, scapolite, apatite, and actinolite. Phlogopite forms nest-like accumulations varying in size from 0.5 to1 m to 1.5 to 6 m, with an average of 1 to 2 m. Phlogopite rarely occurs in thin veins. Phlogopite content ranges from 15 to 86.9 kg/m3. Almost all deposits are associated diopside-magnetite skarn. Local diopside and diopside-scapolite-plagioclase metasomatite contain molybdenite. The deposit is large with resources of about 7,000 tonnes grading 45.1 kg/m3 phlogopite. Origin and Tectonic Controls forTympton Metallogenic BeltThe belt is interpreted as forming during a late-stage or post-collisional tectonic event. Deposits occur in diopside and phlogopite-diopside schist, marble, and calciphyre that are metasomatized into coarse-grained phlogopite-diopside skarn. REFERENCES: Murzaev, 1974; Arkhipov, 1979; Parfenov and others, 1999, 2001. Tyrkanda-Stanovoy Metallogenic Belt ofAu in Shear Zone and Quartz Vein Deposits(Belt TS) (Russia, Aldan-Stanovoy Shield)This Paleoproterozoic(?) metallogenic belt is hosted in the Tyrkanda tectonic melange zone between the East Aldan superterrane and Central Aldan superterrane. The zone consists of tectonic slabs of paragneiss and anorthosite that are bounded by narrow blastomylonite zones with local abundant granite bodies. The age of the belt is interpreted as 1.9 Ga. The belt extends for 700 km and varies from 20 to 150 km wide. The main deposit is the Au in shear zone Kolchedannyi Utyos deposit and the belt contains several Au occurrences. Kolchedannyi Utyos Au in Shear Zone and Quartz Vein DepositThis deposit (Karsakov and Romanovsky, 1976; Moiseenko and Eirish, 1996) consists of a northwestern-trending linear system that contains close-spaced quartz-pyrite veins with irregular, indistinct contacts. The veins are hosted in pyroxene, biotite-pyroxene, and hornblende-pyroxene gneiss and schist interlayered with amphibolite, marble, and garnet-and graphite-bearing rocks. The ore minerals occur in disseminations, masses, and local breccia, and are mainly pyrite (20 to 90%) with lesser chalcopyrite (5 to 15%), and magnetite, sphalerite, and pyrrhotine. Quartz (from 30 to 70%) occurs in honeycombed frameworks, veinlets and nests, and sometimes crystal druses. The deposits are separated by silicified barren gneiss and pegmatoid microcline-plagioclase metasomatite. At the surface, deposits are oxidized to limonite, lazurute, malachite, and jarosite. The average grade ranges from 1-2-120 g/t, Au, 6-20 g/t Ag, and locally up to 64.1 g/t Ag. Origin and Tectonic Controls forTyrkanda-Stanovoy Metallogenic BeltThe belt interpreted as forming during collision between the Tynda composite terrane and Central Aldan and East Aldan superterranes. The reason for collision is unclear. in the Aldan-Stanovoy region and during subsequent collapse of orogenic belt. Au shear zone deposits cut metamorphosed mafic and utramafic bodies and plutonic rocks. REFERENCES: Karsakov and Romanovsky, 1976; Moiseenko and Eirish, 1996; Parfenov and others, 1999, 2001. Davangra-Nalurak Metallogenic Belt ofREE Placer Occurrences and BandedIron Formation (BIF, Superior Fe) Deposits(Belt DN) (Russia, Aldan-Stanovoy Shield)This Paleoproterozoic metallogenic belt is hosted in grabens filled with late Paleoproterozoic clastic and carbonate sedimentary rock. The belt occurs along the southern margin of the Sutam granulite-paragneiss terrane in the Central Aldan granulite-orthogneiss superterrane and in the Tyrkanda tectonic melange zone. The age of the belt is interpreted as late Paleoproterozoic. The belt occurs in the latitudinal Atugey-Nuyam and Davangra-Khugdin grabens filled with thick quartz sandstone, arkose, and gravelstone that are correlated with the Kebekta Formation in the Uguy graben to the west. Middle Proterozoic siltstone in the grabens contains concordant hematite beds that range from 0.3 to 3 m thick and extend for 40 km. The major deposit is at Atugey. Various REE placer occurrences (Arkhipov, 1979) are hosted in in gravelstone and conglomerate in the the Atugey-Nuyam graben and range from 15 to 30 long and a few to 150 m thick. Monazite and zircon comprise up to 95% heavy mineral concentrates. Samples from the conglomerate and gravelstone horizons contain from 0.1 to 0.8% Ce, 0.01 to 0.1% Y, 0.03 to 0.05% La, 0.01 to 1% Tb, and up to 0.005% Nb. Atugey Banded Iron Formation (BIF, Superior Fe) DepositThis deposit (Klimov, 1979) consists of concordant beds of hematite that range from 0.3-3 m thick and extend for 40 km. The beds are interbedded with siltstone in the middle part of Proterozoic sandstone units in the Atugey-Nuyam graben. REE occurrences are in gravelstone and conglomerate horizons that range from 15-30 m long and vary from a few meters to 150 m thick. Principal minerals in the heavy fractions of rocks are monazite and zircon (up to 95%). Samples from the conglomerate-gravelstone horizons contain 0.1-0.8% Ce, 0.01-0.1% Y, 0.03-0.05% La, 0.01-1% Tb, and up to 0.005% Nb. Grade ranges from 29.6 to 70.7% Fe, 0.01 to 0.05% S, and 0.1 to 0.2% P2O5. Origin and Tectonic Controls forDavangra-Nulurak Metallogenic BeltThe belt is interpreted as forming in grabens in a Precambrian intracratonic basin that formed during intracontinental rifting. Source rocks for REE minerals are interpreted as granitoids in the Central Aldan superterrane and alkalic volcanic rocks that erupted during rifting. Placer deposits occur in thick quartz and arkose sandstone, and gravelstone horizons. REFERENCES: Arkhipov, 1979; Parfenov and others, 1999, 2001. |