Siberia - Krasnoyarsk, Russia
Pb Zn Ag
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The Gorevsk, or Gorevskoe, Pb-Zn deposit is located on the south bank of the Angara River, 30 km upstream to the east of its confluence with the Yenisei river, 60 km east of the city of Lesosibirsk, and 250 km north of Krasnoyarsk (#Location: 58° 7' 50"N, 93° 30' 10"E).
It lies within the Yenisei Ridge domain, a NW-SE oriented, 700 x 50 to 200 km, fold and thrust belt, along the southwestern margin of the Siberian craton, marking the boundary with the Palaeozoic Central Asian Fold Belt. The Yenisei Ridge is composed of a basement of Archaean and Palaeoproterozoic high-grade metamorphic and igneous rocks, discordantly overlain by Meso- to Neoproterozoic greenschist-facies metamorphosed sedimentary rocks (Vernikovsky and Vernikovskaya, 2006). These rocks are in turn, overlain by early to middle Palaeozoic sequences. These Proterozoic and Palaeozoic sequences are considered to represent passive continental margins, characterised by accumulation of clastic and clastic-carbonate sedimentary sequences, with minor coeval volcanic rocks, although they could also represent parts of rift basins, with alkaline basaltic dykes (Seltmann et al., 2010).
The Yenisei Ridge domain fold and thrust belt evolved in four major tectonic stages at:
i). 1900 to 1840 Ma, resulting in the high-grade metamorphism (granulite to amphibolite facies) of the Archaean and Palaeoproterozoic basement rocks and emplacement of granites;
ii). 880 to 860, represented by S- and I-type granites, derived from a Palaeoproterozoic crustal source;
iii). 760 to 720 Ma granitoids, mainly A-type, also derived from a Palaeoproterozoic crustal source; and
iv). 700 to 630 Ma, when ophiolite wedges and slices were thrust onto the Proterozoic sequence, and A-type granites, nepheline syenites, alkaline basic rocks and carbonatites of mantle and crustal-mantle origin were intruded.
The southern limit of the Yenisei Ridge segment is marked by the east-west Angara fault, which separates it from the similar Transangara segment. South of the Angara fault, the narrower Transangara segment fringes the southwestern margin of the Siberian craton for ~1000 km to Irkutsk on Lake Baikal. It is composed of two terranes, an older of high grade (granulite facies) Archaean to Palaeoproterozoic gneisses and schists, the Angara-Kan terrane. These have been overthrust from the SW by Neoproterozoic volcano-sedimentary rocks, including greenschist facies basalts, andesite-basalts, andesites, dacites and rhyolites, and gabbroid and diorite-plagiogranite intrusions of the Predivinsk terrane (Vernikovsky and Vernikovskaya, 2006).
North of the Angara fault, the Yenisei Ridge domain is composed of three 200 to 500 km long x 50 to 80 km wide fault bounded blocks, each of a different character, the East Angara, Central Angara and Isakov terranes, chiefly comprising Neoproterozoic rocks (Vernikovsky and Vernikovskaya, 2006).
The tectonically highest Isakov terrane to the NW, is the smallest, ~180 x 30 km, and is composed of Neoproterozoic volcanosedimentary rocks and ophiolites. The central part of the terrane hosts fragments of ophiolites, (metaperidotites, metagabbros, tholeiitic metabasalts), as well as phyllites and calcareous quartz-muscovite schists, with parallel dykes and sills of dolerite and dolerite porphyries. Tectonic slices of rhyolite-andesite-basalt volcanic rocks and associated metamorphosed tuffs, tuffaceous sandstones, sandstones, phyllites and limestones
occur east and west of the ophiolite slabs (Vernikovsky and Vernikovskaya, 2006).
The tectonically underlying Central Angara terrane is 350 to 400 km, and is exposed over a width of 50 to 80 km. The Isakov terrane was thrust over it from the west, while it is separated from the underlying East Angara terrane to the east by the major Ishimba overthrust. It is chiefly composed of metamorphosed Neoproterozoic clastic, clastic-carbonate and carbonate rocks. The lower Teya Group part of the section is metamorphosed to amphibolite to epidote-amphibolite facies high-Al kyanite (andalusite, sillimanite)-staurolite-garnet and biotite-sillimanite gneisses, grading upwards into alternating biotite-amphibole schists, quartzites, amphibolites and marbles. These are overlain by greenschist facies metamorphosed sandstones with interbeds of polymictic conglomerates to grits, silty sandstones, and green to dark-grey to black phyllites and clastic-carbonates of the Sukhoi Pit Group. The uppermost Tungusik Group (also greenschist facies) is a sequence of alternating calcareous and clayey shales at the bottom, which pass up into limestones and dolomites. All of these units are intruded by 880 to 860, 760 to 720 and 700 to 630 Ma granitoids (Vernikovsky and Vernikovskaya, 2006).
The structurally lowest East Angara terrane comprises Neoproterozoic clastic-carbonate deposits (sandstones, siltstones, mudstones, dolomites and limestones), metamorphosed to no more than sericite-chlorite subfacies of the greenschist facies. These sediments are not strongly deformed and are characterised by wide, asymmetric box folds, with steeper western limbs and flexures. This terrane differs from the other two in having no Neoproterozoic magmatism. The sedimentary rocks of this terrane are discordantly overlapped by the
late Neoproterozoic to Cambrian molasse and Cambrian limestones and dolomites (Vernikovsky and Vernikovskaya, 2006).
The Gorevsk deposit is hosted within Neoproterozoic clastic and carbonate rocks of the Central Angara terrane, a few km north of the South of the Angara fault. High grade basement metamorphic rocks of the Angara-Kan terrane.
The host rocks, which have been intensely deformed, are metamorphosed to greenschist facies. Locally they comprise the older Shuntar Group schists, carbonaceous calcareous shale, carbonaceous shale, and the overlying rhythmically-bedded and cross-bedded limestones, with minor calcareous dolomite and thin (a few cm, to a few m thick) seams of marl that constitute the 1000 to 1160 m thick Kirgitei Group. The latter, which host the mineralisation, have been regionally metamorphosed to marble and quartz-sericite-calcareous and quartz-chlorite-calcareous shales (Smirnov, 1977). It is assumed the Shuntar and Kirgitei groups of Smirnov (1977) equate with the Sukhoi Pit and Tungusik groups of Vernikovsky and Vernikovskaya (2006).
The overlying Palaeozoic rocks covering the craton, Yenisey Ridge and to the west are a flat-lying clastic sedimentary sequence of Late Devonian to Early Carboniferous marls, sandstones and calcareous siltstones and gravels.
Near the ore deposits, the country rocks have been hydrothermally altered to sideritic and quartz-sideritic rocks (~70%), dolomitic and ankeritic rocks (~10%) and amphibole-garnet-magnetite skarnoids (~3 to 5%) prior to ore deposition. These alteration styles are all cut by a suite of dolerite dykes (915 Ma ?; USGS - Ryan et al., 2009), which are in turn cut by the ore. Altered rocks form a halo 30 to 50 m wide halo outwards from the ore, and 200 to 150 m up dip. Quartzites and siderite are common immediately adjacent to the ore, while ankeritic rocks are more distal (Smirnov, 1977).
The deposit occurs in a limestone-shale host and occurs as concordant, lens-like sulphide bodies in syncline folds within a larger anticline. The main syncline is symmetrical, with an axial trend of 310 to 320° and steep plunge to the NE. The limbs of the syncline are complicated by smaller folds with amplitudes of 50 to 200 m. A strong 335 to 340° fracture zone on the eastern limb of the syncline is known as the Main fault, characterised by mylonites and tectonites, and a series of small, parallel fractures. The principal controls on ore deposition appears to be both folds and faults, with the principal ore localisation being zones of isoclinal folding, complicated by fractures and shear zones, with the ore following the fold hinge plunges to the SE (Smirnov, 1977).
Three sets of large, steeply to vertical dipping en echelon orebodies have been outlined, with thicknesses varying from 20 to 150 m, strike lengths of up to 1200 m, and down-dip extents of ~1000 m (Seltmann et al., 2010).
The ore minerals include galena, pyrrhotite and sphalerite, with minor pyrite, marcasite, boulangerite-bournonite, jamesonite and arsenopyrite, and trace chalcopyrite, tennantite, argentite, proustite-pyrargyrite, sternbergite, dyscrasite, native Ag and loellingite (Seltmann et al., 2010).
Hydrothermal gangue minerals include quartz, siderite, ankerite and muscovite. The orebodies are characterised by a distinct zonation, with a predominance of pyrrhotite-sphalerite-galena in the footwall, and galena-pyrrhotite in the hangingwall, sandwiching a central zone of galena-pyrrhotite-sphalerite (Smirnov, 1977; Distanov and Kovalev, 1995; Seltmann et al., 2010).
The deposit comprises (Ryan et al., 2009):
300 Mt @ 6.5% Pb, 1.36% Zn, for 19.5 and 4.08 Mt of contained Pb and Zn respectively.
Note: Seltmann et al. (2010) quote a reserve (Russian B+C1 reserve categories) of
~85 Mt @ 7.07 wt.% Pb, 1.37 wt.% Zn, and up to 40 g/t Ag containing 5.8 Mt of Pb and 1.2 Mt of Zn.
The most recent source geological information used to prepare this summary was dated: 2010.
This description is a summary from published sources, the chief of which are listed below.
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