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Panagyurishte district - Elatsite, Medet, Assarel, Vlaikov Vruh, Tsar Assen, Elshitsa

Bulgaria

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Three significant porphyry copper systems Elatsite, Medet and Assarel and a number of smaller occurrences including Vlaikov Vruh and Tsar Assen have been exploited within the Panagyurishte district of the Srednogorie zone in central Bulgaria, some 60 to 80 km east of Sofia.

The main feature of the geology of the Panagyurishte district is the extensive late Cretaceous calc-alkaline magmatism, both intrusive and extrusive volcano-sedimentary rocks which are developed on and through a basement of Proterozoic (mainly granitic gneisses, schists and amphibolites) and late Neoproterozoic to Cambrian (greenschist phyllites, dolerites and mafic tuffs) metamorphic basement, and middle to late Palaeozoic intrusions (granodiorite to granite and smaller peridotite, gabbrodiorite, granodiorite, quartz-diorite to tonalite), overlain by Permian (red bed conglomerates and sandstones) and Triassic (limestone and sandstone) sediments.

The late Cretaceous sequences include:
i). Late Turonian (91-88 Ma) terrigenous sediments, chiefly coal and sandstone,
ii). Lower Senonian (88-86 Ma) volcanogenic complexes, largely extrusives with lesser volcano-sedimentary units and rare sediments, derived from a number of volcanoes, including lava sheets, agglomerates, block tuffs with distal lapilli tuffs, agglomerates, tuffite, sandstone, limestone, argillite and tephroid flysch.   The volcanism is dominantly andesitic although dacitic rocks are more common to the south, while to the north there is a gradation to latite-andesite, latite and eventually trachyte.   The volcanic and sub-volcanic to hypabyssal complexes includes numerous intrusive stocks to dyke like bodies, comagmatic with the extrusives, ranging from monzonite porphyry to granodiorite, quartz-monzodiorite and rarely quartz-gabbro.   There is a possible younging sequence of intrusion from major centres at Chelopech-Elatsite in the north-west to Medet-Assarel to Elshita-Vlaikov Vruh and Pesovets in the south-east.
iii). Late Senonian to Maastrichtian flysch, followed by folding and faulting which produced a series of grabens that preserved the sediments and volcanics, and provided sites for subsequent overlapping Tertiary to Quaternary sedimentation.

Elatsite

The Elatsite deposit is associated with late Cretaceous quartz syenodiorite and granodiorite porphyry dykes cutting late hornfelsed Neoproterozoic to Palaeozoic phyllite and late Palaeozoic granodiorite, some 10 km NW of the Chelopech volcanic centre.   Porphyry copper mineralisation, which was emplaced mainly within the porphyry dykes and basement granodiorite and to a lesser extent in phyllites, occupies a SW-NE elongated ellipsoidal area of 800 x 350 m which plunges south.   K-silicate alteration is developed in association with the ore in all hosts, taking the form of K-feldspar, biotite and quartz replacing original silicates.   This assemblage is surrounded by an annulus of propylitisation (chlorite-epidote-sericite-actinolite).   Local epidote-chlorite-quartz-carbonate alteration is contemporaneous with early magnetite-bornite-chalcopyrite development.   Phyllic (quartz-sericite/illite-pyrite) alteration and small veinlets of fine to coarse pyrite with minor carbonate are developed in the upper levels of the system, with a transitional K silicate-sericite zone.   A particular characteristic of the deposit is the early magnetite-bornite-chalcopyrite mentioned above, which has associated PGE, Co, Ni, Te, Se, Bi, Au and Ag and occurs as sporadic lenses through the deposit.   The main economic assemblage comprises veinlets aggregates and disseminations of quartz-pyrite-chalcopyrite which accompanies the K silicate-sericite transition interval.   Gold occurs as small electrum inclusions in chalcopyrite.   A quartz-pyrite ±chalcopyrite ±calcite vein and veinlet association is found in the upper and marginal sections of the system.   Only minor supergene alteration is observed.

Medet

The Medet deposit was emplaced in the apex of the Medet quartz monzodiorite to granodiorite porphyry intrusive in the north to NE part of the Assarel-Medet district.   The intruded country rock is predominantly Palaeozoic granitoids and gneisses.   The best copper mineralisation is developed in the most intensely fractured and faulted sections of the host intrusive in its eastern sections to form an extensive, NW-SE trending stockwork with a pipe like shape which persists over a vertical interval of more than 1000 m.   Two main alteration assemblages are described, the first being a K silicate association of metasomatic K feldspar-biotite-quartz-apatite, and the second propylitisation (chlorite, epidote and carbonate).   Epidote, chlorite and lesser sericite accompany the sulphide mineralisation at Medet.   Sericitisation is limited and is found around the K silicate zone.   The earliest ore association is quartz-magnetite-hematite accompanying K silicate ±propylitic alteration with Ti bearing minerals.   The main pervasive quartz-pyrite-chalcopyrite mineralisation is found in association with different assemblages through the deposit, with well defined quartz-pyrite veins and veinlets in the centre of the system, grading out to small veins of quartz-galena-sphalerite in the outer periphery and upper sections.   Secondary copper minerals are rare.

Assarel

The Assarel deposit is partly hosted by volcanics which are coeval with the main intrusive and is located in the central part of the main Assarel volcano in an area of intense radial and concentric faulting.   The central part of the volcano is occupied by massive and brecciated andesitic and latite-andesitic lava sheets and pyroclastics, while the Assarel granodiorite porphyry is found in the centre of the stratovolcano as two apophyses which join at depth.   Post ore faulting has displaced the eastern part of the structure upwards to juxtapose weakly altered basement along-side advanced argillic alteration.   The ore is present as a cone inclined at 80 to 85° S, with a surface expression as an ellipsoid elongated in a N-S direction.   Alteration is present within the sub-volcanic intrusives, volcanics and Palaeozoic granitoids as  i). propylitic,  ii). propylitic-argillic,  iii). propylitic-sericitic,  iv). sericitic,  v). sericitic-advanced argillic, and  vi). advanced argillic-acid chloride and acid sulphate types.   Relicts of K silicate assemblages suggest an earlier K silicate and K silicate-propylitic phase.   Epithermal sericitisation and advanced argillic alteration overprint these earlier K silicate assemblages in the lithocap.   The ore and alteration assemblages at Assarel are more complex than at the other deposits, although the early quartz-magnetite-hematite seen at the other deposits is only present to a limited extent while the late quartz-molybdenite association is rare.   The principal ore assemblage is quartz-chalcopyrite ±pyrite accompanied by sericite and transitional sericite-propylitic alteration, with quartz-pyrite with lesser chalcopyrite in both the centre and marginal parts of the system.   Rare galena-sphalerite are found at the top of the system, but are in well defined veins with chalcopyrite at depth.   High sulphidation assemblages including enargite are found in the upper sections of the system associated with sericitic and advanced argillic alteration.   It is also the only deposit in the district with a well developed 60 to 70 m thick supergene enrichment blanket of chalcocite and covellite, below a remnant 10 to 15 m leached cap.   Native gold is rare in the hypogene ore, although it shows elevated concentrations at the contact between the base of oxidation and the zone of secondary enrichment.

Tsar Assen

The small Tsar Assen deposit is to the south-east of the Radka ore field in the eastern most section of the Panagyurishte district and occurs in an area of andesitic volcanics (lapilli-agglomerate tuff, lava and lesser ash-flow tuffs and lava breccias) derived from the Elshitsa volcano-plutonic structure.   These volcanics are cut by sub-volcanic dacite and granodiorite porphyries.   Ore is related to two stock like bodies of granodiorite porphyry, with a zone of secondary enrichment overlying hypogene ore.   The ore associations are similar to those at Assarel.

Vlaikov Vruh

This small deposit occurs near the southern margin of the Elshitsa graben in the eastern most part of the Panagyurishte district. The deposit area comprises Proterozoic gneisses and overlying andesitic volcanics cut by an E-W trending sub-volcanic dacite dyke.   The porphyry-copper mineralisation is mainly hosted by a granodioritic to quartz-monzodioritic stock, emplaced along the contact between the southern parts of the Elshitsa volcanic formation and the Proterozoic gneisses and granitic basement. The major axis of the intrusion trends at 115 to 120° over a strike length is >2 km. The intrusion is cut by later dacitic dykes, which were interpreted by Bogdanov et al. (1972b) as ore-controlling. Up to 30 cm thick late-magmatic aplite-pegmatite dykes crosscut the intrusion.
  Mineralization occurs as four vertical stockwork bodies at depth, coalescing into a single ore body in the upper part of the deposit (Strashimirov et al., 2003). The main ore body has been oxidised to a depth of 10 to 20 m forming malachite-azurite ores, underlain by a 30 to 40 m thick secondary enrichment zone of bornite-chalcocite-covellite ores (Bogdanov et al., 1972). Hypogene alteration includes potassic, phyllic and propylitic zones and mineralisation occurs in all rock varieties in the deposit. The Vlaykov Vruh granodiorite and the two-mica gneiss from the basement underwent potassic alteration (stage I), resulting in the formation of shreddy biotite replacing mafic phenocrysts and the formation of tiny K feldspar-magnetite veinlets. Aplite-pegmatite dykes, at the southern margin of the open pit were propylitically altered and cut by early stage quartz-rutile-molybdenite veins (stage II). Along the western and northwestern sides of the open pit, both the relatively late NNW-striking quartz-pyrite veins and the hydrothermal breccias with phyllic alteration have very similar textures to that of the neighboring Elshitsa epithermal deposit (see below). The main economic copper mineralisation (stage III) occurs as thin veinlets of quartz-chalcopyrite-magnetite±pyrite±pyrrhotite or is disseminated. Polymetallic veins of quartz-sphalerite-galena-chalcopyrite±barite (stage IV) were deposited as open-space filling in extensional fractures and were later cut by quartz-pyrite-chlorite veins (stage V). The latest hypogene mineral assemblage consists of sporadic carbonate–zeolite veinlets (stage VI).

Elshitsa

The Elshitsa epithermal deposit is located on the SW flank of the Elshitsa volcano-intrusive complex and occupies an area of 2 to 2.5 km in length by 0.5 to 0.7 km in width, NW of the Vlaykov Vruh porphyry Cu deposit. The deposit was one of the first mines that was exploited in the Panagyurishte district, operating from 1922 until 1999.
  The structure of the deposit is controlled by a sub-volcanic dacitic body emplaced along the Elshitsa fault, elongated in a NW direction (110 to 115°) and dipping almost at 75 to 80°NE, cutting an andesitic and dacitic volcanic sequence that dips at 10 to 30°N (Bogdanov et al., 1972). The dacite is limited by the Elshitsa fault to the north and by an 80 to 120 m thick breccia zone to the south, which is the main host of the epithermal mineralization. The latter dips steeply at 65 to 70°NE, and is subparallel to the intrusive contact. At depth, it is cut by the Elshitsa fault.
  Two compositionally distinct types of ores have been recognized:
i). massive pyrite, mainly in the eastern sector of the deposit, closer to the Vlaykov Vruh porphyry Cu system, occurring as more than ten lenticular to columnar massive ore bodies which are discordant to the host rock and are structurally controlled by the NW-trending normal fault set, subparallel to the contact of the dacitic subvolcanic body. These sassive lens-like bodies generally show tectonic contacts, due to later Alpine reactivation of the main ore-controlling faults. This stage rpresents an early high-sulphidation pyrite±enargite±covellite±goldfieldite assemblage,
ii). pyrite-chalcopyrite-quartz or copper-pyrite bodies, mainly in the central and western sectors of the deposit. These result from the superposition of an intermediate-sulphidation copper-rich mineral paragenesis upon the early massive pyrite ores, characterised by a Cu-Bi-Te-Pb-Zn signature forming the main economic parts of the ore bodies.

Production to 2002 from the porphyry deposits of the district total:
    460 Mt @ 0.42% Cu, for 1.9 Mt of recovered Cu metal and 77 tonnes of Au
Reserves & production quoted in 2002 were:
    Assarel, Reserve - 254 Mt @ 0.41% Cu, + historic production - 100 Mt @ 0.53% Cu, trace Au.
    Elatsite, Reserve - 154 Mt @ 0.33% Cu, + historic production - 165 Mt @ 0.38% Cu, 0.21 g/t Au.
    Medet, Reserve - Mined out 1964-1993, + historic production - 163 Mt @ 0.32% Cu, 0.1 g/t Au.
    Vlaikov Vruh, Reserve - Mined out 1962-1979, + historic production - 9.8 Mt @ 0.46% Cu.
    Tsar Assen, Reserve - Mined out 1980-1995, + historic production - 6.6 Mt @ 0.47% Cu.

Figures published in von Quadt et al., 2005 are:
    Elatsite, Resource - 185 Mt @ 0.4% Cu, 0.3 g/t Au, 0.68 to 1.9 g/t Ag, 0.07 g/t Pd, 0.02 g/t Pt
        + historic production - 165 Mt @ 0.38% Cu, 0.21 g/t Au.

For detail consult the reference(s) listed below.

The most recent source geological information used to prepare this summary was dated: 2009.     Record last updated: 2/11/2012
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
 References to this deposit in the PGC Literature Collection:
Bogdanov K, Tsonev D, Kuzmanov K,   1997 - Mineralogy of gold in the Elshitsa massive sulphide deposit, Sredna Gora zone, Bulgaria: in    Mineralium Deposita   v32 pp 219-229
Ciobanu C L, Cook N J and Stein H  2002 - Regional setting and geochronology of the Late Cretaceous Banatitic Magmatic and Metallogenetic Belt: in    Mineralium Deposita   v37 pp 541-567
Heinrich C A, Neubauer F  2002 - Cu - Au - Pb - Zn - Ag metallogeny of the Alpine - Balkan - Carpathian - Dinaride geodynamic province: in    Mineralium Deposita   v37 pp 533-540
Kouzmanov K, Moritz R, von Quadt A, Chiaradia M, Peytcheva I, Fontignie D, Ramboz C and Bogdanov K,  2009 - Late Cretaceous porphyry Cu and epithermal Cu–Au association in the Southern Panagyurishte District, Bulgaria: the paired Vlaykov Vruh and Elshitsa deposits: in    Mineralium Deposita   v.44 pp. 611-646
Lips, A., Herrington, R., Stein, G., Kozelj, D., Popov, K. and Wijbrans, J  2004 - Refined tuning of porphyry copper formation in the Serbian and Bulgarian portions of the Cretaceous Carpatho-Balkan Belt: in    Econ. Geol.   v99 pp. 601-609
Moritz R, Kouzmanov K and Petrunov R,  2004 - Late Cretaceous Cu-Au epithermal deposits of the Panagyurishte district, Srednogorie zone, Bulgaria: in    Schweizerische Mineralogische und Petrographische Mitteilungen   v84 pp 79-99
Stefanova E, Driesner T, Zajacz Z, Heinrich C A, Petrov P and Vasilev Z  2014 - Melt and Fluid Inclusions in Hydrothermal Veins: The Magmatic to Hydrothermal Evolution of the Elatsite Porphyry Cu-Au Deposit, Bulgaria: in    Econ. Geol.   v.109 pp. 1359-1381
Strashimirov S, Petrunov R, Kanazirski M  2002 - Porphyry-Copper mineralisation in the central Srednogorie zone, Bulgaria: in    Mineralium Deposita   v37 pp 587-598
Tarkian M, Hunken U, Tokmakchieva M, Bogdanov K  2003 - Precious-metal distribution and fluid-inclusion petrography of the Elatsite porphyry copper deposit, Bulgaria: in    Mineralium Deposita   v38 pp 261-281
von Quadt A , Moritz R, Peytcheva I and Heinrich C A  2005 - Geochronology and geodynamics of Late Cretaceous magmatism and Cu-Au mineralization in the Panagyurishte region of the Apuseni-Banat-Timok-Srednogorie belt, Bulgaria: in    Ore Geology Reviews   v27 pp 95-126
von Quadt A, Peytcheva I, Fangera L and Heinrich C  2005 - The Elatsite porphyry Cu–Au deposit, Bulgaria: in    Ore Geology Reviews   v27 pp 128-129
Zimmerman A , Stein H J, Hannah J L, Kozelj D, Bogdanov K and Berza T,  2008 - Tectonic configuration of the Apuseni-Banat-Timok-Srednogorie belt, Balkans-South Carpathians, constrained by high precision Re –Os molybdenite ages: in    Mineralium Deposita   v43 pp 1-21


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