(Map) Bulgaria

BULGARIA (BG: България; RU: Болгария), the People's Republic of Bulgaria (Narodna Republika Bulgaria) is the state within the south-eastern Europe, within the eastern part of the Balkan peninsula. It borders Romania to the north, Yugoslavia to the west, Greece to the south, Turkey to the south-east. It is washed by the Black sea to the east. The area is 110.9 thousand square kilometres. The population is 8.9 million persons (1982). The capital city is Sofia. Bulgaria is divided into the 28 districts, including the Sofia city (with the rights of the district). The official language is Bulgarian. The monetary unit is lev. Bulgaria is the member of the CMEA (since the 1949).

General characteristic of the economy. The national income during the 1981 has amounted to approximately 21 billion leva; within its structure, 60% is accounted for the industry, 14% for the agriculture and forestry, and 9% for the construction. Within the gross national product during the 1939-79, the share of the industry has increased from 19 to 68% thanks to the rapid tempos of the growth of the chemical industry, electronics, mechanical engineering, and instrumental engineering. The share of the mining industry within the volume of the industrial production of the country is approximately 1.3% (1980). The generation of electricity is 37.0 billion kilowatt-hours (1981). Bulgaria participates within the "MIR" united energetical system of the socialistic countries, thus obtaining the electrical energy from the USSR through Romania. The length of the railways is 4.3 thousand kilometres (1981), of which 1.49 thousand kilometres have been electrified; the length of the automotive roads is 31.4 thousand kilometres (1977). The major sea ports are the Varna and Burgas cities.

Nature. Bulgaria is situated within the temperate climatic zone, and occupies the transitional region between the Eastern and Central Europe at the north and the Mediterranean region at the south. The main mountain chain is the Stara Planina (Balkan, Hemus). Between the Stara Planina and the Danube river, there is situated the Danubian hilly plain. From the middle part of the Stara Planina to the south, there extends itself the Sredna Gora mountain chain (Middle Mountains). There occupy the south and west of Bulgaria the Rila mountains (the highest peak within Bulgaria is Musala, 2925 metres), Pirin and Rhodope mountains. Between this massif and Sredna Gora, there is situated the region of the small mountains, basins, and lowlands, including the Sofia field (550 metres above the level of the sea). At the east, this region transitions itself into the Upper Thracian lowland, which is the drainage basin of the Maritsa river. At the south-east, there are situated the northern spurs of the Strandja mountains. With the exclusion of the large navigable Danube river, the rivers of Bulgaria are small. The climate of Bulgaria is moderate continental, at the south is with the features of the Mediterranean climate. The average temperature of January on the plains is from -2 to 2 degrees Celsius, at the mountains is down to -10 degrees Celsius; the average temperature of July on the plains is 19-25 degrees Celsius, at the mountains within certain places is less than 10 degrees Celsius. The quantity of the athmospheric precipitation is 450-600 millimetres on the plains and 850-1300 millimetres within the mountainous regions. At the mountains, there is observed the altitudinal climatic zonation. The slopes of the mountains are covered with the broadleaf deciduous forests (oak, beech, linden), and the high parts of the Rila-Rhodope massif are covered with the coniferous forests.

The view onto the Stara Planina mountains

Geological structure. The territory of Bulgaria belongs to the structure of the young Alpine-Himalayan folded region and of the Moesian craton. On the territory of the country, there are distinguished the Moesian tectonic plate, Balkanides folded system, and Rhodope median massif. The Moesian tectonic plate, which is occupying the Danube lowland, has the block structure, and is represented by the two structural complexes: the lower complex (the basement of the tectonic plate), which is formed by the pre-Paleozoic rocks, and the upper complex, which is embedded unconformably, and is formed by he Upper Paleozoic, Mesozoic, and Cenozoic depositions (the cover of the tectonic plate), to which there are confined the deposits of petroleum and gas, coal, ores of manganese, fire clays, kaolin, gypsum, and so on.

The Balkanides folded system is situated between the Moesian tectonic plate and the Rhodope median massif, is represented by the several tectonic zones, namely, the fore-Balkan, Kulian (the fragments of the Southern Carpathian mountains), Western Balkan, Eastern Balkan, Sredna Gora, Kraishtide, Sakara-Strandja. There are confined to the Western Balkan and Eastern Balkan zones the deposits with the ores of iron, copper, lead, zinc, which are embedded among the carbonatic rocks of the Triassic, and also the deposits of the mineral coal of the Upper Cretaceous age. For the Sredna Gora zone, there are characteristic the pyrite porphyritic and veinous deposits with the ores of copper, which are confined to the effusive rocks of the Upper Cretaceous. Within the Sakara-Strandja zone, among the rocks of the Archean, Triassic, and Late Jurassic age, there are embedded the deposits with the ores of iron, copper, lead, and zinc. The Rhodope median massif occupies the south-eastern part of the Balkan peninsula, and represents by itself the ancient consolidated section of the Earth's crust, which is formed mainly by the pre-Cambrian rocks. During the Paleozoic - Mesozoic, the massif has undergone the uplift, which has been replaced during the Upper Eocene by the subsidence, during which there have accumulated themselves within the depressions up to 2000 metres of sediments. At the north, the Rhodope massif terminates itself with the steep high ledge along the Maritsa deep fault. There are associated with the Rhodope median massif the lead-zinc deposits within the Madan ore region, the deposits of fluorite, and so on. There are confined to the Kraishtide zone the lead-zinc deposits, which are embedded within the rocks of the Paleozoic.

Seismicity. The territory of Bulgaria is the part of the active in the seismic sense region of the Balkan peninsula, which belongs to the structure of the Mediterranean seismic belt. There have been identified the seismically active zones: Struma (Blagoevgrad - Sandanski), Maritsa (Plovdiv - Chirpan), Sofia, Gorna Oryahovitsa (Tarnovo), Shabla (Varna), Yambol, and Rhodope mountains. Since the 1900, there have been registered within Bulgaria 12 destructive earthquakes.

Hydrogeology. The Moesian tectonic plate and fore-Balkans zone form the Lower Danubian artesian region, within which there prevail the layered karstic waters within the limestone-dolomite complex of the Malmian-Valanginian. The aquifer layers of the sedimentary rocks of the Pliocene, Eocene, Aptian, and Lower Triassic have the subordinate significance. The layers are almost horizontal, with the slight crackedness. Within the eastern part of the tectonic plate (Dobrudja), the waters within the alluvial and Sarmatian sedimentary rocks are slightly mineralized, the temperature is 14-26 degrees Celsius. Within the western part (Vidin), the waters of the Valanginian are more mineralized (mainly with the hydrogen sulfide, the temperature is 45 degrees Celsius); within the region of the mouth of the Kamchiya river, the waters contain the iodine-bromine components. There have got great fame the resorts, which are associated with the mineral waters: Narechenski Bani at the Rhodope mountains (the water is rich in radon, the temperature is 30 degrees Celsius), Gorna Banya near Sofia (the temperature is 41 degrees Celsius), Mihalkovo at the Rhodope mountains (carbonated water, the temperature is 28 degrees Celsius), and others.

(Table) The extraction of the major types of the mineral raw materials
Mineral raw materials 1939 1950 1960 1970 1980
Coal, million tonnes 2.3 5.8 17.1 31.4 31.5
   including lignites, million tonnes 0.1 1.1 5.3 22.0 24.1
Iron ores, thousand tonnes 17.3 59.4 415 2823 1886
Manganese ores (*) - - 83 100 140
Copper ores (*) - 6 27 100 113
Lead-zinc ores (*):
   lead - 34 99 100 89
   zinc - 31 101 100 77
Kaolins, thousand tonnes 14 20 252 820 1771
Facing stone, thousand cubic metres - - - 4.3 75.4
Plates of facing stone, thousand square metres - - - 30 734
(*) The extraction during the 1970 is taken as 100%.

Useful minerals. The most important useful minerals are lignites, ores of iron, lead, zinc, and copper. The fields of petroleum and gas, which are non-significant in reserves, and are confined to the carbonatic and clastic depositions of the Triassic, Jurassic, Lower Cretaceous, Paleogene, and Neogene, are situated at the north of Bulgaria within the limits of the Moesian tectonic plate and fore-Balkans. The petroleums are low-sulfur, heavy, medium, and light-weight. The gases contain small amounts of nitrogen and carbon dioxide.

Bulgaria possesses relatively small reserves of mineral coals (the Dobrudja and Balkan coal basins). Within the Dobrudja coal basin, there are available 4 coal-bearing strata of the Upper Carboniferous, which are embedded at the depth of 1300-1800 metres. Each stratum (the thickness is from 90 to 580 metres) contains 5-35 coal layers with the thickness of 0.1-12.3 metres (the average thickness is 1.5-2.0 metres). The quantity of the coal layers is 17, with the total thickness of 31.55 metres. The content of S is from 1 to 1.5%, the ash content is from 13.7 to 34.2%, the calorific value is up to 20.9 megajoules per kilogram.

The Balkan coal basin is formed by the coal-bearing very dislocated stratum of the Upper Cretaceous age, with the thickness of 80-120 metres, which is including 3-8 coal layers with the thickness of 0.2-1.5 metres. Within the Upper Cretaceous Svoge (Svoge basin) deposit of anthracite, there have been identified 15 coal layers with the thickness of 0.8-2 metres. The reserves of the brown coal are enclosed within the Pernik and Black Sea basins, and also within the Bobov Dol, Oranovo, Bistrita deposits. Within the Pernik basin, there are 4 layers of the brown coal, of the Cenozoic age, with the thickness of 0.3-3 metres, which are embedded at the depth of up to 200 metres. At the east of the basin, they connect themselves into one layer with the thickness of 16 metres. Within the Black Sea basin, the series of the contiguous layers of the Upper Eocene age is embedded at the depth of up to 350 metres. There have practical significance the 2 layers with the average thickness of 1.5 metres, which are distanced one from another for 20-30 metres. The average ash content is 28.6%.

The Bobov Dol deposit is formed by the very dislocated coal-bearing stratum of the Paleogene age, which is embedded at the depth of up to 700 metres along the axis of the syncline. The stratum contains 3-14 coal layers with the thickness of 0.8-12 metres. Their ash content is 13-52%, the calorific value is 14.6 megajoules per kilogram. The coals are gas-bearing. There hold the leading place among the combustible useful minerals the lignites of the Pliocene age mainly of the lacustrine-liman type. The humidity is up to 60%, the ash content is from 28 to 38% and more. The calorific value is up to 6.6 megajoules per kilogram. More than 90% of the reserves of lignites are concentrated within the East Maritsa, West Maritsa, Elhovo, Sophia, and Lom basins. The East Maritsa basin (with the area of 230 square kilometres) is represented by the 3 layers of lignite (the average thickness is 1.1 metres, 12 metres, 1.6 metres), which are embedded at the depth of 25-116 metres. Within the West Maritsa basin, the 2 series of the lignite layers of the Pliocene age are embedded at the depth of 100-160 metres. There have practical significance the 2 layers, namely, the upper layer (Hafuzian), and lower layer (Kiprenian), the average thickness is 2 metres. Within the Elhovo basin, the 3 layers (the average thickness is 3.2 metres) are embedded at the depth of 10-70 metres. The Sophia basin is formed by the series of the lignite layers with the average thickness of 12-40 metres, which are embedded at the depth of 400 metres; the Lom basin is formed by the 2 layers of lignite (1-11 metres) at the depth of 130 metres. The deposits of the petroleum shales, namely, Krasava, Gurkovo, Koprinka, and others, are of the lacustrine-paludal type.

The Rudozem underground mine

Within the Rila-Rhodope massif, there are known approximately 70 sources of the thermal waters, which are confined to the zones of the deep faults. Among their number, there are the hypothermal sources with the temperature of 70-100 degrees Celsius (for example, Sapareva Banya), the thermal sources with the temperature of 50-70 degrees Celsius (for example, Kostenetz) and 37-50 degrees Celsius (for example, Gorna Banya), and the subthermal sources with the temperature of 20-37 degrees Celsius (for example, Bankya).

On the territory of Bulgaria, there are distinguished the 3 main metallogenic units: North-Bulgarian, Balkan - Sredna Gora - Kraishtide, and Rhodope. The mineralization proceeded during the Baikal, Caledonia-Hercynian, Cimmerian, Alpine metallogenic epochs. The iron ores are enclosed mainly within the Kremikovtzi deposit. The ore body is of the lenticular shape, with the length of 800 metres, with the thickness of up to 267 metres. The ores are complex, and contain (%): iron (30.7), manganese (6.2), lead (0.4), barite (18.9). There may be found as impurities copper, silver, and mercury. The main ore minerals are hematite, limonite, siderite. The reserves of the ore are 215 million tonnes. There has been explored the Chiflik deposit of the iron ore with the content of iron of 23%. The deposits of the manganese ores are confined to the 3 ore zones, namely, Southern (covers the region of the Varna city), Northern (the region of Dobrudja near the Black Sea), Tyulenovo (the coast of the Black Sea). There are ore-bearing the Oligocene depositions (clays, aleurites, sandstones); the thickness of the ore-bearing horizons is 0.8-14 metres on average, the depth of embedment is up to 480 metres, the content of manganese is 10-37%. The largest deposit (northern zone), namely, Obrochishte, is represented by the layer of the carbonate-silicate ore (the average thickness of the layer is 10 metres, the content of manganese is 27.8%).

The excavation of overburden

The deposits of the copper ores are represented mainly by the interspersed and venulous mineralization of the stockwork type and by the ore veins. The oldest copper ore region, namely, Burgas, includes the Rosen, Meden-Rid, Vyrli Bryag, Zidarovo deposits. The vertical ore veins with the thickness of 0.5-2 metres are embedded within the effusive rocks of the Late Cretaceous age, and have been traced by the mine workings to the depth of 800 metres. The post-magmatic mineralization in the form of pillars occupies approximately 1/3 of the volume of the veins. The major ore minerals are: chalcopyrite, pyrite, galena, sphalerite, and others. Within the south-eastern part of Bulgaria, there have been explored the Gramatikovo and Malko Tarnovo deposits. The length of the Gramatikovo ore zone is 1500 metres, the thickness is up to 10 metres, the angle of the dip is 50 degrees. The country rocks are the chlorite schists of the Upper Jurassic (Tithonian). The deposit is of the stratiform type, metamorphosed. The major ore minerals are chalcopyrite, pyrite, sphalerite, magnetite, galena.

The Malko Tarnovo deposit is of the contact-metasomatic type. The mineralization is confined to the contact of the Jurassic limestones with granitic intrusions. The ore bodies of the lenticular and columnar shapes are embedded within the skarnous zones with the length of up to 1500 metres. The thickness of mineralization is from 2-3 metres to 15-20 metres. The main ore minerals are: magnetite, pyrite, chalcopyrite.

The deposits of the interspersed copper ores of the stockwork type are Elatsite, Medet, of the copper-pyrite ores are Chelopech, Elshitsa, Radka, of the oxidized ores are Tsar Asen.

The Elatsite mining-beneficiation combined enterprise

The Elatsite deposit is represented by the ore body of the irregular shape, with the inclination of the main axis at the angle of 50 degrees; the country rocks are granodiorites, schists, and hornfels of the Paleozoic age; the ore minerals are pyrite, chalcopyrite, bornite, molybdenite, and others.

The Medet deposit is confined to the intrusions of the quartz-monzonite-diorites and granodiorites of the Late Cretaceous age, which have breached the Paleozoic granites; the ore body is of the columnar shape; the ore minerals are chalcopyrite, pyrite, bornite, molybdenite, magnetite, sphalerite, galena, hematite, and others.

The Chelopech postmagmatic deposit is confined to the volcanogenic complex of the andesitic and agglomerate tuffs and andesites, which is overlain by the sedimentary and volcanogenic-sedimentary depositions (sandstones, tuffs, argillaceous shales); the ore minerals are pyrite, tennantite, chalcopyrite, enargite, gold, and others.

The Elshitsa and Radka deposits are associated with the magmatism of the Upper Cretaceous and Paleogene; the ore bodies are embedded among the dacites and dacitic tuffs; the ore minerals are pyrite, chalcopyrite, bornite, enargite, tennantite, sphalerite, and others. More than 80% of the reserves of lead and zinc are enclosed within the veinous deposits, mainly within the Madan ore region.

The Sedmochislenitsi deposit within the region of the Vratsa city is represented by the tabular and lenticular ore bodies, which are embedded within the limestones and dolomites; the interspersed mineralization transitions itself into the country rocks and does not have the clear boundaries; the cutoff grade content of zinc is 0.5% (or 0.5% of lead, 0.3% of copper); the minimal thickness of the ore interval is 1 metre.

The tungsten-molybdenum ore manifestations have been identified at the Rhodope mountains. The placer gold is known within the Panagyurishte, Kyustendil, and Mikhailov-Gradskij regions, where the share of the flake high-grade gold accounts for 70%. Within the ores of the lead-zinc deposits, there are always present as the accompanying components gold, silver, and sometimes antimony. The scattered elements are contained within the lead-zinc deposits of the Rhodope massif; according to the paragenetic associations, they distinguish Se, Te, Bi, and Cd within the ores, which are associated mainly with the effusive rocks, and Cd, Bi within the ores, which are associated with the silicate rocks.

The Medet open pit mine

The fluorite deposits are Slavyanka and Mihalkovo. The fluorite mineralization is confined to the faults; the bodies of the fluorite ores have the lenticular shape and the thickness of 0.25-1 metres. Perlites have been identified within the Studen Kladenets and Jebel deposits. The Goliamo Kamenyane asbestos deposit is known at the south-eastern Rhodope mountains, and is represented by the thin veins (up to 0.6 metres), which are formed mainly by the tremolite and anthophyllite asbestos. The ore zone extends for 600 metres. The magnesial anthophyllite asbestos has the longitudinally-fibrous structure. The Gluhar agate deposit is situated within the Kardzhali region. There represent the industrial interest the placer agates, which are associated with the alluvial-diluvial depositions within the eastern part of the deposit. The maximal content of agates is 0.8 kilograms per cubic metre, the minimal content is 0.2 kilograms per cubic metre. Most agates are of the jewellery grade. There are known the deposit of gypsum with the reserves of 200 million tonnes within the region of the Vidin city, kaolin sands within the karsts of the limestones at the north-east of Bulgaria, quartzous feldspathic sands, which are rich in potassium, within the region of the Shumen city, bentonites and zeolites within the region of the Kardzhali city, rock salt within the region of the Provadia city, marble at the Pirin mountains (the Ilindentsi deposit). Barite is extracted along the way with iron at the Kremitskovi deposit.

History of the mastering of mineral resources. The start for the mastering of mineral resources on the territory of Bulgaria dates back to the Lower Paleolithic (700-500 thousand years ago), when flint was used for the crafting of primitive implements. The processing of flint on the large scale continued during the Upper Paleolithic, Neolithic, Copper-Stone Age, till the Early Bronze epoch (3rd millennium BC). Along with this, for the crafting of the polished tools, everywhere were used crystalline rocks. During the 7-6 millenniums BC, there has emerged and was conducted on the large scale the extraction of clays for the crafting of crockery and construction of dwellings. During the 5-4 millenniums, on the territory of Southern Bulgaria, there were being developed certain deposits of graphite, which was used for the application of the complicated ornamentation onto the crockery, which has been made of clay. During the 5th - start of the 4th millenniums BC, the territory of Bulgaria was one of the most powerful mining-metallurgical centre within the Old World. On the base of the copper and polymetallic deposits within the Northern Thrace, there has emerged very developed mining-metallurgical production.

The mechanized complex within the stope

The outstanding monument of the most ancient ore-mining extraction business during the start of the epoch of metals is the "Aybunar" mine. The archaeological findings witness, that during this same period, the local population possessed very large quantity of the gold products (the ore sources for the extraction of gold have not yet been identified). During the subsequent periods of the Bronze Age (end of the 4th - start of the 2nd millenniums BC), the volumes of the mining-metallurgical production have noticeably decreased. The new increase was observed during the 2nd half of the 2nd millennium BC, and especially since the 8-6 centuries BC, when there has started the extensive operation of the iron ore deposits, and also continued the development of the copper and lead ores. The largest centre of the mining-metallurgical production during the antique time (till the 5th century BC) has moved itself to the Strandja mountains. Here have been noted up to 600 copper ore workings (open pit mines, underground mines). The depth of certain mines has reached 110 metres. The technique of the mining craft has risen onto the higher level: there has increased the total length of the underground workings, has expanded the scheme for their placement, were used wooden fixtures, water pumping, compulsory ventilation, were headed special adits for the hauling of the ore, and so on. There is known the series of the specialized settlements of the miners and metallurgists near the mines.

The further perfecting of the mining-metallurgical production has started since the 12th-13th centuries, when there migrated into the Balkans the Saxon professional miners and metallurgists, who have practically monopolized this branch of the industry. The centre for the mining production within Bulgaria has shifted to the north-west of the country, into the region of the mountainous Balkan (the major copper and lead mines are Plakalnitsa, Sokolets, Chiprovtzi, and others). This extraction business continued not only during the time of the 1st and 2nd Bulgarian tsardoms, but also after the inclusion of Bulgaria into the structure of the Ottoman empire during the end of the 14th century. During the end of the 17th century, the mining-metallurgical production on the territory of Bulgaria goes extinct in association with the process of decay of the Ottoman empire, and with the departure of the Saxon metallurgists from this place.

By the middle of the 19th century, during the preparation for the Crimean War of the 1853-56, the Ottoman empire, for the provision itself with lead, has built the "factory" for the smelting of this metal at the Rhodope mountains. Even till now this territory is the centre for the extraction of the ores of the non-ferrous metals of one of the ore-mining administrations of the "Gorubso" combined enterprise. The extraction of the lead-zinc ore was conducted at the "Strashimir" mine. There existed also the attempts to extract mineral coal at the Stara Planina (near the Sliven city).

The mechanized extraction of petroleum

The first geological searches on the territory of Bulgaria have been conducted by the French geologist A. Bue, who during the 1840 has published within the Paris city the "European Turkey" fundamental work. One of the sections of this work under the title of the "Geological sketch of the European Turkey" has been issued later as the separate volume, and till the end of the 19th century was practically the single reference book on the geology of Bulgaria. After the liberation of Bulgaria from the Turkish yoke, on the initiative of the Russian administration, during the 1878 within Pernik, they started to extract coal for the needs of the population of the new capital city, namely, Sofia. During the 1890, there has been created within Bulgaria the governmental Geological service. During the 1902, with the help of the foreign capital, there is created the "Plakalnitsa" Joint Stock Company for the extraction of the copper and lead-zinc ores within the region of the Eliseina village. Within the smelting furnace of Eliseina, there was smelted the crude copper, and at the beneficiation plant, they obtained lead and zinc concentrates. During the 1912, there has been created the "Granitoid" Joint Stock Company for the production of the concrete products. The majority of the shares of the company belonged to the foreign owners. As the result of the competition fight, "Granitoid" becomes the main owner of the promising regions for the extraction of coal and lead-zinc ores. During the 1939, it concludes the contract with certain firms of the Nazi Germany for the joint operation of the lead-zinc deposits within the Madan region. There have been built the beneficiation plant within the Kardzhali city, and the Borieva-Kardzhali ropeway (45 kilometres). During the 1927, there has been formed the "Rodopski metal" Joint Stock Company for the extraction of the lead-zinc ores at the Rhodope mountains. During the 1947, all private property for the means of production within Bulgaria has been nationalized.

Mining industry. General characteristic. Within the structure of the mining-extracting industry of Bulgaria, there hold the major place the fuel-energy industry and the non-ferrous metallurgy, are prominent the iron ore industry, extraction of the non-metallic useful minerals, facing stone, and so on. Bulgaria imports petroleum, gas, iron ore, coke, and coal from the USSR. The dynamics for the extraction of the major types of the mineral raw materials within Bulgaria is given within the table (see on the map the placement of the mining facilities).

Within the structure of the fuel-energy industry of Bulgaria, there hold the major place lignites and brown coal, 75% of which are being developed by the opencast method. The import of the mineral coal and anthracite is approximately 6.3 million tonnes per year, and of coke is approximately 360 thousand tonnes per year. The extraction of coal within Bulgaria has started during the 1878 as the development of the 6 near-surface layers within the Pernik coal basin (near the Sofia city), on the base of which there has been organized the "Pernik" governmental mining enterprise. Before the start of the 2nd World War of the 1939-45, the maximal annual extraction of coal has been reached during the 1939. There conduct the extraction of coal the economic mining-energetical combined enterprises, which have been created during the 1975: "Maritsa-East" (the development is being performed since the 1961, 3 "Troyanovo" open pit mines), "Balkanbass" (since the 1852, 6 underground mines), "Marbass" (since the 1896, 6 underground mines), "Bobov Dol" (since the 1891, 6 underground mines, and 2 open pit mines), named after Georgi Dimitrov (since the 1878, 3 underground mines, and 3 open pit mines). Within Bulgaria, the extraction of coal is the basis of the national energy base. There is being developed by the opencast method the largest basin, namely, the Eastern Maritsa (the extraction was 19.5 million tonnes during the 1980). The excavation of coal is conducted mainly from the layer with the thickness of 17-20 metres, which is embedded at the depth of 20-100 metres. They use at the open pit mines the highly productive bucket-wheel and chain excavators. At the "Troyanovo-1" and "Troyanovo-2" open pit mines, the transportation of coal and overburden is performed by the electrical locomotives, while at the "Troyanovo-3" open pit mine, the transportation is performed by the belt conveyors. The prospects are associated with reconstruction, and with the creation of the "Troyanovo-North" (19.5 million tonnes per year) and "Troyanovo-South" (26 million tonnes per year) large open pit mines.

Coal is extracted by the underground method within the Pernik, Western Maritsa, and Balkan basins. Most of the layers, which are being developed, are embedded within the complicated mining-geological conditions, namely, non-orderly thickness, increased rock pressure, and tectonic disturbances. The mechanized extraction of coal has increased from 2.7% during the 1965 to 43.4% during the 1980; at the "Marbass" combined enterprise, the complex-mechanized extraction has amounted to 81%, and the mechanized conduct of the preparatory workings has amounted to 69%. The introduction of the mechanized extracting complexes has provided the increase for the productivity of the labour by 3-4 times throughout the place, and by 2-3 times throughout the mine. The usage of the mechanized complexes during this time amounted to 81.1% (1980), the average daily working load onto the complex amounted to approximately 400 tonnes (1980), the maximal working load was 1100 tonnes per day (at the "Marbass" combined enterprise). The increase of the scales of the underground extraction is associated with the mastering of the Dobrudja coal basin, where the significant reserves have been identified at the depth of 1300-1800 metres.

Within the Pernik, Bobov Dol, Balkan, and Svoge basins, there have been built the beneficiation plants, at which there is being beneficiated 40-45% of the coal, which is being extracted, and brown coals are also being briquetted.

The industrial extraction of petroleum has been started during the 1954, of the natural gas has been started during the 1965: there are being developed 5 petroleum and 3 gas reservoirs. The extraction of petroleum is performed using both the fountain method, and the mechanized method. They use the methods for the maintenance of pressure, and the complex of the methods for the intensification of the yield within the drilled wells. The quantity of the petroleum, which is being extracted, does not provide the needs of Bulgaria. The import of petroleum is 11.7 million tonnes per year (1977).

The need of Bulgaria for the iron ore is satisfied both at the expense of the extraction within the country, and at the expense of the import (approximately 1.7 million tonnes per year). The major volume of the extraction (1.5 million tonnes) is accounted for the "Leonid Brezhnev" mining-metallurgical combined enterprise (has been commissioned during the 1963 on the base of the "Kremikovtsi" open pit mine, beneficiation and sintering plants). The peculiarity of the open pit mine (has been built during the 1962) is the high water flooding (there are pumped out annually up to 6 million cubic metres of water). The system of development is with transportation of overburden, and with external dumps for the waste rocks; there have been created special separate dumps for the rocks of overburden with high content of lead, for barite, and substandard iron ores; the annual production of the iron ore concentrate is 700 thousand tonnes, of the barite concentrate is 90 thousand tonnes; there are being conducted the works for the achievement of the designed productive capacity of the open pit mine (5 million tonnes per year). There are being developed also the small deposits of the magnetite ores, namely, Martinovo (Mihaylovgrad), and Krumovo (Yambol). The extraction at the "Martinovo" mine is performed by the underground method, using the system with sublevel caving, and with the breaking of the ore by boreholes; the ore with the content of iron of 29% is beneficiated by the wet magnetic separation (the content of Fe within the concentrate is 59%). At the "Krumovo" mine, there is used the system of development with the filling of the goaf space. After the dry beneficiation at the magnetic separators, there is obtained from the ore with the content of Fe of 39% the concentrate with the content of Fe of 48%.

The extraction of the manganese ores is conducted on the limited scale. Before the 1970, there were being developed the layers of the oxidized ores. At the same time, there were conducted the geological-exploratory works at the Obrochishte large deposit of the carbonate-silicate ores (during the industrial tests, there has been obtained the agglomerate for the production of the ferro-manganese). The deposit has been unsealed by 2 shafts. There are conducted the experimental operational works with the excavation by the long wall stopes within the long pillars. The prospects for the increasing of the reserves of the deposit are associated with the exploration of the north-western and north-eastern flanks. The extraction of the copper ores is conducted since the 1901 within the Burgas district by the "Burgas Copper Mines" mining-beneficiation combined enterprise, which includes 6 mines and 3 coal preparation plants (the industrial centre is the Burgas city); the deposits have been unsealed by the vertical mine shafts with the depth of up to 850 metres (the deepest underground mines within Bulgaria); at the depth of up to 400 metres, there are used the systems of development with the filling of the goaf space, with the shrinkage of the ore, and with the collapse of the layers; at the greater depths, there is used the excavation of the horizontal layers, with the filling of the goaf space from the bottom up to the top. The extraction of the copper ore is performed also at the Chelopech deposit, which has been unsealed by 3 mine shafts with the depth of 650 metres, and by the field drifts at every 50 metres; the system of development is with the sublevel collapse, with the usage of the deep blasting boreholes. The copper ores are being developed by the "Medet", "Asarel", and "Elatsite" open pit mines, which have been built during the end of the 80-ies. The peculiarity of the last mine is the placement of the building for the coarse crushing near the edge of the open pit mine, from where the ore (in the form of the lumps with the sizes of up to 300 millimetres) arrives onto the belt conveyor with the length of 6700 metres within the tunnel, which has been headed within the northern slope of the Stara Planina, into the "Mirkovo" beneficiation plant. The tailings of the copper flotation are subjected to the magnetic separation for the obtainment of the iron ore concentrate. The "Rosen" beneficiation plant works with the usage of the sea water. The copper concentrate arrives into the copper smelting plant within the Pirdop city at the Sredna Gora mountains, the iron ore concentrate arrives into the "Leonid Brezhnev" metallurgical combined enterprise, the pyrite concentrate arrives into the chemical plants. The wastes of the beneficiation plants accumulate themselves within the dumps for the storage of the tailings.

The extraction of the lead-zinc ore is performed mainly by the "Gorubso" combined enterprise (GOK "Gorubso"), to the structure of which there belong 5 ore-mining administrations of the former joint Bulgarian-Soviet ore-mining society, with 4 beneficiation plants, geological-exploratory enterprise, mechanical repair plant, equipment of the ropeways, and so on. Altogether, there exist within the system of the combined enterprise 18 mines (the industrial centre is the Madan city), which develop the veinous deposits of the Madan ore region. There also undergo operation the deposits at the western Stara Planina mountains within the Vratsa district. There is promising for the maintenence of the level of extraction of the ore the Osogovo ore region at the Kraishtide mountains.

Of the non-metallic mineral raw materials within Bulgaria, they extract kaolin, quartzous sands, marble, refractory and ceramic clays, veinous quartz, feldspar, fluorite, barite, zeolite, talc-magnesite, dolomite, and salt. The total extraction is approximately 3.6 million tonnes per year, includes 30 types of the raw materials, which are delivered into the metallurgy, chemical, food, and silicate industries, are used for the production of the refractory materials, rubber, building materials, electronic means. There performs the extraction and processing of the non-metallic raw materials the Productive Consortium for the non-metallic useful minerals of the Ministry for the metallurgy and mineral resources, which includes 6 combined enterprises for the extraction and beneficiation of various useful minerals, and the enterprise for the extraction of salt from the sea water.

Of the non-metallic useful minerals, there has significance the extraction of kaolin, which is performed by the combined enterprise, which has been named after D. Blagoev (Razgrad district). The depositions, which are containing kaolin (12-21%), fill karst formations within the limestones of the Moesian tectonic plate. The extraction is conducted by the opencast method. The kaolin-containing depositions are beneficiated by the disintegration of the raw materials within the aqueous environment, and later by the three-stage separation within the hydrocyclones. The sands, which have been obtained, are separated into the fractions, and are sent to consumers (glass, porcelain, metal-casting, and faience industries). The kaolin slurry is dewatered at the filtering presses. The major consumer of kaolin is the industry of refractories, and also the faience, ceramic, paper, and other industries. There develop refractory clays the "Voshod" (the Pleven city), "Zhablyano" (the Pernik district), and "Vatia" (from the Sofia city to the east) combined enterprises. Gypsum is extracted within the Vidin district (GOK "Koshava"), and is delivered into the cement industry. The deposits of bentonite, trass, zeolite, and perlite are being developed at the eastern part of the Rhodope massif (GOK "Rodopi"). Basalt is extracted for the stone casting (the "Petrurgiya" enterprise, within the Gabrovo district), pipes, and plates. Marble is extracted since the most ancient times, within the Sakara-Strandja region, and at the Rhodope mountains. There performs the extraction of the marble blocks the "DOSOM" combined enterprise, which produces 800 thousand square metres of the plates per year. The increase of the production is associated with the development of the Ilindentsi (the "Murat" and "Erlepovets" quarries), and Petrovo new deposits. For the separation of the blocks from the massif, they use the chain and rope stone cutting machines. They produce from the marble the facing plates, white and gray mosaics, marble flour, and so on. Bulgaria exports bentonite, kaolin, perlite, talc-magnesite, quartzous sands, decorative facing plates.

Protection of the natural resources and recultivation of the lands include the maximal extraction of the reserves of the useful minerals, which have been explored, from the underground resources, and the rapid restoration of the places of the land, which have been disturbed as the result of the mining works. There are subject to recultivation the places of the land, which have been disturbed during the opencast and underground development. The protection of the underground resources has been imposed onto the mining-extracting enterprises. The example of the successful recultivation is the Pernik city (the underground coal mines and open pit coal mines are located within the limits of the city), where there are created the forest parks on the territory of 700 hectares. At the "Medet" mine, on the slopes of the dumps for the waste rock, there have been constructed terraces, and have been planted pine trees. The monitoring over the protection of the underground resources is performed by the Governmental inspectorate for the protection of the underground resources at the Committee for the protection of the environment. During the development of the new deposits, the Inspectorate monitors the coefficient of extraction for the balance reserves, and the level of the wastelessness for the adopted technology. The organization, which is extracting minerals, finds the consumers for the overburden rocks and tailings.

Mining mechanical engineering. Within the Kardzhali city, the "Komsomolets" plant produces the equipment for the beneficiation plants, namely, the "Denver" (according to the American license), and SFK-1,2 (USSR) flotation machines, thickeners, classifiers, hydrocyclones, TPV and KAVO slag and rotating machines, drilling equipment (according to the license from the "Simba Unior" firm), scraper winches. Within the Pernik city, the "Mineralmash" enterprise issues the SK-70 drilling rigs for the ore-mining industry, filtering presses for the kaolin production, and other machines. Within the Pavlikeni city (the Veliko Tarnovo district), they issue the mine carts, within the Debelets city (the Veliko Tarnovo district), they issue the lifting machines for the inclined underground mines. Within the Ruse and Giurgiu (Romania) cities, there is being constructed (1981) the joint Bulgarian-Romanian enterprise for the production of the non-standard equipment, including the machines and mechanisms for the mining industry.

Scientific institutions. In the field of geology and mining craft, there conduct the researches: Geological Institute of the Bulgarian Academy of Sciences (has been founded during the 1947 within the Sofia city); the Scientific-Research Institute for Useful Minerals within the system of the Committee for Geology; the Geophysical Institute of the Bulgarian Academy of Sciences; the Integrated Scientific-Research and Design Institute (has been founded during the 1962 within the Sofia city, the subsidiary is within the Plovdiv city) within the system of the Ministry for the Metallurgy and Mineral Resources; the Minproekt is the Mining Scientific-Research and Design-Construction Institute (has been founded during the 1956 within the Sofia city) within the system of the Ministry for the Energetical Industry; the Institute for the Mining Construction (has been founded during the 1965) within the system of the Ministry for the Energetical Industry, and others. The scientific institutions within Bulgaria maintain the comprehensive international relations, primarily with the scientific institutions within the USSR and other socialistic countries, and also within the Great Britain, France, Italy, and other countries.

Training of the cadres. Before the 1947, there were within Bulgaria 127 mining engineers, of whom 107 worked within the industry. During the 1953, there has been created the Higher Mining-Geological Institute. There are within the institute 2 faculties (mining, and geological), and 24 cathedras. The institute prepares annually approximately 300 engineers in the field of the mining craft and geology for the specialities: technology of the mining production, mining electrical mechanics, beneficiation of useful minerals, mine surveying, and others. There prepares the cadres for the mining industry the University within the Sofia city for the specialities: geology, geochemistry, geophysics and geomorphology. There prepare the mining technicians three colleges for the mining craft, and one college for the open pit transport, within the system of the Ministry for the Energetical Industry.