Reserves at Kremikovtsi were estimated a number of years ago to contain from 200 million to 250 million tons of ore. An official Russian-language survey of Bulgaria, published in 1969, cited a figure of 317 million tons for total iron ore reserves but mentioned only the Kremikovtsi deposit as one being mined. In a review of the country's natural resources, published in a Bulgarian technical journal in mid-1970, it was stated that known reserves of iron ore would last another fifty years. At the average annual rate of iron ore output in the years 1968 and 1969 the reported life span of the deposits indicates a reserve of only 133 million tons as of 1970. Whatever the actual reserves may be, domestic iron ore has had to be supplemented by imports of about 1 million tons per year from the Soviet Union and Algeria to meet the requirements of the metallurgical industry. Reserves of steel-alloying minerals are reported to be available, particularly manganese, chromium, and molybdenum. The quality of the manganese ores, however, is low, and reserves of chromium are insufficient for the needs of the economy. Output data are available only for manganese ore. Production of this mineral declined by about 60 percent in the 1957-70 period, which suggests the depletion of known reserves. The metal content of the manganese ore mined in 1970 amounted to 10,300 tons. In that year the discovery of new manganese deposits in the Obrocha area was reported, the eventual exploitation of which, it was said, would not only provide for all domestic requirements but would also make it possible to export manganese for an entire century. Although small amounts of ferroalloys are also obtained as by-products of copper, lead, and zinc smelting, imports must be relied upon to cover substantial deficits. Imports of manganese ores and concentrates in 1969 and in 1970 were more than double the volume of domestic production, and imports of chromium and chromite amounted to 3,400 tons in 1969. Nickel and titanium were also imported. Steel is produced at the integrated Kremikovtsi metallurgical combine and at the smaller integrated Lenin Steel Works in Pernik. With Soviet assistance the Kremikovtsi combine is being expanded to a planned annual capacity of 2 million tons of steel and 2.2 million tons of rolled products by the end of 1975. A third coking plant was put into operation in the spring of 1971, and the production of coke is scheduled to reach 1.4 million tons in 1975, compared to an output of 837,000 tons in 1970. The steel mill at Pernik is to be modernized, also with Soviet assistance.