Industry in Kigali formed only 14 per cent of the city's GDP in 2014, focused on a small industrial zone set up in the 1970s. Challenges for the sector include the high cost of importing raw materials into a land-locked country, as well as substandard infrastructure and a lack of skilled workers. In 2011, the parliament passed a law establishing special economic zones in Rwanda, the first of which was established in 2014 on Masoro Hill in Gasabo district, close to Kigali International Airport. Companies operating within the zone benefit from good infrastructure, availability of land and transport links, as well as tax breaks. It attracted 61 businesses in its first year of operation, manufacturing products such as paper and foam mattresses. As the zone grew over subsequent years, further businesses relocated there from other parts of the capital such as the Gikondo Industrial Park. The city sits close to deposits of cassiterite, an ore used to obtain tin, as well as tungsten. Cassiterite is mined in the town of Rutongo, around north of Kigali, while tungsten is mined at Nyakabingo, a similar distance away. Much of the raw mineral is exported out of Rwanda for processing, but there are some local processing facilities. This includes the Karuruma smelter in the northern suburbs of Kigali, which was built in the 1980s and was able to produce up to of pure tin per year as of 2019.