Initially the mine will process 70,000 tonnes of rock per day, ramping up to 85,000 tonnes from both the open pit and the underground mine (underground mining is to be done by block caving). The yield from the first phase of mining will be ground through one semi-autogenous grinding mill (SAG mill). Expansion to new underground areas will result in an additional increase of up to 140,000 tonnes per day with a possible increase to 170,000 tonnes per day. As of 2010, the estimated cost of bringing the Oyu Tolgoi mine into production was US$4.6 billion, making it (financially) the largest project in Mongolian history; however, by 2013 costs had ballooned to $10 billion, which caused some concern for the Government of Mongolia, which borrows its 34 percent share of investment from the foreign investors with interest. The mine is said to account for more than 30% of Mongolia's GDP upon completion. In early 2010 global mining company Rio Tinto owned 22.4% of Oyu Tolgoi owner Ivanhoe Mines (now Turquoise Hill Resources), and gave both technical assistance and financial support to the project. At the time Rio Tinto had the option of increasing their stake to 46.6%. On 31 March 2010 the Government of Mongolia approved an investment agreement where they would purchase 34% of the project. In October 2010, Ivanhoe announced a new US$1 billion share offering in order to raise funds to develop this mine. Rio Tinto increased its ownership of Ivanhoe in December 2010, also assuming direct management of the design and construction of the project, however without fulfilling another aim, to achieve direct ownership of the mine. Disagreement between the Mongolian government and Rio Tinto came to a head in 2013, with the government urging Rio Tinto to settle the US$340 million tax issue and the cost overruns from the initially planned US$5.1 billion to US$7.1 billion during the initial stage of the project. In July 2013, the shares in Turquoise Hill Resources (Rio Tinto's unit that controls 66% of the mine) dropped 20% after a dispute between Tserenbat Sedvanchig, the executive director of Erdenes Oyu Tolgoi (the state-owned company that controls the other 34%), and Rio Tinto. Sedvanchig was fired in August and replaced by Davaadorj Ganbold, a former deputy minister and member of parliament.