EQT Corp. (NYSE:EQT) will buy Range Resources (NYSE:RRC) in an all-stock deal valued at more than $50 billion, including debt. The combined company will produce more than 9 billion cubic feet equivalent a day of Appalachian gas, and the two companies call it the largest vertically integrated natural gas producer in the United States. Range shareholders will receive 0.987 EQT shares for each share they hold, an implied $54.91 a share and a 20.6% premium to Friday’s close. That values Range’s equity at about $12.8 billion, according…