(IDEX Online) - Kiran Gems has moved staff out of the new Surat Diamond Bourse (SDB) just months after it opened, and back to Mumbai's Bharat Diamond Bourse (BDB). It's a blow for the brand new $388m SDB - the world's largest office building - which opened last November but has so far failed to attract major tenants aside from Kiran.Kiran Gems is a privately-owned company, described as the world's largest rough diamond manufacturer.It employs 48,000 diamond workers across its eight factories, all in Surat, and buys over 5.7m carats a year.It relocated its headquarters, together with 1,200 employees to SDB as it opened, but has already moved many of them back to Mumbai.It was "was barely making Rs. 20 for every Rs. 100 they earned in Mumbai," an anonymous SDB source told The Blunt Times.Kira Gems confirmed that it had moved its operations back to Mumbai, but declined to provide further details.It is, however, understood that it will maintain a presence at SDB.Pic courtesy SDB