OM Asset Management plc (NYSE: OMAM) is buying  a 60 percent stake in private equity and real estate secondary market specialist Landmark Partners.OMAM will pay about $240 million, plus potentially more based on the growth of Landmark through 2018, and the deal is expected to close by Sept. 30.

Acquiring the stake in Landmark, based in Simsbury, Connecticut, will help OMAM diversify its earnings by increasing participation in Landmark’s alternative investment strategies, says James Ritchie, chairman of OMAM, which is based in Boston.

Since its start in 1989, Landmark has completed more than 500 transactions with committed capital of $15.5 billion, acquiring interests in more than 1,900 partnerships, including re al estate, real asset, venture, mezzanine and buyout limited partnerships. The firm has a staff of 89 professionals.

Related deals include: In June, Colony Capital Inc. (NYSE: CLNY) announced its merger with NorthStar Realty Finance Corp. (NYSE: NRF) and NorthStar Asset Management Group Inc. (NYSE: NSAM) to form a $58 billion real estate investment trust with $58 billion of assets under management. In April, real estate investment trust Annaly Capital Management Inc. (NYSE: NLY), agreed to acquire Hatteras Financial Corp. (NYSE: HTS) to expand its property business. In March, Carlyle Group (Nasdaq: CG) acquired a majority stake in insurance brokers JenCap Holdings and Wholesale Trading Co-Op Insurance Services, two insurance brokers . Also in March, State Street Corp. (NYSE: STT) agreed to buy GE Asset Management to expand its private equity and real estate alternative investments business.