A majority interest in Silver Medallion, the El Camino Real Derby winner, was sold Thursday to Blackrock Racing Partners, a partnership headed by oil entrepreneur Steve Marshall, according to both Marshall and Michael Ryan, who previously owned 100 percent of the colt.\r\n&ldquo;I&rsquo;ve sold a little over 50 percent,&rdquo; Ryan, a bloodstock agent based in Kentucky, said from Ocala, Fla., where he is attending a 2-year-old sale. &ldquo;The horse will remain with Steve Asmussen.&rdquo;\r\nMarshall, the managing partner of the oil firm Western Energy Capital, said his share of Silver Medallion would race as Blackrock Stables.\r\n&ldquo;It&rsquo;s myself and some buddies,&rdquo; Marshall said from Bakersfield, Calif., where he was on business. Marshall lives in Rancho Santa Fe, Calif., inland from Del Mar.\r\nKENTUCKY DERBY NEWS: Track all the 3-year-olds on the Triple Crown trail\r\nSilver Medallion has won three times in six starts. After racing four times with trainer Chad Brown in New York and Kentucky, he was moved to Asmussen, for whom he is 2 for 2. In his start prior to the El Camino Real Derby, Silver Medallion won the Eddie Logan Stakes on the turf at Santa Anita.