NEW YORK (AP) â¿¿ Stillwater Mining Co. will replace JDA Software Group Inc. in the S&P SmallCap 600 index, Standard & Poor's said Monday. The change will take place on Dec. 13. JDA Software is being acquired by RedPrairie Corp. in a deal expected to close on or near that date. Stillwater Mining, based in Billings, Mont., produces palladium and platinum. Shares of the company rose 16 cents to close at $11.47, then added 30 cents, or 2.6 percent, to $11.77 in after-hours trading.