The Bureau of Mines conducted research on the flocculation of various minerals with insoluble cross-linked starch xanthate (isx) to determine its potential as a beneficiation technique for low- grade, highly disseminated ores and for selective desliming. Covellite, chalcocite, pyrite, pyrrhotite, chalcopyrite, bornite, sphalerite, galena, and molybdenite fines flocculate with isx. Floc formation, floc size, and settling rate are dependent on ph, with the ph dependence differing for each mineral. Quartz is not flocculated by isx. Experiments to obtain selective flocculation of sulfides from quartz were attempted. Good selectivity was only obtained for the bornite-quartz system. Postflocculation separations resulted in flocculated bornite in grades as high as 92 pct. Evidence is presented that the flocculation of many of the sulfide minerals with isx may involve covalent bonding of the xanthate group to lattice metal site(s).