In continuance of the previous report dealing with the intergrowth of chalcopyrite, sphalerite, galena and pyrite found in the complex sulphide ores from Yonaihata Mine, with respect to their occurrence and natures, the results obtained from flotation experiments of these ores will be reported in the following. A system of flotation illustrated in Fig. 1 C, was chosen for this experiments after due consideration had been given to the preliminary tests and the nature and grade of the sample ores. The most serious difficulty encountered in differential flotation of complex sulphide ores lies in the separation of copper sulphide from zinc sulphide minerals. In this experiments, the stress was laid upon this. Trials with a variety of conditioning agents, collectors and frothers revealed that best results might be obtained by the use of 30 g/t of NaCN, 2.000 g/t of ZnSO_4, 3, 000 g/t of Na_2SO_3, 300 g/t of CaO, 30 g/t Aerofloat No. 25, and 100 g/t Nikko No. 134. For separation of chalcopyrite from galena, 500 g/t of K_2Cr_2O_7, 10 g/t of Aerofloat No. 25 and 50 g/t of Nikko No. 134 might be used most effectively. Table 3 shows the results in collation. For an activating flotation of sphalerite, the use of 600 g/t of CuSO_4, 50 g/t of sodium ethyl-xanthate and 60 g/t of Takasago Senpaku No. 1 is recommended and for the activating flotation of pyrite, the use of 1.5 l/t of H_2SO_4, 60 g/t of sodium ethyl-xanthate and 70 g/t of Takasago Senpaku No. 1, in view of the results given in Tables 5 and 6 respectively. These results show that they are far better in recovery of these minerals than those of past experiments and of the current operations in practice at flotation plants. Also tests on simple flotation with ethyl-xanthate as frother of low grade ores, such as 0.7 per cent copper, 1.8 per cent lead and 0.8 per cent zinc ores were conducted. The results are illustrated in Table 8. The products of the above experiments, agglomerated and polished, were subjected to observation under a metallographic microscope for further scrutiny
