The treatment of a hydrobiotite containing 064 per cent copper with various soluHons showed that a high percentage (up to 90 per cent) of the copper can be extracted under mild conditions (1 M BCI, 85C) or withsaline solutions (20 per cent by weight NaCI or NH4F, 400C). The latter results suggest that the copper is incorporated in the interstratified vermiculite of a vermicuHte-biotite mica and the solutions (NaCl and NH4F) which reacted with the vermiculite without attacking the biotite gave the highest extraction yields.In general, extraction yields with saline solutions increased with the temperature (between 100 and 400C) and duration (3 or 6 days) of the treatment but were not appreciably affected by the initial pH of solutions.The results of RCI treatment especially may have a bearing on the hydrometallurgical treatment of refractory copper ores where copper is tied to gangue silicates.