NOVELTY - Control scale deposition in a geothermal power plant having at least one binary heat exchanger (34) which receives geothermal brine, comprises combining a predetermined amount of gas-rich vapor (18) that contains carbon dioxide and is derived from a geothermal fluid which has not passed through a steam turbine with the geothermal brine before the geothermal brine leaves the binary heat exchanger.    USE - The method is useful for controlling scale deposition in a geothermal power plant.    ADVANTAGE - The method: allows deposition of scale from flashed geothermal brine to be controlled at small cost, thus eliminating operational problems while decreasing the need for costly treatment chemicals, and enhancing the quality of the environment; and operates with greater thermodynamic efficiency and generates more power.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (1) a geothermal power plant (I) having at least one main stage steam separator where geothermal brine is flashed, producing flashed geothermal brine (32) and producing steam which is provided to a steam turbine, and the binary heat exchanger which receives the flashed geothermal brine from the main stage steam separators, comprising a gas separator (16) which separates gas-rich vapor containing carbon dioxide from geothermal brine, and fluid conductive means for conducting the gas-rich vapor to at least one location where the gas-rich vapor is combined with the flashed geothermal brine, and at least one of the locations is before the flashed geothermal brine leaves the binary heat exchanger; and    (2) a geothermal power plant (II) comprising the main stage steam separator, at least one binary heat exchanger which receives the flashed geothermal brine from the main stage steam separators, an auxiliary heat exchanger (44) where a predetermined portion of the steam which has not passed through a steam turbine is partially condensed producing gas-rich vapor containing carbon dioxide, and fluid conductive means for conducting the gas-rich vapor to at least one location where the gas-rich vapor is combined with the flashed geothermal brine, and at least one of the locations is before the flashed geothermal brine leaves the binary heat exchanger.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of steam-binary hybrid geothermal power plant.    Gas separator (16)    Gas-rich vapor (18)    Flashed geothermal brine (32)    Binary heat exchanger (34)    Auxiliary heat exchanger (44)