The Bureau of Mines, as part of its goal of helping maintain an adequate supply of minerals to meet national economic and strategic needs, is evaluating alternative technologies to treat oxidized taconites. Since process control is an essential element in the application of these process technologies, research was performed on a prototype monitoring system utilizing a californium-252 (252-cf) neutron source and a thermal neutron capture-gamma ray spectra analysis method to measure the amount of iron and percent solids in process slurries. The prototype system was used to monitor the concentrate and tailing streams in a 900-lb/hr flotation pilot plant during continuous around-the-clock tests. The iron content of the process slurries was determined by measuring the total peak areas under the capture spectrum peaks at 7.626-7.632 Mev, the associated escape peaks at 7.136-7.122 and 6.626-6.612 Mev, and the iron doublets at 4.900 and 4.998 Mev. A potential method for determining the percent solids in process slurries using the 2.22-Mev hydrogen capture peak is discussed. Results of this work demonstrate a potential method for providing process control parameters using the data from thermal neutron capture-gamma ray reactions.