This article extends the earlier work (Haavisto et al. 2008. Optical spectrum based measurement of flotation slurry contents. Int. J. Miner. Process. 88 (3-4), 80-88), where visible and near-infrared (VNIR) reflectance spectroscopy was used together with an X-ray fluorescence (XRF) analyzer to improve the assaying of zinc flotation concentrate. Especially the sampling interval of the assay could be drastically reduced by the presented approach. In this study, a multichannel VNIR spectrum analyzer is utilized to measure the spectrum of the seven most important slurry lines in copper and zinc flotation circuits. Recursive data-based modeling is applied to the VNIR spectrum data and XRF assays to calculate and adaptively maintain the calibration model. The accuracy of the VNIR assays is evaluated in all the lines, and the benefits of the obtained high frequency assays in detecting oscillations and sudden grade changes are demonstrated. (C) 2009 Elsevier B.V. All rights reserved.