We report on experiments we have performed using a rotating drum to investigate the core dynamics and transport properties of granular mixtures with different particle sizes and different fluid viscosities. We used six different fluid viscosities in the experiments, obtained using air and five different fluid mixtures of water and glycerin, and we used particles of three different sizes. Image processing technology was employed to analyze the core dynamics and particle tracking velocimetry was used to measure the dynamic properties. The experimental results indicate that both the fluid viscosity and the particle size significantly affect the creeping flow of slurry granular flows. For a given particle size, an increase in the fluid viscosity causes the erosion and precession of the core to increase, while all the transport properties appear to decrease. However, the effects of variations in the particle size on the core dynamics and the transport properties are more complicated. It was found that the erosion rate can be expressed as an exponential function of the Stokes number, while the precession rate is a linear function of this parameter. (C) 2019 Elsevier Ltd. All rights reserved.