The effect of basicity on the viscosity of blast furnace slags has been discussed in the literature in terms of the ionic structure of these melts. Concerning the liquidus temperatures, it might be useful to check the phase diagram information of the key multicomponent system.
A good starting point to approach these issues might be the book by E.T.Turkdogan on physical chemistry of the iron- and steel making process, his papers in Metallurgical Transactions and the book on physical chemistry of melts in metallurgy by F.D.Richardson.