We consider the category of smooth W (k)[GLn(F )]-modules, where F is a p-adic field and k is an algebraically closed field of characteristic ` different from p. We describe a factorization of this category into blocks, and show that the center of each such block is a reduced, `-torsion free, finite type W (k)-algebra. Moreover, the k-points of the center of a such a block are in bijection with...