Skeena Sawmills is closing down for an unknown length of time as of Feb. 8, citing high operating costs, lack of a secure fibre supply and weak markets combining to make its operation uneconomical.    The announcement follows a halt to log deliveries just over a month ago so that the mill could run down the inventory of what it had in its yard.    The closure includes the next-door pellet plant subsidiary, Skeena Bioenergy, which uses residue from the mill.    More than 150 people are affected, a number ...