Chase says Joseph told him the plates were 40-60 pounds.
Willard Chase, Statement, 1833 in Eber D. Howe, Mormonism Unvailed (Painesville, OH: the author, 1833), 246
After about ten days, it having been suggested that some one had got his book, his wife went after him; he [Joseph Smith] hired a horse, and went home in the afternoon, staid long enough to drink one cup of tea, and then went for his book, found it safe, took off his frock, wrapt it round it, put it under his arm and run all the way home, a distance of about two miles. He said he should think it would weigh sixty pounds, and was sure it would weigh forty.