A chisel of copper would have needed frequent re-sharpening.  In Ancient Egypt, chisels were issued to the workmen, and frequently weighed and examined to ensure that no valuable copper was pilfered.  Sometimes valuable tools were buried in pits as Foundation Deposits at a temple, but the excavation reports written by H.R. Hall in 1912 suggest that somehow tools, baskets, and even remains of the workers' lunches from the time of Ramesses II's restorations were simply 'left' on the site, "lost, or perhaps thrown away."