Re-logging core samples is predominately a visual process to consider a different interpretation of the geology that may not have been considered before. Re-logging occurs almost routinely when dealing with complex structural relationships or when additional in-fill drilling has produced new or other information that may have been overlooked in earlier logging efforts.

As far as the geochemical analysis - when a core is split - half goes to the lab, is crushed, pulverized and assayed, while the remaining half is the what is available to re-log when necessary.

Hope this helps. :)