A topic from AEG's L5R CCG Rules forum, copied for Oracle of the Void from a copy of the forum saved in October 2015, so pages it didn't save are missing. Players' names are left out; the rules officials are named. Rulings are as they stood on these dates; later rulings, the rulebooks and the Rules Archive may differ.
Relevant Text: Platinum mine Text: Bow this card: Produce 5 Gold, or 6 Gold if paying for an attachment.
Celestial Sword of the Mantis Battle: Pay zero or more Gold: Give this Personality a Force bonus equal to the amount paid plus two, or Melee Attack with strength equal to twice the amount paid.
Does platinum Mine produce 5 or 6 gold when paying for this action?
Relevant Text: Platinum mine Text: Bow this card: Produce 5 Gold, or 6 Gold if paying for an attachment.
Celestial Sword of the Mantis Battle: Pay zero or more Gold: Give this Personality a Force bonus equal to the amount paid plus two, or Melee Attack with strength equal to twice the amount paid.
Does platinum Mine produce 5 or 6 gold when paying for this action?
You answer the question yourself. The force bump/melee attack on the Mantis Sword is paid for by paying for an action, not an attachment (in that sense, a holding that produces extra for an action will pay extra for it). Platinum Mine will only produce 5 for the action.