About that legislative authority to mint the coin:
The story starts in 1995, when Rep. Michael Castle, then the Republican at-large representative for Delaware, took over as head of the House Financial Services subcommittee on domestic and international monetary policy. Issues of coinage were part of that subcommittee’s jurisdiction, and so Castle — who tells me that he personally has never collected coins or previously hadn’t had much interest in coin issues — started working with coin collectors and others to draft legislation on the topic.
Castle’s biggest accomplishment in the role was the 50-state quarter program, which involved issuing 50 differently designed quarters in the order the states were admitted to the Union (it isn’t a coincidence that Castle’s home state of Delaware was the first admitted). But he also drafted a bill, the Commemorative Coin Authorization and Reform Act of 1995, that included this provision:
The Secretary may mint and issue bullion and proof platinum coins in accordance with such specifications, designs, varieties, quantities, denominations, and inscriptions as the Secretary, in the Secretary’s discretion, may prescribe from time to time.
There’s a slight problem here. The law stated that the Secretary may issue “bullion and proof platinum coins,” but does not state explicitly that the bullion he issues must be platinum. This was later corrected by the United States Mint Numismatic Coin Clarification Act of 2000, written by Rep. Spencer Bachus (R-AL), who until this start of this Congress chaired the Financial Services committee. That act struck the word “bullion” and replaced it with “platinum bullion coins.”
When I told Castle — who, following a defeat by tea party activist Christine O’Donnell in the 2010 Republican Senate primary, became a partner in the lobbying division of DLA Piper — about the platinum coin solution for the debt ceiling, he was baffled. “That was never the intent of anything that I drafted or that anyone who worked with me drafted…It seems to me that whatever’s being proposed here is a stretch beyond anything we were trying to do,” he said, audibly astonished.
http://www.washingtonpost.com/blogs/wonkblog/wp/2013/01/04/michael-castle-unsuspecting-godfather-of-the-1-trillion-coin-solution/