Yes, it is actually well know in Australian numismatic circles.
The obverse designed for the $200/2oz gold or platinum coin was accidentally paired with the $1/1oz Silver proof reverse. Struck on the silver planchet, the coin could be described as $200/1oz silver proof mule. The denomination for these coins is on the obverse thus the coin shows the value 200 DOLLARS while the reverse shows 1oz. 999 SILVER.
McDonald's 15th edition lists it at $6,000 Australian.