Proof Quality 99.9% Pure Silver. Stunning Butterfly Reverse Design. Issued as Legal Tender of Cook Islands. Pure Gold Gilded Coin? Limited mintage of 2000. Monetary Denomination (NZD) 5. Fineness (% purity) 92.5. Minimum Gross Weight (g) 25. Maximum Diameter (mm)38.61 Maximum Thickness (mm)4.00.