Yes, it applies to them regardless of the form – as long as purity is:
• gold not less than 99.5%
• silver not less than 99.9
From the IRD website covering GST exemptions:
http://www.ird.govt.nz/gst/additional-calcs/calc-spec-supplies/calc-exempt/#gsp
Supply of fine metals
Fine metal is any form of:
- gold with a fineness of not less than 99.5%
- silver with a fineness of not less than 99.9%
- platinum with a fineness of not less than 99%.
The supply of fine metal is an exempt supply, such as any sale of fine metal by a dealer, or anyone importing fine metal.
Exception: When newly-refined fine metal is supplied by a refiner to a dealer as an investment item, it is a zero-rated supply.