You need to pay 3% GST (Goods and Services Tax) on gold if you are buying a gold coin or a gold biscuit. But, if you are buying gold jewellery then you need to pay 3% GST on gold and 5% GST as gold jewellery making charges additionally.
Further, it's important to understand that GST is lost at the consumer end.
For example, if you buy gold worth Rs.1000 then you have to pay Rs.30 as 3% GST on it and your total bill amount will be Rs.1030/-. But, when you sell the same gold back to the jewellery (or to anyone else for that matter) and we assume that the gold rate remains unchanged then you will get back Rs.1000 only. The 3% Good and Services Tax that you paid while purchasing gold is lost at your (consumers) end.