I have 50 grams gold jewellery, and no other Zakaatable assets, no silver, no cash and no merchandise.

Answer

The Nisaab of gold is 87.48 grams. In other words if the only Zakaat taxable assets are gold, there being no other Zakaat assets, and if the gold is less than the gold Nisaab, then strictly speaking Zakaat is not Waajib. In terms of this reasoning and view Zakaat is not Waajib on your 50 grams gold.

However, there is a principle in the Shariah which states that the Nisaab which is best in the interests of the Fuqara (the poor) should be adopted. The silver Zakaat Nisaab is approximately R3,000. The value of your 50 grams gold is about R13,000. You should therefore pay Zakaat in terms of the aforementioned principle and obtain the considerable thawaab which you will most need on the Day of Qiyaamah.