Hi Jongar,
Virgin awards the different levels via Tier Points. You will earn different levels of tier points depending on destination an dclass. For your J class RTN to SA you will get 24 Tier points.
You need 10 Tier Points in 12 months to get to silver, and 70 in 12 months to get Gold, and then you need 50 Tier Pints each successfive year to keep Gold.
I'm silver and I'm impressed with the benefits I get as it partners my Platinum card welll from American Epxress as I can get in to the Clubhouses around the world regardless of class, which is one of the main adavantages of Gold. However, Gold members are allowed to take in a guest where I can't they must have a card on my Platinum account ot get access.
A J (Upper Flight) will get you anywhere between 20 and 28 points per return.
A W (Premium Ec) will get anything from 6 from 16 points per return.
a Economy will get you anything form 4 points to 8 points.
In Premium or Economy, the points awarded also depends on what you paid for your ticket, whether it was full price or discounted.
You can also get points from airline partners, but up to a maximum of 6 for First/Business return for over 6000 Miles.
Full details are in the handbook and on the back of statements.
Let me know if you have any other questions,
Rich
Enjoy your J Flight