Stannous chloride (tin chloride) a test for gold in solution, the stannous chloride testing solution is tin dissolved in an HCl solution, this chemical reagent makes a very sesitive test for gold in solution,
A drop of solution suspected to contain gold on a filter paper (Q-tip), or in a white spot plate, will turn a violet color when a drop of the stannous chloride is added if the solution contains gold).
other metals will not produce this reaction.
Too much oxidizer (nitric in aqua regia), or (chlorine in solution) will also keep this reaction from working, as the purple color comes from the stannous chloride reducing the gold in solution to metal colloids that do not settle but reflect light to give the violet color.
Too much SMB can produce a brown reaction (false positive).
Iron can give a yellow color to solution, that can look like the yellow solution we get from having gold in solution, if in doubt if the solution is gold or iron you can use the stannous test for gold and another test for iron.
Test for Iron II and Iron III Ions, In the identification tests for the Fe2+ and Fe3+ ions use ferrocyanide, (deep blue reaction).
Sodium or potassium or ammonium thiocyanate solution) to a solution containing iron(III) ions, you get a (blood red solution) if positive for iron.
Black sand is high in iron so I would tend to believe the yellow solution is iron until a test proved differently.