Just had a quick look on bullion by post and at 62g if 9ct they will give you £938, and 18ct £1876. No doubt there are better deals out there, but that was just a quickie.
If it is foreign gold there may not be an actual hallmark, but I'd have thought on something that chunky there should be a mark of some sort somewhere. 375 would denote 9ct, and 750 18ct for instance, or even just 9ct or 18ct (or kt). Apologies if I'm teaching my grandmother to suck eggs here. Go over it with a loupe if you have one, theres a lot of links there for a mark to be hiding amongst.
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