An imported Gallo-Belgic E (Ambiani) gold-plated uniface stater. Gallic War type. Van Arsdell dates the issue to circa 60 BC.
The absence of copper corrosion products around the blistered obverse plating suggest that the core is silver, as the VA reference cited below. Van Arsdell comments thus on the type:
Ancient forgery made by wrapping gold sheet around a silver core, and bonding with heat.