Forgery. Probable core of plated denarius. Alternatively it could be a smaller denomination struck in bronze.
Die-axis: 6 o’clockWeight: 3.09 grammes
IMP CARAVSIVS P F AVG, Laureate, draped and cuirassed bust of Carausius, right. (obverse)
[EXPE]CTATE VEN[I], Britannia (wearing mural crown) clasping hands with Carausius. (reverse)
Thank you British Museum for images and text