Medellin, Colombia, silver proof pattern 1/2 decimo, 1873, very rare, NGC Proof details / obv scratched. Restrepo-34 (p. 207). Bright and flashy with luster, lightly toned at rims, the obverse scratches light but evident, otherwise comparable to the Eldorado example in SP66 (misattributed to Restrepo-26, a much less rare type with just denomination on reverse) that hammered for $1,700 in 2018.
Estimate: 500 - 750 USD