Short answer. One-half. Article 438 of the Civil Code provides that when hidden treasure is found by chance on the property of another, the finder is entitled to one-half of the treasure. The other half belongs to the landowner. This applies only when the discovery was accidental — not the result of deliberate searching.
What the law says
when the discovery is made on the property of another, or of the State or any of its subdivisions, and by chance, one-half thereof shall be allowed to the finder.
Civil Code, Article 438 — Who Owns Hidden Treasure. Read the full provision →
The general rule and the finder's exception
Article 438 of the Civil Code starts from the position that hidden treasure belongs to the owner of the land, building, or other property on which it is found. This is the baseline. The exception — and it is a meaningful one — applies when the treasure is found on someone else's property and the discovery is by chance. In that situation, the finder receives one-half of the treasure. You were lawfully present on the land and stumbled upon the treasure accidentally; you are entitled to half.
By chance means accidental — not deliberate searching
The word 'chance' is crucial. If you were specifically searching for hidden treasure — with a metal detector, based on a tip, or after researching the history of the land — the discovery is not by chance, and the 50-50 split does not apply. The full treasure would belong to the landowner. The law rewards the lucky finder who unexpectedly uncovers something while doing ordinary work: digging for construction, farming, or performing repairs. If you were doing your normal job and the treasure appeared, the chance requirement is satisfied.
Trespassers get nothing
Article 438 explicitly bars trespassers from any share of the treasure. If you were on the property without the owner's permission or any lawful basis, you are not entitled to the finder's half regardless of how you found the treasure. The provision protects landowners from having their property invaded in the hope of finding hidden valuables. Since you were lawfully working on the property, this bar does not apply to you — but it underscores why your lawful presence is an important part of your entitlement.
When the State has an interest
Article 438 adds a further rule for items of scientific or artistic interest: the State may acquire them at their just price. If what you found is culturally or historically significant — ancient artefacts, numismatic coins, or objects of archaeological value — the government may step in and buy the treasure. In that case, the price paid by the State is divided in conformity with the same rule: half for the landowner, half for you as finder. The State's acquisition replaces the market distribution but does not change your proportionate entitlement.