As reported at the beginning of last month, the deal was struck with Exploraciones del Altiplano SA de CV and is to earn a 100% right, title and interest in and to Altiplano's Buenavista claims in Durango state.
As part of the deal Altiplano will retain a 2% net smelter return royalty (NSR).
Prospero president and chief executive Tawn Albinson owns or controls, indirectly, via his consulting company Microtermometria y Asesoria Geologica Minera SA de CV, over 20% of Altiplano.
To exercise the option and earn 100%, Prospero must issue 750,000 shares to Altiplano over 48 months - 75,000 shares of which must be within five business days of approval from the TSX Venture Exchange approval.
Precious metal group Prospero aims to discover world-class projects in the major mineral belts of Mexico.
Its exploration programs are run by a small geological team based in Mexico.
Last month it said it had started drilling at the Petate project in Hidalgo state, Mexico - its most advanced project - after receiving thefinal permission.
A rig is now on site and was due to begin turning overnight on Sunday, September 17.
Prospero plans to drill 12 holes at Petate to test four targets - Apartadero SE, Apartadero Central, Tajo and Petate No. 3
It is being carried out as part of its continuing 6,950m reconnaissance drill campaign financed by strategic partner Fortuna Silver Mines Inc