Cerro Crucitas

The 176 sq km Crucitas gold deposit is located in north central Costa Rica, in Alajuela province. The project lies 105 km north of the capital of San José, and 16 km north east of the small town of Coopevega.

Mining will be by the open pit method with conventional shovel and truck operations and it will be conducted on 5 metre benches, with a pre-strip totalling 440,000 cubic metres, planned to gain barren saprolite waste to be used in construction of the tailings dam. The planned strip ratio during mine production is 1.35. The company plans to use a contractor to carry out its mining operations.

Loading will be carried out by a Cat 365 backhoe excavator with a 4.4 m3 bucket capacity. Cat D400 35t capacity articulated trucks are proposed due to the expected working conditions and local climate. Three track dozers, Cat D8's, are proposed for the bench cleaning, road building, waste dump and stockpile levelling and other earthmoving operations. Additional support equipment comprises one 140H grader and one water truck. Drilling equipment will be two Atlas Copco ROC F9 rigs.

After ramping up to plant capacity, a nominal plant feed consisting of a blend of 75% saprolite and 25% hard rock, is planned to continue until the completion of the saprolite reserves. The plant capacity is designed for 7,500 ore tonnes per day (2.50 Mtpa) within saprolite, whereas within hard rock the plant capacity is 5,000 tonnes per day (1.82 Mtpa).

The gold extraction testwork confirmed that the ore is readily amenable to agitated cyanidation, at an optimum grind size of 150 microns. The low levels of silver and its limited recovery through cyanidation, the absence of deleterious elements consuming cyanide, and robbing the pregnant solution of the dissolved gold favour a treatment scheme with a CIP process.

A plant capable of processing 5,000 t/d of competent rock was selected for the basis of the design criteria. A mineral sizer will be used for initial crushing with the predominantly saprolite ore. The grinding circuit incorporates a SAG mill and a ball mill in series. Any saprolite mixture with the competent ore allows for an increase in the actual throughput capability. The leach and CIP circuits are designed to handle a maximum of 7,500 t/d during periods when almost 100% saprolite is being treated.

Water will be pumped from the tailings pond to the plant process water pond. The area of the proposed tailings facility is partially covered with jungle vegetation and is characterized by a series of hills surrounding the basin.

The basic dam design incorporates a homogeneous saprolite fill section with internal chimney, finger and toe drains to intercept seepage and control pore pressures. The main dam crests will ultimately be constructed to typically elevation 80 m and will be some 18 m wide. The upstream slopes are provided with a 1 m thick blanket of waste rock for erosion protection. The downstream slopes are provided with rock fill and a robust geotextile for erosion protection.

The Coopevega road will be the main access to the Crucitas Project and the upgrading of this road is one of the responsibilities of the company set out in the environmental operating permit.