The Calibre Borosi Concessions are located approximately 275 kilometres northeast of the capital city of Managua and 80 kilometres west of the coastal town of Puerto Cabezas. The concessions cover 87,627 hectares (876km2 ) of the highly prolific but underexplored Mining Triangle defined by the three historic mining towns of Bonanza, Rosita, and Siuna of northeastern Nicaragua. Calibre has entered into two joint ventures; Iamgold Corp (176 km2 ) and Santa Rita Mining (33 km2 ). Calibre has maintained 100% control over a total of 665 km2 including the Santa Maria Gold-Silver Project and the Primavera Gold-Copper Porphyry Project.
The Mining Triangle of Nicaragua, one of the most prolific mining districts of Central America, has an estimated historical production of 7.9 million ounces of gold, 4 million ounces of silver and 305 million pounds of copper (Arengi, 2002). Two major historic mines operated on the Borosi concessions as recently as the early 1980s; the La Luz-Siuna gold mine (100% Calibre) and Rosita copper mine (–Joint Venture with Rosita Mining). The La Luz-Siuna mine produced approximately 2.3 million ounces of gold during its operation while the Rosita mine produced approximately 305 million pounds of copper. Both deposits were of the skarn model type. A number of smaller past producing gold deposits are located on the Borosi concessions including the La Luna, Riscos de Oro and Blag historic mines (currently under option to Iamgold). Of the three historic mining towns that make up the “Golden Triangle” only Bonanza is currently producing gold (others towns are Siuna and Rosita).
The Borosi concessions have the potential to host several major deposit types including Low Sulphidation epithermal veins (gold and silver), Skarns (gold, silver, copper, zinc, and iron), Porphyry (gold and copper) and Intrusion Related deposits (gold, silver and copper).
The underlying geology of the region consists of northeast trending sequences of interbedded limestone, calcareous mudstone, and greywacke of the early Cretaceous Todos Santos Formation. These units host most of the reported skarn mineralization. Sedimentary rocks may be locally interbedded with pre-Matagalpa andesitic tuffs and flows of Cretaceous age. Near continuous volcanism from the late Cretaceous to mid-Tertiary resulted in the emplacement of numerous felsic to intermediate stocks, plugs and dikes. Porphyry style mineralization has been confirmed in some of these intrusions (e.g. the Calibre-B2Gold Primavera Project). The associated Matagalpa andesitic to basaltic volcanics and pyroclastics are widely distributed through the region and host most of the low-sulphidation style epithermal mineralization.