The Central America isthmus form a parallel arc system with the subduction trench of the region, where the Cocos plate is being subducted underneath of the Caribean plate. Nicaragua has been also divided into five geological terranes: The Pacific Coast (Paleozoic to Pliocene volcanic and sedimentary sequences), the Nicaragua Depression (emplacement of an ocean crust nature terrane during the late Miocene and covered by Pliocene-Pleistocene volcanic rocks), Central Nicaragua (Tertiary volcanic rocks), the Northern terrane (Paleozoic and Mesozoic rock units of continental nature); and Atlantic Coast (Miocene-Recent sedimentary and volcanic units).
The rocks in the area of study are belonging to an active continental margin environment, which has originated an intense cal-alkaline volcanic activity forming an association of intermediate to felsic volcanic rocks. Mineralization is mainly hosted into Middle to Upper Miocene andesitic volcanic sequence (Coyol Group) and younger intrusive rocks.
Mineralization is related to gold bearing pinch and swelling mesothermal-epithermal quartz veins hosted into Tertiary andesitic volcanic rocks (Somotillo sector) and gold bearing mesothermal-epithermal quartz veins and stockwork mineralization related to Tertiary volcanic and intrusive rocks (Cinco Pinos sector). Historically, in the region, gold has been mined from three deposits—Limon, Bonanza, and La Libertad. Nicaragua is the leading gold-producing country in Central America and the Caribbean Basin. Significant interesting gold and silver grades are more related to veins; but, the stockwork (disseminated gold mineralization) deposits yielded low grades in general.
The Iberominas Company mining concessions comprise two main blocks: Iberominas I and Iberominas II. Both blocks add in total about 145,000 Hectares. The Block of Iberominas I is the most explored/mined while Iberominas II block needs additional exploration.
IBEROMINAS I: Composed of four mining polygons with the corresponding mineralized/vein prospects:
a) Polygon A: La Hoya and El Chaparral.
b) Polygon B: San Diego, El Achiote, Chilamatillo, Loma Verde, El Puercal, El Nancital and Las Carolinas.
c) Polygon F: Danto, Chamuscada
d) Polygon G: Los Cocos, Las Minitas and La Chaperna.
“Iberominas I” has been the subject of detailed geological exploration activities and mining. Regional Geological mapping, detailed geological mapping, geochemistry, exploratory trenches, ground magnetometry, reverse air circulation drilling (about 5,000
The exploration carried out in the block of Iberominas I comprises mainly regional recognition/mapping, detailed geological mapping (scale 1:10,000), stream sediments geochemical survey, geophysics (ground magnetometry), trenching in the main discovered veins and drilling (about 5,000 m of reverse circulation) in the main targets. Unfortunately drill logs are not available and chip trays have not been adequately preserved.
The mining area has been approach by Iberominas Company with superficial (open pit) mining method using excavator and bulldozer. The mining works reached in the best case 20 m of depth at maximum. The mineral potential at depth is being preserved and matter of further exploration drilling and evaluation.
Based on the geological characteristics, mineralization, textures and nature of gold bearing veins it is believed that they correspond to mesothermal-epithermal vein structures with a strong structural control.
Considering the pinch and swelling behavior of veins and the fact that gold grades are very variable along vein strike, the evaluation process (calculation of resources/reserves) will not be easy.
Considering that significant gold and silver grades (during this field visit sampling, April 2012) are confined to some vein structures, it could be inferred that gold mineral potential for stockwork structures (potential open pit) is very limited. However it has to be highlighted that few samples do not show the real potential of a large area and it deserves further exploration.
The tectonism (faulting) affects the vein structures braking up the continuity of them. The structural control of the area is remarkable and needs special attention and future specialized mapping to recognize the direct relationship between the structural component and mineralization.
The size of the area (145,000 Ha) makes this property a very interesting sector for exploration and the possibility of finding new targets is really high.