The Rosita D Joint Venture is a joint venture between Calibre Mining (33%) and Rosita Mining (67%).
The town of Rosita and the Rosita D Joint Venture are located in the North Caribbean Coast Autonomous Region (RACCN) of northeastern Nicaragua, approximately 275km northeast of the capital city of Managua. Rosita is one of the original towns in the historic mining triangle of Nicaragua (Triangulo Minero) which together with Siuna and Bonanza have combined to produce more than 5.0 million ounces of gold, 4.0 million ounces of silver and 305 million pounds of copper (Arengi, 2002). The Bonanza Mine located 24 kilometers to the northwest of Rosita is currently in operation.
The historic Rosita (Santa Rita) open pit copper mine (skarn) is located at the eastern end of the town of Rosita, within the Alder optioned Rosita D concession. The concession covers a 33.6 km2 area and is located in the center of Calibre’s eastern Borosi concessions. Formal mining in the Rosita area dates back to 1906 with total historic production from the mine estimated at 305 million pounds of copper, 177,737 ounces of gold, and 2,629,720 ounces of silver from 5,924,572 tons of ore. Average historic grades from the mine were calculated at 2.06% Cu, 0.925 g/t Au, and 15.08 g/t silver (Arengi, 2002). The Rosita D concession is prospective for Cu-Au skarn and porphyry Cu-Au mineralization.
Work completed by Rosita Mining includes trenching, surface sampling, geologic mapping and diamond drilling at five high priority targets (Santa Rita, R13, R13 West, Tipispan and T3). A map of the prospects is shown below. The mineralization is related to mid-Cretaceous or later multi-phase intrusions that lie in contact with the early Cretaceous calcareous host sediments. The mineralized zones show a strong northeast and northwest structural control with grades and widths being higher near structural intersections.
Results from the Rosita D exploration program include: 12.1 metres grading 5.21% Cu, 4.4 g/t Au and 44 g/t Ag (Tipispan); 29.0 metres grading 2.09% Cu, 0.19 g/t Au and 14.6 g/t Ag (T3); 30.0 metres grading 0.8% Cu, 0.31 g/t Au and 14.7 g/t Ag (Santa Rita); 8.0 metres grading 29.54 g/t Au (Santa Rita gold zone). Work has identified a series of targets including Santa Rita, R13, R13 West, Tipispan and T3 prospects with multiple mineralized zones ready for additional drill testing.
In February 2016 the Rosita D Resource Update included; Stockpile resources upgraded to Indicated category, Total gold and copper resources increased from the 2012 estimate by 24% and 8% respectively, and the maiden tailings resources estimated.
The resource estimate in stockpiles totals 70.9 million lbs. of copper and 96,660 oz. of gold and 46.2 million lbs. of copper and 50,330 oz. of gold in the Indicated and Inferred categories respectively. Indicated resources total 6.46 million tonnes grading 0.47 grams gold per tonne and 0.5% copper per tonne whilst Inferred resources total 3.44 million tonnes grading 0.46 grams gold per tonne and 0.61% copper per tonne in a series of stockpiles located near the former producing Santa Rita gold-copper open pit mine. These estimates have been based on a US$10 net smelter return (“NSR”) cut off. In addition, the Company is also reporting maiden Inferred resources of 1.96 million tonnes grading 0.56 grams gold per tonne at cut-off of 0.3 g/t gold in tailings located proximal to the Santa Rita stockpiles.
The results of these resource estimates, which are summarized in Table below, were prepared by Yungang Wu., P. Geo., an independent Qualified Person as defined by NI 43-101.
Table- Indicated and Inferred Mineral Resource Estimate, Santa Rita Stockpiles and Tailings
|ZONE||Class||AuEq g/t||Au Eq oz|
1. The quantity and grade of reported Inferred resources in this estimation are uncertain in nature and there has been insufficient exploration to define these Inferred resources as an Indicated or Measured mineral resource and it is uncertain if further exploration will result in upgrading them to an Indicated or Measured mineral resource category.
2. A gold price of US$1,200/oz, copper price of US$2.5/lb and silver price of US$16/oz were utilized in the NSR calculations of block values with process recoveries of 80% for gold, 35% for Cu (10% deducted for smelting) and 65% for silver. These values were equated against a cut-off grade of US$10 for stockpiles and 0.3 g/t Au for tailing mineral resources.
3. For the cut-off grade, mining costs were assumed at US$1.00/t, process costs at US$7.50/t and G&A costs at US$1.50/t
4. CIM definition standards were followed for the resource estimate.
5. Numbers may not add exactly due to rounding.
6. Mineral Resources that are not mineral reserves do not have economic viability
7. The quantity and grade of reported inferred resources in this estimation are uncertain in nature and there has been
insufficient exploration to define these inferred resources as an indicated or measured mineral resource and it is uncertain if further exploration will result in upgrading them to an indicated or measured mineral resource category.
The updated NI 43-101 resource estimates incorporated the results of a reverse circulation drilling campaign completed by Rosita in the fourth quarter of 2015. This work included 1,040 m of drilling in 55 vertical in-fill holes on five stockpiles located near the former Santa Rita open pit and 87 auger holes totaling 460 metres in a portion of the tailings piles, drilled in 2012 and 2013. Drilling to test the tailings only tested a small portion of the overall tailing piles which remain open for possible resource expansion
The stockpiles at the project were generated over a 17-year operating life from 1959 to 1975 at the Santa Rita open pit mine. A total of 5.4 million tonnes averaging 2.06% copper, 0.93 grams gold and 15.08 grams silver per tonne were mined. In addition to the stockpile resources, the concessions also include 15 exploration targets for gold-copper skarn and porphyry mineralization.