Siuna Project

Calibre's 100% owned Siuna Project is located approximately 230 kilometres northeast of Managua, Nicaragua. The concession includes the past producing La Luz Mine that produced 17.1 million tonnes of ore grading 4.14 g/t Au (2.3 million oz. gold) from a garnet-epidote skarn system (Arengi, 2002). The town of Siuna is located within the concession.

There are two main prospects on the Siuna Project. The Cerro Potosi prospect in the north hosts near-surface, gold-bearing garnet-epidote skarn mineralization parallel to and in the footwall of the historically exploited ore body of the La Luz Mine. In 2008, Yamana Gold Inc. completed a drill program here that was highlighted by a 16.2 metre intercept grading 4.18 g/t gold.

The Cerro Aeropuerto prospect is located one kilometre south of Cerro Potosi . The system contains gold and base metal bearing quartz veins and replacement style mineralization. Drilling by Yamana Gold Inc. suggests that the system follows a north-trending, steeply west-dipping zone that can be traced for over 500 metres along strike and over 300 metres down-dip. Drilling highlights from 2007/2008 included an intercept of 24 metres grading 5.75 g/t gold. In 2011, Calibre used the existing drilling data to prepare an NI 43-101 compliant inferred resource estimate of 707,750 ounces of gold and 3,144,500 ounces of silver at Cerro Aeropuerto (details below).

View of Cerro Potosi and the historic La Luz Mine
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History of Gold Mining at Siuna

Gold mineralization was first discovered in the Siuna area in the late 1800's by indigenous people that reported "favourable results" from gold panning. The first organized, small-scale mining was carried out by the La Luz and Los Angeles Mining Company from 1908 -- 1928, during which time an estimated 523,000 short tons grading 0.25 oz/ton gold was produced. The property was purchased in 1936 by La Luz Mines Ltd. who operated the gold mine continuously by underground and open pit methods until 1968. Production was only halted when a hurricane permanently damaged the mine's hydroelectric plant. During this period, an estimated 17 million short tons grading 0.12 oz/ton gold was produced. In recent times, only small scale mining by open pit methods was carried out by CODEMINA from 1979 -- 1983, during which approximately 840,000 short tons grading 0.054 oz/ton gold was produced.

Due to the unplanned shut-down of mining operations at the La Luz mine in 1968, it is believed that significant underground and open pit gold resources remain. Rosario estimated in 1974 that the La Luz Mine contained and estimated that the underground portion of the deposit contains 8.2 million tons grading 0.078 oz/ton gold, for approximately 640,000 ounces of gold. Rosario's historic estimate incorporated a 0.05 oz/ton cut-off and 10% dilution. In 1997, Greenstone Resources Ltd. estimated near surface mineralization at the La Luz Mine of 720,000 tons grading 0.049 oz/ton gold, totaling approximately 35,000 ounces of gold. The resource estimates produced by Rosario and Greenstone pre-date NI 43-101 standards but are believed to be relevant as they are based on surface and underground drilling and drift sampling. However, the historic resource estimate should not be relied upon until verified. Both historic resources are open at depth and along strike.

Recent Exploration

Following the 2006 purchase of the mining and exploration concessions from RNC Gold Inc., Yamana Gold Inc. conducted a two-stage approach to developing the area. In conjunction with drill testing of several key, high-priority prospects in the Siuna district, traditional-style regional exploration was carried out in other areas to evaluate existing mineral prospects and locate new gold targets. Two of the most encouraging drill targets are the Cerro Potosi and Cerro Aeropuerto prospects, located along a 1.5 kilometre long strike length of the Potosi Fault near the historic La Luz Mine.

Located immediately east of the historic La Luz open pit, the Cerro Potosi prospect contains gold-silver-copper skarn style mineralization associated with epidote-rich zones containing hematite, pyrite, chalcopyrite, sphalerite, and native gold. Past work by Greenstone Resources Ltd. indicated good potential for additional economic mineralization in the area, proximal to the historic La Luz Mine. Work by Yamana during 2007/2008 included surface geochemical sampling and drill testing of 1,465 metres in five diamond drill holes. Numerous significant drill intercepts were returned, as noted in the highlight drill table below. Drilling was primarily designed to evaluate the possible connection of gold mineralization in the near surface at Cerro Potosi with remaining estimated historic underground mineralization. The gold-rich skarn mineralization at Cerro Potosi is open for expansion along strike and to depth.

Geology and Mineralization

La Luz Mine

In the Siuna area, the Todos Santos interbedded sedimentary-volcanic sequence forms a 12 km long, 1-2 km wide northerly-trending belt, forming a series of syncline-anticline couplets tightly folded around north-northwest trending fold axes. Locally the sequence is offset by several sets of faults.

Mineralization at the La Luz mine is hosted by a sediment-dominant sequence of the Todos Santos Formation, comprising interbedded massive limestone, thin bedded impure limestone, limy mudstone, greywacke, breccia, arkose, quartzite and conglomerate together with lesser tuffs and andesite volcanics, which are referred to as the Mine Series. These units have been altered to a prograde garnet-silica skarn assemblage, locally overprinted by a retrograde epidote±chlorite skarn. Within areas of epidote-rich skarn, smaller zones with disseminated pyrite, chalcopyrite, sphalerite and hematite host the gold-bearing zones previously mined at La Luz (Plecash, 1963).

The most important of the interbedded volcanic units at La Luz is the Hanging Wall Andesite, a massive to porphyritic andesite with local pyroclastic and tuffaceous textures, which is conformable with the Mine Series sediments and cores a tight syncline. It has been traced in mine workings for over 1100 metres strike length and 230 metres width (Arengi, 2003).

The principal zone (No. 1) mined at La Luz lies in the immediate footwall of the Hanging Wall Andesite on the east limb of the syncline, which dips to the southwest at about 65°. Plecash et al (1963) suggest that the Hanging Wall Andesite acted as an impermeable boundary which focused the mineralizing fluids within the subjacent Mine Series calcareous sediments. Other impermeable dikes and sills, in particular the K Dike serpentinite, also controlled fluid flow and the distribution of gold-bearing mineralization.

The La Luz Mine was developed initially from an open pit and then underground from seven levels to a depth of 440 metres, with reported production of 2.3 million ounces of gold. With depth, as the andesite/skarn contact flattens out towards the trough of the syncline, gold grades drop off and the base of the No. 1 zone rakes toward the northwest, parallel to the fold axis. The highest gold grades in the No. 1 zone were immediately adjacent to the Hanging Wall Andesite contact; they generally decreased with distance from it and the footwall of the No. 1zone was an assay cut-off (Plecash, 1963). The geometry of the No. 2 zone is more complicated; it lies in the footwall of the No. 1 zone is controlled by lithologies of the calcareous sediments and by orientations of the K dike and other impermeable bodies. The two zones were connected by an envelope of lower-grade skarn mineralization.

Cerro Potosi

Cerro Potosí is the small hill that lies immediately northeast of the water-filled La Luz Mine open pit. It covers the Mine Series sedimentary/volcanic package in the footwall of the previously exploited No. 1 zone. The style of mineralization is identical to that of the La Luz Mine, with prograde garnet-skarn-diopside skarn developed extensively within the Mine Series calcareous sediments and more localized epidote-rich retrograde skarn locally accompanied by sulphides. Several mineralized northwest-trending gold-bearing zones have been recognized proximal to hornblende-feldspar porphyry dikes at Cerro Potosí. The sediments consist of a package of well-laminated mudstone, calcareous mudstone, marble and lesser arenite which show varying degrees of folding and disruption. Depending on the attitude of the sediments, the dikes vary from slightly to highly discordant. The northwest trending andesite dikes are transected by north to northeast trending faults with left lateral displacement.

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Montes de Oro

Calibre's recent exploration programs have concentrated on the northern portion of the mineralized belt which extends for 10 to 40 kilometres north of the past producing La Luz mine. Calibre has delineated two main gold targets; Montes de Oro and La Virgen which are defined by strong gold-copper soil anomalies which have now been tested by trenching.

The Montes de Oro gold project was discovered by Calibre through prospecting, stream sediment sampling and a soil survey which delineated a strong coincident Gold-Silver-Copper-Lead-Zinc anomaly over a 400 metre by 650 metre area which remains open. Detailed mapping and excavation of trenches and pits has defined a variably shaped diorite body intruding porphyritic andesite as well as minor siltstone and limestone which is similar geology as found at the 2.3 million oz past producing La Luz gold mine. A strong, steeply dipping northeast oriented fault system bounds the prospect to the south and appears to have concentrated fluids resulting in extensive propylitic and skarn style alteration and the development of a 200 metre by 500 metre northeast oriented gossan zone containing areas of massive sulphides.

Montes de Oro Project - Trench Results for MTR13-009 and MTR13-019

Trench ID Trench (m) From (m) To (m) m Au (g/t) Ag  (g/t) Cu  (%) Zn  (%)
MTR13-009   0.0 26.2 26.2 12.54 15.63 0.097 2.32
26.2 0.0 17.0 17.0 17.95 20.51 0.124 2.75
  2.0 11.0 9.0 23.31 21.88 0.120 0.224
MTR13-019   2.5 22.0 19.5 3.91 7.12 0.048 0.224
22.0 4.8 21.0 16.2 4.68 6.85 0.050 0.221
  9.0 15.0 6.0 10.14 9.06 0.049 0.198

Trench MTR13-019 is located approximately 25 metres southwest of trench MTR13-009 and is an extension of the previously released Pit #11 which returned a 2.00m channel sample grading 27.18 g/t Au. Gold assays within the high grade 17.0 metre intercept in trench MTR13-009 are distributed continuously over the intercept ranging between 3.89 and 45.4 g/t Au averaging 17.95 g/t Au and the high grade gold zone remains open for further expansion.

The geology and mineralization at Monte de Oro is similar to the Cerro Aeropuerto Gold Deposit located approximately ten kilometres to the south. The structural setting at both Monte de Oro and Cerro Aeropuerto is dominated by N-S oriented faulting and mineralization with dips ranging between 72 and 90 degrees to the west.

Click Here for Montes De Oro Trench Location Plan Map

The 100% Calibre owned Cerro Aeropuerto Deposit hosts a NI 43-101 compliant Inferred resource of;

Tonnes Grade
(Au g/t)
(Ag g/t)
(Aueq g/t)
Contained Au (ounces) Contained Ag (ounces) Contained Aueq (ounces)
6,052,000 3.64 16.16 3.89 707,750 3,144,500 757,000
  1. Resource models used Inverse Distance grade estimation within a three-dimensional block model with mineralized zones defined by wireframed solids and a base cutoff grade of 0.6 g/t.
  2. Resource Estimate for Cerro Aeropuerto detailed in Technical Report titled NI 43-101 Technical Report and Resource Estimation of the Cerro Aeropuerto and La Luna Deposits, Borosi Concessions, Nicaragua by Todd McCracken, dated April 11, 2011.
  3. Numbers may not add exactly due to rounding.
  4. Gold Equivalent (AuEq) for Cerro Aeropurto was calculated using $1058/oz Au for gold and $16.75/oz Ag for silver, and metallurgical recoveries and net smelter returns are assumed to be 100%.
  5. Mineral Resources that are not mineral reserves do not have economic viability

Mr. Gregory Smith, P. Geo., president & CEO for Calibre Mining is the qualified Person as defined by NI 43-101 and has prepared and approved the technical data and information on this webpage.