Siuna Project
Siuna Project
Calibre's 100% owned Siuna concession 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 concession. 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 historic 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).
Inferred Resource at Cerro Aeropuerto
The Cerro Aeropuerto resource was calculated using data from 2,937 metres of HQ drill core from 9 holes over a 500 metre strike length. Further exploration on the Cerro Aeropuerto deposit will focus on along strike extensions (including towards the past producing La Luz Mine) as well as along parallel mineralized structures identified during the 2008 drill program, but not incorporated into this resource calculation. The Cerro Aeropuerto gold-silver deposit remains open for resource expansion along strike and to depth.
A summary of the inferred resource calculations for the Cerro Aeropuerto deposit at different cutoff grades is summarized below:
| Tonnes and Grade | Total Contained Metal | ||||||||
|---|---|---|---|---|---|---|---|---|---|
| Cutoff Grade Au Eq (g/t)1 |
Tonnes | Gold (g/t ) |
Silver (g/t ) |
Au Eq 1 (g/t) |
Gold (grams) |
Silver (grams) |
Gold (ounces) |
Silver (ounces) |
Au Eq 1 (ounces) |
| 0.2 | 6,850,000 | 3.24 | 14.69 | 3.47 | 22,228,000 | 100,599,000 | 714,640 | 3,234,350 | 765,290 |
| 0.4 | 6,219,000 | 3.55 | 15.95 | 3.80 | 22,078,000 | 99,203,000 | 709,820 | 3,189,470 | 759,780 |
| 0.6 | 6,052,000 | 3.64 | 16.16 | 3.89 | 22,013,000 | 97,805,000 | 707,750 | 3,144,500 | 757,000 |
| 0.8 | 5,656,000 | 3.86 | 15.95 | 4.11 | 21,845,000 | 90,205,000 | 702,330 | 2,900,150 | 747,750 |
| 1.0 | 5,396,000 | 4.02 | 15.93 | 4.27 | 21,676,000 | 85,980,000 | 696,910 | 2,764,320 | 740,210 |
2 Mineral resources that are not material reserves do not have economic viability.
3 Metallurgical recoveries and net smelter returns are assumed to be 100%.
4 The resource was completed by Wardrop. Several factors were considered in the definition of a resource classification including: National Instrument 43-101 requirements, Canadian Institute of Mining, Metallurgy and Petroleum guidelines, and the report author's experience with Tertiary skarn and epithermal deposits. Individual block models were established in Datamine. Drill hole spacing varies, with the majority of the drilling at 100 metres at Cerro Aeropuerto. Block size of 4x10x10 metres was selected in order to accommodate the nature of the mineralization. Sub-celling of the block models was used to allow the parent blocks to be split once in each direction to more accurately fill the volume of the wireframes, thus more accurately estimate the tonnes in the resource. Grade capping was applied where appropriate using the Parrish analysis. The interpolations of the deposits were completed using the Inverse Distance Squared (ID2) estimation method with a three pass spherical search ellipse. The global block model statistics for the ID2 model were compared to the Nearest Neighbour (NM) model. In general there is agreement between the two models and discrepancies were reflected as a result of lower drill density in some portions of the model.
A copy of the complete report as filed on SEDAR is available below:
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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. A historic resource estimate completed at the La Luz Mine by Rosario Resources Corporation in 1974 estimates 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 resource incorporated a 0.05 oz/ton cut-off and 10% dilution. In 1997, Greenstone Resources Ltd. estimated an historic open pitable resource 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 resources defined by Rosario Resources in 1974 (640,000 ounces of gold). The gold-rich skarn mineralization at Cerro Potosi is open for expansion along strike and to depth.
| Cerro Potosi Hole ID |
From (m) |
To (m) |
Interval (m) |
Gold (g/t ) |
|---|---|---|---|---|
| CP-08-13 | 30.00 | 34.00 | 4.00 | 0.93 |
| and | 56.00 | 88.0 | 32.00 | 2.50 |
| CP-08-14 | 81.00 | 85.30 | 4.30 | 1.52 |
| and | 113.00 | 120.00 | 7.00 | 1.32 |
| CP-08-15 | 39.30 | 55.50 | 16.20 | 4.18 |
| and | 62.00 | 68.50 | 6.50 | 2.46 |
| CP-08-18 | 27.00 | 30.00 | 3.00 | 0.72 |
| and | 39.00 | 54.00 | 15.00 | 1.78 |
| and | 70.45 | 76.30 | 5.85 | 0.95 |
The Cerro Aeropuerto prospect is located approximately one kilometre south of the Cerro Potosi prospect and along the strike length of the Potosi Fault. Gold and copper mineralization at Cerro Aeropuerto appears to be an extension of the same hydrothermal system encountered further north at the La Luz Mine. Interest in this prospect was sparked by anomalous surface samples and based on the results of one RC drill hole completed in 1998. Follow-up work included the collection of surface geochemical samples, the excavation of four trenches, and drilling of 3,230 metres in nine diamond drill holes. Significant drill intercepts related to structural zones containing pyrite, chalcopyrite, sphalerite, and native gold in quartz-carbonate veins were encountered. This drilling by Yamana returned numerous significant drill intercepts, as noted in the highlight drill table below. The structural zone hosting significant gold mineralization at Cerro Aeropuerto is open for expansion along strike and to depth.
| Cerro Aeropuerto Hole ID |
From (m) |
To (m) |
Interval (m) |
Gold (g/t ) |
|---|---|---|---|---|
| CA-07-01 | 194.80 | 197.80 | 3.00 | 19.72 |
| and | 242.80 | 266.80 | 24.00 | 5.75 |
| CA-07-02 | 242.00 | 244.00 | 2.00 | 25.08 |
| and | 257.50 | 259.70 | 2.20 | 16.94 |
| CA-07-03 | 303.00 | 306.00 | 3.00 | 4.16 |
| and | 316.00 | 318.00 | 2.00 | 7.34 |
| CA-08-04 | 237.00 | 240.00 | 3.00 | 2.10 |
| CA-08-08 | 263.80 | 266.40 | 2.60 | 2.01 |
| CA-08-16 | 9.00 | 13.95 | 4.95 | 2.50 |
| and | 111.00 | 116.00 | 5.00 | 7.23 |
| and | 174.70 | 177.20 | 2.50 | 6.56 |
Geology and Mineralization
La Luz Mine
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 orebodies 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 orebody (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 orebodies.
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 orebody rakes toward the northwest, parallel to the fold axis. The highest gold grades in the No. 1 orebody were immediately adjacent to the Hanging Wall Andesite contact; they generally decreased with distance from it and the footwall of the No. 1 orebody was an assay cut-off (Plecash, 1963). The geometry of the No. 2 orebody is more complicated; it lies in the footwall of the No. 1 orebody, is controlled by lithologies of the calcareous sediments and by orientations of the K dike and other impermeable bodies. The two orebodies were connected by an envelope of lower-grade skarn mineralization.
Cerro Potosi
Cerro Aeropuerto
The local geology is similar to that of La Luz and Cerro Potosí, with the Hanging Wall Andesite coring the southern extension of the same syncline as at La Luz. Mineralization is hosted within altered Mine Series sedimentary rocks and feldspar±biotite porphyry dikes. The dikes are strongly sericitized and commonly pyritic; the sedimentary rocks are variably skarned with local epidote alteration. Gold mineralization commonly occurs with coarse brown sphalerite, both in discrete quartz-sulphide veinlets and in patchy sulphide replacement of sericitized porphyry.