Geology
The San Simón Project is located in the Precambrian Shield of northeastern Bolivia. It is an extension of the Central Brazil Shield and a geotectonic extension of the Amazonic Craton believed to have consolidated during the Trans-Amazonic Orogeny which ended around 1700 Ma (million years). The shield was affected by two younger orogenies, those of San Ignacio (~1300 Ma) and Sunsas (~1000 Ma). The major part of the shield area is underlain by a sequence of schists, gneisses and granulites of Lower to Middle Proterozoic age (2,500 to 1,300 Ma) with over 10,000 m thickness.
The San Simón project concessions cover a plateau that rises up to 300 m above the late Tertiary lateritic Amazonian peneplain. The plateau is made up of the Proterozoic Serranía San Simón Group of a low to high grade greenshist facies metamorphic arenaceous sequence. The group is divided into the lower El Cerrito Argillite Formation (300-350 m thick), the middle El Colorado quartzite formation (1,300-1,350 m thick) and the upper Bonanza metagreywacke formation (1,600-1,650 m thick).
The Bonanza Formation is deposited in alternating high and low energy shallow water, shallow depressions and paleotrough features in an oxygenated environment. Local fine lamina with sulphides and carbonates are deposited in stagnant water under anaerobic conditions.
Intraformational conglomerates indicate shoaling and temporary withdrawal of the water followed by desiccation and cracking of the surficial muds. Fragments within the sediments suggest an origin from a gneissic basement, volcanic successions and banded iron formation.
The paleocurrents during deposition for the group are principally from the north. Both the El Cerrito and El Colorado Formations had a northwest source of the sediments while the Bonanza Formation had a northeast source. The main metallogenic feature is late kinematic gold mineralization in the schist belt. It includes banded iron formations, shear hosted quartz +/- carbonate gold veins and sediment hosted gold.
There are numerous lode and alluvial gold occurrences within the 52.5 km2 San Simón property; however, Colombia Crest Gold has focused on two primary areas of gold mineralization: the Doña Amelia and the Paititi-Buriti zones. A major portion of the project has yet to be thoroughly explored.
Early work included drilling at Trinidad (Doña Amelia zone) and Paititi in 1996, drilling at Paititi in 1999-2000and a 197 tonne surface bulk sampling at Paititi in 1999-2000 that yielded an average grade 1.62 grams/tonne gold.
Colombia Crest Gold has most recently drilled for an underground mineable resource in the Doña Amelia zone while also pursuing new targets with open pit mine potential in the Paititi-Buriti zone.
Since 2003, Colombia Crest Gold has drilled 328 holes to a maximum depth of 760 meters into the Doña Amelia Zone, which has a 4.2 kilometre strike length. Recent sampling in the Paititi-Buriti region has produced rock-chip samples with gold grades up to 160 g/t within the 7 km long zone.
Gold Mineralization Model
Gold mineralization occurs in and around a thrust fault and is associated with quartz veins, hematite and green sericite; drilling has indicated quartz veins up to 15.9 metres thick. The first 3D drill hole Geosoft model, completed in early 2007, demonstrated that gold in the Doña Amelia Zone is located in high-grade vertical gold shoots and pockets concentrated along a the south-dipping, near-vertical, thrust fault zone. After completing the 3D Geosoft model, Colombia Crest Gold drilled 17,997 metres in 80 holes in an effort to delineate gold mineralization in the L463 gold shoot, which is one of at least eight recognized gold shoots in the Doña Amelia Zone at San Simón. One-third of these drill holes returned high-grade intercepts with over 10 grams per tonne gold.
Gold Resource Calculation
Using the compiled drill hole data from the model above, SRK completed a gold resource calculation for one gold shoot in the Doña Amelia Zone. On December 14, 2010 the Company announced that SRK Canada ("SRK") completed a National Instrument 43-101 resource estimate on the L463 Gold Shoot in the Doña Amelia Zone, San Simón Project, Bolivia. The capped Indicated Mineral Resources show 262,300 tonnes grading 5.15 grams per tonne gold and the capped Inferred Mineral Resources show 251,800 tonnes grading 5.46 grams per tonne gold classified, at a 3 grams per tonne cut-off.
In 2007, the drill program focused in the L463 Gold Shoot with infill and step-out holes at a nominal spacing of 25 metres. The increased data density enabled in-house modeling by Eaglecrest in 2008 and the preparation by SRK, of the resource estimate presented above. Based on this new resource model, SRK recommends that future exploration drill holes maintain a nominal spacing of 25-metres and should concentrate in areas where the strike or dip of the structures change abruptly as such changes may represent dilation zones favourable for gold deposition.
Mineralization Style
Fine and coarse gold, free and associated with a "mineralized envelope" around the thrust faults which includes hematite, both pervasive and disseminated after arsenopyrite, sericite and silica flooding. This alteration is now included in core logs as a guide to finding more gold. Gold is found in fractures and in sites that were previously arsenopyrite but are now hematite, thus there was an association of gold to arsenopyrite during the mineralizing event.
Similar Gold Deposits
Crixas Deposit, Brazil (Kinross Gold Corp, 1M oz gold) & Saõ Francisco Deposit, Brazil (Yamana Gold Inc., 1.4M oz gold) and Ashanti type gold deposits in the Birimian greenstone belt, Ghana (production of more than 55 M oz gold over 100 years).
