The Buriticá deposits are classified as intermediate sulphidation epithermal using the terminology of Sillitoe and of Hedenquist (in Simmons et al, 2005). Corbett and Leach (1997) recognized a specific sub-class of low sulphidation epithermal deposits with high base metal contents and carbonatebearing gangue, which they named CBM association. Although such mineralization is perhaps better described as “base metal carbonate sulphide-rich”, and may occur over depth extents much larger than many low sulphidation epithermals, the Buriticá systems are referred to as the CBM association.

Mineralization at Buriticá is a porphyry related, carbonate base metal (CBM) gold vein/breccia system. High-grade precious metal mineralization in CBM systems may occur over substantial vertical intervals, to well in excess of a kilometre, from the porphyry level to below the shallow epithermal range. Compared to low sulphidation epithermal styles CBM mineralization is sulphide-rich, with abundant pyrite ± pyrrhotite + sphalerite + galena along with minor sulfosalts, chalcopyrite and quartz-carbonate gangue mineralogy. Gold in CBM systems may be free-milling or refractory. Mineralization in CBM systems typically comprises sheeted veins, stockworks and mineralogically similar breccias with some fracture-related dissemination in wallrocks.

CBM systems are widespread in circum-Pacific magmatic arcs, and include the supergiant Porgera deposits in Papua New Guinea (25 million ounces of gold, previous production plus remaining reserves and resources) and the Kelian deposits (7 million ounces (Moz) of gold produced + resources) in Indonesia. Gold mineralization at Porgera has been mined over a vertical range of 500 m but potentially economic mineralization extends over more than 1,000 m depth range.

CGI recognized the strong similarities of the Porgera and Buriticá mineralized systems and this gave CGI the confidence to drill extensively and deeply at Yaraguá and Veta Sur.

Precious metal mineralization in Yaraguá and Veta Sur appears to be related to two main depositional stages. Stage I is represented by banded base metal (iron, zinc and lead) sulphide-rich mineralization with variable amounts of quartz-carbonate gangue and bands. As well as in subparallel narrow vein arrays, Stage I mineralization also occurs in veined (dilational) breccias in places occupying substantial areas of both Yaraguá and Veta Sur, but at grades typically lower than those of the high-grade veins. CGI’s experience at the Yaraguá mine indicates that Stage I mineralization is non-refractory and recoverable by simple gravity and flotation circuits, flotation concentrates being cyanided, gold and silver then recovered by the Merrill Crowe process. Wall-rock alteration around Stage I veins comprises narrow phyllic assemblages ± K-feldspar. Stage I mineralization evidently overprints earlier potassic, phyllic and propylitic alteration.

Stage II mineralization is a texturally and chemically distinctive high-grade gold mineralization that locally cross-cuts and overprints Stage I mineralization as veins and breccia veins. Stage II mineralization is characterized by abundant free (and commonly visible) gold in siliceous and carbonate gangue, associated with arsenical pyrite and with low zinc and lead contents, relatively high arsenic and antimony but low bismuth contents. Stage II mineralization is, to date, largely known from the Veta Sur system in which this style of mineralization contributes to some very highgrade precious metal subzones, but has also been encountered in the Yaraguá system.

Three underground mining methods were selected for Buriticá; longhole open stoping (LHOS), cut & fill (C&F), and shrinkage stoping. Mining method selection was driven primarily by geomechanical rock quality, vein geometry, depth, proximity to old workings, stope margin and vein continuity. Unless geomechanical and geometry characteristics required either C&F or shrinkage, longhole mining was the preferred mining method due to higher productivities and lower mining costs compared to either C&F or shrinkage.

The process design follows these steps: Crushing > Grinding > Gravity Concentration > Cyanide Leach > Counter-Current Decantation (CCD) > Merrill Crowe > On-site refining to doré bars.

ROM mineralized material will be trucked from the underground mines by 30 and 40-tonne rear dump haul trucks to stockpiles to be blended as needed prior to feeding primary crusher. The ROM mineral stockpile will be designed to contain 14,000 t. A front-end loader (FEL) will feed a stationary grizzly over the crusher dump hopper.

The covered coarse ore stockpile will have a 3,400 t live capacity and a 5,400 t total capacity. A bulldozer and/or a front-end loader will recover dead storage. There will be a concrete tunnel containing two draw points below the crushed material stockpile that will provide material to two reclaim feeders, one operating and one standby, which will discharge onto a mill feed conveyor. The mill feed conveyor will transport the crushed mineral from the stockp ........