Summary:
According to Pearson and Speirs (2009), El Limón’s vein system is classified as a low sulphidation epithermal system.
Gold mineralization in the Limón district is structurally controlled and forms veins that occupy pre-existing fault structures and extensional openings formed during mineralization. The veins are quartz dominant with lesser and variable quantities of calcite, and minor adularia. Pyrite is the predominant sulphide, but with a content of less than one percent. Trace amounts of chalcopyrite, sphalerite, arsenopyrite, altaite, gold tellurides, and native gold are also reported to occur. Gold is present in both banded quartz and silicified breccias that form the veins. Gold is very fine grained within the quartz vein and is relatively uniformly distributed throughout the higher grade parts of the veins. Only once has visible gold been reported on the Project concession.
The productive vein systems are approximately one to two kilometres long, with vein widths from less than one metre up to 25 m. Individual mineralized shoots within the veins range from 60 m to 450 m long horizontally, and from 40 m to 290 m vertically. Strike orientations vary from north-northwest through northeast to east-west, and dips are from 40° to nearly vertical. All economic gold mineralization discovered and mined to date lies within 400 m of surface. The productive and prospective elevations within the vein systems vary across the district. Post-mineral faults locally disrupt and offset the vein.
The gold bearing veins and attendant alteration are hosted within volcanic flows, volcaniclastic strata, and possibly hypabyssal intrusions of the lowest volcanic unit. The other three gently dipping volcanic units are variously altered by the same hydrothermal fluids that deposited the gold veins, locally quartz stringers with low gold values are found in the massive porphyritic andesite flows that immediately underlie the unconformity contact with the youngest flat lying unit. The youngest volcanic unit appears to post-date gold mineralization because no veins or vein related alteration has, as yet been identified within this unit.
The most extensive areas of argillic and quartz alteration form a corridor that crosses the Project mineral concession along a roughly west to east trend, this alteration corridor is mostly located to the south of the Talavera, Limón, and Santa Pancha-Panteón vein systems and is partially capped by the young, flat lying volcaniclastic unit. Much of this alteration is part of the upper, near-paleosurface component of the low sulphidation epithermal system that formed the productive gold veins. Preliminary mapping indicates the presence of both distal and proximal alteration facies related to the epithermal system.
The identification of the proximal alteration facies, combined with the presence of auriferous quartz vein boulders and silicified, steeply inclined structures, provide exploration guides for the discovery of new gold bearing vein systems, and increase the exploration potential along this corridor.