The Property is contained within Colombia's Cordillera Central and is underlain by rocks of the Aleluya Complex and the Saldaña Formation that are intruded by rocks of the Ibagué Batholith.
The Aleluya Complex consists of an elongated belt, extending in a north-northeast to south-southwest direction, and of varying width, that extends from El Porvenir and passes through the Yaya and Baché rivers to the southwest. The best exposure is observed in the Palermo-Los Guásimos--El Carmen highway, especially in the section between Aleluya and La Lindosa. The majority of the active mines in the area exploit marble within this unit. The rocks that comprise the Aleluya Complex exhibit abrupt topography with steep escarpments. Karst topography is also evident. The Complex comprises marbles, metaarenites and quartzites of Proterozoica age (Fuquen and Nuñez, 1989).
The Saldaña Formation corresponds to a volcano-sedimentary sequence in which effusive igneous rocks predominate, especially pyroclastics (comprising vitreous tuffs, lithic tuffs and agglomerates), lava flows and some hypabyssal bodies. The Saldaña Formation, in the Property area, is intruded by the Ibagué Batholith with the development of slight contact metamorphism.
The age of the formation, determined by stratigraphic position, fossil content and radiometric dating, is determined as being between late Triassic and early Cretaceous. In the area of El Carmen, La Julia road, and near Las Mariposas bridge, on the San Luis-Aipecito road, is exposed a sequence of tuffs, siltstones and arenaceous tuffs, well stratified, in layers of 10 to 20 cm thickness. At the junction of the San Luis-Aipecito and San Luis-Chapinero highways, volcanic agglomerates, ochre coloured rocks with oval amygdules between 1 cm and 5 cm in diameter are observed, some filled with quartz and chalcedony.
In the area of San Luis, lavas outcrop predominantly and form a north-northeast trending belt between the Avila and El Cocal roads and on the San Luis-Aipecito highway. These lavas comprise dark grey to green coloured, moderately to highly weathered rocks that form reddish ochre coloured clays in areas where they are exposed.
To the southwest of the Property is exposed a 1 km2 area of hypabyssal rocks comprising dykes of andesitic to dacitic composition occasionally cutting the volcanic rocks of the Saldaña Formation.
The Ibagué Batholith compositionally varies between granite and tonalite. Dominant are rocks of intermediate composition that correspond to granodiorite and tonalite, with lesser amounts of quartz-diorite and quartz-monzonite. The Ibagué Batholith is cut by dykes of quartzofeldspathic, andesitic and dacitic composition. In the area of the Property, an apophysis of the Ibagué Batholith is known as the San Luis Stock.
Three fault systems or lineaments have been identified, affecting all the geologic units, with azimuths trending northwest to southeast, northeast to southwest and east to west. These are related to a period of extension, probably of Jurassic age, and are occasionally filled with dykes of varying composition. All fault systems show a relationship with regional metallogenetic events in the area.
The east-west fault system was probably reactivated during a Paleogene compressional phase, resulting in the overthrust to the east of Precambrian units (Aleluya Complex) and Jurassic units including the Saldaña Formation and Ibagué Batholith over Tertiary units and displacing previous faults. This thrusting has created the present morphology of the area. Regionally the Property is delimited by El Fraile - La Pava Fault to the west and the
Corazal Fault to the east. These have a general direction of 020° to 030°, dip to the east, and have been identified as reverse thrust faults of the Chusma Fault System (Marquínez and Velandia, 2001).
To the south is the Jerusalem Fault, which trends 300° with an apparent high dip given its straight line. To the north, an unnamed fault trending 315° limits the zone.
- La Plata-Chusma Fault limits the system to the east and trends 020° with a dip to the northwest.
- The Corazal Fault, trends 020° to 030°, dips steeply and divides regional structural styles. To the east, fracturing to the northwest predominates, and to the west fracturing to the northeast predominates.
- The San Luis Fault trends east-west with a high dip angle cutting the above faults.
Parallel to this fault, to the south, lies a normal fault, to the west of the Corazal Fault. Between these two large structures is found a large system of fractures trending between 070° to 310°.
The fracturing in the region is intense, and several systems of pre- and post-mineralization shears have been identified. The larger magnitude faults are of the normal type and appear to be a result of the extension generated as a result of the compression originated during the orogenic event. The main directions of fracturing in the region are 030°, 070° and 050° to 070°, of which the latter is apparently the most recent.
All these fault systems created the necessary spaces for the introduction and localization of mineralizing fluids. It is probable that movement in the 030° direction generated strong displacement of the veins and the creation of en echelon veins and minor reverse faulting.