Summary:
Epithermal Au and Ag mineralization at Cerro Bayo is contained in veins, stockworks, and breccias. The deposits show multiple stages of mineralization and display open-space filling and banding, typical of lowsulfidation style epithermal mineralization. Mineralogy is complex and is associated with alteration assemblages that suggest at least three types or stages of precious depositional environments.
The principal epithermal gold-silver mineralization event with local bonanza grades is hosted mainly in NNW and N-S to NNE structural trends, such as the Cerro Bayo, Cascada and Coigues Este (in the Laguna Verde sector) veins.
This event was predated by a more likely mesothermal event with silver, gold and base metal mineralization hosted in arcuate N-S to NNE veins and tectonic breccias. This style of mineralization is only known to exist in the Laguna Verde sector and is interpreted to be a result of igneous intrusions, doming, and subsequent collapse. A third mineralizing event is interpreted to coincide with the emplacement of a porphyritic stock and related apophyses at Rodados Colorados, which is characterized by a porphyry-style alteration pattern. This includes moderately extensive propylitic alteration with chlorite, epidote, disseminated cubic pyrite, and specular hematite. Structures contain gangue dominated by calcite with locally abundant oxides and relict pyrite.
Epithermal mineralization is characterized by Au and Ag associated with minor copper, lead, and zinc. Over 90 major veins have been identified to date within the property. Vein mineralogy consists of predominantly quartz with a minor, but complex, sulfide mineral suite and accessory gangue minerals. The veins pinch and swell following pre-mineral faults and fractures. Exposed strike lengths vary from 300 to 2,200 m and widths vary from 0.5 to 5.0 m, with local pods up to 7 m wide. The control of mineralization is mostly structural. The mineralizing fluids were channeled along pre-mineral faults or fracture zones that were in-filled during successive hydrothermal pulses, locally punctuated by syn-mineral fault movement. Lithology also plays a role in mineral control. Brittleness and plasticity of the host units control the width of the veins, the degree of development of sheeted zones, and variations in the dip of the veins due to refraction. Mineralized shoots typically are sub-horizontal, extending up to 1 km or more in length, with a vertical extent of as much as 200 m.