Summary:
The geology of the Mercedes area is dominated by two northwest trending arches, cut by numerous northwest trending high-angle structures, which have exposed older marine sediments and overlying interbedded volcaniclastic sediments and lithic to quartz crystal lithic tuff units.
Gold-silver mineralization on the Mercedes property is hosted within epithermal, low-sulphidation (adularia-sericite) veins, stockwork, and breccia zones. These deposits form on predominately felsic subaerial volcanic complexes in extensional and strike-slip structural regimes. Near-surface hydrothermal systems, including surface hot springs and deeper hydrothermal fluid-flow zones, are the sites of mineralization. Mineral deposition takes place as the fluids undergo cooling by fluid mixing, boiling and decompression.
The veins at Mercedes are typical of most other epithermal silver-gold vein deposits in Mexico in that they are primarily hosted in the Tertiary Lower Volcanic series of andesite flows, pyroclastics and epiclastics, overlain by the Upper Volcanic series of rhyolite pyroclastics and ignimbrites.
Eleven individual deposits have been mined or are currently in production, and seven additional deposits have been identified and are currently in the early exploration or drill definition stage. These deposits occur in three main areas: the prolific Mercedes trend – a major vein that hosts the Mercedes, Aida, Barancas, Gap, Laguna and Marianas deposits; the Rey de Oro area that hosts the Rey de Oro and Klondike deposits; and the Diluvio area that hosts the Diluvio, Lupita and San Martin deposits. Additional mineralized zones proximal to existing workings have been identified and are at the exploration or drill definition stage. Mineralization at Mercedes is primarily hosted in epithermal veins and related structures.
A total of 16.5 km of gold-silver bearing epithermal low sulfidation veins have been identified within a width of some 6 km across the northwest-trending Mercedes corridor or along the margins of the andesite-filled basins, which constitute the primary exploration target on the property. Major veins, like those of the Mercedes vein system, typically trend N30º -70ºW at 60º to 90º dips northeast or southwest, following the major regional structural pattern. Other veins trend variably from east-west to north-south, or even northeast. Veins typically dip at greater than 60º but locally range as low as 25º.
Mercedes Vein System
The Mercedes gold-silver vein system, emplaced into and associated with the Mercedes fault, is the most prominent and continuous mineralized zone identified on the property, consisting of multiple-event quartz-carbonate veining, traced almost continuously on strike for nearly 4.2 km. The Mercedes fault system consists of numerous anastomosing strands within a zone over 50 m wide, where complex, multistage, anastomosing vein/breccia/stockwork zones from 1 m to 15 m wide are emplaced in extensional open areas.
The vein mineralogy (multiple quartz and carbonate stages) and morphology is quite variable along strike and down dip, where highly brecciated mineralized green-grey sugary to chalcedonic quartz is found cemented by 15 to 80% late-stage grey calcite, rhodochrosite, and/or brown-black manganese-iron carbonates.
Klondike Vein System
The Klondike vein system trending N70ºW, dipping 65º to 80º southwest and approximately 800 m long, differs from that at Mercedes in that it forms within a tectonic breccia zone rather than a fissure fill structure. Variable lenses of brecciated white to green or grey quartz and abundant manganese carbonates and calcite are found within the breccia zone.
The overall width of this ´crackle´ brecciation zone which includes stockwork veining in association with silicification and strong manganese-iron oxide content, may be up to 50 m in width. Associated but rare fissure-filling veins over 0.5 m wide can be observed. The Klondike system is developed over a maximum vertical range of approximately 300 m and ranges in width from 0.5 to over 50 m.
Diluvio-Lupita-San Martin Vein System
The Lupita vein zone outcrops on the surface for a distance of 1,800 m, ranging from 1 to 5 m in thickness. Consisting of multi-stage quartz-carbonate ± adularia veining, the vein follows a contact between the overlying andesite package and underlying felsic package and extends continuously down dip in places more than 450 m along most of the western half of the surface outcrop. Results from ongoing exploration activities towards the east identify eastwards extensions over a distance more than 2 km into the Margarita East area. This prospective area remains open towards the north and east.
Most importantly, at depths of 200 m to 300 m, Diluvio reveals an extensive zone of multistage quartzcarbonate ± adularia vein breccias, stockwork, and hydrothermal breccia up to 150 m thick that is primarily hosted in a lithic tuff-volcaniclastic sequence underlying the traditional andesite exploration target for new discoveries.
The vein mineralogy exhibits:
- Multiple stages of quartz-carbonate and adularia/cemented by quartz pulses, as well as multiple stages of rhodochrosite and siderite pulses and barren calcite;
- A complex paragenesis: hydrothermal brecciation, multiple stages pre-syn and post-mineral tectonic brecciation and faulting;
- Quartz types: cover spectrum in colors, and occurring as chalcedony, sugary, granular and/or coarsely crystalline;
- Textures: crustiform, colloform, banded, lattice etc. (during the boiling);
- Rare specks of visible gold (VG) reported, associated locally to copper carbonates, green quartz, hematite.