Summary:
The two geologic units that are exposed within the Ocampo Project are the LVG and the UVG. These rocks are composed of andesites, rhyolite tuffs, andesite porphyries, flows and agglomerates which have been overlain by porphyritic andesites interbedded with agglomerates and capped by Oligocene tuffs. This system is part of a larger caldera that is about 60 kilometers in diameter. An age date of 28 millions of years is recorded for the upper most volcanic unit making the major part of the mineralization older than that date.
Deposit Types
Ocampo is a classic gold-silver epithermal mining district. The mineralogy and alteration present in both the the Plaza de Gallos Refugio (“PGR”) and the Northeast Ocampo project area are indicative of low sulphidation, quartz-adularia type epithermal systems.
The low sulphidation systems contain quartz veins, stockworks and quartz breccias with gold, silver, electrum, argentite and pyrite with minor and variable amounts of base metal sulphides. These minerals probably were deposited in a high level (epizonal) to near surface environment.
In the northwest portion of the Gammon Lake property, historic mines such as La Fe and other prospects are considered to be of the high sulphidation, quartz enargite type deposits. This type of system has veins, vuggy breccias, and sulphide replacements ranging from pods to massive lenses associated with high level hydrothermal systems. The mineralization in the La Fe area is hosted by rhyolite and dacite rocks. These rocks and mineralization may be stratigraphically lower than the mineralization in the PGR Trend and the Northeast area. This suggests that this type of mineralization may be found at depth under the PGR Trend and the Northeast deposits.
Mineralization
The gold-silver mineralization in the project area is structurally controlled. Structures that strike N, WNW, NW, NE and East to West (“E-W”) all host mineralization that is potentially of economic grade. While the majority of potentially economic mineralization discovered to date is hosted andesite flows and agglomerates, all rock types contain mineralization and no single rock type has been shown to be more receptive to gold and silver mineralization.
The gold-silver mineralization is seldom found in discreet fissure veins at Ocampo. The majority of host structures consist of a core of quartz breccia surrounded by varying degrees of quartz stockworks and silicification. The true thickness of the mineralization exceeds 50 m in some areas such as Plaza de Gallos, San Ramon and Refugio. An argillized halo is often present surrounding the silicified structures.
A second type of gold and silver bearing vein has recently been discovered in the northeast Ocampo Project area. Examples of this type of vein include Esperanza, Chica Rica and deeper portions of the Maria vein. Mineralization in these veins consists of semi to massive sulfides filing fractures and as disseminations in the wall rock sulfide.
The precious metal assemblage consists of fine grained electrum, acanthite and native silver. Occasionally ruby silver and cerargyrite have been noted in hand samples and core. The base metals include sphalerite, galena and chalcopyrite occur in minor varying amounts but have no economic importance. These veins do not appear to increase in concentration at further depths.
A study by MMA suggests that Copper, lead and Zinc along with gold and silver can be indicators for precious metal deposition. The same study found that depletions of Lithium, Barium, Sodium, Potassium and Titanium can also be an indication of precious metal deposition. Argillic or clay caps may be an expression of the very tops of the precious metal depositional horizons.
The gold-silver mineralization is known to occur in this area over a vertical distance of at least 750 m. This vertical distance is not known from just one deposit. It is based on the fact that the lowest productive levels at the Santa Juliana mine were at an elevation of approximately 1,400 m and the vein outcrop at the Plaza de Gallos, the highest point, is at an elevation of approximately 2,150 m.