The Role of Manganese As a Controller of Gold Mineralization/Conclusions and Recommendations

Based on the information available up to this moment, a model has been presented to explain the geochemical characteristics of the ore distribution in the San José de Las Malezas gold-quartz vein deposit, in Santa Clara, Cuba.

This model describes the serpentinization of an ultramafic protrusion, which is later obducted onto the surface to form part of an ophiolitic complex. Special attention has been given to the formation and evolution of different manganese minerals during the serpentinization of the host rocks. The model helps to explain the negative correlation between gold and manganese over the serpentinites.

It has been suggested elsewhere the possibility of a partial melting process of this ultramafic body before its protrusion. This process could have provoked the formation of a gold enriched zone due to the gravitational separation of this mineral. Although the partial melting of these rocks is possible, this idea needs to be tested in the future. The existence of a gold enriched zone in the serpentinites will not only help to explain the remobilization of gold in the hydrothermal-metasomatic fluid, but also it could become a prospecting objective in the area.

After the obduction, the area was affected by hydrothermal-metasomatic fluids along the developed tectonic system. The origin of these fluids is yet to be determined, but due to the presence of H2CO3, H4SiO4, and H2S, it is possible to suggest a magmatic or magmatic-slab origin in preference to a pure slab source.

These fluids reactivated the serpentinization of the host rocks, and provoked the formation of a listwaenitic zone toward the less altered serpentinites. The model assumes that gold was leached from the serpentinites by the fluids and considers two mechanisms for its transportation. The first one is the mechanical transportation of thin scales of native gold by the fluid. This may explain the existence of a gold enrichment zone in the iron-altered serpentinites. The second mechanism is the transportation of gold as thio-complexes and its precipitation in the siliceous zone due to a decrease in pH and/or an increment of the fO2 provoked by the formation of galena, massicot or other lead minerals (chrochoite?), and the loss of temperature due to the mixing of the fluids with meteoric waters.

The same conditions of pH, fO2, and loss of temperature in the siliceous zone, provoked the precipitation of copper, lead, zinc, arsenic and silver from the fluid, and the formation of copper and lead-zinc minerals in the contact of the quartz bodies with the crushed host rocks.

Although this model can presently explain all the known characteristics of the distribution of gold and other ores in this deposit, I am not presenting it as uncontroversial model, but as a working hypothesis to formulate what needs to be tested in future studies.