The Bol©o Cu-Co-Zn deposit is located on the eastern coast of the Baja Peninsula, Mexico and comprises an area of approximately 90 km2. The Bol©o sub-basin is contained entirely within the Santa Rosalía basin and represents a sediment hosted, stratiform copper-cobalt-zinc deposit. Baja Mining Corporation currently holds the mining rights to the area with planned exploitation of the deposit commencing in 2009.
The overriding geological control for the area is the continental rifting that formed the Gulf of California. One of the resultants of this tectonism is that much of eastern Baja is underlain by volcanic rock. Consequently, the Bol©o Formation represents the initial rift fill sedimentary sequence in the Santa Rosalía basin and is approximately 250 to 350 meters thick. There is an initial basal sequence of limestone and gypsum followed by five separate instances of upward coarsening fan-delta cycles. Each cycle can be broadly defined as clay-siltstone-sandstone layer followed by a conglomerate followed by a mineralised layer.
The alteration in the conglomerates can be characterised in two broad patterns. As such, there are alteration trends that can be considered as diagenetic in origin, meaning during and/or as a result of the lithification process. The results of this initial alteration can be further categorised. On the one hand, widespread & pervasive hematisation with an increase in montmorillonite can be observed. On the other hand, calcite alteration can be seen in selected units that are associated with an interbedded gypsum layer. However, the former is not mutually exclusive to the latter.
Conversely, there is another alteration trend only seen specifically that can be considered hydrothermal. In this case, the rocks will have pronounced dolomite alteration combined with the possibility of additional montmorillonite. As a comparison, the tuffaceous claystone in tandem with the conglomerate can be used to define a signature of least alteration.
For more details about this thesis contact Dr. Andrew Conly