The Los Pasos project (317 km2), encompasses the entire Los Pasos Formation polymetallic mineral belt which forms the base of the Cretaceous volcanic arc in Cuba. The Los Pasos concession is host to 3 past producing Cu-Zn-Au-Ag mines with remaining “in situ” resources and 16 mineralized exploration targets some of which are gold and silver rich. The concession is analogous in terms of scale and mine potential to the Abitibi belt in Canada from Val D’Or to Noranda.
The Los Pasos VMS belt correlates with identical Cretaceous volcanic arc rocks which host the Pueblo Viejo, Cerro de Maimón and other large gold and silver enriched VMS deposits in the Dominican Republic.
Millbrook has invested 3 years compiling and validating a digital data base for the project. These data include geological maps; soil (24,825); stream sediment (2,091); rock samples; ground and airborne geophysical surveys; 766 drill holes (68,441 m); core assays (5,392); and, historical mine plans. Resource modelling, estimation and a technical report for the project have been completed.
The San Fernando - Santa Rosa area encompasses the past producing San Fernando mine and the precious metal rich Santa Rosa prospect as well as 10 other defined exploration targets. At San Fernando about 200,000 tonnes of Cu-Zn mineralization were mined from 10 underground levels accessed by a 173 m shaft. Millbrook’s due diligence sampling of the mineralization averaged 6.6 g/t Au and 298 g/t Ag (5 samples). At San Fernando the VMS mineralization occurs in lenses within felsic volcanic host rocks at their contact with overlying mafic volcanic rocks.
The mineralization is open along strike and to depth below 170 m. The high precious metal contents at San Fernando and Santa Rosa combined with elevated “volatile” elements (Ba, Pb, As, Sb, Ge and In) suggest a boiling VMS systems which typically occur at water depths less than 1,900 m.
At Santa Rosa there are two short adits (<15 m) and very few drill holes. High gold and silver grades are associated with copper and zinc mineralization, abundant barite, As, Sb, Ge and In. The mineralization has only been tested at depths less than 50 m below surface and is open in all dimensions.
One drill hole intersected 2.60 m grading 3.84 % Cu, 16.08 % Zn, 8.27 g/t Au and 100.55 g/t Ag (true width undetermined). Significant Ba enrichment suggests Santa Rosa is peripheral to the central core of a VMS system, and dominated by low-T, vapour enriched hydrothermal discharge that interacted with oxidized seawater precipitating gold and silver.
An estimated 50,000 tonnes were extracted from the Antonio open pit in the late 1950s. The mineralization has been traced by drilling to a vertical depth of 190 m and remains open to depth. An under explored Cu-rich stringer zone has been identified at depth. Pb, As, and Sb contents are low and barite is present locally at Antonio. Precious metal content is low (1 g/t Au and 30 g/t Ag) and thus the development of a significant vapour phase through boiling was unlikely. The Antonio deposit is similar to classic deep water Abitibi type VMS mineralization.
The Los Cerros deposit occurs in a bimodal mafic dominated setting similar to other Cyprus type VMS deposits. 25,000 t grading 11% Zn and 3% Cu were mined in the mid-1950s from several open cuts, adits and a 100 m shaft. At Los Cerros, high grade Zn mineralization occurs in seams replacing permeable hyaloclastite beds. Ba, Pb, As and Sb contents and the precious metal grades are low (1-2 g/t Au and 30 g/t Ag).
To the southeast of Los Cerros, trenches at the Barita Revolucion occurrence have yielded widths up to 60 m grading 0.69 g/t Au. It is reasonable to speculate that Los Cerros and Barita Revolution are part of the same hydrothermal system.