VOLCANOGENIC MASSIVE SULPHIDE (VMS) DEPOSITS IN THE LOWER CRETACEOUS LOS PASOS FORMATION, SANTA CLARA REGION, CENTRAL CUBA

In the Greater Antilles, Early Cretaceous island arc tholeiite (IAT) rocks are host to volcanogenic massive sulphide (VMS) deposits. In the Santa Clara region of central Cuba the Los Pasos Formation (IAT) is host to three past-producing VMS deposits.

The San Fernando deposit is a past producer accessed by a 173 m shaft and developed on 10 levels. The mineralization occurs as a series of lenses within an altered felsic lapilli tuff breccia capped by overlying basalt. Extensive pyrite-rich alteration zones occur within the felsic rocks, which terminate at the hanging wall contact with the overlying basalt. The deposit has been defined over a strike length of about 800 m and to a vertical depth of 175 m. Both the volcanic rocks and the mineralized lenses are cut and by a swarm of near vertical mafic dykes.

The Antonio deposit is a past open pit producer. Three stacked mineralized bodies occur in highly altered felsic rocks stratigraphically below their contact with overlying basalt. The deposit has been traced 300 m along strike, 190 m vertically and averages 11 m thick. A thin barite-rich exhalite caps the massive sulphides. A debris flow containing abundant massive sulphide clasts occurs adjacent to the pit. Three types of mineralization are recognized at Antonio; massive pyrite in the upper part of the deposit; central VMS mineralization with high Cu-Zn grades; and, the poorly explored underlying disseminated and vein type of mineralization.

The Los Cerros deposit is a small past producer accessed by open cuts, several adits and a 100 m shaft with 3 levels. The mineralization at Los Cerros occurs in an intensely altered, basaltic hyaloclastite. The deposit comprises two narrow semi-concordant zones of high grade Zn mineralization, each averaging about 1 m in thickness. All of the mineralization occurs at the same stratigraphic horizon.

The Santa Rosa prospect was accessed by 2 short adits and tested by several shallow drill holes to a vertical depth of 50 m. The mineralization occurs in silicified basalt and is associated with high contents of barite. Recent sampling has yielded high gold and silver grades (2.3 m grading 9.65 g/t Au and 600.16 g/t Ag). These high gold and silver grades in association with barite suggest a shallow water depositional environment where the hydrothermal fluids likely boiled during exhalation onto the sea floor.