Cuba - Cu stockwork and bedded Pb-Zn-Ba mineralization

 

The western end of Cuba, aroung the town of Pinar del Rio, is an area that is host to dramatic magote landforms, karstic remnants standing up above the plains, but also to a series of Jurassic ore bodies (Matahambre, Castellanos, and Sta. Lucia) that combine copper stockwork with bedded lead-zinc mineralization. They may be analogs for the famous Mt Isa deposits in Australia.

 

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Host Rocks

The mineralization is hosted by the San Cayetano Formation, a Jurassic age package of clastics. A finer-grained and more organic facies at the top is referred to as the Castellanos Member. The San Cayetano is conformably overlain by carbonates of the Jagua and Guasasa Formations.

The San Cayetano Formation in the Pinar del Rio province is a deltaic sequence of sandstones and shales, 1000 m thick to as much as 3000 m thick.  The top of the formation has been dated biostratigraphically as middle Oxfordian. The bulk of the formation is dominanted by gray sandstone with subordinate interbedded gray shales, and this is the lithology that hosts the stockwork Cu ore.  The stratiform Pb-Zn-Ba ores are found at the top of the section in a distinct black shale unit, referred to as the Castellanos Member. No volcanic or intrusive igneous rocks are known from the area around the ore deposits.  After the Jurassic, folding and thrusting occurred with displacement from the south to the north. 

Inactive open pit at Sta. Luccia

 

 

 

 

 

 

 

Isotopes

Sr isotopes in the barite-only deposits of western Cuba have an average 87/86 ratio of 0.712015 (Maynard et al., 1995). Castellanos, in carbonate gangue minerals, ranges from 0.71017 to 0.71272, whereas Matahambre ranges from 0.714934 to 0.717794 (Davies, et al. 1998). These value are all more radiogenic than Late Jurassic seawater at 0.7069, Matahambre extremely so, which indicates that continent-derived clastics underlying the Jurassic section must have contributed at least some of the Sr (and hence the Ba) in the deposits.

No published S isotopic data could be found for these deposits. The suite of Sr isotopes found is most similar to modern rift-related barites (see Isotopes in Modern Barite Deposits).

Thermal History

The combination of stockwork Cu with bedded Pb-Zn-Ba makes the Cuban deposits a particularly useful model system (Valdes-Nodarse, 1998). Are these contrasting styles of mineralization part of the same system, one that operated close to the seafloor, or, as is often advocated for Mt Isa, was the Cu much later, emplaced during peak metamorphism? The thermal history of the Matahambre Cu deposit, as revealed by vitrinite reflectance measurements, indicates that the Cu stockwork is associated with considerably higher temperatures than the bedded deposits (e.g. Sta Lucia) or unmineralized shales (Armas). A late stage thermal event would have produced roughly equal values for these three closely-spaced localities, so the simplest explanation is that these ores are all products of near-sea floor hydrothermal systems (Maynard et al., 2001).

References

Davies, J.F., Prevec, S.A., Whitehead, R.E., and Jackson, S.E., 1998, Variations in REE and Sr-isotope chemistry of carbonate gangue, Castellanos Zn-Pb deposit, Cuba: Chemical Geology, v. 144, p. 99-119.

Maynard, J. B., Morton, J., Valdes-Nodarse, E. L., and Diaz-Carmona, A., 1995. Sr isotopes of bedded barites: a guide to tectonic setting with implications for Pb-Zn mineralization. Economic Geology, 90, 2058-2064.[abstract]

Maynard, J.B., Elswick, E.R., and Hower, J.C., 2001, Reflectance of dispersed vitrinite in shales hosting Pb-Zn-Cu ore deposits in western Cuba: comparison with clay crystallinity: International Journal of Coal Geology, v. 47, p. 161-170.

Valdes-Nodarse, E. L., 1998. Pb-Zn “SEDEX” deposits and their copper stockwork roots, western Cuba. Mineralium Deposita, 33, 560-567.[abstract]

 

 

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