A primer for Cuban-bound geologists

It comes as no surprise that mineral explorers are showing interest in the Santa Clara region of central Cuba. The area contains some of the most prospective geology on the island and hosts several hundred mineral occurrences and deposits.

During an extensive site visit, The Northern Miner examined some of those occurrences in a 1,500-sq.-km concession recently granted to Toronto-listed junior Joutel Resources (T.N.M., Aug. 30/93).

The region, part of a mature island arc terrain, is one of the more geologically complicated areas of Cuba — or for that matter, the Caribbean. According to compilation studies by Joutel and the Cuban government, Santa Clara has the potential to host large deposits of three types: copper-gold porphyry, copper-zinc-silver-gold and epithermal gold. More than 200 occurrences have been catalogued in the Joutel concession to date. Armando Bermudez, vice-director of geology for the state-owned Central Geological and Mining Enterprise, said the most prospective areas have been mapped at 1:50,000; the less prospective areas at 1:100,000. He said a lot more work is required to evaluate deposits and structures in the region, adding that such work will require “new ideas, old experience and new technology.”

On the Joutel concession (see accompanying map, page 6), the simplified stratigraphic sequence consists of the basal, Jurassic-aged, Escambray metamorphic terrain, as well as the Manicaragua granitoid complex and an overlying Cretaceous-aged volcanogenic-sedimentary sequence. The metamorphic terrain hosts the Carlota massive sulphide deposit, which consists of 11 ore lenses and is localized along the contact between schistose rocks and small serpentinite bodies. Alteration near the orebodies consists of chloritization, silicification, dolomitization and weak sericitization and albitization.

The orebodies are 60-155 metres long, extend for 100-140 metres downdip and are 5-14 metres wide. Mineralization consists mainly of pyrite, chalcopyrite, pyrrhotite and sphalerite. The deposit, originally thought to be of the Beshi type, contains geological reserves of 5.5 million tonnes grading 0.79% copper and 0.45% zinc., with minor nickel and cobalt values.

At the Macagua copper-molybdenum deposit, mineralization occurs in a 150-metre-wide linear stockwork in quartz-monzodiorites of the Manicaragua granitoid belt. Mineralization consists of chalcopyrite and molybdenite in 1-10-cm-wide quartz veinlets.

The deposit has been delineated along 800 metres of strike and to a depth of 300 metres. The copper/moly deposit contains geological reserves of about 20 million tonnes grading 0.25% copper and 0.025% molybdenum. The Cretaceous-aged, volcano-sedimentary sequence contains the largest number of showings in the concession. Two of the more interesting occurrences in this sequence are the Antonio volcanogenic massive sulphide deposit and the Arimao copper porphyry deposit.

Antonio measures 400×340 metres with an average thickness of 11 metres. Mineralization consists of massive pyritic ore with greater then 90% sulphides, as well as copper-zinc massive sulphide ore (50-90% sulphides) and disseminated stringer material with less then 5% sulphides.

The deposit contains a geological inventory of about 2.7 million tonnes grading 1.7% copper and 4.5% zinc, with individual gold values of up to three grams per tonne. It is a priority target for Joutel, since the stringer zone has never been delineated and the system may be enriched in gold. Arimao, another priority target, contains a central mineralized zone which measures 500×200 metres and extends to a depth of at least 240 metres. Mineralization, which occurs in a quartz stockwork in altered volcanic rocks, consists mainly of chalcopyrite, pyrite and magnetite.

Work to date has delineated a potential reserve of 83 million tonnes grading 0.27% copper. Limited sampling by Joutel has returned gold values of up to three grams per tonne.

Joutel plans to start an exploration program on the concession by the end of September. Exploration Manager William McGuinty told The Northern Miner that “the first pass will be to evaluate the major deposits already outlined by the Cubans, most of which were surface finds, and then apply airborne electromagnetic techniques to define targets that are blind.” He believes several targets can probably be advanced to the drill stage within a few months.

Other companies acquiring ground in Santa Clara include Holmer Gold Mines (ASE) and Caribgold Mines.