The reserves of marketable chrome ore that have been prospected in Cuba up to the summer of 1918, range from 92,500 long tons to 170,000. The largest known deposits of chrome ore, or at least the largest of those visited by the engineers Burch and Burchard in the spring of 1918, are those of the Caledonia, and the Cayojuan and the Potosi claims, near the northeast coast of Oriente Province, in a region of rather difficult access. According to indications, they will probably yield 130,000 tons of ore, most of which can be brought to the present commercial grade by simple concentration.
The next largest group of chrome ore deposits is near Camaguey. They are very easy of access, but are of a lower grade than those of Oriente. They appear to contain a maximum of about 40,000 tons of ore that can be gathered by hand from the surface.
Near Holguin, Cardenas and Matanzas, are small stocks of ore ready for shipment, perhaps 1,000 tons. The most productive chrome mine operating in the fall of 1918 seemed to be that of the “Britannia Company,” located about twelve miles southwest of Cardenas and about 80 miles from Havana. Two carloads a day were being shipped by rail from Coliseo to Havana, and thence by ferry to Key West and northern smelters.
The manganese ores of Cuba occur principally in sedimentary rocks such as limestone, sandstone and shale, that in places have become metamorphosed, but in the most heavily mineralized zones are associated with masses of silicious rocks, locally temed “jasper” and “byate.” In one locality the manganese and its silicious associates were found in igneous rocks, such as Latite-porphyry and Latite. The sedimentary rocks with which manganese deposits are usually associated are in some places nearly horizontal, but generally show dips ranging from a few degrees to forty-five or more. The inclined beds usually represent portions of local folds. Some faulting is shown in the vicinity of various manganese deposits and may have influenced the localization of the deposits.
Manganese ore is found in Oriente, Santa Clara and Pinar del Rio provinces, but only in Oriente has it been found in large commercial quantities. In Oriente the deposits are in three areas, one north and northeast of Santiago de Cuba, another south of Bayamo and Baire, and the third on the Caribbean coast between Torquino Peak and Portillo. The first two include the most extensive deposits on the Island. In Santa Clara ore has been found near the Caribbean coast west of Trinidad, and in Pinar del Rio Province manganese ore occurs north of the city of Pinar del Rio and farther west near Mendoza.
The deposits of the northeast coast and those south of Bayamo, distant from each other approximately 100 miles, show nevertheless an interesting concordance in altitude. They stand from 500 to 1200 feet above sea level and nearly all of them are at altitude near 600 and 700 feet, suggesting a relation between the deposition of the manganese and a certain stage in the physiographic development of the region. Most of the manganese ore deposits are above drainage level, on the slopes of hills of moderate height, the maximum relief in the immediate vicinity of the deposits seldom exceeding 500 feet.
The deposits of manganese ore examined in Cuba are rather diverse, but may be grouped into three general physical types—buried deposits, irregular masses associated with silicious rock or “jaspar,” and deposits in residual clay. The buried deposits comprise several varieties, one of the most common being of poorly consolidated beds of sandy chloritic material, cemented, with manganese oxides, that fill inequalities in the surface of hard rocks. Other bedded deposits clearly replace limestone, shale conglomerate or other rocks, and tabular masses of ore are interbedded with strata of nearly horizontal limestone. The ore consists largely of Pyrolusite, but many deposits contain Psilomelane, Manganite and Wad, or mixtures of all these materials. The richness of the deposits varies considerably. Most of the richest masses are associated with the “jaspar,” but masses that have replaced limestone are also very rich.
The deposits of manganese examined in the Santiago district comprise the Ponupo Group, the Ysobelita, Botsford, Boston, Pilar, Dolores, Laura, San Andrea, Cauto or Abundancia, Llave and Gloria Mines, together with the Caridad and Valle prospects. All of these properties except the two prospects are producing ore. The Ponupo, Ysobelita and Boston mines were opened many years ago and have produced a large quantity of ore. The Ponupo and Ysobelita are still relatively large producers, though the grade of ore is not so high as that shipped in the earlier days. The Ponupo mine is connected with the Cuba Railroad at La Maya by a branch two miles long, and a narrow gauge track from Cristo, on the Cuba Railroad, runs to the Ysobelita mine three miles distant. Extensions of this line to the Boston and Pilar mines can be made with little additional outlay. The Dolores and Laura mines are near the Guantanamo & Western Railroad, not far from Sabanilla station, and the Cauto mine is adjacent to the Cuba Railroad at Manganeso Station. The other mines are from one to eight miles from the railroad, to which the ore is hauled mainly by oxcarts. In the rainy season these roads are impassable, and even in the dry season they include many difficult places, so that the quantity of the output is much less than could be mined under different circumstances.
The ore is mined by hand, mostly from open cuts, though short drifts and tunnels have been run into lenses of ore at the Ponopu, Cauto and Laura mines, and a slope has been driven on a thin tabular mass of ore between strata of limestone, dipping about 34 degrees, at the Botsford.
High grade ore may be selected in mining the richer parts of these deposits, but most of it requires mechanical treatment, such as long washing and jigging to free it from clay, sand and other impurities. At one mine the ore is cleaned by raking over a horizontal screen in a stream of water. Log washers are in operation at some mines and under construction at others. At one time a system of washing, screening and jigging is employed. They daily production of manganese ore in March, 1918, from this district, was about 300 tons.