GEOGRAPHICAL DISTRIBUTION
The nickeliferous ore deposits of the world may be divided into two main types—the sulphide type, in which weathering has not been of prime importance, and the garnierite or lateritic type, in which weathering has altered and concentrated the nickel as well as the chromium and iron of the original rock. In addition, nickel occurs in some places with ores of precious and semi-precious metals in veins. Nickel may be recovered from such ores as a by-product, but the ores are never mined primarily for their nickel content. The brief descriptions of the known deposits, grouped according to type, which follow, have been taken from the descriptions of the world’s nickel deposits in the report of the Royal Ontario Nickel Commission. A few direct quotations from the text of the report are given.
Deposits of the Sulphide Type.
—The Sudbury district is situated in southeastern Ontario, Canada. In its broader outlines the geology of this district is relatively simple. An immense mass of nickeliferous rock was intruded as a “laccolithic sheet” or sill along an unconformable plane of contact between flat-lying sediments and an underlying complex of ancient rocks. During the intrusion and cooling, or perhaps soon thereafter, the underlying rocks of the central part of the laccolith, covering the reservoirs from which the magma came, subsided. Long periods of erosion then planed down the region until all that is left of the sill occupies a synclinal basin nearly 40 miles long and 10 to 15 miles wide. All of the rocks involved are of pre-Cambrian age.
The laccolithic sheet is approximately 10,000 feet thick. It differentiated on cooling into two kinds of rock—micropegmatite, a rock of the granite group, now forming the upper part of the sill, and norite, a gabbro rock, the lower part. The gradation between these two rocks is rather abrupt. At the bottom of the sill, in some places lying between the norite and the underlying rock and at other places entirely within the underlying rock, are bodies of ore consisting of pyrrhotite, pentlandite and chalcopyrite. These are segregated products of the norite, which in some places solidified at the base of the sill and in others were intruded as dikes in the underlying rocks or in previously solidified portions of the norite. They constitute commercial ore bodies where the sulphides form a preponderant part of the rock.
The ore bodies are classified as “marginal” and “offset.” The marginal deposits occur along the contact of the norite with the underlying rock. Frequently they lie entirely within the rocks adjacent to the norite. The offset deposits occur where faults cut across the limbs of the fold, forming zones of weakness into which ore or mineralized norite was intruded.
The nickel-bearing mineral is pentlandite; the copper-bearing, chalcopyrite. The other sulphide, pyrrhotite, is a sulphide of iron. The ores mined to date average roughly 3.5 per cent. nickel and 2 per cent. copper.
From the opening of the district in 1887 to the end of 1916 nearly ten and one-half million tons of Sudbury ore had been mined and smelted; and, from this, about 285,000 tons of nickel had been produced. It is estimated that there are probably fully 100,000,000 tons of ore reserves. Over a million and a half tons of ore were mined and smelted in 1916.
The Alexo Mine is situated 150 miles due north of Sudbury. The ore occurs at the contact of a large mass of peridotite (now altered to serpentine), with a pillow-lava which the peridotite intruded. The ore consists of sulphide minerals segregated from the intrusive mass. It is of two types, one, a massive, pure sulphide occupying cracks in dike-like relationship, the other, disseminated sulphide in peridotite adjacent to the sulphide ore masses. The ore deposit has a proven length of 700 feet, has been opened to a depth of 120 feet, and drilling has shown ore to extend to a depth of 240 feet. The average width may be taken as approximately 10 feet. By the end of 1916, ore had been raised to the extent of 34,650 tons and more than that amount had been developed. About 12,000 tons of ore were shipped in 1915, averaging about 4.9 per cent. nickel and 0.6 per cent. copper. Several hundred thousand tons are probably available in this deposit.
The nickel ore deposits of Norway are similar mineralogically to those of Sudbury. The deposits are small, their metal content is low, and compared to the Sudbury and New Caledonia deposits they are of little consequence. Up to 1909 there had been mined and smelted in Norway about 400,000 tons of nickel ore. The hand-sorted ore carried 1.4 to 1.7 per cent. of nickel.
Deposits like those of Norway have been found in Sweden, but they have not been worked in recent years. There is evidently a nickeliferous metallographic province in the Scandinavian countries and important ore deposits may yet be found there.
In the United States, near Gap, Lancaster County, Pennsylvania, is a deposit of nickel ore of the sulphide type, which occurs as a segregation from a 300-ft. dike of amphibolite. It was worked spasmodically for copper throughout the 18th century. Nickel was discovered in the ore in 1852 and 4,000,000 pounds of nickel are estimated to have been produced up to 1882. The advent of New Caledonia and Sudbury ores caused the closing of the mine. The ore as mined carried 1 to 3 per cent. nickel and about one-third as much copper.
Near Julian, San Diego County, California, is a sulphide nickel deposit that has never been commercially productive. Assays show the ore to contain nearly 3 per cent. nickel or more.
A small deposit in Tasmania has produced a few thousand tons of rich ore. Diamond drilling has shown that little ore remains.
Nickel-copper sulphides have been found in connection with a large intrusive of basic igneous rock in the Insizwa Range, South Africa. No payable ore has been found.
Nickel sulphide deposits of unknown importance occur in India and in Southwestern China. Small deposits which were worked when nickel was scarce occur in Italy, Scotland, Germany and Austria.
Deposits of the Garnierite and Lateritic Types.
—About one-third of the surface of the island of New Caledonia is occupied by serpentine, this being the weathered product of basic igneous rock. “The ore, noumeaite or garnierite, occurs as a hydrated silicate of nickel and magnesia and may best be described as an alteration product of the serpentine in which the magnesia and iron have been replaced by nickel. * * * The workable deposits always occur on the saddle of spurs from the main mountain ridge, at elevations of 400 to 2,500 feet, the latter elevation being the more common. * * * The replacement of the serpentine by nickel follows the joints and fractures in the serpentine and the undecomposed blocks and boulders of serpentine are as a rule covered by a shell of ore which has to be picked off.” The ores are hand picked to bring them up to a grade profitable to treat. In the past it has not been considered economical to smelt ore of lower grade than 4.5 per cent. nickel nor to ship ore much below 6.5 per cent.
The ore bodies usually contain under 250,000 tons of ore. The largest mine yet worked produced less than 600,000 metric tons (2,204 lb.) of ore. Probably there still remains as much undeveloped ore as has been mined in the forty years of production,—equivalent to 160,000 tons of nickel. This would be equal to about four years’ output of the Sudbury district at the 1916 rate of production. “There are large bodies of lower-grade ores which it has not yet been found feasible to treat.”
Three large blanket deposits of nickeliferous iron ore occur on elevated plateaus in Cuba. These are typical lateritic (residual) deposits. The average depth of the ore is 15 feet and the combined tonnage of the three deposits is placed at one and one-half to three billion tons. The nickel content ranges from about 0.6 per cent. to 2.1 per cent. and shows progressive enrichment from the top downward. Chromium is also present and shows similar enrichment. The presence of nickel and chromium in the iron ores greatly enhances their value for making special steels.
Iron ore on the island of Seboekoe, lying off the southeast coast of Borneo, contains appreciable amounts of nickel and chromium. At least 300,000,000 tons of ore are contained in the deposit, which is a porous limonite, about 15 feet thick, overlying serpentine.
In the United States, nickel deposits of the garnierite type occur in North Carolina and Oregon. Attempts to mine these ores have never been successful.
Small nickel deposits of the garnierite type occur in Egypt, Germany (Prussian Silesia), Greece, Madagascar, Russia and Spain. Nickeliferous iron ores occur in Greece, and it is thought that chromiferous iron ores on Mindao Island, in the Philippines, may, on further exploration, prove to be nickeliferous.
Nickel in Veins.
—Nickel occurs with other metals, precious or semi-precious, in some vein deposits and is recovered as a by-product in the treatment of ores from them. It is notably present in the deposits at Cobalt, Ontario, and has been found in vein deposits in the United States, France, Germany, Austria, Mexico and South America. Several hundred tons are recovered annually in the refining of copper produced in the United States.
Related to the vein deposit type of nickel-bearing ore are the galena deposits disseminated through dolomite in southeastern Missouri. Iron, copper, nickel, and cobalt sulphides occur with the galena. Years ago nickel was recovered electrolytically from matte from these ores.