The ores of Titanium are rutile (TiO2), and ilmenite (FeTiO3). Rutile has been found in quantity in gabbro-pegmatite along with apatite; also with ilmenite in anorthosite. The red or reddish-brown crystals (Fig. 39) of rutile are not likely to be overlooked; it is used mostly in electrodes of are lamps. The market price for rutile is 10 cents a pound (1955) for 94% concentrates.
Ilmenite, often called titanic iron ore, although not used as an ore of iron, is found in gabbro and anorthosite, usually mixed with magnetite, which it very much resembles in appearance. But pure ilmenite is non-magnetic or only slightly magnetic. It contains over 52% titanic acid (TiO2), and the market price (1955) for the best ore is $20 to $22 a ton; for ore containing 32% to 35% of Ti02, $7 to 8 a ton. An ilmenite-magnetite containing 32% or upwards of TiO2 is saleable. Deposits of pure ilmenite are not common, but deposits of very large size are now being mined at Allard lake, near the Gulf of St. Lawrence, 450 miles northeast of Quebec City. There are large quantities of the ilmenite- magnetite mixture in Quebec, Ontario, and Alberta. Sometimes the percentage of titanic acid is high, on account of the presence of rutile. Every discovery of titanic ore should be assayed for titanium; it may be high enough to use as an ore of titanium.
Manganese, like iron, is present in all rocks, but not so plentifully as iron. In the weathering process, manganese is more easily dissolved than iron; but, on the other hand, the iron is more easily precipitated from the solution. These differences account for the separation of manganese ores from iron ores in sedimentary deposits. Nearly all manganese deposits of importance have been formed by sedimentation, or through enrichment by leaching (residual deposits).
The principal ores of manganese are:
Less common ores are braunite containing about 70% manganese, manganite (Mn2O3. H2O) with 62%, and rhodochrosite (MnCO3) with 48%. Rhodonite, (MnSiO3), is sometimes found mixed with other manganese ores.
Bog manganese (also called wad) is of variable composition. It is like bog iron, but is darker, often quite black. As it is much more valuable than bog iron, any black, earthy, or glossy, fairly heavy mineral should be assayed for manganese.
Pyrolusite may be found as a surface deposit. The greatest known manganese deposit, in Trans-Caucasia, consists of layers of pyrolusite in clay, marl, and sandstone. At Tennycape, Nova Scotia, and at Markhamville, New Brunswick, it has been found in veins, pockets, and large masses in limestone of Carboniferous age. At Markhamville, the pyrolusite is accompanied by manganite and psilomelane. Near New Ross, Nova Scotia, it occurs along with manganite and psilomelane in veins in granite. Workable deposits have been found in and above slate.
Psilomelane often accompanies pyrolusite, from which it can be distinguished by its greater hardness. In prospecting in regions where there are sedimentary rocks, particularly limestone, these minerals, of a black or dark brown color, should be looked for on the surface. To be merchantable, a manganese ore must carry at least 40% of manganese ; but iron ores high in manganese may sometimes be profitably mined as manganese ores, even when the manganese content is much less. In British Columbia, near Cowichan Lake, a deposit of psilomelane mixed with pyrolusite and manganite, was worked for several years.
The only important ore of chromium is chromite or chrome iron ore, FeCr2O4. It is found in peridotite and in serpentine rock derived from peridotite. It occurs in irregular bunches, in vein-like masses, and often mixed with magnetite. The discovery of masses of black, hard, heavy metallic mineral in serpentine or peridotite is not necessarily a find of chrome iron ore; it may be magnetite. On the other hand, chromite that is mixed with a little magnetite might be mistaken for magnetite. In Quebec, chromite is found in the asbestos district, principally near Thetford, where it occurs in a rock intermediate between peridotite and pyroxenite. The ore is in grains and larger bodies scattered through the rock. In Ontario and British Columbia, it has been found in peridotite. It may carry microscopic diamonds. In South Africa, chromite has been found in norite near its contact with granite, and in the neighborhood of extensive deposits of titaniferous magnetite, Disseminated chromite deposits have been found in similar rocks at Oiseau River in southeastern Manitoba. It is possible that chromite may be found elsewhere in the Precambrian, as a segregation at the edges of norite or gabbro intrusions.
To be merchantable, chrome iron ore must contain not less than 40% of chromium oxide (Cr2O3), but leaner ores are sometimes concentrated.
The chief ores of tungsten are:
- Wolframite (Fe,Mn)WO4, an iron-manganese tungstate. The parentheses enclosing Fe and Mn and the comma between them mean that the iron and manganese in the mineral vary in proportion, the sum being equal to what would amount to Fe alone or Mn alone. When it has little or no iron, the mineral is hübnerite, MnWO4, much like wolframite, but of a reddish brown color, and yellowish brown when powdered. Wolframite is black or brownish black, and is red-brown when powdered. Both are very heavy, G = 7 or more.
- Scheelite, calcium tungstate, CaWO4. It is white, cream-yellowish, or brownish in color; easily scratched by knife; heavy, G = 6; easily mistaken for quartz, but good cleavage and softness distinguish it; also, when a piece is obtained that is large enough to try its weight, it is found to be much heavier than quartz.
- Tungstite, H2WO4, is a weathered product of wolframite or scheelite, of a canary or golden yellow color. At the Kootenay Belle Mine, it is found in considerable quantities; but usually it occurs only in small quantities with the original minerals.
Tungsten ores are found along with tinstone, and in quartz veins in gold regions. In Nova Scotia, at Moose River and Waverley, the quartz veins in which the tungsten ores are found are mostly barren of gold: but in the Porcupine area, Ontario, scheelite has been found in considerable quantities, closely associated with the gold; and the tungstite of the Kootenay Belle, B.C., carries good gold values. In New Brunswick, at Burnt Brook on the Miramichi River about 25 miles above Boiestown, are narrow quartz veins carrying wolframite and molybdenite, and mining is now being carried on successfully. The veins are in schisted sedimentary rocks near an intrusion of granite. Scheelite has been mined successfully at the Emerald Tungsten property near Salmo, B.C., from large, irregular deposits in altered limestone near granite intrusions. The quartz veins in gold regions should be carefully examined for tungsten minerals, especially those veins of “bull” quartz which appear to be unmineralized. Scheelite, even in considerable quantities, is easily overlooked. Wolframite is more easily spotted.
In panning for gold, a very heavy white or yellowish tail may be scheelite, or a dark brown tail may be wolframite. Where gold is being concentrated on Wilfley or other tables, scheelite or wolframite would appear with the other heavy minerals. It is always possible that, in some exceptional case, it may pay to save the tungsten mineral as a by- product, A tungsten ore containing 3% or 4% of WO3, or about 5% of tungsten mineral, could probably be worked for its own sake.
Tungsten ores are also found with tinstone in the vein-like, pegmatite and quartz bodies which cut through slate, schist and intrusive granite.
The principal ore of molybdenum is the sulphide, molybdenite, (MoS2). This may be changed by weathering into the yellow oxide, molybdite (MoO3) or to molybdic ocher, a yellow molybdate of iron. Where galena and molybdenite occur together, wulfenite PbMoO4, of a bright orange color, may be a product of weathering; and it is sometimes plentiful enough to be of importance. Another product of the weathering of molybdenite is powellite, CaMoO4, of a grayish-white color.
Molybdenite is found in the contact zone of pegmatite, granite, etc., with crystalline limestone, where it is commonly associated with pyrite, pyrrhotite, pyroxene (diopside), and scapolite. Numerous deposits of this kind have been mined in a small way on both sides of the Ottawa River, west of Ottawa.
It is also found in the pegmatite dikes themselves, and sometimes in aplite dikes, as in many places in Eastern Ontario and Western Quebec. In South- eastern Manitoba, in the Falcon-Star Lakes area, molybdenite is found in pegmatite dikes and in quartz veins. At Quyon, Quebec, the molybdenite is found in bunches and scattered flakes in fine-grained syenite, or in bodies of rock high in quartz and pyrite in the syenite. Ores containing as low as 1% of molybdenite can be worked at a profit.
Molybdenite and graphite are very much alike, but molybdenite is blue-black, while the graphite is gray-black. Molybdenite is very much heavier than graphite. When the marks made on rough porcelain are compared, the molybdenite shows a bluish or greenish tint, while the graphite mark is pure gray; this difference can be seen when the marks are made on white paper and rubbed until they are spread out thin, when the molybdenite mark shows a greenish tint.
The Vanadium ores of this important steel- alloy metal are:
Patronite, vanadium sulphide, found with a mineral pitch in Peru. The ash of coal is sometimes rich in vanadium. Bitumen from several localities in the United States has been found to contain vanadium, the ash carrying from 4% to 20%.
Carnotite, an ore of uranium, radium, and vanadium, is found as a bright yellow, powdery mineral in sandstone in Colorado and Utah. It has also been noticed as a yellow incrustation on ilmenite. Most titaniferous iron ores contain a small percentage of vanadium and it is possible that some such deposit may be discovered unusually high in vanadium.
Roscoelite or vanadium mica, is a clove-brown, greenish brown, or greenish mineral, like mica in appearance, but more like chlorite in its softness and lack of elasticity. It has been found in commercial quantities in sandstone in Colorado.
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