II.—The Genesis of Tungsten Ores

Abstract

From the descriptions already given, and from a general survey of the literature of the subject, it is apparent that scheelite is a frequent associate of wolframite in the lodes of magmatic origin. In fact, a certain number of the occurrences already cited, especially in the second part of this paper, might almost as well have been described as scheelite deposits, since the two minerals are found in something like equal quantities. This applies, for example, to a large number of the American and Canadian occurrences, to those of the Malay States, and others. This is only to be expected from general considerations, since gases or solutions containing chemically active tungsten compounds coming in contact with calcareous material would naturally tend to form calcium tungstate. The same applies to lead-bearing minerals; hence in a few instances lead tungstate, stolzite, has been found in association with scheelite. It is of interest to note that scheelite often contains from 1 to 3 per cent of molybdenum. Wolframite and scheelite are often found in lodes and other masses very closely intergrown, and in many cases there is evidence of much pseudomorphism. In some cases scheelite has clearly replaced wolframite, while in other cases the reverse holds. The law governing the paramorphism of these minerals is somewhat obscure, and it is not easy to say anything definite on the subject. In this direction further investigation is required, although the point is not perhaps of much practical importance.