I.—The Genesis of Tungsten Ores

Extract

As already stated in the first part of this paper, a regular gradation may be traced from the cassiterite-wolframite lodes to wolframite-quartz veins without cassiterite, a type which appears on the whole to be more common in America than elsewhere. In many cases this difference is clearly due to a more complete differentiation of the magma, but in other instances a purely igneous origin is less conclusively established. In Cornwall and other granitic areas a tin-wolfram lode can sometimes be traced continuously into a wolfram lode, and this again into a pure quartz vein. Here the pegmatitic origin of the lodes is demonstrated, and as a rule the wolfram is accompanied by'fluorite and other recognized pneumatolytic minerals, as well as by sulphides similar to those found in the tin lodes. Thus the genetic connexion with the tin-bearing types is beyond doubt. In a few instances only wolfram is found in association with gold ores; the significance of this will be discussed in a later section.