294 R. H. Rastall — The Genesis of Tungsten Ores. 



Althoagh sclieelite occurs along with wolframite in Cornwall it is 

 only in small quantity and of no practical importance. The only 

 workable scheelite deposit known in the British Isles is at Grainsgill 

 in Cumberland, on the north-eastern side of the Skiddaw area. 

 Here the lodes are highly mitieralized quartz veins connected with 

 the pneumatolytic phase of the Skiddaw granite ; they are in close 

 association with the greisen of Grainsgill, which is certainly a 

 differentiation product of the granite magma. Unfortunately a good 

 deal of uncertainty still exists as to the relation of the lodes to the 

 surrounding rocks, and especially to the gabbro and granophyre of 

 Carrock Fell. This is a very important point in relation to the age 

 of the latter, which is a matter of dispute. The minerals found in 

 association with the scheelite ores are molybdenite, arsenopyrite, 

 pyromorphite, galena, blende, native bismuth, bismuth teliuride 

 (with a little gold), and tourmaline, while crystals of fluorite 

 have been observed in joint plaaes in the greisen ; it is notable 

 also that arsenopyrite occurs in considerable quantity in the same 

 rock. It is not know^n whether the lead-zinc-bismuth minerals 

 are contemporaneous with the quartz and wolfram minerals or 

 whether they belong to a later phase of mineralization related to the 

 post-Carboniferous lead-zinc deposits of the North of England. The 

 presence of tourmaline and fluorite indicates pneumatolytic influences, 

 and in any case the genetic connexion with the Grainsgill greisen 

 seems clear. ^ 



In Spain and Portugal scheelite is found together with wolframite 

 in many of the deposits. At the La Sorpresa mine in the province 

 of Cordoba it occurs in this way in quartz veins, running from 

 granite into slate, and the ores tend to occur especially at the 

 junction of the two rocks. This fact appears to bring them into the 

 category of contact deposits. In a somewhat similar waj^ scheelite 

 is found in Haute Vienne, France,^ in veins Avith wolframite, 

 cassiterite, molybdenite, arsenopyrite, and pyrite in a gangue of 

 quartz. This is an example of its occurrence in the normal tin- 

 wolfram lode type. 



An interesting occurrence of scheelite with cassiterite is found at 

 Pitkaranta in Finland, to the north of Lake Ladoga.^ Here gneisses 

 and schists containing beds of limestone are intruded by Rapakiwi 

 granite, and it is in the limestones that the ores principally occur. 

 The ores include three principal types: (1) magnetite, (2) copper 

 ore, and (3) tin-scheelite ore. All the ores are intergrown with 

 a remarkable variety of contact-metamorphic calcareous minerals, 

 including diopside, garnet, vesuvianite, chondrodite, and calcite. 

 Topaz and fluorite have also been observed in small quantity. This 

 is a particularly instructive case, since here, where the ores are so 

 closely associated with limestone, scheelite is found without 



^ Finlayson, Geol. Mag., 1910, p. 19. The Mineral Resources of Great 

 Britain, vol. i : "Tungsten and Manganese Ores" (Mem. Geol. Surv.), 

 1916, p. 3. 



" Hurd, Bull. Soc. Industrie Min^rale, vol. ix, p. 99. 



^ Triistedt, "Die Erzlagerstatten von Pitkaranta am Ladogasee " : Bull. 

 Comm. Geol. Finlande, 1907, No. 19. 



