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



The wolframite ores of Cornwall are always ia association with 

 p;ranite intrusions ; they occur in the granite itself, in pegmatite 

 dykes, in lodes, and disseminated in a more or less irregular way in 

 certain rocks in the immediate neighbourhood of the granite ; the 

 associatioQ with greisen is particularly close, and is of much genetic 

 sigaificance with regard to the mode of distribution of the ores. 



It is quite clear that the pegmatite veins carrying wolfram are 

 earlier than either the lodes in the country rock or the greisens. 

 The list of minerals found in connexion with the wolfram ores is 

 long, but the following are the most characteristic and significant : 

 cassiterite, mispickel, chalcopyrite, tourmaline, topaz, and fluorspar. 

 In the greisens of St. Michael's Mount and elsewhere uranium 

 minerals also occur in association with wolfram.' The importance of 

 this fact will be referred to again later. To sum up, the whole 

 mineral association forms an excellent example of the tin-tungsten- 

 fluorine paragenesis, which, as will be seen in the sequel, is so widely 

 spread in many parts of the world. 



In connexion with the tourmaline granites of Brittany wolframite 

 is found along with cassiterite, molybdenite, mispickel, chalcopyrite, 

 blende, and fluorspar. The ores occur iu a network of veins (stock- 

 work) in the granites, near their contact with mica-schists. The 

 resemblance of this mineral assemblage to that found in Cornwall is 

 obvious, and both evidently form part of one petrographical province 

 from the point of view of the metallic contents of the magma, and 

 both are characterized by the presence of fluorine and boron among 

 the non-metallic constituents. 



Although so far as is known the German resources of tungsten 

 ores are but small, the occurrences are of considerable interest, and 

 i^ood descriptions, have been published. The principal output is 

 from the -well-known mining district of the Erzgebirge in Saxony 

 and Bohemia. The ancient crystalline rocks of tlie fractured district 

 between Dippoldiswalde and Teplitz are penetrated by great masses 

 of quartz-porphyrv of Permian age (Teplitz quartz-porphyry); into 

 this are intruded domes and bosses of granite of somewhat later date. 

 The rocks surrounding the granite are highly mineralized, and in 

 particular tlie quartz-porphyry, above the granite intrusions, is more 

 or less converted into greisen and penetrated by innumerable veins 

 and stringers carrying a great variety of ores. The districts richest 

 in mineral veins are those of Altenberg, Zinnwald, Graupen, Ehren- 

 friedersdorf, Geyer, Kibenstock, and Johanngeorgenstadt. At 

 Altenberg the ores occur in the form of a stockwork in the quartz- 

 porphyry above the granite dome to the depth of about 750 feet. 

 The mines of Zinnwald are said to be very rich in wolfram, and are 

 also worked for lepidolite. Here the veins are in the quartz- 

 porphyry and run parallel to the upper surface of the granite dome. 

 The principal minerals are wolfram, scheelite, tinstone, arsenopyrite, 

 galena, blende, chalcopyrite, tourmaline, topaz, and apatite. The 

 impregnation with tin and other ores occurred before the last aplitic 

 phase of the granite intrusion. At Ehrenfriedersdorf many tin- 

 Avolfram lodes of a similar type occur in mica-schist. The whole 



1 The Geology of the Land's End District (Mem. Geol. Surv.), 1907, p. 53. 



