THE ORIGIN OF THE WOLFRAM AND OASSITRRITE ORES 53 



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tions rich in silica and other substances (hiring the final consolida- 

 tion of the pegmatite." 1 Harkei has discussed the vexed question 

 as to whether pegmatites have an igneous or aqueous origin and re- 

 marks 2 :— ■" From our point of view., as already sufficiently indicated, 

 the antithesis marked by these terms finds no place. The magma 

 or solution from which the pegmatites crystallized was igneous, 

 in that it was the residual part of a granitic or syenitie or other 

 igneous magma, of which the greater part had already crystallized 

 under plutonic conditions. It was aqueous, inasmuch as it con- 

 tained, perhaps very richly, magmatic water, concentrated (with 

 other volatile constituents) in the residual magma by continued 

 crystallization of anhydrous minerals. The pegmatites themselves 

 represent this watery residual magma, except that the greater part 

 of the water and other volatile substances was expelled in the final 

 crystallization. This final crystallization from a solution rich in 

 water and perhaps in other fluxes may have taken place at quite 

 low temperatures, but genetically it is impossible to separate the 

 resulting product from igneous rocks. Logically, indeed, we might 

 include under the same head simple quartz veins crystallizing 

 from solution in water (at perhaps 200T), if both quartz and water 

 were of direct intratelluric origin, the final residuum of an igneous 

 rock magma." 3 Lindgren, in discussing juvenile waters, makes the 

 following observations, "the best evidence of the existence of 

 juvenile water is furnished, not by observation of its present springs, 

 but by the study of old intrusive regions. Here the granites merge 

 into pegmatite dykes and the latter change into pegmatite quartz 

 and this into quartz carrying metallic, ores, such as cassiterite 

 and wolfram. Here we have evidence difficult to controvert that 

 dykes consolidated from magmas gradually turn into deposits the 

 structure and minerals of which testify to purely aqueous deposition." 

 And, later, " yet when we note how veins rich in quartz are at 

 places directly connected with pegmatite dykes, and how strong the 

 evidence is against their deposition by leaching from surrounding 

 rocks, we may well wonder whether this silica in the thermal waters 

 is necessarily' derived by solution of rock comparatively near the 

 surface." 4 



' Thomaa and MaoAlister, " Geology of Ore Deposit* " p. 31. 

 -Marker; "The Natural BQrtory of igneous Hocks, p. TO*. 

 •Earlier, lor. c&, p. 295. 

 •Lindgren, "Mineral Deposits," 1010, pp. 88 au<l 9i. 



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