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



in the elements which act as " carriers ". In the case of the 

 tungsten ores the most important of these is undoubtedly fluorine ; 

 boron is a very common associate, but it is not known whether it 

 plays any actual part in the formation of wolframite or scheelite. 

 A detailed study of the literature does not lend any support to the 

 statement sometimes found in textbooks that apatite is a common 

 associate of this group. In fact, minerals containing phosphorus or 

 chlorine seem to be conspicuously absent. 



Another point of interest is that the tungsten minerals are all 

 characterized by a high degree of stability and consequent resistance 

 to chemical action of any sort. Hence they do not undergo any 

 alteration in the zone of oxidation and are not carried down in 

 solution into the zone of cementation. This is equivalent to saying 

 that they do not undergo secondary enrichment. It follows from 

 this that tungsten lodes are always primary in the narrowest sense 

 of the term, and this is a fact which should be taken into considera- 

 tion in the valuation of such deposits. The behaviour of tungsten 

 lodes in this respect is on the whole very similar to that of the tin 

 lodes, and shows no resemblance to the characters of the copper lodes, 

 for example. 



To sum up, it may be said that the tungsten ore-deposits are of 

 magmatic origin, being formed by the natural and normal con- 

 centration in certain fractions of the magma of a group of 

 constituents, metallic and otherwise, which tend to occur together 

 owing to the similarity of their chemical and physical properties 

 under the conditions that prevail during the later stages of magmatic 

 consolidation. Of these constituents the most important are tungsten, 

 tin, molybdenum, arsenic, fluorine, and boron. These constitute the 

 general paragenesis, while certain regional subtypes can be dis- 

 tinguished, characterized by uranium, mobium, tantalum, and possibly 

 others not yet specifically distinguished. In certain cases transitions 

 can be traced to other groups of ore-deposits containing gold, silver^ 

 copper, zinc, and lead. Some of these mixed deposits may be 

 explainable by deposition of metals in the same locality at two or 

 more distinct periods, while in other instances the differentiation of 

 the original magma may have been incomplete and ill-defined. . At 

 any rate, it is clear that in the typical cases the prime factor at 

 work has been differentiation of igneous magmas, and the study of the 

 genesis of the tungsten ores lends the strongest support to modern 

 views as to the origin of ore-deposits in general. It is now 

 becoming increasingly manifest that the study of the characters and 

 origin of the metalliferous rocks is an extraordinarily interesting 

 and important branch of the science of petrology, and that in the 

 past this branch has been unduly neglected by workers on the purely 

 scientific and theoretical side. A detailed investigation of the 

 chemical and physical laws governing the formation of the oxides 

 and sulphides of the igneous rocks, on the same lines as already 

 applied by many workers to the silicates, could not fail to yield 

 results of the highest scientific interest and of the utmost practical 

 value. 



