ORES DEPOSITED BY GASEOUS SOLUTIONS. 1055 



all the characters of ordinary water-deposited veins, and which are substan- 

 tially alike both in the granite and in the limestones. Were it not for the 

 cassiterite there would be no reason to suggest that these deposits differ in 

 any way from other vein deposits produced by underground water. (See 

 pp. 1058-1065.) As already pointed out, about 75 per cent of the tin of 

 the world is produced in the Malay Peninsula and from Banca and Billiton. 

 The product is mainly a mechanical concentrate, but the cassiterite for 

 this concentrate is derived from the veins in the limestone and granite. 

 Therefore probably 75 per cent of the present product of tin was deposited 

 from aqueous solutions. 



Lindgren finds from his study of metasomatic processes in fissure veins 

 that topaz, garnet, tourmaline, and biotite occur as important metasomatic 

 minerals in connection with .certain ore deposits. But the metasomatic 

 minerals which are found in an overwhelming preponderance in ore deposits 

 are those which are produced by water action in the belt of cementation, 

 viz., hydrous silicates, carbonates, oxides, etc. 



The metallic ore deposits which contain anhydrous minerals Lindgren 

 divides into three classes, (1) topaz-cassiterite veins, (2) tourmalinic gold- 

 copper veins, and (3) biotitic gold-copper veins." Lindgren's description of 

 these veins shows that usually they are not in the igneous rocks, but 

 are largely replacement deposits in adjacent rocks. Pyrrhotite and chal- 

 copyrite carrying gold are found as replacement products in feldspar, and 

 by gradual extension of the processes finally replace the whole rock. The 

 process of formation of the biotitic gold-copper veins is "more characteristic 

 of dynamic metamorphism than of ordinary fissure veins." b Lindgren 

 describes the ores between Signal Peak and Meadow Lake as consisting of 

 pyrite, pyrrhotite, and sphalerite, with some galena, with a gangue con- 

 sisting of quartz, epidote, and tourmaline, with some mica. He says "the 

 ores occur intimately intergrown with this gangue." c Lindgren divides the 

 copper deposits of the gold belt of the Blue Mountains of Oregon into 

 various "types." The Seven Devils type, he says, is a contact deposit of 

 chalcopyrite and bornite between limestone and diorite, which has a gangue 

 of garnet, epidote, and other contact minerals. The tourmaline type has 



« Lindgren, Waklemar, Metasomatic processes in fissure veins: Trans. Am. Inst. Min. Eng., vol. 

 30, 1901, pp. 619-645. 



6 Lindgren, cit., p. 645. 



''Lindgren, Waldemar, The auriferous veins of Meadow Lake, California: Am. Jour. Sci;, 3d series, 

 vol. 46, 1893, p. 205. 



