H. W. Fairbanks — Tin Deposits in California. 41 



band specimen appeared to consist wholly of tourmaline, 

 showed bunches of tourmaline crystals radially arranged and 

 embedded in interlocking quartz grains. The crystals are rec- 

 ognized as tourmaline by the hexagonal cross section, parallel 

 extinction, polarization and frequent presence of fibrous termi- 

 nations, although the terminal crystal faces are sometimes 

 present. In the most of the sections prepared the tourmaline 

 appears to be exceptionally opaque, sometimes the border is 

 opaque while the center is feebly translucent. With the blow- 

 pipe the material fused easily with slight intumescence and 

 became magnetic. The reaction for boron was pronounced. 



The large Cajalco vein consists of tourmaline and quartz in 

 almost equal proportions. This aggregate breaks up quite 

 easily, as it is porous, the spaces being lined with drusy crystals 

 of both components. The deposits have evidently been formed 

 in fissures through a gradual replacement of the granite walls. 

 Judging from an examination of the seam-like veins the sili- 

 cates appear to have been attacked easier and removed first. 

 In places the larger veins seem to blend into the granite and it 

 was at first thought that some of the quartz might be a rem- 

 nant of the granite, as it is rarely if ever segregated in bunches. 

 A microscopic examination showed that this view was undoubt- 

 edly false, as the grains interlock in a different manner from 

 those in the granite, and in addition contained fluid and liquid 

 inclusions. The relative proportions of quartz and tourmaline 

 in the Cajalco vein are so constant that it presents a uniform 

 appearance. Although the mine reports speak of the occa- 

 sional presence of arsenical pyrites and copper, nothing of the 

 kind came under the observation of the writer. The bunches 

 in these veins, and especially the enormous one forming 

 Cajalco hill, could have been formed in no other way than by 

 replacement, although it is difficult to conceive of its having 

 taken place on such a large scale. 



With the earlier reports upon this property nearly all the 

 veins were considered tin-bearing, but at the time the writer 

 made the examination shortly before the mine closed, after 

 diligent prospecting the company had succeeded in finding 

 traces of tin in only one or two veins besides the one worked. 

 Tunnels had also been run into Cajalco hill, but in this great 

 body of vein matter nothing was found. The narrower por- 

 tion of the vein to the northeast furnished all that was ever 

 milled. At the time of the examination the vein had been 

 opened to a depth of 180 feet by two working shafts, exposing 

 the vein horizontally for 300 feet. Here the vein has a width 

 of 8 feet or less. The main ore body occurs in the center of 

 the mine between the two shafts and extends down on the dip 

 of the vein. The tin oxide is distributed either through the 



