330 Mr. J. A. Phillips's Notes on the Chemical Geology 



The Norambagua vein is enclosed in a crystalline rock locally 

 known as syenite; but in some parts of the hill its composition 

 would rather entitle it to be classed as a diorite. This vein, 

 which is seldom more than a foot in thickness, is divided by 

 headings into thin lamina? parallel with its walls, and is chiefly 

 composed of greasy-looking quartz, showing rather faint indica- 

 tions of crystallization. Between the several lamina? of silica 

 there are not unfrequently thin deposits of blue slate, which have 

 evidently been subjected to considerable pressure, and which 

 cause the veinstone to be easily separated into parallel bands. 

 In some places iron pyrites and arsenical pyrites are abundant ; 

 but in selecting specimens for analysis those portions of the vein- 

 stone containing a visible amount of sulphides &c. were avoided. 



A microscopical examination of sections cut from this vein 

 showed that it contains fluid-cavities of about ^ qVq of an inch 

 in diameter, in most of which vacuities could be observed. It 

 also encloses a few gas-cavities and some apparently containing 

 clay, together with markings like those observed in the quartz 

 from the Kate Hayes. 



Examination of Quartz from the North-Star Mine. — Some of 

 the ordinary white quartz from the North-Star mine, near Grass 

 Valley, having a specific gravity of 2*61, was next subjected to 

 analysis, and gave the following results : — 



Water lost at 212° F O07 



Water lost by subsequent ignition . 0*03 



Silica 98-61 



Alumina 082 



Peroxide of iron traces 



Potash 0-24 



Soda traces 



99-77 

 This vein, which sometimes thins down to a mere seam, and 

 at others has a width of 6 feet, is one of the most productive in 

 the district, and has been worked to a depth, on the inclination 

 of the lode, of 750 feet. All the specimens were taken from near 

 the bottom of the workings. 



The quartz, of which it is principally composed, is of a milky 

 colour, and presents indistinct crystalline faces in whatever di- 

 rection it may be broken. Like nearly all the auriferous veins 

 of the country, it exhibits a tendency to an arrangement accord- 

 ing to bands parallel to the walls of the enclosing fissure, and, 

 wherever it is most productive, contains iron pyrites and other 

 sulphides. 



Thin sections of this veinstone, examined under a high power, 

 show a few minute fluid-cavities with vacuities, numerous small 



