BY LEO A. COTTON. 



773 



Class viii. — Arsenical Lodes. 



These lodes are of comparatively rare occurrence in this area. 

 The first observed has rather a peculiar association, and will, 

 therefore, be described. 



In one of the typical quartz-quartzose reefs at Elsmore, a band 

 of arsenical pyrites, about 3 inches wide, was found occupying 

 the place of the typical central quartz-rib for about 20 feet along 

 the vein. For a sketch-plan of this, see text-fig. 9. It will be 

 noticed that the arsenical lode commences at the junction of two 

 reefs of the quartz-quartzose type. At this junction is a mass 





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Fig. 9. — Junction of a typical quartz-quartzose vein with a similar one, 

 rendered unique by the presence of arseno-pyrite. Loc. Elsmore. A, 

 Band of arseno-pyrite; B, Bands of ironstone; C, Quartzose zone, con- 

 sisting of granular quartz and mica; D, Massive ironstone; E, Comb-quartz, 

 forming central band of lode. 



of ironstone, from the southern margin of which the arsenical 

 vein emerges. This arsenical band pinches out gradually, and 

 the normal quartz-filling takes its place. On examination, the 

 vein was seen to consist largely of mispickel, some of which 

 had oxidised to arseniate of iron. The vein is cased", on each 

 side, by a band of iron-oxide, about J of an inch thick. It con- 

 tains abundant fragments of quartz, and also double-ended 

 quartz-crystals, such as are common in the central quartz of the 

 quartz-quartzose veins. 



