266 Transactions. 



calcite, &c. An almost opaque streaky substance, nearly white by reflected 

 light, forms much of the groundmass. Such material is often referred to 

 as " kaolinitic," but, as previously remarked, is probably near sericite in 

 composition. 



Of secondary minerals not already mentioned, pyrite, almost invariably 

 in small cubes, is the most conspicuous. Epidote or allied mineral may 

 very rarely be present. 



(c.) Vein- material. 



The vein-material of the Waihi mines largely replaces country, and 

 therefore will be discussed to some extent. In the upper levels of the Waihi 

 Mine the vein-material is quartz, with a little clay, iron and manganese 

 oxides, &c. Some of the quartz is crystalline to the eye, and has obviously 

 been deposited in open spaces. Much, however, is of flinty or chalcedonic 

 appearance. Sections of this chalcedonic material show that it is mainly 

 an indefinite kind of mosaic that resembles the quartz mosaic seen in highly 

 altered wall-rock, and it therefore suggests replacement or silicification of 

 country. This view is supported by a study of the ore from lower levels. 

 The following analysis* of a representative piece of " oxidized " ore from 

 one of the upper levels shows that the material is far from being pure 

 quartz : — 



SiO^ 



AUO3 



Fe'^Oy (including FeO calculated to Fe.,03) 



MnO and NiO . . . . ' . 



H2O at 100° C. 



Loss on ignition 



89-98 

 1-82 

 5-62 

 0-39 

 0-26 

 1-60 



99-67 

 Gold, 2 oz. 5 dwt. 17 gr. per ton. Silver, 10 oz. 2 dwt. 12 gr. per ton. 



Sections made from a portion of the specimen that furnished the material 

 for the above analysis show ore with replacement characters seamed by 

 tiny veins of crystalline quartz. 



In Nos. 5 and 6 levels (445 ft. and 555 ft.) of the Waihi Mine the presence 

 of partly unsilicified country in the veins is easily recognized. In places 

 quite a large proportion of the vem-material is dark-coloured rock, which 

 in some instances is actually less altered than the wall-rock. 



Sections of the less-silicified rock from the veins are very like those of 

 the wall-rocks. Feldspar is the chief original mmeral recognizable. Some 

 individuals with feldspathic outlines are mosaics of quartz and presumably 

 secondary orthoclase or anorthoclase, together with more or less kaolinitic, 

 or more probably sericitic, material. In places fresh, easily recognized 

 valencianite with good cleavage and low index of refraction occurs. Binary 

 twins of apparent orthoclase are observable in at least one section. In 

 several slides traces of repeated albite twmning are quite distinguishable 

 in the feldspars, and in one section acid labradorite, and perhaps andesine, 

 can be identified. Some original quartz in rounded grains is present in all 

 the slides. Ferro-magnesian minerals are in general even more altered than 

 in the -wall-rocks, and are represented by somewhat indefinite masses of 

 chlorite and othe* minerals, particularly pyrite, so that the original species 



* See 7, p. 182. 



