Haeuslek. — Mlcroficopical Struct tire of Gold. 335 



Art. XXXIII.— 0/; the Microscopical Structure of the Ohinc- 

 muri Gold. 



By Dr. Eudolf Haeuslek. 



[Read before the Auckland Institute, ith August, 1890.] 



Plates XXXIII., XXXIV. 



DuKiNG my long residence in Ohinemnri I visited most of the 

 mines, and many localities where gold and other minerals 

 occur in more or less considerable quantity, with the view of 

 collecting a complete series of microscopical specimens for a 

 monograph to be published in co-operation %\ith several con- 

 tinental mineralogists and chemists. The material accumu- 

 lated during fourteen months affords good examples of almost 

 every known variety of gold and silver, and a number of speci- 

 mens which may help to throw light on some yet obscure 

 points in connection with the origin and distribution of these 

 metals. The subject bearing special relation to New Zealand 

 mineralogy, these short remarks may be of interest to the 

 members of the Institute. 



To show the structure of the gold, and the various modes 

 of occurrence in a pure or alloyed state, coloured plates are 

 absolutely necessary, and the specimens have to be drawn on 

 a very large scale ; which methods could not be adopted in 

 this paper, through want of space, and difllculties in the exe- 

 cution of the coloured illustrations. Tho granular or finely 

 crystalline nature of the surface could consequently not be 

 represented in all its minute details. 



Nearly all the specimens were obtained by myself on the 

 spot, to prevent any mistakes about the exact localities and 

 nature of the rock and surroiniding country. A few were 

 picked out from prospects brought by miners and prospectors 

 for microscopical examination, but only in those cases where 

 full particulars were given, and where the composition of the 

 material left in the dish showed the mineralogical character 

 of the rocks or the loose debris in which the gold was deposited 

 mechanically after the disintegration of its original matrix. 



The ordinary process of washing out a prospect in the dish 

 causes, of course, distortions, striation, or compression of the 

 soft, delicate specimens, which, especially in the fine arbo- 

 rescent and filiform varieties, destroy most of the primitive 

 shape and surface. Even the most careful manipulation pro- 

 duces often a slight flattening or scratching, which may easily 

 be mistaken for imperfect crystallization, though under higher 

 power the cause is generally easily detected. The gold found 

 in loose debris has undergone many changes (Jirough me- 



