28 Transactions. 



of great importance on account of the evidence which they 

 furnish in connection with the genesis of solfataric ore- 

 deposits. 



The basement rocks consist of marly clays and greensands 

 of Lower Tertiary or Upper Cretaceous age, which are covered 

 with Hows of basalt and beds of scoriae. It is agreed by all 

 geologists that the basalt constitutes the youngest rock-forma- 

 tion in the district. The surrounding country is studded with 

 old craters, and there is everywhere evidence of former intense 

 volcanic activity. 



The hot springs around which the quicksilver-deposits are 

 clustered are situated about two miles south-east of Lake 

 Omapere, which itself occupies the site of an old crater. 

 They occur along the edge of a flow of basalt, which is over- 

 lain at this point by deposits of calcareous and siliceous sinter 

 and solidified siliceous and carbonaceous muds, through which 

 sulphur and cinnabar are finely disseminated. There are also 

 deposits of pyrites with or without cinnabar, in some cases 

 containing traces of both gold and silver. :;: The sinters also 

 contain gold and silver. 



The ground around the springs is generally very hot, and 

 all attempts to develop the quicksilver-deposits have been 

 frustrated by the large volumes of hot water encountered at 

 shallow depths below the surface. 



The district has been examined at different times by Cap- 

 tain Hutton, Sir James Hector, A. McKay, and the author; 

 but the best description is that of Andr6 P. Griffiths, who con- 

 ducted extensive prospecting and mining operations there in 

 1895 and 1896. The mining operations and borings disclosed 

 many important details which could not be gathered from a 

 surface-examination. 



The iron-pyrites occurs in masses near the basalt, and also 

 filling cracks and fissures in that rock. The thickness of the 

 pyritic masses varies from 3 in. to 3 ft., but their other dimen- 

 sions are extremely irregular. Close to the pyritic masses 

 there is a hard white siliceous sinter from 8 in. to 10 in. thick, 

 which Griffiths found to contain gold and silver in places. 

 One assay of the sinter gave a value of £3 per ton, but unfor- 

 tunately the proportion of gold and silver is not given.! The 

 cinnabar generally occurs lining small cavities and cracks in 

 the solidified mud's and sinters surrounding the original fissures 

 in the basalt. It also occurs impregnating the sinter in an 

 extremely finely divided form. Sulphur occurs throughout the 

 sinter in larger proportion than either the cinnaoar or pyrites. 



* Andre P. Griffiths, "The Ohaeawai Quicksilver-deposits," Trans. 

 N.Z. Inst. Min. Eng., vol. ii, p. 48. 



f Andre P. Griffiths, loc. cit., p. 50. 



