150 KEPORT— 1891. 



margins are doubly refracting, and so are also two of the small fragments 

 that resulted from the fracture ; the remainder is perfectly isotropic, with 

 the exception of the small prismatic particle marked with a star, which is 

 doubly refracting in the upper half. Cracks, crevices, and spaces in and 

 between the fragments are filled with dusty black iron-ore, and vapour- 

 cavities are abundant in all the particles. 



2. On the Occurrence of some Bare Minerals in Netv 

 Zealand. 



By James Paek, F.G.S., Lecturer, Thames School of Mines. 



CoTUNXiTE (Lead-chloride). — This mineral came under my 

 notice last May while conducting some experiments on a 

 three-ton parcel of ore from the Golden Gem Mine at Waiomo, 

 a place on the coast about ten miles from the Thames, where 

 a considerable amount of prospecting is being carried on with 

 very encouraging results. 



The country rock at Waiomo is a tough greenish-coloured 

 tufaceous sandstone or tufa, which weathers at the surface to 

 a yellowish-brown colour. In places it passes into a harder 

 green and grey-coloured brecciated rock, which contains sub- 

 ordinate beds of soft blue mud-rock, much resembling a fine 

 tufa. On the Thames side of the Waiomo stream the first- 

 named green tufas are intercalated with distinct sheets of 

 hornblende-andesite, locally known as diorite dykes. 



The ore from the Golden Gem Mine consisted of rusty- 

 coloured mullocky quartz containing both gold and silver, the 

 latter in the form of kerargyrite (horn silver) , and the former 

 as free gold of fine quality. 



The ore was crushed wet, and then passed over amal- 

 gamated copper plates, in order to ascertain what proportion of 

 the gold could be saved by this mea.ns. The tailmgs were 

 collected in settling-pits, and afterwards treated by pan 

 amalgamation. 



During the first operation a yellowish-coloured mineral 

 collected in considerable quantities on the blankets, and on 

 examination it proved to be lead-chloride. 



When dry the cotunnite possesses a pale yellowish-green 

 colour, but when wet it assumes a bright-yellow tinge, at a 

 distance resembling that of gold. Streak, white or grey ; 

 hardness, about 1-5 ; specific gravity, 5-32. Slowly soluble in 

 hot water, giving a white precipitate with sulphuric acid. 



Teirahedrite. — A sample of this ore occurs in the mineral 

 collection at the School of Mines, marked as from Koputauahi 



