TEANSACTIONS OF SECTION C, 151 



Bay, Coromandel. The prevailing rocks iu that district, which 

 was examined by me last year, consist of grey and brown 

 decomi30sed white-speckled tufaceous sandstones, which are 

 traversed in all directions by veins of siliceous haematite , and 

 are in places intruded by dykes of augite and hornblende- 

 andesite. 



The tetrahedrite is found on the north-west side of Kopu- 

 tauahi Bay, on Mr. Davis's farm, in a soft grey mullocky clay 

 and quartz vein exposed on the beach between high- and low- 

 water marks. The vein trends E.S.E. - W.N.W., with a 

 southerly dip at high angles ; and varies from 9in. to S^in. 

 in width. 



The tetrahedrite occurs as imperfectly-formed tetrahedrons, 

 on which the faces of the rhombic dodecahedron just appear. 

 The crystals are generally studded with clusters of small but 

 well-developed crystals of pyrites iu the form of pentagonal 

 dodecahedrons, and grains of blende. Hardness, about 4 ; 

 specific gravity, 4-81 ; lustre, metallic ; colour, dark lead-grey; 

 streak, dark ; brittle. 



The following analysis of a selected sample, by Mr. William 

 Climo, a student of the School of Mines, shovvs that a large 

 proportion of the copper has been replaced by silver, iron, and 

 zinc, and the antimony by arsenic : — 



Sulphur 



Antimony ... 



Arsenic 



Copper 



Iron 



Zinc 



Silver 



99-57 



This would be represented by the general formula, — 

 [(CuFeZnAg)oS] -f (SbAs)2S3. 



A massive variety of fahl-ore has been described by Mr. 

 William Skey, F.G.S., Colonial Analyst, from Eichmond 

 Hill, Collingwood, where it occurs as a narrow segregated vein 

 in a gneiss rock. At that place it is often highly argentiferous ; 

 but the sample from Coromandel is poor in silver. The asso- 

 ciation of the latter with auriferous andesitic lavas, tufas, 

 and breccias is highly interesting. 



Nagyagite. — During the past year several specimens of an 

 ore from the Sylvia Mine, Tararu Creek, Thames, rich in lead, 

 gold, and silver, have been analysed at the School of Mines. 

 Careful experiments proved that the gold did not exist in a free 

 state, and a subsequent exhaustive analysis showed the ore to 



