50 H. I. JENSEN. 



tain native copper 1 and "Cupriferous Tuffs of the Passage 

 Beds between the Triassic Hawkesbury Series and the 

 Permo-Carboniferous Coal Measures of New South Wales." 2 



Vogt in his contribution to the Posepny-Van Hise discus- 

 sion on ore deposits, maintains that copper deposits are 

 occasionally due to magmatic differentiation. G. A. Waller 

 considers most copper veins and deposits to be due to 

 magmatic extraction, therefore to be primarily derived 

 from igneous rock, from which it has been in the first place 

 removed by heated magmatic waters. 3 



My specimen being of considerable size, and mining 

 operations having been commenced in the vicinity of 

 Lautoka at the time when I was testing the mineral the 

 occurrence seemed to me to be of sufficient interest to 

 publish the results which I arrived at. 



A microscopical examination of a thin slice of the ore 

 showed it to consist essentially of two metallic opaque 

 minerals, one of which is of a fine blue-black colour by 

 reflected light, the other of a soft brown tone. The blue- 

 black mineral consists of chalcocite (Ou 2 S), with perhaps 

 more or less magnetite (Fe 3 4 ). The brown mineral is 

 bornite (copper iron pyrites Ou 3 FeS 3 ). Both minerals are 

 crystalline and are graphically intergrown. They form a 

 crystalline meshwork with a dendritic or mossy appearance, 

 in the interspaces of which are found microlites of felspar, 

 corroded hornblende crystals, and a little biotite. In some 

 places small aggregates of hornblende and felspar are 

 included in the metallic mineral. 



1 Records Geol. Surv. of N.S.W., Vol. vin. 



8 Kept. Aust. Assoc. Adv. Science, 1888. 3 hoc. cit., 1902. 



*" There has been a find of copper ore at Navilawa, about 12 miles from 

 Lautoka. Mining operations have commenced, and five tons of ore have 

 been shipped. The ore is said to be turning out well, and this may 

 perhaps be the starting of a large industry." — Daily Telegraph, Sydney, 

 March 30th, 1907. 



