Bartrum. — Geology of Great Barrier Island. 127 



with the divisions accepted by Fraser and Adams for those beds in the 

 Coromandel Peninsula, but these authors adduce several arguments in 

 favour of the view that many of the similar intrusions in the district referred 

 to must have been pre-Tertiary (1907, pp. 88-89). There can be little 

 doubt that those of Great Barrier Island are substantially contemporaneous 

 with these latter. 



Origin of Copper Lodes. 



Unfortunately the writer has not had the opportunity for a very close 

 study of the copper deposits ; the main lode has been worked out, and 

 only a few remnants of the lode-material are visible here and there in the 

 workings. Such information as is available makes Hutton's view of the 

 origin of the deposit untenable, in spite of the fact that he had the advantage 

 of examining the lode whilst mining operations were in progress. Hutton 

 (1869) considered that it originated superficially as a breccia filling a surface 

 fissure. 



The present writer's view is that the lode is due to the metallization 

 of an irregular shatter-zone trending approximately north and south. The 

 solutions depositing the cupriferous material were almost certainly genetic- 

 ally related to the numerous porphyrite intrusions near by. This view has 

 very weighty support from the presence of small veins of mixed sulphides 

 — largely chalcopyrite with galena, blende, and pyrite — which are exposed 

 actually on the walls of porphyrite dykes in old prospeeting-drives on 

 the north shore of Mine Bay, and up a rill entering Mine Bay Creek 

 from the north about 15 chains up-stream from its mouth (the " New 

 Lode " of Hutton's map). 



In the deposit at Miner's Head the ore-minerals are mainly chalcopyrite 

 with its oxidation products ; these have been deposited in the crevices 

 of the shattered vein-filling, which is predominantly a somewhat altered 

 argillaceous rock. Hutton considered that the presence of fragments of 

 " diorite " in the vein-filling showed that the intrusions were earlier than 

 the lode, and therefore had no genetic relations to this latter. He apparently 

 failed to appreciate the possibility that the intrusions are not all absolutely 

 contemporaneous. 



List op Literature cited. 



Bartrum, J. A., 1920. The Conglomerate Band at Albany, Lucas Creek, Waitemata 



Harbour, Trans. N.Z. Inst., vol. 52, pp. 422-30. 

 Cotton, C. A., 1916. The Structure and Later Geological History of New Zealand, 



Oeol. Mag. (n.s.), dec. 6, vol. 3, pp. 243-49 and 314-20. 

 Fraser, C, 1910. The Geology of the Thames Subdivision, N.Z. Oeol. Surv. Bull. 



No. 10 (n.s.). 

 Fraser, C, and Adams, J. H., 1907. The Geology of the Coromandel Subdivision, 



N.Z. Oeol. Surv. Bull. No. 4 (n.s.). 

 Hector, J., 1870. On Mining in New Zealand, Trans. N.Z. Inst., vol. 2, pp. 361-84. 

 Hutton, F. W., 1869. Report on the Geology of the Great Barrier Island, Rep. 



Oeol. Explor. during 1868-69, pp. 1-7. 



1889. The Eruptive Rocks of New Zealand, Jour, and Proc. Roy. Soc. N.S.W., 



vol. 23, pp. 102-56. 

 McKay, A., 1897. Report on the Silver- bearing Lodes of the Neighbourhood of 



Blind Bay, Great Barrier Island, Auckland, N.Z. Pari. Paper C.-9, pp. 75-80. 

 Park, J., 1893. On the Occurrence of Granite and Gneissic Rocks in the King-country, 



Trans. N.Z. Inst., vol. 25, pp. 353-62. 



1897. The Geology and Veins of the Hauraki Goldfields, New Zealand, Trans. 



N.Z. Inst. Min. Eng., pp. 1-105. 

 Sollas, W. J., and McKay, A., 1905. Rocks of Cape Colville Peninsula, vols. 1 and 2. 



