The geology of the Coromandel subdivision, Hauraki, Auckland . ard. Quartz, calcite, and pyrite form the principal gangue-minerals, but the hydrous oxides of manganeseare in places not uncommon. The calcite exists in much greater quantity than in the veins of theHauraki and Kapanga Mines, a fact which is doubtless due to the different nature of the country gold occurs with silver in the average proportion of 100 to 50 by weight; the latter metal is there-fore more abundant here than in most of the veins connected with andesites. The bonanza ore has been found to occur as definite shoo
The geology of the Coromandel subdivision, Hauraki, Auckland . ard. Quartz, calcite, and pyrite form the principal gangue-minerals, but the hydrous oxides of manganeseare in places not uncommon. The calcite exists in much greater quantity than in the veins of theHauraki and Kapanga Mines, a fact which is doubtless due to the different nature of the country gold occurs with silver in the average proportion of 100 to 50 by weight; the latter metal is there-fore more abundant here than in most of the veins connected with andesites. The bonanza ore has been found to occur as definite shoots and irregular patches. In the upperlevels of the mines the ore-shoots are said to have been intimately associated with what are termed mineral heads or bars. These are apparently layers of the sedimentary rock, which originallyproved more permeable to the circulating ground-waters than the general mass of the rock, and suppliedaqueous precipitants of gold and silver to the vein-channels. These mineral heads now carry a To accompany Bulletin JV & 4<. By Authority : John Mackay, Gouernment Pnnte< 1-23 high percentage of pyrite, cherty silica, and a clayey material, and often present a greenish colorationwhich may be due to sulphate or silicate of iron. In the lower levels the patches of highly auriferousore generally occurred at the intersections of flinties with the veins, or occasionally in connectionwith faults of slight displacement. Vugs or cavities occurring within the actual veins, and oftenassociated with bonanza ores, are not an uncommon feature in these mines. A specimen from one oithese cavities shows (a) the wall-rock, a light-grey felsitic tuff or tufaceous mudstone, seamed withveinlets of bright pyrite ; (b) white crystalline quartz—this contains a considerable amount of goldin a very fine state of division, and is deposited directly on the wall-rock without any intervening selvageor parting ( frozen on, to use the expressive phrase of the miner) ; (c) an
Size: 1837px × 1359px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, bookidgeolog, booksubjectgeology
