MoROAN. — The Ifjncoifs l{ricl-K of the Woihi (Unldfeld. 261 



of Waihi and other parts of the Hauraki goldfields. His work on the silici- 

 fied rocks plainly pointed the way to a theory of metasoniatic replacement 

 of country* by vein-material. 



The next year Park (6) described a hypersthene-andesite stated to be 

 from the 300 ft. level (probably No. 3 or 279 ft. level) of the Waihi Mine. 

 He noted as original minerals plagioclase, some (probable) orthoclase, hy- 

 persthene (much decomposed), a little enstatite, a little possible augite, 

 some magnetite, and perhaps quartz. The possible presence of original 

 hornblende (indicated by lozenge-shaped spaces crowded with dark dust) 

 was also observed. Secondary minerals were magnetite, haematite, ser- 

 pentinous matter, calcite, and quartz. 



Park's determination of orthoclase in this, perhaps the first specimen 

 of rock from the Waihi Mine ever microscopically examined, is noteworthy, 

 but, as will be shown on later pages, the primary origin of much or perhaps of 

 all the orthoclase in Waihi andesites and dacites may be strongly questioned. 



In 1902 the writer, without having made any microscopic examinations, 

 but relying on the statements of previous observers and on the results of 

 analyses made by himself and others, stated that " the Waihi reefs lie in a 

 decomposed andesite or propylite, which there is some reason to believe 

 is older than the bush-clad andesite of the hills to the north and west." 

 This latter is " of a different character to that forming the [Martha] hill 

 itself " (7, p. 165). 



Two years later, the writer, having examined a number of sections of 

 Waihi rocks, incidentally mentions that the " comitry " in which the lodes 

 occur is " decomposed quartz-andesite " (8, p. 429). 



In 1905 Mr. Waldemar Lindgren, the well-known economic geologist, 

 made a visit to Waihi. In a subsequent article on the Hauraki goldfields (9) 

 Lindgren states, " Mr. Park determines it [the country of the Waihi Mine] 

 on authority of Mr. Hutton [? Professor Ulrich] as hypersthene-andesite ; 

 all of it, however, is not of that character, for specimens collected on the 

 500 ft-, levelf in the footwall of the Martha lode consist of a dark-green 

 porphyritic rock with recognisable phenocrysts of corroded quartz and 

 orthoclase. The ferro-magnesian silicates, probably pyroxene, are altered 

 to serpentinoid aggregates. Lime-soda feldspars could not be definitely 

 recognized, while the groundmass is micropoikilitic, and certainly contams 

 much quartz. The rock is thus either a dacite or is intermediate between 

 a dacite and a quartz-bearing trachyte." 



Lindgren also says, " The rock adjoining the sulphide ore [at the 500 ft. 

 level, Martha lode] has suffered great alteration, although seemingly fresh. 

 Pyrite and a carbonate, probably calcite, are abundant in metasomatic 

 development, as is a brownish-green serpentine. The veinlets traversing 

 it contain much secondary orthoclase or valencianite, together with quartz 

 and calcite." 



A letter ^vritten by the writer commenting on Lindgren 's article remarks 

 that the lode-bearing rock at Waihi " might perhaps be more correctly 

 called quartz-andesite or dacite " (10, p. 861). 



In 1905 and 1906 appeared " The Rocks of Cape Colville Peninsula, 

 Auckland, New Zealand" (11). In this important work, consisting of 



* The term " country rock," now so commonly employed by writers on economic 

 geology, is, strictly speaking, tautological. The miners of the Hauraki Goldfield, as a 

 rule, employ the more correct expression, " country." 



t Probably the No. 6 or 555 ft. level. 



