234 University of California Publications in Geology [Vol. 13 



sulphides, are, as a rule, somewhat rounded and smoothed as if by corrosion, 

 and are frequently penetrated by the sulphides in distinct embayments, which 

 resemble those so common in the magmatieally resorbed quartz phenocrysts of 

 rhyolitic roeks.55 



The sulphide-augite mixture constituting the ore grades out to a 

 quartz monzonite in a distance of from six to twelve feet. The quartz 

 monzonite is of normal composition and appearance. Its plagioclase 

 varies from Ab 00 An 40 to Ab 33 An 33 . The rocks of the transition zone 

 are such as would be obtained by mixing the quartz monzonite and 

 the ore in varying proportions. Their textures are hypidiomorphic 

 granular and the lack of idiomorphism of their augite individuals is 

 as pronounced as it is in the augite of the ore body. The plagioclase 

 of the transition zone varies from Ab 63 An 35 to Ab 07 An 33 , a less calcic 

 feldspar than that of the normal quartz monzonite. It would appear 

 from his descriptions that pyrrhotite and chalcopyrite give way to 

 magnetite, titanite and pyrite as accessory constituents at about four 

 feet from the edge of the ore body proper. 



Knopf concludes that the primary igneous origin of the sulphide 

 ore body .... is believed to be established by the following facts, 

 stated summarily : 



(1) All the rocks, including that which composes the ore body and those 

 which surround it, show an entire lack of pneumatolytic or hydrothermal alter- 

 ation, such as the development of tourmaline, sericite, chlorite, carbonates, or 

 other secondary minerals. They are fresh unaltered rocks in which the ferro- 

 magnesian minerals are notably lustrous and the feldspars clear and vitreous. 

 Such minor alteration as was noted is plainly owing to slight post-mineral action. 



(2) There is a textural relation of the sulphides to the augite as shown by 

 the tendency of the pyroxene to show idiomorphic boundaries against the 

 sulphides. This is a feature not easily explainable other than by the hypothesis 

 of an igneous origin. 



(3) The zonal arrangement of basic phases of the quartz monzonite around 

 the ore body indicates that a marked differentiation has taken place in the 

 magma concurrently with the segregation of the sulphides. This differentiation 

 is expressed' mineralogically by the decrease of plagioclase, orthoelase, and 

 quartz, and the concurrent increase in ferromagnesian mineral as the ore body 

 is approached. The increase of ferromagnesian content, instead of appearing 

 as hornblende or biotite/ however, appears almost exclusively as augite in the 

 ore body. It is noteworthy in this connection that if the differentiation took 

 place through the agency of the mineralizers or the volatile fluxes of the magma, 

 as believed by Michel-Levy, there is a conspicuous absence of flourine-bearing 

 and hydroxyl-bearing minerals in the final product. Contrary to what might 

 be expected under this hypothesis, the minerals biotite and hornblende decrease 

 in amount with increasing proximity to the ore body. 56 



55 Ibid., p. 330. 



56 Ibid., pp. 335 and 336. 



