REVIEWS 279 



lar type; shear zones filled with quartz stringers; disseminations of 

 sulphides in amphibole schists. They are in greenstone, granite, gneiss, 

 or amphibolite. Some of these deposits are accompanied by sericiti- 

 zation and the development of horny silicates in the wall rock. Some 

 have been subjected to the stresses of dynamic metamorphism and show 

 the effect of pressure in lenticular development of quartz and in the 

 development of minerals like biotite. The values are gold, silver, and 

 copper. Minerals represented in these deposits are quartz, calcite, 

 siderite, flourite, tourmaline, biotite, epidote, garnet, chlorite, specu- 

 larite, pyrite, pyrrhotite, chalcopyrite, galena, zinc blend, molybdenite, 

 tetrahedrite, bornite, and chalcocite. It is suggested that these ores 

 are genetically related to the granite magma. The pre-Cambrian 

 deposits are not extensively developed. 



Contact metamorphic deposits are developed where the early Ter- 

 tiary intrusives, consisting of monzonites, quartz monzonite, grano- 

 diorites or their porphyries, cut through limestone or calcareous shale. 

 Metamorphism is not excessive and rarely extends more than a few 

 hundred feet in a horizontal distance. Mineralization usually accom- 

 panies metamorphism. Copper, as chalcopyrite, is most common in 

 the contact metamorphic deposits, but is usually accompanied by zinc 

 blend. Magnetite is locally developed. With two exceptions, gold and 

 silver are present as traces only. Galena is generally subordinate; 

 pyrrhotite is not common. Other minerals are quartz, calcite, garnet, 

 epidote, wollastonite, tremolite, specularite, magnetite, pyrite, molyb- 

 denite. Some of these deposits are important. Indicating a transi- 

 tion between contact metamorphic deposits and fissure veins formed 

 by magmatic solutions under conditions of less temperature and pres- 

 sure, there are fissure veins in limestone, the walls of which are in part 

 converted to garnet and other heavy silicates. The magmatic solutions 

 causing contact metamorphism added silica and the metals to the 

 rocks intruded. 



Certain veins, not replacements in limestone, are in close genetic 

 relation to the same early Tertiary intermediate porphyries, which 

 locally produced contact metamorphic mineralization. Perhaps $20,- 

 000,000 gold has been derived from these veins, which are believed to 

 be of deep-seated origin. In a few of these veins silver is the most 

 important metal. Quartz, pyrite, and gold are almost always present; 

 barite is exceptional. Tourmaline, specularite, pyrrhotite, magnetite, 

 flourite, molybdenite, have been noted. Other minerals are calcite, 

 dolomite, chalcopyrite, galena, zinc blend. Wall-rock alterations are 



