252 H. W. TURNER GEOLOGY OF THE SILVER PEAK QUADRANGLE 



Granite-porphyry, specimen number 653. — Locality: Silver Peak range, 10.3 

 kilometers south of Piper peak. 



Macroscopically, a dark gray fine grained porphyry. Microscopically, a por- 

 phyry with a micro-granular spherulitic groundmass of quartz and feldspar in 

 which are imbedded crystals of plagioclase, orthoclase, quartz, biotite and 

 iron ore. 



Granite, specimen number 348. — Locality : North slope of the Palmetto moun- 

 tains, 8 kilometers south of west from Barrel spring. 



Macroscopically, a fine, even grained granolite composed of feldspar and 

 quartz with some biotite. Microscopically, the feldspar, quartz, biotite, iron 

 oxide, and apatite. The feldspar is both plagioclase (oligoclase) and ortho- 

 clase, the former showing an idiomorphic tendency. 



Soda-granite, specimen number 349. — Locality : Same area as number 348, in 

 the Palmetto mountains 8 kilometers south of west from Barrel spring. 



Macroscopically, a nearly white fine grained granite. Microscopically, a 

 soda-granite made up of feldspar quartz, biotite, and titanite. The feldspar 

 is chiefly albite and oligoclase. 



QUARTZ-DIORITE 



The dioritic areas in or near the granite area north of Weepah contain 

 at some points quartz and may he designated as quartz-diorite. Some of 

 the rocks of these areas contain biotite, titanite, magnetite, and apatite. 

 In one specimen the feldspar is labradorite in lath forms with later inter- 

 stitial amphibole, forming an amphibole-diabase, but this appears to be 

 merely a f acies of the diorite. 



GRANULAR DIKE ROCKS 



These have already been briefly described under the head of "pre- 

 Cambrian complex" as certain greenstone dikes that cut all the other 

 members of the complex. Sometimes these dike rocks are softer than the 

 surrounding granite, gneiss, and schist, and their courses are then indi- 

 cated by troughs, as the large dike 1.5 miles north of Silver Peak. This 

 is probably the trap dike referred to by Lieutenant Lyle in his travels 

 through this region in 1871. 22 These dikes are composed chiefly of 

 plagioclase and green-brown hornblende and may in general be designated 

 basic diorite. In true diorites, however, the feldspar is oligoclase and 

 andesine, while in some of these dikes it is in part labradorite. By loss 

 of feldspar and increase of hornblende, some of the greenstone dikes of 

 the pre-Cambrian complex pass into hornblendite. An example of this is 

 the large east-west dike before referred to, 1.5 miles north of Silver Peak. 



The dioritic dikes in the Silver Peak formation to the south of the 

 diorite areas above referred to, in the northeast portion of the quadrangle, 

 contain as their most abundant constituent plagioclase. The amphibole 



23 Exploration in Nevada and Arizona. War Department, Washington, 1871, p. 49. 



