KING TONOFAH SHAFT. 

 AGE OF THE VEINS. 



The veins clearly belong to a period subsequent to the formation of the veins 

 in the earlier andesite, as shown by their having the Tonopah rhyolite-dacite for 

 a wall rock. The relatively high content in gold as compared with silver seems 

 to be very common in these post-andesitic veins connected with the dacite- 

 rhyolites. 



KING TONOPAH SHAFT. 

 GEOLOGICAL SITUATION. 



The King Tonopah shaft lies at the contact of the Tonopah rhyolite-dacite with 

 the later andesite. At many points along the irregular contact of these two rocks 

 phenomena were observed indicating that the rhyolite-dacite is intrusive into the 

 andesite. The rhyolite-dacite sends out intrusive irregular projections into the 

 andesite, and isolated dikes or necks appear in the andesite some little distance away 

 from the contact. 



The shaft starts in the later andesite, and at a depth of 38 feet passes into 

 silicified rhyolite-dacite. The total depth of the shaft is 300 feet, and from the 

 bottom a drift was run to the north arid, at the time of the writer's visit, extended 

 48 feet from the shaft. 



VEIN MATERIALS. 



At a depth of 226 feet a zone of silicified rhyolite-dacite with quartz stringers 

 was cut in the shaft. It is several feet in thickness, but was practically barren of 

 values, the highest assay reported being only about $2. Some of this vein material 

 contains, besides quartz, abundant adularia, as is shown by microscopic study. 

 There is also some finely striated feldspar, which may be albite. Some of the 

 adularia shows the characteristic rhombic cross sections, and many of these crystals 

 are entirely inclosed in quartz. 



NATURE OF ROCK INCLOSING VEIN MATERIALS. 



The rock in which this material lies and in which the entire shaft and drift has 

 been driven below a depth of 38 feet is the Tonopah rhyolite-dacite. It is a glassy 

 lava made up for the most part of a glassy grounduiass, usually more or less devitri- 

 fied and altered to quartz, kaolin, and sericite aggregates. In some specimens 

 abundant fine adularia of secondary origin has been found in the groundmass. 

 Scattered small crystals of feldspar usually occur, but they are mostly nearly or quite 

 altered to sericite and sometimes to adularia. The blunt form of some of these 

 crystals shows probable original orthoclase, while some are more elongated, suggest- 

 ing a more basic species. 



