Bisbee daily review., 1905-12-17

dacite occurred at intervals for a long
 time and produced several of the for
 nations mapped, which include tuffs
 and flows.
 The structure is so complicated
 that no general cross sections have
 been made. Some interesting infor-
 nation on faulting has, however.
 been obtained, chiefly from mine
 workings.
 The most important mineral veins
 occur in the early andesite. and do
 not extend into the overlying rocks.
 The naturalization was probably
 caused by hot ascending waters inl-
 mediateiy after the earlier andesite eruption. The primary ores have
 gangue of quartz, adularia. and
 some sericite and carbonatesI and contain silver sulphides-such as ar gentite, polybasite, and stephanite- silver selenide, gold in a yet undeter- mined form, chalcopyrite, pyrite, and some galena and blende. The depth ot oxidation is irregular. In the ore or the oxidized zone no important changeS in the amount of gold or sil- yer, as compared with the primary ore, have taken place. The ore near the surface is not truly oxidized ore. however, but is an intimate mixture Of original sulphides (and selenidesl together with secondary sulphides, chlorides and oxides. Secondary sui bhldes include argentite and pyrar- gyrite
 A series of veins of small import ance commercially within the Tono- pah district was formed after the eruption of one of the members of thei iShYolite-6acita Gylriest-the Tonopah shyolte-dacite. These veins may be large, but are usually of low grade or barren. They frequently contain a greater proportion of gold than the earlier andesite veins, and have otherl distinguishing characteristics.
 A series of veins of still less import ance was formed after the eruption or one of the later members of the rhyollt dacite series-a siliceous shy ohte, which makes up some of the nils near Tonopah. One of these Mount Ararat, a denuded volcanic neck, IS traveTsed by Assure veins mat carry very little values.
 Fart Of the earlier andesite is pro foundly altered. The maximum ef- feet of the waters which caused these alterations was the formation of theI mineral veins along their circulation channels. The discussion of these processes is followed by the detailed study of analyses of typical speci- mems. The conclusion is drawn that the mineralizing waters were charged with an excess of silica, and probably Of potash, together with silver. gold. | anumony, arsenic. copper. lead. zinc | and selenium; that they also contain. ed carbonis acid and sulphur. with some chlorine and flourine, but that they were noticeably deficient in iron.
 The alteration of the later andesite by thermal waters is also discussed. By comparison of analyses and by studies it is concluded | that the waters which produced the were highly charged with acid and sulphureted hydro gen, and contained magnesia, iron and lime.
 The two theories of the origin of hot springs gs-atmdspheric and mag matic-are discussed by MT. Spur in connection with the Tonopah phe- nOmena. The meaning of the nature of the metals in the Tonopah veins is also discussed. The conclusion is reached that the waters which pro- duced the veins were largely given off from the congealing lava below.
 It is interesting to note that Mir. Spurr finds close resemblance be- tween the Tonopah ore deposits and the deposits of the Comstock lode in Nevada and on the Pachuca district h Mexico. The ores of Silver City and the De Lamar districts in Idaho are also similar in many respects to hose of Tonopah. These deposits all occur in Tertiary iavas, chiefly lndesitic.