Show hi history story production products i on and geology of esmeralda district di ct the aurora consolidated mines comi pany of aurora esmeralda district min P eral county nevada the construction of wh whose ose modern and up to date milling plant was fully described in the mining review of september 15 1914 has resumed operations again since closing down for the pur pose of making some changes in the plant the output for april according to reports being in the neighborhood of the old esmeralda mining district at aurora nev is twenty eight miles in an air line southwest of thorne a town on the hazen tonopah branch of the southern pacific and its nearest railroad point the town of aurora is three miles east of the california nevada boundary sixteen miles north of mono lake and one and one half miles east of bodie canyon the region is shown near the center of the west side of ulm a af ch a n cc ra real del mantle shaft ja and chihuahua caved op n M SA ka lk af A au k owl Z nevada showing gentle slopes of andesite flows hill aurora plate XV last chance in view of the fact that the aurora has settled down to a period of regular production thus insuring the continued prosperity of the camp after so many years of idleness the following interesting article on its history past production and geologic fea J tures from the pen of james M hill and J published in bulletin of the united i united states geological survey is sure to g be of interest to a v great many of our readers the hawthorne topographic sheet of the united states geological survey history and production the old esmeralda near the southern limit of the productive area was the first vein discovered in the aurora district according to wasson james AT M brawley J AT cored corey and E R hicks made the discovery on august 22 1860 and immediately located four claims the town of esmeralda was built in the gulch just east cast of the i tat j discovery but later in the year the present town site of aurora one and one half miles north was laid out the first mill owned by edmund green was put in operation in 1861 and was followed shortly by several arrastres arras tres and mills in 1864 there were seventeen amalgamation mills in the district the largest which had thirty stamps being the real del monte in bodie canyon up to the year 1864 the camp was very prosperous aurora a about and was the county seat of mono county cal during the year 1864 however misfortunes befell the camp the call california fo ania nevada boundary was run and showed that the esmeralda district lay in nevada the rich bonanzas in the wide west vein on last chance hill became exhausted and bitter litigation over the ownership of the veins on last chance hill developed the camp however continued to prosper z until though the supply 0 ore re which in earlier times could tined was then becoming deputed hi in M 0 O an english company acquired possession of the main group of claims on last chance lill hill I it began operations in 1887 starting the real del monte shaft and connections with the durant vein on oil middle hill but suspended work in 1892 after a vain effort to keep tile alie lower workings of tile the foot shaft free from water most of tile the claims in the esmeralda district were owned in july 1913 by two companies tile the cain consolidated co and the aurora mines co the aurora mines co s chief group containing eleven claims lies on silver 1 hill 1111 though they own five claims on oil aurora hill the cain consolidated co controls about forty claims among which are some of the famous producers in the district in the summer of 1912 these holdings were under option to certain financiers of tonopah To nev who have according to reports of the mining journals taken up the ground and started operations most of the productive ground of the district has now been acquired by the goldfield consolidated mining co A ton cyanide mill has been built and there is every prospect that aurora will gain again a be a producing camp the records of production are incomplete according to a statement of wells fargo co the bullion shipped through them up to 1869 had a value of mr wasson gives the following table of gold bullion shipped without insurance bullion shipped from aurora without insurance from 1861 to 1869 inclusive 1861 1862 1863 1864 1865 1866 1867 1868 1869 he further says that between seven and eight million dollars worth of bullion was shipped by express in 1864 and about 12 prior to the year 1869 it if the reports of production of some of the slopes are taken into consideration even so large a sum as seems a small showing for the camp topography there are four rather low hills south and east of the town of aurora see pl PI XIV known as silver middle last chance and humboldt the town has an elevation of feet above sea level silver and middle hills are separated by esmeralda gulch they are long northward sloping spurs from the brawley peaks which rise to a height of feet about two and one A quarter m miles lies t S south of the town v last cliance chance I 1 hill 1111 east of aurora is a low divide less t than hall feel above the valley which separates willow willo w creek from the gregory flat drainage basin I 1 humboldt hill a low rounded knob about three fourths of a mile northeast of aurora rises t to 0 a height of a little over I 1 feet the mines of the aurora district bare are located on these four hills though at 4 the east end of the hat flat north of town and about feet higher there are a few veins near humboldt and last cliance chance hills geology character and distribution of the rocks the rocks exposed in the esmeralda district are with a single exception of vol V S geological surey BULLETIN 59 PLATE XI XIV GEORGE OTIS H DIRECTOR E E LEGEND 78 quaternary Quater nry wash 6 Z aurite basail cap rock L g 0 rhyolite tuffs and flows daout quatia and associated andesite porphyries ries no i granite ory veins N I 1 kers refer to list ar no esl fault U LIST OF VEINS 1 antelope 2 bald eagle spotted diget ef 3 durant 8 4 humboldt silver lining 6 5 live yankee in 6 martinez juanita 7 old esmeralda 3 r is 8 prospectus 7 9 radical A 10 real del monte R 28 E J 11 sonora 12 summit GEOLOGIC SKETCH MAP OF THE VIC VICINITY OF AURORA MINERAL COUNTY NEVADA 13 utah cortez base from topographic map of 0 the hawthorne quadrangle t 14 wide west last chance vt g 0 1 2 3 v 4 4 1 5 I 1 la 13 g jad comtoi tr IT interval feet E by w wa 14 1 lu 7 i 1311 1 canic origin in the bottom of willow gulch about two miles southwest of aurora see pl PI XIV there is a small indistinct exposure of a rock that appears to be the basement on which the flows were extruded it is a coarsely granular rock and is probably to be correlated with tile the and associated rocks of the sierra nevada at least three series of flows overlie this granular rock the oldest of these flows consists of grayish green altered rocks that are largely quartz arites together with some ande sites this series is exposed on silver middle last chance and humboldt hills and extends couth southeast east up willow gulch for an unknown distance these rocks which are at le 1 feet thick all the veins ot athe ati e district none being found in the young rocks above these flows of intermediate che ical composition lies a series of light i gray era to brownish gray that are particularly well exposed on the flats north anil and northwest of aurora along bodle bodie creek where they are 1000 feet thick and also on oil granite mountain about one mile southeast of town where there is a relli remnant nant of tile the series about feet thick above both the ande sites and lies a black blac kVes vesicular basalt that forms aurora crater see pl PI XIV and covers a large expanse of country to the west of granite moun aloun tain it ranges from about ten to feet in thickness its weathered surfaces are brown all these flows appear to have a gentle dip to the north northwest it seems probable that there was a time of erosion between the andesite and rhyolite eruptions as tile the rhyolite flows rest on an uneven surface that looks like an erosion sur surface fact there was unquestionably an ail inter interval of rhyolite e considerable length between the tile ti of and basalt eruptions for tile the base later flows rests in the bottoms of gu lelles in some places and on the alie tops of n at other places andesite addesi 5 the and associated aein to lave have been exposed by the erosion f the capping rhyolite along the willow streek leek drainage basin the granite moun main ain seems to be a remnant of this capping aich escaped erosion it does not seem probable that the basalt ever extended much its present limits as shown on plate ate XIV for the edges of the flows are afresh esh and in some places along the gulch northeast orth east of gregory flats show the piled up P overturned marginal portions of quickly cooled lava sheets topographic expression of the different rocks r the oldest flow rocks are all much altered alered and are rather easily eroded except where here they have been near the veins eins As a consequence the mineralized ills hills have as a rule even and rather gentle slopes lopes as is shown in the view of last la t chance hill PI XV at the southern end af f silver hill where the rock is much bilici red fied near the bald eagle spotted tiger and radical veins the generally smooth andes ite te surfaces are interrupted by steep cliffs the rhyolite series weathers in rough lifts cliffs and the surfaces of the flows are marked by small steep sided gullies on the long ridge northwest of aurora near bodle bodie creek the topography suggests the badland forms at many points especially on an the northeast side of the ridge the surface of the basalt flows is very rough making the crossing of these areas difficult even on foot aurora crater is a basaltic vent the northwest rini rim of which has las been cut through by erosion it is a beautiful example of a small volcano with he successive flows clearly traceable on its rough ough scarred sides petrography granite the single expos espos re ire of granite in the district lies ies in the bottom of willow gulch about one me and one quarter miles southwest of aurora arora its boundaries are not well shown on n account of the wash but the lows flows clearly rest on this basement the outcrop is small and deeply weathered icalla no fresh rock being visible numer us large pink orthoclase crystals the max mum length being two inches are present 11 the residual sand covering part of the rea irea the weathered surfaces have a light greenish gray color owing to the alteration of f the constituents the rock is rather coarsely soar sely granular throughout and contains very ery large built pink orthoclase in thin sections the groundmass of this coarse porphyry is seen to be ar none of the minerals except the phen and accessory minerals show any crystal form the minerals present in this ock named in the order of their abundance re orthoclase quartz green hornblende lorn orn blende brown microcline mus avite and the accessory mill rals are magnetite and apatite the minerals are somewhat and the feldspars feld spars are more or less some of the muscovite appears to be primary but part at least is bleached the and magnetite are closely associated and inter growths of these two minerals are common quartz the general country rock on the hills in the vicinity of aurora in which the veins are found is a greenish gray to gray altered porphyry which ranges from rather fine to medium grain few of the are more than an eighth of an inch in diameter and most of them are less the most widely distributed type of rock has a fine grained greenish gray groundmass thickly studded with small white lath chapped all the rock of this type carries some disseminated semina ted pyrite which is particularly abundant near the veins the thin sections show that this rock originally consisted of of and possibly pyroxene set in a fine grained matrix of with some minerals small interstices of the groundmass contain inter growths of quartz and orthoclase the rock is a quartz all the rocks are very much altered presumably by the hot calcareous solutions which deposited the veins the are altered to calcite some quartz and some ome of them show a little green the minerals are completely altered to chlorite and some magnetite the groundmass is altered to an aggregate of chlorite and quartz near the veins the alteration has been much more intense than at a distance of to feet from them in these highly altered zones quartz has been added to the body of the rock which is also cut by stringers of quartz and calcite and are also much more abundant in the rock near the veins whereas chlorite is more commonly developed in the rock at a dis stance from the veins andesite near the bottom of esmer alda gulch one mile south of aurora there is a fine grained light green porphyry apparently patently ly intrusive into the quart though it may be an all underlying flow this fine grained dark rock is exposed in several other localities in the district and it is probably rather widespread in distribution this rock is much altered and contains disseminated pyrite in small quantities and is cut by quartz and calcite stringers thin sections of this rock show that its groundmass is composed of microscopic lath shaped crystals of and the latter mineral altered to clil chlorite in this groundmass are set small well de of built and of both of which are altered the aug 1 t e to logreen green chlorite and the feldspars feld spars to grayish aggregates of and chlorite rhyolite the rhyolite series is made up of a number of relatively thin flows all of which are glassy they range in color from gray through green to purple some of them appear to be but the majority are typical flow on the flat north of aurora some pearl gray rhyll tes are seen near the top of the series flakes of are seen in all of these rocks and quartz can usually be detected with the unaided eye thin sections show that the rock consists of a glassy base having as a rule distinct flow structure which contains a few of quartz orthoclase and some of the slides show that the groundmass suffered some cation accompanied by the development of chlorite and about one fourth of a mile southeast of the old esmeralda tunnel a small indistinct body of rhyolite has been altered to a soft white mass by hydrothermal action but the flows at other places show no alteration by hot waters basalt the basalt of aurora crater is a very fresh vesicular black rock showing a few small green olivine crystals to the unaided eye under the the groundmass is seen to be composed of microscopic ro laths baths and grains or nearly colorless set in a black glass paste the flow structure is well shown by the rough parallel orientation of the long dimensions of the plagioclase laths baths many of which bend around the vesicular openings quaternary gravels the quaternary deposits on lower bodie bodic creek shown at the top of plat XIV consist of unconsolidated sands gravels and silts which a little north of the area shown on the map are quite thick and extensive the surface is covered by fine sandy loani loam which under irrigation lias has produced excellent crops on last chance hill there is a small area underlain by roughly stratified volcanic material shown in the caved chilita chihuahua this material ranges from a few feet to a maximum of twenty feet in thickness and appears to have been reworked by streams in the canyon northwest of gregory flats and about one and one half miles due north of aurora a warm spring issues from beneath the basalt of aurora crater this spring deposits limonite and aragonite the aragonite forms crusts from one fourth inch to four inches in thickness though most of the crusts are less than two inches thick the entire deposit covers an area about feet square to a maximum depth of fifteen feet ore deposits distribution of the |