Show geology and ore deposition in in luo lucin n mining m ng district by GEORGE H RYAN A very interesting problem in geology and ore deposition is presented in the old lucin district lying in the pilot range of mountains along the utah nevada line about seven miles south of the southern pacific railway the district being along the line of the first railroad activity through this country was found in the early seventies and the mining confined principally to the fissures containing the lead silver ores especially in the old tecoma property although an attempt was made to mine and ship to the salt lake smelters shelters sm elters for fluxing flexing flu xing the iron found outcropping cropping out on the summit of the mountains on the utah side of the line A lead was built at the foot of the hill on the west side and an attempt made to reduce the ore but probably the high cost of operating together with the crude methods and not very abundant supply of ore caused the abandonment of this line of endeavor for several years the work was of an intermit tent character until attention was centered on the copper deposits at the summit of the hill and east of the scene of the earliest activities tivi ties in the district that part of the range containing the developed ore deposits is composed of limestone probably lower carboniferous dipping to the east at various angles averaging in the neighborhood of 25 to 35 degre degrees from the horizontal the entire sedimentary formation rests on granite which shows along the base of the hill both east and west and the north end of the range is composed of an overflow of later igneous rock radiating eastward from an old volcanic cone situated on the west slope of the range about three miles north of the old tecoma mine the lime stones composing C Om Posing the ore bear ing area range from a thin bedded argil mining lining 1 engineer salt lake city lacious lime on the east to the massive blue and gray lime on the west and they are cut by a series of almost vertical fault fissures having a northeast southwest strike these fissures are filled with a porous oxidized iron and quartz gangue containing irregular shoots and bunches of lead ore principally the oxides and carbonates although some galena is encountered showing that the ores have been greatly altered from the old tecoma mine situated at the foot of a small hill on the west side of the range a wide and easily traceable faul fissure runs in a southeasterly direction paralleling a gulch and crossing the hill in a rather low saddle this fissure has A 1 slight dip to the south and at the tecoma it contains the largest deposits of lead ore so far discovered in the district on account of the barren filling in this fissure east ea st of the tecoma there is a question as to whether it was the seat of ore deposition COPPER MOUNTAIN EW dhru mr e If ELATION OF ORE TO hoew wf alp or whether the ore occurs in or along the other system of fissures where they cross the large one the writer did not have an opportunity to examine the workings closely enough to determine this point but the question presented itself after observing conditions to the east however it is evident that the lead silver ore has been deposited along the lines indicating the most recent geological changes in this district except the NS N S faulting on the summit of the mountain about one and one half miles east of the tecoma is situated a copper deposit of unique interest from a geological standpoint which presents a rather complicated problem in the determination of the origin and probable continuance of the ore along the summit of the hill outcrop ping on the east side is the large body of iron ore previously mentioned but owing to the high percentage of which it contains it did not prove successful whet when it was used in the early smelting smelling sm elting opera eions along the summit of the hill a MI wide stratum of dark blue lime outcrops having havin the characteristic dip and strike and ca con three developed deposits of a rather soft reddish brown copper ore nijah mixed a with a gangue of soapy material ranging in color from milk white to reddish brown brow n and containing as high as 27 per cent with an occasional specimen sho chov ing nuggets of native copper in sc places the ore is partially surrounded by a mass of porous iron or a yellowish brown brow mud the latter condition obtains more bior however on the east side of the deposit where the dip of the strata carries it lower and the mud has filled a good deal of that I 1 part of the original cavity not occupied by the ore these three deposits are located within a distance of two thousand feet along the strike of the particular stratum buano but no actual connection has ever been found between them the central deposit is tm the largest and is the one cited in this discussion as it offers the chance for a more extended observation this central body out cropped originally for about one hundred and fifty feet along the west slope of th the e L hill and about three hundred feet down the slope from the top extending some distance north and south along the stratum but did not come to the surface except in the one place in the development of the deposit a tun T nel was run into it from the west and drifts sent along the boundaries next to the lin the main tunnel entered the north of the outcrop about feet from the POP po tal and was continued through the ore for about feet where a slip was encounter cd having a dip to toche the west of about 20 1 grees with a north south strike drw on this slip each way showed the ore t be broken a good deal and one or two raises disclosed small isolated bunches of ore indicating that the block of ground containing the ore has slid down to the west k 4 41 R na 6 0 7 5 arv west slope of copper mountain Looking South showing upper tramway terminal from the position occupied by the enclosing strata at the time they were thrust up the drifts through the disclosed a banded or stratified structure corresponding in dip and strike with that of the lime while the drifts along the boundary showed the walls to be irregular and not in any way except for a slig t tiomir in places leaving a I 1 le alcose ose lime sand beleen the pre and the e all ordinarily the valls aref hard una U ered ill lime le having of 0 noramary or nary amary water worn cavities yf the maia mai was about forty to fifty feet beet anick but extended up and down w in ir zeular cavities or pot holes of various sizes there was also an outcrop of the characteristic ore on the east side of the north of the big body of iron the eary development of this east was mm thelast the east side of the hill and at that ime me iloco no connecting ore had been found be lyeen the two bodies although scattered aad broken bunches of ore were found in raising along the fault plane from the west side bide i in the development of the east ore body I 1 etwas it was followed down on the dip of the lime S vail until the ore was abruptly cut but off by an dike of about forty feet wade 1 standing almost vertical with a nori south strike the ore in this body is id identical e a with that on the west except that ahe the lower portions of the bed are composed principally of a re deposition of the t leached beached contents from the upper part of the deposit sometimes being a secondary enrichment of the existing bedded ore and I 1 again appearing as a precipitate partially i filling the channels and crevices in the gangue and along the outer edge of the which otherwise does not carry 7 values this dike also cuts one of the north east southwest fissures which shows on both sides of the dike but the intrusion was evidently at a much later date and no connection can be traced between the occurrence of the dike and the ore in the lead silver fissure or the bedded copper deposit A tunnel from the west cuts this dike about feet from the surface where it has the same appearance as that shown in the upper workings the lime strata in contact with the do not show any alteration other than crushing which would indicate that the was thrust up in a comparatively cool condition in fact the condition of the sides of the dike prove this as they are seamed with crevices running in downward curves which gradually assume a course parallel with the sides such as may be noticed in a column of stiff brick clay issuing from a pug mill on the west side of the ahe hill some work MR 14 r KW 4 IL MC I 1 OP A east slope of copper mountain looking south showing bench caused by faulting dotted line shows approximate outcrop of dike has been done on another intrusive dike about six feet wide which is composed of a clear white talcy dalcy material somewhat similar to the gangue found in the ore some minute particles of iron pyrite are discernible but no trace of copper is found this dike strikes east west just south of the main ore body and stands almost vertical there is some evidence tending to show how that this intrusion was war prior to the bauit which separated the large larg 1 ore body and it may therefore have existed prior to the up raising of the strata and have had some connection with th the e origin of the ore but so far neither point has been fully demonstrated st rated the throw w of the fault is in the neighborhood of feet and it seems to be merely a minor mino r slip occasioned by the displacement ofa of a large section of the west erly portion of the hill or tecoma ridge S which is composed in part of the same kh kini of limestone as that found at the summit of copper mountain subsequent to the time when the writer was at the property development work by lessees lessels under the direction of george I 1 wilson disclosed a small body of ore ly lying ing between the main fault AA A A and another fault BB B B having a steeper dip than the former one after locating the B BB B fault with relation to the other one mr wilson drove the upper tunnel through the first fault ault f and opened the ore in the block or of ground lying between the two the main fault between tecoma ridge and copper mountain has a strike about north south possibly bearing a little to the west of north ane s alt be somewhat A the present 19 steeper ohp th what the dip a 0 tu dually is has not been 39 39 as there is no alon along 9 39 itly na no prospecting or 39 cons conse equer que 40 anora to 10 expose the fault plane tt t 40 m v 40 the evidence is all seen in the of corr corresponding e sp strata exposed in the dif ferent blocks or sections of the hill the distance of throw is in the neighborhood of 2500 feet downward and westward on the summit of tecoma ridge near its west end the strata similar sij nilar in character to those surrounding and containing the copper ore near the top of the hill are exposed and at one place the ore has been opened and is identical in appearance with the other deposit the dip and strike of the formation are about the same as ain m the main vart part of the hill to the east but the extent of the downward course of the limes along the bedding i magical ma owing to the fact that the grana comes to the surface for some distance up the north slope of tecoma ridge the lat 05 A A F looking north from copper mountain showing schowine how the east slope conforms to the dip of the strata ter may therefore be a comparatively thin section of lime resting on a granite base various theories have been advanced as to the or origin agin of these bedded deposits of copper ore among them bet being g that erosion carried away the greater portion of the mountain containing the original deposit or that the present is the result of leaching and deposition re by wafers percolating through a larger deposit of sulphide ore in the mythical top of the hill which has been removed by erosion again the afie origin was sought in a fissure which it was hoped would be found leading in into the present existing deposit from a sulphide ore body presumably at much greater depth there has been an enormous amount of erosion beyond a doubt as is evidenced by the great depth of the detritus in the surrounding vallar balbo t nt the arguments ad V van tt t of the character of occurrence of the g copper somrith relation to the brence of the he of th thor r ore thel tha faulting an ah d the g arup the in point of time an T q the evidence tends to shaw sh 6 nv h a t pird rs particular copper copp er deposit was contain ed in the enclosing strata at tile the time they were tilted into their present position and therefore the origin is so remote as to be almost out of consideration it may be that the iron filled the entire cavity and on account of its peculiar composition offered a favorable precipitant for the copper from whatever solution carried the latter this is quite possible but could only have occurred prior to the elevation of the strata as the ore is stratified in conformity with the enclosing lime strata if the iron and acted as the i precipitant the sm small all percentage of iron d Ii he ehigh high percentage of in the bre is accounted for due to the fact that the iron would be replaced by the copper I 1 while the would not be destroyed 1 but remain in the ore the main point to be deduced after a study of existing conditions is that this copper deposit had its origin prior to any uplift and if such origin was from solutions rising through fissures the fissures are not in any part of the so far explored and must certainly have antedated all of the present fissures summing the situation up in chronological order it appears that the bedded copper ors ore Z deposited while the rocks still lay in a horizontal position then came the tilting of the strata accompanied by the EW E W fissuring in which the lead silver ore was deposited and lastly the intrusion of the erupt ives which may have caused the NS faulting which cuts all the deposits as does the dike previously mentioned and which parallels the Ns fault these last disturbances were probably y occasioned by the death throes of the ol 01 old d volcano when it belched forth its last streams of lava possibly into the waters of prehistoric lake bonneville |