Show I 1 j the geology of J by george H dern r an article on the geology and of mercur is bound to be more or less unsatisfactory alike to writer and reader because of the uniqueness of the deposit and the consequent difficulty in reaching incontrovertible co conclusions regarding its origin it is essential for the miner to have a practical working knowledge of the geology of his property whether GEORGE H DERN this knowledge be technical or merely the result of experience and observation if he would be successful in prospecting for ore he must know fhe peculiar characteristics of his vein and must learn to understand its behavior at all times and under all conditions but it is not strictly necessary for him to be familiar with theories as to where his mineral came from and how it got into the rock and if he has evolved adequate rules and methods of his own for finding ore he is apt to give little thought to the probable genesis of the metal in mercur prospecting for ore is a most interesting pursuit and requires constant careful study the nature of the veins is such that conditions are not regular or uniform and the unexpected frequently happens what is true in one mine may be untrue in another or in a different part of the same one though the veins are identical such theories as have been advanced advance dhave have not availed to overcome the confusing obstacles and seeming inconsistencies that are encountered hence consideration of these theories forms no considerable part of the fhe miners work in this camp in 1894 mr S F emmons of the united states geological survey began an examination of the mercur district for the avowed purpose of discovering some characteristic by which the gold ledge could be more readily traced before the inspection was completed mr emmons was obliged to return east and the completion of the work devolved upon his assistant mr J E spurr who made the detailed study and deduced the conclusions the investigation was oca careful reful and thorough and the scholarly rb report which res resulted bulted has not been superseded by any marei more recent utterance this publication has been valuable in calling dt attention to certain phenomena which are important and wh which iseli might otherwise have passed unnoticed and if mr spurrs theory as to the probable origin of mercur gold Is not unanimously accepted by operators in the district it is at least fair to say that no more plausible hypothesis has yet been put forth A summary of mr spurrs report will be instructive and appropriate in connection conne etian with a general description of bf conditions which obtain in this interesting gold camp As is well known the structure of the oquirrh mountains in which mercur bissit bated is mainly quartzite and limestone in the mercur district the latter exclusively prevails as the country rock the producing part of the camp is located on the eastern slope of an anti fold the strata having a dip of 15 to 20 degrees it is customary to say that the formation and veins dip northeast but as a matter matte of fact the stratification frequently conforms closely to the contour of the surface and we f ind find synclines syn clines and basins with the result in such cases that the general dip of the camp is entirely lost or changed I 1 overflows of igneous rocks are found at two points porphyry peak is a pointed mountain of birdseye birds eye porphyry toward the northerly end of the district it is not believed that this eruptive rock is in any manner connected with the of the camp south of mercur is found a large body of white porphyry which has been designated as eagle hill porphyry it seems probable that this volcanic rock played a part when the values were deposited as will hereinafter be recited generally speaking it has been customary to say that there are three ve veins I 1 n S or lodes in mercur the lowest of these Is popularly known as the silver ledge because in the early it was vigorously worked for silver though seemingly with rather ather indifferent success this ledge beng ing chiefly composed of limestone is s very hard and has resisted erosion so that is is characterized by a bold outcrop where it comes to the surface the silver ledge is 19 the best guide to the location of the gold ledges from to feet above the silver ledge occurs the lower gold ledge which in the light of more recent developments is now generally called the middle vein usually about forty feet higher than this is the upper gold ledge the distance between these two veins is i S not constant and in some instances cnstance they come together and form immense ore bodies in practice we find another gold bearing stratum which is designated the third gold ledge this is a large low grade deposit lying immediately upon the silver ledge the accompanying cross section for which I 1 am indebted to mr A H brown engineer for the consolidated mercur company shows the occurrence of the ledges in a particular portion of the Mer mercur curmine mine it may be taken as typical of of the formation of the camp camp except that the unusual features upper gold led ledge ae low third th blirer zed leage ya L ime go cr of faulting and junction of the two upper gold ledges are here delineated it is true that variable quantities of gold have been found in strata below the silver ledge this has at least been demonstrated in the sacramento and marlon marion mines some little ore has been taken from these layers but the values so far have b been een too irregular to class them as veins or to say that they contain ore bodies of any consequence consequences As a matter of fact only an insignificant amount of prospecting has been done below the sil 11 ver ledge As a rule the gold ledges are all composed of soft friable material although sometimes the ore is hard in a few places bodies of almost raw unaltered limestone have carried good values but this is exceptional in such cases the limestone is more or less seamed and the values are supposed to be in th the e seams it Is an axiom in mercur that the values are in the fine stuff the alne fine stuff being the soft mit material erial which crumbles readily when mined the ore especially in the two upper gold ledges is mostly decomposed limestone although according to the report already cited portions of the veins consist of altered porphyry the presence of porphyry in the veins is generally not alpar apparent i ent by examination mr spurr admits that this porphyry is so greatly altered that frequently field observation could not determine with certainty whether a given portion of the material was of sedimentary or igneous origin and then recourse was had to and chemical examinations As already indicated mr spurr attaches lm importance to the presence of this porphyry formulates his theory for the deposition of the ores he discovered three thin sheets of eagle hill porphyry which had been intruded between the limestone strata these sheets frequently had a shale like appearance pe arance and formed the roof of the ore he further noted that while the sheets are practically parallel yet they sometimes cross from one bedding plane to another mr spurrs conclusions with regard to the ore deposits are thus summarized by mr emmons there have been two distinct periods of in this district during the first what is called the silver ledge ore was formed and during the second the minerals of the gold ledge were deposited in each period the minerals constituting the ore were deposited mainly along the lower contact of a porphyry sheet where a somewhat t porous or brez brec dated elated zone had been formed by the intrusion of the igneous mate material fial which the mineralizing mineral izing solutions reached through fractures or or fissures extending downward from the respective sheets that the minerals of the silver ledge were pressed out of the cooling body of porphyry with the included water and brought to their present position in an aqueous ro solution lution that the characteristic minerals of the gold ledge however were at an entirely later period brought to their present position through the system of northeast fractures by vapors proceeding from some unknown body of igneous rock which did not reach the surface mr spurr himself states his general theory for far the gold ores more mor 6 fully in the te following words subsequent to the introduction of the porphyry 7 and the formation of the silver ores dres a comparatively local disturbance brought about the formation of a set ot of nearly vertical northeast fissures or trac frac aured zones these fissures established a communication with a body of igneous rock at an uncertain depth below and afforded a vent for moist vo volcanic leania vapors the decomposition of the gold ledge sheet of porphyry was already far advanced at the time of the formation of the fissures 6 these e s e ii fissures s sur ea therefore did not continue into the porphyry as open channels the movement produced in the porphyry only a slight rearrangement of the individual grains in the lowest sheet however that of the silver ledge the porphyry had bad become so indu rated at the period of the primary that in only a few cases in in the vicinity of the principal mines does it show any subsequent softening due to oxidation in this hard altered porphyry the fissures are as clean cut as in the limestone the ascending vapors therefore found no impediment to their progress till they reached the second sheet but this offered no open passages and so interposed a blanket like barrier to further upward in motion the limestone at the lower contact of the porphyry however had been partly at the period of primary and in the succeeding period had been rendered porous bythe leaching out of a large part of the rest residual dual lime I 1 along this porous zone the vapors ars spread out and becoming cooled depo deposited sited the gold and the associated minerals they also penetrated pent rated to a small degree upward into the less permeable altered porphyry this is mr spurrs theory of the origin of the mercur gold and while a number of weighty objections might be offered it will not be worth while to state them since there is nothing more tangible to offer in its stead his explanation of the formation of the silver ledge is not questioned there are those who think the gold ledges were enriched by a similar means but mr spurr argues that certain phe phenomena 3 which he points out render such a position untenable it is true that the theory of the deposition of metals by vapors is one that is rejected by very many m affy geologists and it is quite possible that the presence of gold in limestone at mercur has not yet been correctly de accounted counted for for discussion of thi the e genesis 9 anesis of the ores Is more interesting than profitable perhaps it will be more pertinent in this article to complete the short description already begun of the ledges and the ores we may leave the silver ledge proper out of of the discussion for this deposit does not carry enough silver to be profitably worked and its gold content is trifling fing the lower or third gold vein already mentioned as lying immediately above the silver ledge is probably nothing more or less than the lowest of the three sheets of bf porphyry referred to by mr spurr together with some of the adjacent limestone greatly altered the ore in this lode is usually low grade and it has not been so extensively worked as the upper veins for that reason occasionally however bodies of good ore are encountered in it and the sacramento geyser marion and mercur mines mine shave have taken considerable tonnages ton nages from it however the tie material is frequently very talcy dalcy making it an undesirable leaching article because c use of imperfect percolation and conse quent poor extraction of values by the era nide process the other two gold ledges are in all respects alike neither of these two tw lodes has any peculiar characteristic whereby its ore may be distinguished from that of theother in the mercur mine the lower is asua usua usually lly the larger and richer while in the golden gate the reverse is the case As has already been stated in some places the two veltis veins come together forming ore bodies of great thickness this is the experience jn the upper portion of the golden 6 ate anine where ore was founds found ninety feet thick I 1 in the mercur mine also a similar condition has been encountered d from the electric tunnel up to the lulu workings the theore ore being continuous for nearly seventy fek feet there are two classes el asses of ore the oxidized and the base or sulphide the latter averages the richer the oxidized an excellent cyaniding cyan iding material in its crude state except when bodies of clayey or taley material are encountered the rhe base however is refractory and must be roasted he be fore becoming amenable to the cyanide process mr spurr laid it down as an indisputable fact that the ores of the camp were originally all sulphides sulp hides and that the present oxidized bodies are due to weathering which ia probably pr bably true although I 1 believe some of the operators of the district reject this theory and maintain that the oxidized ores never were base vie tae ore runs in shoots just as in other formations the veins or ledges are continuous tin lious throughout the camp and were readily found by prospectors in numerous properties while small quantities of gold are always present the is not so general or uniform that the discovery of the vein means the discovery of ore As a general thing the largest ore bodies are the richest provided the locality is within the boundaries of an ore shoot some of the highest grade ore of the camp has come from the thick ore body in the golden gate mine already referred to in the mer cur mine likewise the best ore has usually come from places where the vein is thickest while the values often drop below pay when the vein pinches down to five or six feet this rule does not mean that a great thickness of vein n necessarily implies im plies a big body of bf ore to illustrate an exception the bric brickyard byard mine may be cited for where this property was first opened up the foreman frequently expressed the wish that the gold which was disseminated through about sev bev enty five feet of vein material might nave JIM been concentrated in about fifteen feet this emphasizes the vital issue of mercur which is how low grade ore can be made to pay though new devices improved mechanical ch appliances and perfected metal metallurgical lurg c 0 methods are continually making it possible to produce a profit out of lower jower and I 1 lower ower grade ore yet there are ni millions I 1 lyions upon millions of dollars worth of gold in mercur which will never be extracted because too many tons of rock would have to be handled in proportion to the gold recovered few people have any conception of the quantity of gold that may be contained in the mercur hills one operator whose property has not yet become productive has made the assertion that he has a billion tons of ore that will run per ton if this is true of one small group where may not calculations for the entire district lead us this paper has been restricted to the camp of mercur proper the west dip is the recurrence of the mercur formation on the western slope of the anticline general conditions here are very similar to those which obtain at mercur the work has all been done on only one vein however and this vein is not so large as at mercur besides being t lower grade it stands much steeper than in the main camp the dip being about 35 degrees westerly at sunshine three miles south of mercur the formation and seem se em to be identical with mercur the silver ledge can be traced almost the entire distance and between the two camps cameos the gold bearing strata in the sunshine and overland mines are doubtless the same as in mercur |