Show tungsten ten mining mi n ng in n boulder county colorado colored 0 by leroy A PALMIR PALMER the increasing use of the rare metals has brought boulder county colorado into prominence in the mining world as the leading tungsten district of the united states and in fact of the world and the only one in this country where the metal is found in the form of boulder county made a record as a bonanza silver district soon after sam P conger discovered the caribou mine in 1883 but no one paid any attention to the black iron that occurred in large quantities and spoiled much otherwise good agricultural ground on several ranches located near the mines discoveries in this locality have been made over a range of eight miles east and west and sixteen miles north and south but the developed mines lie in a belt extending for eight miles in a general northeasterly and southwesterly direction in the southwest part of boulder county the mineral the only important source of production is a black to brownish black ferrous distinguished from similar minerals by its fusibility 5 specific gravity 71 to 75 and perfect cleavage it has a hardness of 4 to 45 and crystallizes in been eroded into the precambrian pre cambrian formation of the front range and the divide the tungsten district lies three miles west of the nearest sediment aries in the precambrian of the front range geology the most important rocks are a granite and a schist which grades into quartz mica schist and mica schist occasionally casio nally bodies of one rock are found within another showing no distinct contact but usually each has a well defined area intrusive granite in irregular bodies cuts the gneiss and granite and dikes varying malj a ap N mama 6 ae EMU fig K 1 dike and surface working star mine fig 2 dike congor mine pig fig 3 shaft house conger mine in 1900 a former partner of mr conger returned from arizona where he had seen f tungsten Sten mined and first recognized the value of the long neglected ore that year two shippers commenced work on the tungsten ore mr conger through a lease on one of the ranches and the great western exploration V and reduction company the output for 1900 being forty six tons averaging about 60 per cent WO in 1912 the output was s equal to tons of the go 60 per bent cent product or 60 per cent of the total output of the county for that year mining engineer san F francisco ran cisco cali tornia fornia the monoclinic system the deposits in this field are notable for the absence of the minerals usually found associated associated with tungsten pyrite and galena have been found in rare instances and there is one instance of an occurrence of native copper analyses from the southwestern part of the field show from per cent to per cent with a slight excess of feo and per cent to per cent mno from the northeastern part of the field the mno alno has been found as high as per cent boulder county extends from the western edge of the plains westward to tile the continental divide passing through up tilted sedimentary rocks in which steep canyons have from basalt to acidic porphyry are found in the northern and western portion of the field the granite and the gneiss are complex being made up of a primary rock mass and many intrusions that form a large part of the whole except for the dike rocks there are few that do not show metamorphosis but as the age of the varied there is a corresponding variation in the degree and the older have been so metamorphosed that they are distinguished from the enclosing rocks with difficulty originally the granite and the gneiss old granite were intrusive and their structure varies from massive to one in which diorec dional structure is very noticeable with marked segregation of mica the granite is of the ordinary hornblende variety with orthoclase the principal constituent of the granite proper and quartz becoming prominent as the rock grades into gneiss the gneiss which lies in the western and northwestern part of the field has the general chemical composition of the granite and frequently resembles it physically but is much older evidence is that it is of sedimentary origin neither gneiss nor granite shows any regularity of dip or strike pegmatite occurs both coarse and fine grained the coarse as dikes which frequently hold large masses of country rock in suspension and the fine along seams and fracture lines where it was formed by the solution and crystallization re of the surrounding country rock into which it grades this form usually being found in connection with ore bodies the ore is usually found as a breccia which includes a chalcedonic quartz or hornstone dike granite and pegmatite country rock and location of Ore bodies the best ore bodies are found in the granite granite and the more parts of the gneiss most of the mines are in the granite or near the granite gneiss contact there being very few instances where they are located any distance within the gneiss and valuable ore bodies in the more pronounced or the schistose portions of the district are extremely rare when a vein reaches the latter formations it pinches and is usually barren As the chemical composition of the gneiss and the granite is almost identical the explanation of this point is undoubtedly physical the were more or less plastic and the forces that caused fracturing and consequent opening of channels in the pegmatite and gneiss old granite resulted in crumpling and shearing in the schist so that what openings were formed were small and were frequently closed again by the plastic schist in this way restricting the circulation of the mineral solutions or shutting them off entirely A similar condition has been noted in gilpin county a few miles to the south in the nederland beaver creek southwestern portion of the field fissuring seems to have been subsequent to the intrusion of the pegmatite dikes and to have followed them as lines of least resistance the general strike of the veins is from due north to north 80 degrees east although no regular vein systems can be defined the dip is rarely less than 45 degrees and usually approaches the vertical history of ore deposition prof R D george in his excellent report on this field has summarized the history of the ore deposition as follows a the first opening of the fissures accompanied compa nied by much crushing and the formation of angular fragments b the of the rock frag in ments ants and their partial cementation with slight local breccia into an open deposition of tungsten mineral c the second movement and d the first important deposition of tungsten mineral movement crushing the e the third breccia ore and mingling it with much rock matter and in places forming a new breccia by pressure f the second deposition local of chalcedonic silica important tungsten deposition g the second partially cementing the breccia it is possible that this was a secondary enrichment but evidence to that effect is not definite 7 7 vl 41 1 1 4 K ile I 1 A fig 4 open clyde mine h the contemporaneous deposition of silica and tungsten i L local solution of the tungsten and deposition of silica j locally movement later than any recognizable deposition of tungsten and silica resulting in siding and brec clation particularly noticeable at the clyde mine mining As mentioned above many of the veins follow the general course of the pegmatite pet dikes sometimes on one wall sometimes on t the he other and occasionally splitting a dike fig 1 shows through the trees in the background the dike at the star mine of the wolf tongue mining company and pig 2 shows the prominent dike north of the conger shaft of the primos mining corn cora pany the soft nature of the rendered the veins susceptible to erosion which impregnated the soil with float in their vicinity and made their location comparatively easy such a condition naturally led to surface mining and the entire district is marked by open cuts trenches and shallow shafts as illustrated by figs I 1 and 4 the latter shows an open at the clyde mine which was worked downwards from the surface and upwards from a drift at the 80 foot level of the clyde shaft the timbering shown illustrates the style usually used in the narrow veins of the district much aluch high grade ore has been shipped in the past that was obtained simply by picking up float which was found abundantly ar in pieces as large as ones fist and after this supply was pretty well worked over the surface soil near the outcrops was shovelled shovel led up and hand jigged A three good sized mining companies have been organized to work the tungsten ores the primos primes mining company wolf tongue mining company and colorado tungsten corporation all with head offices at boulder colorado the latter is at present closed down and the production is from the wolf tongue and primos primes and several leases on smaller properties and groups of claims primos mining company the primos mining company is a sub sillary of the primos chemical company of primos pennsylvania one of the large dealers in rare metals in the country its holdings c consist of 1680 acres scattered over an area of five square miles in the northern pa portion artion of the field about three fourths of this land was originally patented by the government under the homestead laws but after the true nature of the black iron was discovered the primos company bought the ranches to secure the mineral land thereon the company has its ers and mill at lakewood on north boulder creek this point being about central to its holdings three mines are operated the quaker and oregon four miles from lakewood with a foot shaft the lone tree half a mile from lakewood with a foot shaft and the conger two miles from lakewood with a foot shaft the latter works about forty five men but the forces at the other two mines are small the output of the quaker and oregon and the lone tree is small and is delivered to the mill by wagons the latter proved an exception to the general rule of ore occurrence in the fact that a high grade feet long seventy feet high and a width as great as twenty feet was found in the schist the principal producer the conger Is probably the largest tungsten mine in the world it was originally opened by an ir dine cline on the vein and later a vertical shaft was sunk feet from the incline and sixty feet lower at feet this shaft gives feet of backs it is tapped at the foot level by a tunnel ft feet long which is continued to the incline where a 15 horsepower electric hoist has been installed so that the incline may be used for hoisting while the main shaft is being sunk deeper in fig 3 can be seen the main shaft house at the left and the incline shaft house and dump in the middle background the mine has been opened by seven levels through the shaft which is ft with and the surface equipment consists of a inch hendrie and bolthoff duplex second motion hoist with a rope speed of feet per minute with full load norwalk two stage straight line air compressor air and in steam with a capacity of cubic feet of free air per minute working to 90 pounds and a horsepower return tubular boiler the water problem is not serl then to follow it until it opens out it is then scoped up about eight feet and 14 or 16 in round put in and round lagging laid on them then the usual practice is to follow a regular system of shrinkage chutes are put through holes left in the lagging and uppers are drilled in the ore which is broken down on to the lagging and drawn off only in sufficient amount to allow working room for the miners As the ore is broken down it is given a rough hand sorting orting s and any high grade streaks are carefully scoped out by hand drilling instead of with the hammer sto pers when a is worked out to the level above the ore is drawn off and it is abandoned at first after a was emptied waste was run into it and the hanging wall was shot down to fill it but it was found that the hard and almost perpendicular walls would stand without this support and no filling is now practiced on the level the big was opened up feet fee i t long ninety feet high and eight feet wide and stands with only a few feet of filling V ai Z aw 7 I 1 13 N lt Z i aj xv a X woj VW fig 5 ore bin and tram conger mine ous although the flow has been increased by one of the drifts being extended under a creek A in deming duplex pump geared to a 10 horsepower fort wayne motor on the level handles all of the water working half time development has opened three veins the conger middle and east these are expected to unite at depth and the conger and middle veins have united on their strike on the level a large being found at the intersection the ore occurs more or less lens shaped pinching to narrow seams and then opening out to from four to eight feet frequently for a considerable length as shown above the level where a continuous body feet long has been scoped the general width is such as to give good working room with simple timbering usual mining method r the usual system of mining is to drift from the shaft until a vein is reached and the ore is hoisted to the tunnel level and crammed to a bin at the mouth figure 5 here it is dumped over grizzlies grizzlier grizz lies hand sorted and loaded to cars of 1 tons capacity which are hauled to the mill in trains of five by a 3 ton 10 horsepower general electric company storage battery locomotive the tramway is laid with 30 pound steel on 24 inch gauge is a little over two miles long and has an average grade of two per cent to be continued |