Show DOMESTIC FLINT PEBBLES an item of seeming insignificance in the boorts of mineral products is the orth of flint pebbles that have been dolight into the united states annually dur ng lg the last few years the importance of imports to some of the collateral hese ese Sr k ranches anches of the mining indus industry try is however ever much greater than the value e stated 1 light indicate certain industrial pro esses such as the milling of gold ores the manufacture anu facture of cement and of mineral pig imenes ants involve the grinding of the material L an almost impalpable powder this portion of the process is best accomplished ly y the use of these pebbles in revolving tube jube mills american dependence upon europe for flint pebbles and other specialties was brief lly discussed in bulletin published early last september by the united states geological survey and as since the outbreak of the european war considerable difficulty has been encountered in maintaining the supply the search for substitutes utes therein suggested has been actively prosecuted most of the imported pebbles have been obtained from denmark and as the quantity required by the trade was not I 1 jarge arge compared to the work accomplished ittle attention had been given to searching I 1 for or domestic sources of supply it was only I 1 hen the supply of danish pebbles was practically cut off that the dependence upon them hem became exigent the blessing bright cued when it failed to appear A study of possible domestic sources of pebbles leb bles and of other materials that may be substituted for them has been made by frank J katz of the geological survey domestic localities the principal american localities at which hica flint pebbles have been noted in par nicular icolar abundance are in texas mississippi arkansas Ar gansas and missouri oneff one of these which J az Z considered specially worthy of ion cioll is the area of flint bearing cretaceous limestone bestone in central texas other kinds of 0 4 stough augh siliceous pebbles which are abend at at in some parts of the united states are gate agate I 1 carn carnelian ellan chalcedony land petrified od stream beds or shore beaches conning tain ilig pebbles of this character should be searched marched selected well rounder quartz pebbles of from rom two to six inches in diameter from 1 gravels have been used at a gold 1 in amador county oal these pebbles st 5 a ton delivered at the mill against a ton for danish flint pebbles they are re used mixed with the danish pebbles in proportion of two to one the ity T of local pebbles required appears to be ut three times what would be needed of nish pebbles or in other words 15 worth th compared with 30 worth the grindt e efficiency is reported to be satisfactory re are enormous deposits of these quartz pebbles in and flanking the sierra nevadas ise vadas but as the deposits contain also much material that is unsuitable for tube mill us use hand sorting is necessary one of the large lC alifornia rock crushing plants which uses dredge tailings is sorting from tue the tailings pebbles suitable fo for tube mill use at one of the cement mills in california porphyry pebbles have been successfully aused these pebbles occur in in great quantities in gravel along the coast in the smooth surfaces but many are flat and irregular in shape rather than rounded which may increase the power required for revolving t the mills other california cement mills have used local pebbles at various times during the last ten years but no specific data on the results are at hand artificial substitutes for flint the successful experiments which have been made with substitutes for the flint pebbles are possibly of even greater interest than the discovery of natural pebbles ay as heralding a completer independence on the part of the american grinders of the pebbles obtained from abroad among these materials are artificially rounded lava pebbles stream and beach gravels which are composed chiefly of lava or quartz pebbles basaltic lava blocks not rounded at first but which become so after brief use in grinding and chunks of flinty gold ore at manhattan nev the manufacture or of pebbles from rhyolite a species of lava or volcanic rock had already begun in the early part of 1914 this rock although and largely filled with seams and patches of chalcedony is uniformly tough and resistant to wear it was broken into blocks of suitable size and these were rounded off by tumbling in a chamber the roughly rounded pebbles so made have been tested in several of the large harge tonopah mills and have met with a large degree of success they are delivered f 0 ib tonopah at 25 per short ton in the latter part of 1914 danish pebbles via san francisco were quoted at 41 per ton the effect of the use of artificial pebbles as reported arted in a recent letter to the director 0 the geological survey is that in the la latter t part of january 1915 danish pebbles were offered off ered in tonopah at 27 a ton the manufacturer of the artificial pebbles states that by another year it will be possible to deliver his product at tonopah at 20 per ton one of the gold mills at tonopah has recently adopted the south african practice ol 01 0 making the ore do its own grinding that is enough large chunks of flinty ore aro arc kept in the charge to act as grinders further experiments along this line will doubtless be made by other mills and if proved satisfactory may eff effect act considerable changes in grinding practice the successful use of angular blocks of basaltic lava is reported at a gold mine in eastern oregon where a dike of tough mineralized trap rock was encountered in mining and blocks of this material were substituted for flint pebbles in the tube mill this resulted not only in economical grinding but in the recovery of the mineral content of the itral rock 0 |