DRILLING FOR PLACER GOLD HARRON, RICKARD & MeGONE SOLE AGENTS AN FRANCISCO Work continues in spite of snow DRILLING FOR PLACER GOLD ^KEYSTONE, KEYSTONE DRILLER COMPANY BEAVER FALLS, PENNA. A deep hole in the High Sierras, California CONTENTS PART I PROSPECTING FOR PLACER GOLD WITH THE KEYSTONE DRILL BY WALTER H. GARDNER Chapter 1 The Advantages of the Keystone Drill Page 11 Keystone drills have confidence of engineers. Wide range of use. Keystone results given preference. Prospecting with shafts. Open cuts. Small hand- drills. Keystone drill fits needs of engineer. Incident of Keystone usefulness. Use of Keystone with operating dredges. Summary of Keystone advantages. Chapter 2 Proper Drilling Methods Page 20 The crew. The Operator. The Fanner. The Fireman and the Waterbuck. Four-man crew. Selection of machine. Fuels. Extra equipment. Packing and shipping. Drive pipe, care and kind. Drive pipe, longer lengths. Drive pipe, inspection. Moving drill. Setting up drill. Starting the hole. Use of water. Drilling tight ground. Drilling loose ground. Use of jars. Pumping. Checking Volume of material pumped. Driving. Finishing hole. Pulling pipe. Panning. Tin prospecting. Platinum. Fire assays improper. Precautions to be observed. Frozen ground. Unusual condi- tions. Chapter 3 Laying out the Ground and Estimating the Values Page 44 Survey. What map should show. Plotting drill holes. Exploration with drill. Laying out holes in stream deposit. "Blanket" deposits. Treatment of amalgam. Determining fineness of gold. Value of milligiam of gold. Calculation of cubic contents of drill-hole. Compensation for excessive cores. Other constants in common use. Constant of .3333. Keystone constant of .27. Reasons for the Keystone constant. No one constant invariably proper. Combining value of various holes. Principle of evaluation. Calculation when holes are spaced equidistantly. Other methods. "High Holes". Calculation of stream channel values. Summary of calculation methods. What report should cover. Chapter 4 Reliability of Keystone Samplings Page 65 Keystone estimates now checked. Agreement on Oregon property. Check on a California property. Another check from large acreage. Check from small dredge operations. Example from operations of Natomas Cons, of Cali- fornia. Montana property. Tabulation of available comparisons. Ac- curate prospecting possible. How different conditions affect accuracy. Sum- mary. Conclusion. Keystone creek placers. Plates "B", "C", "D", "E", -F", "G", "H", "I", "J". Field log. PART II AUTHORITATIVE ARTICLES ON MINERAL PROSPECTING The Prospecting and Valuing of Dredging Ground Page 88 by Norman C. Stines. Laying off the ground. Operation of drilling the hole. Treatment of material from the hole. The log book. Tables "1", "2". Calculating values. Final calculations. Value of tests. Accuracy of the tests. 562." CONTENTS Continued Prospecting for Copper with Churn Drills Page 111 by F. S. Pheby. Blasting Tight Placers Before Dredging Page 117 by Oliver B. Finn. PART III MINERAL PROSPECTING MACHINERY Mineral Prospecting Machinery Page 124 by R. M. Downie. Core drills. Things which cannot be done' with a revolving core drill. What cannot be done with Keystone drills. Directions for the Operation of Keystone Machines and Use of Accompanying Appliances Page 135 by R. M. Downie. Moving and setting up. To string the drilling tools. Keystone cut drive pipe. The drive pipe. Exploring from a float or flat boat. Driving the pipe. Dressing the drilling bits. Caution. Pulling the pipe. Pipe pulling ring. The Science of Zinc and Lead Prospecting with the Churn Drill Page 171 by R. M. Downie. Two Prime Requisites in a Prospecting Drill: Page 173 A Long Quick Stroke. A Vacuum Sludge Pump. Quick stroke how obtained. Tendency of drillings to settle on bottom. Trituration of drillings by slow motion drills. How to prevent drillings from settling on the bottom. Keystone drill travel 360 feet per minute. A sim- ple experiment. Another simple test. An incidental advantage of this quick stroke. The suction sludge bucket. Still another test. False assays caused by imperfectly cleaning out the hole. Keystone vacuum sand or sludge pump. Examination of the sludge. Drilling Costs in Potash Prospecting Page 183 by E. E. Free. Cost of data of prospect drilling. Successful Salting of Alluvials Page 188 by C. S. Haley. Preliminary examination of alluvials. An unsuccessful attempt. Keystone and Empire drilling. Drill sampling. Field log. Record of formation. PAT i PLACER PROSPECTING FOR PLACER GOLD WITH THE KEYSTONE DRILL ^^^^ T3ADE HACK. ^^H .KEYSTONE, COMPILED BY WALTER H. GARDNER And after being critically reviewed by the original designer of this process and compared with the findings of a wide circle of authentic and practical engineers who have used the process, it is PUBLISHED BY KEYSTONE DRILLER COMPANY Beaver Falls, Pennsylvania DEDICATION This Manual of Information for the Placer Engineer is dedicated to the hardy men who have carried the Keystone to the edges of the world; who have cleared a path for it with machete through the matted jungles; who have forgotten frost-bitten fingers in Alaskan Tundras to finish "one more hole"; who have lived and toiled in far lands and outlying camps that they might reveal new sources of treasure and open new fields of human endeavor. PREFACE "The chum drill is, however, rtie besfr device, gnownfor prp*pe^tinR ground having the necessary condition* Sot gQld dredging.-.'./. .-. J ,?. t .- Engineering and Mining Journal The Keystone Drill, as universally used, is not an instru- ment of precision. Gold particles are not distributed with mathematical symmetry. One drill hole to an acre in ground that is 50 feet in depth only yields for examination Hw.ooo part of the whole! Ordinary common sense and care on the part of the operator and panner are sufficient to insure acceptable field work. Meticulous precision or elaborate core measurements are generally absurd. For after the depths have been recorded and the gold weighed, there comes the calculation of the values of precious metal in great blocks of gravel. There is no fixed formula. The experienced Engineer, to whom such work should be entrusted, will compensate for high variations, for loose and swelling ground, for sand and clay, for rusty gold and his calculations will of necessity contain approxima- tions that eclipse minor errors of the field and nullify minute measurements . Indeed, field work with the Keystone Drill need not be conducted by men of profound skill. Just so the work is done in a consistent manner under the occasional eye of a competent engineer; just so the results are interpreted in the light of experience then will the final figures carry the full weight of authority. There is no mystery about field work and should there be, the following pages will clarify the mode of procedure. 10 DRILLING FOR PLACER GOLD But there can be no standard of practice in interpreting the drill rettjrnst-thi&bcto^jcan here only serve as a manual of suggestions 1 and reminders "to the experienced engineer. And, &rei -is herein CQn:gaine.cl a review of a generation of Keystone* use in the light of the actual recovery from subse- quent mining operations. Hitherto unpublished tables are offered for the files of all interested in the exploration for placer gold. May you find this little book worthy of preservation ! THE AUTHOR. CHAPTER I THE ADVANTAGES OF THE KEYSTONE DRILL KEYSTONE DRILLS HAVE CONFIDENCE OF ENGINEERS To " Keystone" a gold dredging field is to "prospect" it! So closely has the Keystone Drill identified itself with the examination and calibration of auriferous gravels that its very name has grown into the jargon of the Engineer as a synonym of thorough and conscientious exploration. For the past twenty-five years have seen extensive areas of river gravels accepted for exploitation or cast into the discard on the strength of no other information than that revealed by the Keystone Drill in competent hands. With a serene con- fidence in its reliability, men have invested hundreds of thou- sands of dollars in the purchase of land and dredge machin- ery or accepted an unfavorable verdict without a question. WIDE RANGE OF USE The Keystone Drill was first used for the determination of gold values in a placer deposit in Idaho, in the spring of 1898. Since that time many hundreds of drills have been shipped to all parts of the world and used in the testing of bench and bottom land ; of old channels ; of the bars of live streams; of lake and river bed. It has clattered in the depths of the Columbian jungles where it paved the way for the Nechi and Pato dredges ; it has probed the frozen gravels 11 12 DRILLING FOR PLACER GOLD The Canadian Klondyke Mining Company used KEYSTONE DRILLS in their extensive exploration work DRILLING FOR PLACER GOLD 13 of Alaska and Siberia ; it has charted the wide areas of the Oroville, Yuba and Natoma districts of California; it has explored innumerable of the lesser streams of Oregon and Montana, of the Philippines and the Malay States. It has sought for gold; for platinum; for diamonds and for tin. It has been transported under its own power; by horses; on the backs of mules ; on snow-sleds ; in crude dug-outs even on the backs of human carriers. Sometimes a half dozen machines have been purchased and used to hasten the work on a promising property there were at one time more than 40 Keystone Drills operating simultaneously on the prop- erty of the Lenskoi Mines. It has been used to determine the presence or absence of precious metals ; it has been used to carefully appraise the contents of whole tracts; it has lo- cated limits of dredging possibilities both as to values, depths and bedrock reefs. It has proved that its results are the best index to dredging possibilities. And it has estab- lished a reputation for sturdiness and reliability that few machines enjoy. KEYSTONE RESULTS GIVEN PREFERENCE The Engineer who faces the task of correctly determining the recoverable gold content of a placer field will ordinarily have several alternatives of procedure. He may put down shafts. Open cuts or exposed walls may give access to the various strata. Ke may depend on a small and flimsy "hand-drill." Or he may elect to do a thorough and ac- curate exploration with a Keystone Drill. We briefly re- view the various shortcomings and advantages of these methods: 14 DRILLING FOR PLACER GOLD PROSPECTING WITH SHAFTS Sub-surface waters usually prevent extending a shaft to bedrock. Uneven and improperly completed shafts do not yield reliable data. The same inaccuracy attends the at- tempt to sink a shaft below water level by the use of pumps or other appliances. The inflow of water will carry values. To be sure, if water did not interfere, a property might be thoroughly prospected by shafts and by shafts alone but at an unnecessarily high cost. And while the final data would of course be accurate, it would, despite the greater size of the samples, be little more authoritative than the Keystone evaluations. So the Keystone Drill holes, miniature shafts as they are, are today recognized as preferable from the standpoint of the time and money that they save and as accurate to nearly the same degree. But the careful Engi- neer will usually check the operations of his Keystone with one or more shafts to bedrock if possible and at least to water-level. He sinks the shaft around one of the early drill-holes. It gives him a better visualization of the strata that the drill has already indicated it yields sufficient gold to obtain a test as to the nature and purity of the particles it supplies some data for the decision as to the proper "con- stant" to be employed in his later calculations. And it also more surely indicates the exact level of the sub -surface water; it reveals something of the configuration of the bed- rock; it more clearly tells of clay streaks and buried bould- ers. But the experienced Engineer will rarely waste time and energy on more than one such check shaft. OPEN CUTS A thorough exploration of a placer field will often dis- DRILLING FOR PLACER GOLD 15 cover open cuts, old shafts, exposed banks and other oppor- tunities to cross-cut the gravels to some depth. But such exploration can seldom be more than casual and is either merely supplementary or in advance of the determination to drill thoroughly. For the random nature of such oppor- tunities does not permit the systematic operations that alone carry the assurance of accuracy. SMALL HAND-DRILLS Standard equipment for use with the Keystone Drill is Extra Heavy Pipe 6 inches in diameter. It is generally held that a smaller sample cannot be error-free. Two and a quarter times as much material is recovered for examination from the Keystone Drill holes as from a 4-inch pipe. While there have been cases where the exigencies of transportation seemed to encourage the lighter machine, and while it may be permissable for preliminary work, it is of record that few dredges have been purchased without adequate Keystone results as the basis for the confidence of the investors. In- deed, it has become almost an axiom that capital will not be attracted to a placer field unless it has been thoroughly "Keystoned"! Nor can the "hand-drill" cope with condi- tions of hard ground. Dredge operators say that they can work any gravel that can be broken by a man with a pick and the operations at Natoma, California, certainly prove the truth of this contention. But it requires a sturdy ma- chine to probe such compact gravels heavy enough to scorn the boulders that are inevitably encountered. The Keystone Drill is of as light a design as may be confidently entrusted to test with truth and accuracy the average de- posit of auriferous or value bearing gravels. 16 DRILLING FOR PLACER GOLD DRILLING FOR PLACER GOLD 17 KEYSTONE DRILL FITS NEEDS OF ENGINEER The Engineer who wishes his work to carry the full flavor of accuracy or the promoter or property owner who wishes to collect data that will command the respect and belief of others will not be satisfied with any but Keystone Drill re- turns. Nor is the Keystone so heavy as to be difficult to transport or to operate. Quite the contrary. The Key- stone No. 1, with the boiler sectionalized, may be trans- ported by pack-train. The Keystone No. 3, the standard model for placer prospecting, is designed for speedy moving and "setting up"; for the rapid drilling of holes that are but rarely more than 60 feet in depth ; for hard work far afield from machine-shop and organized repair facilities in short, for the peculiar and arduous work of the pioneer Placer Engineer! INCIDENT OF KEYSTONE USEFULNESS There is on record an example of the untrustworthiness of shafts when they do not go to bedrock. One property was once prospected to the depth of about ten feet when water was encountered. These shafts revealed promising values which had only to be maintained to a reasonable depth to make an attractive dredging proposition. Indeed, so gratify- ing were the returns that a company was formed and stock sold. But cautious capital wisely demanded that the ground be Keystoned and it was discovered that the lower gravels were absolutely barren ! It seemed that an old and filled-up lake bed, or settling basin, had been covered in recent times with an all too thin layer of auriferous gravel. Here the Keystone saved a very considerable sum of money for some one ! Most Engineers prefer, if conditions at all permit, to 18 DRILLING FOR PLACER GOLD rely on a Keystone even for preliminary work. It is dis- concerting to arrive at a property after a long trip with noth- ing more adequate than a "hand-drill" for equipment and find ground that is too hard for it to attack and containing too much water for shaft sinking ! USE OF KEYSTONE WITH OPERATING DREDGES There is yet another angle to the situation. In the event that preliminary work prompts a complete campaign of evaluation, the Keystone is absolutely necessary. And when the dredge is finally completed and at work, the Keystone has not outlived its usefulness. Modern practice suggests the continued use of the drill in front of the dredge, blasting hard ground, determining the boundaries of barren areas, charting the "pay-streak", seeking out reefs of hard bedrock, tracing the sub-surface bench line, even forecasting the cur- rent dredge returns. A large dredging company now follow this practice, for, as they say, "There is nothing more foolish or expensive than to prospect with a dredge!" SUMMARY OF KEYSTONE ADVANTAGES Here, then, are many reasons why a property under ex- amination for its gold content should be Keystoned at as early a date as may be possible 1. Keystone Drills are not too heavy to transport to properties that are at all accessible. 2. Keystone Drills are able to cope with severe conditions of deep bedrock, boulders and hard or frozen gravels. 3. Keystone Drills achieve very nearly the accuracy of shaft work at the cost of less money and time. DRILLING FOR PLACER GOLD 19 4. Keystone Drill returns command confidence and re- spect. Their use adds weight to any report on a placer property. 5. Keystone Drills are practically certain to be specified on the final examination it is a matter of economy and efficiency to use them even for preliminary work. 6. Keystone Drills do not outlive their usefulness with the passing of the period of exploration. CHAPTER II PROPER DRILLING METHODS THE GREW Efficient operation of the Keystone Drill will in most cases require a crew of three men the drill-operator, the panner and a fireman. Usually a man with a team is necessary to bring water and fuel as well as to aid in moving. Sometimes the Engineer in charge will prefer to perform most of the duties of a panner; sometimes, with oil-burning equipment, one man may be eliminated. THE OPERATOR The man who actually runs the drill should be expe- rienced. On him largely depends the accuracy and certainly the expedition of the work. He should be capable of the re- pair, replacement and bit-sharpening which must all be sometimes conducted under the difficulties of limited con- veniences afar from shop and machine equipment. The Engineer will largely be occupied with exploration, survey- ing, securing supplies, correspondence and manifold duties his drill-operator should be a dependable lieutenant and a resourceful mechanic. THE PANNER The panner, also, should be an experienced, discreet and trustworthy man. His duties are to keep the records, check the core, collect the recovered gravels and slimes, clean up the sluice-box and make a full report to his superior on all drilling operations. He is often asked to supplement the 20 DRILLING FOR PLACER GOLD 21 operator's pipe and rope measurements with an independent check of his own. But the ideal man will do more than that he will turn a willing hand to whatever chore presents it- self, for he will have unoccupied moments. It is of impor- tance that he be provided with shade in hot weather and shelter and warmth in cold; otherwise his work can not be kept free from variables incidental to cold and discomfort and can not be prosecuted with full accuracy it being unavoidable that his hands be in water much of the time. THE FIREMAN AND THE WATER-BUCK The work of keeping up steam and driving the team may be entrusted to such labor as can be secured in the field of operations. Ordinarily such men need not be skilled to any degree but the very nature of prospecting work suggests that there be some assurance of the loyalty and discretion of every employee. The fireman should be required to start his work on each shift in such season that a full head of steam will be available upon the arrival of the rest of the crew. FOUR-MAN GREW In the extensive operations of one large company, the em- ployment of a fourth man has been found a justifiable ex- pense. With such a crew it becomes the duty of the fireman to care for the fuel, water and lubrication; to act as mechan- ical inspector, keeping all bolts tight ; and to keep a full head of steam. The fourth man, or "helper", acts as assistant to both panner and operator ; cleans casing threads ; prepares roads in advance of moving ; runs needful errands, and in general serves to keep lost time at a minimum. 22 D R I L L I NG FOR PLACER GOLD DRILLING FOR PLACER GOLD 23 SELECTION OF MACHINE For these many years the Keystone No. 3 Traction has been the favored Model for placer prospecting. It is amply powerful for all depths and all gravels likely to be encount- ered. The friction-hoist is to be preferred. The No. 3 Non-Traction may be used, of course, but the traction ma- chine soon earns back in saved time its somewhat greater cost. Where transportation into regions difficult of access must be provided, the lighter Keystone No. 1, with its boiler sectionalized, may be carried in by pack-train. On those rare occasions when the holes run beyond 300 feet in depth, the Keystone No. 5 is specified. FUELS The standard fire-box of the Keystone Drill will take wood of about 18 inches in length by 6 to 8 inches in thickness. Seasoned wood is the best, of course, but a clever fireman can keep up steam with damp and green fuel that would appear almost useless. It is often possible, and always desirable, that supplies of wood fuel be prepared in advance. Coal may be used interchangeably with wood, the Keystone grate being suited to either, but a supply of extra grates is advisa- ble if coal is to be burned. The machine can easily be equipped with an oil-burner where proper fuel is secur- able and when so fitted the costs of operation are mate- rially lowered. In many parts of Alaska, Keystone Drills fitted with gasoline engines serve best. The drill will use a little less than half a cord of wood to a ten-hour shift if the wood be of average worth, and the operations require four to six barrels of water. 24 DRILLING FOR PLACER GOLD EXTRA EQUIPMENT There are listed hereafter not only the standard equip- ment for placer testing, but also a selected list of extras and spares, with the accessories, that intimate acquaintance with field conditions prescibe as proper and necessary adjuncts to speedy and efficient work. Let it be borne in mind that the search for gold is carried on in the far places of the world, and that, except in those few instances where operations are amid the conveniences of civilization, placer prospecting parties must rely largely on their own resources. Indeed, it is the ruggedness of the Keystone Drill and the simplicity of its upkeep that have raised it so high in favor! Again, speed in carrying out the work is invariably to be desired; there is always an overhead expense in maintaining the crew that counts heavily in the event of lost time. The simple precaution of carrying a complete outfit and ample replace- ment parts will insure against excessive expense and irksome delay. The drill-bits must be sharpened in the field that must be provided for. Sand pump valve packings wear out even an extra valve assembly should be carried as precau- tion against embarrassment due to breakage. Continued use eventually * 'fatigues" the bolts for the driving clamps. Connecting-rod brasses require replacement there are many possible mischances of minor nature incidental to the strenuous work of drilling into impacted gravels. It will be found that the Keystone list of extras as appended cannot be safely curtailed if there is to be provision against ordinary hazards; and, indeed, it may well be increased if the expe- dition is likely to work for a long time far from the beaten track. A complete set of carpenter and blacksmith tools will then be found a worthy addition. DRILLING FOR PLACER GOLD 25 PACKING AND SHIPPING For domestic use the Keystone Drill will generally be shipped completely assembled. For use abroad or in dis- tant fields it may be partially dis-assembled and crated. The new machine, ordered from the branch of the Keystone Driller Company, will be carefully inspected to insure imme- diate readiness for operation. A machine once used, that is to be transported to a new field of work, should be carefully and thoroughly looked over by the Engineer so that possible delay or confusion at time of delivery may be obviated. The machinery and tools should be checked as complete and in perfect working order. Packages and crates should be num- bered and listed to permit of ready identification. All should be plentifully greased to prevent oxidation in transit. The rope should be protected from moisture. Steam en- gine oil and greases should be included in the shipment if there is any uncertainty as to the availability of these in the field. Four 3" by 12" planks are often shipped with the drill, and prove useful in unloading, moving and blocking. The sluice-box can be made in the field if a piece of 30" by 60" Galvanized Iron, 20 Gauge, be rolled up and included. The rocker had best be fabricated on the ground from the best available soft pine for it is almost sure to be dried out or broken in transportation. Wise forethought will yield large dividends in saved time and lowered cost of work ! DRIVE PIPE CARE AND KIND The pipe recommended for placer testing is the Extra Heavy Drive Pipe (28 pounds to the foot), for the lengths are driven and pulled and used over again many times. A generous supply is most desirable on far expeditions three 26 DRILL ING FOR PLACER GOLD DRILLING FOR PLACER GOLD 27 times as much as would be required for one average hole may well be purchased and transported. Short lengths are ad- vised for greater ease in handling an accepted length is about six feet for each piece, though the first joint may well be seven or eight feet. The threading must be accurate and true ; that there be no waste of time in screwing and un- screwing ; that the joints will butt in the middle of the coup- ling, thus avoiding danger of thread -stripping, and so that all pieces will be interchangeable. Threaded ends should at all times be protected by couplings or short sleeves. Pipe ordered from the Keystone Driller Company is threaded to the "Keystone Standard Cut." DRIVE PIPE LONGER LENGTHS However, if the holes are to be more than 60 feet in depth, longer lengths are advisable. To permit their use, provided that the ground is dry, the hole is started in a pit about 6 feet in depth and 5 feet by 7 feet in width and length. This pit is cribbed lightly at the top to prevent the jar of the opera- tion of the machine from breaking it down; it is covered with substantial planks and the weight of the drill is sup- ported on wide and heavy boards. With such a pit 10-foot lengths may be comfortably used. In wet ground where timber is plentiful the drill is often cribbed up so as to be 4 to 6 feet above the surface and the same lengths may be employed. There are then fewer joints to provide the pos- sible cause of a "crooked hole" when the gravel is compact, and less time is taken up in making pipe connections. DRIVE PIPE INSPECTION In the field it is customary to use certain pieces of pipe in a regular sequence, numbering them for identification. It 30 DRILLING FOR PLACER GOLD be taken to examine the material removed for possible val- ues, although the hole will usually be started in barren silt or loam. The stem is then lowered into the pipe and the driv- ing-blocks bolted on. The attendant, mounted on one of the cross-pieces of the derrick, will steady and balance the otherwise unsupported stem, while the panner will hold the pipe until driven to a depth where it can support itself. Or- dinarily, in surface soil the first drive may be for two feet, when the depth and core should be read off and recorded. A little water may then be added (not too much, on account of the possibility of its washing down through the loose soil) and a pumping made without drilling. In hard compact gravel it is sometimes necessary to drill first but this is a procedure to be avoided if it is at all possible. USE OF WATER The contents of the pipe should be kept thoroughly mixed with water as the work progresses. In dry ground no more should be added than is necessary perhaps three or four feet of it in the pipe. But in wet ground the water- level should be kept above the water-level outside the casing. This higher head has been found to be efficacious in largely preventing the inrush of too great a core and the intrusion of extraneous values. The Engineer will some- times find this to be a troublesome point, but one that must be insisted upon. The operator should continually have be- fore him the fact that he is not there to make progress, but to gain a correct sample! Care must also be taken to flood the drill-stem with a bucket of clean water as it comes up after the drilling and before the pumping, and to give the sand- pump a final flush on the conclusion of each pumping. The DRILLING FOR PLACER GOLD 31 boiler water should be kept in a separate barrel where no dirty buckets are plunged into it. The water used in the drill hole should be absolutely free from oil or grease of any kind. DRILLING TIGHT GROUND The pipe will have been carefully measured and marked at intervals of 6 inches with a water-proof crayon. The assembled drilling tools will also have been measured and marked so that at any instant the operator will know the exact relation of the edge of the bit, at the limit of its down- ward stroke, to the bottom of the cutting-shoe. Drilling will proceed until the bit is from 1 to 4 inches above the lower end of the cutting-shoe; this thickness of impacted gravel prevents the intrusion of too much material from without the path of the pipe. This thickness of gravel is alluded to as the "core". The drill-stem should be turned slightly by the hand of the operator to keep the blade from striking in exactly the same place and packing the contents of the pipe or becoming stuck. If a boulder is encountered it may be broken up by drilling ahead of the pipe proper notation being made in the log. Drilling below the pipe is always a bad and a dangerous practice in placer testing, ex- cept that in heavy ground or coarse gravel it may be neces- sary to drill a few inches ahead after pumping to clear the pipe of a plugged core. Before resorting to this expedient, it should be ascertained that the water-level in the pipe is above the water-plane in the ground. Fortunately, in such heavy, tight gravel there is ordinarily found a stiff clay which serves to protect the walls of the hole below the drive- shoe. 30 DRILLING FOR PLACER GOLD be taken to examine the material removed for possible val- ues, although the hole will usually be started in barren silt or loam. The stem is then lowered into the pipe and the driv- ing-blocks bolted on. The attendant, mounted on one of the cross-pieces of the derrick, will steady and balance the otherwise unsupported stem, while the panner will hold the pipe until driven to a depth where it can support itself. Or- dinarily, in surface soil the first drive may be for two feet, when the depth and core should be read off and recorded. A little water may then be added (not too much, on account of the possibility of its washing down through the loose soil) and a pumping made without drilling. In hard compact gravel it is sometimes necessary to drill first but this is a procedure to be avoided if it is at all possible. USE OF WATER The contents of the pipe should be kept thoroughly mixed with water as the work progresses. In dry ground no more should be added than is necessary perhaps three or four feet of it in the pipe. But in wet ground the water- level should be kept above the water-level outside the casing. This higher head has been found to be efficacious in largely preventing the inrush of too great a core and the intrusion of extraneous values. The Engineer will some- times find this to be a troublesome point, but one that must be insisted upon. The operator should continually have be- fore him the fact that he is not there to make progress, but to gain a correc t sample! Care must also be taken to flood the drill -stem with a bucket of clean water as it comes up after the drilling and before the pumping, and to give the sand- pump a final flush on the conclusion of each pumping. The DRILLING FOR PLACER GOLD 31 boiler water should be kept in a separate barrel where no dirty buckets are plunged into it. The water used in the drill hole should be absolutely free from oil or grease of any kind. DRILLING TIGHT GROUND The pipe will have been carefully measured and marked at intervals of 6 inches with a water-proof crayon. The assembled drilling tools will also have been measured and marked so that at any instant the operator will know the exact relation of the edge of the bit, at the limit of its down- ward stroke, to the bottom of the cutting-shoe. Drilling will proceed until the bit is from 1 to 4 inches above the lower end of the cutting-shoe; this thickness of impacted gravel prevents the intrusion of too much material from without the path of the pipe. This thickness of gravel is alluded to as the "core". The drill-stem should be turned slightly by the hand of the operator to keep the blade from striking in exactly the same place and packing the contents of the pipe or becoming stuck. If a boulder is encountered it may be broken up by drilling ahead of the pipe proper notation being made in the log. Drilling below the pipe is always a bad and a dangerous practice in placer testing, ex- cept that in heavy ground or coarse gravel it may be neces- sary to drill a few inches ahead after pumping to clear the pipe of a plugged core. Before resorting to this expedient, it should be ascertained that the water-level in the pipe is above the water-plane in the ground. Fortunately, in such heavy, tight gravel there is ordinarily found a stiff clay which serves to protect the walls of the hole below the drive- shoe. DRILLING FOR P LACER GOLD Drilling in China behind the protection of a fence and barricade DRILLING FOR PLACER GOLD 33 DRILLING LOOSE GROUND If there is loose and running ground there may be but little drilling necessary, and the utmost skill and experience of the operator will be called into play to prevent the pump- ing of too much material. In fact, there will frequently occur a stratum where the amount of silt and sand pumped out of the hole will be greater than the theoretical displace- ment of the drive-shoe a careful recording of volumes will then give the Engineer data for the approximations and allowances that must be made. Fortunately, such loose material seldom contains heavy enrichment. If too thick a core is maintained, there is a possibility of its becoming a plug in the pipe and crowding other material aside as it is driven. The whole science of accurate drilling consists in pumping as nearly as possible the entire material in the path of the pipe and no more! No two pieces of ground will react to drill operations in just the same way; indeed, data have been collected which show that no two skilled operators will secure exactly parallel results in the same hole! Here, as elsewhere, crops up the personal factor which the Engi- neer will study and reflect in his final calculations. In most work, however, variations will be so slight as to be ignored, or will largely compensate. USE OF JARS After some depth has been reached, or where boulders threaten to ' 'stick" the drill bit, there may be occasion to put on the jars not only to afford the impact necessary to loosen the bit by the jerk they can exert, but also for their added weight. Generally, however, they are quite unnec- essary. 34 DRILLING FOR PLACER GOLD PUMPING When the operator has broken up and loosened the mate- rial nearly to the bottom of the pipe he will throw the crank wheel out of gear and the cable reel into gear, thereby hoist- ing the tools clear of the pipe, and will swing the stem out of the way usually throwing it over and behind the cross-arm. One pail of water should be dashed over the stem as it rises ; more water should be added before pumping, as previously described. The Vacuum Sand Pump is then dropped into the hole, and rapidly raised and lowered two or three times to suck in the material. This pump contains a plunger which travels through its whole length. The rapid dropping of the pump forces this down and when the sand reel is thrown into gear, this ' 'sucker" is drawn up so rapidly as to produce a vacuum in the lower part of the pump, thus opening the valve and drawing in the loosened contents of the pipe. The secret of successful pumping lies in impart- ing a properly rapid motion to this plunger and the power and control of the Keystone Drill enable the operator to re- cover the gravel, slimes, sand and mineral enrichment with a remarkable thoroughness. Two pumpings are usual in ordinary work where progress is made a foot at a time. Of- ten time can be saved by pumping immediately after driv- ing, drilling only when there remains more than 2 or 3 inches of core. The two pumpings, the one before and the one af- ter drilling, are preferably caught in the same pan and con- centrated in one operation. When extraordinary care is not required the material may be poured directly into the pan which will have been placed across the frame of the sluice - box, the slimes being allowed to accumulate in the box for the final * 'clean-up" on completion of the hole the panner DRILLING FOR PLACER GOLD 35 making proper record of the values therein contained. This sluice-box, a wooden frame with a half-round trough of gal- vanized iron, is mounted on wooden supports directly in front of the drill and extending forward away from the pipe. The attendant will carry the valve end of the pump out from the pipe as the operator easily slackens the cable (not enough but that the line still carries most of the weight of the pump) until he can lay it over the box; then he will raise the valve end and dump its contents into the pan. The pump should then be washed clean, both inside and out, with clear water and allowed to rest on top of the sluice-box (so that sand-line and drilling cable do not touch) ready for the next pumping. CHECKING VOLUME OF MATERIAL PUMPED If variable cores and unusual conditions suggest a greater accuracy in the observation of the relation of the recovered material to theoretical displacements, the entire pumping may be at once emptied into the sluice-box. At its lower end will be placed a large tub of water containing a pail into which the material falls. The contents of this pail will be measured before panning the tub will gradually collect the slimes for the final accounting. The pail had better be cali- brated and a chart prepared showing the cubic feet of mate- rial for each inch which the surface lies below the top of the pail. There is here given (Plate "E") an actual record of such data as presented in the report of a well-known Engi- neer. DRIVING After the pumping, the drill-stem will be swung back into the hole and carefully lowered to rest on the surface of the 36 DRILLING FOR PLACER GOLD DRILLING FOR PLACER GOLD 37 material within the pipe. A measurement should then be taken to ascertain the amount of material above the drive- shoe and record made thereof as "core after pumping." The drive-blocks are then bolted on and the pipe driven the proper distance, usually a foot, more in loose and easy ground where no values are anticipated; less in very hard and refractory gravel or resistant sand. It has already been noted that there are occasions when lack of progress indi- cates that one may reluctantly drill ahead to facilitate driv- ing, but the Keystone Drill has ample power to cope with exceptionally hard formations and the logs of Keystone drill-holes are singularly free from record of this expedient. FINISHING HOLE Most holes are continued to the hard rock, shale, de- composed granite, tufaceous lava, or barren stratum that marks the limit of recoverable values. The Engineer will usually prefer to be present at the conclusion of a hole, not only on account of the greater concentration of material usually encountered on bedrock, but to observe what he may of the character of this formation. The pipe should be driv- en to a depth that makes certain of bedrock and of the total absence of values but not to a depth into the bedrock that will make pulling a slow and tedious process. The full pur- pose of the test hole having been supposedly now accom- plished, the operator may, at will, drill a few feet into the bedrock. This will prove whether his supposed bedrock is or is not a large boulder. PULLING PIPE The long stroke of the Keystone Drill, together with its responsive control, facilitates the withdrawal of the heavy 38 DRILLING FOR PLACER GOLD drive pipe for use over and over again. The stem is de- tached from the rope-socket and the "puller" screwed on tightly. The puller knocking-head is then attached to the top length of pipe and the machine started with the slack so controlled as to strike a forceful upward blow. If the pipe yields but slowly, the pulling ring and lifting jacks may be employed. The water-level in the hole is usually meas- ured during this operation, although, if the hole "stands up", more nearly accurate information may be obtained by delay- ing this reading for a day or so. When the last joint is removed, the drill-stem is again fastened to the rope-socket, loaded into the bed of the machine, the jacks removed, and the outfit moved to the next hole. PANNING Under ordinary conditions the panner will concentrate the recovery of each pumping in his pan. After removing all but the minerals and black sand, he will estimate the weight of gold in milligrams and also count and record the colors. It is customary to record these as of the "First", "Second" or "Third" grade. A "Third" grade color is one that is large enough to be individually counted, yet below two milligrams in weight. A color between 2 and 7 milli- grams is of the "Second" grade above 7 of the "First" grade. This counting of colors and estimate of weight serves several purposes. It shows the occurrence of values according to the depths ; it gives data for the Engineer if the recovery of a pumping is to be later discarded or discounted ; it gives some idea of the worth of the ground if by accident the recovered values are lost or contaminated. The gold from the various pannings as the hole progresses will be ac- DRILLING FOR PLACER GOLD 39 cumulated in the same globule of mercury. This, preserved in a glass tube, will be kept on the person of the panner. On finishing the hole the tailings will all be re-run through the rocker, together with the slimes from the sluice-box and tub, and any values added to the mercury. This will then be handed to the Engineer, together with the log of the hole which it is also the panner's duty to keep. When the drill- ing is being prosecuted by a night-shift it has proved unwise to attempt panning by artificial light. Under such circum- stances the pans are preserved for concentration on the fol- lowing day, being marked by a wooden "paddle" on which the proper identification of the pumping may be pencilled. The panner is held responsible for the correct recording of the progress of the work, of the cores and for the recovery of every particle of metal. TIN PROSPECTING The procedure in evaluating tin placers is practically the same as for gold except that the panner will screen his ma- terials and grind the larger particles of tin to determine a sample and gain an assay that will declare as to the propor- tion of dross in the heavy tin-stones. Placer gold particles are ordinarily unadulterated with quartz not so with tin "nuggets". PLATINUM Inasmuch as platinum is not picked up by the mercury, it is necessary to save for assay the heavier concentration of the pannings. In rare cases, the platinum will represent no small proportion of the values in all placer fields it is a wise precau- tion to make a careful test of its presence in commercial quan- tities. For the ordinary gold-saving, tables of the modern dredge make a remarkable recovery of these heavy particles. 40 DRILLING FOR PLACER GOLD FIRE ASSAYS IMPROPER Every Engineer has heard of instances where through ignorance the concentrate from auriferous gravels has been sent to the assay office for a fire test. This grave error is even today not uncommon. It should be remembered that the heavy quartz pebbles carry gold that no washing device can recover and that while field panning and hand concen- tration methods may be crude, that they are of comparable efficiency to the gold-saving devices of the dredge and that more nearly accurate recovery from the sample will be dan- gerous and misleading. The ' 'black sand" concentrate from the bottom of the pan, after the mercury has picked up all visible yellow particles of gold, will often yield a high fire assay but the recovery of these values by washing or amal- gamation is even more nearly impossible on a large scale than it was in the prospector's pan! PRECAUTIONS TO BE OBSERVED On leaving the work at the end of a shift, it is an excellent idea to throw into the hole a few handfuls of tailings that are known to be barren. This is pumped out and inspected on beginning the next day's work an effectual safeguard against tampering. In fact, it is impossible to salt a Key- stone Drill hole if even moderate watchfulness is employed. It is rumored that on one occasion particles of virgin gold were inserted into the fibres of the drill-rope, these gradual- ly falling into the hole as the work progressed. The sight of a few flakes of bright gold on the top of the driving-head revealed the trick. It is also said that once an interested property owner loaded a cigarette with precious dust and flicked the ashes into the pan as concentration was being DRILLING FOR PLACER GOLD 41 carried on. Salting is only possible by some such fantastic and wholly unlikely ingenuity. However, the careful Engi- neer will from time to time check the purity of the quick- silver which he uses. FROZEN GROUND A new technic of drilling in the frozen gravels of the Arctic has been developed. This work requires experience if it be done with accuracy; we can only touch on the method em- ployed. When the pipe reaches frozen strata, drilling and pumping and panning proceed below it a foot at a time. There will be some caving, and an irregular hole is pretty sure to result as thawing proceeds. After bedrock is reached, the tools are withdrawn and a measured quantity of water kept at a temperature just above freezing is poured into the hole. A careful record is kept of the volume necessary to raise a float one foot vertically and thus is secured an equiv- alent measurement of the cubic feet of gravel actually re- moved in each foot of progress. With the new science of "cold-water thawing" and the renewed interest in Arctic gravels, this ingenious method of insuring reasonable accura- cy in prospecting becomes particularly noteworthy and here again is the power of the Keystone Drill of signal value ! UNUSUAL CONDITIONS The vast differences encountered in probing the placers of the world cannot all be dwelt upon in this short treatise. Indeed, there will be unprecedented conditions now and then arising that will tax the resourcefulness of Engineer and op- erator alike. But the ruggedness and yet splendid flexi- bility of the Keystone Drill adapt it to the hardest tasks. It can be cribbed up high above marshy ground when long 42 DRILLING FO R PLACER GOLD DRILLING FOR PLACER GOLD 43 pipe lengths are to be handled. It can be operated from a scow afloat in lake or river. It is a sturdy machine for hardy men in rough country! Here might be introduced a paragraph on the Keystone as a Shaft-Sinker in frozen strata. The advantage and process are that : A six-inch hole is first drilled through the frozen strata. Two or three returns of one-inch pipe connected to the boiler serves overnight to thaw the material out to shaft size. The drill-stem having been removed, the cable and cable reel are, without other change, used to elevate the mining bucket for the thawed material or the accumulated water. The machine and its accessories in fact make it a complete shaft-sinking outfit. HARRON, RICKARO * MeCONE SOLE AGENTS CHAPTER III LAYING OUT THE GROUND AND ESTIMATING THE VALUES SURVEY The careful examination of a placer deposit requires a thor- ough survey and an adequate map this being made with sufficient accuracy and to so large a size that distances may be scaled with precision. It is not always possible to secure such a survey in advance the Engineer will often prosecute such work while supervising the beginning of drill work. WHAT MAP SHOULD SHOW On the map should appear property lines, roads, bedrock outcroppings, and physical limitations of dredging areas; and it should represent a complete picture of the property not only for purposes of prospecting, but for later use in buying par- cels of land and for dredge operations: Perhaps such thor- ough work will not be completed until there is some assur- ance as to the desirability of actual exploitation, but the initial survey may quite as well be conducted so as to be made full use of if the property ''proves up". PLOTTING DRILL HOLES Usually the first drillings will render a verdict as to the ultimate value and dredgability of the property. Accord- ingly, it is often desirable that they be well scattered so that they may roughly reveal the worth of the entire acreage. Yet, if the results are favorable, this first work should have been so done that it fits into the complete campaign of prospecting. DRILLING FOR PLACER GOLD 45 EXPLORATION WITH DRILL In a channel deposit the Engineer will often stake out lines at right angles to the stream flow and mark proposed holes just as if he were assured of favorable results. Then he will start drilling by driving alternate holes on alternate lines with the purpose of later completing the work when the value of the area has been reasonably established. In a "blanket" deposit he may chart his entire scheme of drilling then actually drill here and there over the entire acreage until a complete exploration has been justified. LAYING OUT HOLES IN STREAM DEPOSIT In all ordinary deposits a Keystone Drill hole to every two to four acres will be adequate to yield complete data as to values. The plotting of proposed drill-holes will be made with this in mind. Several "channel" or stream deposits have been appraised by drilling holes at a distance of 150 feet on lines that are 1000 to 1500 feet apart. The location of holes on Plate "A" is typical. "BLANKET" DEPOSITS As is hereafter described, the marking of a wide acreage of auriferous gravels into equilateral triangles, placing drill- holes at their apices, is an excellent method of conducting an exploration. The final calculations are then quite simple and the chance of confusion and error is eliminated. Some Engineers prefer to plot the field in rectangles, drilling at the corners of each parcel. Still others divide the field into squares and drill at the center of each square. This brief treatise does not attempt to argue the merits of various methods but to fully present one method for the uniniti- 46 DRILLING FOR PLACER GOLD DRILLING FOR PLACER GOLD 47 ate and record the several angles of consideration as memo- randa for the more experienced. TREATMENT OF AMALGAM The Engineer will receive from the panner a small phial in which he has preserved the mercury containing the gold from the sample. This he will treat with dilute nitric acid (Sp. Gr. 1.42 plus an equal volume of distilled water) in a test tube over the flame of an alcohol lamp wash well with boiling water to which a few drops of alcohol have been added dry and anneal in a small annealing cup or porcelain crucible and weigh the clean dust on scales that are accu- rately sensitive to a milligram. Pocket scales are made that are sufficiently precise for this work. These operations should be carried out in a room free from dust or air currents and with clean reagents and containers. Then the Engineer, with the weight of the gold and the log of the hole before him, proceeds to the calculation of values in "cents per cubic yard" the accepted basis for the evaluation of placer prop- erties. DETERMINING FINENESS OF GOLD To properly translate his gold values he must appraise the fineness of the metal peculiar to the property in question. Many Engineers insist on sending a sample of the gold col- lected to the nearest available authority on quantitative analysis to determine with accuracy the proportion of gold and silver. Sometimes, if platinum be expected as occur- ring in the sands, as large as possible a sample of the panner's concentrate is also sent and a determination of that metal likewise requested. 48 DRILLING FOR PLACER GOLD VALUE OF MILLIGRAM OF GOLD A customary approximation, when accurate data are lack- ing, is to call a milligram of gold worth .06 cents. This is based on gold that assays $18 . 66 worth of pure metal to the troy ounce of 480 grains one grain being equal to 64 . 8 mil- ligrams. CALCULATION OF CUBIC CONTENTS OF DRILL-HOLE A 1 foot hole yields .3068 cubic feet of material. If that material produces 1 milligram of gold then a cubic yard will produce 2 7 /. 3068 times as much or 8.8 milligrams. But, on a basis of gold that is worth $18 . 66 per ounce; one milligram is worth . 06 cents. Therefore a hole one foot in depth that yields one milligram of gold proves a value of 8 . 8 times . 06 or 5 . 280 cents. Then, since this figure repre- sents the yield of a hole of the unit depth of one foot and the unit recovery of one milligram we have only to divide it by the depth in feet and then multiply it by the number of mil- ligrams recovered to learn the indicated values in cents per cubic yard for any hole ! A table is included in this booklet which reduces this arithmetical calculation to one operation. (Plate "G"). It is based on the working out of the following formula : 3068 X x P t p,, x Mgms. = Value in Cents per Cubic Yard. . 3068 Equals area of drive shoe in square feet. 27 Equals conversion factor to cubic yards. . 06 Equals value of gold in cents per milligram. "D" Equals recorded total depth of hole in feet. Mgms. Equals number of recovered milligrams. In this appended table there have been substituted vari- ous depths for the factor "D" there remains only to multi- DRILLING FOR PLACER GOLD 49 ply the partial result opposite to the actual depth to bedrock by the number of milligrams to find the indicated value in cents per cubic yard. COMPENSATION FOR EXCESSIVE CORES Occasionally a hole will be reported that varies in a marked manner from normal. For instance, suppose that between the 20 and 25 foot marks there was trouble with a defective pipe joint or a plugged core that kept out the proper amount of material or an inrush of far too much sand and gravel. The panner's log would show an estimate of 18 milligrams of gold in this five feet of progress and extracted from either too little material or too much. Suppose that the amount of material actually recovered and the theoreti- cal recovery do so fail to coincide, what then? Some Engi- neers prefer to throw out this portion of the hole ; it is surely not necessary to discard the whole drilling by reason of this mishap, nor yet should such unreliable data be incorporated as part of the whole. In this hypothetical case the Engineer would subtract five feet from the recorded depth and 18 mil- ligrams from the weight of the gold as finally wieghed ; then calculate his values. Other Engineers will credit values to this five feet of hole according to the average of a like dis- tance above and a like distance below the error. This seems a likely way to approximate the truth. OTHER CONSTANTS IN COMMON USE But the constant of . 3068 (based on the calculated volume of a cylinder 1 foot high with a base l l /2 inches in diameter) is only one of several that have been widely used in the past and are more or less favored today. 50 DRILLING FOR PLACER GOLD CONSTANT OF .3333 It was once a favorite practice to estimate values on the above basis and then to discount the completed returns on the appraisal of the property by 10 or 15 per cent as a meas- ure of safety and conservatism. However praiseworthy this desire to err only on the side of safety, this procedure is hardly professional or sensible. At least one serious error has occurred where the values were so discounted twice through a misunderstanding. But this desire to lean to the safe side led to the adoption of an arbitrarily fixed constant of .3333. This was widely used by those who insisted on ultra-conservatism in the estimating of dredging values and also by those who maintained that the beveled edge of the Keystone drive -shoe as well as the entire method of opera- tion allowed more material to enter the drill-pipe than strict theory would indicate. The use of the constant . 3333 gave final values that were 8.7% less than when the .3068 factor was employed. KEYSTONE CONSTANT OF .27 But from the very earliest day of the development of the technic of prospecting, there have been many Engineers who have favored the constant of . 2 7 (one cubic yard of material to each 100 feet of pipe). This has been widely called the "Radford Factor" or the "Keystone Constant." Its use was first scouted as too likely to exaggerate values, but in the light of recent comparisons of estimated prospecting to- tals and the actual recovery of subsequent dredge returns, this "Keystone Constant" climbs back into secure favor. One large Company that has successfully operated many dredging properties in different parts of the world for a long DRILLING FOR PLACER GOLD 51 time preferred the conservative constant of . 3333 but it is noteworthy that their estimates today are usually worked up on the basis of the " Keystone Constant." REASONS FOR THE KEYSTONE CONSTANT The churn drill, functioning by impact", continually acts to drive the gravel downward before the pipe and to settle the heavier particles of gold and precious metal. If any metal ever does escape the action of the pump, it is more likely to be these same heavier particles. At the conclusion of the hole the last drilling may have driven a few particles of the metal down out of reach into the bedrock. The panner may always, despite the most scrupulous care, lose a tiny proportion of the values from the splash of the pumping or in the rocker. There is more likelihood of missing some of the values than of getting more than the due amount. There are many sound reasons to justify the practice of crediting the recovered gold to a volume of material some- what less than the theoretical amount and the "Keystone Constant" does just that. NO ONE CONSTANT INVARIABLY PROPER Few Engineers will use the same constant under all con- ditions. For there are many variables to consider in trans- lating the work of a drill to a well considered prophecy of the values that the dredge will recover. The Engineer, in choosing his constant will weigh many things. The per- sonality of his crew cannot be ignored. The time of the year in which the work is done will have an effect a panner can- not work in freezing weather with the same accuracy as in the pleasant days of summer. Rich and streaky channels of 52 DR I LLING FOR PLACER GOLD DRILLING FOR PLACER GOLD 53 heavy gold concentration will usually drill higher than the expected recovery a small gold content evenly distributed in loose ground will often show to the drill as less than what the dredge will later actually save. These matters will be discussed more at length in the final chapter of this article "Chapter IV Reliability of Keystone Samplings". Most Engineers today will use the "Keystone Constant" as the proper basis for their estimates. COMBINING VALUE OF VARIOUS HOLES When the Engineer has correctly evaluated the various holes he faces the problem of combining them to gain his tract values. It is customary to plot the holes on a large map, noting dredging limits as determined by surface con- tour, by exposed rimrock or reefs and also marking proper- ty lines. If the values fade off into barren areas there should be marked the probable boundaries of dredging values roughly estimated at the probable cost of the dredging operations. This may vary from 5 cents where a large dredge is to work under the most favorable conditions to 1 5 cents or even more where inaccessibility, expensive power or frozen ground offers difficulties. If the ground shelves to shallower depths the limiting depths should also be plotted. These vary for different dredges, but the average dredge can hardly dig its flotation in ground that is not at least 12 feet in depth. The yardage should be estimated from this com- pleted plat with all possible accuracy. It is perhaps true that a little carelessness or a wrong conclusion at this point will affect the figure of total recoverable gold more than any other error that is likely to be made. It may be noted in passing that most Engineers add to their yardage calcula- 54 DRILLING FOR PLACER GOLD tions the amount of ground that the dredge buckets will handle in digging bedrock to the depth of one foot. This is a necessary procedure in actual dredging and one that dilutes the auriferous gravels with barren material. PRINCIPLE OF EVALUATION The only principle involved in calculating the value of a tract of ground lies in the necessity of giving proper "weight" to each drill-hole in that area that is, in letting a drill-hole affect the final result in proportion to the area which it rep- resents, or "governs." Merely to add the values of the holes and divide by the number of them is an elementary error. CALCULATION WHEN HOLES ARE SPACED EQUIDISTANTLY If the area of auriferous gravels is a "blanket" deposit and it has proved feasible to lay out the holes so that they are equi -distant, this calculation is a simple one indeed. The ground is then divided into equilateral triangles, and the depth of each area, and its values in cents per cubic yard is the average of the product of the depths and values of each hole. Thus, the deeper the hole, the greater its effect on the values of the area. The value of the tract is the average of the products of the volume of the triangles and their values. If the holes are not evenly spaced, to connect them by lines, to figure the area of the enclosed triangle and to allot to it the average of the products of the depths and values of the three holes at its apices is not far wrong. . To be sure, there is a slender factor of error that increases as the "triangle" departs from the equilateral, but this is a compensating variation that may often be ignored. DRILLING FOR PLACER GOLI> 55 OTHER METHODS There are Engineers who favor other and more compli- cated calculations but the principle to be followed is a sim- ple matter of common sense that lends itself to translation in ordinary arithmetical terms. Discussion of the infinite number of special problems that the prospecting Engineer will meet can only bring one back to the starting point. It has been shown by actual test that rarely will two Engineers go about combining the results of two or more drill-holes in exactly the same way. But there is little chance to go far wrong. If there be a large area and many holes, the result will surely be within the limits of error of the entire technic of field work ! Set several men to counting a pile of nails some will count one at a time ; some two at a time and some five at a time but the complete tally will be the same no matter what system best fitted the idiosyncrasy of the coun- ter! The best argument against meticulous precision or vast elaboration in the calculation is the admitted fact that the same Engineer cannot get the same results from the evaluation of the same scattered holes at two different times. But the percentage of disagreement will be well within safe limits. To be sure, there are occasional per- plexing problems where the odd areas at the side are of un- usual shape, or where it becomes necessary to separate the value of some particular tract or acreage from the calcula- tion of the whole area. But these, too, yield to arithmetic and to the elementary principle of allowing each .drill-hole to influence only that territory to which it is the nearest. "HIGH HOLES" Two or three of the holes are most likely to be very much higher than the others. Sometimes, they are so large in com- 56 DRILLING FOR PLACER GOLD DRILLING FOR PLACER GOLD 57 parison with surrounding holes that there is a very natural suspicion of a grave error. There is no standard method of treating these "high holes" in the final calculation differ- ent Engineers favor different methods. In fact, nowhere does the "personal" factor enter more strongly than in mak- ing the decision as to how such high holes shall be counted. Some hold it advisable to put down a check hole about six feet from the high hole. The check hole rarely shows values as great sometimes it is surprisingly low. Usually, the average of the high hole and check hole is taken and figured into the final result as though there were but one hole at that point. It may be here noted that the gold content of more than one property has been padded by figuring in the check holes on an equal basis with the other drillings, the fact being forgotten or ignored that these holes were put down at favored locations and were not equally representa- tive samplings. Usually, the Engineer is content to check one or two of the high holes and to regard the others in the light of what the first check holes reveal. If the property as a whole is of even enrichment, there is little likelihood that a second hole will confirm exceptionally high results of a first. On the other hand, if it is known to be "spotted", an occasional high hole can be accepted at full value without question. Indeed, the plotting of the several high holes will sometimes indicate a rich streak or channel. Extra holes are often put down to determine the course and extent of such an area of attractive concentration not as check holes, but as supplementary drillings. Once that such an enrichment is established, there is of course no argument against accepting the higher values of the holes within such territory. If the high yield of a hole can be traced to a 58 DRILLING FOR PLACER GOLD single large piece of gold, or a nugget, it is customary to leave out the weight of this persumably accidental bit in calcu- lating the value. Some Engineers, in what is perhaps an over-anxiety for conservatism, do not include the high holes in their final calculations. Still others cancel them against the low holes in the apparent conviction that the very high and the very low are due to errors which may be bal- anced. Another method is to take half the result of a high hole which is more a concession to timidity than to com- mon sense. Most dredge operators will report that a high hole is never proved up by the work of the dredge. Yet from actual results it seems to be an established and a safe and proper practice that the occasional high hole may be included in the calculations if it was correctly drilled and if there is no mechanical error to be detected. For if the drill caught a stray bit of concentration behind a boulder or tapped a random streak of enrichment, there are quite cer- tain to be many scattered areas of similar values that the dredge will recover. It seems fallacious and hypercautious to count out the one or two holes of most attractive result. But it must be remembered that only very rarely does such a high hole actually reveal a definite area of surrounding yardage of a corresponding richness only adequate check- ing could prove that! But it does have a proper part in the summation of the whole! CALCULATION OF STREAM CHANNEL VALUES If the auriferous gravels follow a comparatively narrow and well-defined channel, it will have been prospected by lines of holes that cross it at intervals of a thousand feet, more or less, the holes spaced rather close together, depend- DRILLING FOR PLACER GOLD 59 ing on the width of the channel. The calculation of the values of the line may be made as is outlined and exemplified on Plates "A", "B," and "C." The principle is exactly the same as has been above outlined. Each drill-hole governs the length of "line" that is nearer to it than to any other drill hole. The figuring is facilitated by making a diagram of this channel cross-cut being careful to lay out the dredg- able limits at the side with due regard to the surface contour, bedrock elevation, barren gravels and practical digging depths. Ordinarily, the line will end at an actual drill-hole, but sometimes it will seem reasonable to extend it somewhat beyond a hole with acceptable values and depth part way to another hole that is either shallow or barren, or toward a further and approximated dredging limit. It is then nec- essary to credit to this "proportionate point" or "fictitious hole" a calculated value and depth these assumptions to be made with due regard to the comparative distance of the two drill-holes that govern the estimate. This is shown on Plate "A" there are such "proportionate points" at the right limit of Line 9 and at the left limit of Line 10. No matter if the holes be spaced irregularly, the area which each governs may be visualized and correctly calculated. To simplify calculations, the method exemplified in Plates "A" and "B" is often resorted to the value of the area be- tween two holes is estimated by multiplying the distance by the average depth and the value. A study of the Plates will reveal the whole process as reproduced from an actual report. To obtain the value of the "block", or the dredga- ble area between the two lines, the procedure as illustrated on Plate "D" may be followed. The calculation is some- times called the determination of block values by the "Cen- 60 DRILLING FOR PLACER GOLD ter of mass" formula. The lines are projected (by using the cosine of the angle which they make with an ' 'altitude" line connecting their centers) and the average area of the pro- jected bases, multiplied by this altitude, gives the volume of the "block." It should be noted that the lines affect the total value of the enclosed block not by their comparative lengths but by the area of the channel that they cut. In the same way, the blocks may be added to find the total yardage and total gold content in a property but the average value per cubic yard must be figured by allowing each block to affect the result in proportion to its yardage. Thus, the block yardages times the block value, added, di- vided by the sum of the yardages will give the value of the tract. It is often desirable to estimate as nearly as may be the value of a piece of land within certain property lines often so bounded as to have only one or two holes actually within its confines. The calculation may be made by the use of "proportionate points" or fictitious holes which are credited with a depth and a value that are derived from com- bining the value and depth of the two nearest holes in a pro- portion that is in inverse value to their distance away. Such estimates can be called little more than "intelligent guesses." SUMMARY OF CALCULATION METHODS In the discussion above, the plotting of the cross-cut of a channel has been pre-supposed. Referring to this drawing, the Area between two holes, which is ordinarily a trape- zoid, is the average of their depth multiplied by the distance between them ; the Value of this Area is the average value of the two holes multiplied by the Area ; the Value of the Line is the sum of all these products divided by the Area ; DRILLING FOR PLACER GOLD 61 the value of the Block is the sum of all these products in one Line, plus the sum of all these products in the second Line, divided by the added Areas of the two cross-sections, and multiplied by distance between the lines. WHAT REPORT SHOULD COVER The experienced Engineer will include in his final report of the property much beyond the mere calculation of yardage and values. For it is quite possible that that very report will be the dredge designer's sole source of accurate data re- garding the physical conditions with which the dredge must cope. Modern firms prefer to design a dredge to fit the property. Even a used dredge, if torn down and trans- fered to a new property must be largely altered to meet the somewhat different conditions of soil and depth. Accord- ingly, there are here suggested the various bits of infor- mation upon which a thorough report will touch : Character of bedrock. Water-level with reference to surface and to bedrock. Are boulders present? Their maximum size. Character of gravel loose, cemented, clay, etc. Kind of gold large or fine ; flaky or rusty. Are special gold-saving devices indicated for nuggets or for flour or oxidized gold? What are climatic conditions on property? Must dredge be specially equipped to lengthen its working season? What are transportation conditions with special refer- ence to heavy dredge machinery? What power is available for dredge construction and operation? Its probable cost? 62 DRILLING FOR PLACER GOLD DRILLING FOR PLACER GOLD . 63 What is recommended size of dredge for efficient operation and for proper exploitation of available yardage? What about water supply? What is maximum grade of ground in which dredge will be called upon to work? Where may dredge be best built with relation to greatest conveniences for construction and good values as well as in accord with the best economic plan for future operations? 64 DRILLING FOR- PLACER GOLD CHAPTER IV RELIABILITY OF KEYSTONE SAMPLINGS Actual Instances of Comparison Between Drill Estimates and Dredging Returns KEYSTONE ESTIMATES NOW CHECKED If gold particles were uniformly distributed, uniform samplings would exactly determine the value of the whole. But the precious flakes are laid down according to no mathe- matical law; rather by the uncertainties of shifting currents, of spring freshets, of endless reconcentrations. Even a defi- nite ' 'pay-streak" begins unexpectedly and ends abruptly. Seldom will a dredge recover a comparative amount of gold in two successive days of operation. Yet the records of a generation of placer gravel exploration have proved that a reliable appraisal is quite possible with the Keystone Drill. Yet Engineers rarely expect a second drill-hole, sunk a few eet from a first, to yield values that are in close accord; nor are they surprised when a shaft, put down around a drill-hole, presents a considerable discrepancy in values. No one expects a flake of ore, chipped from one part of a vein, to assay the same as another flake from near-by. Yet the average of several such flakes will approximately reveal the proportion of mineral in the ore-body. The the- ory of Keystoning is the theory of averages let the sam- ples be fairly collected, correctly measured and properly assayed and they will collectively indicate the values of the whole. Once this was purely theory today it is fact. 65 66 DRILLING FOR PLACER GOLD For in the last few years the results of vast dredging operations have been totaled and analyzed, and it is now possible to check them with the predictions of those who drilled the same areas in earlier years. AGREEMENT ON OREGON PROPERTY A placer deposit in Oregon which was the result of stream action was systematically drilled by lines of holes at right angles to the flow. The work was carefully done by com- petent Engineers and the calculations carried out by the methods illustrated in Plates "A" to "D." This property, consisting of 121 acres, has today been completely mined by a modern dredge. Its average depth was 18 feet and there was an overburden of almost barren tailings covering a "streaky" enrichment. The original estimates gave the average value per cubic yard as 16.8 cents and the value recovered by the dredge was 15.63 cents or 93% of the estimate. The constant used in computing the drill re- sults was . 3333 ; had a constant of . 3068 been used, the esti- mated and actual values would have agreed quite closely. There were here put down one hole to every 2 . 4 acres. Yet hardly any two of the eight "blocks", into which the area was divided by the drill lines yielded the identical values which the drill forecast in one of them the recovered value per cubic yard exceeded the estimate by 49 . 4% and in another it was less by 68 . 2%. CHECK ON A CALIFORNIA PROPERTY We reprint from the Engineering and Mining Journal an account of the balancing of prospecting estimates and dredg- ing results on a California property section of 118.5 acres DRILLING FOR PLACER GOLD 67 where the results of 38 drill-holes were used in making the forecast 14 of the holes being outside but adjacent to the area dredged. "The estimated value per cubic yard in this tract was 29.88 cents and the dredge returns were 31.55 cents, a gain of 5 . 6%. We believe the constant used in figuring the drill returns on this property to have been .3068. Some years ago on another and undredged portion of this property consisting of 493 acres an estimate was made to determine the gold content. The results from 53 drill holes, which were within the limits of the tract, were used by taking 70 per cent of their recorded value. Consideration was then given and use made of the values obtained from dredging operations which had been conducted adjacent to and around about two thirds of the tract. Since then 402 acres of this tract have been dredged and the returns per cubic yard averaged 12.73 cents. The data used in making the original estimate were applied to the portion now dredged and the proportionate values found to be 12.70 cents per cubic yard." ANOTHER CHECK FROM LARGE ACREAGE From the same article we quote another example that shows a recovery closely corresponding to the estimate, giving the results produced by operations on three separate tracts in a large California property, the third tract having been mined by three dredges: Average No. of Acreage to Each Value per Cubic Yard Dredge Per- Tract Depth Acres Holes Hole Drill Recovery centage A 22 .5' 173. 5 x 57 3.2 6.8 7 .82 115% B 44 .5' 84. 20 4.2 5.9 6 .7 113% CDr. #1 51 .8' 183 120 1.5 11.1 9 .64 87% CDr. #2 60 .6' 106 41 2.6 11.2 9 .44 84% CDr. #3 56 .4' 135 58 2.3 11.6 11 .30 97% 68 DRILLING FOR PLACER GOLD DRILLING FOR PLACER GOLD 69 x 37 shafts and 20 Drill-holes On Tracts A and B Constant Used in Calculating Drill Results . 27 On Tract C Constant Used in Calculating Drill Results . 30 CHECK FROM SMALL DREDGE OPERATIONS "The average results of all the above, proportioned to the acreage, is a drill value of 9.48 cents per yard, and the dredge recovery 9.12 cents, or 96 . 2%". And we quote yet another instance: "Dredging operations on one property in California have produced returns which, taken as a whole, correspond quite closely with the original estimates, and the following de- tails have been presented covering the work done in the past three years: Year Average Depth Acres No. of Holes Acreage to Each Hole Value per Cubic Yard Dredge Per- Drill Recovery centage 1918 1919 1920 32 34 29 I 7 4' 8' 19 20 20 94 90 43 11 10 7 1.8 2.1 2.9 10 9 10 39 69 .69 10.64 9.22 14.34 102.4' 95. 2< 134.0' 3 1 EXAMPLE FROM OPERATIONS OF NATOMAS CONS. OF CALIFORNIA "The average results proportioned to the acreage show an estimated value of 10.25 cents and a dredge recovery of 11 .39 cents, or an increase of 11 . 1%". Perhaps the dredging problems of the Natomas Company of California have been the most difficult encountered on large scale operations. Here, on the American River, are high benches of gravel that is so compact and cemented as almost to defy the dredge buckets and, down in the bottom lands, wide areas of softer and shallower ground. A check, made five years ago on the operation of three of their many dredges gives a reasonably close agreement. 70 DRILLING FOR PLACER GOLD Percentage of Area in Years of Estimate Dredge Acres Operation Recovered No. 5 180 10 86 No. 8 106 4 87 No. 9 135 6 101 These results are based on an original calculation using the constant .30. During the last five years these dredges, as a whole, have produced about 101 per cent of the cal- culated recovery ! MONTANA PROPERTY A portion of a Montana property consisting of 300 acres was prospected with 77 drill holes spaced at irregular dis- tances. The average value per cubic yard indicated by the drilling was 15.83 cents, and the dredge recovery 13.55 cents or 85 . 6%. The average depth of the ground was 40 feet and the larger portion of the values was contained in the three feet of gravel next to the bedrock. Such a deposit offers obvious difficulties to accurate calibration. TABULATION OF AVAILABLE COMPARISONS The article from the Engineering and Mining Journal partly reproduced above, written by Mr. Charles W. Gard- ner, Manager of the Mines Operating Department of the Hammon Engineering Company, probably the first Engi- neer to use a Keystone Drill for placer prospecting, con- cludes with a summary that is of striking interest : "From all of the properties above mentioned we are able to segregate 3,743 acres to which we can apply data given in fairly accurate reports. This combined area was pros- pected by means of 1,749 drill-holes, or one to every 2.1 acres. The average value per cubic yard obtained by DRILLING FOR PLACER GOLD 71 drilling was 15.4 cents and the average dredge recovery 13 . 55 cents, or 88%. A comparison of returns, segregated as to values, is as follows : Average Value per Cubic Yard Percen tage Drill Values per Per Centage Drill Dredge Cubic Yard Acres of Whole Value Recovery Gain Loss Underll^ 27.9 0.7% 9.2M 8.60^ 6.6% Underll^ 1638.1 43.8 7.68 9.34 21.6% Between 11 and 12 c 424.0 11.3 11.28 10.12 10.3 Between 11 and 12 e 480.0 12.8 11.61 16.44 41.6 Between 12 and 20 c 582.5 15.6 16.92 13.10 22.6 Over 20 c 392.0 10.5 45.86 20.93 54.4 Over20c 198.5 5.3 33.15 35.97 8.5 Totals 3743.0 100.0% AVERAGES 15.40 13.55 12.0 Here is spread before us the work of different Engineers at different times in many fields. There has been no at- tempt to trace out the avoidable error in either prospecting or mining. Suffice it to say that there is included in this tabulation the exploration of at least two properties where the excavated material was a clean washed sand and gravel with little clay and many boulders ; making the forecasting of the values exceedingly difficult by any method and the recovery of certain dredges that fall short of the highest standard of modern efficiency. ACCURATE PROSPECTING POSSIBLE Mr. Gardner closes his article with; "We feel that a safe conclusion to be drawn from all of the above is that when a property has been sufficiently prospected by an experienced Engineer, the results intelligently interpreted and the cal- culations accurately made, the result obtained will indicate within reasonable limits the gold content. 72 D R I LLING FOR PLACER GOLD DRILLING FOR PLACER GOLD 73 "Full consideration should be given all these points and then if the estimated gross value safely and sufficiently ex- ceeds the cost of acquisition, equipment and operation, there should be nothing to deter or discourage the invest- ment of capital in such an enterprise." HOW DIFFERENT CONDITIONS AFFECT ACCURACY Mr. James W. Neill, in an article in the Mining and Sci- entific Press, says, "If the driller keeps his bit behind his shoe, and sees that he gets a correct amount of core, there should be little question of the correctness of a large gen- eral average, and the Engineer can use such factors of safety as his experience and the character of the ground in- dicate. In very loose ground, I personally look for a recov- ery of full drill values where the gold is coarse and is entirely contained in the foot or two above bedrock. I think one will also usually overrun the drill, provided the bedrock can be dug. That is about the sum of our experience at Snelling. ' ' We quote an extract from an article by the compiler of this booklet that recently appeared in the Engineering and Mining Journal; "It may be observed that the accuracy of results gained by drilling is surprising, considering the com- paratively small size of the sample. For example, one hole to two acres in 50-ft. ground would mean that 1 /328,000 part of the gravel was examined. Of course one hole by it- self means nothing it is only a carefully charted series that reliably represents actual conditions. "All available data seems to point to the following facts regarding the accuracy of drilling : 1. Drill results give high assays where the gold is fine. 74 DRILLING FOR PLACER GOLD 2. Estimates will tally with returns where gold is reasona- .bly heavy; ground is compact with a little clay; and prospecting and dredging are intelligently done. 3. The drill will exaggerate the value of very loose ground where sand and water pressure crowd material into the bottom of the pipe. 4. The drill will signally' fail to show recoverable gold in areas of moderately loose ground where gold is dis- tributed and in comparatively small amount." SUMMARY The whole problem is squarely up to the discretion of the Engineer. He may compensate for the co-efficient of the personal accuracy of his crew; he may use the proper con- stant in his calculations ; he may use his own experience and the now recorded findings of others and translate the results of his Keystone Drill work to a forecast that bears the stamp of conviction and accuracy ! CONCLUSION The Keystone Driller Company sells more than a mere machine it sells service! Orders are carefully filled with selected materials and shipments forwarded with all possible expedi- tion for we are keenly alive to the difficulties and hazards of field work. During the score of years in which Keystone Drills have been the reliance of prospectors the world over, we have collected a considerable knowledge of the technic of placer testing and of the proper equipment therefor. That data we shall gladly share ; and we offer our experience to any Engineer, be he out- fitting for a proposed campaign of prospecting or meeting a knotty problem in the field! 75 76 DRILLING FOR PLACER GOLD PLATE "A" LINE No. 9 Hole 29 49.5' Hole 30 Hole 31 Hole 32 HoleX 30' 189' 192' 197' 116' 20' Width at top 744' Width at bottom 694' 51.6' 49.5' 45.0' 40.0' 4.56c 11.23c 29.75c 14.19c S.OOc LINE No. 10 Hole Y 55.0' 18.89c 27.5' Hole 33 55.5' 18.89c 100' Hole 34 49.5' 18.02c 200' Hole 35 40.0' S.OOc 200' 20' Width at top 547.5' Width at bottom 500' KEYSTONE CREEK PLACERS (From actual drill records) Key Chart to Estimate of Line 9 on Plate "B"; of Estimate of Line 10 on Plate "C"; of Block Estimate on Plate "D." NOTE Left limit of Line 9 determined by low value actual drill-hole. Right limit of Line 9 determined by approximation of dredging limit and marked by "fictitious" drill-hole "X." Left limit Line 10 determined by some physical factor probably an irregular rim. "Fictitious" Hole "Y." Right limit Line 10 determined by too low value of Hole #35. Engineer has approximated limit of values 20 feet inside of this Hole and marks "fictitious" hole #35' giving it a limiting value of 5^. DRILLING FOR PLACER GOLD 77 PLATE "B" KEYSTONE CREEK PLACERS Valuation of Line 9 Area of Square Cubic Block Feet Yards Cents A equals 49 5 2 x3 742.5 or 27.5 x 3.04 = 83.6 B equals 49 5&516 x 189 9553.9 or 353.8 x 7.89=2791.4 C equals 51 6 ^ 49 5 x 192 9705.6 or 359.5 x 20 49 = 7366.1 D equals 49 - 5 2 &45 x 197 9308. 2 or 344.8 x 21.97 = 7575.2 E equals 45 & 40 x 116 4930.0 or 182.6 x 9.59=1751.1 F equals 40 * 20 400.0 or 14.8 x 3.33 = 49.3 34640.2 1283.0 15.25 19616.7 One foot into bedrock 694.0 35334.2 1308.7 14.99 19616.7 NOTES There is given to Areas "A" and "F" a value equal to only two thirds of their governing drill-hole. These small areas are the approximation of the departure from the vertical of the dredge bank. Under the "Cents" column is the average value of the two bounding drill holes. To the yardage total has been added the barren material resulting from dredging one foot into bedrock. The figure 14.99 represents the value in cents per cu. yd. of the line and is gained by dividing 19616 . 7 by 1308 . 7. 78 DRILLING FOR PLACER GOLD PLATE "C 1 KEYSTONE CREEK PLACERS Valuation of Line 10 Area of Square Cubic Block Feet Yards Cents A equals 55x 2 27 ' 5 756 or 28.0 x 12.59 = 352.5 B equals 55 & 2 55 5 x 100 5525 or 204.6 x 18.89 =3864.9 C equals 55 5 ^ 49 5 x 200 10500 or 389.0 x 18.46 = 7180.9 40 'i flr 4ft D equals x 200 8950 or 331.5 x 11.51 =3815.5 E equals 40 * 20 400 or 14.9 x 3.33 = 49.7 26131 968.0 15.72 15263.5 One foot into bedrock 500 18.4 26631 986.4 15.48 15263.5 NOTES See Notes on Plate "B." The figure 15 .48 represents the value in cents per cu. yd. of the line and is gained by dividing 15263 . 5 by 986 . 4. DRILLING FOR PLACER GOLD PLATE "D" KEYSTONE GREEK PLACERS Estimate Gross Value of Block Between Lines 9 and 10 Area of Projected Gross Cubic Section Area Value Yards Line 10 = 26131 x .9925 (Cos. 7)= 25935 15263.5 968 Line 9 = 34640.2 x .9563 (Cos. 17) = 33126 19616.7 1283 2)59061 34880.2 2251 29530.5 29530.5 (Average area projected base) multiplied by 945 (Surveyed or plotted distance between middle of both lines which is altitude of "block") gives a total cubic content of 27,906,522 Cubic Feet. 27,906,522 Cu. Ft. equals 1,033,367 Cu. Yds. The Gross Value Factor, divided by Cu. Yds. Factor equals: 2251 )34880 . 2 ( 1 5 . 49 cents Value of block Total Value of Block equals 1,033,367 times 15.49 or $160,099.70. As a check on Calculations we may figure the same Total by using the products of the Line Calculations after adding "One Foot Into Bedrock." Area of Section Line 10= 986.4 Cu. Yds. x .9925 (Cos. 7)= 979.0 Line 9 = 1308.7 Cu. Yds. x .9563 (Cos. 17) = 1251.5 2)2230.5 1115.25 1115.25 x 945 = 1,053,911 Cu. Yds. Total Value of Block equals 1,053,911 x 15.19c = $160,089.08. NOTE A line is drawn connecting the centre of the Lines 9 and 10. These lines are then projected so as to form a 90 angle with this "altitude" line. The projected base areas are added, averaged, and multiplied by the altitude to find content of block in Cu. Yds. Additions and sub- tractions might have been made for irregular rim. DRILLING FOR PLACER GOLD PLATE "' CORE MEASUREMENTS KEYSTONE PLACERS Total Core Measured on Surface Cubic Core Measured in Pipe Without Slimes With Slimes Feet as per Hole Depth Drive Total Per Ft. Total Total Average Total Average Const. No. Ft. Ft. Ins. Ins. Cu. Ft. Cu. Ft. Cu. Ft. Cu. Ft. Cu. Ft. .27 1 110 110 1446 14.32 21.69 30.27 .2752 (Not Measured) 29.70 2 105 98.5 1539 15.83 23.08 25.18 .2556 39 .53 .401 26.60 3 105 98.5 1521 15.44 22.82 26.30 .2669 37 .80 .384 26.60 4 105 97.6 1477 15.14 22.16 24.87 .2547 38 .82 .398 26.35 5 105 96.1 1600 16.65 24.00 26.33 .2740 38 .02 .396 25.95 6 105 97.4 1493 15.33 22.40 24.35 .2499 36 .00 .369 26.30 7 107 99.7 1529 15.34 22.94 22.36 .2243 28.75 288 26.91 8 98.5 83.0 1402 16.90 21.03 25.24 .3041 32.30 .389 22.41 840.5 12007 15.34 180.12 204.90 .2621 251.22 .3746 210.81 NOTES Figures under "Depth" represent total from surface under "Drive" they represent actual drilling. (Holes were started in a pit.) This Chart, taken from the Report of an Engineer, was prepared by him that he might compare the core records of various similar holes. It shows work that is reasonably uniform, with no outstanding discrepancies, and proves that the material actually re- covered, if discounted for the "swelling" of the gravels, checks very closely with the theoretical displacement of the drive-shoe. DRILLING FOR PLACER GOLD 81 PLATE "F" KEYSTONE DRILLER COMPANY TABLE FOR FINDING VALUE PER CUBIC YARD (When depth of drill-hole and weight of gold in milligrams are known) CONSTANT .27 Depth to Depth to Depth to Bedrock in Bedrock in Bedrock in Feet Factor Feet Factor Feet Factor 10 .6000 26.5 .2264 43 .1395 10.5 .5714 27 .2222 43.5 .1379 11 .5455 27.5 .2182 44 .1364 11.5 .5217 28 .2143 44.5 .1348 12 .5000 28.5 .2105 45 .1333 12.5 .4800 29 . 2069 45.5 .1319 13 .4616 29.5 .2034 46 .1305 13.5 .4444 30 .2000 46.5 .1290 14 .4286 30.5 .1967 47 .1277 14.5 .4138 31 .1935 47.5 .1263 15 .4000 31.5 .1905 48 .1250 15.5 3871 32 .1875 48.5 .1237 16 .3750 32.5 .1846 49 .1224 16.5 .3636 33 .1818 49.5 .1212 17 .3529 33.5 .1791 50 ' .1200 17.5 .3429 34 .1765 50.5 .1188 18 .3333 34.5 .1739 51 .1177 18.5 .3243 35 .1714 51.5 .1165 19 .3158 35.5 .1690 52 .1154 19 5 .3077 36 .1667 52.5 .1143 20 .3000 36.5 .1644 53 .1132 20.5 .2927 37 .1622 53.5 .1121 21 .2857 37.5 .1600 54 .1111 21.5 .2791 38 .1579 54.5 .1101 22 .2727 38.5 .1559 55 .1091 22.5 .2667 39 .1539 55.5 .1081 23 .2609 39.5 .1519 56 .1071 23.5 .2553 40 .1500 56.5 .1062 24 .2500 40 5 .1481 57 .1053 24.5 .2449 41 .1463 57.5 .1044 25 .2400 41.5 .1446 58 .1035 25.5 .2353 42 .1429 58.5 .1026 26 .2308 42.5 .1412 59 .1017 Diameter of Cutting -Shoe 7>2 inches. Value of gold 0.06 cents per milligram $18.66 per ounce. To find value in cents per cubic yard, multiply number of milligrams of gold recovered from drill-hole by the factor in the table opposite the depth to bedrock 82 DRILLING FOR PLACER GOLD PLATE "G" KEYSTONE DRILLER COMPANY TABLE FOR FINDING VALUE PER CUBIC YARD (When depth of drill-hole and weight of gold in milligrams are known) CONSTANT .3068 Depth to Depth to Depth to Bedrock in Bedrock in Bedrock in Feet Factor Feet Factor Feet Factor 10 .5280 26.5 .1992 43 .1228 10.5 .5029 27 .1955 43.5 .1214 11 .4800 27.5 .1920 44 .1200 11.5 .4591 28 .1886 44.5 .1187 12 .4400 28.5 .1853 45 .1173 12.5 .4224 29 .1821 45.5 .1160 13 .4061 29.5 .1789 46 .1148 13.5 .3911 30 .1760 46.5 .1136 14 .3771 30.5 .1731 47 .1123 14.5 .3641 31 .1703 47.5 .1112 15 .3520 21.5 .1676 48 .1100 15.5 .3407 32 .1650 48.5 .1089 16 .3300 32.5 .1625 49 .1078 16.5 .3200 33 .1600 49.5 .1067 17 .3106 33.5 .1576 50 .1056 17.5 .3017 34 .1553 50.5 .1046 18 .2933 34.5 .1530 51 .1035 18.5 . 2854 35 .1509 51.5 .1025 19 .2779 35.5 .1487 52 .1015 19.5 .2707 36 .1467 52.5 .1006 20 .2640 36.5 .1447 53 .0996 20.5 .2575 37 .1427 53.5 .0987 21 .2514 37.5 .1408 54 .0978 21.5 .2456 38 .1389 54.5 .0969 22 .2400 38.5 .1371 55 .0960 22.5 .2347 39 .1354 55.5 .0951 23 .2296 39.5 .1337 56 .0943 23.5 .2247 40 .1320 56.5 .0935 24 .2200 40.5 .1304 57 .0926 24.5 .2155 41 .1288 57.5 .0918 25 .2112 41.5 .1272 58 .0910 25.5 .2071 42 .1257 58.5 .0903 26 .2031 42.5 .1242 59 .0895 Diameter of Cutting-Shoe 1Y^ inches. Value of gold 0.06 cents per milligram $18.66 per ounce. To find value in cents per cubic yard, multiply number of milligrams of gold recovered from drill-hole by the factor in the table opposite the depth to bedrock. DRILLING FOR PLACER GOLD 83 PLATE "H" KEYSTONE DRILLER COMPANY TABLE FOR FINDING VALUE PER CUBIC YARD (When depth of drill-hole and weight of gold in milligrams are known) CONSTANT Depth to Depth to Depth to Bedrock in Bedrock in Bedrock in Feet Factor Feet Factor Feet Factor 10 .4860 26.5 .1834 43 .1130 10.5 .4629 27 .1800 43.5 .1117 11 .4418 27.5 .1767 44 .1105 11.5 .4226 28 .1736 44.5 .1092 12 .4050 28.5 .1705 45 .1080 12.5 .3888 29 .1676 45.5 .1069 13 .3738 29.5 .1647 46 .1057 13.5 .3600 30 .1620 46.5 .1045 14 .3471 30.5 .1593 47 .1034 14.5 .3351 31 .1568 47.5 .1023 15 .3240 31.5 .1543 48 .1013 15.5 .3135 32 .1518 48.5 .1002 16 .3037 32.5 .1495 49 .0992 16.5 .2945 33 .1472 49.5 .0982 17 .2895 33.5 .1450 50 .0972 17.5 .2777 34 .1429 50.5 .0963 18 .2700 34.5 .1408 51 .0953 18.5 .2627 35 .1388 51.5 .0944 19 .2558 35.5 .1369 52 .0935 19.5 .2492 36 .1350 52.5 .0925 20 .2430 36.5 .1331 53 .0917 20.5 .2371 37 .1313 53.5 .0909 21 .2314 37.5 .1296 54 .0900 21.5 .2260 38 .1279 54.5 .0892 22 .2209 38.5 .1262 55 .0884 22.5 .2160 39 .1246 55.5 .0876 23 .2113 39.5 .1230 56 .0868 23.5 .2068 40 .1215 56.5 .0860 24 .2025 40.5 .1200 57 .0853 24.5 .1984 41 .1185 57.5 .0845 25 .1944 41.5 .1171 58 .0838 25.5 .1906 42 .1157 58.5 .0831 26 .1869 42.5 .1143 59 .0824 Diameter of Cutting-Shoe 7M> inches. Value of gold 0.06 cents per milligram $18.66 per ounce. To find value in cents per cubic yard, multiply number of milligrams of gold recovered from drill-hole by the factor in the table opposite the depth to bedrock. 84 DRILLING FOR PLACER GOLD PLATE "I" KEYSTONE DRILLER COMPANY GOLD DREDGE CAPACITY CHART Cubic Yards Elevated per Month of 30 Days at Various Efficiencies for Different Sizes (Bucket Speed at 50 Feet per Minute) Figures are based on an actual operating time of 20 hours out of each 24. Size of Dredge 100% Efficiency 80% Efficiency 60% Efficiency 2^Cu.Ft. 89,000 71,000 53,000 3^ Cu. Ft. 108,000 . 86,000 65,000 5 Cu. Ft. 140,000 112,000 82,000 7^Cu.Ft. 182,000 146,000 110,000 9 Cu. Ft. 213,000 171,000 129,000 15 Cu. Ft. 304,000 244,000 184,000 From this table the Engineer may roughly approximate the yardage of a proposed dredge once he knows the physical and climatic condi- tions to be encountered and general working conditions. DRILLING FOR PLACER GOLD 85 fOVOOPOVOOCOVOOPO COVOOCOOOCOIOOPO co*oocovooco*o cTco^ ^HCS^"l/3VOOOO\OCSfO o o o o o ^ ^_^ o" n" to oo" o" CN" t" vo" oo* o" tnOinOVO"*VO"*VOCN ^ w co oo^ c^ t>^ i-j^ W fx 10 m * PO CN -i T W o" ^H" rOOOCOOOfJiOOc'O CO IO O CO VO O^COVO^O^CO oT oo* oo" tC 10" *o m" * TJ-* co cNinoo^^t^ocovoo^ I-H^ e^ co_ in vp^ t>- w O i-^ e^ r* CN" en TJ" in" vo t^T oT o" i-T ogooooooo; OOOOOOOOOi OfOOVOCOOVOCOOVO VOCOOOCOOVOCOO>O vo^co cTvo co o~*o co^cT^o' . l- CN CO ^- ^ l/ (O t 00 t^o VOO cot^ocot^oco CO*OOCOVOOCO cooocovooco H" 10 of tC CN" oo" of oocNr^i-ivoom r- t- o co co ^- i/ in v 00 00 ^oocNvooTtoocsno" OOVOIOCO!NOXVOUT T^o^'*w^o^coooco! IH i- t^ COO ^ COO t^ > VO CO O VO CO O *O i VO CO O VO CO O VO r o" co" vo" oo" .-* <*" vo" o> 1-1 co m oo o M *H i- i- c< CN c co co vo < co^vp^i ^oT' VOCN( m 10 oo o> o CM co So vo CN o* in i-H 00 Ol iH CM Tt- IO X ^ lsi?i? s y co in co m 86 DRILLING FOR PLACER GOLD FIELD LOG No. of Hole Date Commenced.... Date Finished. DEPTH FEET No. of COLORS FORMATION CORE REMARKS Size 1 Size 2 Size 3 Total Depth feet. Bedrock feet. Water level feet. ABBREVIATIONS T. Tailings S. Sand St. Sticky F. Fine G. Gravel Md. Medium C. Coarse Cl. Clay M. Much V. Very Sm. Some L. Loose PART II AUTHORITATIVE ARTICLES ON MINERAL PROSPECTING iKEYSTONE/ Reprinted from the Keystone Driller Com- pany's Catalog No. 2, Edition 1907, and from various technical Journals. THE PROSPECTING AND VALUING OF DREDGING GROUND Written for the Mining and Scientific Press By Norman C. Stines (Published in the Issues of Feb. 3 and Feb. 10, 1906.] The prospecting of gravel deposits to test their fitness for dredging purposes is done by boring holes with a drilling machine, by sinking shafts, or by making a trial run with what is known as a prospecting 'dredge. It is such work by means of the Keystone drill that this article attempts to describe. In prospecting a piece of ground, the following data must be ascertained: 1. The average value of the ground per cubic yard and the distribution of the gold. 2. The character of the gravel. 3. The character of the bedrock and its approximate contour. 4. The position of the water level as referred to the sur- face. 5. The amount of water obtainable for the pond. 6. The nature and cost of the power obtainable. 7. The length of the working season. 8. The cost of the land. The first four points are determined directly by the use of the drill, and the last four by a careful study of the prevailing conditions. As this paper is to describe the method of using DRILLING FOR PLACER GOLD 89 the drill and the interpretation of the results thus obtained, it will treat of the first four points only. The machine used in the greater part of this work in California is the Keystone Driller No. 3, Traction. It is made by the Keystone Driller Company, Beaver Falls, Pa., and costs (at present, 1923) complete f. o. b. at the factory, about $2700.00. The driller consists of a walking-beam arrangement operated by a steam engine of 1 1 h.p. This pro- duces the required motion for raising and dropping the drill, and for transporting it from place to place. The engine, with the drilling cable reel, the sand-reel and the socket, drill-stem and bit, is suspended by a \%" cable which passes over the rear sheave and over the front one, continuing over the sheave at the top of the derrick and then down. As the walking beams are put in motion, the drill is alternately raised and dropped. The machine makes about 52 strokes per minute in drilling and about 54 in driving. LAYING OFF THE GROUND For the preliminary work, to determine if the gold is scattered over a large area or if it is confined to a narrow winding channel, a few holes are sunk from 500 to 700 ft. apart. If the gold is found to be pretty evenly distributed over the whole tract, it is divided into five or ten-acre squares, according to the amount of drilling to be done. A flag is placed in the center of each of these squares, and this marks the site of the hole. If the gold is found to be confined to a narrow winding channel, the ground is crossed, at right angles to the channel, by series of holes. These series are from 400 to 800 ft. apart. At every 100 ft. in each series a flag is placed and this, as ?0 DRILLING FOR PLACER GOLD DRILLING FOR PLACER GOLD 91 before, marks the place to be drilled. On drilling, the first hole in any series is placed as near the center of the channel as possible, and then drilling to one side or the other is only carried as far as the results warrant. Every fourth or fifth series is drilled across the tract to be sure that there are no splits in the channel. This method insures the least amount of work spent in valueless ground. The series are desig- nated by letters and the holes by numbers. In this way they are recorded in the transit notes. When a hole is drilled, the number in the log-book is also placed in the transit book and the number from the transit book is placed in the log-book. OPERATION OF DRILLING THE HOLE The machine is moved to one of the flags and set up there. A hole is then dug to a couple of feet and the shoe-joint is dropped, then plumbed, and finally the dirt filled around it. The next operation varies according to the nature of the ground. Where the soil is deep, the driving blocks are put on and the casing is driven as far as possible, or to the gravel. Where the gravel commences at the surface, the drill is first lowered and the ground immediately beneath the shoe is drilled. The casing generally settles as the drilling pro- ceeds; but if it does not, when a sufficient depth has been drilled, the blocks are put on and the casing driven to a point about three inches below the depth drilled. The lower end of the shoe-joint is protected from injury by a steel shoe, 7K" in diameter, tempered at the cutting edge and slightly beveled on the inside. It is the area of this shoe which represents the area excavated. 92 DRILLING FOR PLACER GOLD DRILLING FOR PLACER GOLD 93 The casing is nearly always driven to gravel. If the first joint does not reach, a second, and sometimes a third, is put on. As soon as the first joint has been driven to head, the driving cap is removed, the threads brushed off and greased (being careful to use only graphite and linseed oil for the purpose so as not to allow any oil to get into the bore hole, K. D. Co.). The second joint is then put on, cinched tight, the driving cap placed on that and the driving continued. The depth driven at first usually varies from three to twelve feet. In driving, the stem on which the driving blocks have been placed acts as the weight in a pile-driver. The weight of the stem is about 800 Ibs. and the drop ranges from 28 to 36 inches. After the casing has been driven as far as desired, the driving blocks are removed, the stem is lowered into the casing, the core is measured, water is poured in and the walk- ing beams are set in motion. When the machine man measures and reports the length of core to the panner, he also reports the depth of the casing in the ground. The core is measured in the following manner: The length of connected casing is measured on the drill-stem and rope, commencing at the bit. This point is marked in chalk. The stem is then lowered into the hole, and the difference between where the top of the casing is and where the mark on the stem is, is the core. The core then is the material in the casing. This is important and will be fully explained later. While there is yet some core in the casing, the drill-stem is removed and the sand-pump is placed in the hole. This is a piece of 4-in. pipe about 8 ft. long, in which a rod or plunger fits the pipe closely. At its lower end there is HARRON, RICKARD MeCONE 94 DRILLING FOR PLACER GOLD a valve. On raising the plunger suddenly, a vacuum is formed and the material in the hole is forced in through the valve at the bottom. This is repeated until all the ma- terial is thought to be in the pump. The pump is then reeled out of the hole, and its contents is caught by the panner. The stem is then lowered into the casing, the core is measured, the stem is hoisted, the driving blocks are put on and the casing is driven again. This is repeated for each foot of the hole until the desired depth has been reached. The desired depth is generally bedrock or the lower limit of a known pay-streak. The depth to which the hole is sunk in bedrock depends upon the occurrence of gold. Some bedrock carries gold for a con- siderable depth. The hole is generally put down until no colors are found in the pan. It may happen that the casing has come on bedrock in such a way as to cross a seam. This seam may be particularly rich and gold might come into a number of pans after bedrock has been reached. When this occurs, it is well to be wary of the results of that hole if it gives a yield above the general average. The gold is plainly coming from a seam and so we have no measure of the volume of dirt from which it is coming. There is one way to guard against this danger. When approaching bedrock, use two or more small pans for receiving the concentrate from each foot panned. The concentrate for, say, the first 27 ft. .is placed in a pan. On driving the 28th foot and pan- ning, there is found to be more gold than usually comes with bedrock. This is then put in a separate small pan, as is each succeeding pan of concentrate; if there seems to be more gold than usual, it is saved separately and the results of the ground above bedrock and that below bedrock are then DRILLING FOR PLACER GOLD 95 known. This is not often necessary, but it will save dis- trust of the high returns, which sometimes appear in a hole among a lot of other lower results, which are fairly close together. The hole being drilled as far as desired, the drill is placed on the ground, the rope-socket taken from it and placed on the pipe-jars. These pipe or pulling-jars consist of an iron ram or boss on the end of a stem about four feet long. On this stem is a threaded knocking-head with a square opening through which the stem passes, up and down, in striking the blow. The threaded knocking-head is screwed to the cas- ing and the ram is drawn up so that it will strike against the knocking-head when put in motion by the walking-beams. The walking-beams are then set in motion and the jar of the ram against the pipe causes it to be loosened and to be drawn up. As the pipe comes up, the slack is taken by the runner. When the top joint is removed from the ground, the machine is stopped, the threaded knocking-head is removed and the pipe-jars are pulled from the casing. The top joint is then removed and the operation is repeated for each succeeding joint. When all of the joints are out of the ground, the drill-stem is again put on the rope-socket, loaded into the bed of the machine, the jacks removed from under the machine, the engine thrown into gear for propelling mechanism and the whole is moved to the next flag. TREATMENT OF MATERIAL FROM THE HOLE The material brought up by the sand-pump may be treated in different ways. It may be caught in a pan held over the sluice-box, the slime going to the sluice-box; it is 96 DRILLING FOR PLACER GOLD then washed in the panning tub. It may be caught in the pan, the slime going to the sluice-box as before, then washed in a rocker, the material caught on the apron being panned separately; or it may be dumped into the sluice-box and all of it swept into the rocker, the concentrate being panned. The second way seems to answer the purpose best. It gives quickest results and is the easiest for the panner. It uses a minimum of water, and at all times the water in the tub is comparatively clear, thereby preventing the loss of gold unavoidable when panning in thick water. The apparatus required is a sluice -box about eight feet long and 12 in. square in cross-section, a small rocker, pans and panning tub. Each foot is pumped and panned; the gold is estimated carefully. The amount is then inserted on the log opposite the foot from which it came. This is more fully explained when describing the log-book. The gold is classed in three sizes, 1, 2 and 3. Number 3 is the finest and consists of all pieces which weigh less than one milligram. Number 2 gold would be any piece weighing one milligram or over, up to four milligrams, and Number 1 is such that any piece weighs over four milligrams. As mentioned above, the concentrate from each washing is put in a small pan, and, when the hole is completed, the gold is amalgamated and put by itself. In special cases, we would have more than one "pill", as explained already. The gold is separated from the mercury by nitric acid and thoroughly washed, dried, annealed and weighed. If the drying is done in the annealing cup, there is no danger of loss due to sputtering, but the addition of a few drops of alcohol to the last wash water, when using the porcelain cups, pre- DRILLING FOR PLACER GOLD 97 vents sputtering. From the weight of gold obtained, and the volume of dirt from which it came is figured the value of the ground immediately adjacent to the hole. Not only the gold obtained from the pannings is recorded, but the character of the gravels. This would include a note on the size of particles and whether there was sand, clay or cementing material present. This is ascertained by a close examination of the screenings, as left in the hopper of the rocker. Then, too, the panner carefully notices his con- centrate and records anything of interest, such as the amount of black sand, any gem stones, and the appearance of amalgam. These are all recorded in the log-books, oppo- site the foot in which they were found. THE LOG BOOK It is in the records that the engineer finds his data for valuing ground. The log-book as kept by different men varies, but for practical utility I have found the accompany- ing to be best ; Table I is a page from a log-book as kept by a panner. All linear dimensions are in feet and tenths. At the head of the page is placed the number of the hole as drilled and the number as recorded in the transit-book. Following this is the name of the tract on which the hole was drilled. In column "A", we have recorded the depth to which the casing has been driven. Everything on the same horizontal line as that refers to that foot in the section of the ground. This is measured by the machineman and recorded by the panner. In column "B", we have the depth of core after driving. This is a measure of the amount of material which has been forced into the pipe by the last drive plus the core left in the pipe before driving. It gives 98 DRILLING FOR PLACER GOLD the panner an idea of the kind of ground to expect and occasionally it indicates the character of bedrock. In drill- ground in which the bedrock is volcanic ash (such as that at Oroville), a large core after a hard drive is a very good sign of bedrock. Its importance, however, lies in the fact that it acts as a check on the amount of material coming into the pipe. Column "C" is also important. In it we can see if the bit has been below the casing and at what point. If we see that it has been below and has found an abnormal amount of gold for that pumping we can be sure that something was wrong some gold has run into the pipe. In this hole, the bit is never below the casing except after the casing has been driven 0.5 ft. into bedrock. The reason for this is, that the machine-man is under orders to cease drilling while there is yet 0.3 ft. of core in the casing. There is only one reason for the bit to be below the casing; the ground is so tight or so coarse that the casing will not drive unless the ground is loosened below the casing. And in no case where the ground is drilled below the casing should the material be pumped before the casing is again driven deeper. This core is to act as a plug to prevent any material from outside the limits of the shoe from running into the casing. Its length will depend on the ease with which the ground runs. In sand, a larger core is required than in gravel. The proper length of core to leave can be determined only in the ground itself and will vary not only for different holes but also for different depths in the same hole. This must be regulated by the man in charge. The length of core left in the pipe before driving should always be such that only the right volume of material will be forced into the casing. By the right amount is meant that DRILLING FOR PLACER GOLD 99 amount which corresponds to the volume of a cylinder one foot long and 7/^ in. diameter at the base. This amount, when forced into the pipe, should be somewhat longer than one foot, as it has been reduced at the base to a circle only six inches in diameter. This cylinder, to have the same volume as the one of larger cross -sect ion, not allowing for the expansion due to the loosening of the gravel, would be 18.7 in. long, or 1.555 ft. But only in those cases where the ground is classed as "very firm" does the length of core ap- proach this value. (See column "B" for the following feet: 15-19 and 27-30). In column "D" is placed the core after pumping, and its importance in one way has been shown. Its further im- portance will be indicated later. In column "E" is placed the depth of the hole. It is obtained by subtracting the core in "D" from the depth of the casing as seen in "A." It is the least important of all, and is only retained as a con- venience. TABLE I In column "F" are recorded the estimated amounts of gold, which are classified as explained above and are re- ported by weight, not by number of colors. For example: 3 7 means that seven milligrams of No. 3 gold was found in that pan; 2 9 means nine milligrams of No. 2 gold, and I 18 indicates 18 milligrams of the largest size were in the pan. This estimating of weights tells a great deal more than the mere number of colors. It is remarkable how expert a man will become in estimating the gold, especially in the smaller sizes. In looking at the log-book one can immediately tell how the ground is running and how many cents it will pan per cubic yard. Each milligram of gold per running foot 100 DRILLING FOR PLACER GOLD S J I S I || cl O I . 0| d . * * . c ! -o a .^ * * a ^^ . y o.wz* 9^0 g, , a c8cd co coco co* d cococo fc lid cococodd ffi E *orhrj-NNOfovo t^oioc^^OrHfoooint^fjinpoPO^^^-^'Oo IO Ol O\ O 6 H fH ^H H -i CS H tH rH iA .t^ t^ o m o o o o o vnm in t^ o t^ t^ t^ oot^t^mmm cs o o o^tN W "" -i^OOOO^'r-i (N rH >-i ^' rH i-l o ^H o I-H CN PO * mt^oooi rt r-i ^ I-H 1-1 IH i-i i-c IH cs CN | TTT ^ C4 fH |H IH l-l rH Ol CS CS IH rH <-l IH rH f-H I-I |H CS C4 i-H l-H 1-H CM ; ;? ; I CS CS CN (N CN CM CS CN CS DRILLING FOR PLACER GOLD 101 means that that foot corresponds* tc ground of a -Value of 6c. per cu. yd. For example, in the: 15th foot -the: patmer recorded two milligrams of gold arid one immediatciy knows that that corresponds to 12 -cent ground; in the 17th foot there were 11 milligrams or that ground was 66-cent ground. This value is obtained thus: Each running foot means 0.01 cu. yd. Therefore, if we get one milligram from 0.01 cu. yd., from a yard we should get 100 mg. ; and as a gram of gold (as ordinarily found in the gravels of the San Joaquin and Sacramento Valleys) is worth about 60c., 100 mg. is worth six cents. This method of recording weights em- phasizes the occurrence of pay-streaks much better than that of recording colors only. In column "G" is recorded the amount of material ob- tained by pumping, as measured in the pan. It is a rough check on the volume extracted and its use is shown later. In column "H" is given the time of each pumping. It helps to afford an idea of the stiffness of the ground by a measure of the time it takes to drive, drill, and pump a foot. In column "I" is recorded the character of the ground in regard to its tightness. Ground is classed as "loose", "firm" and "very firm." "Loose" ground is that which can be drilled and pumped at the rate of one foot every 5 to 9 minutes; "firm" ground would be such as required from 10 to 14 min. for the same operations, and "very firm" that which required a longer time. In column "J" is recorded the for- mation as passed through. This is classified under the following heads : Clay, sand, cemented material, fine gravel, medium gravel, coarse gravel and large boulders. Under the head of remarks, almost anything important or unusual is recorde