UNIVERSITY of NEVADA Reno PLACER EXAMINATION

UNIVERSITY OF NEVADA

Reno

PLACER EXAMINATION

PRINCIPLES AND PRACTICE

A thesis submitted in partial fulfillment of the requirements for the degree of Engineer of Mines

by

John H. Wells

June 1970 The thesis of John H. Wells is approved:

Thesis advisor

University of Nevada

Reno

June 1970 placer examination PRINCIPLES AND PRACTICE

TECHNICAL BULLETIN 4

UNITED STATES DEPARTMENT OF THE INTERIOR BUREAU OF LAND MANAGEMENT

Washington, D.C. July 1969 placer examination

PRINCIPLES AND PRACTICE

by John H. Wells Mining Engineer Bureau o f Land Management CONTENTS

Page PREFACE ...... vii PART I - REVIEW OF PLACER THEORY AND GEOLOGY ACKNOWLEDGEMENTS 1. Placers Defined ...... 3 The author is indebted to the Bureau o f Land 2. Study of Placers — General ...... 3 Management for making the publication o f this book 3. Sources o f Valuable Mineral ...... 3 possible. a) Lodes or mineralized z o n e s ...... 3 A book of this type would not be complete without the b) Erosion o f pre-existing placer deposits ...... 3 illustrated description o f placer drilling and related data c) Low-grade auriferous conglomerates or glacial debris ...... 4 contained in Appendix D. These were provided by Mr. Cy d) Magmatic segregations and associated basic rocks ...... 4 Ostrom of C. Kirk Hillman Company, whose generosity is e) Regional rocks containing particles of valuable mineral .... 4 appreciated. 4. Weathering and Release Processes ...... 4 a) Ground water ...... 4 b) Temperature change ...... 4 c) Plant growth ...... 5 d) Surface erosion ...... 5 5. Stream Processes Related to Placers ...... 5 6. Concentration of Valuable Minerals ...... 6 a) Bedrock concentrations...... 6 b) Types of bedrock ...... 6 c) Pay streaks ...... 6 7. Preservation o f the Deposit ...... 6 a) A b a n d on m en t...... 7 b) Regional uplift ...... 7 c) Burial ...... 7

PART II - TYPES OF PLACERS 1. Residual Placers ...... 11 2. Eluvial Placers ...... 11 3. Stream Placers ...... 11 a) Gulch placers ...... 11 b) Creek placers ...... 12 c) River d e p o s it s ...... 12 d) Gravel plain deposits ...... 12 4. Bench P la c e r s ...... 12 5. Flood Gold Deposits ...... 12 6. Desert Placers . . 7. Tertiary Gravels 8. Miscellaneous Types a) Beach placers b) Glacial deposits

For salo by the Superintendent ot Documents, c) Eolian placers . U.S. Qovornmont Printing Offlce Washington, D.C. 20402 - Price $1.50 PART III - SAMPLING AND EVALUATION PART VII - CHECK LIST FOR PLACER INVESTIGATIONS 1. General C on sid eration s...... 21 1. General Considerations ...... 79 a) Problems ...... 21 2. Field Guide and Check List (example) ...... 80 b) Industry practice ...... 22 c) Minerals other than gold ...... 22 PART VIH - GLOSSARY OF PLACERS TERMS ...... 93 d) Other factors to be considered ...... 22 e) In brief ...... 23 APPENDIX 2. Sampling Guides ...... 23 A. Placer Sampling Forms ...... 115 a) Reconnaissance ...... 23 B. Gold Price and Value Data ...... 121 b) Choosing a sampling method ...... 23 C. Water Data ...... 125 c) Number and size o f samples ...... 24 D. Placer Drilling Data ...... 129 E. General Information and Cost Data ...... 143 3. Sampling Methods ...... 25 a) Existing exposures ...... 25 F. Conversion Tables ...... 147 b) Hand-dug e x ca v a tio n s...... 26 c) Machine-dug shafts ...... 28 d) Backhoe excavators ...... 31 e) Bulldozer trenches ...... 32 f) Sampling with churn drills ...... 32 g) Bulk samples ...... 43 h) Grab samples ...... 43 i) Drift mine sampling ...... 44 j) Hydraulic mine sampling ...... 44 4. Special Problems ...... 45 a) Large rock or boulders ...... 45 b) Erratic high values ...... 46 5. Uncased or Small-diameter Drill H o l e s ...... 47 6. Salting ...... 48 7. When Sampling Fails ...... 49

PART IV - SAMPLE WASHING EQUIPMENT 1. General C on sid eration s...... 53 2. Miner’s Pan ...... 53 3. Sluice Box ...... 53 4. R o c k e r s ...... 55 5. Special Machines ...... 58 6. Dry Washers ...... 58

PART V - PANNING AND ASSAY PROCEDURES 1. P a n n in g ...... 63 2. General Notes on Panning with Suggestions For Improving Procedure ...... 64 3. Fire Assay o f Placer Samples — Misleading Results ...... 65 4. Procedure For Determining Recoverable Gold in Placer Samples . 66

PART VI - NOTES ON GENERAL PRACTICE 1. Description o f S a m p le s ...... 71 2. Reduction o f Sample Vo lu m e s ...... 71 3. Reporting V a lu e s ...... 72 4. Cost Estimates ...... 73 iv 5. New or Unproven Processes ...... 74 PREFACE As the title suggests, the subject matter in this book deals for the most part with the examination and testing o f placers. It is intended primarily as a guide for the professional mineral examiner who examines mining claims located on public lands o f the United States. The book has been divided into eight parts or sections. Parts I and II, which deal with placer-forming processes and types o f placers, are intended as a review o f placer fundamentals. Other sections bring together the fundamentals o f placer investigation and industry-proven testing procedures. Part VIII is a glossary o f the placer industry, setting out more than three hundred placer-related terms and definitions, many of which have not previously appeared in glossary form. In scope, this book covers problems o f placer investigation from initial reconnaissance to computing the value o f a blocked-out placer. It is intended to serve as a reference book as well as a manual for day-to-day work. Its use should help the mineral examiner identify his sampling problems and select procedures appropriate to the purpose o f his examination and to the deposits involved. While this book has been prepared specifically for use by Bureau o f Land Management personnel, it is hoped that it will at the same time be useful to the mining profession generally. PARTI

REVIEW OF PLACER THEORY AND GEOLOGY 1. PLACERS DEFINED placer-forming processes will be taken up under In the United States mining law, mineral deposits the following headings: that are not veins in place are treated as placers Sources o f valuable mineral. so far as locating, holding and patenting are Weathering and release processes. concerned. But for the purposes o f this book, the Stream processes related to placers. term “ placer” is applied to deposits o f sand, Concentration o f valuable minerals. gravel, and other detrital or residual material Preservation o f the deposit. con tain in g a valuable mineral which has 3. SOURCES OF VALUABLE MINERAL accumulated through weathering and mechanical The source o f gold or other minerals found in a concentration processes. Prerequisites for a placer placer may be one or more o f the following: are: a. Lodes or mineralized zones. A valuable mineral which is relatively b. Erosion o f pre-existing placer deposits. heavy and is resistant to weathering and c. Low-grade auriferous conglomerates or abrasion. glacial debris. Release o f the valuable mineral from its d. Magmatic segregations and associated parent rock. basic rocks. Concentration o f the valuable mineral e. R egion a l rocks containing scattered into workable deposits. This step usually particles o f valuable mineral. involves water transport. a. Lodes'. Although placers are commonly The term “ placer” as used in this book applies to found in lode mining districts, experience has ancient (Tertiary) gravels as well as to recent shown that there is no fixed relation between deposits, and to underground (drift mines) as the richness o f the parent lode and the well as to surface deposits. richness or size o f resultant placers. Some o f 2. STUDY OF PLACERS - GENERAL the most noted gold mining districts such as The study o f placers is not simple—it involves G o ld fie ld , Nev., contain no significant many o f the disciplines o f geology, with special placers. On the other hand, some highly emphasis on the theory and habits o f streams. productive placer areas are not associated Although the location, size, and shape o f a placer with valuable lodes, the Klondike region will reflect the regional forces of erosion, being an example. In some cases the lode transportation, and deposition which created it, source may have been completely removed its final form will be controlled or modified by by erosion, while in others, it can be purely local conditions. As a result, each placer demonstrated that the gold or other valuable deposit can be expected to be unique in one or mineral was not derived from a single source, more ways and the field investigator should but instead, from many small mineralized approach his work with this in mind. seams or zones scattered through the bedrock. Although individually unimportant, All placers begin with weathering and these smaller sources can collectively furnish disintegration o f lodes or rocks containing one or substantial amounts o f gold. more heavy, resistant minerals such as gold, platinum, magnetite, garnet, zircon, cassiterite, b. Pre-existing placers: In many localities old monazite, etc. It should be stressed that the end placers have been destroyed by erosion and richness and size o f a placer deposit will depend their gold content reconcentrated in present more on there being an abundant supply of day streams. Excellent examples are found in source materials, and on conditions favorable for the Sierra Nevada region o f California. Here, their concentration, than on the actual richness in Tertiary times, beginning some 60 million o f the primary source. While the following years ago, there existed an extensive river paragraphs refer largely to gold placers, the system, a prolonged time o f rock decay, and principles set forth apply to all types. A t the risk a good balance between erosion and of oversimplification, a brief discussion o f basic deposition. These factors combined to form widespread gold placers and some extremely degrading, and where there is a net they can be important, as shown by tl in some cases, is an effective agent o f rock rich bedrock concentrations in the Tertiary deposition it is said to be aggrading. G oodnews Bay platinum deposits whet destruction. streams. Later, as the present Sierra Nevada dredging has been carried on since 1937. c. Plant growth: Plants contribute to rock b. It can be stated generally that streams do range was elevated by mountain-building e. Regional rocks: Monazite placers of the typ destruction and mineral release in two ways. most o f their transporting while in flood, disturbances, new streams flowing toward dredged in central Idaho, provide j (1) R oot growth forces open and extends and most o f their depositing when the the west cut across the ancient channels and excellent example of a placer miner, surface and near-surface cracks and floods recede. In general, the coarse swept some of their gold concentrations into originating as small, sparsely distribute; crevices. material transported by a stream moves today’s streams where new, and sometimes particles in the country rock. Hert (2) Decaying plants contribute rock solvents intermittently and much o f the coarsest richer, concentrations accumulated. monazite, which is a rare-earth minen to th e p ercola tin g ground waters. material may be at rest for all but brief Som ew hat similar reconcentrations were chiefly valuable for its thorium content Decomposing vegetation is a very periods o f time. Other things being found in parts o f Alaska, the Klondike, and originates as an accessory mineral in th powerful agent of rock decay and, other places. equal, the length o f time between moves regional granitic rocks. Following liberatio: consequently, wet, humid climates favor and the distance moved is largely a c. Auriferous conglomerates and glacial debris : by the usual weathering processes it finds it the development of deep mantles of function o f particle size. In some placer areas the immediate source o f way into stream deposits, where because ol decomposed rock and the liberation of gold is found to be a low-grade auriferous c. Stream conditions wherein the entire its moderately high specific gravity, i placer-forming minerals. conglomerate or a glacial deposit. With few b ed loa d is shifted or is agitated accumulates in placers along with othe d. Surface erosion: On the steeper slopes exceptions such material is too poor to be sufficiently to allow a downward heavy minerals. Similarly, most o f thi surface erosion becomes more effective and, worked but where appreciable quantities movement of gold particles may occur magnetite, ilmenite, rutile, garnet and zircoi in turn, chemical rock decay assumes a lesser have been eroded, superficial placers may only during extreme flood conditions or associated with gold placers, could be traceo role in the weathering process. The rapid form on the erosion surface or within the periods o f regional climatic change, to the regional bedrock where such mineral surface erosion o f relatively unweathered local drainage. Wind erosion o f an auriferous many years or centuries apart. commonly occur as scattered particles a rocks in desert regions can result in the conglomerate occasionally creates an Nevertheless, bed scour or movement of accessory minerals. formation of placers, but as shown by enriched surface veneer amenable to the whole contents o f a stream bed, or Lindgren (1933, p. 219), such placers are not small-scale, selective mining. Under favorable 4. WEATHERING AND RELEASE PROCESSES o f all except the large boulders, is often rich or highly concentrated. essential to formation o f the typical conditions, gold derived from low-value The first step in placer formation is release ol STREAM PROCESSES RELATED TO stream placer. Concentration o f gold on glacial debris is carried into streams and valuable mineral from its parent rock. Thi PLACERS the bedrock would not be possible reconcentrated into minable placers and various phenomena which combine to decompos Because streams are the dominant agent in the without channel scour or a general although some o f these reconcentrations and disintegrate rocks are embraced in the have an appreciable extent, most are general term “ weathering.” formation of most placer deposits, the field agitation o f the bed load. relatively small and spotty. engineer should understand the fundamental d. T o d a y ’s climate and present stream The chief agents o f rock weathering are: p rocesses in volved in the movement and c o n d itio n s m ay have little or no Examples o f placers derived from low-grade a. Ground water. deposition o f sediments by flowing water. In resemblance to those which controlled auriferous conglomerates are found in the b. Temperature change. particular, he should be able to relate stream formation o f a given placer. Also, it R ed R ock , Goler, and Summit mining c. Plant growth. processes to the mechanics of placer formation. should be borne in mind that old stream districts o f Kern County, Calif., (Hulin, d. Surface erosion. Actually this is a complex subject but several o f 1934) 1/ . At Breckenridge and at Fairplay, deposits such as those of Tertiary age the more important concepts o f stream processes Colo., gold derived from glacial moraines has a. Ground water: The great solvent o f rocks is, may have no relation to today’s been successfully dredged along the Swan, o f course, water; particularly ground water related to placer formation are: topography or drainage pattern. a. Stream bed erosion occurs only when Blue, and South Platte Rivers. According to that has become charged with products ol e. In the case o f desert placers, the usual the flow has the ability to transport MacDonald (1910), a gold-bearing glacial till mineral and vegetable decay. Some rocks rules o f stream deposition and o f placer more material than is being supplied, and in the Weaverville district o f Trinity County, such as limestone may be completely concentration are often subordinate to conversely, deposition will begin when Calif., is an important source o f gold for the dissolved but the majority are more other factors. These conditions are the stream becomes overloaded or has its Trinity River and its tributaries, commonly decomposed through the discussed under the heading o f DESERT velocity sufficiently checked. Temporary d. Magmatic segregations: Disseminated processes of oxidation, carbonation, and PLACERS. deposits associated with magmatic hydration. or semi-permanent deposits are usually Longwell, Knopf and Flint (1948) present in segregations in basic rocks seldom generate b. Temperature : C hange o f temperature formed where velocity is locally reduced concise language, a broad picture o f fluvial significant placers but a notable exception is combined with frost wedging plays a part in on the downstream side o f rocks or processes and the movement o f alluvial material found at Goodnews Bay, Alaska, where rock weathering, particularly in desert other channel obstructions and along the by streams. Although this reference does not extensive platinum placers have been derived regions where changes may be rapid and inside banks o f curves. Although at any discuss the formation o f placers it can serve as a from a large mass o f dunite and related basic extreme. The effects of frost wedging are one point in a stream the balance may be quick review o f fundamental principles. Jenkins rocks. Although minable placers from basic readily apparent where it loosens large precarious, alternating between erosion (1946), in an article titled “ New Technique or ultrabasic rocks may be few in number, blocks, but its lesser-known and more and deposition, the net effect will be one Applicable to the Study o f Placers,” discussed important function is the wedging apart o( or the other. Where there is a net 1/ References cited will be found at the end of Part I. stream processes and their relation to placers in minute rock scales and mineral grains, which reduction the stream is said to be Covering by landslide material. considerable detail. This well illustrated article is coarse gold has settled to the bedrock it is geologic controls responsible for the creation of a Covering by flood-plain gravels following possibly the best single reference on the subject. very difficult for the current to dislodge it. particular placer may persist for a long period o f regional subsidence or a net change in 6. CONCENTRATION OF VALUABLE For this reason coarse gold is generally found time (as measured by the affairs o f man), the climate. MINERALS near its source. deposit itself is transitory. Unless preserved by Burial under alluvial fans or outwash some disruption o f the normal erosion cycle, the In theory, the richest part o f a placer should be b. Types of bedrock : The ultimate richness of a very forces which create the placer will in time detritus in desert regions. found near bedrock and, because o f this, many placer is dependent to a large extent on the destroy it. Knowing how and why a particular Needless to say, a knowledge o f past geologic people think that gold placers invariably are physical characteristics o f the bedrock. Slates deposit was preserved is important to the or physiographic events is an important tool richer on bedrock than elsewhere within the and jointed rocks, particularly those dipping prospector or mine operator and, obviously, such in the study o f placers. deposit. On this basis, they believe that if at steep angles are considered most effective knowledge is also important to the examining indications o f value are found in the upper in capturing and holding gold. Compact clay, engineer—particularly when he is called upon to horizons, pay gravel will surely be found on clayey volcanic tuff and decomposed granite project the course o f a buried channel or appraise bedrock and countless mining ventures have been make effective bedrocks. A smooth, hard REFERENCES CITED (PART I) launched on this premise. Needless to say, many bedrock such as serpentine is generally its potential. The more common causes of failed. In practice, it is not uncommon to find considered to be a poor gold saver. In some preservation are: deposits in which the pay is scattered through a important placer fields, the pay gravels rest a. Abandonment: This is probably the most Hulin, Carlton D., 1934, Geologic features of the dry gravel mass without a significant bedrock on a false bedrock. In the Folsom, California, frequently encountered form of preservation. placers of the northern Mojave Desert: Thirtieth enrichment. Some deposits, in fact, have their area, for example, this is usually a layer of It is brought about where a stream, by Report of the State Mineralogist, pp. 417-642, concentrations at the surface rather than on volcanic tuff found well above the true change o f course or rapid downward cutting, California Division o f Mines. bedrock. bedrock. This type of occurrence is explained in abandons its former bed and the placers Jenkins, Olaf P., 1946, New technique applicable to the section titled “ Flood Gold Deposits.” Gold works its way into soft or decomposed therein. The abandoned placers are preserved the study o f placers: California Division of Mines Another popular idea is that concentration of bedrocks and settles into the cracks and in the sense that they are no longer subject Bull. 135, Placer mining for gold in California, to erosion by the parent stream. High bench gold in a stream is analogous to concentration in crevices o f hard formations. It commonly pp. 149-216. a sluice box. But in nature the process is by no migrates downward to an extent requiring and terrace gravels provide typical examples First published in California Journal o f Mines and means this simple as will be shown in following the mining o f several feet o f bedrock to o f abandoned placers. Geology, Vol. 31, No. 2, 1935 pp. 143-210. paragraphs. effect a complete gold recovery. In some b. Regional uplift: Elevation o f the ocean Reprinted as a series o f 8 articles in Mineral cases, inability to dig a hard, rough bedrock a. Bedrock concentration: The development of shoreline has in some places preserved beach Information Service, Vol. 17, Nos. 1, 2, 3, 4, 5, 6, has been the direct cause for failure of bedrock concentrations in simple stream placers by raising them above the active surf. 8 and 9, Jan.-Sept., 1964. California Division of dredging ventures. In others, having to dig deposits may be generalized as In some localities, such as Nome, Alaska, Mines. unexpected amounts of soft bedrock has follows: Consider a down-cutting stream in elevated beach placers are now several miles Lindgren, Waldemar, 1933, Mineral deposits, 4th ed: seriously upset the initial cost estimates. which the bed load o f sand, gravel and inland. McGraw-Hill Book Co., New York. Such possibilities should always be boulders is progressively shifting downstream c. Burial: The lava-capped Tertiary channels co n s id e re d w hen evaluating a placer Longwell, Chester R.; Knopf, Adolph and Flint, and subjected to general agitation during fo u n d in the Sierra Nevada region o f property. Richard F., 1948, Physical geology, 3rd ed: John times o f high water. During high-water California offer some o f the best examples o f c. Pay Streaks : Bedrock enrichments known as Wiley & Sons, New York. periods some o f the smaller and lighter buried placers but there are means other than “ pay streaks” usually follow a sinuous course MacDonald, D.F., 1910, The Weaverville-Trinity particles will be picked up and advanced by v o lc a n ic flo w s b y w h ich burial and and sometimes have no discernible relation Center gold gravels, Trinity County, California: the current, usually in a series o f short preservation may be affected. Among these to the present stream channel. A pay streak U.S. Geol. Survey Bull. 430, pp. 48-58. jumps, while the heavier rocks and boulders are: roll and slide along the bottom. Each time may split or terminate suddenly and its the bed load moves or is generally agitated, lateral limits may be irregular or indefinite, the contained gold particles can work its location and eccentricities being dictated downward toward bedrock. Under favorable by lo c a l controls. Bear in mind that conditions this may be quite rapid but in conditions which caused the pay streak, many deposits, such bed movements occur particularly in the case o f older deposits, only at long-spaced intervals—perhaps not may no longer be in evidence. Pay streaks in within the lifetime o f any one observer. gravel-plain or similar widespread-type Nevertheless, it must be realized that without placers are usually less definite than those in stream placers. such movement and rearrangement o f the entire bed load, a downward migration o f the 7. PRESERVATION OF THE DEPOSIT g o ld and, in p a rticu la r, its eventual Placer deposits do not suddenly come into being concentration on bedrock would not be but, instead, they are progressively accumulated possible. Under flood conditions fine gold and enriched by a succession o f stream actions may be swept up and carried away but once and interactions. Although the land forms and PART II

TYPES OF PLACERS Perhaps the best known schemes for classifying placer moves the gold and weathered detritus down hill, deposits are those by Jenkins (1946, p. 161) and allowing the lighter portions to be removed by Brooks (1913, pp. 25-32) 1I, the former being based rain wash and wind. As the detrital mass on conditions o f deposition and the latter on present gravitates downhill, a rough stratification or position o f the deposit. The field engineer should concentration o f values may develop but this is acquaint himself with these schemes, particularly that rarely perfected to the degree found in stream by Jenkins which has been developed in some detail. placers. Eluvial placers are typically limited in For the usual field investigation a somewhat simpler extent but there have been cases such as at classification will be found suitable. This is: Round Mountain, Nevada, (Vanderburg, 1936, 1. Residual placers. pp. 133-145) where this type of placer supported 2. Eluvial placers. large-scale mining operations. 3. Stream placers. 4. Bench placers. 3. STREAM PLACERS 5. Flood gold deposits. Stream placers are the most widespread type in 6. Desert placers. the Western States and, accordingly, are the type 7. Tertiary gravels. m ost fre q u e n tly en cou n tered in mineral 8. Miscellaneous types. examinations. Individual deposits vary so much a) beach placers. that few general statements can be made b) glacial deposits. concerning them but for the purpose o f this c) eolian placers. review, they can be conveniently divided into: a. Gulch placers. 1. RESIDUAL PLACERS b. Creek placers. A residual placer is, in effect, a concentration of c. River deposits. gold (or other heavy mineral) at or near its point d. Gravel-plain deposits. of release from the parent rock. In this type of a. Gulch placers: Gulch placers are placer the e n rich m en t results from the characteristically small in area, have steep elimination o f valueless material rather than from gradients and are usually confined to minor concentration o f values brought in from an drainages in which a permanent stream may outside source. Residual placers may be rich but or may not exist. This type o f placer is, as a they are not likely to be large and as a class, they rule, made up o f a mixture o f poorly sorted have been relatively unimportant. The “ seam gravel and detritus from adjacent hillsides. diggings” in El Dorado County, Calif., (Clark and B ecause o f steep gradient, the gravel Carlson, 1956, p. 435) offer an example of accumulations are often thin and residual gold placers. discontinuous. Boulders are commonly 2. ELUVIAL PLACERS found in quantities that preclude all but simple hand mining operations. The gold is Eluvial placers usually represent a transitional likely to be coarse and well-concentrated on stage between a residual placer and a stream bedrock. Gulch placers were usually the first placer. Where one type merges into another, they to be found by the early miners and because cannot be clearly distinguished. They are most can be worked with simple hand tools, characteristically found in the form o f irregular unworked remnants of shallow gulch sheets o f surface detritus and soil mantling a deposits are not likely to contain material hillside below a vein or other source o f valuable that would yield a profit today. The mineral. It should be noted that the parent vein early-day miner was generally well-schooled or lode may or may not outcrop at the actual by experience, and a dilligent worker. Any ground surface. Eluvial placers differ from pay gravel that he left was usually cleaned up residual placers in that surface creep slowly by the patient Chinese who followed. This 1/ References cited will be found at the end of Part II. was particularly true in gulch placers. The best-known flood gold occurrences in the b. Creek placers: In many districts creek plaeers gravel-plain deposits are built by shifting United States are found along a 400-mile stretch have been important sources o f gold but like stream channels, their gold is apt to have i o f the Snake River in western Wyoming and the gulch placers most were carefully wide lateral and vertical distribution and southern Idaho. Here they are called “ skim bars” prospected by the early miners and worked because o f the relatively low velocities ol (Hill, 1916) and have been intermittently worked out, where worthwhile to do so. Many of the streams flowing over flood plains, theii since about 1860. See Figure 1. They were first lower-grade remnants left by the early hand placers are commonly made up ol exploited by transient miners employing rockers miners have since been exploited by some smaller-size gold compared with that found and simple sluicing operations and, by cleaning form of mechanized mining, notably by in the main stream deposits. Any larger gold up the richer spots, a few did fairly well. It was dragline dredges during the depression years carried by the main channel will likely bt inevitable that some would proceed to install o f the 1930’s. Creek placers as a group no dropped close to the upper edge o f the flood dredges or other large washing plants and launch longer contain significant economic reserves plain where the stream’s velocity decreases ambitious mining schemes on the strength of in the Western States but some in Alaska are and its transporting ability is reduced. surface showings. Needless to say, following the mined with nonfloating washing plants and Although subject to surface wash and flood FIGURE I. — Sketch showing the location o f flood gold on exhaustion o f superficial pay streaks, most of movea hie sluices utilizing various e r o s io n , m ost gravel-plain deposits are accretion, or skim bars. (From USGS Bull. 620-Lj these large-scale mining schemes proved combinations o f hydraulic and mechanical relatively permanent. Examples o f this type excavation equipment. unprofitable. The foregoing is pointed out o f d e p o s it are the dredging fields al mineral examiner should recognize the true because flood gold concentrations are still to be c. River d e p o s its : River deposits are H a m m on ton , and those near Folsom, nature o f flood gold deposits so that he can guard found and without doubt, new mining ventures represented by the more extensive gravel California. Each produced gold valued al against being misled by their seemingly-rich will be proposed and attempted from time to flats in or adjacent to the beds o f present-day approximately $ 100,000,000. surface concentrations. time, particularly by advocates of suction rivers and as a class, they have been our most 4. BENCH PLACERS As a stream sweeps around a curve, the water is dredges. The mineral examiner should learn to important source o f placer minerals. They subject to tangential forces which cause a relative recognize flood gold deposits and equally are generally similar to creek placers but the Bench placers are usually remnants o f deposits increase in velocity along the outer radius o f the important, he should be fully aware o f their gold is usually finer, the gravel well-rounded fo rm e d during an earlier stage o f stream curve with a corresponding decrease along the pitfalls. and large boulders fewer or absent. Although development and left behind as the stream cuts inside radius. The bottom layer o f water is the over-all deposit may be low-grade, pay downward. The abandoned segments, particularly retarded by friction and as a result, it has a 6. DESERT PLACERS streaks and bedrock concentrations capable those on the hillsides, are commonly referred to tendency to flow sideways along the bottom Desert placers in the Southwest occur under o f supporting dredging or other large-scale as “ bench” gravels. Frequently there are two or toward the inner bank. This, in turn, causes sand widely varying conditions but taken as a whole, mining operations are not uncommon. At more sets o f benches in which case the miners and small gravel to accumulate in the form o f an they are so different from normal stream placers many places in California, the early miners refer to them as “high” benches and “low" accretion bar along the inside bank o f the curve as to deserve a special classification. When dealing diverted rivers through tunnels or bypassed benches. In California and elsewhere, most bench and where flood-borne particles o f gold are being with the usual desert placer the mineral examiner the water in flumes to permit mining the deposits were quickly found by the early miners carried down the stream, some will be deposited must learn to disregard some o f the rules of river bed. In this manner, many miles o f the who proceeded to work the richer1 bedrock near the upper point o f such bars, as shown in stream deposition, or at least, he must learn to streaks by primitive forms of underground middle and upper reaches o f the principle apply them with caution. Desert placers are Figure 1. gold-bearing rivers were effectively cleaned mining. At the time these were referred to as The foregoing is an oversimplification of a found in arid regions where erosion and out. The lower reaches o f many o f these “ hill diggings.” Following the development of complex stream process but the fact is, in streams transportation of debris depends largely on streams were systematically dredged and, at hydraulic mining in the 1850’s, many o f the draining a gold-bearing region, seemingly rich fast-rising streams that rush down gullies and dry one time, where conditions were favorable, larger bench deposits were worked by deposits of fine-size gold may be concentrated washes following summer cloudbursts. During gravels returning five cents per cubic yard hydraulicking and the smaller ones by ground near the upper point o f the inside bars, between intervening periods, varying amounts o f sand, were dredged at a profit. Needless to say, few sluicing. During the depression years o f the the high and low water marks. G ood surface gravel or side-hill detritus is carried in from the important river deposits remain unknown in 1930’s, much of the so-called “sniper” mining showings o f fine-size gold are not uncommon and sides by lighter, intermittent rain wash which is was carried out on remnants o f bench gravels and the United States. sufficient to move material into the washes but it should be noted that these hard-working although they may appear to be valuable, d. Gravel-plain deposits: These are somewhat not carry it further. When the next heavy rain individuals seldom recovered more than 25 or 30 experience has shown that in most cases the difficult to define as they may grade from comes, a torrential flow may sweep up all of the cents per day. gravel a few inches beneath these surface river or bench deposits, into flood-plain or concentrations is nearly worthless. accumulated detrital fill, or only part o f it, d e lta -ty p e d e p o sits and they can be depending on intensity and duration of the storm 5. FLOOD GOLD DEPOSITS In many gold-producing areas, particularly in geologically old, or recent. Gravel plains are and depth o f fill. It should be obvious that the A s a rule, finely-divided gold travels long parts o f South America, river bars have been found where a river canyon flattens and intermittent flows provide scant opportunity for distances under flood conditions. This gold which skimmed by natives year after year from time widens or, more often, where it enters a effective sorting o f the gravels or concentration can best be referred to by the miners’ term of immemorial. These are not permanently wide, low-gradient valley. The contained o f gold. Under such condtions the movement and “ flood gold”, consists mostly of minute particles exhausted because floods deposit a new supply of placers are generally similar to those in river concentration of placer gold will be extremely so small that it may take 1,000 to 5,000 colors to gold and the renewal will continue indefinitely. deposits except for greater size and a more erratic. Moreover, where the entire bedload is not be worth 1 cent. With few exceptions such gold These are called Charcas de Oro which KteraHy 12 general distribution of gold. Because moved, any gold concentration resulting from a 13 has proven economically unimportant. The translates “ Gold Farms.” some future date. For this reason a brief the United States Geological Survey. Seismic, sudden water flow will be found at the bottom o f Tertiary Channels (Clark, 1965, pp. 39-44). discussion and some selected references are resistivity, gravity, magnetic, the temporary channel existing at that time.This This article contains a brief-history o f rnininc offered here. electromagnetic, and induced polarization may be well above bedrock. operations and descriptions o f the Tertiaij a. Beach placers: Beach placers may form geop h ysica l methods were applied and Desert miners have learned from experience that ch ann els o f the Sierra Nevada region. where gold-bearing material is carried into evaluated. 22 p p ., maps, illus. gold enrichments are sometimes found resting on Contains indexed map with list of principal the ocean by streams, or along the wave-cut Gold Resources in the Tertiary Gravels o f caliche layers, particularly those near the ground deposits and bibliography. base o f a gold-bearing coastal plain. With California (Merwin, 1968). One o f a series o f su rfa ce, bu t such surface or near-surface exception of the highly productive beach California’s Gold-Bearing Tertiary Channelj reports presenting results o f investigations concentrations are commonly small, residual-type placers discovered at the turn o f the century (Jenkins & Wright, 1934). A condensed but conducted by the United States Bureau of accumulations o f gold left behind where lighter at Nome, Alaska, none have been o f great e x c e lle n t discussion o f the origin oi Mines under the Department o f the Interior’s material has been removed by rain wash and wind importance in the Western States. Typical C alifornia’s Tertiary gravels and related Heavy Metals Program. It reviews the history action. In other words, such enrichments result beach placers along the Pacific coast are geology. Highlights factors in gold of hydraulic and drift mining in California’s from the removal o f valueless material rather found as erratically distributed, somewhat accum ulation and discusses methods of Tertiary gravels and the reasons for cessation than from the concentration o f gold by normal lenticular concentrations or streaks o f black geologic exploration and proposed o f large-scale mining o f these deposits. The stream processes. It should be stressed that in sand minerals with varying amounts o f geophysical techniques as aids to future rep ort d iscu sses general geology, the some desert placers the only economically finely-divided gold and in some places, with exploration work. distribution o f gold within the gravels, past minable ground is related to superficial platinum-group minerals. Beach-placer black production, and gold reserves. 14 pp., illus., concentrations and, at best, the chance o f finding Tertiary Gravels o f the Sierra Nevada oj sands can be expected to consist largely o f pay gravel is to a great extent fortuitous and California (Lindgren, 1911). A classic on bibliography. magnetite and ilmenite but significant largely dependent on careful prospecting. Tertiary gravels and related subjects. Most amounts o f chromite are found in some Most of the foregoing references are of a Oregon beach sands. In the case of Descriptions o f many desert placer areas in the writers on placer subjects have drawn heavily technical nature and primarily o f interest to gold-bearing beach placers, the individual Southwest can be found in a number of from this source o f information and as a engineers and geologists. black sand concentrations are seldom over publications among which are those published by result, quotations from and references to 100 feet long or more than a few feet thick. the Arizona Bureau o f Mines (Wilson and L in d g ren ’s work are prominent in the The term ‘Tertiary gravel” is used broadly to Those found on the active beaches are the F a n sett, 1 9 6 1 ), the University o f Nevada literature. designate extensive gold-bearing gravel d e p o sits laid down in ancient streams result o f storm and tidal action, and they (Vanderburg, 1936) and the California Division The Auriferous Gravels o f the Sierra Nevada approximately 50 million years ago. These come and go with changing conditions of the o f Mines (Haley, 1923, pp. 154-160). o f California (Whitney, 1880). Discusses in often-rich channels were subsequently buried beach. Some of the most productive placers considerable detail, the concepts (circa under as much as 1500 feet of younger have been found in ancient, elevated beaches 1879) o f origin and deposition o f Tertiary 7. TERTIARY GRAVELS gravels and volcanic material which that are now several miles inland. gravels. The book is best suited to advanced effectively sealed and preserved the original Beach mining reached its height following Gold-bearing gravels o f Tertiary age are abundant study. Also contains maps and excellent placers. The present Sierra Nevada range and discovery of the rich gold placers at Nome, in the central Sierra Nevada region o f California descriptions o f important Sierra Nevada its Tertiary deposits have since been elevated Alaska, in 1898. Here, over two million and to a lesser extent in northwestern California placer mining districts and offers some of the by mountain-building disturbances and, dollars were produced from a 20-mile section and southwestern Oregon. A few are found in best available data on individual mining today, the dissected channels are typically of modern beach about 200 feet wide, and northeastern Oregon and central Idaho. In operations of the day. Includes chapters by found as lava-capped segments high above another 15 million from a series o f inland California, many miles o f these ancient river W.A. Goodyear and W.H. Pettee. the present streams. Parts o f the Tertiary elevated beaches. Subsequent discoveries on channels have been mined and according to The Ancient River Beds of the Forest Hill deposits were worked extensively by the other Alaskan beaches, and elsewhere along figures offered by (Clark 1965, p. 44), seven of D ivid e (Browne, 1890). One of many hydraulic method during the latter half o f the Pacific coast, resulted in other gold the California deposits have together produced excellent articles describing Tertiary gravel the 1800’s and in many places, the richer rushes but little production. Some beach gold amounting to more than 232 million dollars. deposits and related mining operations that bedrock gravels were exploited by tunneling placers along the California-Oregon coast The total production is not on record but it is have been published by the California State operations known as “ drift mines” , some of have been worked in the past by simple hand known to far exceed this figure. Although few, if Mining Bureau. which followed the ancient channels for mining methods and although a number of any, o f the remaining Tertiary deposits can be Tertiary Gold-Bearing Channel Gravel in miles along their subterranean course. Parts large-scale operations have been attempted, mined at the present price o f gold, the possibility Northern Nevada County, California of California’s Tertiary channel system none, to this writer’s knowledge, have been o f mining some at a future date is real and must (Peterson and others, 1968). A report on remain buried and unexplored; these are successful. be given serious consideration. Because o f this studies o f the San Juan Ridge Tertiary' believed to contain a large gold reserve, Over the years a number o f attempts have fu tu re potential and today’s sporadic but channel in Nevada County, California, made available for mining at some future date. been made to mine magnetite-rich beach continuing mining efforts, it is important that the as part o f the Department o f the Interior’s sands for their iron content and during World mineral examiner have a clear concept o f this Heavy Metals Program. It describes the 8. MISCELLANEOUS TYPES War II some chromite was recovered from special type o f placer. The subject o f Tertiary geology and physical characteristics o f a There are other less publicized types o f gold ancient beach deposits in Oregon. (Kauffman channels is too extensive for review here and, for 15-mile section o f this channel and also placers that are not economically important this reason, the reader is directed to the following and Baber, 1956, pp. 12, 13). 15 discusses geophysical investigations o f the today, but which may achieve importance at selected references: channel gravel carried out by personnel of When investigating a beach placer, all reports Gold derived from the outcrops of small Two districts having glacier-related placers Browne, Ross E., 1890, The ancient river beds o f the and sampling data relating to the property veins is thus mixed with large masses ol that are well described in the technical Forest Hill divide: State Mineralogist Rept. X, should be examined critically. First it should barren earth. Attempts to mine gold in literature are now near Breckenridge and California State Mining Bureau, pp. 435-465. be ascertained if the samples represent a glacial moraines, where bits o f rich but Fairplay, in Colorado. At Fairplay (Singe- Clark, William B., 1965, Tertiary Channels: Mineral minable volume, o f if they actually represent widely scattered float have been found, wald 1950), the actual moraines were mined Information Service Vol. 18, No. 3, March 1965. selected or scattered streaks o f enriched are for that reason foredoomed to locally but the most extensive and productive California Division o f Mines. material. Second, it should be ascertained failure. placers were found in outwash aprons extend­ whether or not the reported gold values were Clark, William B. and Carlson, Denton W., 1956, ing away from the true moraines. At Brecken­ determined by fire assay. In the absence o f “ If a glacier advances down a valley Mines and mineral resources o f El Dorado ridge (Ransome, 1911,pp. 175-181), bench information to the contrary, it must be which already contains gold-bearing river County, California: California Journal o f Mines gravel associated with Pleistocene glacial assumed that the reported values were gravel, it is apt to gouge out the entire and Geology. Vol. 52, No. 4, October, 1956. deposits were mined by ground sluicing and obtained by fire assay. Little or no credence mass, mix it with much other debris and California Division o f Mines. hydraulicking while younger gravels derived can be given sample results, or the reliability deposit it later as useless till. Under some from glacial moraines have been extensively Clifton, H. Edward, Hubert, Arthur, and Phillips, R. o f a report, based on fire assay returns. There circumstances, however, it merely slides dredged along the Swan and the Blue Rivers. Lawrence, Marine Sediment Sample Preparation are persistent stories that beach deposits over the gravel and buries it without distributing it. Both districts are well described in the for Analysis For Low Concentrations of Fine contain gold and platinum in forms not literature referred to. Detrital Gold: U.S. Geol. Survey Circular 545, amenable to recovery by conventional “ On the other hand, the streams born ol In general, glacial debris that has been 1967. 11 pp. processes, in fact, many o f the larger-scale glaciers or slowly consuming their scoured from highly mineralized bedrock attempts to work beach deposits have been moraines have the power to winnow the Dasher, John; Fraas, Foster and Gabriel, Alton, 1942, areas may be expected to contain gold but it based on some kind of “revolutionary” or particles o f rock and mineral matter M ineral dressing o f Oregon beach sands. will probably have little or no economic secret process intended to recover this elusive according to size and heaviness. Such Concentration o f chromite, zircon, garnet and value unless resorted by post-glacial streams, gold. The fact that few such schemes have streams may form gold placer deposits in ilm enite: U.S. Bureau o f Mines Report o f c. Eolian placers: In desert regions the wind gone into commercial production and none the well-known way by churning the Investigations 3668, 1942, p. 19. may act as an agent o f concentration by have become sustained operations is load they carry and allowing the heavy Haley, Charles S., 1923, Gold placers o f California: blowing sand and the lighter rock particles significant. minerals to sink to the bedrock. Placers Bulletin 92, California State Mining Bureau, p. away from a body o f low-value material and A number o f excellent technical articles may therefore be found in the deposits leaving an enriched surface veneer containing 167. relating to beach deposits in Oregon, Alaska o f glacial rivers if there are gold veins gold or other heavy minerals in a somewhat Hill, J.M., 1916, Notes on the fine gold o f Snake and California are available, among which are exposed in the glaciated area upstream. concentrated state. There have been many River, Idaho: U.S. Geol. Survey Bull. 620-L, pp. those by Pardee (1934); Dasher, Fraas and Nearly all the gravel which has been cases where wind-caused surface enrichments 271-294. Gabriel (1942); Twenhofel (1943); dredged for gold along the foothills of supported the activities o f itinerant miners Thompson (1915); Thomas and Berryhill the Sierra Nevada was deposited by Jenkins, Olaf P., 1946, New technique applicable to using hand tools and simple dry washers. (1962); and by Jenkins (1946). Recent work rivers derived in part from glaciers along the study o f placers: California Division o f Mines Although commercial-grade eolian placers are by the United States Geological Survey the crest o f the range, but most o f the Bull. 135, Placer mining for gold in California, pp. not likely to be encountered by today’s (Clifton, 1967) points out the problems gold was probably picked up in the 149-216. mineral examiner, he should be aware o f normally encountered when sampling and lower courses o f such rivers. Since glacial First published in California Journal o f Mines and their existence and should be alert to their analyzing beach or marine deposits rivers choke themselves and build up Geology, Vol. 31, No. 2,1935 pp. 143-210. misleading appearance. In other words, when containing detrital gold. their channels progressively, their Reprinted as a series o f 8 articles in Mineral taking near-surface samples from desert Glacial deposits: The mineral examiner deposits are likely to be thicker and not Information Service, Vol. 17, Nos. 1, 2, 3, 4, 5, 6, placers, he should guard against working in the Western States may seldom so well concentrated as those of the 8 and 9, Jan.-Sept., 1964. California Division of unintentional salting which could result from encounter a placer directly associated with more normal graded rivers which are not Mines. the inclusion of non-representative, glacial deposits but, on the other hand, it is associated with glaciers.” wind-caused surface enrichments. Jenkins, Olaf P. and Wright, Quinby W., 1934, not unusual for a miner to assert that a California’s gold-bearing Tertiary channels: Where a glacier-related placer is encountered, particular deposit, particularly if its origin is Engineering and Mining Journal, Vol. 135, No. the field engineer should, as an early step in obscure, is a “ glacier” placer. For this reason REFERENCES CITED (PART II) 11, November, 1934, pp. 497-502. his investigation, search out and study all the engineer should know about glacial available technical literature relating to the Kauffman, A.J., Jr. and Baber, K.D., 1956, Potential deposits as they relate to placers. Blackwelder, Eliot, 1932, Glacial and associated glacial history o f the region. In particular, he o f heavy-mineral-bearing alluvial deposits in the The fundamentals have been well set out by stream deposits o f the Sierra Nevada: California should seek any reliable information on past P a cific N orth w est: U.S. Bureau o f Mines Blackwelder (1932) as follows: Div. o f Mines, Mining in California, State mining o f the deposit or similar deposits in Information Circular 7767, p. 36. Mineralogist Rept. 28, pp. 309-310. “ Since it is the habit o f a glacier to the district, the object being to determine if Lindgren, Waldemar, 1911, Tertiary gravels o f the scrape o ff loose debris and soil but not significant gold concentrations are to be Brooks, Alfred H., 1913, The mineral deposits o f Sierra Nevada o f California: U.S. Geol. Survey, to sort it at all, ice is wholly ineffective expected and, if so, under what conditions Alaska: Mineral Resources o f Alaska, U.S. Geol. as an agency o f concentration for metals. Professional Paper 73, p. 226. they are likely to be found. Survey Bull. 592, 1914. Merwin, Roland W., 1968, Gold resources in the Eastern Gulf o f Alaska: U.S. Bureau o f Mines Tertiary gravels o f California: U.S. Bureau o f Report o f Investigations 5986, p. 40. Mines Technical Progress Report, Heavy Metals Program, 1968. Thompson, Arthur G., 1915, Yakalaga beach placers: Engineering and Mining Journal, Vol. 99 Pardee, J.T., 1934, Beach placers o f the Oregon No. 18, May 1, 1915, pp. 763-765. coast: U.S. Geol. Survey Circular 8, 1934, p. 41.

Peterson, Donald W., Yeend, Warren E., Oliver, Twenhofel, W.H., 1943, Origin o f the black sands ol Howard W., and Mattiek, Robert E., 1968, the coast of Southwest Oregon: State of Oregon Tertiary gold-bearing channel gravel in Northern Dept, o f Geology and Mineral Industries Bull. 24 Nevada County, California: U.S. Geol. Survey 1943. PART III Circular 566, 1968. Vanderburg, William 0 ., 1936, Placer Mining in Ransome, Frederick L., 1911, Geology and ore Nevada: University o f Nevada Bull, Vol. 30 No. 4, deposits of the Breckenridge district, Colorado: May 15, 1936, p. 180. U.S. Geol. Survey Professional Paper 75, 1911, p. SAMPLING AND EVALUATION Whitney, J.D., 1880, The auriferous gravels of the Singewald, Quentin D., 1950, Gold placers and their Sierra Nevada o f California: Contributions to geologic environment in Northwestern Park American Geology, Vol. 1: Harvard University County, Colorado: U.S. Geol. Survey Bull. 955-D, Press, Cambridge, Mass. 1950, pp. 103-172. Wilson, Eldred D. and Fansett, George R., 1961, Gold Thomas, Bruce I. and Berryhill, Robert V., 1962, placers and placering in Arizona: Arizona Bureau Reconnaissance studies o f Alaska beach sands, o f Mines Bull. 168, p. 124. FIGURE 2. - Typical placer material showing the wide variation in particle sizes to be dealt with in sampling.

If the reader will pause and study Figure 2, he can they occur in the parent mass. But look better visualize the more pertinent placer sampling at Figure 2. This deposit is a mixture of problems, as they are taken up in the following fine sand, pebbles and boulders varying paragraphs. from a few tens o f pounds to hundreds o f pounds, and in this respect, is typical o f many placers. A little study o f Figure 2 will show why when dealing with such 1. GENERAL CONSIDERATIONS deposits, it is virtually impossible to take a. Problems: Contrary to popular belief, a small sample representative o f the representative placer samples are seldom easy whole mass, and why the evaluation o f to obtain and in almost all cases sample such a deposit can tax the ability o f an results need a large measure of expert. interpretation. Some of the underlying (2) High unit-value of gold. When dealing reasons are: with the typical placer sample containing (1) Large particle sizes to be dealt with. A a high-value mineral such as gold, any er­ representative sample should contain all ror in mineral content o f the sample will o f the constituents o f a deposit and in be h igh ly m a gn ified in the end result. exactly the same proportion in which Consider that in a commercial placer the 21 relative amount o f gold (by volume) may T h is is particularly true when used in b. Industry practice: How do the establish^ amounts o f sticky clay, large boulders or be on the order of one part gold to a stereoscopic pairs. Aside from providing a p la cer mining companies evaluate tk other factors that would adversely affect a h u n d red -m illion parts o f gravel. To quick, overall perspective o f the lands, good prospects? First, the prospecting is put. placer mining operation. A good sampling the m ineral examiner this means that a aerial photographs reveal details of charge o f an employee who has had wii program will provide the information needed single fly speck o f gold in a pan o f gravel topography, drainage and other features not experience with the type o f deposit q to evaluate adverse physical conditions, is equivalent to say, 2 to 5 cents per mining project involved. Second, the should they exist, but here again experience easily discernible on the ground. cubic yard, depending on the exact size recognize that any one sample is rare) is needed to interpret the information and A review o f published material relating to the of the speck. The actual separation of representative o f the overall deposit andk make correct decisions. lands under study should be part o f any small amounts of such gold from itself may mean little. Third, after studying e. In brief: Placer samples yield limited reconnaissance because information thus overwhelming quantities o f sand and the combined prospecting data and perhap information. Correct interpretation o f this o b ta in e d can be a great time saver, gravel seldom presents a serious problem; taking special check samples information depends upon the engineer’s particularly where the regional or local the real problem is to take a sample that experience-based adjustments known * powers of deduction and experienced geology has been worked out by qualified is representative in the first place. “ correction factors” are applied to the initii ju d g em en t, rath er than on the rigid observers and reported in authoritative (3) Erratic distribution o f values. Obtaining sample data where needed and, finally, tit application o f formulae. publications. On the other hand, too much a satisfactory placer sample would be a ca lcu la te d values are based on these reliance on published material can lead to comparatively simple undertaking if the “ a d ju s te d ” data. Here, it should k SAMPLING GUIDES erroneous prejudgements, particularly among valuable minerals were uniformly emphasized that the successful place: For practical reasons, placer sampling younger engineers not in a position to weigh distributed throughout the whole mass. In companies place as much reliance on the incorporates a series o f steps which may be the statements and conclusions o f others almost all placers, however, the heavy experience and insight o f their prospectini carried out one at a time or in some cases are against their own experience. minerals and particularly the gold are and management personnel as they do on the more or less combined. These may be defined as: The history of a mining district can play an more or less segregated. For example, in sample results. If there is a mathematical Reconnaissance o f the lands. important role in the selection and cases where economic values are formula or a general rule which will replace Sampling. interpretation o f placer samples and should confined to pay streaks, these are likely experience-based judgement, the operating Sample processing. be considered an element of the to occur as narrow, discontinuous companies have not found it. Data processing. reconnaissance. Any old diggings on the accumulations with perhaps little or no c. Minerals other than gold: Parenthetically, it Evaluation o f results. lands to be sampled merit careful value in between. Where coarse gold is should be noted that placers chiefly valuable The first step can be further divided into three consideration, particularly those from which present it can be expected to be even for minerals such as monazite, rutile, parts which will be discussed here under the some production has been made. Where more erratic in distribution and it should cassiterite, ilmenite, etc., are generally easier production records are available, they often following headings: be evident that under such conditions to sample and evaluate than gold placers. serve as a useful guide in the selection and a. Pre-sampling reconnaissance. relia b le v a lu a tion will depend on There are several reasons. First, the valuable interpretation o f new samples. Nearby mines b. Choosing a sampling method. something more than taking a few small mineral makes up a larger part o f the mass. should also be visited and examined where c. Number and size o f samples. samples and an exercise in arithmetic. Second, the mineral sought has a relatively possible to do so. a. Reconnaissance: A preliminary inspection o f In theory, these problems can be low unit value which means that extraneous Because the reconnaissance must be tailored the lands should precede any placer sampling o v e rco m e by taking samples large particles o f such mineral (in a sample) may to suit the job at hand, no fixed procedures work. If the property is small this may take enough to offset the eccentricities of a have little effect on the calculated value. can be set out here. The effort and time less than an hour but if it is large or if it deposit, but to do so, would mean taking Third, deposits containing such minerals are required for an adequate job will depend on con ta in s significant mineral exposures, samples measured in tons rather than often made up of well sorted, small-size the examining engineer’s experience and several days o f pre-sampling reconnaissance pounds and it is seldom possible to take detrital materials such as beach sands and, in perception. may be in order. The importance o f this such large samples in actual practice. such cases, the mechanics o f sampling may preliminary work should be self-evident for, b. Choosing a sampling method: What sampling Some approach the problem by arguing be simplified by permitting the use o f augers obviously, before the engineer can make method should be used? This question comes that if enough small samples are taken, or jet drills in lieu o f churn drills. Speaking intelligent sampling plans he must have some up early in most placer investigations but the highs will balance the lows and the generally, the sampler has considerably more idea o f the size, shape and the general there is no easy answer. Because each deposit end figure will represent the average latitude when dealing with minerals o f low characteristics of the deposit being has unique characteristics there is no single value of the deposit even though no one unit-value than when dealing with gold and investigated. Unfortunately, this first step “ best” method of sampling and no procedure his mistakes are less likely to seriously affect sample is correct. This may be can be applied universally. In some cases, the end results. appears short-changed in many sampling statistically true but here again, practical d ecision s will have to be made on a d. Other factors to be considered: Many things programs. considerations seldom permit taking the sample-by-sample basis but a good other than mineral content have a direct If aerial photographs o f the lands under number of samples needed to achieve pre-sampling reconnaissance will usually bearing on the commercial value o f a placer study are available, copies should be this end. indicate if the ground should be tested by deposit. The mineral value in itself may be of obtained before starting the reconnaissance. means o f pits, shafts, churn drilling, or other 1/ Ground having a gold-gravel ratio o f 1:100,000,000 (by secondary concern where sampling or Photographs o f the type available from the means. It is a paradox that the very things volume) is worth approximately 15 cents per cubic yard examination of the lands for example, show U.S. Geological Survey or Forest Service are 22 (@$35/oz.) which are to be determined by sampling are 23 unfavorable bedrock conditions, excessive often the most useful reconnaissance tool. often things which govern the type o f sample which the gold or other valuable mineril to be taken in the first place. This is a closer and closer intervals, the areas o f intermediate drilling along the 800’ lines. distributed somewhat uniformly? Or, isj “ chicken-and-egg” type of situation in which influence become progressively smaller and Each step, progressively taken, was designed boulder-strewn, stream-type depo, we sometimes cannot tell which comes first. the combined sample results progressively to furnish the amount o f information needed containing coarse, erratically district, for evaluation at that stage. Had the results Something to keep in mind is the fact that more representative until, in theory, a point gold? It is a generally accepted principle tk from any one step been unfavorable the today’s placer sampling is expensive. Because is reached where the combined average the smaller and more uniform the size oft project would have been dropped at that o f this, the method or sampling program equals the true value o f the whole. This is gravel, and the more evenly distributed t: point. It should be apparent that a high adopted should be no more elaborate than known as sampling to a uniform average. mineralization, the fewer samples neededl; degree o f training and diagnostic skill is needed to provide the amount o f detail and Sampling to a uniform average is simple in an intelligent estimate o f value. While \ needed in this work. the end accuracy required for a particular concept but its objective can seldom be may accept this principle as fact, the dege determination. For example, the prospector, reached in practice. In other words, for In the foregoing example, a reliable placer to which such characteristics affect samfl whose main concern is to expose enough o f a practical reasons the desired number o f valuation was based on a sampling density of size and the number o f samples requirt “ showing” to interest a second party or samples can rarely be taken and in the end, one hole for each 3 1/2 acres o f dredge remains largely a matter o f judgement. I mining company in his prospect, would he the placer operator must either reject a ground which in this case was equivalent to a put it another way, textbooks tell us thatfo foolish to expend his own time and money property or go forward on the strength o f a volumetric sample factor of about ordinary gold ore, the size o f the large a ttem p tin g to carry out an elaborate valuation which is not 100 percent reliable 1/500,000. For comparison, there are cases piece o f rock in the sample determines tli sampling program; that is, sampling which and, hence, he must always accept some in which one hole for each 10 acres was weight o f sample needed. According i any cautious mining company would do over degree o f risk. Realistically then, the found adequate and some in which no Woodbridge (1916, p. 57) if the large again fo r th eir ow n satisfaction and minimum number o f samples might be amount of drilling would suffice. piece is one inch, the minimum samp!, protection. Very often the first placer considered the number required to hold this In summary: We can seldom, if ever, weight should be 2,000 pounds. Where tb sampling is o f a cursory nature sufficient risk within acceptable limits. A method for predetermine an optimum sampling pattern largest piece is two inches, the minimur only to indicate if further interest in the graphically examining this problem has been or the total number o f samples required to weight should be 10,000 pounds, etc. If tin property is warranted or to serve as a guide described by Herr (1916, pp. 261,262). evaluate a placer. For this reason initial progressive scale were applied to place in future sampling or exploratory work. As a practical example, consider an actual sampling programs should be tentative or at gravels, the required weights for typia Some methods to be considered are: sampling program carried out by an least should be flexible enough to samples would be measured in tens of ton- Sampling existing exposures. experienced gold dredging company. In this accommodate any changes dictated by the This points out that sampling procedure Use o f hand-dug excavations. case the ground had a history o f superficial work as it progresses. In any case, detailed based on pure theory are too unwieldy fa Machine-dug shafts. hand mining operations going back many placer sampling is expensive and for this if no placer application and, in turn, it shows wh; Backhoe pits or trenches. years and the g e o lo g ic and physical other reason, even the most comprehensive the placer sampler must to a large extent rek Bulldozer trenches. conditions indicated a possible depth and sampling program should progress from a on his own judgement and good sense ti Churn drill holes. volume sufficient to support a bucket-line simple beginning to its final form in a series determine what is an adequate-size samplet Bulk samples. o f carefully evaluated steps. a given case. dredge. A comprehensive drilling program Grab samples. was needed to determine the average tenor Also, it is important that a distinction be Now, consider a single sample. While asingl* The order in which these methods are and to define possible mining limits. made between sampling for the purpose of sample may provide much information aboil presented has no bearing on their relative As a first step,a 6-inch placer drillwas moved to initial valuation and sampling to block out a the material it actually penetrates, it rarel; im p orta n ce or applicability in a given the property and four holes drilled at finite parcel of mining ground. It sometimes if ever, provides sufficient information (# situation. Their applications are described in random points to test the depth, character o f takes only a few judiciously selected samples the valuation o f a deposit. Where a single the section titled “ Sampling Methods.” material, and to get some idea o f its gold to determine that a property has no sample is taken its assumed area o f influemt Number and size of samples: When content at depth. Results from the four economic value while, on the other hand, an will reflect the insight or optimism of tit investigating placers, th,e problem o f how preliminary holes enhanced the overall area showing good potential may require a viewer. But, how do you measure these' many samples are needed and where they prospect and indicated a need for further thorough sampling in order to determine the There are placer deposits o f such a charactei should be taken, and how large they should sampling. value and other information needed to plan a that it is safe to project sample data several be, is often a perplexing one. Here there is no successful mining operation. hundred feet and there are others where tit At this point a rectangular grid in the form formula, rule o f thumb, or pat answer to Parenthetically, it should be pointed out that gold distribution is so erratic that a ten-fool o f 800’ x 1600’ rectangles was laid out and reliably guide the sampler; in fact, placer there is no final proof o f the accuracy o f projection would be a dangerous assumption holes were drilled at each intersection. This sampling procedures may vary not only with initial wide-spaced drilling over a 1500-acre p lacer sampling because in an ensuing But now suppose we take a second, third and operation, the mining and metallurgical every property but with the purpose o f the tract was d esign ed to determine the fourth—or an extended series o f samples losses can never be fully identified or examination and, to some extent, with the approximate size, shape, and possible value type o f mining contemplated. Obviously as each sample is taken, its area of measured. This is particularly true in the case o f the deposit. Using results from this drilling influence extends only part way to adjacent o f gold dredging. How can the mineral examiner cope with this as a guide, the prospect data were further samples and as more samples are taken at problem? First, he must know what he is refined by drilling intermediate holes along 3. SAMPLING METHODS 24 dealing with. Is it a large, regular deposit in a. Existing exposures: During the early stage o f 1/ References cited are listed at the end of Part III. some o f the 1600’ sides and, in turn, a selected area was divided into 400’ blocks by a placer investigation a quick answer may be 25 TABLE I. The effect o f a single small gold particle on placer material for panning and unless he is a reservation until proved valid. The vet\ The use o f hand-dug shafts for general placer samples o f typical size. trained placer sampler capable o f applying offering of this type of data, without sampling was common practice at the turn of The values shown are those which would result from one experience-based judgement to the findings. gold particle in a 1-foot sample increment. q u a lifica tio n , may be good reason to the century when labor was cheap and Values shown are based on gold weights determined by the question the expertness or intent of the experienced shaft men were readily available A somewhat similar procedure but one in author, and gold at $35 per ounce. vendor. but, today, because o f the high cost o f labor w h ich the personal factor is in part eliminated may be carried out as follows: SIZE OF GOLD PARTICLE In brief, samples from existing exposures and a scarcity of experienced men, they are Carefully deepen the pit or shaft in uniform, And Effect on Sample taken in conjunction with a placer seldom used on a wide scale. But they may Size of Drill still be used to advantage in special measured drops o f say one foot at a time. Hole or 20-Mesh 40 Meash investigation can, if properly evaluated, 60-Mesh Just prior to each deepening, carefully Channel (6.57 mg.) (0.91 mg.) (0.27 mg.) provide valid, useful data. But, for the situations; for example, by prospectors who expect to find good bedrock values in ground remove a sample by digging below the 7 / 2” dia. 58c/cu.yd. 8c/cu.yd. 2!4c/cu.yd. inexperienced or the unwary sampler, bottom of the pit or shaft to a depth exactly 5K” dia. SI.1 8 ” 16c ” 5c ” existing exposures offer an inviting and too deep for effective use o f pits or trenches. 3” dia. equalling the distance the bottom is to be $3.60 ” 50c ” 14c ” sometimes unrecognized trap. In such cases one or more shafts will usually 3” x 6” $1.42 ” 20c ” 6c be put down to test the gravels lying on dropped during the next deepening step. The 6” x 6” 7 1 c” 10c ” b. Hand-dug excavations: Hand-dug excavations 3c bedrock. This approach is common where minimum-size sample that can be 6” x 12” 35c ” 5c ” 114c ” in the form o f pits, trenches or small shafts the owner or a promoter’s main concern is to conveniently taken in this manner will be 12” x 12” 18c ” 2 He ” 3/4c ” are generally suited to dry, shallow ground. one having a ” x ” cross section but if 16-inch pan 1/ $1.18 ” 16c ” 5c convince someone that the property should 12 12 They are most effectively used to depths of be more thoroughly prospected by drilling or many rocks are present it may be somewhat about 7 feet which is the depth from which 1 / @ 180 pans per cubic yard. other means. larger. A sheet-iron caisson 18 or 24 inches in material can readily be thrown with a shovel. Hand-dug shafts are commonly used to check diameter by about 12 inches long can be n e e d e d to determine if a significant Where practicable, they may provide the best used to advantage when the bottom sample expenditure of time or money is justified for selected churn drill holes and in many cases means for sampling a placer. They generally must be taken from wet or ravelling ground. further investigation. At this stage, practical they are essential to correct interpretation o f do not require such close supervision as This type of sample may be taken from the considerations may limit initial testing to a the overall drilling results. This is taken up in drilling nor do they require the high cost, center o f the pit or shaft bottom or from any few samples taken from existing exposures the section dealing with sampling by means specialized equipment or highly trained suitable place but once started, its location such as creek or dry wash banks, road cuts, o f churn drills. personnel needed for placer drilling. An extra should remain fixed. By following this old mining pits, etc. These can be Most engineers agree that where feasible all bonus is offered by hand-dug excavations in procedure, a progressive sample can be informative if properly used. o f the material taken from a test pit or shaft cases where they remain open for some time, obtained from undisturbed material ahead of permitting resampling at a later date. In the should be washed. If the ground stands well Existing exposures are usually tested by the main excavation. panning, particularly where the exposure is case o f dredge prospects, the principal point and the walls o f the excavation are cut Where the excavation walls stand reasonably small. In most cases the bedrock will not be in favor o f pits or shafts, where applicable, is square and parallel, it is an easy matter to well, a sample can be obtained by cutting a exposed and the distribution o f available the fact that they provide a much better idea determine the in-place volume o f material vertical channel up one side o f the pit or sample points will be far from ideal and, in o f boulder content and gravel sizes than do removed and to directly compute its value shaft. The excavated sample material can be either event, it should be obvious that small-diameter drill holes. Boulders are after washing. An excellent description o f a allowed to fall on a canvas placed at the extreme care is needed when evaluating the always an important factor in dredging sampling program employing this procedure bottom o f the pit or it may be caught in a sample results. On the other hand, the only operations. is found in an article by Sawyer (1932, pp. 381-383). The use o f hand-dug shafts to bucket or box held close to the point of preparation needed may be the cleaning The simple equipment needed for hand-dug prospect ground worked by the Wyandotte cutting. Where conditions permit taking a away o f sloughed or weathered material to sample pits or shafts is a particular advantage Gold Dredging Company of California has true channel, the sample volume can be expose fresh surfaces and, because o f this, in remote areas or where only a limited been described by Magee (1937, p. 186). determined by direct measurement but in the use o f existing exposures offers a cheap, amount of sampling is anticipated. A few Where an excavation cannot be measured any case it is best to weigh each sample as a fast method for preliminary testing. strategically located pits or shafts may show accurately, it will be necessary to weigh the check. By themselves, small samples obtained from that the ground is entirely unfit for mining sample material or to measure its loose The first step in channel sampling is existing exposures can seldom be expected to or that it will not warrant the expense of volume in a box or other container. In either to clear away all foreign material from the indicate the actual value o f the ground. They drilling. On the other hand, if they return case the indicated gold value will have to be ground surface above the place to be m ay, h ow ev er, prove or disprove the good prospects and the ground is converted to in-place or “ bank” value by use sampled. Next, thoroughly clean the sample presence o f gold and, if correctly interpreted, su b seq u en tly d rille d , the expense of o f suitable conversion factors. area by scaling down the face to be cut. they can indicate the range o f values to be preliminary hand work will be but a small Following this, remove any loose material expected. Nevertheless, many reports part o f the overall cost. Successful mining Where it is not practicable to wash all from the bottom of the pit where it might intended to prove or disprove the actual companies learned long ago to approach material, a good approximation o f the interfere with the sampling operation and, value o f placer lands are based on a few placer prospects cautiously and to make a ground’s worth may be made by washing finally, check the bottom for bedrock. A pan-size samples taken from existing few diagnostic tests before putting their several pans per foot o f depth as the piece o f heavy canvas or a tarp is then spread exposures and offered at face value. Such money in an expensive sampling program. In excavation advances. But, this method is at the bottom o f the face to be sampled and reports and sample data must always be many cases hand-dug excavations adapt well always risky unless the man in charge is this is positioned to catch all material falling 26 viewed critically and accepted with to this need. completely impartial in his selection o f from the sample cut. Starting at the bottom, popular belief, there is no minimum # a uniform rectangular channel is cut upward The successful use o f rotary bucket drills to optimum size which by itself will insure an sample dry placers has been described in to the top o f the prospect pit or in some adequate sample. cases, to the top o f a particular formation or articles by Draper (1932, p. 537) and by In ground where the water level is several sample increment. When starting a sample, Frommel (1937). Prommel describes a feet below the surface, it is sometimes the cuttings are usually allowed to fall on the sampling project in which 1,239 test holes 28 possible to sink pits or small shafts to canvas but when sufficient room becomes inches in diameter were drilled in 147 days. bedrock using only buckets or a small pump available, it is best to catch them in a suitable Their combined depths amounted to 16,705 to remove the water. These wet excavations box or metal container held close to the feet. The cost o f this work using two rotary are usually difficult to keep squared up but, point o f cutting. As the sample channel bucket drills was 98.6 cents per foot o f hole in any case, some form of ground support advances upward, the cuttings are but this did not include engineering or may be needed to eliminate the working periodically transferred to one or more sample testing charges and, it should be hazard and to minimize sampling errors noted that the low cost reflects sample sacks which should be kept in the which result when inflowing water carries sampler’s possession or under surveillance depression-level prices o f 1935. values into the pit. A simple, easily-framed throughout the sampling operation. In most Two clamshell-type machines designed style of cribbing suitable for most shallov situations an ordinary prospect pick will be specifically for placer prospecting are: An work is shown in Figure 3. found satisfactory for cutting channel-type air-actuated unit sold under the trade name In loose, water-logged ground it may be placer samples. KLAM, and a cable-actuated unit known as impracticable to sink prospect shafts without the PAR-X Placer Sampler. The KLAM is How large should the channel cut be? There the use o f telescoping steel caissons. Certain essentially a manganese steel clamshell is no simple answer because like other problems and special procedures associated bucket o f 1 cubic foot capacity, fitted with aspects o f placer sampling there may be with caisson work have been discussed by replaceable teeth and actuated by special factors to consider in each case. Steel (1915, pp. 66-68) and Dohney (1942, compressed air. The digging unit consists of Speaking generally, however, it will be found pp. 48-49). that experienced placer samplers usually the bucket, an air cylinder placed directly A t first glance the use o f hand-dug pits or select a size somewhere between 3” x 6” and above the bucket and a 15-foot stem as shafts would seem to be an effective, 12” x 12” in cross section but, contrary to shown in Figure 5. The combined digging inexpensive way of prospecting shallow FIGURE 4. — Rotary bucket drill making a 24-inch diameter unit which weighs one ton is suspended from placers but this approach is too expensive for hole in desert placer material The average drilling rate for the mast o f a drill truck by means o f a wire general use today, where a high dollar value 90 foot holes was about 70 fe e t per shift. Progress was 3"- ■3' & 5 ‘ Lengths ■ line spooled on a suitable hoist. According to -3" m ust be placed on time. Nevertheless, slowed by the presence o f numerous hard, caliche- the manufacturer, the standard unit digs a hand-dug excavations intelligently used can cemented layers. 3 " x 6" Rough F ir round, vertical hole 24 inches in diameter serve a useful purpose in that, under DETAIL OF CRIBBING t _ o II and is efficient to a depth of 100 feet. It is li -J favorable conditions, a few well located pits usually designed to dig a hole 24 or 36 inches said to dig from 2 to 20 feet per hour 2" x 4" Each corner, or shafts may indicate the value o f a prospect in diameter and to depths of 60 feet or more. depending upon depth, formation, and on length optional before any great expenditure o f money is The digging unit can best be described as a whether or not casing is used. Ground Surface made. straight-sided bucket which has two radial The PAR-X machine differs from the KLAM c. Machine-dug shafts: Machine-dug shafts have openings in its bottom and excavating blades in that the clamshell is attached to a been found both useful and economic in a extending below the openings. Rubber flaps telescoping stem or bucket carrier which number o f instances but they are not a fitted over the openings allow cuttings and limits the depth o f hole to about 30 feet. cure-all for placer sampling problems. The rocks to 6-or 8-inch size to pass into the The opening and closing action is controlled equipment used can broadly be divided into bucket but seal the openings when the by wire ropes. The unit is truck-mounted tw o ty p e s: rota ry bu ck et drills and loaded bucket is being hoisted. The bucket is and, according to Huttl (1941, pp. 55, 56), clamshell-type excavators. To be effective, rotated by means o f a square “ Kelly” bar its digging speed averages 35 feet per day in either type must be capable o f doing three which, in turn, is rotated by a ring gear on Excelsior normal ground. It digs a hole 28 inches things: ( 1) dig a hole large enough for a man the drill rig. See Figure 4. to enter and inspect the ground or to cut square without casing. Attempts to adapt this type o f drill to placer samples from the shaft walls; ( 2) have a Machine-dug shafts are best suited to bulk Space between cribbing and sampling have met with mixed success but reasonably fast digging rate; and ( 3) be sampling, that is, sampling in which the test pit walls to be backfilled speaking generally, rotary bucket drills have self-contained, freely mobile and capable of entire volume o f material removed from the with excelsior when exploring been found useful where the ground is dry loose ground. negotiating rough terrain. shaft is run as a sample. Where the ground and firm and where there are few rocks too Truck-mounted bucket drills have been in stands well channel samples can be cut from large to pass through the bucket openings. FIGURE 3. — Test pit cribbing suitable for use in shallow use for many years by excavation the shaft walls but there is hardly room for a On the other hand, they have been found placer ground. (From U.S. Bureau of Reclamation Con­ contractors, particularly those specializing in man to work effectively in a 24-inch crete Manual, 7th edition, 1963). poorly suited to the hard, rocky ground foundation test work. Their equipment is diameter hole. However, the fact that encountered in many gold placers. machine-dug shafts can be entered for To cite an actual case, a dry, desert p|a(t in s p e ctio n is a point in their favor, uniform this local enlargement would be of was sampled by means o f 24-inch-diamelt particularly in new fields where little is no consequence, but it was found that the machine-dug shafts ranging from 60 to 9; known about the sub-surface conditions. enlarged sections were often in feet deep. Both rotary-bucket and Klam-typ Something proponents o f this method o f magnetite-rich sands. As an end result, excavators were used. The valuable minen placer sampling seldom mention is the fact samples (representing 30-foot shaft was magnetite occurring in the form of blad that an uncased, machine-dug shaft passing increments) contained too large a proportion sand. When the completed shafts wen through alternating hard and soft layers or o f the richer material which in effect entered for inspection, it was found that tly th rou gh ravellin g ground will have a amounted to unintentional salting. Had this shafts had passed through a series o f had non-uniform diameter, that is, it may be been a gold prospect the errors caused by c a lich e -ce m e n te d gravels separated h appreciably larger in the softer horizons than non-uniform hole size would have been relatively loose sand and gravel strata and, ii in the hard. T h is means that where substantial. all cases, the shaft diameters wen over-diameter shaft sections occur in ground Backhoe excavators'. The development of appreciably larger in the softer materials th® that is above average or below average com pact, tractor-mounted backhoe in the cemented horizons. Sections wen mineral value, the end result will be an excavators in recent years has given the found enlarged to as much as 2 1/2 times th unintentional salting or an impoverishment mineral examiner a tool which adapts well to normal 24-inch diameter. If the grade o| o f the bulk sample. many o f his placer sampling needs. These material throughout the shaft had been go-anywhere, high-performance machines dig, load and backfill. The combination most frequently employed is a hydraulically-operated backhoe unit mounted on the back end o f a rubber-tired tractor plus a scraper or loading bucket at the front end. See Figure 6. A typical rig will dig 10 feet deep, reach more than 15 feet from the pivot point and will load into a truck 11 feet high. The backhoe bucket has more than 7,000 pounds digging force and generates a pryout force o f 15,000 pounds or FIGURE 6. — Back hoe excavator digging trench in placer more. Most placer ground is handled with ground. Hand-dug channel samples were later taken from the trench walls. ease. A 1 1/2-yard, track-mounted backhoe (Thew-Lorain) has a depth capacity of 27 feet and is available with a range o f buckets and the travel time was two hours bringing that provide cutting widths from 12 to 38 the total charge to $88. This amounted to a inches. little less than $1 per foot o f shaft and In most areas, this type o f equipment is provides a good example of the cost and available on a rental basis from contractors work accomplishment that can be expected who will be found listed in the yellow pages when using this type o f machine. o f the telephone book under “ excavating In m ost p la cer gravels the walls o f contractors.” Rental rates vary with locality backhoe-dug pits or trenches stand well and and machine size but $10 to $14 per hour is can be sampled by cutting a vertical channel not unusual. This price includes the operator. in the fa ce o f the standing material. On short-term jobs the charge starts at the Depending on requirements and conditions, time the equipment leaves the contractor’s the sample channel can be cut with the yard so it is well to have the work well backhoe bucket (usually 24” wide) or by planned and laid out in advance. hand. Where the presence o f much large rock In connection with a placer sampling job or ravelling ground precludes the use o f near Grants Pass, Oregon, in 1966, thirteen channel cuts, either all excavated material or shafts ranging from 4 to 12 feet deep were alternate buckets can be set aside as a bulk dug using a tractor-mounted backhoe sample. See pages 71, 72. equipped with a 38-inch “graveyard” bucket. The tractor-mounted backhoe is probably FIGURE 5. — Air-actuated excavator manufactured under trade The backhoe with operator rented for $11 the most versatile placer sampling tool 30 inches in diameter to depths o f 100 feet or more. per hour. The 13 shafts were dug in 6 hours available to the mineral examiner today. 31 e. Bulldozer trenches: The use of bulldozers to particularly those exploited by bucket-lit, dig trenches for prospecting shallow placers dredges, have been sampled by churn drills is too common and too well known to need and it can be said generally that this methot more than passing mention. adapts well to the dredge operator’s needs. Because o f its design, the bulldozer is more The basic drilling equipment consists of, effective as a pusher than as a digger and for heavy casing, a chisel-shaped bit suspends this reason it is best suited to ground less from a drill line and a vacuum-type said than 10 feet deep and to a working (pushing) pump. The overall operation can be divided distance not exceeding 200 feet. Two types into five steps as follows: o f blade control are in general use; the blade Driving. may be raised and lowered hydraulically or it Drilling. may be operated by a cable control. For Pumping. digging prospect trenches the hydraulic blade Panning. is considered best as it provides a positive Pulling and moving. downward pressure; in fact, it allows much o f the tractor’s weight to be put on the blade The first step provides a measured core ol while digging hard ground. The gravel which serves as the sample. The gravel cable-controlled blade has only its own c o re is obtained by driving the cask weight to hold it down and as a result its (commonly referred to as the drive pipe) into cutting edge has a tendency to ride over any the ground by striking it with a driving blod hard spots in the bottom o f the trench. attached to a heavy drill stem. The botton The cost of bulldozer-dug trenches depends end o f the drive pipe is fitted with an so much on the type and size o f machine alloy-steel shoe made with a sharp, beveled used and on the depth and hardness o f the cutting edge. The effective diameter of this fo r m a tio n , and the operator’s skill; any beveled edge determines the area of gravel or estimate o f working speed or costs must be sample cut by the drive shoe as it is forced made on a case-by-case basis. Lorain (1944, downward. p p . 1-8) has tabulated field data for A second step breaks up the core anij trenching with bulldozers but his 1944 cost prepares it for removal from the pipe. This is figures cannot be used without updating. done by chopping the core with the drill bit Possibly the greatest advantage to be gained which is repeatedly raised and dropped by in prospecting placers by means o f bulldozer means o f a walking beam or crank acting on trenches, where applicable, is that they the drill line. Water is added during the permit first-hand inspection o f the ground. drilling operation and when the material is This makes it possible to visually determine reduced to a size that will permit pumping, the character and size o f gravel to be dealt the resultant sludge is removed from the hole with and, in addition, the pay or barren with a special vacuum-type sand pump. The sections can sometimes be found by simple cuttings are transferred to a measuring inspection and panning o f the trench walls. bucket which serves as a check to indicate if Another feature is that a considerable area of excess core is being removed or if extraneous bedrock can be exposed for inspection or material is running into the pipe. testing as compared to pits or drill holes. In The cuttings are washed in a rocker and the many cases, even where the ground is more rocker concentrate further reduced by than 10 feet deep, the results obtained from panning. The panner counts the gold colors a few days of trenching with a bulldozer will recovered from each drive, estimates their provide the information needed to decide weight and enters this information in the whether or not a more extensive (and drill log. Examples o f placer drill logs will he expensive) sampling program is warranted. found in Appendix D. f. Sampling with churn drills: Drilling is usually The driving, drilling and pumping steps are resorted to in deep or wet ground where successively repeated for each drive (usually sampling by means o f pits, trenches or shafts 1 foot at a time) until the hole is completed. 32 is not practical. Many western gold placers, The engineer in charge then weighs the whom the reader is referred. From these it combined gold and calculates the value o f But in practice a perfect core is rare and*, is that if a placer drill sample is to be will be seen that placer drilling requires the hole. find the measured core rise and the voli® meaningful it must take into account the specially trained personnel and that As a final step, the drive pipe is recovered by o f material recovered from each drive to b> amount o f material actually obtained from “ correcting” the drill results is a specialty pulling. The drill is then moved to the next greater or less than their theoretical amount the sample point in question. Stated simply, that is not within the experience range o f h ole. When drilling gold placers, any deviatioj if a drillhole increment contains too much most mining engineers. For this reason, any from the norm is important because whei core its value will have to be downgraded. If An illustrated, step-by-step description o f the placer valuation based on drilling should be basing value calculations on small-diametn it contains too little core its indicated value placer drilling process will be found in viewed critically until the qualifications of holes, any deviation between the theoretic may be upgraded. Most placer engineers base Appendix D, to which the reader is referred. the engineer in charge have been established. sample size and the actual sample sin their adjusting procedures on either the ratio The basic equipment is illustrated by Figure This is particularly true where the original becomes critical. For this reason, any exces between theoretical and actual core rise, or 7. drill logs are not available for inspection, or or deficiency of core should be taken into theoretical and measured core volume. As the pipe is driven downward it will, in where drilling cannot be compared against consideration during the calculation Depending on which is used, the basic theory, cut a cylinder o f gravel having an past production from the particular deposit procedure and suitable corrections applied formula would be: area equal to that o f the drive shoe and a or area. length equal to the drive. A short length o f Erratic drill cores are caused by a variety of Something should be said about the so-called core left in the bottom o f the pipe to serve as things. A rock partially blocking the drive “Radford” factor which, when used, corrected gold weight a plug will, also in theory, prevent run-ins o f shoe may move downward with the pipe and applies an arbitrary plus correction to the extraneous material when pumping. force material beneath it to one side. The drill hole calculation. Early placer drillers theoretical core rise^ estimatedi weighl Assuming ideal conditions and a perfect core, resu lt w ou ld be a deficient core. A soon became aware that their actual core actual core rise the value o f the hole (or the sample normal-length drive in tight ground often recoveries were something different than the increment) would be determined by use of gives less core than it should. This is caused theoretical amounts and it was reasoned that the following equation: by material packing in the pipe and as it because o f progressive rounding o f the corrected gold weight cents per cubic yard = ^ x ^ x ~ ‘ becomes more difficult for the core to enter, cutting edge, a 7 1/ 2-inch drive shoe will in A x D some will be pushed aside. The experienced normal use cut something less than 0.3068 theoretical core volume^ weighl driller sometimes prevents this by drilling] sq. ft. o f material. Mr. Radford, on the basis 1'C^1 W = weight o f gold in milligrams. actual core volume short distance ahead o f the shoe. He should V = value o f gold in cents per milligram. of his experience and observations, not, however, “ drill ahead” without A = effective area o f drive shoe in sq. ft. concluded that the sample taken in by a permission o f the engineer in charge because D = length o f sample in ft. In general practice both core rise and volume 75'2-inch shoe driven 1 fo o t will, on an there are cases where drilling below the shoe 27 = cubic feet in a cubic yard. corrections will be considered, but the most average, be 0.27 cu. ft., or as more creates more problems than it solves. conservative correction will be used. commonly stated, 1/100 of a cubic yard per To illustrate the above equation, assume a When a drive is made through tailings or Experience has shown that adding large plus fo o t o f drive. This figure was widely 32-foot hole drilled with a standard 6-inch through loose, rocky ground, the initial core corrections at their full value is likely to accepted by the early drillers. drive pipe and 7 1/2-inch (outside diameter) rise may be normal but subsequent pounding result in an overestimate and for this reason drive shoe with an effective area of 0.3068 The Radford factor is applied by substituting by the drill bit tends to push the core some engineers limit any “ corrected” figure sq. ft. Also assume a recovered gold weight 0.27 for “ A ” in the basic equation where material back down the pipe and out of the to an amount not more than double the o f 50 milligrams. As a matter o f convenience cents per cu. yd. hole. As a result, the pump may get little or initial uncorrected figure. They will, the gold will be considered 887-fine, which is W x V x 27 no core recovery. In loose, wet ground there however, apply the full amounts o f all minus equivalent to l/ 10c per milligram. A x D is always danger of overpumping, that is. corrections, this being considered a form of Substituting we would have: pulling excess material in from under the safety factor. Actually, in the case o f gold Using our earlier example this equation would become: cents per cubic yard = 50 x 0,1 x 27 drive shoe. In “ running” ground the driller placers, there are no universal rules for 50 x 0.1 x 27 0.3068 x 32 should keep the drive pipe full o f water to interpreting or “ correcting” the samples cents per cubic yard = q 07 x 30 offset outside ground water pressure (which obtained from churn drilling. Validity o f the cents per cubic yard = 13.7 cents per cubic yard = 15.6 tends to push loose material into the pipe) end result will depend largely on insight and It should be emphasized that drill hole values but in spite of such precaution, excess cores the experience o f the engineer in charge. drive shoe area o f 0.3068 sq. ft. for “ A ” gave calculated in this manner would be correct can be expected. Many o f the details to be considered when a value o f 13.7 cents. Substituting 0.27 gave only if all drives were perfect, that is, if the Ideally, a 1-foot drive should produce a logging placer drill holes and processing the a value o f 15.6 cents. It is seen that use o f effective area o f the drive shoe were exactly 1.7-foot core rise; this 0.7-foot increase data have been given by Harding (1952, pp. the Radford factor increased the calculated 0.3068 sq. ft., and if the correct length o f reflecting the difference in diameters 96-98) and Daily (1962, pp. 80-88), to value by 12 percent. core had entered the pipe with each drive. In between a 6-inch drive pipe and its Th In some cases other factors were applied to the preceding example, the 50 milligrams of inch shoe. But in practice we rarely get decrease rather than to increase the gold would have been obtained from a the theoretical amount o f core. Instead, we 1/ In practice the corrections are usually applied to the estimated gold weight for each drive. The individual cylinder o f gravel exactly 7 1/2 inches in get too much or too little for a given drive. corrections are carried forward for use when calculating 1/ Also known as the Keystone Constant. 35 34 diameter by 32 feet long. Now, the most important thing to remember an end value for the completed hole. calculated value. Usually, the Radford or he provides the information needed by the other factor was applied to the entire hole, engineer for “correcting” the indicated that is, they were not applied on a values. The panner who should have some drive-by-drive basis. It should be obvious that technical as well as practical training, often the use o f any arbitrary correction factor is serves as the crew foreman. hazardous because ground character will vary As a rule, when prospecting narrow, in different properties and for that matter in stream-type deposits the holes are drilled at different parts o f a single drill hole. relatively close intervals along lines laid out Today, considerable difference of opinion at right angles to the general trend o f the exists concerning the validity or use o f the deposit as shown in Figure 11. Hole spacing Radford factor. It has been mentioned here along the line is commonly 100 feet or less, to alert readers who may not be familiar with while the distance between drill lines is placer drilling that many o f the placer greater, often on the order o f 500 feet or valuations found in reports, particularly in m ore. This type o f drilling pattern is old reports, have been based on calculations designed to search out and delineate employing the Radford or other arbitrary relatively narrow pay channels. upgrading factors. In widespread placers, particularly those In arctic regions, permanently frozen ground having a som ew h a t u n ifo rm mineral is drilled without casing with exception o f a distribution, holes are usually put down at short length at the surface to serve as a collar the intersections o f a rectangular grid pattern and tool guide. Sample volumes are designed to cover the deposit as shown in determined by measuring the displacement Figure 12. The drilling ratio will vary from of known quantities of water poured into the one hole for every acre to one hole for every hole. Arctic drilling and the special procedures 2, 3 or possibly 10 acres, depending on the em ployed have been well described by distribution o f mineral, previous experience Doheny (1941, pp. 47-49). in similar ground and other factors. In the Most placer-type churn drills used in the Folsom, California dredge field the average FIGURE 8. — Truck-mounted Keysto ne Model 70 place FIGURE 9. - Hillman 4-inch Airplane drill. This compact, hole density was about 1 hole for every 4 U nited States are powered by gasoline drill skid-mounted machine is widely used for reconnaissance- engines and designed for use with 6-inch type prospecting. acres. On the other hand, there are placers drive pipe and tools. Typical arrangements Hand-powered drills are widely used ii are illustrated by Figures 8 and 9. Drills in foreign fields and regions where access i common use are the Keystone Model 70 1/, a difficult and labor cheap. The Banka « truck-mounted unit for use with 6-inch pipe; Empire dri]l employs a rotating casin' equipped with a serrated cutting shoe. Tl* the Keystone Model 71, a 6-inch traction Ward 4/ hand-powered drill employs 4 a drill mounted on a crawler base, the BE 5-inch drive pipe and standard tools. 22-T 2/ a crawler-mounted 6-inch drill; the Hillman Prospector 3/, a 6-inch truck or A drill crew usually consists o f the drilkt cra w ler-m ou n ted rig and the Hillman who is responsible for operation of the drill Airplane Drill, a compact, skid-mounted a helper to assist with general work ami machine designed for use with 4 or 5-inch handling the tools and a panner who musl drive pipe. A crawler-type traction drill process the samples and keep an accurate Iffi complete with 40 lengths (about 240 ft.) of o f the hole as it progresses. A typical place drive pipe and the necessary tools will weigh drilling set-up is shown in Figure 10. 1 10 to 15 tons. fourth man may be required where water must be hauled or drill sites prepared. Ai experienced driller has become so accustomed to the sound o f drilling and the 1/ Now called “ Speedstar” ; manufactured by Buffalo- feel o f the drill line, he can usually tell just Springficld Co., Enid, Oklahoma (successor to Keystone what is happening in the hole. By keeping Driller Co.). careful watch and logging all pertinent dal), 2/ Manufactured by Bucyrus-Erie Co., South Milwaukee, Wisconsin. 3/ Manufactured by C. Kirk Hillman Company, Seattle, 4/ Available from New York Engineering Co., New York Washington. New York. FIGURE 10. - A typical placer drilling set-up. Note rocker for washing samples. 37 o o o o o o o o o o o o ro IT) CO o- O' O' o

FIGURE 12. - An example o f holes drilled on a rectangular grid to sample a heavy-mineral deposit. In this case, holes are on the corners o f 400-foot squares that com pose the drilling grid. (From USBM I.C. 8197)

and the average value o f a deposit which has Where Va = average value o f block or been drilled on a grid pattern, the drill holes triangle expressed in are first connected by imaginary lines to cents/ cubic yard, divide the deposit into blocks or triangles. d = depth o f each bounding The volume and value o f each triangle or hole in feet. block is then calculated using weighted drill V = prospect value o f each hole h ole values and standard ore reserve in cents/cubic yard. calculation procedures. The procedural details will not be set out here as they are A value for the deposit is subsequently well known to most field engineers and have arrived at by combining the individual been adequately covered in the technical triangles as shown in Figure 13. literature. Daily (1962, pp. 86, 87) and For the valuation of narrow, stream-type which cannot be adequately sampled by any either the higher or the lower-grade areas, Doheny (1942, Part II, pp. 43,44) have deposits where the holes are drilled at close amount ol drilling. | |le selection o f a drilling pattern and the described the applications to placers. In intervals, say 50 or 100 feet apart on relatively far-spaced drill lines, a calculation Although a regular drilling pattern may be initial placement o f holes is normally a principle, the value o f each block or triangle based on the mean-area formula is usually preferred, there are situations in which an responsibility o f the engineer in charge, is calculated by the following formula: employed. This relies on a formula used for irregular drill pattern should be employed. In Assuming a completed drilling project with Va = Sum of products (d x V) making cut and fill estimates in road work in any case, it is important to avoid placing the favorable results, the next step is to make an Sum of depths (d) which it is inferred that the volume o f a 39 holes in a way that would tend to exaggerate overall evaluation. To calculate the yardage Step 1-GRAPHIC DISPLAY OF PROSPECT DATA Step 1-GRAPHIC DISPLAY OF PROSPECT DATA Step 2—DETERMINE SEGMENT AREAS AREA DRILL BOUNDING DEPTH AVER. WIDTH AREA SEGMENT SQ. YDS. LINE HOLES FT. DEPTH FT. SQ. FT.

Step 3-VALUE CALCULATION C-l 40 50 90 4,500 500 bl C-2 60 C-2 60 55 100 5,500 611 TOTAL VOLUME = 2,012,305 cubic yards2/ s 2 C-3 50 C-3 50 45 100 4,500 500 GROSS VALUE = $684,0652/ a C-4 40 C-4 40 35 120 4,200 466 =4 C-5 30 AVERAGE VALUE = x 100 2 ,0 1 2 ,3 U 5 D-l 30 40 100 4,000 444 ^5 D-2 50 = 34.0c per cubic yard D-2 50 45 100 4,500 500 h6 D-3 40 2/ From Step 2. D-3 40 30 75 2,250 250 h7 D-4 20

Scale in feel

Step 2—DETERMINE VOLUME AND VALUE FOR EACH TRIANGLE A DEPTH HOLE VALUE AVER. WEIGHTED AREA 1/ VOLUME NO. FT. D x V VAL. $ c DEPTH VAL. c SQ. YDS. CU. YDS. B-4 40 33.4 1336 B-5 40 20.5 820 A-5 30 25.2 756 36.6 26.52 20,500 250,100 66,326 110 2912 Step 3 - DETERMINE WEIGHTED VALUES C-4 22 37.2 818 B-4 40 33.4 1336 WEIGHTED 2 34.0 DRILL DEPTH VALUE D x V SQ. YDS.1/ A x V B-5 40 20.5 820 29.16 17,700 200,010 58,323 SEGMENT HOLE VALUE LINE FT. 102 2974 C-l 40 9c 360 500 6,300 C-4 22 37.2 818 c C-2 60 15c 900 12.6c S1 Step 4-BLOCK VOLUME AND VALUE B-5 40 20.5 820 1260 3 qh 100 D-5 28.4 o5z 30.7 27 06 90 ^00 u6,o82 C-2 60 15c 900 11,365 92 2490 C-3 50 23c 1150 18.6c 611 C s2 Area of line C ♦ B-4 40 33.4 1336 BLOCK VOLUME = area x distance between lines A-3 40 41.8 1672 C-3 50 23c 1150 4 500 10,800 A-5 30 25.2 756 36.6 34.24 30,100 367,220 125,736 C-4 40 20c 800 21.6c C S3 n o 3764 90 1950 = 2'077 ??• r^8-* 1’ 194 8

40 41 FIGURE 13. Use o f the “ triangle” method for calculating prospect values where deposits are drilled on a grid pattern. FIGURE 14. - Use o f the “ mean area” method for calculating prospect values in narrow, stream-type deposits. prism having somewhat similar end sections many things in placer valuation which ret can be expressed by the equation: scarcity o f qualified placer drillers and represent the deposit as a whole, because heavily on experience-based judgement. Volume = A j + A 2 x L panners, drill crews are hard to find and, as a high costs usually limit this type o f testing to In a like manner, shafts sunk over drill hold result, they can demand and usually receive a few points. 2 should be expected to show appreciaU, premium wages. Other expenses include the One school o f thought gives great importance variations in value when compared with thei purchase or rental o f a drill rig, tools and to the supposed superior accuracy of bulk Where A j = the cross sectional area o f respective drill holes. This is particularly tna supplemental equipment such as flatbed and samples as compared to smaller samples such one end of the block. in loose formations or in old tailings when pickup trucks, transportation to the job, as those provided by churn drills or channel A2 = the cross sectional area o f drilling conditions may be far from ided supervision, engineering, insurance, fuel, cuts. While bulk sampling per se is a valid the opposite end. Check shafts put down over drill holes da supplies and incidental labor. Today, in the method and bulk samples do, in many cases, L = distance between ends. however, allow inspection of the gravel a United States the minimum direct cost for offer the most satisfactory method o f testing place thus providing the examining engines Applied to placer valuation, the average operating a standard 6-inch placer churn drill erratic, high-value ground, they are at the with a wealth of information not available prospect value o f the two end sections o f a on a one-shift basis will be about $125 per same time open to certain criticism. For from drilling alone which in turn results ini gravel block is calculated and this value day, based on rental o f the drill rig and tools example, bulk samples must be more accurate evaluation o f the deposit. applied to the block volume derived from the at $50 per day and other expenses. Applying representative o f the deposit, a feat not foregoing equation. T he average rate and c o s t o f placet the average figure o f 10 feet per calendar day easily achieved where they are few in drilling are topics which have received little When computing the average prospect value over the life o f a project, a minimum cost of number. Another important consideration is attention in the technical press, none 0! of each end section it will, of course, be $12.50 per foot o f drilling is indicated but the fact that all facets o f a bulk sampling which is recent. This largely reflects 1 necessary to consider the area o f influence when incidental expenses are considered, the program cannot have personal supervision all tendency for operating companies to keep exerted by each drill hole. At the risk o f overall drilling cost may be nearer $15 per o f the time and, for this reason, salting can their prospecting data confidential plus the oversimplification, a commonly used foot. A company operation utilizing be perpetrated with comparative ease. It is difficulty in identifying hole-by-holt procedure can be described as follows: permanent personnel or a contractor working important that all such possibilities be performance and cost data among general for an extended period of time could quite considered during the evaluation of bulk C o n sid e r an elongated block o f gravel operating records. bounded on its two ends by drill lines possibly lower costs but the point being sampling results or when considering any Drilling rates when figured on a day-to-day containing relatively close-spaced holes. The made here is that placer drilling today, if actions based on this type o f sampling. cross-sectional area between each pair o f or a hole-to-hole basis will be found to vary properly done, is expensive. If improperly Bulk samples are sometimes used to check holes is found by multiplying their average widely. The variations reflect many factors done it is worse than useless, as shown by the reliability o f other types. In placer d ep th b y th e distance between them. including moving and set-up time, actual too many cases where inadequate drilling drilling, for example, shafts may be put drilling, stuck or lost tools, breakdowns, pipe M u ltiplyin g this area by the weighted that was intended to save money led to the down over selected drill holes to establish a pulling, etc. T o be meaningful, any average prospect value of the two bounding holes equipping o f sub-economic deposits with correction or “ shaft” factor which when figure must take all such contingencies into gives an area x value figure. This procedure is resultant loss o f large capital investments. combined with experience-based judgement account, but few do. For those who must repeated for each pair o f holes across the line Speaking generally, the chum drill today is can be used as a basis for adjusting the make preliminary estimates, a good and the same is done at the opposite end o f too expensive for casual or indiscriminate use calculated drill values as a whole, experience-based figure to use is feet per the gravel block. T o find the average value o f 10 as a placer sampling tool but it still offers the h. Grab samples: One thing to avoid or to use calendar-day over the life of a drilling the two drill lines, divide the sum o f area x on ly feasible means for sampling some with caution when investigating placers is the project. This may appear conservative but it value products (from both lines) by the sum placers. so-called grab sample. This method o f also reflects an actual average daily ^ o f th e individual areas. The resultant g. Bulk samples: Bulk samples may be called sampling relies on a theory that if enough footage obtained under a variety of drilling weighted prospect value for the combined for when dealing with placers having an small “ grabs” or portions o f material are conditions in the United States, Canada and ends is then applied to the entire volume South America. erratic distribution o f values, especially impartially taken and then combined into a between the drill lines to arrive at a dollar where the pay is found as coarse gold or single sample, the combined material will be A word o f caution. Where placer drilling is value for the gravel block. The procedure is nuggets. Depending on conditions, samples representative o f the deposit or o f the illustrated by Figure 14. contracted and the contractor’s payment is containing a portion of a cubic yard, or as exposure, as the case may be. But in practice based on footage drilled, there may be a When drilling a gold placer, two holes put much as tens or hundreds o f cubic yards may the average person fails to make allowance tendency to sacrifice accuracy for speed. down in close proximity will rarely check be needed for a reliable estimate o f value. for the large rock or boulders normally Under such conditions the engineer in charge found in bank-run material and, as a result, and, in fact, the divergence in value will The so-called “plant rim” is a form of must be constantly alert and he should insist th eir grab samples contain a deceptive probably be too great to be reconciled by the large-volume bulk sample in which a portion layman. This problem is not necessarily a on having full authority over all aspects of proportion o f fines. Such oversight can cause the work. o f the deposit is mined and processed under serious error in the estimated value, reflection on the drilling itself but, instead, actual working conditions. A pilot plant The cost of placer drilling where no unusual particularly when based on a few pans o f reflects the small sample area encompassed employing full-scale processing and recovery p ro b le m s are encountered will directly by a 7 1/2-inch drive shoe and the typically equipment is sometimes used. But when material. reflect the cost o f labor. Because o f the irregular distribution o f gold in placers. relying on plant runs, good judgement must Every mineral examiner will at one time or 42 Interpreting “ check” holes is another of the another run into a situation where systematic 1/ One 8-hour shift per day. be used to insure that the points or areas selected for large-scale sampling actually sampling is not practicable or is not called 43 A small hydraulic mine on Fox Creek, for. For example, a property may have no Typical drift mines are not amenable form a pretty good idea whether the gravel is Alaska, was prospected and simultaneously discernible mineralization or mineral-bearing sam pling with churn drills and this i, likely to pay for working; but this is not by worked in the following manner: The structure, or the mineral examiner may for particularly true where the values art any means the same as ascertaining the exact deposit, consisting o f low bench gravels other reasons be sure that no significant confined to sinuous, deeply buried pai amount o f gold which it contains.” flanking a small creek, was superficially values exist. Here, a few check samples can streaks. In deep ground the cost ol A s indicated above many o f the early tested by panning and its 15 to 20-foot serve as “ written proof” and as such carry7 far close-interval drilling can be expected to hydraulic operators relied more on qualified depth was determined by use o f 3-inch, more weight than a bald statement of fact. outweigh its benefits. Drilling can, however, estimates o f value than on a formal sampling hand-driven drive pipes. Several hand-dug Grab samples, if fairly taken, serve this be o f great value in guiding an underground program. Such estimates were based largely pits and shafts were put down in the more purpose well. Grab samples can sometimes be exploration program when dealing with this on the production records or estimated gold promising areas and those returning the best used to check the presence or the type o f placer. A relatively few well-placed yield o f nearby or similar properties but, in prospects were expanded into ground sluice distribution o f gold in a gravel exposure and drill holes may indicate the course o f the par most cases, the question o f actual gold value cuts. Pay areas exposed by ground sluicing thus used as a guide for subsequent sampling channel, depth and character o f the gravel, was (and remains) secondary to such factors were, in turn, expanded into pits and worked and, judiciously used, they provide an grade of bedrock, etc. This type ol as the area o f minable ground, its character, excellent check against salting. out by hydraulicking. Once a pit was started, inform ation is essential to a successful width and course o f the deposit, the depth the hydraulic mining proceeded from Other uses for grab samples could be cited development program where drain tunnel; and slope o f bedrock, facilities for washing, clean-up to clean-up without further but the novice will be better served by and haulage levels are to be kept below the dump room, water supply, cost of water, etc. sampling. When the ground stopped paying, stressing the fact that in nonexpert hands lo w e st point o f the pay channel. An It is obvious that some factors cannot be the pit was expanded in another direction or they are almost sure to be misleading. With application of this type of churn drilling at readily appraised without some underground abandoned. In other words, this was a few exceptions, grab sampling cannot be the Vallecito Western drift mine has been exploration. Such work, where provided, is considered a valid method for testing placers. described by Steffa (1932, pp. 4-6). usually in the form o f a few shafts and some hand-to-mouth operation (as are many small placer mining ventures) and it illustrates the When evaluating drift mines, prospect data drifting or small-scale operations. Churn type and extent o f sampling or testing Drift mine sampling: Underground mining are usually meager and the mineral examiner drilling may be employed to a limited extent g en era lly relied on for working small procedures are collectively known as “ drift should take into account the fact that drift to investigate the course o f the channel or hydraulic mines. mining” where applied to placer gravels. mining, by its very nature, is typically a bedrock contours. Some examples follow: P lacers bu ried under deep masses o f In most cases the initial prospect work has high-risk venture. He should also recognize The initial sampling and exploratory work at been engulfed or otherwise eradicated by low-value gravel or capped by lava flows that sampling, in the usual sense, may not be the Malakoff mine (one o f California’s largest subsequent mining and, today in most have been extensively worked in this manner. practicable. hydraulic operations) consisted essentially of hydraulic areas, there remains little to see Drift mining presupposes the concentration four shafts and 2,000 feet of drifting along but abandoned pits and their sloughed faces. o f values in a well defined stratum or j. Hydraulic mine sampling: Determining the the channel, which, according to Bowie W hat d o e s th is mean to the mineral channel. Pay streaks in these channels are mineral value o f large deposits o f the type (1885, p. 88), cost a total of $63,956.20. It typically confined within narrow limits, both examiner? It means that in the absence of worked by hydraulic mining is perhaps the should be noted that at the time (circa laterally and vertically, and are commonly prospecting shafts or other openings in the most difficult task faced by today’s mineral 1880), the expenditure o f this great a sum related to troughs or other depressions in the unworked gravels, it is necessary to use what examiner. A typical large hydraulic deposit for prospecting and sampling was considered past records are available and a large measure bedrock. But it is not unusual to find several presents most o f the sampling problems somewhat remarkable. generations o f “ pay leads” , as the miners call o f common sense in making an evaluation. encountered in drift mines plus a few of its According to Eassie (1944, p. 93), the initial them, within a given deposit where several own. Anyone familiar with the immense prospecting and sampling for a medium-size 4. SPECIAL PROBLEMS periods o f erosion and deposition have masses o f Tertiary gravels that have been hydraulic property (150-foot banks) in a. Large rock or boulders: A t this point superimposed successive channels over one partially worked in California’s Sierra Nevada British Columbia was done hydraulically, something should be said about large rocks another. Such complications are usually region need not be told that detailed with exception o f a small amount o f churn quite difficult to decipher and speaking or boulders—nemesis o f the placer sampler. sampling o f such deposits ahead o f mining drilling undertaken to determine the course generally, drift-mine deposits seldom lend When sampling placers there is a natural would be too costly for practical application. o f the channels. In all, six exploratory pits th em selves t o th e usual investigative tendency to bypass areas of heavy boulders The California hydraulic miner was no were opened but only one supported a procedures. or, at least, to take the finer material from stranger to mining risks and, for the most continuing operation. These deposits are usually explored by adits among them without considering the end part, he concurred with Whitney (1880, p. Existing faces in old hydraulic pits can, in or shafts from which drifts are driven into effect on indicated values. In many cases the 3 6 9 ), who in assessing hydraulic mine some cases, be sampled by conventional the richer portion o f the gravels. Crosscuts effect is the same as salting the sample, a fact sampling said: “ . . . the amount o f gold in means. At the McGeachin mine in Placer are run from the main drifts to establish the which does not seem to be recognized by the gravel cannot be accurately determined County, California, old hydraulic banks outer pay limits and at the same time to some mineral examiners. by assay or any other proper method. All roughly 50 feet in height were sampled by block the ground for mining. In the usual Consider that the gold particles or other that can be positively known is the amount means o f vertical hand-dug cuts 2 feet wide drift mining venture, exploration, sampling, valuable minerals in placers are found among obtained in the clean-up.” Whitney went on by 1 foot deep. The sampling crew worked development and mining are o f necessity the finer-size material while on the other to say: “The miner, by panning a sufficient from long ladders propped against the gravel integral parts o f an overall package. hand, the large rocks or boulders contain no 45 number o f samples, judiciously selected, can faces. by an experienced dredging company using a recoverable values within themselves. For estimated boulder content. In other words handling erratic high values should be Keystone placer drill and qualified crew. this reason, when the sampler takes too 13.3 cents minus 10 percent equals 12 cents govern ed by conditions found in the much fine material or fails to make an per cubic yard, bank-run value. particular deposit being investigated. The mineral examiner should always view allowance for valueless boulders, he is likely Needless to say, no method o f discounting The sample notes and subsequent data sheets critically any placer evaluation based on gold to report an incorrect, high value. To put it high values should be adopted until the values obtained from uncased or small-diameter must, of course, clearly show all such another way, where all bank-run material reason for their occurrence is understood. drill holes. Figure 15 shows why, in the case o f adjustments and they should preferably show including boulders will be handled in a small-diameter holes, the indicated values are not both the uncorrected and corrected figures. mining operation, the prospecting should 5. UNCASED OR SMALL-DIAMETER DRILL always reliable. Before leaving this topic it will be pointed reflect this fact by including a proportionate HOLES While some gold dredging companies occasionally out that while the foregoing correction amount o f large material in the samples. Various attempts to sample gold placers by use o f e m p lo y 4-inch churn drills for preliminary procedure is generally reliable, there are A direct approach to sampling the type o f uncased or small-diameter drill holes have for the prospecting, the 6-inch size equipped with a placers having boulder problems so severe, ground under consideration would be to cut most part generated more problems than they 7}4-inch diameter drive shoe is considered they cannot be effectively sampled by any samples large enough to include the fair have solved. As noted earlier, the volumetric means short o f mining the entire deposit, standard. proportion o f large-size rock and thus obtain gold-to-gravel ratio in 15-cent ground is about b. Erratic high values: The usual methods for Under certain conditions, small-diameter drill samples which truly represent the mine-run one to a hundred million (1:100,000,000). This calculating the value o f placer ground rely on holes may be both practical and adequate. As an material, boulders and all. But where the tells us that calculated drill hole values are an assumption that the value found in a example, when evaluating beach-type deposits mineral examiner must work alone or where extremely sensitive to stray gold particles or particular sample extends halfway to the valuable for their chrome or titanium-bearing a limit is placed on the size o f his samples incorrect sample volumes. The effect o f one gold next sample. In effect, this assumes that the minerals it is often possible to rely on through the use o f hand tools or for other particle too many or one particle too few is mineral content changes at a uniform rate small-diameter (say 2-inch) holes for sampling. reasons, the taking o f very large samples may shown in Table II. . betw een sample points. While valuation Here the fine-grained nature o f the deposit, the not be practicable. In such cases, he must It can be seen that any sloughing o f an uncased procedures based on this concept work well relatively large proportion o f valuable mineral settle for something less than optimum size, drill hole, should it occur in a gold-bearing zone, for ground having a general low or uniform and its low unit value combine to eliminate some but he can guard against possible error in his will tend to upgrade the calculated value by average, the finding o f erratic high-value o f the uncertainties normally associated with end valuation by first carefully evaluating the significant amounts. If one knew with certainty samples can create problems. In practice it small-diameter drill holes. As another example, problem and, second, adjusting his calculated how much excess material entered a sample and has been found that to include them at full sample values (if necessary) to correspond exactly where it came from, the discrepancies value will often result in an over-valuation of with those which might be obtained from a might be appraised and allowances made during the lands involved. There are several ways to suitably large-size sample. the calculation process. But experience tells us approach this problem: In practice this can often be achieved by that this is not always practicable and that when First, the sections in which they occur visually estimating the boulder content o f a dealing with the usual gold placer, uncased drill should preferably be resampled. If the piece o f ground and, where needed, inserting holes just do not give reliable results. More often resulting value is low, it is safer to use the a correction factor in the end sample than not the ground will be over-valued and this low' figure and this is sometimes done. Where calculations. seems to be particularly true when rotary drills the two results are about the same, most are employed, especially those using roller-type Consider a case where it was estimated that engineers will use the average. 10 percent o f the bank-run material was too bits. In one case, placer ground reported to run Another commonly used method for large to be represented by material taken 26 cents per cubic yard on the basis o f samples adjusting erratic high values is to decide what from a 3” x 6 ” x 4 ’ channel cut. The 55.9 obtained from rotary' drill holes was found to the highest value reasonably expected from pounds o f material removed from this cut contain 1 1 /4 cents per cubic yard when checked the particular ground might be. This is contained 2.70 milligrams o f gold. The estimated after considering the type of indicated value based on these weights was deposit being dealt with, the overall sample 13.3 cents per cubic yard. TABLE II. — Error in calculated value cased by one gold results and in particular the neighboring particle too many or one particle too few , in a 1-foot Now, to include a proportionate amount of samples. This might be called the “ normal” drive. Values shown are based on gold weights determined boulder material this particular sample would high value expected in a given property or by the author, and gold at $35 per ounce. have to be 10 percent heavier. In other locality. The erratic “ too-high” value is then words, it would weigh 55.9 pounds plus 10 downgraded to match this figure. percent, or a total o f 61.5 pounds. Using this Diameter SIZE OF GOLD PARTICLE But where it is reasonable to believe that the new weight and the same 2.70 milligrams of of ‘ Gold @ $35.00/oz. property as a whole is made valuable by Drill Hole 20-Mesh 40-Mesh 60-Mesh gold, the calculated bank-run value becomes occurrence o f erratic, high-value areas, it may (6.57 mg.) (0.91 mg.) (0.27 mg.) 12 cents per cubic yard. FIGURE 15.— Curve showing change in calculated value be proper to use all sample results at their T / i" 58c /cu.yd. 8c /cu.yd. 2Yic 1 cu.yd. caused by plus or minus I milligram o f gold in a 1-foot In practice the same end figure can be full value. 5/4" $1.18 ” 16c / « 5c ” sample. It can be seen that accidental loss or addition o f a obtained by simply reducing the uncorrected 3” $3.60 ” 50c / >> 14c ” single gold particle can cause serious error when dealing There are, of course, other approaches to the 47 value by a percentage factor equal to the with small-diameter drill holes. problem but in any event the method for consider a tin placer containing 1/10 lb. Clean and carefully inspect all equipment cassiterite per cubic yard. With tin at $1.50 per WHEN SAMPLING FAILS and when this happens, it is important that the before sampling. pound, the indicated value would be 11.6 cents Not all placers lend themselves to the usual forms fact be recognized. Check equipment at appropriate intervals. per cubic yard and the volumetric ratio of of sampling and there are some which cannot be Complete the cutting and processing during) cassiterite to gravel 1:114,000. In other words, sampled by any means short o f mining the entire single work-day if possible. the volume o f valuable mineral in this case would deposit. This problem usually reflects one o f two REFERENCES CITED (PART III) When sampling is completed, go back and be approximately 1,000 times greater than the things: (1) The gold or other mineral occurrence take a few check samples from selected volume of gold in a comparable gold-placer and is so erratic that usual sampling or evaluation Bowie, A.J., 1885, A practical treatise on hydraulic points, particularly those showing unusually this illustrates why low-value placer minerals are, methods break down hopelessly. (2) There are mining in California: D. Van Norstrand Co., New high values. in general, easier to sample. physical co n d itio n s which make sampling York. Some placer drillers place barren material in the 6. SALTING impracticable. Daily, Arthur, 1962, Valuation of large gold-bearing bottom o f the drill hole at the end o f the shift Excellent examples o f the latter condition can be There are two kinds o f salting—intentional and placers: and test it for values when resuming operations. found in California’s drift mines. Sampling innocent. Intentional salting can be defined as Engineering and Mining Journal Vol. 163, No. 7, The black sand concentrate obtained from a problems inherent in this type o f deposit have the surreptitious addition o f valuable material to July, 1962, pp. 80-88. sample should be examined with a hand lens ot, already been brought out under the heading o f a sample with intent to deceive. Innocent salting, preferably, with a low-power microscope because “ Drift Mine Sampling” but the point to be made Doheny, L. C., 1941, Placer valuation in Alaska, which can have the same end effect, can be at this point the careful observer can usually here is that the physical characteristics o f such Part I. accidental or the result o f carelessness or Engineering and Mining Journal, Vol. 142, No. detect any anomolous or foreign material in the deposits when combined with an almost improper working procedures. Although 12, Dec., 1941, pp. 47-49. sample. Figure 16 is a photomicrograph showing complete absence o f surface guides to their intentional salting is seldom encountered, only gold shavings found in a placer sample. In this underground location makes sampling in the Doheny, L. C., 1942, Placer valuation in Alaska, Parts the engineer who is constantly alert can feel case, the shavings were small enough to be missed normal sense impracticable. Historically, the II and III: secure about his sample results. A few o f the in a cursory inspection of the pan concentrate successful exploration and development o f this Engineering and Mining Journal Vol. 143, No. 1, salting methods applicable to placers are: but examination under a 20X binocular type o f deposit has relied on the practical Jan., 1942, pp. 43, 44 and Vol. 143, No. 3, Secreting gold in the material to be sampled. microscope revealed the fraud. application o f bits and pieces o f information March, 1942, pp. 48, 49. Placing gold in sample containers or in the Another give-away may be sample results that are gleaned from limited surface exposures or Draper. Marshall D., 1932, Placer ground sampled by sample itself. consistently too high or too regular in value. The underground workings. This is another way of well-digging equipment: Engineering and Mining Secreting gold in the excavating or washing mineral examiner should always compare his saying the old-time drift miner relied largely on Journal Vol. 133, No. 10, Oct., 1932, p. 537. equipment. sample results with the known or expected tenor geologic inference tempered by good judgement. Eassie, W.H., 1944, What does hydraulicking cost? Dropping bits o f gold in the pan during final of the district and where marked discrepancies Today’s mineral examiner, when confronted by a processing. Engineering and Mining Journal, Vol. 145, No. 6, appear, the cause should be ascertained. deposit that cannot be readily sampled, may also June, 1944, pp. 92-94. Where the volume o f material obtained from a While the possibility o f samples being tampered have to fall back on his powers o f observation drill hole or from a channel cut is comparatively with must never be disregarded, the possibility of and other resources. Harding, James E., 1952, A new way to interpret the small, it takes very little gold to appreciably alter the sam pler “ sa ltin g ” h im se lf through Where factual sample data cannot be obtained results of placer sampling: Engineering and the value. It should be noted that in bulk carelessness or through use o f an incorrect without extensive and costly explorations, which Mining Journal Vol. 153, No. 1, Jan., 1952, pp. sampling a substantial amount o f gold may be procedure is usually much greater. except in isolated cases will probably never be 96-98. required to achieve the desired effect but, at the made, authentic production records will generally Herr, Irving, 1916, Sampling placer-gravel deposits: same time, the opportunity for salting may be be found a useful source o f information. And Engineering and Mining Journal, Vol. 102, No. 6, greater. This is because the larger the sample the even where the actual records are not available, it Aug. 5, 1916, pp. 261, 262. more it is handled, and the more it is handled, may be possible to obtain enough statistical Huttl. John, 1941, Unique portable sampler for the more difficult it becomes to provide adequate information from state mining bureau reports or shallow placers: safeguards or keep it under constant surveillance. other government publications to ascertain the Engineering and Mining Journal Vol. 142, No. 9, Ironically, it may be easier to detect salting after past production o f better-known mining districts Sept., 1941, pp. 55,56. it has happened than to prevent it in the first and to appraise tbeir remaining potential. To place. varying degrees, this type o f statistical data can Jarman, Arthur, 1927, Report o f the Hydraulic But there are many precautions that can be taken be applied to individual properties. Noteworthy Mining Commission upon the feasibility o f the to discourage salting, most o f which require little examples are found in studies o f California’s resumption of hydraulic mining in California (a more than common sense. Some are: hydraulic mine reserves (Jarman, 1927) carried report to the California Legislature o f 1927): Keep the exact location o f the point to be out by state and federal agencies, preparatory to Twenty-third Report o f the State Mineralogist, sampled a secret until the actual cutting construction o f the North Fork and Yuba Jan., 1927, pp. 44-116. begins. FIG URE 16. — Photomicrograph o f gold shavings used to salt Narrows debris retention dams. A lso se e —Jadwin, Edgar, Hydraulic mining Clean and carefully inspect all faces before a placer sample (X 100). This fraud tons detected by micro­ But, the point to be stressed is that sooner or investigations in California (a report o f the War sampling. scopic examination o f black sand concentrates obtained from the sample. later the mineral examiner can expect to Department, Board o f Engineers for Rivers and encounter a placer deposit where sampling fails Harbors, dated April 20, 1928): 49 Senate Doc. No. 90, 70th Cong., 1st Sess. Sawyer. Dwight L., 1932, Sampling a gold place. Also see—Bradley, Walter W., Dams lor hydraulic Engineering and Mining Journal Vol. 133, No ] mining debris: July, 1932, pp. 381-383. Calil. Jour, o f Mines and Geol., Vol. 31, No. 3, July, 1935, pp. 345-367. Steel. Donald, 1915, Prospecting wet placer ground by shaft sinking: Mining and Scientific Press, Vol Lorain, S.H., 1944, Prospect trenching with 110, No. 2, Jan. 9,1915, pp. 66-68. caterpillar-mounted angledozers: U.S. Bureau o f Steffa, Don, 1932, Gold mining and milling costs at Mines Information Circular 7294 (Sept., 1944), 8 the Vallecito Western drift mine, Angles Camp p p . California: U.S. Bureau o f Mines Information Magee, James F., 1937, A successful dragline dredge: Circular 6612 (1932), 14 pp. Amer. Inst, o f Min. and Met. Engr., Trans. Vol Whitney, J.D., 1880, The auriferous gravels of the 126(1937). Sierra Nevada o f California: Contributions to Prommel, H.W.C., 1937, Sampling and testing a American Geology, Vol. 1; Harvard University- gold-scheelite placer deposit in the Mojave Desert, Press, Cambridge, Mass. Kern and San Bernardino Counties, California: Woodbridge, T.R., 1916, Ore-sampling conditions in U.S. Bureau o f Mines Information Circular 6960 the West: U.S. Bureau o f Mines Tech. Paper 86 (1937), 18 p p . (1916). indicate the actual returns to be expected from a 1 g e n e r a l considerations commercial operation. In this connection it is Equipment used for the recovery o f placer gold noteworthy that the pan, rocker, and the sluice has changed very little over the years and, in when used by experienced placer operators fulfill general, remains relatively simple. Most devices this requirement. employ some form o f riffled surface to hold the gold or other heavy mineral after it has been MINERS’ PAN separated from the valueless material. The actual The miners’ pan, better known as a gold pan, is separation relies on the ability o f heavy minerals perhaps the most widely used device for washing to resist the action o f moving water while the small placer samples and from the standpoint of lighter materials are carried away. In dry washers simplicity it has no peer. A separate article where a current o f air is used as the transporting describing its use and manipulation will be found medium, the same principle applies. Although in Part V under the heading of “ PANNING.” In many have tried, no one to date has devised a the hands o f an expert the pan is both a versatile gold-saving d ev ice or system which can and a highly efficient concentrator well suited to economically replace the ordinary riffled sluices washing small amounts o f gravel but where or placer jigs used on today’s dredges or in other individual samples weigh more than about 30 comparable large-scale placer operations. It is pounds, or where a large number are to be true that sluices may lose some o f the fine gold washed, something which provides a greater but this is normally offset by their low operating throughput with less expenditure o f time and cost and their high unit capacity which combine labor is needed. to return the greatest dollar profit. SLUICE BOX When selecting a machine for washing and Another widely used sample washing device is the concentrating placer samples, the first ordinary' sluice box which in its smaller form is consideration should be whether or not it will sometimes loosely but erroneously called a “ long indicate the commercially recoverable gold tom ” . A sluice in its simplest form is no more content o f the sample. Other desirable features than an elongated, rectangular trough fitted with would be: transverse cleats or some other form o f riffled Low first cost. bottom. It is operated by essentially allowing a Easy to maintain or repair in the field. stream o f water to carry the sands and gravel over Easy to transport and set up for operation. the riffles which, in turn, detain any gold or Will a c c e p t bank-run material without heavy minerals as they settle to the bottom . pre-screening. Small sluices o f the type used for sampling are Will thoroughly wash and reject the oversize commonly 8 or 12 inches wide with 6 or 8-inch material. sides and are usually 6 to 12 feet in length. Makes efficient use o f water. Construction details and the materials used are Will efficiently process small as well as large largely a matter o f personal choice, but the samples. simpler ones are no more than an open-ended Will effectively reduce the sample to a trough made o f planed 1-inch lumber and small-volume residue or concentrate. provided with cross bracing where needed. Some Can be quickly and completely cleaned samplers prefer a sluice made o f heavy-gauge between samples. sheet metal (made rigid by bracing) and others Is time-tested and accepted by prefer exterior-grade plywood painted with knowledgeable mine operators or engineers marine varnish or spar. The longer sluices are familiar with placer sampling requirements. usually sectionalized to facilitate transportation. It should again be stressed that no dredge or The primary' function o f a riffle is to retard heavy other large-scale placer equipment saves 100 minerals giving them a chance to settle and, at percent o f the values and because o f this it is the same time, to provide pockets in which the important that the sample washing process values are retained. A well designed and properly 53 working riffle will create eddies along its catchers. Expanded metal riffles do not have a water is seldom reclaimed or reused and, for this amount of gold anticipated by the property downstream edges and the so-called “ boiling” large holding capacity, that is, they may soon fill* reason, the water requirement for a typical owner or vendor, it is sometimes argued that he action in these eddies will do two things. First, it with concentrate, but this is seldom a problem in sampling operation can easily be several thousand failed to recover the hoped-for value because his will prevent packing o f the black sand or other sampling work where close watch and frequem gallons per day. It should be apparent that the sluice was too small or the sample was put material caught by the riffle, and, second, it will clean-ups should keep the riffles working sluice is best suited to testing stream placers. through too fast. While it is true that a sluice box provide a classifying effect which further efficiently. Hungarian-type riffles, such as those Supplemental equipment is often needed. This crowded beyond its optimum capacity will lose concentrates the gold and heavy minerals. While shown in Figure 17, can hold a comparatively may be a water pump, a puddling box or tub, or some o f the gold, a quick look at the facts will this boiling action must he strong enough to large amount of concentrate and for this reason some kind o f screening arrangement. Because o f usually show that there is little or no room for prevent packing it must not be so strong that may be preferred where the gravel contains mucli the relative short length o f the usual sampling argument in most cases. flake or fine gold cannot settle. It should he black sand. On the other hand, expanded metal sluice, cemented gravel or gravel containing much For example, modern gold dredges provide about obvious that proper riffle action is the key to riffles leave a minimum amount o f concentrate to clay must be thoroughly broken up in a puddling 10 square feet o f riffle area for each hourly yard good recover)'. An easily built and effective riffle be panned at the end o f a sample run and this box or tub before being fed into the sluice. o f material passing over the gold-saving tables. By suitable for use in a small sampling sluice can be time-saving feature makes them easy to clean up. Screening out the plus 54-inch rocks ahead o f the direct comparison it can be shown that it would made from 54” x 'A” wood strips placed across Many engineers compromise by equipping the sluice will conserve water and will generally be necessary to feed an 8-inch x 10-foot sampling the bottom o f the sluice at right angles to the upper 2 or 3 feet o f a sampling sluice with improve the entire operation. sluice at a rate o f 1 1/2 cubic yards per hour to flow, with 3 /4 ” spaces between each riffle bar. Hungarian-type riffles and the remainder with The slope or grade o f a sluice depends on a attain this degree o f riffle loading. But experience The boiling action can be improved by expanded metal lath. number o f factors including rock size and shape, tells us that the rate o f feed for a sampling sluice undercutting the downstream face o f each bar on In commercial-scale placer operations, mercury is the amount and composition o f sand, type o f o f this size is more likely to be on the order o f a 30-degree bevel. The individual riffle bars are usually placed in the riffles to assist holding the riffle and depth o f water flow. In each case the 154 cubic yards per day rather than per hour. It tacked to wooden side rails and the whole gold over extended periods of time but in proper grade must be determined by trial and this can be seen that in a sampling sluice the riffle assembly held in place by means o f cleats and small-scale sampling work where clean-ups are can be best done by initially setting the sluice on area provided for each unit o f sample material is wedges as shown in Figure 17. The riffle frequent, mercury is not needed for this purpose a grade o f about 1 inch fall per foot o f length and considerably greater than the riffle area provided assemblies are made a little narrower than the and is seldom used. then adjusting the grade as found necessary. in standard mining practice. In other words, the inside width o f the sluice and o f convenient length. It should be noted that when a particle o f golds When in doubt it is better to have the grade too small sampling sluice usually favors the sample. “wetted” by mercury, the mercury actually steep than too flat, as too flat a grade will result This is borne out by long experience which shows penetrates the surface and causes the gold to in sanding o f the riffles which in turn will impair that a properly constructed and carefully SIDE RAILS TACKED } become brittle. Depending on the size o f the gold their ability to recover fine gold. Where fine gold operated sampling sluice will save all o f the gold TO CROSS BARS / i particle and length o f exposure, the penetration is to be saved the depth o f flow over the riffles o r other heavy minerals which can be / (d ir e c tio n <- LOF FLOW may be superficial or complete. The ductility is should be as shallow as possible while still economically recovered by standard placer not restored when the mercury is removed with sufficient to carry o ff the pebbles and maintain a methods. acid and in the case o f small gold particles, a loose bed between the riffles. T o do this the ROCKERS delicate crystalline structure is often induced. It sluice grade is steepened and it can be said can be seen that amalgamation within the generally that the grade for very fine gold should Rockers are widely used for washing placer WOODEN RIFFLE SUITABLE FOR USE sampling sluice would either impair or prevent a be steeper than for coarser colors. Increasing the IN SMALL SAMPLING SLUICE samples and under most conditions they are well later study o f particle size, the surface texture, or grade will, to a point, offset a deficient water suited to the needs o f the field engineer. It FIGURE 17. — Wooden riffle suitable for use in a sampling other physical characteristics o f the gold, any of supply but, in any case, the riffle action should sluice. should be noted that since its inception, the which could prove important in a placer tell the operator when the proper balance has American gold dredging industry has, for the Heavy wire screen o f the type used for screening investigation. been reached. most part, used rockers in preference to other gravel, and expanded metal lath are sometimes The feed and water flow should be regulated to The daily capacity for a sampling sluice varies types o f sample washing equipment. The fact used as riffles in small-size sluices, particularly maintain proper riffle action and it can be said widely with the type o f gravel, degree o f that the rocker has survived in direct competition where much fine gold is present. This type of generally that where this is not done more fine cementation, amount o f clay, etc. These factors with a variety of more “modern” or “improved” riffle is usually installed over burlap mats, cocoa gold will be lost by its inability to penetrate individually and collectively determine the machines which have been introduced over the matting, or similar rough-surfaced fabric which packed riffles, than will be carried o ff by amount of material that a man can prepare for years attests to the reliability o f results which can helps hold the fine gold. Because burlap and suspension in the water. The quantity o f water y washing in a day’s time and, in many cases, the be obtained. cocoa matting are difficult to clean, ordinary required varies considerably according to the preparation time will exceed the actual washing Rockers are usually homemade and are built in a canvas should be substituted in sampling sluices. character o f material being washed and the rate time. Under favorable conditions with an variety o f sizes and designs depending on the It will be noted that metal webs forming the o f feed, the type o f riffle, width and grade of efficient sluice set-up, two men can handle 1 to 3 ideas and experience o f the builder. Figure 18 diamond-shaped openings of expanded metal lath sluice, etc. Because o f these variables the water cubic yards per day taking into account time shows a lightweight rocker which is easily built have a noticeable slope in one direction. When requirement is difficult to predict but as a rough needed for clean-ups between samples, processing and is suitable for general use. Individual the expanded metal is placed in the sluice so this guide, a minimum flow o f about 50 gallons per \ the sluice concentrate, logging sample data, etc. components are a screen-bottomed hopper for slop e leans downstream, small eddies form minute should be provided for a 6 or 8-inch When the mineral examiner washes a placer receiving and sizing the feed material, a canvas 54 beneath the over-hangs and make excellent gold sampling sluice. Unlike panning or rocking, the sample in a small sluice box and fails to find the apron for deflecting the feed to the head-end o f 55 the rocker, the rocker body which is equivalent the advantage o f lighter weight and they ^ The apron consists o f a simple wooden frame to be determined by trial but if it is initially set to a sluice, and a bed plate or frame upon which strong and durable if the joints are sealed wij covered with loose-fitting canvas or similar at 1 1/2 inches fall per foot o f length, a few short the entire assembly is mounted. A rocker may be waterproof glue. The exposed surfaces ol s material. The resultant sag or “ belly” in the trial runs will suffice to make any needed made any convenient size because within limits, plywood rocker should be protected with mar* apron functions as a gold and black sand trap and adjustment. Insufficient grade may cause sand to its size will determine throughput capacity rather varnish or spar. when large amounts o f material are put through a blanket the riffles and result in loss o f fine gold. than its efficiency as a gold saver. Although there The hopper should be made 1/2 to 3/4-intl rocker, the apron’s gold-holding ability permits If the hopper is filled too full, gravel will slop are no fixed size criteria, a rocker 1 foot wide by narrower than the inside width o f the rocker; longer runs between clean-ups. In normal over the sides when rocked and it will be difficult 3 feet long would generally be referred to as results in a bumping action as the rocker t sampling work where short runs are made, the to regulate the flow o f material through the “ small” and one more than 18 inches wide or 5 operated and assists scouring and screening tit apron is less important and is sometimes screen and, for this reason, the hopper should not feet long as “ large.” When made o f wood (which gravel. The amount o f open area in the screw dispensed with. be filled over half full and preferably the screen is usually the case) clear lumber without cracks plate is important. A screen with too much opea plate should be left partially exposed at one end. or flaws must be used and the bottom should he area allows the fines to pass through too fast and It is noteworthy that most old-time prospectors Starting at the exposed end o f the screen plate, made o f vertical-grained stock which will not where much sand is present this can cans employed by dredging companies wash their water is poured over the gravel while the rocker is shred or rough-up when scraped. Heavy-duty overloading o f the riffles with resultant gold loss, samples in rockers without riffles. Experience shaken vigorously and the amount o f material fed rockers and those which are in continuous use are A plate with 1/4-inch holes drilled or punched® and practice enable these men to concentrate the to the riffles is regulated by shifting the point of preferably made o f sugar pine reinforced with an alternate pattern at 1-inch intervals and or gold and black sand directly on the smooth water application back and forth between the suitable metal fittings. Where sugar pine is not 1/2-inch centers will provide a screen with 10 wooden bottom o f the rocker and, as a final step, gravel and the exposed screen plate. Most available, redwood makes a fair substitute. percent open area. This has been found to tt to tail out the black sand and bring the gold to a pictures illustrating the use o f a rocker show the Rockers made o f exterior grade plywood have about right for small prospecting rockers. point in a manner somewhat similar to panning. water being applied with a long-handled dipper This technique is particularly useful when applied such as a gallon can on the end o f a stick. In to small-volume churn drill samples and is practice one finds that it takes considerable mentioned here to point out that a properly dexterity to use a dipper and at the same time operated rocker is an excellent gold saver which operate the rocker smoothly and maintain a unlike the sluice, does not rely on riffles for its uniform flow o f material over the riffles. For this effectiveness. But it should be pointed out that a reason, a water hose supplied by a pump or a rocker equipped with good riffles will forgive gravity-flow should be provided where possible. much mishandling and, for this reason, the The flow of water obtainable from an ordinary average person should use them. Parenthetically, garden hose (about 5 gallons per minute) is it should be noted that even the experienced usually enough for operating a rocker but where rocker operator, in certain cases, may find it this is not available, two or three barrels o f water more expedient to use riffles than to explain to a used in a closed circuit will generally be sufficient layman why they are not essential. A simple riffle for a day’s work. When water must be dipped, arrangement suitable for general use can be the water barrel should be placed next to the provided by covering the rocker bottom with head-end o f the rocker within easy reach o f a heavy-gage expanded metal lath placed over a short-handled dipper. canvas mat and held down by several transverse wooden slats as shown in Figure 18. When rocking is periodically stopped to discharge rocks from the hopper, the material passing over The length o f the rocker handle is important—it the riffles will settle and tend to pack, should be waist-high to the operator in a standing particularly if much black sand is present. If position. The long leverage thus provided makes washing is resumed without first loosening this the rocker much easier to handle and materially material, any fine gold that has not penetrated reduces the physical effort which, at best, is the packed sand will be lost with the tailings. To MAKE ROCKER BODY AND HOPPER FROM 1/2-INCH EXTERIOR GRADE PLYWOOD. considerable. Anyone who has attempted to N guard against this, the material behind each

ASSEMBLE WITH WATERPROOF GLUE AND SUITABLE WOOD operate a short-handled rocker from a sitting transverse riffle should be loosened and scraped SCREWS. position will appreciate the foregoing comment. back toward the head-end of the rocker with a PAINT ROCKER WITH MARINE SPAR OR PLASTIC VARNISH. Like panning, rocking relies to some degree on fla t, straight-edged scoop. This loosening PROTECT MOVING AND SLIDING SURFACES WITH SUITABLE METAL STRIPS. subtle techniques which must be learned by procedure is the key to effective rocking. The

SECURE RIFFLES WITH CLEATS AND REMOVABLE WEDGES experience but the following pointers may help loosened material is subsequently washed down AS SHOWN. the novice get o ff to a good start. The first step is and re-concentrated with the next run and if the to set the bed plate and secure it so that it will rocker is kept free o f packed sand in this manner, FIGURE 18. - Prospecting rocker suitable for general use. With this rocker, one man working under normal conditions can wash the equivalent o f eight 80 pound samples per day. This includes the time needed for clean-ups, panning, and logging sample not shift or move around when the rocker is in it will effectively recover flour gold particles 56 data. operation. The best slope for the rocker will have running 1,000 or more to the cent. 57 After the entire sample has been washed, the T hese are manufactured bv the Denver be the logical choice for processing samples. A 1 /4 " SCREEN concentrate remaining behind the transverse Equipment Company and known as the “ D enver number o f small, hand-powered machines are on riffles is picked up with the scoop and placed in Mechanical Gold Pan” and the “ Denver Gold the market and most work quite well within the upper end o f the rocker and then carefully Saver” respectively. The mechanical pan has been certain limits common to all dry washers. re-washed once or twice with clear water to well received in the industry over a 30-year First, consider two identical gold particles, one in remove surplus sand and further reduce the period and is generally referred to simply as a a dry washer and the other submerged in water. concentrate volume. The apron, riffles and canvas “ Denver Pan.” It comprises an assembly of three It will be shown that the relative weight o f the mat are then removed and washed out in a pan or shallow, nested pans 2 feet in diameter with two dry gold particle is substantially less than its wet tub o f water and the combined concentrate superimposed screens arranged to wash and reject counterpart. This is illustrated by the following panned to a finished product. the plus /4-inch material. The combined assembly equations in which the specific gravity o f gold is Although reference books state that from 1 to 3 is mounted on a horizontally gyrating base driven 19, the specific gravity o f gravel 2.65, and the cubic yards can be washed in a rocker per by a small gasoline engine and the resultant specific gravity o f water is 1: man-shift, it should be noted that these figures motion is said to duplicate hand panning. The apply to production-type work and give little minus !4-inch material after passing through the indication of what should be expected when screens, progressively flows over the three pans, Gold in air, 19 7 processing samples. Experience has shown that one discharging into the next. The uppermost Gravel in air, 2.65 1 one man using a 12-inch x 4-foot rocker similar pan is provided with an amalgamating plate, and to the one illustrated in Figure 18 can wash the the two successive pans with special rubber mats equivalent o f eight 80-pound samples per day or cocoa matting held down by coarse wire whereas where conditions are favorable. This includes the FIGURE 19. — Schematic diagram showing the arrangement screen. Capacity o f a single unit ranges up to 2 o f a typical hand-operated dry washer. In use, the dirt is time for clean-ups, panning, and logging sample cubic yards per hour and water consumption is moved over the riffles by puffs or air forced through the data. The total amount will, o f course, vary with said to be as little as 1 to 2 parts (by weight) per cloth bottom by the bellows. The gold lags behind and Gold in water, 19-1 11 accumulates along the upstream edges o f the riffles. the size or number o f individual samples and with part o f gravel which would indicate an average of the character o f material being washed. Material about 1,000 gallons per cubic yard. Single or Gravel in water, 2.65-1 1 Fansett (1961, p. 108) in referring to tests made containing much clay can halve this figure double units are available and these can be at the University o f Arizona sum these up by whereas loose, free-wash type material may provided with a scrubber and a trommel-type saying: double it. Dredging companies occasionally use screen. The largest (Duplex) unit when so This shows the gold to be eleven times heavier large, engine-powered rockers in which the total equipped has a rated capacity o f 4 to 6 bank-run “ A dry concentrator will not make as high than gravel when immersed in water, as compared gravel excavated from a shaft can be washed yards per hour and weighs 2100 pounds. The recovery as a wet concentrator. Under to 7:1 in air. Simply stated — the relative weight rapidly and economically. A typical power-driven single (Simplex) unit without the trommel weighs favorable conditions, the recovery will be of gold is about 1!4 times greater when passing rocker having a capacity o f 5 cubic yards or more 675 pounds. The Denver Mechanical Gold Pan is approximately ten to fifteen percent less through a wet process than when passing through per 8-hour shift is illustrated and described on sturdily built and is suitable for continuous use with a dry machine as compared with a wet a dry washer. The lesser ratio in air is not too pages 334 and 335 o f the August 25, 1923, issue such as would be encountered in a mining machine.” apparent when processing coarse or “shotty” o f Engineering and Mining Journal-Press. operation. gold but it no doubt contributes to the dry This tells us that in cases where a dry processing The Denver Equipment Company’s second plant is proposed for the recovery o f gold in a 5. SPECIAL MACHINES washer’s often poor recovery of fine or flaky machine, sold under the name o f “ Denver Gold gold. commercial-scale placer operation, it might be Saver” , is well suited for general sampling work advisable to process the initial samples with a A variety o f small mechanical gold washers have To respond to dry washing the material treated in that it can be quickly and easily cleaned thus small dry washer. Figure 19 illustrates a type o f been manufactured and put on the market over must be almost completely dry. In most cases 3 eliminating the danger o f carry-over o f values machine found suitable for this purpose. If all the years and although most were intended to be percent moisture is considered a maximum. The from one sample to the next. It consists o f a feed else is equal, the recovery obtained from the dry used for small-scale mining operations, some were gold particles must also be completely liberated hopper, a combined scrubber and trommel to (sample) washer should indicate the recovery to advertised and sold as prospecting or sampling and free o f cementing material such as caliche. In wash and screen out the plus 14-inch material, a units. The typical machine consists o f a small addition , effectiv e separation is usually be expected from the full-scale operation. On the special vibrating molded riffle, a reserve water trommel screen with a feed hopper for shoveling dependent on use o f a closely-sized feed, other hand, if the samples are washed in a rocker storage tank and a centrifugal pump with suitable in, a short sluice (which is usually provided with sometimes not larger than 54” screen-size. One or other wet device, a suitable recovery piping sprays, etc., all powered by a 1 Vi HP a shaking motion or some kind o f “ special” might say that the amenability o f a dry placer to “correction” factor may have to be applied to gasoline engine. The complete assembly weighs riffle), a pump, and a water distribution system, working by the usual (dry) methods varies in the indicated sample values. 750 pounds and has a rated capacity o f 2 to 3 all run by a small gasoline engine. The typical proportion to its suitability to sizing by cubic yards per hour. machine weighs more than 500 pounds and screening. REFERENCES CITED (PART IV) 6. DRY WASHERS requires a pickup truck or a trailer for Besides the well-known difficulties related to transportation. Most are no longer manufactured In arid districts where water is scarce or drying placer material prior to dry washing and Wilson, Eldred D. and Fansett, George R., 1961, Gold and have passed from the scene but two o f the expensive and a “ dry” plant is proposed for the using small-mesh screens, there are other placers and placering in Arizona: Arizona Bureau better-known machines are still on the market. recovery o f placer gold, a small dry washer may problems less generally appreciated. Wilson and o f Mines Bulletin 168 (1961). 59

I

1. PANNING above water and move the hands slightly back o f center (allowing the pan to tip Panning is a simple operation but, at the same forward with the low side away from the time, it is difficult to describe. Although the panner) and change from the twisting motion subtle techniques o f panning vary with the o f Step 2 to a flat circular motion. While individual and with the material being washed, keeping the pan partially submerged and its the overall operation can be divided into six basic contents loose, gradually work the steps as follows: lighter-weight material over the low side o f a. Preparation: A fte r fillin g the pan the pan. The rate o f discharge is regulated by approximately level full, carefully submerge raising or lowering the pan rim and by using it in quite water, preferably resting it on the a side to side motion along with the flat bottom o f a shallow pool or tub with the top circular motion. Alternate Steps 2 and 3 and of the pan just below the water surface. wash until the bed begins to pack or until After the material has become thoroughly heavy minerals begin to crowd to the surface, wet, work over the contents with both hands d. Cleaning: The fourth step involves selectively and break up any lumps. If clay is present, washing away surface grains and, in effect, it knead and stir the material until the clay is can be compared to the action o f wash water dissolved and floated away. It is important on a concentrating table. To prepare the now that all clay be eliminated before actual partially concentrated material for this step, panning begins. Wash o ff and throw out all the pan is given a short, quick side to side large rocks. In this first step the eye and motion of sufficient vigor to thoroughly hands substitute for a screen. loosen the bed and further stratify the b. Suspension and stratification: Commence material. During this shaking phase the pan is this stage by grasping the pan with hands on tipped gradually forward until the surface o f opposite sides and while holding the the mineral bed becomes flush with the lip. submerged pan level, twist it back and forth At this point the shaking is stopped and the (clockw ise and counterclockwise) with mineral bed allowed to settle. Next, a thin sufficient vigor to keep the contents loose. layer o f the lighter material is removed by This allows the heavier minerals to migrate to carefully dipping and raising the pan with a the bottom o f the pan and is similar to the forward-and-back motion which will wash action in a jig in which heavy mineral grains o ff the surface grains a few at a time. The are separated from lighter grains by their washing can be effectively controlled by use ability to sink through a semi-fluid bed. If o f a somewhat circular motion as well as the this second step is properly executed, the forward-and-back dipping motion. When the smallest and heaviest grains will migrate panner decides that further washing would toward the bottom and the larger and cause a loss o f values, the bed is re-stratified lightest to the top. This will allow many of and more light material brought to the the pebble-size rocks to be manually surface by repeating the vigorous side-to-side removed by raking them out o f the pan with motion. Repeat the washing and shaking the fingers. operations until the heavy-mineral c. Washing: The third step is one which, concentrate is clean or until it is reduced to a depending on the nature o f the material volume small enough to permit inspection or being washed, may take on many variations. removal o f the gold. During the finishing It is like Step 2 in that the entire contents of steps the panner can save time by raking any the pan are kept in motion, but as remaining pebbles out o f the pan with his stratification o f the bed develops, the lighter fingers and flicking out smaller particles with particles are allowed to escape over the rim his thumb. These and other tricks come with o f the pan. To do this, raise the pan partially practice. 63 Inspection and estimating: At the end o f the 2. GENERAL NOTES ON PANNING WITH gravel swell. Experience has shown that two low-grade tailing. Usually two or three panning operation the original material will SUGGESTIONS FOR IMPROVllu half-size pans can usually be washed in less repannings will make an acceptably clean normally have been reduced to a small TECHNIQUE time than one full-size pan. tailing. quantity of concentrate consisting mostly of d. Use of perforated pan: Panning, at best, is a black sand minerals. After putting a little a. New pan - preparation for use: The film 0| h. Supplemental data: When panning a sample tedious, back-breaking job and anything clear water in the pan, the experienced grease or other rust preventative found oru the experienced engineer will note a variety done to speed the operation or improve panner will fan out the concentrate on the new pan must be removed before use. This is o f things among which are: Its amenability working conditions will be repaid many bottom o f the pan and by “ tailing” the gold best done by passing the pan over a gas stove to washing, particularly where clay or he can inspect or count the colors. At this burner or other suitable flame until the metal times over in the form o f more reliable cem en tin g materials are present; the point he can estimate the tenor o f the turns blue. Although this process results. The beginner and experienced panner proportion o f coarse to fine material; any alike can profit by use the use o f a sieve 1/ sample. There are perhaps as many ways o f sometimes called “ burning” , care should be evidence o f unusual muddy water problems; tailing the gold as there are panners but this taken to avoid excessive heat. Blueing a pan made by drilling Vi-inch holes in the bottom the composition and angularity o f rocks; the is usually accomplished by moving the pan in not only frees it o f grease but equally of a pan o f the same size and shape as the relative ease o f concentration; the quantity a way that causes the water to gently swirl important, the resulting dark color make; one used for panning. T o use the sieve, place and composition o f black sand; indications around the trough formed at the intersection fine specks o f gold much easier to see in the it inside o f the regular pan and then fill with o f valuable or potentially valuable accessory o f the bottom and side o f the pan. This swirl pan. The “burning” process should be gravel and submerge in water in the usual minerals; the size, shape and other physical o f water carries the lighter particles ahead o f repeated as often as necessary to keep the way. When the material is thoroughly wetted, characteristics o f the gold including “ rust” , tarnish or other factors which would affect those which are heavier or finer and with pan free o f body oil films which accumulate lift the sieve slightly and twist it back and its amalgamation. Any o f the foregoing could careful manipulation, brings the gold colors on a pan in normal use. forth (under water) until all minus Vi-inch into view at the tail o f the slowly moving fan material has passed into the regular pan. The be important factors in a placer mining of concentrate. b. Pan factor: Gold pans are made in a variety plus Vi-inch material is discarded and the operation. o f sizes but the size generally referred to as fines which dropped into the regular pan are i. Use as a geologic tool: Although the miners’ Removing the gold: Final separation o f the “ standard” has a diameter o f 16 inches at tbe washed in the usual way. Aside from pan is normally associated with gold gold from other heavy minerals can be made top, 10 inches at the bottom and a depth of speeding the overall panning operation, the deposits, it can be profitably employed when in a number o f ways. Larger pieces can be 2Zi inches. A typical pan will hold 336 cubic use o f a sieve enables the engineer to investigating a variety o f heavy minerals such picked out with tweezers or the point o f the inches or 0.0072 cubic yard. The numberof conveniently inspect the plus Vi-inch rocks as monazite, scheelite, magnetite, ilmenite, knife and small colors or specks can be pans representing a cubic yard o f material in and to estimate the proportion o f corase cassiterite, chromite, cinnabar, etc. In picked up by pressing down on them with place (bank-measure) is called the pan factor. material. general, it should be borne in mind that with Pan factors vary according to the size and the end o f a wooden match or a dry finger e. Use of safety pan: Allowing the pan tailings few exceptions the pan can be employed in shape o f the pan, the swell o f the ground tip. Remove the gold by placing the finger to fall into a second pan generally referred to the study o f either lode or detrital-type when excavated, and the amount o f heaping tip over a vial o f water and washing it o ff as a “ safety” pan will guard against losing the deposits containing finely divided minerals of when filling the pan. In practice, factors fora with a splash o f water. sample by accident and will greatly expedite relatively high specific gravity. The use o f a 16-inch pan range from 150 to 200 but an A small globule o f clean quicksilver repanning where this is called for. miners’ pan as a geologic tool has been approximate figure o f 180 is often used. This studied and reported in detail by Mertie (mercury), if rolled around in the pan, will f. Panning large samples: When a large is based on a struck pan (i.e., level full) and pick up the gold providing it is untarnished multi-pan sample is to be washed, rather than (1954) and by Theobald (1957). an assumed 20 to 25 percent gravel swell. and free o f oil or grease. Tarnished gold can complete each successive pan, it is best to 3. FIRE ASSAY OF PLACER SAMPLES - be brightened by rubbing it in the pan. c. Recommended pan size: The average panner reduce them only to a rough concentrate. MISLEADING RESULTS Where there is a considerable amount o f should not use a 16-inch pan but instead The rough concentrates are accumulated and Fire assaying, in essence, is a minature smelting black sand, particularly if it is fine and should use the so-called “ half-size” pan are eventually combined for finishing in the process which recovers and reports the total gold densely packed, it may be easier to separate which has a top diameter of 12 inches, a usual manner. content o f the assay sample, including gold the gold by blowing. This is done by first bottom diameter o f 7Vi inches and a depth of g. Stage panning: Where a large amount o f combined with other elements or locked in the drying the concentrate and then removing 2 inches. 1 he half-size pan level-full weighs heavy black sand is encountered, a ore particles. Because o f this, a fire assay may the magnetite with a common horseshoe approximately 9 pounds compared to about stage-panning procedure can be used to report values that cannot be recovered by placer magnet, and finally, by blowing the 20 pounds for the standard 16-inch pan. I advantage. This is done by panning and methods and it cannot be too strongly stressed non-magnetic black sand residue away from Halving the sample weight by use of the repanning to successive high-grade that when dealing with gold placers, the sample the gold. I'o do this, place the non-magnetic smaller pan not only reduces fatigue, concentrates without attempting to make a values should not be determined by fire assay. residue in a dry gold pan or on a suitable particularly when much panning is to be complete saving o f black sand or values at Furthermore, no credence should be placed in sheet o f stiff paper and holding it level, blow done, but the fact that it is much easier to any one stage. As the proportion o f heavy placer valuations or reports that are based on the gently across its surface while tapping the carry in the field and to use in a small stream minerals decreases with each successive results o f fire assays. Although this should be pan or paper. This take some practice but or tub is an important consideration. The h repan, it becomes progressively easier to common knowledge among mineral examiners, a with care a clean separation can be made in a pan factor for a 12 x T/i x 2-inch pan make a high-grade concentrate with a surprising number seem unaware that fire surprisingly short time. is about 400. assuming a 20 to 25 percent assaying although accurate per se yields 1/ Sometimes referred to as a “ grizzly” pan. misleading results when applied to placers. gold is present, provisions should be made to scour There are other reasons: First, consider the small over a safety pan reduce the black sand ton or otherwise brighten the gold prior to quantity o f material used in a fire assay. The small-volume concentrate. Near the end o| amalgamation. This may be done by rubbing it on usual amount o f sample taken for a crucible panning process the mercury may tend to the bottom o f the pan or adding a few pebbles to charge is either 29.166 grams (one assay-ton) or ride over the top o f fine-size or hard-packing the amalgamating jar. Fine grinding or pulverizing half o f this amount. Next, consider that a particle materials but by this time all gold should should be avoided. o f placer gold only 1/32-inch in diameter may have been picked up by the mercury. weigh about 1/4 milligram. Now if the bank-run d. Remove the mercury and place it in a 250 ml material from which it came averaged 10c per Pyrex beaker. Add 40 or 50 ml diluted nitric REFERENCES CITED (PART V) cubic yard, 1/ the 1/4-milligram gold particle acid (Note 3) and digest until the mercury would be contained in about iVt pounds of sand globule is reduced to the size o f a match Gardner, E. D. and Allsman, Paul T., 1938, and gravel. But suppose this same 1/4-milligram head. Transfer to a # 0 glazed porcelain Power-shovel and dragline placer mining: U.S. gold particle found its way into a 29-gram fire parting cup, add fresh acid and complete the Bureau o f Mines Information Circular 7013, assay charge. The resulting assay-value would be digestion using low heat if necessary. 1938. 1/4 ounce per ton or about S54fo-per cubic Fine-size gold will be left as a coherent, Janin, Charles, 1918, Gold dredging in the United yard.l/ It is seen that a single small particle of sponge-like mass if rapid digestion or boiling States: U.S. Bureau o f Mines Bulletin 127, 1918. gold, by placer standards, will cause an is avoided. intolerable error when injected into a standard e. After decanting o ff the acid, carefully wash Mertie, John B. Jr., 1954, The gold pan; a neglected fire assay charge. the gold three or more times with warm geologic tool: Econ. Geology, Vol. 49, No. 6, FIGURE 20. — A folding assay balance widely used in placer Experience tells us that with few exceptions no water. Add a drop or two o f alcohol (to Sept. — Oct., 1954, pp. 639-651. work. Capacity 10 grams, sensitive to V* milligram. amount o f mixing or careful division can produce prevent spattering) and dry in the parting Complete in mahogany case with set o f weights 10 grams Theobald, Paul K. Jr., 1957, The gold pan as a a fire assay charge representative o f bank-run cup at low heat. by 1 milligram. Size when closed, about 6x3x11/2 inches. quantitative geologic tool: U.S. Geol. Survey Bull. placer material. The practice o f first panning a f. Anneal the gold by bringing the bottom o( 1071-A, 1957. 5. The described procedure will extract all free gold sample to reduce its bulk, and then fire assaying the parting cup to a low red heat. This step recoverable by commerical placer methods. With Vanderburg, William 0 ., 1936, Placer mining in the resultant black sand concentrate does not will eliminate any residual mercury and is care, extremely low gold values can be Nevada: University o f Nevada Bull. Vol 30, No. 4, entirely resolve this problem. essential when working with very small gold determined. Where so-called “ rusty” or coated May 15, 1936. Even if we assume that a representative crucible weights. charge could be obtained, the fire assay will g. Transfer the annealed gold to a' balance pan detect all gold including that which is locked up and weigh. A balance widely used by placer in rock particles or is too finely divided to be engineers is shown in Figure 20. recovered by placer methods. This in itself NOTES precludes the use o f fire assays for evaluating 1. Number 3 colors consist of gold particles weighing placer ground. less than 1 milligram. Number 2 colors weigh In brief, experience has shown that fire assay between 1 milligram and 4 milligrams. Number 1 results applied to placers usually results in a colors weigh over 4 milligrams. Gold particles substantial over-valuation o f the ground. This weighing 10 milligrams or more should be fact has been set out by Janin (1918, p.38), individually weighed and recorded. Vanderburg (1936, p. 33), Gardner and Allsman 2. Placer gold loses its original surface texture when (1938, p.61) and others. amalgamated. In the case o f fine-size gold, its end 4. P R O C E D U R E F O R D E T E R M IN IN G form may assume the shape o f fine needle-like RECOVERABLE GOLD IN PLACER SAMPLES crystals which are actually pseudomorphs after a. Reduce the original sample to a black sand gold amalgam. concentrate by panning, rocking, or other 3. Prepare a parting solution by diluting commercial suitable means. nitric acid with water to a strength which will b. Place the concentrate in a pan, then count dissolve mercury without violent action. A 1:1 and record the gold colors as #3, #2 or #1 — dilution is usually satisfactory. size (Note 1). At this point, manually remove any gold particles which are to be kept in 4. Large-volume or hard-packing black sands that are their natural form (Note 2). difficult or tedious to pan may be amalgamated in c. Add a globule o f clean, gold-free mercury a glass jar rotated about its longitudinal axis at a (about the size o f a small bean) and working peripheral speed o f 500 inches per minute. The addition o f a small amount o f lye will counteract o il or grease and will generally assist 67 66 1/ Based on gold at $35 per ounce. amalgamation. PART VI

NOTES ON GENERAL PRACTICE description o f s a m p l e s 320 lead shot mixed as A mining claim may be validly located and held thoroughly as possible in a bucket of sand and only after the discovery o f a valuable mineral deposit. When it becomes necessary to determine the validity o f a claim and the sufficiency of discovery is in doubt, the Government will initiate contest proceedings during which the testimony is given by parties to the contest and their witnesses. During such proceedings, assay certificates or other sample data are submitted as evidence o f value, or lack o f value. The sample and assay data are important in that the hearings examiner or the court must rely on them to a large extent to determine if a valid discovery has been made. A A A A 57 30 38 28 42 31 51 43 But numerous decisions have pointed out that in AAAAAAAA order to fully understand the results o f these 32 2519 11 17 21 8 20 17 25 11 20 25 26 22 21 assays, the method in which samples were taken and tested must be considered. Without such FIGURE 21. — Diagram showing erratic distribution o f metallic particles in successive splits o f a placer-type information they have little probative value and, sample. accordingly, are entitled to little evidentiary weight. Referring to Figure 21, assume that the bucket o f sand weighs 60 pounds and that instead o f lead In brief, an accurate and systematic record shot it contains 320 particles of placer gold should be kept o f each sample through the weighing 0.1 milligram each. cutting, processing, and calculation stages. The use o f suitable printed forms will expedite the The initial sample will have a value o f S I.60 per data recording process and, equally important, cubic yard.l/ will serve as a check list and lessen the risk of The first split yields two 30-pound samples with oversight. Three such forms prepared specifically indicated values o f S1.53 and $1.67 per cubic for BLM use are included in the appendix. yard, a spread o f 14 cents per cubic yard. Complete, accurate and signed sample records are The second split yields four 15-pound samples in effect legal documents and they should be with indicated values o f $1.74, $1.32, $1.46 and prepared and preserved with corresponding care. $1.88 per cubic yard; a spread o f 56 cents per cubic yard. REDUCTION OF SAMPLE VOLUMES The third split yields eight 7V2-pound samples In typical gold placers the variations are so great with values ranging from a low o f $1.12 to a high and the values are so low, any attempt to divide a o f $2.28 per cubic yard; a spread o f $1.16. sample by taking alternate shovels, mechanical The fourth split yields sixteen 3-3/4-pound splitting, or by other means will invariably yield samples with values ranging from a low o f 64 erratic results. Rather than set out supporting cents to a high o f $2.56 per cubic yard; a spread theory which at best would he academic, two o f $1.92. examples are offered to show what actually As splitting continues, the spread in indicated happens. One is based on a laboratory value becomes progressively greater. On the fifth experiment and the other on field practice at an operating mine. First consider the laborabory 1/ Using a weight to volume ratio of 3,000 lbs. per cu. yd. experiment. and figuring 10 milligrams of gold to the cent. TABLE III. — Erratic values resulting from 1:1 splits o f gold-bearing gravel Two equal-volume samples were COST ESTIMATES similar property where mining operations have obtained from each shaft by placing alternate buckets in half “A ” and half “B”. One of the mineral examiner’s functions is to give been conducted and costs established. But just a qualified or expert opinion as to whether a how to obtain these cost data and how to equate given mining claim or mineral deposit has present them to today’s inflated prices is one o f the or potential value. Among the evidence to be practical problems encountered in applying the Indicat ed Value % o f Actual Value Value examined and weighed in forming his judgement comparative cost method. Shaft No. c per cu. yd. Half “ A ” will the question o f costs. In many cases there is First, we find that because o f the depressed state Half “ B” Half “ A ” Half “B” a factor so obviously weak that a detailed cost o f the placer mining industry there are few 1 27.0 17.4 36.6 64 136 ~ study is not necessary, in fact, it would be operations from which up-to-date costs might be 2 26.7 24.8 useless. Here, a rough approximation based on extracted. Second, anyone who has tried to 28.7 92 108 3 31.0 experience and common sense will usually obtain detailed cost data from a responsible 35.0 27.0 113 87 operating company has soon found that such 4 34.6 33.7 suffice. 35.6 98 102 But in other cases a careful consideration o f this . information is considered confidential and 5 31.0 26.6 35.5 86 114 seldom released for outside use. While the small 6 question will be necessary. If the deposit has not 13.0 13.2 12.8 102 98 been completely blocked out and sampled, or if operator may be freer with his information, it 7 38.3 36.5 40.2 95 105 the mining method and working rate have not will usually be found that he did not bother to 8 54.9 61.2 keep systematic records and his cost figures may 48.6 112 88 been firmly established, an accurate cost estimate 9 19.1 be little more than a guess. 17.7 20.6 92 108 is not possible. In the absence o f such 10 26.5 development work, all the mineral examiner can This means that for the most part, the mineral 24.0 29.0 90 110 examiner will have to rely on the few placer cost 11 25.3 23.8 do is to make a qualified estimate based on 26.8 94 106 12 comparative data from reliable sources, or from data available in the technical press, most o f 29.5 26.6 32.4 90 110 his own experience with similar properties. which are fragmental and over 30 years old. A list 13 26.8 28.0 25.6 104 96 o f the more useful and readily available sources 15.7 Basically, he must decide whether the deposit 15.2 16.2 97 103 has been placed at the end o f this section. 14 contains enough gold or other salable mineral to To update the older figures, a year-by-year cost cover: index will be needed. The annual index for Cost o f operation. various classes o f construction, construction Cost of all equipment. materials, labor, and machinery can be obtained split, for example, (not shown) the indicated likely to fol ow. Any divergence from normal Royalties or cost o f land. from Engineering News-Record magazine. The values ranged from 16 cents to $2.72 per cubic procedure should, of course, be noted in the All exploration, sampling, and March (quarterly review) issue will be found sampling records and in subsequent reporting. pre-operating costs. particularly helpful. Data from a recent study by the United States When dealing with fine-size placer materials Cost o f borrowed captial. In the absence o f comparative data the estimator Geological Survey (Clifton, 1967) confirm that having a low unit-value, such as magnetite or is on his own. In such cases he may have to work variances shown in the foregoing example are Cost of start-up delays and ilmenite sands, a substantial reduction of the up estimated costs based on a hypothetical typical o f those found in practice. contingencies. bulk sample or o f its concentrate by mixing and operation using a method or combination of Reasonable profit. The second example has been taken from the splitting is generally a proper procedure and a methods proven effective in similar deposits common practice. In turn, some o f the factors influencing the prospecting records of an operating company. In elsewhere. This estimating procedure has been this case the gold-bearing gravel excavated from operating cost will be: REPORTING VALUES illustrated by Staley and Storch in a two-part each o f 14 shafts was divided as carefully as Type of operation (dredge, hydraulic, article titled “ Choosing a mining method for In the United States, the volume o f placer possible by taking alternate buckets as the work sluiceplate, etc.) gold-bearing gravels.” This article has been listed material is always reported as bank-measure cubic progressed. The hand-dug shafts were 40 inches Size and tenor of the deposit. among the selected references which follow. in diameter and ranged from 30 to 40 feet deep. yards and the value is customarily reported as Character o f the gravel and bedrock. Examples o f 1964 costs are given in Appendix E. The individual halves, averaging 7)4 cubic yards cents per cubic yard. Water supply. each, were washed separately. Results are shown In addition to the calculated value, the actual Grade for sluices. in the above tabulation. weight o f gold in milligrams, its fineness or SELECTED REFERENCES CONTAINING The foregoing examples show that the splitting o f estimated fineness, and the price o f gold used in Disposal area for tailings and muddy PLACER COST DATA gold placer samples should be strictly avoided the value calculation should be noted on the water. unless there is some very special reason to divide sample sheets as well as in subsequent reporting. Working season. Averill, Charles V., Dragline dredging in Siskiyou a sample or reduce its volume before washing or Minerals other than the precious metals are Regulatory laws (land restoration, etc.) County: Thirty-seventh Report of (Calif.) State other treatment. In cases where this must be reported as pounds per cubic yard, percent, or If the foregoing are kept in mind and weighed Mineralogist, pp. 328-331. April, 1949. Costs o f done, the mineral examiner should be fully aware the particular unit customarily used for the intelligently, a fair cost estimate can usually be principal items o f equipment noted. Also cost o f 72 o f the erratic and probably misleading results commodity in question. made by comparing the subject property with a a resoiling project. 73 Bureau o f Mines Staff, Minerals Yearbook,, annual Contains detailed operating data for a typjCl| operations. These devices or schemes seem to today’s methods and equipment. Operating volumes. Current economic trends and effects on dragline dredge. have an unfailing attraction for miners as well as economies made possible by the large capacity mining industry. and the simplicity o f conventional riffles and Patman, Charles G., Methods and costs o f dredginj for the general public. placer jigs more than offset the dollar value o f _____ Production potential of known gold deposits in auriferous gravels at Lancha Plana, Amaifa But despite the many “improved” placer the gold they may lose. On this basis, they yield the United States: U.S. Bureau o f Mines County, California: U.S. Bureau of Mine; machines and the new gold-saving methods that Information Circular 8331, pp. 11-14, 1967. Information Circular 6659, 17 pp. 1932, have been offered, the simple Hungarian-type the greatest operating profit. Notes current cost estimates for dredging, Describes construction, operation, and operating riffle has held its place in the placer industry Even where a new or improved recovery method drift-mining and hydraulicking. Also capital cost costs of a 6-cu. ft. bucket-line dredge. while most o f its rivals have been discarded. A may be shown to possess some potential, if it is for bucket-line dredges. notable exception is the placer-type jig which has not yet at the stage where it can be presented as a Romanowitz, Charles M., Floating dredges used fa Chellson, Harry C., What will it cost to work a gold supplemented the riffled tables (sluices) in some proven method or technique, the mineral mining purposes: Mineral Information Service placer o f medium size? Engineering and Mining dredging operations and has replaced them in examiner has little choice but to rely on standard Vol. 20, No. 7, pp. 82-87. July, 1967. (Published Journal, Vol. 135, No. 10, pp. 441-445. October, anaytical and recovery methods when making his by California Division o f Mines and Geology), others. 1934. Costs for various size operations using a evaluation. Discusses onshore and offshore dredging including It can be said generally that the success o f a mobile dryland washing plant. tin and other minerals. Compares hydraulic placer operation will hinge on the throughput, a Daily, A.F., Chapter 13.5 (Placer Mining) in AIME (suction) dredges and bucket-line dredges. Notes high throughput being the key to low costs. In Surface Mining volume: Published by Amer. Inst, dredging costs in South America and Yukon other words, the greater the throughput the REFERENCES CITED (PART VI) o f Mining, Metallurgical and Petroleum Engineers, Territory. Reviews history of dredging and latest lower the unit cost. Experience has shown that to Inc., New York. 1968. developments. achieve the optimum working rate some recovery Clifton, H. Edward, Hubert, Arthur, and Phillips, R. must be sacrificed, or put simply, it is cheaper to Lawrence, Marine Sediment Sample Preparation Eassie, W. H., What does hydraulicking cost? Staley, W. W., and Storch, R. H., Choosing a mining lose a certain amount o f gold than to save it. for Analysis For Low Concentrations of Fine Engineering and Mining Journal, Vol. 145, No. 6, m eth od for gold-bearing gravels, Part 1: To date no one had demonstrated a placer Detrital Gold: U.S. Geol. Survey Circular 545, pp. 92-94. June 1944. 1939-1941 costs for a Engineering and Mining Journal. Vol. 138, No.7. recovery system that can economically replace 1967.11 pp. medium-size hydraulic mine in British Columbia, pp. 342-346; also p. 359, July, 1937. Part II: Vol. Canada. 138, No. 9, pp. 43, 44. Sept., 1937. Develops Gardner, E. D., and Allsman, Paul T., Power-shovel hypothetical mining programs and comparative and dragline placer mining: U.S. Bureau o f Mines costs for working a placer (in Alaska) by Information Circular 7013, 68 pp., 1938. hydraulicking, power drag-scraper, and dredging. Detailed cost data for floating and stationary A good example of a placer cost study. plants. Thomas, Bruce I., Cook, Donald J.. Wolff, Ernest, Gardner, E. D., and Johnson, C. H., Placer Mining in and Kerns, William H., Placer mining in Alaska: the W estern U n ited States. I. General U.S. Bureau o f Mines Inforamtion Circular 7926, Information, hand-shoveling, and ground sluicing: 34 pp. 1959. Describes mining methods and gives U.S. Bureau o f Mines Information Circular 6786, unit operating costs at operations where hydraulic 73 pp. 1934. and mechanical equipment is used with nonfloating washing plants, including sluiceplatc ------Placer mining in the Western United States. II. mining operations. Hydraulicking, treatment o f placer concentrates, and marketing o f gold: U.S. Bureau o f Mines Thurman, Chas. H., Costs in dragline gold dredging: Information Circular 6787, 88 pp. 1934. Contains A.I.M.E. Technical Publication No. 1900 (1945), o p e ra tin g and cost data on small-scale 6 pp. Compares bucket-line and dragline dredge hydraulicking. costs. Gives examples o f equipment and operating costs. ------Placer mining in the Western United States. III. Dredging and other forms o f mechanical handling o f gravel, and drift mining. U.S. Bureau o f Mines 5. UNPROVEN PROCESSES Information Circular 6788, 81 pp., 1935. Many special placer machines or secret recovery Lord, Harry S., Modern dragline dredging: Mining processes have been “ invented” or proposed. World, Vol. 3, No. 10, pp. 14-16. Oct., 1941. Some claim the ability to extract microscopic or Cost o f principal items o f equipment for lki cu. colloidal gold from materials that show little or yd. to 12 cu. yd. dragline dredges. no value when tested by fire assay or by the normal methods o f testing placer material. Others Magee, James F., A successful dragline dredge: are intended to recover the varying amounts of A.I.M.E. Trans., Vol. 126 (1937), pp. 180-200. fine gold admittedly lost in large-scale placer 75 PART VII

CHECK LIST FOR PLACER INVESTIGATIONS •vl 6 G xs, a poe xesv o cue premature cause or expensive prove can exist, muddy water disposal problems, where they they where problems, examiner. disposal mineral water the assessor tailings muddy properly to or recognize to concern Failure be prime always should of distribution and number, size, disastrous to a placer operation their maximum maximum their operation placer a to disastrous dredging project. Because boulders can be be can boulders Because to one than project. failure more to and dredging fatal proved has known this to consider be and up hardness its taken must cases be such irregularities In must pay. the bedrock recover f o commercial feet a several in value the f o most Sometimes a develop will investigation mineral adequate An placer is found on or in the bedrock; perhaps perhaps bedrock; the example: in or For on found prospect. is placer a the assessing f o when vital worth found actual be will which considerable body o f information in addition to to addition in information f o body considerable that obtainable from samples alone, some o f f o some alone, samples from obtainable that NRL CONSIDERATIONS ENERAL The following check list is intended first as a field field aas first isintended list check following The guide and second, to show the range o f inquiry inquiry f o range the show to second, and guide be can rule no alike, are deposits two no Because more considering or f o much the as placer a determine f o failure often or details success operation. physical profitable brief, In otherwise an f o shutdown investigation. The user should, o f course, tailor tailor course, needs. f particular his o suit to list this placer should, user adequate an The for investigation. necessary be may which gathered. be should well-informed a report afor data value sufficient required, be here, even not prospective but may or investigation field value adetailed no that has evident clearly property is it Where vary will investigation. inquiry f o degree placer the a in Also, included list. be check should what to as made overemphasized. be cannot iey eedn o te ups of the f o purpose the on depending widely importance The itself. content mineral the than all factors and their possible effect effect possible their and factors 2. FIELD GUIDE AND CHECK LIST FOR PLACER INVESTIGATIONS 14. Gradient o f deposit: Less than 5% ( ); More than 5% ( ).

1. Date o f examination______Remarks.------

2. NAME OF CLAIM(s) OR PROPERTY ______

15. Is the deposit dissected by deep washes or old workings? Y es( ); No ( ).

Remarks------3. State , County District

4. Township ______Range______Section(s)

5. REASON FOR EXAMINATION______16. Type and extent o f overburden

6. EXAMINED BY 17. Depth to permanent water table

7. Assisted b y ____

8. Others present _ 18. Depth to bedrock

9. Number o f claims or acres 19. Kind o f bedrock (rock type)

10. NAMES OF LOCATORS AND PRESENT OWNER 20. Hardness o f bedrock ______

21. Bedrock slope or contour to be expected

11. Owner’s Address

12. TYPE OF DEPOSIT (stream, bench, desert, etc.)

22. Are high bedrock pinnacles or reefs in evidence? ^ es ( ), No ( ).

Remarks

13. Terrain 23. Gravel is: Well-rounded ( ); Sub-rounded or Sub-angular ( ); Angular ( ). 31. Cemented gravel? Y es( ); No ( ). Remarks

Remarks .______

24. Does gravel contain rocks over 10-inch ring size? Y es( ); N o ( ). 32. Caliche? Y es( ); No ( ). Remarks

Remarks .______

25. BOULDERS (Max. size, number, distribution, etc.) 33. Permafrost? Yes ( ); No ( ). Remarks

34. Buried timber? Y e s( ); N o ( ). Remarks

26. Rock types noted in gravel 35. Hard or abrasive digging conditions? Y es( ); No ( ). Remarks

27. Predominent rock type (if any) 36. Character o f gold: Coarse ( ); Flaky ( ); Fine ( ); Rough ( ); Shotty ( ); Smooth ( ); Bright ( );

Stained or coated ( ). R em arks------

28. SAND (kind, amount, distribution, etc.)

37. Can good recovery be expected by use of riffles or jigs? \ es ( ); No ( ). Remarks

29. Sorting or bedding patterns (if apparent)

38. Is recovery said to depend on secret process or special equipment? Yes( ); No ( ). Remarks

30. STICKY CLAY? Yes( );N o( ). Remarks

39. Are black sands said to contain locked gold values? ^ es ( ); No ( ). Remarks 40. Have black sands been checked for valuable minerals other than gold? Y e s( ); No ( ). 48. Present work (if any)

49. APPLICABLE MINING METHOD

50. Possible cost to bring property into production

51. POSSIBLE MINING COST

44. Are old workings in evidence? Yes( ); No ( ). Remarks

52. Dimensions of (physically) minable ground

45. Past production (if known)

53. Possible extensions

46. Date o f last production or work

54. Maximum yardage indicated to date

47. Reason for quitting 55. Mining equipment on ground 51 pish and Game regulations? Y e s( ); N o ( ). Remarks

56. Accessory equipment or improvements on ground 62. CAN SETTLING PONDS BE BUILT TO EFFECTIVELY RETAIN OR CLARIFY THE MUDDY WATER? Yes ( ); No( ). Remarks ______

63. IS PROPERTY SUBJECT TO RESOILING OR OTHER SURFACE RESTORATION REGULATIONS?

Yes ( ); No ( ). Remarks ------. 57. Water supply

64. Elevation o f property

65. Climate ------58. Power supply

66. Working season -----

67. Season governed by

59. DOES PROPERTY HAVE ADEQUATE TAILINGS DUMP ROOM? Yes ( ); No ( ). Remarks 68. Surface cover and its effect on mining

60. Would mining in this area come under County, State or Federal water quality control regulations? 69. Merchantable timber or other surface values

Yes( ); No ( ). Remarks

87 70. Nearest town 71. Access 7h Other reference sources

72. Reference maps 77. SAMPLING (describe or attach notes)

i 3. Aerial photos (USGS, Forest Service, etc.)

78. Additional information and remarks

74. Reference literature

75. Previous examinations or reports

79. Attach suitable map or sketches (if needed). ------

80. Attach photographs o f pertinent features (if available).

89 PART VIII

GLOSSARY OF PLACER TERMS Many of the following terms have universal Institute. Doubleday & Company, Garden City, definitions, that is, they have definitions common to N.Y. 1962. all branches o f the mineral industry. On the other hand Brooks. Brooks, A. H., The Gold Placers o f Parts some are unique to the placer industry or at least o f Seward Peninsula, Alaska. U.S. Geol. Survey they have placer-related meanings different from Bull. 328, pp. 114-145, 1908. those in general use. For example: The term FLOTATION, as used in the general mining industry, Duim, E. J. Dunn, E. J., Geology o f Gold. Charles relates to a mineral separation process. But in placer Griffin & Co., London. 1929. mining, the term FLOTATION is applied to the minimum water depth needed to move an operating Dunn, R. L. Dunn, Russell L., Drift Mining in dredge. California. In Eighth Report o f the (Calif.) State Mineralogist, pp. 736-770. 1888. It should also he noted that the definitions given here are intended to be descriptive rather than legal, and Fay. Fay, Albert H., A Glossary o f the Mining and they should be used accordingly. Mineral Industry. U.S. Bureau o f Mines Bull. 95. 1920. Names in parentheses refer to sources as follows: AGI. Dictionary o f Geological Terms. Prepared McKinstry. McKinstry, Hugh E., Mining Geology. under the direction o f the American Geological Prentice-Hall, New York. 1948.

ACCRETION BAR. A low-level deposit o f sand and AIRPLANE DRILL. A compact, engine-powered gravel formed in a stream by gradual addition o f placer drill designed for use in areas o f difficult new material. Accretion bars are typically formed access. The term AIRPLANE DRILL is actually a along the short, or inside radius o f curves. See - trade name which through common use, has Skim bar. become part o f the placer vernacular.

ADJUSTED VALUE. A sample value that has been ALLUVIAL. 1. Deposited by a stream. 2. Relating increased or decreased by an amount deemed to deposits made by flowing water. (Fay) necessary to offset known variables or other factors that may cause discrepancies in the ALLUVIAL FAN. A cone-shaped deposit of initially indicated value. In placer drilling, the alluvium made by a stream where it runs out onto adjusted value is also known as a CORRECTED a level plain or meets a slower stream. The fans VALUE. To be valid, such adjustments must be generally form where streams issue from based on careful diagnosis o f sampling problems, mountains upon the lowland. (AGI) and must reflect sound judgement. See ALLUVIAL GOLD. Gold found in assocation with Indicated value. water-worn material.(Fay) AINLAY BOWL. A wet, gravity concentrator used ALLUVIAL PLAIN. 1. Flood plains produced by for the recovery o f gold and other heavy minerals the filling o f a valley bottom are alluvial plains and from alluvial materials. It consists essentially o f a consist o f fine mud, sand, or gravel. 2. A plain howl-shaped vessel, rotated about its vertical axis resulting from the deposition o f alluvium by and provided with circular riffles. Feed entering at water. (AGI) the center is carried upward and outward by the flow o f water and centrifugal force. Tailings ALLUVIUM. A general term for all detrital deposits overflow the rim while gold and other heavy resulting from the operations o f modern rivers, minerals are retained by the riffles. A somewhat thus including the sediments laid down in river similar howl-shaped concentrator is known as the beds, flood plains, lakes, fans at the foot o f KNUDSEN BOWL. mountain slopes, and estuaries. (AGI) 93 AMALGAM. An alloy of mercury with gold or man or animal-powered sweep attached to tht another metal. In the case o f placer gold, a “ dry” overlaying red gravels. Actually, these blue gravels is equipped with buckets having a struck capacity upper section. Men standing on an attached amalgam, that is, one from which all excess represent unoxidized portions o f the gravel o f 18 cubic feet each. Compare with Dragline platform, chop up the drill core and remove it mercury has been removed by squeezing through channels whereas the red gravels represent the dredge; also Suction dredge. from the casing by means o f hand-powered tool* chamois leather will contain nearly equal oxidized portions o f the same material. Also known as an EMPIRE DRILL. BULLION. Unrefined gold that has been melted and proportions o f gold and mercury. BLUE LEAD, (pronounced leed) See — Blue gravel. cast into a bar. In placer mining, the gold sponge BAR. A deposit o f alluvial material above or below AMALGAMATION. The extraction of the precious BOOMING. A variation o f ground sluicing in which obtained by retorting amalgam, is commonly the water line o f present streams. Bars may form metals from their ores by treatment with mercury. water is stored in a reservoir and suddenly released melted with borax or other fluxes, then poured where the current slackens or changes direction. into a bullion bar. See — Sponge. ANCIENT BEACH PLACER. Deposits found on the See — Accretion bar. to provide a rush o f water, in a large volume, coastal plain along a line o f elevated beaches. which erodes and transports the gravel. Booming is BURIED PLACER. Old placer deposits which have (Brooks) BATEA. A wide and shallow, cone-shaped vessel, generally employed where water is scarce. In become buried beneath lava flows or other strata. usually o f wood, used for panning gold. The batea! California the contrivances for collecting and ANCIENT CHANNEL. See Tertiary channel. (Fay) See — Tertiary Channel. is in common use in Mexico, Central and South discharging water are termed SELF-SHOOTERS. ANNUAL LABOR. See Assessment work. America, and Asia. BY-WASH. In many cases, hydraulic giants are See - Ground sluicing. capable o f cutting more material from the bank, ASSAY.(verb) T o determine the amount o f metal BEACH PLACER. See Sea-beach placers. BRAIDED STREAMS. 1. A braided stream is one than can be swept into the slucies by means o f the contained in an ore. (McKinstry) BED LOAD. Soil, rock particles, or other debris flowing in several divided and reuniting channels giants alone. In such cases supplemental water 1. The act of making such a determination. rolled along the bottom o f a stream by the movin« resembling the strands o f a braid, the cause o f may be brought into the pit by means o f a ditch, 2. The result o f such a determination. water, as contrasted with the “ silt load” carried in division being the obstruction by sediment to assist carrying the material to the sluices. This is See — Fire assay. suspension. (AGI) deposited by the stream. 2. Where more sediment locally called BY-WASH, BY-WATER or BANK is being brought into any part o f a stream than it WATER. ASSAY VALUE. The amount o f gold or silver, BEDROCK. The solid rock underlying auriferous can remove, the building o f bars becomes contained in an ore or other material, as shown by gravel, sand, clay, etc., and upon which the alluvial BY-WATER. See-By-Wash. assay o f any given sample. excessive, and the stream develops an intricate gold rests. (Fay) In placer use, the term bedrock network o f interlacing channels, and is said to be CABLE DRILL. See — Churn drill. ASSESSMENT WORK. The annual work upon an may be generally applied to any consolidated braided. (AGI) 3. Conditions which cause braiding CABLEWAY SCRAPER. See — Slackline scraper. unpatented mining claim on the public domain formation underlying the gold-bearing gravel. are common in glacial areas where much sediment necessary under the United States law for the Bedrock may be composed of igneous, CAISSON. A metal cylinder used to sink prospect is added by the melting ice and in semiarid regions maintenance of the possessory title thereto. Same metamorphic or sedimentary rock. See — False shafts in loose ground or in the presense o f a large where the transporting power o f streams is as ANNUAL LABOR. (Fay) bedrock. quantity o f water. Caissons are usually provided in reduced by seepage and evaporation. In general, sets o f 4 or more telescoping units. AURIFEROUS. Containing gold. BENCH PLACER. Gravel deposits in ancient stream such conditions are not conducive to the channels and flood plains which stand from 50 to BAJADA PLACER. Placers found in confluent formation o f placers. CALICHE. A brown or white material commonly several hundred feet above the present streams. alluvial fans along the base o f a mountain range or found as a subsoil deposit in arid or semi-arid (Brooks) BREAKOUT. A point where a ravine or canyon cuts in a mantle of rock debris along the lower slope of climates, and which is composed largely o f into, but not through, a channel. (Dunn, R. L.) a mountain range, in arid regions. The deposits BLACK GOLD. Alluvial gold coated by black oxide calcuium carbonate. It is commonly encountered Usually applied to buried Tertiary channels. are mainly residual detritus and poorly sorted o f manganese. (Dunn, E. J.) in desert placers where its cementing effect Compare with Outlet, and with Inlet. adversely affects the mining and washing alluvium found in gulches and on slopes that are BLACK SAND. Heavy grains o f various minerals BREAST. The working face of a prospect drift on the processes. subject to occasional torrential rain wash. Bajada which have a dark color, and are usually found pay lead; the face o f a gangway being mined. is the Spanish term for slope. This term has not accompanying gold in alluvial deposits. (Fay) The CANNON CONCENTRATOR. See — pinched sluice. found general use in placer mining, most bajada (Dunn, R. L.) heavy minerals may consist largely o f magnetite, CAPPING. Volcanic flow materials or agglomerates placers being referred to collectively as “Desert” BUCKET-ELEVATOR DREDGE. See - ilmenite and hematite associated with other that cover and in some cases, conceal underlying placers. Bucket-Line dredge. minerals such as garnet, rutile, zircon, chromite, auriferous gravels. Commonly found associated BANK-MEASURE. The measurement o f material in amphiboles, and pyroxenes. In Western gold BUCKET-LINE DREDGE. A dredge in which the with Tertiary channels in California’s Sierra place, such as gravel in a deposit before placers, the black sand content is commonly material excavated is lifted by an endless chain of Nevada region. Also called CAP ROCK. excavation. In placer work, values are normally between 5 and 20 pounds per cubic yard of buckets. (Fay) Also known as Connected-bucket CASING. Steel tubing or pipe used to case a drill reported as cents per cubic yard and unless bank-run gravel. dredge. The type o f bucket-line dredge generally hole. In placer sampling it is usually driven into specified otherwise, this means a cubic yard in employed in placer mining is a self-contained BLUE GRAVEL. Some of the deeper, the formation ahead o f the drill bit and when so place, or bank-measure. digging, washing and disposal unit, operating in a water-saturated gravels found in California’s used, is commonly called a “ drive pipe” BANK WATER. See By-Wash. Tertiary channels have a distinctive bluish-gray pond and capable o f digging, in some cases, more than 100 feet below water. Its machinery is CASING FACTOR. The depth to which a churn color and for this reason early miners referred to BANKA DRILL. A placer drill consisting essentially mounted on a shallow-draft hull and the dredge drill casing must be driven to take in a sample them as “ blue gravel” or more commonly, as the o f a flush-jointed casing equipped with a serrated backfills its working pit (pond) as it advances. The volume o f I cubic yard. For example, a standard “ blue lead” . At one time they were believed to cutting shoe. The casing is rotated by means o f a capacity o f individual buckets is used as a measure 6-inch drive pipe equipped with a new, 7Vi-inch represent a separate gravel flow, distinct from the of dredge size. For example, an “ 18-foot” dredge drive shoe would be driven 88 feet to cut out a 95 CORE RISE. The measured length of the cylinder of DISCOVERY. The finding o f a valuable mineral theoretical volume of 1 cubic yard. This is COCOA MATTING. A heavy, coarse-woven fab^ crravel entering a churn drill casing as it is driven deposit in place upon a mining claim. Although sometimes called PIPE FACTOR, but it is most made o f jute-like material and commonly placej downward. For example, a standard 6-inch casing “ Discovery” and “ valuable” , as they relate to commonly known as the DRIVE SHOE FACTOR. on the bottom o f a sluice to aid in saving fjne fitted with a 7J4-inch drive shoe should produce a mining claims, have not been defined by statute, a See — Radford factor. gold. core rise of 1.7 feet per foot of drive. The long history o f court decisions have held that in CEMENT. The Material that hinds together the sand COLLOIDAL GOLD. Gold in an extreme stated difference between the actual core rise and the order for a location to be valid, there must be a and gravel particles in an indurated placer or other subdivision. In a true colloid, the individual theoretical rise is sometimes used as a factor for discovery o f mineral within the limits o f the claim formation. The cementing material can be particles are o f almost molecular dimensions. adjusting drill hole sample values. and the discovery must be such as would justify a calcareous, silicious or ferruginous. Also used person o f ordinary prudence in the further COLLUVIAL. Consisting o f alluvium in part and CORRECTED VALUE. See — Adjusted value. when referring to the hardened formations as a expenditure o f time and money, with reasonable also containing angular fragments o f the original whole. Cemented gravels must, in some cases, be rocks. (Fay) CRADLE. See - Rocker. prospect of success in developing a profitable milled to release their gold content. mine. In some decisions the word “valuable” is CREEK PLACER. Gravel deposits in the beds and COLOR. A particle of metallic gold found in the interchanged with “ profitable” . CEMENT CHANNEL. A channel depression intermediate flood plains o f small streams. prospector’s pan after a sample o f earth has been completely filled with lava, no auriferous gravel. washed. Prospectors say, “ The dirt gave me so I (Brooks) DISCOVERY CLAIM. (Alaska) A claim covering the (Dunn, R. L.) many colors to the pan” . (Fay) CREVICING. A small-scale mining method in which initial discovery on a creek. Subsequent claims are commonly designated as one above, two above, CHALK. Volcanic tuff or ash, largely rhyolitic in CONCENTRATE, (verb) To separate a metal or the miner removes detrital material from cracks three above; one below, two below, etc., composition, is commonly found as mineral from its ore or from less valuable material, 1 and crevices in the bedrock, usually by means o f depending on their position in relation to the intraformational strata or masses in Tertiary (noun) The product of concentration. pry bars and long-handled spoons, and washes the channels o f California’s Sierra Nevada region. The material to recover its gold content. discovery claim. CONCENTRATION. The removal by mechanical whiter, fine-grained and homogeneous beds are means o f the lighter and less valuable portions of CRIBBING. Close timbering, as the lining o f a shaft. DOODLEBUG. 1. Miners’ term for a dragline locally called “ Chalk” ore. (Fay) (Fay) In placer work, cribbing may be needed to dredge. 2. A divining rod or similar device CHANNEL. A stream-eroded depression in the support the walls o f shaft or test pits down in supposedly useful for locating gold or other CONFLUENCE. A junction or flowing together o( bedrock, ordinarily filled with gravel. See valuable minerals. See — Dragline dredge. streams; the place where streams meet. (Fay) loose or wet ground. Tertiary channel. DEBRIS. The tailings from hydraulic mines. DRAGLINE. A power shovel equipped with a long CONGLOMERATE. Rounded waterworn fragments CHURN DRILL. A portable drilling machine boom and a heavy digging bucket that is of rock or pebbles, cemented together by another DEEP LEAD, (pronounced leed) A gold-bearing arranged to successively raise and drop a heavy suspended from a hositing line and is pulled mineral substance. (AG1) alluvial deposit buried below a considerable string o f tools suspended from a drill line. By toward the machine by means o f a “ drag” line. By CORE. See — Drill core. thickness o f soil, lava or other barren material. See means o f the successive blows the formation is manipulating the two lines (wire ropes), the bucket -Tertiary channel. chopped up and the hole deepened. The type of CORE FACTOR. In churn drilling, when the casing can be caused to dig, carry, or dump the excavated churn drill designed for placer sampling is often is driven downward ahead o f the drill bit, it should ! DESERT PLACER. See — Dry placer. material. Such a machine is more properly called a referred to as a “ Keystone” drill or “ placer” drill. take in a cylinder o f gravel having a diameter equal DETRITUS. A general name for incoherent dragline excavator. See — Dragline dredge. A hand-powered type, used extensively in South to the effective diameter (cutting edge) of the j sediments, produced by the wear and tear o f rocks DRAGLINE DREDGE. A dragline dredge consists America, is known as a “ Ward” drill. drive shoe. If the effective diameter o f the shoe through the various geological agencies. The name o f two units; a self-propelled power shovel were the same as the inside diameter o f the casing, is from the Latin for “ worn” rock waste. (Fay) A CLAIM. See — Mining claim. equipped with a dragline bucket, and a floating a 1-foot drive would produce a 1-foot core rise deposit o f such material. CLEAN-UP. 1. The operation of collecting the gold inside the casing. But this is not so. Take for washing plant which is similar to, but usually or other valuable material from the recovery example a standard 6-inch casing equipped with a DIP BOX. A modification o f the sluice box used for smaller than that o f a bucket-line dredge. The system o f a dredge, hydraulic mine or other placer new, 7/2-inch drive shoe. The effective area of the small-scale mining where water is scarce. It washing unit contains a hopper for receiving gravel operation. 2. The valuable material resulting from shoe is 44.17 square inches while that of the generally consists of a short sluice made of 1 x dug by the dragline; a revolving screen; riffled a clean-up. casing is about 26 square inches. As a result, when 12-inch lumber, and standing on legs arranged to sluices or orther gold-saving equipment, and a driven, the core should rise 44.17/26 = 1.7 or, in provide a steep slope. The gold-bearing material is tailings stacker. Dragline dredges are generally COARSE GOLD. The word “ coarse” , when applied other words, there should be a 1.7-foot core rise washed in batches by first shoveling it into the employed to mine relatively small, shallow to gold, is relative and is not uniformly applied. inside the casing for each foot o f drive. Here the upper end o f the dip box and then pouring water deposits that are too small to amortize a Some operators consider coarse gold to he that over it, usually from a dipper. bucket-line dredge. which remains on a 10-mesh screen. Others CORE FACTOR is 1.7. The core factor will, of c o n s id e r individual particles weighing 10 course, vary according to the combination of DIRT. A miner’s term for auriferous gravel or for DREDGE. A machine, operated by power, and milligrams or more to be coarse gold. Some apply casing and drive shoe used, and it will vary with the material being worked. See — Pay dirt. usually mounted on a flat-bottomed hull provided the amount o f wear on a given shoe. The core rise the term “ coarse gold” to any particle that is DISCHARGE HEAD. The vertical distance from the with the equipment necessary to dig, process, and per foot o f drive is less commonly referred to as relatively thick as compared to its diameter and center o f a pump to the center o f the discharge dispose o f alluvial or other unconsolidated the SHOE FACTOR, but to do so, invites risk of can be easily picked up with the fingers. outlet where the water is delivered, to which must materials o f a type found at the bottom o f rivers confusing it with other factors or terminology. See be added the loss due to friction o f the water in or in certain terrestrial and offshore deposits. See COBBLE. A smoothly rounded stone, larger than a Drive shoe factor; Pipe factor; Casing factor; the discharge pipe. — Bucket-line dredge; Dragline dredge; Jet dredge. 97 pebble and smaller than a boulder. (Fay) Drill factor; Radford factor. DREDGE SECTION. The depth o f gravel, or a sample volume of 1 cubic yard. For example to 7 cubic yards per miners' inch per 24 hours. 2. overhangs, thus creating conditions well-suited for particular vertical section within a placer deposit, standard 6-inch drive pipe equipped with a new The effectiveness o f water generally. the saving o f fine gold. When used as riffles, that will pay to mine by dredging. 7/4-inch drive shoe would be driven 88 feet to cut expanded metal is generally placed over cocoa out a theoretical sample volume o f 1 cubic yard ELECTROSTATIC SEPARATOR. A device DRIFT, (geol.) Any rock material, such as boulders, matting or similar material. A flat-lying style o f This is less commonly called the PIPE FACTOR employing charged fields with little or no current till, gravel, sand, or clay, transported by a glacier expanded metal (without overhangs) is less-suited flow, and used to extract or separate the and deposited by or from the ice or by or in water or CASING FACTOR. See — Radford factor. component minerals o f sands or heavy mineral for this use. derived from the melting o f the ice. (Fay) DRY DIGGINGS. In the 1850’s, placers inoralonj concentrates. Speaking generally, electrostatic FALSE BEDROCK. A hard or relatively tight DRIFT, (mining) 1. A sub-tunnel running from the the banks o f California’s rivers were known as I separators do not make sharp separations and they formation within a placer deposit, at some main tunnel to prospect for the pay lead; 2. A “ Wet diggings” , and those in the dry ravines are sensitive to humidity, temperature, and other distance above true bedrock, upon which gold sub-tunnel run from the main tunnel across the adjacent to the rivers were referred to as “Dry variables. Electrostatic separators have not found concentrations are found. Clay, volcanic ash, pay lead to block out the ground and to facilitate diggings” . Compare with DRY PLACER. wide application in placer mining. Compare with caliche or “ tight” gravel formations can serve as its working; 3. Generally, a sub-tunnel. (Dunn, R. DRY PLACERS. Placers in arid or semiarid regions High Tension separator. false bedrocks. A deposit may have gold L.) or generally where surface water is not available. ELEVATED SLUICE. See — Trestle sluice. concentrations on one or more false bedrocks, DRIFT MINING. A method o f mining gold-bearing DR\ WASHER. A device for recovering gold or with or without a concentration on true bedrock. ELEVATOR. A device for ejecting gravel or tailings gravel by means o f drifts, shafts or other other heavy minerals from dry alluvial material from a hydraulic mine pit. See — Hydraulic FANNING CONCENTRATOR. See - pinched underground openings, as distinguished from without the use o f water. The typical dry washer elevator; Rubel elevator. sluice. surface methods for placer mining. is a small, hand-powered machine employing a DRILL. See — Churn drill. sloping riffle board and a bellows or blower ELUVIAL DEPOSIT. See — Eluvium. FINE GOLD. 1. Pure gold, i.e., gold of arrangement. The bottom o f the riffle board is ELUVIUM. L o o s e material resulting from 1000-fineness. 2. Gold occurring in small particles DRILL CORE. A cylindrical core o f sand and gravel made o f some porous material such as heavy cloth. decomposition o f rock. Eluvial material may have such as those which would pass a 20-mesh screen forced upward into the drill casing as the casing or Puffs of air forced up through the bottom by the slumped or washed downhill for a short distance but remain on 40-mesh. “ drive pipe” is forced into the deposit, usually bellows or blower, cause the lighter materials to but it has not been transported by a stream. ahead o f the drill hit. See — Core rise. FINENESS. The proportion o f pure gold in bullion hop over the riffles and work their way through EMPIRE DRILL. See — Banka drill. or in a natural alloy, expressed in parts per DRILL FACTOR. A figure used to designate the the machine, while the gold or other heavy thousand. Natural gold is not found in pure form; effective area o f a drive shoe used in placer EOCENE. One o f the earliest o f the epochs into materials lodge behind the riffle bars. it contains varying proportions o f silver, copper sampling. For example: A new, 7/ 2-inch drive shoe which the Tertiary period is divided; also the series DRY WASHING. The extraction of gold or other and other substances. For example, a piece of has an open area o f 0.306 sq. ft. but to allow for of strata (and auriferous gravels) deposited at that minerals from dry sand and gravel by the use of natural gold containing 150 parts o f silver and 50 wear and other variables, some engineers use a time. Specifically, an epoch of the Tertiary machines in which air is employed as a separating parts o f copper per thousand, and the remainder lesser figure (com monly 0.27) in their value between the Paleocene and Oligocene. medium. pure gold, would be 800-fine. The average fineness calculations. The figure so used is referred to as EROSION CYCLES. The Earth’s erosional land of placer gold obtained in California is 885. DRYLAND DREDGE. A mechanical washing plant, the DRILL FACTOR. See — Radford Factor; Core forms develop in successive stages which can be sometimes o f appreciable size, designed to follow 1 FINES. 1. The sand or other small-size components factor; Volume factor; Drive shoe factor. divided into three broad categories — youth, a dragline, or other excavator, as the mining cut o f a placer deposit. 2. The material passing DRILL LOG. The record o f a drill hole, usually maturity, and old age. Youthful land forms in the advances. Some are equipped with trommel-type through a screen during washing or other recorded on a prepared form as the work erosion cycle are featured by steep, narrow, revolving screens and rock stackers, and are processing steps o f a placer operation. progresses. The usual placer log, in addition to V-shaped canyons and fast-cutting streams. In mounted on crawler-type tracks. showing the drilling progress, type o f material time, as the valleys deepen, they become wider FIRE ASSAY. The assaying o f metallic ores, usually penetrated, its mineral content, etc., will also DUMP. 1. The fall immediately below a and have gentler slopes. In early maturity they are gold and silver, by methods requiring furnace heat. show the type and size o f equipment used, hydraulic mine outlet and in particular, the area roughly U-shaped instead o f V-shaped. In late (Fay) Fire assaying, in essence, is a miniature personnel employed, cause o f delays, and other available for tailings storage. 2. A specially maturity downcutting has become slow, and smelting process which recovers and reports the details o f the work. A complete log will also show prepared place outside of a drift mine, usually conspicious flats develop. Old age is marked by total gold content o f the assay sample, including near the portal, where the pay gravel is deposited , the essential calculations and all factors used in wide, flat valleys or peneplains, over which gold combined with other elements, or preparatory to washing. 3. A pile or heap of ' arriving at the reported value. sluggish streams follow meandering courses. The mechanically locked in the ore particles. material, usually waste material, extracted from a 1 mature stage is m ost fa v o ra b le for the Consequently, the gold value indicated by fire DRIVE PIPE. See — Casing. mine. development o f extensive placers. assay is not necessarily recoverable by placer DRIVE SHOE. A hardened steel protective shoe DUST. See — Gold dust. EXPANDED METAL. (Expanded-metal lath) A methods. For this and other reaons, the gold attached to the lower end o f a drive pipe or casing. type o f p u n ch ed -m eta l screen. The style content o f placer material is not normally The drive shoe is usually slightly larger in diameter DUTY. 1. A measure o f the effectiveness of watti commonly used in placer mining, for saving fine determined by fire assay. See — Free gold assay. than the casing and is provided with a beveled employed in hydraulic mining, usually expressed gold, consists o f a latticework o f diamond-shaped cutting edge. See — Casing. as the number o f cubic yards o f gravel washed per FLAKY GOLD. Very' thin scales or pieces o f gold. miners’ inch per day (M.I.D.). The duty varies openings (about 3 /4 ” x IF2” ) separated by raised DRIVE SHOE FACTOR. The depth to which a FLASK. The unit o f measurement for buying and with the coarseness o f gravel, height of bant metal strands that have a decided slope in one churn drill casing must be driven to take in a selling mercury (quicksilver). A standard iron flask grade, available head, etc., usually varying from 1 direction. When installed as riffles, with this slope leaning downstream, eddies form beneath the contains 76 pounds of mercury. 99 FLAT. An essentially level gravel bar or deposit FLUVIO-MARINE. Formed by the joint action ofa GRAIN. A unit o f weight equal to 0.0648 part o f a feet below the intake point (o f the pipe) would be along the banks o f a river. river and the sea, as in the deposits at the mouth, gram, 0.04167 part of a pennyweight, or said to be working with a 200-foot head. o f rivers. (Fay) FLOAT. A term much used among miners and 0.002083 part o f a troy ounce. There are 480 HEAVY GOLD. 1. Gold in compact pieces that grains in a troy ounce. A grain of fine gold has a geologists for pieces of ore or rock which have FOOL’S GOLD. A substance which superficially appear to weigh heavy in proportion to their size. fallen from veins or strata, or have been separated resembles gold; usually pyrite, a sulphide of iron value of 7.29 cents (@$35/oz.). 2. Rounded, “shotty” or “ nuggety” gold. from the parent vein or strata by weathering GRAM. A unit o f weight in the metric system equal FeS2 . H EAVY MINERALS. The accessory detrital agencies. Not usually applied to stream gravels. to 15.432 grains, 0.643 pennyweight, or 0.03215 FREE GOLD. Gold uncombined with other minerals o f a sedimentary rock, o f high specific (Fay) troy ounce. There are 31.103 grams in a troy substances. Placer gold. (Fay) gravity. (AGI) The black sand concentrate ounce. A gram o f fine gold has a value o f S I.12 (@ FLOAT-GOLD. Flour gold. Particles o f gold so common to placers, would more properly be FREE GOLD ASSAY. A procedure carried out to $35/oz.). small and thin that they float on and are liable to called a ‘heavy-mineral’ concentrate. determine the free gold content o f an ore. In the I he carried o ff by the water. (Fay) See — Flood GRAVEL. A comprehensive term applied to the HIGH-GRADE. 1. Rich ore. 2. To steal or pilfer ore gold. case o f placer material; a procedure to determine | water-worn mass o f detrital material making up a or gold, as from a mine by a miner. (Fay) the amount o f gold recoverable by gravity placer deposit. Placer gravels are sometimes FLOOD GOLD. Fine-size gold flakes carried or concentration and amalgamation. arbitrarily described as “ fine” gravel, “ heavy” redistributed by flood waters and deposited on I (large) gravel, “ boulder” gravel, etc. HIGH-GRADER. One who steals and sells, or gravel bars as the flood waters recede. Flood gold FREE-W ASH GRAVEL. Gravel that readily otherwise disposes o f high-grade or specimen ores. sometimes forms superficial concentrations near disintegrates and washes in a sluice. Loose, GRAVEL MINE. A placer mine; a body o f sand or (Fay) the upstream end o f accretion bars. See — Float clay-free gravels such as those found in accretion gravel containing particles of gold. (Fay) gold. bars are generally free-wash gravels. HIGH TENSION SEPARATOR. A machine, GRAVEL-PLAIN PLACERS. Placers found in gravel essentially consisting o f a rotating drum, upon FLOOD PLAIN. That portion o f a river valley, GIANT. See — Hydraulic giant; also Intelligiant. plains formed where a river canyon flattens and which a thin layer o f dry sand or mineral grains adjacent to the river channel, which is built of widens or more often, where it enters a wide, GLACIAL. Pertaining to, characteristic of. produced are fed, and an electrode suspended above the sediments during the present regimen o f the low-gradient valley. or deposited by, or derived from a glacier, (AGI) | rotating drum, or rotor. The electrode furnishes a stream and which is covered with water when the GRIZZLY. An iron grating which serves as a high voltage discharge at high current flow. High river overflows its banks at flood stages. (AG I) GLACIOFLUVIAL. Of, pertaining to, produced by, heavy-duty screen to prevent large rocks or or resulting from combined glacier action and river tension separators employ a high rate o f electrical FLOTATION. The minimum working draft of a boulders from entering a sluice or other recovery action. (Fay) See — Fluvioglacial discharge to separate various minerals according to dredge. When a dredge “ digs flotation” it equipment. their relative conductivity. Some are pinned to the excavates the ground to the minimum depth GOLD DUST. A term once commonly applied to rotor while others are attracted toward the GROUND SLUCING. A mining method in which required for floating the dredge. This is usually placer gold, particularly gold in the form of small electrode, with a resultant “ lifting” effect. The the gravel is excavated by water not under done when passing through tailings or moving colors. pinning and lifting effects, imparted in varying pressure. A natural or artificial water channel is between nearby working areas. degrees to different minerals, flattens or heightens GOLD PAN. See — pan. used to start the operation and while a stream of their respective trajectories as they leave the rotor. FLOUR GOLD. The finest gold dust, much of water is directed through the channel or cut, the GOLD-SAVING TABLES. The sluices used aboard a | Adjustable splitters placed in the trajectory are which will float on water. (Fay) Flour gold, such adjacent gravel banks are brought down by picking dredge are customarily called gold-saving tables, employed to cut selected minerals or groups of as that found along the Snake River in Idaho, at the base o f the bank and by directing the water rather than sluice boxes. minerals from the thus stratified stream o f commonly runs 3 million colors to the ounce. flow as to undercut the bank and aid in its caving. material. High tension separators differ from GRADE. 1. The amount o f fall or inclination from | Sluice boxes may or may not be used. Where not FLOURED MERCURY. (QUICKSILVER). The electrostatic separators in that the latter employ the horizontal in ditches, flumes, or sluices; , used, the gold is allowed to accumulate on the fin e ly granulated condition of quicksilver, charged fields with little or no current flow. High usually measured in inches fall per foot of length bedrock awaiting subsequent clean-up. A produced to a greater or less extent by its tension separators are extensively used for or inches fall per section o f sluice. 2. The slope of substantial water flow and adequate bedrock grade agitation during the amalgamation process. The separating heavy minerals recovered from beach a land or bedrock surface; usually measured in j are necessary. See — Booming. coating o f quicksilver with what appears to he a percent. A one percent grade is equivalent to a rise sands, monazite placers, etc. thin film o f some sulphide, so that when it is GUTTER. The lowest portion o f an alluvial deposit; or fall o f one foot per hundred. 3. The slope of a HILLSIDE PLACERS. A group of gravel deposits separated into globules these refuse to reunite. commonly a relatively narrow depression or stream, or the surface over which the water flows; j intermediate between the creek and bench placers. Also called Sickening and Flouring. (P ay) trough in the bedrock. In some placers the pay usually measured in feet per mile. Streams having Their bedrock is slightly above the creek bed, and streak is largely confined to a narrow streak or FLUVIAL. Of, or pertaining to rivers; produced by a grade o f about 30 feet per mile favor the the surface topography shows no indication o f “gutter” . river action, as a fluvial plain. (Fay) accumulation o f placers, particularly where a fair j benching. (Brooks) balance between transportation and deposition is HAND DRILL. See — Ward drill. Also see — Banka FLUVIATILE. Caused or produced by the action of HORN SPOON. See — spoon. maintained for a long time. 4. The relative value or drill and Empire drill. a river; fluvial. (Fay) tenor o f an ore, or o f a mineral product. HUMPHRYS SPIRAL. See — Spiral concentrator. HEAD. 1. A measure o f (water) pressure. 2. The FLUVIOGLACIAL. Produced by streams which GRADED STREAM. A stream in equilibrium, that height o f a column o f water used for HYDRAULIC DREDGE. A dredge in which the have their source in glacial ice. (Fay) See is, a stream or a section o f a stream that is . hydraulicking. For example, a hydraulic mine in material to be processed is excavated and elevated 100 Glaciofluvial. essentially neither cutting or filling its channel. which the point o f water discharge is 200 vertical from the bottom o f a stream or pond by means o f 101 openings, a fine-size concentrate will be collected MARINE MINING. The exploitation of sea-bottom a pump or a water-powered ejector. Large INLET. The point where a channel is cut off by a ' in a hutch beneath the screen. mineral deposits, including placers. See — Marine hydraulic dredges may he equipped with a digging ravine or canyon on the upstream end. (D u n n placer. ladder which carries the suction pipe and a R.L.) Usually applied to buried Tertiary channels. KEYSTONE CONSTANT. See — Radford factor. motor-driven cutter head, arranged to chop-up or Compare with Breakout; and with Outlet. k eysto n e d r i l l . See —Churn drill. MARINE PLACER. A deposit of placer-type otherwise loosen material directly in front o f the minerals on the ocean or sea bottom beyond the INTELLIGIANT. The trade name for a hydraulic knudsen BOWL. See — Ainlay bowl. intake pipe. Dredges having this configuration low-tide line, as distinguished from beach placers. giant that is provided with water-powered piston 1 employ a deck-mounted suction pump and they LACUSTRINE DEPOSITS. Deposits formed in the Some marine placers may contain material related and cylinder arrangements to control its vertical I may carry the mineral recovery equipment on bottom o f lakes. (Fay) Compare with Lake-bed to beach deposits formed during periods of low and horizontal traverses. Some models can be board the dredge or more commonly, they may placers. sea level. Others may contain stream-type placers rigged for automatic operation and can run | transport the excavated material, by means o f a LAKE-BED PLACERS. Placers accumulated in the or mineral concentrations formed on land and unattended in a preset arc or pattern. See - I pipe line, to a recovery plant mounted on beds of present or ancient lakes that were later drowned by a lowering o f the coastal region. independent barges or on the shore. See — Jet Hydraulic giant. generally formed by landslides or glacial damming. dredge; also bucket-line dredge. MATURITY (MATURE VALLEY). See - Erosion IRON SAND. 1. Magnetite or ilmenite-rich sand. 2. ^ (Brooks) It should be noted that a lake-bed (or cycles. HYDRAULIC ELEVATOR. A near-vertical pipe Black sand concentrate containing an abundance I lake-bottom) placer might actually be a drowned employed in hydraulic mining to raise excavated o f magnetite. stream placer. MEANDER. One o f a series o f somewhat regular material from the working place to an elevated and looplike bends in the course o f a stream, JET DREDGE. A form o f hydraulic dredge. Jet j LAVA. The term ‘Lava’ as used by a placer miner, sluice, or to a disposal area, by means o f a developed when the stream is flowing at grade, dredging equipment may range from a simple, may designate any solidified volcanic rock high-pressure water jet inducing a strong upward through lateral shifting o f its course toward the self-contained pipe-like venturi containing riffles, ! including volcanic agglomerates. current in the elevator pipe, see — Rubel elevator. convex sides o f the original curves. (Fay) that is carried by a diver and operates entirely 1 LEAD, (pronounced leed) Deeply buried placer HYDRAULIC GIANT. The nozzle assembly used in underwater to larger and more elaborate surface , MEDIUM-SIZE GOLD. Gold o f an approximate size gravel, where rich enough to work, and hydraulic mining. The giant is provided with a units carried on inflated rubber tubes or ■ that will pass through a 10-mesh screen and particularly when in a well-defined bed, is often swivel enabling it to be swung in a horizontal styrofoam floats. These devices, operated by one remain on a 20-mesh screen. Compare with Coarse termed the “ lead” or, “ pay lead” plane, and it may be elevated or depressed in a or two men, are similar in two ways: 1. They rely gold; also Fine gold. vertical plane. Nozzle sizes range from 1 to 10 LIGHT GOLD. Gold that is in very thin scales or on a water jet and venturi effect to pick up j MERCURY. A heavy, silver-white liquid metallic inches in diameter and the larger sizes are provided flakes or in pieces that look large as compared to unconsolidated stream-bottom materials and carry | element, useful in placer mining where its their weight. See — Flood gold. with a deflector, enabling them to be moved with them to a gold recovery device, usually riffles. 2. chemical affinity for gold is taken advantage o f to little effort. In California, giants discharging as The suction intake is normally hand-held and is I LITTORAL. Pertaining to the shore o f a lake, sea, help detain gold in a sluice box. Mercury placed in much as 15,000 gallons per minute in a single guided by a diver working on the stream bottom. 1 or ocean. the riffles forms a gold amalgam which is removed stream at a nozzle pressure o f over 200 pounds per The typical jet “ dredge” entails a small or modest LOCATION. See — Mining claim. at the time o f clean-up and then retorted to square inch, have been used. The giant is also capital outlay and is typically used for | recover the gold. The miners’ term for mercury is LONG TOM. 1. A small, sluice-type gold washer known as a “ Monitor” . Both terms stem from recreation-type mining. See — Hydraulic dredge, j “ Quicksilver” or simply, “ Quick” . Symbol, Hg; manufacturer’s trade names. See — Intelligiant. widely used in California during the 1850’s and specific gravity, 13.54. JET DRILL. A churn-type drill employing a string | 60’s. The early long tom was built in two sections; HYDRAULIC MINING. A method of mining in of reciprocal hollow rods equipped with a drill bit. a washing box equipped with a perforated plate to MILLIGRAM. The one-thousandth part o f a gram. which a bank o f gold-bearing earth or gravel is Water is pumped through the rods and discharged screen out the rocks; followed by a short sluice As a matter o f convenience, the milligram is washed away by a powerful jet of water and through an orifice near the bit. Cuttings resulting containing riffles. 2. A short auxiliary sluice used widely used as the unit for reporting gold weights carried into sluices, where the gold separates from from the chopping action o f the bit are carried to aboard a dredge to further reduce concentrate in placer samples. There are 31,103 milligrams in a the earth by its specific gravity. (Fay) the surface by wash water rising between the drill taken from the dredge riffles at clean-up time. 3. troy ounce. With gold at $35 per troy ounce, 1 HYDRAULIC MONITOR. See — Hydraulic giant. rods and casing. Rods are added as the hole A short sluice used to wash placer samples. milligram o f fine gold is worth 0.112 cent and 1 deepens, thus the drill cable does not go down the milligram o f ordinary placer gold is worth about HYDRAULICKING. Mining by the hydraulic LOW-GRADE. A term applied to ores relatively hole as would be the case in conventional churn 0.1 cent, or in other words, 10 milligrams to the method. Note spelling. poor in the metal for which they are mined; lean drilling. Jet drills are well suited to sampling cent. ore. (Fay) INCHES OF WATER. A common expression low-value minerals, such as ilmenite, occurring in MINERS’ INCH. A unit o f water measurement. denoting the quantity of water (in miners’ inches) beach deposits. MAGNETIC SEPARATOR. A device in which a Originally it represented the quantity o f water available or being used in a placer operation. See — strong magnetic field is employed to remove that will escape from an aperture one inch square Miners’ inch. JIG. A machine in which heavy minerals are magnetic materials from a sand or a concentrate, through a two-inch plank, with a steady flow of separated from sand or gangue minerals on a or to selectively remove or separate their INDICATED VALUE. The value of a placer sample, water standing six inches above the top o f the screen in water, by imparting a reciprocating constituent minerals. Magnetic separators are derived by formula, before making adjustments to escape aperture. The miners’ inch is now defined motion to the screen or by the pulsation of water commonly used in conjuction with high tension compensate for excess or deficient core rise, in the through the screen. Where the heavy mineral is separators to process the heavy mineral by statute in various states. case o f churn drilling; or before applying shaft larger than the screen openings, a concentrate bed concentrates obtained from beach sands, monazite 1 second-foot = 40 miners’ inches in Arizona, factors, boulder factors, or other empirical will form on top o f the screen. Where the heavy i placers, tin placers, etc. California, Montana and Oregon. 103 102 corrections. See — Adjusted value. mineral particles are smaller than the screen = 50 miners’ inches in Idaho, Nevada, NATIVE GOLD. 1. Metallic gold found naturallyjg PATENT. A document by which the Federal PINCHED SLU IC E . A film -ty p e gravity New Mexico and Utah. that state. 2. Placer gold. Government conveys title to a mining claim. To concentrator employing a wedge-shaped trough, = 38.4 miners’ inches in Colorado. obtain a mineral patent, the applicant must among tapering to a narrow vertical opening at its NUGGET. 1. A water-worn piece o f native gold. The I miners’ inch equals 11.25 gallons per minute other things, (1) make a valid mineral discovery discharge end. In use, heavy-gravity minerals term is restricted to pieces o f some size, not mere when equivalent to 1/40 second-foot. (2) invest $500 in improvements, (3) pay for a migrate toward the bottom and are removed from ‘colors’ or minute particles. Fragments and lumps 1 miners’ inch equals 9 gallons per minute when boundary survey if lode minerals are applied for, the stratified discharge stream by means of of vein gold are not called ‘nuggets’, for the idea equivalent to 1/50 second-foot. (4) pay $2.50 per acre for the lands in a placer splitters. Pinched sluice-type concentrators are o f alluvial origin is implicit. (Fay) 2. Anything application, or $5.00 per acre for the lands in a used to remove heavy minerals, such as rutile and MINERS’ PAN. S e e -P a n . larger than, say, one penny-weight or one gram lode application. See — Discovery. ilmenite, from beach sands. The CANNON may be considered a nugget. See — Pepita. MINERS’ SPOON. See - Spoon. CONCENTRATOR and FANNING PAY DIRT. Auriferous gravel rich enough to pay for NUGGETY. Like or resembling a nugget; occurring CONCENTRATOR are o f this type. MINING CLAIM. That portion o f the public mineral washing or working. (Fay) in nuggets; also abounding in nuggets. (Fay) PIPE CLAY. Miners’ term for clays or clay-like lands which a miner, for mining purposes, takes PAY LEAD, (pronounced leed) Where gravel is OLD AGE. See — Erosion cycles. materials found in finely-laminated beds within and holds in accordance with the mining laws. found rich enough to work, and if there is a (Fay) A mining claim may he validly located and the Tertiary gravels o f California’s Sierra Nevada OUTCROP. The exposure of bedrock or strata well-defined bed o f it, it is often termed the “ pay region. Some may consist o f volcanic material held only after the discovery o f a valuable mineral projecting through the overlying cover of detritus lead” or, “ lead” . Compare with Pay streak. which has fallen into water, in the form o f ash, deposit. See — Discovery. and soil. (AGI) PAY STREAK. A limited horizon within a placer and taken on a stratified form resembling clay in deposit, containing a concentration of values or OUTLET. The point where a channel is cut off by a appearance. MONAZITE. A phosphate o f the cerium metals ravine or canyon on the downstream end. (Dunn, made up o f material rich enough to mine. Pay PIPE FACTOR. The depth to which a churn drill (cerium , didymium, lanthanum) and other R. L.) Usually applied to buried Tertiary channels. streaks in gold placers are commonly found as casing must be driven to take in a sample volume rare-earth metals. Monazite-bearing alluviums have Compare with Breakout; and with Inlet. more or less well-defined areas on or near bedrock been mined for their thorium content (by and are commonly narrow, sinuous, and of I cubic yard. For example, a standard 6-inch OVERBURDEN. Worthless or low-grade surface dredging) in Idaho and elsewhere. discontinuous. Compare with Pay lead. drive pipe equipped with a new, 754-inch drive material covering a body o f useful mineral. The shoe would be driven 88 feet to cut out a MONITOR. See — Hydraulic giant. PEDIMENT. Gently inclined planate erosion frozen muck covering dredge gravels in Central theoretical volume of 1 cubic yard. This is Alaska is an example of placer overburden. surfaces carved in bedrock and generally veneered MORAINE. An accumulation o f earth, stones, sometimes called the CASING FACTOR but it is with fluvial gravels. They occur between mountain boulders, etc., carried and finally deposited by a most commonly known as the DRIVE SHOE OFFSHORE DEPOSITS. Mineral deposits on the fronts and valley bottoms and commonly form glacier. A Moraine formed at the lower extremity FACTOR. See — Radford factor. ocean or sea bottom beyond the low-tide line. See extensive bedrock surfaces over which the erosion o f a glacier is called a TERMINAL Moraine; at the — Marine placer. products from the retreating mountain fronts are PIPER. The man operating a hydraulic giant and side, a LATERAL Moraine; in the center and PAN. 1. A shallow, sheet-iron vessel with sloping transported to the basins. (AGI) directing its stream. parallel with its sides, a MEDIAL Moraine and sides and a flat bottom, used for washing PIPING. Washing gravel with a hydraulic giant. beneath the ice but back from its end or edge, a PENEPLAIN. A land surface worn down by erosion auriferous gravel or other materials containing GROUND Moraine. (Fay) Placer gold is found in to a nearly flat or broadly undulating plain; the PITCH. Used in connection with the bedrock in the heavy minerals. It is usually referred to as a ‘Gold some glacial Moraines and deposits o f reworked penultimate stage o f old age o f the land produced channel or rim to express decent. (Dunn, R. L.) pan’, but is more properly called a ‘Miners’pan’. Morainal material, that is, material reworked by by the forces of erosion. (AGI) Pans are made in a variety o f sizes but the size PITTING. The act of digging or sinking a pit, as for streams; some have been dredged and worked by PENNYWEIGHT. A unit o f weight equal to 24 generally referred to as “ standard” has a diameter sampling alluvial deposits. (Fay) other placer methods. grains, 0.05 troy ounce, or 15552 grams. A o f 16 inches at the top, 10 inches at the bottom, pennyweight o f fine gold has a value o f $1.03, PLACER. A place where gold is obtained by MOSS MINING (Mossing). The gathering o f moss and a depth o f 2/2 inches. Pans made o f copper, or with gold at $20.67 per ounce. A pennyweight of washing; an alluvial or glacial deposit, as o f sand or from the banks o f gold-bearing streams for the provided with a copper bottom are sometimes fine gold has a value o f $1.75, with gold at $35.00 gravel, containing particles o f gold or other purpose o f burning or washing it, to recover its used for amalgamating gold. 2. (verb) To wash valuable mineral. In the United States mining law, gold content. Under certain conditions, moss or earth, gravel, or other material in a pan to recover per ounce. mineral deposits, not veins in place, are treated as similar vegetation will capture and hold small gold or other heavy minerals. PEPITA. (Spanish) A nugget; usually a smaller size. placers, so far as locating, holding, and patenting particles o f gold being carried downstream by PAN FACTOR. The number of pans of gravel are concerned. (Fay) The term “ placer” applies to flood waters. See — Flood gold. PERMAFROST. Permanently frozen ground in equivalent to a cubic yard in place. Pan factors Alaska, up to 100 or more feet in thickness. See — ancient (Tertiary) gravels as well as to recent deposits, and to underground (drift mines) as well MUCK. (Alaska) A permanently frozen overburden vary according to the size and shape o f the pan, Muck. overlying placer gravels in the interior o f Alaska. It the amount o f heaping when filling the pan, the as to surface deposits. PILOT SLUICE. A small, auxiliary sluice operated is composed o f fine mud, organic matter and swell o f ground when excavated, and other intermittently aboard a dredge to determine the PLACER DEPOSIT. A mass o f gravel, sand, or small amounts o f volcanic ash. It varies in depth factors. In practice, factors for a 16-inch pan range amount o f gold being recovered by the dredge similar material resulting from the crumbling and (thickness) from seldom less than 10 feet to 100 from 150 to 200; a factor of 180 is widely used. during a given interval o f time, or from a erosion of solid rocks and containing particles or feet or more in places. This overburden (muck) PANNING. Washing gravel or other material in a particular gravel section. The ratio o f pilot sluice nuggests o f gold, platinum, tin, or other valuable must be removed and the underlying gravels Miners’ pan to recover gold or other heavy recovery to dredge recovery is determined for each minerals, that have been derived from the rocks or thawed before dredging is possible. minerals. dredge by empirical means. veins. (Fay) 105 PLACER MINING. That form of mining in which RARE EARTH MINERALS. A group of widely ■ RIM ROCK (or RIM). The bedrock rising to form rich in mineral. It is done with intent to defraud. the surficial detritus is washed for gold or other d istrib u te d but relatively scarce mineral; the boundary of a placer or gravel deposit. (Fay) 2. Unintentional or innocent salting. The valuable minerals. When water under pressure is containing rare earth compounds, usually jn unintentional or accidental enrichment of a employed to break down the gravel, the term combination with uranium, thorium, and other RIVER-BAR PLACERS. Placers on gravel flats in or sample through erroneous procedure or HYDRAULIC MINING is generally employed. elements. Monazite and other rare earth mineral, adjacent to the beds o f large streams. (Brooks) There are deposits o f detrital material containing carelessness, without intent to defraud. are obtained from placers i n Idaho, and elsewhere RIVER MINING. The mining o f part or all o f a river gold which lie too deep to be profitably extracted See — Monazite; also Radioactive blacks. SAMPLE. A portion o f the ore systematically taken, bed after by-passing the stream by means of by surface mining, and which must be worked by by which its quality is to be judged. (Fay) R/E. See — Recovery. flumes or tunnels; or by use o f wing dams to drifting beneath the overlying barren material. To divert the river from the working area. SAMPLING. Cutting a representative part o f an ore the operations necessary to extract such auriferous RECOVERY. 1. The amount or value o f mineral deposit, which should truly represent its average material the term DRIFT MINING is applied. ROCKER. A short, sluice-like trough fitted with recovered from a unit volume; in the case of gold j value. Honest sampling requires good judgement (Fay) transverse curved supports, permitting it to be placers, expressed as cents per cubic yard. 2. The and practical experience. (Fay) Parenthetically, it rocked from side to side, and provided with a amount o f mineral extracted, expressed as a I should be noted that in the case o f gold placers, POINT BAR. See — Skim bar. shallow hopper at its upper end. The hopper percentage o f the total mineral content. 3. In gold the high unit-value o f gold, its extreme dilution POINTS. See — Thaw points. bottom consists o f a punched-metal plate dredging, the expression “ R over E” (designated within the gravel mass and its typically erratic containing holes about J4-inch or Fi-inch diameter. PROSPECT DRILL. See - Churn drill. R/E) is used to compare actual recovery to | distribution are factors which individually or This is for the purpose of holding back the larger expected recovery where R represents the actual I combined, make it virtually impossible to obtain a PROSPECTING. 1. Used to qualify work merely rocks which when washed, are discarded. A flow returns and E represents the estimated recoverable I truly representative sample. To this extent, the intended to discover a pay lead in a drift mine, or of water, aided by the rocking motion, carries the value, after allowing for known or expected 1 usual definitions of sampling do not apply to gold to locate the channel. (Dunn, R. L.) 2. (generally) fine material down the trough where the gold or mining and metallurgical losses, etc. When placers. Searching for new deposits. 3. Drilling a known other heavy minerals are caught by riffles. Rockers recovery exceeds the initial estimate, the R/E will ! placer deposit to determine its value or delineate a are generally operated by hand but large, SAND PUMP. A special plunger-type vacuum pump be shown as something greater than 100%, such as minable area. used to remove the chopped-up drill core from a 105%, 110%, etc. power-driven rockers are sometimes employed. QUATERNARY GRAVELS. Gravels deposited When washing churn drill samples, rockers are chum drill hole. REPRESENTATIVE SAMPLE. See - Sampling. from the end o f the Tertiary, to and including the often used without riffles, the recovery being SAUERMAN EXCAVATOR. See - Slackline made on the smooth wooden bottom much in the present time. RESIDUAL PLACER. Essentially, an in situ scraper. manner o f panning. CRADLE is an obsolete term QUICKSILVER (or ‘Quick1). See — Mercury. enrichment o f gold or other heavy mineral, caused | SCALY GOLD. Small, rounded, flattened gold by weathering and subsequent removal of the lode ! for rocker. RADFORD FACTOR. An arbitrary' factor used by particles; usually quite thin in proportion to their or other parent material, leaving the heavier, j ROCKING. The process o f washing sand or gravel in some engineers in the calculation o f drill hole diameter. valuable mineral in a somewhat concentrated a rocker. volumes and in turn, the drill hole values. This SCHIST. A crystalline rock that can be readily split state. In some cases, a residual placer may be factor is based on an assumption that due to wear, ROUGH GOLD. Gold that has not been appreciably or cleaved because o f having a foliated or parallel essentially an area o f bedrock, containing 1 etc., a 7/ 2-inch drive shoe will take in 0.27 cu. ft. worn or smoothed by movement and abrasion. It structure. (Fay) Schist bedrocks, because o f their n u m erou s gold-bearing veinlets that have o f core per foot o f drive instead o f the theoretical may be more angular than rounded and may have rough, platy structure, generally make excellent disintigrated by weathering to produce a detrital I 0.306 cu. ft. In other words, it assumes a core included or attached quartz particles. As a rule, gold catchers. mantle rich enough to mine. In some parts o( I volume o f 1/100 cubic yard per foot o f drive. rough gold is found near its place o f origin. California, such areas are known as SEAM SCHISTOSE. Characteristic of, resembling, Using this factor, the equation for calculating the DIGGINGS. RUBEL ELEVATOR, (pronounced Roo-bull) A pertaining to, or having the nature o f schist. (Fay) drill hole value becomes: value o f recovered gold form o f elevator used in hydraulic mines, SEA -B EA CH PLACERS. Placers reconcentrated in cents times 100, divided by depth o f hole in RETORT. A vessel with a long neck used for i particularly those having insufficient bedrock from the coastal-plain gravels by the waves along feet, equals cents per cubic yard. Use o f the distilling the quicksilver from amalgam. (Fay) grade for effective tailings disposal. It is Radford factor will upgrade the theoretical value the seashore. (Brooks) RIFFLE. 1. The lining o f a bottom o f a sluice, made essentially a large, inclined flume, through which by about 12 percent. The Radford factor is SEAM DIGGINGS. (California) Residual deposits of blocks or slats of wood, or stones, arranged in gravel or tailings are driven by a strong water jet sometimes called the KEYSTONE CONSTANT. consisting of decomposed bedrock filled with such a manner that chinks are left between them. | furnished by a hydraulic giant. A grizzly When reviewing drill logs or reports, care should irregular seams o f quartz containing gold. In The whole arragement at the bottom o f the sluice j arrangement removes the fines for treatment in be taken to determine the factor used. See — Drill California, seam diggings have been worked by the is usually called THE RIFFLES. In smaller conventional sluices while the rocks are factor. hydraulic method. gold-saving machines, as the rocker, the slats of discharged from the upper end. RADIOACTIVE BLACKS. A group o f dark colored, wood nailed across the bottom are called j RUSTY GOLD. Free gold, that does not readily SECOND-FOOT. A unit of water measurement heavy minerals recovered by placer mining RIFFLE-BARS, or simply RIFFLES. (Fay) 2. A , amalgamate, the particles being covered with a equivalent to one cubic foot per second or 448.83 methods in Idaho and elsewhere, and valuable for groove in the bottom o f an inclined trough or silicious film, thin coating o f oxide o f iron, etc. gallons per minute. Commonly used to report the their contained uranium, thorium, or rare earth sluice, for arresting gold contained in sands or , (Fay) flow o f streams. components. They include such minerals as gravels. (Fay) 3. A shallow extending across the SELF-SHOOTER. See — Booming. SALTING. 1. Intentional salting. The surreptitious brannerite, euxenite, davidite, betafite, and bed o f a stream; a rapid o f comparatively little SHAFT FACTOR. A correction factor applied to samarskite. See — Rare Earth minerals. fall. (AGI) placing o f gold or other valuable material in a working place or in a sample to make it appear drill-hole values after a shaft has been sunk over 107 TENOR. The percentage or average metallic content the drill hole. The factor is based on the difference SLICKENS. A word sometimes used to designate SPONGE. The somewhat porous mass of gold of an ore. (Fay) As commonly used, it is in values obtained from the drill hole and from the the finer-size tailings, or mud, discharged from a remaining after the mercury has been removed synonymous with an approximate, or a general shaft; the shaft value generally being considered placer mine. Sometimes synonymous with Slime from a gold amalgam by heating. the more reliable o f the two. value rather than a precisely known value. SLUDGE. The fluid mixture of chopped up cote SPOON. A shallow, oblong vessel, at one time made SHINGLE. 1. The flatter pebbles and cobbles in a and water that results from the drilling action in a from a section o f ox horn but now made o f metal. TERRACE. A relatively flat, and sometimes long stream deposit will often come to rest with their churn drill hole. When the sludge is pumped from Used to test small samples o f gold-bearing material and narrow surface, commonly bounded by steep uppermost edge leaning slightly down-stream. This the hole, it becomes the sample for the particular by washing, in a manner similar to panning. More upslopes and downslopes on opposite sides. Gravel "shingling’ effect is used by placer miners to section of hole that produced it. properly called a MINERS’ SPOON or, HORN terraces may be stepped, and they are commonly determine the direction o f flow o f ancient streams dissected by transverse drainage patterns. SLUICE BOX. An elongated wooden or metal SPOON. and it can be particularly useful when working trough, equipped with riffles, through which SPOTTED GRAVEL. Where gold is erratically drift mines. 2. Beach gravel, especially if consisting TERTIARY. The earlier o f the two geologic periods alluvial material is washed to recover its gold or distributed through a deposit, the term “ spotted” o f flat or flattish pebbles. comprised in the Cenozoic era, in the classification other heavy minerals. Small sluice boxes are or, “ spotty” gravel is sometimes applied to it. generally used. Also, the system o f strata SHOE FACTOR. See — Drive Shoe factor. commonly, but erroneously, called “ L o n g Toms”. STRIP. To remove the overlying earth, low-grade, or deposited during that period. (AGI) SHOTTY GOLD. Small granular pieces o f gold SLUICEPLATE. A shallow, flat-bottomed steel barren material from a placer deposit. resembling shot. (Fay) Any small, more or less hopper arrangement at the head-end o f a sluice STRUCK CAPACITY. Level-full, that is, the capac­ rou n d ed g old particle that is somewhat box. A bulldozer is generally used to push ERA PERIOD YEARS AGO ity of a container filled even with its rim or top. equidimensional rather than platy. gold-bearing gravel onto the sluiceplate, from where it is washed into the sluice by water issuing SICK MERCURY. See — Floured mercury. SUBMARINE PLACER. See — Marine placer. from a large pipe or by means o f a small hydraulic RECENT SKIM BAR. An area near the upstream end o f an giant. SUCKER. 1. A syringe used to remove material from underwater crevices in the bedrock. 2. A PLEISTOCENE accretion bar from which superficial SNIPER. An individual miner, usually a transient, concentrations of flood gold are mined by small, hand-held jet dredge o f the type carried who gleans a living from gravel remnants not underwater.

‘skimming’ o ff a thin layer o f gravel. They are QUATERNARY worth working except by someone content with 1 000.000 sometimes known as POINT BARS, probably very modest gains. He usually works with simple SUCTION DREDGE. See — Hydraulic dredge; also Pliocene because o f their proximity to the upper point of hand tools and washes his gravel in a short sluice Jet dredge. the accretion bar. See Flood gold; also Accretion or dip box. Being transient and generally 11.000.000 bar. SUCTION LIFT. The vertical distance from the level innocuous, he seldom owns or leases the land he of the water supply to the center of a pump, to SKIN DIVING. The use o f wet-type diving suits, works. o Miocene which must be added the loss due to friction of o with or without self-contained underwater N SODIUM AMALGAM. Mercury that has been the water in the suction pipe. o 30.000.000 breathing apparatus. Skin diving gear is generally treated with small amounts o f metallic sodium to z SURF WASHER. A small sluice, somewhat similar w used by the operators o f small hydraulic dredges increase its affinity for gold and other metals. CJ to a long tom; used to recover gold from beach Oligocene and by divers who search for underwater bedrock ed SPECIFIC GRAVITY. The specific gravity of a sands. The surf washer is placed so the incoming crevices from which gold-bearing materials may be < 40.000.000 substance is its weight as compared with the surf rushes up the sluice, washing material from a H retreived. See — Jet dredge. as weight o f an equal bulk o f pure water. For hopper and upon retreating carries it over the w H Eocene SLACKLINE SCRAPER. Consists essentially o f a example, placer gold with a specific gravity of riffles. head tower and a movable tail tower or tail block, about 19 is 19 times heavier than water. The SWELL. The expansion or increase in volume o f 58.000.000 supporting a track cable. A bucket or scraper specific gravity o f a mineral largely determines its earth or gravel upon loosening or removal from running along the track cable can be raised and susceptibility to recovery in simple gravity Paleocene the ground. The average swell o f gravel is around lowered by tightening or slackening the track concentrators such as sluice boxes. 25% and sometimes as high as 50%. cable. The digging bucket or scraper runs out by SPECIMEN GOLD. Nuggety gold or other forms 00 000 000 gravity and is pulled in by a drag cable. The suitable for the manufacture o f natural-gold TAIL. (verb) Manipulating the concentrate product hoisting machinery and in some cases a screening jewelry or for display purposes. in a gold pan in such a way that the heavier CRETACEOUS or washing plant are incorporated in the head minerals and in particular the gold colors string SPIRAL CONCENTRATOR. A wet-type gravity tower. This arrangement is also known as a out in the bottom o f the pan in a long, narrow concentrator in which a sand-water mixture, CABLEWAY SCRAPER. The SAUERMAN “ tail” , where they can be readily inspected or flowing down a long, spiral shaped launder, EXCAVATOR is o f this type. counted. This is referred to as “ tailing a pan.” separates into concentrate and tailings fractions. SLATE. A fine-grained rock formed by the The concentrates are taken o ff through ports TAILINGS. The washed material which issues from compression o f clay, shale, etc., that tends to split while the tailings flow to waste at the bottom. The the end o f a sluice or other recovery' device in a along parallel cleavage planes and to form a rough,

HUMPHREYS SPIRAL, which employs this placer operation. The tailings from hydraulic MESOZOIC platy bedrock, well suited for the retention o f principle, is widely used for recovering heavy mines are generally referred to as “ debris” in 108 placer gold. minerals from beach sands. legislative documents. and bacteria and the mechanical action o f changes YARDAGE. 1. The number o f cubic yards o f gravel TERTIARY CHANNELS. Ancient gravel deposits, sluice, but being much wider than the latter of temperature, whereby rocks on exposure to the mined or put through a washing plant in a shift or often auriferous, composed o f Tertiary stream allows the water to spread out in a thin sheet over weather change in character, decay, and finally a day. 2. A measured block o f gravel. alluvium. Tertiary gravels are abundant in the its surface, thereby so abating the velocity of the crumble into soil. (Fay) YIELD. The quantity or gross value o f minerals Sierra Nevada gold belt of California where many current that the very fine gold, including the rusty extracted from a deposit. have been covered by extensive volcanic eruptions particles, is more apt to be caught here than in the WING DAM. A dam built partially across a river to and subsequently elevated by mountain uplifts, sluice. (Fay) Undercurrents are usually fed with YOUTH. See — Erosion cycles. deflect the water from its course. (Fay) See — and are now found as deeply-buried channels, high fine-size material taken from the main sluice by ZIRCON. A mineral o f widespread occurrence as River mining. above the present stream beds. means o f a grizzly placed in the sluice bottom small crystals in igneous rocks. Composition, near the discharge end. zirconium silicate, ZrSiC>4. Because o f its TEST PIT. S ee-P IT T IN G . WING FENCE. A V-shaped wall, usually made o f resistance to weathering, and moderate specific THAW POINTS. Water pipes driven into frozen UPPER LEAD, (pronounced leed) A pay lead in a heavy timber and attached to the head o f a sluice gravity (4.68), zircon is a common constituent of gravel, th rou gh which water at natural top wash or in the gravel deposit considerably and arranged to guide gravel into the sluice as it is the black sands associated with gold placers. temperature is ciculated for weeks or months, to above the bedrock. (Dunn, R. L.) swept from the pit by a hydraulic giant. thaw the ground ahead o f dredging. Where used in VALUES. The valuable ingredients to be obtained, Alaska, points are usually spaced 16 feet apart. by treatment, from any mass or compound; Once thawed, the ground does not freeze again specifically, the precious metals contained in rock, and thawing is usually carried one or two seasons gravel, or the like. (Fay) ahead o f the dredge. VOLUME FACTOR. The volume o f sample which TIGHT GRAVEL A hard, or compact gravel that is should be taken into a churn drill casing for each not cemented, but requires something more than foot o f drive. For example, a standard 6-inch drive normal effort to excavate. Compare with pipe equipped with a new, 754-inch drive shoe will CEMENTED GRAVEL. theoretically take in a volume of 530 cubic inches, TILL. Nonsorted, nonstratified sediment carried or or, 0.306 cubic foot per foot o f drive. See - Core deposited by a glacier (AGI) factor; Drive shoe factor; Drill factor.

TOP WASH. A deposit o f gravel, not in a channel on WARD DRILL. A lightweight, hand-powered churn the bedrock, but resting on cement overlying the drill widely used in South America, particularly in bottom deposit. (Dunn, R. L.) remote areas where access is difficult and manpower is cheap. The drilling tools are TRACE. A very small quantity o f gold; usually a suspended from a tripod and the reciprocating speck too small to weigh. In reporting samples it is motion provided by a simple spudding arm known abbreviated tr. as a “Diablo” . Sometimes referred to as a HAND TRESTLE SLUICE. A moveable steel sluice DRILL. constructed on a skid or track-mounted trestle; WASH. 1. A Western miners’ term for any loose, usually provided with a hopper, grizzly and wash surface deposits o f sand, gravel, boulders, etc. 2. water system, and fed by a dragline or similar The dry bed o f an intermittent stream, sometimes excavator. Also called an ELEVATED SLUICE. at the bottom o f a canyon. Also called Dry wash. TROMMEL. A heavy-duty revolving screen used for 3. T o subject gravel, etc. to the action o f water to washing and removing the rocks or cobbles from separate the valuable material from the worthless placer material prior to treatment in the sluices, or less valuable; as to wash gold. (Fay) In drift gold-saving tables, or other recovery equipment. mining (California), the term “ Wash” is used TROY OUNCE. The one-twelfth part o f a pound o f indifferently in describing channel gravel, volcanic 5760 grains, that is 480 grains. It equals 20 mud flows, or masses of lava boulders. (Dunn, R. pennyweights, 1.09714 avoidupois ounces, L.) 31.1035 grams, or 31,103 milligrams. This is the WASTE. Valueless material such as barren gravel or ounce designated in all assay returns for gold, overburden. Material too poor to pay for washing. silver or other precious metals. (Fay) WATER TABLE. The upper limit o f the portion of TUNNEL. The nearly horizontal excavated opening the ground wholly saturated with water. This may from the surface into the mine. (Dunn, R. L.) be very near the surface or many feet below it. UNDERCURRENT. A large, flat, broad, branch (Fay) I l l sluice, placed beside and a little lower than the WEATHERING. The group o f processes, such as the 110 main sluice. This apparatus is riffled like the chemical action o f air and rain water and o f plants

PLACER SAMPLE

FIELD RECORD

Sample N o. 1/ Date . State ------. C ounty. . Serial No. C laim . Legal description: Sec.. . Twp.. , Range.

Type of deposit:______

Type of sample:______Dimensions of cut:

Place taken:

Reference tie :.

Photograph:___

INTERVAL FORMATION

_to .

.to .

.t o .

.t o .

.to .

Bedrock: No( ) Yes( ) Type_

Overburden: Feet______Type. .Water level. .ft.

Sample Weight: Gross______lbs. N et______lbs.

Sample Volume:______loose measure ( ) bank measure ( )

Boulders: N o ( ) Y es( ) Aver, size______Max. size______Est. % o f bank-run.

Cement: No ( ) Y es( ) Remarks______

Clay: N o ( ) Y es( ) Est. %___ . Remarks.

Caliche: No ( ) Y es( ) Est. %___ . Remarks.

Hard digging: N o ( ) Y es( ) Remarks.

Sampled bv______. Title.

Others present______

Time: Arrive______. Depart .Weather.

Remarks:______

Place sketch on back o f this sheet.

1/ Carry this number forward to PROCESSING RECORD SHEET, which see. Sample No. f / ______115 PLACER SAMPLE

PROCESSING RECORD

Sample No. 1I ______Date______

Serial N o .______

Dry Weight------lbs.; V olum e______; How measured__

How Processed______

Processed b y ______Title______

Others present______

A isible gold ^ :------# 3 colors;______# 2 c o lo r s ;______# 1 colors. No visible gold ( );

Gold weight______milligrams Estim. fineness______

Gold removed: Manually ( ); By amalgamation ( ); Other______

Character of Gold: Fine or flaky ( ); Coarse or shotty ( ); Smooth ( ); Rough ( );

Remarks______

When panning, does Gold tend to ride over top o f black sand ( ); or stay down on pan ( );

Remarks______

Does Gold amalgamate readily: Y es( ); N o ( );

Remarks______

Weight o f black sand in sample------; Lbs. black sand per cubic yard______.

Amount o f black sand is: Large ( ); Medium ( ); Small ( );

Screen was used in washing process: N o ( ); Y es( ); Size o f openings______DATA SUMMARY SHEET

■------% Oversize:______% Undersize;

Remarks______

Material washed: Easy ( ); Normal ( ); Difficult ( );

Remarks______

Muddy water indicated by washing: Little ( ); Moderate ( ); Much ( ).

Grade o f sluice or rocker------in./ft.; Source o f wash water______

Notes:______

1/ Number the same as FIELD RECORD sheet, which see. 2/ # 3 colors consist of gold particles weighing less than 1 milligram; # 2 colors weigh between 1 and 4 milligrams; #1 colors weigh over 4 milligrams. Weigh and note individual colors weighing 10 milligrams or more.

Sample No. 1/

116 FIELD LOG

SHAFT NO______LOCATION

Cu.Ft. Cu.Ft. Box Gold Value Date Formation Sampl. Depth Excavation Measure Recovered Per Cu. Yd. Workmen

Shaft Hoist Rocket 1

2 3

4 5 APPENDIX B 6

7

8 9 GOLD PRICE AND VALUE DATA 1 0 11 12 13 14 15 16 17 18 19 20 21 22 24 25 26 27 28 29 30

NOTES:

DEPTH VALUE W. L.

B. R.

118 »7 T'^'AKrr/rf^f- ^ ‘ 1

U. S. PRICE OF GOLD TROY WEIGHT (FOR GOLD & SILVER)

Value Per 1 pound troy = 12 oz. troy = 5760 grains Date of Law Fine Oz. Troy = 373.2417 grams

April 2,1792 $19.393939 1 ounce troy = 20 pennyweights = 480 grains June 28,1834 $20.689656 1 ounce troy = 31.1035 grams = 31,103 milligrams Jan. 18, 1837 $20.671835 Mar. 4,1900 $20.671835 1 pennyweight = 24 grains = 1.5551 grams Jan. 31, 1934 $35.000000 Mar. 17, 1968 U.S. Treasury regulations VALUE OF GOLD, c PER MILLIGRAM published in the Federal Register $ Price x fineness x 0.1 on March 19,1968, allow = 31,103 domestic gold producers to sell Example: newly mined gold to persons regularly engaged in an industry, Gold @ $70 per ounce and 825-fine. profession, or art, who require gold for legitimate, customary, 70 x 825 x 0.1 = 0.185c per mg. and ordinary use, or persons 31,103 hold Treasury gold licences. The price of such gold is no longer MILLIGRAMS OF GOLD EQUIVALENT TO 1 c regulated by the Treasury. The 1 price o f monetary gold remains fixed at $35.00 per ounce. The c per mg. U .S. Mint will no longer purchase gold in the private Using foregoing example: market nor sell it for industrial, 70 x 825 x 0.1 = 0.185c per mg. professional or artistic uses. The private holding o f gold by U.S. 31,103 citizens continues to be 1 prohibited except pursuant to = 5.4 mg. equivalent to lc . existing regulations. 0.185 121 GOLD FINENESS AND VALUE EQUIVALENTS (based on $35/oz.)

VALUE PER

FINENESS TROY OZ. PENNEYWEIGHT GRAIN MILLIGRAM

1000 $35.00 $1.75 7.29c 0.112c

975 $34.12 $1.71 7.11c 0.109c 950 $33.25 $1.66 6.93c 0.107c APPENDIX C 925 $32.38 $1.62 6.74c 0.104c

900 $31.50 $1.57 6.56c 0.101c

875 $30.63 $1.53 6.38c 0.098c

850 $29.75 $1.49 6.20c 0.096c WATER DATA

825 $28.88 S I.44 6.02c 0.093c

800 $28.00 S I.40 5.83c 0.089c

775 $27.13 $1.36 5.65c 0.087c

750 $26.25 $1.31 5.47c 0.084c

725 $25.38 $1.27 5.29c 0.082c

700 $24.50 $1.22 5.10c 0.079c

675 $23.63 $1.18 4.92c 0.076c

650 $22.75 $1.14 4.74c 0.073c

625 $21.88 $1.09 4.56c 0.070c

600 $21.00 $1.05 4.38c 0.067c

TO FIGURE THE VALUE OF GOLD AT ANY PRICE OR FINENESS:

New price x Fineness x 0.112 = c per milligram 35 1000

New price x Fineness x 7.29 = c per grain 35 1000

New price x Fineness x 1.75 = $ per penneyweight 35 1000 WATER REQUIREMENTS 2-monitor mines operated by individual owners or The source, amount, and delivered cost o f water are lessees, usually have a water duty o f less than 1 important elements in a placer operation. In many cubic yard per miner’s inch-day. cases they determine the type o f equipment or Stationary washing plants: These are typically mining method used. Water estimates for new or owner-operated plants, fed by a dragline or a small proposed operations are generally based on power shovel. Most employ a trommel or other experience or working data obtained from screening device ahead o f the sluice. Incomplete comparable operations. figures indicate a range o f 650 to 2,000 gallons per cubic yard. The water required for various working methods varies widely and depends on many factors. Examples Moveable washing plants and dryland dredges: In that folow are intended only to show the possible same category as stationary plants and same range. remarks apply. Water requirements ranging from a. Rockers: A steady flow o f 4 or 5 gallons per 480 to 3200 gallons per cubic yard have been minute is sufficient to operate a small ( l ’x4*) noted. Plants equipped with Ainlay bowls (in place rocker. Water can be dipped from a barrel where o f sluices) generally have good water economy. steady flow is not available. Net water Dragline dredges: Net water required for washing consumption may be as low as 50 to 100 gallons gravel and maintaining the pond is governed by the per cubic yard, if carefully saved and reused. amount o f clay, porosity o f the gravel, and other b. Small-scale hand mining: Where material is factors. Wash water which is commonly supplied loosened by picking, and shoveled into a sluice by an 8-inch centrifugal pump working against a box by one or two men, 170 to 225 g.p.m. are 40-foot pressure head, may range between 570 to required for a 12-inch box with steep grade. 2,500 gallons per cubic yard. c. Ground sluicing: Water duty varies widely but Bucket-line dredges: Water in circulation aboard may range between 1/10 and 3/4 cubic yard per a dredge may range from 3,500 g.p.m. to over miners’ inch-day at small mines. This would be 10,000 g.p.m. depending on digging capacity of equivalent to about 22,000 to 162,000 gallons per dredge and type o f material being washed. Dredges cubic yard. are usually provided with independent high pressure and low pressure w'ater systems, the high d. Hydraulicking: Water duty varies widely and pressure being used for screen sprays and bucket reflects the coarseness o f gravel, degree of nozzles, and the low pressure for the gold-saving cementing, height of bank, grade of bedrock, tables and general service. When working in available head, etc., and is commonly between 1/2 land-locked ponds, a fresh water input o f 1,000 and 7 cubic yards per miner’s inch-day. This g.p.m. to more than 2,000 g.p.m. will be needed would be equivalent to about 2,000 to 32,000 to replace muddy water which must be pumped out gallons per cubic yard. The better efficiencies are o f the pond (to prevent excessive mud build-up) and obtained at large, well-equipped mines. Small, 1 or to maintain pond level. 125 ___ ...... ______......

UNITS OF WATER MEASUREMENT

1 gallon (gal.) = 231 cubic inches . = 0.1337 cubic feet. 1 gallon of water weighs 8.33 pounds. 1 million gallons (m.g.) = 3.0689 acre feet. 1 cubic foot (cu. ft.) = 1728 cubic inches. = 7.48 gallons. 1 cubic foot of water weighs 62.4 pounds. 1 acre foot (ac. ft.) = amount of water required to cover one acre one foot deep. APPENDIX D 43,560 cubic feet. 325,850 gallons. 12 acre inches. 1 gallon per minute (g.p.m.) = 0.00223 cubic feet per second. 1440 gallons per day PLACER DRILLING DATA (24 hrs.). 1 million gallons per 24 hours (m.g.d.) 1.547 cubic feet per second. 695 gallons per minute. 1 cubic foot per second (sec. ft.) 7.48 gallons per second. 448.8 gallons per minute. 646,272 gallons per day (24 hrs.). .992 acre inch per hour. I. 983 acre feet per day (24 hrs.). 40 miner’s inches (legal value) in Arizona, California, Montana and Oregon. 50 miner’s inches (legal value) in Idaho, Kansas, Nebraska, Nevada, New Mexico, North Dakota, South Dakota and Utah. 38.4 miner’s inches in Colorado. 35.7 miner’s inches in British Columbia. 1 miner’s inch (mi. in.) = II. 25 gallons per minute when equivalent to 1/40 second foot. 9 gallons per minute when equivalent to 1/50 second foot. 1 miner’s inch-day (24 hrs.) = 16,200 gallons when equivalent to 1/40 second foot. 1 miner’s inch-day (24 hrs.) = 12,960 gallons when equivalent to 1/50 second foot. Setting Up The Drill Starting a Hole

IHE drill is placed in the desired location for the AT THE SITE marked for drilling, a hole is dug hole, leveled, and the derrick raised. One end o f the approximately 16 inches deep. The gravel removed is sand line is attached to the vacuum sand pump; the examined to see whether it contains gold. A drive other end is placed over the sand line sheave in the shoe is placed on one end of a length of drive pipe derrick and attached to the sand line drum. The drill and a drive head on the other. line is placed over the crown sheave of the derrick, After carefully measuring the length o f the pipe and laced through the walking beam, and attached to the shoe they are placed in the hole in a vertical position mainline drum, the cable socket being on the other with the drive shoe on the bottom. Dirt is packed end of the line. around the pipe to hold it in position. Where long For most placer operations, a string o f tools usually lengths o f casing are used, a well is usually dug consists o f a rope socket, a stem, and a bit. When directly in front o f the drill. This is very difficult to assembling a string o f tools, lay the stem on the do in wet ground. ground at the front o f the drill; screw on the rope socket with the attached cable; then screw the bit on DRIVING THE PIPE the lower end o f the stem. A light wire brush and gasoline is recommended to clean the threads before THE TOOLS are lowered, allowing the bit to enter assembling. A few drops o f light oil are desirable on the casing, the drive clamps are clamped on the the threads. square on the bit. It is important to see that the drive clamp bolts are kept tight. Loose nuts mean certain Great care must be exercised in assembling a string of breaking o f bolts. tools to see that the joints are tight. Screw the tool The engine o f the drill is started and operated at slow joints up by hand, then apply tool w enches and set speed. the joint up firmly by means o f the chain wrench bar. The drive clamps are lowered to within three inches Remember, most fishing jobs are due to improper o f the drive head, the spudding lever is moved to the setting o f joints. “ On” position, and the casing gently tapped into the Many drillers use a stone in polishing the shoulder ground. The impact blow and feed are adjusted by portion o f the box and pin, before assembling. After gently raising the brake lever. a joint has been set up perfectly solid, a mark is If the top soil is valueless, the pipe is driven to gravel. sometimes made with a sharp cold chisel, half on the When the drive head reaches a point a few inches pin collar and half on the box. Each successive time from the ground, it is removed and another length of this joint is screwed up, the mark on the box should pipe is carefully measured and coupled to the first go a little farther past the mark on the pin collar. By length, care being taken to couple the pipe so that this method one can check and see that the joint is they butt in the center o f the coupling. The drive set up firmly. If, at the next fitting the joint does not head is then placed on the top o f the next section o f go far enough, it is indicative that there is dirt on the p ip e and the operation resumed, core in the face of the joint — or in the threads, which dirt must meantime is being removed as the pipe is driven he removed. deeper.

After the stem and bit have been assembled, the tools Whenever pipe is added, the threads arc carefully are hoisted, the operator being careful not to kink the cleaned and then greased with graphite and linseed oil cable where it enters the socket. Check the frame to and securely tightened by means o f chain tongs. It is see that the tools hang directly above the center line very important to grease the pipe and not the of the drill and approximately 24 inches out from the couplings. The portion of the thread one-quarter inch front of the drill. You are now ready to start the back from the end o f the pipe is the part usually hole. lubricated. 129 As soon as the hole has reached a prevent any values being carried into (|^ deptli sufficient for the bit and casing. opening the valve and washing the contents out on In extreme instances where the burden o f jarring the stem to enter the casing, the drive When drilling through boulders greater speed caul, [he ground. The driller must be careful, however, not pipe is too great for normal blow delivered and the clamps are placed on the top square obtained by using an ordinary rock bit or a four-win; to throw away the contents when gravel is reached. upward tension of a hand hoist line is insufficient, a o f the stem. After driving pipe to type bit, than with a placer bit. Extreme care should be exercised so that the last pipe pulling ring should be used. By placing the ring the desired depth, the drive clamps three or four inches o f the core is left in the bottom o f on the casing-head and hand jacks beneath the flange PUMPING OUT THE CORE are removed. the drive pipe to form a plug. on the ring, a tremendous upward pressure is added THE TOOLS are hoisted out o f the pipe and held out Records are made o f the depth of After the stem has been lowered into the pipe, and to the jar ring effect o f the stem which starts the pipe o f line o f the drill casing by means o f the tool guy. the drive pipe and also the core. By the depth o f the remaining core checked and upward. While the tools are being hoistered, a bucket-of way starting at the bit and measuring re c o rd e d in the log book, the tools are raised. The is usually poured on the rope and stem to wash oil back along the stem, the total drive clamps are bolted on and the operations PIPE PULLING WITH CASING any values that might be clinging to the tools. Tl* length o f pipe is marked with chalk re p e a te d . After the first drive, the clamps are bolted SPEAR sand pump is raised by pulling on the sand pump or a piece o f string on the line. The on the top square. It is impossible to do this at the lever. When the lever is released, a brake keeps tht stem is lowered into the pipe and start, as bit would strike the core when driving. THE C. KIRK HILLMAN Company sand drum from turning, and holds the pump in the distance between chalk mark makes a three-jaw casing spear. position. When the sand pump lever is half wa\ and the top o f the pipe represents Three jaws are used to eliminate between the brake position and the hoist position, the core remaining in the hole. PIPE PULLING distortion o f the pipe as is usually the drum is free, allowing the pump to fall freely to the case when two jaws are used. the bottom o f the hole. A SPECIAL FEATURE o f the Hillman Drills is their Four jaws do not work as When the pump is at the bottom o f the hole, tl* remarkable pipe pulling ability. DRILLING PROCEDURE well as three jaws for six- piston type plunger is at the bottom o f the pump. ft Using a top puller, the operation o f pulling the pipe is inch casing and smaller, DRILLING proceeds in the follow­ pulling on the sand drum lever, the plunger is rapidly as follows: The drive head is removed from the top of for not enough stock is ing manner: raised, creatinga strong vacuum, sucking in the gold the casing. The knocking head is slipped over the pipe then left in the center of The driller measures and reports the sand, mud, cuttings, etc. The efficiency of a sand pulling jar. The rope socket is attached to the pin of the spear to withstand the length o f core to the panner. This, pump depends on the speed with which the plungers the pipe pulling jar. Some operators prefer to use the DRIVING constant hammering. and the depth o f casing in the raised. rope socket and stem above the The operation of pulling ground, are recorded in the log The foot valve in the bottom of the pipe pulling jar but a sharper blow book. the pipe by means o f the seems to be obtained when it is pum p p rev en ts material from spear is as follows: The Water is poured into the casing, the b e lo w . T he knocking -head is escaping, Holding the sand drum string o f tools is assem­ spudding lever thrown in the “ On” screwed on the top of the pipe in lever out and keeping the sand bled, consisting of a rope position, and the core chopped up. place o f the driving head. The drill drum engaged, brings the pump socket, a stem, a set o f is placed in the spudding position Some operators place a spoonful of containing the core to the surface. long stroke jars and the lye in the drill hole when churning. and the string o f tools is raised far Engineers very often drop several trip casing spear. The jaws Lye cuts any grease from the fine enough so that by means o f the lead shot in the hole without the o f the spear are set by us­ gold and prevents it floating away. spudding action they are thrown at operator’s knowledge, and then ing the spider furnished There are times when there is a the driving head. A sharp blow is count them after the pumping to with the spear for pulling certain amount of vegetable oil in obtained rather than a straight pull. JARS see that everything was removed. back the jaws and com­ the ground or grease from pipe This is exactly the reverse action o f It is common practice to pump be­ pressing the spring. The threads or wire line. pipe driving, the blow being fore and after driving. In loose anvil block directly on top directed at the lower face o f the In p la ce r testing it is always ground it is often possible to pump o f the spring has a key which slides knocking head instead o f the top o f customary to try to drive the casing out the core immediately after into a notch on the lower end of ahead o f drilling. Three or four the driving head. driving. When the two pumpings SPEAR the spear; this key is pressed in. The inches o f core are always left in the are made before and after driving, Sometimes con­ spider is then removed. The string casing to form a plug. This is con­ they are caught in the same bucket siderable time is o f tools is then lowered into the casing. Pulling is trasted with other types o f drilling and concentrated in one operation. saved by using a usually done from the last length. When the spear is where the churning is done below T he pu m pin gs are ordinarily hand hoist in con­ in the last length o f pipe it is hoisted up, sinking the the casing. emptied into a mud box. junction with the jaws into the casing. The drill is placed in the When large boulders are encount­ When prospecting a deposit having bumping action. PULLING RING spudding position and the string o f casing jarred ered, it is necessary to drill below a deep overburden o f valueless By thus having a upwards. T o release the casing, the spear is struck a the drive shoe; then the operator material, a one-inch rod is driven ten sion on the sharp blow from the top. This causes the anvil block should check to see that the water into the ground and as the pump is line, the pipe does not have a to strike the top o f the jaws, which releases the spear. level in the pipe is at least as high as brought up, the foot valve of the chance to drop back after each The tools are then hoisted out o f the casing. The CHURNING the water plane in the ground, to PUMPING sand pump is set on the rod, thus blow and a continuous upward lengths o f casing out o f the ground are uncoupled and tension on the pipe is maintained. the operation repeated. After all values have been recorded and the bottles is added to the cup and the contents heated over the TREATMENT OF THE CORE not always check with the theoretical volume or 4 are again setn out in the field, the writing is removed flame o f an alcohol lamp. The mercury goes into volume as measured by the rise of the core in tl( by a scouring action with the thumb, using sand and solution with the nitric acid, leaving the natural alloy WHEN the sand pump is hoisted out o f the casing, pipe. water. This method eliminates the danger o f lost o f gold and silver. The acid should be heated only the helper, or panner. grasps the lower end o f the The material in the volume bucket is thorough labels. R em em b er: relia b le evidence inspires enough to accelerate the reaction. Excessive or puinp, walks hack from the drill, and lays the lower stirred to break up any sticky lumps and then tlie confidence in the crews’ reports. continual heating will dissolve the alloy in the gold end on the saddle o f the dump (or mud) hox. The water is poured off. Records are made in the log bool and change its fineness. This loss o f weight may cause hail end o f the sand pump is then lowered into the o f the measured volume o f the core. Directly beside the ROCKER an error, as the values are computed on the basis o f bottom o f the dump (or mud) hox. When the pump the volume bucket is the panning table. natural fineness o f the gold. The mercury nitrate is in this position the foot valve is approximately on an DIRECTLY beside the panning table is the rocker. carefully washed from the gold and silver alloy, using even height with the panner’s eye. THE PANNING TABLE The rocker, as used for checking drill samples, is very a wash bottle with hot water. After adding a drop or While the pump is in this jackknifed position, it is similar to the one used by the small individual placer two of alcohol to the annealing cup to prevent thoroughly washed both inside and out. A dipper, THE Panning Table is usually 28 inches high by 3d operator. Som e of the differences are: sputtering, it is heated over the alcohol lamp to a red formed by fastening a handle on a gallon tin can, is inches wide by 60 inches long. It has two wash tub three-eight-inch holes in place o f half-inch-holes in heat or to a point as hot as the lamp will alllow. The used for pouring water in the foot valve and slushing on top. A safety pan is placed in the bottom of each the punched plate; punched portion o f plate only operation removes the moisture and burns away any out the material. The pump is hoisted and jackknifed tub. A shelf is directly under the table top to hold the two-thirds o f half size used in the ordinary rockers, carbon or lint which would salt the weight o f the in the other position. The lower end o f the pump on dish for holding the concentrates. The grizzly pan and preventing all the material from being washed gold. The gold is then weighed and values recorded in the previous washing is now the top. The second regular pan are also part o f the equipment for the through with the first dipper o f water. As the rocker the log book. washing is not always essential, hut is advisable, panning table. The grizzly pan has three-eight-inch is cleaned up so often, only two or three riffles are especially when working in rich ground. Directly holes. This allows the small material to wash through, necessary. LOG BOOK below the lower end of the mud box is located a tub and speedily eleminates the coarse material. containing the volume bucket. An accurate systematic record should be kept of each The material is taken out o f the volume bucket with TREATMENT OF GOLD hole drilled. Neat, accurate and carefully kept, and the gold scoop and placed in the grizzly pan which h MUD BOX OR DUMP BOX signed drillers logs are o f the utmost importance and in the second pan. The pans are usually filled A FEW o f the operators take the bottles o f should be as carefully prepared as banking or legal two-thirds full. The stones and large cuttings are concentrate from the hole, carefully pan them down THE LEGS and sides o f the dump hox are made of papers. The reliability o f a report on any placer washed clean while the small particles fall through the as far as possible, dry them, remove the magnetic surfaced fir, two inches by four inches. The trough is deposit depends on the care with which the grizzly pan into the second pan. The rocks are looked material with a magnet, blow the remaining black formed o f 16-gauge steel. The top end o f the hox is examination is conducted and recorded. over and examined for nuggets before thrown out and sand off and then weigh the gold. welded solid. The lower end is also welded and fitted The driller and panner have a good opportunity to the rough panning is done in the first tub. The fine The usual procedure is to use a six-inch gold pan, pan with an adjustable gate which can be set to control examine all the conditions relative to the deposit. All panning is done in tub No. 2, where the water is clear. the material down to a high concentrate, and them the flow into the volume bucket and avoid splashing. factors which may in any way have any bearing on By having the water slightly warmed, the working amalgamate the gold. This is done by rubbing the the cost o f the operation should be noted in the logs. conditions are more pleasant for the operator and black sand and concentrate with mercury, then THE VOLUME BUCKET Any corrections or compensation for lack of core also the clay tends to disintegrate more readily. The carefully panning o ff the black sand. This is usually should also be made in the field at the time, as later panner classifies the gold in one, two, and three caught in another pan and checked to see that no THE Volume Bucket, holding one in the office, engineers might not fully understand all colors. No. 3 is the finest, and consists of all particles values have been lost. The samples are then usually cubic foot, is 13/2 inches in diameter the conditions. weighing less than 1 Mg; No. 2 is gold consisting of all placed in bottles marked for future reference. At this and 12 inches in height. The measuring particles weighing between 1 Mg. and 4 Mg.; while time it is well to qualitatively inspect the contents of stick is calibrated in tenths and No. 1 gold is any particle weighing over 4 Mg. The the pan and black sands for platinum or unusual Explanations of Headings on Log Sheet hundredths of a cubic foot. A good colors are recorded in the log book. The concentrate amounts o f any o f the other valuable metals or p ra ctice is to measure the total The following data is usually recorded on the log is placed in a bottle, and marked with a Line Number, minerals which are apt to be found in placer deposits. quantity o f material pumped from Hole Number, and Depth. sheets: each hold and to compare the results There are times when the gold does not readily 1— Name o f property from all holes drilled in similar material. A fair amalgamate, due to oil or grease from the sand pump, 2— Location average can be obtained and used as a check on each THE SAMPLE BOTTLES pipe joints, vegetation, et cetera. Adding a little separate property. Some operators calculate twenty caustic potash usually eliminates this trouble. To 3— Date FOR handling samples, some of the cubic feet o f material so measured to represent one amalgamate the gold, some operators add one or two 4— Line Number companies use small bottles similar to a vase­ cubic yard actually drilled. drops o f dilute nitric acid to the amalgam and line jar. The cover is made o f aluminum and 5— Hole Number concentrates and stir vigorously was a glass stirring The volume bucket measurement entails complete o f the screw type. The top o f the cover is 6— Elevation rod until all the gold has been absorbed by the disintegration o f the material and its reaggregation flat and has a dull finish, similar to a sand 7— Time: Entries are made in this column o f the mercury. before measurement takes place. The escaping slimes time of day each pumping is made. At the bottom of blasted surface. Writing with lead pencil is The ball o f amalgam is then carefully placed in a may or may not fill the interstices o f the sand with the page the time consumed in drilling, pulling, very legible on this type surface. The Line Number, porcelain annealing cup or test tube. Dilute nitric acid doubtful increase o f the volume o f the sand. moving, repairs, and delays is recorded. These records 133 Hole Number, Depth, and the panner’s signature are (specific gravity 1.42, plus an equal volume o f water) 132 Therefore, measurements made by this method will all written on top o f the bottle. are helpful in determing the cost of prospecting records the weight o f the different colors in the |0, similar ground. on lines corresponding with the depths at which they 8 - Depth o f the cutting edge o f the drive shoe:are found. Ihis is helpful in following pay streasks ° i S 3 5 < The last item in this column is the total depth drilled. § E 2 o Z o 17-Form ation: The nature o f the formatio, 9 - Depth o f pumping: Care must be taken to see corresponding with the various depths is also note! J u.' 2 (j 2 o that pumping is not continued farther than within Very often the pay streak has a distinctive color.Itj, two inches o f the lower edge o f the drive shoe until advisable to make a notation o f this. The size anj bedrock has been reached or when a boulder is quantity of boulders have a definite bearing on ho* encountered. Notation should always he made when the property should be worked. Properties contain® FORMATION drilling below the shoe. an unusual amount o f clay require special wash® 1 0 - Entries are made o f each individual drive. equipment to prevent the clay from going throudi a 2 s * * o 3 o y i s 1 1 - The rise o f the core in the pipe for eachthe boxes and picking up the gold. Some properties drive: This is the distance from the bottom o f the contain black sand which has a tendency to pack tin

drive shoe to the top o f the core. riffles and decrease the amount o f material which can i f ( j VI i > s o a m s be handled. z JO 12- Core after pumping: The amount of core left o UOTOD in the pipe is naturally less than before pumping. This 19— Depth and nature o f over-burden: Very often 1H0I3M is the distance from the bottom o f the drive shoe to the over-hurden is removed by a different methoi 031VWI1S 3 the top o f the core and is termed the plug. It usually than that used for working o f the gravel. Information varies from two to four inches. such as buried logs, large boulders, etc., have a direct

bearing on the cost, and records should be made of of OJ 1 3 - The length o f core removed: The difference §»2iSil Number

them. COLORS between the core before pumping and the core after - pumping shows the rise o f the core in the pipe. Some 20— Labor conditions, transportation facilities. w » 5 1 3 fi­ operators use this in computing the volume. Volume 21— Depth o f the pay gravel. by computed by this method is known as the core 22— Depth to bed rock. BUCKET Measured volume by pipe measurement. VdLUfofc VOLUME 23— Nature o f bed rock. 1 4- Volume Bucket measurement. This is exactly 24— Depth of pay in bed rock. as the name implies, the volume as measured in the t s 25— Diameter o f the drive shoe. volume bucket. 2 5 j 8 26— Theoretical volume o f the core removed. 3AIUO 15- Classification of colors: The number of s u m a o j 27— Measured volume. colors are classified in the No. 1, No. 2, and No. 3 3U0Q \ O Ut m v! 0 sizes. No. 3 is the finest and consists o f all particles 28— Weight o f gold in milligrams, (mg.) 0V3HV weighing less than one milligram. No. 2 is the gold 29— Fineness o f the gold.

03TTIU 0 Inches consisting of all particles weighing between one 30— Constant used in making calculations. milligram and four milligrams. No. 1 gold is any 31— Value in cents per cubic yard. ONidwna 3 U 3 U V particle weighing over four milligrams. These are | 32— Price o f gold at which values were computed. o m d recorded on the lines opposite the depths o f drive, so co 33— Signatures o f the driller, panner and helper. 3SIH -C that the various pay streaks will be known. DRILLERS O FIELD LOG z 3U03 16- Estimated weight of gold: The panner A list o f abbreviations is included at the top of becomes very proficient in estimating weight. He 4 Z the log sheet which simplifies the recording. £Z Inches £

E DRIVE © z 5 u_ Inches

© PUMPING

DEPTH OF u. Inches

PIPE © u.

u faJ

Z z < OF

«/> o TIME PUMPING DRILLING REPORT

Name of Property VALUE: CENTS PER CU. YD^ Location of Property.. .. Line No...... Hole No.... Location of Hole

""•7 Depth of Tails . Depth of Overburden...... CROSS SECTION OF MATERIAL- Depth of Gravel...... Depth of Bedrock.... Depth of Dredge Section...... Depth o f Hole: Casing Open

Cold @ per Ounce...... per mg Black Sands: Much ...... Some Little Coarse...... Medium ... Fine Size Casing ELEVATIONS Size Shoe ...... Surface...... Volume from Shoe Constant...... Volume from Core Rise ...... Volume from Bucket ...... ;

Volume from Water Displacement 3edrock Volume for Estimate .. . Gold, Actual W t...... MjrS

F ro m ...... T o Mgs., Constant...... , Cu. Yds...... , 4 per Y d...... F ro m ...... To... Mgs., Constant...... , Cu. Yds...... , 4 per Yd...... F ro m ...... To. Mgs., Constant...... , Cu. Yds...... , 4 per Yd...... _ F ro m ...... To... Mgs., Constant...... , Cu. Yds...... , 4 per Yd. F rom T o Mgs., Constant...... , Cu. Yds...... , 4 per Yd. F rom T o Mgs., Constant...... , Cu. Yds...... , 4 per Y d...... _ F rom T o ...... M gs.,\ C on stan t...... , Cu. Y ds. , 4 p er Yd. F rom T o Mgs., Constant , Cu. Y d s ...... 4 p er Y d. TIME LOG

D rillin g H rs. D riller

P u llin g ...... P anner M ovin g H elper

R epairs ...... H rs. Field Supt.

D elays H rs. Metallurgist or Engineer T otal T im e H rs. Checked by: USE OF HILLMAN MULTIPYING FACTORS prospect drilling factors (see following page). In the TABLE OF MULTIPLYING FACTORS FOR DETERMINING GOLD VALUE PER CUBIC YARD FOR VARIOUS DIAMETER DRIVE SHOES FOR DETERMINING GOLD VALUE PER above example it will be found that 40 feet x 20.3” = 812” , the theoretical core rise. But suppose the actual CUBIC YARD To determine the value in cents per cubic yard, multiply the number of Mgs. of gold recovered from the hole by the factor shown in the following measured core rise was 893 inches. The value in cents which corresponds to the depth o f hole and the proper diameter of drive shoe. These are computed from the following formula: v , , Mg. recovered x price per Mg. Using the theoretical value: Suppose that from a per cubic yard based on a 100% core would then be Value per cu. yd. =— £------L------l------Volume (in cubic yards) 40-foot hole using a 7/4” drive shoe, 100 milligrams adjusted by multiplying it by 812, the ratio of actual This value is equal to K x Mg. recovered, where K is the proper multiplying factor. The factors are based on the following values: of gold are recovered. From the table of multiplying 8 9 3 VALUE OF GOLD $35.00 PER OUNCE. FINENESS OF GOLD 1000 factors on the preceding page, find opposite the to theoretical core rise. In our example the adjusted DEPTH OF DRILL HOLES EXPRESSED IN FEET - DIAMETER OF DRIVE SHOE EXPRESSED IN INCHES depth of 40 feet the factor .2475. Also suppose the These factors are computed with the assumption that the volume of core obtained is represented by a cylinder whose length is equal value would be to the depth of hole and the diameter of the drive shoe. The volume of ground obtained is usually somewhat less than the volume relative fineness o f the g old is 9 0 0 . T h e value o f the represented by this cylinder. When this is true, the gold actually recovered is credited to a larger volume o f ground than that from which 22.3c x 812 = 20.3c per cubic yard. hole w ould b e fo u n d as fo llo w s : it was actually obtained. The actual value per cubic yard is then slightly greater than that shown by calculating using the following table. 8 9 3 Depth to 5 K” 6ft” 7ft” 9K” Depth to 5/4” 6ft” 7ft” w 100 x .2475 x 900 = 22.3c per cubic yard. The same type of adjustment can be made using Bedrock Shoe Shoe Shoe Shoe Bedrock Shoe Shoe Shoe Shoe 1000 volume measurements in place of core rise. Some 6 3.368 2.1972 1.651 .9766 33.5 .6032 .3935 .2955 ■ I741) 6.5 3.109 2.0282 1.523 .9015 34 .5943 .3877 .2912 .172.1 engineers calculate the adjustment both ways and 7 2.888 1.8833 1.415 .8371 34.5 .5857 .3821 .2870 .16911 The above value would be correct providing a 100% apply the one giving the least plus correction. There 7.5 2.694 1.7577 1.320 .7813 35 .5774 .3767 .2828 .1674 8 2.526 1.6479 1.237 .7324 35.5 .5692 .3714 .2789 .1651 core had been ob ta in ed . are times when the correction is applied only to 8.5 2.378 1.5509 1.165 .6894 36 .5613 .3662 .2750 .1628 certain portions of a drill hole, that is, to sections 9 2.245 1.4648 1.100 .6510 36.5 .5536 .3612 .2713 .1605 Using a correction factor: The theoretical core rise 9.5 2.127 1.3877 1.042 .6168 37 .5462 .3563 .2675 .15114 containing significant values. per foot of drive will be found in the table of 10 2.021 1.3183 .9903 .5860 37.5 .5389 .3516 .2640 .1363 10.5 1.925 1.2555 .9430 .5581 38 .5318 .3469 .2004 .1542 11 1.837 1.1985 .9003 .5327 38.5 .5249 .3424 .2571 .1522 11.5 1.757 1.1463 .8612 .5096 39 .5182 .3380 .2539 .1503

12 1.684 1.0986 .8250 .488.3 39.5 .5116 .3337 .2506 .1-18.3 12.5 1.619 1.0547 .7922 .4684 40 .5052 .3296 .2475 .1165 13 1.554 1.0141 .7617 .4507 40.5 .4990 .3255 .2415 .1417 13.5 1.498 .9767 .7335 .4340 41 .4929 .3215 .2415 .1429 14 1.444 .9416 .7074 .4186 41.5 .4869 .3177 .2385 .1412 14.5 1.393 .9092 .6829 .4042 42 .4811 .3139 .2358 .1395 PROSPECT DRILLING FACTORS 15 1.347 .8789 .6602 .3906 42.5 .4755 .3102 .2329 .1379 15.5 1.304 .8505 .6389 .3781 43 .4699 .3066 .2302 .1363 554” Drive Shoe 16 1.263 .8239 .6187 .3663 43.5 .4645 .30.31 .2275 .1347 4” Drive Pipe 16.5 1.225 .7990 .5999 .3551 44 .4593 .2996 .2250 .1332 Cutting Edge dia. 5!4” Inside dia. 3.826 17 1.189 .7755 .5824 .3447 44.5 .4541 .2963 2!>!M .1317 17.5 1.155 .7533 .5658 .3348 45 .4491 .2930 .22(H) .1302 21.6475 Sq. In. . 11.4969 Sq. In. Cross-sectional 259.7700 Cu. In. 18 1.123 .7324 .5500 .3255 45.5 .4441 .2897 .2176 .12118 137.9628 Cu. In. 18.5 1.092 .7126 .5351 .3167 46 .4393 .2866 .2152 .1274 .1503299 Cu. Ft. .079835 Cu. Ft. 19 1.064 .6938 .5215 .3084 46.5 .4346 .28.35 .2129 .1260 .00556777 Cu. Yds. 19.5 1.036 .6761 .5077 .3005 47 .4300 .2805 .2106 .1247 .00295695 Cu. Yds. 20 1.011 .6592 .4950 .2930 47.5 .4254 .2775 .2084 .1234 20.5 .9858 .6431 .4829 .2858 48 .4210 .2746 .2063 .1221 Depth to which 5/ 4” drive shoe must be driven to cut out a

21 .9621 .6278 .4717 .2790 48.5 .4167 .2718 .2041 .1208 theoretical volume of one cubic yard • • 21.5 .9399 .6132 .4605 .2725 49 .4124 .2690 .2020 .1196 Theoretical rise in 4 ” drive pipe using a 5/4” drive shoe driven 22 .9185 .5992 .4500 .2664 49.5 .4082 .2663 .2000 .11114 22.5 .8981 1 .1 r ...... 22.0 .5859 .4400 .2604 50 .4042 .2637 .1980 .1172 to a a ep in 01 o n e iu u i . . . . 23 .8786 .5732 .4.304 .2548 50.5 .4002 .2611 .1961 .1160 23.5 .8599 .5610 .4216 .2495 51 .3962 .2585 .1941 .1149

24 .8420 .5493 .4125 .2442 51.5 .3924 .2560 .1922 .1138 24.5 .8248 .5381 .4041 .2392 52 .3886 .2535 .1903 .1127 F ” Drive Shoe 25 .8083 .5273 .3960 .2344 52.5 .3849 .2511 .1886 .1116 5” Drive Pipe 6 2 25.5 .7925 .5170 .3882 .2298 53 .3813 .2487 .1868 11(H) Cutting Edge dia. / ” Inside dia. 4.813’ 6 2 26 .7772 .5071 .3810 .2254 53.5 .3777 .2464 .1850 .1095 26.5 .7626 .4975 .3740 .2211 54 .3742 .2441 .1833 .1085 33.1832 Sq. In. 18.1938 Sq. In. Cross-sectional 398.1978 Cu. In. 27 .7485 .4883 .3670 .2170 54.5 .3708 .2419 .1816 .1075 218.3255 Cu. In. 27.5 .7348 .4794 .3600 .2131 55 .3674 .2397 .1800 .1065 .1263394 Cu. Ft. .2304585 Cu. Ft. 28 .7217 .4708 .3540 .2093 55.5 .3641 .2375 .1784 .1056 .0085355 Cu. Yds. 28.5 .7091 .4626 .3475 .2056 56 .3609 .2354 .1768 .1046 .0046795 Cu. Yds. 29 .6968 .4546 .3417 .2021 56.5 .3577 .2333 .1752 .1037 29.5 .6850 .4469 .3358 .1986 57 .3545 .2313 .1737 .1028 Depth to which 6/ 2” drive shoe must be driven to cut out a 30 .6736 .4394 .3300 .1953 57.5 .3514 .2293 .1722 .1019 theoretical volume of one cubic y a r d ...... 1 1 7 .1 ’ 30.5 .6620 .4322 .3246 .1921 58 .3484 .2273 .1707 .1010 31 .6519 .4253 .3194 .1890 58.5 .3454 .2254 .1692 .1002 T heoretical rise in 5” drive pipe using a 6/ 2' ' drive shoe driven 31.5 .6415 .4185 .3142 .I860 59 .3425 .2234 .09932 .1678 ...... 2 1 .9 ” 139 32 .6315 .4120 .3094 .1831 59.5 .3396 .2216 .1664 .09048 to a depth of one foot ...... 32.5 .6218 .4056 .3047 .1803 60 .3368 .2197 .1651 .09766 33 .6124 .3995 .3000 .1776 60.5 .3340 .2179 .1638 .096.36 ? S • ;&

PROSPECT DRILLING FACTORS I I

6” Drive Pipe 7/4” Drive Shoe Inside dia. 5.761” Cutting Edge dia. 7)4” Cross-sectional A r e a ...... 26.0666 Sq.In. 44.1788 Sq.In. Volume in Cu. In. per Ft. depth 312.7997 Cu. In. 530.1450 Cu. In. Volume in Cu. Ft. per Ft. depth .181019 Cu. Ft. .3067968 Cu. Ft. Volume in Cu. Yds. per Ft. depth .00670433 Cu. Yds. .0113628 Cu. Yds.

Depth to which 7J4 drive shoe must be driven to cut out a theoretical volume of one cubic y a rd ...... 88 00’ APPENDIX E 1 heoretical rise in 6 drive pipe using a 754” drive shoe driven to a depth o f one foot ...... 20 ’i”

8” Drive Pipe 9%” Drive Shoe GENERAL INFORMATION Inside dia. 7.625” Cutting Edge dia. 9%” Cross-sectional A r e a ...... 45.6636 Sq. In. 74.6621 Sq. In. Volume in Cu. In. per Ft. depth 547.9632 Cu. In. 895.9450 Cu. In. AND COST DATA Volume in Cu. Ft. per Ft. depth .3171086 Cu. Ft. .5184867 Cu. Ft. Volume in Cu. Yds. per Ft. depth .0117447 Cu. Yds. .01920321 Cu. Yds.

Depth to which 9% drive shoe must be driven to cut out a theoretical volume o f one cubic y a r d ...... 52 08’

1 heoretical rise in 8 ” drive pipe using a 934” drive shoe driven to a depth of one foot ...... [ 95 ”

140 approximate w e ig h t s o k e a r t h a n d g r a v e l data precludes the formulation o f specific rules. The

ORDINARY GRAVEL Rank measure .’{,000 lbs. per eubic yard following figures should be used with this in mind. DRY GRAVEL loose measure 2.000 lbs. per eubic yard Distance from Source Nature o f G old11 DRY SAND loose measure 2.200 lbs. per cubic yard 5 miles Rough nuggety ORDINARY EARTH Rank measure 2.000 lbs. per cubic yard 8 miles Small nuggety, DRY EARTH loose measure 2.000 lbs. per eubic yard water-worn (XAY bank measure 2.200 lbs. per eubic yard 11 miles Fine granular 25 miles Fine scaly

1/ Gold in Adelong Creek, New South Wales. Data from ar­ APPROXIMATE SWELL OF EARTH AND GRAVEL11 ticle by N. H. Fisher; Fineness of Gold With Special Re­ ference to the Morobe Gold Field, New Guinea: Econ. ORDINARY GRAVEL 20 to 30% Geol., Vol. 40, No. 7, November, 1945. CEMENTED GRAVEL 40% SAND AND GRAVEL 15% HEAVY MINERALS FOUND IN GRAVEL AND CLAY 35% WESTERN GOLD PLACERS1/ LOAM 20% SPECIFIC GRAVITY DENSE CLAY 50% MINERAL FROM TO

Magnetite 5.2 1/ The volume increases shown here may change appreciably Ilmenite 5.6 5.7 under varying conditions, the amount of swell being in­ fluenced by the moisture content, size o f gravel and its Garnet 3.2 4.3 ratio to sand, and other conditions. Zircon 4.2 4.7 Hematite 4.9 5.3 GRAIN SIZE Chromite 4.3 4.6

AVERAGE DIAMETER Epidote 3.2 3.5 NAME OF PARTICLES IN MILLIMETERS'/ Olivine 3.3 boulders Greater lliau 250 mm (10” ) Cobbles 04 mm to 250 mm (214” to 10” ) Limonite 3.6 4.0 Pebbles 4 mm to 04 min (3 /10” to 254” ) Rutile 4.2 Gravel Greater than 2 mm Sand 2 mm to 1/10 mm Pyroxine 3.3 Silt 1/10 mm to 1/250 min Clay Less Ilian 1/250 mm Monazite 4.9 5.3 Platinum group metals 14 19

1/ 25.1 millimeters (mm) I inch. 1/ A partial list, arranged in approximate order of frequency.

CHARACTER OF PLACER GOLD Gold, platinum, magnetite, ilmenite, chromite, gar­ related to n et, z ir c o n , rutile and monazite, when found in DISTANCE FROM SOURCE placers, may be far from their source. Copper It is generally recognized that the shape and angu­ minerals, galena and sphalerite are rarely found in larity o f placer gold may serve as a measure o f placers, and where found, are usually not far from distance traveled. The heavier and more hackly, the their source. nearer the source. The more water-worn and scaly, The black sand content o f gold placers in the Western the further it has traveled from its source. While this United States is commonly between 5 and 20 pounds can be accepted as fact, the near-absence o f statistical o f black sand concentrate per cubic yard o f gravel. i.i Mi " i.~ r r r r r “ ------

APPROXIMATE MINING COSTS, 1964 G

Bucket-line dredge 11c 22c per cubic yard Dragline dredge 22c 45c ” ” ” Hydraulic 25c 45c ” ” ” Drift $9.00 $18.00

BUCKET-LINE DREDGE COST, 1964 2/

Maximum Cost Cost, Annual capacity, Bucket size, digging depth Weight, per ton, erected, million cubic yards cubic feet below water tons erected, dollars level, feet dollars (million)

8.4...... 22 150* 5,000 1,300 6.5 APPENDIX F 10.4...... 27 120 4,000 1,370 5.5 6.9...... 18 100 3,000 1,400 4.2 3.8...... 10 80 2,000 1,600 3.2 3.0...... 8 50 1,300 1.850 2.4 2.3...... 6 40 700 2,000 1.4 1.6...... 4Z< 25 460 2,175 1.0 CONVERSION TABLES * A bucket-line dredge of this digging capacity has not been built; bucket size may be restricted by engineering requirements.

FLOATING GRAVEL WASHING PLANT COST, 1964 2/ 3/

Annual capacity, Weight Cost per ton, Cost, erected, million Trommel size short tons erected, thousand cubic yards dollars dollars

0.6...... 54-inch diameter, 76 1,380 105 by 30 feet. 1.5...... 72-inch diameter, 207 1,210 248 by 47 feet. 3.0...... 120-inch diameter, 488 1,270 620 by 63 feet.

1/ U.S. Bureau of Mines I.C. 8331, p. 13,1967. 2/ U.S. Bureau of Mines I.C. 8331, p. 14,1967. 3/ Washing plant for dragline dredge. Lengths

' 8 furlongs i rod = J5 5 yards 80 chains \ 16.5 feet 1 mile = • 320 rods i i _ 13 feet 1,760 yards 1 yard { 36 inches . 5,280 feet 1 vara = 33 inches (approx.) I 10 chains 1 furlong = 1 foot = 12 inches l 220 yards 1 link = 7.92 inches (6.06 rods 1 inch = 0.0833 foot 1 station = | 33.3 yards \ 100 feet 4 rods 22 yards 1 chain = ( 66 feet 100 links

Square Measure

1 township = 36 sq. miles (600 ft. x 1,500 ft. 1 section 1 sq. mile = Lode Claim = {20.661 acres (640 acres (3305.78 sq. rods 4,840 sq. yards Placer Claim = 20 acres 43,560 sq. feet 1 acre = (1 locator) 10 sq. chains 1 sq. rod = 27254 sq. feet 160 sq. rods 1 sq. yard = 9 sq. feet 1 sq. foot = 144 sq. inches

Cubic Measure

1 cubic yard = 27 cubic feet 1 cu. ft. = 7.48 U.S. gallons 1 cord (wood) = 4 x 4 x 8 ft. = 1 bushel = 2150.42 cu. in. 128 cu. ft. 1 bushel = 1.244 + cu. ft. 1 ton (shipping) = 40 cubic ft. 1 gallon = 231 cu. in. 1 cubic foot = 1.728 cubic inches

Weights (Commercial) 1 long ton = 2,240 lbs. 1 pound = 16 ounces 1 short ton = 2,000 lbs. 1 ounce = 16 drams

Troy Weight (for Gold and Silver)

12 oz. troy = 1 lb. troy = 0.823 pounds av. = 5760 grains 16 oz. av. = 1 lb. av. = 7,000 grains 31.1035 grams = 1 oz. troy = 20 pennyweight = 480 grains 28.350 grams = 1 oz. av. 1 kilogram = 2.2046 lb. av. 1 pennyweight = 24 grains = 1.555 grams

Dry Measure

1 bushel = {Ji>ed “ 1 quart = 2 pints 132 quarts 1 bushel = 1.2445 cubic feet 1 peck = 8 quarts 147 Metric and U.S. Weights and Measures

Lengths

MilesX 1.6093 = Kilometers KilometersX 1093.6 = Yards YardsX.9144 = Meters KilometersX 3280.9 = Feet FeetX.3048 = Meters MetersX 1.094 = Yards FeetX 30.48 = Centimeters MetersX 3.281 = Feet InchesX2.54 = Centimeters MetersX 39.37 = Inches lnchesX25.4 = Millimeters CentimetersX.3937 = Inches i KilometersX.621 = Miles MillimetersX .03937 = Inches

Areas

Sq. mileX2.59 = Sq. kilometers AcresX .00405 = Sq. kilometers AcresX.4047 = Hectares INDEX Sq. YardsX.8361 = Sq. meters Sq. feetX.0929 = Sq. meters Sq. InchesX 6.452 - Sq. centimeters Sq. inchesX645.2 - Sq. millimeters Sq. kilometersX.3861 = Sq. miles Sq. kilometersX247.ll = Acres HectaresX 2.471 = Acres Sq. metersX 1.196 = Sq. yards Sq. metersX 10.764 = Sq. feet Sq. centimetersX.155 = Sq. inches Sq. millimetersX.00155 = Sq. inches

Volume Cu. yardsX.765 = Cu. meters Cu. feetX.0283 = Cu. meters Cu. inchesX 16.383 = Cu. centimeters Cu. metersX 1.308 = Cu. yards Cu. metersX 35.3145 = Cu. feet Cu. centimetersX.06102 = Cu. inches

Liquid Measure

U.S. gallonsX.8333 = Imperial gallons GallonsX 3.785 = Litres QuartsX.946 = Litres Imperial gallonsX 1.2009 = U.S. gallons LitresX .2642 = Gallons LitresX 1.057 = Quarts

Weights

PoundsX.453 - Kilograms KilogramsX 2.2046 = Pounds A b and o n ed placers, 7 Bench placers, 11, 12 Check samples—Continued Accretion bar, 13, 93 Black gold, 94 to detect salting, 48 Accuracy of sampling, final proof of, 25 Black sand, 94 use in valuation, 22 Adjusted sam ple data, use of, 22 constituents, of, 94, 143 Check shafts, use in placer drilling, 27, 42, Adjusted value, 93 content, in Western gold placers, 94 43 Adjustment of values, from chum drill, extraction of gold from, 64, 66 Chellson, Harry C., cited, 74 34-36,139 treatment in amalgamating jar, 66 Chum drill, 96 Adverse physical conditions, shown by Black sand minerals, in beach placers, 15 multiplying factors for, 138-139 sa m p lin g , 23 Blackwelder, Eliot, quoted, 16 use in drift mine prospecting, 44 Aerial photographs, use of, 23 Blowing, to separate gold from black sand, use in hydraulic mine prospecting, 45 Agents o f rock weathering, 4, 5 64 use in sampling, 32-43 Aggrading stream, 5 Blue gravel, 94, 95 Chum drill, as a method for testing placers, Aim in placer sampling, 23 Blue lead (see blue gravel) 32-43 Ainlay bowL, 93 Blue River, Colorado, gold from glacial computing values from, 3436, 138-139 Ainlay centrifigual concentrator (see moraines, 4,17 cost of, 42-43 Ainlay bowl) Booming, 95 equipment for, 32-34, 129-133 Airplane placer drill, 36, 93 Boulders, allowance for in samples, 43, excess or deficient core, causes of, 34 illustrated, 33, 37 45-47 frozen ground, 36 Alaska, beach placers, 15 as a factor in dredging, 26 hole spacing, 36-42 Alluvial deposits, classification of, 11 consideration of, 79 holes per acre, 25, 37 Alluvial fan, 93 Bowie, A. J., cited, 45 pattern, for narrow deposits, 37, 38, in preservation o f placers, 7 Braided streams, 95 39-42 Alluvial plain, 93 Breckcnridge, Colorado, gold from pattern, for widespread deposits, 37, Amalgam, gold, 94 glacial moraines, 4,17 38-39, 40 sodium, 108 Brooks, Alfred H., cited, 11, 93 personnel for, 36 Amalgamation, definition of, 94 Browne, Ross E., cited, 14 procedure, 32-34, 129-133 effect on gold texture, 54, 66 Bucket drill, use in sampling, 28-31 rate of drilling, 42 in glass jar, 66 Bucket-elevator dredge (see bucket-line ratio, holes per acre, 25, 37 in pan, 64, 66 dredge) ratio, sample to gravel, 25 in sampling sluice, 54 Bucket-line dredge, described, 95 supervision of, 36-37 of gold in black sand concentrate, cost of, 144 value adjustments, 3436,139 66-67 water requirements for, 125 without casing, 36, 47 Ancient channels (see Tertiary Channels) Bucyrus placer drill, 36 Choosing a sampling method, 23-24 Angularity of placer gold, related to Bulk samples, 43, 48 Clamshell-type excavator, use in sampling, distance from source, 143 Bulldozer, use in sampling, 32 28, 29-30 Appraisal, of drift mines, 44 Buried placers, 7, 95 Clark, William B., cited, 11,14 of placer potential, where sampling Burlap, use in sluice, 54 Clean-up, definition of, 96 fails, 49 Cable drill (see churn drill) Clifton, H. Edward, cited, 16 Area of influence, in sampling, 24, 25 Caisson, 95 Climatic change, effect on placers, 5 Assay, definition of, 94 use of, 27, 28 Coarse gold, 96 Assay, fire, described, 99 Calculation of reserves, grid system, 38-40 effect on samples, 22, 43 misleading results from, 65, 66 line system, 39-42 Cocoa matting, 96 Assay, free gold, definition of, 100 mean-area method, 39-42 use in sampling sluice, 54 procedure for, 66-67 triangle method, 38-39, 40 Colloidal gold, 96 Assay balance, illustration of, 67 Caliche, as factor in dry washing, 59 in unproven processes, 74 Assay value, definition of, 94 cemented gravels, 30 Colluvial definition of, 96 Auriferous conglomerate, as gold source, described, 95 Color, gold, definition of, 96 4 residual-type enrichments on, 14 standard sizes of, 66 Averill, Charles V., cited, 73 California, auriferous conglomerate in, 4 Colorado, gold from glacial moraines, 4,17 Backhoe excavator, use in sampling, 31 beach placers, 15,16 Concentration, dry, principles of, 58-59 Bajada placer, 94 El Dorado County, seam diggings, 11 of gold on bedrock, 5, 6 Balance, assay, illustration of, 67 Tertiary gravels in, 3-4, 14, 15, 44 of valuable minerals, 6 Bank measure, 72, 94 Canvas, use in rocker, 57, 58 Concentrates, extracting gold from, Banka placer drill, 36, 94 use in sampling sluice, 54 64,66 Bar, definition of, 94 Casing, chum drill, 95 Core, churn drill, 96 Basic rocks, as source of platinum drilling with, 32-34,129-131 factor, 96 minerals, 3, 4 drilling without, 36, 47 rise, 97 Batea, 94 Casing factor, 95, 96 Corrected gold weight, in drill samples, Beach placers, 15-16, 107 Cement, 96 35,139 elevated, 7 Channel cut, use in sampling, 27-28, 45 Conversion tables, water, 126 sampling problems, 16 size of, 28 weights and measures, 147,148 sampling with small-diameter drills, Channel obstructions, effect on gold Correction factors, applied to samples, 47-48 deposition, 5 22, 43, 46, 59 Bed Scour, 5 Channel scour, as factor in gold deposition, for chum drill, 139 3ed load, 5, 94 5 Conversion tables, weights and measures, movement of, 5, 6 Character of placer gold, related to 147,148 Bedrock, definition of, 94 distance from source, 143 Cost, factors influencing, 73 concentration of gold on, 5-6 Check holes, interpreting, 42 of bucket-line dredges, 144 conditions, consideration of, 79 Check list, for placer investigations, 79-89 of chum drilling, 42-43 false, 6, 99 Check samples, as “ written proof’ where of sampling, with backhoe excavator, 31 release of gold from, 4-5 no values exist, 44 of washing plants, 144 types of, 6 interpreting, 42 Cost data, sources of, 73-74 Bench gravels, 7, 12, 94

151 Drilling—Continued Goodnews Bay, Alaska, platinum placers, Keystone constant, 35, 103 Moraine, glacial—Continued Cost estimates, making, 73 frozen ground, 36 Failure, of sampling, 49 4 Keystone placer drill, 36 placers derived from, 4,16, 17 based oil hypothetical operation, 73 hole spacing, 36-42 Fairplay, Colorado, glacial moraines, Grab samples, 43-44 illustrated, 36 Moss mining, 104 comparison method, 73 holes per acre, 25, 37 gold from, 4, 17 Grade, definitions of, 100 KLAM, mechanical shaft digger, 29-31 Muck, Alaskan, description of, 104 Cost index, Engineering News-Record, 73 pattern for narrow deposits, 37, 38 False bedrock, 6, 99 ( for rocker, 57 illustrated, 30 Mud box (see puddling box) Costs, related to throughput, 75 39-42 Fay, Albert H., cited, 93 for sam pling sluice, 55 Klondike region, Canada, source of gold Muddy water, consideration of, 79 mining, 144 pattern for widespread deposits, 37, Graded stre a m , 100 in, 3-4 in dredge ponds, 125 Cradle, (see rocker) Field guide, for placer investigations, 79-89 38-39, 40 Field log, shaft, 118 Grain size , ta b le o f , 143 Lacustrine deposits, 103 Narrow pay channel, drilling pattern for, Creek placers, 12, 97 personnel for, 36 Field record, sampling, 115 Gravel, d e f in it io n o f , 101 Landslide material, in preservation of 37 Crevicing, 97 procedure, 32-34,129-133 Fire assay, 74, 99 Gravel-plain deposits, 12, 101 placers, 7 value calculation of, 39-42 Cribbing, 97 rate of drilling, 42 of beach sands, 16 gold distribution in, 12 Large rocks, allowance for in samples, 43 Nevada, Goldfield District, absence of diagram showing, 28 ratio, holes per acre, 25, 37 Grid, sy ste m o f p ro s p e c tin g , 25, 37-40 45-46 placers in, 3 use of, 28 of placer samples, 65-<)6 supervision of, 36-37 Fine (size) gold, definition of, 99 I Grizzly, 101 Lead, 103 Nome, Alaska, beach placers, 7,15 Cutting samples, in pits or shafts, 27-28 Length of sampling sluice, 53, 55 elevated beaches, 7 value adjustments, 34-36, 139 in flood-gold deposits, 12, 13 pan, use of, 65 Daily, Arthur, cited, 35, 39 Lindgren,Waldemar, cited, 5,14 Nugget, definition of, 104 without casing, 36, 47 recovery of, by unproven processes Ground sluicing, 101 Dasher, John, cited, 16 Drills placer, types of, 36 74-75 water requirements for, 125 Line system, for prospect drilling, 37, 38 Nuggety ground, use of bulk samples for, 39-42 43 Data summary sheet, for samples, 117 Drive pipe, 98 recovery of in dry washer, 59 Ground sluice cuts, for sampling, 45 Degrading stream, 5 Lines, spacing of, 36-42 Number of samples needed, 22, 23, 37-38 Drive shoe, 98 recovery of, in rocker, 57 Ground water, function in rock decay, 4 Denver Gold saver, 58 factor, 98 Lodes, related to placers, 3 Operation of churn drill, 129-133 recovery of, in sampling sluice, 54, 55 Gulch placers, 11 Dry placers, 13, 98 Log, drillers, 98 Ore reserves, calculation of, 39-42 Denver Mechanical Gold Pan, 58 Fineness (purity), of gold, 99 Haley, Charles S., cited, 14 Desert placers, discussion of, 13-14 Dryland dredge, 98 Hand mining, water requirements for, 125 example of, 135-137 Oregon, beach placers, 15, 16 Fineness and value equivalents, table of stream deposition rules, subordinate water requirements for, 125 Hand-dug sample pits, 26-28, 45 headings in, explained, 133-134 Tertiary gravels in, 14 in, 5 122 Dry washer, diagram of, 59 Fisher, N. H., cited, 143 shafts, 26-28, 45 use of, by driller and panner, 32, 35, Outwash aprons, placers in, 17 surface enrichments in, 17 Dry washers, 53, 58, 59, 98 Float gold, 100 Hand-powered placer drills, 36 36-37,133-134 Over-valuation, from fire assays, 66 Dip box, 97 Log, shaft, example of, 118 effectiveness of, 59 I Flood gold, 100 Hard bedrock, mining problems, 6 from rotary drills, 47 Discounting, of high values, 46-47 recovery by, 59 deposits, 6, 12, 13 Harding, James E., cited, 35 Long tom 53, 103 Pan, 104 Discovery, 97 Dry washing, problems, 59 Longwell, Chester R., cited, 7 amalgamation in, 66 Flood plain, definition of, 100 Head, definition of, 101 Disposal, of muddy water, 79 Loose volume measure, use in sampbng, 27 requirements for, 59 deposits, 12 Heavy gold, 101 bluing before use, 64 of tailings, 79 Dunite, as source of platinum, 4 Flour gold, 100 Heavy minerals, 101 Lorain, S. H., cited, 32 description of, 104 Disseminated deposits, as a source of Dunn, EJ., cited, 93 Lord, Harry S., cited, 74 Floured mercury, 100 I in placers, 3 factor, 64, 65,104 placer minerals, 4 Dunn, R.L., cited, 93 Low-value minerals, effect on sample, 22, grizzly, use of, 65 Folsom district, California, drill hole list of, 143 Duty, ofwater, 98, 99 47-48 perforated, use of, 65 density, 37 source of, 4 Distance from source, related to Eassie, W. H., cited, 45, 74 MacDonald, D. F., cited, 4 removing grease from, 64 false bedrock in, 6 Herr, Irving, cited, 25 character of placer gold, 143 Machine-dug shafts, use in sampling, 28-31 Electrostatic separation, 99 Fools’ gold, 100 High tension separator, 101 safety, use of, 65 Dohney, L. C., cited, 28, 36, 39 Elevated beaches, 15 High-value minerals, effect on sample, Magee, James F., cited, 27 use as geologic tool, 65 Forest Hill Divide, California, Tertiary Doodlebug, 97 Magmatic segregations, as source of placer use for washing sample, 53 Elevated sluice, 110 gravels, 14 21-22 Dragline dredge, 97 minerals, 4 Panner, for placer drill, 32, 36-37 Elevator, hydraulic, 102 Free gold, definition of, 100 Hill, J. M., cited, 13 washing plants, cost of, 144 Rubel, 107 Magnetic separator, 103 Panning, procedure described, 63-65 Free-gold assay, 100 Hillman Airplane placer drill, 36, 93 water requirements for, 125 Eluvial placers, 11 Magnetite, in beach sands, 15 notes and suggestions to improve, 64-65 procedure for, 66 iUustrated, 33, 37 Draper, Marshall D., cited, 29 Eluvium, 99 Malakoff hydraulic mine, sampling at, 45 testing by, 26, 27, 44, 45 F'ree-wash gravel, 100 i Hillman Prospector placer drill, 36 Dredge, 97 Empire placer drill, 36, 94, 99 Marine placer, definition of, 103 PAR-X mechanical shaft digger, 29 Frozen ground, churn drilling in, 36 Holes per acre, for prospect drilling, 25, 37 bucket-line, 95 Eolian placers, 17 Market, for placer gold, 121 Pardee, J. T., cited, 16 Gardner, E. D., cited, 66, 74 Holes spacing of, in prospect drilling, dragline, 97 Erosion, of pre-existing placers, gold Mat, use in rocker, 57, 58 Patent, 105 Geophysical investigation of Tertiary 36-42 hydraulic, 101, 102 from, 3-4 use in sampling sluice, 54 Particle size, as function of stream pro­ channels, 14-15 Hulin, Carlton D., cited, 4 jet, 102 Erosion cycles, 99 Materials, weights of, 143 Giant, hydraulic, 100 Humphreys spiral concentrator, 108 cesses, 5 suction, 109 Erosion surfaces, placers on, 4 McKinstry, Hugh E., cited, 93 Particle sizes, to be dealt with in sampling, Glacial debris, as placer gold source, 3-4, Hungarian-type riffles, 54, 75 Dredge section, 98 Mean-area method, for calculating value of Erratic distribution of values, effect on 16, 17 Huttle, J ohn, cited, 29 21 Drift, definitions of, 98 samples, 22, 49 Hydraulic dredge, 101,102 placer ground, 39-42 Parting solution, preparation of, 66 Glacial moraines, placers derived from, 4, Drift mines, appraisal of, 44 Measurement of samples, by weighing, 27 Patman, Charles G., cited, 74 Erratic high values, sampling of, 43, 16, 17 Hydraulic elevator, 102 sampling, 44, 49 46-47 Hydraulic giant, 102 Mercury, 103 Pay lead, 105 Glacier-related placers, 16,17 Drift mining, 98 Error in calculated value, amounts caused by Hydraulic mines, sampling of, 44-45 effect on surface texture of gold, 54, in drift mines, 44 Glossary, of placer terms, 93-111 Drill, Airplane, 33, 36-37, 93 extraneous gold particles, 47 66 Pay streak, 6, 13, 22,105 Gold, amalgam, 94 Hydraulic mining, 102 Banka, 36, 94 Estimate of value, from production Idaho, Monazite placers in, 4 “ floured” and “ sickened” , 100 Pediment, 105 character, related to distance from Bucyrus-Erie, 36 records, 45, 49 Snake River, flood gold in, 13 penetration of gold by, 54 Pennyweight, 105 source, 143 Empire, 36, 94, 99 Evaluation, of bulk samples, 43 Tertiary gravel in, 14 use in pan, 64 Perforated pan, use of, 65 extraction from mercury, 66 Hillman, 36 of prospects, 22, 25 Hmenite, 22 use in riffles, 54 Permafrost, 105 fineness, 99 jet-type, 102 of sample results, 25-26 Indicated value, definition of, 102 use in sampling sluice, 54 Peterson, Donald W., cited, 14 fineness and value, table of, 122 Keystone, 36, 103 Examination of placers, check list for, Initial sampling programs, 25 Mertie, John B. Jr., cited, 65 Pilot plant, use in sampling, 43 flour, 100 Ward, 36, 110 79-89 Initial valuation, 25 Merwin, Roland W., cited, 15 Pilot sluice, use on gold dredge, 105 Drill core, 98 milligrams equivalent to lc, 121 Existing exposures, samples from, 25-26 Interpretation of samples, 23 Metric weights and measures, table of, 148 Pinched sluice, 105 pan, description of, 104 Drill factors, 35, 36, 95, 96, 98,105,106 Expanded metal lath, Investigations, placer, checks list for, Microscope, use to detect salting, 48 Pipe clay, 105 108, 110 panning, instructions for, 63-65 use as riffle, 54, 57 79-89 Microscopic gold, 74 Pipe factor, 105 price, changes, in, 121 Drill holes, number per acre, 25, 37 Experience factor, in churn drill sampling, Iron sand, 102 Miner’s inch, 103,104, 126 Placer, definition of, 105 recovery, in dry washers, 59 spacing of, 36-42 35 Janin, Charles, cited, 66 Miner’s pan, used for washing samples, 53 deposits, classification of, 11 recovery, in rockers, 57 Drill log, examples, of, 135-137 in evaluation of placers, 22-23, 42 Jarman, Arthur, 49 Mining costs, 144 drill, basic equipment, illustration of, recovery, in sampling sluice, 54, 55 explanations of headings in, 133-134 Extraneous mineral particles, effect on Jenkins, Olaf P., cited, 7, 11, 14, 16 factors influencing, 73 33 sale of, 121 use of, 32, 35, 98, 133-134 sample, 22, 26, 47 Jet-type dredge, 102 procedures for estimating, 73 drill, typical set up, illustration of, 37 separation from black sand, 64, 66 Drilling, as a method for testing placers, curve showing, 47 Jig, description of, 102, 103 Monazite, 22, 104 drills, types of, 36 sources of, 3-4 32-43, 129-133 Factor, shaft, 107,108 placer type, 53, 75 placers, 4 geology, review of, 3-7 value per milligram, how to figure, 121 computing values from, 34-36, 138-139 Factors, churn drill, 95, 96, 98, 105, 106 Judgement, required in sampling, 23, 24, Monitor, hydraulic, 102,104 machines, small scale, 58 Gold particle size, effect on sample, 26, 47 cost of, 42-43 108,110 42 Moraine, glacial, 104 material, typical, photo of, 21 Gold-saving tables, 100 equipment, 32-34, 129-133 in hydraulic mine evaluation, 45 Kauffman, A. J. Jr., cited, 15 as gold source, 3-4,17 mining, definition of, 106 excess or deficient core, causes of, 34 in placer investigations, to be Goler mining District, California, considered, 79 auriferous conglomerate in, 4 152 153 Placer—Continued Regional uplift, preservation of placers Sample washing equipment, 53-59 terms, glossary of, 93-111 by, 7 ' desirable features in, 5? ~ie 0f placer deposit, related to source, Thurman, Charles, H., cited, 74 theory, review of, 3-7 Reporting values, 72 Trace, gold definition of, 110 dry washers, 58-59 3 Placers, accretion, 13, 93 Representative samples, 21-23,107 Trained personnel, need in placer beach, 15-16,107 general considerations for, 53 ^kin diving, 108 Reserves, calculation of, by grid system, miner’s pan, 53 1 Siam bar, 13,108 drilling, 35, 36 bench, 12, 94 38-39, 40 rockers, 55-58 Slackline scraper, 108 Trestle sluice, 110 burial, preservation by, 7 by line system, 39-42 Triangle method, for calculating reserves, buried, 95 sluice box, 53-55 Sluice box, 108 by mean-area method, 39-42 for washing samples, 53-55 38-40 classification of, 11 special machines, 58 by triangle method, 38-39, 40 water requirements for, 54-55,125 Trommel, 110 creek, 12, 97 Samples, area of influence, 24-25 Residual placers, 11, 106 Sluiceplate, 108 Troy ounce, definition of, 110 defined, 3, 105 description of, 71 Richness of placers, factors in, 3, 5, 6 Small-diameter drill holes, sampling pro­ Troy weight, conversion table for, 121 desert, 13-14 minimum number of, 25 River bar placer, 107 representative, 21-22, 45-46 blems, 47-48 Twenhofel, W. H., cited, 16 dry, 98 River deposits, 12 required number of, 22, 23, 24-25 Smooth bedrock, as gold saver, 6 Types of placers, 11-16 eluvial, 11 River mining, 107 Uncased drill holes, sampling problems, eolian, 17 size of, 22, 23, 24, 26, 28, 46 Sniper, 12, 108 Riffle, action in, 53, 54 Sampling, accuracy, proof of, 25 Snake River, Idaho and Wyoming, flood 47 flood goH 12, 13, 100 expanded metal type, 54 Undercurrent, 110 glacial, 4, i6, 17 check list for, 115 gold in, 13 for sampling sluice, 53-54 cost of, with churn drill, 42-43 Sodium amalgam, 108 Unproven processes, 74-75 gravel-plain, 12, 101 for sampling sluice, drawing of, 54 Ultrabasic rocks, as platinum source, 4 gulch, 11 data summary sheet, 117 Soft bedrock, mining of, 6 Hungarian type, 54 definition of, 107 Source of placer gold, related to character, Valuable minerals, sources of, 3-4 marine, 103 wire screen type, 54 density, for dredge ground, 25, 37 “ 143 Valuation, area of influence in, 24 residual, 11,106 Riffles, for fine gold, 54 drift mines, 44, 49 Sources of valuable mineral, 3-4 factors, other than mineral content, resorted, 4 function of, 53, 54 effect of gold particle size, 26 South America, flood gold deposits in, 13 22-23, 79 river, 12 use of, in proven processes, 75 erratic, high-value ground, 43 South Platte River, Colorado, gold from initial, 25 skim bar, 13, 108 use of in rocker, 57 of placer deposits, calculating stream, 11-12 existing exposures, 25-26 glacial moraines, 4 Rock weathering, agents of, 4, 5 procedures, 38-42 study of, 3-7 failure of, 49 Specific gravity, definition of, 108 Rocker, 55-58,107 Value of deposit, calculated by mean-area Tertiary, 14-15,110 field record for, 115 Speedstar placer drill, 36 construction details, 55-57 method, 39-42 Plant run, use in sampling, 43 frozen ground, with chum drill, 36 Spiral concentrator, 108 drawing of, 56 Split samples, misleading results from, 72 calculated by triangle method, 38-40 Platinum placers, 4 engine-powered, 58 general considerations, 21-23 guides, 23-25 chart showing, 71 Values, definition of, 110 Platinum-group minerals, in beach placers, for washing samples, 53 hydraulic mines, 44-45 table showing, 72 reporting, 72 15-16 grade for, 57 problems, 21-22 use for fine-size, low-value material, 72 Vanderburg, William 0., cited, 11,14, 67 Point bar, 108 key to effective use, 57 projection of data, 24-25 Sponge, gold, 109 Volume, error in, effect on sample value, Pre-existing placers, as source of gold, 3-4 operation of, 57 proof of accuracy, 25 Stage panning, 65 47 Presampling reconnaissance, 23 saving fine gold in, 57 reconnaissance for, 23 Staley, W. W., cited, 73, 74 factor, chum drill, 110 Preservation of placers, 6-7 sizes of, 56 special problems, 45-47 Statistical information, use where sampling measurements, in sampling, 27 Processing record, for samples, 116 slope for, 57 stream-type deposits, with drill, 37, 38, fails, 49 Ward-type placer drill, 36,110 Production records, use of, 23, 45, 49 throughput capacity, 58 39-42 Steel, Donald, cited, 28 Wash, definitions of, 110 Prommel, H. W. C., cited, 29 use of scoop in, 57 to block out ground, 25 Steffa, Don, cited, 44 Washing equipment, for samples, 53-59 Prospecting, definition of, 106 use of, with and without riffles, 57 to a uniform average, 25 Stray gold particles, effect on sample, 47 Washing plants, cost of, 144 Prospecting rocker, construction details, water requirements for, 57, 125 water requirements for, 125 55-57 use of backhoe excavator, 31 curve showing, 47 Romanowitz, Charles M., cited, 74 Water duty, 98-99 Puddling box, use with sampling sluice, use of bulk samples, 43 Stream balance, 5 Rotary bucket drill, use in sampling, 28-29, use of bulldozer trenches, 32 Stream bed erosion, 5 Water head, 101 55 30-31 measurements, units of, 126 Quaternary gravels, 106 use of channel cuts, 27-28 Stream placers, 11 Rotary drills, over-valued samples from, Stream processes, related to placers, 5 Water requirements for, bucket-line Quicksilver (mercury), 103 47 use of chum drill, 32-43,129-133 use of clamshell-type excavators, 28, Stream-type deposits, prospecting with dredges, 125 effect on surface texture of gold, 54, 66 Rough gold, 107 dragline dredges, 125 use in pan, 64 29-31 churn drill, 37-38, 39-42 Roughness of placer gold, related to dryland dredges, 125 use in riffles, 54 use of grab samples, 43-44 Stream-type deposits, value calculation by distance from source, 143 ground sluicing, 125 use in sampling sluice, 54 use of hand-dug excavations, 26-28 mean-area method, 39-42 Round Mountain, Nevada, eluvial placers, hand mining, 125 Radford factor, 35-36, 106 use of machine-dug shafts, 28-31 Streams, deposition in, 5 11 hydraulicking, 125 Radioactive blacks, 106 use of rotary bucket drills, 28-29 Struck capacity, definition of, 109 Rubel elevator, 107 moveable washing plants, 125 Ransome, Frederick L., cited, 17 Sampling and evaluation, 21-50 Suction dredges, 13, 109 Rusty gold, 107 placer operations, 125 Rare earth minerals, 106 Sampling methods, 25-45 Surf washer, 109 treatment of, 66 rockers, 57,125 Ratio of gold to gravel, 21-22, 47 choice of, 23, 24 Surface concentrations, 6, 13, 14, 17 Safety pan, use of, 65 Surface veneers, enrichment in, 4, 17 sampling sluice, 54, 55 R/E, explanation of, 106 Sale of gold, 121 Sampling programs, initial, 25 Sampling sluice, effectiveness of, 55 Summit mining District, California, stationary washing plants, 125 Reconcentrations, from older deposits, Salting, 17, 30-31, 43, 44, 45, 48, 107 3-4 grade for, 55 auriferous conglomerates in, 4 Weathering, 110-111 detection of, 48 Superficial placers, 4, 14 Weathering and release processes, 4-5 Reconnaissance, in placer examinations, innocent, 48 throughput capacity, 55 23 Swan River, Colorado, gold from glacial Weaverville, California, gold from glacial intentional, 48 water requirements for, 54-55 Recovery, definition of, 106 Saucrman excavator, 107 moraines, 4 till, 4 methods, 48 Swell, definition of, 109 Weight of sample, as volume check, 27 in proven and unproven processes, precautions, 48 Seam diggings, 11,107 74-75 Secret processes, 16, 74 of earth and gravel, table of, 143 Weights of materials, 143 Sample, definition of, 107 Wet ground, cribbing for, illustrated, 28 Rectangular grid system, for sampling, 25 Self-shooter, 107 Tailings, 109 processing record, form, 116 consideration of, 79 use of caissons in, 28 use in prospecting, 37-38, 39, 40 record, need for, 71 Selling gold, 121 Shaft factor, 43, 107 Tenor, 109 Whitney, J. D., cited, 14 Red Rock mining District, California, results, evaluation of, 26 Shaft log, form, 118 Terrace, definition of, 109 quoted, 44-45 auriferous conglomerate in, 4 results, qualification of, 26 Shingle, 108 gravels, 7 Widespread placers, prospecting by use of References cited, in Part I, 7 splitting, erratic results from, 71-72 in Part II, 17-18 Shoe factor, 108 Tertiary gravels, 7, 11,14-15, 44 rectangular grid, 37-38, 39-40 splitting, results, diagram showing, 71 in Part III, 49-50 Shotty gold, 108 Tertiary period, geologic chart showing, Wilson, Eldred D., cited, 14 splitting, results, table showing, 72 109 quoted, 59 in Part IV, 59 typical, 21 Sierra Nevada region, California, Tertiary in Part V, 67 gravels in, 3-4, 14-15, 44 Tertiary River systems, 3-4, 110 Wind-caused surface enrichment, 4, 14,17 values, adjustment for large rock or Woodbridge, T. R., cited, 24 Regional rocks as source of placer Singewald, Quentin D., cited, 17 Theobald, Paul K., Jr., cited, 65 boulders, 46-47 Wyoming, Snake River, flood gold in, 13 minerals, 3, 4 Size of gold particles, effect on sample, 26 Thomas, Bruce I., cited, 16 volume, reduction of by splitting, Thompson, Arthur G„ cited, 16 Yardage, definitions of, 111 71-72 Zircon, 111 154 155

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