H I N TS

— ON

A M A LGA M AT I ON

AND T H E

GENE! AL CA! EOFGOLD MILLS

A E . M . W . J . AD AMS, . M

'

G radu a of h l f n of Col i a. n iv i te the Sc oo o Mi es uxfib U ers ty.

New Yo rk .

A Bmm mBOO K o r A U L GO LD - M L L P! CT CE AS c CT A I A I , D ETE! MIN ED BY AN E! PE! IENCE OF TWENTY YEABB W! ITTEN IN L ANGUAGE TH AT CAN BE

UND E! STOO D BY AL L .

A I LLUST! TED .

CHICAGO M D O E! N MACH I N E! Y PUBL I SHING CO MP ANY.

1899 . f 1 8 En te red A cc ordi n g to Act o Co n gress i n the Ye ar 80 ,

W J . AD AMS BY . .

f h L i r ria n f o n ess W hi n I n the Offi ce o t e b a o C gr at as gton , D . C . TABLE O F C E O NT NTS.

— ChapterZI General Process

Arrangement of Mortars P lates Concentrators

for Canvas P lant 2— Care of Quicksilver Amal gamation

— - 3 Cleanin g up 4— ! etorting an d Melting 5— Concentration 6 Sampling

7 Conclusion

INT! O D UCTION.

Gold has been known from the earl iest ages , from its occurrence in a metall ic state in sedim enta ry deposits as well as in veins . On account of its great specific l i gravity , it can be col ected from placers and r ver beds , by separation with water alone , and in veins after the m atrix i s crushed , a great am ount i s saved by the same simple method . When only rich deposits were exploited , an ybody could manage as it apparently required only

labor and opportu nity , w hile as lon g as money was

s made , the lo ses tha t occurred did not trouble the own

ers . Fro m this very s implici t y of working , the maj or ity of owners and i nvestors i magined that no special

training wa s requisite to insure success , but that any

tru stworthy man , skilled in m ercantile pursuits , was th e proper person for the place of general manager .

- To day the sam e opinion is held by very many , in spite of the warnings from hosts of disastrous failures . One ca use for thi s belief has been the lack of literature for thi s speci al branch of metallurgy ; in fact , very near

1 890, there was practical ly no works written at all which spoke of gold except as a subsidiary prod uct

rac of the m etall urgy of other metals . Volumes , both p

i a t c l and scientific , have been published which deal with the special branches of the metall urgy of lead , copper , H I NT 8 S ON AMALGAMATI ON .

an d silver, but the metallurgy of gold seemed so simple , it only requi red an occasional article in a paper or magazin e.

In spite of this deart h of w ritten knowledge , practical m en in all parts of the world were rapidly improvin g the methods of treatment, both mechanically and with

aid r a i the of chemist y , in their sever l localit es ; but ,

th rough lack of exchange of thought , ea ch section had f a di ferent process , on which faith was pinned to the

exclusion of all other proces ses .

As the rich deposi ts gave out , attention was turned

to those of lower grade , which are now found to be very profita ble with improved machinery and increased

- are knowl edge, but , even to day , we in the infancy of

this sci ence . The treatises on gold , now before the

n public , can still be counted on the fingers of one ha d , and are either devoted to the scientific discussions of processes now in vogu e , the history past and present

c of gold m ill ing, or the m e hanics pure and simple of the

various machinery used . Th ey are all good for the edu

of direc cation the world , but are lacking i n definite ti ons of the best way to employ the methods they describe , and are generally understood by those only who h ave enj oyed a previous technical educat ion . This absence of intelli gent application of these known p rin ciples in the great m aj ority of the mills in this Sta te

s (the hom e of gold m illing) , has been a con tant source

n of wonder to m e, a d yet I have a fellow feeling from HINTS ON A MALGAMATION . u

o - G my first experiences in g ld m ill practice . raduating i from a celebrated school of min ng engineering, I thought myself em inently fit to at once assume the absolute managem ent of the biggest m ining concern on earth , but , thank s to the kind influence of an elder

brother, already well known in the m ining world, I was started at the bo ttom of the ladder in a gold mill , to l begin my rea education. I very soon found that t here was no bigger tenderfoot in California , as my technical education had only taught the chem istry and s in t r es cientific mechanics general , with no prac ical ul

u s of how to apply this knowledge . These practical r le

i in have been learn ed through bitter expe r ence, extend g

are through many year s , and to try and help others who

s j ust beginning , I have set down in the following page

c the results of the observations I have made , all of whi h have be en practically demonstrated as correct by appli

ou i lt cation several very d fi i cu ores , with marked suc

to cess in every case . It has been a work of pleasure

in su u contribute th is m ite of knowledge , and if I am mental in increasing the production of only one gold mill , I will feel amply repaid for my labor .

he the I ask the indulgence of t reader , to overlook absence of rounded sentences and polished language ,

est an d take the will for the deed . I have done the b

m to c. I a able , and can only leave the verdict the publi

M. M . W . J . A DA S , E

San Franci sco .

C HAPTER I .

GENE! AL P ! O C ESS .

I t i s not t he purpose , in t his book to enter i nto a ny detailed description of gold milling , as the ground has already been amply covered by E . B . Preston , in h is re “ ” r on M “ po t G old illing , publi shed by the State Min ” of eralogist , C alifornia . Som e other points also may seem too well known and appreciated to be m entioned , but these require con stant repetition , and even then very little practical ap plication seem s to be m ade by th e average m ill man .

In order clearly to understand the en tire me thod . we must start with the ore as it com es from the m ine . This ore m ust first be carefully exa m ined , as its character i and structure as well as its value , determ ne t he most

. ma advantageous method to pursue First , the ore y be hard and tough , requiring force to disintegrat e it , though

- o entirely free milling ;sec nd , the ore may be soft , giving a great deal of slimes ; third , the ore may be a m ixt ure of the above two divisions . o re First ! Here , the i s first dumped over a grizzly , 1 1 with the bars set 76 i nch apart , the coarse lumps goi ng

- through a rock breaker of som e form , to m ix with the

fines in the ore bin . Fro m this bin it m ust be carried to stamps , preferably of heavy weight , notwithstanding all as sertions to the contrary by patentees and makers “ of other pulverizing device s which are j ust a s good as ” stamps .

Second ! When th e ore is soft , it also requires t o be passed t hrough a breaker, to enable the part i cles to be 12 HINTS ON A MALGA MATION .

of uniform size ; but here , very frequently any kind of stamp , and always those of heavy weight , will slush through the bed of pulp , wearing out iron uselessly , and increase the proportion of slimes , always to be avoided as m uch as possible . Here we find a great advantage in f l the di ferent types of th e Chilian mil , such as the Hunt in ton g and Bryan , from both of which the pulp escapes as soon as i t is reduced to the requisite size , as de termin ed by the screen , and with t he mini mum of slimes to hinder future operations .

! Third In an ore containing both soft , clayey or talcose m ateri al , and hard bunches of quartz , sta mps are gener of s ally the be st , as the grit the hard quartz prevent i s u fi i ien t pound ng of iron on iron , and causes c splash to keep the screens fro m choking , while all operations can

a be kept under close observation , which c nnot be done — with any pan or roller mill o n e of the greatest obj ec

I n tions to the general use of these mills . som e few di cases , however, where the output from the m i ne is su i n i c e tly large to warrant the outlay of capital , it w ll be found of great benefit to separate the ore parti ally and automatical ly into two classes. Dumping the ore over l a long grizzly , the soft and fine wil go into one bin , while the coarse , after being put through the breaker , to fall s i nto a second b in . That from the first bin is fed

- l s one or m ore roller pan m i l , while the hard broken quartz goes to the stamp m ill , very largely increasing i n th is way the outp ut through the two methods com blued. u The p lverized ore , technically known as battery ” - p ulp , i s now carri ed by wat er down silver plated copper plates , by which means as much of the gold as possible f is abstracted , varying very considerably under dif erent

’ millmen s e methods ; a low percentage saved , b ing ex HINTS ON A MALGA MATIO N . 13

” cused by such term s as floured gold , that floats in “ ” a w ter, rusty gold , plumbago i n the ore , or a si milar

state of afi airs .

‘ However , there i s generally sufii cien t gold left in this

pulp , which could never be saved with quicksilver , to

require further treatment , while the value i s too low to

all a . treat the pulp en m sse This gold is either , me chan icall mt L y or chemically , locked up with other e a lif rou s e substances , generally sulphides or m ineral s of a

higher specific gravity than the accompanying gangue . This specific gravity is the keystone to all the con centratin g devices , and the special m ethod required is de termin s ed by only two facts , the value of the concentrate th when pure , and the percentage of them carried by e

ore . Should these concentrates be of low value and mod eratel a G y co rse , a simple bu mping table , l ike the ilpin ilfi e County bu mpi ng table , or its improvement , the W y, e could be used , as they require little care , are reasonabl

i n price , and save concentrates free from foreign mat

ter, while the final tailings , though still carrying a large s percentage of m ineral , will be econom ically valueles

owing to the intrinsically low value of the sulphurets . ih When , however , the concentrates are of value , for

stance above $50 per ton , a mechanism of much greater

a ll delicacy must be employed , a nd of the devices , none

has proved so sati sfactory as an endless movi ng belt ,

shaking without a j ar . A s a rule , the higher the grade

of sulphurets th e more friabl e they are , and the finest f slimes , most easily a fected by agitation , carry the rich

est particles , reaching a culmination in the tellu ri des . Should the “ battery pulp” carry a high percentage of 1 2 be sulphurets , that is , above per cent i t very often i com es necessary to use a double concentration , and n

thi s case two machines of the sam e type are used , th e 4 T 1 HIN S ON AMALGA MATION .

a t ilings from the first passing directly to the second , after removing the surplus water if there i s t oo much added on t he first machine .

In spite of all these precautions , it is very frequently found that the concentrator tailings still carry an ap reci abl e p value , and most thorough tests must be made to determine whether or not t his can be econom ically saved . The first and commonest method is to allow the ail t ings to run over a la rge surface , covered with canvas , but which i s cleaned and swept several ti mes a day , , l genera ly , thi s only saves a small percentage of the los s , and its only advantage i s its cheapness . With prope r care and experience the concentrators should save all t reduc hat the canvas plant could do , and any further tion m ust treat economically with the entire mass . So far the onl y way to do thi s is by employing some “ ” of the modifications of the cyanide process , and t his requires a large tank capacity , so that the tailings can flow directly to the fil tering tanks .

This i s concisely the method of gold m illing , but t here are several points to observe , to i nsure complete success on the maj ority of ores .

First , foremost and at all times i s the question of grease . Guard against i ts excessive use day and night , K e month and year . eep all the b arings and machinery where it i s used a s scrupulously clean as a New Eu gland housewife does her home ; do not grudge the use of clean waste , but see that the employees observe the a r m ximu m of cleanliness . Bits of candles do n o ha m , or very little , if made of steari c acid , but beware of t tallow dips . Star i n wi th the roc k breaker , and place dripping pans underneath the j ournals , m aking frequent e xam inations to see that all the drops are caught . See that none of the oil used on the running gear of the M HINTS ON A ALGA M ATION . 15

- fi oor self feeders drops on the feeder , being very careful about working the leakage of ore always found under t nea h the feeders , if there i s the slightest possibility of its b eing fouled . Clean the stem s of the stamps , the a r c m s and tappets ve y frequently , and do not use liqui d oil on them , but make a swab of blanket and apply a a m inimum of axle gre se, t o th e cam s several times a day , to the stems only as needed . When applied to the stem s , only touch them above the guides . It i s gen erally better to tack som e canvas between th e cam fi oor shaft and the top of the lower guides , giving to it a decided belly , to prevent any grease thrown by the cam s from falling into the feeder or throat of mortar, or on th e plates . I n on e m ill , where very poor work had been done , though the builder and superintendent claimed most thorough knowl edge , we found boards placed below the cam s to prevent the grease from falling on the plates , and set at such an angle that there was a constant rolli ng of pellets of grease directly into the throat of the m ortar .

We now come to the concentrators , and it can be safely stated , with hardly an exception , that the cleanliness of the m ach ines i s a sure indication of the quality of work done , an d the closeness of saving accomplished .

Where rubber belts are used, the oil rots them , the sand and grit get into the bearings , causin g bumping , inequality of the plane of the table, and a li ttle grease getting i nto the pulp will prevent the saving of the finest and richest of the sulphurets . Th e very act of cleaning the machines brings all parts under close scrutiny , and many a seriou s break - down is averted,observed in tim e he during this cleaning at regular intervals . Therefore , t sure and watch for grease , daily cau ion the employes about it , spare no pains nor expense to have every part HINTS O N A MALG AMATION .

Modern Ma chi n ery .

1 . FI G . — — Wo o d ac k n . 2 l ro n s r . 3 b 1 Co p p e r p l a t e . t i p i g HINT S O N A MALGA MATIO N . 17

of the m ill at all ti mes as if on parade , and the close saving and freedom from break - downs will amply repay all the troubl e and outlay . Within certain li mits the shape of the mortar does not affect the economic results nearly as much as has been supposed— that depending m ostly on the man attending to them . A mort ar must be narrow , as the obj ect is to get th e ore out of the battery as fast as crushed . The back should be c urved from the throat , so as to throw “ ” the ore directly on the center of the die . Thi s back must be soli d m etal , and on no account have copper plates in the back . Their advantage i s very dubious , and in nine cases out of ten their use i s a very great detri ment to successful work . Without them the copper “ ” plates on the chuck - blocks catch as m uch amalgam as both combined ;there i s less surface to scour, particular

- ly with low grade ore , and with them the additional width of the mortar prevents the splash being exerted exclusively against the screen , and reduces the crushing capacity of the battery . (See Fig .

The discharge , that is , the distance bet ween the top of die an d bottom of screen , should be within a fraction of four inches , new dies requiring wooden strips under “ ” the screen s to keep this height . The drop of the 1 stamps should be 4 75 t o 5 inches , and the speed always

1 00 . above 95 drops per m inute , preferably above drops i A slow drop , besides decreas ng the duty of the s tamps , allows the quicksilver to settle an d dim inishes its com min ution so that too m uch is l iable to be used at one

. time , a sure loss i f the gold is floured A quick , short drop more nearly approaches the action of the pan in pan amalgamation , keeping all the pulp in constan t agitation , and m ixing the quicksilver uniformly , so that all parts of the ore com e i n contact with it before leaving the battery . 18 HINTS ON AMALGA MATION .

- The chuck block , covered with t he copper plate , should be entirely separated fro m t he st rip of wood on which the screen rests . The plate should touch the bot tom of th e screen itself , at as sl ight an angle as possible , and should be very nearly vertical and five inches deep .

It s backing , generally of wood , m ust be as slight as

. possible , so as to place it far from the dies It i s held

FI G 2 .

P i c . 3.

B odera Ma chi n ery .

Fro . 4 . i n place by a strip of iron , which extends into the shoul ders on each side of the m ortar . Two chuck - blocks should be m ade with the blocks to conform t o the height of the screen as the dies wear o down , as with dies half worn the wo den strip under i neat h the screen i s removed , b ring ng the discharge down to normal height , and the copper must not project

- above the bottom of the screen discharge .

This sketch , made without a scale , as the width of i 2 t. mortars varies , will better explain Figure shows

- both cross section and longitudinal section .

20 HINT S ON A MALGAMATION .

moved . In fact , as my first great point was avoid ” “ s grea e , my secon d is , Never remove the screen of a battery ti ll the run i s ended , if it can p ossibly be an d avoided , the finer the gold the more important this ” is . a It t kes a very appreciable time , after a battery i s ar s t ted , no m atter how short the stop may be, before all a the pulp is in const nt agitation , and the quicksilver mixed with it. This rule also brings us to the proper material of which to have the screens made , and in this as well as t every h ing else , the best i s always the cheapest . Theo reti al l c y, wire screens expose the most dischar ging sur face , but they clog the qu ickest , and have to be removed to be cleaned by a wire bru sh , a very serious fault , as

- stated above . Round punched holes present too much th dead surface, being exactly the reverse of e wire “ l - scree ns . Thi s on y leaves us the burr slot and the ” - - punch ed slot , and of these the burr slot , though clog l ging the least of any , wears coars er more quick y th an

- the punched sl ot. Therefore the advice we give i s to “ ” i - use in stamp batter es p unched slot screens , of the i best m aterial to be had . Of mater al we have tinplate ,

! ussia i ron an d steel . Tinplate is the cheapest, but the an d scree ns are worn out within a few days , are really the m ost expensive in the results that can possibly be i l a l employed . Russia i ron w l not break e si y , but the r orifices wea r so coar se with in 48 hours , particula ly on t iz d hard quar z , that the ore will not be pulver e as fine as required . This leaves us only the steel , which brea ks

its . before it wea rs coarse , on account of hardness Of course there is stee l and steel , but if a point is made about it, steel screens can be procured which w ill n ot f break or over a m onth under rough u sage , and even in HINT S O N A MALGA MATION . 21

that tim e the size of the apertures has not appreciably

e . ff i increased , i . , su i c ently to cause any loss in free gold .

Here we have the best condition , the battery i n steady i n operation for a month , the pulp steady and constant

agitation , no disturbance of the hard amalgam , by re moving a screen ; and the greater the quantity of am a l

fi o r gam in the batte ry , the more of the fine and u ed gold “ - is caught there . Therefore use a steel , punched slot ” - screen , of the size found by experim ent to be the best .

Several factors determine this size .

With coarse gold this is not of so much m oment , but

should the gold be fine , it i s necessary to crack the ore

that much m ore to free it . Thi s degree of pulverizin g

depends on the grade of the ore , as in many cases it costs

more to save the finest gold than the total am ount saved , and it then becomes necessary in practical reduction to

use a larger sized screen , put through more rock , and

pay little attention to additional loss in the tailings .

However, it i s best to use as fine a screen as is conform

able with a profit i n working the m ine . The outside of the screen mu st be scraped several

times a day , and as good a device as any i s a copper spade with the edge turned over at an angle of 45 de

grees ; wooden handle , copper riveted , as shown in

Fig . 4. There should be a long expanse of copper- plate surfac below each battery , though some of it is only of use in case of faulty amalgamation . These plates are techn ically divided into

K - L K INSID E COPPE R CHUC B O C , a description of h t which as already been given , and here is only to add

- that it i s an unnecessary expense to have it silver plated .

LI P - L at P ATE , which must be heavily silvered , least

three ounces of silver to the square foot being put on it . 22 HINTS ON AMALGA MATION . This plate is j ust the length of the m ortar and is wide enough to extend from the inside-edge against which

- the bottom of screen is braced , to a half inch beyond the iron lip of mortar . Two rectangular holes are cu t in it, to allow the shoulders of lower keys to project , and

' the wooden s trip on which the screen rests is placed on top of the plate and holds it solidly in position . L L — a S P ASH P AT E This is r rely found , even in the

bu o o cr it . t o Nofi u n q Woc am Sa ck Woo J Ba t hi n g

pa t h n D / ! o id c Q -4 O I” i l ‘ ) La d af d }h plo i Q

Apr-o w plot;

Modern Machi n ery. best mills , but i s of the utmost importance ;the more so . as the gold is floured . In fact , it i s absolutely necessary 1 2 if very fine gold is to be saved . It should be inches wide , by a length j ust sufficient to fill the space between the shoulders of the mortar . There are several ways of n in adj usti g, but every one the point to be observed is , 23 HINTS ON A MALGAMATION . that it shall stand in front of the screens at an angle never less tha n forty - fi v e degrees and better if over fifty degrees from horizontal ; that the bottom shall be at

least an inch below the bottom of the screen , and the

space between the screen - frame and it shall not exceed

- nd three quarters of an inch . Take this plate a fasten

it to an inch board , leaving a margin of the board below

the copper plate , to act as a brace to the stalactites

slowly formed , and then by back supports , stand it on the edge of the next plates , so that it is held firmly against the mortar and yet can be instantly removed , as shown in Fig . 5.

Another way of great simplicity , which , however , has the objection of causing to o much j ar , i s to rivet a piece t of rack iron on each shoulder , at the angle the plate shall stand , and slide the plate down , keeping it away from the screen by a false strip tack ed to the front of the board , along each side of the plate itself . By studying the effect of this its advantages can easily be seen . Twenty years ago it was universal to have a spray of clear water consta ntly dropping on the apron plate to form a slight stoppa ge of the pulp a n d cause t he a malgamated gold to settle and attach itself to the plate . but , as future working of the pulp was very much hin

it . dered by thi s excess of water, is now rarely used t ih Again , to a certain ex ent , the output of the mill is creased the greater thc amount of water allowed to fl ow into the battery , and as a result, all the water that could be used and not h inder future operations , is allowed to run i nto the mortars . it No matter how fine the gold may be, if is free , under proper amalgamation , it will adhere to an amalgamated surface if brought into actual contact with it, and thi s

- the splash plate does i n two ways . First, half of the 24 HINTS ON AMALGAMATION .

pulp i s thrown against it in a coarse spray, aiding adhe sion by the force ; second , it then runs down the plate , dropping off the bottom exactly similar to the spray from the clear water troughs used i n earlier times , forming l a dam and eddies , which cause the other ha f of the pulp to precipitate its fine amalgam at this point .

From here, the obj ect to be attained is to have no rap id and strong currents . To turn the pulp over and over , so that all parts are frequently brought in contact with S the amalgamated surface, and to pread this pulp as thin as consistent with keeping it i n constant motion and allowing no settling of even the heavy sulphurets on the plates . It is also found that an occasional drop of one

- inch to one and one half inches is a benefit . Now we come to one of the greatest mistakes made by 90 per cent. of all amalgamators , an error held to like n the grip of death by men of broad technical educatio , causing the failure of many properties which should be

successful .

This is the grade given to the large plates . These should never be placed w ith less than inches to 3 better each foot , and i n most cases inches would be , and even more, while better work can be done at an angle of forty - fi ve degrees than with a grade less than

inches .

Take a case w here the plates are set below inches , we find an excess of water required to keep all the pulp ovi g and th refor m n , e w great a depth , so that th e mmarid e fine gold is held never touch s the amal amated fi g surface , when we truly have oat gold , while an equally bad feature, almost universal, is that it allows too much quicksilver to be used, and fine gold will never d be save with even a slight excess of quicksilver . This point will be more fully explain ed under the discussion of amalgamation . ' ON HINTS A MALGA MATION . 25 With the plates at the proper grade and the requisite '

amount of water, the pulp travels down the plates in

a succession of waves , the lower edge of each wave rolling over and over and bringing every particle of

water even , in contact several times with the amalga

mated surface. The m ore sulphides the ore carries , the

steeper m ust be the grade of the plates , to clear them and h still not interfere wit the concentration of the tailings . After this explanation we can continue the descrip

tion of the plates . From the lip- plate the pulp has a drop of nearly tw o inches and falls on the first plate separate from the mor

tar .

- The apron plate should be divided into two sections, l the first easily removed at a l times . This should be the

full length of the mortar, and tw o feet wide, and that end nearest the battery resting on the wooden shelf fast

- ened to wooden m ortar block , and held in place by the lip of the mortar or a strong hook on each side, while the lower end rests on the second section . This second sec 4 6 tion m ust have the same width , and be from to feet o e e to long . It is supported by extensi n legs firmly s cur d the floor. By using this form of support the grade of the table can be changed to suit the ore, after practical ex im z per en t. Start with a grade of yfi to 3 in ches , and , if too much water is required to keep all the pulp in steady motion , lower the second s ection (the first assuming the same grade, as it rests on it) , until the pulp i s seen to m ove freely an d in successive waves with a minimum of water. On most ores this amount of p late surface is all that is

necessary , but if there is still sufficient fall to allow the o tailings to be rea dily carried away aut matically, the “ ” pulp is now passed over sluice plates , as a safeguard 26 HINTS ON AMALGA MATION .

against accidents, after passing through a quicksilver trap . These sluice plates are 1 8 inches wide and from 8 to

1 0 feet l ong, and are set at a minimum angle of 1 35 inch per foot. All the plates should have a coating of silver of three ounces to every square foot, although on the o n sluice plates tw ou ces will do .

There are several devices for traps, but most of them are only receptacles where a slight obstruction to the flow n of the current is given and this is not e ough . We want to accomplish two obj ects ! first, retain all the amalgam and quicksilver that may h ave escaped the of copper plates ; second , secure this with a minimum sand and sulphurets . A large open box is always filled with sand which i s gradually replaced by coarser sand and sulphurets ac cording to the lengt h of time before its complete re

o . moval , while nly a modicum of loss is arrested here The next result of experimenting caused the pulp to de scend on one side and rise on the other of a pa rtition , the higher specific gravi ty of the valuable portions aid ing their retention , and it is on this principle , that the most successful traps are now constructed ; the best of “ ” all bein g those used in the mills of the Homestak e in “ the Black Hills , and designated as the Black Hills ” Trap . This can easily be constructed of wood by any good carpenter, as i t consists of a wooden box with sheet iron partitions , loosely set in grooves cut in the sides of the box . A trap for five stamps is given here . It is 1 made of 1 76 i nch clear lumber ; in side measure horizon 1 0 tally inches wide by 8 inches ; depth at inlet, 1 8 6 i P inches ;at outlet, nches . lough three grooves equally in an distant each side d inch deep , m akin g them

28 HI NTS ON A MALGAMATION .

high specific gravity as quicksilver , even if very finely comminuted and sti ll not enough to prevent the escape of all the pulp and sulphurets except a slight layer less than two inches , which also is in constant agitation as

' Per s p e c fax/ e

long as the same amount of water i s employed . Should

' e l ck this water g t s a from an y cause, the first divisi on s at once become choked , but the trap is quickly freed 29 HINTS ON A MALGA MATION .

by rai sing the first partition . W hen the trap is cleaned

all the partitions are withdrawn and the residue, very

small in quantity , is removed .

- The pulp , on leavin g the apron plate, falls into a

' box w ith the bottom sloping from each side to a central

vent , from which it flows directly into the trap , and on

- leaving the trap , either flows over the s luice plates , or,

n ModemMachi er y. o in their absence , into wooden or ir n launders , to be con

ve ed o 7 - y to the c ncentrators . Fig . shows two cross sec

- tions of the box i n front of apron plates .

t - The ba tery tailings , after leaving the sluice plates ,

or, if they are absent, the amalgam trap , fall directly into t the concen rating launders . These are preferably m ade as of wood , iron pipes , if choked by broom straws ,

e . pi ec s of blanket, etc , have to be disj ointed to be cleaned .

These W ooden boxes , troughs or launders measure inside 4 inches wide by 6 inches high , and m ust have at the

very least a grade of 3g inch per running foot . Now , a a under the most ca reful m n gement, a little amalgam

and quicksilver escapes all the devices mentioned above , “ ” and it is advisable to put in a couple of rifi i es in each 1 2 box length of feet . This is done in this way ! Before

o n - the b ttom piece i s ailed to the sides , make a saw cut at right angles to the length equally distant and a half inch s deep , and then gouge out to it from the upper ide . This

is s hown in Fig. 8 . he If t water used is always the same in quantity , a

Vrshaped box will carry the sand with the smal lest 30 HINTS ON AMALGAMATION .

amount , but should the water slacken at all the sand at once makes a broader surface and then from the ih creased fr iction and breadth the launder i s at once filled

a V - to the top . To gain some adv ntage from the shaped form we have found great benefit i n putting angle strips

” Cr o as M 7 7 0

m a hine Mode M c ry. 1 1 along each side of the box , inch wide and inch high , e i n giving a 2 inch bottom with fl aring sid s , as shown

Fig . 9 . When the pulp is divided over two m achines a division with a long swinging finger i s put in and each launder 2 reduced to a W i dth of inches , from the end of which it i s carried by a rubber hose to the concentrators . — THE CONCENTRATOR S . As stated in the beginning , ' all sulphurets of a value above $50 per ton require a shakin g table wi th an endless bel t that m us t work without a j ar, and be at all times completely under the control of the operator . in Two classes of machines are vogue , one shaking sidewise or across the stream , the other with an end Y shake against and with the stream . ears of practical experience have proved that the end - shake concentrators cannot produce concen trates free from foreign matter, M N HINTS ON A MALGA ATIO . 81 though in som e cases the tailings have a very low valu n atio , while any attempt to make clean hea dings results in excessive loss . This can readily be seen as the up stroke against the current exerts too great a force against the clear water regulated for the downstroke , while if regulated with suffi cient force to keep the sand back on the upstroke, it washes down the finer and lighter sul hur t t p e s during he downstroke. This has been ack n ow l

n of - edged by the inve tors the end shake machines , from the fact of the universal application of the side—shake si nce that spec ial patent has expired . The first of these side - shake machines is still tak en s as the standard , being super ior in the e ti mation of the world in its operation and ease of adj ustment, and far ahead in the quality of material employed in its con e s struction . This mak s it, however, the m o t expensive a t first cost , though the cheapest in the end . This i s “ F ” known as the rue Vanner , and the general applica tion of all being the same , it will be taken to illustrate the general m ethod of concentrati on. However , we wish

first to explain the reason for the use of a wooden frame , to which some obj ection is made . It is this , that there i s sufficient spring to a wooden frame to prevent any j ar n to the table as it is thrown a inch each way , and this j ar is always very perceptible on all the m achines resting on a rigid iron frame . We will now continu e the course of the battery t ail ings . The concen trator is set with a grade regulated by screws at the foot , up which and against t he cur rent the endless belt travels , and this grade is arranged 1 4 so that there is at all ti mes a thickness of pulp of 72 inch which i s neither stiff nor sticky . The speed of the shaking motion for average ores i s started at 1 90 revo o luti ns per minute, and then the proper grade is deter 82 HINTS ON AMALGAMATION .

t . l mined only , after ac ual experiment The pulp fa ls on

i trib the machine near its upper end , being uniformly d s “ ” uted by the ore- spreader over the entire width of

- ! the belt . On this ore spreader it is well to have a silver the i plated copper plate, as this is last opportun ty to catch s eparately any amalgam or quicksilver that may e have escaped all the other devic s . — The ore spreader must deliver the pulp to the belt w ith as little splash as possible so as not to disturb the sul phurets that have al ready settled . To do this there 1 0 should be a step added , as shown in Fi g . , to break the the fall , and this step must j ust clear surface of the pulp already on the machi ne. In front of this ore - spreader is placed a clear water dis tributer , which supplies j ust enough water to sepa of rate the remnants sand from the sulphurets , and take the place of the water com ing down w ith the pulp . The water should be j ust enough to keep all the field be tween the water distributor an d the ore- spreader cov ered with water without a cu rrent . Too little water is shown by a series of dry fingers against which the fines t sulphurets shake, become dry and float down the ma chine uncaught . Should some sand come up with the sulphurets and no dry fingers be exposed, do not turn on more water , but either decrease the speed of the uphill travel of the belt if the bed of pulp is the right depth n o the n and t sticky , or give m achi e a steeper grade by lowering the foot . The tailings from the concen trators under proper m anagement should show by panning tests no m ore sulphurets , though perhaps an assay by fi re will still show that too m uch i s being lost , either i n sul phurets too finely slimed to be collected by hand tests i r or in tellurides , oxidized m ne als or carbonates . Very f e e e w o ten thes fine sli m s can be sav d ith coarse canvas , HINTS ON A MALGAMATION . 38

Cleo r W f ! ! a Or fi ‘ e fi p eo cle r

h ” vhf,

' Coal r >¢ 5An d f 7 /(J rc c

( O A v a g.

. A Tuf mq boo c d

T l n de r 5 u hn q } La u

+lm Lamb C, >¢ f q ; 84 HINTS ON AMALGA MATION . requiring very little additional expense except the first n outlay i n erecting the plant. We can safely say that i

- al l ninety ni ne per cent . of these cases the value i s i n n the slimes , so that our first duty i s a mecha ical separa tion or sizing . This separating i s done with the well “ ” - - known spitz kasten , a V shaped box divided by a par titi on . Here the coarse sand i s drawn out through a hole at the point of the V, while the slimes overfl ow a t

o . the top , clear water being added to help the separati n

- 1 1 . The cross section i n Fig . will explain the principle The slimes and water are n ow carried in launders to the canvas plates, always made in duplicate to allow the cleaning of one set while the slimes are flowing over the other. The cleaning is done with a broom and in some cases a spray of clear water under pressure . The tables 4 1 2 are made of matched lumber , varying from feet to 1 feet wide and 0 feet long . They are set at a grade of t inches for each running foo , and are covered with

No . 6 canvas . As stated above , the tables must either be n made in duplicate or , i n a large pla t, a couple of extra

- l n tables are provided , to be used while cleaning those steady use . The slimes and water flow down one series e of tabl s for a definite time, generally one to three hours , when the pulp is turned off and a small amount of clear water is used to carry off a little of the waste . Then a tilting board is placed under the fo ot of the table and t he concen trates swept and washed i nto the settling box . The con centrates , i f rich enough , are shipped with o out further handling , but it is found occasi nally to be of benefit to reconcentrate them over a machine set with d very little grade , and running at a very low spee . We 1 2 show in Fig . the method of saving the washings of in the canvas plates , as generally adopted California ,

36 HINTS ON A MALGA MATION . When the practical adaptation of the solubility of gold in cyanide of potassium became generally known , the an maj ority of m illmen , d more especially the owners of mines , were afraid to use any cyanide in their opera tions , as they believed they were liable to lose much of

e . the fine gold in the ore, dissolv d by the cyanide This is a very erroneous impressi on , except in a case where cyanide i n solution was mixed with th e ore previous to the i ntroduction of quicksilver . In other words , cy an ide of potassium has the greatest afii n ity for grease and copper , and will also dissolve quicksilver, if present , without affecting the gold at all . This enables us to use this chemical in conj unction with quicksilver to great advantage in all our operations . Always , then , before using any of the quicksilver , add to it a solution of cyanide , and a strong solution is better than a weak one ; in fact, we have used a saturated solution with i benefit . Some of the quicksilver i s poured into a ch na bowl and the surface is covered at least to a depth of — n one half i ch with the solution , with which it m ust always be kept covered . As each spoonful of quick silver is fed into the batteries it is thoroughly brightened a and cleansed in passing through the supern tant liquid , and is in the best condition to catch the gold . After it fr the quicksilver has been in use in the mill , is e e qu ntly spoiled by certain elements in the ore, or some accidental foulin g, such as the heating of a j ournal and

fi in - the consequent ow g of babbit m etal into the ore bin .

From the elements in the ore, we find lead , tellurium , and selenium . The worst fouling , however, comes from babbit metal . This turns the quicksilver black , mak

ing it slimy and frothy . In this case retorting of the t quantity contamina ed must be resorted to , but a partial l ulh uri he p can be had by using s p c acid , allowing the T HIN S ON A MALGAMATION . 37

fuming to go on for several hours , with occasional stir n ring . The loss is very great . Should the ore comntai tellurium or selenium , it will always be found eces sary to purify the quicksilver after retorting , as these metals are carried over with the quicksilver in dis till ing the quicksilver from the amalgam . Here we must a employ nitri c acid , llowing it to fum e for several hours .

Then , after washing thoroughly , a solution of cyanide is added , turning the liqu id black . On removing this wi th a o t sp nge, the quicksilver is found to be in perfec condi tion . Some advise the addition of a small amoun t of sodium amalgam to the quicksilver , but personally we are very averse to usi ng it on account of its causing even the iron of the mortar to be amalgamated , while the amalgam on the plates is kept too soft . Turning then to the room especially set apart for

- chemicals and quicksilver , and specifically known as the

- u clean p room , we need to k eep in stock all our supplies; which consist of the following list ! Com mercial cyanide P l hi 1 of potassium , C . . nitric acid , 0 . P . Su pu c acid , 0 1 pounds of copperas or sulphate of iron , 0 pounds of

- blue stone or sulphate of copper, some pieces of soft n chalk for lini g the retort, a heavy horseshoe magnet , a 40- mesh screen 1 8 inches in diameter for sieving wood ashes, a mortar and pestle of one quart capacity and one of two quarts , two gold pans and one copper bottom pan , two white enameled iron pails , two porcelain lined kettles with bales , of one gallon capacity and two of half gallon , several pint and quart stoneware bowls , and several cups wi thout handles , a large carriage sponge and several smaller sponges , a few yards of fine

- canvas , one half dozen whisk brooms of better quality than the ordinary clothes brushes , a couple of scrubbin g - z s brushes , one half do en hand whitewa h brushes , 8. HINTS ON AMALGAMATION .

Modern Machi n ery. HINTS ON A MALGA MATION . 89

couple of square rubber scrapers , or , what is better , new t rubber belting with sharply cut edges , h aving at leas e a dozen already prepar d , and a small platform scale for weighing the quicksilver and amalgam . This should i n use av ordup o s weights , as it is only the bullio itself that is weighed in troy ounces .

Make the floor of matched lumber , on top of the reg ular flooring , with a tightly fitted baseboard all around the room , remembering that quicksilver is very elusive and disappears from no apparent cause . This room is placed to one side of the battery floor wi th one win dow that commands a full view of the batteries on one side, and a window letting in light from the outside,

- h directly in front of the clean up tank , while t e door, th secured by a padlock , leads from inside e m ill and never from the outside, so that all persons before get ting to this important room must pass before the obser vation of the m ill employees . A ground plan is given in 1 Fig . 3 .

- - The work bench i s made of 2 inch lumber, w ith solid legs that will not j ar the room when heavy ham mering is done . On this old screens are removed from their an frames d new ones put on , and as there is always some amalga m attached to the old screens , the top of the table m ust be tight so that the residue can be col lected and planned . The implements required , each of which should have its place j ust above the table , are , a light hammer , a steel scraper (home made, either from a n old file or a putty knife) , a tack extractor, a pair of s snips or tin shear , and a punch to enable the tacks to enter the steel . The only tacks of any account are n r ih those know as upholstery , ordinary ca pet tacks variably losing their heads , while small wire nails are held too firmly by the wood for subsequen t withdrawal 40 HINTS ON A MALGA MATION .

o n . replacing the screens The punch is made of steel .

- 1 4 si milar to a scratch awl , or according to Fig . . There must also be here , ready to hand , a piece of blanket of good quality and strips of wood of various sizes , for n patchi g a hole in a screen temporarily , when it is not a to dvisable remove i t j us t then , as , for instance , during the night when nearing the end of a run , with so much a amalgam inside the battery that , to s ve any further w a dispute , i t will be as ell only t o open t he b t tery i n t he presence of the party who is directly responsible . A stock of screen frames w ith n ew screens on and ready ‘ for use must always be kept on hand , and this reserve should never be less than three , as in no instance i s the “ ” old adage so exemplified of time being money tha n the moments lost in stopping a battery from i ts work .

In putting the new screens on the frame , be sure that the rough side, presenting t he s mallest openings is on the inside . The cupboard m ust be arranged to be kept under t all the lock and key , be fi ted wi th shelves on which supplies , scrapers , chemicals , assortment of wire nails

a re and quicksilver kept , but n o oil or grease must be a llowed in this room .

I n ta n k arranging the tray and panning , we mus t an d get the best light possible on our work , therefore they must be placed in front of the window on the out of 4 6 s ide the building . The tank m ust be feet inches 2 by feet on top an d tapering to the bottom , where the 4 2 6 dimensions are feet by 1 8 inches . It m ust be feet

a n inches deep . Six inches from the top is placed over flow pipe , discharging outside the building i nto a sluice rifi i s a few i nches wide, either set with e or covered w ith ai a copper plate, while a dr n hole, stopped with a plug , is bored j ust above the bottom . A slat is tacked along M M HINT S ON A ALGA ATION . 41

each side , a foot from the top , on which a movable wooden grate can be placed, to rest a pan while breaking up the lumps , or a screen that requires washing .

On the left side , and proj ecting an inch over the tank , is placed the tray solidly built and absolutely water 4 6 tight . This should be feet inches long, and at least 1 8 inches wide, have a bottom preferably of one pi ec e

l - 2 of yé inch clear lumber, having edgings inches high on three sides , and open in front of the tank with a gutter along this open side to collect an y quicksilver th at may

l - t. run down . The slope should be /2 inch to each foo

- Over this tray must be placed a clear water pipe, or f - ig inch , fitted w ith a globe valve and a piece of rubber 1 2 1 8 hose to inches long . This is explained in the sketch of Fig . 1 5. On this tray the chuck blocks are scraped and all the amalgam put through its final cleaning . The scrapers are made from old files of all lengths and shapes . One edge is hammered flat and ground to a chisel edge, whi le the other end is bent to nearly a right- angle before 1 6 it is ground . Shown in Fig . . The brooms are improved by a small scraper inserted

1 7 . in the handle, as shown in Fig

Be sure an d keep a large stock of file scrapers , sharp ened and ready for use, always on hand , but also keep them all under lock and key till wanted in cleaning up . We will now start with a mill newly built and note the final preparations necessary before the run i s begun . We put a half inch of dry sand in the mortars and place the dies , the sand being required to act as a cush ion to the blows of the stamps to prevent the cracking h of either the mortar itself or t e dies . Then the shoes are placed on top of the dies , the shank being sur oh rounded with soft pine wedges tied with a string . 42 HINTS ON A MALGAMATION .

40 0 In cas e the m ill i s a very large one, say of to 8 stamps , much time is saved by preparing th is circle of ! wedges beforehand . It i s done in this way A shoe is taken and the wedges placed around it , and then a strip of cloth i s stretched over them and fastened to ea ch wedge with a tack . This circle is then withdrawn and a sufficient number made for all possible use . After e that, it i s only n ecessary to slip one of th se circles over the shank of the shoe, and it i s at once ready . n ' in l After the shoes are ready they are driven o s g y, by the power employed , a board being placed between

an , n er the shoe and the die , to eliminate y da g of chippin g fi the iron . They are then hung up by the ngers on the

- cam shaft floo r. The chuck block is taken to the clean up room and amalgamated . First , i t is thoroughly scoured with a weak solution of nitric acid till the true color of pure copper i s shown . Then washed with a satu rated solution of cyanide of potassium and quicksilver sprayed from a bottle over the mouth of which a piece of canvas has been stretched . The quicksilver is rubbed into “ ” the copper by the exertion m ainly of elbow grease, as sisted by a cloth and sand , but it must be very thor re oughly attached to the copper , the surplus being “ ” f at moved by one o the rubbers . The splash pl e and lip plate are also dressed i n the clean - up room and the operation with them is that which is employed on all the remainder of the plates . They are first thoroughly scoured with cyan i de of potassium and then the quick silver is sprayed over them and rubbed hard with a cloth , avoiding all the use of sand or grit of any kind . Cyanide of potassium is added frequently until the eu tire surface looks not only bright but wet . Then the surplus quicksilver is again squeezed out with the rub bers and the plates are ready for use .

44 HINTS ON AMALGAMATION .

of the apron plate must also be dry, hard and immov u able to press re by the finger, while below it gradually should becom e softer , and , when pushed by the finger, have the consistency of putty ; while at the very bottom of the apron a si milarity to thick molasses is not too soft. The color of all must not be dull , like frosted sil a ver, nor as bright as quicksilver alone , but nearly p roaches p the appearance of a looking glass . Of the two extremes , however, the dull frosted appearance is far preferable, as quicksilver is always being carried by the attrition of the sand and where quicksilver goes there is lost also the fine gold held i n solution . The finer the gold , the drier must be kept the plates , the less quick silver put in at one ti me and the shorter the interval a between the dditions of the feed into the mortars . If too much quicksilver is added it is at once noticed from e the small amount collected near the batt ry , and its accumulation increasing as it travels down the plates . When the plates are kept in proper shape near the battery t the proper wetness can be con rolled at all times, on the lower part of the apron , by an oc casional sprinkling of t quicksilver, and this will at ract the last of the flour gold that may have escaped previous amalgamation without j eopardizing the gold already amalgamated and collected in and near the battery . Even to- day som e p eople advocate only outside amal amation g , putting n o quicksilver at all into the battery , but we believe that as m uch gold should be caught in side the battery as possible and for fi our gold especially the h ighest efficiency is attained with dry amalgam a tion in the battery and a soft but not wet amalgamation on the lower apron plate and the sluice plates . Even on s r ore that run nea ly the same in value, day in and day n out, consta t watchfulness and observation of the condi HINTS ON AMALGA MATION . 45 tion of the plates must be exercised and it is generally advisable to examine each plate with the aid of a very small stream of clear water each time any quicksilver is to be added . Sometimes a touch of the finger is suf fi ci n h e t to inform the adept , but t is takes a long time to acquire , so as to place any trust in it . In addition to e observation of the outside plates , daily f el the chuck an d in block , by removing the canvas over t he screen serting the arm very carefully . As each watch of men will rem ove the chips , etc . , before qui tting time , of t s t0 in course withou pp g the m ill, they can then feel the

- chuck block , see that everything i s fastened properly , the t hat amalgam is accumulating , and has the proper touch and hardness . The touch of am algam should not be slippery , neither should it be sandy . It m ust show n a u iform hard , dry , and solid surface on the chuck block , splash and lip plates , but can be moved i nto a pas ty ridge on the apron plate . In regard to the interval of time to allow between the feeding of the quicksilver r All several facto s mus t be considered . gold i s only

a a am lgam ted on i ts surface, and , therefore, coarse gold a requires less quicksilver per value th n fine gold , which i presents a larger area per unit of value, and , in addit on to this , the finer the gold the more frequently the qui ck s ilver m ust be added . If it is found that the size of the grain s of gold in the ore have diminished rather than add the necessary addition to the regular dose reduce the

- a . interval of time one half , or as found most benefici l 1 0 e . 8 We generally exp ect on average ore, i . , $ to $ i of moderate coarseness , to feed quicks lver once every

fi o r - hour , but if very fine and u ed, once every half hour u is not too often . The superintendent m st allow som e to discretion his amalgamators , as even on ore of very uniform quality it is not politic to give an order for a 46 HINTS ON AMALGAMATION .

a cert in feed of quicksilver for m ore than two hours . n a d. therefore , it i s very necessary that thoroughly com petent men alone be employed in this capacity . We feed the quicksilver and know it is in its best condition , but our labor is lost unless we keep it in that condition as far as possible all the ti me . Our watchful t ness h as prevented its contamination by grease and ye , ’ in many cases , even after only a few hours run , we find the plates coated with various colors that would sicken an y subsequent amalgam or quicksilver , so that it will not be attached , but flows on to waste. This coating must be removed , even if the mill is stopped “ ” every three hours to dress the plates . If the amalgam is removed from the plates too f re too quen tly or close , the silver coating disappears very rapidly and j ust as soon as the copper is exposed the plates are always tarnished with verdigris , the colors starting as a pale golden yellow , but rapidly becoming a o d rk , greenish and brown . For this there are only tw

- remedies , one to remove the plate and have it re sil e vered , and the other, which we consid r far better, to a malgamate it with gold amalgam and be more careful in the future from removing the amalgam so thoroughly .

a n d o First, clea n scour till the pure color of c pper is

n shown with cyanide of potassium , or a solution give a l ter . Then amalgamate w ith quicksilver , rubbing it i n thoroughly and then , after removing the surplus quick silver, take a little am a lgam of fi oured go l d a n d coat the w plate t horoughly with it . After ard bot h in dressing the plates and cleaning up , push the amalgam from other parts of the plate to this spot until it is foun d to k eep as bright a s all other parts .

With the ores of this State, California , we find a pur lish a p brown st in , caused by telluride of gold , a black H I NTS ON A MALGAM ATION . 47

or very dark brown , from selenide of gold , and a most

- beauti ful steel blue shee n which com es from iri dosmium . t These stains hemselves are all rich in gold , and unless

b e saved at the tim e and place noted , will m ainly lost , as n they defy concentratio , are apparently soluble in im water and , without spec ial chem ical treatment, are pervious to the action of cyanide of potassium . It is , therefore, useless for us to use simple cyanide , w hi ch , though m aking the plates and quicksilver bright, would a llow all this scum to flow to waste . n i a There is one m ixture, however, that helps us very teriall y, known to very few , as far as we are informed , a n d only employed by the two or three possessin g i ts simple formula . Even where there is no special need for its employmen t we always use it in preference to a si m ple solution of cyanide . It only consists of a mixture of copperas and cyanide, form ing a solution of both ferro an d ferri cyanide of potassium . The preparati on of this mixture has never been put in an exact formula , and can either be made freshly d each day or in quantity . Our metho has been to take two quarts of water and add to it two to four ounces of a cyanide of potassium , and when this has p rtially dis solved , we add a pint of a saturated solution of copperas and stir the mixture thoroughly ; but on using this mix ture or part of it, we do not clean out the sediment until n ecssar y, but add at first fresh water and the next day more of the diff erent in gredients and fresh w ater as

o . needed . Crude , but satisfactory results are btained The method of application is the same for the daily s i dre s ng of the plates as well as to remove stains . The on e ' batter stamps of y are hung up , then the water is turned off and the concentrators attached to that bat ter i y are stopped, so as to keep their load un form and

4 CN a 50. K 48 HINTS ON A MALGAMATION .

lose as littl e of the sulphurets as possible . A stream of clear water of considerable strength is now directed first on the screens and then over the plates till all the sand an d slimes are removed . Starting at the bottom of the first section of the apron plate a whisk broom is dipped i nto the mixture and the plate rubbed with a circular m otion , of which the stronges t movement is upwards towards the battery and carries the amalgam that way . This is repeated until the entire secti on hams been scrubbed with the m ix ture an d the whisk broo . The splash pl ate is then tilted over and the mixture brushed lightly over it , and afterwards the broom i s drawn l ightly over the lip plate, but any am alga m disengaged is brushed to the apron plate . Very little of th e m ixture has left the plates and has been acting on the gold bearing stains and the sulphurets whi ch have been attached to the plates by the particl es of gold mechanically adhering to them . The plates are now brushed up in a straight s line , and all the loo e amalgam sulphurets , etc are col l ected into a small heap , when they are taken up with a rubber and small iron scoop and put into a china bo w l which has some cl ear water in it . If the lower apron is also stained , it is treated i n the same way, but gen erall th re y e stains a kept on the upper plates . Careful ness has been taken to disturb and remove as little of t he amalgam as possi ble , and m ost of i t is saved in the china bowl ; but every tim e the broom is dipped into the mixture a little am algam is washed ofi into the kettle ; so that it must all be saved mand once a week or so , poured out and cleaned . The a algam now lies on e the plates with microscopic ridges caus d by the broom , parallel with the cu rrent, and to change these to trans verse ridges , the whitewash brush is taken and drawn 4 HINTS ON A MALGAMATION . 9

continuously across the plates , back and forth , till the the battery i s reached, when water in the battery is turned on , the stamps are dropped and the concentrators G started . enerally this treatment is sufficient when n done at 7 a . m . a d 5 p . m . each day , but as stated t n e above , should the pla es agai b com e stained , han g up and dress them in this same way , even as often as u tr every three hours . O n no acco nt y to rem ove the stains with the battery running and the sand passin g a over the plates , as mu ch amalgam is carried way and the gold in the stains lost forever . Should the plates r require d essing every three hours , it i s not necessary o to rub them so hard with the whisk bro m , except in the mo rning and evening , but this double dressing must not be neglected , even if the plates are apparently clean and bright . They always are improved by it , and with practice ten to fifteen m inutes is all that is r equired on each battery . Whenever it i s found that considerable amalgam i s collecting at the lower part of the plates , brush i t up with the broom towards the head of the plates , and once a week lightly remove the surplus from the lower apron and the sluice plates with a rubber, but do not touch the am algam on the splash , lip and upper apron till the tim e for the general clean up of the t e mill , as the hick r the amalgam that is there, the more of the fine gold i s caught and nearer to the battery as well . It is also a fact that gold amalgam is less liable to tarnish than any other amalgam . We occasionally fi n d another difificulty to contend “ ” With , in that the gold is rusty , that is , coated with a fi lmrendering its surface impervious to the attack of o f q uicksilver . This is rarer occurrence than im agined, a s the loss of gold is very often laid to this cause , when the gold i s capable of being amalgam ated i f proper care 50 HINT S ON A MALGA MATION .

. and knowledge are employed In some oxidized ores , taken above water level , a laboratory test of amalga mating will show gold not touched by quicksilver, but here the ore is fi rst ground by itself and then the qui ck silver and water (and a good deal of wa ter) are added and it i s shaken in a bottle or stirred in a w edgwood mortar, after which the amalgam i s separated by pan w ning . In a battery it h stamping , coarse gold i s hit and cracked and an inside bright surface exposed , s which is at once attacked by the quicksilver , pre ent at c the same time , before it can again be o me tarnished ; wh ile fine gold is ground temporarily bright by the vio lent agitation of coarse and fine rock throw n against I n the s ides of the mortar and the screen surface . this n ot way a great deal of gold, reported as rusty , and ti available for amalga mating, is found to act very sa s

‘ f toril ac y when actually worked , while this result is helped by the use of our sovereign mixture , the high specific gravity of gold causing it to remain on the plates mechanically , when it is taken up for future treatm ent in our daily dressing of the plates . If we know positively that we are dealing with rusty gold , we can help ourselves a little by throwing into the bat fery every hour a piece of bluestone the size of a wal nut , but our principal work should be on the outside plates . It is not a very good plan to put any cyanide into the battery , as it may dissolve free gold before the quicksilver has coated its surface or dissolved it .

After the dressing of the plates , the kettle, broom s , rubbers , and bowl of amalgam and dirt, are taken to

- u an d the clean p room ; the rubbers brooms are washed , and th n put awa . f th ll a mall on t e y I me mi is s e , en stamps or less , the amalga collected at one time is so small , it is better to put the bowl away as it is , and only

52 HINTS O N AM ALGAMATION .

s l ittle water kept , not more than a couple of tablespoon full, as we require the mixture to be thick for proper r in grinding . It i s now g ound for several minutes , fact, a till it seems to be nothing but a slime, when the mort r a is placed in a gold pan, and a stre m of clear water e under pressure is turn d on , the m ix ture being rapidly sti rred wi th the pestle, till the water flows clear, over the sides of the mortar . The su rplus water, except a off very little , is then poured , an d the grinding renewed unti l this clear water is dark and possibly has become n thick once more, when the operation of washi g with clear water is agai n employ ed . After this second wash ing there should only rem ai n with the amalgam , the iron from the battery and a little coarse sulphurets . L eaving the water in th e mortar the iron is removed wi th the horse-s hoe magnet an d then the water re moved , when the amalgam coll ected can be carefully added to that in the bowl, l eaving the sulphurets behind th i n e mortar . If this las t amalgam still has a bluish

- or brownish coating, it is a gold bearing stain and o should be added to the general amalgam . Th e dr ss ,

are the - sulphurets , etc . , now put into copper bottom h m e pan , which as been a algam at d , shaken in this and washed into the tan k . A piece of the fine can vas is taken an d th oroughly wet on both sides and then placed i n a bowl of clear water . Into this som e of the quicksilver an d amalgam is poured , but only a quantity that can be handled con v en ien tl y, the canvas is twisted tightly and the quick it silver squeezed through , adding the amount to , un til either it is all in one ball or the ball is of a size not to be cumbersome . Now, it is not necessary to exert great e i a str ngth to elim nate the l st of the quicksilver , as more can t i be ex racted by rubb ng the hand or the thumb , H I NT M L S ON A A GA MATION . 53

with a steady pressure over the ball , with frequent e imm ersions in the water , than by viol nt twis ting . When the amalgam is squeezed dry the ca n vas is laid

- open on the gold pan , the bottom covered wi th water, a s a the ball of amalg m pre sed into solid sh pe , all de tached d t pieces adde , and the ball is hen rolled over t i every part of the canvas . In tha way t collects every a t speck of am alg m , and has its surface smoo hed with the small amoun t of quicksilver remainin g in the in

r ts te s tices of the canvas , while any dirt or sulphure is kept from being attached , owing to the water in the pan . D ry am algam , even wi th a little free quicksilver , 24 t becomes very h ard in hours , and the sligh addition of mercury to the surface of the ball , from rolling over the canvas , acts as a cement to keep the ball together n in a compact mass . The ca vas is washed in the pan , T he squeezed dry and hung up . floured quicksilver is b th o collected, rubbed y e finger into a gl bule and added

o t that i n the bowl . The ball is now weighed in avoir o dupois ounces , and put int the safe or strong box , and entered into the book for mill reports , as the product for

e . one day or num b r of days , as the case may be It may seem that this work is not required and that the amalgam can be saved and cleaned with that col

- lected from the general clean up , but it will be found

e to be money saved , to att nd closely to the instructions ti a given above , and par cul rly where we have to contend w ith tellurides . The foreman of the mill , or the super in ten den t of a small plant , have ample ti me each day to devote to this work ; more gold will be acquired , and a the retort m etal alone, in its cle nliness and the sm all t loss from the subsequent mel ing , will more than repay I f im the attention to the small details advocated . this perfectly amalgamated muck i s roughly panned and 54 HINTS O N A MALGAMATI ON .

al n a the a m a lgam o e saved , the loss in a month is p i l p rec ab e, and it is forever gone , while this is the only a a n d a lloy of gold which i s hard to cle n , not tha t from

- the chuck blocks or inside the bat tery . ca r We see the mint saving the dus t on the roof , the

an pets , d the clothes of the workmen , and g etting a mar

e a o d v lons qu ntity of g l , and yet , in a mill , t he amal

m th a n d a re all a d as g a , e scrapings refuse h ndle if of L a no more value than the sand on the ocea n beach . tely a report w as made by a responsible consulting mining an engineer , that he estimated the value of old mill a n d o the gr und on which i t stood , to be over a a an d in m lgam , quicksilver sulphurets , and it has been o ur experience that in the m aj ority of mills which have been in opera tion for several years a s tonishing results a re obta ined from scraping the cracks i n the flo or a n d working over everything a bout the m ill or under it a s

a - all well as the t il sluice below the property . Save the e an d a chips , scr en frames any wood t h t has been in

an use in the battery and slui ces , burn them to ashes on iron plate and amalgamat e the ashes . After the cast

o i an d i ngs have bec me dry , exam ne them thoroughly , a remove every speck of amalg m , even if some of the off e iro n i s broken w ith it . Hammer the old scre ns and scrape off all the rust ; while all small bits of iron , even a n be e t h t saved by the mag et , should mix d with salt a n d e o o a dampen d ccasi n lly , and spread ou t in the sun where it i s exposed to the weather . Every six months

- u a - u i this is run through the clean p barrel or cle n p pan , whichever is emp loyed .

a e The floor , on which are pl c d the pla tes , is given a slope towards the concentrators , and a t the end of this floor a gutter is placed which will catch all the sweep a n d ings water that may flow down . This gutter must 55 HINT S ON A MALGAMATI ON .

d have a slight grade , ending in a woo en box or a pipe , ff to carry o the waste, but i n each gutter one or two rifi fles a couple of inches high , are placed before the

r - fl oor overfl ow pipe is reached . Each m o ning the plate is swept thoroughly to this gutter, or in sum mer washed t down with the hose, and a stream of water of modera e s trength is occasionally run through the gutter, and the fi l concen trated material at the ri es rem oved . Every leak from the plates is a t once calked and stopped , as where the sand goes some of the quicksilver and amal n t ga m will go , even if a panning test m ight o show an n t appreci able qua ity . We can safely handle all the dirt on this fl oor , as we have taken especial pains to e prevent any drippings of grease, coal oil , or other d le terious subs ta nces from coming in contac t with the plates or their environs .

One other question has properly to be considered , and that is the temperature of the air, and the battery water, t in regard to its ac ion on the amalgam . We see the effect of heat in the expansion and con tracton of m er cury in therm ometers without changing the weight i n the least . We also find that our bowl of cleansing quicksilver will have a very appreciable amount of crystalline amalgam after the first cold night . There fore , we have these deductions to m ake ! As the cold i e ncreas s , the quicksilver becomes more viscous and slower in motion , and it will not dissolve amalgam , and to increase the cold beyond a certain point the mass i re is so lacking i n its lively characteristic , that t will quire more in quantity and with the leas t beneficial re ul s ts . According to actual exp erience thi s temperature prohibitive to good work i s that of 2 5 degrees Fahren i heit or lower . With an ncrea se of temperature , the n quicksilver expands , becomes m ore flue t, runs easier 56 HINTS ON AMALGAMATION .

and will carry much more fine gold in solution , and we are enabled to keep more perfect control o ver our op eration s . To any one accustomed t o amalgamating “ ” wet, a low temperature will be of mos t benefi t though i n no case will perfect work be done . In wet amalga m ation the cold viscous quicksilver will form a pasty mass , easily collected with a rubber , but as soon as the temperature rises to sum mer heat , there is a great di vergence be tw een the coarse amalgam and the fluid h quicksilver , and , as a result, t e upper part of the plates becomes incomprehensibly hard and dry , in spite of an i ncrea se in the Quantity added , while the m ore lively ff and thinned qui cksilver runs rapidly o the plates , is

a floured and lost, carrying with it the incre sed quantity of gold i t is now capable of dissolving , lost forever . . i s t As a result, there a poor effi ciency of work tha the amalgamator cannot explai n even to himself .

- In pan amalga mation of silver ores , t he pulp is heated to the boiling point of water , either by live steam , or a es false bottom , and all have acknowledged this to be sen tial even on pure chloride o res , not only on account of the chem ical action , but also to pu t the quicksilver in its m os t efficient condition . In the cheaper gold n o i amalgamating this can t be done , economically , ow ng to the steady infl ux of cold water through the batteries , but com mon sen se will show the benefit of having the battery water as warm as consistent with expense and th the heal of the employes . In summer , for all prae o suffi tical purp ses , the ditch or spring water becomes cien tly wa rm i n passi ng through the water - tank and e pip s , not to i nterfere with the efficiency of the quick silver . But i n winter, except in the tropics , the water i e z com es from melting snow , and it s very li ttle above fr e b ing , and unless rem ed ied , it is etter to hang up th! 5 HINTS ON AMALGA MATI ON . 7

m ill during the cold weather . In som e places it is very nl dangerous to do this , n ot o y on account of the burst z ing of pipes , but when once fro en up it will be difficult im to start again before warm weather arrives . It is erativ e p then , to keep the mill moving and thorough

preparations should be completed during the early fall ,

Modern Machi n ery.

to provide against a cold snap , even if of rare occur rence . If the mill i s run by steam , this is very easily

- attended to , but wherever possible , mill power i s now derived either directly from water under pressure, or indirectly from water at a dist an ce , driving an electri c plant .

If steam is employed, the waste steam is conducted through the water tank , never i nto it on account of the O 58 HINTS ON AMALG AMATI N .

. x grease This is generally sufficient , but in an e cep tion all y cold locality , rather than add fresh live steam directly to the tank , we advise the following arrange ! ment Before carrying the water to the battery , pass it through a coil of pipe placed aroun d the steam - drum of the boiler where it will be amply warmed by the waste heat emanating from the surface of the drum . As this will make the water uncomfortably warm in e summ r , have two sets of pipes , one to go direct to the batteries from the tank , and the other for winter use, leading to the coil . The water leaves the tank in one “ ” pipe, but within a couple of feet thi s pipe enters a T . With short nipples from the other two ou tlets and e glob valves on each n ipple, the water can be diverted either way desi red . These separate pipes are j ointed together again j ust before the battery pipe is reached “ by another T , the water being under control by two globe valves arranged as in the first instance . Figure 1 8 will partially explain the plan. In a mil l where the power is ei ther water or elec tricit y, the building is made tight by battening all the

h v m cracks , keeping the doors shut , and a g all the panes of glass in the windows . Have a large wood stove, at least three feet long , and have plenty of wood , not only h for the comfort of t e employes , who will attend to a their work better, but also for the benefit of the am l amation g . In a cold country i t is necessary to have a small boiler solely to generate stea m to heat the water the in tank . In som e localities where water is scarce or requi res pumping to elevate it above t he m ill , the wa ter tha t e comes from the mine is us d in the battery . Th is does not require h eating unless the reserve tank is very large and the weather very cold . In most mines the

CHAPTE! III .

P C LEAN ING U .

As the amalgam accumulates in battery and on the t plates , a cer ain time in each m onth must be taken to remove it all , not only to get the money locked up , but to do the necessar y rep airing to the m ill for a comin g ru n . It i s far better to appoint a regular day and adhere to it a s near as possible, as the cleaning up when the owner happens to be at the mine , or the superintendent feels like it , always comes when new shoes and dies are not required , and often when the ore i s j ust i n the best condition for profitable work in that month . According to the size of the mill and the richn ess of the ore , this day should be set aside either once or twice a month . Of course, in certain local ities it i s not advisable , for obvious reasons , a to have exactly the s m e day in each month , and it cannot be too strongly impressed on those in power, to keep the exact day to them selves until the morning that has been set , when instructions are given to the m illmen to hang up , and the night shift to work over ln r t ime , the effort to finish the actual cleaning and e pairing and start the m ill as soon as possible . If the mining property is isolated , with little com munication with the outside world , a regular day , once or twice a month , does no harm ! but in a com munity where there are numerous persons unconnected in any way with this particular property , and a section subj ect to a constant influx and outflow of persons , whether tramps or people HINTS O N AMALGA MATIO N . 61

on special business , it is on the safe side to keep the date secret when the lon g accum ulations are reduced to a portable shape . For this reason we have advised the prelim inary

- preparations of a goodly stock of scrapers , sharply cut rubbers , and the making of the wooden wedges for the

’ shoe s , to be always on hand and ready at a moment s notice , so that no estimate of the special day can be made from observing the preliminary preparations .

In all mines we find rich ore , medium grade, and poor fi i i n ore , and an e c e t superintendent will try to work all these together in the proper proportions to insure dividends , and yet leave no ore carrying val ue i n the ” mine . A tenderfoot owner will be highly pleased with large profits as long as they last, but i s always unwilling to part with some of thi s profit for future development , when the mine has been robbed of its richest ore .

Therefore , it is advisable , in the beginning of a run , to work up for som e ti me the poorer ore of the m ine , bringing the product up to a regular amount by extract ing more or less of the richest ore as required . Now it depends not only on the size of the m ill , but also on the value of the ore , whether the m ill is stopped for

- u clean p once or twice a month . Should all the ore be f low grade , we cannot a ford to lose any more time than we can possibly help , and should only take one day in each m onth , a s our dies and shoes can be a rranged to last that time without renewal . Even if we remove them before thei r usefulness has ended we m ake m ore money owing to the increased production . In a custom t o mill , af er each lot of ore i s worked , of c urse a thorough

- and general clean up m ust be made, as gold ores are ac not safe to buy outright , with the lim ited means of curate sampling which is general ly at our service i n countries remote from s melters. 62 HINTS O N A MALGAMATION .

l a In a m i l running ste dily on ore from one m ine , we can afford to allow a little of the value to remain n u

- u taken at each clean p , as it will have an average result in six months or a year , and in reality give more money from a greate r production . Most superintendents , on

- u clean p day , remove all the dies from all the batteries . to get the amalgam in the sand and ore wh ich is packed a ’ round them , from two weeks work , and then replace these partly worn dies for another run . We consider s ’ this to be a great lo s in a year s run , and a case of greatly m i staken economy for several reasons .

When we first put i n the new dies , they were very heavy , and so kept their position , and the tops were absolutely tru e . Before there was a chance of changing position they becam e cemented with the rock and sand so as to becom e an integral part of the mortar . Though the stamps turn at each revolution of the cam shaft , both the shoe and die wear unevenly , but each shoe after a few days will form the greatest crushing surface t with its own particular die , in its original posi ion , which has become as fixed as if it were welded to the mortar . Thi s situation will continue till either the shoe or die break fro m the thinness attained through the steady

. d wearing away of the iron In ad ition to this , the quantity of amalgam which settles through this cement

will not be of sufi i cien t amount in any one battery , to diminish the total output to such an extent as to be

of special moment to secure at that particular time , ’ while in a year s work i t will ret urn a much better aver age . Now suppose partially worn dies are removed , the gravel extracted and the mortar prepared for their re

placing . Th e tops of the dies are now uneven , perhaps

worn more on one side than the other, or cupped , but

the shoe corresponding to each die is worn the sam e , HINTS ON A MALGA MATI ON . 68 and to replace the dies exactly in the sam e relative p o u ' sitio is well nigh impossible , even with the greatest care , and a useless waste of time as well . The result i s , that a point or edge of a shoe strikes on a point or

f a edge of a die , o fering m inim um of crushing surface for several days , and using up unnecessarily a great

deal of i ron , with no benefit per ton of ore worked . The lessened weight of the die also allows it to j ump from the blow of the stamp , before the gravel has be com e cemented , and we are specially liable to a cracked die , or , at any rate , one tilted at an angle to its base .

After a couple of months at the longest , we find som e of the batteries with worn out dies , while others will con

- tinne till our next clean up day . We replace those worn out , and leave the others , after digging out most of the cemented gravel around them , and we get ready for a fresh start in the shortest possible time , and are agai n making money . We certainly earn no additional money on clean - up day ; we only collect that which we have previously earned .

The previous day to that one agreed on , we exam ine all the shoes and mark those batterie s where we have

r - to e shoe and put in new dies , while other shoes which are too far worn to last a whole run are also marked ao for rem oval , and partially worn ones which have cumulated are prepared for these stamps . A close ex amination is also m ade of every part of the mill , includ ing the engine , if run by steam , and whether the boilers require cleaning . In the case of steam power , the order t to clean up is given the night before , as the m ill m us suffi be stopped at 4 a . m . to allow the boilers to cool cien tl ff y to be blown o . A regular system m ust be drilled into the m inds of the employees , so that each one knows exactly what he is expected to do . The firem en 64 HINTS ON A MALGAMATION . attend to the boilers ; the engineer cleans and repairs the engine , taking up all lost motion , an d then looks over all the line shafts and pulleys , tightening up the bolts on wooden pulleys , relaces or rivets those belts that require it , and does all the other m echanical re pairing , assisted by the night engineer . The coneen trator men t horoughly clean the machines ; go over the plane of the table with straight edge an d level , replace all worn out castings , lace the drivin g belts , and get ev er thin i n - y g apple pie order . The man who attends to the rock - breaker cleans it of all grease and replaces worn out shoes and dies , assisted in this or any babbit ing by the engineer . The battery men and all others connected with the m ill , who have no special duty , are under the direct supervision of the forem an , and help hi m , first in removing the amalgam plates to the clean up room , and then to extract the sand from the batteries , clean ofi all the amalgam from the apron s and get the batteries in general , ready for as speedy a return to starting as possible , and it is with their work that spe cial instructions mu st be given .

Orders are given to stop the mill at a certain time , off and a few mi nutes before, the feeders are shut , and boards put over the throats of the mortars to prevent any more rock being j arred into the batteries . W hen the stamps begin to strike iron , two methods can be pursued , either hang up all the stamp s or reduce the speed of the m ill down to about thirty - fi v e drops per minute , and allow the stamps to drop till the water comes through the screens clear , though still carrying some sand . We prefer this last method for several — reasons ! we have less gravel to handle , the chuck blocks and all parts of the mortar are clean , and therefore visible , and any quicksilver or amalgam which i s i n t he HINTS O N A MALG A MATION . 65 rock on top of the dies has been thrown out or settled

. below the tops The m ethod advocated by som e, to hang up all but one battery , and feed this surface rock through it , not only takes a longer ti me , but requires the workmen to expose them selves to a possible but not probable accident , by working under the stamps with the cam shaft i n motion , and they do th e work in con sequence carelessly , and take a m uch longer time . As soon as the stamps are hung up the water i s turned ff o , and preparations at once started to clean up th e mill .

First, the splash plates are washed and laid across the lower apron plate . Second , the screens are removed ,

- washed over the plate an d carried to the clean up room .

Third , the lower keys are driven out and the chuck blocks carefully removed and washed over the plates

- and carried to the clean up room . Fourt h , the lip plate is washed on both sides and placed on the lower apron .

The mill crew i s now divided . One m an is put in the clean - up room and chisels off th e am al gam from the

- chuck blocks directly into the tray . A second m oves the upper halves of the apron plates down over the lower halves , after thoroughly washing down all the gravel and dirt to the trap . He then scrapes the am al gam from lip plate and splash plate on the upper apron .

These tw o are the day and night shift amalgam ators . The others of the crew remove the top gravel from the mortars and dump it into the feeder of one batterv . When this top gravel is taken out to th e top of the

' dies the balance of the gravel i s picked out around the

. dies , and those dies extracted which require removal Thi s cemented gravel is dumped into the barrel or placed

- in a box alongside of the clean up pan , and the m ortar

a , is thoroughly cleaned , all adhering am alg m o n shoes 66 O N H INTS A MALG AMATI O N .

sides and lip of mortar being chiseled off. The worn out on shoes are driven the stems , an d the worn out wedges put into a box for examination and future burni ng .

The new dies are placed in position , and the new shoes

with the circle of wedges placed on top of the die s .

The partitions are taken out of the traps , the water re moved with a sponge and the settlings added to the pulp taken from the battery . The old shoes and dies a re washed in a tub , the amalgam roughly chipped off and the sediment added to that in the barrel . These m en now tighten all the bolts around the bat tery and clean the stem s and cam s of every particle of grease , using a table knife , coal oil and old sacks .

When thi s i s done , wooden blocks are put on the dies , the exact height the drop of the stamps is required to be .

- The feed stamp is given a h alf inch more drop , and the two end stamps a quarter inch more than the others ,

. 2 4 viz , No . and No . , and these stamps are set by their tappets .

The amalgamators and foreman have , in the sam e ff time , scraped o all the amalga m from the chuck block s and all the plates , and it is stored in kettles and

- u pans , ready for the clean p barrel ; i n fact , should be dumped into the barrel a s fast as collected to get it out ’ of harm s way . The upper apron i s put in place , and the

- lip plate , splash plate and chuck block for each battery

- put on the lower apron . The engine or water wheel is now started slowly and the shoes driven on , and these shoes are now set by the blocks as the others h a ve been .

- All the am algam and gravel i s in the clean up barrel . Some water and at least 40 pounds of quicksilver are added , though the amount of quicksilver depends on the 1 00 quan tity of amalgam to be cleaned , and sometimes

68 HINTS ON A MALGAMATION . M We consider that r. Preston m akes a great m istake in his treatise , where he advises a speed of 70 revolutions per m inute , as this speed should never be over 1 5 revo lutions , and our practice has been to u se from 7 to 1 0 , when the pulp i s thoroughly ground inside of twelve hours .

As soon as the barrel i s started , the night shift go off duty , and if it is late in the day , the day shift remain on duty till midnight . The day shift now dress all the plates with the dressing m ixture , thoroughly amalga

- mate the ch uck block , lip , and splash plates with quick silver , throw som e rock into the battery, replace every thing, i ncluding new screens , and start on a fresh run . All the i mplem en t s used are cleaned and taken to t he

- u clean p room , the floor i s cleaned and all the mill put

- in appl e pi e order once more .

- In scraping the chu ck blocks , we take everythin g down to the clean copper , but great care must be exercised in scraping the silvered plates , not to go into the silver difi i cult coating at all . Thi s i s not so very , but for this reason th e work should be done by the amalgamators , or those who are careful in their operations . There is a great difference i n the “ feel” of the scraper when going through a malgam or into the silver the latter being very m uch harder and smoother . In fact it very frequently feel s like the surface of glass . The scrapers must have perfectly true edges and be very sharp , with an end like a wood chisel . The flat side is put again st the plate and a steady pressure exerted , never a chip ping or striking motion . The barrel is allowed to run till there is a steady swish and no grinding is heard .

To be on the safe side , it i s better not to open it till the next morning when it is certainly ground most OE thoroughly . The belt is thrown and the barrel turned HINT S O N A MALGA MATIO N . 69

till the manhole is on top . The cap i s removed and washed over the manhole , and the enameled p ail (placed

- on top of the die directly under the screw plug) , and the o box , are filled with water fr m a hose , which hose i s

th - fastened to and kept in e pail . The screw plug i s removed , and as the amalgam , quicksilver and slimes tin flow ou to the pail , it i s constantly stirred with a wooden or iron paddle , so as to keep the contents in constant

Our/ 1 7

Modern Maohi n crv.

agitation . W henever no more will run out by itself , the hose i s turned in to the barrel , and the pieces of iron taken out , each piece being thoroughly washed . All thi s time the contents of the pail are kept agitated , so that only the heavy amalgam and iron remain , all the sand flowing into the big box and from there over the waste sluice plate . After all the iron i s removed , the inside of the barrel is thoroughly cleaned with a broom and

clear - n a l the water, and our cl ean up i s fi l y collected in 70 HINT S ON A MALGA MATI ON .

the pail , but it still requires some work which m ust now

. r l be done by hand We give a cross section of ba re , pail 1 and box in Fig . 9 .

The pail i s carried to the clean - up room and the super i mposed sand and iron panned in small quantities at a time . The sand i s washed away and the iron picked out by hand and extracted with the magnet , until n nothi g but the q uicksilver and amalgam i s left . This is squeezed into balls of convenient size , and , with that collected each day , i s now ready for retorting . In some ex ception ally u nsafe localities it might not be advisable

- u to delay the retorting till the day after the clean p , and in that case all the dirty amalgam is kept separate from the gravel and sand , and i s first cleaned by itself in the barrel . In thi s case there is only need of putting i n the cannon ball s . The m achine will clean and soften the amalgam in less than an hour, when it can be drawn fl o as described above , the iron extracted and retorted at once . After this is done , all th e sand and gravel i s f put into the barrel , together with the di ferent sized pieces of iron , and is ground till the next day . The amalgam result ing from this is st ored in the strong box

- till the next clean up .

Though the ba rrel i s more generally used in gold mills , som e mill men prefer a grinding pan , which i s at all ti mes open to inspection , and can be fed with fresh ma terial without stopping and cleaning out the previous

- a charge . D iffering from a s il ver amalgam ting pan , this on e co mbines the work of b oth the grinding and amalga

mating pan and the settler . The pan should have iron difl eren t shoes and dies , and three outlets at height s ,

closed by wooden plugs , i n addition to the m ain duct

set below the bottom of the die . The overflow outlets sluice late conduct the tailings directly over a p , while HINTS O N AMALGAMATIO N . 71

- the main duct discharges into a water tight box , fixed with old die and pail . The overflow from thi s i s carried

to the same silvered plate that the slim es ran over . Thi s

- 2 is shown in a cross section , Fig . 0, which represents the only the outlet part of pan . The speed should be 30 about revolutions per m inute , and the modus Oper andi is as follows ! The am algam alone i s first ground with the m uller down an d a sufi i eien t a ddition of quick silver to thin it and only a littl e water . When thor oughly ground , which should be done i n an hour a t t he

longes t , water i s added, the m uller slightly raised , and the overfl ow plugs opened in succes sion , with cl ear water constantly running in til l there are no more slimes running out . Then the main duct is Opened and the amalgam and quicksilver run into the pail . After ' all has run out that will , the machine is stopped and the balance swept out with the whisk broom . After the a amalgam i s cle ned , a charge of the gravel is put in and 40 pounds of quicksilver , and ground moderately , when all that will run down to the lowest overflow plug , after thinn ing with water, is allowed to escape . The plugs are then put i n and it is filled up with more of the gravel . Thi s is continued till all of the scrapings are in the pan . When this i s all ground , the main duct is opened at th e very last , and the am al gam , quick silver and iron are run into the pail , and w hen the iron is separated the amal gam is panned and squeezed . ! The advantages of the barrel over the pan are First , i t takes less power to run . Second , it does not requi re so much skill to handle . Third , it i s a thorough gri nder and amalgamator . Fourth , the cost of wear and tear is practically nothing , as worn out castings are used .

Fifth , its contents cannot be tampered with , unless the

machine is stopped . 72 H INTS O N AMALGAMATION .

! The disadvantages are First, it can only be run by hearing . Second , only one charge at a time can be run , and not conti nuously as in a pan . Third , the separation of sand from amalga m has to be done on discharging the a contents , when the pulp is thick and cap ble of carry n! ing o values . As the advantages considerably more than balance the obj ections to it , we would advise the employment of a barrel . P ! CHA TE IV .

! ! AND M ETO TING ELTING .

- The kind of a retort we require in our m ill plant , depends entirely on the amount of amalgam we

- u have to distill at each clean p . There are two varieties in use, the stationary ones , always used in s ilver mills , but only employed in gold mills when the amount of amalgam runs over ounces ; and port able retorts i n sizes holding from 30 ounces and up I f wards . the number of stamps exceeds 40 , and the o ore i s of go d grade, we will require a stationary re i tort , but its use s of much less importa nce in general mill work than the portable ones .

Where retorting of large quantities is required , we i l must have a building entirely separate from th e ml . Thi s building will contain one room for the retorting and melting furnaces , and one for the assaying and chemical department , with a small room in which the delicate balances , assay accounts and such things w hich require care, are kept . The retort is in the center of the room and th e o utlet from the fire box extends to a chimney placed to one side . Into this chimney , from the other side come the fines from the two melting furnaces and the muffle furnace . All around the fur naces the floor i s covered with iron plates at least four feet wide, th e rem ainder of the flooring being brick set very closely together . The retort i s placed hori zontally and i s closed by a cap covering the whole ln terior diameter, while the outlet for the escape of the 74 HINTS ON AMALGAMATI ON .

quicksilver , is a small orifice at the top of the rea r

- end, from which it is conducted by a water j acketed pipe to a receiver , which is an iron tank filled with b ll water. The a s of amalgam are placed loosely in trays which j ust fit the contour of the bottom of the retort . These trays are first thoroughly coated with chalk to prevent the gold sticking to the iron when softened by all the heat . W hen the trays are pushed in , the cap is put on and keyed very tightly . Now a tight j oint cannot be made with i ron against iron , and no gaskets f will stand the heat , so we m ust find a j oint una fected by the heat or the action of the quicksilver . There are several substances at our disposal , and the choice de pends only on the presence of one or the other and its relative cost . The luting material can be pure clay , either white fire clay or colored , as the heat is not suf fi i c en tly high to melt or even thoroughly bake it . The a w oodashes most comm on materi l employed i s sifted , either m ixed with water alone or with the addition a of s lt . Either m aterial i s first screened through the 4 0 mesh sieve , and all lumps in the clay or cinders in the a shes thrown away . A small portion i s mixed and puddled with a little water , until it can be moulded in any form without breaking , and yet carries no surplus water. As the puddling i s carried on , either water or ashes are added till the right quantity of the proper consistency is obtained . At first a novice is apt to add . too much water, th e paste seeming to be too dry , but on working it with a knife , it grows softer and more liquid , so that only after considerable puddling and slight additions of ashes is it possible to get it thick and at the sam e ti me soft . When ready the cover is laid in a horizontal po sition and the lute put all around the edge in the recess made for it . It i s put on quite

76 HINTS ON A MALGAMATI ON .

noon , and finish the retorting during the night . As soon as i t has become thoroughly heated , it is safe to leave in the care of the watchman as no one i s able to open the retort or abstract the metal as long as it t e mains so hot . It i s rarely cool enough to open with

m. safety till 7 a . , the next day , and it should not be t touched till the arrival of the one in authori y . When ready , the cap i s removed and the trays taken out and r placed on the iron plates to cool still more . If the e tortin g has not bee n don e too rapidly and with too . u high a heat , hard to get with wood f el , the gold should still be in its pristine balls , now , however, porous and spongy . In the bottom of each tray we always find i som e of the gold j oined together, being part ally m elted from its proximity to the red - hot iron ; but it can be easily broken with a blow of the hammer into con ven i t ent weights to handle for the subsequent mel ing.

( ‘ IP Q n At most m ines , the amount of amalgam at each u p i s small in actual bulk , and can be handled with the a portable retorts . Each m ill should have two on h nd , diif eren c of t sizes , the largest according to the apacity h of t he mill and the richness of the ore , capabl e of old

- ing in one charge the total of the clean up . A retort must never be filled more than th ree- quarters of its

- r capacity . The danger from over loading i s not app e ciated by the average person till a serious accident occurs . Under the influence of the heat the whole ma ss swells very m uch , and we have seen , from putting too m uch am algam i n first the co plete choking of the , m, m outlet pipe by amalga , and then when the pressure became too great the sudden forcing of several pounds a of amalg m with quicksilver vapor, into the receiving tank . In some cases if the retort was old or the cap improperly fastened , a very serious and dangerous acci M HINTS O N A MALGA ATIO N . 77

dent would happen from the explosion of the retort

itself.

The portable retorts are in two shapes , those w i th

a flat cover, and those with a curved cover and known

as the Nevada retort . Th e latter style i s very m uch

preferable , as i t gives , under all circum stances , a re serve space for the quicksilver vapor and allows a little more latitude in filling the retort , besides giving a m uch stronger keyway and general fastening .

Before putting in the am algam , every part of the re tort m ust be exa mined . First see that the pipe is tightly screwed into the cover , and i s perfectly clear, tapping ’ it with a ham mer and blowing through it . With a

new one , be sure and coat it thoroughly , because , if the gold adheres to the iron i n any one place , in sub sequent cooking with every care taken , it is generally attached to the same place . If the retort has been in use , remove all adhering particles of gold with a chisel and coat most thoroughly . We have a choice of two coatings , one , which we consider the best,i s of soft chalk , rubbed on dry from the chunk or powdered , mixed into a paste with water , and plastered smoothly all over the inside ; the other , a thin paste of sifted o wo d ashes and water, which is thoroughly daubed all over the interior . If a paste i s used , the retort should i n be dried before putting the amalgam . The quicksilver

- condensing pipe should always be water j acketed , and can be bought already prepared in thi s way . Thi s j acket consists of an iron or tin pipe two to fou r inches in diameter, and m ade water tight at each end , through which the condensing pipe passes . At the lower end , the furthest from the retort , there i s put in a part of a hose coupling to which the hose conveying the cold is water can b e screwed . At the upper end a small 78 HINTS ON A MALGA MATION .

outlet , to which a piece of quarter inch pipe is screwed . This pipe is bent and carried down on top of the con denser , discharging into the kettle which receives the m etallic quicksilver . If not bought with the retort , any tinsmith or capable engineer can make a t in cyl inder of the required size , solder i n a hose coupling at t he lower end, and s older the whole tightly to the pipe

a t a a e ch end , The constan t flow of w ter will preven t n a y melting o f the solder (See Fig . ‘ e - en d o f o Wh re a w ater j acket i s used , the the utlet pipe is placed a little below the surface of the water in the receiving ket tle, an inch being ample . Sometimes

a a i t is necess ry to use a retort , having only the n ked pipe over which water is poured from a dipper . In th is case care must be ta ken that the o rifice of the con den s in an d g pipe is partly out of the water , this i s very

a dimin u rarely looked into by mill men . The d nger of a tion in the heat consists in the cre a tio n of a partial vacuum in the retort, which then sucks up water from the kettle if the pipe is wholly i mmersed . This water is converted into steam an d causes an explosion of great HINTS O N A MALGAMATIO N . 79

danger . With part of the orifice out of the water , only e air is suck d up , which causes no sudden increase in the internal pressure ; but we are confronted with another danger, that of sali vation from the escaping quicksilver n gas , u less we close the orifice in some way . Now we wish to impress this poi nt very , very strongl y on all those i ntending to retort the amalga m without a water are jacket. Even if they fortunate, time after time , in in hav g no serious accident , they will always be more or less salivated , and it takes a very slight exposure to quicksilver fumes to find the teeth becoming loose and e other eviden c s of quicksilver poisoning . Th e way to prevent i t i s this ! The pipe is wrapped with burlaps or V gunny sacks , and a of tin placed underneath , sus pended by wire , to carry the water poured over the upper part of the pipe , away from the fire . This sack ing is extended several inches beyond the end of the pipe and into th e water of the receiving kettle . In this case the pipe m ust be straight from the retort to the kettle , with no bend , as shown in the sketch of the

- water j acketed pipe . The wet sacking prevents any escape of the quicksilver fumes , and yet part of the orifice of the pipe i s out of water . Should a partial f vacuum be formed inside the retort , the only e fect is to suck the gunny sack against the mon th when the air enters freely through the web .

The retort has been chalked , all parts exam ined , and the amalgam in balls ready to be packed in it . This packing depends on the subsequent handling of the re

- tort metal . Where not convenient to m elt into a bar at the mine , it is j ust as well to ship th e gold j ust as it comes from the retort , but in that case we want to have a t it as compact a m ass as possible . I f i t is melted once it is bett er to keep it i n its original balls from 30 HINTS ON AMALGA MATIO N .

which the quicksilver has been distilled . When the re tort metal i s shipped , the balls are broken and the amalgam packed with the iron pestle into one solid mass , that around the sides particularly being smooth , so as to leave no thin ridges to break away . When i t i s all smoothed , a hole i s bored i n the center to the bottom , a with an iron rod , to ct as a vent for the escaping gases and to prevent the entire mass from being raised by the pressure underneath before it makes its own vent . In this case also the heat during the last of the operation is raisedto a bright red so a s to anneal and parti ally m elt the gold and so hold it together . When it i s melted on the spot , the balls are put in unbroken , and sometimes each ball i s wrapped in a piece of cloth or paper. The wrapping is unnecessary and only a false idea of ex ces s ive carefulness , which results i n the distillation along with the quicksilver of pyroligneous acid , and this very quickly chokes the condensing pipe and flours the quick silver , hindering the operation considerably .

- After all i s ready , the iute of wood ashes, with or without salt , is m ixed and put on the cover, not on the retort ; the cover is put in place and keyed tightly , and all the oozing luting i s scraped off and smoothed around the j oin t .

t . The nex question ari ses , how and where to retort

Retort out of doors , or under an open shed , where there is no danger of tire . D o not use the blacksmith forge , because too m uch heat is unconsciously given with the bellows, nor a furnace into which the retort i s set , as the heat is not under control , while it i s hard to remove a heavy and hot retort , and in both the se cases no direct heat can be applied to the bottom . Make a tripod with a ring into wh ich the retort j ust fits , and high enough to allow a good fire place underneath . This can be HINT S O N A MALGA MATIO N . 81

made by any blacksm ith , and the only point to be oh served i s that the legs shall be extra thick and strong, to withstand any bending from the heat and weight .

In addition to the welding of the legs to the ring, put one or two rivets in each leg , for additional security . Fig . 22 shows this tripod . Th e tripod is set within distance of the water pipe and the retort put in place , the h ose connected and th e re ceivin g kettle , partially filled with water, i s put at a slight inclination with the end of the condensing pipe submerged in it an inch . A small fire of shavings and a little oi ly waste is started directly under the retort . This is gradually increased with either pine bark or wood , but slowly until all the air i s driven out , and a ln little quicksilver begins to run . Then the fire i s creased and the retort kept at a cherry red till no more quicksilver can be collected, after tapping the pipe .

When this i s shown to be the case , the fire i s withdrawn , k tl the pipe taken out of the et e, and the cover of the retort taken off . To prove that no m ore quicksilver i s w t left , take a cold shovel , e it and hold over the open retort, when it will be covered with a white fil m if any of the quicksilver remains . Before the retort has a chance to cool , dump out th e retort m etal i nto a pan set on an iron plate or directly on the plate , and scrape out any adhering gold . The gold must now be cool it enough to handle with the bare hands , before is oh weighed , or a correct estim ate of its weight is not tain e d. It should be porous and bright , or the amalgam has not been properly cleaned .

The question as to what fuel to use is of some moment .

Do not use charcoal or coke , even though on account of the greater heat it would be surm ised that tim e can be gained . The top of the retort m ust be kept as hot as the 82 HINT S ON AMALGA MATION .

t bottom , and his can only be done with a fuel ow hich gives strong flames . The best fuel i s pine bark , but if l i this i s not easi y ava lable , dry wood , either p ine or other soft wood , will do as well . The wood is sawed

- into two foot lengths and split to small s ize . When t he

fire i s well started , some pieces are placed under the retort between the legs of the t ripod , and a complete circle of the wood , placed on end , i s stacked against the ring of the tripod, which form s a chimney for draught and a gradually increasin g heat . Frequently only one firing i s necessary when placed in this way .

The retort m etal , if shipped direct , i s now wrapped carefully in paper and then sewed and sealed i n an ore sack of canvas . If melted on the premises into a bar , we can use the assay furnace , provided there is no special furnace . The fuel used for melting is either charcoal or coke , t he latter good English and not gas house coke . The coke is very m uch to be preferred .

- The black lead crucible , for a long tim e before use , should be put bottom up on the boiler or other hot place , to get thoroughly dried out . I t i s then put into the fur nace where there is a hot fire dying out . Here i t is put bottom side upwards , and left to be annealed till everything is cold . It is then ready for the m elting of t he gold attended by a m inim um of danger as regards cracking . Before the retorting i s completed a fire is started i n the furnace , and the cru cible , resting on a piece of brick , is placed in posit ion . The fire is gradually increased till t he crucible is heated almos t to a whi te heat , and t he supply of i ncandescent fuel j ust reaches ta to the top of the crucible . The retort me l i s now put in from an iron scoo p . This can be home made from rolling a thin sheet of Russia iron so that it has a smaller a diam eter at one end , or a scoop t hat can be purch sed

84 HI NTS ON AMALGAMATION .

fineness of bullion or its value . In any and all circum stan ces the buyer will have it remelted and assayed , and it is bet t er for the seller not to publish so widely his own knowledge of its value . Practically all gold bullion from placers and quartz mines , saved by amalgamation , contains some silver , and this has to be separated before the gold is ready for coining or other purposes . This cannot be done at the mine , and as some gold is lost to the seller in remelting , it i s of advantage to ship the bullion as retort meta l , save the expense of fuel and the loss in melting . Under any ci rcumsta nces a fixed charge has to be paid to the refiners . L t ouis Falkenau , S ate assayer of San Francisco , tells us that if the slag dipped off is powdered and panned and old crucibles treated in the same way , there i s no o l ss in melting . And also , if the bar has been properly melted and m ixed , the chips will ensure a control which he considers important . C HAPTER V.

C C ! ON ENT ATION .

In the begi nni ng of th is series of articles , a rapid summ ary w as given of all the various processes em ployed in m illing that seemed t o be of m om ent . The most m inute details have been explained in con nection with the extraction of the free gold . We com e now to the consideration of the valuable residues sti ll remaining in the pulp , to which the generic name of sulphurets has o been given . As the financial standing of g ld mining — to day depends exclusively on the ability to extract all i the value in the ore, m ost careful attention s paid to the concentration of these sulphurets at a small expense from the worthless rock into a paying and portable product. Rival states have waged a bitter controversy over this ’ tt s e ma er of concentr ation , contending that each one s p cial process is the best and should be m ore largely adopted in other places . We refer to the radical variation in mill practice as pursued in certain localiti es of 0 0 10 a rado n d in Cal iforn ia . The author is free to confess that he is prej udiced in favor of the California method , as giving a higher percentage ultimately , in all the sections a so far investigated . However , the method must be ab o lutel y correct and not a partial adaptation . In iron and copper pyrites (the commonest gold - bearing minerals) the maj ority of the gold is still in a meta llic state , microscopic leaves in the fractu res of the mineral, and if pulverized to sufii cien t fineness can be cau ght 86 HINTS ON AMALGA MATION .

l is i c a with quicksi ver, but the expense n re sed i n a pro o er hibitiv e ratio , wing largely to the small duty p formed

- by each stamp per horse power consumed . Again , the sulphurets have been so depleted of their values that it is only possible and advisable to save them where they have more value than the gold they still contain , and where the cost of concentration can be done w ithout additional expense beyond the first outlay in plant. The first condition is obtained by the demand of lead an d copper smelters for an iron flux , and their nearness to l the m ines . This , and this on y , has brought the Gilpin county method into a prominence which it does not war it rant. R em ove the smelters from Denver , and w ill be found to be ec onomically impracticable to save the con cen trates of that distri ct after the method of milling em ployed . We are not try ing to convert the millmen of that district to our way , but the maj ority of gold m ills have not the good fortune to be in such close proximity to smelters , and it is suicidal to pursue such a method any Bl where unless as propitiously situated . The ack Hawk m ills save an average of 80 per cent . , according to trust worthy sources , and , we honestly believe , this percenta ge can be raised to over 90 per cent . and at a less expense per ton , if they will stop trying to corrall every spec k of the free gold inside the m ortar . We wish to be very te minu . so that the other districts of the world can j udge in regard to the feasibility of the process . We ha e min s in this state in whic the ore i s very m v e , h si ilar to that of G ilpin county , the value all in the l 0 su phurets , which are working over 9 per cent. of the a assay v lue, and at a less cost per ton . Of these the G G T most notable is the olden ate, of uolumne county . We would advise any person who is considering the rela s tw o tive merit of the processes, to make some inquiri es 87 HINTS O N AMALGAMATIO N .

first, not from the manufacturers of the machinery , but from the own ers or superintendents of some of the sui phuret m ines in this State . It is not a question of slow fi ne or fast drop , but of high or low discharge, and the ness of the mesh of the screen . We are all trying to save as much of the value in the mill as possible and at a m inimum of expense, and to do this we have to harmonize the two distinct processes e of amalgamating and conc ntrating , and not unduly favor one at the expense of the other. Now gold has a very high specific gravity and yet be i l comes so fine that t floats . It is a so malleable, but n not often brittle, and , therefore, is commi uted very little after being freed from its enclosing gangue. Sulphurets , th on e other hand , have m uch less specific gravity , and are always brittle, which brittleness in creases di re tl in c y as their richness the precious metals . Expose fine sulphurets for an instan t only to the air and they will float on the surface of the water for m iles or till i submerged by the water fa ling an inch or more . G0 at any time below any of the mi lls of the Black _ i Hawk district, except immed ately after a heavy storm , and the banks of the gu lch will be found lin ed with sul hurets p , while in the eddies , all the detritus is composed of pure concentrates . G o below a California mill, prop erly handled, and only traces are found on pan nin g, and none is seen with the naked eye. The assay of the tail G ings for each ton in ilpin county may be low , but the aggregate in a year that can be saved , is so large that it seems almost crim inal to allow such a loss to exist. The keynote of this loss is owing to the unnecessary sli-ming of these very brittle sulphurets . First, the 14 inches or more that the pulp has to rise through , before dis charging, keeps all the ore to be struck so m any times 88 HINTS ON A MALGA MATION . by the stamps that the sulphurets are ground to a slime and this is secondarily aided by the fineness of the fre screen openings , but only partially , as we have very

1 2 - quently had to employ a No . punched slot screen on

California ores , to save all the values . The output of

- this is as fine as that of a 50 mesh wire screen .

Now , the greatest trouble to be found in concentration , e are is to save th slimed m ineral , and often the slimes rem oved with a point box an d settled separately in order e to make any showing at all satisfactory . It is , ther fore, obligatory to crush as coarsely as is consistent wi th the loss i n the tailings , which loss must be located , whether i n the sand or slimes . If in the sand , finer crushing is required till we are satisfied we h ave reach ed the m ost practical, that is, economical efficiency . Of course it is advisable to save all free gold possible with i the qu cksilver , but not to such an extent as to ruin the r concentration of the remaining values . No matte how ai fine the sulphurets are pulverized , they will still cont n free gold , and even after roasting this free m etal will not be absorbed by quicksilver ; but it is only with a th chemical agent that e gold is saved . If impartially considered , all will agree that the obj ect of stamping is to save all possible value in the m ill , and the observa tion that can be m ade by any one below the mills em f ploying the di ferent methods, should practically prove the advantage of the process employed in this state .

As there are tricks in all trades , there are certai n points in regard to the handling of concentrators and their pro duct which will m aterially add to the efficien cy of the work performed . With some styles of machines , a great advantage is gained by sizing the material to be treated “ ” w ith the aid of spitzlutten or as cending columns of a r i w ter under va y ng pressure , but this is not neces sary 89 HINTS O N A MALGA MATION .

with a shaking table working without a j ar . In fact,

unless there is an undue proportion of clay slimes , the

- - side shake , endless belt , machine will do its best work

on ore j ust as it leaves the battery screens , and sulphurets will be separated by the machine which require great care and ingenuity to save after its deposition in the

concentration tank . A vann er in perfect working order should show the fol

lowing state of aff airs ! First, no j ar whatever, on plac

ing the hand on any part of the upper frame ; second, a I thickness of pulp on the bed below the ore- spreader of A

inch , slowly flowing towards the foot of the machine,

with a smooth surface and no ripples , and this curren t

must not be faster on on e side of the machine ; third, a

sand edging on each side, along the flange of the belt , 2 of equal width and not to exceed inches ; fourth , at

the foot of the machine, the tailings to escape towards

the middle of the belt , leaving the flanges and a small tri angular s ection of the belt free from sand and exposing n clear rubber ; fifth , the sa d to be kept in view up to the rear side of the clear water box , but showing no dry

fingers ;sixth , the sulphurets to be passing over the head of the machine in bands between the clear water j ets and

showing absolutely no sand or slimes ;seventh , when the belt leaves the concentration t ank , that it shall be cleaned i th h of all the sulphurets ; e g t , that the concentrates de posited in the box and saved by the machine shall be also saved by the operator, and not allowed to escape in the overflow water.

First , no j ar . In setting up the m achine , the posts and sills are mortised and placed in position , with the key s driven i n on the outside of each post. Then the shoul ders on each post are cut to scant width and full depth ; 4 that is, for a foot machine the measurem ent between 90 HINTS ON AMALGAMATI ON .

o s 5 p sts call for feet inches , but the shoulders are cut an d to give a distance of 5 feet inches , when the lower frame of the machine is put together the bolts are driven in with a sledge, almost cementing frame and n posts . If through shri kage, later on , the m achine gets loose, iron or hard wood wedges m ust be driven in to t form a ight j oint . The two rollers underneath the an d machine must have no lost motion , must not strike the sides of the lower frame . The lost motion is taken up by tightening the two cross tie rods equally . The pre v en tion of striking is accomplished by moving the roller i either way t ll it clears each side . This is done by loosen n u ing the t of the rod , on the side the roller should go , and tightening the nut on the opposite side (the one which See is striking) . that the flat springs , on which the a shak ing t ble rests , do not strike the lower frame, and where one does , drive in the lower spring suppo rt . Take up all los t motion of the end rollers , by the gudgeon caps , and see that there is none also in the j ournals and brasses of the shaft , nor in the spur wheel and spring

. L but crank shaft ast , m ost frequently overlooked , ex amine each one of the little rollers over which the belt travels , and move the chairs till there i s no side motion , r but that they will still tu n easily , and then fasten each chair by driving a wire nail or two into the upper rail, in front of the chair .

Second , have a proper bed of pulp . Put a straight edge across top of lower frame and with spirit level make it practically level across , and then place machine on dead center. Take a piece of wood j ust two inches long and place between upper rail and top of each cross piece of lower frame , and raise or depress lower supports by the bolts passing through lower frame , ti ll this wood j ust

' passes easily un der lower rail everywhere . The small

92 HINTS ON AMALGA MATI ON .

of the crank - shaft than on the other and the sand is sensitive to the slightest vari ation . To overcome this , d we have two rem e ies , the first and si mplest to remove

- and bend the spiral drive spring, at the head of the machine , inclining the point the way the sand is wanted

a . to t r vel The second is , to move the entire main

1 - 32 1 - 1 6 shaft , to inch , in o r out , as the case requires ; out, i f the heavy sand corner i s on the sam e side as the shaft , and in if the reverse is the case .

Seventh . In order to be sure that the belt is cleaned of sulphurets after leaving the main tank underneath the machine , two series of j ets are directed agai nst it above and below , and the pipes must be frequently watched to see that the holes do not clog , most particularly dur ing the tim e when the accum ulated deposits are with drawn , and the water rapidly lowered in the tank till it may not subm erge the belt . It is also very necessary to observ e when we lower or raise the machine , that the belt is not ei ther raised completely out of the wash water, or sunk so deep as to cause undue agitation .

When raised out of the water , the conclusion is obvious .

If sunk too d eep , the belt and flange throw the water back and forth so violently that it slops over the sides of the box , carrying sulphurets as well as making everything sloppy ; but the chief fault lies in the fact that the concentrations do not settle here but are carried a way with the overflow water . With the least agitation too much escapes in thi s way! This overflow contains the richest in value as well as the finest in size of all which is saved by the m achine, and this brings us to the consideration of the very important subdivision No .

8 , namely, for the operator to collect that which the ma o chine has saved . I t is i mp rtant , but frequently over O HINTS O N AMALGA MATI N . 98

is looked . Th e mill doing good work , according to the

assay of the final tailings , but the product does not

tally with these assays , owing to lack of care of the concentrates after the machine ha s extracted them from

the pulp . Some m inerals , notably nagyagite and black i tellu r de , largely saved by the machine , will float as a

scum on the water of the tank , and run away with the

overflow unless it is forced under the water, and the

sam e is true in a lesser degree , of all the sulphurets .

To overcom e t his , we always place a piece of rubber

- belting in a sem i circle , around th e inside of the over

flow orifice , which extends at least two inches below the

surface of the water in th e tank . This requires all the material to be thrust under the water before i t can escape ;but that which does escape should flow through

- a very long series of dead water boxes , in which are placed num erous obstruction s to the flow . One obstrue tion is to place cross - pieces at intervals which extend nearly to the bottom of the box ; while another obstru c tion is to frequently transfer the current through a sur face orifice to another box in which the cu rrent runs in the opposite direction , and the two together are very i efli c en t. A peculiar slime box was lately brought to our i observation , in conj unct on with a patented slim e con e c n trator, which appears to be of exceptional value , as presenting great obstruction to the flow of th e solid

material in the water. We append a sketch of this as i of interest , only rem ark ng that the wings are remova

ble . (Fig. These devices prevent as much loss as possible in the

slimed material while the machine i s running , but there

are other losses to be guarded against as well . Each machine has constantly on its bed a greater weight of

sulphurets than i s comm only supposed , which remains 4 9 HINTS ON A MALGAMATI ON . uniform as long as th e pulp flows on it and i t i s kept in agitation . Stop th e machine and pulp and allow the water to run and this accumulated load i s rapidly

- washed into the tail race , a total loss , unaccounted for t i by the assays of the a ilings , and t i s a very great loss as well . So that on stopping the machine temporarily , always turn off the water and when stoppi ng for some

- fl tim e , as durin g clean up , always work o the load on

P ig

Modern Machi n ery.

the belt before stopping the m achine . A third source of loss is the careless removal of the concentrates . Twice a day the accum ulations are hoed out into a drain box , placed in front of each machine , and the surplus water , after settling by blows or stirring, thrown back into the

- concentration box . Be sure that the wheel barrow or

- e car i s water tight , and do not fill it more than thre fourt hs full , as in moving it becomes almost a liquid , from the water held i n suspension . Have a separate room for storage which is tight , and save all spillings ’ from shoveling, etc. , as they count in a year s ti me .

In spite of the most careful settling , the concentrates r 1 will car y at least 0 per cent . of moisture , which should M M HINTS O N A ALGA ATION . 96 be eliminated as a m atter of economy if for no other

ea s . h r on If th e sulphurets are c lorinated on the ground , thi s excess of water increases the consumption of fuel in l roasting . Genera ly, however , the concentrates of one m ine are too l imited in quantity to warrant the erec tio n of a reduction plant , and therefore , they are period ically shipped to sm elter or other custom reduction works . This shipment requires long wagon hauls , be sides ra il road transportation , for which the expense charges are always based on gross wei ght . It i s easy to see the loss in cash returns on the ore when at least

- -fi fth one tenth , and often one , of the gross weight is barren . water, which can b e removed at the m ill before shipment with only a little trouble and at a very small expense . If dried as soon as removed from the machine, th e sulphurets do not oxidize , cli nker and cement to gether, but allow such a thorough m ixing at all times as to get accu rate sampling and assays .

The sun is , of course , th e cheapest drier, but its use i s of doubtful value , if th e concentrates are dried on a the l platform in the open air, as wind will very quick y scatter several per centum , as soon a s they become dry . e To us e sun heat , a room must be construct d , with the three sides consisting of panes of glass and ventilators in the roof . In other words , have a conservatory with ou t the glass roof . This room need not be very large, as the concentrates , as soon as dried , are shoveled into a storage bin , where they are sacked , sampled , weighed

- 20 and shipped . For a 20 stamp m ill , make the floor the if feet by 30 feet , putting room , possible , on the sunny side of the concentrator room , and place the bin at a lower elevation than thi s floor . l e and it For artificial drying, very litt e heat is requir d , ca n be procured from waste steam , or any scraps of 96 HI NTS ON AMALGAMATI ON .

s wood chip , etc that are handy . The top of the drier is

made of sheet iron with raised sides . When the sulphur t ets are nearly d ry , hey will run li ke quicksilver on

being touched or sti rred . In using steam , a coil of pipe

is placed underneath the plate , which comes from the engine and whi ch discharges the condensed wate r and

steam outside the building . In using fire direct , i t i s w necessary t o build a regular drying furnace , ith a rela

- tiv ely large fi re box . The simplest form i s to place the fi r - iron tray directly on the e box , and create the

draught with a short piece of pipe at the further end .

However, as in all cases it is better to do well anything th that is undertaken , we would advise e erection of a

‘ l fi r - regular drying furnace . Thi s wi l consist of a e box an d bridge at one end of the plate and a shallow space

under the plate from the bridge to the flue , all to be

built of red brick and fi re clay .

As soon as the sulphurets are dry , they are shoveled

into a storage bin , till wanted for shipping . In sacking

them the closest woven canvas should be used , and before each sack is sewed a sample is taken with a tryer

such as used to sample butter, or made by splitting

- a half inch gas pipe . Another satisfactory method i s

- to use a quarter inch auger . Do not expect any check on the value when a pinch is taken from t he top of each sack , as a sample must extend clear to the bottom .

As stated above , the slimes taken from the overflow settling boxes are invariably very much richer than

the coarser concentrates which are collected each day ,

but they are generally very lim ited in quantity . On o account of the small amount , these boxes are nly cleaned occasionally , once a month or less frequently .

When these are dried by them selves , it is imperative that they shall be uniformly scattered over and m ixed HINTS ON A MALGAMATION . 97 s with the accumulations already in the storage bin , or the m ine i s never credited with its full value . If sacked by themselves , the one or two samples taken of them an d m ixed with the 1 00 or more samples from the vaster amount of the coarser accumulati ons , will not be nearly as accurate in giving the average value as if all had been thoroughly mixed in the first place , and the 1 00 o r m ore samples should each contain their proper proportion of these rich slimes . If the space at the m ill will allow it , we would advise sampling as done by the smelters . The concentrates are shoveled into sacks , but every third , fift h or tenth shovelful is put into a separate pile till all the concentrates are sampled . If the result r ing pile i s still bulky , eve y other shovel i s put into the sacks , and then the remai nder is shoveled into a cone , spread out , and quartered down till the assay weight i s obta ined . With the necessary appliances this can be done very quickly . Beside a broom and square

-n pointed shovel , there are requi red a sack iler, and i ron cross for both of which ideas we are indebted to a well

- known sm elter near San Francisco . The sack fi ller has been copied from that in u se on potato ranches , and i s an iron cylinder with a funnel top , which i s inserted into each sack . (Fig . The iron cross is made of two pieces of i ron at right d angles , an two sizes shoul d be kept on hand , both i n height and circumference . With this cross , each shovel ful is dum ped direc tly over the center of the cross , and on smoothing the resulting cone , the quartering divis i ions are already accurately determined , of uniform s ze and p osition . (Fig. CHAPTE R VI .

MP SA LING .

I t is of very rare oc currence to find an assay oflice attached to a gold m ill , but if any intelligent work is done, it is imperative to have absolute technical t accuracy at frequent in ervals , and not trust entirely e to the eye, which is d ceptive , no matter how finely trained . In silver mills and other reduction works a qualified assayer who also po ssesses an i nsight of t he methods in metalliferous chemistry, is absolutely essen techn i tial to the success of the enterprise . Such wide

n - cal knowledge is ot demanded in gold mill practice , s u though , of cour e, of appreciable benefit ; but, th e s perin ten dent or one of the employes of a company must be able to make an accurate determination by

fire of the values i n the ore and tailings when required .

G old is worth per ounce, and occurs very i rreg rl ula y dis sem inated in the accompanying gangue, when its t in a free state . O n account of value, a small par icle in that piece assayed , might enhance the estim ated value of the body of ore under investigation m uch beyond the working value afterwards determined in practice, and the opposite results m ight also erroneously be obtained .

For th is reason , the determ ination of the value of free

- gold bearing quartz in place, by sampling and assay , is a very uncertain method of fixing the value of a mine , an d yet it is the one universally employed by experts , and these experts in gen eral , are entirely unfamiliar with the existing conditions of that particular section . As pre

100 HINTS ON A MALGAMATION .

cretion or selection , as that is the way it would be prac tically worked in a mill . If practicable, have a small assay crusher, and reduce the coarse uniformly , as the quartering proceeds , thoroughly mixing after each reduc A tion in the size of the pieces . diagram of the m ine where each place is sampled , with its corresponding num er is entered in the note ook , an d the samp es a e b , b l mr sacked and sent to the assayer for tests , but each sa o 1 ple should weigh 5 p unds , and 5 pounds is better. We wish to state at this point that the value of a m ine i s not always determined by sampling, but it is the only resource on which an expert foreign to the conditions of a certain section , can rely for his first j udgment i of the property , wh le it is the natural preli minary to a

- a practical mill test . Should the vein be too large to d mit of taking one sample across its width , a series of samples are taken in each cros s- section at absolutely equal distances apart in every case. After the assayer returns the individual values to the expert, he i s able to lay out accurately the length and

- direction of the ore shoot or shoots , in the mine, and

- i whether the ledge matter ntervening, has a value that would warrant its exploitation w ithout reducing the t total output prohibitively . He now instru c s the a ss ayer to take a weighed proportion of each sample, good or

t - o bad, hat occurs in the ore shoot, and make a laborat ry

- on n working test, on amalgamation an d subsequent c ce i trat on . This will serve as a guide for a final mill test,

but only as a guide, as the mechanical work of the mill will generally give better results than any hand-test made, though only in total value saved , and not n ec essarily in an increase of either the free gold or sul p hurets . Unless frequent and large samples from the

mine are taken as stated above , the resultant mill work HINTS ON A MALGAMATION . 101

r will be very disappointing to the owne s , and detrimental h to the reputation of the expert imself, unless the bla me is laid on a supposedly faulty mill . This is frequently done, and very unj ustly , if a good amalgam ator is in

. G e charge rab samples of a few select d pieces , j udged by the eye, to be both average, poor and the highest

- grade, can be assayed , and a test of the ore in 25 ton lots run through the mill, and the resulting product be found to be not over 60 per cent. of what was expected from the average of the selected samples , w hen accusa tions of dishonesty are hinted at and often e xpressed . It seems to be an accepted axiom amongst mine owners “ ” that a custom mill will always cheat, when the fault lies entirely with themselves i n estim ating what ought of to be returned , according to the assays one or two little pieces of rock , and hum an nature will force them to take , if not the better looking rock , at least, clean ore, neither of which , it i s readily seen , can be any criterion of a mass of ledge blasted dow n and always carrying m ore or less of the barren country rock whi ch has to W h be handled with the clean quartz , on ich they form their j udgment . I have gone so fully into a matter that does not seem e the to be pertinent, because, as mention d above, mills are generally so unj ustly blamed . Several years ago ,

I was requested by a prominent railroad man , to make 2 a working test in a neighboring mill , on 5 tons of ore from a mine he held under bond . While the ore was I being brought to the m ill , was asked to make three assays , one of a highly mineralized piece of rock weigh

- ing less than a pound , and suppo sed to be so high grade n t that similar rock was o shipped to the m ill , but was sorted out for sale to smelter . The second sample was one piece of about pound weight, taken from the 102 HINTS ON A MALGAMATION .

th e mine and considered about average, while third sam ple w as their average of this entire lot an d consisted of four little pieces of clean quartz . After m aking the as says and finding the highest grade did not go over ih $1 0 per ton , while the average of the three , even I e cludin g this one, was under $8 per ton , examin d the ore that had already been stored in the bin and was positive it would not stand up to the assays . Therefore, to protect myself beforehand , I informed this gentleman that I wished him to bear in mind a comm on report that custom mills invariably retained a part of the proceeds n for their personal aggrandizement . O the completion ten of the test, the resultant amalgam netted per ,

n 50 . the concentrates $1 per to , and the final tailings 3 per ton , giving a total of per ton of ore treated . On making my report the question was i mmediately asked , why the returns were so low , when the average of the prelim inary assays showed $8 per ton ; but, calling to my help the previo us statement and the required ex planati on placed the situation most forcibly before this gentlem an . It is , therefore , well to have a most thor o l ugh sampling of the mine, or trust entire y to the sam ples taken in the mill . Assays during the steady ru n of a mining property are n rarely taken in Califor i a , ex cept in the case of foreign corporations , and it i s a very great mistake . The ex pense of an adequate outfit is very slight , at a maximum 500 price of $ , and the cost of all the assays per month ,

‘ would make no m aterial difference i n the profit, while n an m y cases great losses would be prevented . The com

mon practice i s to guess at the value of the ore, and the

s . n im lo s i n final tailings , by panning Though it is ot perativ e to assay by fi re all the ore of a free-gold mine i da ly , yet an occasional assay of a new stope opened, or

104 HINT S ON A MALGAMATION . e hand sampling is as corr ct, gives less trouble, and is always available . Hand sampling has its points to be observed to ins ure accuracy and very few appreciate the wherefore that it should be done in one way more than another. To get a sample of the quartz before entering the battery , it must be taken as it leaves the feeder to enter the throat of the mortar . Use a dipper, a n d see that the same quantity each time drops into it .

- Be sure and be regular in time, either a half hour or hour , that each sample is taken , and at the end of the d specifie number of hours , reduce the whole systematic ally by finer crushing , mixing and quartering . The reason that the outlet of the self- feeder is the only safe place, is that the ore is here the m ost thoroughly mixed are and crushed to a more uniform size . Car camples only grab samples , a little taken at random from the top , generally the finer pieces , or, if a coarse piece is taken , too great a proportion for that time. From the car the ore is separated by the grizzly into the fines and coarse, but the coarse is broken by the crusher, and , in passing through the ore bi n becomes fairly well mixed with the fines . It is then remixed in passing through the automatic feeder, and , being delivered by that to the battery in such a small quantity and thin t stream , all of the ore for that instant is caugh in each a sample . We consider this s m ple of small importance , as we get immediate returns from the free gold , and it is onl y the value locked up in the sulphurets that would probably escape us , which we can only determine after the free gold is extracted . Therefore, the important sampling begins at the end of the plate surface . We have two places at our command , at the inlet and at the outlet of the trap . It is unsafe to trust a sample taken below !the lower apron plate as there is always the p os 0 HINTS ON A MALGAMATION . 1 5 sibility of a little amalgam being broken off in passing the dipper along the edge of the plate. If it can be done and the whole stream covered , the inlet to the trap is the better place, as the outlet may carry more sulphurets than the average at one tim e or the other . The under current will accumulate sulphurets to a ceratin depth , whe n the increased pressure will throw them out in a o bunch , and the pr cess is begun over again . In takin g all these samples , a separate dipper must be kept for pulp, as well as for tailings . No overflow whatever is n allowed , and the sample is put in a covered ca , while the dipper is thoroughly rinsed out each time. The jar of the mill will very rapidly settle all the solid matter w ff i hen the clear water is very carefully poured o , a o th lowing none f e slimes to escape . In very exceptional cases it will be advis able to evaporate all this water i n for a comparative test , but the d fi ere ce will be found ima r iable to be pp ec . At the end of the time set, the resultant sample is thoroughly dried , m ixed , quartered down and assayed . Should a regular daily assay be made, which will give a correct weekly average , i t is only necessary after pouring off the supernatant liquid , to mix most thoroughly the residual slim es into a con sistent mass , and then , while stirring , take out a dip pertul and dry that for the assay . o The most importa nt sample, and the only one abs aliin s lutely necessary in a gold mill, is that of the t g as they leave the mill . These should be taken each hour i from the foot of each m ach ne, and never, under an y circumstances , from the waste sluice where there might n i be a partial reconcentration of th e taili gs . The d pper is drawn steadily across the foot with no pause at either end where a great proportion of the tailings leave the machine . This sample is settled and manipulated as O 106 HINTS ON AMALG AMATI N .

' o n e described for t he pulp , but at the time each is taken , a duplicate should be examined by panning , to see the amount of visible sulphurets escaping . The fore man should compare the assays of a sample with a panning test of the same, and after several examples can approxim ately determine the good or bad working of any particular m achine, from panning alone . In mak f ing these tests, the color of the sulphurets are so di ferent

Modern Machi n ery. FI G . 27.

from that of gold , that they do not show on a dark ground, and they are so fine an d light that more care f must be exercised , and , in reality , a di ferent method employed . The best color is pure white, and where

t ff - nothing bet er o ers , a tea saucer i s far preferable to

- i a gold pan . However, now , there can be procured white n e ameled pans of all sizes , but choose those with very

fl aring sides . A patented instrumen t is now specially

’ l l CHA I TE R V .

CONCLUSION .

With the suggestions in the foregoing pages taken . . s a basis , it should not be difficult for any one to adapt them to the local conditions so as to increase the effi cien P ut cy of the work , and to correct unknown losses . in a concise form , the summary would be .

l st. Beware of grease. 2 n d. Am algamate dry .

3 rd. Turn over the pulp as frequently as possible near the battery . 4 h t . Use all necessary water inside the battery , and do not divide it with a spray outside. th 5 . Have the battery water warm , at least above a minimum temperatu re of 50 degrees , better above 70 degrees .

6 th. l n Use no acids on the p ates , or lye or cyanide , inside the battery . 7 th . Dress the plates at least one a day , but remove

th - as little of e am algam as can be prevented till clean up .

8 th . Most thoroughly clean the daily amalgam at once .

9th - . Systematize regular clea n ups and do not remove e unn cessary dies . l 0 th . Retort out of doors and do not use charcoal or coke for fuel . 1 h 1 t . See that the concentrators work noiselessly and withou t a j ar . 1 2 th . Watch the tailings of the concentrators and see

that the loss from the m ill is kept at a mini mum , 109 HINTS ON AMALG A MATION .

t e 1 3 th . Be very sure hat your ore is adapt d to the

- free milling process . All gold- bearing ore is not adapted to the free -milling

an d i i i i ; u defi process, on open ng a m ne th s po nt m st be

n itely determined before the reduction works are erected .

An assay will determine the value, a panning test will

demonstrate if any of the gold is free , and a laboratory working test will inf orm us of the amount that can be expected to be saved by amalgamation and concentra

tion ; but if the final tailings are still very high , some t method has to be found o recover this value. Should

the high est percentage remain in the tailings, cyaniding t must be ri ed , or chlorination , if the gross value of the

ore will stand the expense, while sometimes a combina

- tion of all must be used . If the ore i s very high grade

and refractory as well , smelting of the mass is the

proper procedure . Neither cyanogen or chlorine will

economically act on coarse gold , and both processes

req uire crushing . If our panning tests show coarse gold , and the value is too low for smelting, we have to crush ,

and then , either before or after the chem ical work , can

secure the coarse gold by amalgamati on . The great es t detriment to successful milling is the presence of tel l urium compounds , except the telluride of lead and cop per . These cannot be amalgamated or concentrated to f a practical e ficiency, and yet if these ores as usual , show

great richness in free gold and coarse gold , they are n m illed , and , as a consequence , hu dreds of thousands of

dollars are run to waste, all of which would have been

saved if the whole m as s had been shipped to a smelter .

Therefore, examine the ore for tellurium , and if of suf fi cien t richness , ship , even though at the same time rich

in free gold . C the s In Tuolumne ounty, California , many of mine 1 10 HINTS ON AMALGAMATI ON .

an have chimneys of ore very rich in free gold d tellurides . and the early history of a few of them , show that they were formerly abandoned, though known to be rich , because so little of the value could be saved . One mine can be specially mentioned as a type, namely, the Black

Oak . This mine very nearly ruined its owners , by the

- attempt to work by free m illing alone , was bonded twice and abandoned , and within two years from this time, had been ofl ered on long bond for a small figure . To a day , it c nnot be bought, since means have been found to save the $ 10 to $50 per ton previously lost. No special method has been devised , but reduction was at last adapted to com mon sense . Instead of using the mill r l process as the sine qua non , the ore is now pa tia ly sort a ed , the richest shipped direct to the smelter, the bal nce crushed wet by mill , amalgamated an d concentrated . The tailings are impounded and worked by cyanide pro cess, and the concentrates shipped to smelter .

On ores which are purely adapted to concentration , it ' becomes very frequently a delicate question w hether to employ stamps or some other crushing device . In this case, the obj ect is to have the grain s of sulphurets , while absolutely freed from the gangue, in as large a size as possible, and wi th a m inimum of slimes . Stamp mills d for amalgamating, make a larger proportion of slime mineral than Cornish rolls and devices of the type of the

Chilian mill, for the reas on that the pulp will escape re from the latter form s, as soon as crushed to the quired fineness , while , owing to the height of discharge in a stamp mill , quite a proportion is struck several times before escaping . Here the character of the ore can s be divided into two classes ! Cla s A , in which , if it is found that the ore carries enough free gold to pay s e working expen s, the process as minutely described in