P-36 Prospecting For Gold Ores

\ ?

First Second Third Fourth Fifth

Pamphlet No. 36

STATE OF IDAHO C. A Botto .i'sen, Governor It

IDAHO BUREAU ¥' 1~INES APD G~~OLOGY A. H. Fah enllald, Director

PROSPECTTI' G FOR GOID ORES By

John HeJlington Finch

Univerpity of Idaho HOGCp"T, Idaho

T::dition, Edit.ion, :Cc1i tion, Edition, ~di tion,

June

1932

1933 Hay 1934 Hay 1939 Harch 1953 IvJay

T

IE OF CONT::!HTS

Page 1 1 1

Introduction - - - Tho

pros~octor

w

Pioneer clays Preparations for prospcc ingKn ovrlodgc of :>rncti al mining des irable Honey for r>rospocti gGrub stakes - - - - - - -' - ~ Equipment an0. suppl as - - Usefplnoss of tho g ologistGcophycics - - - - ... -,.. .... Main kind of ::--oc1cs - - - - - - - Dofinj.*::,:tons of torr. - ... - - .. Books upon rocks un ~ ~''',incrals ... Structp.I'o nnd toxb'''o of rocks - ,.. Pedimentnry }:'ocks - - - - - - :Sros:i.on o.nd GO i:- 1onta tiOlT Conglomornto, a.nc:otono, 0;10.10, liT'10stono Stroam c1.cpos:tt - - - - Hind doposi ts - Glacial doposi s - I'otane>I'Dl1ic rocks - - Gneiss, schist T1.D.rblc, sorpcniijnoIgnoouo rock~ - - - - - - - '!"" - - - - - - - &gm - - - - - - . - - - - - - - - Batholiths, st C2CS, dikos, oi11s, Gho;:;ts-

..

2 2 2 2

- ...

3 4 4 5 5 5 5

--

VOICD..l100S

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-

-

-

-

-

-

-

G ("j. (,.)

8

- ...

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Finspro voins - - - - - - TJcddcd (l11d bIn: .1~0~t veins

G011utry rocks

u

xtJ:'"l~'[Jivc

rocks- - })o~~"'1!hyrlos - - - - - - - - - - ~fft'.Glvo and 0 pJOGj.vo volcanoes Broccias, trLff , obciJ.:tan, :,!ur'liceRolo.tions of roc!m and 0 os Tho o3rth t c intorlo" Gold Ol"OS and ,.cic1 rocks .., ,';oll~t:i.ons and "f<"octs of hoatOros and nngr'1D.S - - - - ,.. - - - - F].uid 0:':'0 rosi ~"()S from mo.r;F!.o.S ~. Gaces j.l1 oro s JJ:t~.ons Voin structnro - - .. - - - - - Frn,ctrros, ?:·"p.l ts, .'. i:)s11.ros -

(""~.

.......... .-

Intr",rJivo and

G011gC -

6 6 6 6 6 7 7 7 7 8 8

.. -

~

..... .., -

8 9 9 9 9 9 9 10 10 10 10 10 10 10

11 Voin matorj.o.ls 2nd torml ology - - ...., Oro, T;"'inornli Z t tl.on, gal1.gl1o ... 11 11 ntriko o.nd clip - - ,.. - - 11 /jano of O~'.iC.Cl t: .on .:mel ~:n.1.1 ;.>!"").ido zone ... Prim.o.ry (hypog no) cmd so ~ondo..ry (CUpG rg:no) oros- 11

"'"

TABIE OF CONTENTS (Cont'd) Page 8ubdivis:i.on of the prima sulphide zone - - - - _ - __ Zones of depth nnd emperaturo at timo of depooitionTemperaturos at tim of doposit:i.on and at preGont __ Bpi tho rna 1 oros __________ ... __ • ____ _ Hosothormal oros ______ .. ______ .. __ _ Hypothermal oros _ _ _ _ .. _ _ _ _ _ .. _ _ _ _ _ _ Other inflv.onccs cat sine dOlmHo.rd changos in 01"00 __ Contlnnity of lall rock _______ .. Chango of Hall rock _ _ _ _ _ .. .. Erosion of veins __ .. _____• ___ _ Effects of dopth of orocion Tolesco~od veino _ Blind veins _ _ _ ... _ Tho oxidized zono _ _ __ _ Oxid1z:od oros load a SUlphide oros Processes and rosul :J of o::~idD.tion __ ..

11 12 12

13 13 14 14 14 1L,.

- ........ -'

14

- .. - -

16

15 16 16 16

17 Leaching _ .. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 17 Iron cD.3F)ing, gossa __________ .. __ .. __ _ 17 Oxidation of count rocks ______ ... - - - - - - - 17 Honey-comb 0.110. cugo. qnartz _ .... __________ _ 17 TJonthering _____________ _ 17 B10vT-outs _____ 17 18 Zones of un.dorground ,,,a.tl,,,i"·r gathered from tho surface Ground Hator, 'to tel" table __ _ 18 ~

de:~incd

I

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-

-

-

-

-

-

-

-

-

-

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Tho gathering (Hoat ring) zone __ Secondary Gu12)h· do enrichmont _ Gold onrichmentl nonr surfaco _

_ _ -

Lea.ching ___ _______ _ ~

Tho zone of diochnrg and circulation}SQcondnry Gl1.1ph· do cmrichmont - - Cementation __ The cto.rrnnnt zone -1Th; Zono of tC:L"od sl1.1nhidos Dopth of oxido..tion - - -I •• - Gold voin outcroDs _ - -:, Tho }Ie". of,L to~) of 0.1 vein- -. - - Topo~rD.!,hic indj.cn.tipns - - Other indicntionc ofl voj.ns - - ... - - - Forms cnd couroos of! ou-'ccrops- - Tracing f10nt - - - - - -! :. - - - - - The gold pan - - - -1- - - - - - - - - Penning f.loat, t,oil, g11.1ch travolsExceptiona.l conditio 0 - - - - - - - - In nl1oHoJ.j_de do of.!lts - - - - - - In landslidos In ctroC1.l11 grave s - - .~ - ~. - - - I

-

-

_ _

-

J.8

18

IG 19 19 19

_

I

tUlnr.

u.

-

-

8.,

- - - - - - - - - - -

-

- - -

-

-

- - - - - - -

-i- - - - - - - - - - -- -- --

In glacial drif· Surface oros

- - - - - - - - - - - - - - - -

- - - - - - - - - - - - - - - - - - - - - .Surfnce gold oros in coppor voins- - - ... Tel111.:~ido voins

Ie

18 18 18

20 20 20 20 20 20

21 21 21 21 21 22 22

22 22 22

;

TABlE OF CONTENTS (Conttd) Page

Favorable and unfavorable conditions tor gold ores- - - ...... Unfavorable: ,Great plains, plateaus, and shields- - Limestone regions- - ... - - - - ... - - - Excessive erosion since depos1 tion'" - Favorable: Presence of igneous rocks- ... - - - - - Combination of igneous and older rocks Small amount of erosion- ... - - ... - ... - !locky Hts., Coast and Cascade ranges 1.n

- 23 ... 23 - 23 - 23 - 23 ... 23 - 23

Ca21ad.ll - - - - ... - - - .. - - - .. - .... .. - ...

Nountnin ranges in tvestern United States ..

- - - - - - - ... ... ... 23-n - ...,. ~ - - - - 24. - ... - - - - - ... - - '/.4 - ... - - ..... - - - ... 24 ... - - - - - - - 24 - - - ... - - ... - - - 24 24 - - - - - - - - - - 25 - - - - - ... - - - ... ... 25 ... - - ... - ... - - ... - - 25 ...... - - - - - - ... - ... 25 - - -- ...... - - ... - ... - 25 - - ... - - - - - - - - 25 - - - - ... ... - - - - - 26 ...... - - - - - - - - ... 26 - ... - - - - - - ... - - 26 - - - - - - - - - - .. 26

Central Idaho -- -Igneous epochs and gold deposits of Idaho The Idaho batholith - - ... - - ... The gncissic8hell ... - - - ... Later i~noous epochs - - - - Age of gold de,onits - .. Kinds of gold depositsNorth-central Tdaho- - M ••

Pro0.tlction - - - -

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-

- - ....

Hinorals in veins - - VaJ.uos of oros- - - - South-central Idaho- - Volcanic rocks- - - - - - Kinds of veins- - Locnlities _ ... - ... • Dif2':'iculties of discovery - Other gold districts- - - ...... - National foroots - .. - - ............ - - The value of gold ,.. ... - - - ... - - ... ... Fooll s goM - - .. - - •. - - - - - - - The fire aosay- - - - ... - ... - - ... - - l.,That to do vrith a vein vThen it is found Locating a mining claim- - - - - Development - ... - - - - - - - Stay uith the ore- - ........ Trial chipmont - - Terms "lith finun~j.ors - _ Promotion - - - - - - - - - - - - - - Gold mines in Hootern History - - - - wo

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23 23-a

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... ... -

...

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...... ... - - ...... - - ...

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- - 27 - - 27 - - 27 - - 27 - - 27 - - 28 28 - - 28 ... - 28 29 - - 29 - - 29 -

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ILLUSTRATIONS :B'ollovTing Page Figures 1, 2, 3, 4, and 5 - - - - - - - - - - - - - Map showine gold lode districts - - - - - - - - - - - - - - -

20

24

+.

PROSPEC

11~G

FUn GvLD ORES

Th0DUCTION This pamphlet was prepared i response to an urgent demand from citizens interested in the up-building of he btate of Idaho, and from a host of mining people to whom the low prices of he base metals have brought great distress in recent times a.nd have roused a ne interest in the mining of gold" the one metal. for which the market does not fai. Unemployed e~erienced miners are search.- .• ing for gold .. a.nd many inexperien ed men \'-dsh to learn the art of prospecting •. The Idaho Bureau of ~dnes ana Geo ogy has received a constant stream of request~ for suggestj.ons and guidance in p ospectingl and the correspondence has becone " so voluminous that pamphlets cove ing the whole subt,iect had to be prepared for distribution to inquirers. The first of this seri~s of amphlets dealt with the search for and the operation of placer mines.:; Th call for it continues and it is now in its tenth· edition. ' . There have been so many quee ions upon t he methods of saving gold that a separate pamphlet has been writte by Professor A. vv. Fahrenwald upon the recovery of gold from its ores. 2 A fourth edition, revised and brought up to date, has been issued~

ROSPi1CT0R 'Ihe prospector of pioneer dars has passed into history and has not handed down his skill to the present gen ration. Up to this century he found practically all of our gold mines. His cr it had developed from oent\~ie~ of experience. Under his methods 1 the cost of f" ding our gol~ was less than it ever is likely to be again. Although often ting d 'W ith super,stitions and fallacies; such as fantastic theories of nature, fai h in t he divining rod, and other mystic devices that sometimes caused unnecess ry effort and led to disappointments, his . conceptions and his methods were n the whole sound and effective 1 and their revi val would be of great b.enefit t this state. In pioneerdaysj placers wer the easiest gold deposits to find, to test for value, and to work. Upon then the beginnings of Ielaho history were founded. Probably the b'e~t placers have be·n discovered;, yet important deposits may remain in out-of-the-way places.. Also, nost of t he gold veins that could be found easily, especially those near the old placer camps, have been developed and opera.ted, but it is believed tha.t gold mines are still to be discovered in central Idaho in regions offering le~s physical difficulties than confronted prosp~ctors of the old days, on a count of now forest roads and trails) the absence of hostile Indians, and t E; nearness of towns where supplles an°cl equipment can be obtained. v~alla Viall was the nearest supply point for the pioneers • . Also, deep mining was not d.one in the:: early days. The art of recovery of gold has made important advances ~ Ore not profitabl~ .for.erly may now be ;successfully treated·. All these conside ati.ol1s reCOml1Y~nd the search for gold. Some of the reasons for believing that gold rer,:.ains to be discovered in Idaho will be given., also the slirroundings in w ich it may be found will be described. --,-_.. .. .. Y Staley, '~h U~, u ~lementary nLet o(~s of placer mining," Idaho Bureau of ~dnes and Geology, 'Pamphlet No. 35 Fahrenwald, A~ W~, ttReco~ery·o gold from its or{;s," Idaho Bureau of hines and Geology, Pamphlet No. 37. \ .. ~

y

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The immense profits made up 0 the last year or two by the great base metal miners had diYerted attention from old mining. Along with this the pioneering spirit had waned .. both among miner and f'inanclal people. Now that the base metals appear to have been over-de eloped, it is an appropriate time to stimulate miners and men of money to find no gold. It is needed in the business of' Idaho and of the world" This pamphlet is intended fo for gold, even though he has had n

the use of' anyone who has the urge to explore technical training or mining e~p~rience.

Technical or scientific educ tion, alt;lough it would be helpful, is not necessary for the prospector. Howev~r highly he is educated, he has to learn by experi~nce. He cannot, by reading books, set forth into the mountains as a full~ fledged prospector. The bost this pamphlBt can accomplish may be to help any man to get started, who has n~ver pros ected before, and keep him from making certain mistakes. ' ;' Certain personal qualities a prospector must have: Courage, natural resourcefulness, good powers of obse vation" but, most of all, a tireless patience and physical energy. A new mine '5 not likely to be found on a sunner's holiday or a casual vacation. It was not unusual for the skilled old timers to hunt ovor great areas many years for veins b~fore anything satisfactory was located, and that was at a tim~ whel'l conspicuo s gold veins remained to be di.scover(;d. A knowledge of practical mining is more important probably than geological or engineering education. If' it is entirt':ly lacking, one bent upon prospecting should get a job for a time, if possible, around a sliall mine wh0re there is a variety of work going on, in orde to learn how to drill holes by hand and use explosives to blast rock, how to repare and put in mine timb0ring, how to sharpen steel, and to do otrwr ro h blacksmithing. If such employmt;;nt is impossibl~ to get in these days whe~ mining jobs are scarce, it would be wise to hire a practical miner for a time,1 or 'join one as a partner. i

for prospE;;cting

l~oney!

!

iVlining financiers and tho bilg mining companies possibly are now more inclined than usual to invest in thel (;xploitation of authf.mtic gold discoveries already located. But they ar8 r0~uctant, as th{;;y always havo been, to put up money toward the primc'1.ry search for nevi deposits, although gold has extra purchaSing power just now, market fO~ it is unlimited, and labor is plentiful. I

The prospector should f'inani himself in the hills, if possible, and thus avoid E;lntangling allianc~s. In 0 der to do thi.s, it was a conilllon custom in former times to work around the m· uS somewhere for a. part of tho year ana to use the savin's from wages tho ba~anco of tht,;; year soarching in the hills. qrub stakes I

Some men, however, prt;f~rre~ to s. pend all their time prospecting and sought a friend to supply money for .food rnd equipmunt. This \vas the "grub stake. If One or more people, having mon\,";.~y to e~arG and a confidence in the prospector, paid the actual cost of thE:; search 'in epcchan?e for a half interest in anything discovered. The prospector gave his Iskill and hard work. This idea was elaboratbd in various ways. Money was advancled sometiml-s by a group or s:yndicate. Partnerships in the field work Were commop, and wore vf;ry dGsirable on account of the !

2

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I

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possibility of accidents and sickness in remote places~ If the~e w~re two men working togeth~r in the fi<::ld. J the intt;:r~st of each was reduced to a. quarter, but. if both m~n were competent, doubl~ the amount of territory could be covered, and, because two heads are better thap one, the chanc~s of discovery were increased. Equipmwt and

suppli~s

It is a good plan to purchase essentaal food supplies befor~ starting into the hills. Such supplies can b0 6upp10mcntE::d from timt.: to timo by fish and game, and by fresh v~getables from st:ttl(jrs in the mountains •. A man working in thtJ hills consumes as much as four pounds of food a day. Flour, corn meal, beans, ham and bacon, dried fruits, coff~e, tea" sugar, canneq milk, salt, pE:pper, buttor, and syrup are the essentials to take along. Caution should be used regarding drinking wator. It is not so safe as it once was to drink from every l.llountain stream, The water Of springs and brooks at high altitudes may not be contaminat(;d, but if tht,:;re are human beings or live .. stock at any point up struam, it is ~dse to boil water befor~ drinking it~ Springe and wells in the desert occasionally contain injurious or poisonous mineral matter~ In desert regions, CaLl") should not be moved until a satisfactory wat(;;r supply for men and animals is assurod in advance. In IdCl-ho, c lothiI'l:g should be durablG a nd warm, o.nd ttwr~ should be one or . more complete changos,! It SOf!l(;tim(;;;S snows in mid-summer in the high mountains of Idaho and there are fr~quent cold rains. Boots are most important of &11. Cheap and uncomfortabl<:: boots have ofton d ef\.~ated thE'.: best of intentions in exploration. Strong, water-right, mining boots, hobnailud for climbing rocks, are tht: best. Heavy socks are n(.;c(;;ssary for foot prot~ction. Ther{; should b~ a t.,;;nt for shelt0r of hGavy enough canvas to shed hard mountains rains and to rBtain the h~nt of n stoV(; in cold weath!;:r. A knock-down sheet-iron stov<;; with oven, pipe, and sleeve to protect tent r~of is satisfactory for heat, cooking, and drying wet clothi.ng. Th(;l follo"'ing tools and camp equipment are desirable for one man: One gold pan, mortar and pestl~, one good axe, a round-pointed shovel, a good compass, medium s i.zed miner! s pick, prospecting pick, hGavy jack-knife .. magnifying gluss, na.ils, wuter-tight Ilk'ltch box, candl~s, acctyl~nQ minE:r' 5 lamp with two fivepound cans of carbide, two frying pans, covered kettle, coff~e pot, can opt:ner, baking pan, water bucket, small galvanized wash tub, tin platos and cups, knives, forks, spoons, soap, towels, cc.nV[1,S to cover bod and to protect packs wh~n traveling, a reliable untis0ptic, roll 0 f gauze bandage, C?nd a ft:;w simple household remedies. A man should not.slcep on tho ground in northorn latitudes, is convenient to carry. Tht;re should be pll;)nty of warm bedding,

A folding cot

Haps A good map sholrJing settl,;H0nts ,. streams, mOtlntFlins and trails, sho,.ld be taken along; also, if possible, a guologic0-1 map. il,iost of the ge;:ologicu.l maps of central Ic.~aho are out of print. They may be consulted in city libra,ries~ The maps havt; bt.Hm publisher by the t:. S. G(;.;ologico.l Survey" or by this bureau, with reports upon 10c(1.1 arQus .. and art;; bound in ,dth th~m. Tr~nsportati.on

In IClaho, automobiles c['"n novl bv drivcln to points within r~asonablt; dispro~pp.~t.}n~ +.et'rit.orY,~J_tbou!!h tri.D9 I")f ]00 rrdJeC\ or more ~o1l1d be :.,

t2.nce"')f

made beyond the ends of roads if a ithe possible gold-producing areas were covered. Away from the roads" pac animals (burros or horses) can travel to all points where camps might be established. From camps as headquarters, much rough olimbing afoot is necessary. In the Canadia.n wilderness, where a canoe and man himself take the place of ack animals, all equipment and supplies must be iOparcela that can be carried n a man's back over portages. The airplane has come into c in this country, Alaska., and Canad operations in Idaho to carry mail, dinary prospecting they are too e for real prospecting on foot. Sue the airplane only by a geologist.

romon use by government and company geologists • They are used in connection with mining light supplies, and men in winter. For orensive, Thoy only serve to spot loc~lities places would generally be recognized from

TH.l£

G~uLOGI8T

Probably the geologistts gre test usefulness in the search for gold is to assist prospectors in the folloYjin::> ways:

1. By describing features 2.

the surface tInt indicate veins.

0

By clarifying coneepd_on of veins and ore deposits, so that the diecoverer may be aided' estimating the possibilities in what he finds and develop or bandon it accordingly.

3. l'viost impor-tant of all, b mapping rocks accurately on the surface and explaining which of them, or which combinations of them, offer the best promise of co t.:lin:tng gold veins. In this way, geol..;. ogists have succeeded' blockirig off great areas in which ore is improbable, and in arrot-dng down to small regions the most favorable spots in wh '.ch to work. In cooperation vJith the u. S. GfJological Survey, and independently.t the geologists of this oureau' are in t 16 fiold for thf:.: purpose of aiding ore discovery and the mr..king of nevJ mintls

A field in which geologists ecessarily have a monopoly" and the prospect~ or is practically helpless, is fin .ing ore tr~t does not show on the surface. This they have done in the Tintic istrict in Utah and in the Butte district. But that is a separate story and d as not Some of the conceptions of f "'those relating to tht:: forroation of used ;successfully, particularly in this will involve conclusi.ons upon but space is not used to set forth belief is the Irk'ljQrity vi.ew or the cal science. The difficulty of . " highly technical subj~ct as the ge

b~long

in this pamphlet.

damental geological processos, especi&lly ores, are outlined because th(jy are being the valu().tion of prospects. In,some cases, \Jhich tht:re art) some differences of opinion. all of these, The wri tvr gives wha.t in his present decid~d trend of opinion in goologipresenting in brief and simple form such a. logy of oro deposits is fully realized. ·~OPHYSICS I

Tht1 study of forces in the e tion, and the transmission of soun instruments for measnring these th some of the large invisible and de the slight differonces between the ordinary rocks. Hitherto geophysi

rth, such 8.S electricity, magnetism, gravitaLnd shock, is ~EhY.SiC6, and geophysical ngs ho.ve begun to be successful in finding ply buriE;d mineral d epo["ii ts, by determining cffC:lcte of these forces in such bodies and in (11 m~thods have not been widely useful in the

4

discovery of ordinary gold veins., Poss~bly they ma.y be in the fU'~ure. Th(;:y have no relation, of course, to the 01 -t~me divining rod. The various kinds of apparatus are necessarily of delicate construction, exp~nsive, and require experts to operate them. They a. re not as yet of much use to prospectors. Geophysic~l prospecting is m~ntioned because . quiri~s indicate th~t th(;:re is n wide-spread impression that such methods havo een perfected and are an easy route to fortun~ .. making no longer necessa.ry the la~or and hardship of the search for gold, 1Jhen '; .this time comes, if it does, it w~ll be known and widely published, Secret divining methods and apparatus, r~presented as operating upon scientifiC principles not generally known to I.s clentists, are to be avoided ~ " ,

i

This pamphlet is restricted,1 50 far as possible, to a description of gold veins, but much of the discussion lapplies to all metal-bearing veins. I

IvIA IN ~INL6 (; F RO CKS

As this discussion proce~ds", it is hopod that the significanc(-) of certain rocks may grow upon tho reader an
Dana f S NanlUal of lliiineralogy, 4th il:di t ion. John 'VJileV & Sons, New York.

$4.00

J. W. Anderson:

ProspectorJ~ Handbook, 12th E9ition. D, Van Nostrand Co., New York.

A. F. Rogers:

Introduction to the study of min~rD.ls and rocks 2nd Edition,. $4.00. lVicGraw-Hill Book Co" New York.

G. Nontague Butler:

$2.00

Pocket l,Io.ndbook. of Blow-Pip(;: An;.7..lysis.

J.<)ltrl",l Hilf..:Y & Sons, New York H~ "VV. von Bernevlitz:

Handbo()k for prospectors. ':;3,00 McGraw-Hill Book Co., New York.

5

::Pl.25 ,

ine'er'

Robert .Peele':

}lining En, s Handbook, 2nd ~ditiOi1. John viile & Sons, 'New York

J,

Geology applied to mining~ 2nd Edition, McGraw-H 11 Book Co" New York

Ei Spurr:

;WlO ,00 '."

$3.00

I

James F. Kemp:

$3~OO

Handbook pf ro. cks, 5th Edition. D. Van Nolstrand & Co., New York

v;aldemar Lindgren: Nineralldeposits" 4th Edition. NcGraw-H~ll Book Co., New York

$6.00

As one reads about rocks, he Iwill note two terms are often used, struc~ure and texture. Structure· refers to ~he shap~ of. a rock mass or of its larger divi~i.p Texture has to do "Jith the particles of wh~ch l. t is made and the arrangement of them. A bolt of cloth is a rollediup, sheet-like body in structure, its texturei~ the weave or fabric of it. Rocks group themselves into ~hree ma.in classes according to the way they were made: Sedimentary, metamorph~c, and igneous. (1) Sedimentary r2~: Thos~ rocks that have a bedded structure and in tex~ ture are oamposed ot worn rock fragments, or of, chewical deposits, that generally have been laid down under water, a~e called sedimentary rocks " The ocean extended at times over' parts of the 40ntinent that were lower then than now, There' were also lakes that do not exist ~oday. Some sedimentary beds were spread out by streams, or by winds, over land smtfaces. It required great periods of tin.e to " make the large bodie~ At' sedi.::lent.aty rocks, and their bedded forms are due to mor~ rapid accumulation at one time tha~ another, according to the am9unt of material :' being moved by 6tO~S and streams trom high ,to low regions and ultimately to lakes and seas. The process of breaking !down solid rock and moving the resulting loose material from elevated places is c~lled erosion, to be discussed more fully later, The deposition of the material in +owlands ind water bodies is called sedimenta- . tl.2n; hence, the name sedimentary Ito cks. Those rocks made up by worn f'ragniet1 ts particles may be of any coarseness or fineness of texture. If composed of bould~", ere and pebbles, they are cel.lled c$nglomerate beds:; if of sand, they are sand... ' stones, if of very fine sand, clay~ or mud; they are ~hales. .

or

Another kind of sedimentary ~ockJ refer~ed to above as chemical deposits; is generally a mixture of fine partic+es of silt cemented by lime, deposited from solution in sea water, often b:T th$ aid of minute sea animals that build shells and house their colonies in limy structures. Such rocks may be nearly pure lime. This whole group, pure or impure, is called limestone. It dissolves and effervesces if dilute hydrochloric acid in put upon it. There' are other chemically deposited sedimentary beds, but lime,tone is the most common of them. The sedimentary beds so far ~amed are usually solid, ~ementedJ and hard, mostly because they have been deepfY buried for long periods, Vie now find them at the surface because they have b~en uncovered by erosion, which has in some places removed many thousands of fflet of overlying beds, Certain sedimentary rocks, h¢>wever, are still unconsolidated beca.use ~hey have been deposited more recently and still lie at or near the earth' s ~urface and have not been squeezed and pressed; d01tJn by a hea~J burden of overlying rocks. Of these, there are alluvial deposits spread out OV6r broad valleys and plains during flood stages of slowly flowing rivers. Coarser sand and gravel beds accumul along swifter streams, ~uch may cCl>ntain conUllercial gold placers.i~ There are also *FOr explanation of--placers,· . ·s-e"e-famphlet No'. Ge('.lc?'y •

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Bureauof

Nines ani

comparati~Arhick 1aY&1\&. Gf wind blown dust, such as the soil of the Palouse hills, or of wind-blown sand, as· the dunes of barren sea coasts or desert plains. Wind-laid accumulations s ch as these are never gold placer depOSits, but the coarser materials left beh· d by them along beaches may be richer because the barren sand has been blown awa. The enormously rich diamond-bearing beach placers of Southwest Africa have b en enriched in this way by winds, Other unconsolidated deposit along the northe~n edge of the United States, and allover Canada, were left by he great ice sheet of the Glacial Period, which extended southward from the rctic country advancing and retreating s~ver­ al times until the main ice sheet inally withdrew some twenty to thirty thousand years ago. Some of these deposits were spread out by the slowly moving ice itself and are given various names s ch as till, boulder clay, moraines, etc., or they ma.y be grouped under one name the drift. It is mainly a j\.Dllble of grEjat boulders, sllJ.8.l1 pebbles, and fine lay, unassorted and not bedded. It may contain a little gold here and there, but the gold does not pay for the working of such deposits. Vigorous streams t at poured from th(; front of the ice did l however, in places along valleys 1 Bor . such mat(;rial, carried away grvat volumes of clay and find sand, and left grave s (placers) that contain ~nough gold to be profitable. Small mountain glacio s at about th~ same time, and even in recent times, have existed around mountai summits and in high valleys in Idaho, Washington, J:.iontana, Colorado, Ore on, and C.lifornia, as ttwy do today in Switzerland. Outwash glacial rav:.ls in gulcht;s and vallt:ys below places wht;:r~ SU( glaciers have been are profitable lacers in some localiti~s where the glaciers wore away parts of gold veins. (2) Metamorphic rocks: It h s been stated that rocks ar0 connected after they have been very deeply buried. Some gruat rock masses have be ,n buried to depths where they susta'ined enormo 5 loads of ov(;;rlying rock, and whbre the earth was hot, and may also have b 'cn subjected to strains caused by movements in the earth's crust. These, whvn exposed at the surface, have structures and textures decidedly different from heir original character. This has b~en brought about nminly by new crysta lization or re-arrangement of rock materials. Thus, a body may be squeozed thinn~r and caused slowly to flow, or to become banded, by the shifting and re-ali nmcnt of minerals, By such processes, shales and shaly sandstones become banded schist; purer sandstones become quartzite; granites become gneiss; limwstones turn into marble and serpentine. Heat sufficient to alter existing beds pro oundly has been brou'~ht up from great dt;pths by large bodies of molten rock, su h as the Idaho batholith, now exposed in central Idaho. This will be discu sed more fully in the description of Idaho gold ores. (3) Igneous rocks: As tho n m0 implies, heat took part in the making of rocks of this kind. It v.]Quld be . possiblfJ in a brief space to explain everything about igneous rocks; in fact, nobody knows all about them., A few things are fairly well understood and the e will be outlined becat;.se thuy have to do with the origin of ore deposits.

The temperature of the increases from the surface downward, so also does pressure, merely by the incre sing load of rock. Pressure t0nds to make rock still more solid. At a depth 0 f ten to fifteen miles the heat is great enough to melt most rocks, but pre sure generally keeps t hem solid. In fact, physicists have shown that they ar' increasingly rigid all the way to the earth' 6 center. But, if pressure is in an way r~lieved at depths where the rocks are sufficiently hot, thoy melt. Eros· on by its age-long mothods shifts the wei~lt of earth masses on the outer shell. A wide belt along thQ Rocky l'Jiountain system, for instance, became so much lightened at tinlt;S in the past thiJ.t heavy masses

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ot the continental body on both sides crowded against it, and probably at great depth were squeezed beneath it. Under sufficient pressure and heat, it is known as already stated, that rocks slowly flow. Such stresses from the aides of belts lightened by erosion cause upward bending arches and cracks penetrate to great depthl relieving pressure. Rock becanes molten and fluid, and walls up under the arches and bursts out a.long the cracks, bringing with it the hea.t of regions perhaps miles below the surface. The fluid rock is called magnta. Great bodies of deep magma that accumulated under broad domes or arches beoame batholiths when cooled to solid rock. Considerable bodies, fornwd in the srune way, upthrust into existing rocks of the cru~t q.re etocks. If the magma filled cracks and fissures, it made ~; if it pushed' in between beds, sills or sheets; if the magma reached the surface along cracks, volcanoes erupted" the magma was blown into the air or poured over the surface as lava. These terms relate mostly to the structure of the resulting rock body. Ore deposits are found associated \-Jith all these kinds of igneous rock. The igneous rocks are also named according to the textures resulting from the way they cooled. Every igneous rock is wade up of several distinct minerals, in coarse crystals if they cooled slowly. If they cooled rapidly, they hardened . without much crystalliza.tion. They are either intrusive or ~usive, terms that express where they stopped on their way up from the depths. 'l'he intrusive magrnaa thrust themselves into rocks that existed before them, but failed to reach the ' surface and hardened into batholiths, stocks, dikes, and sills. The' extrusive magmas are those that poured out on the surface. The kinds of rock in the greater masses that were deep-seated when they were, ade, the batholiths and stocks are ' granite" syenite l diorite, gabbro, etc. They are coarse in texture (granitic). Rocks of the sanle composition in dikes and sills are generally finer grained and are given names that express their finer textures; rhyolite, porphyry, quartz porphyry, granite porphyry, andesite porphyry, diorite porphyry, and many others. These chilled rapidly because they were small volumes of magma in contact "Jith the cooler rocks that they were invading. Porphyrtes are intrusive rocks in which one or two minerals fonned large crystals, while other minerals formed a matrix of smaller crystals. Thus certain crystals stand out conspicuously among the very small ones produced by rapid cooling. There is a great variety of extrusive or volcanic rocks, also named according to the way in wffi-ch they came up from the depths: (1) Effusive, those that poured out as fluid lavas; (2) explosiv~, those ejected violently as rock fragments by the expansion of steam and other fases, The fragmental volcanic rocks of explosive eruptions are called breccias, if coarse, and ~, if fine. The fragments may be of intrusive rocks that had hardened below the surface and afterwards were blown out by repeated eruptions from cracks and pipes whic h they had previously fillod. Volcanoes also generally tear off fragments from the walls of the passagev.Tay-s through which they di.scharge. So the volcanic rock may include in it sedimentary" metarllorphic,. other igneous rocks, anything mot on its way to the surface. Lavas may vary in texture, from porphyry, with considerable crystalline texture, to gla.ss which is magma that was chilled albost instantly .. so that no crystals even started to gro\-J. The name obsidian covors most of the massive glasses. Pumice includes glasses that coOled while full of gas bubbles, so are porous I some of them so light that they will float on v/at8T. No attempt ~Jill be made to describe further any of the sedimentary or igneous rocks mentioned. Specimens of th\,;;Tll can be found in any good university'

s

geological museum and the eye soon le,arn.s to distinguish between the main kinds. The first thing to note is that the principal varieties of igneous rock generally contain sharply definod angular crystals and sedimentary rocks do not, but usually have in them rounded or worn particles. Even though they are finegrained} a good pocket magnifying lens will show the distinction. Some of the cr.ystalline metamorphic rocks are more likely to be confused with the crystallized igneous rocks, but in the field most of the' metarllorphic rocks can be recognized by their banded structures~ Quartzite usually shows surviving grains of sand. The volcanic glasses are harder than the massive sedimentary rocks like limestone. Limestone, and marble, the metamorphic rock made from it, are ea.sily scratched by a knife" R~TI(iNS

GF HOCKS

A!~D

OHBS

Veins and deposits of gold would not be found at all on the earth's surface if, throughout the billion years or more of knovm earth history, the magmas of some igneous rocks had not at some tinie pushed up to the surface or toward it in what are n01J the gold-bearing districts. These magrnas brought with th~m gold and other metals from the great depths, where they really belong in the earth. Strictly speaking, they are out of place on the surface and are th0re only because igneous magmas and the gases and fluids in them are the speoial vehicles that give the metals transportation. That gold and many other metals have come up with the igneous rocks has b~(;n demonstrated beyond question. The earth's interior Physicists and geophysicists in recent years have found lnethods not only of weighing the earth as a whole, but can detoct the differences of weight between separate layers from the surface down. It has been found that there are distinct layers, probably diffe:t:ing from one another because of what they contain, and that they are successively heavier from the outer shell downward. So heavy is thE':: greater part of tht;; deep masses of the earth that we naturally assume that in thc;;m the metals are much more abundant than in surface rocks. Gold ores are associated with the lighter-colored acid or siliceous rocks from the magma-forming laY0r just belo,,! th€j thick out~rust. Diamonds and the platinum group of metals probably come from a deeper layer with magmas that cooled as dark-colored ~ rocks. Solutions Solutions will be mentione;d frequently" 50 the term ShOl. lld be defined. A solution is a uniform mixture or combination togeth0r of two or more substances. They are usually in definite proportions, because one substance will absorb just so much of another, and', if there is any of it left over, it "dll drop out of the solution. For example, watc;r will tnke up in solution just so much sugar and is then said to be saturated 'ttfith it, and any more put in vlill not dissolve, but rumain in solid form. If the solution is heated, more can be dissolved; as heat is reduced, some will be dropped and will crystallize as a solid. It is important to keep this in mind because dlfferent ore;:s were formed at' different temperatures in veins by this behavior of solutions. Ores and magmas As the magmas crowded u~~ard, came to rest and cooled to solid rock, as batholiths for instance, it is believod that it was still so hot around these hardening rock masses that certain minerals left over as fluid residues refust::d for a time to orystallize or solidify. Those solutions contain~d metals such as

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gold, silver, nickel, tin, t~gste~rirdP, copper, lead, zino, and 6~hers. They also contained much silica, hlt:h ir\ its solid fonn miners know as quartz, and smaller amounts of other non. etallic substances, and with them there was a great deal of steam and less ounts of various other gases, also containing some of the metals in solution. he bases were;:: also very useful in supplying the driving power to force the f uids toward the surface wherever they could find a way. Through fissures, heated ore-b ring fluids, l~ft over as t he magmas turned to rock, moved upward, and as the reached cooler rocks along channels of circulation, and, as time elapsed, t e metals and other minerals in them began one by one to be deposited from solution. Long before they reachbd the surface the vein metals had mostly bean droPP'd and the remaining fluid was mainly water with a few substances such as are found around the mouths of the hottest of the hot springs, such as lime, magnesia, carbonic and sulphyrous gases, possibly some silica and iron" and i.n some places quicksilver, arsenic and antimony sulphides. Vl£IN 5TRUCTURE

The routes supplied for oro fl . ds werlcl cracks fornicd deep through the outer crust along dikes or wherer the rocks had b~en strain~d beyond th~ir strength. Probably the shrinking of deep intruding magmas, as they contmued to cool and became rock, was one f the causes of such cracks. In gold-mining districts, we find fractures that cut through older rocks before magmas came up, others that "lere later than t e solidifying magmas and cut the resulting rocks themselves 4p There are ott. 0r cracks along "Jhich great nl[;.sses of rock slipped upon one ano ther. Those re nc',med faults by geologists and miners. They are generally fillE.;d VJit. h gr~und-rock clay call~d gouB.£. £.tuners gene:t;ally speak of fractures and faults, gr~'at or sIllall, as fissures. A fissure may be a simple fracture or a system of . ractures more or less complex. Fissure veins a.re deposits of 'neral IIlc'ltter in or along a fissure or system as just defin~d. f unusually large or complex, th~y nre c~lled "lodes".. A fissure vein is also nown as a ~, ledge, or ~, in some districts. A vein m£~y occupy a faul fissure, although in som~ faults the tight gouge appears to have prevented 0 e fluids from circulating. In othlclr cases" faults were formed after c.ll ma s hf),d congealed and all are deposition ended. The majority of gold veins are fa d in fissures along which thbre has b0en no great movement. Hiners use the t nn Ittrue fissure vein". Behind the use of this term is the b()lit:f th:::.t D. v~1n occupying a 'W011-defined fissurt:: can be relied upon to continue for a Ion distanCE:: down into th0 earth. It is not a very good generalization, because many important gold deposits art: not in big fissures, but in complex, interse ting, smD.ll frc.ctures, and great fault fissures are guncrally barrf::n. fiss~e

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Bedded veins are thoso that li0! along beddj_ng pl8.nes. llilint,;rs n~un~ them blanket veips, if th€.y lie fla.t. Th(;y may lie a.gainst sills and sheets that are intruded between sedimt:ntary ~eds as in Leadville. The mineral dt:posit may permeate a porous bGd or may rave eatt~n into soluble beds (limestones, dolomites and quartzites), dissolvingl th0m and r0placing thwm \iiith ore materials. II

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The rock adjoining a vein is tht, ~ry rock. It is also c Q.lled wall rock and the sides of a vein are its 'VI lis. If the vt:in is inc1in0d" th e upper wall is the hanginr; ~ and the . ower the f2.2.i....will.:,

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V~IN hA~}ililALS AND T~Ri>J.INvLOGY

A few other terms commonly el.Lp oyed should ['.180 be defint:d. easy in some cases because usage,diffBrs in various places.

This is not

I

~ has a legnlized mccming in Ithis country. It is Ci.n aggregate of minE-ral matter containing v~luable metal in such qu~ntity that it can be mined and the metals removed from it and sol<;1 t a. profit. Profitable non-metallic materiul~ like clays, gypsum, sr'.lts, etc., Gore not CElled ores.

For the md.terial in a vein or qeposit which does not yield [~ profit, ml.nlng people use such names as ~~~l zation ,ve~n matte~J ledge or lead. matter , waste. Veins may be barren of g Id in some parts and rich in others. Gangue !'S"tI1e general name for elll the ~inerals that contCl.in no recoverablf..; metals, the unprofitable and waste mat~:rin.ls in ;:l vein. I

In describing the position of ~ vein in the ground, two terms are necessary. Its strike is the direction the tbin takes horizontally or on a level. Tho strike is not usually its course !or direction on the surface.~r The dip has a direction square, or at right [l.na1cs, \dth the strike, and is the inclination of the vein downwn.rd into th0 eatt,h. A 90-degree dip is vt;,;rticc..l or th~ dip of a plumb-line, a O-degrf.!e dip is p(;rfoctly level. All other anglbs or dip lie betw8en these. ZONJ.!S

In working dmmward on a vein, it is found thL',t, at certain depths there are changos from one kind of or\;.; to qmother. Il'rora the surface downward each segment of the v(.~in thc>t conto.ins a, distinct ve.riety of ore is called o. zone. Also a district with mr1.ny veins u5uJ,lly shows different ores from 0. center of ore deposition outw2.rd to the IMrgin$ of the district ~ nut prt~ctic[11ly nIl voins have two Inc'lin zones, the !Q!l£ .2£.. oxidation c.t or near tlw surfQcG, lnter to be described, and tho sulphid~!Q!l£i contC1.ining com,pounds of sulphur and metals (sulphides). At the timu vJht;n vpins 'H(;;)re fonned" they were entir()ly in the sulphide zone, "Jhich includes al~ those ore deposits th!l.t W0re brought~p from deop magl11c'1. regions r-\.nd hn.vo not been ch:'lnged since they "vere ori[in211y deposited. The zone of oxidation was made nftf.!rwards gVDE::rally "ii th the :lddition of materials 9arri0d ~ into it. Gvologists hc.v~ termed the original sulphide ores hypogeno, but mini~ people gen8r.::~11y cP,ll tht:m prim2.ry, and ores tho.t formed l(J.ter, ~condqry. Gtologj.sts nnme secondary ore supergene. The supergene, or secondn.ry, ores ar~ hypogene or primary ores nl.Qde ov(;r by pro,c~sseet operating at and niJar thu surface. To understand them, the primary or sulphide ores need first to be I::~pla.ined, Sulphide zone is not B,n accurate term bf;!cD.ttse it includes m3.ny met[~llic minerals thc.t are not sulphides, but thE; sulphides ar(;;) tJhe most important and the most conspicuous, nnd tho nalne hD.s become established. SUBDIVI~)lGN0

OF THE PHlhAHY SULPHIDE ZONE

In the primary sulphide zone, n1inercJ.ls forr'.;.ed in groups at different distances from thbir sourc(Js bect'..us~ of the b(;hr;,vior of orE;;: solutions p.s th~y cooled. Geologists recognize threo mD-in di visit.ins of thu sulphide zone, ea.ch huving its speci~l minorals. Each main eroup, when formttd, occupied D. zone nora or less by it self, which HClS 0. part of the larger sulphide zone. \Ii. H. Ermllons -l<50E;

Figure -1--------· - - '-- ·..·--3:-1--·--·--

olassed these groups as made at var ous depths and called them the 9!!2, ~­ ately deep, and ehaliow zones, hav' g in mind their distance below the surface at the time they were deposited. W Idemar Lindgren, a famous leader in the study of ore deposits, advanced the idea a few years ago that these m4neral groups were caused by the decrease f temperature upward when veins grew from solutions. The groups of minerals ores that were deposited at the hotte~t pOints in fissures were forned ther because they would stay in solution only when th,e flui~s in which the, y were proug~t up we~e very hot, a nd those hi,:~her up were deposl.ted because they rematned l.n solut~on until heat dropped to a certain lowt)r point~ So Lindgren a~so divided the sulphide ,zone into three smaller zones, as did Emmons. The groups of minerals described by the two authors are practically the same. ' These three main zones, as now ~enerally recognized by ing from the greatest depths, are: :

geologists~

1.

The hypothermal or hottest primary zone

2.

The mesothermal or moderate-temperature primary zone

start-

3. The epithermal or lOl'I+o-temperature primary zone At lease some mention of these ~ones appears to be called for, because mining people now have some kno1rfledge of them and they are considered in reports upon mining properties. Also a working knO\~ledge of the zones is proving to be more and more useful to geologists and minin; engineers in estimating the probably value of newly discovered veins. The prospector, if he is not interested, can disregard the discussion: of this subject. He can probably. best judge the merits of his discovery by the amount of gold he finds in his vein. Later on, if he thinks he has a val~abl$ gold deposit, heJnay be wise to employ a geologist, who specializes in mintug geology, to give an opinion upon its probably persistence and to estimat~ its future possibilities. This may help to obtain money for opening it up, or· cause him to drop it; if it is promising, help in judicious planning of equipment and development. Gold is found in all three temp~rature zones, but in each the ores ~ave special peculiarities. The low-temperature zone best suit s the prospector. In it are bonanza ores, as those of Cr~pple Creek, the Comstock Lode, and Goldfield, Neva.da. In such depoei t~ it is sometimes possible to make money from the start with little or no eqp.ipment. Single deposits have yielded as much as $50,000,000; the Comstock deposit nearly :~400,OOO,OOO. Such mines are spectacular, but may be short lived. Their ores are geologically comparatively young. They are found in or near volcanic areas. ' '," ., The ores in the other two zones were deposited at greater depths, where solutions were hotter, are, COIliTnOnly' found in much larger bodies than those of the low-temperature zones, but they, are;: generally low-grade, They are difficult fora prospector to finance. Only great amounts 'of g3.pital can develop them, equip them, and put them into condition for profitable production. Yet when worked on a large scale, they may be immensely profitable and hav~ produced a large part of the worldts stock of gold. Temperature at time of ore deposition and at present It is to be clearly understood that all this dlscussion of temperature relates only to the temperature '\rfhen the veins were being made. l\.{uch time has generally elapsed Since, except in the case of certain ~uicksilver deposits

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tha.t a.re still fonning. The Co tock,. Lode and some others remain hotter than the wall rocks # but most of them have cooled down approximately to the natural te~peratures of the coUntry, rock. The natural increase of earth temperature . downward from the surface, ·howev. r, stops mining work at a certain depth in any district, although ores may stil be good in the bottom levels. Further characteristics of he three zones are briefly as follows:

These generally contain ope with vein minerals, The princip erately coarse crystals, but mor crystalline chalcedony, or as no gangue minerals are adularia, fl quantity of gangue matter is gen uous. The ores in some pl~ces, than country rock with metallic pores, with but a small amount 0 may be short and irregular or By tinctly the gold ... silver zone. T generally not much of it. Certa such as the rich tellurides of g and the gold-coDper telluride go found in Cripple Creek and south (cinnabar) and bismuth sulphides silver, is found in v~ry fine pa difficult to catch in the gold p to be important in the oxidized more valuable for silver than fo a.nd silver sulphide (argentite).

cracks and cavities (vugs or druses) lined 1 gangue mineral is quartz, sometimes in modoften encrusting surfaces as very finely -crystalline opal in vugs and seams. Other orite, barite, calcite, and gypsum., The rally small, in some deposits very inconspics in Cripple Creek, appear to be little else . nerals on faces of seanlS or filling rock other vein matter. The vein fissures also tems of intersecti~g fractur~s. This is disere may be a little iron pyrite, but there is n metal compounds are peculiar to this zone, Id 'and silver (slyvanite, calaverite, hessite, dfieldite), antimony sulphide (stibnite) is . central Idaho, as w~ll as mercury sulphide Free or native gold, always alloyed with ticles in quartz or included in sulphides, and n~ Resi.dual na.tive and rusty gold is likely , res, as will be explained later. In veins gold, there are compl~x silver-lead min~rals ores

The'main marks of identific tion of the gold ores of this zone in Idaho are: milky, coarse, crystalline quartz, lime, magnesium and iron carbonates (calcite, dolomite, siderite). here are some unfilled cavities, but less of these than in the low-temporatur zont;;;. Vt;)ins are likely to be wider and are often of great length and regUla ity. The quantity of vein matter, especially quartz and other gangue material , greatly exceeds the amount of these found in ercs of the low-temperature zone Th~ ores contain complex aggregates of various metallic minerals. It is t e important base-metal zone. It contains the great majority of th0 commercial sulphide ores of copper, l~ad and zinc, in many of which gold and silver ar important by-products Antimony is not g~n­ erally in the form of stibnite" this zono, but as a sulphide of antimony and copper (tetrahedrive), or of ant" ony and lead (boulangerite) and in other combinations. Ars~nic is found in similar sulphid8s of arsenic and copper (enargite and tennantite). Important mounts of silvlJr a.nd some gold are contained in these antimony and arsenic "~rals. If thb deposit is mostly lead sulphide (galena) the by-product 1s likel to contain morE-j silver and less gold. SilvtJr .. though always pres(;nt in some amo t with gold, ~lso occurs separate;ly in a variety of minerals and is a cons icuous prod-..:lct 0 f mines in tLis zone. All ores of the base metals are usually mo e v aluabl~ for th0sE:. mt::tals than the associated gold or silver~ 0

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, Other veins, however, proper~y to be classed as gold veins and valuable principally for gold may yield a potable amount of copper. Iron as pyrite is "

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is always present. Gold seems to ~a natural companion of iron and copper. So most of the veins primarily val ble for gold in this zone are gold-silver!!:2.n-guartz veins, or gold-eilver- ron-coEper...quart,z veins. I

HfPotherrnal ores This zone has the following m~in characteristics: The quartz is coarsely crystalline, compact and generallyi clear and glassy; gangue minerals peculiar to the zone are feldspar, tourmalipe, biotite, hornblende, epidote, garnet" graphite, chlorite; certain metall~c minerals such as magnetite, specularite, and ilmenite in gold ores might al~o be regarded as gangue because t hey are of no commercial importance, Tin, moo..ybdenum, and tungsten minerals are found in this zone, although tungsten .oecu.t, also in other zones. '~v"here any of these exist in quantities sufficient to ~ke an ore, they contain little gold, although it is usually present in some amount. Arsenopyrite, pyrite, and pyrrhotite (magnetic iron sulphide) are ~he important metallic minerals found with the gold. Particles of gold are erclosed in these and in the vein quartz. Little veinlets of gold, in the b~st ore, out across the sulphides and quartz crystals. In such cases" which arte conunon, the vein was cracked and fractured after it was first made and a. ne\,l Igeneration of gold-bearing solutions flowed through it. This later gold deposlition was necessary to make gold ores profitable in many districts. Veins in rthesame districts not affected by it are too lean to be worked. Other influences causing downwa.rd changes in ores The downward continuity" or jmterruption, 0 f any kind of ore is dependent upon many factors besides the temperature zones. Important among these are: 1.

Continuity of the sam~ "all. rock. Having thiS, ther,., can be a reasonable expectation that ore will continue downward subject only to zonal changes •

2.

Change of country rock. Geologists, by the study of dips and strikes of rock fornations, faults and contacts between forations in the viciniti, before mining is carried downward, can often predict \'!hethera vein will cut into or thro ugh other formn.tions th n that showing at the surface. A change to another wall rock maybe beneficial or may lnake the vein worthless. Soft or pliable rocks like shales or schists yield and adjust themselves to fissuring strains rund fissures on them are not likely to be good channels for are deposition, Harder and stronper rocks that form self~supporting fissure walls and do not crush easily to clay, such as granite, gneiss, many of the volcanic rocks, quartzite, and limestone, supply better channels for circulatlon and for deposition from ore-forming solutions. A low-temperature vein in volcanic rocks is likely to become poor as it ~s mined down into underlying sedimentary beds.

3. ThE: a.mount of erosion that has affected the vein is important and is discussed below: EHOS 10N

(j F

VEINS

Although apparently slow processes, yet., if given eriough time, weathering and erosion do astonishing things~ One of the practical results is that lowtemperature deposits may have beun entirely destroyed and removed, In other

places they have been worn down only' a few hundred feet f Although. the lowtemperature' gold ores are among the youngest of vfjin deposits J yet the time elapsed, since some of them were rr~de~'has been 20,000,000 or 30,000,000 years~ Hence, if they are in uplifted mountain country, there is a good chance that they have been eroded deeply.' In their original form these ores extended 4,000 to 6,000 feet along the dips of veins'. If such a deposit shows even an occasional mineral that belongs to the moderate-temperature group, it has been deep-, ly eroded and ~-grade gold ore cannot generally be expected to continue far below the surface, In Cripple Creek, at about 3,000 feet depth, base metal sulphides begin to appear and ores assay much less in gold than they did high~r up. In some districts there are indications thnt the moderate-temperature ores may follow in the sarne vein below the low-ter,lperaturo zone; as in the Camp Bird vein, San Juan Mountains, Colorado, and c~rtain veins in the Horseshoe Bend Boise Basin regions, Idaho Some veins never contained any but ores 0 f the low-temperature zone I" as in Goldfield, Nevada. The solutions that made them were not hot enough to bring up the highe.r.temperature minorals and drop them in the deeper parts of such veins. There was no way to foretell this in workings near the surface. So, if erosion has ren~oved a vein close to the bottom of th.is zone, very little ore may remain to be mined. Ores of the mesother.mal, or moderate-temperature zono, probably extended before erosion from 5,000 to 10,000 feet along the dips of veins,' If a vein is wide, and shows great length at the surface and contains profitable ore with the minerals mentioned as belonging to this zone, with here and there a few minerals of the low-temperature group, it may become an important producer. Then the zone is probably practically intact and can be minud to great depth. There are such veins in south central Idaho. If, on the othEir hand, occn.sional hightemperature minerals are found, then very little of the moderate-temperature zone may be left, Such a. diagnosis is chiefly useful in the case of ores in which silver minerals and the complex sulphides containing silver constitute the ores. Such ores are not likely to extend downward below the moderatetemperature zone. Thr::refore, it is important, if poss ible, to determine how much of this zone has not been eroded and ranains to be mined. Ivlining geologists can in some cases arrive at a good opinion upon this question,. In ~.o,;ld-A!9.n"'"9.).l?r.~N~ ores, the determination of position in the zone is less important. ..L(, it;; not serious if one finds he is working nenr the bottom of the mOderate-temperature oros downward into high-temperature ~R,;Ld-q..~t?:t;,'~J.­ pyrite or simple gold-quartz ores, because the high-tempe;rature OL'es maya Iso be profitable. Noderate-temperature ores are likely to pass dO\-JIl into hightemperature ores in the same vein. If a prospector finds in a vein ore exposed that belongs near the bottom of tht; moderate ...temperature zone or nunr the top of the high-temperature zone, it may continue down to great depth. If h~ finds gold ore in the top of the moderate-temp6rat.ur~ zone, he rI11y have a. mine tha.t can be \-Jorked downward until normal a1.rth heat stops him. This depth in some districts is as little as 3,000 feet; in others, it may be Ct mile, and in the South African plateau or eastern Canada, mining can be done dov·m to as much as a mile a.nd a half below the surface. In the case of high-tempernture ores, it is especially desirable to learn, if poss:i.ble, how deeply erosion ha.s reduced this zone, becc.use b0low it there will be no conullercial gold ores. Reference has be~n maGe to the striking effects of erosion in certain places. In other places, it has done surprisingly little. SOIlle important high,...; temperature veins are known to have been deposited close to a billion years ago} and one '\tvould not expect to fiI}d such ancient V0inS at all., All the

15

reasons why these ancient veins ha not been work away would make a long story, but the principal one is that thro out most of their existence certain areas in whioh they are found were early reduced approXimately to a level, at little elevation above the sea,and were ever again lifted into high lund where erosion could work deeply upon the. Such ancient veins, thus protected am preserved, are the gold veins of 0 tario. Oth~rs, equally old, were uplifted with the Appalachian 140untains and have been eroded away "down to their roots." Their gold ores are only remnants nd snk~.ll shoots of formerly more extensive ore bodies. No deep gold mining w'11 ever be done upon such veins.

In some districts, ore was de such places, after the earliest or terval of erosion t hat cut the vei. Then the circulation of ore soluti posited along openings in the meso lower-temperature ore, thus overla telescoped voins. They are, as a the repeated deposition in them.

sited at two or throe different times. In s were formed, there has b~cn a long ins down deeply into the mesothurmal zon0. ns was revived and epitheI'lllUl ore was dehennal ores. Veins conto.ining younger, ping older, higher-temperature ore, are called eneral thing, more profitable on account of

This is the name given by min that do not extend to th8 surface •. Some blind ore bodies were fonEed that encountered barriers on their upw~rd way, .such as beds or orE!.atl.Ons too tight to be passed; other blind veins once o.ppearedCl t the s rface and hnve since been buriE:d by sedimentary beds (Jerome" Arizona), or by L'lva beds (parts of the Hother Lode, C(ilifornia). Many such ore ~dies have bet.-;n found, some by accident o.nd a few by geological rtjasoning. In the gent district of Leadville, discovered over fifty years ago, only one minor or body extended to the surface •. The rich, big ones were formed deep in the g ound under impervious beds and sills that drunmed back the rising ore fluids. These \'oTerE: discovered by sinking sha.fts at random and driving levels tll1til ho e and there the miners stumbled upon the ore. Another kind of blind vein is foun in Butte, Montana, where rich ores were deposited in certain fault fissures ull of clay. Solutions wer~ abl~, in the time they had to operate before th cooled too much, to work their way upwn.rd only to a certain height, by disso ving and replacing the clay wi th are.. They stopped 500 to 1,000 feet bBlow th· ~)resent surface. urcs in thE-;sC have been found at intersections "lith veins previously discovered or developed by. underground work carefully directed by geologists. In other places blind veins are 10 cat ed by drilling. THr£ OfID IZ£D Z(;NE

vie shall now soon consider thel actual things tlw.t the prospector must hunt for and find, if he is to open up 0. mine that contains any of th6 ores we have been considering.. Tho foregoing discussion, justifies itself becLusE.; the primary ores of the sulphide zone are, after :).11, the ultimn.te ob~iective of the prospector. Upon them the long life of a mint must depend. But th~y generally cannot themselves be found on the surface, only those things tba t lead to them by prospecting and mine developnKmt. The ores of the oxidized zonlo: are l.UJ.de from the sulphide ores.- vfuen the alteration is complete, they resemble the sulphide ores very little. They may be value.ble in thems~lves or chiefly useful as guides to sulphide ores. In any event they are generally not extensive and arE; usuC\lly found only at and near th~ surfac~.

Air is a mixture of oxygen and nitrogen. Its oxygen attacks and combines with most met~llic substances and this process is known as oxidation. To learn even roughly how oxides are fornted is the best way to understand how they indicate what mD.y be the kinds of more extensive sulphides below. The sulphides of metals are especially subject to attack by oxygen of the air, which pushes t.ll or pa.rt of their sulphide aside and unites itself with the remaining elements in the mineral, forming oxides, if nllthe sulphur is removed, or" sulpho.tes, if part of it rerun.ins. The sulph~rr also. combines with oxygen and forms gas. The gas pas,ses into the air or is dissolved in water and washed away_ T11e odor of sulphur gus is usunlly pE;rceptible around sulphide ore bodies exposed to the air underground. host of th~ oxidized compounds of the metals are soluble, and are [.1150 carried nwny from the veins. This is called leaching. The oxide of iron i S exception~l and a lo.rge pr:rt 0 fit remains with the vein. At and nenr the top of many veins th~re are deposits of iron oxide (limonite), pOl/dery or solid, and everything nOt'.r at hand is more or less stc.ined bright yellow, brown, or red, by the various iron pigments. The iron oxides in and around the top of [.. v~in form the tfiron c['.pping," so useful in the search for ores. It is en.lled "iron he.tlt by thE::: Germnns, "gossan" by tht: Cornish, a.nd various names having the same meaning in otht:Jr languages. Thtl iron oxides and the accompanying qunrtz '\'li11 conte-in gold if it is a gold vein in the sulphide zone. If no gold is found in the iron capping, gold is not to be exp~cted deeper in t he vein in the sulphide zone. Some gold veins of moderate-temperature orJ.gJ.n have bll1.ck outcrops where the primary sulphide zone con.'Lainbtl manganese minerals, rhodochrosite (the curbonate) and rhodonite (the silicate). The black lllc'1.ngnnese oxide acts SOU1(;;whut like iron, is not easily soluble, so clings around the tops of voins. Another kind of iron stain is due to the weathuring of iron-betl.ring minerals of certain country rocks, espGcinlly some of thE,; lavns and porphyrids. This iron stain often looks like vein gossan, but, by experience it will be rt;lcognized thc.t it is mixed with earthy clay" is gel1l;)rally only a stain with no solid iron oxide, such as is found in gossnns. Also, of course, it does not contain vein qQ~rtz or oth~r v~in minerals. Qua.rtz resists effects of o,ir and wnter. Many ores, which underground are made up of br:tght.. shiny, metallic mine;r[',ls with quartz and other gangue" show at the surface only the iron-stained quartz sk0leton, with many cavitiE:::s where once were sulphides, This 1.s "honE;y-combll quartz. The quartz may have become so porous thnt it has collapsed to srtndy 11 suer.lor quartz," from thE: pressure of the vein walls. These t",O kinds of surface quartz may themselves be rich oxide gold ores J easy to mine, (l.nd under them at some depth there is liktlly to be good sulphide ore. ~weathering is a term much used to include nll the effects of air, "'Je.ter, heat and cold; in fact, every infl.uence th'1, t :J.ffects rocks and ores on the earth's surface. So intense hns been the disintegration by weath~ring, c.nd so striking the "burned" nppeart".nce produced by oxidation on some outcrops, tha.t the idea prevails among miners thc~ th~y have been ejected violently frol~l the hot interior of the earth. They are cc.lled "blow-outs,U although they arc r~ally caused only by exposure to the weather. Such conspicuous effects may indicate a specially promiSing part of n. vein,

17

THE ZONlS OF UNDERGROUND

HAT~R GAT~MD

FRUh The; SURFACE

Water 'that falls as rain, or melts from snow, sinks, if it can, into the soil and the rocks below. If enough w~ter falls on the surface, part of it percolates downward to make an underground water body, genern.lly co.lled ground ~, filling at some depth all the cracks and pores in the rocks, as we find it in wells. The top of this body is cc:lled ttwater level," D. bad nClne because it is seldom level 4 A better one is used by geologists, tht:- ~ter t~ The gathering zone All the zone above the water table is c~lled the gatherin~ ~ where we.ter is accunlulated and carried do\vn to the underground storage. This zone, r.~st of the time, is filled only with air and moisture, but during a storm, and for a time afterward, descending water passes through it. The gathering zone is ~lso the zone oLweatherin .~ In it vein sulphides are c.tta.cked c.nd oxidized, c.nd these oxid~tion products oxides and sulphates) are l~.ched out as they are at the surface. Some of these compounds c::.re carried down to the wo..ter table in solution and come out in sprin;.:;s and seepages; some are left in the veins. In copper veins important additions are JDade to the copper ores just below the water table. Here copper as sulphate is re-deposited 3.S sulphide when a solution of it comes in contact with sulphide minerals. This newly deposited ore is cnlled n secondary sulphide. This is secondary sulphide enrichment of v~ins. In a gold-copp~r vein, it may make important copper ores at the w~ter table ~nd just below it, bec~use of ti addition of copper, but the gold is very little affected. Because few things ccm dissolve it, gold n~ar the surface in veins h~s the habit of relIl3.ining in much the S.3l"ae plo.ce it occupiE:d before the sulphi.des were oxidized. Some of it is, of course, carried awc..y by flo~lI'ing surface water to make placers ~ but only as t he out crop of the vein i s complli~tely destroyed c.nd scattered down the slopes. The gold just below'the surface relll~.;.ins in the vein, It mo.y be washed down the vein by water for short distances along open pc..ssnges. Secondnry gold enrichment Gold veins may become decidedly richer in the zone of weathering by the oxidation and removal of worthless l11.'1terial, quc.;.ntities of heavy iron pyrite for example, thus reducing the volume D.nd w(;ight of vein mntter contC:l.ining the gold. In extreme cas~s three tons mo.y hc..ve been reduced to one J thus enriching ore that was worth, say $10.00 in gold as sulphide ore to ~30.00 a ton us oxidized ore, On account of [~ll the influ0nces of weathbring, it is safe to expect tm t the oxidized gold and Silver ores in a vein will be richer right near the surface th.1.n they are 0. moderate distance below, largely on o.ccount of the ranoval of waste cmd not by the addition of gold p..nd 511 ver. Since so mny substances at-e tnken into solution t,nd so few 3.r(; 10ft around the tops of veins J the weathering zone is also n3.lned the ~ 2.£ solution 2!: 2! leaching .. Tho zone of circli1:·::.tion

~'"nd

discho.rge

In this there is circulating ground watl3r, It circul2.tt:s bE.JcQ.l'.se there are outlets to the surface, perh~ps a long way orf I toward which it slowly flows. This zone is important because in it all secondary dovmward enrichm~nt of the sulphide ores of. the base metals is done, but in gold veins this is generilly of little importance~

18

'Oxfdatiorn:j)Sl15anrld somewhat below the water table because fresh water is regularly added to it with some entrap?ed air; also because the water table changes with seasons and rain cycles, and rises at times into the zone of weathering. Various kinds of minerals, besides the metals, are deposited in this zone. For instance, some weathered rock minerals in solution are carried down into it and re-deposited in pores and spaces. So the zone is sometimes called the !2!!! of cementation. The Stagnant zone Below the lowest point at which water can escape back to the surface by springs or seepage, there is no reason for it to flow and it is at rest in the vein. The ground waters in this stagnant zone accomplish very little, if anything, in changing the sulphide ores. The free oxygen in the water is used up in the zones before it enters the stagnant zone, so the sulphides in it are not oxidized~ There is a bottom t.o this stagnant water body and below it rocks am veins are dry There were conceptions in the past among geologists - some argue for them nO~1 - that "later from the surface reaches down practically indefinitely, or so far as ore deposits go, but deep nrlnes have proved the contrary, and. these ideas are now generally abanconed c The rocks are usually dry" except along open passages" below a thousand feet, at leso depth in many regions. 0

Figure 5 illustrates the ground water zones just discussed. D~FTH

uP QXIDATI0N

Ivlost known veins have been eroded down into the original or primary sulphide zone. In humid climates the Y.rater table and the sulphide ores may be close to thesuri'ace, also in the great plains '\There ground water has little opportunity to discharge and lower itself.. In mountainous mining regions there is generally a considerable zone of oxidation or weathering beneath the sunmdts and high slopes of mountains and mountain ridges, but very little in valley bottoms where the water table comes to the surface or near it. In dry or desert climates the water table is deep, or does not exist at all. Oxidation may extend downward irregularly' several hundred feet, or along open passage wa:rs in veins to 2,000 or 3,000 feets The water along such passages is only temporaryo The main mass of the vein may remain dry, because the :infrequent rain water does not soak into it, neither does air cirCUlate in it; therefore, oxidation is shallow. If an ore deposit does not extend up to the surface, it may not, of course, be oxidized anY\'Jhere. On the contrary) in known cases veins were exposed at the surface and had a normal zone of oxidation in past geologic ages, and were afterward buried by volcanic or sedimentary fonJ.ations, so that oxidized oreS now stand well below the present water table. In the hot, wet climates of tropical countries, weathering is relatively rapid and at the salH~ time not deep because the water tablfj is high. It is rapid and exceptio~ally deep in tropical deserts. In polar &ld northern latitudes, it is very slow and oxidation products may be eroded as they are made. Glaciers stripped off most of the oxidized tops of veins in the northernmost states and over all of Canada. In the 25,000 years or more, sincS" the great continental ice sheet laid bare the sulphides in Canadian veins, they have beon oxidized only a few inches from the surface.

19

Cl-u'D VETIl 0 UTCRCliO

.

The outcrop, or 1t copping" is the top of the vein. Its legal name is the apex." Geologists use the word t\ outcrop" to mean veins or rocks that project and are actU4l1y visible at the surface, The top or apex of the vein, where it is solid or in place, is generally buried by 60il or mountain-side sli.de rock. That is why they are hard to find and why the art of prospecting is necessary. tt

There may be suggestions of the presence of a vein in topographic 0 r ground surface forms.. Some veins, made up mostly of quartz and other minerals that do not yield readily to weathering, are harder to erode than the country rock) and therefore stand above the general surface. These may be covered \'Jith soil and loose rock yet for-m a slight ridge or series of low humps, Other veins, that contain less resistant minerals, or fault clay; or have had abundant sulphides weathered out from them, may collapse or be easier to wash away at their tops than is the country rock. Veins like these may be marked by slight depres6ions. It happens then, that in crossing an elevated area where overburden is thin, a vein may either stand up above the ground or form a notch or saddle. Hard and soft rock formations standing on edge show the same effects, but where the country rock is a single forElation in the district, veins, if of good size, may be 'Clearly indicated in the topography, althoueh buried under considera.ble overburden. Belts of iron-stain colors in the soil or wash of low-lying areas ma.y be caused by scattered small particles of iron gossan or capping, and indicate a concealed outcrop. It was recognized as early as the 15th century, and prospectors in the western states have noticed it also, that some large veins encourage or discourage certain kinds of vegetation, particularly trees, because their disintegrated outcrops make a soil unlike that derived from the country rock. This is occaSionally a helpful sign. A strip of different trees, as aspens in a pine forest, or trees smaller or larger than usual, may indicate a vein beneath. However, it may be only a dike or some rock forLd.ation unlike the prevailing country rock, or a barren fissure that serves as a vJater course. The indications of veins often follow crooked courses on account 0 f the shape of the surface. This will be the case even if the vein itself is straight and regular, but the surface rough anti irreeular. Figures 1 and 2 show some of the reasons for this. The dip of the vein where first uncovered may not be its real dip, but at the top may seem to be in a direction opposite to that to be expected from the course of the outcrop. On any hill slope, especially if the country rock is sHal~' or easily weathered, or thin-bedded and standing on edge, and to some extent whatever the wall rock may be, the top of the vein will be found bent down hill, as shown in Figure 3.· rrhe true dip will appear when it is followed down into solid bed rock.,

Buried or mantled outcrops usually can be found only by tracing fragments that came from them, These fragments are float. To learn the kinds of vein float, study exposed outcrops of veins already discovered. Figure 3 shows h6W float washes down a hill with other loose weathered rock material. Obviously all float will be found bE;llow the outcrop where it is moved by storm \-later or the run-off from melting snow., Huch material may be brought down from above the outcrop and may bury it deeply J also cover all float: for some distance below tbe 20

FAMPHLET No. 86

IDAHO BUREAU OF MINES AND GEOLOGY

Fiq./ Showing 0 vein ofsfroightsfrikeqnd re9u/ar f'lot dip, so eroded that H7e remnonf lert cuts thru a sleep mountoin and outcrops on a/I sides of it

f

, ~...-""

. ",:::'

".

Fiq.~Z- ,ShDWit'1q Ihl1l:tI,~4.1.9ht "'6!/ItIJ"" :,~;6I{)wtll:l .~ dec; ded ,dip. ".c"($).s~e.""id.f/e;J ,Jf/M1.d .(}ukhe,p If!) ,<:I/.I"f:I cr'ooA-ed COI.Il"Je, while "r-ell1 wtlh Q vel' /tcol (90·) dip cOc,,/r'ses t:/C'r'OJJ fhem in "slr't:1iqhl line

PAMPHLET No. 36

IDAHO BUREAU OF MINES AND GEOLOGY

riq. 3-Showinqlhe eff~cf 01 b~ndin9lhe

veil? downhill

b" downlAlQ,.d C'l'"eep ol/oooJ'ened, J'OmewhQf weolhel'ed. /;ec/-I"'ock on ste&p hillslde.s nea" fhe sunbce

nq. 4 - £)oll~d o~as t:1~ fhD.,.ewh~re mel" he 9o/d il?lbs pat7.

f'1t:JCf from fhe vein

round or

t7?Q,!'

~how

PAMPHLET No. 36

IDAHO BUREAU OF MINES AND GEOLOGY

~I

I I

DIAGRAM

~ J

I~<:)I'

rOD II

SHOWING

I

1-8 ' :~ l \j.

,~p 1ft) Cj

Gathering Zone.' ,

Weathering and

ZONf5 Of GI20UND WATE12.

ACCUMULATED F120M THE SUl2fACE

, I

I ~ , '6 I t.~ ~ , I.~~. I ~B' C5~1 •

AND

EfFECTS Of THESE AND Of WEATH EJ21 NG AN 0 EOO510N

leachIng

Zone of circulating

/S«.~vtd

ground water. Cementation

------Stagnant Zone of ground water

---.- . . -~- .......

---- ........,

F.Gv.u.5

-

.... -

- ~ -".-t',,"__

outcrop •. At some place, down hill,. however, float fragments should show on the surface and still more of them be found by a little digging below the surface into the soil. Float on the surface should increase in amount and size of fra.gments up hill toward the outcrop until a point is reached where it is no longer found. Then a. trench should be dug extending up the hillside, It may be shallow so long as it shows float, but where float 1s ~ound only in the bottom of the soil or wash, it should be deepened to bed rock and carried uPhill until the top, of the vein is uncovered. On a level surface float may appear in a broad belt and the vein should be found by trenching across the middle of the belt. If the float that is being traced does not show gold when crushed and panned .. it may be a waste of time to follow it up to an outcrop. . Tracing float may often be puzzling. It is possible to trace it first on one side than on the other of a vein on different slopes in a' hilly country cut by many valleys and gulches. Figure 4 shows such conditions. Contours in this sketch are level lines. Float. is carried down a slope squarely across these be'"cause that is the direction taken by run-orr water. The gold pan The gold pan should be used along with the tracing of float~ In many places where no quartz float is found .. the soil shows the kind of iron fragments and stain that come trom vein outcrops. Dumps from the holes of gophers and other burrowing creatures may show flcat which does not appear elsewhere on the sti:t'~ face. Chunks of quartz float, or samples from the vein after it is found, should be crushed with mortar and pestle and panned. For directions in handling the pan, see Pamphlet No. 35 of this bureau. Smaller gulches that have not been occupied by glaciers are well worth panning up-stream in the hunt for a vein. Colors of gold may first show UP1 then float farther up" then still higher both may stop.. Then it is time to turn aside and prospect up the hill slopes. (See Fi~lre 4.) Samples may be packed dO\'Jn the hill and panned in a stream, or a half-barrel or washtub may be placed on the hillside and occasionally filled by buckets when the water becomes too muddy. By the latter method the location of samples is kept clearer in mind, unless the prospector sets stakes and maps the points where he has taken samples that contained gold" as he worked up the hill. Cases are reported of important discoveries which the prospector could not find again at a later date after he had left them, beca\.!se he had not made an accurate record of their location. Some exceptional conditions in tracing float. l~

In rugged mountains, there are snolV slides (avalanches) that carry down the wash and loose rock with them" sometimes stripping bed-rock bare. These materia.ls" along with uprooted trees and rubbish, are found in summer piled up wherever the slide stopped.. These should be recognized and little attenticn paid to float in them, but t he track of the slide up the mountainside may be a good place to look for exposed outcrops.

2. There are also land slides, rock streams, and mud flows, often great masses of loose surface material that, when ",rater-soaked by rains flow down hills and gulches.. Float in this J.latcrial wher·e it came to rest is of no particular use as a Blide to the location of a vein, except that it indicates a voin somevJhere in the path followed

21

by the mOving material, or above it. If b~d-rock has been left exposed along the path of the flow· or slide, it sho~d be inspected for a possible uncovered outcrop. Float in the rock flow may have been brought down into the soil and wash of the surface from higher points before the flow took place.

3. Rounded and water-vTorn float in the gravels of large streams generally will not lead to the outcrop from which it came. Such float may have traveled score~ of miles. But, although float in main stream channels is useless f or finding the vein from which it has come, panning may show the gravel to be a profitable placer deposit.

4. Glacial till or drift and outwash gravels have bien mentioned. Generally float in them is far: removed from its outcrops. In.Nova Scotia, where drift of the continental glacier is comparatively thin, engineers have found veins by carefully surveying and mapping float localities, dett:rmining direction of ice movement by marks on the bed-rock, and th~reby guessing the localities of veins fairly accurately, but these methods are too elaborate for ordinary prospecting and too expensive to carry out~ Small local mountain glaciers, however, extended down gulches in many places in the high western mountain ranges, south of the continental ice sheet. Float in moraines and out-\t/ash from such glaciers shows that there were vein materials on the ridges where the glaciers had their heads. SURFA CE (; fillS

If the gold ore found in the outcrop is a weathered low-temperature deposit, high-grade ore may begin at the surface and continue downward into th~ sulphide zone and be rich there also. This is especially·" the case in telluride districts 1 such as Cripple Creek, Colorado. In the outcrops of gold telluride veins, tellur* ium has been oxidiz·ed and carried away a s sulphur is from the sulphides, leaving, where the tellurides had b0en, a bro\-!n or powdery residue called "rusty gold," that is easily overloeked. Such gold is difficult to catch in a gold pan and does not combine with mercury (amalgamate). No placers are feund in tht: streams heading in telluride districts, although outcrop eres may be very rich. The powdery geld is too light to' settl(: in flowing water. Gold selenides have been found in IdahO' and a selt.mide vein should weather and exhibit surface ores similar in character to those in telluride veins. Assays are necessary to determine the amount of gold in them. In certain cases, as already suggested, gold may be cencentrated in the oxidized ores near the surface. This is especially true ef the sulphide veins (especially of copp~r) that yield soluble exides, leavirg the associated geld in the zone of weathering. For this reason, there w~y be geld ores for a shert distance down the dip in veins that are not found to' be primarily geld veins in the sulphide zone. The great United V~rde copper mine in Arizona, at its outcrep was a prefitable desert gold min~. Senater v~·, A. Clark bought it whdn its owners were working it for gold. He vias an experienced prospecter, found a great amount of iron capping around the surface, IIhonc;y-comb" and It sugarlt quartz, eccasional flecks of copper sta.ins, and, in the deepE;;r geld workings, seams of secondary copper sulphide, clear signs ef a cO'pp~r depesi t below. In tht: sulphide zone in this mine, geld is an unimpertant by-product. 22

FAVORABLE AND

UNFAV(jHABL~

CuNDIT IvN~ M

GOLD OR.t£S

Gold aeposits ot commercial value are r~re. This is tbe reason why gold is a precious metal. A very l~rge pa.rt of thE; earth r S $urface can bE:; blocktld off and dismissed as unpromising for gold discovery.

Unfavorabla conditions 1. Vast regions like the great plains of this and other countri~s can be dropped from consideration a s prospecting territory, because in th(;m there has been no igneous activity. 2. There are certain oth e1" large ar~as where the conlbina tion of proper conditions is lacking, as in th~ Colorado Plat~au occupying western Colorado, the ~outheastern half of Utah .. northeast'Crn Arizona, and northwest New lJI~x1co.

!I

3. Limestone regions usual11 are not favorable areas for gold prosp~cting, but may contain important deposits of base metals and silvl;;ir, if there are intruded igneous rocks in the vicinity. 4. Excessive erosion

sinc~ veins

were formed ruay have (a) destroyed am removed bonanza low-temperature ores, (b) worn away all or~s of every kind, (c) may have ,lowered the top of tht; vein from a rich zone into a l€an one. Favorable conditions 1. Ign8Qus rocks must be somewhere near at hand. They may not ~how at the surface and only a geologist would suspect th~ir exist~nce below it, or they may appear as large, coarsely crystalline bodi~s (batholiths and stockS), or as dikes, or 10c-a1 bodies of volcanic rocks. 2.

Other rocks besides the i gnt;OUS rocks are also important; in oth(;r wO'rds" rocks that were there before thest; and were intruded or invaded by them, for it is in the favorable invaded fonnations that a great many 0 re deposits are found ~ Although sornl: fissures have fonned ~ batholiths and stocks after they became solid, a much greater number extend upward or outward from the igneous masses into th~ older overlying and surrounding forrnations. These, if tht::y were the right ~inds of rocks, afforded favorable channels tor deposition from ore sol~tions.

:3. A small amount of erosion since veins were formed is quite sure to be i.JI.portant. ~lost rich, low...temperature deposits Were deposited comparatively near the surface when they wer<.: form\;;:d. If the surface has been lowered 5,000 feet or more, there ~ay be little left of them. Erosion has b~en de~p in gr~at valleys and canyons of south central Id~ho and has not been great in som~ cases on high ridges and plateaus since low-temperature ores were made, The extent of erosion is a less critica.l consideration in the case of moderate-t€mp~rature gold deposits, as has already been explained. j

4. The extensions of the Rocky Mountain, Coast, D..nd Cascade ranges in Canada and Alaska contain mt.my large unexplored areas where locally all conditions are right for ore deposits. The glaciers havt;; laid some outcrops here and have covered others with drift. Growths of forest nUl tundra, thb short prospecting season, and the remoteness of likely districts from civilization are relll handicaps" but, for men of fortitude, these Cl.re good fi~lds for exploration.

r;; Buti-t;r,

B. S., COlor;r(0rcientific--Soclety,·proc;~(:finis~- Voi·:-12

23

5. Although they have b~dn pr~tty thoroughly prospected, the mountnins of Colorado, Utah, Arizono., Nevade.. , New 1v1exico, (around the IIlc'1rgins of thE;: Colorado Plateau), California, v~ashington, and Oregon, no doubt contain undiscovered gold veins concealed by drift, wash and slice rock. V~ry thorough, intelligent prospecting, guided by the fine geologic~l field studi~s and mapping that have b~(;n dono lately in Colorado, should be carried on in oth.;;;r states. Gold discoveries will probably result from them, . 6. Of greatest inte;;rest to the pE:ople of Idaho is thu (;xcollunt field for prospt:cting in the central regions of the state, 60 thf.;se will b(;; discuss~d more at lE:::ngth. PROSP:£C'l'S 0F GVLD

DISCl,v.Jl~Y

IN IDA.HO

In gl;:neralj the:re are present in many places in c ~ntr(1l IC.C'Jl0 practi.cally all the conditions thcit havl;;; been described in this pamphl~t as responsible for gold deposits~ The map h<:;;rc1Aith ___. _. _... ___ .___ .. _.._..~ ....._._. _ . _ _

23-a

PAMPHLET No. 36

IDAHO BUREAU OF MINES AND GEOLOGY

DISTRICTS AND LOCALITIES .Moyle-Vahk S2 Owl Creek 2 Hope 33 Moose Creek 3 Murray 34 Darian Creek ~ Kellogg 35 Leesburg 5 Ward 36 Beaver Craek 6 St. Maries 37 Musgrove 7 Warren Creek 38 Yellow Jacket 8 Gold Center 3' Myers Cove 3 Gold HIli 40 Parker Mtn. •10 Pierce 41 Loon Creek " Deer Creek ..2 Yankee Fork 12 Cottonwood 43 Seafoam 13 Harpster "'<4 Stanley Basin 14 Golden <45 Germania IS Elk City 46 Hailey 16 Oro Grande 47 Atl.anta 17 O!.lCie 48 Rocky Bar 18 Buffalo Hump 4' Grimes Pass I' Florence 50 Quartz burg 20 Warren 51 Centerville 21 Marshall Lake 5Z Pearl 2~ Seven Dev/ls 53 Neal 23 Cuddy Mtn. 54 Silver City 2.. Edwardsburg 55 De Lamar 25 Yellow Pine 56 Flint 26 Meadow Creek 57 South Mount~in 21 Thunder Mtn. 58 Carmen Creek 28 Gibbonsville 59 Kirtley Creek 23 Ulysses 60 Pratt Creek 30 Shoup 61 A8encv Creek 31 Pine Creek 62 Caribou I

Scale

%$

MAP OF IDAHO SfiOWING LOCATION

so

7S

=

100 "IlLES

OF GOLD VEINS COlli

iled b Stew.rt Udell

shows localities where gold was found and produced in some quantity from veins. Districts that have produced gold from placers are indicated on another map in Pamphlet 35, cited above.

IGNillUS EPOCHS AND OOLD DEPOSITS In Idaho is one of the world's greatest batholiths. It is now exposed by erosion over large areas, but locally it is still covered by bodies of rock that are remnants of old sedimentary and metamorphic formations invaded by it. One striking effect of the batholith has been the intense alteration of the rocks adjacent to it ~ A banded rock, made up of thin layers of old metamorphic sedimentary beds with narrow bands of granitic magma injected between them, has been named "injection gneiss~n TherG is so much of this that the rocks immediately overlying the batholith have been grouped under the name "the gneissic shell," although this shell contDins other metamorphic rocks such as quartzite, slate, schist, altered limestone, and marble, The gneiss was favorable to the formation of suitable fissures for the circulation of ore solutions. In it gold veins are generally more prevc.lent than in the other rocks of the sheil, or cover, or in the granitic rock of the batholith. The tendency from recent study by Idaho and hontana geologists is to fix the age of the Idaho batholith at a. time a.round the beginning of the Tertiary period. Until the past few years it has been regarded as much older than that. The next igneous epoch came a.round. the early part of the !-iiocene in the middle of the Tertiary period. \fuo.tever the age of the batholith, ther'e "las a great lapse of time between the batholith invasion and this later 6poch. Two-thirds of Idaho was uplifted at the tiMe woon the batholith came in beneath it. In the long interval before th~ Niocene, it was first a high mountain area, then was reduced to a region of low elevation ~nd small relief as a result of removal by erosion of many thousands of feet of the batholith cover. If gold veins were deposited in the cover rocks by solutions from thb batholith magIIlc1., they were mostly destroyed and rer.J.oved in thi s long pbriod of uplift and erosion. The hiocene igneous activity was 'widespread in relaho, and in otht:lr Rocky Nountain states. There were volconic extrusions of rhyolite and andesite, as around Thunder Iviountnin, in western Custt;;r County, :in OvtyhE)o County, and otht;;r parts of south-centro.l Idaho. In several epochs, contempornneous with and later than the volcanic extrusions, there were lintrusions of light colored porphyries and local granitic stocks. After these intrusions, and after t htd..r r elated gold deposits had been formed, dark colored, basic dikes (lC'JD.prophyres, et c.) \'ler0 intruded in the same areas, commonly in and :.:;.long the veins. Still later, from time to time alnlOst to the present (as at thl;., Craters of the lVloon), baso.ltic lava.s have continued to be poured over thf; surface in many localities. No gold deposits are related to, or likely to b~ found, in th~se younger lavas. Nost of the known gold veins of central Idaho were regarded f or many yuars as having an' origin corUlected with the batholith intrusion. The u.ore deta~led geological field study now being done throws doubt upon this. It is possible that the great majority of the veins will be account~d for as originating from the Miocene magmas that solidified in two or thr0e separ[tte epochs as the light colored intrusive and extrusive rocks. Not having been formf;)d at ont; time or from thE;: SDnLU n1'lgnms, and having been variously arfect~d by erosion since they were n~de, the gold deposits differ

24

considerably. Some have been eroded dOvID into th~ mesother.mal zones; others only into the epithermal zone. There is c.. wide difference in the amount of associated silver and busa~etal minerals, ~nd in the abundance of gangue, NORTH-Ccl~TRAL

IDAHO

North-central Idaho is t~ken to include Clenrw~ter County and that part of Idaho County north of the Salmon Riv~r~ The most important gold v~ins are in tho gneissic rocks, particularly at Pierce, Elk Citjr, Buffalo Hump, Dixie, and Florence c, Gold valued at o.bout',)60.,OOO,OOO has bc(;;n produced from both veins and pln.cers in this part of the state. The veins dip steeply and generally stri~e across the gneissic structure~ Th<::se Clnd otrwr chnracteristics will be described by Hessrs. Pe J. Shonon and John C" Heed in their forthcoming report upon the Elk City-Buffalo Hump region/! Most of the ~/eins are of considerable length, but are irregul,s.r in width" Commercial ore is mostly in local shoots that follow the swells in the vbins \) In the grc..nitic rock of thu batholith, th~ veins, or lodes, are in shear zon~s and consist of mor0 or less parallel interconnecting, n~rrow,quartz-filled s~rums. Tho primP,ry ores are chiefly gold~bear1ng iron pyrite scattered irregularly in quurtz gangue. In most of the veins, along with the pyrite, occasional crystals of other sulphides are visible (gal~na~ sphalerite, chalcopyrite). In some of the best ores these are microscopic in size and ~ppear only as bluish bands and irregular blotches in the quartz. These contr~in much of the gold. Hany veins are composed mostly of barren quartz (so-called "bull quo.rtz"). The profitablt;;; ores are .u'). t.ho se parts of veins in which the quartz hns be~n shattered by earti.1 mO";,reme!".t s., Dn.d the cracks filled \'lit 11 younger quo.rtz ~ sulphides and gold. The undi~;>t.u! ~(Od f)J.der qu-'1rtz is coo.rse-tu:xtured;~ clu[1.r or milky, in places showing ~clnib strur.tu.t'e) i oe., qUc.'1.rtz vein filling in which tht: crystals project from the ~!.J'2.._t::.s t;.;c;rOfl S r', fissure openingo ND.tivL! gold is gent;r:.uly seen only in the cx1.di7.ed clres! altb.ough it probably exists dedper in the veins in nearly the same amo'J.nt: but conce~led in the sulphides" Thu veins so far discov(;.~red in north-centra.l IC!2.ho are mesotherrnr",l. Naturally, bonanza bod.ies are absent~ although local srnt;,ll shoots have yielded $20.00 or more per t:)l1: Sc; f J.r as knovm, '.J ~,OO to :;,)15,,00 per ton has be~n recovered fr0m ore ir:~·.1ej Mel nr:~llecl in thE; p."..st Oxi.dized ,~nd p,3.rtly oxidized ores were SUrpf)2~d t. ') bp. s)l;J.e,,~hnt. richer th'1n . sulph:L~e orl~s) but this impression may be a result of the hif~1E;r cxt,:rD.ction of gold from oxidized ores in the stamp mills of former tim{.;s. Prosent-dc,y milling methods can save a high percentage of the gold from both sulphide c..nd oxidized ores, c.s has bben determinf.;d in the laboratory of this burec.u.

,,:J

SOU1H ·-C~h'l1RAL IDAHO

South"cent:c'll Idr,h0. :~"'").cludes ValJ.vy County, acljojning parts of Lemhi, Cust er, and B0ise CC'Ll!l'~5.f';:), s0uthectf1tsrn Gf-;n1 County.> and the northerly pnrts of Blaine and EL11.o::'8,:-;1..:r.L+.i ',3 ,; In t:;~Btern V3.1:::"8Y o.nd -I"restern Cu.ster counties, th~re arE: large c.rec.s of itLoc·:.;ne y~ lc2.nic rocks (, Later there ,';, woro dike G.lld stock intru&ions c:. I:r I).l.,ht:r o.rCdC: the ign\.:ous rocks 01' this time were mostly intrusi va. The H~OC8ng ir.t:~"u3ionb 1,'IJ'8re 10c<'.-1, yet they.~ re found in 3. consid(;rable number of plc.ces no'l, fr~r ~ptl.rt:l Th1s f.uggests tho.t th0y CclITlIJ frorn quite c..n extensive, but d0eply t-uried, magma reservoir. Th(;: lc\rg(;:r intrusives (stocks), unlike the batholith, did not grently ,~,ltcr the invaded rocks and forl~ltjd no conspicuous gneissic shells. :; Thomson.: F-:-A~a-;-;'ilQ-rd~S, H.) Geol~~y 2.ndg~ld r~s~urces of northcentral Idoho, Bull. No.7, Idt\,ho ~ureau 0 f l'i.in(;;s ~~'.lld G80logy.

25

Gold veins in the volcanic territory are epithermal. Southwestward in Boise County, where erosion has been deeper, the majority are mesothermal. In Gem County (Pearl district), they are mesothern~l, but some border on the epithermal. The best ore is in shoots where the country rock, along zones of shearing and fissuring, was more than usually cracked and shattered. The fissures, shear zones, and the intrusive and extensive rocks appear to be arranged in a broad elongated structural area extending from western Lemhi County and eastern Valley County southwest to Gem County. The porphyry dikes and gold veins are in general alignment with the direction of this belt. The country rocks may be any of the older sedimentary forLations, the metamorphic sediments, the granitic rocks of the batholith, or the volCanic flows and tuffs. The gold oreS of the volcanics contain little silver, but those in the other parts of the belt may have important amounts of silver. In some gold deposits of the volcanic area, the eJTe has difficulty in distinguishing mineralized from unmineralized rock. Fissuring may be obscure. The ore may be (1) wide-spread and lying flat in particular beds of lava or tuff, as at Thunder Mountain, (2) the ore may be fine-grained, thin quartz seams, filling simple or complex fractures • Some of the gold is in the form of a selenide. In the vicinity of some of the ore bodies the rocks were somewhat bleached by the hot ore solutions. This may be an aid in prospecting. Generally t hbre is so little to aid the eye that the gold pan and assays are necessary in finding veins.

Underground development sat l'1eudow Creek near Yellow Pint;: disclose important bodies of low-temperature gold ore, with stibnite, arsenopyrite and other sulphides, and little gangue, in seams and replacements of country rock along a broad lode. Just north of Meadow Creek are cinnabar (quicksilver) veins containing some go ld • In the high Salmon River Nountain region of Valley County the surface has not been greatly reduced by erosion since the epithermal ores were deposited. Remnants of flat erosion areas that may have been land surfaces, at about the same time th~ ores were being formed, may be set:n on high ridges and plateaus. Outside the volcanic areas, as in Atlanta, Boise BaSin, Pearl, and ot~ r districts in the southwest half of th~ mineral belt, the mesothermal veins show mineralization for several hundred, even thousands, of feet along their strikes. The light-colored porphyry dikus with which the veins are structurally and genetically associated, are probably of the same age as those of the eruption area. Th~ v~ins contain more gangue, although not large amounts, quartz, calcite, dolomite, barite; also sulphide min~rals, galena, chalcopyrite, tetrahedrite, some ruby silver, and locally bismuth minerals, Usually fin~ gold can be found by panning. Deeper developmdnts in the past few years in the Boise Basin and at . Atlanta, on which thE;re is little published information, have shown that tht:re" is no secondary gold in the veins near th~ surface, and that the sulphide ore shoots yield a good profit. Detailed study of Boise Basin is now being carried on by Dr. Alfred L. Anderson for th~ U.S.Geological Survey and this bureau and a preliminary report is in preparation. A short report by !Vir. Clyde P. Ross (Bulletin 846-d) has been published this yuar (1931~) by tht; U,3. Gt.;ological Survey. OTH~R

GVLD DIGTHICTS

Ores in the Silv~r City and Delamar districts, Owyhee County, are of the same age as those of the mineral belt ,just discussed. Thl:Y arIJ in a volccnic

26

ar~a that is in alignment with tho min~ral belt just des~ribed, but on the south side of the Snake River Plain these districts have produced an important amount of gold, although thby are· chi~fly fwmou6 for their silv~r.

Considerable gold has b~en found in placers around Mount Caribou, Bonneville County. Tht)re ar~ also gold veins in this district, but they have not had much development. The Hurray district, Shoshone County, is on the northerly border oftha great C~ur d'Alene lead-zinc-silver area. There has been a good production from placers in the past. Successful operations are now being conducted on small, but rich, gold vein.s.

NATI0NAL FORESTS Prospecting may be done in the national forests as on other governmt;nt land. Forest officials will be found to be obliging and helpful if regulations for fire protection and other reasonable rules are observed.

THE

VALU~

OF GVLD

The value of gold was formerly fixed at the United States Hint as ~20.67 a. troy ounce. The government now pays ~35 .00 an ounce for newly-mined gold. Good ore under favorable operating conditions c onte.ins 1/15,000 or It:ss of ~old by weight, at present price. Thorefore, it is not to b~ expected that. it will be visible to the naked eye in ordinary ore. Discovery, davtlopm~ntl and mining of gold ore has to be guided by the gold pan, by assaying, or by the app~arance of the vein, or by t he pres~nce of some significant mineral that accompnnies the best oro. One should not b~ excitt;;d OVbr a color of gold becr-use thl;;; gold pan is really surprisingly successful in catching gold worth only a f6\,1 cent s p~r ton of material. This is beeause gold is so very heavy. Fine specks of gold are "colors." They may be SO find that as many as 2,000 are required to be "forth one cent. One cubic inch of gold weighs 10,17 troy ounces, and is now worth about $356.00. A cubic foot of gold w0igh's 1184.7 pounds avoirdupois and a cube measuring l5~ inches in each dimension Weighs about one ton.

FOuL'S O0LD Bright iron pyrite and yello'IJ'i flakes of mica are mistaken for gold by the inexperienced, and ar~ sometimes \~lled "fool's gold." A prospector soon learns to distinguish them under tho magnifying glass or by t heir lighter weight and behavior in the gold pan. Pyrite c~ be easily crushed to a powder. Gold is malleable and is not crushed if pressed or hrunmered. A knife blade will cut a bright yellow mark on gold; on pyrite ['.nd mica, it It:nves a powdery streak. TH~

FIHE ASSAY

The fire assay for gold makes a complete r~covery of it. There are no mysterious or secret methods that can really get any more gold from a sample than does the fire assay. Fraudulent promot~ons of procebses represented to recover more gold than is shown by assay still continue to be attempted.

vvHAT

'rl(j

DO

~'JI1'H

A V.c.;IN

~vH~N

rr IS FuUND

If it is discovered on the public domain, i,e., l~nd .wn~d by the U. S. Government, a discovery monument should b~ erected at once, and a notice of location posted. on the monument. A discov~ry shaft or tunn8l should thbn be d\ll:

27

to a depth or distance of tt..-n f'etolt from th~ surface. The notice can be V'dry simple, printed upon thef'ace of the PO$t used for discovery monumGnt, or writt~n on paper and put into a tin can for protection against weath~r and fastened to the monument. Printed forms may be bought at nt1wspo.ptJr offices and rstation~ry stores in mining regions, but the written notice will hold the claim. The notice should read something like the following:

"1 (or we) hereby loca.te C'.nd cla.im the Bonanza. (or any name

selecte4) lode, running in a course of -~ (whatever direction the compass shows),--- feet, from th~ discovery monument a.nd ....- (in the oppoai te compass direction), - - feet and 300 teet on each side of the lode line. Tht;;; discovery monument bears --- (compass directio'n) teet from (a. 'section corn~r or some pcrmanunt natural object).n Dated. (S1gn~d) Loco.tor or locators.

Distances ann be measured with, a tap~ or paced. Th~ dista.nces from th~ discovery ea.ch way along the assumed course ot th<:; vein must not totc..l over 1,500 feet. The discovery is, Q£ cours~, on the vein or lode line which is supposed to be the cours~o£ t he more or 1~5S concealed vein' on the surface. This line extends along the middle of thb c1a'~. The discovery nv;~y be anywhere between the two ends. Soon after discovery, the corn~rs of th(;: cl[;.im should be marked by posts stariding three' feet nbove ground or by rock monunhmt s of th~ sc.m~ h~ight, The end-lines of the claim Sl10uld be pc.r:lll<:;l or tIl{; locator will not a~cure with th~ c18,im the right to follow th~ vein beyond his side-linea on its dip, under the 50-called "Apextt or extrnlateral law. A v~in outcrop is lik~ly to be crooked so that it m[1.Y be necessary to mrJ.ko bonds or cngl(;:s in the side-lines of tht; claim. If so, place monumt.}nts at theso points. \tlithin 90 dC.i.Ys, filt; with the recorder of the district, or the necr~5t brnnch of the U, S. Land Orfice, 0. notice' of location, giving the srune inforuation as that shown on the location notice ~ The locator now owns thi;,; cl~im so long as he does ~lOO worth of work on it each year, before July 1st, ~ developing the vein or improving the prop~rty, and files affido.vit that he hus done this work, or paid this amount of mon(;:y for wages to emp!o1ee~ who have do~e th~ work for him. claim is found to be vnluabltJ. Patent is Details of this and other legal procedure may be obtain0d from a pomphl(;t tlHining Laws of Idaho," issued b . the State Insptoictor of N.1nes, Stnte Cc,pitol Building, ,Boise, IdC),ho, or abulletin~ "Hin!ng Laws,1t puqlislied by the S:tate Hirl'eraro~ist of California, Ferry Build.ing, San Francisco, ~alifornia. (Price, ~2.00). . Dev~lopm~nt Patent is desirable

wh~never th~

a deed from the government which is generally safe from attack.

In the first stages of devt;lopmt.:nt, it is 'Jise to stay v,li th the ore in incline shafts nnd drifts follov~ing ttl\';: vt::in, and in whatevl:.ir undorground workings the.t are made, howev~r crooked they may be. ThE) t inl'd for more economically design~d workings will comt: later, after the shape 0 f the ore body has b\;;en shown. The prospector should Ull:f3. ov i;;r his outcrop at :.. number of points by pits or sink a prospect shaft on the dip of his v(;:in at th~ plnce of best surface showing, becO,use tht: ore n1~;"y lie in the vein in well defined bodius or "shoots." 1'/1ost v~d.ns cannot mr~ke profitablE;.; production at th~ start, none really exc'ept bonanzas. vlork 'Hithout mining machinery is slow and ~xpensive. Ore may have to be shipp0d on p~ck ~n~~ls. It is advisablu to ship out some of the best ore, if pMning ['..nd n.ssny indicate tl'¥:l t it has good valuti, eVen though it mny not pay r..ll expc:n6~S. Ono or two shipm0nts and sufficient op~ning5 on the

~~enches, then

28

vein, to indicate the position of em or~ shoot and ~nablb it to b~ insp~cted satisfactorily nnd srtlnpllJd by othurs" mt~.y be so convincing thc:..t mon~y cOon be raised to procure effici~nt mining machin~ry to go d~~p~r in th~ v~in, drive levels" and provtl wh~tht:;:r the ore continues as an important body. Aft~r tint, if it do~s prolidse a good tonnng~J there will be no troublv to solI th~ mine, or get cash for a part int~rest, nnd continue to hold a subst.:'..ntiJ.l sh~~rt:: in it. Terms with financiers Developm~t and finc..l equipment, after discovery of 0. promising or~ body" run into large sums of mon~y, Before beginning to m~k~ n profit from a good gold vein, D.nywhere from ~50,OOO to :;)250,000 me.y ht':.vu to bt; sp~nt upon it. This expenditure might yibld ult1mD.tt;;:ly mOllY millions. Yut, in th\j beginning, without this money, the property is of no definite v~,lud to the discoverer. However, he mn.y be in a position to negotiate for fin[.:ncit"l hdlp. He m£.y offer to m.n.ke an outright sr:..le. Some mining fin::tncicrs prefer this. Others expect the discoverer to join in the speculn.tion by wo.iting with them for ultimfJ,te returns. This would be done by his accepting, in lieu of cc..sh, a proper interest in the corpor~tion th~~t \'Jould be orgnnized to develop nnd op~rn.t~ thE; prop~rty't If he is dt:wing with trustworthy people exp~ri~nced in th~ technicalities of mining, this is a good arrangement ~ In this Wtly, great mining fortunvs h[l.ve beGn made.

Somtj mines a.re financed .. through prof~ssionnl promoters or brokt:rs, by sale of stock to the public. The N~tion['.l Securities Act (1934) tt:;:nds to protect the public against misrepre~entation or excessive pron~t0rts commissions, Gold !lIP

min~s

in western history

The place of gold in the history of thu west~rn states is not gener~lly appreciated in tht:s~ d.::.ys. Thu rush ot forty-niners to Cr.li.fomia started the main wo.ve of settloment in the Rocky ~lount:'..ins t.nd to the west of them, The gold of Co,lifornin. had much to do ,,~ith nationo'l r0construction after the Civil~vnr. Then soon thereafter" thE:; Comstock Lode of Nevada enlc;rgud the group of millionaire mining pioneers, distributed woalth for the upbuilding of Cc.lifornia. The early mining fortun~s were nminly responsible for the construction of the transcontinental railway and t~legraph lines. There wc.s a return wave of C~. lifornia prospectors into the northWest c~nd to these we O,\,le the economic beginnings of Idaho ~d Washington, It was interesting to obs~rve in pioneering days the effects of sudden wealth upon individua.l prospectors. lVia.ny of them hnd wandered over mO'Wltains and deserts mostly for the love of such ['.. life. Such m~n ha.d no pdrm1ll1ent interest in conventionnl co~nunities) sold th0ir discoveries for wrr~t th~y could get in ready cash, had a short fling nt the luxuries of citi0s, th~n returnud to th~ wilderness. Others found insFirut ion in the solitudes, c-cquired abundant physic,".l ·'lnd IDuntG.l vigor nnd a sound philosophy of life. Some of these were r.l~n of grutlt vision. Th~y becn.t,~ leaders in business,. civil affairs Gond politics, D.cculcrt,t(;.)d the development c,nd civild.zD.tion of the 'Whole uvest, c.nd achieved pln.ces of honor in the history of the cCJuntry.

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