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TEMPERATURESF FORi,IATIONOF THE CHISEI AKE

sutpHtDEDEPOS|T,NOW [AKE, MANTTOBA

A. E. BENCEercD . C. COLEMAN

tln iaer ity of Sashatchezaan,os atoon,Saskatchaaan

During the winter of 1961-62a study was madeof the ore mineralogyof the chisel Lake Mine by A. E. Benceworking under the supervision

of L. c. coleman.This mine s located n centralManitoba at 84"b0,N.Lat., 100007/ w. Long. specimensfor this work were provided by theHudsonBay Mining and SmeltingCompany.

The sulphides: arsenopyrite, pyrite, sphalerite, chalcopyrite, galena,pyrrhotite, gudmundite, marcasite, and the sulphosalts: meneghinite,tetrahedrite, and a bournonite-seligmannite olid solution, wereobservedas well as small amounts of native gold.

on the basisof textural relationships he following generalsequence fevents for the formation of the metallic componentsof the ore body ispostulated: the crystallization of arsenopyritefollowed by deformation;crystallizationof pyrite;introductionof gold; crystallizationofpyrrhotite,sphalerite, and chalcopyrite, generally in that order but with somereversals and overlapping relationships; fracturing followed by theemplacementof galena, the sulphosalts, gudmundite, and pyrite; andfinally, the formation of marcasiteby the alteration of pyrrhotite.

Two geothermometerswere employed to determine emperatures offormation. Thesewere the FeS-ZnSgeothermometerof Kullerud (lgbg)

and skinner & Barton (195s) and the pyrrhotite geothermometei ofArnold (1962).

All measurementswere made with a Norelco wide angle diffracto-meter using filtered cu radiation for the sphalerite samples and Feradiation for the pyrrhotite samples.An external silicon standard wasemployed and the 2g values measuredare believed to be accurate to+0.005'. corrections for Mns and cdSx in solid solution in sphaleritewere made basedon the curves of coleman (19b7).The amounts of coand Ni* present in the pyrrhotite are less than 400 p.p.m. and

theireffectson the unit cell dimensionsare negligible.

.*Yr and

9d.analyses-of so,haleriteand co and Ni analysesof pyrrhotite were doneby Dr. R. G. Arnold of the saskatchewan Research council uriig r-rt-fluorescencetechniques.

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664 THE CANADIAN MINERALOGIST

Sphalerites rom fourteenspecimenswereanalyzed.Thesesampleshad

been taken at regular intervals along the plunge of the orebody to see f

a temperature gradient existed during its formation.

The correctedunit cell dimensiotr" t.bl" 1) vary from 5.4131A to5.4158A which indicate FeS contents of the sphaleritesranging from

about 8.4-14.3 mol/s. Using data from Kullerud (1953)' a range of

minimum temperaturesof formation of the sphaleritewas determinedas

having beenfrom 275" C. to 425"C.

T"tt" 1. T""""-"tt*a""

F.

MnS and

Sample Meas"red Wl % Wt.To CdS Correqted" N;:* - oo Ai - 'Mir6" caS" correction oo (A)

Minimum

Mol Vo formationFeS Temp. "C.

234o6a

8I

10t l7213L4

5.4153 .675.4140 .695.4160 .405.4157 .275.4160 .595.4151 .485.4157 .295.4163 .485.4161 .295.4140 .48

6.41,45 .545.4161 .735.4152 .735.4135 .36

.08 -.0006

.13 - .0007

.10 - .0004

.L4 -.0003

.13 - .0006

.12 -.0005

.17 - .0003

. r2 - .0005

.L7 - .0003

.13 -.0005

.L2 - .0005.14 - .0007

.17 - .0007

.t7 - .0004

5.4L47 11.855.4133 8.805.4156 13.805.4154 13.356.4154 13.355.4t46 11.605.4154 13.355.4158 74.255.4158 14.256.4135 9.20

5.4140 10.305.4154 13.355.4145 11.405.4131 8.35

3702854L5405405360405425425300

330405360275

Pyrrhotite from two specimenswas analysed n the present study and

d(l}z) spacingsof 2.05-65 and 2.0558A w"r" measured (Table 2)'

These indicate pyrrhotite compositions containing about 46.5 atomic

percent metals and a temperature of formation for the pyrrhotite from

toth specimensof 510+10' C. This is a minimum tempefature offormation but, since n both specimenshe pyrrhotite is closelyassociated

with pyrite, the results are probably very close o the true temperature

of formation.

Tenr-B 2. TsMrsRAruREs op FotuetroN oF Pvnnsortrp

Sample - d'(l}Z)a - Atomic % lemperature of

Nd. Angsirom units metals formation oC'

13 2.0565 46.50 510

The results of this work suggest he following possibilities: first, that

either a temperature gradient existed during the formation of the

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CEISEL LAKE SULPEIDE DEPOSIT 6 6 5

sphalerite or that there was a time-space relationship for sphaleriteformation, and second hat the temperatureof formation of the pyrrhotitewas higher than that of the sphalerite and that, therefore, the physical

conditions were changing during the formation of the deposit.The Fes content of the sphalerites as determined by the unit celldimensionsappears o be a function of the distance from the margins ofthe ore body (Table 1, Fig. 1). This feature could be accounted or if

GLACIAL

o tt":::

\ i,1ffi\ ,. \.1;z\ :i,\ !i .iii

i . f i !. /1 i i

.i".j/t' .i li fi'i.,+ |,iiii "/..1g,"r'1,

E--?i':/MARGINOF OREBODY

SPHALERITEISOTHERMS--35O...-

gAlAUEBrr_EAMPLE JLOCATIONS

LOIIGITUDINAL SECTION

CHISEL LAKE M|NE

LOOKING N.67OE.

SCALE: t INCH32Oo FEET

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666 THE CANADIAN MINERALOGIST

the deposit had formed as the result of hydrothermal solutions which

were introduced along some"channelway" located near its centre and if

such introduction had createda thermal gradient diminishing outwards

from the locus of introduction. An alternative explanation is that theformation of sphalerite extended over a period of time during which

temperatures in the region were progressively changing. In this case,

sphalerite tourard the centre of the orebody would, presumably, have

been formed earliest and the formation of sphalerite would have pro-

gressedoutwards, with time, towards the margins of the deposit.

This study has shown that the pyrrhotite formed at a higher temper-

ature than the sphalerite.On this basis,assumingwhat is considered he

normal sequenceofevents (i.e. decreasing emperature with time), the

pyrrhotite formed earlier than the sphalerite.Age relationshipsof these

minerals deduced rom textural evidencesupport this idea.

RrrBnBNcss

AnnolD, R. G. (1962): Equilibrium reliationsbetween pyrrhotite and pyrite from 325"

to 743oC., Econ. GeoI., 57, 72-90.Cor-sMeN,L. C. (1957): Mineralogy of the Giant Yellowknife gold mine, Yellowknife,

N.W.T.. Econ.Geol'., ,400-42,5.

Kwr-rnr,o, G. (1952) Fe$ZnS system, a geological hermometer, Nmsh. GeoI.T'id'sshr,,32.6L-t47.

SKTNNTR, , J., & BAnroN, P. B., Jn. (1958): Recent work on sphalerite, its.bearing on

the sphaierite geothermometer (abstr.), Geol',Soc. Amerha Bul'|,., 69, L768.

Manuscribt rece'fuedctober 6, 1962