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MISSI ISLAND

Fig . 1 - S ample locality map.

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Flin Flon Base Metals Project

by G. R. Pa.rslo.v and B. R. Watters

'Ihis year's project is a detailed laboratory lithogeoc.hemical study of approximately 900 samples collected during the 1979 field mapping of the area east of Amisk Lake (~Dougall et al, 1979). 'Ihe extent of sanpling is illustrated in Figure 1. 'Ihe stl.dy has been carried out with the objective of characterizing and subdividing geochemically the Amisk Group volcanics. Difficulties were experienced in the field in subdividing these rocks except on the broad basis of older, basic roe.ks to the east and ya.mger, more acid rocks towards the west. Indeed, even after detailed re-mapping, the "mixed basaltic series" of Byers and Dahlstrcrn (1954) is still a term applicable to m:>st of the exposed volcanic rock. 'Ihe post-volcanic regional rretarrorphisn has rendered subtle field subdivision inpossible. Microscopic identification of rock types, other than volcaniclastic types, is also unrewarding due to extensive, pervasive alteration (e.g. arrphibolitization) of mafic and felsic minerals.

An orientation study of sane 80 rocks has been conpleted to establish the procedures to be followed for the main analytical program. Briefly, each sanple is split in two, one half (weighing about 3 kg on average) is crushed to produc.e about 60 g of -200 mesh material. Major elements are determined as follows: ICP: Si02, Al203, total Fe203, cao, r-t::JO, MnO, P205, Ti02: AA: Na20, K:I): Tube furnace: H:tJ+, COz; Titration: FeO. 'Ihe selected trace elements are determined by both ICP and XRF: Ba, Co, OJ, Ni, V, Zn, Y, Nb, Zr, Sr, Rb. Present results clarify certain aspects of the main volcanic sequence and of talc-magnesite roe.ks in the area.

Volcanic Pocks

'lhe major oxide data illustrate that the majority of exposed volcanic roe.ks in the area are basaltic and that true andesites are rare. Standard binary and ternary plots show that the predaninant rock type is a quartz tholeiite, h~ver, insufficient analyses are yet available to distinguish oceanic or island arc affinities. Talcing into account the views

* University of Iegina. Cperating budget provided this year by the Saskatchewan Geological SJrvey in continuance of the previously funded federal-provincial program.

of other authors regarding lithostructural domains (Lewry and Sibbald, 1980) am conparisions with the La lbnge volcanic sequence ( Cbombe, 1979), the authors favour the latter origin.

Major element variation diagrams and field observations indicate tv.0 dominant rock types: a spec.ifically defined grol.(> of quartz tholeiites and a more diffuse group lCXJsely tenned "mixed basalts". fk:Mever, trace element relationships, such as the Ti-Zr binary plot (Fig. 2), indicate cyclical

15

10 Ti(kpprnJ

,,_ 1..L c

o O

,, O o

~ () . ct;o •

0 0 o. 0

o• o •

Ood'I O e

l• t ..... ,

100

Fig. 2 - Ti-Zr binary diagram illustrating the volcanic trend (as open cir­cles) from older (low Ti/Zr values) to younger (high Ti/Zr values} basalts and rare andesi­tes. The dots represent data for "talc-magnesite'' bodies fn the area (corrected for volatiles),

volcanic activity: that is to say rocks of similar major element chemistry occur at different stratigraphic horizons with different Ti-Zr values arD yet all fall CXl a single Ti-Zr evolutionary trend. '!he essentially lineal trend in Figure 2 (open circles) exhibits low Ti-Zr values for basal roe.ks to the east with increasing Ti-Zr towards the upperrrost rocks in the west. 1he suggested stratigraphy is:

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4. Upper Mixed Ilasalts (highest Ti-Zr values)

3. Upper Quartz 'lholeittes 2 . Lo,;er Mixed Basal ts 1. Lo,;er Quartz 'Iholei ttes (lo,1est Ti -Zr

values)

A sinplified geologic map of tli.e area (Fi g . 3) illustrates the di stribution of tli.e lo,1est three units as determined f rou the available data .

'lhese preliminary r esult s suggest that the ongoi ng geochemical program will contribute to a better understanding of the Amisk Gr oup "stratigr aphy" am the evolutioo of the volcanic sequence .

Carb:.:>natized Rocks

Recently, Parslo,J et al (1980) reported the results of a chemical study on "talc-­magnesite" rocks occurring in the area . * The

Table 1: Corrparison of mean values am standard deviations (brackets) of the tv.o groups of "talc-magnesite" material with an average ultramafic (UM) and tasaltic rock . Bare data r ecal culat ed without volatiles fran raw data in A.

Sanple Average Average Average Average Average Average 1-13 1- 13 lM 14-21 14- 21 Basalt

A B A B

Si02 32.30 ( 4 .0) 40 . 5 43.60 ( 3.5) 37. 20 (7.7 43.50 50 .8

Ti02 0 .006 (0 . 009) 0. 008 0 .12 ( 0 . 08) 1.10 (0 . 6 l.30 2 .0

A1.203 0 . 34 ( 0.32) 0 .43 2.30 ( 1. 3 ) 12. 00 (3 .6 ) 14.00 14. 1

Fe203 3 .32 ( l.89) 4 .16 0 . 90 ( 0 .8) 0. 45 (0 . 48) 0 . 53 2.9

[\n() 0 ,08 ( 0.04) 0 . 10 0 .15 ( 0 . 04) 0 .21 (0 . 11) 0.25 0 .18

FeO 2.55 ( 0 .81) 3.20 7. 70 ( 0.96) 6.90 (2 . 3 ) 8.10 9.05

~ 34.10 ( 5.4 ) 42 .70 40. 50 (11. 0 ) 7.90 (2 .4 ) 9.20 6 .34

cao 6.00 ( 5.5) 7. 50 5.90 ( 8. 7) 14 , 10 (5,1 ) 16. 50 10.4

Na20 0 ,39 ( 0 . 11) 0 . 49 0.17 ( 0. 05) l.64 (0 .84) 1.92 2 .2

K20 0. 14 ( 0 . 05) 0 . 18 0 . 05 ( 0.04) 0 . 99 (0.83) l. 16 0 .82

P205 0 .13 ( 0.10 ) 0 . 16 0 .30 (0 .15) 0.35 0.23

C02 15.50 ( 10.1) n/ a 12 . 60 (8 . 5 ) n/a

H20+ 4 . 70 ( 3.8 ) n/a 0 . 6 ( 0. 24) l.82 (1.16) n/a 0.91 H20- 0 .13 ( 0 . 11 ) 0.16 0.13 ( 0 . 06) 0. 07 (0.02) 0.08

(LOI) 20. 70 ( 6.5 ) n/a 15 . 60 (8 . 0 ) n/a

Au 11 18 ) 14 7 18 (41 21

Ba <10 <10 0.40 134 (184 157 150

Co 103 17 129 150 54 (15 63

Cu <40 <40 20 70 ( <40 82 175

Nb 8. 70 5 . 5 11 9 8.90 ( 1. 0 ) 10

Ni 1830 496 2293 2000 81 ( 50 ) 95 100

Rb 3.60 7 . 7 4 . 50 1 11 16 ) 13 5

Sr 35 23 44 10 168 85 ) 196 355

v 28 17 35 40 293 (105 342 275

y 4. 30 6.1 5.40 5 20 ( 9 23 5

Zn 44 77 55 40 93 83 109 80

Zr 8 . 00 6. 4 10 40 77 38 90 30

* Laboratory XRD studies indicate that "magnes ite" is actually an Fe poor ankerite.

Fig. 3 - Simpl i fi ed geol ogical map of the eastern side of Am1sk lake.

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S IMPUFIEO GEOLOGIC MAP O F EAST AMISI\ lAI\E

1 : 50 000

• 3 U,mple location

O m.ne ttl•

SfflATIGRAP'"'Y

p P 6 1'90l OtC

M Ml•i G,oup

,., M fied BasaN.a

tNTRUSIYE ROCKS

b gabbro - dt0nl•

'- UIIUN'llaf)C$

M

~ •16 ~

• 17 ~ ,.M, : ; • : 18 .: .• :. JI -~ ,. .. ,-. ..

... '"' ., ·"· ' ' ' JI II ,.. A " ,. ,. "

,., " · r. ",., JI ,.,

JI -'• JI,. JI

"' b I', ,. ,I. ,, "

p

p

(J

0 0

0 N

~

locations of these rocks are shown on Figure 3. In the field they fall naturally

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into the folla,/ing t1f.O groups: K 20

a) Srre.11 isolated bcdies (generally in the west of the area) associated with basalts and their pyroclastic and sedimentary equivalents.

b) large planar bcdies (e.g. in ~sher Lake) paralleling the regional structure and associated with altered ultrama£ic (possibly intrusive) rocks.

Tentative field identification suggests that type (a) rocks are carbonatized and h~ated basalts, or equivalents, and that type (b) rodes ~e derived fran the ultranafic rocks. 'lhe chemical data confirm this explanation. Fbr exanple, the Ti-Zr values plotted on Figure 2 fall into tv.o obvious groups, one folloong the general volcanic trend, the other givi ng the typical lcw Ti-Zr values expected of ultranafic rocks. Figure 4, a silica variation diagram, illustrates ho.,,, the major oxides also conform to tv.o subgroups -an ul tramafic group and a basal tic group. The single sarrple to the extreme right in ooth Fi~es 2 and 4 was considered at the time of sanpling to be altered Mi.ssi Group sediment: its position oo the graphs vindicates this supposition. Table 1 lists mean elE!'11eflt values .for the t<,,o groups, as analyzed (A) and corrected assuning addition of a:,2 and Hp+ (B), as well as data for an average basalt and an average ultranafic rock . The data ccripare favourably and stq:3est that major and trace element mobilization has been negligible and that the rocks have been altered sinply by introduction of volatiles. The cnly exception is Ca, and its geochemical associate Sr, the fomer being sanewhat erratic and high in value, suggesting sane introduction of calcium in certain sarrples.

Mineralization

An objective of the project is t o gain a better unjerstan::'l.ing of the controls and distr icution of mineralization in the area. 'Tue> observations can be made at this stage:

1. The eex>ncnri.c Cu concentrations of Flexar and Birch Island (Fig. 3) , and subecornnic CU concentrations in the area in general, are apparently restricted to andesitic pyroclastic rocks in the I.o,,,er ~rtz Tholeiite unit. Further stooies around other mines to the east is warranted in order t o see if they are localized in a similar stratigrai;:hic position.

2. Altlnugh the data for Au (by NM) are very erratic, values are clearly higher in carbonatized rocks . The mean and stan::'l.ard

Dt--~-'-~--'.J.!..'-.tm.~...._~u____:~~~L--~...J.....~--1 3

' 0

Cao . . ,o• .

MgO ..

FeO

0 •

oi--~, .~~-'-~---1.~~..___· ~··-·..__~....._~__,..::_--l 12

. .• .. . . .. 0

0

Dt-,~--'-~--'~~-'T~-'-~~......_~-l-~--''-----I 8

. . - . ..

0

"'

0 ~2s~--''--~~3s;""'"_...__.._~,~5~~,.__~~,s~~--'-~_Jes

5102

Fig. 4 - Si lica variation diagram of "ta 1 c-magnes i te" rocks . Open c ircles are analyses of basaltic affinity while dots are analyses of ultramafic affinity {al l analyses recalculated to a vola­til e free basis) .

deviation for fresh rocks are 2 and 3 fPb, \\hi.le for carbonatized rocks the values are 14 and 21 fPb, Further ....ork 01 the Au distributions is desirable .

References

Byers, A.R. and Dahlstran, C.D.A. , 1954. Geol ogy and Mineral Deposits of the J\misk-Wildnest Lake Area. saskatchewan Department of Mineral Resources Report No. 14,

Ccx:m:>e, w., 1979. Mineral De!X)sits and !Egional Metallogeny, Southeastern Shield. in Summary of Investigations, 1979, Saskatchewan Geological &irvey . p 120-133.

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Lewry, J.F. and Sibbald, T. I .I., 1980. 'Iherrrotectonic Evolution of the <llurchill Province in Northern Saskatchewan. Tectonophysics, v. 68. p 45-82.

M::.D?ugall, F. H. , Parslow, G. R. and Watters, B.R., 1979. Flin Flon Base Metals Projec. t . in SUllVMry of Investigations, 1979, Saskatchewan Geological Survey. p 116-119.

Parslow, G.R. , Watter, B.R. and McD:>ugall, F.H., 1980 (in press). <llemistry and Origin of Carbonate Ric.h Ibcks in the Area East of Amisk lake, Saskatchewan. Bull. Can. Inst. Min.