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Newgres: a turbo pascal program to solve a modified version of gresens' hydrothermal alteration equation
Computers & Geosctences Vol. 16, No 7. pp. 925-932. 1990 Pnnted in Great Britain
0008-30o~qO$3.00+ 0.00 Pergamon Press pie
NEWGRES: A TURBO PASCAL PROGRAM TO SOLVE A MODIFIED VERSION OF GRESENS' HYDROTHERMAL ALTERATION EQUATION C. H. B. LEITCH and S. J. DAY Department of Geological Sciences, University of British Columbia. Vancouver. British Columbia. Canada V6T 2B4 (Received 21 March 1989: rerised 23 January 1990)
Abstr+.ct--Chemical compositions of altered rocks cannot be compared directly to the compositions of the unaltered parent rocks because of volume changes attendant on alteration. In order to make such a comparison, the observed chemical changes must be corrected for volume changes, usually by identifying immobile elements that are conserved during alteration. Gresens" equation can be used to estimate the volume changes, and subsequently calculate the chemical changes. A modified version of Gresens' hydrothermal alteration equation has been derived that expresses metasomatic losses and gains as a ratio of component weights rather than a weight difference. The resulting equation is more applicable to comparison of the behavior of components during hydrothermal alteration. In graphical presentations loss of components can be given the same visual weight as component gain. The programs GRES (for Gresens' equation) and NEWGRES (for the modified equation) enable rapid modeling of chemical mass balance during hydrothermal alteration, with the ability to rapidly compare the outcome of selecting different parent rocks or different immobile components. Ket' Word~': Chemical changes, Mass balance, Ilydrothermal alteration. Volume factors, Grescns diagrams.
INTROI)UCTION Studies of hydrothermally altered rocks are concerned necessarily with the chemical losses and gains produced during alteration of the parent rock. It is not possible to compare directly chemical compositions of the altered rocks with those of the fresh rock if there has been a significant volume change accompanying the alteration (Gresens, 1967; Babcock, 1973). In his classic study of this problem Gresens (1967) made the fundamental assumption that one or more components are immobile during alteration. Once these components are identified, the assumption of their immobility must be verified, as suggested by Appleyard (1980). The volume change then can be estimated, and if alteration is pervasive, that is the same volume change applies to all components, gains or losses of the mobile components can be calculated. Gresens" approach has been applied widely (Gibson, Watkinson, and Comba, 1983; Morton and Nebel, 1984; Studemeister and Kilias, 1987; Kerrich and Fyfe, 1981). In this paper we present a Gresens' and modified Gresens' equation, and graphics programs for both which permit rapid modeling of losses and gains during hydrothermal alteration.
where X,, is the change in weight proportion of component n, I.V4. Wn are the weights of component n in parent rock A and altered rock B, w is the initial weight of parent rock, /'; is the volume factor, the ratio of volume of altered rock to parent rock, X.4, Xn are weight proportions of component n in parent rock A and altered rock B, used directly from chemical analyses, and S.~, SA are specific gravities of parent and altered rock, measured on representative rock chips. Usually, w is set to 100 g so that if X.~ and Xs are in percent then X, is in weight percent change of component n. Althot, gh the dcriwLtion is straightforward and sound, the equation can be improved by elimination of the following shortcomings.
MODIFIED VERSION OF GRESENS' EQUATION Gresens" equation is: X,, =
W s -
;V., =
w{[(F,)(XH)sB/s,)]
-
X,}
(I) 925
(a) The equation is dimensionless if X, and Xa are expressed as a proportion, however concentration data for trace elements usually are reported in parts per million whereas data for major elements are given in percent. Therefore. in the situation of a data set containing both trace and major elements, all numbers must be transformed to percent prior to using Gresens" equation if trends for different components are to be compared. This operation requires a data manipulation step which is preferably avoided. (b) In some alteration studies, the effect ofchanging volume factors and specific gravity may be
926
C.H.B. LEITCHand S. J. DAY of interest. Because Gresen's equation was derived specifically to express weight change as a difference, manipulation of factors in the equation expressed as ratios (specific gravity and volume factor) does not produce usable results. (c) It is not possible to manipulate the equation to express XA and XB as a simple ratio or a difference. Therefore, the effect of changes in these factors on X,, for example in checking the impact of analytical or sampling errors, is not obvious.
Furthermore, in a graphical presentation, say of X, vs F,, it is preferable to plot the variables on logarithmic axes so that values less than unity (for example, decrease of component weight or volume factor) are given the same emphasis as values greater than unity (corresponding increase). In Equation (I), the straightline form is not preserved if logs of values are plotted. By expressing X;, as a ratio of the weight of component n in the product rock to the weight in the parent rock and using the same definitions as Gresens' equations, a new equation is produced:
x'.= w.Iw~ =(X.I,V,,).(s.IS,,).F..
(2)
In Equation (2) all changcs tire expressed :is ratios, the equation is dimensionless and taking logs preserves the straightline rehttionship betwcen X;, and F~: Iog(X~, ) = log( Wn/ll'.~ ) = log(#%) +
Iog[(X.lX,).(s.IS,)l.
(3)
Further rearrangement of Equation (3) shows that it is similar to Equation (I): log(Wn) - log( I,V,~) = Iog[F,'(S,/S,)'Xn]-Iog(XA).
(4)
A comparison of results obtained using Equation (4) and Gresens' Equation (1) is provided following description of the program.
transect of variably altered rock (e.g. as a vein is approached). THE PROGRAM
GRES (for Gresens' equation) and N E W G R E S (for the modified Gresens' equation) are Turbo Pascal programs developed for IBM-compatible personal computers. The current versions produce tables of results and draft-quality graphical output for a Hercules graphics adaptor (HGC), color graphics adaptor (GCA), and enhanced graphics adaptor (EGA) using Turbo Pascal G R A P H I X subprograms. Memory requirements are minimal (256 K RAM), and only one floppy disk drive is necessary. The programs are user-friendly, with all instructions provided in the form of menu-type prompts, at all stages of program operation. Every effort has been made to provide assistance with correction of mathematical errors (such as division by zero, or zero or negative arguments in log functions) without aborting the program. Errors resulting from simple keyboard errors can be corrected prior to proceeding. Tile programs, with a user's manual, will be available on floppy diskette (at cost) through the Association of Exploration Geochemists, P.O. Box 523, Rexdale, Ontario, Canada M9W 5L4. Input data can consist currently of concentrations of up to 30 components as well as rock specific gravity and distance from the vein. The input data file is a text file with the fl)rmat shown in Table I. A sample data file used in the tbllowing examples is shown in Table 2. The input file allows selection of dehtult immobile components (indicated by an asterisk in column I). Prompts throughout the program allow reduction of this list. The programs are interactive, giving the user opportunities to test which elements are most likely immobile, to view estimated volume changes produced, to select the elements interpreted as immobile to calculate an average volume factor, and to select the sample (or average) considered as parent rock. Menu option 1: composition-colume diagrams
GRAPHICAL APPROACHES Two graphical approaches have been used to show alteration trends. Grant's (1986) method shows which elements have been lost or gained, and discriminates between constant volume, constant mass, or constancy of an immobile component (such as AI,O~), during alteration. However, it does not show readily the spatial relationships of changes relative to a feature such as a vein. Using this method a separate diagram would have to be plotted for each incremental sample location on approaching a vein. By contrast, Sketchley and Sinclair (1987a), Robert and Brown (1986), and Kerrich and Watson (1984) and the current program produce a single bar diagram showing gains or losses of a given element across a
In Equation (3) there are two unknowns, viz. X~, and F~, all other factors are measured (or assigned). In the composition-volume diagrams, one sample is selected and Equation (3) lines for each element are constructed by choosing values for F, and solving for it';,. The reason for constructing a diagram such as Figure I is that the relative immobility of components may be checked. Ideally immobile components will have common intercepts. In practice, because of measurement errors, if they show a tendency to cluster, it is considered a sufficient demonstration of immobility. Because log(X;,)=0 defines immobile components, the average intercept values for the immobile components gives the volume factor applicable to that sample, compared to the fresh rock
DIST(NSUITE)
SG(NSUITE)
= project title = number o f oxides and elements (integer) = number o f altered suites o f rocks (integer) = number of unaltered rocks (integer) flag for potentially immobile elements or oxides (character) COMPtj) = name o f j t h oxide or element (string o f up to five characters) NAME(i) = name of ith rock (string o f eight characters) DIST(i) = distance o f ith sample from altering conduit in meters (real) SG(i) = specific gravity of ith sample (real) x0,j) = concentration of oxide or element j in sample i (real) NINSUITE(k) = number o f samples in suite k (integer) SUITETITLE(k) = name o f kth suite (string of eight characters) {I = comment line
TITLE NCOMP NSUITE NFRESH
where
NAME(NSUITE)
SG(l)
X(I ,NSUITE)
X(l,l)
X(I,NINSUITE)
SG(NINSUITE)
DIST(NINSUITE)
NAME(NINSUITE)
NINSUITE(NSUITE) SUITETITLE(NSUITE) NAM E(I) DIST(1)
X(I,I)
SG(I)
DIST(I)
XiI,NFRESH)
X(I,I)
COMP(I)
SG(NFRESH)
SG(I)
DIST(NFRESH)
S.G.
{ Distance
DIST(I)
{Column 1 must be either* or blank
{Line I
NAME(NFREStl) NINSUITE( I ) SUITETITLE( 1) NAME(I)
COMP(NCOMP) NAME(I)
TITLE N C O M P NSUITE N F R E S H COMP(I)
Table I. General format for input data file
X(NCOMP,NSUITE)
X(NCOM P,I )
X(NCOMP, NINSUITE)
X(NCOMP, I)
XtNCOMP,NFRESII)
COMP(NCOMP)} X(NCOMP, I)
o
o
g
0
o
0 -I
8. g
O
<_.
O
928
C . H . B . LEITCH and S. J. DAV Table 2. Sample data file BRALORNE 1127
SiO, *AI~O~ *TiO: "Zr
Fe:O~
MgO CaO Na,O K:O LOI Y C093 AVGDI C094 AVGSG C033 8 C033 9 C033 10 7 1551FW C032 1 C032 2 C032 3 C032 4 C032 6 C032 7 C032 8 7 1551HW C033 1 C033 3 C033 5 C033 7 C033 8 C033'10 C033, 9
50 50 50 50 8 9 10
2.85 2.85 2.66 2.67 2.80 2.84 2.92
59.35 55.32 71.83 68.90 55.52 57.03 52.37
II.22 0.23 13.12 0.40 13.68 0.19 13.97 0.20 13.12 0.28 9.29 0.19 15.06 0.47
49 40 86 60 35 28 39
7.80 9.28 3.07 3.88 6.96 7.53 10.39
8.12 7.00 0.44 1.03 3.46 11.12 6.28
7.06 7.02 2.10 3.06 9.95 8.14 7.48
3.88 3.60 5.60 5.78 2.97 2.09 3.17
0.14 0.08 0.69 0.41 0.21 0.04 0.03
0.1 0.5 1.0 2.0 3.5 5.0 I0
2.7645.15 2.75 60.15 2.82 45.25 2.74 53.01 2.75 49.02 2.73 53.66 2.72 48.82
18.85 0.46 17.75 0.22 7.06 0.18 15.47 0.27 14.12 0.34 14.66 0.30 18.63 0.39
41 24 32 38 43 49 49
6.14 3.46 5.72 4.93 7.15 7.65 7.06
3.24 2.07 5.03 3.51 5.57 6.33 3.25
9.22 4.93 16.26 9.82 8.97 6.13 8.43
0.76 0.24 0.03 0.24 2.21 2.57 5.33
3.69 3.70 1.80 3.01 1.73 I.t4 1.55
12.26 7.55 18.81 10.04 II.01 7.28 6.39
13 8 7 8 14 12 6
0.3 1.5 3.5 5.0 8 9 10
2.83 2.74 2.78 2.76 2.80 2.92 2.84
6.53 0.12 14.54 0.22 16.60 0.30 15.02 0.34 13.12 0.28 15.06 0.47 9.29 0.19
28 73 34 42 35 39 28
3.46 4.79 7.69 9.56 6.96 10.39 7.53
2.78 2.83 3.74 5.01 3.46 6.28 11.12
11.300.12 1.31 7.67 0.60 2.69 4.89 1.13 2.39 6.54 2.86 1.18 9.95 2.97 0.21 7.48 3.17 0.03 8.14 2.09 0.04
10.23 9.34 7.68 8.60 6.43 4.14 3.18
6 9 10 13 13 17 17
64.54 57.56 55.65 50.58 55.52 52.37 57.03
[log(F,) = 0.17 in Fig. I]. If the user desires, a separate d i a g r a m may be plotted by the p r o g r a m comparing each sample to the fresh rock. Typically, the lines on the diagram will tend less a n d less to cluster as the vein is a p p r o a c h e d (and the a s s u m p t i o n of BRALORNE
COMPOSITION
SAMPLE: ( 2 0 3 2 / 3 1,2
~
VOLUME DIAGRAM SUITE: 1 5 5 1 F
UNALTERED SAMPLE:
C093
0
1.74 16 2.71 17 2.46 14 2.40 12 6.43 13 4.14 17 3.18 17
immobility is violated increasingly). In addition, the user may eliminate immobile c o m p o n e n t s from the short list defined in the data file (asterisks in c o l u m n I of c o m p o n e n t list, Tables I a n d 2). In its simplest terms, for instance, if AI,O3 is immobile so that none is lost or gained during alteration, then if its c o n c e n t r a t i o n seems to d r o p relative to the unaltered sample, there must have been a volume increase, and vice versa. T h e former leads to a volume factor (F,) of > 1, the latter to a F, of < I .
Menu option 2: t,olume Jiwtor diagrams u.
0.6
,,,
i i co..,.~,
o >
A,,O, rio~ Zr
o.oi
///C'/~'°' ///~,o~
......
i
06 -1.2
/
•
7"
.......
/Co
_.~...;>'~-'
-0.6
0.0
0.6
LOG LOSS/GAIN FACTOR
Figure I. Log composition-volume plot [Eq. (3)] for sample C032/3 (Table 2). Line at log( Vd V ) = 0.17 gives average volume factor calculated using TiO: and AhOy. Diagram is redrawn from program output; lines for AI:O,. Fe:O~. Zr. MgO, SiO:. and TiO: are shown as a shaded region because they are too close to be resolved.
The averaged volume factors for the various samples in an alteration series are o u t p u t in tabular form (each F, in Table 3 is derived from a separate plot like Fig. I) and the volume factors are also plotted vertically, as in Figure 2A, to see if the three supposedly immobile c o m p o n e n t s show similar behavior (i.e. if the curves are relatively flat). If they are not (if they are strongly kinked as in Fig. 2A), this may be cause for rejection of one or more of the "'immobile" c o m p o n e n t s before o b t a i n i n g a final average volume factor for each sample. T h e closer the curves are to the horizontal, the better the assumption of immobility of all three is met, with changes in c o n c e n t r a t i o n s of the three elements resulting from only dilution or c o n c e n t r a t i o n , that is, only by
Solving a modified ,.ersion of Gresens' hydrothermal alteration equation
929
Table 3. Option 2 output (summary of logarithmic volume factors) for Bralorne. Suite: 1551F. unaltered sample C093. Average volume factor based on: AI:O~, l-iO,, Zr Sample
Distance (m)
Density (gcm ' )
AI:O~
TiO,
C0321 C032,2 C03L3 C032,4 C032,,6 C032/7 C032/8
0.1 0.5 1.0 2.0 3.5 5.0 10.0
2.76 2.75 2.82 2.74 2.75 2.73 2.72
-0.2114 -0.1837 0.2058 -0.1224 -0.0843 -0.0975 -0.1999
-0.2871 0.0348 0.1111 -0.0525 -0.1542 -0.0967 -0.2091
addition or leaching of some other component(s). This contrasts with absolute changes in concentration due to real losses or gains of other, mobile, components. The curves may be at different F, levels, because samples close to the vein may have F~ values increasingly far from unity. They also tend to show increasing variability as the vein is approached. This is shown in Figure 2B, where (except for the closest sample to the vein, C032/I, which contained a quartz BRALORNE SUITE 1551F VOLUME CONSTRAINTS UNAkrEnE~ ~.~a,c't.E CO9~
rr O I-O
0.2
co,:
,<,
CO3Z'~
LU ,d
CO~
3
e 2~
O >
-0.2 !
At,~O]
T~Ol
Zr
COMPONENTS
A!~O~ TIO 1 Z"
A
BRALORNE SUITE 1551F VOLUME CONSTRAINTS tt~LrE¢~ SaCUF',.E AW3~
0.3 i
0.2
m
0.!
O~ 0 0
0.0
11201
]'iO 2
COMPONENTS
Z¢
Algo I TiO~t ZF
B
Figure 2. Plot of log(F,) for immobile components. Open boxes are average volume factors of components listed below them (in this example, AI:O~, TiO:. and Zr). Note overestimation of volume factor by Zr; B. as for (A) but using a different fresh host-rock composition. Diagram is redrawn from program output.
0.0913 0.3255 0.1896 0.1275 0.0722 0.0187 0.0202
Average -0.1357 0.0589 0.1688 -0.0158 -0.0554 -0.0585 -0.1296
vein and is therefore not representative of altered wall rock), there is a general trend towards flatter curves, closer to unity, in the series C032/2 and 3, to C032/4, to C032/6, 7, and 8. If sampling were carried out far enough, to the parent rock. the average line would become horizontal at log(F,)= 0.
Menu option 3: loss-gain diagrams The refining of the list of immobile components and fresh rocks culminates in tabulated values of log(X,]) or X, (Table 4) and loss-gain diagrams which show log(X;,) (Fig. 3) or X, (Fig. 4) vs distance from a vein for each component and summarize the selection of frcsh rocks and immobile components. Gains of components are reflected as positive wtlues of ,V'. and vice versa. The example, from the footwall of the major 51 Vein on 15 level of the Bralornc Mine, British Columbia, shows strong depiction of Na,O and concomitant addition of K20 as the vein is approached. This represents the destruction of albite feldspar as it is replaced by muscovite. Strong depletion of MgO and Fe20 ~ also arc indicated, as primary hornblende is destroyed by carbonatcsericite alteration. An additional feature of interest is the general parallel variations in volume factor and loss-onignition (LOI) as alteration increases (compare Fig. 3 and htst column of Table 3). Although not always linear as the vein is approached (sample C032/I is again an exception, possibly bccause of included quartz vein material), it is apparent in the example given. It is better shown by the data, of Skctchlcy and Sinclair (1987a) for the Erickson Mine (northwestern British Columbia), a similar mesothermal gold vein deposit to Bralorne, but located in more homogeneous basaltic host rocks. The underlying reason for the parallel increases in F~ and LOI lies in the type of alteration, which at both deposits involves addition of CO, and HzO in the form of carbonate, scricite, and chlorite (Leitch and Godwin, 1987: Sketchlcy and Sinclair, 1987b). The general agrcement between volume factor and LOI thus gives confidence that the changes in volume estimated from immobile elements are real, and that therefore the calculated losses and gains in other elements also reflect real proccsses.
iiii
-0.1
Zr
930
C.H.B. LEZTCHand S. J. DAY
Table 4. Tabulated losses and gains: Bralome suite 1551F losses and gains (weight percent). Volume factors calculated based on AI:O3, TiO:, Zr. Unaltered sample: AVGDI Distance Density (m) (g/cm~)
Sample C032/I C032,'2 C032/3 C032/4 C032/6 C032/7 C032/8
0.1 0.5 1.0 2.0 3.5 5.0 I0.0
SiO:
AL:O3 TiO:
2.76 -17.07 2.85 2,75 29.37 11.87 2.82 25.08 -0.58 2.74 4.44 4.32 2.75 -5.71 1.17 2.73 -0.86 1.76 2.72 -13.88 2.69
-0.01 -0.09 -0,08 -0.10 -0.06 -0.I0 -0.07
Zr
F e : O ~ MgO
-5.27 -6.21 16.86 2.84 3.51 9.73 1.59
COMPARISON OF GRESENS' EQUATION AND EQUATION (4)
Comparative loss-gain diagrams for the test data are shown in Figure 4 (Gresens' equation) and Figure 3 (modified Gresens" equation). The trends shown by the two equations are similar, for example Na:O is depleted whereas K:O is enriched. However, comparison of values of losses and gains for the various elements are more meaningful on the modified
-4.08 -4.41 0.88 -3.72 -2.04 -1.52 -3.29
-4.26 0.79 -4.09 -0.08 1.94 21.87 -3.04 4.05 -1.36 2.06 -0.58 -0.80 -4.24 0.13
02
Na,O
K:O
LOI
Y
-2.96 -3.26 -3.55 -3.33 -1.36 -0.99 0.92
3.05 5.13 3.12 3.31 1.67 1.08 1.24
7.68 7.92 30.73 8.61 8.43 4.68 2.71
-20.88 -8.12 22.36 -16.56 -17.53 -22.28 -66.74
equation graphs. In particular, gains for AI:O_~ (an immobile component) are greater than the maximum 0.04% loss experienced by TiO z using Gresens' equation but using the modified equation reveals comparable values. It is apparent that Zr should not have been included in the volume factor calculation because it shows considerably greater losses than either AI,O~ and TiO:. It also is clearer that K:O and NazO are the most mobile elements to be expected.
s,o2°-1°11
03
CaO
0.10
TiO 2
A[203
0.1 0.0
i
t
O
-0.1 i
-02 -0.3
Zr
0.1 0
g
i
0
o
o
-02 -03
CaO
0.4
I
0.4 I ~ L . ~
FezO 3
03
06 02
I
o
I
-0.4
BRALORNE
Na20
SUITE:
2 !
t
o
,
o
L
,
t
,,
1551F
VOLUME FACTOR BASED ON AI203 4 t
6 i
8 t
10 i
TiO 2 12 I-
I
-0.5-
!
-0.2
i
i I
S
-06
L~-
0.0
0
00 -0.2
00
0.5"
-,-I ,]
MgO
04
1,0"
0.2
DISTANCE T O VEIN (M)
-1.0-
-0.4
U N A L T E R E D SAMPLE:
-1.5"
K20
LOI
1.o-
CO93
10
!
0.5
05 00
j
-o lo I U
-0.1 -0.2 -0.3 -0.4
-0.1
10
,
02 0.1
02
0.0
I
.O.lO
0.3
OO
0.00
I .oILl I l o
i
oo
O5
I 0
i
0
0
:
! I t
00 ~ V ~ C
-05
-o 5
-05
-1.0
.1 o
.10
Figure 3. Log loss'gain vs distance profile diagr;,ms. Diagram is redrawn from program output, however
program prints eight bar graphs on one page; K:O. LOI. and Y v,ould appear on separate page with tide block repealed.
Y
Sob,ing a modified version of Gresens" hydrothermal alteration equation
SiO 2
20
3.1
AI20 3 0.04
2.
10 i
i
i
I
o.o2
' V'I 0 .t.JU I
•
o,oo
-0.02
-2"
-0.04
m
Zr
.OOlS1
.0025'1,d
Fe203
IL
-2
J
hlT.lI,
II" MgO
4 2
i
I
.~d n
TiO 2
6
4 2
I
I
0
j
-4 -4
__I
-6
L
C,aO
BRALORNE $UffE: 1551F
Na20
3 2
¢,.9
VOLUMEFACTORBASEDON AI20 3 TIO2
1
I:
't
I
K20
0.0
! I
!
, I,
.!15 -2,0] -25
I
-1 -2
2.0 1.5 1.0 0.54
I
I
o
2,
4,
?
~
1,o
DISTANCE TO VEIN (M)
i
UNALTERED SAMPLE: CO93
25 2O 15
LOI o.o04t
10 5
0 -5 -10 -15 -20 -25
931
, =
=
I
I
0o0210 !
i
I
|
!
I
Figure 4. Loss/gain vs distance profile diagrams calculated using Gresens' original equation. Parent rocks and immobile components are identical to Figure 3. Diagram is redrawn from program output as described in Figure 3. CONCLUSIONS Using G R E S and N E W G R E S , hydrothermal alteration can be modeled rapidly by considering a variety of fresh and altered rocks and different immobile components. The modified version of Gresens' hydrothermal equation used in N E W G R E S allows the user to compare readily different components in terms of immobility. Because all changes are expressed as ratios data can be plotted on log axes without losing the straightline form of the equation.
Acknowh'dgments--We are grateful to A. J. Sinclair, D. A. Sketchley, and C. I. Godwin and two earlier referees for critical reading of this paper and helpful suggestions. Work was supported by an I. W. Killam fellowship to Leitch. REFERENCES Appleyard, E. C., 1980. Mass balance computations in metasomatism: metagabbro/nepheline syenite pegmatite interaction in northern Norway: Contrib. Mineral. Petrology. v. 73. no. I, p. 133-144.
Babcock, R. R., 1973, Computational models of metasomatic processes: Lithos, v. 6, no. 3, p. 279-290. Gibson, H. L., Watkinson, D. H., and Comba, C. D. A., 1983, Silicification: hydrothermal alteration in an Archean geothermal system within the Amulet Rhyolite Formation, Noranda, Quebec: Econ. Geology, v. 78, no. 5, p. 954-971. Grant, J. A., 1986, The isocon diagram--a simple solution to Gresens' equation for metasomatic alteration: Econ. Geology, v. 81, no. 8, p. 1976-1982. Gresens, R. L., 1967, Composition-volume relationships of metasomatism: Chem. Geology, v. 2, no. I, p. 47-55. Kerrich, R., and Fyfe, W. S., 1981, The gold-carbonate association: source of CO,, and CO: fixation reactions in Archean lode gold deposits: Chem. Geology, v. 33, no. 4, p. 265-294. Kerrich, R., and Watson, G. P., 1984, The Macassa Mine Archean Lode Gold deposit, Kirkland Lake, Ontario: geology, patterns of alteration, and hydrothermal regimes: Econ. Geology. v. 79, no. 5, p. 1104-1130. Leitch, C. H. B., and Godwin, C. I., 1987, The Bralorne gold vein deposit: an update (92.1/15): British Columbia Ministry of Energy, Mines and Petroleum Resources, Geological Fieldwork 1986, Paper 1987-1, p. 35-38.
tF
932
C . H . B . LEITCl-tand S. J. DAY
Morton, R. L., and Nebel, M. L., 1984, Hydrothermal alteration of felsic volcanic rocks at the Helen siderite deposit, Wawa, Ontario: Econ. Geology, v. 79, no. 6, p. 1319--1333. Robert. F., and Brown, A. C., 1986, Archean gold-bearing quartz veins at the Sigma Mine, Abitibi Greenstone Belt, Quebec: Part II. Vein paragenesis and hydrothermal alteration: Econ. Geology, v. 81, no. 3, p. 593-616. Sketchley, D. A,. and Sinclair. A. J., 1987a. Gains and losses of elements resulting from wallrock alteration a quantitative basis for evaluating lithogeochemical samples: British Columbia Ministry of Energy, Mines and
Petroleum Resources, Geological Fieldwork 1986, Paper 1987-I, p. 413--417. Sketchley, D. A., and Sinclair, A. J., 1987b. Multi-element lithogeochemistry of alteration associated with goldquartz mineralisation of the Erickson Mine, Cassiar District: British Columbia Ministry of Energy, Mines and Petroleum Resources, Geological Fieldwork 1986, Paper 1987-1, p. 57-63. Studemeister, P. A., and Kilias, S., 1987. Alteration pattern and fluid inclusions of gold-bearing quartz veins in Archean trondjhemite near Wawa, Ontario, Canada: Econ. Geology, v. 82, no. 2, p. 429439.
0008-30o~qO$3.00+ 0.00 Pergamon Press pie
NEWGRES: A TURBO PASCAL PROGRAM TO SOLVE A MODIFIED VERSION OF GRESENS' HYDROTHERMAL ALTERATION EQUATION C. H. B. LEITCH and S. J. DAY Department of Geological Sciences, University of British Columbia. Vancouver. British Columbia. Canada V6T 2B4 (Received 21 March 1989: rerised 23 January 1990)
Abstr+.ct--Chemical compositions of altered rocks cannot be compared directly to the compositions of the unaltered parent rocks because of volume changes attendant on alteration. In order to make such a comparison, the observed chemical changes must be corrected for volume changes, usually by identifying immobile elements that are conserved during alteration. Gresens" equation can be used to estimate the volume changes, and subsequently calculate the chemical changes. A modified version of Gresens' hydrothermal alteration equation has been derived that expresses metasomatic losses and gains as a ratio of component weights rather than a weight difference. The resulting equation is more applicable to comparison of the behavior of components during hydrothermal alteration. In graphical presentations loss of components can be given the same visual weight as component gain. The programs GRES (for Gresens' equation) and NEWGRES (for the modified equation) enable rapid modeling of chemical mass balance during hydrothermal alteration, with the ability to rapidly compare the outcome of selecting different parent rocks or different immobile components. Ket' Word~': Chemical changes, Mass balance, Ilydrothermal alteration. Volume factors, Grescns diagrams.
INTROI)UCTION Studies of hydrothermally altered rocks are concerned necessarily with the chemical losses and gains produced during alteration of the parent rock. It is not possible to compare directly chemical compositions of the altered rocks with those of the fresh rock if there has been a significant volume change accompanying the alteration (Gresens, 1967; Babcock, 1973). In his classic study of this problem Gresens (1967) made the fundamental assumption that one or more components are immobile during alteration. Once these components are identified, the assumption of their immobility must be verified, as suggested by Appleyard (1980). The volume change then can be estimated, and if alteration is pervasive, that is the same volume change applies to all components, gains or losses of the mobile components can be calculated. Gresens" approach has been applied widely (Gibson, Watkinson, and Comba, 1983; Morton and Nebel, 1984; Studemeister and Kilias, 1987; Kerrich and Fyfe, 1981). In this paper we present a Gresens' and modified Gresens' equation, and graphics programs for both which permit rapid modeling of losses and gains during hydrothermal alteration.
where X,, is the change in weight proportion of component n, I.V4. Wn are the weights of component n in parent rock A and altered rock B, w is the initial weight of parent rock, /'; is the volume factor, the ratio of volume of altered rock to parent rock, X.4, Xn are weight proportions of component n in parent rock A and altered rock B, used directly from chemical analyses, and S.~, SA are specific gravities of parent and altered rock, measured on representative rock chips. Usually, w is set to 100 g so that if X.~ and Xs are in percent then X, is in weight percent change of component n. Althot, gh the dcriwLtion is straightforward and sound, the equation can be improved by elimination of the following shortcomings.
MODIFIED VERSION OF GRESENS' EQUATION Gresens" equation is: X,, =
W s -
;V., =
w{[(F,)(XH)sB/s,)]
-
X,}
(I) 925
(a) The equation is dimensionless if X, and Xa are expressed as a proportion, however concentration data for trace elements usually are reported in parts per million whereas data for major elements are given in percent. Therefore. in the situation of a data set containing both trace and major elements, all numbers must be transformed to percent prior to using Gresens" equation if trends for different components are to be compared. This operation requires a data manipulation step which is preferably avoided. (b) In some alteration studies, the effect ofchanging volume factors and specific gravity may be
926
C.H.B. LEITCHand S. J. DAY of interest. Because Gresen's equation was derived specifically to express weight change as a difference, manipulation of factors in the equation expressed as ratios (specific gravity and volume factor) does not produce usable results. (c) It is not possible to manipulate the equation to express XA and XB as a simple ratio or a difference. Therefore, the effect of changes in these factors on X,, for example in checking the impact of analytical or sampling errors, is not obvious.
Furthermore, in a graphical presentation, say of X, vs F,, it is preferable to plot the variables on logarithmic axes so that values less than unity (for example, decrease of component weight or volume factor) are given the same emphasis as values greater than unity (corresponding increase). In Equation (I), the straightline form is not preserved if logs of values are plotted. By expressing X;, as a ratio of the weight of component n in the product rock to the weight in the parent rock and using the same definitions as Gresens' equations, a new equation is produced:
x'.= w.Iw~ =(X.I,V,,).(s.IS,,).F..
(2)
In Equation (2) all changcs tire expressed :is ratios, the equation is dimensionless and taking logs preserves the straightline rehttionship betwcen X;, and F~: Iog(X~, ) = log( Wn/ll'.~ ) = log(#%) +
Iog[(X.lX,).(s.IS,)l.
(3)
Further rearrangement of Equation (3) shows that it is similar to Equation (I): log(Wn) - log( I,V,~) = Iog[F,'(S,/S,)'Xn]-Iog(XA).
(4)
A comparison of results obtained using Equation (4) and Gresens' Equation (1) is provided following description of the program.
transect of variably altered rock (e.g. as a vein is approached). THE PROGRAM
GRES (for Gresens' equation) and N E W G R E S (for the modified Gresens' equation) are Turbo Pascal programs developed for IBM-compatible personal computers. The current versions produce tables of results and draft-quality graphical output for a Hercules graphics adaptor (HGC), color graphics adaptor (GCA), and enhanced graphics adaptor (EGA) using Turbo Pascal G R A P H I X subprograms. Memory requirements are minimal (256 K RAM), and only one floppy disk drive is necessary. The programs are user-friendly, with all instructions provided in the form of menu-type prompts, at all stages of program operation. Every effort has been made to provide assistance with correction of mathematical errors (such as division by zero, or zero or negative arguments in log functions) without aborting the program. Errors resulting from simple keyboard errors can be corrected prior to proceeding. Tile programs, with a user's manual, will be available on floppy diskette (at cost) through the Association of Exploration Geochemists, P.O. Box 523, Rexdale, Ontario, Canada M9W 5L4. Input data can consist currently of concentrations of up to 30 components as well as rock specific gravity and distance from the vein. The input data file is a text file with the fl)rmat shown in Table I. A sample data file used in the tbllowing examples is shown in Table 2. The input file allows selection of dehtult immobile components (indicated by an asterisk in column I). Prompts throughout the program allow reduction of this list. The programs are interactive, giving the user opportunities to test which elements are most likely immobile, to view estimated volume changes produced, to select the elements interpreted as immobile to calculate an average volume factor, and to select the sample (or average) considered as parent rock. Menu option 1: composition-colume diagrams
GRAPHICAL APPROACHES Two graphical approaches have been used to show alteration trends. Grant's (1986) method shows which elements have been lost or gained, and discriminates between constant volume, constant mass, or constancy of an immobile component (such as AI,O~), during alteration. However, it does not show readily the spatial relationships of changes relative to a feature such as a vein. Using this method a separate diagram would have to be plotted for each incremental sample location on approaching a vein. By contrast, Sketchley and Sinclair (1987a), Robert and Brown (1986), and Kerrich and Watson (1984) and the current program produce a single bar diagram showing gains or losses of a given element across a
In Equation (3) there are two unknowns, viz. X~, and F~, all other factors are measured (or assigned). In the composition-volume diagrams, one sample is selected and Equation (3) lines for each element are constructed by choosing values for F, and solving for it';,. The reason for constructing a diagram such as Figure I is that the relative immobility of components may be checked. Ideally immobile components will have common intercepts. In practice, because of measurement errors, if they show a tendency to cluster, it is considered a sufficient demonstration of immobility. Because log(X;,)=0 defines immobile components, the average intercept values for the immobile components gives the volume factor applicable to that sample, compared to the fresh rock
DIST(NSUITE)
SG(NSUITE)
= project title = number o f oxides and elements (integer) = number o f altered suites o f rocks (integer) = number of unaltered rocks (integer) flag for potentially immobile elements or oxides (character) COMPtj) = name o f j t h oxide or element (string o f up to five characters) NAME(i) = name of ith rock (string o f eight characters) DIST(i) = distance o f ith sample from altering conduit in meters (real) SG(i) = specific gravity of ith sample (real) x0,j) = concentration of oxide or element j in sample i (real) NINSUITE(k) = number o f samples in suite k (integer) SUITETITLE(k) = name o f kth suite (string of eight characters) {I = comment line
TITLE NCOMP NSUITE NFRESH
where
NAME(NSUITE)
SG(l)
X(I ,NSUITE)
X(l,l)
X(I,NINSUITE)
SG(NINSUITE)
DIST(NINSUITE)
NAME(NINSUITE)
NINSUITE(NSUITE) SUITETITLE(NSUITE) NAM E(I) DIST(1)
X(I,I)
SG(I)
DIST(I)
XiI,NFRESH)
X(I,I)
COMP(I)
SG(NFRESH)
SG(I)
DIST(NFRESH)
S.G.
{ Distance
DIST(I)
{Column 1 must be either* or blank
{Line I
NAME(NFREStl) NINSUITE( I ) SUITETITLE( 1) NAME(I)
COMP(NCOMP) NAME(I)
TITLE N C O M P NSUITE N F R E S H COMP(I)
Table I. General format for input data file
X(NCOMP,NSUITE)
X(NCOM P,I )
X(NCOMP, NINSUITE)
X(NCOMP, I)
XtNCOMP,NFRESII)
COMP(NCOMP)} X(NCOMP, I)
o
o
g
0
o
0 -I
8. g
O
<_.
O
928
C . H . B . LEITCH and S. J. DAV Table 2. Sample data file BRALORNE 1127
SiO, *AI~O~ *TiO: "Zr
Fe:O~
MgO CaO Na,O K:O LOI Y C093 AVGDI C094 AVGSG C033 8 C033 9 C033 10 7 1551FW C032 1 C032 2 C032 3 C032 4 C032 6 C032 7 C032 8 7 1551HW C033 1 C033 3 C033 5 C033 7 C033 8 C033'10 C033, 9
50 50 50 50 8 9 10
2.85 2.85 2.66 2.67 2.80 2.84 2.92
59.35 55.32 71.83 68.90 55.52 57.03 52.37
II.22 0.23 13.12 0.40 13.68 0.19 13.97 0.20 13.12 0.28 9.29 0.19 15.06 0.47
49 40 86 60 35 28 39
7.80 9.28 3.07 3.88 6.96 7.53 10.39
8.12 7.00 0.44 1.03 3.46 11.12 6.28
7.06 7.02 2.10 3.06 9.95 8.14 7.48
3.88 3.60 5.60 5.78 2.97 2.09 3.17
0.14 0.08 0.69 0.41 0.21 0.04 0.03
0.1 0.5 1.0 2.0 3.5 5.0 I0
2.7645.15 2.75 60.15 2.82 45.25 2.74 53.01 2.75 49.02 2.73 53.66 2.72 48.82
18.85 0.46 17.75 0.22 7.06 0.18 15.47 0.27 14.12 0.34 14.66 0.30 18.63 0.39
41 24 32 38 43 49 49
6.14 3.46 5.72 4.93 7.15 7.65 7.06
3.24 2.07 5.03 3.51 5.57 6.33 3.25
9.22 4.93 16.26 9.82 8.97 6.13 8.43
0.76 0.24 0.03 0.24 2.21 2.57 5.33
3.69 3.70 1.80 3.01 1.73 I.t4 1.55
12.26 7.55 18.81 10.04 II.01 7.28 6.39
13 8 7 8 14 12 6
0.3 1.5 3.5 5.0 8 9 10
2.83 2.74 2.78 2.76 2.80 2.92 2.84
6.53 0.12 14.54 0.22 16.60 0.30 15.02 0.34 13.12 0.28 15.06 0.47 9.29 0.19
28 73 34 42 35 39 28
3.46 4.79 7.69 9.56 6.96 10.39 7.53
2.78 2.83 3.74 5.01 3.46 6.28 11.12
11.300.12 1.31 7.67 0.60 2.69 4.89 1.13 2.39 6.54 2.86 1.18 9.95 2.97 0.21 7.48 3.17 0.03 8.14 2.09 0.04
10.23 9.34 7.68 8.60 6.43 4.14 3.18
6 9 10 13 13 17 17
64.54 57.56 55.65 50.58 55.52 52.37 57.03
[log(F,) = 0.17 in Fig. I]. If the user desires, a separate d i a g r a m may be plotted by the p r o g r a m comparing each sample to the fresh rock. Typically, the lines on the diagram will tend less a n d less to cluster as the vein is a p p r o a c h e d (and the a s s u m p t i o n of BRALORNE
COMPOSITION
SAMPLE: ( 2 0 3 2 / 3 1,2
~
VOLUME DIAGRAM SUITE: 1 5 5 1 F
UNALTERED SAMPLE:
C093
0
1.74 16 2.71 17 2.46 14 2.40 12 6.43 13 4.14 17 3.18 17
immobility is violated increasingly). In addition, the user may eliminate immobile c o m p o n e n t s from the short list defined in the data file (asterisks in c o l u m n I of c o m p o n e n t list, Tables I a n d 2). In its simplest terms, for instance, if AI,O3 is immobile so that none is lost or gained during alteration, then if its c o n c e n t r a t i o n seems to d r o p relative to the unaltered sample, there must have been a volume increase, and vice versa. T h e former leads to a volume factor (F,) of > 1, the latter to a F, of < I .
Menu option 2: t,olume Jiwtor diagrams u.
0.6
,,,
i i co..,.~,
o >
A,,O, rio~ Zr
o.oi
///C'/~'°' ///~,o~
......
i
06 -1.2
/
•
7"
.......
/Co
_.~...;>'~-'
-0.6
0.0
0.6
LOG LOSS/GAIN FACTOR
Figure I. Log composition-volume plot [Eq. (3)] for sample C032/3 (Table 2). Line at log( Vd V ) = 0.17 gives average volume factor calculated using TiO: and AhOy. Diagram is redrawn from program output; lines for AI:O,. Fe:O~. Zr. MgO, SiO:. and TiO: are shown as a shaded region because they are too close to be resolved.
The averaged volume factors for the various samples in an alteration series are o u t p u t in tabular form (each F, in Table 3 is derived from a separate plot like Fig. I) and the volume factors are also plotted vertically, as in Figure 2A, to see if the three supposedly immobile c o m p o n e n t s show similar behavior (i.e. if the curves are relatively flat). If they are not (if they are strongly kinked as in Fig. 2A), this may be cause for rejection of one or more of the "'immobile" c o m p o n e n t s before o b t a i n i n g a final average volume factor for each sample. T h e closer the curves are to the horizontal, the better the assumption of immobility of all three is met, with changes in c o n c e n t r a t i o n s of the three elements resulting from only dilution or c o n c e n t r a t i o n , that is, only by
Solving a modified ,.ersion of Gresens' hydrothermal alteration equation
929
Table 3. Option 2 output (summary of logarithmic volume factors) for Bralorne. Suite: 1551F. unaltered sample C093. Average volume factor based on: AI:O~, l-iO,, Zr Sample
Distance (m)
Density (gcm ' )
AI:O~
TiO,
C0321 C032,2 C03L3 C032,4 C032,,6 C032/7 C032/8
0.1 0.5 1.0 2.0 3.5 5.0 10.0
2.76 2.75 2.82 2.74 2.75 2.73 2.72
-0.2114 -0.1837 0.2058 -0.1224 -0.0843 -0.0975 -0.1999
-0.2871 0.0348 0.1111 -0.0525 -0.1542 -0.0967 -0.2091
addition or leaching of some other component(s). This contrasts with absolute changes in concentration due to real losses or gains of other, mobile, components. The curves may be at different F, levels, because samples close to the vein may have F~ values increasingly far from unity. They also tend to show increasing variability as the vein is approached. This is shown in Figure 2B, where (except for the closest sample to the vein, C032/I, which contained a quartz BRALORNE SUITE 1551F VOLUME CONSTRAINTS UNAkrEnE~ ~.~a,c't.E CO9~
rr O I-O
0.2
co,:
,<,
CO3Z'~
LU ,d
CO~
3
e 2~
O >
-0.2 !
At,~O]
T~Ol
Zr
COMPONENTS
A!~O~ TIO 1 Z"
A
BRALORNE SUITE 1551F VOLUME CONSTRAINTS tt~LrE¢~ SaCUF',.E AW3~
0.3 i
0.2
m
0.!
O~ 0 0
0.0
11201
]'iO 2
COMPONENTS
Z¢
Algo I TiO~t ZF
B
Figure 2. Plot of log(F,) for immobile components. Open boxes are average volume factors of components listed below them (in this example, AI:O~, TiO:. and Zr). Note overestimation of volume factor by Zr; B. as for (A) but using a different fresh host-rock composition. Diagram is redrawn from program output.
0.0913 0.3255 0.1896 0.1275 0.0722 0.0187 0.0202
Average -0.1357 0.0589 0.1688 -0.0158 -0.0554 -0.0585 -0.1296
vein and is therefore not representative of altered wall rock), there is a general trend towards flatter curves, closer to unity, in the series C032/2 and 3, to C032/4, to C032/6, 7, and 8. If sampling were carried out far enough, to the parent rock. the average line would become horizontal at log(F,)= 0.
Menu option 3: loss-gain diagrams The refining of the list of immobile components and fresh rocks culminates in tabulated values of log(X,]) or X, (Table 4) and loss-gain diagrams which show log(X;,) (Fig. 3) or X, (Fig. 4) vs distance from a vein for each component and summarize the selection of frcsh rocks and immobile components. Gains of components are reflected as positive wtlues of ,V'. and vice versa. The example, from the footwall of the major 51 Vein on 15 level of the Bralornc Mine, British Columbia, shows strong depiction of Na,O and concomitant addition of K20 as the vein is approached. This represents the destruction of albite feldspar as it is replaced by muscovite. Strong depletion of MgO and Fe20 ~ also arc indicated, as primary hornblende is destroyed by carbonatcsericite alteration. An additional feature of interest is the general parallel variations in volume factor and loss-onignition (LOI) as alteration increases (compare Fig. 3 and htst column of Table 3). Although not always linear as the vein is approached (sample C032/I is again an exception, possibly bccause of included quartz vein material), it is apparent in the example given. It is better shown by the data, of Skctchlcy and Sinclair (1987a) for the Erickson Mine (northwestern British Columbia), a similar mesothermal gold vein deposit to Bralorne, but located in more homogeneous basaltic host rocks. The underlying reason for the parallel increases in F~ and LOI lies in the type of alteration, which at both deposits involves addition of CO, and HzO in the form of carbonate, scricite, and chlorite (Leitch and Godwin, 1987: Sketchlcy and Sinclair, 1987b). The general agrcement between volume factor and LOI thus gives confidence that the changes in volume estimated from immobile elements are real, and that therefore the calculated losses and gains in other elements also reflect real proccsses.
iiii
-0.1
Zr
930
C.H.B. LEZTCHand S. J. DAY
Table 4. Tabulated losses and gains: Bralome suite 1551F losses and gains (weight percent). Volume factors calculated based on AI:O3, TiO:, Zr. Unaltered sample: AVGDI Distance Density (m) (g/cm~)
Sample C032/I C032,'2 C032/3 C032/4 C032/6 C032/7 C032/8
0.1 0.5 1.0 2.0 3.5 5.0 I0.0
SiO:
AL:O3 TiO:
2.76 -17.07 2.85 2,75 29.37 11.87 2.82 25.08 -0.58 2.74 4.44 4.32 2.75 -5.71 1.17 2.73 -0.86 1.76 2.72 -13.88 2.69
-0.01 -0.09 -0,08 -0.10 -0.06 -0.I0 -0.07
Zr
F e : O ~ MgO
-5.27 -6.21 16.86 2.84 3.51 9.73 1.59
COMPARISON OF GRESENS' EQUATION AND EQUATION (4)
Comparative loss-gain diagrams for the test data are shown in Figure 4 (Gresens' equation) and Figure 3 (modified Gresens" equation). The trends shown by the two equations are similar, for example Na:O is depleted whereas K:O is enriched. However, comparison of values of losses and gains for the various elements are more meaningful on the modified
-4.08 -4.41 0.88 -3.72 -2.04 -1.52 -3.29
-4.26 0.79 -4.09 -0.08 1.94 21.87 -3.04 4.05 -1.36 2.06 -0.58 -0.80 -4.24 0.13
02
Na,O
K:O
LOI
Y
-2.96 -3.26 -3.55 -3.33 -1.36 -0.99 0.92
3.05 5.13 3.12 3.31 1.67 1.08 1.24
7.68 7.92 30.73 8.61 8.43 4.68 2.71
-20.88 -8.12 22.36 -16.56 -17.53 -22.28 -66.74
equation graphs. In particular, gains for AI:O_~ (an immobile component) are greater than the maximum 0.04% loss experienced by TiO z using Gresens' equation but using the modified equation reveals comparable values. It is apparent that Zr should not have been included in the volume factor calculation because it shows considerably greater losses than either AI,O~ and TiO:. It also is clearer that K:O and NazO are the most mobile elements to be expected.
s,o2°-1°11
03
CaO
0.10
TiO 2
A[203
0.1 0.0
i
t
O
-0.1 i
-02 -0.3
Zr
0.1 0
g
i
0
o
o
-02 -03
CaO
0.4
I
0.4 I ~ L . ~
FezO 3
03
06 02
I
o
I
-0.4
BRALORNE
Na20
SUITE:
2 !
t
o
,
o
L
,
t
,,
1551F
VOLUME FACTOR BASED ON AI203 4 t
6 i
8 t
10 i
TiO 2 12 I-
I
-0.5-
!
-0.2
i
i I
S
-06
L~-
0.0
0
00 -0.2
00
0.5"
-,-I ,]
MgO
04
1,0"
0.2
DISTANCE T O VEIN (M)
-1.0-
-0.4
U N A L T E R E D SAMPLE:
-1.5"
K20
LOI
1.o-
CO93
10
!
0.5
05 00
j
-o lo I U
-0.1 -0.2 -0.3 -0.4
-0.1
10
,
02 0.1
02
0.0
I
.O.lO
0.3
OO
0.00
I .oILl I l o
i
oo
O5
I 0
i
0
0
:
! I t
00 ~ V ~ C
-05
-o 5
-05
-1.0
.1 o
.10
Figure 3. Log loss'gain vs distance profile diagr;,ms. Diagram is redrawn from program output, however
program prints eight bar graphs on one page; K:O. LOI. and Y v,ould appear on separate page with tide block repealed.
Y
Sob,ing a modified version of Gresens" hydrothermal alteration equation
SiO 2
20
3.1
AI20 3 0.04
2.
10 i
i
i
I
o.o2
' V'I 0 .t.JU I
•
o,oo
-0.02
-2"
-0.04
m
Zr
.OOlS1
.0025'1,d
Fe203
IL
-2
J
hlT.lI,
II" MgO
4 2
i
I
.~d n
TiO 2
6
4 2
I
I
0
j
-4 -4
__I
-6
L
C,aO
BRALORNE $UffE: 1551F
Na20
3 2
¢,.9
VOLUMEFACTORBASEDON AI20 3 TIO2
1
I:
't
I
K20
0.0
! I
!
, I,
.!15 -2,0] -25
I
-1 -2
2.0 1.5 1.0 0.54
I
I
o
2,
4,
?
~
1,o
DISTANCE TO VEIN (M)
i
UNALTERED SAMPLE: CO93
25 2O 15
LOI o.o04t
10 5
0 -5 -10 -15 -20 -25
931
, =
=
I
I
0o0210 !
i
I
|
!
I
Figure 4. Loss/gain vs distance profile diagrams calculated using Gresens' original equation. Parent rocks and immobile components are identical to Figure 3. Diagram is redrawn from program output as described in Figure 3. CONCLUSIONS Using G R E S and N E W G R E S , hydrothermal alteration can be modeled rapidly by considering a variety of fresh and altered rocks and different immobile components. The modified version of Gresens' hydrothermal equation used in N E W G R E S allows the user to compare readily different components in terms of immobility. Because all changes are expressed as ratios data can be plotted on log axes without losing the straightline form of the equation.
Acknowh'dgments--We are grateful to A. J. Sinclair, D. A. Sketchley, and C. I. Godwin and two earlier referees for critical reading of this paper and helpful suggestions. Work was supported by an I. W. Killam fellowship to Leitch. REFERENCES Appleyard, E. C., 1980. Mass balance computations in metasomatism: metagabbro/nepheline syenite pegmatite interaction in northern Norway: Contrib. Mineral. Petrology. v. 73. no. I, p. 133-144.
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