MacFlinCor and its application to fluids in Archean lode-gold deposits

-himica Pergamon

a Cosmochimica Acta,Vol.59, No. 19.pp. 3943-3952.1995 Copyright8 1995Elsevier Science Ltd Printed in the USA. Allrights reserved 0016-7037/95 $9.50+ .OO

00s7037( 95)00254-5

MacFlinCor and its application to fluids in Archean lode-gold deposits* PHILIP E. BROWNand STEFFENG. HAGEMANN Department of Geology and Geophysics, University of Wisconsin, Madison, WI 53706, USA

(Received December 30, 1994; accepted in revised form July 12, 1995 )

Abstract-MacFlinCor was developed to process laboratory data gathered on fluid inclusions and to calculate isochores for geologically important fluids composed of H20, CO*, CH,, NaCl, and Nz. Within the program, interactive diagrams are available to describe those chemical systems which cannot be adequately constrained numerically. The user can choose from various published equations of state describing fluid behavior and can easily compare the results obtained by using different equations. The program, once the basic fluid parameters have been established, allows the data to be used to determine the P-T trapping conditions, to evaluate possible pressure corrections and to compare different depths of formation based on the pressure calculations and given geothermal gradients. For illustrative purposes, MacFlinCor has been utilized here to constrain different physical-chemical parameters of fluid inclusions trapped in ore-related quartz veins and breccias of Archlode-gold deposits in Western Australia. Inferred pressures from individual deposits show a wide range of values which may be due to post-entrapment modifications and/or observational uncertainties including estimation of liquidvapor ratios. 1. INTRODUCTION

of crustal depths from epizonal ( <6 km) to mesozonal (5 11 km) to katazonal ( >lO km) (Hagemann and Ridley, 1993 ). These observations are consistent with the crustal continuum model for lode-gold deposits in Western Australia which proposes that these deposits comprise a single genetic group that formed during the late stages of evolution of the host granitoid-greenstone terrains (Groves et al., 199 1.1992) . A variety of different fluids have been observed in these deposits and provide examples to illustrate the features of MacF’linCor.

Routine microthermometric observations of fluid inclusions are the most common way to gather temperature and compositional data on inclusion fluids. Large amounts of data commonly must be interpreted to obtain quantities such as densities or molar volumes of observed or inferred phases and concentrations of dissolved solutes. Because fluid inclusions generally provide only constraints on minimum pressures and temperatures of trapping, it is necessary to calculate the isochore (extrapolated locus of P and T values) consistent with the observational data. In 1989 a Microsoft Windows program FLINCOR was completed (Brown, 1989) with the goal of providing geochemists with a tool for: ( 1) interpreting laboratory observations on fluid inclusions, (2) calculating isochores for fluid inclusions, (3) calculating isochores for hypothetical mixtures of fluids, and (4) comparing the results obtained for different published equations of state. MacFlinCor+ provides the same functionality for the Macintosh line of computers and, in addition, (5) is designed as an electronic notebook for direct laboratory use, and (6) provides interactive diagrams for those chemical systems that cannot be adequately described numerically. Features of MacFlinCor are presented in this paper using examples from lode-gold deposits in Western Australia. Archean lode-gold deposits are hosted in prehnite-pumpellyite to lower granulite facies metamorphic rocks. Recent research has shown that these deposits have formed over a wide range

2. PROGRAM

STRUCTURE

In deciding how to adapt the Windows program FLINCOR (Brown, 1989) to run on Macintosh computers, several features of the programming environment were considered: ( 1) ease of programming so that additions and corrections could be readily made, (2) the ability to create stand alone applications or make use of features present on all Macintosh computers, and (3) a mechanism to incorporate graphical material so that data reduction procedures requiring use of diagrams could be undertaken. HyperCard appeared to fit these requirements, is expandable, and was provided with all Macintosh computers. It operates on the model of index cards with each card providing an entry in a simple but powerful database. This approach is ideal for working with fluid inclusions because each card in a data stack can be used to record all the information about a single inclusion. The program MacFlinCor is composed of two files: MacFlinCor itself which occupies about 470 K of disk space and FlinCalc which takes up 112 K. The FlinCalc stack is the home to some of the more involved calculations and is called as needed by data cards in the MacFlinCor stack. Calculations that require complicated or iterative solutions were programmed in Pascal, compiled, and exported to the FlinCalc program. The heart of the program, and the only cards that the user should see, are the fortyone (at present) cards making up the MacFlinCor stack.

* Resented at the fifth biennial Pan-American Conference on Research on Fluid Inclusions (PACROPl V) held May 19-21, 1994. at the Instituto de Investigaciones Electricas in Cuemavaca, Morelos, Mexico. ’ Tbe MacFlinCor program is available directly from the first author. Individual copies of MacPlinCor cost $75 which includes future upgrades of the program. The program has built in help and additional information can be obtained from Brown and Hagemann (1994a) and this paper. Suggestions and questions should be addressed to the first author ([email protected]). 3943

P. E. Brown and S. G. Hagemann

3944

FIG. 1. Opening card of MacFlinCor stack.

Nine of these cards are tailored to specific chemical systems that should closely represent individual fluid inclusions and for which sufficient experimental data are available to interpret laboratory observations. These cards serve as templates that are copied automatically from the MacFlinCor stack into a user’s data stack. Each of these cards may be accompanied, at the user’s discretion, by a second card that can be used to: ( 1) record independent P-T data, and (2) calculate trapping temperatures or pressures by applying these independent data to the isochore for the observed fluid. Most of the rest of the cards present figures redrawn from the literature which have been made interactive by the addition of moving crosshairs.

3. MACFLINCOR:

DATA INPUT

After double clicking on the MacFlinCor icon, the first card of the MacFlinCor stack appears on the screen (Fig. 1). In addition to Help and Information buttons, the user may choose between opening a previously created data file or beginning a new one. In this example, we will create a new data file and input representative data from Archean lode-gold deposits to illustrate many of the features of MacFlinCor. Upon clicking the “Start a New Database” button, the user is prompted for a file name and a data stack is created (Fig. 2). This stack

0 Rdd to Existing Fil Mitied-Salt-H20 lsochore

Settings

(I)

Options

( Calculate

before

Printing

lsochores

Rgaln

Stack:

FIG. 2. Initial Index card of a newly created data stack. Clicking on the popup menu in the upper left portion of the card (as shown here) allows the user to choose an appropriate composition from the “Chemical Systems” menu.

3945

Software for the study of fluiff inehtslons

I

H20-NaCl-[KC11

The critical temoerature and preeeure that arr calculated are fo; the composition that is either derived from input obeervetionel date (top right) or directly input (below right, arrows). A fluid of this composition, homogenizing to the liquid, must do eo et e T less then Tcrit. The pressure calculsted along the L-V-NaCl eolubilitycurveat theobserved Th only provides a lower limit on the Pet the time of homogenization. An upper P limit is provided by either the criticel curve (T>374) or the L-V curve for water (Tc374). For example: e Th of 400* corraponds to a L-V-NaCl volubility curve pressure of 165

.-...r-

-

1 nclusion

a

--

I-----------

Number:

11

Freezing pt. depression 0 N&l dissolution temp. J.Frac Vap: m Th (L-V): NaCl / (NaCI + KCl)

T Eutectic:

i) Hydrohalite melting KCI dissolution

rlelt 2 point: temD.: a

0 0 0 :rit. Temp.

Molality Salt Weight % Salt Mole fraction Salt p ros_l Crit. Press. Molar Volume Density t Th alone L-V-N&l Sol Curve

FIG. 3. Data card created for inclusion fluids in the system H20-NaCI-[KC]] which are characteristic of fluids in Archean lode-gold deposits.

initially contains only the Index card shown in Fig. 2. From this Index card, data cards are created for appropriate chemical systems, decisions are made about the format in which data will be exported, and the parameters for calculating isochores may be set. The default settings for isochore calculations are 300” to 1000°C in 100°C intervals. Clicking on the Isochores button allows the user to change these values. The user may return to this card at any time and change the isochore parameters; the changed values will be in effect for any further calculations done in the stack. The “Calculate Isochores Again” button lets one recalculate isochores for every card in the data stack if, after gathering a mass of data, the user decides to change the isochore limits or intervals. The buttons on the bottom left of the card are designed to

Boffhga & RIcrhet

lfolloway

Zhang &Frantz Brown & Lamb

Kenkk& Jacobs Bowers & Helgeson swWW7beijJ Heyen eta/.

Haar et a/.

simplify printing of the stack. HyperCard can print multiple (up to thirty two) cards per page and these pages of small images of cards provide a convenient hard copy of the data gathered on a single sample or population of inclusions. Clicking and holding the mouse button while pointing at the shadowed box in the upper left portion of the screen produces a popup menu that allows one of nine chemical systems to be chosen (Fig. 2). Separate data cards for the various systems have been designed because of the different input parameters and output calculations that are appropriate for different groups of chemical constituents. After highlighting the desired menu item and releasing the mouse button, the sought after data card can be created by clicking on the Create button (Fig. 2). Studies of fluid evolution using fluid inclusions in Archean lode-gold deposits recognize that a number of different fluids are preserved in breccia and vein quartz (Hagemann and Ridley, 1993; Brown and Hagemann, 1994). The most commonly observed fluid inclusions related to ore deposition can be described using the H20-NaCl- [ KC11 , C02-CH4, and H,O-CO&I&-NaCl systems. In the sections below, fluid inclusions representing these chemical systems are used to demonstrate the application of MacFlinCor. One of the most wide spread fluid inclusion types in lode-gold deposits, regardless of crustal depth and host rock type, is an aqueous solution containing various salts (Wood et al., 1986; Robert and Kelly, 1987; Walsh et al., 1988; Ho et al., 1990; Hagemann et al., 1994a,b). We begin here by creating a card for the system H20-NaCl- [ KC11 (Fig. 3). 3.1. I&O-NaCl- [ KCI I

FIG.4. Equations of state applicable to the system H20-NaCI-[KC]] are shown in bold on the drop down menu. Equations which apply only to other chemical systems are shown grayed out. For the sake of clarity here, these grayed out items have been shown in italics.

Every data card (e.g., Fig. 3) has essentially the same screen layout. In the upper left comer, a popup menu permits the choice of an equation of state for the chosen chemical system. This list of equations (Fig. 4) is the same on most of

P. E. Brown and S. G. Hagemann

3946

d

Deposits

Sample

lWiluna

ID:

Inclusion

Number:

i2T

Inputs: VolFrac

Vapor

at Tm:

Th to: @ Liquid 0 Vapor 0 crttical

inclusion being measured.

L-V Homogenization

17.11

Temp.

0 Swanenberg 0

Herskowitz & Kisch

OHeyenetal.

@Thi&yetal.

u

L CO2 Density CO2 Molar

at Th (L-V):

Volume

(pure):

Estimated

XCH4

Bulk Molar

lsochor

‘es

0.1 t 49.f

Volume:

FIG. 5. Data card for fluid inclusions in the system COI-CIi+ Such fluids are locally found at Wiluna but are commonly encountered in katazonal lode-gold deposits.

tures and other inclusions, and other data can be recorded. HyperCard provides a set of drawing tools that are adequate for simple illustrative purposes. This becomes a permanent part of the data record for this inclusion. The right half of the card provides fields for data entry and calculated output. For the undersaturated H20-NaCl- [ KC11 system, two observations serve to characterize the inclusion fluids: a freezing point depression (for salinity) and a liquidvapor homogenization temperature (for density). For halitecontaining inclusions the salinity can be constrained by observing the NaCl dissolution temperature. Clicking on the

the cards with those that are not applicable to the chosen chemical system grayed out. (For clarity here, the grayed out items have been shown in italics.) Below this is a large area designed for two purposes. The default use is as a notebook for recording observations in the laboratory during heating and freezing runs. (Newly created cards contain explanatory information in this field; this may be easily replaced by the users own observations.) Secondly, clicking on the Graphic button above the text box causes the text to be temporarily hidden and to be replaced by a white board upon which simple sketches of the inclusion in question, its relationship to frac-

This hgure is modified from Fig 7b (ThiOry et aL.1994) and can be used to interpret data throughout the C02-CH4 cornpositron range. Click on an appropriate portion of the diagram to access an expanded view of that area. Inclusions that homooenlze to the vaoor (L->G) he in the uppe; portion of the figure. Inclusions which homogenize by melting of the solid to the liquid in the absence of vapor (SQL) he in the lower right part of the figure. Observed

d.0 Oil

olz

0:;

0:4

0:s

o:!J

0:7

Ol9

019

1:o

X CH4

Values

Thi&y

et al.: Choose

an Area

Th to: @liquid OvapoOcritical FIG. 6. The first of two cards needed to estimate methane contents of carbonic fluids (ThiCry et al., 1994). Clicking on one of the quadrants of this diagram brings up an expanded view of that area (Fig. 7). In this example the observed microthermometric data lie in the upper left quadrant.

Software for the study of fluid inclusions

Relatively

3947

flat lines are S+L+V

-> S+L (Th); The steep curves

are S+L -> L

VW

Observed

Values Th (L-VI:

Observed

r:

Values

(D-3

XCH4

High molar vol. low XCH4 Th to: @liquid Ovaporocritical

Q

FIG. 7. Expanded view of low XC&, high molar volume portion of CO&H, system (Fig. 6).

Z button will result in one of three responses: ( 1) a message requesting some additional data that is required for the calculation, (2) an error message requesting a change in one of the inputs because some value is out of range, or (3) the calculation will take place. Error messages are context sensitive and will generally inform the user of the appropriate range of values and, after dismissing the message box, the input cursor will be returned to the offending entry. Output varies with the chemical system; in Fig. 3 salinity data are presented in three different ways, the critical temperature and pressure are calculated, and the density and molar volume are given. In addition, the isochore for the fluid is calculated using the parameters set on the Index card. The field for the calculated isochore is hidden behind the rest of the output. Clicking on the Isochores check box will show the field and its contents. An important feature of MacFlinCor is that it provides the user with an opportunity to calculate derived quantities and isochores for hypothetical fluids. The user may enter as inputs, values for quantities that are normally outpurs when working with fluid inclusions: e.g., in the case of H,O-NaCl- [ KC11 (Fig. 3) molality, wt%, or mole fraction salt. Clicking on one of the arrows next to these outputs produces a dialog box in which a value may be entered. Closing this dialog box results in calculation of the rest of the output parameters. Across the bottom of the card are buttons allowing the user to return to the Index, make a Copy of the current card (retaining the Sample ID and any graphics drawn under the Text Table 1. Carbonic Phase Physical-Chemical XCH4

Equiv

CO2

Density

Thky et al. Swanenberg Heyen et al.

Parameters

Equiv Molar

CO2

Pressure

Volume

300”

0.19

0.63

62.12

666

0.25

0.46

91.69

567

0.29

0.39

92.45

430

window), make a blank card from the current one, and Delete the current card. 3.2. CO&& Some of the hydrothermal quartz from the epizonal Wiluna lode-gold deposit contains carbonic inclusions with low to moderate XCH, (Hagemann, 1993; Hagemann et al., 1994b). Figure 5 shows the data card for the carbonic CO,-CH, system. It is not generally possible to calculate numerically the methane content of the carbonic phase in an inclusion from microthermometric data-this must be done graphically. Therefore, after entering the data and upon clicking the C button, the user is taken to interactive figures (Figs. 6 and 7) contained in the MacFlinCor stack that have been modified from ThiQy et al. ( 1994). As described in detail in van den Kerkhof and Thitry ( 1994) and ThiCry et al. ( 1994), the bulk molar volume and XCH4 in the carbonic phase can be derived from microthermometric data. Clicking on the arrow in the lower right (Fig. 7) returns to the card in the data deck (Fig. 5) and completes the calculations. In addition to the approach taken by Thiery et al. (1994) shown in Figs. 6 and 7, Swanenberg ( 1979). Herskowitz and Kisch ( 1984) and Heyen et al. ( 1982) provide graphical treatments that are applicable to certain compositional and density ranges for this system. These can also be accessed from this card. Table 1 presents results obtained by using three of these data reduction approaches. The three authors’ techniques yield different results (e.g., in bulk density) because they utilize different analytical data and/or graphical presentations.

at c

3.3. H,O-CO,-CH,-NaCI The most common fluid inclusions reported from mesozonal lode-gold deposits are composed of, at least, H20-CO*-

P. E. Brown and S. G. Hagemann

3948

0

-L”“‘l” I__-.___

.l

eL3r--;v

Molalitu s

FIG. 8. Data card for inclusion lode-gold deposits.

H20-NaCl-[KC1

T

P 36

II

500

. 2.

_...

which is typical for fluids in mesozonal

(L-V) equilibria. The output area presents data for both the aqueous and carbonic phases as well as the bulk inclusion. After all the data has been gathered and entered into the stack, it can be exported to a tab delimited file which can be read and manipulated by any spreadsheet or statistical computer program. Returning to the Index Card, a list of data cards present in the stack can be made by clicking the “Click here to update index” field (see Fig. 2). Because each type of card has a different set of input and output data, the Export command has been restricted to one inclusion type at a time. ‘Ibis allows column labels to be associated with each input and

1ttesozonal

2

nber: I1

8 Lamb)

_-_.._:~i:_:.I.:.l_l.L_?.l.,.~.~.:.:.~.:.,.~. I li’;l

-i

(e.c). stratigraphic

reconstruction) ‘pressure

I

3424

information

II

(Brown

10.6921

Wt’11INaClk&%d

fluids in the system H20-CO#&-NaCI,

CI&-NaCl, the most complicated system that can be approximately modeled using experimental phase equilibria (Wood et al., 1986; Robert and Kelly, 1987; Walsh et al., 1988; Ho et al., 1990). Returning to the Index card, choosing this system from the popup menu, and clicking the Create button produces the card shown in Fig. 8. In the absence of a precise nonmicrothermometric determination of the CO,:CI& ratio (e.g., laser Raman), CH, contents of the carbonic phase may be estimated from CO* triple point temperatures. Aqueous phase salinities are determined from clathrate melting observations and carbonic phase densities are deduced from CO2

11 250

NaCl

lsochores

you can generate

correction’

which,

when

a edded to

l-l

/

Average

j/i M

l@l :_:_:

FIG. 9. The “second” card for the system H,O-NaCI-[KCl]. Here independent temperature or pressure data can be entered and applied to the calculated isochore to generate a pressure- or temperature-comction for inclusions trapped under nonphase separating conditions.

3949

Software for the study of fluid inclusions

H20-C02-NaCI

Solvi

This figure is a compilation of several published solvi for the system HZO-COZ-NaCl. The solvus moves to higher temperatures with decreasing pressure or increasing salinity. The asymmetry of the solvus becomes very pronounced at low pressures and moderate to high salt contents. 6% N&l modified lrom Bowers 8 Helgeson (1963). 2.6% NaCl from Hendel 8 Hollister (1961). 0% N&l from Todheide & Franck, (1963). Values

from

Fiqure:

0

20

40

6’0

80

Mole % CO2 0 FIG. 10. MacFlinCor card showing temperature versus XCOz plot of several solvi in the H20-CO?-NaCl

and provides a reasonably compact export file. It is also possible to create multiple files each of which contains data for a single compositional type of inclusion.

output

4. MACFLINCOR:

DATA MANIPULATlON

An inclusion formed in a nonboiling system will undergo total homogenization at a pressure and temperature below that at which it was trapped in nature. Independent temperature or pressure data are required to fix the other unknowns and fully characterize the trapping conditions. Such independent temperature data could be derived from, for example, calcite-dolomite, arsenopyrite, or various silicate geothermometers. Independent pressure data could be derived from sphalerite-pyrite-pyrrhotite geobarometry, stratigraphic reconstruction, or data from other groups of fluid inclusions. To facilitate making these types of corrections, second data cards have been created for each of the important chemical systems. These second cards are created and accessed initially from an individual data card; note the “More PIT Info” button on Fig. 3, and the “More T Info” button on Figs. 5 and 8. Figure 9 shows the result of creating a second card for the system shown in Fig. 3. Isochore information is automatically transferred to the left side and independent temperature data can be entered on the right side of the card. The source of these data can be recorded by choosing from a list on a popup menu; here for example arsenopyrite geothermometry yielded temperatures of 325°C. In mesozonal lode-gold deposits, co-genetic aqueous and CO*-rich inclusions with variable phase ratios are locally observed within the auriferous quartz veins and breccias (Robert and Kelly, 1987; Walsh et al., 1988). Given the wide twophase field in the HzO-C02-NaCl system (Takenouchi and Kennedy, 1%5; Gehrig, 1980), it is important to investigate whether the formation of the different fluid inclusion types, particularly H@- and COz-rich, is related to fluid immisci-

system.

bility processes operating on an originally homogenous fluid during entrapment. In MacFlinCor this can be done using the card shown in Fig. 10 which is a temperature vs. XCOZ diagram that shows several experimentally and empirically determined solvi for the H,O-CO*-NaCl system at varying pressures and eq. wt% NaCl contents. This figure is accessed by clicking a button on the second card for several of the chemical systems in MacFlinCor. Note that the addition of NaCl or CH, to the H1O-CO2 system broadens the limbs of the solvus and raises the crest, thus extending the two phase field by at least 80°C at 1 kbar (Danniel et al., 1967; Hollister et al., 1981). 4.1. kochores, Pressures, and Depth Constraints The P-V-T-X properties of every inclusion studied define an &chore in the P-Tplane. Assuming no post-trapping modifications, the fluid in the inclusion was trapped at P-T conditions constrained by the isochore. Figure 11 shows individual isochores calculated for CO,-CH, inclusions trapped in quartz veins and breccias related to Au-pyrite-Arsenopyrite mineralization at the Wiluna lode-gold deposits in Western Australia (Hagemann, 1993). Trapping pressure estimates from isochores can be obtained by the intercept of the isochore with the vertical projection of a temperature estimate (e.g., arsenopyrite geothermometry ) . The resulting population of pressure estimates displays a distinct range and, therefore, should be interpreted statistically. In order to assign mode, mean, median and/or standard deviation, one has to evaluate whether the population has, for example, a normal (Gaussian) or skewed distribution (Rock, 1988). Pressure data might be best displayed in a notched box plot (Fig. 12). The central black box extends between the two upper and lower hinges (one standard deviation), with the dividing line at the median. The whiskers (thin vertical lines) extend from the hinges to the fences (short horizontal lines), which lie two standard deviations from the me-

P. E. Brown and S. G. Hagemann

3950

Wiluna Type 3 lsochores Stage 1: Au-Py-Apy Type 3: C02-CH4

300 “C 2

z

600,

$ It

600, 400,

3

Type 3: Th CO2 (L) C02-CH4

100

200

Ternpe;zure

500

(‘c’,”

FIG. 11. Isochores for CO&X& fluid inclusions from the Wiluna lode-gold deposits in Western Australia (Hagemann, 1993). Note that dashed lines (some of which are covered by solid lines) represent isochores for fluid inclusions that homogenize into the vapor phase.

dian. Any outliers beyond the fences are displayed individually. The notches indicate the confidence levels on the median. The large spread in pressure estimates, shown here for the Wiluna samples, but generally characteristic of most Archean lode-gold deposits (Ho et al., 1990; Brown and Hagemann 1994) might be attributed to observational uncertainties including estimation of liquid/vapor ratios. The latter represents a common problem with important implications for compositional and pressure determinations. Figure 13 shows the range of calculated isochores for different estimates of the volume fraction of COZ for the same inclusion using the same equation of state. Other possible uncertainties related to phase equilibria include: ( 1) the calculation and location of isochores within a chemical system, (2) the estimation of the trapping temperature, (3) the pressure corrections due to a lack of phase immiscibility, and (4) the entrapment of already phase-separated high-density, liquid-rich and low density, vapor-rich fluids. The relative importance of the latter two points depends upon the fluid inclusion evidence for phase immiscibility in individual cases. Furthermore, in complex hydrothermal systems one must consider (5) post-entrapment modifications of fluid inclusions that result in erroneous pressure estimates, and (6) the petrographic relations within fluid inclusion populations in order to decipher the timing of entrapment. Reviews by Roedder ( 1984) and Roedder and Bodnar ( 1980) contain more detailed evaluation of precision, accuracy, and the limitations of fluid inclusions when used for pressure determinations. Using pressure determinations from fluid inclusions, depth ranges within which these deposits are emplaced in the crust can be inferred providing assumptions are made regarding the load conditions (Roedder and Bodnar, 1980). Two possible endmembers, lithostatic and hydrostatic fluid pressure conditions, with pressure gradients of 3.3 km/ 100 MPa and 10.0 km/ 100 MPa respectively, are considered. Commonly, a wide range in depth estimates is obtained for individual lode-gold deposits (Brown and Lamb, 1986; Hagemann, 1993). This

Type 3: Ti CO2 (V) C02-CH4

FIG. 12. Notched hoxplots for isochores shown in Figure 11 using a temperatureof 300°C. Isochores deduced from fluid inclusions that homogenized to liquid are shown in the left hoxplot while those that homogenized to vapor are shown in the right hoxplot. See text for explanations of the hox plot.

range is largely due to the uncertainties of the pressure estimates and assumptions about load conditions. The latter is especially significant at epizonal(<6 km) depth levels where transient pressure conditions (pressure fluctuations), albeit short-lived, between hydrostatic and lithostatic fluid pressures might occur that make it difficult to define rigorously a single geobarometric gradient (Hagemann et al., 1994b). Using published and unpublished P-T data on Archean lode-gold deposits from the Yilgam Craton and assuming load conditions (i.e., geobarometric gradients), estimates of the depth of mineralization can be made as shown in Fig. 14. Lithostatic pressure conditions were assumed for meso- and katazonal deposits, whereas a mixed litho- hydrostatic pressure gradient was assigned for epizonal deposits. Geological evidence such as the dominant brittle structural style (seismic zone), open-space ore textures, low temperature gangue and ore minerals, and isotopic and fluid inclusion evidence for incursion of surface waters (Hagemann et al., 1994b) supports the possibility of a transient hydrostatic pressure gradient during mineralization in the epizonal deposits. For deeper

4000

3500

3035 ban

3000 z ii

2500

e $j

2ooa

a gj

1500

-I

631 bars

t 1000 500

0 -r 250

300

Temperature

350

400

“C

FIG. 13. Range of calculated isochores for estimated volume fractions of CO2 from 0.3-0.7 for the same inclusion using the equation of state of Kerrick and Jacobs (1981).

3951

Software for the study of fluid inclusions P (MPa) 100 200 300 400 500 600 700

programming of MacFlinCor which was done by Mike Wheatley. SGH acknowledges the support of MERIWA Grant Ml54 while a post-doctoral fellow in Perth. Major support for this project has been supplied by the NSF through grants INT 90-15198. BAR-9305245 and EAR 94-06683. Bob Bodnar, Dave Vanko, and Dominic Channer are thanked for thoughtful reviews which helped focus the paper. Editorial handling: D. A. Vanko

olden Mile (13881)

RJWERENCES

Barnicoat A. C., Fare R. J., Groves D. I., and McNaughton N. J. ( 1991) Synmetamotphic lode-gold deposits in high-grade Archean settings. Geology 19,92 I-924. Bloem E. J. M. and Brown P. E. ( 1991) Fluid inclusion evidence from Amphibolite facies lode-gold deposits: Variations on the greenschist theme (abstr.). Geol. Sot. Amer. Absfr. Prog. 23, A174. Brown P. E. ( 1989) FLINCOR: A microcomputer program for the reduction and investigation of fluid inclusion data. Amer. Mineral. 74, 1390-1393.

FIG. 14. Pressure-depth conditions of Archean epi- meso- and katazonal lode-gold deposits from the Western Australian Yilgam Craton. Depths for different deposits were estimated using ranges of pressures from isochores. Lithostatic and hydrostatic lines assume pressure gradients of 33 and 100 m/Mpa. Note that for the epizonal lode-gold deposits pressures may vary between litho- and hydrostatic values, whereas for meso- and katazonal deposits constant Ii&static pressures are assumed. The ranges given indicate the uncettainties of estimation. The gray bands indicate the assumed transition zone between the different crustal levels. References for individual deposits are: Racetrack: Gebte-Mariam et al. (1993); Wiluna: Hagemann (1993). Hagemann et al. (1994b); Lady Bountiful: WoodaIl (1990). Cassidy and Bennett (1993); Granny Smith: Ojala et al. (1993); Mt Charlotte: Ho et al. (1990); Golden Mile: Ho et al. (1990); VictoryDefiance: Clark et al. (1989); CorinthiaHopes Hill: Bloem and Brown (1991); Three Mile Hill: McCall 19927Knight et al. (1993). Hagemannet al. (1994a); Marvel Loch: Mueller et al. (1991), Hagemann et al. (1994a); Griffins Find: Barnicoat et al. (1991) Hagemann et al. (1994a).

deposits (>6 km) lithostatic fluid pressures are assumed based on the lack of evidence for surface water influx and hydrodynamic considerations such as the total load of rocks overlying the deposits. In summary, MacFlinCor provides a powerful tool for fluid inclusion researchers to input and record data from microthermometric measurements and calculate fluid compositions, densities, and molar volumes. Isochores can be calculated and compared using different equations of state. The program provides convenient interactive diagrams for those chemical systems that cannot be adequately described numerically. The development of the program using HyperCard ensures that new experimental data and equations can be easily incorporated in the future. Acknowledgments-PEES

acknowledges the Gledden Fund, Univ. of Western Australia, which supported portions of a sabbatical leave in Perth which marked the beginning of a very productive collaboration with the research group at the Key Centre for Strategic Mineral Resources under the direction of Prof. David Groves. We would also like to acknowledge the support of the late Nick Rock and the initial

Brown P. E. and Hagemann ( 1994a) MacFhnCor: A computer program for fluid inclusion data reduction and manipulation. In Fluid Inclusions in Minerals: Method and Applications (ed. B. De Vivo and M. L. Fraxzotti), pp. 231-250. VPI Press. Brown P. E. and Hagemann S. G. ( 1994b) Giant Archean lode-eold deposits in the A&tibi Greenstone belt’of Canada: Pressure-&mperature-depth (P-T-d) constraints. 12 Ausrr. Geol. Congress, 4243. Brown P. E. and Lamb W. M. ( 1986) Mixing of H1O-COr in fluid inclusions; Geobarometty and Archean gold deposits. Geochim. Cosmochim.

Acta 50,847-852.

Cassidy K. F. and Bennett J. M. ( 1993) Gold mineralization at the Lady Bountiful Mine, Western Australia: an example of a granitoid-hosted Archaean lode-gold deposit. Mineral. Deposita 28, 388-408.

Clark M. E., Hodgson C. J., and Fu M. ( 1989) Wall-Rock alteration, Victory gold mine, Kambalda, western Australia: Processes and P-T-X CO2 conditions of metamorphism. In The Geology of Gold Deposits: The Perspective in 1988 (ed. R. R. Keays, W. R. H. Ramsay, and D. 1. Groves); Econ. Geol. Monogr. 6,445-459. Danniel A., Todheide K., and Franck E. U. (1967) Verdampungsgleichgewichte und kritische Kurven in den Systemen Athanl Wasser und n-Butan/Wasser bei hohen Drucken. Chemisch Ingenieurwesen Technik, 816-822.

Gebre-Mariam M., Groves D. I.. McNaughton N. J., Mikucki E. J., and Veamcombe J. R. ( 1993) Archaean Au-Ag mineralization at Racetrack, near Kalgoorlie, Western Australia: a high crustal-level expression of the Archaean lode-gold continuum. Mineral. Deposira 28, 375-387.

Gehtig M. ( 1980) Phasengleichgewichte und PVT-Daten tern&rer Mischungen aus Wasser, Kohlendioxid und Natriumchlorid bis 3 kbar und 550°C. Ph.D. Dissertation, Univ. of Karlsruhe.. Groves D. I., et al. ( 1991) Archaean lode-gold deposits: The products of crustal-scale hydrothermal systems. In Proceedings of Brazil Gold’91, An International Symposium on the Geology (ed. E. A. Ladeira) pp. 299-306. Balkema.

of Gold,

Groves D. I., et al. ( 1992) Sub-greenschist to granulite-hosted Archean lode-gold deposits of the Yilgarn Craton: a depositional continuum from deep-sourced hydrothermal fluids in crustal-scale plumbing systems. In Third International Archaean Symposium, Perth 1990 Proceedings Volume (compilers J. E. Glover and S. E. Ho); Geol. Dept. Univ. Ext. Publ. 22,325-337.

HagemannS. G. (1993) The Wiluna lode-gold deposits, Western Australia: A case study of a high level Archean Lode-gold system. Ph.D. thesis. Univ. West. Australia. Hagemann S. G. and Ridley J. R. ( 1993) Hydrothermal fluids in epiand katazonal crustal levels in the Archaean: Implications for PT-X-r evolution of lode-gold minerahsation. In An international conference on crustal evolution, metallogeny and explomtion of the Eastern GoMfields, (ed. P. R. Williams and J. A. Haldane); Austr. Geol. Surv. Org. Ext. Absrr. Rec. 1993154, I23- 130.

P. E. Brown and S. G. Hagemann

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Hagemann S. G., Brown P. E. and Ridley J. R. (1994a) Preliminary fluid inclusion analyses of the katazonal Archean Griffin’s Find, Marvel Loch (Savage Lode) and Three Mile Hill gold deposits from the Yilgam Block, Western Australia (extended abstr.). PACROFI VAbstr.

Pro&

39-40.

Hagemann S. Cl., Gebre-Mariam M., and Groves D. I. (1994b) Surface-water influx in shallow-level Archean lode-gold deposits in Western Australia. Geology 22, 1067- 1070. Herskowitz M. and Kisch H. J. (1984) An algorithm for finding composition, molar volume and isochores of CO?-CH, fluid inclusions from Th and T,,,, (for Th < T,,) . Geochirn. Cosmochim. Acra 48, 1581-1587. Heyen G., Ramboz C., and Dubessy J. (1982) Modeling of phase equilibria in the system CO&I& below 50°C and 100 bar. Application to inclusion fluids. Compte Rendu Acad. Sciences Paris 294, 203-206. Ho S. E., Groves D. I., and Bennett J. M. ( 1990) Gold deposits of the Archean Yilgarn Block, Western Australia: Nature, Genesis and Exploration Guides. Univ. West Austr. Publ. 20. Hollister L. S.. Crawford M. L., Roedder E., Burruss R. C., Spooner E. T. C., and Touret J. ( 1981) Practical aspects of microthermometry. In Short Course in Fluid Inclusions: Application to Petrology (ed. L. S. Hollister and M. L. Crawford), pp. 278-304 Mineral. Assoc. Canada. Jacobs G. K. and Kerrick D. M. ( 198 1) Methane: an equation of state with application to the ternary system H?O-CO*-CH. Geochim Cosmochim Acta 45,607-614.

Knight J. T., Groves D. I., and Ridley J. R. ( 1993) The Coolgardie goldfield, Western Australia: district-scale controls on an Archean gold camp in an amphibolite facies tetrane. Mineml. Deposita 28, 436-456.

McCall C. ( 1992) The timing and controls on gold mineralization in the gabbro-hosted Three Mile Hill deposit, Coo&a&e, Western Australia. Unpubl. Honours thesis, Univ. West. Australia. Mueller A. G., Groves D. I., and Delor C. P. ( 1991) The Savage Lode magnesian skam in the Marvel Loch gold-silver mine, Southem Cross greenstone belt, Western Australia: Part II. Pressuretemperature estimates and constraints on fluid sources. Canadian J. Earth Sci. 28,686-705.

Ojala V. J., Ridley J. R., Groves D. I., and Hall G. C. ( 1993) Granny Smith: An example of a granitoid-hosted Archean lode-gold deposit (abstr.) .2nd National Meeting, Specialist group in Economic Geology,

Geol. Sot. Australia 34, 55-56.

Robert F. and Kelly W. C. ( 1987) Ore-forming fluids in Archean gold-bearing quartz veins at the Sigma mine, Abitibi greenstone belt, Quebec, Canada. &on. Geol. 82, 1464- 1482. Rock, N. M. S. ( 1988) Numerical Geology. Springer Verlag, Berlin, 427 pp. Roedder E. ( 1984) Fluid inclusions; Reviews in Mineralogy 12. Roedder E. and Bodnar R. J. ( 1980) Geologic pressure determinations from fluid inclusion studies. Ann. Rev. Earth Planet. Sci. 8, 263-301.

Swanenberg H. E. C. ( 1979) Phase equilibria in carbonic systems, and their application to freezing studies of fluid inclusions. Contrib. Mineral. Petrol. 68, 303-306.

Takenouchi S. and Kennedy G. C. (1965) The solubility of carbon dioxide in NaCl solutions at high temperatures and pressures. Amer. J. Sci. 263,445-454. ThiCry R., Kerkhof A. M. Van Den, and Dubessy J. ( 1994) VX properties modeling of Cl&CO2 and C02-Nr fluid inclusions (T < 31°C. P < 400 bar). Eur. J. Mineral. ?, in press. Van Den Kerkhof A. M. and ThiCry R. ( 1994) Phase transitions and density calculation in the CO?-Cl&-N? system. In Fluid Inclusions in Minerals: Method and Applications, (ed. B. De Vivo and M. L. Frezzotti), 171-190. VP1 Press. Walsh J. F., Kesler S. E., Duff D., and Cloke P. L. (1988) Fluid inclusion geochemistry of high-grade, vein-hosted gold ore at the Pamour mine, Porcupine camp, Ontario. Econ. Geol. 83, 13471367. Wood P. C., Burrows D. R., Thomas A. V., and Spooner E. T. C. (1986) The Hollinger-McIntyre Auquartz vein system, Timmins, Ontario, Canada: Geologic characteristics, fluid properties and light stable isotope geochemistry. In Proceedings Gold ‘86: Willowdale, Ontario (ed. A. J. Macdonald) Konsult International, 5680. Woodall R. ( 1990) Gold in Australia. In Geology of rhe Mineral Deposits of Australia and Papua New Guinea. (ed. F. E. Hughes) ; Aust. Inst. Mini. Metal. Mon. 14,45-67.