1

GEOLOGICAL NOTE

(to be submitted to Journal of Geology)

2.05 Ga Isotopic Age for Transvaal MVT Deposits: Evidence for Large-Scale

Hydrothermal Circulation Around the Bushveld Igneous Complex, South Africa

James D. Gleason Department of Geological Sciences, University of Michigan, Ann Arbor,

MI, USA

Jens Gutzmer Department of Mineralogy, Technische Universität Bergakademie

Freiberg, Brennhausgasse 14, 09569 Freiberg, Germany

Stephen E. Kesler Department of Geological Sciences, University of Michigan, Ann Arbor,

MI, USA

Horst Zwingmann CSIRO Petroleum, PO Box 1130, Bentley, WA 6102 and School of Earth

and Environment, The University of Western Australia, 35 Stirling

Highway, Crawley, W.A. 6009, Australia

ABSTRACT

The dimensions of hydrothermal fluid circulation associated with emplacement of the Bushveld

Igneous Complex (BIC) are documented with new ages for Paleoproterozoic mineral deposits in

wallrocks (Transvaal Supergroup) surrounding the BIC. A fluorite-rich MVT deposit in the

Zeerust district is dated at 2.05 Ga (Sm-Nd isochron age), and is shown to have a Nd isotopic

composition identical to coeval F-rich Lebowa Granite from late in the BIC intrusive sequence.

2

Hydrothermal illite from the Zn-Pb MVT Bushy Park deposit is dated at 2.05 Ga (K-Ar age),

linking widespread MVT deposits of the Kaapvaal craton to basinal brine circulation associated

with emplacement of the 2.055 Ga BIC. These data, in combination with gold vein and

paleoplacer ages, suggest that a regional Bushveld-age hydrothermal system included basinal,

magmatic, and metamorphic fluids that circulated as much as 500 km outward from the present

margins of the BIC. This hydrothermal system is among the largest documented and appears to

be scaled to the dimensions and heat flow budget of the BIC.

Key words: Bushveld Complex; MVT deposits; Isotopic Ages; Hydrothermal; Paleoproterozoic

Introduction

Hydrothermal systems developed around igneous intrusions are an important agent of

chemical exchange in the upper continental crust. Systems of this type around felsic intrusions

are well documented (Taylor 1997). Mafic intrusions, with their increased dimensions and

higher temperatures (Cawthorn and Walraven 1998), might be expected to produce more

complex fluid flow in the surrounding crust. Hydrothermal effects associated with the largest

igneous complex in the world, the ca. 2.055 Ga Bushveld Igneous Complex (BIC), have recently

been hypothesized to extend >> 100 kilometers outward from the margins of the BIC

(Rasmussen et al. 2007; Gutzmer et al. 2007). Products of such extensive hydrothermal systems

include mineral deposits, which are widespread around the periphery of the BIC. Here we report

isotopic ages that link two important groups of hydrothermal mineral deposits in the

Paleoproterozoic Transvaal Supergroup to the emplacement of the BIC. These data expand the

3

evidence for large-scale hydrothermal activity and multi-component fluid flow around the BIC

ca. 2.05 Ga, with distal effects up to 500 km beyond the margins of the BIC being documented.

Previous Evidence for Bushveld-Related Hydrothermal Effects

The Bushveld Igneous Complex (BIC) was emplaced largely into the upper part of the

Transvaal Supergroup, an unusually well preserved sedimentary shelf sequence of Late Archean-

Early Proterozoic age (2.65-2.06 Ga; Beukes 1987; Eriksson and Altermann 1998). The

Transvaal Supergroup is exposed today in the Transvaal, Kanye and Griqualand West, erosional

remnants of a sedimentary basin that originally extended across the entire Kaapvaal craton (fig.

1A). Emplacement of the BIC took place over a short span of time beginning with eruption of

volcanic rocks of the Rooiberg Group at 2061±2 Ma (U-Pb zircon; Walraven 1997), followed by

the mafic/ultramafic Rustenburg Layered Suite (RLS) at 2054±1 Ma (U-Pb zircon; Scoates and

Friedman 2008) and finally by granites of the Lebowa Granite Suite and related phases (here

called Bushveld granites) at 2054±2 Ga (Pb-Pb zircon; Walraven and Hattingh 1993).

Early work on hydrothermal effects in or immediately adjacent to the BIC by Schiffries

and Skinner (1987) and Schiffries and Rye (1990) demonstrated that rocks of the RLS in the

eastern lobe of the Complex (V, fig. 1B) contain veins that formed at temperatures of 350 to

700ºC from saline fluids derived largely from the surrounding Transvaal Supergroup. The RLS

in the western lobe of the complex (R; fig. 1B) shows similar evidence for invasion by

Transvaal-derived fluids (Buick et al. 2001), as does the Platreef in the northern limb of the

Complex (P; fig. 1B) (Pronost et al. 2008; Roelofse and Ashwal 2008) and the Uitkomst

Complex, a satellite intrusion east of the Bushveld Complex (Sarkar et al. 2008). An Ar-Ar

(biotite) cooling age of 2042±3 Ma (Nomade et al. 2004) from chromitite in the RLS was re-

assessed recently by Scoates and Friedman (2008), yielding an alteration age of ca. 2054 Ma

4

within error of the age of the Bushveld intrusion. Slightly farther outward from the intrusion,

Schweitzer and Hatton (1995) described thermal and hydrothermal effects that extended as much

as 1.4 km from the contact of the RLS around all parts of the BIC, and Reimold et al. (2007)

reported Ar-Ar ages of Transvaal Supergroup rocks along the immediate southern margin of the

Complex (T; fig. 1B), interpreted by Alexandre et al. (2006) to reflect Bushveld-related thermal

effects.

In addition to these features, which are associated with mafic/ultramafic rocks of the

RLS, numerous Sn, F, base and precious metal deposits are found in and adjacent to the

Bushveld granites (Robb et al. 2000; Bailie and Robb 2004). These include the Zaaiplaats,

Union and Rooiberg Sn (ZP, U, R; fig. 1B), Buffalo and Zwartkloof F (B, ZL; fig. 1B),

Vergenoeg Fe-F (VG; fig. 1B) and Spoedwell Cu deposits (S; fig. 1B), all of which are thought

to have been deposited largely from fluids of magmatic origin (Robb et al. 2000; Borrok et al.

1998; Goff et al. 2004; Kinnaird et al. 2004).

The widespread distribution and pervasive nature of proximal hydrothermal anomalies

around the BIC suggest that distal effects of the same age should also be present, although fewer

examples are known and most of these are subtle. For instance, in the Witwatersrand basin as

much as 150 km south of the Complex (fig. 2), Rasmussen et al. (2007) reported U-Pb ages of

2.06 Ga to 2.03 Ga for monazite and xenotime which were interpreted by them to be related to

distal hydrothermal effects from emplacement of the BIC. Farther to the southwest, in the

Griqualand West basin (fig. 1a; fig. 2), Whitelaw et al. (2005) reported a Rb-Sr age of 2014±38

Ma on clinochlore from secondary chlorite and associated wallrocks from the Katlani and

Kalkdam Pb-Zn occurrences (fig. 2), compatible with Bushveld-age hydrothermal activity.

Finally, paleomagnetic data from the Transvaal Supergroup in the Griqualand West region (De

5

Kock et al. 2009) record a distinct Paleoproterozoic overprint that is in agreement with 2.05 Ga

re-setting of Rb-Sr isotope systematics in whole-rock samples of Neoarchean (2.65-2.70 Ga)

shales across the entire Kaapvaal Craton (Schneiderhan et al. submitted).

Hydrothermal Mineral Deposits Related to Emplacement of the Bushveld Igneous Complex

Additional evidence of distal fluid flow associated with the BIC is provided by

widespread occurrences of hydrothermal mineral deposits of Paleoproterozoic age in

sedimentary rocks of the Kaapvaal craton. These occurrences are largely of two main types:

Mississippi Valley-type (MVT), which are found at a wide range of distances from the complex,

and vein-type deposits, which are relatively close to the complex (fig. 2).

Mississippi Valley-type (MVT) Deposits

MVT deposits in the Kaapvaal craton are hosted largely by carbonate rocks of the

Transvaal Supergroup (fig. 1; fig.2) and can be divided into two groups. The first group contains

sphalerite, galena and hydrothermal carbonate typical of many MVT deposits around the world

(including type-locality MVT), though these deposits are also locally enriched in other elements

nearest the BIC. For instance, MVT deposits in the Transvaal basin around the BIC contain

chalcopyrite at Leeuwenkloof and Carletonville, siderite and pyrite at Leeuwbosch, magnetite at

Hendrina, and manganese oxides with silver at Genadendal and adjacent deposits (Martini 1976;

1986; Clay 1986; Bear 1986; Philpott and Ainslie 1986; Ryan 1986; fig. 2). In contrast, Pering,

Bushy Park and numerous smaller MVT deposits in the Griqualand West basin, which is farther

west and south of the BIC (fig. 2), have a conventional MVT mineral assemblage consisting

largely of sphalerite, galena and hydrothermal carbonate (Martini 1990; Martini et al. 1995;

Kruger et al. 2001; Schäfer 2002; Schäfer et. al. 2004; Gutzmer 2006; Huizenga et al. 2006a).

6

The second group of MVT deposits, which is found only in the Zeerust district (fig. 2),

consists largely of fluorite and hydrothermal carbonate with very little galena and sphalerite

(Martini 1976; 1986; Ryan 1986; Bear 1986; Roberts et al. 1993; Martini et al. 1995; Poetter

2001). Although the Transvaal basin MVT deposits have a surprisingly wide range of

compositions, a genetic relation among them is suggested by similar common lead isotope

compositions for Carletonville, Leeuwenkloof, Leeuwbosch and Zeerust (Duane et al. 1991).

Fluid inclusion and stable isotope analyses indicate that both groups of MVT deposits formed

from fluids consisting largely of basinal brines, but with different admixtures of meteoric and

magmatic fluids. In the MVT deposits containing largely lead and zinc, fluid inclusions indicate

that mineralization was formed from basinal brines with admixtures of meteoric water as well as

CO2 and CH4 derived from reaction between the brine and wallrocks, (Schäfer 2002; Kesler and

Reich 2006; Huizenga et al. 2006a,b). Mineralization is estimated to have taken place at

temperatures of 200 to 240ºC and pressures of about 0.8 to 1.5 kb in the upper crust. Fluid

inclusions from the fluorite-bearing Zeerust MVT deposits contain generally similar basinal

brines, but with evidence also for local or sporadic introduction of much higher temperature

fluids of probable magmatic origin (Poetter 2001; Kesler et al. 2007).

Gold and Lead-Zinc-Silver Vein Deposits

Quartz-gold veins of the Sabie-Pilgrim’s Rest and related districts are found along the

east side of the BIC (Harley and Charlesworth 1994; Boer et al. 1995) and similar veins of the

Witwatersberg district (Killick and Scheepers 2005) are located on the west side. The small

Mamre-Slaaihoek deposits farther to the south of Sabie-Pilgrim’s Rest are close to the 2.055 Ga

Uitkomst satellite intrusion (Sarkar et al. 2008). Most of these vein deposits are hosted in the

lower part of the Transvaal Supergroup where the majority of the MVT deposits occur (fig. 2).

7

Fluid inclusion and stable isotope data suggest that the vein deposits were formed from saline

fluids with variable enrichment in CO2 at temperatures of 300 to 350ºC and supra-lithostatic

pressures of 2.2 to 2.5 kb (Boer et al., 1995). The data are consistent with either a magmatic or

metamorphic source for the fluids and exclude involvement of significant amounts of meteoric

water (Boer et al., 1995).

Ages of the Hydrothermal Mineral Deposits

Geologic relations and isotopic age determinations show that the gold veins are

essentially coeval with the ~ 2.05 Ga BIC (Boer et al. 1995), but similar constraints on the age of

the MVT deposits have not been available. Establishing the age of the Transvaal MVT deposits

is important to test their temporal relation to the BIC, but is complicated by the scarcity of

suitable mineral phases for isotopic age determinations. Although Rb-Sr isotopic analyses of

sphalerite have yielded reliable ages for other MVT deposits (Christensen et al. 1995; Schneider

et al. 2007; Heiljen et al. 2003; Leach et al. 2001), Rb-Sr chronology of Bushy Park sphalerite

has not yet been successful (Kesler et al. 2003). Both Zeerust and Bushy Park MVT deposits

contain fluorite and illite, which are amenable to isotopic age measurements by Sm-Nd and K-Ar

age dating, respectively. At Bushy Park, illite is a trace constituent that is intergrown locally

with coarse-grained sphalerite (Schäfer 2002; Gutzmer et al. 2007), and at Zeerust, fluorite is the

most abundant hydrothermal mineral and represents the main stage of mineralization (Martini

1976, 1986; Ryan 1986).

Results

Isotopic ages for Transvaal MVT mineralization were determined for fluorite at Zeerust

by Sm-Nd geochronology (Chesley et al. 1991) and for illite at Bushy Park by K-Ar dating. At

Bushy Park, hand-picked, millimeter-sized monomineralic aggregates of illite yielded K-Ar ages

8

of 2038±40 Ma and 2059±41 Ma (Table 1). At Zeerust, Sm-Nd isotopic data on four hand-

picked fluorite separates (Table 2) generated a 2046±42 Ma isochron (MSWD=2.0) with initial

143Nd/144Ndi = 0.509734±0.000059 (εNd = -4.9; fig. 3). These ages for Bushy Park and Zeerust

are identical within error to the full range of ages obtained for magmatic phases of the BIC

(~2.06-2.05 Ga), though not precise enough to directly link the MVT deposits to a specific

intrusive phase. The ages reported here for Bushy Park and Zeerust are also similar to that of the

Vredefort impact event (2.023 Ga; Kamo et al. 1996) and the Limpopo tectonothermal event

(2.03 Ga; Kramers et al. 2006) of the Kaapvaal craton region. A genetic association with the

latter two events is deemed unlikely, however, because of the short duration of the Vredefort

event (Gutzmer et al. 2007), and because of the apparent limit of the effects of the Limpopo

tectonothermal event (Kramers et al. 2006). Instead, the Kaapvaal MVT deposits have a much

closer spatial association with the BIC, and a mineralogy much more likely to be related to a

regional 2.05 Ga hydrothermal event driven by emplacement of the BIC.

Implications for Hydrothermal Circulation around the Bushveld Complex

Our data linking MVT deposits to the BIC, combined with previous data linking gold

deposits to the BIC, shows that the Bushveld hydrothermal system consisted of several different

fluid types. A close genetic link between Zeerust MVT fluorite and Bushveld-related F-rich

magmatic systems is supported by the similarity of Nd isotopic compositions [εNd (2.055 Ga)] for the

Lebowa Granite suite and Zeerust fluorite (fig. 3, inset). Whole rock Sm-Nd data for the

Lebowa Granite Suite at Dennilton (Hill et al. 1997) plot along the same isochron as the Zeerust

Sm-Nd fluorite separates. Combined, the two sets of data define an isochron age (2050±66 Ma)

that is identical to the Zeerust isochron age (2046±42 Ma), and with the same initial ratio

(143Nd/144Ndi = 0.509722±0.000071; εNd = -5.1; fig. 3) within error. Recognition of the isotopic

9

link between fluorine-rich systems of the Zeerust MVT, and F-rich granites of the BIC,

establishes that hydrothermal fluids at Zeerust resulted from the invasion of Transvaal basinal

brines by F-rich high temperature magmatic fluids (Kesler et al., 2006) of the BIC. At Zeerust,

this invasion is further reflected by zones of F-bearing tremolite and talc surrounding the MVT

deposits (Martini 1976), consistent with their location within the outer greenschist contact

metamorphic aureole of the BIC (Engelbrecht 1990).

From the above discussion, we can infer that a direct link exists between hydrothermal

fluids forming the Sn-F type deposits directly associated with the Bushveld granites, and F-

bearing MVT deposits of the Transvaal Supergroup (Zeerust). A second hydrothermal fluid type

represented by Transvaal Group-hosted MVT deposits (other than Zeerust-type) shows a subtle

spatial zonation outward from the BIC, with unusual enrichments in Fe and Mn within Transvaal

basin deposits (fig. 2). The presence of these geochemical anomalies does not require a direct

magmatic fluid contribution and could instead imply a leached component from the RLS, or

enclosing sedimentary rocks, by circulating basinal brines (Martini, 1990). Migration of

Transvaal basinal brines was localized by several paleoaquifers, including volcanic rocks of the

Ventersdorp Group, which underlies the Transvaal Supergroup (Duane et al. 1991; Kruger et al.

2001; Gutzmer et al. 2007). More distal fluid pathways (also associated with the RLS) probably

account for the Bushveld-like ages observed in Witwatersrand Basin rocks (Rasmussen et al.

2007).

The third hydrothermal fluid type is represented by the gold vein deposits, which are

most easily explained by mixing of Transvaal basinal brines with carbonic fluids produced by

metamorphic devolatilization of BIC wallrocks (Boer et al., 1995). The deposits are just outside

the maximum original extent of the Bushveld Complex, where metamorphic fluids would have

10

been most abundant, and the supra-lithostatic conditions of the mineralizing fluids are consistent

with a metamorphic origin (Boer et al. 1995).

It is likely that all three fluid systems were active simultaneously for at least part of the

full duration of hydrothermal activity ca. 2.05 Ga, but may have overlapped in only a few

locations. As shown in Figure 4, BIC-related hydrothermal activity was focused in the lower

part of the Transvaal Supergroup at 2.05 Ga, with rocks proximal to the complex hosting

overpressured fluids of largely (contact) metamorphic origin. These deposited gold, while fluids

in more distal regions formed MVT deposits with or without direct contributions of magmatic F

and Sn from Bushveld granites. Farther outward in regions most distal to the BIC, hot basinal

fluids reset paleomagnetic, Rb-Sr and K-Ar systematics in the Transvaal Supergroup, and

deposited monazite, xenotime and other low-temperature phosphates as far away as the

Witwatersrand basin sequence more than 500 km from the BIC contact aureole.

ACKNOLWLEDGMENTS

We would like to acknowledge the roles of Markus Schäfer, Lynette Greyling, Phil

Poetter and Craig McClung for their respective contributions during the investigation of the

carbonate-hosted Zn-Pb-F deposits of the Transvaal Supergroup. Sm-Nd isotopic work was

carried out in the Radiogenic Isotope Geochemistry Laboratory (RIGL) at the University of

Michigan (J. Blum, director), and the KECK trace element lab with assistance from M. Johnson

and T. Huston, respectively.

REFERENCES CITED

Alexandre, P.; Andreoli, M.A.G.; Jamison, A.; and Gibson, R.L. 2006. 40Ar/39Ar age constraints

on low-grade metamorphism and cleavage development in the Transvaal Supergroup

11

(central Kaapvaal craton, South Africa): implications for the tectonic setting of the

Bushveld Igneous Complex. South African Journal of Geology 109: 393-410.

Bailie, R.H., and Robb, L.J. 2004. Polymetallic mineralization in the granites of the Bushveld

Complex – examples from the central southeastern lobe. South African Journal of

Geology 107: 633-652.

Bear, L.M. 1986. Note on the Bulhoek fluorspar mine, Groot-Marisco district. In Anhaeusser,

C.R., and Maske, S., eds. Mineral Deposits of Southern Africa. Geological Society of

South Africa (Johannesburg) p. 851–852.

Boer, R.H.; Meyer, F.M.; Robb, L.J.; Graney, J.R.; Vennemann, T.W.; and Kesler, S. E. 1995.

Mesothermal-type mineralization in the Sabie-Pilgrim's Rest gold field, South Africa.

Economic Geology 90: 860-876.

Beukes, N.J. 1987. Facies relations, depositional environments and diagenesis in a major Early

Proterozoic stromatolitic carbonate platform to basinal sequence, Campbellrand

Subgroup, Transvaal Supergroup, Southern Africa. Sedimentary Geology 54: 1-46.

Borrok, D.M.; Kesler, S.E.; Boer, R.H.; and Essene, E.J. 1998. The Vergenoeg magnetite-

fluorite deposit, South Africa: Support for a hydrothermal model for massive iron oxide

deposits. Economic Geology 93:564-586.

Buchanan, P.C.; Koeberl, C.; and Reimold, W.U. 1999. Petrogenesis of the Dullstroom

Formation, Bushveld Magmatic Province, South Africa. Contributions to Mineralogy and

Petrology 137: 133-146.

Buick, I.S.; Maas, R.; and Gibson, R. 2001. Precise U-Pb titanite age constraints on the

emplacement of the Bushveld Complex, South Africa. Journal of the Geological Society

of London 158: 3-6.

12

Cawthorn R. G., and Walraven F. 1998. Emplacement and crystallization time for the Bushveld

Complex. Journal of Petrology 39:1669-1687.

Chesley, J.T.; Halliday, A.N.; and Scrivener, R.C. 1991, Samarium-neodymium direct dating of

fluorite mineralization. Science 252: 949-951.

Christensen, J.C.; Halliday, A.N.; and Kesler, S.E. 1997. Rb-Sr dating of sphalerite and the ages

of Mississippi Valley-type Pb-Zn deposits. Society of Economic Geologists Special

Publication 4:527–535.

Clay, A.N. 1986. The stratigraphy of the Malmani Dolomite Subgroup in the Carletonville area,

Transvaal. Genetic implications for lead–zinc mineralization. In Anhaeusser, C.R.,

Maske, S., eds. Mineral Deposits of Southern Africa. Geological Society of South Africa

(Johannesburg) p. 853–860.

de Kock, M.O; Evans, D.A.D; Kirschvink, J.L; Beukes, N.J.; Rose, E.; and Hilburn, I. 2009.

Paleomagnetism of a Neoarchean-Paleoproterozoic carbonate ramp and carbonate

platform succession (Transvaal Supergroup) from surface outcrop and drill core,

Griqualand West region, South Africa. Precambrian Research 169:80-99.

Duane, M.J.; Kruger, F.J.; Roberts, P.J; and Smith, C.B. 1991. Pb and Sr isotopes and origin of

Proterozoic base metal (fluorite) and gold deposits, Transvaal Sequence, South Africa.

Economic Geology 86:1491-1505.

Engelbrecht, J.P. 1990. Contact metamorphic processes related to the aureole of the Bushveld

Complex in the Marico district, western Transvaal, South Africa. South African Journal

of Geology 93:339–349.

Eriksson, P.G., and Altermann, W. 1998. An overview of the geology of the Transvaal

Supergroup dolomites (South Africa). Environmental Geology 36:179-188.

13

Eriksson, P.G.; Altermann, W.; Catuneanu, O.; van der Merwe, R; and Bumby, A.J. 2001. Major

influences on the evolution of the 2.67-2.1 Transvaal basin, Kaapvaal craton.

Sedimentary Geology. 141:205-231.

Faure, G. 1986. Principles of isotope geology. John Wiley & Sons, New York, 589 p.

Glass, J. 2006. The environmental impact of the abandoned Edendale lead mine near Tshwane,

South Africa. Unpubl. MSc. Thesis, University of Johannesburg, 74 pp.

Gleason, J.D.; Finney, S.C.; Peralta, S.H.; Gehrels, G.E.; and Marsaglia, K.M. 2007. Zircon and

whole-rock Nd-Pb isotopic provenance of Middle and Upper Ordovician siliciclastic

rocks, Argentine Precordillera. Sedimentology 54:107-136.

Goff, B. H.; Weinberg, R.; Groves, D.I.; Vielreicher, N. M.; and Fourie, P. J. 2004. The giant

Vergenoeg fluorite deposit in a magnetite–fluorite–fayalite REE pipe: a hydrothermally-

altered carbonatite-related pegmatoid? Mineralogy and Petrology 80:173–199.

Gutzmer, J. 2006. The Paleoproterozoic carbonate-hosted Pering Zn–Pb deposit, South Africa: I.

Styles of brecciation and mineralization. Mineralium Deposita 40:664-685.

Gutzmer, J.; McClung, C.R.; Beukes, N.J.; Zwingmann, U.; and Schaefer, M.O. 2007. Age and

origin of the Earth’s oldest carbonate-hosted Pb-Zn-(F) deposits. Proceedings of the

Ninth Biennial SGA Meeting, Dublin, 2, pp. 299-302.

Harley, M., and Charlesworth, E.G. 1994. Structural development and controls to epigenetic,

mesothermal gold mineralization in the Sabie-Pilgrim's Rest Goldfield, eastern Transvaal,

South Africa. Exploration and Mining Geology 3:231-246.

Harris, N.; McMillan, A.; Holness, M.; Uken, R.; Watkeys, M.; Rogers, N.; and Fallick, A. 2003.

Melt generation and fluid flow in the thermal aureole of the Bushveld Complex. Journal

of Petrology 44:1031-1054.

14

Heijlen, W.; Muchez, P.; Banks, D.; Schneider, J.; Kucha, H.; and Keppens, E. 2003. Carbonate-

hosted Zn–Pb deposits in Upper Silesia, Poland: origin and evolution of mineralizing

fluids and constraints on genetic models. Economic Geology 98:911–932.

Hill, M.D.; Barker, F.; Hunter, D.; and Knight, R.J. 1996. Geochemical characteristics and origin

of the Lebowa granite suite, Bushveld Complex. International Geology Review 38:195–

227.

Huizenga, J.-M.; Gutzmer, J.; Banks, D.; and Greyling, L. 2006a. The Paleoproterozoic

carbonate-hosted Pering Zn–Pb deposit, South Africa: II. fluid inclusion, fluid chemistry

and stable isotope constraints. Mineralium Deposita 40:686-706.

Huizenga, J.-M.; Gutzmer, J.; Greyling, L.; and Schäfer, M.O. 2006b. Carbonic fluid inclusions

in Paleoproterozoic carbonate-hosted Zn-Pb deposits in Griqualand West, South Africa.

South African Journal of Geology 109:55-62.

Jacobsen, S.B. and Wasserburg, G.J. 1980. Sm-Nd isotopic evolution of chondrites. Earth

Planet. Sci. Lett. 50:139-155.

Kamo, S.L.; Reimold, W.U.; Krogh, T.E.; and Colliston, W.P. 1996. A 2023 Ma age for the

Verdefort impact event and observations from shocked metamorphosed zircons in

pseudotachylite breccias and granophyre. Earth and Planetary Science Letters 144:369-

388.

Kesler, S.E., and Reich, M.H. 2006. Precambrian Mississippi Valley-type deposits: relation to

changes in composition of the hydrosphere and atmosphere. In Kesler, S.E., Ohmoto, H.,

eds. Evolution of Early Earth's Atmosphere, Hydrosphere and Biosphere — Constraints

from Ore Deposits. Geological Society of America Memoir 198:185–204.

15

Kesler, S.E.; Gleason, J.D.; Smith, C.N.; Ahler, B.A.; and Taylor, D.R. 2003. Age and provinces

of Precambrian MVT mineralization, Transvaal Supergroup, South Africa. Geological

Society of America Abstracts with Programs 35(6):234.

Killick, A.M., and Scheepers, R. 2005. Controls to hydrothermal gold mineralization in the

Witwatersberg Goldfield situated in the floor to the south of the Bushveld Complex,

South Africa. Journal of African Earth Sciences 41:235-247.

Kinnaird, J.A.; Kruger, F.J; and Cawthorn, R.G. 2004. Rb-Sr and Nd-Sm isotopes in fluorite

related to the granites of the Bushveld Complex. Geological Society of South Africa

107:413-430.

Kramers, J.D.; Mc Court, S.; and Van Reenen, D.D. 2006. The Limpopo Belt. In M.R. Johnson;

C.R. Anhaeusser; and R.J. Thomas, eds. The Geology of South Africa. Geological

Society of South Africa/Council for Geoscience p. 57-94.

Kruger, F.J.; Duane, M.J.; Turner, A.M.; Whitelaw, H.T.; and Verhagen, B.T. 2001.

Paleohydrology of a ca. 2 Ga old Mississippi Valley-type Pb-Zn deposit, South Africa:

Radiogenic and stable isotope evidence. Information Circular No. 355, Economic

Geology Research Institute, University of the Witwatersrand, Johannesburg, 22 p.

Leach, D.L.; Bradley, D.C.; Lewchuck, M.; Symons, D.T.A.; Brannon, J.; and de Marsily, G.

2001. Mississippi Valley-type lead–zinc deposits through geological time: Implications

from recent age-dating research. Mineralium Deposita 36:711–740.

Maier, W.D.; Arndt, N.T.; and Curl, E.A. 2000. Progressive crustal contamination of the

Bushveld Complex: evidence from Nd isotopic analyses of the cumulate rocks.

Contributions to Mineralogy and Petrology 140: 316-327.

16

Martini, J.E.J.; Eriksson, P.G.; and Snyman, C.P. 1995. The Early Proterozoic Mississippi

Valley-type Pb-Zn-F deposits of the Campbellrand and Malmani Subgroups, South

Africa. Mineralium Deposita 30:135-145.

Martini, J.E.J. 1976. The fluorite deposits in the dolomite series of the Marico district, Transvaal,

South Africa. Economic Geology 71:625-635.

Martini, J.E.J. 1986. The Zeerust fluorspar deposits, western Transvaal in Anhaeusse, C.R. and

Maske, S., eds. Mineral Deposits of Southern Africa, Geological Society of South Africa,

Johannesburg, p. 837-841.

Martini, J.E.J. 1990. The Genadendal Zn-Pb-Mn mineralization, South Africa: A possible Early

Proterozoic alkaline hydrothermal system. Economic Geology 85:1172-1185.

Nomade, S.; Renne, P.R.; and Merkle R.K.W. 2004. 40Ar/39Ar age constraints on ore deposition

and cooling of the Bushveld Complex, South Africa. Journal of the Geological Society

161:411-420

Odin, G.S. and 35 collaborators. 1982. Interlaboratory standards for dating purposes in Odin, G.

S., ed. Numerical Dating in Stratigraphy, Part 1, John Wiley and Sons, Chichester, p.

123-148.

Philpott, G.D., Ainslie, L.C. 1986. Lead mineralization on Leeuwbosch 129 KQ, Thabazimbi

district. In Anhaeusser, C.R., Maske, S. eds. Mineral Deposits of Southern Africa.

Geological Society of South Africa, Johannesburg, pp. 861–866.

Poetter, P.A. 2001. Origin and exploration potential of sedimentary-hosted Mississippi Valley-

type F-Zn-Pb deposits in the Neoarchean platform dolostones of the Transvaal

Supergroup, Northwestern Province, South Africa. Muenster, WWU Muenster, Diplom

thesis (http://general.rau.ac.za/geology/PPM/Abstracts.html).

17

Pronost, J.; Harris, C.; and Pin, C. 2008. Relationship between footwall composition, crustal

contamination, and fluid-rock interaction in the Platreef, Bushveld Complex, South

Africa. Mineralium Deposita 43:825-848.

Rasmussen, B.; Fletcher, I.R.; Muhling, J.R.; Mueller, A.G.; and Hall, G.C. 2007. Bushveld-aged

fluid flow, peak metamorphism, and gold mobilization in the Witwatersrand basin, South

Africa: Constraints from in situ SHRIMP U-Pb dating of monazite and xenotime.

Geology 35:931–934.

Reimold, W.U.; Wittek, A.; and Jourdan, F. 2007. Comment on 40Ar/39Ar age constraints on low-

grade metamorphism and cleavage development in the Transvaal Supergroup (central

Kaapvaal craton, South Africa): implications for the tectonic setting of the Bushveld

Igneous Complex. South African Journal of Geology 109:393–410.

Robb, L.J.; Freeman, L.A.; and Armstrong, R.A. 2000. Nature and longevity of hydrothermal

fluid flow and mineralisation in granites of the Bushveld Complex, South Africa.

Geological Society of America Special Paper 350:269-281.

Roberts, P.J.; Gize, A.P.; Duane, M.J.; and Verhagen, B. 1993. Precambrian hydrocarbon

residues associated with Mississippi Valley-type mineralization in the Transvaal

Sequence, South Africa. South African Journal of Geology 96:57–60.

Roelofse, F. and Ashwal, L.D. 2008. Symplectitic augite from the Platreef-textural evidence for

fluid/rock interaction in the Northern Sector of the Northern Limb of the Bushveld

Complex? Geological Society of South Africa 111: 21-26.

Ryan, P.J. 1986. The Witkop fluorspar mine near Zeerust, western Transvaal in Anhaeusse, C.R.

and Maske, S., eds. Mineral Deposits of Southern Africa, Geological Society of South

Africa, Johannesburg, p. 843-849.

18

Sarkar, A.; Ripley, E.M.; Li, C.; and Maier, W.D. 2008. Stable isotope, fluid inclusion and

mineral chemistry constraints on contamination and hydrothermal alteration in the

Uitkomst Complex, South Africa. Chemical Geology 257:129-138.

Schäfer, M. 2002. Paleoproterozoic Mississippi Valley-Type Pb-Zn Deposits of the Ghaap

Group, Transvaal Supergroup in Griqualand West, South Africa. unpublished Ph.D.

dissertation, Rand Afrikaans University, Johannesburg.

Schäfer, M.; Gutzmer, J.; and Beukes, N.J. 2001. Genesis of carbonate-hosted Pb-Zn deposits in

the Later Archean Transvaal Supergroup, Northern Cape Province, South Africa in

Piestrzykinski, A., ed. Mineral Deposits at the Beginning of the 21st Century. Proceedings

of the biennial SGA-SEG meeting. Swets and Zeitlinger Publishers, Lisse, p. 177-180.

Schiffries, C.M. and Rye, D.M. 1989. Stable isotopic systematics of the Bushveld Complex: I.

Constraints on magmatic processes in layered intrusions. American Journal of Sciences

289:841-873.

Schiffries, C.M. and Skinner, B.J. 1987. The Bushveld hydrothermal system: Field and

petrologic evidence. American Journal of Sciences 287:566-595.

Schneider, J.; Melcher, F.; Brauns, M. 2007. Concordant ages for the giant Kipushi base metal

deposit (DR Congo) from direct Rb–Sr and Re–Os dating of sulfides. Mineralium

Deposita 42:791-797.

Schneiderhan, E.; Zimmermann, U.; Gutzmer, J.; Mezger, K.; Armstrong, R. (submitted) The

relationship of the Limpopo Mobile Belt and the Kaapvaal Craton as deduced from Rb-Sr

model age data of Neoarchean shales. South African Journal of Geology.

Schweitzer, J.K. and Hatton, C.J. 1995. Chemical alteration within the volcanic roof rocks of the

Bushveld Complex. Economic Geology 90:2218-2231.

19

Scoates, J.S. and Friedman, R.M. 2008. Precise age of the platiniferous Merensky Reef,

Bushveld Complex, South Africa, by the U-Pb zircon chemical abrasion ID-TIMS

technique. Economic Geology 103:465-471.

Steiger R.H. and E. Jäger, E. 1977. Subcommission on Geochronology: convention on the use of

decay constants in geo-and cosmochronology. Earth and Planetary Science Letters.

36:359-362.

Taylor, H.P. 1997. Oxygen and hydrogen isotope relationships in hydrothermal mineral deposits.

In Barnes, H.L., ed. Geochemistry of hydrothermal ore deposits, 3rd ed., Wiley, New

York, p. 229-301.

Twist, D. and Harmer, R.E.J. 1987. Geochemistry of contrasting siliceous magmatic suites in the

Bushveld Complex: Genetic aspects and implications for tectonic discrimination

diagrams. Journal of Volcanology and Geothermal Research 32:83-98.

Walraven, R. 1997. Geochronology of the Transvaal Supergroup, South Africa. Information

Circular-University of the Witwatersrand, Economic Geology Research Unit 316, 21 p.

Walraven, F. and Hattingh, J. 1993. Geochronology of the Nebo Granite, Bushveld Complex.

South African Journal of Geology 96:31–41.

Whitelaw, H.T.; de Bruin, H.; Schoch, A.E.; Van der Westhuizen, W.A.; and Kruger, F.J. 2005.

Isotopic relationships of epigenetic Pb-Zn mineralization in the Ventersdorp Supergroup

near Douglas, Northern Cape Province. South African Journal of Geology 108:187-198

20

Figure 1. A) Location of the Neoarchean-Paleoproterozoic Transvaal and Griqualand West

structural basins that preserve part of the Transvaal Supergroup on the Kaapvaal craton in

southern Africa. B) Geologic map of the Bushveld Complex and immediately adjacent

wallrocks in the Transvaal Basin (modified from Martini et al., 1995; Eriksson et al.,

2001), showing the location of areas within the Complex that exhibit evidence of

proximal hydrothermal effects including the layered series (V), Burgersfort bulge (BB)

and Uitkomst (U) in the east, Rustenburg Layered Suite (R) in the west and Platreef (P)

in the north. Also shown are areas of metamorphic effects in proximal wallrocks along

the southern margin of the complex (T), as well as mineral deposits hosted by and

thought to be associated with Bushveld granites, including Zaaiplaats, Union and

Rooiberg Sn (ZP, U, R, Figure 1B), Buffalo and Zwartkloof F (B, ZL, Figure 1B),

Vergenoeg Fe-F (VG, Figure 1B) and Spoedwell (S) Cu deposits. Locations are

discussed in the text.

Figure 2. Distribution and relative positions of exposed and covered rocks of the Bushveld

Complex, Transvaal Supergroup (exposed in the Transvaal, Griqualand West and Kanye

basins – see fig. 1a), and Witwatersrand basin showing location of possible distal

hydrothermal effects of the Bushveld Complex, including MVT and related deposits

(crosses, G = Genadendal, L = Leeuwbosch, H = Hendrina), gold and lead-zinc vein

systems (triangles), and U-Pb ages of monazite and xenotime in Witwatersrand rocks

(circles). Isotopic ages for Bushy Park and Zeerust from this report and for

Witwatersrand samples from Rasmussen et al. (2007).

Figure 3. Main Diagram) Sm-Nd isochron for fluorite separates from the Witkop and

Doornhoek deposits in the Zeerust district. Samples plotted on the main isochron include

coarse and fine-grained fluorite from both stratiform and breccia units at Zeerust. Data

were inputted as 2-sigma values to generate a Model 1 solution (95% confidence interval)

using Isoplot Ex3 (Ludwig 2005). The 2-sigma solution yields an age of 2046±42 Ma

with MSWD = 2.0, and initial 143Nd/144Ndi = 0.509734±0.000059 (epsilon Nd = -4.9).

Inset lower right) Comparison of εNd2.055 values for hydrothermal fluorite from the

21

Zeerust data (isochron value), with averages for rocks of the Bushveld Complex and the

Vergenoeg F-bearing deposit (from data of Buchanan et al. 1999, Maier et al. 2000, Hill

et al. 1996, Goff et al. 2004, and Twist and Harmer 1987). Calculated εNd =

104[(143Nd/144Nd(t)SAMPLE)/(143Nd/144Nd(t)CHUR) – 1] assuming modern143Nd/144NdCHUR =

0.512638 (Bulk Earth) and 147Sm/144Nd CHUR = 0.1966 (Jacobsen and Wasserburg,

1980), where t = 2.055 Ga. Inset upper left) Portion of the Sm-Nd isochron combining

all of our Zeerust fluorite data with data for Lebowa F-rich granites from the Bushveld

Complex (Hill et al. 1996; Dennilton area only; n = 9). The 2-sigma solution yields an

Sm-Nd isochron age of 2050±66 Ma with MSWD = 17, and initial 143Nd/144Ndi =

0.509722±0.000071 (epsilon Nd = -5.1). The two Zeerust data points shown are open

squares; Lebowa data points (Dennilton area) are solid symbols.

Figure 4. Schematic distribution of mineral deposits and inferred fluid flow related to the

Bushveld hydrothermal system. Fluids closest to the intrusion, largely of metamorphic

origin with minor amounts of metals probably leached from the Rustenberg Layered

Suite, generated the quartz-gold veins in the Transvaal Supergroup. Outward from these,

basinal fluids formed MVT deposits in the Transvaal Supergroup with locally significant

contributions of F and heat from the Lebowa (Bushveld) Granites in areas close to the

intrusion and minor contributions of Fe, Mn and possibly Cu leached from the

Rustenberg Layered Suite. Farthest from the intrusion, basinal fluids deposited phosphate

minerals in the Witwatersrand Supergroup and reset paleomagetic and Rb-Sr isotope

systematics as much as 500 km from present contacts. Vertical exaggeration is 10:1

(approximate width of cross section is 1000 km).

22

Table 1. K-Ar1 dating of fine grained illite from the Bushy Park MVT deposit.

Sample ID K Rad. 40Ar Rad. 40Ar Age Error [%] [mol/g] [%] [Ma] [Ma]

BP271-118.2; white friable muscovite/illite 8.38 5.5884E-08 99.53 2059.2 40.77 BP379-243.2; muscovite/illite only 7.75 5.0780E-08 99.54 2037.6 40.38

1 The K-Ar dating technique follows standard methods described in detail by Faure (1986). During the

course of the study, the international standards HD-B1 and LP6 (Odin et al. 1982) were measured. The

error for Ar analyses is below 1.00 % and the 40Ar/36Ar value for airshots averaged 294.54 ± 0.21 (n

=2). The K-Ar ages were calculated using 40K abundance and decay constants recommended by Steiger

and Jäger (1977).

23

Table 2. Sm-Nd isotopic data for Zeerust fluorite used in age interpretation.

Sample Wt. (g) 147Sm/144Nd1 2-sigma2 143Nd/144Nd3 2-sigma4 3 – WT-PK-F - Witkop 0.4497 0.3080 0.0017 0.513867 0.000010 4 – PD-2-(P) 0.1087 0.1893 0.0008 0.512304 0.000010 5 – PD-2-(W) 0.2752 0.1598 0.0005 0.511874 0.000010 7 – DDH31-268 0.1064 0.2651 0.0005 0.513311 0.000009 1 Sm/Nd ratios were determined by single collector magnetic sector ICP-MS using a standard-sample-

standard bracketing technique (Gleason et al. 2007). Two in-house standards of known Sm/Nd

composition (ID-TIMS) gave 147Sm/144Nd = 0.1266 ± .0010 (n=8) relative to a true (ID-TIMS) value of

0.1265; and 147Sm/144Nd = 0.1466 ± .0020 (n=8) relative to a true (ID-TIMS) value of 0.1462 during this

run. Sample solutions were a 1:10 dilution of the same aliquot used for Nd isotope chemistry. 2 2-sigma errors are based on the in-run average of 4 analyses. True reproducibility of 147Sm/144Nd ratios

by this method is estimated to be ± 1%. 3 Nd isotopic data were determined by TIMS static mode on a Finnigan 262 equipped with 8 collectors

following methods of Gleason et al. (2007). Mass 147 was monitored to insure no Sm interference on

mass 144. 143Nd/144Nd ratios were normalized to 146Nd/144Nd = .7219 for online mass bias correction

using exponential law. Multiple measurements of the La Jolla Nd isotopic standard during the course of

this study gave a value of 143Nd/144Nd = 0.511852 ± 9 (n = 23), making corrections unnecessary. Prior to

analysis, Nd was pre-concentrated by digesting cleaned and crushed fluorite samples in a mixture of

HClO4 and HCl following methods of Chesley (1991). Nd was then separated from matrix using

conventional 2-stage column chemistry (Gleason et al. 2007); Nd blanks were < 100 pg. 4 2-sigma errors reflect TIMS in-run precision based on 15 blocks of data on 10 ratios each (150 ratios).

A)

1000 km

GriqualandWest Basin

TransvaalBasin

KaapvaalCraton

Capetown

Durban

Lebowa Granite and Granophyre

Rustenberg Layered Suite

Rooiberg Suite

Bushveld Igneous Complex

Pretoria Group

Chuniespoort Group

Post-Bushveld Complex

Transvaal Supergroup

B)

50 km

V

BB

V

P

RT

U

B

VG S

ZLR

ZP

V

Features Related to:

Layered Mafic SuiteLebowa Granites andRooiberg Suite

Pretoria

Indian

Ocean

100 km

Pering

Bushy Park -20382059

Kalkdam

Katlanai

2121

20322140

H

Witwatersberg

Pilgrim’s Rest

Sabie

Johannesburg

Zeerust

204320432060

2046

Mississippi Valley-type deposits

Witwatersrand Basin(Central Rand Group)

Bushveld Complex

Transvaal Supergroup

Exposed Covered

Witwatersrand Ages (m.y.)

Au and Pb-Zn vein deposits

2043G

L

C

E

Ventersdorp Supergroup

Basement Rocks (including Witwatersrand Supergroup and Dominion Group)

skcoR tsoHxelpmoC dlevhsuBRooiberg Group

Lebowa Granite Suite

Rustenberg Layered Suite

Postmasburg-Pretoria Group

Ghaap-Chuniespoort Group

MVT-(Pb-Zn) DepositMVT-(F) Deposit

Au DepositPhosphate Ages

10 km

WENESW

Granite Related Fluid Basinal FluidsMetamorphic Fluid Meteoric Fluids