Petrography, sulfide mineral chemistry, and sulfur isotope evidence for a hydrothermal imprint on Musina copper deposits, Limpopo Province, South Africa: Evidence for a breccia pipe origin?

Accepted Manuscript Petrography, sulfide mineral chemistry, and sulfur isotope evidence for a hydrothermal imprint on Musina copper deposits, Limpopo Province, South Africa: Evidence for a breccia pipe origin? Jeff B. Chaumba, Humbulani R. Mundalamo, Jason S. Ogola, J.A. Cox, C.J. Fleisher PII:

S1464-343X(16)30149-2

DOI:

10.1016/j.jafrearsci.2016.05.003

Reference:

AES 2562

To appear in:

Journal of African Earth Sciences

Received Date: 19 February 2016 Revised Date:

5 May 2016

Accepted Date: 6 May 2016

Please cite this article as: Chaumba, J.B., Mundalamo, H.R., Ogola, J.S., Cox, J.A., Fleisher, C.J., Petrography, sulfide mineral chemistry, and sulfur isotope evidence for a hydrothermal imprint on Musina copper deposits, Limpopo Province, South Africa: Evidence for a breccia pipe origin?, Journal of African Earth Sciences (2016), doi: 10.1016/j.jafrearsci.2016.05.003. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Petrography, sulfide mineral chemistry, and sulfur isotope evidence for a hydrothermal

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imprint on Musina copper deposits, Limpopo Province, South Africa: Evidence for a

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breccia pipe origin?

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4 Jeff B. Chaumba

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Department of Geology & Geography, University of North Carolina at Pembroke,

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Pembroke, NC 28372, USA, [email protected]

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Humbulani R. Mundalamo, Jason S. Ogola

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Department of Mining and Environmental Geology, University of Venda, Private Bag

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X5050, Thohoyandou, Limpopo Province, 0950, South Africa

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J.A. Cox and C.J. Fleisher

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Department of Geology, University of Georgia, Athens, GA 30602, USA.

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ABSTRACT

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The Musina copper deposits are located in the Central Zone of the Limpopo orogenic belt

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in Limpopo Province, South Africa. We carried out a petrographic, sulfide composition,

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and δ34S study on samples from Artonvilla and Campbell copper deposits and a country

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rock granitic gneiss to Artonvilla Mine to place some constrains on the origin of these

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deposits.

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The assemblages at both Artonvilla and Campbell Mines of brecciated quartz,

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potassium feldspar, muscovite, chlorite, calcite, and amphibole are consistent with

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sericitic alteration. Quartz, amphibole, feldspars, and micas often display angular textures

ACCEPTED MANUSCRIPT 2 which are consistent with breccias. Sulfur concentrations in pyrite from Artonvilla Mine

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plot in a narrow range, from 50.2 wt. % to 55.7 wt. %. With the exception of a positive

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correlation between Fe and Cu, no well defined correlations are shown by data from the

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Musina copper deposits. The occurrence of sulfides both as inclusions in, or as interstitial

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phases in silicates, suggests that hydrothermal alteration that affected these deposits most

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likely helped concentrate the mineralization at the Musina copper deposits. Sulfur

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concentrations in chalcopyrite samples investigated vary widely whereas the copper

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concentrations in chalcopyrite are not unusually higher compared to those from

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chalcopyrite from other tectonic settings, probably indicating that either the Cu in the

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Musina copper deposits occurs in native form, and/or that it is hosted by other phases.

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This observation lends support to the Cu having been concentrated during a later

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hydrothermal event.

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One sample from Artonvilla Mine (AtCal01) yielded pyrite δ34S values of 3.1and

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3.6 ‰ and chalcopyrite from the same sample yielded a value of 3.9 ‰. A country rock

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granitic gneiss to Artonvilla Mine yielded a δ34Spyrite value of 8.2 ‰. For Campbell Mine

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samples, one quartz vein sample has a δ34Spyrite value of 0.5‰ whereas chalcopyrite

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samples drilled from different areas within the same sample yielded values of 0.4 and 0.7

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‰. The same sample also yielded a δ34Sbornite value of 0.4‰. Another Campbell Mine

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quartz vein sample yielded a chalcopyrite δ34S value of -0.3 ‰. Sulfur isotope

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thermometry for one Campbell Mine quartz vein sample with coexisting sulfides yielded

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a ∆34Schalcopyrite-bornite value of 359oC that is consistent with the stability of this mineral

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pair. Thus, δ34S values from Campbell Mine are consistent with an igneous source for the

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sulfur. Based on a simple two-end member isotope mixing model, contamination of the

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ACCEPTED MANUSCRIPT 3 sulfur by sulfur derived from granitic country rocks likely occurred at Artonvilla Mine.

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Based on findings from this study and by other previous investigators, it is concluded that

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features displayed by the Musina copper deposits are consistent with a breccia pipe origin

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for the Musina copper deposits.

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51 1. Introduction

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Although a breccia pipe origin has not yet been suggested as a source for the Musina

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copper deposits, results presented here warrant a re-interpretation of the origin of these

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deposits and we hypothesize that the copper deposits at Musina originated as breccia

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pipes. A breccia pipe is a steeply dipping to subhorizontal, subcylindrical body of broken

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rock that is long in one dimension but relatively short in two dimensions, and generally

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forms at the intersection of tabular features such as dikes or faults (e.g., Guilbert and

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Park, 1986). Breccia is used here as defined in the economic geology context of “a once

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solid rock which is now broken and exhibits fragment rotation” (Taylor, 2009). Although

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brecciation may redistribute and overprint earlier formed orebodies, Taylor and Pollard

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(1983) and Taylor (2009) observed that breccia pipes also have a tendency to provide

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pathways for fluids to permeate through large volumes of rock resulting in high-grade

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deposits. The El Teniente, one of largest Cu-Mo deposits in central Chile (a deposit

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largely classified as a porphyry Cu-Mo deposit, e.g., Klemm et al., 2007), was also

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interpreted as a breccia deposit by Skewes et al. (2002). Other important breccia deposits

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include the Oyu Tolgoi in Mongolia (e.g., Perelló et al., 2001), the Cananea in Mexico

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(e.g., Bushnell, 1988), and the Los Bronces in Chile (e.g., Warnaars et al., 1985; Vargas

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et al., 1999). Breccia pipes commonly occur in porphyry systems (e.g., Skewes et al.,

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ACCEPTED MANUSCRIPT 4 2003; Taylor, 2009) in small porphyritic intrusions thought to be apophyses to larger

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plutons that act as centers to large-scale hydrothermal systems. Breccias contain

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significant parts of orebodies in many porphyry deposits, for example, at Cananea in

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Mexico (e.g., Bushnell, 1988), Los Bronces-Río Blanco in Chile (e.g., Warnaars et al.,

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1985; Vargas et al., 1999), and Oyu Tolgoi in Mongolia (e.g., Perelló et al., 2001). The

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character and origin of these breccias in magmatic hydrothermal environments vary

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widely. Intrusive, magmatic hydrothermal, hydromagmatic breccias, and tectonic

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breccias are distinguished (e.g., Sillitoe, 1985; Zhang et al., 2007; Bertelli and Baker,

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2010; Cas et al., 2011; Li et al., 2012), and different types of breccias can occur in a

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single deposit.

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The Musina copper district, located near Musina in the Limpopo Province, northern South Africa (Figs. 1, 2), is comprised of five mines which are, from west to

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east: Campbell, Harper, Messina, Spence, and Artonvilla (Söhnge, 1945; van Graan,

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1964; Jacobsen and McCarthy, 1976; Bahnemann, 1986). These mines were exploited for

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copper for most of the twentieth century (1906-1991; e.g., Bahnemann, 1986; Wilson,

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1998). In the Musina copper deposits, the metal is hosted in chalcopyrite, bornite, and

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chalcocite, in addition to occurring as native copper in the central parts of the ore bodies

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(e.g., Jacobsen and McCarthy, 1976; Bahnemann, 1986). The Musina copper deposits

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occur as a group of nine pipe-like breccias of varying shapes; they also occur as

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disseminated replacement deposits, vein/fissure deposits, and associated hydrothermal

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copper deposits that were emplaced within high-grade metamorphic rocks of the

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Limpopo orogenic belt (e.g., van Graan, 1964; McCarthy and Jacobsen, 1976; Jacobsen

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et al., 1976; Ryan et al., 1983; Bahnemann, 1986).

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ACCEPTED MANUSCRIPT 5 Despite this long history of exploitation of copper in the Musina area, the origin

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of these deposits is still controversial (e.g., Sawkins and Rye, 1979, 1980; McCathy and

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Jacobsen, 1980; Wilson, 1998). Sawkins and Rye (1979) analyzed five samples from

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Campbell Mine and obtained δ34Schalcopyrite values ranging from -0.4 to 0 ‰, two samples

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from Campbell Mine with δ34Sbornite values of -0.3 ‰ and 2 ‰. They also obtained a

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δ34Schalcopyrite value of 0.1 ‰ for a sample from Messina Fault and another one from

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Spence Mine, and a δ34Sbornite value of -0.1 ‰ for a sample from Spence Mine, as well as

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two samples from Harper Mine with δ34Schalcocite values of -2.1 and -1.0 ‰. Sawkins and

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Rye (1979) interpreted these values to indicate an igneous source for the sulfur in

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hydrothermal fluids.

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Studies of both sulfide mineral compositions and sulfur isotopes are potentially

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useful tools in helping shed light on the genesis of sulfide mineralization (e.g., Ohmoto

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and Rye, 1979; Ohmoto and Goldhaber, 1997; Seal, 2006). In this study, we report on

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petrographic and sulfide mineral composition data, additional δ34S data on sulfides from

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both Artonvilla (the easternmost) and Campbell (the westernmost) Mines, and a bulk-

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rock δ34S value from country rocks to the Artonvilla Mine to try and place some

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constrains on the origin of the Musina copper deposits. No country rock δ34S analyses for

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these deposits have been determined before, and such results may be useful in helping

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constrain the amount of crustal contamination. We specifically aim to document for the

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first time sulfide mineral compositions from these deposits and evaluate if significant

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copper mineralization is hosted in base metal sulfides, and attempt to constrain the

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Musina copper mineralization temperatures from sulfur isotope thermometry.

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ACCEPTED MANUSCRIPT 6 2. Previous work and tectonic setting

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The Limpopo orogenic belt is a Precambrian orogenic belt (e.g., Holzer et al., 1999;

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Barton et al., 2006; Khosa et al., 2013) located between rocks of the Zimbabwean craton

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to the north and those of the Kaapvaal craton to the south (Fig. 1). Based on

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magnetotelluric data, Khosa et al. (2013) recently proposed that the 20-30 km wide

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composite Sunnyside-Palala-Tshipise-Shear Zone represents a collisional suture zone

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between the Kaapvaal and Zimbabwe cratons. According to Khosa et al. (2013), this

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suturing resulted from the collision of the Zimbabwe and Kaapvaal cratons at ~2.6 Ga

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and caused formation of high-grade granulites of the Limpopo orogenic belt. The

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Limpopo orogeny evolved between 2.7 and 2.04 Ga, with its individual terranes having

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experienced different tectonic histories under high-grade granulite facies metamorphism

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(e.g., Barton et al., 2006).

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Folded rocks form the dominant structure in the Musina area whose dimensions

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vary from hand specimen to regional scale (Figs. 2, 3). The Musina copper deposits,

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located within the Central Zone of the Limpopo orogenic belt, occur within multiply

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folded orthogneisses of varying composition (Bahnemann, 1986). These orthogneisses

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have been subdivided into granodioritic and tonalitic varieties which form the basement

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rocks in the area, overlain by metasediments and leucogneisses, garnetiferous schists,

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amphibole and pyroxene granulite, metaquartzites, calc-silicates, and magnetic iron

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formations (Bahnemann, 1986). Both the Singelele granitic gneiss and the Sand River

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gneiss, dated at 2647 Ma and 3282 Ma respectively (Zeh et al., 2007), crop out in the

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vicinity of the Musina copper deposits (Figs. 2, 3). The Sand River gneiss is interpreted

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to have formed from melting of older Archean crust derived from a depleted mantle

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ACCEPTED MANUSCRIPT 7 source at 3.65 Ga (Zeh et al., 2007). The Singelele granitic gneiss, and the 2612 Ma Bulai

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Pluton which crops out to the northwest of Musina (Figs. 2, 3), are both thought to have

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been derived from mixtures of different proportions of reworked 3.65 Ga Paleoarchean

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crust and juvenile magmas extracted from depleted mantle during the Neoarchean at 2.65

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Ga (Zeh et al., 2007).

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The Bulai pluton, a calc-alkaline and dominantly porphyritic granite, was also intruded into the Central Zone of the Limpopo orogeny (Zeh et al., 2007). The Bulai

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pluton is interpreted to represent a magmatic complex of variably deformed charnockites

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and granites, and contains xenoliths of highly deformed metamorphic country rocks (Zeh

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et al., 2007; Millonig et al., 2008). Further to the west of the Musina deposits, the

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Mahalapye Complex, which forms the southwestern-most terrane of the exposed Central

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Zone of the Limpopo orogenic belt in Botswana, is composed of granodiorites, quartz-

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monzonites, migmatitic rocks, and Central Zone gneisses (e.g., Aldiss, 1991, Millonig et

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al., 2010). An overall increase in the former melt fraction in the Central Zone migmatitic

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rocks has been observed to occur from east to west (Van Breemen & Dodson, 1972;

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Chavagnac et al., 2001). According to McCourt et al. (2004), the migmatitic gneisses are

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crosscut by granite dykes and are also intruded by large volumes of granite plutons that

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comprise both the syn-kinematic Mokgware Granite and the post-kinematic Mahalapye

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Granite. A number of terranes in the Limpopo orogenic belt, such as the Franscistown

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terrane in Botswana, are interpreted to represent continental margin arc complexes

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(McCourt et al., 2004).

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At the Musina copper deposits, copper mining is thought to have commenced a couple of centuries ago when indigenous Africans used stone hammers and iron tools to

ACCEPTED MANUSCRIPT 8 mine the ore (e.g., Söhnge,1945; van Graan, 1964; Bahnemann, 1986) and ceased in 1991

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(Wilson, 1998). Nine breccia pipes and associated hydrothermal copper deposits are

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aligned along a northeast trend (e.g., Jacobsen et al., 1976) which forms a southwestern

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projection of the 184-179 Ma Karoo igneous province (e.g., Cox, 1988, 1992; Duncan et

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al, 1997, Jourdan et al., 2007). Both barren and three mineralized breccia pipes (Jacobsen

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et al., 1976) which intrude rocks of the Limpopo orogenic belt (e.g., Barton et al., 2006)

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occur in an area measuring 20 km long by 1 km wide that strikes northeast (e.g.,

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McCarthy and Jacobsen, 1976; Jacobsen et al., 1976). Bahnemann (1986) observed that

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the Musina copper mines occur at the intersection of faults, folds, fractures, and

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lithological contacts (Figs. 2, 3). The Messina Fault and Dowe Tokwe wrench fault (Fig.

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3) have been interpreted to be steep mylonite zones ranging from 2-40 m in width and are

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cut by younger mafic dikes indicating reactivation along these faults (e.g. Bahnemann,

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1986).

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Based on fluid inclusion studies (Sawkins, 1977) and stable isotope data (Sawkins and Rye, 1979), Sawkins and co-workers (Sawkins, 1977; Sawkins and Rye, 1979)

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proposed a model involving formation of the Musina orebodies from circulating meteoric

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waters whereby Cu and S were extracted from now eroded overlying Karoo basalts by

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meteoric waters (with dissolved salts sourced in playa lakes which migrated downward

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along faults). Based on oxygen isotope data of quartz veins with δ18O values of 9.8-14.1

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‰, with the higher values interpreted to have occurred later at relatively lower

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temperatures, Sawkins and Rye (1979) argued that such 18O-enriched values resulted

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from low-temperature interaction of quartz with hydrothermal fluids that had negative

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δ18OH2O values. As these meteoric fluids returned to surface they produced breccia and

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ACCEPTED MANUSCRIPT 9 replacement ore bodies (Sawkins and Rye, 1979). However, McCathy and Jacobsen

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(1980) argued that the quartz that Sawkins and Rye (1979) studied is late in the

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paragenetic sequence, and also that Sawkins and Rye (1979) did not analyze early stage

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quartz on the basis that it was unsuitable for study. Further, McCarthy and Jacobsen

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(1980) interpreted δ34S values {-3.4 to 0.4 ‰} presented by Sawkins and Rye (1979) to

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lend support to a magmatic source for the sulfur in the Musina copper deposits.

A number of workers (e.g., Mihalik et al., 1974; Jacobsen and McCarthy, 1976;

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McCarthy and Jacobsen, 1976; Jacobsen et al., 1976) proposed a magmatic hydrothermal

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origin for the Musina copper deposits. According to Jacobsen and co-workers, copper-

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bearing solutions were derived from a deep-seated alkaline magma of the Karoo igneous

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suite that migrated upward along suitable structures and at several places became trapped,

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enabling reactions between fluids rich in sodium and aluminum, and host granulites.

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These reactions produced the ore deposits (e.g., McCathy and Jacobsen, 1980).

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Paragenetic studies conducted by Jacobsen et al. (1976), Jacobsen and McCarthy

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(1976), and Sawkins (1977) observed a progressive increase in Cu:Fe and Fe:S ratios in

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copper minerals with time, and specularite deposition relatively late in the paragenetic

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sequence. Such observations imply a progressive increase in fO2 with a corresponding

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decrease in fS2 occurred during the mineralization period (Sawkins and Rye, 1979). In the

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Musina copper deposits paragenetic sequence, minerals such as albite, sericite, zoisite,

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and quartz occur as replacement minerals, whereas specularite, sulfides, chlorite, and

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calcite occur as vein filling minerals (Jacobsen et al., 1976). It was observed by Jacobsen

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et al. (1976) that minerals such as albite and zoisite occur as both replacement (during

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brecciation at ~375oC) and vein filling minerals, with the vein filling minerals inferred to

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have been formed at temperatures of 160-210oC (Jacobsen et al.,, 1976).

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The largest mining district is the Campbell Mine area (Figs. 2, 3), and here several lodes such as the Esperanza, Snake Lode, Line Lode, West Lode, Chain Lode,

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and Maverick Lode, were mined for and produced a lot of copper (e.g., Bahnemann,

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1986). These lodes were projected vertically transverse to the Messina Fault in a

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southwest direction (Fig 4a; Bahnemann, 1986). What is striking to us from an

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examination of Fig. 4 is that the main mineralization here is linked to the brecciated West

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Lode which continues at depth. The Esperanza Lode, which appears to be linked to a

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breccia at depth, is one of the most richly mineralized lodes not only in the Campbell

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Mine area but in the whole Musina copper district (Bahnemann, 1986).

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Although not the subject of the present investigation, the Harper Mine, the next mine located approximately 3 km northeast of Campbell Mine, is shown in Fig. 4b to

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demonstrate that the association of ore bodies with breccias is widespread in the Musina

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copper deposits. On a longitudinal projection parallel to the Messina Fault in a north-west

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direction, it can be noticed that a breccia pipe and the ore body are closely associated at

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Harper Mine (Fig. 4b). Indeed, the occurrence of breccias and associated ore zones has

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been documented at all mines in the Musina copper district (e.g., Van Graan, 1964;

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Jacobsen et al., 1976; Jacobsen and McCarthy, 1976; Bahnemann, 1986).

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The observation that the Musina copper deposits are located along the Messina

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Fault, as well as their preferential location where this fault intersects the contact between

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granitic gneisses and metaquartzites, is probably an indication that the mineralization was

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an interplay of a number of factors such as lithological contacts, faults, and folds

ACCEPTED MANUSCRIPT 11 (Bahnemann, 1986). Bahnemann (1986) interpreted these breccias to be the result of

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tension that was created near lithological contacts by stress distribution during faulting

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and this probably aided copper mineralization. Associated with breccia formation was

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hydrothermal replacement and fissure mineralization (Bahnemann, 1986), implying that

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the Musina breccias were cogenetic with the hydrothermal alteration.

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At the Musina copper deposits, copper mineralization is confined to a cordierite-

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biotite-garnet gneiss unit which is hydrothermally altered (e.g., Jacobsen and McCarthy,

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1976). According to Jacobsen and McCarthy (1976), mineral zonation occurs in four

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concentric zones and increases in intensity towards the central part of the ore bodies.

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Sericitization of plagioclase, sillimanite, cordierite, biotite, and quartz together with

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pyrite marks the outermost first alteration zone. Biotite, sillimanite, and cordierite are

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altered to chlorite whereas perthite and plagioclase are partially replaced by albite; garnet

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is partially chloritized and pyrite is replaced by chalcopyrite to comprise the next

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(second) zone further inwards (Jacobsen and McCarthy, 1976). Chalcopyrite is in turn

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replaced by bornite where increasing alteration occurs in the third zone, the next

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alteration zone inwards. Hematite is reported by Jacobsen and McCarthy (1976) to first

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appear together with bornite in this third alteration zone. Where still more intense

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alteration has destroyed original minerals to form the central and fourth alteration zone of

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chlorite, epidote, and albite; associated ore minerals in this fourth alteration zone are

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chalcocite and bornite (Jacobsen and McCarthy, 1976). Hematite and goethite also occur

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in this fourth and most intensely altered zone (Jacobsen and McCarthy, 1976). Further, in

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this fourth alteration zone, an assemblage of chalcocite, native copper, and goethite may

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ACCEPTED MANUSCRIPT 12 252

occur in a host rock that has been altered to gray-green clay (Jacobsen and McCarthy,

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1976). Söhnge (1946) reported that as of June 30th, 1939, ore reserves at the Musina

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copper deposits were estimated at 2.81 million tons assaying 2.09% Cu. In 1960, ore

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reserves at these deposits were estimated at 6.37 million tons at 1.61% copper (Pelletier,

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1964). In 1991, the last mine to operate in the Musina area, Messina-No. 5 shaft, stopped

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production, bringing to an end 88 years of modern copper mining in the region. At the

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time of closure, a total of 42 Mt of ore and 0.75 Mt of copper had been produced from the

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Musina copper mines, with ore production peaking at 1.1 Mt/year in the 1970s (Wilson,

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1998).

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3. Samples and analytical techniques

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Since it is no longer possible to enter the old mine workings as they are currently sealed-

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off, samples were collected from near closed mine shafts and dumps. Although our

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efforts to obtain drill core data from the time when the mines were in operation were not

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successful, our results compare very well to those from previous investigators and thus

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validate our interpretations based on these dump samples. Samples from both Campbell

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Mine and Artonvilla Mine utilized in this study are shown in Table 1 and their

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approximate locations are shown in Fig. 2. Thus, rock and ore samples may not

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necessarily conform to the geological map as they were collected from the rock dumps

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representing the host rocks of the two deposits. Determining the actual levels from which

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the samples originated from is now nearly impossible. However, since our samples were

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ACCEPTED MANUSCRIPT 13 274

obtained from the top part of the dumps, they are most probably from the deepest levels

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of the workings since they are likely to have been mined last, if that was the case.

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Examples of brecciated samples investigated in this study are shown Fig. 5. Slabbing of the samples was carried out in an effort to bring out the textures as

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recommended by Taylor (2009). For samples from Artonvilla Mine, some breccias are

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composed of mostly micas, amphibole and minor calcite and chlorite, potassium feldspar,

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and angular quartz which range in grain size from 2 mm to >4 cm (Fig. 5a). The interval

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between the amphibole and potassium feldspar clasts in Artonvilla Mine breccias is filled

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in with mostly quartz (Fig 5a) and minor calcite in some cases (Table 1). The clear and

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angular textured quartz is interpreted to be infill quartz, occupying the spaces between the

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now altered broken rocks (Fig. 5a). This texture has some resemblance to a jigsaw fit-

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stockwork texture (e.g., Zhang et al., 2007). For samples from Campbell Mine, very

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coarse-grained and sometimes rounded (milled) quartz, angular quartz, amphibole, and

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potassium feldspar clasts range in size from 1 mm to >7 cm (Figs. 5b, c), with quartz

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forming the majority of the breccia clasts. Disseminated mineralization at Campbell Mine

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is in the form of chalcopyrite, pyrite, and bornite which are hosted mostly in quartz veins

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(Figs. 5b, c; Table 1), the quartz veins also being part of infill textures (e.g., Taylor,

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2009). Sulfides in sample CpQv02 from Campbell Mine are very coarse-grained,

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sometimes reaching sizes of up to 2 cm. All these lithologies are hydrothermally altered

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represented by minerals such as chlorite and amphibole. The textures described for the

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Campbell Mine breccias such as rounded clasts (e.g., Fig. 6) composed of different

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lithologies are comparable to breccia pipe textures from Grasberg mine in Papua,

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Indonesia described by Taylor (2009). At Campbell Mine, brecciated macroscopic quartz,

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ACCEPTED MANUSCRIPT 14 micas, and amphibole grains occur in association with coarse-grained copper sulfide

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mineralization (Figs. 5d). Another example of the brecciated sample from Campbell

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Mine is shown Fig. 5d. Here, brecciated macroscopic quartz and amphibole grains occur

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in association with coarse-grained copper sulphide mineralization (Figs. 5d). Pyrite is

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observed mostly in association with sericite. These breccia textures described for the

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Musina copper deposits which show rounded (milled) fragments are consistent with

303

breccia pipes of ‘broken rock’ described by Taylor (2009).

SC

Thin sections were examined first under a petrographic microscope, followed by

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analyzing the major mineral phases and sulfides by electron microprobe on polished thin

306

sections. Mineral compositions of the sulfides (chalcopyrite and pyrite) were obtained

307

with a JEOL JXA-8530F Hyperprobe housed at Fayetteville State University, North

308

Carolina, USA (e.g., Chaumba et al., 2015). For sulfide analyses, the Hyperprobe was

309

operated at a beam current of 30 nA, an accelerating voltage of 30 kV, and a minimum

310

beam diameter of 1 µm. Compositions were analyzed firstly by X-ray energy dispersive

311

spectroscopy (EDS) for qualitative and semi-quantitative analysis, and then by X-ray

312

wavelength dispersive spectroscopy (WDS) for quantitative analysis using Smithsonian

313

standards. At least three spots were collected for each phase. Fifteen-second counting

314

times were used on peak and background measurements. For the calculation of the

315

oxides, the ZAF matrix correction system of Armstrong (1988) was used.

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Minerals for δ34S isotope analyses were separated via manual drilling using a

317

diamond drill bit at University of Georgia, Athens, GA, USA. Between 4 and 6 mg of

318

pyrite, chalcopyrite, and bornite were combined with elemental copper, quartz, and

319

vanadium pentoxide (V2O5) and finely crushed. An offline V2O5 combustion line with

ACCEPTED MANUSCRIPT 15 variable cryogenic temperature trap was used, employing a modified method from

321

Yanagisawa and Sakai (1983). The sample was then heated in a furnace at 1050oC to

322

produce SO2 and other gases. Water was removed cryogenically using a dry ice-ethanol

323

slush, and the remaining sample was collected in a variable temperature cryogenic trap.

324

After raising the temperature from -190 oC to -145 oC to remove CO2, the temperature

325

was raised again to -90 oC to convert solid SO2 to gaseous SO2.

The extraction line cryogenically isolates the SO2 gas from non-condensable

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326

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gases, CO2, and H2O using a dry ice and ethanol slush and a variable temperature trap.

328

The SO2 gas was measured using a calibrated mercury manometer, converted, and

329

reported as actual SO2 yield. SO2 was then collected in a Pyrex breakseal and analyzed

330

using a Finnigan MAT 252 dual inlet mass spectrometer. An accelerating potential of

331

8kV was used, and each sample was measured for 8 seconds for 8 standard-sample cycles

332

against the appropriate SO2 reference gases. Sulfur samples were measured with a 1000-

333

2000mV signal intensity, with an open Variable Ion Source Conductance (VISC) ‘sulfur

334

window’. An error of ±0.2 ‰ (2σ) was determined based upon replicate analysis of

335

Esperanza and ZS495 standards. Results are reported relative to the Vienna Canyon

336

Diablo Troilite Standard (VCDT) defining δ34S as:

338 339 340

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δ34S = {(34S/32sample - 34S/32reference)/( 34S/32reference)} x1000.

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The absolute 34S/32S ratio for VCDT is 4.50045 × 10−3 (Ault and Jensen 1963).

4. Results

341 342

4.1 Petrography

ACCEPTED MANUSCRIPT 16 343 Photomicrographs for samples from Artonvilla Mine area are shown in Fig. 6. Breccia

345

textures are not clearly visible in thin section mainly due to the very coarse-grained

346

nature of the breccias, and also probably due to overprinting events which take advantage

347

of earlier fractured zones (e.g., Taylor, 2009). Some Artonvilla Mine samples are

348

extensively hydrothermally altered such that only amphibole and micas are visible in

349

plane polarized light (Figs. 6a-d). Evidence of a breccia texture is evident in some thin

350

sections as angular points defined by the contacts of micas and amphiboles (Fig. 6b, c). In

351

some instances, some clasts (now altered to micas) in amphiboles are rounded, hinting to

352

milled (rounded) breccias (Fig. 6d). Other samples have high proportions of disseminated

353

sulfides (~10%) which occur together with sericite, muscovite, calcite, and feldspar (Figs.

354

6e, f). In some thin sections, evidence of pathways of hydrothermal fluids can be seen in

355

the form of numerous sulfide stringers and bifurcating sulfides with muscovite crystals

356

occurring between and interfingering with the sulfides (Figs. 6e, f). The sulfides also

357

contain numerous very fine- to fine-grained inclusions of muscovite (Figs. 6e, f). Granitic

358

gneisses, country rock samples to the Artonvilla Mine, which are dominated by altered

359

plagioclase, multiply-twinned plagioclase feldspar, alkali feldspar (Fig. 6g), occur in

360

association with coarse-grained biotite and sillimanite (Fig. 6h).

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Campbell Mine samples show similarly extensive hydrothermal alteration of

362

silicate minerals (Fig. 7). Brecciated muscovite and potassium feldspar (being replaced

363

by sericite) are the dominant phases, with disseminated sulfides occurring as accessory

364

phases (Fig. 7a). The sulfides similarly enclose numerous very fine-grained sericite

365

crystals but the sulfides are not as abundant as in the Artonvilla Mine suite of samples.

ACCEPTED MANUSCRIPT 17 Where it is not sericitized, the alkali feldspar which occurs in association with the

367

mineralization is strongly hydrothermally altered (Fig. 7b). In some patches of Campbell

368

Mine deposit thin sections, sericite and brecciated potassium feldspar are the only

369

minerals present (Figs. 7c, d) whereas in other patches amphibole and feldspar and

370

altered alkali feldspar, chlorite, sericite, and quartz (Figs. 7e, f, respectively)

371

predominate. In certain cases, only isolated remnants of alkali feldspars remain from the

372

sericitization process (Fig. 7d). The lack of clear breccia textures in some thin sections

373

studied is probably due to extensive late-stage hydrothermal overprinting and alteration,

374

as discussed later.

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375 376

4.2 Sulfide mineral occurrence and composition

377

In backscattered electron images (BEIs), pyrite is lighter compared to muscovite, sericite,

379

and potassium feldspar in Artonvilla Mine samples (Figs. 8a, b). Pyrite grain size is

380

highly variable and ranges from less than 0.5 mm across to more than 2 cm in length,

381

occurring as subhedral to polygonal in shape (Figs. 8a, b). As shown in Figs. 8a and b,

382

pyrite neither occurs as inclusions nor as interstitial phases between silicate minerals, but

383

tends to occur as massive, polygonal grains with characteristic pyrite dodecahedral

384

shapes and penetration twinning (e.g., Wenk and Bulakh, 2004). The bifurcating nature

385

of the muscovite and sericite (darker (less dense) portions in Fig. 8a), consistent with

386

hydrothermal alteration, is also visible in BEIs from Artonvilla Mine samples (Fig. 8a).

387

This bifurcating nature of sericite in the Fig. 8a, although it also occurs in the center of

388

the feldspars, is concentrated more near the edges of the feldspars and in feldspars near

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ACCEPTED MANUSCRIPT 18 veins and veinlike textures, an indication that sericitization was triggered by external

390

hydrothermal which gained access through hydraulic fracturing fluids (e.g., Que and

391

Allen, 1996). Pyrite commonly occurs in association with muscovite and sericite (Figs.

392

8a, b). In addition, pyrite also occurs as numerous polygonal grains often less than 10 µm

393

across enclosed in coarser-grained potassium feldspar crystals of >500 µm in size (Fig.

394

8b).

Chalcopyrite is lighter compared to both amphibole and potassium feldspar

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crystals as shown in a BEI in Fig. 8c. In samples from Campbell Mine, chalcopyrite is

397

very fine-grained and tends to occur as anhedral inclusions in brecciated amphibole

398

crystals (Fig. 8c). Further, chalcopyrite also occurs as numerous anhedral crystals often

399

less than 10 µm across enclosed in brecciated and relatively coarser-grained potassium

400

feldspar crystals of >500 µm in size (Fig. 8d). In contrast, in some thin sections,

401

plagioclase is almost completely enclosed by anhedral chalcopyrite of not more than 50

402

µm across (Fig. 8e). Moreover, chalcopyrite grains in plagioclase can occur as inclusions

403

within very coarse-grained amphibole crystals (Fig. 8e). In some cases, interstitial

404

curvilinear to anhedral chalcopyrite grains, typically <50µm, can also occur enclosed

405

within relatively coarser-grained zoned plagioclase crystals of >300 µm in size (Fig. 8f).

407 408

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4.3 Pyrite

Table 2 lists representative pyrite chemical analyses from Artonvilla Mine, with

409

the rest of the results in Appendix 1. Sulfur concentrations in pyrite plot in a narrow

410

range, from 50.2 wt. % to 55.7 wt. % (Table 2, Fig. 9a). In some oxidized sulfides, O

411

replaces S (e.g., Locmelis et al., 2010) but this was not the case in our fresh samples. The

ACCEPTED MANUSCRIPT 19 majority of pyrite S concentrations (64 out of 85 analyses) fall within the 52-54 wt. % S

413

range (Fig. 9a). Very few pyrite S analyses fall in the ranges 50-51.99 wt. % S and 54-

414

54.99 wt. S (Fig. 9a). Nickel contents in Artonvilla Mine samples range from values at or

415

below detection limit to 0.45 wt. % (Table 2, Fig. 9b), and in a plot of wt. % Ni versus

416

wt. % Fe, no correlation exists between the two (Fig. 9b). The Artonvilla Mine country

417

rock gneiss sample, however, has lower Ni concentrations which range from values at or

418

below detection limit to 0.01 wt. % Ni (Fig. 9b). Iron concentrations for both Artonvilla

419

Mine and Artonvilla Mine country rock gneiss samples are comparable and they range

420

from 43-46.3 wt. % (Fig. 9b). Lead concentrations for Artonvilla Mine samples have

421

values at or below detection limit of ~0.03 wt. % to 0.43 wt. %, with the Artonvilla Mine

422

country rock gneiss values falling within the Artonvilla Mine samples (Table 2, Fig. 9c).

423

A plot of wt. % Pb versus wt. % Fe shows that Pb concentrations tend to cluster between

424

values at detection limit and 0.1 wt. % Pb whereas Fe concentrations tend to cluster

425

between 44.5 wt. % Fe and ~46.3 wt. % Fe (Fig. 9c).

426

428

4.4 Chalcopyrite

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Table 3 lists representative analyses of chalcopyrite samples from Campbell Mine, with the rest of the results in Appendix 2. Chalcopyrite was not observed in the

430

Artonvilla Mine thin sections investigated. Chalcopyrite S concentrations are more or less

431

homogeneous with the majority of S analyses plotting in the 33-34.99 wt. % S range (51

432

out of 63 analyses) (Table 3, Fig. 9d). The majority of chalcopyrite S analyses, however,

433

fall in the 33-33.99 wt. % range (Fig. 9d). Very few chalcopyrite analyses plot in the 30-

434

32.99 wt. % S range and in the 35-38.99 wt. % S range (Fig. 9d). In both Campbell Mine

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429

ACCEPTED MANUSCRIPT 20 amphibolites and quartz veins, Fe concentrations range from 26.7 wt. % to 29.8 wt. %

436

(Table 3, Fig. 9e). For both Campbell Mine amphibolite and quartz vein samples, Pb

437

concentrations range from values at or below detection limit to 0.2 wt. % Pb, and show

438

no correlation with Fe (Fig. 9e).

439

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435

In amphibolites, copper (Cu) concentrations in chalcopyrite plot in a very narrow range, from 32.5 wt. % to 33.9 wt. % (Table 3, Fig. 9f) whereas in quartz vein samples,

441

Cu concentrations in chalcopyrite range from 31.5 wt. % to 34.1 wt. % (Table 3, Fig. 9f).

442

In both Campbell Mine amphibolite and quartz vein samples, a good positive correlation

443

exists between Cu and Fe (Fig. 9f).

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440

4.5 Sulfur isotopes

446

δ34S results from the present study are shown in Table 4. One sample from Artonvilla

447

Mine, AtCal01, has δ34Spyrite values of 3.1and 3.6 ‰ and chalcopyrite from the same

448

sample yielded a δ34S value of 3.9 ‰ (Table 4, Fig. 10a). A country rock granitic gneiss

449

sample to the Artonvilla Mine yielded a δ34Spyrite value of 8.2 ‰ (Table 4, Fig. 10a).

TE D

445

For samples from Campbell Mine, one quartz vein sample (CpQv01) has a

451

δ34Spyrite value of 0.5‰ whereas chalcopyrite samples drilled from different areas within

452

the same sample yielded δ34Schalcopyrite values of 0.4 and 0.7 ‰ (Table 4, Fig. 10a). The

453

same sample (CpQv01) also yielded a δ34Sbornite value of 0.4‰ as shown in Table 4.

454

Sample CpQv02, another quartz vein, yielded one δ34Schalcopyrite value of -0.3 ‰ (Table 4,

455

Fig. 10a). Sample CpAm04, an amphibolite, has chalcopyrite samples drilled from

456

different areas within the same sample yielding δ34S values of -1.1 and 0.3 ‰ (Table 4,

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ACCEPTED MANUSCRIPT 21 457

Fig. 10a). From Figure 10a, it can be seen that Campbell Mine samples all plot within a

458

range of -1.5 – 1.5 ‰.

459 5. Discussion

461

Based on both hand specimen descriptions and petrography, it is clear that samples from

462

both the Artonvilla and Campbell Mines are brecciated (Fig. 5). The lack of void spaces

463

in the samples under investigation rule out collapse breccias as collapse breccias are

464

characterized by voids comprising 20-50% of the rock (e.g., Taylor, 2009). The

465

occurrence of rounded (milled) clasts and lack of voids lend support to an intrusive

466

breccia origin. An intrusive breccia origin encompasses breccias that are characterized by

467

rounded fragments exhibiting evidence of upward transport and forceful injection to form

468

a pipe (e.g., Taylor, 2009). It should be noted that other types of breccias such as

469

hydrothermal, magmatic-hydrothermal, fluidized, explosive, phreatic, phreatomagmatic,

470

or hydromagmatic, e.g., are included in this intrusive breccia definition. At Musina, the

471

occurrence of a jigsaw fit-stockwork texture, where the interval between clasts is marked

472

by fractures or quartz veins is consistent with fluidized magmatic-hydrothermal breccias.

473

Further, the occurrence of larger breccias that are supported by smaller breccias and

474

alteration materials, probably indicating that the clasts moved over short distances,

475

creating open spaces with clasts of different lithologies characterized by rounded shapes

476

further supported a fluidized breccia origin (e.g., Zhang et al., 2007). It is speculated that

477

brecciation and mineralization/hydrothermal alteration likely coincided with fault development in

478

the Musina area such as the Messina and associated faults, probably during Karoo times.

479 480

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460

The occurrence of hydrous minerals like amphibole, sericite and biotite in the Musina copper deposits samples investigated is consistent with a hydrothermal

ACCEPTED MANUSCRIPT 22 overprinting phase(s) which affected the breccias. Hydrothermal overprinting (often

482

multistage) is a common occurrence in breccia pipe deposits (e.g., Taylor, 2009). Such

483

hydrothermal overprinting and associated alteration can be very intense to the extent of

484

obliterating the original breccia textures (e.g., Taylor, 2009). The lack of clear breccia

485

textures in thin sections could be due to this hydrothermal overprinting. The mineral

486

assemblages at the two deposits of potassium feldspar, sericite, muscovite, chlorite,

487

calcite, and amphibole are consistent with sericitic or potassium silicate alteration (e.g.,

488

Meyer and Hemley, 1967; Rose and Burt, 1979; Pirajno, 1992; Reed, 1997). The

489

development of sericite in the deposits investigated suggests that the samples are from the

490

outer zones of a hydrothermally system (Jacobsen and McCarthy, 1976). The occurrence

491

of pyrite at Artonvilla Mine as in the Emery Lode also lends support to our interpretation

492

that samples from the Musina copper deposits investigated here are part of the outer

493

zones of a hydrothermal system. The association of chalcopyrite and chalcocite, which

494

are present in the internal parts of hydrothermal systems (Jacobsen and McCarthy, 1976;

495

Bahnemann, 1986), were not encountered in our suite of samples.

SC

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Chalcopyrite-bearing samples from Campbell Mine, the largest of the Musina

EP

496

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481

district (Bahnemann, 1986), are probably from the upper levels of the hydrothermal

498

system where this sulfide is predominant, and where chalcopyrite occurs together with

499

minor bornite (e.g., Bahnemann, 1986). This observation supports the interpretations of

500

Bahnemann (1986) who reported comparable hydrothermal alteration zones between

501

some ore shoots at both Campbell and Artonvilla Mines. This hydrothermal activity,

502

therefore, must have affected a large area of at least 20km by 1 km wide, from Campbell

503

Mine in the west to Artonvilla Mine in the east.

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ACCEPTED MANUSCRIPT 23 504

The occurrence of felsic, porphyritic calc-alkaline rocks in the Central Zone of the Limpopo orogenic belt is consistent with dacites, quartz-feldspar-biotite porphyries,

506

quartz-latite porphyries, and rhyolitic porphyries encountered in porphyry copper

507

deposits such as at Escondida (e.g., Richards et al., 2001) and the Miduk porphyry Cu

508

deposit, Kerman, Iran (e.g., Boomeri et al., 2009). Some younger magmatic rocks

509

associated with, or close to, the Musina deposits are those that are thought to have been

510

emplaced during the break-up of Pangaea. The Limpopo-Lebombo-Sabi triple junction,

511

encompassing an aborted rift and associated sedimentation, formed a thick volcanic and

512

sedimentary succession formed during the Mesozoic (Truswell, 1977; Jourdan et al.,

513

2007). In the Musina area, copper deposits showing evidence of this age include basalt

514

intrusions of Karoo age (Jacobsen and McCarthy, 1975). Ore-related magmatism,

515

however, could have occurred much earlier in which case it was likely to be associated

516

with the intrusion of the porphyritic 2612 Ma Bulai calc-alkaline pluton (Zeh et al., 2007;

517

Millonig et al., 2008) in the Central Zone of the Limpopo orogenic belt. Thus, it is

518

possible that the Musina ores could have been mobilized at least twice after

519

emplacement: first at 1000 Ma based on a Rb-Sr age of Campbell Mine albites (Ryan et

520

al., 1983), and then during Karoo times (Jacobsen and McCarthy, 1975). Dating of

521

sericite, presumed here to be cogenetic with the mineralization phase (and also the

522

brecciation?), would help constrain the age of the mineralization. Occurrence of Cu

523

mineralization in an orogenic belt is not unique to the Musina area. In the Qiyugou

524

breccia pipe, Henan Province, China, brecciation and associated gold mineralization is

525

interpreted to have been related to granite porphyry emplaced at ~134 Ma which occurred

526

during continental collision (Li et al., 2012). The 347 Ma Santa Olalla granodiorite

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505

ACCEPTED MANUSCRIPT 24 complex Cu–Ni deposit, for example, is a breccia deposit which is hosted by quartz

528

diorite to granodiorite-monzogranite rocks (e.g., Ordoñez-Casado et al., 2008). This

529

breccia deposit occurs in calc-alkaline rocks of the Iberian Variscan orogenic belt in

530

Spain (e.g., Casquet et al., 2001; Piña et al., 2006; Tornos et al., 2006).

531

RI PT

527

Sulfide compositions from the Artonvilla and Campbell Mines are not unusual

when compared to those from various settings (Fig. 11). Sulfide compositions from our

533

Musina samples are compared to sulfides from gabbros from the South West Indian

534

Ridge spreading center (Miller and Cervantes, 2002); an ophiolite complex, the south

535

west Oregon ophiolite (Foose, 1986); a layered intrusion, the Duluth Complex (Pasteris,

536

1984); and the metamorphosed Keivitsansarvi Ni-Cu-PGE deposit in the Keivitsa

537

intrusion, Finland (Gervilla and Kojonen, 2002) in Fig 11.

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532

For Artonvilla Mine and gneiss pyrite samples, Ni contents are comparable to

539

those from various tectonic settings (except the Keivitsansarvi deposit) but Fe is only

540

comparable to concentrations from the SW Indian Ridge gabbros (Fig. 11a). Fe, however,

541

is higher than that from the Keivitsansarvi deposit but lower than Fe from the SW Oregon

542

ophiolite (Fig. 11a). This probably reflects less substitution of Fe by both Ni and Co,

543

common substituents for Fe in pyrite (e.g., Vaughan, 2011) in the Keivitsansarvi deposit

544

than the rest of the samples. The Keivitsansarvi deposit, a Ni-Cu-PGE rich deposit,

545

clearly shows this to be the case as it has both elevated Ni (Fig. 11a) and Co (Fig. 11b)

546

concentrations compared to the rest of the samples plotted.

EP

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547

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538

A plot of Fe versus Cu for Campbell Mine samples shows a positive correlation

548

between the two and that Campbell Mine samples have both lower Fe and Cu

549

concentrations compared to other samples plotted (Fig. 11c). The observation that Cu

ACCEPTED MANUSCRIPT 25 concentration from Campbell Mine are lower than other samples may suggest that at

551

Campbell Mine, the Cu mineralization is not hosted by chalcopyrite, but rather either by

552

other sulfides not in the present suite of samples such as bornite, chalcocite, or as native

553

copper (e.g., Bahnemann, 1986). Another possible explanation is that remobilization of

554

the copper (originally hosted in chalcopyrite and bornite) occurred during the

555

hydrothermal process, as in other breccia deposits such the copper-rich Donoso breccia

556

pipe of the Río Blanco-Los Bronces deposit in central Chile, the copper is mostly

557

contained in chalcopyrite and/or bornite (e.g., Skewes et al., 2003).

SC

Another plausible explanation is that the samples studied are not from the ore

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558

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550

zone. This observation also supports our earlier interpretation, based on mineral

560

assemblages from this study, that our samples are most likely from the outer zone of

561

hydrothermal alteration. Further, this observation is also consistent with previous studies

562

that have documented hydrothermal alteration zones whereby native copper occupies the

563

central zone, followed by a zone of chalcocite, followed by a zone of chalcopyrite as one

564

moves from the center of the alteration zone outwards (Jacobsen and McCarthy, 1976).

565

The lack of spread in Cu and Fe concentrations in chalcopyrite is consistent with the lack

566

of significant substitution in chalcopyrite by other cations (Vaughan, 2011). The lower

567

Cu concentrations in Campbell Mine samples, however, may also be due to the lower

568

abundances of sulfides in the crustal rocks (i.e., quartz veins and amphibolites) compared

569

to mantle-derived mafic rocks with higher concentrations of these elements than our

570

samples (Fig. 11). Campbell Mine quartz vein and amphibolite samples are both

571

characterized by chalcopyrite samples with Pb concentrations which show much wider

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559

ACCEPTED MANUSCRIPT 26 572

ranges over smaller Cu ranges with no correlation between Cu and Pb observed (Fig.

573

11d). Pyrite compositions from Artonvilla Mine are plotted on a S-Fe-Ni ternary

575

diagram in Fig. 12a and it can be observed that low Ni+Co wt. % values are characteristic

576

of these samples (Kullerud et al., 1969). The low wt. % Ni+Co concentrations from

577

Artonvilla Mine pyrites plot at and near the pyrite point which is consistent with pyrite

578

crystallization well before both the onset of chalcopyrite crystallization and expansion of

579

the monosulfide solid solution with further cooling (Fig 12a; e.g., Kullerud et al., 1969;

580

Guo et al., 1999). A simplified phase relations diagram in the S-Fe-Cu system at 300oC

581

(Barton and Skinner, 1979) is plotted in Fig. 12b. Campbell Mine chalcopyrite

582

compositions plot close to the ideal chalcopyrite but define a trend from high S and low

583

Fe to low S and high Fe at near constant copper concentrations (~33 wt. % Cu),

584

especially in Campbell Mine quartz vein samples (Fig. 12b). In amphibolites, however,

585

Fe and Cu concentrations define a trend from high Fe and low Cu concentrations of ~31

586

wt. % Cu to low Fe and high Cu concentrations of ~36 wt. % Cu (Fig. 12b). From phase

587

relationships, such a trend shown by amphibolites (Fig. 12b) is consistent with

588

immiscibility of both S and Fe, leading to increased concentrations of Cu in the sulfide;

589

which then likely settled out later, leading to the formation of the Musina copper

590

deposits.

SC

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591

RI PT

574

A probable interpretation for such differing trends is that some of the Cu was

592

probably sourced from minerals such as chalcopyrite and bornite in amphibolites having

593

widely varying Cu concentrations and was then concentrated by hydrothermal fluids

594

which are characterized by more uniform Cu concentrations. This interpretation is

ACCEPTED MANUSCRIPT 27 595

supported by BEI images in which sulfide inclusions and sulfides enclosed in silicates

596

were only observed in amphibolites but not in quartz veins and other crustal rocks such as

597

gneisses (Fig. 8). A plot of the frequency versus δ34S values for samples from both the Artonvilla

599

and Campbell Mines, combined with results from Sawkins and Rye (1979), is shown in

600

Fig. 13a. Data from the present investigation compare very well with data from Sawkins

601

and Rye (1979) (Fig. 13a), and data from the Mantos Blancos breccia copper deposit in

602

Chile are broadly comparable to data from Campbell Mine (Fig. 13a). Of significance is

603

that samples from Campbell Mine are consistent with a magmatic source for the sulfides,

604

even though the sulfides now occur in amphibolites and quartz veins, and these data lend

605

support to the hypothesis that the mineralization in the Musina copper deposits was

606

sourced from hidden magmatic rocks of alkaline affinity most likely related to the Karoo

607

igneous phase (Söhnge, 1945; Jacobsen et al., 1976). If this is the case, hydrothermal

608

fluids could have been triggered by intrusion of these alkaline intrusive complexes,

609

resulting in the Cu being carried upwards towards the surface by heated meteoric waters

610

during the breakup of Pangaea. Sawkins and Rye (1979, 1980) suggested that the source

611

of the magmatic sulfides may well have been Karoo lavas that have since been eroded

612

away, an interpretation not ruled out by the findings from this investigation. However, it

613

would be difficult to explain the origin of the sulfide inclusions in amphibolites (which

614

most likely were formed contemporaneously with their enclosing rocks) if the sulfides

615

were concentrated by meteoric fluids only as suggested by Sawkins and Rye (1979,

616

1980).

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ACCEPTED MANUSCRIPT 28 Artonvilla Mine samples have δ34S values of ~4 ‰, whereas a country rock

618

granitic gneiss to this deposit has a δ34S value of 8.2 ‰ (Fig. 10). Contamination of

619

magmatic sulfur by sulfur from Artonvilla Mine granitic gneisses can produce the

620

measured Artonvilla Mine δ34S values in Fig. 10 if the Campbell Mine sulfides are

621

representative of the sulfur source. The sulfides in Artonvilla Mine could also have been

622

mantle-derived, and the sulfides were then subsequently affected by hydrothermal fluids

623

that had interacted with sulfides from Artonvilla Mine country rocks. The slightly 34S-

624

enriched values in Artonvilla Mine samples allow some interpretations to be drawn based

625

on the timing of mineralization at Artonvilla Mine. If the mineralization predated

626

metamorphism, Artonvilla Mine samples and its country rocks would likely be

627

characterized by similar δ34S ratios, which is not the case here, suggesting that the

628

mineralization most likely occurred after regional metamorphism.

SC

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The mantle is characterized by δ 34S values of 0 ± 5‰ (Ohmoto and Rye, 1979;

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629

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617

Ohmoto and Goldhaber, 1997). Sulfur isotope thermometry carried out for the Campbell

631

Mine quartz vein using a ∆34Schalcopyrite-bornite = 0.3 ‰ value (sample CpQv01) yielded a

632

temperature of 359oC (Li and Liu, 2006) consistent with the stability of this mineral pair

633

(Barton and Skinner, 1979). Such a temperature is broadly comparable with a

634

hydrothermal imprint on the Musina copper deposits where replacement minerals were

635

also inferred to have been formed at temperatures of ~375oC (e.g., Jacobsen et al., 1976).

636

Other copper deposits such as Mines Gaspé in Quebec, Canada (e.g. Shelton and Rye,

637

1982; Yang and Bodnar, 2004), the Ilkwang Mine breccia pipe deposit (δ34S values of

638

between -1.6 to 0.9 ‰), Republic of Korea (So and Shelton, 1983), and Mantos Blancos

639

breccia copper deposit (e.g. Ramírez et al., 2006), record comparable temperatures of

AC C

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630

ACCEPTED MANUSCRIPT 29 formation. This temperature is consistent with the interpretation that the mantle-derived

641

(due to the cluster of Musina δ34S values around 0 ± 2 ‰ in Fig. 13a, e.g. Sakai et al.,

642

1984; Chaussidon et al., 1991) mineralization is related to hydrothermal circulation

643

driven by magmatic intrusions, based on other evidence presented in this work such as

644

petrography and sulfide mineral compositions. Samples from Artonvilla Mine, however,

645

did not yield any temperatures, probably due to resetting of the δ34S ratios at this deposit

646

by hydrothermal fluids which resulted in sulfur isotope disequilibrium. δ34S results for

647

samples from Campbell Mine are within the range of δ34S values expected from mantle

648

reservoirs. It is, thus, concluded that δ34S results for Campbell Mine samples are within

649

the range of typical mantle-derived S, whereas δ34S values of the country rock granitic

650

gneiss at Artonvilla Mine is within the range of metamorphic rocks (e.g., Seal, 2006;

651

Hoefs, 2015). Samples from Artonvilla Mine plot at the high end of samples

652

characteristic of mantle-derived S, and also within the metamorphic δ34S range,

653

suggesting that the Artonvilla Mine samples may well have been formed during

654

metamorphism. The implication of this observation is that some of the mineralization at

655

Musina may have occurred very early, as metamorphism in the Central Zone occurred

656

between 2.7 and 2.04 Ga, during individual terranes accretion under high-grade granulite

657

facies metamorphism (e.g., Barton et al., 2006). The source of the mineralization could

658

also have been associated with the generation of voluminous granitic bodies during

659

Neoarchaean granulite metamorphism at ca 2.6 Ga (Holzer et al., 1999). Later

660

hydrothermal alteration, therefore, would have had little or no effect on the δ34S isotope

661

signatures. Interaction of mantle-derived S, such as encountered at Campbell Mine, with

AC C

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640

ACCEPTED MANUSCRIPT 30 662

fluids that had previously interacted with country rock gneisses could also have produced

663

the enriched 34S values at Artonvilla Mine.

664

Assimilation of country-rock S is considered as the most reasonable mechanism for producing enriched S isotope signatures such as those at Artonvilla Mine (e.g.,

666

Ripley, 1999; Ripley and Li, 2003, 2013). Determination of the extent of assimilation of

667

crustal S by mafic magmas can be modeled using a simple two-component mixing model

668

(e.g., Ripley, 1999). If we assume an isotope composition of a mantle-derived magma of

669

δ34S = 0.0‰, a S concentration of 800 ppm in primitive magma, an Artonvilla Mine

670

country rock granitic gneiss δ34S value of 8.2‰ (Table 4), and a concentration of 1 wt. %

671

S in fresh biotite-garnet-cordierite gneisses (Jacobsen and McCarthy, 1976),

672

approximately 38% to 48% assimilation of fresh biotite-garnet-cordierite gneisses would

673

be required to produce δ34S values of between 3 ‰ and 4 ‰. A curved trajectory for this

674

two-component mixing equation is shown in Figure 13b. However, despite the

675

occurrence of sulfide-bearing country rocks to the Musina copper deposits, assimilation

676

of country rock sulfur was not the only cause of mineralization. At Campbell Mine, δ34S

677

results are indistinguishable from mantle values, indicating no contribution of crustal

678

sulfur or very little to negligible degrees of contamination.

SC

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Due to the hydrothermal alteration that affected the Musina deposits, assessing the

AC C

679

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665

680

assimilation of crustally derived sulfur by the use of two-component mixing models (e.g.,

681

Lesher and Burnham, 1999; Ripley, 1999; Faure, 2001; Ripley and Li, 2003), however,

682

must be interpreted with caution. Physical addition of a contaminant or processes that

683

affect sulfide masses such as the hydrothermal alteration documented for the deposits

684

under study may render such mixing models inapplicable (e.g., Ripley and Li, 2003).

ACCEPTED MANUSCRIPT 31 Sulfur isotope studies in the Limpopo orogenic belt are lacking: however, such

686

data exists for adjacent Archean cratons and intrusions of the Zimbabwe and Kaapvaal

687

cratons. Mineralized samples from the Phoenix and Selkirk Ni-Cu-(PGE) deposits in the

688

Tati greenstone belt in eastern Botswana display slightly positive δ34S isotope values,

689

which range from 0.2 to 0.8‰ (Fiorentini et al., 2012). These S isotope values were

690

interpreted by Fiorentini et al. (2012) to be consistent with a dominantly mantle source

691

for the sulfur. In the Selebi-Phikwe belt, however, a granite-gneiss terrane with abundant

692

amphibolite lenses of either volcanic and/or intrusive nature, mineralized lower grade

693

samples from the Phikwe, Phokoje, and Dikoloti Ni-Cu-(PGE) deposits are characterized

694

by more variable δ34S values ranging from −3.1 to +0.3‰, suggesting that barren sulfides

695

associated with distal or low temperature sea-floor hydrothermal activity contributed

696

sulfur to these deposits (Fiorentini et al., 2012).

SC

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In the Damara orogenic belt located between the Kaapvaal and the Congo cratons

TE D

697

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685

southwest of the study area, Pirajno et al. (1992/93) reported possible granite related

699

mineral deposits (Group 2) composed of a wide range of sulfide minerals characterized

700

by low δ34S values (-1.2 ± 1.9‰). Mineral deposits in this orogenic belt which include

701

the Onguati and Brown Mountain marble-hosted Au-bearing hydrothermal quartz veins

702

and stockworks were interpreted by Pirajno et al. (1992/93) to be orogenic magmatic-

703

related. The formation of hydrothermal mineral deposits in the Damara orogenic belt was

704

related to the northwest subduction of the Kalahari plate below the Congo craton

705

accompanied by the emplacement of more than 200 plutons in the Central Zone (Pirajno

706

et al., 1992/93). The emplacement mechanism proposed for the Damara orogenic belt

707

deposits may also have been broadly comparable to what may have lead to the formation

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ACCEPTED MANUSCRIPT 32 708

of the Musina copper deposits, with crustal contamination having been more pronounced

709

at some of the Musina copper deposits such as at Artonvilla Mine being the exception. Crustal contamination of mantle-derived magmas is widespread even in the

711

Kaapvaal craton. In the northern part of the Kaapvaal craton, crustal sulfur contamination

712

signatures have been documented within all Platreef rock types of the mafic-ultramafic

713

layered intrusion of the Bushveld Complex from sulfur isotopes (e.g., Holwell et al.,

714

2007; Sharman et al., 2013). Further, from sulfur isotopes, Li et al. (2007) document

715

magmatic hydrothermal alteration helped concentrate platinum-group elements in the

716

main mineralized zone of the Great Dyke, a major Neoarchean mafic-ultramafic complex

717

intruding the Zimbabwe craton. Varying degrees of crustal contamination of mantle

718

derived magmas in the Kalahari craton have been described for various mineralized

719

bodies using other stable (e.g., Schiffries and Rye, 1989, Chaumba and Wilson, 1997)

720

and radiogenic (e.g., Kruger, 1994; McCandless et al., 1999; Schoenberg et al., 1999,

721

2003) isotopes. Thus, both hydrothermal alteration and crustal contamination of mantle-

722

derived magmas was widespread in the Kalahari craton and it was therefore not unique to

723

the Musina copper deposits.

SC

M AN U

TE D

EP

724

RI PT

710

Although the Musina breccia pipes are well known and have been described previously (e.g., Bahnemann, 1986, and references therein), a breccia pipe origin has not

726

yet been linked to the origin of the Musina ore bodies and it is hypothesized in this work

727

that these deposits originated as breccia pipes. In the Artonvilla and Campbell deposits,

728

in general >50 % of the volume of breccias we investigated are composed of clasts that

729

are at least 2 mm in diameter, consistent with an origin as fault breccias (e.g., Woodstock

730

and Mort, 2008). The documented hydrothermal event later affected the rocks under

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ACCEPTED MANUSCRIPT 33 study thus overprinting the fault breccias, although it is possible that some breccias may

732

have been formed during the hydrothermal alteration stage (e.g., Jébrak, 1997). A breccia

733

pipe origin may better explain some of the features of the Musina copper deposits.

734

Alteration which has been documented in all previous studies at Musina copper deposits

735

(e.g., Mihalik et al., 1974; Jacobsen and McCarthy, 1976; McCarthy and Jacobsen, 1976;

736

Jacobsen et al., 1976; Bahnemann, 1986) and it is also common in some breccia pipes

737

where it has also been interpreted to be a result of both orthomagmatic and hydrothermal

738

events (e.g., Williams et al., 1999). Although brecciation may redistribute and overprint

739

earlier formed orebodies, breccia pipes also can provide pathways for fluids to permeate

740

through rocks resulting in high-grade deposits (e.g., Taylor and Pollard, 1983; Taylor,

741

2009), such as the high-grade deposits at Musina.

SC

M AN U

742

RI PT

731

Hydrothermal breccias develop early during the formation of veins, probably in response to the process of fracture propagation (e.g., Scholz, 1990). Hydrothermal

744

brecciation is one of the most common mechanisms of brecciation (e.g., Jebrak, 1997).

745

Formation of the Musina copper deposits at collisional tectonic environments that we

746

have suggested in this study is consistent with breccia pipe deposits formed in other

747

collisional tectonic regimes such as the Belif breccias in Tunisia (e.g., Decrée et al.,

748

2013) and the Qiyugou breccia pipe in China (e.g., Zhang et al., 2007; Li et al., 2012).

749

Evidence exists for a breccia pipe origin for the Musina copper deposits.

AC C

EP

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743

750

Numerous ore concentrations in the Musina copper deposits are associated with breccias

751

(e.g., Söhnge, 1945; Van Graan, 1964; Bahnemann, 1986). Breccia pipes are also a

752

common occurrence in porphyry systems (e.g., Skewes et al., 2003), resulting in

753

extensive hydrothermal alteration in both the breccia pipes and porphyry systems. It is

ACCEPTED MANUSCRIPT 34 also possible that the Musina deposits may have originated as a porphyry system as most

755

breccia pipes are associated with porphyry deposits (e.g., Sillitoe, 2010) but the evidence

756

linking the deposit to that origin may have been destroyed during subsequent processes.

757

Although classic porphyry-style mineralization characterized by different alteration zones

758

which are often a guide to ore from series of mineral assemblages which extend into

759

larger adjacent rocks has not been reported in all breccia pipes, a link between the two

760

can often be ubiquitous (e.g., Sillitoe, 1985; Seedorff et al., 2005). Oxygen isotope values

761

of quartz veins of 9.8 ‰ reported by Sawkins and Rye (1979) are also consistent with an

762

igneous origin, although no hydrogen isotopes have yet been performed to help constrain

763

the source of the fluids.

SC

M AN U

764

RI PT

754

On discussing a model for the origin of mineralization at Musina, Bahnemann (1986) concluded that “…it must be able to explain the unusual purity of the ore at

766

Musina that allows the production of fire-refined copper ingots of almost wire-bar

767

quality”. A breccia origin for the Musina copper deposits can help answer this as high-

768

grade copper deposits occur in breccias such as the Donoso breccia deposit at Rio

769

Blanco-Los Bronces (e.g., Skewes et al., 2003) where mineral deposition in the breccia

770

matrix cooled rapidly, resulting in metal deposition due to expansion of magmatic fluids

771

that are released from cooling stocks (e.g., Sillitoe, 1985). Indeed, the El Teniente, one of

772

largest and high-grade Cu-Mo deposits in central Chile (a deposit largely classified as a

773

porphyry Cu-Mo deposit, e.g., Klemm et al., 2007), is now also being re-interpreted as a

774

breccia deposit by Skewes et al. (2002) and here we also suggest a breccia origin for the

775

Musina copper deposits.

776

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6. Conclusions

778 The Musina copper deposits display evidence of hydrothermal activity based on their

780

mineralogy. Hydrothermal alteration products include potassium feldspar, sericite,

781

muscovite, and pyrite. Sulfide mineralogy and sulfide compositions at Artonvilla and

782

Campbell Mines are also consistent with a hydrothermal overprint on earlier formed

783

sulfide mineralization. δ34S values of the Musina copper deposits are consistent with a

784

hydrothermal imprint of mantle-derived sulfur at Campbell Mine. Mantle-derived sulfur

785

affected by either contamination by country-rock sulfides or affected by hydrothermal

786

activity that had interacted with country rocks, or both, may explain the elevated δ34S

787

isotope compositions at Artonvilla Mine. Sulfur isotope thermometry carried out for the

788

Campbell Mine quartz vein using a ∆34Schalcopyrite-bornite = 0.3 ‰ value yield a temperature

789

of 359oC that is consistent with the expected stability of these mineral phases. Features

790

such as the occurrence of faults, breccias, high-grade copper ores, and hydrothermal

791

alteration displayed by the Musina copper deposits are consistent with a breccia origin.

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779

EP

792 Acknowledgements

794

JBC gratefully acknowledges funding from a UNC Pembroke Summer Research

795

Fellowship which covered the costs of S isotope work at The University of Georgia, and

796

a Research Fellowship from UNC Pembroke Office of Graduate Studies and Research

797

which helped cover the costs of microprobe analyses at Fayetteville State University.

798

Mike Roden is gratefully acknowledged for critically reading an earlier version of the

799

manuscript. Doug Crowe commented on an earlier draft of the manuscript and facilitated

AC C

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ACCEPTED MANUSCRIPT 36 800

access to the UGA Stable Isotope Lab. Thoughtful reviews by Joyashish Thakurta and an

801

anonymous reviewer helped improve the manuscript and are acknowledged.

802 References

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hydrothermal fluid of the Qiyugou breccia pipe, Henan Province, China: implication for breccia genesis and gold mineralization, Geochemistry: Exploration, Environment, Analysis, 12: 147-160. Li, Y.B. and Liu, J.M., 2006. Calculation of sulfur isotope fractionation in sulfides: Geochimica et Cosmochimica Acta , 70: 1789-1795. Locmelis, M., Melcher, F. and Oberthür, T., 2010. Platinum-group element distribution in the oxidized Main Sulfide Zone, Great Dyke, Zimbabwe, Mineralium Deposita, 45: 93-109. Maydagán, L., Franchini, M., Lentz, D. Pons, J. & McFarlane, C., 2013. Sulfide composition and isotopic signature of the Alter Cu-Au deposit, Argentina: constrains on the evolution of the porphyry-epithermal system, Canadian Mineralogist, 51: 813-840. McCandless, T.E., Ruiz, J., Adair, B.I., Freydier, C., 1999. Re–Os isotope and Pd/Ru variations in chromitites from the Critical Zone, Bushveld Complex, South Africa. Geochimica. Cosmochimica. Acta, 63: 911-923. McCarthy, T.S. and Jacobsen, J.B.E., 1976. The mineralizing fluids at the Artonvilla copper deposit: an example of a silica-deficient, alkaline hydrothermal system: Economic Geology, 71: 131-138. McCarthy, T.S. and Jacobsen, J.B.E., 1980. Additional geochemical data on the Messina copper deposits, Transvaal, South Africa - A discussion: Economic Geology, 75: 478-483. McCourt, S., Kampunzu, A.B., Bagai, Z. and Armstrong, R.A., 2004. The crustal architecture of Archaean terranes in Northeastern Botswana, South African Journal of Geology, 107: 146-158. Meyer, C. and Hemley, J.J., 1967. Wall rock alteration, in H.L. Barnes (ed.), Geochemistry of Hydrothermal Ore Deposits, Holt, Rinehart and Winston, New York, p. 166-235. Mihalik, P., Jacobsen, J. B. E., and Hiemstra, S. A., 1974. Platinum group minerals from a hydrothermal environment, Economic Geology, 69: 257-262. Miller, D.J. and Cervantes, P., 2002. Sulfide mineral chemistry and petrography and platinum group element composition in gabbroic rocks from the Southwest Indian Ridge: In J.H. Natland, H.J.B. Dick, D.J. Miller and R.P. Von Herzen (eds.), Proceedings of the Ocean Drilling Program, Scientific Results, 176: 1-29. Millonig, L., Zeh, A., Gerdes, A. and Klemd, R., 2008. Neoarchaean high-grade metamorphism in the Central Zone of the Limpopo Belt (South Africa): Combined petrological and geochronological evidence from the Bulai pluton: Lithos, 103: 333-351. Millonig, L., Zeh, A., Gerdes, A. Klemd, R. and Jackson, J.M. Jr., 2010. Decompressional heating of the Mahalapye Complex (Limpopo Belt, Botswana): a response to Palaeoproterozoic magmatic underplating? Journal of Petrology, 51: 703-729. Ordoñez-Casado, B., Martin-Izard, A. and García-Nieto, J., 2008. SHRIMP-zircon U–Pb dating of the Ni–Cu–PGE mineralized Aguablanca gabbro and Santa Olalla granodiorite: Confirmation of an Early Carboniferous metallogenic epoch in the Variscan Massif of the Iberian Peninsula, Ore Geology Reviews, 34:343-353. Ohmoto, H. and Rye, R.O., 1979. Sulfur and carbon isotopes: in H.L. Barnes (ed.),

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Geochemistry of Hydrothermal Ore Deposits, 2nd Ed., J. Wiley and Sons, p. 173235. Ryan, B.D., Kramers, J.D., Stacey, J.S., Deleveaux, M., Barton, J.M. and Fripp, R.E.P., 1983. Strontium and lead isotope studies and K/Rb ration measurements relating to the origin and emplacement of the copper deposits near Messina, South Africa: in W.J. van Biljon and J.H. Legg (eds.) Geological Society of South Africa, Special Publication no. 8: 47-53. Sakai, H., DeMarais, D., Veda, A., and Moore, J.G., 1984. Concentrations and isotope ratios of carbon, nitrogen, and sulfur in ocean-floor basalts: Geochimica et Cosmochimica Acta, 48: 2433-2441. Sawkins, F. J., 1977. Fluid inclusion studies of the Messina copper deposits, Transvaal, South Africa, Economic Geology, 72: 619-631. Sawkins, F. J. and Rye, R. O., 1979. Additional geochemical data on the Messina copper deposits, Transvaal, South Africa: Economic Geology, 74: 684-689. Sawkins, F. J. and Rye, R. O., 1980. Additional geochemical data on the Messina copper deposits, Transvaal, South Africa-A reply: Economic Geology, 75: 481-482. Schiffries, C.M. and Rye, D.M., 1989. Oxygen isotopic systematics of the Bushveld Complex: I. Constrains on magmatic processes in layered intrusions, American Journal of Science, 289: 841-873. Schoenberg, R., Kruger F.J., Nagler T.F., Meisel T., and Kramers J.D., 1999. PGE enrichment in chromitite layers and the Merensky Reef of the Western Bushveld Complex; a Re–Os and Rb–Sr isotope study. Earth Planet Science Letters 172: 49-64. Schoenberg, R., Nagler, T.F., Gnos, E., Kramers, J.D., and Kamber, B.S., 2003. The source of the Great Dyke, Zimbabwe, and its tectonic significance: evidence from Re–Os isotopes, Journal of Geology, 111: 565- 578. Seal, R.R. II, 2006. Sulfur isotope geochemistry of sulfide minerals: Reviews in Mineralogy and Geochemistry, 61: 633-677. Seedorff, E., Dilles, J.H., Proffett, J.M. Jr., Einaudi, M.T., Zurcher, L., Stavast, W.J.A., Johnson, D.A., and Barton, M.D., 2005, Porphyry deposits: Characteristics and origin of hypogene features, in Hedenquist, J. W., Thompson, J. F. H., Goldfarb, R. J., and Richards, J. P., eds.: Economic Geology 100th Anniversary Volume, p.251-298 Sharman, E.R., Penniston-Dorland, S.C., Kinnaird, J.A., Nex, P.A.M., Brown, M., Wing, B.A., 2013. Primary origin of marginal Ni-Cu-(PGE) mineralization in layered intrusions: ∆33 S, evidence from the Platreef, Bushveld, South Africa. Economic Geology, 108: 365-377. Shelton, K.L. and Rye, D.M., 1982. Sulfur isotopic compositions of ores from Mines Gaspé, Quebec: An example of sulfate-sulfide isotopic disequilibria in oreforming fluids with applications to other porphyry-type deposits, Economic Geology, 77: 1688-1709. Sillitoe, R.H., 1985. Ore-related breccias in volcanoplutonic arcs: Economic Geology, 80: 1467-1514. Sillitoe, R.H., 2010. Porphyry copper systems, Economic Geology, 105: 3-41. Skewes, M.A., Arévalo, A., Floody, R., Zuñiga, P.H., and Stern, C.R., 2002. The giant El

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pentoxide-silica glass mixtures for preparation of sulfur dioxide in sulfur isotope ratio measurements: Analytical Chemistry, 55: 985-987. Yang, K. and Bodnar, R.J., 2004. Orthomagmatic deposit for the Ilkwang Cu-W brecciapipe deposit, southeastern Kyongsang Basin, South Korea, Journal of Asian Earth Sciences, 24: 259-270. Zeh, A., Gerdes, A., Klemd, R. and Barton, J. M., Jr., 2007. Archaean to Proterozoic crustal evolution in the Central Zone of the Limpopo Belt (South AfricaBotswana): Constraints from combined U-Pb and Lu-Hf isotope analyses of zircon. Journal of Petrology, 48: 1605-1639. Zhang, Y.H., Zhang, S.H. and Pirajno, F., 2007. Fluidization: an important process in the formation of the Qiyugou Au-bearing breccia pipe in central China. Acta Geologica Sinica, 81: 226-238.

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ACCEPTED MANUSCRIPT 44 Figure captions

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Fig. 1. Simplified geological map of part of Southern Africa showing the location of Musina in the Central Zone of the Limpopo orogenic belt. Abbreviations: GGT – granitic greenstone terranes of the cratons, NMZ – North Marginal Zone, CZ – Central Zone, SMZ – South Marginal Zone. Proterozoic and younger formations are unornamented. The location of Fig. 2a is also shown.

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Fig. 2. (a) Simplified geologic map of part of the Limpopo orogeny showing location of the two groups of samples used in this study. (b) shows detailed geology of an area between Messina Mine and Artonvilla Mine (both maps modified from Jacobsen and McCarthy, 1976). Abbreviations: ZW – Zimbabwe, L.R. – Limpopo River, Undifferenti. – undifferentiated.

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Fig. 3. Generalized geology in the vicinity of the Musina copper deposits showing extent of underground workings (Modified from Bahnemann, 1986). Fig. 4. (a) Vertical projection of various lodes in the Campbell Mine area transverse to the Musina Fault in a SW view, and (b) longitudinal projection of the Harper mining area parallel to the Musina Fault in a NW view (After Bahnemann, 1986). Note the association of sulfide mineralization with breccias in both deposits.

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Fig. 5. Photographs showing textures of brecciated quartz and amphibole macroscopic crystals occurring in association with copper sulfide mineralization from the Musina copper deposits. Pencil shown for scale is ~18 cm long. (a) Samples from Artonvilla Mine showing breccias that are composed of mostly amphibole, potassium feldspar, and angular quartz. (b) Campbell Mine sample showing very coarse-grained and sometimes rounded angular quartz, amphibole, and potassium feldspar clasts. (c) Brecciated sample from Campbell Mine of mostly pyrite hosted in quartz veins. (d) Brecciated sample showing rounded and angular quartz, chalcopyrite, pyrite, and amphibole. Width of photograph is ~25 cm. Specimen from Campbell Mine area. Fig. 6. Photomicrographs for samples from Artonvilla Mine. Scale bar shown in (a) is applicable to all photomicrographs. (a) and (b): The two fields of view are occupied by hydrothermally altered clasts (altered to micas) and amphibole crystals, plane plolarized light (PPL) for both images, sample AtBr02. In (b) angular points are consistent with a breccia texture. (c): photomicrograph showing angular points at the contact of amphibole and mica clasts which is consistent with broken rock, sample ATBr02, PPL. (d) shows rounded (milled) mica clasts in amphibole which are consistent with rotated, intrusive breccias, sample ATBr02, PPL. (e): Field of view dominated by disseminated sulfides (Sulf), calcite (Cal), and potassium feldspar (Kfs) in PPL (e) and crossed polars (XPL) (f), sample AtCal01. Upper left view shows bifurcating sulfides and muscovite. (g) View dominated by altered plagioclase (Pl) and altered alkali feldspar (Kfs) in granitic gneiss, XPL, sample ATGN04. (h): Granitic gneiss showing sillimanite (Sil) together with biotite (Bt) which occupies smaller portions to the right (h) of center and altered Pl and

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ACCEPTED MANUSCRIPT 45 Kfs occupying most of the field of view in the photomicrograph, sample AtGn03. The feldspars in (h) are less altered compared to those in previous photomicrographs (a)-(g).

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Fig. 7. Photomicrographs for samples from Campbell Mine. Scale bar shown in (a) is same for all photomicrographs. (a): Sulfides (Sulf), sericite (Ser), and potassium feldspar (Kfs) in quartz vein in crossed polars (XPL), sample CpQV01. (b) shows an orthoclase (Or) crystal displaying typical Carlsbad twinning together with other alkali feldspar crystals (Kfs), XPL. (c) shows hydrothermally altered Kfs crystals with sulfides associated with the veinlets together with altered Kfs being replaced by sericite (Ser), sample CpQv01, XPL. (d): view dominated by Ser with remnant Kfs at center of photomicrograph, view of a breccia dominated by Ser and Kfs in XPL, sample CpQv01. (e) Highly altered amphibolite showing field of view dominated by amphibole and minor feldspar (Fsp), XPL, sample CpAM04. (f): muscovite (Ms) and chlorite (Chl) at center of photomicrograph in breccia, together with Kfs in XPL, sample CpQv02.

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Fig. 8. Backscattered electron images (BEI) from Artonvilla and Campbell Mines. (a) and (b) are BSE images showing coarse-grained disseminated pyrite occurring together with Ser, Ms, and Kfs and from Artonvilla Mine, sample AtCal01. Upper left view of (a) shows bifurcating sulfides and muscovite. (c): BEI showing very fine-grained chalcopyrite (Ccp) crystals completely enclosed in an amphibole crystal, sample CpQv02. (d): BSE image showing fine-grained chalcopyrite crystals completely enclosed in feldspar crystals (Kfs), sample CpAm04. (e): BSE image showing fine-grained chalcopyrite crystals occurring in association with amphibole (amp) and plagioclase feldspar crystals (Pl), sample CpAm04. Note one chalcopyrite crystal in center right “enclosing” a very fine-grained Pl crystal. (f): BSE image showing fine-grained chalcopyrite crystals completely enclosed in plagioclase (Pl) crystals, sample CpAm04.

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Fig. 9. Plots of pyrite and chalcopyrite compositions from Artonvilla and Campbell Mines. Plot of wt. % Fe versus wt. % S (a), wt. % Ni versus wt. % Fe (b), and wt. % Co versus wt. % Fe (c) from Artonvilla Mine. Plot of wt. % Fe versus wt. % S (d), wt. % Cu versus wt. % S (e), and wt. % Fe versus wt. % Cu (f) from Campbell Mine. Fig. 10. (a) Frequency plot of pyrite or chalcopyrite δ34S values for samples from both Artonvilla and Campbell Mines. (b) Frequency plot of pyrite or chalcopyrite δ34S values for samples from both the Artonvilla and Campbell Mines.

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Fig, 11. Plots of pyrite and chalcopyrite compositions from Artonvilla and Campbell Mines compared to compositions from Southwest Indian Ridge (Miller and Cervantes, 2002), Southwest Oregon ophiolite (Foose, 1986), the Duluth Complex (Pasteris, 1984), and the Keivitsansarvi Ni-Cu-PGE deposit, Finland (Gervilla and Kojonen, 2002). Plot of wt. % Ni versus wt. % Fe (a), wt. % Co versus wt. % Fe (b), and wt. % Fe versus wt. % Cu (c) from Artonvilla Mine. Plot of wt. % Cu versus wt. % Pb (d) from Campbell Mine. Fig. 12. (a) Pyrite compositions, in wt. %, from Artonvilla Mine plotted on S-Fe-Ni ternary diagram. The labeled dashed fields and the shaded field are high-temperature monosulfide solid solution (mss) fields of Kullerud et al. (1969), Py – pyrite. (b)

ACCEPTED MANUSCRIPT 46 Simplified phase relations for Campbell Mine chalcopyrite samples in the S-Fe-Cu system at 300oC (Barton and Skinner, 1979). Abbreviations for phases are bn – bornite, iss – intermediate solid solution, py – pyrite, po – pyrrhotite, cc – chalcocite, ccp – chalcopyrite, and cv – covellite, The composition of an ideal ccp is also shown.

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Fig. 13. (a) Frequency plot of δ34S values for samples from both the Artonvilla and Campbell Mines together with results from Sawkins and Rye (1979) for pyrite, chalcopyrite, bornite and chalcocite. Mantos Blancos breccia pyrite δ34S data from Ramírez et al. (2006) and Ilkwang breccia pipe, South Korea, data from So and Shelton (1983) and Yang and Bodnar (2004). (b) δ34S mixing diagram for the Artonvilla and Campbell Mines using δ34S value of 0 ‰ and a S concentration of 800 ppm; a fresh biotite-garnet-cordierite gneisses contaminant with a S concentration of 10,000 ppm (Jacobsen and McCarthy, 1976) and a δ34S value of 8.2 ‰ (Table 4).

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Table 1. Description of samples from Campbell and Artonvilla Mines for sulfur isotopes

Mafic

Medium

Mafic

Low

Coarse grained

Medium to coarse grained, gneissic foliation Coarse grained, foliated

Atgn05

Quartz-feldsparthic gneiss

Low

Felsic to mafic felsic

CpQv01 CpQv02

Quartz vein Amphibolite with mineralization within quartz veins Amphibolite: minor quartz veins hosting sulfides

Medium Low

Felsic Mafic

Coarse grained Coarse grained

Low

Mafic

Medium to coarse grained

CpAm04

Mineral composition

RI PT

Low

Mafic

Texture/ structure Medium to coarse grained, veinlets of quartz/calcite Medium to coarse grained

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Atgn04

Color

Amphiboles, mafic minerals, calcite, quartz, disseminated sulfides within amphibole Amphiboles, quartz, minor micas, low content of sulfides

SC

Atgn03

Amphibole with elongated calcareous and quartz crystals forming veins Brecciated amphibole with angular and veined quartz grains Biotite garnet gneiss with disseminated sulfide mineralization Biotite gneiss with disseminated sulfides

Degree of alteration Low

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Campbell

Artonvilla

Atbr02

Rock type

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Sample ID Atcal01

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Deposit

1

Amount sulfide mineralization Medium

Low

Layers of mafic and felsic minerals, micas and spotted garnets

Medium

Alternating layers of mafic and felsic minerals, minor spots of garnets, sulfides disseminated No fully developed interlayers of quartz feldsparthic and minor mafic minerals Quartz , chalcopyrite, pyrite Quartz , amphibole, chalcopyrite, pyrite, bornite,

Low

Amphiboles, Chalcopyrite- pyrite, quartz, chalcopyrite partly oxidized

Very low

Medium-high Low

Low

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Table 2. Representative pyrite chemical analyses b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. 0.0053

Pb (wt.%)

b.d.l. b.d.l. b.d.l. b.d.l. 0.025 0.009 0.014 b.d.l. b.d.l. 0.01 b.d.l. 0.012 0.0044

0.056 0.068 0.149 0.155 0.158 0.064 0.148 0.189 b.d.l. 0.142 0.097 0.068 0.0273

Fe (wt.%)

1

Co (wt.%)

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Cu (wt.%)

46.037 46.073 45.332 45.005 46.058 45.93 46.255 46.104 44.72 45.194 44.549 45.434 0.0027

SC

b.d.l. b.d.l. b.d.l. 0.438 b.d.l. b.d.l. b.d.l. 0.008 0.005 0.074 0.062 0.07 0.0043

Zn (wt.%)

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53.784 53.086 52.815 53.193 53.268 52.697 53.176 53.285 51.436 53.934 55.959 52.238 0.003

Ni (wt.%)

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ATCA1-P76 ATCA1-P77 ATCA1-P78 ATCA1-P79 ATCA1-P81 ATCA1-P82 ATCA1-P83 ATCA1-P84 ATCA1-P85 ATGN04-P1 ATGN04-P2 ATGN04-P3 M.D.L.

S (wt.%)

EP

76 77 78 79 81 82 83 84 85 1 2 3

Comment

AC C

Point

0.078 0.071 0.088 0.228 0.094 0.1 0.086 0.072 0.074 0.113 0.215 0.145 0.0033

Mn (wt.%)

b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. 0.0032

Total

99.958 99.298 98.39 99.028 99.613 98.805 99.681 99.663 96.235 99.467 100.882 97.967

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CPQV01-P17 CPQV01-P18 M.D.L.

0.007 b.d.l. 0.006 b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. 0.006 b.d.l. b.d.l. b.d.l. 0.0043

SC

33.706 33.088 33.813 33.794 34.115 34.034 33.589 33.697 34.101 33.673 35.706 36.34 0.003

Zn Cu (wt.%) Pb (wt.%) Fe (wt.%) Co Mn Total (wt.%) (wt.%) (wt.%) b.d.l. 33.474 b.d.l. 29.432 0.057 b.d.l. 96.68 b.d.l. 33.591 0.214 29.051 0.074 b.d.l. 96.018 b.d.l. 33.405 0.038 29.489 0.053 b.d.l. 96.804 b.d.l. 33.722 0.1 29.742 0.069 b.d.l. 97.427 b.d.l. 33.452 b.d.l. 29.477 0.067 b.d.l. 97.128 b.d.l. 33.473 0.079 29.475 0.058 b.d.l. 97.126 b.d.l. 33.501 0.147 29.488 0.046 b.d.l. 96.771 b.d.l. 33.702 0.108 29.63 0.074 b.d.l. 97.23 b.d.l. 33.626 0.048 29.584 0.055 b.d.l. 97.42 b.d.l. 33.438 0.03 29.336 0.059 b.d.l. 96.557 b.d.l. 33.798 b.d.l. 29.117 0.053 b.d.l. 98.718 b.d.l. 32.861 0.108 28.096 0.066 0.004 97.479 0.0053 0.0044 0.0273 0.0027 0.0033 0.0032

M AN U

CPAM04-P1 CPAM04-P2 CPAM04-P3 CPAM04-P4 CPAM04-P5 CPAM04-P13 CPAM04-P14 CPAM04-P15 CPAM04-P16 CPAM04-P17

Ni (wt.%)

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S (wt.%)

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Table 3. Representative chalcopyrite chemical analyses

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Table 4. δ34S(CDT) data for Artonvilla Mine and Campbell Mine samples Mine Sample Phase δ34S (‰, VCDT) Artonvilla AtCal01py pyrite 3.1 Artonvilla AtCal01py2 pyrite 3.6 Artonvilla AtCal01Ccp chalcopyrite 3.9 Artonvilla AtGn04 wr whole-rock 8.2 Campbell CpQv01py pyrite 0.5 Campbell CpQv01Ccp2 chalcopyrite 0.7 Campbell CpQv01Ccp chalcopyrite 0.4 Campbell CpQv02Ccp chalcopyrite -0.3 Campbell CpAm04Ccp chalcopyrite 0.3 Campbell CpAm04Ccp2 chalcopyrite -1.1 Campbell CpQv01bn bornite 0.4

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