0361-0128/07/3659/347-32 347 Introduction OVER THE PAST DECADE, the Archean Midlands greenstone belt of Zimbabwe has been subject to several research and ex- ploration programs due to its high gold potential. Extensive exploration in the central part of the Midlands greenstone belt, the Kwekwe district, has led to the discovery of new gold ore reserves (mainly bulk mineable ores), including open-pit operations near Indarama (Buchholz et al., 1998)—the Globe and Phoenix, Chaka’s Pride, and Dalling mines. However, not much research has been carried out on the genesis and met- allogeny of the gold deposits in the Kwekwe district. A special feature of the Kwekwe district is that the Archean gold deposits are anomalously rich in antimony. Similar Archean vein-type deposits have been described from the “Antimony Line” in the Murchison greenstone belt of South Africa (Pearton, 1982; Davies et al., 1986), the Blue Spec/Golden Spec and Wiluna districts in Australia (Gifford, 1990; Hagemann et al., 1992, Hagemann and Lüders, 2003), and the Signal Hill deposits in Botswana (Audet, 1995). This study investigates the gold-antimony association of the Kwekwe district, using modern microanalytical and geochem- ical techniques. Four representative gold-antimony deposits were selected for study: the Indarama, Jojo, Primrose and Globe, and Phoenix mines. The deposits were of exploration interest in the late 1990s, and their structural geology is well documented from previous studies. Although the deposits are located only a few kilometers apart, they show distinct differ- ences in deformation style and mineralization. Geologic surface and underground mapping was carried out from regional to hand-specimen scale. Sampling focused on the various reefs and mineralization stages wherever ac- cessible underground. Detailed petrography of the mineral- ization stages and host rocks was carried out on 241 samples in support of the microanalytical and geochemical studies, and each selected sample was used for a range of analytical techniques. Previously published data (e.g., detailed fluid in- clusion studies at Indarama from Buchholz et al., 1994, and at Globe and Phoenix from Porter, 1993) are integrated with new data from this study. At Indarama and Globe and Phoenix, the same sample sites used by Buchholz et al. (1994) and Porter (1993) were also selected for this study for better comparison of the data. Multistage Au-As-Sb Mineralization and Crustal-Scale Fluid Evolution in the Kwekwe District, Midlands Greenstone Belt, Zimbabwe: A Combined Geochemical, Mineralogical, Stable Isotope, and Fluid Inclusion Study PETER BUCHHOLZ, † THOMAS OBERTHÜR, Bundesanstalt für Geowissenschaften und Rohstoffe (BGR), Stilleweg 2, D-30655 Hannover, Germany VOLKER LÜDERS, GeoForschungsZentrum Potsdam, Telegrafenberg, D-14473 Potsdam, Germany AND JAMIE WILKINSON Department of Earth Science and Engineering, Royal School of Mines, Imperial College London, Exhibition Road, London SW7 2AZ, United Kingdom Abstract The Kwekwe district comprises the central part of the Archean Midlands greenstone belt of Zimbabwe and represents one of few Archean gold provinces in the world hosting gold deposits associated with massive anti- mony mineralization. The deposits typically occur along late Archean transcrustal deformation zones. Mineral- ization is characterized by an early Au-As stage 1, followed by a pronounced Au-Sb stage 2, and a low-grade Sb-bearing stage 3. Four gold deposits within the Kwekwe district have been studied. The Primrose and Globe and Phoenix gold deposits display typical features of Archean orogenic lode gold systems such as fluid inclusions with low salin- ity, mixed aqueous-carbonic fluids, formation temperatures between 300° and 400°C, and a common stable iso- tope composition of fluid and mineral precipitates. Deposits of this type formed in the brittle-ductile crustal transition zone at 1.5 to 3.0 kbars. In contrast, gold mineralization at Jojo and especially the Indarama gold de- posits probably formed at lower temperatures (<<300°C) and from dominantly aqueous, early moderate- to late high-salinity fluids. At Indarama, microthermometric studies indicate stibnite-gold mineralization at tem- peratures between 120° and 230°C at about 0.8 to 1.8 kbars. Low formation temperatures and extremely low δ 34 S values of pyrite (–52‰) and stibnite (–36‰) of the latest mineralization stage at Indarama reveal reacti- vation of the hydrothermal system within a near subsurface, organic-rich epithermal or hot spring-type envi- ronment during the late Archean or even early Proterozoic. Such low δ 34 S values have not been reported pre- viously from gold deposits in Archean greenstone belts. We propose that hydrothermal activity and gold mineralization has not only taken place at different crustal levels but also at different times. † Corresponding author: e-mail, peter.buchholz@bgr.de 1 We would like to dedicate this paper in memorandum to our colleague Tim Nutt, who performed fundamental work in the Kwekwe district. ©2007 Society of Economic Geologists, Inc. Economic Geology, v. 102, pp. 347–378