Isr. J. Earth Sci.; 48: 195–208 © 1999 Laser Pages Publishing Ltd. 0021-2164/99 $4.00 *Author to whom correspondence should be addressed. E-mail: matthews@mail.gsi.gov.il Sedimentary and epigenetic copper mineral assemblages in the Cambrian Timna Formation, southern Israel Naama Shlomovitch, a Miryam Bar-Matthews, a, * Amit Segev, a and Alan Matthews b a Geological Survey of Israel, 30 Malkhe Yisrael Street, Jerusalem 95501, Israel b Institute of Earth Science, The Hebrew University of Jerusalem, Jerusalem 91904, Israel (Received 13 December 1999; accepted 20 December 1999) ABSTRACT Shlomovitch, N., Bar-Matthews, M., Segev, A., Matthews, A. 1999. Sedimentary and epigenetic copper mineral assemblages in the Cambrian Timna Formation, southern Israel. Isr. J. Earth Sci. 48: 195–208. Copper mineralization in the Timna Formation occurs in the dolomitic, sandy, and shaly lithofacies of the Upper Sasgon Member. Scanning electron microscope, chemi- cal, and isotopic studies of the copper mineral parageneses indicate an evolution from diagenetic, neutral reducing conditions through stages of epigenetic alteration at oxidizing and progressively more acid conditions. Primary copper sulfide minerals are djurleite (Cu 1.93 S) and covellite (CuS) with minor chalcocite (Cu 2–1.93 S), digenite (Cu 1.8 S), and anilite (Cu 1.75 S) randomly dispersed in the dolomitic lithofacies. δ 34 S values of –14‰ are consistent with their formation by reduction of marine sulfate. Subsequent evolution of the ores involves their replacement by malachite (Cu 2 (OH) 2 CO 3 ), which armors and replaces the sulfide minerals, followed by the develop- ment of paratacamite (Cu 2 (OH) 3 Cl) as veins emanating from the altered sulfides. The malachite alteration stage represents a change to oxidizing conditions; paratacamite develops with a decrease in pH and in the presence of chloride ion, which allows the development of stable aqueous copper chloride complexes. The first copper mineral to form in the sandy and shaly lithofacies is chrysocolla (Cu 2–X SiO 5 (OH) 3 ·yH 2 O), which forms by the dissolution of precursor silicate minerals (quartz, clays, feldspars). The chrysocolla subsequently evolves into plancheite (Cu 8 (Si 4 O 11 ) 2 (OH) 4 ·yH 2 O), pseudomalachite (Cu 5 (OH) 4 PO 4 ), and dioptase (CuSiO 3 ·H 2 O). Thermodynamic calcu- lation indicates that copper silicate formation was brought about by a decrease in pH and/or increase in aCu and is thus consistent with the evidence for epigenesis in the dolomitic lithofacies. INTRODUCTION Copper mineralization occurs in the Early/Middle Cambrian (~525 Ma) Timna Formation, Timna Val- ley, southern Israel, ~25 km north of Elat (Fig. 1). Due to the economic potential of the copper mineralization, the Timna Formation was the subject of a significant amount of research from the 1960s (e.g., Bentor, 1952; McLoad, 1959; Bartura, 1966; Milton, 1966; Bartura and Würzburger 1974; Ayalon et al., 1983, 1985; Bar- Matthews, 1986, 1987; Segev, 1986; Segev and Sass, 1989a,b; Bar-Matthews and Matthews, 1990; Segev, 1992; Shlomovitch, 1995). The copper was mined dur- ing this period and until the 1980s. The Timna Formation is exposed in several locali-