SAMPLES AND METHODS

Chemical and isotopic analyses were undertaken at the Commonwealth Scientific and Industrial Research Organisation (CSIRO) (Australia) on two of these core pieces; Sample 193-1189A-12R-1 (Piece 16, 120–122 cm; CSIRO reference number 142701), representing a possible example of subhalative mineralization within a former pumiceous volcaniclastic horizon in Hole 1189A (Shipboard Scientific Party, 2002), and Sample 193-1189B-1R-1 (Piece 1, 0–4 cm; CSIRO 142703) collected from immediately below the cased interval of Hole 1189B and potentially derived from the sulfide mound presumed to underlie the Roman Ruins chimney field (Shipboard Scientific Party, 2002).

In addition, a thick semimassive pyrite vein broken from altered wallrock in Sample 193-1189B-3R-1 (Piece 4, 34–37 cm; CSIRO 142705) was chemically analyzed, whereas Pb isotope analyses were conducted on a similar vein in breccia Sample 193-1189B-5R-1 (Piece 2, 12–22 cm; CSIRO 142706). Although somewhat richer in quartz, these two subsamples were visually comparable with Sample 193-1189B-6R-1 (Piece 6, 56–67 cm) cataloged on board as massive sulfide but not sampled by the author. Like the latter, considered on this basis to be derived from an unusually thick vein rather than a horizon of massive sulfide, they represent the dominant vein style within the stockwork zone intersected in the upper part of Hole 1189B (Shipboard Scientific Party, 2002). Chemical analyses were also performed on two related samples, a 2-cm lump of massive pyrite (closely resembling Sample 193-1189B-6R-1 [Piece 6, 56–67 cm] and likely derived from the stockwork zone) caught on the bowspring of the logging tool during a geophysical survey of the uncased section of Hole 1189B (CSIRO 142808) and a sample of sand packed on the hammer drill during placement of casing at commencement of the same hole (CSIRO 142807). Details of all six samples are provided in Table T1.

For chemical analysis, representative portions (avoiding conspicuous host rock fragments or layers) were broken or sawn from the samples and the sawn surfaces were cleaned with sandpaper. After ultrasonic cleaning, washing in deionized water to remove sea salt, and drying, these were finely ground under acetone in a mechanical agate mortar and pestle. Analyses were performed by inductively coupled plasma–atomic emission spectrometry (ICP-AES) and mass spectrometry (ICP-MS) and also by instrumental neutron activation (INAA) using the CSIRO methods outlined in Miller et al. (this volume). The complete analytical data set is provided in Table T2, whereas preferred compositions taking into account precision and sensitivity of the various methods are provided in Table T3.

Lead isotope ratios (Table T4) were analyzed on separately agate-ground fragments by thermal ionization mass spectrometry on a VG54E single-collector mass spectrometer at CSIRO. Precision, based upon two relative standard deviations in 1192 analyses of the standard reference material 981, is estimated as Pb^206/204 = 0.16%, Pb^207/204 = 0.21%, and Pb^208/204 = 0.28%. Sulfur isotope ratios (Table T4) were determined for individual pyrite grains in polished slices by laser ablation mass spectrometry at the Central Science Laboratory, University of Tasmania, following the methods of Huston et al. (1995). Estimated precision of ³⁴S relative to Canyon Diablo troilite is 0.4–0.5.