Samples utilized in this study are a subset of samples used for petrographic (standard light microscopy and cathodoluminescence) study of calcite veins (Morgan and Milliken, this volume). Trace-element analysis was performed on the same thin sections used for petrographic study. Backscattered electron imaging was routinely employed for sample navigation in the electron microprobe. Powders for isotopic analyses were obtained from rock slabs taken adjacent to the thin-section blanks. Powders were excavated with a micro-drill bit (approximately 0.5 mm diameter) from specific calcite types identified on the basis of their petrographic characteristics. This method allows only a relatively crude discrimination of the myriad complex zones within the calcites. All isotopic values necessarily represent mixtures of calcite types, construed to be dominated by some specific type that was the target of microdrilling.
Wavelength-dispersive analysis of trace elements was performed on a JEOL 733 electron microprobe at the University of Texas at Austin. Cathodoluminescence and plane-polarized light images of vein calcites (Morgan and Milliken, this volume) were used as a guide to beam placement. Analysis was performed with a 15-kV accelerating voltage, a sample current of 12 nA (measured on brass), and a 10-μm spot. Calibrations were performed using standard carbonate materials: dolomite (for Ca, Mg), siderite (for Fe, Mn), and coral (for Sr) that are part of the standard collection in the University of Texas Electron Microprobe Laboratory. Analysis times employed were 60 s for Sr and 20 s for all other elements. Totals between 97 and 103 were accepted. Detection limits were approximately 340 ppm for Mg, 450 ppm for Fe, 310 ppm for Mn, and 185 ppm for Sr.
Powders obtained by microdrilling were reacted under vacuum with 100% phosphoric acid at 25°C (method of McCrea, 1950) and analyzed on a VG Prism gas-source mass spectrometer (University of Texas at Austin).
Powders obtained by microdrilling were analyzed on a FinniganMat 261 thermal ionization mass spectrometer. For comparison to values for seawater Sr on the Burke curve (Burke et al., 1982; Koepnick et al., 1985) it is necessary to subtract 0.0001 from the values reported here (L.M. Mack, pers. comm., 1994).