Jörg Ostendorf, Friedhelm Henjes-Kunst, Nicola Mondillo, Maria Boni, Jens Schneider, and Jens Gutzmer

Transcription

1 GSA Data Repository Supplemental Information for: Formation of Mississippi Valley type deposits linked to hydrocarbon generation in extensional tectonic settings: Evidence from the Jabali Zn-Pb-(Ag) deposit (Yemen) Jörg Ostendorf, Friedhelm Henjes-Kunst, Nicola Mondillo, Maria Boni, Jens Schneider, and Jens Gutzmer Analytical Techniques Mineralized parts of drill core J 125 (western part of the Jabili deposit; cf. Mondillo et al., 2011) were extracted, crushed and sieved ( µm). Sample fractions of host dolostone were hand-picked under a binocular microscope. Ore minerals sphalerite and galena were preconcentrated by heavy-liquid separation using diiodmethane and subsequently purified by careful hand-picking. For Rb-Sr geochronology, sphalerite separates (cleaned overnight in 3 N CH 3 COOH) were crushed using a boron carbide (BC) mortar and pestle and ~1.5 ml of deionized water was added after crushing in order to sample the liberated fluid inclusions. Care was taken to grind the aliquots thoroughly in order to avoid or at least minimize the problem of contributions from unopened fluid inclusions (Pettke and Diamond, 1996). The leachate was recovered from the residual sphalerite by repeated centrifuging. Only the first supernate was kept as the fluid inclusion leachate sample and a known weight of a mixed tracer containing highly enriched 87 Rb and 84 Sr was added to the leachate after its separation from the sphalerite residue. The residual sphalerite was once more alternatingly leached and sonified in 2 N HCl and 2 N HF to remove possible interstitial carbonate and silicate inclusions, with a water wash in between. Prior to digestion in 6N HCl, a mixed 87 Rb- 84 Sr spike was added. Sr and Rb separation was carried out with Teflon micro-columns (50 l) and Eichrom Sr resin, following the methods of Deniel and Pin (2001). For a number of sphalerite samples, Pb for isotopic analysis was subsequently stripped from the Sr columns with 6N HCl (Deniel and Pin, 2001). The Rb cuts from the sphalerite residues were further purified using standard cation-exchange procedures (Birck, 1986). Additional lead for isotopic measurement was obtained dissolving single galena grains of ~ µg using one drop of HBr 8N and subsequent dilution in 13.7N HNO 3 and deionized H 2 O, without further purification. For mass spectrometry, Sr was loaded with a TaF 5 activator onto W single filaments. Rb was run with Re double filaments. For Pb isotopic measurements, loads of approximately 75 ng Pb were loaded with silica gel onto Re single filaments. Isotope analyses were carried out at the Federal Institute for Geosciences and Natural Resources (Hannover) and performed in static multicollection mode using a Finnigan MAT261 thermal ionization mass

2 spectrometer for Rb and Sr, and a ThermoFinnigan TRITON TIMS for Pb. Reproducibility of Sr standard NBS SRM 987 was 87 Sr/ 86 Sr = ± (2 ; n = 19). Sr isotope ratios were corrected for mass fractionation to 88 Sr/ 86 Sr = and are normalized to for the NBS SRM 987 standard. All Rb and Sr values were blank corrected (mean blanks 12 and 32 pg for Rb and Sr, respectively; 87 Sr/ 86 Sr blank = ). Reported 2 m errors on the Sr isotope ratios include the run statistics, an uncertainty of 50 % for the blank correction and the 2 deviation of the NBS SRM 987 standard runs. The 2 m errors on 87 Rb/ 86 Sr ratios include the run statistics, blank uncertainties and an uncertainty for instrumental mass bias (runs of natural Rb gave ± ; n = 16). Furthermore, an averaged uncertainty of 0.42% is added which was derived by repeated measurements of spiked standard solutions (n = 5). For Rb and Sr concentrations, individual errors (2 m ) are reported and include the blank uncertainties, an assumed weighing error of 1%, measurement statistics and an uncertainty of 0.73% and 0.96% for the Sr and Rb spike concentrations, respectively. Rb concentrations include the uncertainty for instrumental mass bias. Rb-Sr isotope ratios and elemental concentrations of the 8 sphalerite residues ( 87 Rb/ 86 Sr: ; 87 Sr/ 86 Sr: ; Sr: ppb; Rb: ppb) have broadly similar dimensions like previously published data (e.g., Brannon et al., 1992; Christensen, 1995a, 1995b; Nakai et al., 1990, 1993). Pb isotope analyzes were corrected for instrumental mass fractionation with a factor of 0.11% per atomic mass unit; reproducibility of NBS SRM 981 (n = 6) is 206 Pb/ 204 Pb = ± 0.006, 207 Pb/ 204 Pb = ± and 208 Pb/ 204 Pb = ± The sulfur isotope composition of fifteen sphalerite and galena samples was analyzed with a ThermoQuest-Finnigan DELTA PLUS mass spectrometer using standard techniques by a commercial laboratory (Erz & Stein, Freiberg). Rb-Sr model isochron regressions were calculated after Ludwig (2012) using the ISOPLOT/Ex version 4.15 program. For iterative planar paleomixing line regressions according to Schneider et al. (2003), an internal FORTRAN subroutine «MIXING LINE 3 D» was used. The decay constant used for the age calculations was 87 Rb = 1.42 x a -1 (Steiger and Jäger, 1977) and errors on Rb-Sr model ages are quoted at the 2 level. The goodness of fit of linear and planar regressions has been tested by means of the MSWD parameter (Wendt and Carl, 1991). Analytical Results

3 Table DR1. Rb-Sr isotope data of crushed sphalerite residues (R), corresponding fluid inclusion leachates (L) and dolostone samples (d) from Jabali deposit. Quoted errors for Rb- Sr isotope ratios and elemental concentrations are in the last digits listed. Rb and Sr concentrations of fluid inclusion leachates (L) are not reported since the total amount of trapped fluid in the sphalerite samples is not known. sample Rb (ppb) (± 2 m ) Sr (ppb) (± 2 m ) 87 Rb/ 86 Sr (± 2 m ) 87 Sr/ 86 Sr (± 2 m ) sphalerite J125 4A Sp A R L J125 4A Sp B R L J125 5A Sp A R L J125 5A Sp B R J125 7A Sp A R L J125 7A Sp B R J125 7A Sp C R J125 7B-2f Sp A R sample Rb Sr (ppm) 87 Rb/ 86 Sr Sr/ 86 Sr (± 2σ m ) (± 2σ m ) host dolostone J125 1A d n.d n.d J125 2A d n.d n.d J125 4A d n.d n.d J125 5A d n.d n.d J125 6A d n.d n.d

4 Table DR2. Pb isotope ratios obtained on sphalerite and galena from Jabali sample 206 Pb/ 204 Pb 207 Pb/ 204 Pb 208 Pb/ 204 Pb sphalerite J125 1A Sp A J125 2A Sp A J125 4A Sp A J125 4A Sp B J125 5A Sp A J125 6A Sp A galena JS-Mar-2 Gal JS Mar 2C JS_Mon-33 Gal J138-6 Gal J138-10A Gal J125-2A Gal J125-4A Gal J125-6A Gal

5 Table DR3. Sulfur isotope analyzes of sphalerite and galena from Jabali sample 34 S [±0.3; 1σ] sphalerite J125 1A Sp 0.9 J125 2A Sp 9.0 J125 4A Sp 22.0 J125 5A Sp 9.6 J125 6A Sp 9.2 J125 7A Sp 10.4 galena J125-2A Gal 9.8 J125-4A Gal 1.5 J125-5A Gal 2.2 J125-6A Gal 0.7 J125-7A Gal 6.0 J138_6 Gal 5.0 J138_10A Gal 1.5 JS_MAR2 Gal 2.5 JS_MON 33 Gal 7.4

6 oxidized ore Sp dolostone 5000 µm Figure DR1. Transmitted light (plane polarized) photomicrograph showing sphalerite (Sp) in dolostone from Jabali. Partly oxidized ore occurs at the upper right corner.

7 Figure DR2. Representative BSE images of separated sphalerite grains. The majority of sphalerite grains (> 95%) used for Rb-Sr isotopic analyses contained no (A, B) or negligible mineral inclusions (C). Larger mineral inclusions (accounting for > 5 Vol. % of the hosting sphalerite grain) were only observed in few grains of sample J125 4A Sp A (D).

8 References Cited Birck, J.-L., 1986, Precision K-Rb-Sr isotopic analysis: Application to Rb-Sr chronology: Chemical Geology, v. 56, no. 1-2, p , doi: / (86) Brannon, J.C., Podosek, F.A., and McLimans, R.K., 1992, Alleghenian age of the Upper Mississippi Valley zinc-lead deposit determined by Rb-Sr dating of sphalerite: Nature, v. 356, p , doi: /356509a0. Christensen, J.N., Halliday, A.N., Vearncombe, J.R., and Kesler, S.E., 1995a, Testing models of largescale crustal fluid flow using direct dating of sulfides: Rb-Sr evidence for early dewatering and formation of Mississippi Valley-type deposits, Canning Basin, Australia: Economic Geology and the Bulletin of the Society of Economic Geologists, v. 90, p , doi: /gsecongeo Christensen, J.N., Halliday, A.N., Leigh, K.E., Randell, R.N., and Kesler, S.E., 1995b, Direct dating of sulfides by Rb-Sr: A critical test using the Polaris Mississippi Valley-type Zn-Pb deposit: Geochimica et Cosmochimica Acta, v. 59, p , doi: / (95) Deniel, C., and Pin, C., 2001, Single-stage method for the simultaneous isolation of lead and strontium from silicate samples for isotopic measurements: Analytica Chimica Acta, v. 426, no. 1, p , doi: /s (00) Ludwig, K. R., 2012, User's Manual for Isoplot 3.75: A geochronological toolkit for Microsoft Excel. Berkeley Geochronology Center Spec. Pub. 5, 75p. Mondillo, N., Boni, M., Balassone, G., and Grist, B., 2011, In search of the lost zinc: A lesson from the Jabali (Yemen) nonsulfide zinc deposit: Journal of Geochemical Exploration, v. 108, no. 3, p , doi: /j.gexplo Nakai, S.i., Halliday, A.N., Kesler, S.E., and Jones, H.D., 1990, Rb-Sr dating of sphalerites from Tennessee and the genesis of Mississippi Valley type ore deposits: Nature, v. 346, p , doi: /346354a0. Nakai, S.i., Halliday, A.N., Kesler, S.E., Jones, H.D., Kyle, J.R., and Lane, T.E., 1993, Rb-Sr dating of sphalerites from Mississippi Valley-type (MVT) ore deposits: Geochimica et Cosmochimica Acta, v. 57, p , doi: / (93) Pettke, T., and Diamond, L. W., 1996, Rb-Sr dating of sphalerite based on fluid inclusion-host mineral isochrons; a clarification of why it works: Economic Geology, v. 91, no. 5, p , doi: /gsecongeo Schneider, J., Haack, U., and Stedingk, K., 2003, Rb-Sr dating of epithermal vein mineralization stages in the eastern Harz Mountains (Germany) by paleomixing lines: Geochimica et Cosmochimica Acta, v. 67, no. 10, p Steiger, R. H, and Jäger, E., 1977, Subcommission on geochronology: Convention on the use of decay constants in geo- and cosmochronology. Earth and Planetary Science Letters, v. 36, no. 3, p , doi: / x(77) Wendt I., and Carl, C., 1991, The statistical distribution of the mean squared weighted deviation: Chemical Geology, v. 86, no. 3, p , doi: / (91)90010-t.