| Abstract: | Secondary ion mass spectrometry (SIMS) measurement of sulfur isotope ratios is a potentially powerful technique for in situ studies in many areas of Earth and planetary science. Tests were performed to evaluate the accuracy and precision of sulfur isotope analysis by SIMS in a set of seven well-characterized, isotopically homogeneous natural sulfide standards. The spot-to-spot and grain-to-grain precision for ??34S is ??0.3??? for chalcopyrite and pyrrhotite, and ??0.2??? for pyrite (2SD) using a 1.6nA primary beam that was focused to 10??m diameter with a Gaussian-beam density distribution. Likewise, multiple ??34S measurements within single grains of sphalerite are within ??0.3???. However, between individual sphalerite grains, ??34S varies by up to 3.4??? and the grain-to-grain precision is poor (??1.7???, n=20). Measured values of ??34S correspond with analysis pit microstructures, ranging from smooth surfaces for grains with high ??34S values, to pronounced ripples and terraces in analysis pits from grains featuring low ??34S values. Electron backscatter diffraction (EBSD) shows that individual sphalerite grains are single crystals, whereas crystal orientation varies from grain-to-grain. The 3.4??? variation in measured ??34S between individual grains of sphalerite is attributed to changes in instrumental bias caused by different crystal orientations with respect to the incident primary Cs+ beam. High ??34S values in sphalerite correlate to when the Cs+ beam is parallel to the set of directions <uuw>, from [111] to [110], which are preferred directions for channeling and focusing in diamond-centered cubic crystals. Crystal orientation effects on instrumental bias were further detected in galena. However, as a result of the perfect cleavage along {100} crushed chips of galena are typically cube-shaped and likely to be preferentially oriented, thus crystal orientation effects on instrumental bias may be obscured. Test were made to improve the analytical precision of ??34S in sphalerite, and the best results were achieved by either reducing the depth of the analysis pits using a K??hler illuminated primary beam, or by lowering the total impact energy from 20keV to 13keV. The resulting grain-to-grain precision in ??34S improves from ??1.7??? to better than 0.6??? (2SD) in both procedures. With careful use of appropriate analytical conditions, the accuracy of SIMS analysis for ??34S approaches ??0.3??? (2SD) for chalcopyrite, pyrite and pyrrhotite and ??0.6??? for sphalerite. Measurements of ??34S in sub-20??m grains of pyrite and sphalerite in ~3.5Ga cherts from the Pilbara craton, Western Australia show that this analytical technique is suitable for in situ sulfur isotope thermometry with ??50??C accuracy in appropriate samples, however, sulfides are not isotopically equilibrated in analyzed samples. ?? 2010 Elsevier B.V. |
| Genre: | Article |
| ProdID: | 70037382 |
| Citation Author: | Kozdon, R.; Kita, N. T.; Huberty, J. M.; Fournelle, J. H.; Johnson, C. A.; Valley, J. W. |
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| Citation End Page: | 253 |
| Citation Issue: | 3-4 |
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| Citation Language: | English |
| Citation Larger Work Title: | Chemical Geology |
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| Citation Number Of Pages: | 11 |
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| Citation Search Results Text: | In situ sulfur isotope analysis of sulfide minerals by SIMS: Precision and accuracy, with application to thermometry of ~3.5Ga Pilbara cherts; 2010; Article; Journal; Chemical Geology; Kozdon, R.; Kita, N. T.; Huberty, J. M.; Fournelle, J. H.; Johnson, C. A.; Valley, J. W. |
| Citation Start Page: | 243 |
| Citation Volume: | 275 |
| Citation Year: | 2010 |
| Type: | citation/reference |
| Text: | In situ sulfur isotope analysis of sulfide minerals by SIMS: Precision and accuracy, with application to thermometry of ~3.5Ga Pilbara cherts; 2010; Article; Journal; Chemical Geology; Kozdon, R.; Kita, N. T.; Huberty, J. M.; Fournelle, J. H.; Johnson, C. A.; Valley, J. W. |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/outside_thumb.jpg |
| URL (DIGITAL OBJECT IDENTIFIER): | http://dx.doi.org/10.1016/j.chemgeo.2010.05.015 |
| Date Other: | Fri, 1 Jan 2010 00:00 -0600 |
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