Narrow Results

Trace elements in thick samples of aluminum metal reference standards were analyzed by means of PIXE and ICP-AES. The samples were SRM1258 and SRM1259 from National Institute of Standards and Technology (U.S.A.) and 1-A, 3, 4-A and 83 from Japan light metal association. The observed PIXE spectrum was converted “into that of a hypothetical thin target and it was analyzed using a relative intensity database for thin target. A good agreement was obtained between the certified and the found amount of the trace elements. The analytical results for SRM1258 and SRM1259 obtained by ICP-AES method also agreed well with the present results confirming the analytical accuracy.

We have examined tin-polymetallic ore, a complex mixture of cassiterite (SnO₂) and sulfides, by micro-PIXE. Tin-polymetallic ore is one of the major sources of technologically important “rare metals”, especially of indium and bismuth, usually as trace elements. In addition to such rare metals, silver is another important trace component in the ore. But the trace elemental distribution of tin-polymetallic deposit has not well been described due to the small size of constituent minerals, complex ore texture, and lack of analytical method to detect trace elements in a small area. PIXE with a proton microbeam could be an effective tool to solve this problem by delineating the distribution of these trace elements among carrier minerals with the required sensitivity. Thus we have applied PIXE with the CSIRO’s proton microprobe to a tin-polymetallic ore from Canada. The result showed that micro-PIXE is an essential tool to study trace element distribution in such a complex ore.

Praseodymium is one of the most important pigment materials for high-quality china and ceramics but its source minerals are not well known to geologists. Allanite, one of the REE-bearing minerals in nature, has a large coordination polyhedra for cations and favors the larger LREE ions such as praseodymium than other REE-bearing minerals that favor the smaller HREE. We have tested some allanite crystals by CSIRO’s micro-PIXE to examine its possibility as a praseodymium source. Our result showed that allanite incorporates praseodymium at the order of 4000 to 5000 ppm and thus it is one of the good host of this element. We conclude that micro-PIXE is a viable quantitative tool for determining REE in allanite and other conventional REE sources in spite of the relatively poor minimum detection limit compared to that for other elements.

We have applied the micro-PIXE technique to determining the cadmium content in sphalerite (ZnS) and galena (PbS) for use in geothermometry in the Bulawan gold-silver telluride deposit, Philippines. This geothermometry is based on the temperature control on the cadmium distribution between sphalerite and galena. For the analyses by the micro-PIXE, a beam of 3MeV protons was used at CSIRO, Sydney. The size of the beam was between 10-30μm such that during analysis, points within sphalerite-galena pairs which are located very close to the rims of the grains were analyzed and also pairs which are located farther away from each other. The X-rays obtained were deconvoluted for peak areas and converted to concentration using the Geo-PIXE software. The results for rim and non-rim pairs are indistinguishable. The micro-PIXE was capable of analyzing Cd to the level of about 100ppm in galena and 150ppm in sphalerite. Six pairs of galena-sphalerite at the earliest stage of mineralization were examined and only three pairs could be used for our purpose. The obtained temperatures, 402 to 527°C are about 90 to 210°C higher than estimates for the later stage of mineralization in the deposit. Thus, using micro-PIXE we concluded that deposition of early sphalerite and galena in the Bulawan deposit probably occurred at around 500°C before waning down to around 300°C.