Recent work has highlighted the need to distinguish the contribution(s) of different populations of petrographically and isotopically distinct pyrites to interpret bulk δS sedimentary values. To address this, we developed a method for micron-scale isotopic characterization of petrographically diverse sedimentary pyrites within a multimineralic matrix using ion imaging with a 7f-GEO secondary ion mass spectrometer (SIMS), aiming to rapidly and precisely analyze the isotopic composition of pyrites over relatively wide fields of view. By using primary beam currents in the range 1–11 pA and raster widths of 15–80 μm, precise data can reproducibly be acquired over a relatively large field of view, with negligible penetration into underlying mineral phases. Instrumental artifacts are a factor in cases where phosphate or halide minerals are intergrown with pyrite or where surface topographic variation is significant. However, a 1 pA beam method with smaller rasters can eliminate these artifacts if those situations cannot be avoided. The precision (1σ) on individual regions of interest (ROI) is <1‰ at all beam currents tested, provided the total accumulated number of measured S counts exceeds one million. Isotopic gradients within grains can be resolved across areas as small as 20 μm (5 μm diameter) and features as small as 1.5 μm (∼1.4 μm diameter) can be resolved with a precision of 1.5‰ (1σ). The achievable sub-micron spatial resolution with a 1pA primary current allowed for data to be extracted from specifically desired regions within pyrite (e.g., distinguishing primary/early diagenetic pyrite from late-stage components), with minimal contamination from neighboring minerals.

中文翻译：

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使用 7f-GEO SIMS 评估黄铁矿 δ34S 中的晶内梯度


最近的工作强调需要区分不同岩相和同位素不同黄铁矿群体的贡献，以解释大量 δS 沉积值。为了解决这个问题，我们开发了一种使用 7f-GEO 二次离子质谱仪 (SIMS) 进行离子成像对多矿物基质内岩相多样化沉积黄铁矿进行微米级同位素表征的方法，旨在快速、精确地分析黄铁矿的同位素组成视野相对较宽。通过使用 1-11 pA 范围内的主束电流和 15-80 μm 光栅宽度，可以在相对较大的视场内重复获取精确数据，而对底层矿物相的渗透可以忽略不计。在磷酸盐或卤化物矿物与黄铁矿共生或表面地形变化显着的情况下，仪器伪影是一个因素。然而，如果这些情况无法避免，则具有较小光栅的 1 pA 光束方法可以消除这些伪影。如果测量的 S 计数的累计总数超过 100 万，则在所有测试的束流中，各个感兴趣区域 (ROI) 的精度 (1σ) 为 <1‰。晶粒内的同位素梯度可以在小至 20 μm（5 μm 直径）的区域内进行解析，小至 1.5 μm（∼1.4 μm 直径）的特征可以以 1.5‰ (1σ) 的精度进行解析。使用 1pA 一次电流可实现的亚微米空间分辨率允许从黄铁矿内特定所需区域提取数据（例如，区分原生/早期成岩黄铁矿与后期成分），同时将邻近矿物的污染降至最低。