Potassium (K)-rich feldspars are one of two mineral types typically used for optical dating. Feldspar grains can contain up to ~14 wt% K that gives rise to an internal dose rate component. This internal component can comprise a significant proportion of the total environmental dose rate to which a mineral grain is exposed. The environmental dose rate term—the denominator in the optical age equation—determines the rate at which electronic charge is transferred into the crystal lattice of a mineral grain over its period of burial. Not all feldspar grains have the same K concentration, so internal dose rates differ between individual grains. K concentrations can range from 0 to 14 wt% due to the variable compositions of feldspar phases, differing proportions of discrete feldspar phases and/or the presence of other mineral inclusions in grains. Numerous techniques are available for determining the K concentrations of individual grains, but are time-consuming, and either lack the spatial resolution to classify discrete mineral phases within multi-phase grains, or the coverage to obtain whole-of-grain average K concentrations. Quantitative evaluation of minerals using energy dispersive spectroscopy (QEM-EDS) is a time-efficient and automated mapping technique that has the spatial resolution to classify most mineral phases, as well as the coverage to determine their area proportions. QEM-EDS can also be used to determine elemental concentrations based on spectral matches to EDS reference spectra. It is, however, difficult to determine accurate elemental concentrations for minerals such as feldspars, where solid solutions exist. To overcome this, we establish a QEM-EDS calibration using EDS spectra from six feldspar reference standards to define five solid solution regions along the alkali and plagioclase feldspar series. We test this calibration through comparisons of the K concentrations of discrete phases of three feldspar varieties (orthoclase/microcline, albite and sanidine), derived using both QEM-EDS and wavelength dispersive spectroscopy (WDS). We assume that the WDS-derived K concentrations represent the ‘true’ K concentrations of the phases, and calculate, from a best-fit weighted regression of the two data sets, a correction and uncertainty estimate that can be applied to the QEM-EDS-derived K concentrations, taking into account instrument irreproducibility and any measurement bias. We also test alternative mapping step sizes to optimise efficiency, and apply this time-efficient technique to individual luminescent feldspar grains from two samples. We propose that QEM-EDS is capable of (1) classifying the range of mineral phases in grains, (2) determining the area proportions of each of these phases, and (3) obtaining accurate whole-of-grain average K concentrations of individual feldspar grains using the calibration and correction presented here.

富含钾（K）的长石是通常用于光学测年的两种矿物类型之一。长石晶粒可包含至多约14 wt％的K，从而产生内部剂量率成分。该内部成分可以占矿物颗粒所暴露的总环境剂量率的很大一部分。环境剂量率项（光学年龄方程中的分母）确定了在埋葬期间电荷转移到矿物晶粒的晶格中的速率。并非所有的长石晶粒都具有相同的K浓度，因此各个晶粒之间的内部剂量率不同。由于长石相的组成变化，离散的长石相的比例不同和/或晶粒中存在其他矿物夹杂物，钾的浓度范围可以为0至14 wt％。有许多技术可用于确定单个晶粒的K浓度，但很耗时，或者缺乏空间分辨率来对多相晶粒内的离散矿物相进行分类，或者缺乏获得全谷物平均K浓度的覆盖范围。使用能量色散光谱法（QEM-EDS）对矿物进行定量评估是一种省时，自动的制图技术，具有可对大多数矿物相进行分类的空间分辨率，以及可确定其面积比例的覆盖率。QEM-EDS还可以根据与EDS参考光谱的光谱匹配来确定元素浓度。但是，很难确定存在固溶体的矿物（例如长石）的准确元素浓度。为了克服这个问题 我们使用来自六种长石参考标准品的EDS光谱建立QEM-EDS校准，以定义沿碱金属和斜长石长石系列的五个固溶体区域。我们通过比较使用QEM-EDS和波长色散光谱法（WDS）得出的三种长石品种（原长石碱/微晶石，钠长石和山梨糖苷）的离散相的K浓度来测试该校准。我们假设源自WDS的K浓度代表了相的“真实” K浓度，并根据两个数据集的最佳拟合加权回归来计算可应用于QEM-EDS的校正和不确定性估计-得出的K浓度，要考虑仪器的不可重复性和任何测量偏差。我们还测试了替代的映射步长，以优化效率，并将这种省时的技术应用于两个样品中的单个发光长石晶粒。我们认为QEM-EDS能够（1）对谷物中矿物相的范围进行分类，（2）确定这些相中每个矿物相的面积比例，以及（3）获得各个个体准确的全谷物平均K浓度长石晶粒使用此处介绍的校准和校正方法。