Fe-oxides in jasperoids from two gold districts in Nevada: Characterization, geochemistry, and (U-Th)/He dating
Fe-oxides in jasperoids from two gold districts in Nevada: Characterization, geochemistry, and (U-Th)/He dating
复制标题
DOI：
10.1016/j.gca.2020.07.014
复制
发表时间：
2020-10
影响因子：
5
通讯作者：
Dante E. Huff;E. Holley;W. Guenthner;J. Kaempfer
中科院分区：
文献类型：
--
作者：
Dante E. Huff;E. Holley;W. Guenthner;J. Kaempfer
本文通过对碧玉类岩石全岩地球化学特征、氧化铁结构和晶体形态特征、氧化铁（U-Th）/He年龄变化特征及其相互关系的研究，评价碧玉类岩石作为金矿化的指示标志。从内华达州的两个金矿区收集了具有一系列纹理、外观和预期金浓度的碧玉状样品：北方卡林趋势（金矿）和巴特尔山地区（万寿菊矿;巴特尔山前景）。在我们的碧玉样品中，全岩Au浓度与As、Ag、Pb、Sb、U、W和Tl呈正相关。以下氧化铁纹理与异常金浓度：浸染，亚微米晶体;羽毛状和针状晶体形态;同心环带从赤铁矿针铁矿;和botryoidal纹理。在我们的数据集内观察到的碧玉状氧化铁形态中，计算出的（U-Th）/He系统的闭合温度范围为26至136 °C，表明在近地表条件下对He扩散的敏感性不同。Fe氧化物（U-Th）/He年龄范围为29.4 ± 0.5Ma ~ 0.11 ± 0.01Ma，显示出样品内和样品间的差异。我们将日期变化归因于多种因素，包括He注入、母体同位素交换以及He通过闭合温度敏感性和α-喷射的损失。铁氧化物（U-Th）/He测年的样品内和样品间变化限制了我们进行地质解释的能力。我们的案例研究确定了（U-Th）/He方法在碧玉中的重要局限性，并提供了有关如何在未来研究中避免He日期变化的见解。
This study examines the whole-rock geochemistry, Fe-oxide texture and crystal morphology, and Fe-oxide (U-Th)/He date variation of jasperoids, as well as the relationships between these characteristics, in order to evaluate jasperoids as an indicator for gold mineralization. Jasperoid samples with a range of textures, appearances, and expected gold concentrations were collected from two gold districts in Nevada: the northern Carlin trend (Gold Quarry Mine), and the Battle Mountain district (Marigold Mine; Battle Mountain prospect). In our jasperoid samples, whole-rock concentrations of Au are positively correlated with As, Ag, Pb, Sb, U, W, and Tl. The following Fe-oxide textures are associated with anomalous gold concentrations: disseminated, submicron crystals; feathery and acicular crystal morphologies; concentric zonation from hematite to goethite; and botryoidal textures. Calculated closure temperatures for the (U-Th)/He system in observed jasperoid Fe-oxide morphologies within our dataset range from 26 to 136 °C, indicating variable susceptibility to He diffusion at near-surface conditions. Fe-oxide (U-Th)/He dates range from 29.4 ± 0.5 Ma to 0.11 ± 0.01 Ma, displaying intra- and intersample variation. We attribute the date variation to multiple factors including He implantation, parent isotope exchange, and He loss through closure temperature sensitivity and alpha-ejection. The intra- and intersample variation within the Fe-oxide (U-Th)/He dates limits our ability to make geologic interpretations. Our case study identifies important limitations of the (U-Th)/He method in jasperoids and provides insight on how He date variation might be avoided in future studies.