Mineralogy, fluid inclusion and isotope signatures: Implications for the genesis of the Early Paleozoic Yangjiashan scheelite-quartz vein deposit, South China
Mineralogy, fluid inclusion and isotope signatures: Implications for the genesis of the Early Paleozoic Yangjiashan scheelite-quartz vein deposit, South China
复制标题
DOI：
10.1016/j.oregeorev.2021.104136
复制
发表时间：
2021-03
影响因子：
3.3
通讯作者：
Wei Li;Guiqing Xie;J. Mao;Huichao Zhang
中科院分区：
文献类型：
--
作者：
Wei Li;Guiqing Xie;J. Mao;Huichao Zhang
破解白钨矿—石英脉矿床的形成机制，对于推进对石英脉钨矿化体系的认识至关重要。本文以早古生代杨家山白钨矿—石英脉矿床为例，应用电子探针、He-Ar-H-O同位素、流体包裹体、激光拉曼光谱等分析方法，探讨成矿流体的性质、成因及白钨矿沉淀条件。石英和白钨矿中的流体包裹体包括富气型和富液型。在第一阶段，白钨矿中两种类型流体包裹体的均质温度和盐度分别为215°~ 336°C（平均250°C）和2.4 ~ 13.2 wt% NaCl当量（平均9.3 wt% NaCl当量）；在第二阶段，分别为195°~ 290°C（平均231°C）和1.2 ~ 12.8 wt% NaCl当量（平均6.6 wt% NaCl当量）。所有这些数值与两个阶段的石英相当，表明两个阶段之间的温度差距不明显。拉曼光谱证实了水的存在，并在流体包裹体中检测到CH4、co2和n2。原生铋、磁黄铁矿和马氏铁矿的矿物组合以及包裹体中ch4的存在表明成矿流体减少，logfo2和logfs2的计算值分别在-45 ~ -40和-15.0 ~ -7.0之间。与白钨矿平衡的δD和δ 18oh2o值分别为-84 ~ -56‰和3.2 ~ 5.1‰。两阶段毒砂3He/4He比值在0.13 ~ 0.69 Ra之间（Ra，空气3He/4He比值= 1.39 × 10-6）；40Ar/36Ar和40Ar*（非大气）的百分比分别为556%至1327%和47%至78%。这些同位素特征均支持岩浆流体与幔源成分混合以及大气水参与了杨家山矿床的形成。与沸腾和混合过程相关的流体pH值变化是白钨矿沉淀的原因。
Decoding the formation mechanism of scheelite-quartz vein deposits is critical for advancing the understanding of quartz vein tungsten mineralization systems. In this study, we take the Early Paleozoic Yangjiashan scheelite-quartz vein deposit as an example, applying electron probe, He–Ar–H–O isotopes, fluid inclusions, and laser Raman spectroscopy analyses, to investigate the nature and origin of mineralizing fluids and the conditions of scheelite precipitation.Fluid inclusions in quartz and scheelite from both greisen and quartz vein stages include vapor-rich and dominant liquid-rich types. The measured homogenization temperatures and salinities of the two types of fluid inclusions within scheelite from both stages range from 215° to 336 °C (mean 250 °C) and 2.4 to 13.2 wt% NaCl equiv (mean 9.3 wt% NaCl equiv), respectively, for Stage 1, and from 195° to 290 °C (mean 231 °C) and 1.2 to 12.8 wt% NaCl equiv (mean 6.6 wt% NaCl equiv), respectively, for Stage 2. All these values are comparable to those of quartz from both stages, indicating an insignificant temperature gap between the stages. Raman spectroscopy confirms the presence of H2O with detectable CH4, CO2and N2within the fluid inclusions. The mineral assemblage of native bismuth, pyrrhotite, and marcasite and the presence of CH4in the fluid inclusions suggest reduced ore-forming fluids, and the calculated logfO2and logfS2values vary from approximately -45 to -40 and -15.0 to -7.0, respectively. The δD and δ18OH2Ovalues in equilibrium with scheelite range from -84 to -56‰ and 3.2 to 5.1‰, respectively, for the two stages. The3He/4He ratios in arsenopyrite for both stages are between 0.13 and 0.69 Ra (Ra,3He/4He ratio of air = 1.39 × 10-6);40Ar/36Ar and the percentages of40Ar* (non-atmospheric) range from 556 to 1,327 and from 47 to 78%, respectively. All these isotope signatures support the involvement of magmatic fluid mixing with mantle-derived components and meteoric water in the formation of the Yangjiashan deposit. Fluid pH change associated with boiling and mixing processes is responsible for scheelite precipitation.