| 青海松树南沟金矿区西矿床磁铁矿地球化学特征及成因意义 |
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| 引用本文：叶紫枫,郎兴海,仲世新,王旭辉,董维财,罗超,李善财,王登科,李科,汤永江.2026.青海松树南沟金矿区西矿床磁铁矿地球化学特征及成因意义[J].地球学报,47(5):1150-1166. |
| DOI：10.3975/cagsb.2026.102821 |
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| 基金项目:本文由国家自然科学基金项目(编号: 42572103)、新一轮找矿突破战略行动科技支撑项目(编号: ZKKJ202427)、四川省自然科学基金项目(编号: 2024NSFSC1954)和中央引导地方科技发展资金项目(编号: XZ202401YD0006)联合资助。 |
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| 中文摘要:青海松树南沟金矿区西矿床是北祁连成矿带重要的Au矿床之一, 赋存于晚奥陶世石英闪长斑岩及其接触带附近的玄武安山岩内, 目前探明金资源量已达大型金矿床规模。然而, 其成因类型缺乏系统的矿物学证据支持, 且成矿流体演化过程尚不明确, 制约了深部及外围找矿工作的开展。本文以松树南沟金矿区西矿床阶段I钾硅酸盐化(Mt1)和青磐岩化叠加钾硅酸盐化(Mt2)蚀变带中的磁铁矿脉为研究对象, 开展了矿物学、电子探针(EPMA)和激光剥蚀电感耦合等离子体质谱(LA-ICP-MS)分析。结果显示: Mt1含有较高的Ti(2 830×10–6~18 797×10–6)、Al(1 309×10–6~19 165×10–6)、Si(1 851×10–6~24 993×10–6)、Mn(130×10–6~2 982×10–6)和低含量的Co(0.53×10–6~280.01×10–6)、Ni(37.08×10–6~135.71×10–6)、Sn(3.52×10–6~39.90×10–6); Mt2的Ti(614×10–6~4 464×10–6)、Al(539×10–6~7 268×10–6)、Si(2 155×10–6~10 544×10–6)、Mn(137×10–6~467×10–6)含量则明显低于Mt1, 而Co(90.97×10–6~196.58×10–6)、Ni(20.95×10–6~163.04×10–6)、Sn(2.70×10–6~77.02×10–6)含量略高于Mt1。Mt1形成于相对高温环境(平均温度395 °C), 而Mt2(平均温度337 ℃)则受到后期中-低温热液蚀变的改造, 呈现出温度降低、氧逸度升高的趋势, 表明了成矿流体演化过程中温度下降与氧逸度升高的过程。元素地球化学图解显示西矿床为斑岩型Au矿床, 两类磁铁矿均属热液成因型, 且高Ti、Al、Mn含量的磁铁矿(Mt1)可作为识别蚀变矿化斑岩体的重要标志之一。 |
| 中文关键词:磁铁矿地球化学 成因类型 成矿流体演化 松树南沟金矿区 北祁连成矿带 |
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| Geochemical Characteristics and Genetic Implications of Magnetite from the Western Deposit in the Songshunangou Gold District, Qinghai Province |
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| Abstract:The western deposit in the Songshunangou district is a large-scale gold deposit within the North Qilian metallogenic belt. Mineralization occurred within the Late Ordovician quartz-diorite porphyry and adjacent basaltic andesite near the contact zone. However, genetic classification lacks systematic mineralogical support, and ore-forming fluid evolution remains poorly constrained, impeding deep and peripheral exploration. This study focused on magnetite veins within potassic alteration (Mt1) and potassic alteration overprinted by propylitic alteration (Mt2) in the western deposit. Mineralogical studies, combined with electron probe microanalysis (EPMA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses, revealed distinct compositional differences. Mt1 exhibited higher concentrations of Ti (2 830×10–6–18 797×10–6), Al (1 309×10–6–19 165×10–6), Si (1 851×10–6–24 993×10–6), and Mn (130×10–6–2 982×10–6), with lower levels of Co (0.53×10–6–280.01×10–6), Ni (37.08×10–6–135.71×10–6), and Sn (3.52×10–6–39.90×10–6). In contrast, Mt2 exhibited significantly lower Ti (614×10–6–4 464×10–6), Al (539×10–6–7 268×10–6), Si (2 155×10–6–10 544×10–6), and Mn (137×10–6–467×10–6) content compared to that of Mt1, while containing slightly higher Co (90.97×10–6–196.58×10–6), Ni (20.95×10–6–163.04×10–6), and Sn (2.70×10–6–77.02×10–6). Formation temperatures indicate that Mt1 crystallized at relatively high temperatures (395 °C on average), whereas the lower temperature of Mt2 (337 °C on average) reflects overprinting by later moderate-to low-temperature hydrothermal fluids. This fluid evolution is characterized by a temperature decrease and an increase in oxygen fugacity. Elemental geochemical diagrams exhibited the diagnostic characteristics of a porphyry gold deposit. Both magnetite types (Mt1 and Mt2) are of hydrothermal origin. Furthermore, the high Ti, Al, and Mn contents of magnetite (Mt1) can be diagnostic altered and mineralized porphyry systems in exploration, providing a key vector for exploration targeting. |
| keywords:magnetite geochemistry genetic type ore-forming fluid evolution Songshunangou gold district North Qilian metallogenic belt |
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