福建姑田斑岩矿床成矿岩浆形成演化与铜钼富集研究

The Gutian porphyry Cu-Mo deposit is the second porphyry deposit found in Southeast China coastal area, which located north-east 80 km to the Luoboling porphyry Cu-Mo deposit. Multi-stages magmatic activities have been found in the Gutian porphyry ore-field. The Gutian porphyry is different from Luoboling porphyry deposit in ore-hosted rocks and ore-forming element compositions. Based on the field observation and microscopic identification of different intrusions, alteration and mineralization, this project plan to analyze the isotopic ages of deposit and the different intrusions, the geochemistry characteristics and isotopic compositions of the intrusions, the differences of fertile and barren intrusions in their zircon Ce4+/Ce3+ ratios, apatite Mn2+/Mn3+ ratios as well as apatite trace element compositions, iron oxide mineral assemblage of different intrusions, melt inclusions and fluid inclusions in quartz and accessory mineral such as apatite and zircon. Through the above work, the spatial and temporal distribution of Yanshanian magmatism in the area will be revealed, the porphyry mineralization age and fertile intrusion will be determined, the source characteristic of ore-forming magma will be discussed, the geochemistry index indentifying the fertile intrusion from barren intrusions will be established, and the factors controlling the difference ore-forming element compositions between Gutian and Luoboling porphyry deposit will be proposed..The project plays an important role in understanding the Mesozoic magmatism and porphyry mineralization in Southeast China coastal area. It will also help to develop the porphyry mineralization theory in the south China. Besides, the fertile intrusion index established in this project will provide supervisions in ore prospecting in the district.

姑田矿床是我国东南沿海新近发现的斑岩型铜钼矿床，对其成矿时代、成矿岩浆特征及形成过程均了解甚少，特别是其与邻区白垩纪斑岩矿床（罗卜岭矿床）和华南侏罗纪斑岩矿床（主要沿十杭带分布）构造背景异同尚不清晰。本项目拟通过详细的野外考察和系统的室内分析，特别是成岩成矿高精度定年、锆石原位Hf-O同位素、锆石Ce4+/Ce3+比值、磷灰石Mn2+/Mn3+比值及矿化剂元素含量、铁氧化物组成及岩浆出溶挥发相特征等研究，确定矿床形成时代及与矿化有关的斑岩特征；查明成矿与非成矿岩体地球化学特征异同，建立成矿岩体地球化学指标；分析姑田与罗卜岭斑岩矿床Cu/Mo比值差异的主要控制因素；探讨姑田斑岩Cu-Mo矿床与东南沿海白垩纪斑岩矿床和沿十杭带分布中-晚侏罗世斑岩矿床动力学背景异同。本项目对认识东南沿海中生代斑岩矿床成岩成矿过程、深入了解华南斑岩成矿时空分布规律及分析不同时期斑岩矿床动力学过程异同等有重要意义。

姑田斑岩Cu-Mo矿床是福建东南沿海新近发现的矿床。本项目分析了姑田矿区岩浆岩的锆石U-Pb年龄、辉钼矿Re-Os年龄、黄铁矿Re-Os年龄、全岩主微量元素、锆石微量元素及Hf同位素组成，阐明矿区岩浆活动期次及其与成矿的关系，揭示成矿岩浆的地球化学特征。本项目还对比分析了邻区的紫金山高硫型浅成低温Au-Cu矿床及罗卜岭斑岩Cu-Mo矿床的形成时代和成矿岩浆的锆石Hf同位素组成，探讨姑田、紫金山和罗卜岭三个空间相近的矿床元素组合差异的控制因素。分析结果显示，姑田矿区的中细粒花岗岩，钾长花岗闪长斑岩，斜长花岗斑岩和碱长花岗斑岩的形成时代相近，都在164.4±5.4Ma-160.3±8.1Ma之间；而闪长玢岩的年龄为131.1±2.0Ma，表明区内发生了侏罗纪和白垩纪两期岩浆活动。黄铁矿Re-Os模式年龄为124.4±0.9Ma 至139.1±133.9Ma，与白垩纪的岩浆年龄基本一致。结合前人的辉钼矿Re-Os年龄（~162 Ma），表明姑田矿区发生了和侏罗纪、白垩纪岩浆作用有关的两期矿化作用。侏罗纪岩浆相较白垩纪岩浆具有高Sr/Y比值（>30）及高的锆石Ce4+/Ce3+比值（平均574），表明侏罗纪岩浆为富水高氧化岩浆，有利于斑岩成矿，可能是主要的成矿岩浆。邻区的紫金山高硫型浅成低温Au-Cu成矿期云母Ar-Ar年龄为113.4±1.1Ma和110.4±1.3Ma，明显早于罗卜岭Cu-Mo矿化斑岩的103.8±0.9Ma，因此，紫金山矿田高硫型浅成低温矿床与斑岩矿床并不属于同一斑岩成矿系统，而是两次岩浆成矿作用的产物。姑田成矿斑岩的锆石εHf(t)为 -13.5 ~ -19.7，低于罗卜岭成矿斑岩的-1.2 ~ -4.6和紫金山矿化火山岩的0.3 ~ -4.6，表明三者的源区存在明显的差异。其中姑田成矿岩浆主要来自于地壳，形成了低Cu/Mo比值（<3）的斑岩矿床；紫金山的成矿岩浆含有较多幔源物质，形成了Au-Cu矿床；罗卜岭的成矿岩浆较姑田的含有更多幔源组分，但较紫金山的含更多壳源组分，形成了高Cu/Mo比值（>12）斑岩矿床。本研究表明，源区是控制研究区内矿床元素组合和元素比值差异的主要因素，福建东南沿海在侏罗纪和白垩纪分别发育与太平洋板块俯冲及折返作用相关的多期斑岩成矿作用。