Magnetite texture and trace element evolution in the Shaquanzi Fe-Cu deposit, Eastern Tianshan, NW China
Magnetite texture and trace element evolution in the Shaquanzi Fe-Cu deposit, Eastern Tianshan, NW China
复制标题
DOI：
10.1016/j.oregeorev.2023.105306
复制
发表时间：
2023-03
影响因子：
3.3
通讯作者：
Xia Hu;B. Xiao;Hongjun Jiang;Jianhan Huang
中科院分区：
文献类型：
--
作者：
Xia Hu;B. Xiao;Hongjun Jiang;Jianhan Huang
沙泉子矿床是东天山雅曼苏铁矿化带中重要的铁铜矿床。根据结构和矿物组合划分出3种类型的磁铁矿，即板状蘑菇石(TA)、与钾长石和绿帘石共生的粒状磁铁矿(TB)和与黄铁矿共生的粒状磁铁矿(TC)。在BSE观察下，塔磁铁矿由三个世代组成，即亮核(TA-1)、深灰色内缘(TA-2)和浅灰色外缘(TA-3)。由于氧逸度的急剧降低，Ta-1磁铁矿由原生赤铁矿转化而来，并保留了其板状假象。随着温度的变化(升高或降低)，TA-1磁铁矿经历了溶解和再沉淀(DRP)过程，形成了TA-2和TA-3磁铁矿。Tb磁铁矿由两代(Tb-1和Tb-2)组成。TB-1磁铁矿中含有丰富的矿物包裹体和微孔隙。随着氧气和温度的降低，TB-1磁铁矿经历了流体辅助重结晶过程，形成了具有泡沫结构的TB-2磁铁矿。TC磁铁矿由TC-1、TC-2、TC-3和TC-4四个不同世代组成。TC-1磁铁矿具有密集分布的振荡分带(一般小于1μm)，被较暗的TC-2磁铁矿包围。TC-1磁铁矿重结晶可形成泡沫结构的TC-2磁铁矿。TC-3磁铁矿交代或切割TC-2磁铁矿，表明其形成于TC-2磁铁矿的DRP过程。根据氧和温度的周期性变化，在TC-3磁铁矿周围形成具有振荡带的TC-4磁铁矿，提出了一种区分热液磁铁矿和岩浆磁铁矿的新的Fe/(Mg+Al+Fe-Mn)-Ti判别图。沙泉子矿床的磁铁矿成分与岩浆磁铁矿有很大不同，但与IOCG、矽卡岩型矿床等热液系统中观察到的磁铁矿非常相似，表明沙泉子矿床的磁铁矿是由热液作用而不是岩浆分异作用形成的。
The Shaquanzi deposit is an important Fe-Cu deposit in the Yamansu Fe mineralization belt, Eastern Tianshan. Three types of magnetite were distinguished based on the textural and mineral assemblages, including the platy mushketovite (TA), granular magnetite coexisting with K-feldspar and epidote (TB), and granular magnetite intergrown with pyrite (TC). TAmagnetite consists of three generations, including a bright core (TA-1), a dark-gray inner rim (TA-2), and a light-gray outer rim (TA-3), under BSE observations. TA-1 magnetite was transformed from the primary hematite due to a sharply reduced oxygen fugacity and retains its platy pseudomorph. With the changing temperature (increase or decrease), TA-1 magnetite underwent dissolution and re-precipitation (DRP) processes to form TA-2 and TA-3 magnetite. TBmagnetite consists of two generations (TB-1 and TB-2). TB-1 magnetite contains abundant mineral inclusions and microporosity. With the decrease offO2and temperature, TB-1 magnetite underwent a fluid-assisted recrystallization process to form TB-2 magnetite with foam texture. TCmagnetite consists of four different generations (TC-1, TC-2, TC-3, and TC-4). TC-1 magnetite with densely-distributed oscillatory zonings (generally smaller than 1 μm) is surrounded by the darker TC-2 magnetite. TC-2 magnetite with foam texture may be formed by recrystallization of TC-1 magnetite. TC-3 magnetite replaced or cut TC-2 magnetite, indicating that it was formed by the DRP process of TC-2 magnetite. Following periodic changes offO2and temperature, TC-4 magnetite with oscillatory zones formed around TC-3 magnetite.This study proposes a new Fe/(Mg + Al + Mn) vs Ti discrimination diagram to distinguish hydrothermal and magmatic magnetite. Magnetite compositions of the Shaquanzi deposit are quite different from those of magmatic magnetite, but very similar to those observed in the hydrothermal system such as IOCG and skarn deposit, indicating that magnetite of the Shaquanzi deposit was formed by hydrothermal process rather than magmatic differentiation.