Geology of the Gushan iron oxide deposit associated with dioritic porphyries, eastern Yangtze craton, SE China
Geology of the Gushan iron oxide deposit associated with dioritic porphyries, eastern Yangtze craton, SE China
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DOI：
10.1080/00206810902823941
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发表时间：
2009-01-01
影响因子：
2.6
通讯作者：
Li, Shunting
中科院分区：
文献类型：
--
作者：
Hou, Tong;Zhang, Zhaochong;Li, Shunting
姑山铁矿存款位于扬子克拉通东部，是长江中下游典型的铁矿床。这类矿床一般被认为与燕山期次火山-火山岩有关，在时间和空间上与约1000万年前的火山岩有关。129.3-137.5 Ma闪长斑岩。后者具有非常窄的87 Sr/86 Sr范围（0.7064 ~ 0.7066）和较低的Nd（t）值（-5.8 ~-5.7），表明斑岩是由幔源岩浆在岩浆上升过程中受到地壳混染而形成的。矿体主要沿着闪长斑岩与沉积围岩的接触带产出。最重要的矿石类型是块状和角砾状矿石，共占90体积%。存款。块状型通常以主要由磁铁矿（赤铁矿）和少量磷灰石组成的大型矿脉出现。角砾岩型的特征是围岩的棱角状碎块被细粒磁铁矿胶结。网脉状铁矿石呈不规则的脉状和网状，特别是具有梳状结构;它们由低温矿物（如方解石）组成，这表明热液过程。块状矿石、角砾状矿石和斑岩中磷灰石的稀土元素模式相似，加上高温流体（1000 ℃），表明它们是岩浆成因的。此外，块状矿石中普遍存在的熔体流动结构以及硅酸盐矿物和堆积结构的缺乏表明，铁矿石是由不混溶的氧化物熔体从硅酸盐熔体中分离出来的，而不是由晶体分馏形成的。结合理论和实验研究，我们提出，引入磷由于地壳污染在幔源岩浆上升可能是一个关键因素，导致形成不混溶的氧化物熔体的硅酸盐岩浆。
The major Gushan iron oxide deposit, typical of the Middle-Lower Yangtze River Valley, is located in the eastern Yangtze craton. Such deposits are generally considered to be genetically related to Yanshanian subvolcanic-volcanic rocks and are temporally-spatially associated with ca. 129.3-137.5 Ma dioritic porphyries. The latter have a very narrow 87Sr/86Sr range of 0.7064 to 0.7066 and low Nd(t) values of -5.8 to -5.7, suggesting that the porphyries were produced by mantle-derived magmas that were crustally contaminated during magma ascent. The ore bodies occur mainly along the contact zone between dioritic porphyries and the sedimentary country rocks. The most important ore types are massive and brecciated ores which together make up 90 vol.-% of the deposit. The massive type generally occurs as large veins consisting predominantly of magnetite (hematite) with minor apatite. The brecciated type is characterized by angular fragments of wall-rocks that are cemented by fine-grained magnetite. Stockwork iron ores occur as irregular veins and networks, especially with pectinate structure; they are composed of low-temperature minerals (e.g. calcite), which indicate a hydrothermal process. The similar rare earth element patterns of apatite from the massive ores, brecciated ores and the porphyries, coupled with high-temperature fluids (1000 degrees C) suggest that they are magmatic in origin. Furthermore, melt flow structure commonly developed in massive ores and the absence of silicate minerals and cumulate textures suggest that the iron ores formed by the separation of an immiscible oxide melt from the silicate melt rather than by crystal fractionation. Combined with theoretical and experimental studies, we propose that the introduction of phosphorus due to crustal contamination during mantle-derived magma ascent could have been a crucial factor that led to the formation of an immiscible oxide melt from the silicate magma.