Thermomechanical erosion at the Alexo Mine, Abitibi greenstone belt, Ontario: implications for the genesis of komatiite-associated Ni–Cu–(PGE) mineralization
Thermomechanical erosion at the Alexo Mine, Abitibi greenstone belt, Ontario: implications for the genesis of komatiite-associated Ni–Cu–(PGE) mineralization
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安大略省阿比蒂比绿岩带 Alexo 矿的热机械侵蚀：对与科马提矿相关的 Ni-Cu-(PGE) 矿化成因的影响
DOI：
10.1007/s00126-011-0371-6
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发表时间：
2011
影响因子：
4.8
通讯作者：
P. C. Davis
中科院分区：
文献类型：
--
作者：
M. Houlé;C. Lesher;C. Lesher;P. C. Davis
典型的科马提岩型Alexo Ni-Cu-（PGE）存款产于安大略省安大略Dundonald镇西部Abitibi绿岩带2720 - 2710 Ma的Kidd-Munro组合中。一个200米长的冰川抛光露头的详细测绘提供了明确的证据，表明宿主科马提岩流热机械侵蚀下盘安山岩：（1）科马提岩与安山岩之间的接触非常尖锐，但呈精致的扇形，以<1cm厚的黑色隐晶质科马提岩镶边为标志，在安山岩中明显地海侵枕状构造和枕间角砾岩，没有任何风化层的证据，剪切，（2）安山岩沿露头的整个长度沿着发生接触变质和蚀变，在海湾周围变质/蚀变程度较厚、较强烈，（3）科马提岩中的安山岩捕虏体在海湾内较常见;（4）科马提质岩脉向下渗透到下伏安山岩中，主要是沿海湾的侧缘沿着;（5）许多岩脉和边缘岩石显示出混染的地球化学证据。热机械侵蚀的物理和地球化学证据，结合矿石中非岩浆围岩S的主要成分的S同位素证据，提供了额外的支持热机械侵蚀的作用和掺入围岩S的成因科马提岩相关的Ni-Cu-（PGE）矿床。详细的绘图还显示，矿区的地层比以前报道的要复杂得多，表明硫化物在几个阶段中侵位，证实了与科马提岩有关的Ni-Cu-（PGE）矿床的矿石侵位过程的动态性质。
The archetypical komatiite-hosted Alexo Ni–Cu–(PGE) deposit occurs in the 2,720–2,710-Ma Kidd-Munro Assemblage of the western Abitibi greenstone belt in Dundonald Township, Ontario. Detailed mapping of a 200-m long glacially polished outcrop provides unequivocal evidence that the host komatiite flow thermomechanically eroded footwall andesites: (1) the contact between komatiite and andesite is very sharp but delicately scalloped, marked by a <1-cm-thick selvedge of black aphanitic komatiite and clearly transgresses pillow structures and interpillow breccias in the andesite without any evidence of a regolith, shearing, or folding, producing multiple nested embayments on scales from hundreds of meters to a few centimeters; (2) the andesites have been contact metamorphosed and altered along the entire length of the outcrop and the degree of metamorphism/alteration is thicker and more intense around embayments; (3) xenoliths of andesite in komatiite are more common within embayments; (4) komatiitic dikes penetrate downward into underlying andesites, primarily along the lateral margins of embayments; and (5) many of the dikes and marginal rocks exhibit geochemical evidence of contamination. This physical and geochemical evidence for thermomechanical erosion, combined with S isotopic evidence for a major component of non-magmatic country-rock S in the ores, provides additional support for the roles of thermomechanical erosion and incorporation of country-rock S in the genesis of komatiite-associated Ni–Cu–(PGE) deposits. The detailed mapping also reveals that the stratigraphy of the ore zone is considerably more complex than previously reported, indicating that the sulfides were emplaced in several stages, confirming the dynamic nature of the ore emplacement process in komatiite-associated Ni–Cu–(PGE) deposits.