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首页> 外文期刊>Chemical geology >Interaction of magmatic fluids and silicate melt residues with saline groundwater in the footwall of the Sudbury Igneous Complex, Ontario, Canada: New evidence from bulk rock geochemistry, fluid inclusions and stable isotopes
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Interaction of magmatic fluids and silicate melt residues with saline groundwater in the footwall of the Sudbury Igneous Complex, Ontario, Canada: New evidence from bulk rock geochemistry, fluid inclusions and stable isotopes

机译：加拿大安大略省萨德伯里火成岩联合体下盘的岩浆流体和硅酸盐熔渣与盐水的相互作用：大量岩石地球化学，流体包裹体和稳定同位素的新证据

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摘要

Along the northern margin of the 1.85. Ga Sudbury Igneous Complex (SIC), Canada, a volumetrically minor rock type known as the footwall granophyre (FWGP) preserves evidence of the interaction of magmatic fluid and groundwater. The FWGP comprises veins, dikes and irregular bodies of a quartz-alkali feldspar-plagioclase intergrowth that are most abundant near footwall-style Cu-Ni-platinum-group element mineralization. Textures and cross-cutting relations show that the emplacement of the FWGP created favourable sites for the later deposition of sulfides. Geochemical and physical evidence show that the FWGP did not form by in-situ partial melting of the Archean country rocks in the footwall beneath the SIC. It represents a mobilized (injected) silicate residue from either the contact between partially melted country rocks and the SIC, or from the crystallizing SIC itself. Its bulk composition can be modeled as the product of fractional crystallization of a liquid with an initial composition equivalent to granophyric matrix (trapped liquid) in the lowermost units of the SIC (norite and sublayer).Primary fluid (saline, H_2O-poor) and melt (silicate, H_2O-rich) inclusions hosted in quartz from the FWGP have bulk and trace element compositions consistent with those hosted in quartz from the granophyric matrix of the lower units of the SIC (norite, sublayer). Fluid inclusions contain mixtures of a high salinity (44-70wt.% NaCl_(equivalent); n=39), Na-Fe-rich aqueous magmatic fluid and a lower salinity, Ca- and Sr-rich groundwater. The magmatic end-member is thought to be an SIC-derived volatile phase. Estimates of the mixing proportions show that primary and secondary inclusions in the FWGP contain 60-100% and 30-80% of the magmatic end-member by mass, respectively. Fluids responsible for the remobilization of ore metals represent mixtures containing a much higher proportion of the groundwater end-member (not less than 70% by mass) compared to the fluids trapped in the FWGP. At considerable distance (~400m) from the SIC, the chlorine isotope composition of biotite in the FWGP is enriched in ~(37)Cl (δ~(37)Cl=0.98‰ to 1.61‰). Scapolite from the high temperature veins and the interstices of rock types in the main mass of the SIC shows similar enrichment in ~(37)Cl (up to 1.34‰) whereas biotite from the Archean country rocks (δ~(37)Cl=-0.88 to -0.53‰) and associated groundwater are ~(37)Cl-depleted.The results of this study lead to two important conclusions concerning genetic and exploration models for the footwall ore zones. First, magmatic end-member fluid introduced into the footwall with the melt from which the FWGP crystallized contained very little Cu (rarely >~100. ppm), the main ore metal in the footwall ores. This result questions hydrothermal models for footwall ore formation that hypothesize that Cu and other ore metals were remobilized from sulfide deposits along the SIC contact by magmatic-hydrothermal fluids and redeposited in the footwall. It is more likely that ore metals were only locally remobilized in the footwall ore zones when metal-poor hybrid fluids interacted with pre-existing sulfide veins of magmatic origin. Second, inclusions containing the hybrid fluid occur in the FWGP rock type throughout the footwall, in both mineralized and unmineralized areas. Therefore, although the FWGP preserves stable Cl isotope and fluid inclusion evidence that magmatic fluid was introduced into the footwall, detection of this magmatic component alone will not serve as a useful exploration method. In contrast, mapping the distribution and abundance of FWGP may be ore-predictive since FWGP emplacement and its higher abundance in mineralized areas appears to have been a structural and textural prerequisite for footwall ore emplacement.
机译：沿1.85的北缘。加拿大的Ga Sudbury火成岩体（SIC）是一种体积较小的岩石类型，被称为下盘面花岗石（FWGP），保留了岩浆流体与地下水相互作用的证据。 FWGP包括脉，堤和石英-碱长石-斜长石共生体的不规则体，在下盘式Cu-Ni-铂族元素矿化附近含量最高。纹理和横切关系表明，FWGP的位置为以后的硫化物沉积创造了有利的位置。地球化学和物理证据表明，FWGP并不是通过SIC下方下盘中的太古代乡村岩石的原位部分熔融形成的。它代表了部分融化的乡村岩石与SIC之间的接触或结晶的SIC本身中动员的（注入的）硅酸盐残渣。可以将其总体组成建模为液体的分步结晶产物，其初始组成与SIC最低单元（黑土和亚层）中的粒状基质（捕获的液体）等效。主要流体（盐水，H_2O贫乏）和FWGP石英中包含的熔融（硅酸盐，富含H_2O的）夹杂物的体积和微量元素组成与SIC下部单元（norite，亚层）的粒状基质中石英所包含的相同。流体包裹体包含高盐度（44-70wt。％NaCl_（当量）; n = 39），富含Na-Fe的岩浆水液和较低盐度，富含Ca和Sr的地下水的混合物。岩浆末端成员被认为是SIC衍生的挥发性相。混合比例的估算表明，FWGP中的主要和次要夹杂物分别占岩浆端部质量的60-100％和30-80％。与FWGP中捕获的流体相比，负责矿石金属迁移的流体代表的混合物中所含的地下水端构件的比例要高得多（按质量计不少于70％）。在距SIC相当远的距离（〜400m）处，FWGP中黑云母的氯同位素组成富含〜（37）Cl（δ〜（37）Cl = 0.98‰至1.61‰）。 SIC主体中高温脉型的闪锌矿和岩石类型的空隙在〜（37）Cl（至1.34‰）处富集相似，而在太古代的岩石中的黑云母（δ〜（37）Cl =- （0.88至-0.53‰）和相关的地下水贫化了〜（37）Cl。这项研究的结果得出了有关下盘矿带成因和勘探模式的两个重要结论。首先，岩浆末段流体与FWGP从中结晶出来的熔体一起进入底壁，其中所含的铜很少（很少>〜100。ppm），是底壁矿石中的主要矿石金属。该结果质疑了下盘矿形成的热液模型，该模型假设铜和其他矿石金属是通过岩浆热液从沿SIC接触的硫化物矿床中迁移出来并重新沉积在下盘壁中的。当贫金属的混合流体与岩浆成因的硫化物脉络相互作用时，矿石金属更有可能仅在底盘矿带中局部迁移。其次，在矿山和非矿山地区，贯穿整个底盘的FWGP岩石类型均含有混合流体包裹体。因此，尽管FWGP保留了稳定的Cl同位素和流体夹杂物的证据，表明岩浆流体已被引入底盘，但仅对岩浆成分进行检测将不能用作有用的勘探方法。相比之下，绘制FWGP的分布和丰度可能是矿石预测的，因为FWGP的位置及其在矿化区的较高丰度似乎是下盘矿石安置的结构和质地前提。

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