Petrogenesis of gold-bearing listvenites from the carbonatized mantle section of the Neoproterozoic Ess ophiolite, Western Arabian Shield, Saudi Arabia
Petrogenesis of gold-bearing listvenites from the carbonatized mantle section of the Neoproterozoic Ess ophiolite, Western Arabian Shield, Saudi Arabia
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沙特阿拉伯西阿拉伯地盾新元古代埃斯蛇绿岩碳化地幔部分含金列表岩的岩石成因
DOI：
10.1016/j.lithos.2020.105679
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发表时间：
2020
期刊：
影响因子：
3.5
通讯作者：
Al-Kahtany, Khaled M.
中科院分区：
文献类型：
--
作者：
Gahlan, Hisham A.;Azer, Mokhles K.;Asimow, Paul D.;Al-Kahtany, Khaled M.
晚新元古代Ess蛇绿岩（沙特阿拉伯西部）中的蛇绿岩化地幔橄榄岩沿着剪切带和冲断面高度蚀变，形成抗侵蚀的蚀变橄榄岩。从岩石学和地球化学特征上可区分为碳酸盐型、硅碳酸盐型和硅（水硼岩）型三种类型。地球化学分析与岩相学的预期一致：碳酸盐钙铝榴石的SiO2含量低，但MgO、Fe 2 O3和CaO含量相对于硅碳酸盐和水硼钙石高，后者的SiO2含量显著高，而其他所有成分都不高。硅质碳酸盐岩和碳酸盐蚀变岩中稀土元素总量较低，而水硼岩中稀土元素含量较高，具有较大的Eu正异常。寄主蛇纹岩具有与超俯冲弧前环境中高度亏损的地幔方辉橄榄岩原岩典型相关的所有特征：体相成分低Al 2 O3和CaO，高Mg# [摩尔Mg/（Mg + Fe）]，残余Cr尖晶石高Cr# [摩尔Cr/（Cr + Al）]和低TiO 2，残余橄榄石高Mg#和NiO含量。铬尖晶石遗迹也被发现在listvenites;那些在蛇纹岩和碳酸盐listvenites有显着较高的Mg#比那些在硅碳酸盐和birbirite，这表明铬尖晶石再平衡在listvenitization的后期阶段。各种各样的钙钛矿捕获流体介导的置换反应的连续阶段。碳酸盐钙钛铁矿似乎与蛇纹石化同时发育，而硅碳酸盐钙钛铁矿和水硼镁石则形成较晚。钙钛矿的形成导致了一些组分的浸出和去除，同时伴随着其他组分在固体产物中的沉积，特别是CO 3、SiO2、REE（特别是Eu）、Au、Zn、As、Sb和K。我们的数据表明，铁硅脉石化集中了次经济到经济级别的金;在寄主蛇纹岩中测得的金浓度为0.5-1.7 ng/g，而在碳酸盐铁硅脉岩中为4-2569 ng/g，在硅-碳酸盐铁硅脉岩中为43-3117 ng/g，在水镁石中为5-281 ng/g。Jabal Ess地区的铁橄榄石矿床值得进一步勘探。
The variably serpentinized mantle peridotites of the Late Neoproterozoic Ess ophiolite (Western Saudi Arabia) are highly altered along shear zones and thrust planes to form erosion-resistant listvenites. The listvenites are distinguished petrographically and geochemically into three types: carbonate, silica-carbonate and silica (birbirite) listvenites. Geochemical analyses are consistent with expectations from petrography: carbonate listvenite is low in SiO2content but high in MgO, Fe2O3, and CaO relative to silica-carbonate and birbirite, which is remarkably high in SiO2at the expense of all other components. The total REE contents are low in silica-carbonate and carbonate listvenites but highly enriched in birbirite, with a large positive Eu anomaly. The host serpentinites have all the characteristics typically associated with highly depleted mantle harzburgite protoliths in supra-subduction fore-arc settings: bulk compositions are low in Al2O3and CaO with high Mg# [molar Mg/(Mg + Fe)], relict Cr-spinel has high Cr# [molar Cr/(Cr + Al)] and low TiO2, and relict olivine has high Mg# and NiO content. The Cr-spinel relics are also found in the listvenites; those in serpentinite and carbonate listvenites have significantly higher Mg# than those in silica-carbonate and birbirite, suggesting re-equilibration of Cr-spinel in the later phases of listvenitization. The varieties of listvenite capture successive stages of fluid-mediated replacement reactions. The carbonate listvenite appears to have developedsyn-contemporaneously with serpentinization, whereas silica-carbonate listvenite and birbirite formed later. The listvenite formation resulted in leaching and removal of some components accompanied by deposition of others in the solid products, notably CO3, SiO2, REE (especially Eu), Au, Zn, As, Sb and K. Our data show that listvenitization concentrated gold at sub-economic to economic grades; measured gold concentrations in the host serpentinite are 0.5–1.7 ng/g, versus 4–2569 ng/g in carbonate listvenite, 43–3117 ng/g in silica-carbonate listvenite and 5–281 ng/g in birbirite. The listvenite deposits in the Jabal Ess area merit further exploration for gold.
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DOI：
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期刊：
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