Tellurium, magmatic fluids and orogenic gold: An early magmatic fluid pulse at Cononish gold deposit, Scotland
Tellurium, magmatic fluids and orogenic gold: An early magmatic fluid pulse at Cononish gold deposit, Scotland
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DOI：
10.1016/j.oregeorev.2018.05.014
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发表时间：
2018-05
影响因子：
3.3
通讯作者：
C. Spence-Jones;Gawen R. T. Jenkin;A. Boyce;N. J. Hill;C. Sangster
中科院分区：
文献类型：
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作者：
C. Spence-Jones;Gawen R. T. Jenkin;A. Boyce;N. J. Hill;C. Sangster
在许多造山型金矿床中发生显著的碲富集，但造成这种情况的因素知之甚少;一些作者认为这需要岩浆输入，而另一些人则认为不需要。Te从Se和S中的分馏可以提供含金流体的源/通道过程的见解。与许多造山型金矿床相比，苏格兰变质沉积岩中的Cononish脉金矿床异常富含Te，Te/Au ≈ 2.4，而大多数造山型金矿床的Te/Au < 1。在这里，通过共生，Au-Ag合金中的Ag从0.10%增加到90wt%，与降低的六方铁镁矾（Ag 2 Te）丰度相关。这表明Au-Ag合金成分受流体Te活性控制，并且随着时间的推移而降低。这与黄铁矿δ 34 S通过共生作用从−2.0‰增加到+11.4‰有关。因此，该存款是由低δ 34 S、高Te + Au + Ag的原生流体演化为高δ 34 S、低Te、Pb + Cu的流体形成的。晚期流体的高δ 34 S值表明其只能来自附近特定的变质SEDEX层位。沉积大部分金的早期流体可能来源于地层中的其他变质沉积单元或岩浆成因。我们认为，两个观察一起表明，这是最有可能的流体是岩浆，矿化的年龄是相同的结晶附近的花岗岩基的最后阶段，和流体有一个S-同位素签名与岩浆源一致。造山带中的金矿床几乎肯定是多成因的，这项研究证明了富Te的“造山”矿床具有显着的岩浆成分的证据。
Significant tellurium enrichment occurs in many orogenic gold deposits but the factors causing this are little understood; some authors suggest this demands a magmatic input whereas others suggest it need not. Fractionation of Te from Se and S could offer insight into source/pathway processes of auriferous fluids. The metasedimentary-hosted Cononish vein gold deposit, Scotland, is unusually Te-rich compared to many orogenic gold deposits with Te/Au ≈ 2.4 whereas most orogenic deposits have Te/Au < 1. Here, Ag in Au-Ag alloy increases from ∼10 to 90 wt% through the paragenesis, correlating with decreasing hessite (Ag2Te) abundance. This suggests the Au-Ag alloy composition was controlled by the fluid Te activity, and that this decreased through time. This is coupled to an increase in pyrite δ34S from −2.0‰ to +11.4‰ through the paragenesis. Thus, the deposit formed from a primary fluid with a low-δ34S and high Te + Au + Ag that evolved to a high δ34S-low Te, Pb + Cu bearing fluid. The high δ34S of the later fluid suggests it can only be sourced from specific nearby metamorphosed SEDEX horizons. The early fluid that deposited most of the gold could be sourced from other metasedimentary units in the stratigraphy or be magmatic in origin. We argue that two observations taken together suggest it is most likely that this fluid was magmatic; the age of the mineralisation is identical to the last stage of crystallization of nearby granite batholiths, and the fluid has a S-isotope signature consistent with a magmatic source. Gold deposits in orogenic belts are almost certainly polygenetic and this study demonstrates evidence for Te-rich “orogenic” deposits having a significant magmatic component.