The crustal continuum model for late-Archaean lode-gold deposits of the Yilgarn Block, Western Australia
The crustal continuum model for late-Archaean lode-gold deposits of the Yilgarn Block, Western Australia
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DOI：
10.1007/bf02431596
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发表时间：
1993
影响因子：
4.8
通讯作者：
D. Groves
中科院分区：
文献类型：
--
作者：
D. Groves
大多数西太平洋金矿属于一个连贯的成因组的构造控制的矿脉矿床，其特征是富集Au与可变富集的Ag，As，W，Sb，Bi，Te，B和Pb，但很少Cu或Zn，并包围围岩蚀变晕富集K，LILE和CO2，与可变Na和/或Ca的补充。来自西澳大利亚Yilgarn地块的证据，结合来自加拿大和其他地方的类似证据，表明这些矿床代表了一个地壳连续体，它是在各种地壳制度下形成的，至少有15公里的地壳剖面，PT条件从180°C <1 kb到700°C 5 kb。个别矿床，相隔数十至数百公里，共同显示过渡变化的结构风格的矿化，静脉纹理和矿物学的围岩蚀变，涉及到他们的形成在不同的地壳深度的PT条件。总光谱内的具体过渡也可以通过金营地内的矿床来显示，尽管没有任何地方记录到来自单个金营地或甚至绿岩带的整个矿床连续体，但对矿床地壳连续体的认识暗示了巨大的晚白垩世热液系统的存在，该热液系统具有原生矿液的深源。一些深部流体和溶质储层是可能的，包括基底段的绿岩带，深层次侵入花岗岩类，中低地壳花岗岩片麻岩，地幔岩石圈，甚至俯冲洋岩石圈，考虑到可能的收敛边缘设置的主机绿岩。个别稳定和放射性同位素比值的流体和溶质成分牵连流体的演变，或平衡，这些水库的数量，强调潜在的复杂性的途径，流体平流沉积网站。铅和锶同位素比值的矿石伴生矿物提供了最有说服力的证据，流体平流通过深层次侵入花岗岩类或花岗岩-片麻岩地壳，而初步的氧同位素数据表明，深源流体和地表沃茨的混合只发生在最高的地壳水平记录的矿脉金矿床。
Most Archaean gold ores belong to a coherent genetic group of structurally controlled lode-deposits that are characteristically enriched in Au with variable enrichments in Ag, As, W, Sb, Bi, Te, B and Pb, but rarely Cu or Zn, and are surrounded by wallrock alteration haloes enriched in K, LILE and CO2, with variable Na and/or Ca addition. Evidence from the Yilgarn Block of Western Australia, combined with similar evidence from Canada and elsewhere, indicates that such deposits represent a crustal continuum that formed under a variety of crustal régimes over at least a 15 km crustal profile at PT conditions ranging from 180°C at <1 kb to 700°C at 5 kb. Individual deposits, separated by tens to hundreds of kilometres, collectively show transitional variations in structural style of mineralisation, vein textures, and mineralogy of wallrock alteration that relate to the PT conditions of their formation at varying crustal depths. Specific transitions within the total spectrum may be shown also by deposits within gold camps, although nowhere is the entire continuum of deposits recorded from a single gold camp or even greenstone belt.Recognition of the crustal continuum of deposits implicates the existence of giant late-Archaean hydrothermal systems with a deep source for the primary ore fluid. A number of deep fluid and solute reservoirs are possible, including the basal segments of greenstone belts, deep-level intrusive granitoids, mid-to lower-crustal granitoidgneisses, mantle lithosphere, or even subducted oceanic lithosphere, given the probable convergent-margin setting of the host greenstone terranes. Individual stable and radiogenic isotope ratios of fluid and solute components implicate fluid evolution from, or equilibrium with, a number of these reservoirs, stressing the potential complexity of pathways for fluid advection to depositional sites. Lead and strontium isotope ratios of ore-associated minerals provide the most persuasive evidence for fluid advection through deep-level intrusive granitoids or granitoid-gneiss crust, whereas preliminary oxygen isotope data show that mixing of deeply sourced fluid and surface waters only occurred at the highest crustal levels recorded by the lode gold deposits.