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在太古代岩石中,硫酸盐矿物、赤铁矿和同位素已分馏的硫化物相对很少见。然而,几个太古代金矿床却含有作为氧化热液流体指示剂的这些特征矿物的一种或多种。这些太古代金矿床包括赫姆洛、麦金太尔-霍灵格、马卡萨、莱克肖尔和罗斯等金矿床,它们都位于加拿大安大略省和澳大利亚卡尔古利。较小的金矿床例子位于加拿大安大略省希斯洛普区和马塔奇文地区。除了赫姆洛金矿床之外,其余这些金矿床都是在空间上和时间上与长英质深成作用有关的石英-碳酸盐脉型矿床。因为变质流体和太古代地表水基本上是还原的,所以流体的最可能的总来源是长英质岩浆。 母岩浆都是相对氧化的、含水的和富CO_2的。这种氧化特征可能有利于Au加入到部分熔融的熔体中去,从而有利于把Au分配到岩浆水流体中。CO_2含量高有助于水流体与来自深度比其他地方还深的岩浆分离开来。流体包体数据支持主要的太古代脉型Au矿床是在深度比大多数现代岩浆-热液矿化(如斑岩铜矿床)大的壳层形成的。在较高的温压条件下,富CO_2流体不能分离成两个相:盐水流体相和低盐度H_2O—CO_2流体相。这可使Cl配合的贱金属与包括Au、Sb和As在内的其他金属分离开。在大多数金矿床周围发生的广泛的碳酸盐化具有在原生岩浆CO_2能及的范围内一致的δ~(13)C值。
Sulfate minerals, hematite and isotope-fractionated sulfides are relatively rare in the Archean rocks. However, several Archean gold deposits contain one or more of these characteristic minerals as an indicator of the hydrothermal fluid. These Archean gold deposits include the gold deposits of the cities of Hmulus, MacIntyre-Hollingh, Makassar, Lake Shore and Rose, all located in Ontario, Canada and Kalgoorlie, Australia. Smaller gold deposits are located in the districts of Hesloop and Matakivin in Ontario, Canada. Except for the Helmut Gold Deposit, the rest of these gold deposits are quartz-carbonate vein deposits that are spatially and temporally related to the deep-quartz metamorphism. Because metamorphic fluids and Archean surface water are essentially reduced, the most likely total source of fluid is felsic magma. The parent magma is relatively oxidized, hydrous, and CO 2 -rich. This oxidation characteristic may favor the addition of Au to the partially melted melt, thereby facilitating the distribution of Au into the magma fluid. The high CO 2 content helps to separate water fluids from magma that is deeper than elsewhere. Fluid inclusions data support that the major Archean vein Au deposits are formed at deeper shells than most modern magma-hydrothermal mineralization (eg, porphyry copper deposits). At higher temperature and pressure, the CO2-rich fluid can not separate into two phases: saline fluid and low-salinity H 2 O-CO 2 fluid. This allows Cl complexed base metals to be separated from other metals including Au, Sb and As. The extensive carbonation occurring around most gold deposits has a consistent δ ~ (13) C value within the range of CO 2 energy of primary magmas.