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靠近安大略省马拉松(Marathon)镇的赫姆洛(Hemlo)矿床,是北美最大的金矿床之一。该矿呈层状赋存在太古界变质火山岩—沉积岩中,主要的矿带由黄铁矿绢云母片岩和块状重晶石组成。这是北美太古界层状重晶石的首次报导。但是,赫姆洛以西,此后也曾发现过其他的赋存状态。矿化体实质上富含Au、Mo、Sb、Hg、Tl和V而缺乏碳酸盐。由于地质体的变质和变形作用,其成因尚未确定。该矿床重晶石中的~(87)Sr/~(86)Sr比值为0.7017近似于赫姆洛西部的沉积重晶石和同期火山岩的初始比值。在主矿带的底部,δ~(34)S为+8到12‰的重晶石与-5～0‰的黄铁矿均为同期沉积而成。由此向上,在形成矿带上部的不含(层状)重晶石的片岩中,重晶石和黄铁矿两者的同位素值均较低,其黄铁矿的最小值达-17.5‰。在钻探剖面中。Au的品位与黄铁矿的同位素组成为对应关系。这是由于分离的硫化物和硫酸盐相结合之故,这暗示着金、黄铁矿以及重晶石为同期沉积的产物。含硫矿物的链状不对称分布和其同位素值的分布,以及赫姆洛和其西部重晶石中同位素值的相似性与同生沉积模式完全一致。考虑到硫化矿物有两个来源:第一个来源是来自局限性盆地中的外生硫酸盐,在地热系统中被部分地还原,形成了~(34)S减损的硫化物;第二个来源是,硫化物和硫酸盐都是岩浆—热液成因。硫酸盐和分离的硫化物,在太古界岩石中非常少见;但其中之一或二者却以不寻常的同时出现在太古界的金矿床中,中高氧逸度(fo_2)的热液。所含硫酸盐由于氧化与还原作用,硫的种属之间常发生同位素的分馏,因而有利于金的分解、迁移和沉淀。
The Hemlo deposit near the town of Marathon in Ontario is one of the largest gold deposits in North America. The deposit is hosted in the Archean metamorphic volcanic rocks - sedimentary rocks, the main ore belt from the pyrite sericite schist and massive barite composition. This is the first report of stratiform barite in North America. However, west of Hermlo, other states of existence have also been discovered since then. The mineralized body is essentially rich in Au, Mo, Sb, Hg, Tl and V and lacks carbonate. Due to the deterioration and deformation of the geological body, its cause has not been determined. The ~ (87) Sr / ~ (86) Sr ratio of barite in this deposit is 0.7017, which is similar to the initial ratio of sedimentary barite and contemporaneous volcanic rocks in the west of Helmro. At the bottom of the main ore belt, barite with δ ~ (34) S of +8 to 12 ‰ and pyrite of -5 ~ 0 ‰ are all deposited in the same period. From the above, the isotopic values of both barite and pyrite are lower in the unconsolidated (stratiform) barite-forming schist of the upper part of the ore belt, with the minimum value of pyrite reaching -17.5 ‰. In the drilling section. Au grade and pyrite isotopic composition of the corresponding relationship. This is due to the combination of the separated sulphide and sulphate, suggesting that gold, pyrite, and barite are co-precipitated products. The asymmetric chain-like distribution of sulfur minerals and their isotopic distribution, and the similarity of the isotope values of the Hemler and its western barites, are completely consistent with the synsedimentary patterns. Considering there are two sources of sulphide minerals: the first source is exogenous sulphates from localized basins that are partially reduced in the geothermal system to form ~ (34) S detrimental sulphides; the second source Yes, sulfides and sulfates are all magmatic-hydrothermal causes. Sulfates and isolated sulphides are rare in Archean rocks; however, one or both of them are unusual hydrothermal fluids with moderate to high oxygen fugacity (Fo_2) in the Archean gold deposits. Contained sulfate due to oxidation and reduction, sulfur species often occur between isotopic fractionation, which is conducive to gold decomposition, migration and precipitation.