Cu–(Ni–Co–Au)-bearing massive sulfide deposits associated with mafic–ultramafic rocks of the Main Urals Fault, South Urals: Geological structures, ore textural and mineralogical features, comparison with modern analogs
Cu–(Ni–Co–Au)-bearing massive sulfide deposits associated with mafic–ultramafic rocks of the Main Urals Fault, South Urals: Geological structures, ore textural and mineralogical features, comparison with modern analogs
复制标题
DOI：
10.1016/j.oregeorev.2012.03.005
复制
发表时间：
2013-08
影响因子：
3.3
通讯作者：
I. Melekestseva;V. Zaykov;P. Nimis;G. Tret'yakov;S. Tessalina
中科院分区：
文献类型：
--
作者：
I. Melekestseva;V. Zaykov;P. Nimis;G. Tret'yakov;S. Tessalina
与乌拉尔主断裂带（MUF）南部镁铁-超镁铁岩有关的富铜块状硫化物矿床的特征是镍的富集程度不同（高达0.45wt.%），Co（高达10重量%）和Au（在单个手标本中高达16 ppm）。MUF矿床的富Cu（Ni-Co）成分，与沿马格尼托哥尔斯克弧西侧沿着大致相似年龄的更向东的块状硫化物矿床的富Cu（Zn）成分相反，反映了早泥盆世马格尼托哥尔斯克前弧最外部的海底暴露的富Ni-Co超镁铁质岩的丰度。个别矿床之间的形态，结构和成分差异被解释为硫化物沉积风格的结果，部分，原始海底岩性。一种主要由海底热液作用产生的存款的特征是黄铁矿-白铁矿-磁黄铁矿，锌品位不太低（有时高达2 wt.%），碎屑相丰富，周期性浅表氧化作用。以海底热液作用为主的矿床，其特征为磁黄铁矿>黄铁矿，Zn含量极低（一般<0.1wt.%），体积较小的碎屑相和多层存款形态。海底存款中非常低的Ni/Co比值可能表明主要金属来自镁铁质而不是超镁铁质来源。硫化物矿化与寄主超镁铁岩和镁铁岩的广泛热液蚀变有关，导致形成了丰富的滑石、滑石碳酸盐和滑石岩。在蛇绿岩带中大量出现这种蚀变岩型，可作为寻找MUF型（Cu、Co、Ni）矿床的潜在标志。尽管地球动力学环境不同，但MUF矿床的地质、地球化学、结构和矿物学特征在许多方面与沿着大西洋中脊的超镁铁质块状硫化物矿床相似。在地质时代，超俯冲带的设置似乎已经更有效地保存超镁铁岩托管的块状硫化物矿床比洋中脊的设置。
Cu-rich massive sulfide deposits associated with mafic–ultramafic rocks in the southern portion of the Main Urals Fault (MUF) are characterized by variable enrichments in Ni (up to 0.45wt.%), Co (up to 10wt.%) and Au (up to 16ppm in individual hand-specimens). The Cu (Ni–Co)-rich composition of MUF deposits, as opposed to the Cu (Zn)-rich composition of more eastward massive sulfide deposits of broadly similar age along the western flank of the Magnitogorsk arc, reflects the abundance of seafloor-exposed, Ni–Co-rich ultramafic rocks in the most external portion of the Early-Devonian Magnitogorsk forearc. Morphological, textural, and compositional differences between individual deposits are interpreted to be the result of the sulfide deposition style and, in part, of the original subseafloor lithology. One deposit produced by dominantly on-seafloor hydrothermal processes is characterized by pyrite–marcasite≫pyrrhotite, not so low Zn grades (occasionally up to 2wt.%), abundant clastic facies and periodical superficial oxidation. Deposits produced by dominantly subseafloor hydrothermal processes are characterized by pyrrhotite>pyrite, very low Zn (generally < to ≪0.1wt.%), volumetrically minor clastic facies, and multi-layer deposit morphology. Very low Ni/Co ratios in the on-seafloor deposit may indicate a dominant metal contribution from a mafic rather than ultramafic source. The sulfide mineralization was associated with extensive hydrothermal alteration of the host ultramafic and mafic rocks, leading to formation of abundant talc, talc–carbonate and chlorite rocks. Occurrence of large volumes of such altered lithotypes in ophiolitic belts may be considered as a potential searching criteria for MUF-type (Cu, Co, Ni)-deposits. In spite of the contrasting geodynamic environment, geological, geochemical, textural and mineralogical peculiarities of the MUF deposits in many respects are similar to those of ultramafic-hosted massive sulfide deposits along the Mid-Atlantic Ridge. In geological time, supra subduction-zone settings appear to have been more effective than mid-ocean ridge settings for preservation of ultramafic-hosted massive sulfide deposits.