Geology of the Sari Gunay Epithermal Gold Deposit, Northwest Iran
Geology of the Sari Gunay Epithermal Gold Deposit, Northwest Iran
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DOI：
10.2113/gsecongeo.101.8.1455
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发表时间：
2006-12
期刊：
影响因子：
5.8
通讯作者：
J. Richards;D. Wilkinson;T. Ullrich
中科院分区：
文献类型：
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作者：
J. Richards;D. Wilkinson;T. Ullrich
Sari Gunay浅成低温热液金存款矿床位于伊朗中西北部的一个弱碱性的粗面质火山杂岩中。侵入岩和火山岩的寄主存款已被定年为11.7和11.0马之间（8.0Ma时的一个较年轻样品;火成黑云母和角闪石的~（40）Ar/~（39）Ar定年）而与早期热液活动有关的绢云母蚀变发生在~10.8 ~ 10.3Ma之间（绢云母40 Ar/39 Ar测年得到的最佳年龄为10.7Ma）。主要热液系统在结构上由以Sari Gunay山为中心的角砾岩复合体定位。最早的热液活动仅在深度（地表以下>300 m）出现，产生了弱钾质蚀变和石英硫化物磁铁矿脉，具有低品位的Cu和Au矿化，使人联想到浅层（≤ 1.5 km深度）斑岩金矿系统。同生晚期的石英-电气石角砾岩和脉体遵循远晶角砾岩的南-西南-北-东北走向，并在火成岩碎屑和围岩中产生强烈的绢云母蚀变和硅化作用。流体包裹体表明，在与低密度、含CO2气相包裹体共存的高盐包裹体中，温度为246° C至360°C，盐度为34.4至46.1重量% NaCl当量。这些流体似乎没有沉积金，但角砾岩提供了进一步的结构渗透性流动的后来成矿浅成热液。在石英-冰长石-黄铁矿-辉锑矿脉的早期阶段，以固溶体形式存在于细粒砷黄铁矿和少量砷黄铁矿中。这些矿脉中的晚期矿物包括雄黄、雌黄、朱砂和极其罕见的金丝。这些矿脉中的富液流体包裹体的平均均一温度（捕集温度）为199° ± 24°C，盐度为3.6 ± 1.1wt%NaCl当量，并与低密度含CO2的气相包裹体共存，表明处于低压条件下。相分离可能是金沉积的一个贡献原因，但硫化物的沉淀反应系统的快速冷却可能是沉积的黄铁矿托管金的主要控制。Sari Gunay金存款及其寄主火山系统构成了构造控制的中中新世弱碱性火山-深成复合体的塔卡布带的一部分。Zarshuran沉积物型金存款矿床位于该带西北偏北沿着约190 km处，也与中中新世岩浆活动有关。塔卡布带比广泛的始新世-中新世乌鲁木齐-多克塔尔钙碱性火山弧稍年轻，并向西南移动，该火山弧承载着几个大型斑岩铜矿（例如，Sar Cheshmeh，Meiduk）.塔卡布带的岩石也明显比乌鲁木齐-多克塔尔带的岩石碱性更强。从非洲-阿拉伯板块和欧亚板块之间新特提斯洋的新近纪闭合的板块构造模型来看，这些差异可能反映了乌鲁木齐-多克塔尔弧的正常俯冲带起源，并含有斑岩铜矿，但对稍年轻的塔卡布带火山岩和浅成低温热液金矿床则是碰撞起源。因此，Sari Gunay存款可以被归类为碰撞相关的碱性型浅成热液系统，尽管它的碱性低于该组的经典存款，如Porgera，皇帝，或Cripple Creek（后者显然与碰撞后或弧后伸展，而不是同碰撞过程）。
The Sari Gunay epithermal gold deposit is located within a mildly alkaline latitic to trachytic volcanic complex in central-northwest Iran. Intrusive and volcanic rocks that host the deposit have been dated at between 11.7 and 11.0 Ma (with one younger sample at 8.0 Ma; 40Ar/39Ar dating of igneous biotite and hornblende), whereas sericitic alteration associated with an early stage of hydrothermal activity occurred between ~10.8 and ~10.3 Ma (the best age estimate is 10.7 Ma obtained by 40Ar/39Ar dating of sericite). The main hydrothermal system was structurally localized by a diatreme breccia complex centered on the Sari Gunay hill. Earliest hydrothermal activity, only encountered at depth (>300 m below surface), produced weak potassic alteration and quartz-sulfide-magnetite veining with low grades of Cu and Au mineralization, reminiscent of shallow-level (≤ 1.5-km depth) porphyry gold systems. Paragenetically later quartz-tourmaline breccias and veins followed the south-southwest–north-northeast trend of the diatreme breccias and produced strong sericitic alteration and silicification in igneous clasts and wall rocks. Fluid inclusions indicate temperatures of 246° to 360°C and salinities of 34.4 to 46.1 wt percent NaCl equiv in hypersaline inclusions coexisting with low-density, CO2-bearing vapor-phase inclusions. These fluids do not appear to have deposited gold, but the breccias provided further structural permeability for flow of later mineralizing epithermal fluids. Invisible gold occurs in solid solution in fine-grained arsenical pyrite and minor arsenopyrite, deposited in the early stages of quartz-adularia-pyrite-stibnite veins. Late-stage minerals in these veins include realgar, orpiment, cinnabar, and extremely rare wire gold. Liquid-rich fluid inclusions in these veins have an average homogenization temperature (≈ trapping temperature) of 199° ± 24°C, salinities of 3.6 ± 1.1 wt percent NaCl equiv, and coexist with low-density CO2-bearing vapor-phase inclusions, suggesting low-pressure conditions. Phase separation may have been a contributory cause of gold deposition, but precipitation of sulfides in response to rapid cooling of the system may have been the main control on deposition of pyrite-hosted gold. The Sari Gunay gold deposit and its host volcanic system form part of the Takab belt of structurally controlled, middle Miocene, mildly alkaline volcano-plutonic complexes. The sediment-hosted Zarshuran gold deposit, located ~190 km to the north-northwest along the belt, is also related to middle Miocene magmatism. The Takab belt is marginally younger than, and displaced to the southwest of, the extensive Eocene-Miocene Urumieh-Dokhtar calk-alkaline volcanic arc, which hosts several large porphyry Cu deposits (e.g., Sar Cheshmeh, Meiduk). Rocks of the Takab belt are also distinctly more alkaline than the Urumieh-Dokhtar rocks. Viewed in the context of plate tectonic models for Neogene closure of a Neo-Tethys ocean between the Afro-Arabian and Eurasian plates, these differences may reflect a normal subduction zone origin for the Urumieh-Dokhtar arc and contained porphyry Cu deposits but a collisional origin for the slightly younger Takab belt volcanic rocks and epithermal gold deposits. The Sari Gunay deposit may thus be classified as a collision-related alkalic-type epithermal system, although it is less alkaline than classic deposits of this group such as Porgera, Emperor, or Cripple Creek (the latter apparently being related to postcollisional or back-arc extensional rather than syncollisional processes).