Geology and genesis of Nalunaq Palaeoproterozoic shear zone-hosted gold deposit, South Greenland
Geology and genesis of Nalunaq Palaeoproterozoic shear zone-hosted gold deposit, South Greenland
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南格陵兰纳鲁纳克古元古代剪切带金矿床的地质和成因
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发表时间：
2000
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通讯作者：
L. Kludt
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作者：
K. Kaltoft;D. Schlatter;L. Kludt
Nalunaq存款是一个剪切带托管金存款的特点是非常高的品位（高达5240克Au/吨超过0.8米）。容矿岩石为纳诺尔塔利克推覆体的古元古代变基性岩，该推覆体是柯提里甸移动的带的一部分。纳诺尔塔利克推覆体由层状块状磁黄铁矿/石墨燧石层组成，上覆细粒变玄武岩，具有枕状结构和变白云岩，随后是变凝灰岩和变集块岩。该序列被一个斑状黑云母花岗岩（约1755 - 1725百万年）侵入。然后是环斑花岗岩金矿化发生在一个0.5 - 2.0 m宽的剪切带中，剪切带由片状石英脉和相关的钙硅酸盐蚀变组成。矿化剪切带在Nalunaq山东侧出露800 m，北侧出露1200 m。地表测绘、金刚石钻探（78个孔，共计11 452米）和平硐开发（288米）表明，承载含金主脉的剪切带是一个连续的结构。这个结构随后被轻微旋转的右旋走滑断层所取代。金主要以自然金和少量的辉绿石的形式存在。游离金主要以包裹体形式存在于石英、透辉石、斜长石中，少量的包裹体存在于硫砷铜矿和毒砂中。金也存在于石英、硫砷铜矿和毒砂的裂隙和晶界中。这些金的出现表明发生了几次金的流入和/或再活化阶段。金颗粒的大小从1微米到4毫米不等，其分布是不规则的，这使得很难从1.5到5公斤的样品中估计存款的品位。石英和透辉石中金的流体包裹体包含三种类型的流体：水相流体、碳相流体和碳水混合流体。中度至高度含盐（14 - 26重量% NaCl + CaCl2当量）含水流体，推断成分为H2O-NaCl-CaCl/MgCl ± LiCl。平均均质化温度为201 ° C。所述含碳流体含有小于5摩尔%的CH 4，并且具有在45 - 60 cm 3/摩尔范围内的密度。近源蚀变矿物（如透辉石、富钙角闪石、富钙斜长石）和不透明组合（如硫砷铁矿、毒砂和磁黄铁矿）表明该存款是在上绿片岩-角闪岩相条件下形成的。毒砂镶边的勒灵石结构表明，该存款形成于高温，金矿化结构随后也在较低温度下活动。剪切带形成于韧性条件下，石英脉的主要侵位发生在随后的脆-韧性体系中，在多次流体流入的过程中。剪切带明显晚于角闪岩相区域变质作用，因为它与变质面理不一致。这种矿化作用，以及东南沿海Xutseq类似的高温剪切带托管金矿化和通常金含量高度异常的水系沉积物，表明在Ketilidian移动的带演化的后期阶段，格陵兰南部可能存在一个广泛的金矿化系统。
The Nalunaq deposit is a shear zone-hosted gold deposit characterized by very high grades (up to 5240 g Au/t over 0.8 m). The host rocks are Palaeoproterozoic metabasic rocks of the Nanortalik Nappe, which is part of the Ketilidian Mobile Belt. The Nanortalik Nappe consists of bedded massive pyrrhotite/graphitic chert horizons overlain by fine-grained metabasalts with pillow structures and metadolerites followed by metatuffs and meta-agglomerate. This sequence was intruded by a porphyritic biotite granite (ca 1755-1725 m.y.) and subsequently by rapakivi granites. The gold mineralization occurs in a 0.5-2.0 m wide shear zone consisting of sheeted quartz veins with associated calc-silicate alteration. The mineralized shear zone is exposed for 800 m on the east face and 1200 m on the north face of Nalunaq Mountain. Surface mapping, diamond drilling (78 holes totalling 11 452 m) and adit development (288 m) have shown that the shear zone that hosts the gold-bearing Main Vein is a continuous structure. This structure was subsequently displaced by slightly rotating dextral strike-slip faults. Gold is present mainly as native gold and as minor maldonite. Free gold appears mainly as inclusions in quartz, diopside, plagioclase and as minor inclusions in löllingite and arsenopyrite. Gold also occurs in fractures and at grain boundaries of quartz, löllingite and arsenopyrite. These occurrences of gold indicate that several influxes of gold and/or stages of remobilization took place. The gold grains vary in size from 1 µm to 4 mm and their distribution is irregular, which makes it difficult to estimate the grade of the deposit from 1.5-to 5-kg samples. Fluid inclusions associated with gold in quartz and diopside contain three types of fluids: aqueous, carbonic and mixed carbonic-aqueous. Moderate to highly saline (14-26 wt% NaCl+CaCl2 equivalent) aqueous fluids with the inferred composition H2O-NaCl-CaCl/MgCl±LiCl predominate. The average homogenization temperature is 201°C. The carbonic fluid contains less than 5 mol% CH4 and has densities in the range 45-60 cm3/mole. The proximal alteration minerals (e.g. diopside, Ca-rich amphibole and Ca-rich plagioclase) and opaque assemblages (e.g., löllingite, arsenopyrite and pyrrhotite) show that the deposit was formed under upper greenschist- to amphibolite-facies conditions. The texture of löllingite rimmed by arsenopyrite suggests that the deposit was formed at high temperatures and the gold-mineralized structure was subsequently also active at lower temperatures. The shear zone was formed under ductile conditions and the major emplacement of quartz veins occurred in the subsequent brittle-ductile regime during multiple influxes of fluids. The shear zone clearly postdates the amphibolite-facies regional metamorphism as it is discordant to the metamorphic foliation. This mineralization, together with the similar hypothermal shear zone-hosted gold mineralization at Xutseq on the southeast coast and stream sediments that are generally highly anomalous in gold, indicates that a widespread gold-mineralizing system may have been active in South Greenland in the late stages of evolution of the Ketilidian Mobile Belt.