Shear-hosted base metal mineralisation at the Dana Peaks, Murchison Mountains, Fiordland, New Zealand
Shear-hosted base metal mineralisation at the Dana Peaks, Murchison Mountains, Fiordland, New Zealand
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新西兰峡湾默奇森山脉达纳峰的剪切贱金属矿化
DOI：
10.1080/00288306.2010.498406
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发表时间：
2010
影响因子：
2.2
通讯作者：
D. Craw
中科院分区：
文献类型：
--
作者：
A. Allibone;P. Ashley;D. MacKenzie;D. Craw
默奇森山脉中部达纳峰的Darran套闪长质、英云闪长质和花岗闪长质深成岩和片状洛赫伯恩组火山岩受到广泛的黑云母-绢云母-绿泥石-钠长石-石英-黄铁矿±碳酸盐±绿帘石/斜长石±钛铁矿/金红石±阳起石蚀变的影响。沿着橙子风化剪切带，绢云母-钠长石-石英-黄铁矿±碳酸盐蚀变更强烈，颜色更浅。蚀变组合是在通常所称的长角闪岩、钾质岩和千枚岩之间的过渡。蚀变岩含有铜、铅、锌和银的异常富集，覆盖面积为c。2.5×6公里。金属浓度是Darran Suite深成岩和洛赫伯恩组典型值的2-5倍，通常与更广泛的弱至中等强度蚀变有关。更高的金属等级可达C。0.5%的铜、1%的锌、1.3%的铅和30 ppm的银集中在1-5 m宽、蚀变更强烈的剪切带中或附近，剪切带中含有黄铁矿化围岩、角砾岩和石英±钾长石±碳酸盐±赤铁矿±电气石脉的夹带透镜体。某些矿化岩石还含有微量钨（2-7 ppm）、砷（<5-35 ppm）和碲（0.2-5.4 ppm）。大多数样本缺乏可检测到的钼（<3 ppm）、金（<0.004 ppm）或铋（<0.2 ppm），非典型的较高值（分别为40、0.03和50 ppm）通常仅限于蚀变和/或变形最强烈的岩石。成矿岩石与几条狭窄的韧性剪切带在时间和空间上有着密切的关系，这些韧性剪切带可能发育于早白垩世，128和110 Ma。矿化剪切带形成了较大剪切带的较小倾斜，这些剪切带是主要弧内断层系统的一部分，此时沿沿着或靠近中柱岩内侧和外侧部分之间的边界活动。类似的铅矿化痕迹存在于中烧c的头部。沿沿着向东北方向8公里处，与达纳峰所在地相同的区域规模断层系统。流体和金属很可能来自于洛赫伯恩地层和/或邻近的深成岩石的变质作用。岩浆热液成因被认为是不可能的，因为金属组合缺乏Mo、Bi、Au、Sn和W，并且邻近的深成岩可能在蚀变和矿化之前结晶了几百万年或更久。
Abstract Darran Suite dioritic, tonalitic and granodioritic plutonic rocks and schistose Loch Burn Formation volcaniclastic rocks in the central Murchison Mountains at the Dana Peaks have been affected by widespread biotite-sericite-chlorite-albite-quartz-pyrite±carbonate±epidote/clinozoisite±titanite/rutile±actinolite alteration. More intense, paler coloured sericite-albite-quartz-pyrite±carbonate alteration is concentrated along orange weathered shear zones. Alteration assemblages are transitional between those commonly referred to as propylitic, potassic and phyllic. Altered rocks contain anomalous concentrations of copper, lead, zinc and silver over an area of c. 2.5×6 km. Metal concentrations 2–5 times those typical of Darran Suite plutonic rocks and the Loch Burn Formation are commonly associated with more extensive weak to moderate intensity alteration. Higher metal grades up to c. 0.5% copper, 1% zinc, 1.3% lead and 30 ppm silver are concentrated in or adjacent to the 1–5 m wide, more intensely altered shear zones which contain entrained lenses of pyritised country rock, breccias and quartz±K-feldspar±chlorite±carbonate±hematite±tourmaline veins. Some mineralised rocks also contain traces of tungsten (2–7 ppm), arsenic (<5–35 ppm) and tellurium (0.2–5.4 ppm). Most samples lack detectable molybdenum (<3 ppm), gold (<0.004 ppm) or bismuth (<0.2 ppm), with atypical higher values (40, 0.03 and 50 ppm, respectively) generally restricted to the most intensely altered and/or deformed rocks. The mineralised rocks show a close spatial and temporal relationship with several narrow ductile shear zones that probably developed in the Early Cretaceous between c. 128 and 110 Ma. Mineralised shear zones form minor splays off larger shear zones that are part of a major intra-arc fault system, active along or near the boundary between inboard and outboard parts of the Median Batholith at this time. Traces of similar lead mineralisation are present at the head of the Mid Burn c. 8 km to the northeast along strike on the same regional-scale fault system as the Dana Peaks locality. Fluids and metals are likely to have been derived from metamorphism of the Loch Burn Formation and/or adjacent plutonic rocks. A magmatic hydrothermal origin is considered unlikely as the metal assemblage lacks Mo, Bi, Au, Sn and W and the adjacent plutonic rocks probably crystallised several million years or more before alteration and mineralisation.