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Abstract
The Kangaroo Caves volcanic-hosted massive sulfide deposit is located in the Archean Panorama district in the northern Pilbara Craton, Western Australia. The deposit contains an indicated and inferred mineral resource of 6.3 Mt at 3.3% Zn, 0.5% Cu and 12.1 g/t Ag. The Kangaroo Caves area is characterised by predominantly tholeiitic volcanic rocks of the ca 3240 Ma Kangaroo Caves Formation, which is overlain by turbiditic sedimentary and volcanic rocks of the Soanesville Group. Zinc–copper mineralisation is hosted mainly by the regionally extensive Marker Chert, the uppermost unit of the Kangaroo Caves Formation, and structurally controlled by D1 synvolcanic faults. The upper area of the deposit is characterised by quartz–sphalerite ± pyrite ± barite ± chalcopyrite, whereas the lower area contains mainly chlorite–pyrite–quartz–carbonate–sericite ± chalcopyrite ± sphalerite.
Laser-ablation inductively coupled-plasma mass-spectrometry analyses show that pyrite in the Marker Chert is enriched in Zn, Ag, Pb and Sb when compared with dacite from the Kangaroo Caves Formation, Paddy Market Formation, and Dalton Suite. Pyrite from the Marker Chert also displays a negative correlation between Zn and As, i.e. with increasing Zn levels As is decreasing. The Co/Ni ratios in pyrite are significantly greater in the upper, Zn-rich area (median ratio = 0.4) of the deposit than the lower, Zn-poor area (median ratio = 5). Copper is low irrespective of the host rocks. Sphalerite displays low Fe (<10 000 ppm), Cu (<100 ppm), Ag (58 ppm) but high Cd (<500–1000 ppm). Some elevated Cu values suggest the presence of chalcopyrite inclusions, whereas elevated Cu and Sb values suggest tetrahedrite–tennantite inclusions.
Structural analysis of the Kangaroo Caves area, combined with three-dimensional modelling of ore element distribution, shows that the deposit is predominantly an elongate pipe of Zn mineralisation, which plunges ~30° to the northeast and is approximately 1000 m in length. The morphology of the Kangaroo Caves deposit was largely retained from its original formation, despite rotation of the host rocks and deposit during the D2 event. Variations in hydrothermal alteration assemblages, including the Co and Ni contents of pyrite within the deposit and underlying dacite, are interpreted to be the result of variations in the influx and mixing of seawater with upwelling volcanogenic fluids during Zn–Cu mineralisation. In the Kangaroo Caves area, the Co/Ni of pyrite can be used as an exploration vector towards high-grade Zn–Cu mineralisation.
袋鼠洞穴火山岩中的大型硫化物矿床位于西澳Pilbara克拉通的太古宙Panorama区。该矿床含有明示的和推断的矿产资源6.3百万吨，包括 3.3 ％的锌、0.5 ％的铜和12.1%的银。袋鼠洞穴区的特征是约3240Ma的袋鼠洞穴组主要为拉斑玄武岩火山岩，被Soanesville群的浊流沉积和火山岩所覆盖。锌 - 铜成矿作用主要发生于该地区广泛出现的硅质岩标记层，这是袋鼠洞穴组的最顶部单元，并且构造上由D1同时火山断层控制。矿床的上部区域以石英闪锌矿±黄铁矿±重晶石±黄铜矿为特点，而下部区域主要含有绿泥石，黄铁矿，石英 - 碳酸盐 - 绢云母±黄铜矿±闪锌矿。激光剥蚀电感耦合等离子质谱分析表明，与袋鼠洞穴组、Paddy Market组和Dalton岩套中的英安岩相比，硅质岩标记层中的黄铁矿富含锌、银、铅和锑。硅质岩标记层中的黄铁矿也显示锌和As之间的负相关，即随锌含量的上升，As的含量下降。黄铁矿中钴/镍的比率在矿床上部的富锌地区（中数比¼ 0.4 ）比下部锌含量低的地区（中位数比¼5 ）高出很多。无论主岩是什么，铜含量都是低的。闪锌矿显示低含量的铁（ < 10000 PPM ） 、铜（ < 100 ppm） 及银（ 58 PPM ），但高含量的镉（ < 500〜1000 ppm） 。一些铜升高的值表明黄铜矿包裹体的存在，而升高的Cu和Sb的值指示黝铜矿 - 砷黝铜矿包裹体。袋鼠洞穴区域的结构分析，综合矿石元素分布的三维模型，表明该矿床主要是长管状锌矿。它向东北向降低约30度，长约1000米。袋鼠洞穴矿床主要还保留着它的原始形态，尽管D2活动期间主岩和矿床发生旋转。热液蚀变组合的变化，包括矿床和下伏英安岩中黄铁矿的Co和Ni含量，被解释为Zn-Cu矿化过程中海水的涌入和海水与上涌的火山成因流体混合的变化的结果。在袋鼠洞穴区，黄铁矿的钴/镍比率可作为高等级锌-铜矿化作用的勘探指示值。
ACKNOWLEDGEMENTS
The authors would like to thank Sipa Resources for their financial support and excellent work on the geology of the Panorama District, which laid the foundation for this project. In particular, we would like to thank Michael Doepel and Dr Leigh Bettenay for initiating this study and Dr Carl Brauhart for his thoughtful reviews of the manuscript. The generous support provided during laser ablation ICP-MS analyses by the Centre for Ore Deposit and Exploration Studies (CODES) at the University of Tasmania is also greatly appreciated, and we would like to thank Sarah Gilbert in particular. F. Pirajno, S. Stephens and an anonymous referee are thanked for their detailed and thorough reviews.