In 2013, a diamond drill program tested an extensive advanced argillic alteration lithocap within the Hu’u project on eastern Sumbawa Island, Indonesia. A very large and blind copper-gold deposit (Onto) was discovered, in which copper occurs largely as disseminated covellite with pyrite, and as pyrite-covellite veinlets in a tabular block measuring at least 1.5 × 1 km, with a vertical thickness of ≥1 km.Copper and gold are spatially related with a series of coalesced porphyry stocks that intrude a polymictic diatreme breccia capped by a sequence of intramaar laminated siltstones, volcaniclastic and pyroclastic rocks, and overlain by andesite flows and domes. The porphyry intrusions were emplaced at shallow depth (≤1.3 km), with A-B–type quartz veinlet stockworks developed over a vertical interval of 300 to 400 m between ~100 and 500 m below sea level (bsl), 600 to 1,000 m below the present surface, which is at 400 to 600 m above sea level.In the area drilled at Onto, the diatreme breccia, all porphyry intrusions and, to a lesser extent, the surrounding older andesite sequence have all been overprinted by intense subhorizontal advanced argillic alteration, zoned downward from illite-smectite, quartz-dickite to quartz-alunite and quartz-pyrophyllite ± diaspore alteration. The alteration package includes two particularly well-developed zones of residual quartz with vuggy texture in subhorizontal zones at shallow depth, the upper one is still porous but the lower horizon, ~100 m thick, is largely silicified and is located at or near the top of the quartz-alunite alteration.Mineralization starts below the lowermost silicic horizon with more than 90% of the current resource in quartz-pyrophyllite-alunite and quartz-alunite alteration. Mineralization is dominated by a high-sulfidation assemblage of covellite-pyrite ± native sulfur largely in open-space fillings and replacements, but also as discrete pyrite-covellite and covellite only veins down to at least 1 km. Although the greatest amount of copper occurs as paragenetically late covellite deposited during formation of the advanced argillic alteration, approximately 60% of resource at 0.3% Cu cutoff still occurs within the porphyry stocks, indicating the porphyry stocks are a fundamental control on mineralization. There is considerable remobilization and dispersion of copper and, to a lesser extent, gold into the surrounding pre-mineral breccia and the late intermineral intrusions from the two earliest porphyry phases, resulting in quite consistent copper and gold grades throughout the currently delineated mineral resource. The very high sulfidation state of the mineralization is thought to be a consequence of the metal-bearing ore fluids cooling in the advanced argillic-altered host rocks in the absence of a rock buffer.Early chalcopyrite-bornite ± pyrite mineralization with potassic ± chloritic and sericitic alteration is only preserved on the margins of the system and more rarely at depth in a few holes 600 m bsl (~1,100 m below surface) but makes up only a small proportion (~8%) of the current resource.The Onto system is exceptionally young and formed rapidly in the middle Pleistocene and is not significantly eroded. A U-Pb zircon age for the andesite that caps the volcanosedimentary host rocks provides a maximum age of 0.838 ± 0.039 Ma, with a slightly younger porphyry zircon crystallization age of 0.688 ± 0.053 Ma. Re-Os dating of molybdenite that is associated with both the quartz vein stockwork and high-sulfidation assemblage copper mineralization shows overlap between 0.44 ± 0.02 and 0.35 ± 0.0011 Ma. ⁴⁰Ar/³⁹Ar ages for alunite within the advanced argillic alteration block ranges from 0.98 ± 0.22 to 0.284 ± 0.080 Ma, and alunite closely associated with covellite spans a period from 0.537 ± 0.064 to 0.038 ± 0.018 Ma.

中文翻译：

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印度尼西亚东苏巴瓦东古铜金矿发现：大型中新世岩性盖层高位硫化高锰锌铁矿-硫铁矿斑岩矿床

2013年，一个钻石钻探计划在印度尼西亚Sumbawa岛东部的Hu'u项目中测试了一个广泛的先进的泥质蚀变岩盖。发现了一个非常大的，盲目的铜金矿床（Onto），其中铜主要以散布的黄铁矿和黄铁矿的形式出现，并且在尺寸至少为1.5×1 km的板状块体中以黄铁矿-鹅卵石的细纹出现，垂直厚度≥ 1公里处的铜和金在空间上与一系列聚结的斑岩储层相关，这些斑岩储层侵入多学科的角砾岩角砾岩，这些角砾岩层积有一系列的层积内层积粉砂岩，火山碎屑岩和火山碎屑岩，并覆盖有安山岩流和穹顶。斑岩侵入体浅埋（≤1.3km），AB型石英细脉细木桩厂在海平面以下（bsl）〜100至500 m的垂直间隔为300至400 m，在海平面以上400至600 m的当前表层以下为600至1,000 m。在Onto钻出的地区，即角砾岩角砾岩，所有斑岩岩体侵入物，以及在较小程度上，周围的较老的安山岩层序，都被强烈的水平亚斜向高级泥质蚀变覆盖，从伊利石-蒙脱石，石英-白闪石到石英-石英亚矾石和石英叶蜡石±辉石蚀变。蚀变组合包括两个特别发达的残留石英带，它们在浅水平的亚水平带中呈孔状纹理，上面的仍然是多孔的，但是下面的水平，厚约100 m，矿化作用始于最低硅质层以下，矿化作用始于最低硅质层位以下，目前石英-叶蜡石-铝质和石英-铝质蚀变中的资源超过90％。矿化作用主要由露天矿填充物和替代物中的黄铁矿-黄铁矿（天然硫）的高硫化组成，但也包括离散的黄铁矿-黄铁矿和仅在至少1 km处的黄铁矿脉。尽管最大数量的铜是在高级泥质蚀变形成过程中沉积的方铅矿后期晚鹅卵石而出现的，但斑岩储量内仍有约60％的资源以0.3％的铜截断率存在，这表明斑岩储量是矿化的基本控制。铜的迁移和分散相当大，在较小程度上，金会进入周围的矿山前角砾岩，并且从两个最早的斑岩相开始进入后期的矿床间，从而在目前划分的矿产资源中产生相当一致的铜和金品位。矿化的极高硫化状态被认为是由于在没有岩石缓冲层的情况下，先进的改变了泥质的母岩中含金属的矿石流体冷却的结果。早期的黄铜矿-黄铁矿±黄铁矿的矿化与钾的±氯酸和浆液性蚀变仅保留在系统边缘，很少在深度600 m bsl（约地下1,100 m）的孔中保留，但仅占现有资源的一小部分（〜8％）。是异常年轻，并在中更新世迅速形成，并没有显着侵蚀。覆盖火山成岩主岩的安山岩的U-Pb锆石年龄最大年龄为0.838±0.039 Ma，斑岩锆石的结晶年龄稍年轻，为0.688±0.053 Ma。与石英脉储层和高硫化组合铜矿化作用有关的辉钼矿的Re-Os测年显示出0.44±0.02和0.35±0.0011 Ma之间的重叠。晚期泥质蚀变块体中亚铝石的⁴⁰ Ar / ³⁹ Ar年龄为0.98±0.22至0.284±0.080 Ma，与陨石紧密相关的亚铝石的周期为0.537±0.064至0.038±0.018 Ma。