Abstract The Southwest Pacific region, and Papua New Guinea in particular, is spectacularly endowed with mineral resources, including some of the youngest and richest porphyry Cu-Mo-Au deposits in the world. Among them is the giant porphyry-epithermal Ladolam Au deposit on Lihir Island in the Tabar-Lihir-Tanga-Feni (TLTF) island chain, northeast of New Ireland. Its setting within a former forearc basin is very different from most Southwest Pacific porphyry and epithermal deposits. Our synthesis of published and previously unreleased data from ship-based multibeam and seismic studies, satellite gravimetry, geochemistry and geochronology reveals a far more complex crustal structure and composition than is presently understood from the geology of the islands alone. We show that the unique regional Au endowment results from the alignment of various preconditions that are prolific to ore formation: i) hydrous and metal-rich metasomatic veins in the mantle source, ii) second-stage, low volume partial melting due to incipient rifting, iii) high volatile contents and oxygen fugacities of the melts due to preferential melting of hydrous phases in the metasomatic veins, and iv) in the specific case of Lihir, unroofing of the volcanic edifice that led to boiling and rapid metal deposition. This study shows that the location of the Ladolam deposit on Lihir is controlled by large-scale structures that can be traced offshore and are the site of continuing submarine volcanism and epithermal-style Au mineralization. The observed structural framework is dominated by the emergence of trans-lithospheric faults that provided pathways for the melts to the seafloor, near-surface structural focusing of the ascending melts and fluids, and a regional tectonic stress regime that stabilized the conditions over a significant period of time and/or repeatedly. Marine seismic data confirms the complex structure of the TLTF island chain. Each island group sits on tilted blocks that form horst structures separated by half grabens developed due to regional NW-SE-directed extension. Regional compression perpendicular to the extension continues as a result of the transition from subduction to collision at the leading edge of the Ontong Java Plateau. The protracted, transtensional motion between distinct crustal blocks controls the location and timing of magmatism and mineralization. A kinematic link between volcanism at the location of Lihir and the splitting of New Ireland by NE-directed propagation of seafloor spreading in the Manus Basin is suspected. By combining onshore and offshore geology, we propose a new model of the evolution of the New Ireland Basin, magmatism along the TLTF island chain and ultimately ore deposit formation. This study demonstrates the importance of integrating offshore geology and geophysics into models that aim to explain the structural, magmatic, and sedimentary evolution of marginal basins that are host to economic mineral deposits.

中文翻译：

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Tabar-to-Feni岛链中Cu-Au赋存的海底构造岩浆框架，PNG

摘要 西南太平洋地区，特别是巴布亚新几内亚，矿产资源得天独厚，其中包括一些世界上最年轻、最丰富的斑岩铜钼金矿床。其中包括位于新爱尔兰东北部 Tabar-Lihir-Tanga-Feni (TLTF) 岛链 Lihir 岛上的巨型斑岩-浅成热液 Ladolam Au 矿床。它位于前弧前盆地内的环境与大多数西南太平洋斑岩和浅成热液矿床大不相同。我们对来自舰载多波束和地震研究、卫星重力测量、地球化学和地质年代学的已发表和以前未发表的数据进行了综合，揭示了比目前仅从岛屿地质学中所理解的地壳结构和组成要复杂得多。我们表明，独特的区域金禀赋是由于各种促成矿石形成的先决条件的排列：i) 地幔源中的含水和富含金属的交代脉，ii) 由于初期裂谷而导致的第二阶段、低体积部分熔融, iii) 由于交代脉中水相的优先熔化，熔体的高挥发性含量和氧逸度，以及 iv) 在 Lihir 的特定情况下，火山建筑物的屋顶开裂导致沸腾和快速金属沉积。这项研究表明，Ladolam 矿床位于 Lihir 的位置受大型构造控制，这些构造可以在海上追踪，并且是持续的海底火山作用和低温热液型 Au 矿化的场所。观察到的结构框架主要是跨岩石圈断层的出现，为熔体提供了通往海底的通道，上升的熔体和流体的近地表结构集中，以及在很长一段时间内稳定条件的区域构造应力状态时间和/或反复。海洋地震数据证实了 TLTF 岛链的复杂结构。每个岛群都坐落在倾斜的块体上，形成地垒结构，由由于区域 NW-SE 定向延伸而形成的半地堑隔开。由于 Ontong Java 高原前缘从俯冲过渡到碰撞，垂直于伸展的区域压缩继续存在。旷日持久的，不同地壳块体之间的张力运动控制着岩浆作用和成矿作用的位置和时间。怀疑 Lihir 位置的火山活动与马努斯盆地的海底扩张的 NE 定向传播导致的新爱尔兰分裂之间存在运动学联系。通过结合陆上和海上地质，我们提出了新爱尔兰盆地演化、TLTF 岛链沿线岩浆作用以及最终矿床形成的新模型。这项研究证明了将近海地质学和地球物理学整合到旨在解释拥有经济矿床的边缘盆地的结构、岩浆和沉积演化的模型中的重要性。怀疑 Lihir 位置的火山活动与马努斯盆地的海底扩张的 NE 定向传播导致的新爱尔兰分裂之间存在运动学联系。通过结合陆上和海上地质，我们提出了新爱尔兰盆地演化、TLTF 岛链沿线岩浆作用以及最终矿床形成的新模型。这项研究证明了将近海地质学和地球物理学整合到旨在解释拥有经济矿床的边缘盆地的结构、岩浆和沉积演化的模型中的重要性。怀疑 Lihir 位置的火山活动与马努斯盆地的海底扩张的 NE 定向传播导致的新爱尔兰分裂之间存在运动学联系。通过结合陆上和海上地质，我们提出了新爱尔兰盆地演化、TLTF 岛链沿线岩浆作用以及最终矿床形成的新模型。这项研究证明了将近海地质学和地球物理学整合到旨在解释拥有经济矿床的边缘盆地的结构、岩浆和沉积演化的模型中的重要性。