Abstract

The Matangkaka manganese deposit is an unusual Quaternary epithermal stratabound manganese oxide deposit from Ambitle Island in the Feni Island Group, New Ireland Province, Papua New Guinea. Ambitle is a small volcanic island that has undergone Quaternary explosive and effusive volcanic activity. Oldest volcanic rocks on the island consist of mafic–intermediate lavas and epiclastic rocks of the Pleistocene Ambitle Volcano (Waramung Volcanics). These rocks rest unconformably on Oligocene calcilutites of the New Ireland Basin. The summit of Ambitle Volcano is now modified as a semi-circular topographic rim around Nanum Valley, known as the Nanum Valley Crater. This crater formed during gravity induced failure (or sector collapse) of the southwest flanks of the summit of Ambitle Volcano. Ambitle Crater is a resurgent Pleistocene–Holocene crater located within the summit crater of Ambitle Volcano. Deposits of resurgent volcanism include block and ash deposits, mafic–intermediate lavas, trachyte lavas, tephra and lacustrine sediments (Babamis Volcanics). Two new members are described from the Babamis Volcanics (Nanmikit Trachyte Member and Danmagal Tephra Member). The tephra member is the youngest deposit in the Plio-Pleistocene Tabar–Lihir–Tanga–Feni alkalic volcanic arc. Three new intrusive units are described (Kabang Syenite, Matangkaka Monzonite and Saddle Monzonite). The Saddle hydrothermal system (new name) is an active geothermal system, elongated along the arc-parallel northwest-trending Niffin structural zone. The Matangkaka occurrence is classified as a Mn–Fe–Cu–Mo deposit. Active northwest-trending structures and northeast-trending faults allowed sea water to circulate to depth, leach metals from basement and overlying volcaniclastic rocks and ascend to shallow levels. Manganese mineralisation was deposited in shallow marine conditions, focussed in porous and permeable volcaniclastic units and forming 3–4 m-thick bedded deposits. Circulating neutral chloride waters of the Saddle hydrothermal system played a key role in the deposition of manganese in porous and permeable volcaniclastic units. Mineralising fluids were probably $\le$120 °C.

1. KEY POINTS

2. The Matangkaka manganese deposit is an unusual Quaternary epithermal stratabound manganese oxide deposit on Ambitle Island in the Feni Island Group, Tabar–Lihir–Tanga–Feni alkalic volcanic arc, New Ireland Province, Papua New Guinea.

3. Ambitle Island is a small volcanic island that has undergone Pleistocene–Holocene explosive and effusive volcanic activity. Active fractures have allowed sea water to circulate to depth, leach metals from basement and overlying volcaniclastic rocks and convect to shallow levels.

4. Manganese mineralisation was deposited by neutral chloride waters, probably $\le$120°C. Y/Ho ratios indicate there was a sea water component to mineralising fluids. The manganese occurrence is classified as a Mn–Fe–Cu–Mo deposit.

5. Manganese mineralisation was deposited in shallow marine conditions, focussed in porous and permeable volcaniclastic units, and forming 3–4 m-thick bedded deposits.

摘要

Matangkaka 锰矿床是巴布亚新几内亚新爱尔兰省费尼岛群 Abitle 岛的一个不寻常的第四纪浅成热液层状氧化锰矿床。Ambtle 是一个小火山岛，经历了第四纪爆发和喷涌的火山活动。岛上最古老的火山岩由更新世 Ambitle 火山 (Waramung Volcanics) 的镁铁质中级熔岩和史诗碎屑岩组成。这些岩石不整合地位于新爱尔兰盆地的渐新世方解石上。Ambitle火山的山顶现在被修改为围绕Nanum Valley的半圆形地形边缘，被称为Nanum Valley Crater。这个火山口是在 Ambtle Volcano 山顶西南侧的重力引起的破坏（或扇区坍塌）期间形成的。安比特尔火山口是一个复活的更新世-全新世火山口，位于安比特尔火山的山顶火山口内。复活火山的沉积物包括块状和灰烬沉积物、镁铁质中质熔岩、粗面岩熔岩、火山灰和湖相沉积物（巴巴米斯火山）。描述了来自 Babamis Volcanics 的两个新成员（Nanmikit Trachyte 成员和 Danmagal Tephra 成员）。tephra 段是 Plio-Pleistocene Tabar-Lihir-Tanga-Feni 碱性火山弧中最年轻的矿床。描述了三个新的侵入单元（Kabang Syenite、Matangkaka Monzonite 和 Saddle Monzonite）。马鞍热液系统（新名称）是一个活跃的地热系统，沿弧平行西北向的尼芬构造带延伸。Matangkaka 矿床被归类为 Mn-Fe-Cu-Mo 矿床。活跃的西北向构造和东北向断层使海水循环到深处，从基底和上覆火山碎屑岩中浸出金属并上升到浅层。锰矿化沉积在浅海条件下，集中在多孔和可渗透的火山碎屑单元中，形成 3-4 m 厚的层状沉积物。萨德尔热液系统的循环中性氯化物水在多孔和可渗透火山碎屑单元中锰的沉积中发挥了关键作用。矿化流体可能是 集中在多孔和可渗透的火山碎屑单元，形成 3-4 米厚的层状沉积物。萨德尔热液系统的循环中性氯化物水在多孔和可渗透火山碎屑单元中锰的沉积中发挥了关键作用。矿化流体可能是 集中在多孔和可渗透的火山碎屑单元，形成 3-4 米厚的层状沉积物。萨德尔热液系统的循环中性氯化物水在多孔和可渗透火山碎屑单元中锰的沉积中发挥了关键作用。矿化流体可能是$\le$120℃。

1. 关键点

2. Matangkaka锰矿床是巴布亚新几内亚新爱尔兰省Tabar-Lihir-Tanga-Feni碱性火山弧Feni岛群Ambitle岛上的一个不寻常的第四纪浅成热液层状锰氧化物矿床。

3. 安比特尔岛是一个小型火山岛，经历了更新世-全新世爆发和喷涌的火山活动。活跃的裂缝使海水循环到深处，从基底和上覆的火山碎屑岩中浸出金属，并对流到浅层。

4. 锰矿化是由中性氯化物水沉积的，可能 $\le$120℃。Y/Ho 比率表明矿化流体中存在海水成分。锰矿被归类为 Mn-Fe-Cu-Mo 矿床。

5. 锰矿化沉积在浅海条件下，集中在多孔和可渗透的火山碎屑单元中，形成 3-4 m 厚的层状沉积物。