Primary source of titanomagnetite ores at the Orokolo Bay placer deposit: Implications for petrogenesis

IF 1.1 4区 地球科学 Q3 GEOLOGY
Resource Geology Pub Date : 2024-08-13 DOI:10.1111/rge.12337
Leeysmon Hulijeli, Yasushi Watanabe, Osamu Nishikawa, Carmela Alen J. Tupaz
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Abstract

Coastal and river sand sequences of Holocene age at Orokolo Bay in Papua New Guinea are host to secondary titanomagnetite ore deposits. The resource developer (Mayur Resources) declares a measured orebody of 139 million tons at grades of 11.35% Fe, 1.94% Ti, and 712 ppm Zr. Orokolo Bay is located near the boundary between the Papuan Thrust and Fold Belt and the Aure Fold Belt. This region is characterized by sedimentary rocks of the Papuan Basin, which are intruded and overlain by a diverse array of magmatic intrusive and volcanic rocks, ranging from mafic alkaline to felsic calc‐alkaline types related to arc–continent collisions in the Cenozoic. The Vailala and Purari rivers located to the east and west of Orokolo Bay, respectively, are the main sediment pathways. Earlier provenance studies have suggested that the deposited sediments mainly come from the erosion of volcanic rocks found within the catchments of these two rivers. However, these studies did not specifically identify the primary source of the Fe‐Ti ores within this region. Here, we report on a potential primary source of the Fe‐Ti ores by examining the occurrence and chemical compositions for detrital titanomagnetites, and associated pyroxene and amphibole minerals. The purpose of this was to discern specific attributes of the primary source for its identification. Lithic sediments comprised of magnesio‐hornblende (Mhbl), tschermakaite (Tsr) and magnesio‐hastingsite (Mhst) amphiboles, clinopyroxene (Cpx), and Fe‐Ti oxide minerals dominate the heavy sands. Feldspar is more abundant than quartz, and Cr‐spinel is rare. Two primary titanomagnetite types were categorized based on their homogeneous grain textures and TiO2 content, Tmt1 (average 28 wt% TiO2) and Tmt2 (average 7 wt% TiO2). Pleonaste exsolutions and zircon inclusions distinguish Tmt1 from Tmt2, while apatite and quenched glass inclusions occur in both. A portion of both primary titanomagnetites exhibits hydrothermal overprinting, this subset was categorized as Tmt3 (average 12.5 wt% TiO2). Fe‐Ti oxides are associated with Cpx and amphiboles as inclusions, and as pseudomorphs in opacitic amphiboles. Tmt1 coexists predominantly with Mhst‐Tsr but also appears less frequently with Mhbl and Cpx. Tmt2 occurs almost exclusively with Mhbl and Cpx. Titanomagnetite chemistry is low in Cr, Mg, and V content suggesting crystallization from evolved melts. Tmt3 is shows enriched Si, Ca, Al, and Mg concentrations that are characteristic of late‐stage fluids derived from calcareous rocks. Amphibole and Cpx chemistry indicate they were derived from a subalkaline source magma of arc affinity. Fe‐Ti thermobarometry reveals Tmt1 (990 to 967°C, −0.51 to −0.18 ΔNNO) formed at higher temperatures and in less oxidized conditions than Tmt2 (834 to 689°C, 0.33 to 3.2 ΔNNO). Amphibole thermobarometry reveals Mhst‐Tsr and Mhbl formed under similar conditions as Tmt1 and Tmt2, respectively. The lack of Cr‐spinel, olivine, and the abundant occurrence of zircon and Mhbl indicate an evolved subalkaline source characterized by felsic rocks related to arc magmatism. The only volcanic source which aligns with these characteristics is Mount Yelia within the Vailala River catchment. Compositional variation between Tmt1 and Tmt2 titanomagnetites and associated silicate minerals is attributed to heterogeneous temperature and ƒO2 conditions within the melt during crystallization. The provenance of Ti‐rich titanomagnetite ores from sources related to arc magmatism indicates the potential of other areas associated with arc activity in Papua New Guinea to host secondary deposits rich in Fe‐Ti ores.
奥罗科洛湾块状矿床榍石矿石的主要来源:对岩石成因的影响
巴布亚新几内亚奥罗科罗海湾全新世时期的海岸和河沙序列是次生钛磁铁矿矿床的所在地。资源开发商(Mayur Resources)宣布,该矿床的实测矿体储量为 1.39 亿吨,铁品位为 11.35%,钛品位为 1.94%,锆品位为 712 ppm。奥罗科罗湾位于巴布亚推覆褶皱带和奥雷褶皱带的边界附近。该地区的特征是巴布亚盆地的沉积岩,这些沉积岩被各种岩浆侵入岩和火山岩侵入和覆盖,这些岩浆侵入岩和火山岩从岩浆碱性岩到长纤维钙碱性岩类型不等,与新生代弧-大陆碰撞有关。分别位于奥罗科洛湾东部和西部的维拉拉河和普拉里河是主要的沉积物通道。早期的出处研究表明,沉积物主要来自这两条河流流域内火山岩的侵蚀。但是,这些研究并没有具体确定该地区铁钛矿石的主要来源。在此,我们通过研究碎屑钛磁铁矿以及相关辉石和闪石矿物的出现和化学成分,报告了铁钛矿石的潜在主要来源。这样做的目的是为了识别原生矿源的具体属性。由菱镁角闪石(Mhbl)、菱镁辉石(Tsr)和菱镁霞石(Mhst)闪石、辉石(Cpx)以及铁-钛氧化物矿物组成的石质沉积物在重砂中占主导地位。长石的含量高于石英,而铬尖晶石则很少见。根据均匀的晶粒纹理和 TiO2 含量,将钛磁铁矿分为两种主要类型:Tmt1(TiO2 平均含量为 28 wt%)和 Tmt2(TiO2 平均含量为 7 wt%)。辉石外溶体和锆石包裹体是 Tmt1 和 Tmt2 的显著特征,而磷灰石和淬火玻璃包裹体在两者中均有出现。两种原生钛磁铁矿中都有一部分呈现热液叠印,这部分被归类为 Tmt3(平均 TiO2 含量为 12.5 wt%)。Fe-Ti氧化物作为包裹体与Cpx和闪长岩伴生,并作为乳白闪长岩中的假象体。Tmt1 主要与 Mhst-Tsr 共存,但也较少与 Mhbl 和 Cpx 共存。Tmt2 几乎只与 Mhbl 和 Cpx 共存。钛磁铁矿化学成分中的铬、镁和钒含量较低,这表明它们是从进化熔体中结晶出来的。钛磁铁矿化学成分中的硅、钙、铝和镁含量较高,这是钙质岩后期流体的特征。闪石和Cpx的化学成分表明,它们来自与弧岩亲缘的亚碱性源岩浆。铁-钛热压仪显示,Tmt1(990 至 967°C,-0.51 至 -0.18 ΔNNO)是在比 Tmt2(834 至 689°C,0.33 至 3.2 ΔNNO)更高的温度和更低的氧化条件下形成的。闪石热压计显示,Mhst-Tsr 和 Mhbl 分别是在与 Tmt1 和 Tmt2 相似的条件下形成的。由于缺乏铬尖晶石和橄榄石,而锆石和 Mhbl 又大量存在,这表明该地区是一个以与弧状岩浆活动有关的长英岩为特征的演化亚碱性岩源。唯一符合这些特征的火山源是维拉拉河流域内的耶利亚山。Tmt1 和 Tmt2 钛磁铁矿及相关硅酸盐矿物之间的成分差异归因于结晶过程中熔体内部的异质温度和 ƒO2 条件。与弧岩浆活动有关的富钛钛磁铁矿的来源表明,巴布亚新几内亚与弧岩活动有关的其他地区有可能蕴藏着富含铁钛矿石的二次矿床。
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来源期刊
Resource Geology
Resource Geology 地学-地质学
CiteScore
2.30
自引率
14.30%
发文量
18
审稿时长
12 months
期刊介绍: Resource Geology is an international journal focusing on economic geology, geochemistry and environmental geology. Its purpose is to contribute to the promotion of earth sciences related to metallic and non-metallic mineral deposits mainly in Asia, Oceania and the Circum-Pacific region, although other parts of the world are also considered. Launched in 1998 by the Society for Resource Geology, the journal is published quarterly in English, making it more accessible to the international geological community. The journal publishes high quality papers of interest to those engaged in research and exploration of mineral deposits.
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