Magnetite geochemistry as a proxy for metallogenic processes: A study on sulfide-mineralized mafic–ultramafic intrusions peripheral to the Kunene Complex in Angola and Namibia

IF 4.4 2区 地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS Mineralium Deposita Pub Date : 2024-06-19 DOI:10.1007/s00126-024-01288-x
Lorenzo Milani, Lize Oosthuizen, Trishya M. Owen-Smith, Grant M. Bybee, Ben Hayes, Jérémie Lehmann, Hielke A. Jelsma
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Abstract

Trace element concentrations in magnetite are dictated by the petrogenetic environment and by the physico-chemical conditions during magmatic, hydrothermal, or sedimentary processes. This makes magnetite chemistry a useful tool in the exploration of ore-forming processes. We describe magnetite compositions from Ni-Cu-(PGE)-sulfide mineralized rocks from seven mafic–ultramafic intrusions peripheral to the Mesoproterozoic AMCG (anorthosite-mangerite-charnockite-granite) suite of the Kunene Complex of Angola and Namibia to investigate metallogenic processes through the geochemical characterization of Fe-oxides, which were analyzed in-situ via Electron Probe Microanalysis (EPMA), and Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS). We identified magmatic magnetite, segregated from both a silicate liquid and an immiscible sulfide liquid. Elements like Cr, Co and V suggest that the sulfide-related magnetite segregated from a relatively primitive Fe-rich monosulfide solid solution (MSS). Secondary Cr-rich magnetite appears in intrusions with abundant chromite or Cr-spinel. Two types of hydrothermal magnetite were identified, related to the pervasive replacement of sulfides and a late-stage, low-T fluid circulation event. Magnetite replacing sulfides is associated with serpentinized ultramafic rocks and is preferentially observed in the intrusions with the highest base and precious metal tenors. The high concentration of Ni, Co, Cu, Pd, As and Sb in these grains is corroborated by the identification of micron-size PGE mineral inclusions. We infer that serpentinization during hydrothermal fluid circulation was accompanied by desulphurization of sulfides with metal remobilization and reconcentration to generate magnetite carrying Pd microinclusions. We suggest that the highly serpentinized ultramafic rocks in the Kunene Complex region may become a possible target for economic Ni-Cu-(PGE) mineralization.

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磁铁矿地球化学作为成矿过程的替代物:对安哥拉和纳米比亚库内内复合体周边硫化物矿化黑云母-超黑云母侵入体的研究
磁铁矿中的微量元素浓度取决于岩浆、热液或沉积过程中的成岩环境和物理化学条件。这使得磁铁矿化学成为探索成矿过程的有用工具。我们描述了来自安哥拉和纳米比亚库内内复合体中新生代 AMCG(阳起石-芒硝-石榴石-花岗岩)岩组外围七个黑云母-超黑云母侵入体的镍-铜-(PGE)-硫化物矿化岩的磁铁矿成分,以通过铁氧体的地球化学特征研究成矿过程、通过电子探针显微分析法(EPMA)和激光烧蚀-电感耦合等离子体质谱法(LA-ICP-MS)对其进行了现场分析。我们发现了从硅酸盐液体和不溶硫化物液体中分离出来的岩浆磁铁矿。铬、钴和钒等元素表明,与硫化物有关的磁铁矿是从相对原始的富铁单硫化物固溶体(MSS)中分离出来的。次生富铬磁铁矿出现在具有丰富铬铁矿或铬尖晶石的侵入体中。已发现两种类型的热液磁铁矿,分别与硫化物的普遍置换和晚期低T流体循环事件有关。取代硫化物的磁铁矿与蛇纹岩化的超基性岩有关,并优先出现在贱金属和贵金属含量最高的侵入体中。这些晶粒中含有高浓度的镍、钴、铜、钯、砷和锑,微米级的 PGE 矿物包裹体也证实了这一点。我们推断,热液循环过程中的蛇纹石化伴随着硫化物的脱硫,金属的再移动和再富集生成了携带钯的磁铁矿微包裹体。我们认为,库内内复合区高度蛇化的超基性岩可能成为经济镍-铜(PGE)矿化的目标。
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来源期刊
Mineralium Deposita
Mineralium Deposita 地学-地球化学与地球物理
CiteScore
11.00
自引率
6.20%
发文量
61
审稿时长
6 months
期刊介绍: The journal Mineralium Deposita introduces new observations, principles, and interpretations from the field of economic geology, including nonmetallic mineral deposits, experimental and applied geochemistry, with emphasis on mineral deposits. It offers short and comprehensive articles, review papers, brief original papers, scientific discussions and news, as well as reports on meetings of importance to mineral research. The emphasis is on high-quality content and form for all articles and on international coverage of subject matter.
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