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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 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
IF 4.8 2区 地球科学 Q1 Earth and Planetary Sciences 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

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.

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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引用次数: 0
Magmatic to aqueous phase transition in Li-pegmatite: microtextural and geochemical study of muscovite–lepidolite from Boam mine area, Uljin, South Korea 锂辉石中从岩浆到水相的转变:韩国蔚珍 Boam 矿区麝香石-鳞片岩的显微质构和地球化学研究
IF 4.8 2区 地球科学 Q1 Earth and Planetary Sciences Pub Date : 2024-06-14 DOI: 10.1007/s00126-024-01286-z
Woohyun Choi, Changyun Park, Chul-Ho Heo, Seok-Jun Yang, Il-Hwan Oh, Kyung Su Park, Sung Hwa Choi

This study investigated the Boam mine area, a prominent Li-pegmatite deposits located in South Korea, using Li-bearing micas to determine the magmatic–aqueous transition involved in rare-element pegmatite formation. Muscovite–lepidolite series micas from the layered pegmatite exhibited six textures, classified into three stages (early, intermediate, and late) based on compositions of major and trace elements. The substitution mechanisms of muscovite–lepidolite series micas follow lithium fixation (Si ↔ Li + Al) and phengitic substitution (Aliv + 2Alvi ↔ Li + (Fe2+, Mg2+, Mn2+) + Si) vectors. Early-stage micas displayed a large grain size due to rapid crystal growth due from low undercooling. Diffusional zonation of these micas with the higher Nb–Ta and lower Li concentrations compared with later-stage lepidolite indicate a lower degree of fractionation. These features suggest a silicic melt origin for early-stage micas. Intermediate-stage micas are distinctly separated from the early-stage type and feature erratic boundaries with higher Li composition. B enrichment reduced the melt viscosity and increased the H2O solubility, resulting in an increase in growth rate and retardation of mineralization. The inhibition of HFSE partitioning by B lead to a lower Nb–Ta concentration than the silicic melt, suggesting the existence of an aqueous melt. Fine-grained late-stage mica coexists with microcrystalline quartz, and is characterized by Cs enrichment and Nb–Ta depletion that exclusively occur in flux-rich aqueous fluids. Non-Rayleigh behavior of K-Rb-Cs indicates a deviation from fractional crystallization unlike melt phases, suggesting an aqueous fluid origin for late-stage micas. Consequently, the formation of Li-pegmatite in the deposit was predominantly controlled by the immiscibility of silicic melt–aqueous melt–aqueous fluid and fractional crystallization within each medium.

这项研究利用含锂云母对位于韩国的著名锂辉石矿床 Boam 矿区进行了调查,以确定稀有元素伟晶岩形成过程中的岩浆-水转变。层状伟晶岩中的麝香石-鳞片岩系列云母表现出六种质地,根据主要元素和微量元素的组成分为三个阶段(早期、中期和晚期)。黝帘石-鳞片岩系列云母的置换机制遵循锂固定(Si ↔ Li + Al)和辉石置换(Aliv + 2Alvi ↔ Li + (Fe2+, Mg2+, Mn2+) + Si)矢量。早期阶段的云母由于低过冷度导致晶体快速增长而显示出较大的晶粒尺寸。与后期的鳞片岩相比,这些云母的扩散带具有较高的铌-钽浓度和较低的锂浓度,表明其分馏程度较低。这些特征表明早期云母起源于硅质熔体。中期云母与早期云母截然不同,边界不稳定,锂含量较高。硼的富集降低了熔体的粘度,增加了H2O的溶解度,导致生长速度加快,矿化速度减慢。B 对 HFSE 分配的抑制导致 Nb-Ta 浓度低于硅质熔体,这表明存在水熔体。细粒晚期云母与微晶石英共存,其特征是铯富集和铌钽贫化,而这只发生在通量丰富的水成岩流体中。K-Rb-Cs 的非瑞利行为表明,与熔融相不同,它偏离了部分结晶,这表明晚期云母起源于水流。因此,矿床中锂辉石的形成主要受控于硅熔体-水熔体-水液的不溶性以及每种介质中的分部结晶。
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引用次数: 0
Petrogenesis of Ni-sulfide mineralisation in the ca. 3.0 Ga Maniitsoq intrusive belt, western Greenland 格陵兰岛西部约 3.0 Ga 的 Maniitsoq 侵入带中硫化镍矿化的成岩作用格陵兰西部 3.0 Ga Maniitsoq 侵入带中的镍硫化物成矿作用
IF 4.8 2区 地球科学 Q1 Earth and Planetary Sciences Pub Date : 2024-06-13 DOI: 10.1007/s00126-024-01282-3
Wolfgang D. Maier, D. D. Muir, S-. J. Barnes, K. Szilas

The ca. 3.0 Ga Ni sulfide mineralisation at Maniitsoq, SW Greenland, is hosted by a cluster of relatively small, irregularly shaped mafic-ultramafic intrusions, typically 10s of m to a few km across, that are lodged within broadly coeval gneiss. Many of the intrusions are fault bounded and fragmented so that their original sizes remain unknown. The sulfides form disseminations and sulfide matrix breccia veins displaying sharp contacts to the host intrusives. The mineralisation has relatively high Ni/Cu, with 4–10% Ni and 1–2% Cu. Correlations between Ni and Cu with sulfide content are strong, consistent with a magmatic origin of the mineralisation. PGE contents are mostly below 0.5 ppm, and Cu/Pd is typically above primitive mantle levels, interpreted to reflect equilibration of the parent magma with segregating sulfide melt prior to final magma emplacement. Sulfide segregation was likely triggered by assimilation of crustal sulfur, as suggested by whole rock S/Se ratios of 7000–9000. The sulfide melt underwent extensive fractionation after final emplacement, caused by downward percolation of Cu-rich sulfide melt through incompletely solidified cumulates. We suggest that the exposed Maniitsoq intrusions represent the Ni-rich upper portions of magma conduits implying that there is potential for Cu-rich sulfides in unexposed deeper portions of the belt.

格陵兰西南部马尼特索克的约格陵兰岛西南部马尼特索克的3.0 Ga硫化镍矿化物是由一组相对较小、形状不规则的黑云母-超黑云母侵入体形成的,这些侵入体的直径通常在10米到几千米之间,被固定在大致共生的片麻岩中。许多侵入体受到断层的束缚而支离破碎,因此它们原来的大小仍然不得而知。硫化物形成散布和硫化物基质角砾岩脉,与主侵入体有明显的接触。矿化物的镍/铜含量相对较高,镍含量为 4-10% ,铜含量为 1-2%。镍和铜与硫化物含量之间的相关性很强,这与矿化的岩浆起源相一致。PGE 含量大多低于 0.5 ppm,Cu/Pd 通常高于原始地幔水平,这反映了母岩浆与分离硫化物熔体在最终岩浆喷放之前的平衡。整个岩石的S/Se比值为7000-9000,这表明硫化物分离可能是由地壳硫同化引发的。硫化物熔体在最终喷出后经历了广泛的分馏,这是由于富含铜的硫化物熔体通过未完全凝固的堆积物向下渗透造成的。我们认为,裸露的马尼措克侵入体代表了岩浆导管的富镍上部,这意味着在该岩带未裸露的深部可能存在富铜硫化物。
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引用次数: 0
Using zircon and apatite chemistry to fingerprint porphyry Cu – Mo ± Au mineralization in the Delamerian Orogen, South Australia 利用锆石和磷灰石化学特征描述南澳大利亚德拉梅利亚造山带斑岩铜-钼±金矿化过程
IF 4.8 2区 地球科学 Q1 Earth and Planetary Sciences Pub Date : 2024-06-07 DOI: 10.1007/s00126-024-01287-y
Wei Hong, Adrian Fabris, Sarah Gilbert, Benjamin P. Wade, Alan S. Collins, Tom Wise, Anthony J. Reid

To evaluate the fertility of porphyry mineralization in the Delamerian Orogen (South Australia), zircon and apatite from four prospects, including Anabama Hill, Netley Hill, Bendigo, and Colebatch, have been analyzed by LA-ICP-MS and electron microprobe. The zircon is characterized by heavy REEs enrichment relative to light REEs, high (Ce/Nd)N (1.3–45), and weak to moderate negative Eu/Eu* (0.2–0.78). The apatite has right-sloped REE patterns with variably negative to positive Eu anomalies. Low Mg (< 670 ppm) and Sr/Y ratios (< 5) in apatite likely illustrate fractional crystallization trends for the granitic melts in shallow crust. The Yb/Gb and Eu/Eu* in zircon reveal that intrusions at Anabama Hill, Netley Hill, and Bendigo underwent fractional crystallization controlled by amphibole (< 50–60%), garnet (< 15%), apatite (< 0.6%), and/or titanite (< 0.3%). These stocks have average fO2 values reported relative to fayalite-magnetite-quartz buffer (ΔFMQ), from 0.7 ± 0.9 to 2.1 ± 0.4, ascribed to prolonged magmatic evolution or sulfur degassing during post-subduction processes. Our data imply that both Anabama and Bendigo complexes experienced prevalent (garnet-) amphibole crystallization from hydrous melts that have moderately high oxidation (ΔFMQ + 1 to + 3) and elevated sulfur-chlorine components (Anabama, 37 ± 9 to 134 ± 83 ppm S and 0.30 ± 0.24 to 0.64 ± 0.89 wt% Cl; Bendigo, 281 ± 178 to 909 ± 474 ppm S and 0.45 ± 0.47 to 3.01 ± 1.54 wt% Cl). These are crucial ingredients to form porphyry Cu–Mo ± Au ores with economic significance, which provides encouragement for mineral exploration in this orogen.

为了评估德拉梅里安造山(南澳大利亚)斑岩矿化的富集程度,我们采用 LA-ICP-MS 和电子微探针对 Anabama Hill、Netley Hill、Bendigo 和 Colebatch 等四个探矿区的锆石和磷灰石进行了分析。锆石的特征是重型 REEs 相对于轻型 REEs 富集,(Ce/Nd)N 高(1.3-45),Eu/Eu* 为弱至中等负值(0.2-0.78)。磷灰石具有右倾的 REE 模式,Eu 异常由负变正。磷灰石中较低的镁(670 ppm)和锶/钇比值(5)很可能说明了浅地壳花岗岩熔体的碎裂结晶趋势。锆石中的Yb/Gb和Eu/Eu*显示,Anabama Hill、Netley Hill和Bendigo的侵入体经历了由闪石(50-60%)、石榴石(15%)、磷灰石(0.6%)和/或榍石(0.3%)控制的分块结晶。据报道,相对于辉绿岩-磁铁矿-石英缓冲区(ΔFMQ),这些储量的平均 fO2 值从 0.7 ± 0.9 到 2.1 ± 0.4 不等,这归因于岩浆演化时间过长或俯冲后过程中的硫脱气。我们的数据表明,Anabama 和 Bendigo 复合物都经历了从水化物熔体中普遍(石榴石-)闪石结晶的过程,这些熔体具有中等程度的高氧化性(ΔFMQ + 1 至 + 3)和较高的硫-氯成分(Anabama,37 ± 9 至 134 ± 83 ppm S 和 0.30 ± 0.24 至 0.64 ± 0.89 wt% Cl;Bendigo,281 ± 178 至 909 ± 474 ppm S 和 0.45 ± 0.47 至 3.01 ± 1.54 wt% Cl)。这些都是形成具有经济意义的斑岩铜-钼-金矿石的关键成分,这为在该造山带进行矿产勘探提供了动力。
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引用次数: 0
New insights on the formation of the polymetamorphic Felbertal tungsten deposit (Austria, Eastern Alps) revealed by CL, EPMA, and LA-ICP-MS investigation 通过CL、EPMA和LA-ICP-MS调查揭示多变质Felbertal钨矿床(奥地利,东阿尔卑斯山)形成的新见解
IF 4.8 2区 地球科学 Q1 Earth and Planetary Sciences Pub Date : 2024-06-02 DOI: 10.1007/s00126-024-01284-1
Cordula P. Haupt, Joachim Krause, Bernhard Schulz, Jens Götze, Johannes Chischi, Jasper Berndt, Stephan Klemme, Steffen Schmidt, Karsten Aupers, Nils Reinhardt

The Felbertal tungsten deposit is the only economic scheelite mine in Europe, yet its genesis is not fully understood. It has been argued recently that the formation of the deposit is most likely related to granitic intrusions of Variscan age, contrasting a previously suggested syn-depositional stratabound origin of Early Cambrian age. Solving this controversy remains challenging due to the polymetamorphic evolution of the deposit, which experienced both Variscan and Alpine metamorphism. In this contribution we present a comprehensive new data set of scheelite major, minor, and trace element concentrations from multiple scheelite generations of the Felbertal deposit along with microstructural observations. Our results show that Mo, Mo/Mn, REE, Y/Ho, Nb, and Nb/Ta in scheelite are variable within the different scheelite generations and are predominantly controlled by the host-rock lithologies on the local scale, whereas in general the data show a strong response to the shift of P, T, and pH upon changing magmatic-hydrothermal to metamorphic conditions. For the first time, we identify remnants of primary scheelite in the Western Ore Zone. The presented data support a magmatic-hydrothermal origin of the first scheelite mineralization during the Variscan orogeny with primary scheelite being characterized by wing-shaped REE patterns with a negative Eu-anomaly, high trace element concentrations, non-chondritic Y/Ho, and high Nb/Ta. Primary scheelite underwent metamorphic/hydrothermal alteration (recrystallization and dissolution-reprecipitation processes) during the Variscan and Alpine orogeny. This case study highlights that indicative mineralization-controlling geochemical ratios like Sr/Mn cannot be applied for polymetamorphic tungsten deposits like Felbertal.

费尔伯塔尔钨矿是欧洲唯一具有经济价值的白钨矿,但其成因尚未完全明了。最近有观点认为,该矿床的形成很可能与瓦利斯坎时代的花岗岩侵入体有关,这与之前提出的早寒武纪时代的同步沉积地层起源形成了鲜明对比。由于该矿床经历了瓦里坎期和阿尔卑斯山期的多变质演化,解决这一争议仍具有挑战性。在这篇论文中,我们提供了一套新的白钨矿主要元素、次要元素和微量元素浓度的综合数据,这些数据来自 Felbertal 矿床的多代白钨矿,同时还进行了微观结构观察。我们的研究结果表明,白钨矿中的钼、钼/锰、稀土元素、Y/Ho、铌和铌/Ta在不同的白钨矿世代中是可变的,在局部范围内主要受主岩岩性的控制,而在总体上,当岩浆-热液条件转变为变质条件时,数据显示了对P、T和pH值变化的强烈反应。我们首次在西部矿带发现了原生白钨矿的残余。所提供的数据支持在瓦里斯山造山运动期间首次白钨矿成矿的岩浆-热液起源,原生白钨矿的特征是具有负Eu-异常的翼形REE模式、高微量元素浓度、非软玉Y/Ho和高Nb/Ta。原生白钨矿在瓦里斯山和阿尔卑斯造山时期经历了变质/热液蚀变(重结晶和溶解-再沉淀过程)。该案例研究强调,像Sr/Mn这样的指示性成矿控制地球化学比率不能用于像Felbertal这样的多变质钨矿床。
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引用次数: 0
Polyphased gold enrichment as a key process for high-grade gold formation: Insights from the 10 Moz Jundee-Bogada camp (Yilgarn Craton, Western Australia) 多相金富集是高品位金形成的关键过程:10 Moz Jundee-Bogada营地(西澳大利亚伊尔加恩克拉通)的启示
IF 4.8 2区 地球科学 Q1 Earth and Planetary Sciences Pub Date : 2024-05-31 DOI: 10.1007/s00126-024-01274-3
Sumail, Nicolas Thébaud, Quentin Masurel, Laura Petrella, Peter le Roux, Chris Stott

High-grade (> 10 g/t) gold mineralization in orogenic gold deposits is of significant economic importance. Understanding the formation of such enriched ore zones is critical for gold exploration success. The world-class Jundee-Bogada gold camp in the Yilgarn Craton of Western Australia comprises both high-grade (avg. > 10 g/t, Jundee deposit) and low-grade (avg. < 3 g/t, Bogada prospect) lodes, despite shared host stratigraphy. The paragenetic framework established for the Jundee gold deposit suggests that the overall gold endowment developed over three deformation events. An early episode of low-grade gold mineralization is associated with colloform-crustiform veins that formed during extensional deformation (DJB2A). A switch to transtensional deformation (DJB2B) resulted in brecciation of the colloform-crustiform veins and coeval deposition of native gold. Late reverse faults record evidence for a third mineralization stage resulting from a NE-SW-directed shortening (DJB3). Mineralization during this late stage was dominantly low-grade, with local occurrences of ultra-high-grade ore zones (> 100 g/t). Each event records transient changes in fluid chemistry during continued hydrothermal activity that spanned local deformation histories. We argue that at the Jundee gold deposit, protracted gold enrichment during three polyphased mineralization episodes resulted in the formation of high-grade gold ores. Whereas the complete metallogenic history is recorded at the Jundee deposit, gold within the Bogada prospect was introduced solely during the late contractional stage (DJB3), resulting in a bulk low-grade endowment. We hypothesize that gold enrichment in high-grade orogenic gold deposits is a direct consequence of the spatial superimposition of protracted ore-forming events.

成因金矿床中的高品位(> 10 g/t)金矿化具有重要的经济意义。了解这种富集矿带的形成对金勘探的成功至关重要。世界级的 Jundee-Bogada 金矿区位于西澳大利亚的 Yilgarn 克拉顿,由高品位(平均每吨 10 克,Jundee 矿床)和低品位(平均每吨 3 克,Bogada 探矿区)矿床组成,尽管有共同的寄主地层。为 Jundee 金矿床建立的准成因框架表明,金矿的整体禀赋是在三次变形过程中形成的。早期的低品位金矿化与延伸变形过程中形成的胶状壳状矿脉(DJB2A)有关。转为横断变形(DJB2B)后,胶结-壳状矿脉发生了角砾化,并同时沉积了原生金。晚期逆断层记录了东北-西南方向缩短(DJB3)导致的第三个成矿阶段的证据。这一晚期阶段的矿化主要是低品位的,局部出现了超高品位矿带(> 100 g/t)。每个事件都记录了在跨越局部变形历史的持续热液活动期间流体化学的瞬时变化。我们认为,在 Jundee 金矿床,三次多相成矿过程中长期的金富集导致了高品位金矿石的形成。Jundee金矿床记录了完整的成矿历史,而Bogada探矿区内的金仅在晚期收缩阶段(DJB3)被引入,从而形成了大量的低品位赋存。我们假设,高品位造山型金矿床中金的富集是长期成矿事件空间叠加的直接结果。
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引用次数: 0
Paleozoic orogenic gold mineralization from metamorphism of volcanic sequences in the North Qinling terrane (central China): Insights from the Yindongpo gold deposit in the Tongbai area 北秦岭地层(中国中部)火山岩序列变质作用中的古生代造山运动金矿化:桐柏地区银洞坡金矿床的启示
IF 4.8 2区 地球科学 Q1 Earth and Planetary Sciences Pub Date : 2024-05-28 DOI: 10.1007/s00126-024-01265-4
Ming-Chun Chai, Jian-Wei Li, Ya-Fei Wu, Xiao-Ping Xia, Huai-Yu He, Wei Fu

Phanerozoic orogenic gold deposits worldwide are commonly considered to be formed from metamorphic devolatilization of marine carbonaceous sedimentary rocks. Here we show that the Yindongpo gold deposit from the Qinling orogen (central China) is genetically associated with the metamorphism of volcanic rocks during the late Paleozoic orogeny, which involved the closure of the Shangdan ocean. Gold mineralization at Yindongpo is hosted in lower Paleozoic metavolcanic-sedimentary sequences and occurs mainly as lenticular to stratiform ore bodies that formed in three paragenetic stages represented by quartz-ankerite-pyrite (stage I), quartz-carbonate-sulfide (stage II) and quartz-calcite assemblages (stage III), respectively. Rutile grains coexisting with auriferous pyrite from stage II yield U–Pb ages of 395 ± 9 to 400 ± 13 Ma (2σ). Fluid inclusions in quartz of stages I and II are dominated by CO2-rich (~ 10 mol%) aqueous fluids with low salinities (< 4.9 wt% NaCl equivalent) and total homogenization temperatures ranging from 241 to 352 ºC, whereas the values for H2O-rich inclusions of stage III are 0.2 to 2.6 wt% NaCl equivalent and 151 to 164 °C. Based on secondary ion mass spectrometry analysis of oxygen isotopes of quartz (Qz-1 to Qz-4), the calculated δ18Ofluid values for the quartz-forming fluids are 1.3 to 7.0‰ in stage I, –3.1 to 6.6‰ in stage II, and –9.6 to –3.7‰ in stage III. These data indicate a metamorphic origin of ore fluids that underwent Rayleigh fractionation and incursion of meteoric water. The large variation in 40Ar*/4He ratios (1.7–30.0), caused by accumulation of radiogenic Ar* and He loss within some pyrite samples, can be ascribed to regional metamorphism and deformation. Ore sulfides have sulfur (δ34SV-CDT = –2.1 to 3.3‰) and lead (206Pb/204Pb = 17.008–17.152, 207Pb/204Pb = 15.402–15.493, and 208Pb/204Pb = 38.254–38.564) isotopic compositions that are consistent with those of pyrite in the metavolcanic host rocks. Results presented here suggest that the ore fluids and, by inference, gold of the Yindongpo deposit were derived primarily from the volcanic sequences during regional metamorphism and deformation in response to the Early Devonian Qinling collisional orogeny. The Yindongpo deposit represents the first recognized Paleozoic orogenic gold deposit in the Qinling orogen, and thus has important implications for regional metallogeny and gold exploration.

世界范围内的新生代造山运动金矿床通常被认为是由海相碳质沉积岩变质脱落形成的。在这里,我们展示了秦岭造山带(中国中部)的银洞坡金矿床与晚古生代造山带火山岩变质作用(包括商丹洋的关闭)的基因相关。银洞坡的金矿化赋存于下古生代的变质火山岩-沉积岩序列中,主要以透镜状至层状矿体的形式出现,形成于三个成因阶段,分别以石英-红柱石-黄铁矿(第一阶段)、石英-碳酸盐-硫化物(第二阶段)和石英-方解石组合(第三阶段)为代表。第二阶段的金红石颗粒与含金黄铁矿共存,产生的 U-Pb 年龄为 395 ± 9 至 400 ± 13 Ma (2σ)。第一和第二阶段石英中的流体包裹体主要是富含二氧化碳(约 10 mol%)的含水流体,盐度较低(< 4.9 wt% NaCl 当量),总均化温度为 241 至 352 ºC,而第三阶段富含 H2O 的包裹体的温度值为 0.2 至 2.6 wt% NaCl 当量和 151 至 164 °C。根据对石英(Qz-1 至 Qz-4)氧同位素的二次离子质谱分析,计算得出的石英形成流体的 δ18Ofluid 值在第Ⅰ阶段为 1.3 至 7.0‰,在第Ⅱ阶段为-3.1 至 6.6‰,在第Ⅲ阶段为-9.6 至-3.7‰。这些数据表明,矿石流体起源于变质岩,经历了瑞利分馏和陨水侵入。在一些黄铁矿样品中,由于放射性 Ar* 的积累和 He 的损失,40Ar*/4He 比值变化很大(1.7-30.0),这可以归因于区域变质和变形。矿石硫化物的硫(δ34SV-CDT = -2.1-3.3‰)和铅(206Pb/204Pb = 17.008-17.152,207Pb/204Pb = 15.402-15.493,208Pb/204Pb = 38.254-38.564)同位素组成与变质岩主岩中黄铁矿的同位素组成一致。本文介绍的结果表明,银洞坡矿床的矿石流体以及推断出的金主要来源于早泥盆世秦岭碰撞造山作用下的区域变质和变形过程中的火山岩序列。银洞坡矿床是秦岭造山带首次发现的古生代造山型金矿床,对区域成矿作用和金矿勘探具有重要意义。
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引用次数: 0
Melt infiltration in a crystal mush and pegmatoid formation in the platiniferous Merensky Reef, Bushveld Complex, South Africa 南非布什维尔德岩群铂髓质梅伦斯基礁水晶蘑菇和埙状岩层中的熔融渗透
IF 4.8 2区 地球科学 Q1 Earth and Planetary Sciences Pub Date : 2024-05-27 DOI: 10.1007/s00126-024-01278-z
Ben Hayes, Reza Maghdour-Mashhour, Lewis D. Ashwal, Albertus J.B. Smith, Henriette Ueckermann, Jaco Vermeulen

Giant mafic-ultramafic layered intrusions of Archaean-Proterozoic age are the fossilised remnants of huge injections of silicate magma in the Earth’s crust and are our most important repositories of platinum-group elements. Magmatic PGE-rich ore deposits, such as the Merensky Reef, are typically hosted in stratiform reefs at the contacts between ultramafic and feldspathic cumulates. The Merensky Reef is commonly characterised by coarse-grained and pegmatoidal textures that may provide important clues to its origin. We present textural and in situ geochemical data for Merensky pegmatoids at Styldrift Mine (Impala Bafokeng) in the Western Bushveld Complex of South Africa. This region is adjacent to an inferred magmatic feeder zone to the Bushveld. The Merensky pegmatoids are characterised by (i) amoeboid olivine inclusions in zoned orthopyroxene megacrysts with increasing molar Mg# of orthopyroxene towards olivine, (ii) fine-grained chains of orthopyroxene in compositional equilibrium with adjacent orthopyroxene megacrysts, (iii) increasing molar Mg# of orthopyroxene megacrysts and increasing molar An with decreasing 87Sr/86Sri (at 2.06 Ga) of plagioclase oikocrysts in pegmatoids laterally across a 10-km section distal to the feeder, and (iv) highly variable molar An and initial 87Sr/86Sri of interstitial plagioclase proximal to the feeder. We interpret the coarse-grained and pegmatoidal textures, their dissolution-reprecipitation features, and lateral chemical variations as the product of lateral melt infiltration and mixing in a crystal mush. We suggest that the platiniferous Merensky Reef was not formed at the base of a large melt-filled magma chamber but was instead the product of non-sequential magma emplacement that rejuvenated the crystal mush.

太古宙-新生代的巨型黑云母-超黑云母层状侵入体是地壳中硅酸盐岩浆巨大喷射的化石遗迹,是我们最重要的铂族元素储藏地。富含铂族元素的岩浆矿床,如梅伦斯基礁,通常赋存于超基性岩积和长石岩积接触处的层状岩礁中。梅伦斯基礁通常具有粗粒和辉绿岩质地的特征,这可能为其起源提供了重要线索。我们展示了南非西布什维尔德复合体 Styldrift 矿(Impala Bafokeng)的梅伦斯基伟晶岩的纹理和现场地球化学数据。该地区毗邻推断的布什维尔德岩浆给矿带。梅伦斯基辉绿岩的特征是:(i) 带状正长辉石巨晶中的amoeboid橄榄石包裹体,正长辉石的摩尔Mg#向橄榄石方向递增;(ii) 与相邻正长辉石巨晶成分平衡的正长辉石细粒链;(iii) 正长辉石巨晶的摩尔Mg#递增,摩尔An随87Sr/86Sri(2.06 Ga时)的递减而递增。(iv) 在馈源附近,间隙斜长石的摩尔安和初始 87Sr/86Sri 变化很大。我们将粗粒和柱状纹理、其溶解-再沉淀特征以及横向化学变化解释为晶体泥浆中横向熔体渗透和混合的产物。我们认为,含铂的梅伦斯基礁并不是在一个充满熔融物的大型岩浆腔底部形成的,而是非连续性岩浆喷出的产物,它使晶泥重新焕发了活力。
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引用次数: 0
Geochemical implications of uranium-bearing thucholite aggregates in the Upper Permian Kupferschiefer shale, Lubin district, Poland 波兰卢宾地区上二叠统库珀弗谢费页岩中含铀褐铁矿集合体的地球化学影响
IF 4.8 2区 地球科学 Q1 Earth and Planetary Sciences Pub Date : 2024-05-25 DOI: 10.1007/s00126-024-01279-y
Marcin D. Syczewski, Paweł Panajew, Leszek Marynowski, Marta Waliczek, Andrzej Borkowski, Jan Rohovec, Šárka Matoušková, Ilona Sekudewicz, Malwina Liszewska, Bartłomiej Jankiewicz, Aliya N. Mukhamed’yarova, Mirosław Słowakiewicz

New inorganic and organic geochemical data from thucholite in the Upper Permian (Wuchiapingian) Kupferschiefer (T1) shale collected at the Polkowice-Sieroszowice Cu-Ag mine in Poland are presented. Thucholite, which forms spherical or granular clusters, appears scattered in the T1 dolomitic shale at the oxic-anoxic boundary occurring within the same shale member. The composition of thucholite concretions and the T1 shale differs by a higher content of U- and REE-enriched mineral phases within the thucholite concretions compared to the T1 shale, suggesting a different mineralising history. The differences also comprise higher Ntot, Ctot, Htot, Stot contents and higher C/N, C/S ratios in thucholite than in the T1 shale. The hydrocarbon composition of the thucholite and the surrounding T1 shale also varies. Both are dominated by polycyclic aromatic compounds and their phenyl derivatives. However, higher abundances of unsubstituted polycyclic aromatic hydrocarbons in the thucholite are indicative of its pyrogenic origin. Pyrolytic compounds such as benz[a]anthracene or benzo[a]pyrene are more typical of the thucholite than the T1 shale. Microscopic observations of the thucholite and its molecular composition suggest that it represents well-rounded small charcoal fragments. These charcoals were formed during low-temperature combustion, as confirmed by semifusinite reflectance values, indicating surface fire temperatures of about 400 °C, and the absence of the high-temperature pyrogenic polycyclic aromatic hydrocarbons. Charred detrital particles, likely the main source of insoluble organic matter in the thucholite, migrated to the sedimentary basin in the form of spherical carbonaceous particulates, which adsorbed uranium and REE in particular, which would further explain their different contents and sorption properties in the depositional environment. Finally, the difference in mineral content between thucholite and the T1 shale could also have been caused by microbes, which might have formed biofilms on mineral particles, and caused a change in the original mineral composition.

本文介绍了在波兰 Polkowice-Sieroszowice 铜金矿采集的上二叠统(武奇亚平统)Kupferschiefer(T1)页岩中的褐铁矿的新的无机和有机地球化学数据。形成球状或颗粒状团块的褐铁矿散布在 T1 白云质页岩中,位于同一页岩成分的缺氧-缺氧边界。褐铁矿凝块与 T1 页岩的成分不同,与 T1 页岩相比,褐铁矿凝块中富含铀和稀土元素的矿物相含量更高,这表明其成矿历史不同。与 T1 页岩相比,Thucholite 中的 Ntot、Ctot、Htot、Stot 含量更高,C/N、C/S 比率也更高。苏合香岩和周围 T1 页岩的碳氢化合物成分也各不相同。两者都以多环芳香族化合物及其苯基衍生物为主。不过,苏合香岩中未取代的多环芳烃含量较高,这表明苏合香岩起源于热成岩。苯并[a]蒽或苯并[a]芘等热解化合物在苏赫岩中比在 T1 页岩中更为典型。对褐铁矿及其分子组成的显微观察表明,褐铁矿代表了圆形的小木炭碎片。这些木炭是在低温燃烧过程中形成的,半透明反射率值证实了这一点,表明表面着火温度约为 400 °C,而且不含高温致热多环芳烃。烧焦的碎屑颗粒可能是褐铁矿中不溶性有机物的主要来源,它们以球形碳质颗粒的形式迁移到沉积盆地,尤其吸附了铀和 REE,这进一步解释了它们在沉积环境中的不同含量和吸附特性。最后,Thucholite 和 T1 页岩之间矿物含量的差异也可能是由微生物造成的,微生物可能在矿物颗粒上形成生物膜,并导致原始矿物成分发生变化。
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引用次数: 0
Tracing the magmatic-hydrothermal evolution of the Xianghualing tin-polymetallic skarn deposit, South China: Insights from LA-ICP-MS analysis of fluid inclusions 追溯华南祥华岭锡多金属矽卡岩矿床的岩浆-热液演化过程:对流体包裹体进行 LA-ICP-MS 分析的启示
IF 4.8 2区 地球科学 Q1 Earth and Planetary Sciences Pub Date : 2024-05-24 DOI: 10.1007/s00126-024-01281-4
Yong-Kang Chen, Pei Ni, Jun-Yi Pan, Jian-Ming Cui

The Xianghualing large tin-polymetallic skarn deposit is located in the Nanling W-Sn metallogenic belt, South China, showing distinct spatial zoning of mineralization. From the contact between granite and carbonate rocks, the mineralization transitions from proximal skarn Sn ore to cassiterite-sulfide ore and more distal Pb–Zn-sulfide ore. This study reveals the fluid evolution and genetic links among these different ore types. The physical and chemical characteristics of fluid inclusions from each ore types indicate that the skarn Sn ore, cassiterite-sulfide ore, and Pb–Zn-sulfide ore all originated from the identical magmatic fluid exsolved from the Laiziling granite. Their formation, however, is controlled by diverse fluid evolutionary processes and host rock characteristics. The Sn–Pb-Zn-rich fluids were primarily derived from cooled and diluted magmatic brine, which is generated by boiling of initial single phase magmatic fluid. Mixing of magmatic brine with meteoric water is crucial to form skarn Sn ore. Redox reactions of aqueous Sn (II) complexes with As (III) species and/or minor CO2 during short cooling period of ore-forming fluid is likely an effective mechanism to form high-grade cassiterite-sulfide ores, accompanied by favorable pH conditions maintained through interaction with carbonate host rocks. The later stage addition of meteoric water prompts the formation of Pb–Zn-sulfide ore. Comparing these findings with the characteristics of initial or pre-ore magmatic fluids in both mineralized and barren granitic systems indicates that high Sn content in the pre-ore fluids and the suitable fractional crystallization degree of the parent magma may determine high Sn mineralization potential in granitic magmatic-hydrothermal systems.

湘华岭大型锡多金属矽卡岩矿床位于华南南岭W-Sn成矿带,矿化空间分带明显。从花岗岩与碳酸盐岩接触处开始,矿化从近端矽卡岩锡矿过渡到锡石硫化矿和更远端的铅锌硫化矿。这项研究揭示了这些不同矿石类型之间的流体演化和遗传联系。各矿石类型流体包裹体的物理和化学特征表明,矽卡岩锡矿石、锡石硫化矿石和铅锌硫化矿石均起源于来子岭花岗岩溶出的相同岩浆流体。然而,它们的形成受控于不同的流体演化过程和母岩特征。富含锡铅锌的岩浆流体主要来自冷却和稀释的岩浆盐水,而岩浆盐水是由初始单相岩浆流体沸腾产生的。岩浆盐水与陨石水的混合是形成矽卡岩锑矿的关键。在成矿流体短时间冷却过程中,水性锡(II)络合物与砷(III)物种和/或少量二氧化碳发生氧化还原反应,这可能是形成高品位锡石-硫化物矿石的有效机制,同时通过与碳酸盐主岩的相互作用维持有利的 pH 值条件。后期陨石水的加入则促进了铅锌硫化物矿石的形成。将这些发现与矿化和贫瘠花岗岩体系中的初始或矿前岩浆流体特征进行比较后发现,矿前流体中的高含锡量和母岩浆的适当分晶度可能决定了花岗岩岩浆-热液体系中的高含锡矿化潜力。
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Mineralium Deposita
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