Due to the multiple and poorly-crystallized phases in ferromanganese (Fe–Mn) nodules, research on the variability of micro-layers in nodules is limited and the accumulation of various elements with the growth of micro-layers have not been well documented. To address this gap, we examined the spatial distributions of elements in cross-sections of nodules from the Northwestern Pacific Ocean using in-situ electron microprobe analyses coupled with backscattered electron imaging and high-resolution X-ray elemental intensity mapping. Results suggest their significant selective enrichment of metal elements is similar to that of typical hydrogenetic nodules and diagenetic nodules. Moreover, W_Mn+Fe of Fe–Mn oxyhydroxide is equal to 50% after normalization and Co and Ni show positive relationships with Mn/Fe ratio, suggesting Fe oxyhydroxide would serve as a diluter at exposed surface during nodule growth. In suboxic conditions, Mn, Ni, and Co start to release, and the remaining Fe oxyhydroxide may react with the surrounding sediment to form Si-rich layers. Our studies reveal the diverse growth processes and show a much larger chemical heterogeneity of individual layers, which extend the models about the mechanisms of chemical precipitation and environmental conditions that existed during nodule growth.

The Huangyangshan super-large graphite deposit is located in the Qitai area of East Junggar in Xinjiang Province, China. This deposit is well known for its distinguishing properties, including the alkaline granite complex that hosts the graphite ore, the dominantly orbicular structure developed in the graphite ore, and the association of graphite with metal sulfides in the orbicular ore. This study aims to determine the genetic relationship between graphite and metal sulfides in order to better understand the graphite mineralization process of the Huangyangshan deposit. The methods applied in the study include X-ray micro-CT scanning and scanning electron microscopy (SEM) analyses of the orbicular graphite ore and in situ inductive laser ablation-coupled plasma mass spectrometry (LA-ICP-MS) trace element analyses of the pyrrhotite and chalcopyrite associated with the graphite. The analytical results show that the graphite ore is composed of crystalline graphite, K-feldspar, albite, quartz, biotite, amphibole, and metal sulfides. The metal sulfides in the orbicular ore include pyrite, pyrrhotite, pentlandite, and chalcopyrite. According to the color, crystalline shape, texture, and occurrence, pyrrhotite can be classified into four types (I, II, III, and IV), and chalcopyrite into two types (I and II), of which types I, II, and III pyrrhotite and type I chalcopyrite have a close genetic relationship with graphite. The granular types (I, II, and III) of pyrrhotite are enriched in Co, Ni, Se, Ge, and Te and are depleted in As, Sb, Ag, and Au; they also have a high value of Co/Ni, indicating that these types of pyrrhotite have a magmatic origin. Low values of Co/Ni suggest that type IV pyrrhotite has a hydrothermal origin. The similar contents of Co and Ni and the values of Co/Ni compared with the chalcopyrite from the magmatic Co–Ni sulfide deposits imply that type I chalcopyrite has a magmatic origin. In summary, the metal sulfides of the Huangyangshan deposit are genetically related to graphite mineralization and formed predominantly by magmatic processes.

Enrichments of critical metals in ferromanganese (Fe–Mn) nodules have received increasing attention in both deep-sea research and mineral exploration. To better assess the controls on the resource potential of Fe–Mn nodules, we conducted a comprehensive and detailed study of twelve nodules from the Philippine Sea collected from water depths of 4400 to 6000 m by investigating their microstructures, bulk geochemistry, and in situ Fe–Mn oxyhydroxide geochemistry, using XRF, ICP-MS, EMPA, and LA-ICP-MS coupled with BSE images. We successfully resolved different controls on the element enrichments, of which significant selective enrichment of metal elements in seawater is similar to that of typical hydrogenetic nodules. An enhanced supply of iron hydroxide due to calcite dissolution resulted in a dilution effect on Co, Ni, and Mn but an enrichment effect on rare earth elements plus yttrium (REE + Y) and Fe in nodules near topographic highs close to the carbonate compensation depth. While the supply of diagenetic Mn resulted in a dilution on Co and REE + Y, it resulted in enrichment on Ni, Cu, Li, and Mn on nodules on the seafloor. Moreover, via micro-layer analyses we confirmed the growth rate is a major determinant for the correlations of Co and REE with Fe-oxyhydroxides in these Philippine Sea nodules.

In the Huanggangliang–Ganzhuermiao metallogenic belt in the southern Great Xing’an Range, the Haobugao Pb–Zn deposit is the most widespread skarn-type polymetallic deposit. The observed mineralization processes in this area are closely associated with both magmatic and tectonic activity. The zircon U–Pb ages of two granitoid phases are 134.0 ± 0.6 Ma and 133.4 ± 0.9 Ma (Early Cretaceous). High SiO₂ content (average mass fractions of 77.98 wt.% and 73.25 wt.%), high alkalinity (average mass fractions of 6.19 wt.% and 8.78 wt.%), and low CaO levels (average mass fractions of 0.16 wt.% and 0.12 wt.%) are characteristic of these rocks. They are also enriched in high-field-strength elements (HFSEs) (Th, U, Ta, Zr, Hf, etc.) and depleted in large ion lithophile elements (LILEs) (Ba, Sr, etc.). Furthermore, the Nb/Ta ratios (7.80~8.82, 10.00~10.83) point to a crustal origin of the magma. The zircon Hf isotopic compositions suggest that the melting of young crust derived from Meso-Neoproterozoic and Neoproterozoic depleted mantle gave rise to the magma in these granite porphyries. These rocks formed in an extensional environment driven by the subduction and retreat of the Paleo-Pacific plate during the Early Cretaceous.

The Zhangxuan district in North China, also known as Northwestern Hebei “Golden Triangle,” develops many intrusion-hosted lode-gold deposits. The Dongping gold deposit in the Zhangxuan district is well known for its unique hosting of rocks and ore mineral assemblages. Magnetite and pyrite are common minerals that widely exist in ores of the Dongping deposit. To get a better understanding of the evolution of the ore-forming fluids responsible for mineralization, we report on an integrated study on the electron microprobe analysis (EMPA) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analysis of magnetite and pyrite from the deposit. The major results are as follows: The magnetite grains from the Dongping deposit show a variable content of major and trace elements such as Ti, Al, Si, Fe, Mn, Cr, Na, V, and Co, and the majority of the magnetite contain low Ti contents, revealing potential properties of hydrothermal magnetite. The flat time-resolved signals of LA-ICP-MS imply that the majority of trace elements in magnetite exist in the form of isomorphism, except for some incompatible trace elements. Magnetites from the Dongping deposit have compositional characteristics of hydrothermal origins, and the genetic discriminant diagrams of Ti–V, Ti–Ni/Cr or (Ca + Al + Mn)–(Ti + V) show that they may be originated from magma differentiated hydrothermal solutions. Co, Ni in pyrite from Dongping mainly enter the lattice via isomorphism, and Cu, Zn, Ag, W, Sn, Au, Pb, and Bi are partitioned into pyrite as micro/nano- mineral inclusions. The Co, Ni content, and the Ni/Co ratios, indicated that the temperature of the ore-forming fluids has decreased from Py-1 to Py-2, and the enrichment of Au in Py-2 may be related to the cooling and boiling of the fluids.

The Dajing giant Cu–Sn polymetallic deposit is located in the Cu–Sn–Ag–Pb–Zn polymetallic belt of the southern Great Xing’an Range, NE China. Research on its ore genesis is of great significance for understanding Sn polymetallic mineralization in this region. In this study, pyrite, arsenopyrite, and sphalerite were analyzed by electron-microprobe analysis (EMPA) and in situ S–Pb isotope analysis. Previously published fluid-inclusion microthermometric and H–O isotope data were also incorporated to constrain fluid evolution and ore genesis. Both in situ S and Pb isotopic compositions fall within short ranges. The δ³⁴S values suggest a sulfur reservoir with possible magmatic contribution, whereas Pb isotopes indicate a mainly crustal Pb signature in an orogenic setting. Arsenopyrite records variations in As, S, Fe, and Co contents from core to rim. The Co-rich core shows Co enrichment accompanied by Fe depletion, consistent with Co-for-Fe isomorphous substitution. These features indicate changes in local fluid chemistry during arsenopyrite growth. Sulfur isotope geothermometry based on coexisting late-stage pyrite–sphalerite pairs yields 118–233 °C, with an average of 159 ± 49 °C, indicating medium- to low-temperature hydrothermal activity during the late sulfide stage. The Dajing deposit is interpreted as a fault-controlled hydrothermal vein-type Cu–Sn polymetallic deposit formed in a Late Jurassic extensional setting. Ore precipitation was likely promoted by cooling during upward fluid migration away from the magmatic heat source, pressure release, meteoric-water mixing, and fluid–rock interaction with granitic rocks and Linxi Formation wall rocks. This study provides mineral-scale constraints on fluid evolution and ore genesis in the Great Xing’an metallogenic belt.