Carbonaceous material (CM) is common in meta-sediments and is generally interpreted to be intimately associated with gold mineralization. For the Bumo deposit in Hainan Province, South China, CM is mainly hosted by greenschist facies—to amphibolite-facies metamophic rocks of the Paleo—to the Mesoproterozoic Baoban Group, and by auriferous veins which could be used as an important gold prospecting indicator. However, the genesis of CM and its relationship with gold mineralization are still unclear. From the field work and thin section observations two types of CM occur, i.e., layered and veinlet. The layered CM occurred in CM-bearing black shales, up to meters thick, and prevails in the deposit. More importantly, Au-bearing sulfides are commonly distributed along the boundary between the quartz veins and layered CM. In contrast, the veinlet CM, co-precipitated with native gold and sulfides, has the thickness of micro- to centi-meters, and these thin veins occur in quartz veins and hydrothermally altered rocks. In addition, layered CM has a stringy shape and laminate structure, while veinlet CM occurs as isometric particles based on the Scanning Electron Microscope (SEM) analysis. The Raman carbonaceous material geothermometer indicates that layered CM with a high maturity is formed at elevated temperatures of 400–550 °C, consistent with X-ray diffraction (XRD) analysis. In contrast, veinlet CM with a low maturity is formed at 200–350 °C and generally consistent with gold mineralization. In addition, layered CM has ^δ13C values ranging from −30 to −20%, demonstrating a biogenic origin. Consequently, it is interpreted that layered CM is formed by a pre-ore metamorphic event during Caledonian, and its reducing nature promotes gold precipitation via destabilization of aqueous Au complexes or facilitating sulfidation. Veinlet CM is of hydrothermal origin, and its precipitation modified the chemical conditions of ore fluids, leading to the destabilization of Au complexes, which therefore are favorable for mineralization.

The Jiangnan Orogenic Belt is a world-renowned metallogenic region for Au-W-Sb mineralization, with the Wangu deposit being a representative one. Previous research has demonstrated that tungsten in this Au-W-Sb deposit is sourced from the hosting metasedimentary rocks, but the specific mineral that provides tungsten is still unclear. This study evaluates the tungsten source by conducting petrographic observations and geochemical and geochronological analyses on the rutile from the host slate the Wangu deposit. The results show that rutile from wall rocks of the Wangu deposit yields an age of 955 ± 13 Ma, which is older than both the ore-forming age of the deposit and the age of the host strata. Electron microprobe analyses (EMPA) and laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) elemental analyses show that detrital rutile is enriched in elements such as Fe, Cr, V, and W, as well as high-field-strength elements (HFSE) including Nb, Ta, Zr, and Hf. The total rare earth element (ΣREE) ranges from 3.37 ppm to 156.85 ppm. The samples are generally enriched in light rare earth elements (LREEs) and exhibit distinct negative Eu anomalies. These geochemical features and a geochronological age of 955 ± 13 Ma suggest that the rutile is of detrital origin and they are possibly derived from the Grenvillian rocks. It is concluded that the detrital rutile in the metasediments could be an important source for hydrothermal tungsten enrichment.

Carbonaceous material (CM) is common in meta-sediments and is generally interpreted to be intimately associated with gold mineralization. For the Bumo deposit in Hainan Province, South China, CM is mainly hosted by greenschist facies- to amphibolite-facies metamophic rocks of the Paleo- to Mesoproterozoic Baoban Group and by auriferous veins and is used as an important gold prospecting indicator. However, the genesis of CM and the relationship with gold mineralization are still not clear. Field work and thin section observation indicates that two types of CM occur, i.e., layered and veinlet. Layered CM, up to meters thick, prevails in the deposit. More importantly, Au-bearing sulfides are commonly distributed along the boundary between the quartz veins and layered CM. In contrast, veinlet CM, co-precipitated with gold and sulfides, has the thickness of micro- to centi- meters, and these thin veins occur in quartz veins and hydrothermally altered rocks. Scanning Electron Microscope (SEM) analysis indicates that layered CM has a stringy shape and laminate structure, while veinlet CM occurs as isometric particles. Raman carbonaceous material geothermometer indicates that layered CM with high maturity is formed at elevated temperatures of 400 – 550°C, consistent with X-ray diffraction (XRD) analysis. In contrast, veinlet CM with low maturity is formed at 200 – 350°C, generally consistent with gold mineralization. In addition, layered CM has δ13C values ranging from -30 to -20%, demonstrating a biogenic origin. Consequently, it is interpreted that layered CM is formed by a pre-ore metamorphic event during Caledonian, and its reducing nature promotes gold precipitation via destabilization of aqueous Au bisulfide complexes or facilitating sulfidation. Veinlet CM is hydrothermal origin, and its precipitation modified the chemical conditions of ore fluids, leading to the destabilization of Au complexes and thus favorable for mineralization.

The Huangjindong gold deposit, located in the central segment of the Jiangnan Orogen, is partly hosted by carbonaceous slate of the Neoproterozoic Lengjiaxi Group. However, the origin of carbonaceous material (CM) in host rocks and its relationship with gold mineralization remain poorly understood. Field investigations demonstrate that orebodies occur in both carbonaceous and CM-free slates Petrographic observations indicate that gold predominantly occurs as invisible or lattice-bound gold within sulfides, implying that sulfidation, rather than simple fluid reduction by CM, is the dominant gold precipitation mechanism. In addition, statistical analysis reveals no significan correlation between total organic carbon (TOC) values and gold grades in the mineralized carbonaceous slate (r = −0.104, p = 0.533). The δ¹³C_V-PDB values of CM in host rocks range from −25.58‰ to −21.75‰, with an average of −23.24‰, indicating a predominantly marine sedimentary organic matter source. The hydrothermal carbonates have the δ¹³C_V-PDB values of −6.49‰ to −3.59‰, δ¹⁸O_V-PDB values of −15.38‰ to −12.20‰, and δ¹⁸O_SMOW values of 15.06‰ to 18.33‰. Although the carbon isotopic compositions of these carbonates could potentially result from isotopic fractionation of CM, mass balance calculations demonstrate that the extremely low CM content (<1%) is far insufficient to form the abundant pre-ore Fe-bearing carbonates that constitute favorable chemical traps for gold mineralization. Consequently, the association between gold mineralization and CM at the deposit scale is insignificant. Based on this study, we propose that host-rock CM is not a prerequisite for gold mineralization and that future exploration should prioritize structural controls and sulfidation processes over lithological controls.

The Bou Azzer and Bleïda deposits in the Anti-Atlas of Morocco are geographically close and occur within the same Neoproterozoic Pan-African tectonic framework, yet they host contrasting styles of metal mineralization. Bou Azzer hosts economically important Co–Ni mineral deposits linked to serpentinized ultramafic formations, whereas Bleïda is mainly characterized by Cu–Fe sulfide mineralization hosted in volcanic units. Despite their close geographic and tectonic relationship, the geological and geochemical controls responsible for these different mineralization styles remain insufficiently understood. This study integrates geological and petrographic observations with compiled published geochronological data, fluid-inclusion microthermometry, and S isotopic compositions to better understand the evolution of mineralizing systems and ore formation processes. The results suggest that Bou Azzer is a polyphase serpentinite-hosted Co-Ni hydrothermal system with high-temperature, saline fluids, and sequential arsenide and sulfarsenide deposition. Bleïda, in contrast, is associated with a structurally controlled volcanic-sedimentary copper system characterized by low-salinity hydrothermal fluids, fluid–rock interaction, and remobilization of pre-existing sulfide mineralization. Despite their contrasting mineralization styles, Bou Azzer and Bleïda exhibit broadly similar S-isotope ranges and possibly overlapping mineralization ages. Their wide isotopic variations are interpreted to reflect redox-controlled fractionation under relatively oxidizing conditions rather than differences in sulfur source. The contrasting metal assemblages were therefore probably controlled by differences in fluid–rock interaction, local redox evolution, structural setting, and metal precipitation mechanisms. The genetic model integrating magmatism, structural deformation, and hydrothermal mineralization is proposed in this study.

The Xiangshan ore field is characterized by extensive alkali metasomatism, which represents the early-stage hydrothermal event before the acidic metasomatism during major U mineralization. However, the mineralogical and geochemical characteristics of alkali metasomatism, as well as its association with uranium mineralization, remain poorly understood. This study evaluates these scientific problems by conducting petrographic and geochemical analyses on feldspar, together with thermodynamic modeling. Hydrothermal feldspars are present as veinlets, differing from the magmatic ones with granular and subhedral structures. Hydrothermal albites have lower Na but higher K content than magmatic ones, while hydrothermal K-feldspars have lower K but higher Na content than magmatic ones. In addition, hydrothermal feldspars are significantly depleted in Ca and Sr, likely associated with the consumption of Ca in fluids by fluorite and calcite precipitation. Furthermore, alkali metasomatism is accompanied by intense hematitization, indicating the oxidized properties of ore fluids that are favorable for uranium transport. Thermodynamic modeling further demonstrates that continuous K⁺ consumption during fluid–rock interaction leads to a pH increase in the fluid, which is buffered by quartz–muscovite–K-feldspar (QMF). Given that quartz solubility is positively correlated with pH, this process induces extensive quartz dissolution in the host rocks. Such dissolution significantly enhances the porosity and permeability of the host rocks, creating ideal physical traps for the subsequent accumulation of uranium-bearing fluids. Consequently, alkali-metasomatized rocks associated with quartz dissolution and hematitization serve as critical indicators for regional uranium exploration.