Conference Agenda

The Karambusel vent field on the western flank of the polymetallic Au-mineralized Conical Seamount in the New Ireland Basin of Papua New Guinea was discovered in 2023 during research cruise SO299. The active vent field sits on top of a volcanic center that is ~200 ka younger than the Conical main edifice. Recently, we could demonstrate that the magma forming the Karambusel system rejuvenated the crustal magma chamber under Conical, feeding water-rich melt into the system and triggering epithermal-style mineralization at both edifices. This early, high temperature ore-forming event was followed by low-temperature As-Sb-Tl-Hg-rich mineralization related to the current venting. However, the Karambusel vents are characterized by a high proportion of CH₄ (>80 vol.%) relative to CO₂, which is uncommon for volcanic-hosted systems. Furthermore, the hydrocarbons are most likely of thermogenic origin although the maturation of organic matter is rapid and incomplete. Recent analyses of the composition of noble gases are consistent with a direct extraction from the mantle (³He/⁴He ~6.9 R_a). This is in line with the B-enriched nature of the fluids (relative to K and Sr) that points towards a potential magmatic vapor origin. However, we cannot rule out that connate fluids released from the breakdown of clay minerals also contribute to the vent fluid. Altogether, Karambusel is a highly complex system where a magmatic-hydrothermal system interacts with the lithology and fluids of a sedimentary basin. The result is a complex ore-forming system that shares some similarities with epithermal, Carlin-type and volcanogenic massive sulfide deposits.

Interest in lithium as a critical raw material is continuously increasing due to its key role in battery manufacturing and the energy transition. The co-production of lithium and geothermal energy may contribute to domestic raw material supply and energy security. However, there is still a lack of understanding of enrichment processes and spatial distribution of lithium in potential sedimentary reservoirs, such as Bunter sandstone of the North German Basin. The study aims to compile a regional database of formation water analyses from the previous research and archival data, construct geological and hydrogeochemical models of lithium enrichment (fluid evolution and migration, water-rock interaction, etc.) in Bunter sandstone, conduct the resource assessment with Monto Carlo simulation and identify the factors controlling elevated lithium concentrations. The particular focus of the research is Altmark region, which has a dense network of wells, providing data availability and opportunities for further exploration and development. Special attention was paid to the geochemical composition of formation waters, sediment provenance, potential fluid source areas, inherited tectonic structures, fluid migration pathways, and long-term water-rock interaction processes controlling lithium enrichment. The study is expected to improve the understanding of geological controls on lithium enrichment and help identify areas with elevated lithium potential in the Altmark region.

Differentiating between diagenetic and hypogene assemblages is a major challenge in sedimentary rock hosted mineral systems. In the sedimentary rock hosted Cu deposits of the Kupferschiefer district (central Europe), oxidation of footwall sandstones has been described at the core sample scale and variably attributed to diagenetic reddening or hypogene (Rote Fäule) iron-oxide/hydroxide alteration. Here, we present results from a combined Scanning Electron Microscopy (SEM) and Transmitted Electron Microscopy (TEM) study of samples from the Spremberg-Graustein deposit (Brandenburg, Germany), to resolve these assemblages at the micro to nanoscale. The SEM observations constrain at least three formation mechanisms of Fe-oxide/hydroxide: open-space growth as acicular, botryoidal, and radial aggregates within pores and microcavities; spheroidal aggregates in framboidal arrangements; and replacement of sheet silicates and titanium oxide phases. The TEM data reveal a mineralogical complexity not previously reported in the Kupferschiefer district. Magnetite and hematite coexist at the nanoscale, and oriented goethite needles are intimately intergrown with hematite plates, suggesting either a sequence of hypogene alteration or a transition between diagenetic and hypogene assemblages. An amorphous Fe-Si-Ti phase occurring as rims around iron oxide crystals may represent a possible metastable precursor in a low-temperature crystallisation sequence. These findings point to a protracted, multi-stage iron oxide/hydroxide formation sequence rather than a single oxidation event, providing valuable constraints on fluid rock interaction during sedimentary rock hosted Cu metallogenesis.

The Paleozoic Selwyn Basin (Canada) hosts some of the world’s largest clastic-dominated (CD-type) massive sulfide Zn deposits. Conventional studies have investigated δ³⁴S values to reconstruct different pathways of sulfur enrichment; however, interpretations remain challenging due to overlapping signatures from organoclastic sulfate reduction (OSR), anaerobic oxidation of methane coupled with sulfate reduction (AOM-SR), and thermochemical sulfate reduction (TSR). In this study, we compare the multiple sulfur isotope composition (³²S, ³³S, ³⁴S) of mineralized and unmineralized host rock samples from the Tom and Boundary Zone deposits to resolve different pathways of diagenetic and hydrothermal sulfate reduction.

The sulfide paragenesis is characterized by early, fine-grained framboidal pyrite, euhedral pyrite, and barite, later overgrown and partially replaced by hydrothermal subhedral to anhedral pyrite and sphalerite. Bulk rock sulfur was extracted from pyrite (CRS; n=23), sphalerite (AVS; n=9), and barite (n=8). Relative to Late Devonian seawater, the isotopic composition of sulfate shows a small increase in δ³⁴S values (20.6 to 28.6 ‰) and decrease in Δ³³S values (0.01 to −0.04 ‰), diagnostic of sulfate influenced by methane seep activity. Correspondingly, the isotopic composition of CRS in samples from the unmineralized drill-hole plots on a curvilinear array that describes mixing between sulfide derived from OSR and AOM-SR. The isotopic composition of CRS and AVS in mineralized samples plots along a steeper array, which could indicate a greater contribution of AOM-SR or TSR. These results demonstrate how multiple sulfur isotopes can be used to constrain the sources of reduced sulfur in the metal trap of CD-type deposits.

Zinc and other base metals are critical for our modern society and the technological transformation towards a carbon-neutral future, but major new discoveries are rare. Notable are recent discoveries of clastic dominated deposits in Proterozoic sedimentary basins of northern Australia that highlight the potential for additional future discoveries that may be facilitated by refined mineralisation models. A long-standing debate encompasses syngenetic base metal precipitation in the water column and epigenetic replacement mineralisation. Sedimentary-exhalative models readily explain the stratiform mineralisation characterised by micrometre scale alteration between mineralised and non-mineralised zones. However, recent studies provide compelling evidence for subseafloor mineralisation in Australian ZnPbAgS deposits such as HYC McArthur River and Teena.

We provide a new hypothesis for explaining the intricate small-scale lamination of ores often considered as evidence for syngenetic mineralisation: microbial mats are key ingredients in the epigenetic mineralisation process. Our mineralisation model builds on the physical characteristics of modern microbial mats and the details of selective silicification of fossil microbial mats outside the mineralisation zone of Proterozoic sediments hosting ZnPbS deposits in northern Australia. Fossil mats contain abundant pyrite and organic matter, providing critical reducing power for oxidised metal-rich brines. Their laminated structure with steep physicochemical gradients provides small and large-scale seals and migration paths for diagenetic fluid-flow. The microscale layering with carbonate, organic matter, pyrite, and clay mineral-rich laminae induces selective burial mineralisation evocative of SEDEX-laminations. While microbial mats have been described in many stratiform deposits, we highlight for the first time their potential importance in epigenetic mineralisation processes.

Volcanogenic massive sulphide deposits are major sources of base metals and are actively mined worldwide. Often these deposits have undergone a complex alteration history, including hydrothermal alteration by ore-forming fluids and metamorphic overprinting. The analysis of accessory minerals is a promising tool to constrain the mineralization/alteration processes and the hydrothermal fluid flow paths, as they retain textural evidence and geochemical signatures of the mineralizing fluids. We investigated the accessory minerals in samples from the world-class VMS deposit Kidd Creek located in the Archean Abitibi Greenstone Belt, Canada. The Cu-Zn-Pb mineralization is hosted by felsic volcanic rocks and was caused by multiple hydrothermal fluid influxes related to submarine volcanic activity. The mineralization and later regional metamorphic processes altered the whole succession to greenschist-facies metamorphic conditions.

Distinct mineral assemblages of primary igneous zircon together with hydrothermal zircon and REE-phosphates monazite and xenotime were found to be paragenetically related to the Kidd Creek sulfides. Using geochemical (EMPA) and microstructural (TEM) analyses, we confirmed the hydrothermal origin of the latter phases and their formation by dissolution-reprecipitation processes likely concomitant to the precipitation of bornite and chalcopyrite in the stockwork of Kidd Creek.

We demonstrate the use of accessory phases in VMS deposits to trace hydrothermal alteration processes in ore-forming systems, which has potential to be applied to volcanogenic hydrothermal mineralization systems worldwide.