Wall rock alteration in part of the Sarnak gold deposit, SE Bulgaria. Preliminary data

This short communication presents preliminary data on а wall rock alteration in part of the Sarnak epithermal gold deposit based on host rock samples from drill hole cores. Methods used are powder X-ray diffraction as well as optical and scanning electron microscopy. The most pronounced alterations related to the epithermal mineralization are vein silicification, adularization and pyritization.

Specific features of postmagmatic and hypergene kimberlite rock alteration research

Methods of studying postmagmatic and hypergene kimberlite rock alteration, as well as identifying secondary minerals and their associations are characterized. It is shown that secondary mineral formation processes took place in a wide temperature range and they are caused by their downward change of medium reaction from alkaline to acidic followed by neutralization, which resulted in dissolution, additional growth and emergence of new secondary mineral generations.

Microstructure and fluid flow in rift border fault-bounded basins – insights from the Dombjerg Fault, NE Greenland

In this contribution, we elucidate the interaction of structural deformation, fluid flow, and diagenesis in hanging wall siliciclastic deposits along rift basin-bounding faults, exemplified at the Dombjerg Fault in NE Greenland. Due to fault-controlled fluid circulation, fault-proximal syn-rift clastic deposits experienced pronounced calcite cementation and became lithified, whereas uncemented clastic deposits remained porous and friable. Correspondingly, two separate deformation regimes developed to accommodate continuous tectonic activity: discrete fractures formed in cemented deposits, and cataclastic deformation bands formed in uncemented deposits. We show that deformation bands act as partial baffles to fluid flow. This led to localized host rock alteration, which caused a chemical reduction of pore space along the bands. Where cemented, porosity was reduced towards zero and fracture formation created new pathways for fluid migration, which were subsequently filled with calcite. Occasionally, veins comprise multiple generations of microcrystalline calcite, which likely precipitated from an abruptly super-saturated fluid that was injected into the fracture. This suggests that cemented deposits sealed uncemented deposit bodies in which fluid overpressure was able to build up. We conclude that compartmentalized fluid flow regimes may form in rift fault-bounded basins, which has wide implications for assessments of potential carbon storage, hydrocarbon, groundwater, and geothermal sites.

Metamorphic gabbro and basalt in ophiolitic and continental nappes of the Zermatt region (Western Alps)

The composition of meta-gabbro and meta-basalt occurring abundant and widespread in all nappes of the nappe stack exposed in the Zermatt region of the Western Alp shows distinct patterns related to the geodynamic origin of metamorphic basic rocks. Eclogitic meta-basalts of the ophiolitic Zermatt-Saas Unit (ZSU) show enriched MORB signatures. The meta-basalts (eclogites) of the continental fragment of the Theodul Glacier Unit (TGU) derive from pre-Alpine metamorphic continental intraplate basalts. Meta-basalts (eclogites) from the continental basement of the Siviez-Mischabel nappe (SMN) derive from MORB thus a genetic relation to the TGU eclogites can be excluded. All basic igneous rocks experienced post-magmatic alteration by fluid-rock interaction ranging from processes at the seafloor, in the shallow crust, during subduction zone hydration, in the exhumation channel and late Alpine regional metamorphisms. The consequences of these alteration processes can be identified at various levels in the rock composition data. It was found that the REE data are little affected by fluid-rock alteration. Some trace elements, notably Cs, Rb, and Ba are typically massively altered relative to igneous compositions in all three groups of meta-basalts. Generally, meta-basalts from the TGU and the SMN preserved the features of the original composition whilst the ZSU meta-volcanic rocks experienced massive alteration. For the ZSU meta-volcanic rocks it is evident that Zr was gained and Y lost during high-pressure fluid-rock interaction indicating a mobile behavior of the two elements during HP-metamorphism in contrast to their behavior in hydrothermal near-surface fluid-rock interaction.

Geological mapping and mineral prospectivity using remote sensing and GIS in parts of Hamissana, Northeast Sudan

In recent years, various geological activities and different mineral prospecting and exploration programs have been intensified along the Red Sea hills in order to elucidate the geological maps and to evaluate the mineral potentials. This study is therefore aimed at testing the viability of using remote sensing and geographic information system (GIS) techniques for geological mapping and prospecting for gold mineralization in the area. The study area is located in northeast Sudan and covers an area of about 1379 km2. Different digital image processing techniques were applied to Landsat 8 Operational Land Imager image in order to increase the discrimination between various lithological units and to delineate wall rock alteration which represents target zones for gold mineralization. Image sharpening was performed to enhance the spatial resolution of the images for more detailed information. Contrast stretching was applied after the various digital processing procedures to produce more interpretable images. The principal component analysis transformations yielded saturated images and resulted in more interpretable images than the original data. Several ratio images were prepared, combined together and displayed in RGB color composite ratio images. This process revealed the existence of alteration zones in the study area. These zones extend from the northeast to the southwest in the acid meta-volcanic and silica barite rocks. The enhanced satellite images were implemented in the GIS environment to facilitate the final production of the geological map at scale 1:400,000. X-ray fluorescence analyses prove that selected samples taken from the wall rock alteration zones are gold-bearing.

Trace Element Concentrations Associated with Mid-Paleozoic Microfossils as Biosignatures to Aid in the Search for Life

Identifying microbial fossils in the rock record is a difficult task because they are often simple in morphology and can be mimicked by non-biological structures. Biosignatures are essential for identifying putative fossils as being definitively biological in origin, but are often lacking due to geologic effects which can obscure or erase such signs. As such, there is a need for robust biosignature identification techniques. Here we show new evidence for the application of trace elements as biosignatures in microfossils. We found elevated concentrations of magnesium, aluminum, manganese, iron, and strontium colocalized with carbon and sulfur in microfossils from Drummond Basin, a mid-Paleozoic hot spring deposit in Australia. Our results also suggest that trace element sequestrations from modern hot spring deposits persist through substantial host rock alteration. Because some of the oldest fossils on Earth are found in hot spring deposits and ancient hot spring deposits are also thought to occur on Mars, this biosignature technique may be utilized as a valuable tool to aid in the search for extraterrestrial life.

Porphyry-Related Metamorphosed Au-Ag and Cu-Mo Deposits in the Precambrian of the Fennoscandian Shield

The Pellapahk Cu-Mo and Oleninskoe Au-Ag deposits in the western segment of the Russian Arctic in the Kolmozero–Voronya greenstone belt are considered two parts of an Archean (2.83–2.82 Ga) porphyry-epithermal system, probably the oldest one defined in the Fennoscandian Shield. Formation of the Oleninskoe Au-Ag deposit at the epithermal stage of the system is indicated by the spatial and genetic relationships with the sills of granite porphyry, the geochemical association of ore elements (Au, Ag, Cu, Pb, Sb, As), an Au/Ag ratio of <0.2, and the multiplicity of silver mineralization with different Ag, Cu, Pb, Sb sulfosalts. The geological–structural characteristics of the Oleninskoe and the Pellapahk, i.e., their location in a shear zone, the morphology and size of ore bodies, the scale of the deposits, and the intensity and zoning of rock alteration, do not oppose this model. Mineralized rocks of the Pellapahk Cu-Mo and Oleninskoe Au-Ag deposits were amphibolite metamorphosed in the Neoarchean and again in the Paleoproterozoic. Structures of sulfide melt crystallization formed in the ores during metamorphism, those are fine intergrowths of galena, argentotetrahedrite, pyrargyrite, pyrrhotite, ullmannite, stutzite, and other mineral phases of low-melting-point metals such as Ag, Cu, Pb, Sb, As, Bi.