Ultramafic Igneous Rocks Research Articles

Reduced partition function ratios of iron, magnesium, oxygen, and silicon isotopes in olivine: A GGA and GGA + U study

Olivine, typically occurring as a forsterite-fayalite solid solution, is a major rock-forming mineral in mafic and ultramafic igneous rocks, and it is important for understanding the genesis, evolution, and alteration of its host rocks. In this study, both GGA and GGA + U methods were employed to calculate the reduced partition function ratios of Fe, Mg, O, and Si isotopes for the forsterite-fayalite solid solution, aiming to elucidate the impacts of Fe content and Hubbard U correction on the isotope fractionation signatures of Fe, Mg, O, and Si in olivine. On the whole, the βFe-factor, βMg-factor, βO-factor, and βSi-factor decrease with increasing Fe content. The linear correlations between β-factors and bond lengths obtained from GGA + U are better compared to those from GGA. The Hubbard U correction can increase the βFe-factor. When Fe/(Fe + Mg) ≤ 1/8, ≤ 1/2, and ≤ 1/2, the effect of Hubbard U correction on βMg-factor, βO-factor, and βSi-factor can be considered negligible, respectively, suggesting that the βMg-factor, βO-factor, and βSi-factor of Fe-bearing olivine calculated using GGA + U and those of Fe-free minerals calculated using GGA can be combined to derive 103lnα and trace geological processes. Furthermore, equilibrium fractionation of Fe, Mg, O, and Si isotopes between olivine and other minerals, including troilite, clinopyroxene, and garnet, were also calculated. Our results are helpful in interpreting the observed data regarding Fe, Mg, O, and Si isotopic compositions of olivine, leading to a comprehensive understanding of relevant geological processes.

Emplacement of shergottites in the Martian crust inferred from three‐dimensional petrofabric and crystal size distribution analyses

AbstractShergottites are mafic to ultramafic igneous rocks that represent the majority of known Martian meteorites. They are subdivided into gabbroic, poikilitic, basaltic, and olivine–phyric categories based on differences in mineralogy and textures. Their geologic contexts are unknown, so analyses of crystal sizes and preferred orientations have commonly been used to infer where shergottites solidified. Such environments range from subsurface cumulates to shallow intrusives to extrusive lava flows, which all have contrasting implications for interactions with crustal material, cooling histories, and potential in situ exposure at the surface. In this study, we present a novel three‐dimensional (3‐D) approach to better understand the solidification environments of these samples and improve our knowledge of shergottites' geologic contexts. Shape preferred orientations of most phases and crystal size distributions of late‐forming minerals were measured in 3‐D using X‐ray computed tomography (CT) on eight shergottites representing the gabbroic, poikilitic, basaltic, and olivine–phyric categories. Our analyses show that highly anisotropic, rod‐like pyroxene crystals are strongly foliated in the gabbroic samples but have a weaker foliation and a mild lineation in the basaltic sample, indicating a directional flow component in the latter. Star volume distribution analyses revealed that most phases (maskelynite, pyroxene, olivine, and oxides/sulfides) preserve a foliated texture with variable strengths, and that the phases within individual samples are strongly to moderately aligned with respect to one another. In combination with relative cooling rates during the final stages of crystallization determined from interstitial oxide/sulfide crystal size distribution analyses, these results indicate that the olivine–phyric samples were emplaced as shallow intrusives (e.g., dikes/sills) and that the gabbroic, poikilitic, and basaltic samples were emplaced in deeper subsurface environments.

Nickel as A Strategic Mineral and Its Potential Resources in X-Field, North Konawe, Southeast Sulawesi, Indonesia

Indonesia is the world's largest producer of Nickel laterite deposits. By the regulation of UU No. 3 2020, due to its utility as the main component of batteries on electric vehicles (EV), nickel is one of the metal minerals that play important role in energy transition issues. It will drive the increasing demand for Nickel and Indonesia needs a massive exploration and specific regulation, especially for this deposit. The focus of this research is to discuss how important Ni is as a strategic mineral and its potential resources in North Konawe, Southeast Sulawesi. The methods are based on field data analysis and references study.X-Field is located in Lasolo Island, North Konawe, Southeast Sulawesi. This area has potential resources of Ni-laterite deposit. The lithological condition consists of a massive ultramafic igneous rock complex. The host rock has already been enriched by the serpentinization process. The geochemical analysis shows various ranges of 0.87-2.43% Ni content from different soil zone. To this day, the government regulation of Ni in a specific way as a critical mineral is still not present. The lack of data transparency (supply chain) and policy synchronization urgently need to be solved.

Identification of recycled oceanic crust in the mantle source of sulfide-bearing lower crust of the Gangdese magmatic arc, Southern Tibet: Constraints from Sr–Nd–Li isotopes

Post-collisional porphyry copper deposit (PCD) is a new genetic type of PCDs discovered in the Himalayan–Tibetan orogenic belt. It is believed that the formation of ore-forming magmas results from the re-melting of a sulfide-bearing, thickened, juvenile mafic lower crust in a magmatic arc associated with the oceanic plate subduction. However, the material contribution of subduction processes to the formation of this particular arc magma remains unclear. In this paper, we attempted to present a study that includes petrology, mineral geochemistry, whole rock Sr–Nd–Li isotopes, of Late Cretaceous Lilong ultramafic igneous rocks, south Lhasa sub-terrane, Tibet. The target ultramafic igneous rocks are sulfide-bearing cumulates. They show relative depletion in whole rock Nd isotopic compositions, slightly elevated (87Sr/86Sr)i ratios (0.7043–0.7059), and variable δ7Li values (2.8–9.0‰). Simulation results showed that trace element of melts in equilibrium with cumulus hornblende grains exhibit typical arc-like trace element distribution patterns, indicating that these ultramafic igneous rocks crystallized from arc magma. Additionally, the modeled melts showed enrichment in melt-mobile elements such as Ba, Pb, Sr, Th, and light rare earth elements (LREE), and higher Th/Yb ratios, as compared with normal mid-ocean ridge basalt (MORB). These geochemical properties can be explained by the metasomatism of depleted MORB mantle peridotites by hydrous melts derived from subducted seafloor sediments. Whole rock Sr isotopes show correlations with Ba/Nb and Th/La ratios for the modeled melts, showing that fluids from the basaltic igneous crust, in addition to hydrous melts from the seafloor sediments, contribute to their mantle source. In addition, the heterogeneity of whole rock δ7Li values for ultramafic igneous rocks also indicates that their mantle sources have been metasomatized by terrigenous sediment- and altered oceanic crust-derived fluids. Depleted MORB mantle peridotites react with the mixed fluids at sub-arc depths to produce ultramafic metasomatites, and model calculations for trace element contents and Sr–Nd–Li isotopic compositions further validate that the geochemical compositions of the Lilong ultramafic rocks can be clarified by this process. The results show that the deeply subducted oceanic crust may have played an important role in the formation of sulfide-bearing juvenile mafic lower crust of this magmatic arc.

Petrogenetic Study on Ultramafic Rocks from Waturapa and Surrounding Areas, South Konawe Regency, Southeast Sulawesi Province

The petrogenesis study of ultramafic igneous rocks in the South Konawe Region has been carried out by several previous researchers, however, petrogenesis of ultramafic igneous rocks in the Waturapa Region has never been carried out in detail. This study aims to determine the characteristics and petrogenesis of ultramafic igneous rocks in the Waturapa area using petrographic and geochemical analysis using the XRF method. Petrographic analysis was carried out to determine the relative abundance percentage of primary minerals in the form of olivine, clinopyroxene, orthopyroxene, and opaque minerals as well as secondary serpentine minerals which were formed later. Meanwhile, XRF geochemical analysis is used to determine the major and minor oxide content in rocks. This geochemical data is used to determine ultramafic rock types, and magma series and to interpret the tectonic setting of the research location. The results showed that the ultramafic rocks in the study area consisted of olivine websterite and lherzolite, both of which have been serpentinized which is characterized by the presence of serpentine minerals such as lizardite and chrysotile. These serpentine minerals are present as replacement minerals and fracture-filling minerals. The geochemical characteristics of the analyzed rocks showed a SiO2 content of less than 45%, high MgO content, and low K2O, TiO2, Na2O3, and P2O5 compounds. The igneous rocks in the study area are classified as ultrabasic or ultramafic rocks (peridot gabbro). Ultramafic rocks in the study area belong to the tholeiitic magma series that formed in oceanic islands or oceanic intraplate margins.

Analysis of Empirical Bayesian Kriging Methods for Optimization of Measured Resources Estimation of Laterite Nickel

Laterite nickel deposits are formed from the intense weathering of ultramafic igneous rocks. The distribution of Ni content in an area does not always have a stationary data. One method of resource estimation and precise geological modeling is the Empirical Bayesian Kriging (EBK) method which is known to be able to perform precise estimates for stationary and non-stationary data. The results of this study were found that thickness of the limonite layer will increase as the slope decreases, while in the saprolite zone the thickness will increase with increasing the degree of slope up to the limit of 16°-25° then the thickness will decrease when crossing that limit. In the limonite zone, the concentration of Ni is maximally concentrated at a high degree of slope (>16°), while in the saprolite zone, Ni content is maximally concentrated on a slope of 16°-25° and then decreases in Ni content when passing through a slope of 25°. Validation of the estimation results and geological modeling using RMSE, MAE, MAPE, and linear regression in the limonite and saprolite zones indicate that the EBK method is a precise method for resource estimation and geological modeling.

La Queglia carbonatitic melnöite: a notable example of an ultra-alkaline rock variant in Italy

Very primitive ultramafic igneous rocks occur at Mt. La Queglia (Abruzzo, Italy). They form a strongly deformed sill–dyke system now tilted vertically. These rocks were initially classified as alnöite and, subsequently, have been suggested to be a carbonatitic olivine melilitite. However, further investigation and interpretation of these rocks is needed due to the presence of hand-specimen-scale textural variation suggesting a complex petrogenesis. We study the texture, mineral chemistry, and whole-rock geochemistry to define three main rock-types. (1) A brecciated rock with an ocellar texture composed of calcite pseudomorphs after olivine and melilite, plus fresh diopside in a groundmass of mica, aegirine, garnet, calcite, apatite, perovskite, titanate and chlorite. Zoned ocelli in this rock show an amoeboid shape, agglutination, and menisci typical of a plastic state. (2) A quenched rock showing a spinifex texture containing long feathery phenocrysts of cpx and mica suspended in a groundmass of nepheline, aegirine, apatite, Ti–rich magnetite, plus abundant calcite and some K-feldspar and zeolites. (3) A coarse-grained rock is composed of calcite plus intergranular glauconite, a mixture of spinel mineral group and Ti–rich magnetite, accessory barite, pyrite, and chabazite-K. The igneous rocks at Mt. La Queglia show extreme SiO2-undersaturation (33.5–37.3 wt% SiO2), high MgO contents and TiO2/Al2O3 ratios. Rock-type 1 has a lower Mg number Mg# = 100 × [Mg/(Mg + Fe2+)], higher Ca number Ca# = 100 × [Ca/(Ca + Mg)], high Cr (up to 720 ppm) Ni (up to 379 ppm), higher rare earth elements (REE) contents as well as La/Lu ratio, compared to rock-type 2. Perovskite and chromite accumulation seems an important agent during rock differentiation. Rock-type 3 shows REE cross-over with rock-type 2 suggesting light (L)REE concentration in a carbothermal residuum. Mt. La Queglia rocks are an end-member compared to other Upper Cretaceous and Paleogene Italian lamprophyres, suggesting a low degree of melting of a HIMU (a colloquialism for “high-μ”; referring to mantle domains with high 238U/ 204Pb) garnet-bearing mantle source.

Source-to-sink analysis of Mesozoic–Cenozoic sandstone-type uranium deposits in the Qaidam Basin

Accurate evaluation of uranium sources and identification of their spatiotemporal correlations with uranium deposits (or sinks) in sedimentary basins are important for exploring sandstone-type uranium deposits. This study examines the source-to-sink system of Mesozoic–Cenozoic sandstone-type uranium deposits in the Qaidam Basin (QB) through a literature review in conjunction with logging and seismic data and yields the following findings. (1) The uranium-supplying capacity of a source rock in the uranium source area depends on primarily its type and to a lesser extent, the tectonic zone where it is located and the episode during which it formed. (2) The initial uranium content, U0, is the core parameter for classifying and evaluating the uranium-supplying capacity of a source rock. At U0 > 1.5 ppm, uranium begins to migrate from a source rock. The uranium variation coefficient, ΔU, and the amount of uranium migration, ΔUt, decrease continuously to –55 % and –5 ppm respectively as U0 increases up to 9.5 ppm, which suggests that at most 5 ppm of uranium in the source rocks can migrate away. As U0 increases beyond 9.5 ppm, ΔU and ΔUt fluctuate around –55 % and –7 ppm respectively, which suggests that approximately 7 ppm of the uranium in the source rocks can migrate away. (3) Of the different types of rocks, silicic igneous rocks (including both intrusive and volcanic igneous rocks) and granitic gneisses have the highest uranium-supplying capacity; intermediate igneous rocks and gneisses come second; mafic–ultramafic igneous rocks and the other metamorphic rocks (except granitic gneiss and gneiss) come third. Of the sub-source areas (tectonic zones), the western segment of the Eastern Kunlun and the Qiman Tagh have the highest uranium-supplying capacity; the Central and Southern Altyn Tagh come second; the others come third. (4) Uranium sources are the fundamental prerequisite for the formation of uranium sinks. Other geological factors control the specific formation process of uranium sinks as well as their spatiotemporal distribution patterns. For QB, the most economic and prospective uranium sink, Neogene formations of Gy anticline, was fed by the source areas which had the highest uranium-supplying capacity. This suggests that the Neogene of WEK anticline belt, Quaternary of Kumukol Basin and Qarqan River Basin are the most noteworthy metallogenic prospective areas. The uranium-source evaluation scheme and “source-to-sink” ore exploration approach introduced in this study have practical value for advancing the exploration of uranium deposits in sedimentary basins in northern China and other parts of the world.

Transformation of low-molecular-weight organic acids by microbial endoliths in subsurface mafic and ultramafic igneous rock.

A growing body of work indicates that continental subsurface rocks host a substantial portion of the Earth's biosphere. However, the activities of microbial cells inhabiting pore spaces and microfractures in subsurface rocks remain underexplored. Here, we develop and optimize microcosm assays to detect organic acid transformation activities of cells residing in mafic to ultramafic igneous rocks. Application of this assay to gabbro core from the Stillwater Mine, Montana, USA, revealed maximal methane production from acetate at temperatures approximating that of the mine. Controls show that these activities are not due to contamination introduced during drilling, exhumation, or laboratory processing of the core. The assay was then applied to rocks cored from the Samail Ophiolite, Oman, which is undergoing low-temperature serpentinization. Production of (i) carbon dioxide from acetate and formate and (ii) methane from formate were detected in a dunite/harzburgite rock core interfacing pH9.6 waters, and estimates of microbial activities were up to three orders of magnitude higher in the rock core pore space than in corresponding waters. The detection of endolithic microbial activities in igneous rocks has implications for life detection on other planetary bodies where similar rock types prevail, such as Mars, Europa and Enceladus.

A Random Forest approach to predict geology from geophysics in the Pontiac subprovince, Canada

Current “visual” integration approaches to map geology from geophysics are challenging, biased toward user assumptions, and time consuming. Applying a supervised machine learning Random Forest method to airborne geophysical data sets is an alternative solution to quickly generate interpretative maps, which can later be validated through targeted and therefore more efficient field campaigns. The approach is tested in the Malartic–Cadillac area of the Pontiac subprovince, Canada. Available airborne geophysical data sets include magnetic, frequency-domain electromagnetic, and radiometric data. Unlike the western part of the area, many studies have been done in the eastern part where the world-class Canadian Malartic gold deposit is located. The eastern part has abundant field observations and well-documented geology that are used as training data for Random Forest learning. A predicted map is built after preprocessing the data, gridding the area into a mesh of nodes and training using known geological knowledge. The results provide new information about the spatial distribution of lithological units, including diabase dikes, felsic-intermediate igneous rocks, mafic–ultramafic igneous rocks, and sedimentary rocks. Comparison between the predicted map and previous geological maps could suggest locations where future field mapping efforts should focus in the Malartic–Cadillac area.

Quantitative verification of 1:35 diluted fused glass disks with 10 mg sample sizes for the wavelength-dispersive X-ray fluorescence analysis of the whole-rock major elements of precious geological specimens

Herein, an improved wavelength-dispersive X-ray fluorescence (WD-XRF) analytical technique for determining the major elements (including SiO2, TiO2, Al2O3, TFe2O3, MnO, MgO, CaO, Na2O, K2O, and P2O5) in precious geological samples, particularly extraterrestrial basaltic rock samples, was developed. For WD-XRF analysis, undersized (approximately 11 mm in diameter) glass disks were prepared by fusing 10 mg of a powdered sample with 350 mg of lithium borate flux at a sample-to-flux ratio of 1:35. Specialized PtAu crucibles and molds were crafted for glass disk preparation to facilitate automatic fluxer mounting. This procedure enabled the automatic preparation of undersized glass disks, with repeatability between sample batches. Calibration curves were constructed for 30 certified reference materials (CRMs), including felsic, intermediate, mafic, and ultramafic igneous rocks. Regular-sized CRM disks with large sample sizes were prepared at the same sample-to-flux ratio as the test samples to avoid issues caused by CRM heterogeneity. The influence of various factors, including glass disk thickness and homogeneity, releasing agent amount, and interference between lines (Br Lα with Al Kα, Rh Lγ2 and Rh Lγ3 with K Kα, and K Kβ with Ca Kα), on analytical accuracy was investigated. Two homogeneous synthetic reference glass samples (ARM-2 and ARM-3) were pulverized and used to verify the analytical results for small samples using the WD-XRF method, which could eliminate the uncertainty caused by sample homogeneity. Subsequently, three CRMs (JB-1b, JA-3, and JR-1) were used to validate the accuracy and precision of the method. Finally, two lunar meteorite samples (NWA4898 and NWA4734) were assayed by the proposed method, and comparison with inductively coupled plasma optical emission spectroscopy results confirmed the reliability of the method. The proposed small sample protocol, which involves the destructive pretreatment of precious and limited extraterrestrial basaltic samples, has great application potential for precious samples such as lunar soil samples.

Multi-proxy provenance of the lower Pennsylvanian Pottsville sandstone of the northern Appalachian basin in Pennsylvania, U.S.A: Paleodrainage, sources, and detrital history

ABSTRACT The lower Pennsylvanian Pottsville Formation, in the Appalachian foreland basin, constitutes a late Paleozoic clastic wedge formed close to the Appalachian orogenic belt. In this study, we analyzed Pottsville sandstone from the western bituminous and eastern anthracite fields in Pennsylvania to evaluate the detrital history of the sediments. Petrographic modal analyses show that sandstone in the western bituminous field ranges from quartzarenite to sublitharenite, with mean composition of Qt84F1L15; sampled sandstone from the eastern anthracite field is dominated by sublitharenite to litharenite with mean composition of Qt70F2L29. Heavy-mineral assemblages from both fields are dominated by ultrastable minerals (zircon, rutile, and tourmaline), apatite, sphene, spinel, siderite, and abundant opaques. Almost all the studied sandstone samples are garnet-depleted except one from the eastern anthracite field. The chemical composition of chromium- and zinc-rich spinel in samples from both fields might suggest exhumation of an arc terrane and ophiolitic belt with ultramafic igneous rocks. Particularly, the ternary plot of Fe3+–Cr3+–Al3+ end members for the chrome spinels possibly suggest a derivation from an alpine-type peridotite complex. Laser 40Ar/39Ar analyses of detrital muscovite from eastern anthracite fields and western bituminous fields record separate ages, with the former characterized by prominent Middle to Late Ordovician Taconic and Middle Devonian Acadian ages with two discrete modes at 463 and 369 Ma, and the latter dominated by Late Ordovician Taconic, Middle Devonian Acadian, and Late Devonian Neoacadian ages with discrete modes at 445, 397, 360, and 351 Ma. The new data suggest that early Pennsylvanian sedimentation in the Appalachian foreland basin was controlled by southward, southwestward, and westward drainage systems that originated in the Appalachian orogenic belt to the east and northeast.

Texture and Trace Element Composition of Rutile in Orogenic Gold Deposits

AbstractRutile from a wide range of orogenic gold deposits and districts, including representative world-class deposits, was investigated for its texture and trace element composition using scanning electron microscopy, electron probe microanalysis, and laser ablation-inductively coupled plasma-mass spectrometry. Deposits are hosted in various country rocks including felsic to ultramafic igneous rocks and sedimentary rocks, which were metamorphosed from lower greenschist to middle amphibolite facies and with ages of mineralization that range from Archean to Phanerozoic. Rutile presents a wide range of size, texture, and chemical zoning. Rutile is the dominant TiO2 polymorph in orogenic gold mineralization. Elemental plots and partial least square-discriminant analysis suggest that the composition of the country rocks exerts a strong control on concentrations of V, Nb, Ta, and Cr in rutile, whereas the metamorphic facies of the country rocks controls concentrations of V, Zr, Sc, U, rare earth elements, Y, Ca, Th, and Ba in rutile. The trace element composition of rutile in orogenic gold deposits can be distinguished from rutile in other deposit types and geologic settings. Elemental ratios Nb/V, Nb/Sb, and Sn/V differentiate the rutile trace element composition of orogenic gold deposits compared with those from other geologic settings and environments. A binary plot of Nb/V vs. W enables distinction of rutile in metamorphic-hydrothermal and hydrothermal deposits from rutile in magmatic-hydrothermal deposits and magmatic environments. The binary plot Nb/Sb vs. Sn/V distinguishes rutile in orogenic gold deposits from other geologic settings and environments. Results are used to establish geochemical criteria to constrain the source of rutile for indicator mineral surveys and potentially guide mineral exploration.

Preferential groundwater flow directions in a pseudokarst system in Colombia, South America

The correct identification of recharge zones and understanding of groundwater flow through fractured and karstic media are some of the main issues in hydrogeology and are of utmost importance for managing groundwater resources. The Aburra Valley is an excellent example of a promising aquifer system for future water supply in Colombia, with recharge zones and hydrogeological units (HGU) still not well understood. One of those HGUs, the Medellin Dunite, is an ultramafic igneous rock with significant secondary porosity due to the high grade of fracturing and the presence of a pseudokarst system formed by the dissolution of magnesium-rich minerals. In this study, we aimed for the first approximation of this unit's hydrogeologic characteristics by performing a hydro-structural analysis based on a systematic collection of structural data in rock outcrops and secondary information available on karstic landforms. In order to improve the understanding of the relations between the analyzed HGU and the other units in the Aburra Valley, the main objective of our investigation was to calculate the hydraulic weight of discontinuities and determine the associated preferential groundwater flow directions. The results showed that the predominant directions of groundwater flow are WNW and ENE, which imply that lateral flows from the Dunite not only recharge the alluvial aquifers of the Aburra Valley Aquifer System (AVAS) but could also be recharging the San Nicolas Valley Aquifer System (SNVAS), another region with high rates of population growth. However, detailed studies are needed to establish the connections of the Dunite with the Medellin Amphibolite and other hard rocks of the SNVAS. Our findings show the importance of studying the Medellin Dunite and implementing management and protection measures for this aquifer unit.

Petrology and geochemistry of early Permian mafic–ultramafic rocks in the Wajilitag area of the southwestern Tarim Large Igneous Province: Insights into Fe-rich magma of mantle plume activity

The majority of global Fe–Ti-oxide deposits hosted in mafic–ultramafic layered intrusions are closely related to mantle plume activity. The metallogenesis of these Fe–Ti-oxide deposits is still debated, especially with regard to their mantle source and relationship to magmatism. Here we report detailed petrology and geochemistry for early Permian (ca. 280 Ma) mafic–ultramafic igneous rocks in the Wajilitag area of the western Tarim Large Igneous Province (TLIP) to establish the relationships among mantle source, magmatism, and metallogenesis in mantle plume activity. The mafic rocks (i.e., gabbro and diabase) show alkaline affinities and OIB-like trace-element patterns. Clinopyroxenites closely related to Fe–Ti-oxide deposits were derived from the same magmatic system as that of the mafic rocks. The primary magma of the Wajilitag mafic rocks was enriched in FeOT and TiO2 and depleted in SiO2, and has high FC3MS (FeOT/CaO − 3MgO/SiO2) and Fe/Mn, indicating the involvement of Si-poor pyroxenite/eclogite in the mantle source. Primary olivines from the Wajilitag gabbro have consistently high NiO and Fe/Mn. Wajilitag mafic rocks have variable Sr–Nd–Hf isotopes owing to their derivation from a hybrid mantle source with the involvement of subducted oceanic crust and sediments. Subducted slabs within the upper mantle are inferred to have been entrained by the upwelling mantle plume and preferentially melted to produce mainly Fe-rich magma. The occurrence of an adjacent oceanic subduction event just prior to the operation of a mantle plume played a crucial role in the formation of large-scale Fe–Ti-oxide deposits in LIPs.

PENAMBANGAN BATU SPLIT YANG MENYISAKAN KELERENGAN TERJAL DI DAERAH AWANGBANGKAL, KECAMATAN KARANGINTAN, KABUPATEN BANJAR, PROVINSI KALIMANTAN SELATAN

Mining of split rock or ultramafic igneous rock, located in the Awangbangkal area, Karangintan District, Banjar Regency, South Kalimantan Province, causes steep slopes. The formation of the Meratus Mountains is an oceanic bedrock that is exposed to the earth's surface and is mined by local residents using simple tools or semi-mechanical equipment carried out by the company. Positive impacts arise but negative impacts will also build up over time. Day by day more dangerous slopes were formed. The local government became worried because it was dangerous. This writing is compiled based on the results of direct measurements in the field using the Theodolith unit. The measurement results are processed using Autocad Landesktop 2009 software. The analysis is by classifying the slope of the formed slopes according to the data that is already in digitized form. The result is a dangerous area on the east side, because it has a slope of 25% -45% (steep). Although from a geological point of view this area is stable because it is formed by igneous rocks, from the local government side this is a concern for the people who do work in the area.

Storing CO2 in buried volcanoes

Australia contains rich natural gas resources, but many of Australia’s currently producing and undeveloped gas fields contain relatively high CO2 contents; if not captured and stored, the venting of co-produced CO2 could hinder efforts to meet Australia’s emission reduction targets. The most mature technology for isolating produced CO2 from the atmosphere is by containing it in deep sedimentary formations (e.g. saline aquifers or depleted oil and gas reservoirs). The effectiveness of this approach is dependent on factors such as reservoir capacity, the presence of low-permeability seals that physically impede vertical migration of injected CO2, the chemical reactivity of both reservoir and seal minerals, the risk for leakage, and a gas-entrapping structure. An alternative and attractive mechanism for permanent storage of CO2 is geochemical or mineral trapping, which involves long-term reactions of CO2 with host rocks and the formation of stable carbonate minerals that fill the porosity of the host rock reservoir. Natural mineral carbonation is most efficient in mafic and ultramafic igneous rocks, due to their high reactivity with CO2. Here we review the outcomes from a series of recent pilot projects in Iceland and the United States that have demonstrated high potential for rapid, permanent storage of CO2 in basalt reservoirs, and explore the practicalities of geochemical trapping of CO2 in deeply buried basaltic volcanoes and lava fields, which are found in many basins along the southern (e.g. Gippsland Basin) and northwestern (e.g. Browse Basin) Australian margins, often in close proximity to natural gas fields with high CO2 content.

Neoarchean A-type acid metavolcanics in the Keivy Terrane, northeastern Fennoscandian Shield: Geochemistry, age, and origin

The Lebyazhka acid metavolcanics occupying 40% of the Keivy Terrane in the Arctic Region of the Fennoscandian Shield belong to mainly alkali-calcic and calc-alkaline series and are classified as peraluminous to metaluminous metadacites, metarhyodacites, metarhyolites and metatrachyrhyolites. Geochemical characteristics of most of these metavolcanics are very close or identical to those discriminative of A-type granites. Compositionally these rocks are similar and often identical to the Keivy A-type peralkaline granites. On variation plots and geochemical spider and discriminant diagrams the Lebyazhka acid metavolcanics and Keivy peralkaline granites share the same trends and patterns and fall into fields of post-orogenic, within-plate and A-type granites. A U–Pb (SHRIMP II) zircon age of the Lebyazhka acid metavolcanics is 2678 ± 7 Ma. The first thermal event recorded by the U–Pb isotope system of magmatic zircon occurred at ca. 1.90 Ga, an age corresponding to the termination of the Paleoproterozoic Lapland-Kola collisional orogeny. The youngest zircon generation is dated at 1805 ± 23 Ma ago and is assumed to have grown during metasomatic or hydrothermal alteration.The finding of relics of baddeleyite, a mineral crystallizing only in mafic and ultramafic igneous rocks, in zircon from the Lebyazhka acid metavolcanics along with the chemical similarity of these metavolcanics and the Keivy peralkaline granites and their emplacement simultaneously with the Keivy gabbro-anorthosites 2.68–2.66 Ga ago, obviously suggests that these three types of rocks should have a common origin. Based on new data and existing tectonic models, the origin of the Lebyazhka acid metavolcanics as well as the Keivy peralkaline granites, gabbro-anorthosites and nepheline syenites is concluded to be linked with underplating by basaltic magma of the lower crust of the eastern Kola Province 2.68 Ga ago. This underplating led to anorogenic bimodal magmatism including the 2678 Ma Lebyazhka acid metavolcanics, the 2674–2663 Ma Keivy peralkaline granites, the 2674–2659 Ma Keivy gabbro-anorthosites, and the 2645 Ma Sakharjok nepheline syenites and subalkaline gabbro. The underplating also caused partial melting of the Mesoarchean continental crust and involvement of this older crustal component into felsic melts parental for the Lebyazhka acid metavolcanics and the Keivy peralkaline granites.

Carbonates at the supergiant Olympic Dam Cu-U-Au-Ag deposit, South Australia. Part 1: Distribution, textures, associations and stable isotope (C, O) signatures

The supergiant Olympic Dam Cu-U-Au-Ag deposit in South Australia is a type example of the iron-oxide copper–gold (IOCG) deposit family. Hosted entirely within heterogeneous breccia in 1.59 Ga granite, the deposit contains a volumetrically substantial and mineralogically diverse component of carbonate minerals. Carbonate minerals are always associated with ore minerals (sulfides, uraninite), implying a genetic relationship and providing an opportunity to use gangue carbonates to better understand ore formation. This study provides the first detailed and comprehensive petrographic and chemical/isotopic study of Olympic Dam carbonates, with a particular emphasis on petrography and texture, and an attempt is made to relate carbonate formation to local and regional events that have affected Olympic Dam.Based on a set of 196 carbonate-bearing samples, carbonate minerals are observed in all lithologies present at Olympic Dam. Carbonates occur as cement in breccia and conglomerates, as breccia clasts, in veins crosscutting ore-rich breccia and other rock types, in pores and ooids, and in the form of laminated carbonate. Siderite and siderite-rhodochrosite-magnesite solid solution are by far the most common carbonate types, whereas calcite, dolomite-ankerite solid solution and REE-fluorocarbonates are locally abundant. Single carbonate grains typically show compositional zones (simple or oscillatory) and replacement textures (including mutual replacement of carbonates with other carbonates and with hematite) are common. In the absence of consistent, deposit-wide paragenetic relationships, the carbonates were placed in seven associations based on host rock, mineralogy and texture: (1) coarse-grained calcite veins in weakly brecciated granite and rhyolite, (2) carbonates in strongly brecciated granite, (3) carbonate veins in bedded clastic facies, (4) carbonates in mafic and ultramafic igneous rocks, (5) massive barite-fluorite-dominated veins with minor carbonate, (6) laminated siderite, and (7) carbonate matrix in conglomerate-breccia-sandstone above the unconformity. Some of these associations can be related to regional tectonic events based on local context and relationships with dated assemblages. δ13C (−6.5‰ to −2‰) values for the carbonates show a relatively limited range whereas δ18O is more variable (+9.4‰ to + 20.9‰). C-O isotopic compositions for the various carbonate associations tend to overlap, suggestive of mixed fluid sources, recycling of older carbonate and perhaps other fractionation processes. The C-O isotope data overlap the compositional fields of several major carbon–oxygen reservoirs (magmatic, sedimentary) and carbon sources in local granite, felsic volcanics, older BIF and sedimentary rocks are all possible at different stages of carbonate deposition.

Characteristics of Ultramafic Igneous Rock Ofiolite Complex in Asera District, North Konawe Regency Southeast Sulawesi Province

The research area is located in Asera District, North Konawe Regency, Southeast Sulawesi Province which has ultramafic rock lithology. The purpose of this study is to determine the characteristics of ultramafic igneous rocks using petrographic and geochemical analysis. Petrographic analysis aims to determine the types and abundance of minerals present so that rock types can be determined based on the classification of Travis (1955) and Streckeisen (1976). The geochemical analysis aims to determine the oxide/major element so that it can determine the type of magma based on the AFM classification according to Irvine and Baragar (1971) and the origin of the magma / original rock formation environment based on Pearce (1977). Petrographic analysis results showed that ultramafic rocks in the study area consisted of 2 types of rocks namely peridotite consisting of wherlit and lherzoite and serpentinite. The results of geochemical analysis indicate that the type of magma in the study area is thoellitic series and the origin of the magma/rock formation environment comes from the expansion of the oceanic floor or mid oceanig ridge (MOR) which is ultramafic.