Igneous Rock Samples Research Articles

Quantitative analysis of major and trace elements in NH4HF2-modified silicate rock powders by laser ablation - inductively coupled plasma mass spectrometry

In this paper, we described a NH4HF2 digestion method as sample preparation for the rapid determination of major and trace elements in silicate rocks using laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS). Sample powders digested by NH4HF2 at 230 °C for 3 h form ultrafine powders with a typical grain size d80 < 8.5 μm, and various silicate rocks have a consistent grain morphology and size, allowing us to produce pressed powder pellets that have excellent cohesion and homogeneity suitable for laser ablation micro-analysis without the addition of binder. The influences of the digestion parameters were investigated and optimized, including the evaporation stage of removing residual NH4HF2, sample homogenization, selection of the digestion vessel and calibration strategy of quantitative analysis. The optimized NH4HF2 digestion method was applied to dissolve six silicate rock reference materials (BCR-2, BHVO-2, AGV-2, RGM-2, GSP-2, GSR-1) covering a wide range of rock types. Ten major elements and thirty-five trace elements were simultaneously analyzed by LA-ICP-MS. The analytical results of the six reference materials generally agreed with the recommended values, with discrepancies of less than 10% for most elements. The analytical precision is within 5% for most major elements and within 10% for most trace elements. Compared with previous methods of LA-ICP-MS bulk analysis, our method enables the complete dissolution of refractory minerals, such as zircon, in intermediate-acidic intrusive rocks and limits contamination as well as the loss of volatile elements. Moreover, there are many advantages for the new technique, including reducing matrix effects between reference materials and samples, spiking the internal standard simply and feasibly and sample batch processing. The applicability filed of the new technique in this study was focused on the whole-rock analysis of igneous rock samples, which are from basic rocks to acid rocks (45% < SiO2 < 73%). However, we thought that the NH4HF2 digestion method can be used as a new alternative in LA-ICP-MS for a wider range of geological samples, and will significantly accelerate the application of LA-ICP-MS for the whole-rock analysis.

Geochemical modelling of terrestrial igneous rock compositions using laboratory thermal emission spectroscopy with an overview on its applications to Indian Mars Mission

We attempt geochemical modelling of igneous rock samples with a range of compositions using laboratory-generated thermal emission spectra. Igneous rock samples, plutonic and volcanic variants of alkaline and sub-alkaline composition were used for the analysis. The collected rock samples were analysed for mineralogical composition, mineral chemistry, and bulk rock chemistry using various techniques. Laboratory thermal emission spectrometer was developed by attaching an in-house fabricated emissivity apparatus to FTIR spectrometer thus, modifying the optical path of FT-IR spectrometer. Rock samples, chipped for the fresh surface, of fist size, were used to generate emissivity spectra. The emissivity spectrum of each rock sample so generated was deconvolved into its constituent minerals with the help of a spectral library of end-member minerals and using simple linear retrieval algorithm. The deconvolution was achieved by reducing RMS error while matching the measured spectrum to the modelled spectrum. Mineral chemistry and bulk rock chemistry was derived from the modelled spectrum with the help of the spectral library of end-member minerals developed by ASU, USA. We applied the existing IUGS classification scheme for all the analysed rock samples based on bulk rock chemistry derived using thermal emission spectroscopy and compared with measured bulk chemistry from XRF. The method is found to be useful in the classification of both plutonic and volcanic rock types within an error limit of 1σ. The classification is effective in differentiating alkaline rock types from sub-alkaline varieties. Measured and modelled silica percentage is found to be closely matching whereas total alkali shows over and under estimation. The emissivity spectra of collected rock samples were resampled to 12 bands corresponding to the spectral bands of Thermal Infrared Imaging Spectrometer (TIS) onboard Indian Mars Orbiter Mission. The analysis shows that TIS will be able to differentiate major Martian surface compositions. Consequently, we believe that the instrument will help us to improve our understanding on Martian surface in particular and its evolution and crustal differentiation in general.

Analysis and Discrimination of Sedimentary, Metamorphic, and Igneous Rocks Using Laser-Induced Breakdown Spectroscopy

This study deals with the analysis of rocks using laser-induced breakdown spectroscopy (LIBS) coupled with principal component analysis. The spectra of sedimentary, metamorphic, and igneous rock samples were recorded in the 200–900 nm spectral range. The atomic lines of elements such as Si, Ca, Mg, Fe, Na, and K along with lighter elements, namely C, H, N, and O, were observed in these spectra. Multivariate analysis in combination with LIBS was used to classify the samples. For principal component analysis, a 12 × 5849 data matrix was formed using the results of LIBS. The plot of the analysis revealed similarities between the sedimentary and metamorphic rock samples compared with the igneous rock sample. Thus, the present study demonstrates that LIBS coupled with principal component analysis can become an important tool for rapid classification and in-situ discrimination of rock samples.

Gamma Radiation Measurements of Naturally Occurring Radioactive in Igneous Rocks and Its Radiological Complications

The concentrations of natural radioactivity were measured in igneous rock samples collected from Albaha region in the south west of Saudi Arabia. A high purity germanium (HPGe) detector was used for analysis. The average activity concentrations for 226Ra, 232Th and 40K were 35, 31.52 and 843.63 Bq kg−1, respectively. The average absorbed dose rate was 70.86 nGy⋅h−1 with a corresponding average annual effective dose 0.09 mSv⋅y−1. The average radium equivalent activity value was 145.84 Bq⋅kg−1, lower than the international limit 370 Bq⋅kg−1. The external and internal indices average values were 0.39 and 0.49, respectively. The average results obtained in this study are lower than the average national and world recommended values, therefore, there is no health risk to the populace of the area. This study provides a baseline map of background radioactivity levels in the Saudi environment and will be used as reference information to assess any changes in the level background due to geological processes.

The paleolacustrine evolution of Juventae Chasma and Maja Valles and its implications for the formation of interior layered deposits on Mars

Juventae Chasma, Mars, is an approximately 7km deep basin located in close vicinity of Valles Marineris. It extends for ∼190km east-west and ∼270km north-south and exhibits several light-toned interior layered deposits (ILDs). These deposits form four large and distinctive light-toned mounds referred to as mound A, B, C, and D, from south to north. The deposits, with thicknesses up to several kilometers, consist dominantly of Mg-, Fe-rich anhydrous, or simple hydrated sulfate minerals at the base partly overlain by hydrated sulfates, suggesting precipitation as a result of evaporation processes related to chemical reactions of sulfate solutions with martian rocks. Results of experimentally produced sulfate solutions containing Mg, Na, K, Ca, Fe, and Al cations are used to simulate such evaporation processes in Juventae Chasma. Rock/fluid interactions were studied by leaching igneous mineral and rock samples including the martian meteorite Tissint with pH 1.3 sulfuric acid solutions. The resulting fluids were then chemically analyzed and numerically evaporated at 25 °C, 75 °C, and between 100° and 200 °C using the Geochemist's Workbenchۛ software. The resulting sulfate precipitations were similar to those sulfates observed in Juventae Chasma. This enabled the development of a paleolacustrine model of the Juventae basin including the evolution of the Maja Valles outflow channel system. The results indicate that sulfuric acid solutions were in contact with olivine minerals to form these sulfate-rich outcrops on the surface of Mars or olivine-bearing rocks with a mineral composition of a peridotite on or within the martian regolith at the time of the late Noachian or Hesperian. Simulated moderate to warm conditions (25° ̶ 200 °C) were used to explain the characteristic stratigraphy of multiply hydrated sulfate precipitation above anhydrous or less hydrated sulfates in lake water, with a water volume large enough to fill Juventae Chasma and to form Maja Valles.

ANALÝZA LABORATORNÍCH HODNOT RADIOAKTIVITY HORNIN NA MAPOVÉM LISTU 15-11 ZLATÉ HORY

Natural radioactive elements (potassium, uranium and thorium) abundances were measured in 769 samples of metamorphic and igneous rocks and pre-Cenozoic sedimentary rocks from all geological units on the map sheet 15-11 Zlaté Hory, using a laboratory gamma-ray spectrometer. Metamorphic rocks belong to two geological units of the Silesicum: to the Vrbno Group (a volcanosedimentary complex composed mainly of phyllites, quartzites, amphibolites, greenschists, acid to intermediate metavolcanites and their metatuff s) and the Desná Group (metagranites and blastomylonites). Unmetamorphosed pre-Cenozoic sedimentary rocks are represented by three Variscan flysch formations – the Andělská Hora, Horní Benešov, and Moravice Fms. (rocks of the first formation are unmetamorphosed to anchimetamorphosed), only in small areas by Cretaceous sandstones of the Peruc-Korycany Formation and Devonian limestones of the Líšeň Formation. Unmetamorphosed magmatites are represented by granitoids, lamprophyres andmicrogabbro. From calculated values of mass activity of 226Ra equivalent it is evident that natural radioactivity of most of the studied rocks is low. Slightly increased mass activity values were found in feldspar-rich quartzites (186 Bq.kg-1 on average), metakeratophyres (200 Bq.kg-1) and felsic metatuff s (229 Bq.kg-1) of the Vrbno Group.

Log‐ratio transformed major element based multidimensional classification for altered High‐Mg igneous rocks

AbstractA new multidimensional classification scheme consistent with the chemical classification of the International Union of Geological Sciences (IUGS) is proposed for the nomenclature of High‐Mg altered rocks. Our procedure is based on an extensive database of major element (SiO2, TiO2, Al2O3, Fe2 , MnO, MgO, CaO, Na2O, K2O, and P2O5) compositions of a total of 33,868 (920 High‐Mg and 32,948 “Common”) relatively fresh igneous rock samples. The database consisting of these multinormally distributed samples in terms of their isometric log‐ratios was used to propose a set of 11 discriminant functions and 6 diagrams to facilitate High‐Mg rock classification. The multinormality required by linear discriminant and canonical analysis was ascertained by a new computer program DOMuDaF. One multidimensional function can distinguish the High‐Mg and Common igneous rocks with high percent success values of about 86.4% and 98.9%, respectively. Similarly, from 10 discriminant functions the High‐Mg rocks can also be classified as one of the four rock types (komatiite, meimechite, picrite, and boninite), with high success values of about 88%–100%. Satisfactory functioning of this new classification scheme was confirmed by seven independent tests. Five further case studies involving application to highly altered rocks illustrate the usefulness of our proposal. A computer program HMgClaMSys was written to efficiently apply the proposed classification scheme, which will be available for online processing of igneous rock compositional data. Monte Carlo simulation modeling and mass‐balance computations confirmed the robustness of our classification with respect to analytical errors and postemplacement compositional changes.

The Lake Krasnoe obsidian source in Chukotka (Northeastern Siberia): geological and geochemical frameworks for provenance studies in Beringia

Basic data on the geology and geochemistry of obsidian from the Lake Krasnoe source in Chukotka (Northeastern Siberia) are reported for the first time. The data are based on 2009 fieldwork and analytical studies of igneous rock samples. The lake shore and surrounding parts of the Rarytkin Range were thoroughly examined. Two geochemical types of rhyolitic obsidian were recognized for the first time: (1) metaluminous obsidian related to the fine-grained crystalline rocks and (2) peralkaline obsidian corresponding to ignimbrite ash-flows or lapilli-tuffs composition. Both types are related to the final phase of acidic volcanism in the Western Kamchatkan-Koryak Volcanic Belt. Based on the results obtained, we conclude that accumulation of obsidian pebbles in the lake’s modern beach deposits is related to silicic melts that erupted during the late Eocene-early Oligocene in the form of extrusive domes or pyroclastic flows, which are now either covered by Quaternary sediments or located below the water level. The Lake Krasnoe obsidian was intensively used by the ancient populations of Chukotka as a raw material for making stone tools. It was also occasionally transported to Alaska across the Bering Strait in later prehistory. The distances between source and utilization sites are up to 700–1100 km. Geochemical data for Lake Krasnoe obsidian, based on neutron activation analysis and X-ray fluorescence that are presented here, can now be used for provenance studies in the Northeastern Siberia and adjacent regions of northern North America.

A ca. 2.60 Ga tectono-thermal event in Western Shandong Province, North China Craton from zircon U–Pb–O isotopic evidence: Plume or convergent plate boundary process

Voluminous Neoarchean plutonic and supracrustal rocks are well developed in the Western Shandong Province of the North China Craton, which has been divided into a late Neoarchean crustally-derived granite belt, a middle to early Neoarchean ancient rock belt and a late Neoarchean juvenile rock belt. Earlier studies provided reconnaissance evidence for ∼2.60Ga metamorphism in some areas. This study presents SHRIMP zircon U–Pb dating and O isotope analysis on nine metamorphosed igneous rock samples (gneissic tonalite, gneissic trondhjemite, gneissic quartz diorite and meta-gabbro) from the ancient rock belt. Magmatic zircons vary in age from 2.74Ga to 2.60Ga, whereas metamorphic and anatectic zircons vary in age from 2.63Ga to 2.59Ga, with an age peak of 2.61Ga. In this study, we identified 2.69–2.67Ga metamorphic zircons for the first time. Most of zircons, whether magmatic or metamorphic, have δ18O values of +4.5‰ to +6.5‰ (V-SMOW). However, the oldest tonalite sample with a protolith age of 2735Ma has zircons showing low δ18O (V-SMOW) values, particularly in recrystallized domains and overgrowths. This suggests at least in local crustal extension and influx of meteoric water during the evolution of the rocks. Combined with data from earlier studies, we draw the conclusion that the Western Shandong Province experienced a regional tectono-thermal event at ∼2.60Ga, as a result of high heat flow and crustal extension, perhaps caused by a mantle plume or mantle overturn activity. Therefore we conclude that 2.60Ga can be regarded the break between early and late Neoarchean crustal accretion. The O isotope study indicates that in some cases, trondhjemitic leucosome was not derived from nearby gneissic tonalite, although they show a close relationship in outcrop.

Multiple sources for volcanic rocks dredged from the Western Australian rifted margin

Abstract Igneous rock samples recovered during the 2008–09 Australian Southwest Margin Marine Reconnaissance Survey (GA-2476), off the Western Australian coast from Perth to the Wallaby Plateau, come from a variety of tectonic settings reflecting a complex magmatic history of this margin. Cretaceous rhyolite and basaltic andesite samples most likely erupted in a continental extensional setting, while younger volcanic samples reflect a transition to a mature passive continental margin with the generation of mid-ocean ridge basalt. During the last phase of volcanism, a series of volcanic cones and mounds with ocean island basalt geochemical signatures formed along the margin. The pre-rift sedimentary rocks sampled on the Wallaby Plateau support the viewpoint that it is an extended block of continental crust, overlain by syn-rift and post-rift volcanic rocks.

Tracking deep crust by zircon xenocrysts within igneous rocks from the northern Alxa, China: Constraints on the southern boundary of the Central Asian Orogenic Belt

The southern boundary of the central segment of the Central Asian Orogenic Belt (CAOB) with the Precambrian Alxa Block is not well constrained due to poor recognition of deep crust. Statistical analysis of zircon xenocrysts within igneous rocks from the northern Alxa and its adjacent regions was applied to resolve this problem. We compiled new and previously published geochronological zircon age data obtained by SHRIMP, SIMS, TIMS, and LA-ICP-MS for 316 igneous rock samples of which 61 samples contain zircon xenocrysts. New and previously published Hf isotopic compositions of these zircon xenocrysts are combined with zircon ages in this study. The zircon xenocrysts are mainly contained within Permian rocks from the Yabulai–Nurgong–Honggueryulin (YNH) zone and igneous rocks from the northwestern margin of the North China Craton (WNCC). A few xenocrysts were also found in Permian igneous rocks from the Zongnaishan–Shalazhashan (ZS) zone, Neo-proterozoic and Paleo-proterozoic intrusive rocks in the YNH zone, as well as Devonian to Carboniferous granitoids and volcanic rocks from southern Mongolia. Altogether we analyzed more than 270 zircon xenocrysts and considered only ages that are less than 10% discordant. Xenocryst ages within the Permian igneous rocks from the ZS zone are mainly around ca. 350Ma, ca. 600Ma and ca. 1400Ma. The oldest age of zircon xenocrysts in this zone is similar to those of zircon xenocrysts from the CAOB (∼1.1Ga). By contrast, abundant zircon xenocrysts within Permian igneous rocks from the YNH zone show highly variable age populations at ca. 2.6–2.1Ga, 1.8–1.6Ga, 930–750Ma and 460–300Ma. Zircon xenocrysts from the ZS zone have positive εHf(t) values of +6.3 to +13.9, whereas those from the YNH zone display highly variable εHf(t) values from −16.1 to +11.6. From the southern CAOB and the ZS zone to the YNH zone, the zircon xenocrysts show a significant shift from juvenile to crustal Hf isotopic compositions, suggesting that the area between the ZS and the YNH zones constitutes the southern boundary of the CAOB in the deep crust within this region. Our study indicates that statistical analysis (or isotopic mapping) of zircon xenocrysts is an effective method to trace the nature of the deep continental crust and to separate between newly-formed orogenic domain and ancient cratons.

Determination of divalent iron content in igneous rocks of ultrabasic, basic and intermediate compositions by a wavelength-dispersive X-ray fluorescence spectrometric method

This paper proposes the quantitative wavelength-dispersive X-ray fluorescence (XRF) technique of divalent iron content determination in igneous rocks and reports specifics of this technique in terms of classifying rocks into ultrabasic, basic, intermediate and acid ones. Unlike the widely used technique of titration, the proposed XRF technique does not require a labor-consuming procedure for sample preparation. In the fields of FeKβ5 line, and FeKβ′ and FeKβ″ satellites relative intensities of XRF emission spectrum lines are dependent on the valence state of iron in minerals. The ratio FeKβ5/FeKβ1,3 is preferred as the analytical parameter. The XRF method allows divalent iron content (expressed as FeO oxide) over 1.5% to be measured in igneous rocks of ultrabasic and basic compositions by the common calibration equation with the error below 10rel. %, that is comparable with the error of titrimetric analysis. The samples of igneous rocks of intermediate composition and granodiorites should be analyzed using calibration equations obtained with certified reference materials corresponding in composition to the study samples. For the samples of alkaline rocks the errors of FeO content determination might be in excess of 50rel. %.

A new high-precision method for determining stable chlorine isotopes in halite and igneous rock samples using UV-femtosecond laser ablation multiple Faraday collector inductively coupled plasma mass spectrometry

A new analytical protocol for measurement of stable chlorine isotopes was proposed for LA-MFC-ICPMS.

Reaction of Hydrothermally Altered Volcanic Rocks in Acid Solutions

Rock matrix stimulation has been used to clean, to recover and to enhance well productivity in oil systems. Recently, for the same purposes this methodology began to be applied in geothermal systems. In order to investigate the solubility of altered volcanic rocks in acid solution used in rock matrix stimulation; experiments were carried out on samples of igneous hydrothermal altered rocks from the Los Humeros geothermal reservoir. Industrially, the common acid solutions used during acid well stimulation are HCl 10% and a mixture of HCl 10% and HF 5%. In this work, experiments were conducted in the laboratory using the referred acid solutions at atmospheric pressure and temperature of 110 ± 5°C. The chemistry, the mineralogy and the permeability of selected rocks from Los Humeros geothermal field were determined before and after the reaction with each acid solution. Mineral dissolution is selective and depends on the permeability of the rocks, the type and the intensity of hydrothermal alteration. As it is expected, Calcite readily reacts with acids leaving empty cavities, veins and micro fractures (worm holes). Calc-silicates are resistant to acid solutions. If Calcite is absent dissolution of minerals is observed in the external surfaces of the specimen in contact with the acid solution giving rise to a rough texture and leaving the rock matrix unreacted

Estimation of Sound Level Produced During Drilling of Igneous Rock Samples Using a Portable Drill Set-up

The mechanical strength of rock is one of the most important factors of concern to engineers involved in mining operations. Information about rock strength is used in rock excavation planning and design operations in civil and mining engineering. Drilling is widely carried out in hard rocks for blasting the rock mass so that the blasted material can be easily loaded by the excavators. The drillability of rock depends on many factors including rock properties whereas properties such as compressive strength, porosity, density etc. are uncontrollable parameters during drilling process. A number of studies have been reported recently on the application of sound level which have been concentrated on using either CNC or jack hammer machine for drilling purpose. It is worth mentioning that neither CNC machine nor jack hammer drill set-up is the normal way of drilling in rock, nor in mining, civil or any other operations, not even in working with rock in installation of countertops. Therefore, it is difficult to exactly say whether the noise generated during drilling is only from the rock drilling or from the drilling unit itself. In view of the above, it is important to fabricate a new drilling set-up which is a silent unit in itself. Such unit when used for drilling purpose will clearly indicate the change in sound level produced with different rock properties.

Laser-induced breakdown spectroscopy for in situ qualitative and quantitative analysis of mineral ores

In this work, the potential of laser-induced breakdown spectroscopy (LIBS) for discrimination and analysis of geological materials was examined. The research was focused on classification of mineral ores using their LIBS spectra prior to quantitative determination of copper. Quantitative analysis is not a trivial task in LIBS measurement because intensities of emission lines in laser-induced plasmas (LIP) are strongly affected by the sample matrix (matrix effect). To circumvent this effect, typically matrix-matched standards are used to obtain matrix-dependent calibration curves. If the sample set consists of a mixture of different matrices, even in this approach, the corresponding matrix has to be known prior to the downstream data analysis. For this categorization, the multielemental character of LIBS spectra can be of help. In this contribution, a principal component analysis (PCA) was employed on the measured data set to discriminate individual rocks as individual matrices against each other according to their overall elemental composition. Twenty-seven igneous rock samples were analyzed in the form of fine dust, classified and subsequently quantitatively analyzed. Two different LIBS setups in two laboratories were used to prove the reproducibility of classification and quantification. A superposition of partial calibration plots constructed from the individual clustered data displayed a large improvement in precision and accuracy compared to the calibration plot constructed from all ore samples. The classification of mineral samples with complex matrices can thus be recommended prior to LIBS system calibration and quantitative analysis.

Mineralogical and geochemical responses of coal to igneous intrusion in the Pansan Coal Mine of the Huainan coalfield, Anhui, China

The Huainan coalfield, where magma is commonly intruded into the coal measures in the northern section, (e.g., the Zhuji, Dingji, Pansan, and Panbei mines), is the largest energy base in eastern China.To investigate the mineralogical and geochemical responses of coal to igneous intrusion, minerals, major and trace elements in sandstone, thermally-altered coal, igneous rock, sandy mudstone, and unaltered coal samples were collected from a representative profile of the No. 1 Coal of the Pansan Coal Mine. The samples were analyzed using an optical microscope, powder X-ray diffraction, scanning electron microscopy in conjunction with X-ray energy dispersive spectroscopy, X-ray fluorescence, inductively coupled plasma atomic emission spectrometry and mass spectrometry. The results indicated that the thick sill transformed from mafic rocks at the bottom, via intermediate rocks in the middle to felsic rocks at the top of the profile. The moisture, total sulfur, and carbon contents of the coal increased, whereas volatile matter, hydrogen, and nitrogen decreased during contact metamorphism caused by igneous intrusion. Epigenetic minerals (i.e., dolomite, quartz, and pyrite) occurred in the thermally-altered coals. Three stages of hydrothermal fluids (i.e., Ca-, Mg-, and Fe-rich; Si-rich; and Fe- and/or H2S-rich solutions) were identified. Iron, Ca, S, Si, Mg, Zn, Cd, and Pb were transported into the thermally-altered coal by hydrothermal fluids. The concentrations of Co and Ni in the thermally-altered coal increased in relation to the increase of ash yields that were caused by contact metamorphism, whereas the B in the coal was volatilized. Manganese is directly related to the intrusive magma. Phosphorus, Ge, and Sr might be introduced into the coal by groundwater; however, K, Na, Ga, and Ba were leached out. Titanium, Sc, Cr, V, Cu, Zr, Nb, and rare earth elements and yttrium (REY) in the coals originated from terrigenous input and were not influenced by igneous intrusion.

Measurements of Naturally Occurring Radioactive Materials for some Granite Rocks samples in the Eastern Desert Egypt

The distribution of natural radionuclide γ-ray activities and their respective annual effective dose rates, produced by 238 U, 226 Ra, 228 Ra, 235 U, 232 Th and 40 K were determined for igneous rock samples collected along the road between Idfu and Marsa Alam in eastern desert of Egypt. This subject is important in environmental radiological protection, since igneous rocks are widely used as building material. The variation in concentration of radionuclides for thirty igneous rock samples was determined. A HPGe spectrometer was used for quantification of gamma emitting radionuclides in the samples. All igneous rocks contained radionuclides from the uranium and thorium series as well as 40 K. 238 U concentrations in samples ranged from 12.03±0.88 to 19.34±1.41 Bq.kg -1 , 235 U from 1.16±0.11 to 4.83±0.44, Bq.kg -1 , 226 Ra from 9.69±0.82 to 18.97±1.33 Bq.kg -1 , 228 Ra ranged from 10.24±0.70 to 17.35±1.29, 232 Th range from 9.99±0.67 to l7.65±1.23 Bq.kg -1 and 40 K from 298.58±21.74 to 955.78±69.58 Bq.kg -1 .

Research on fabric characteristics and borehole instability mechanisms of fractured igneous rocks

There are favorable exploration prospects in igneous rock reservoirs. However, problems of borehole instability occur frequently during drilling igneous formations, which is a serious impediment to oil and gas exploration and production. The lack of systematic understanding of the inherent instability mechanisms is an important problem. A series of experiments were conducted on several igneous rock samples taken from the sloughing formations in the Tuha area in an attempt to reveal the inherent mechanisms of wellbore instability when drilling in fractured igneous rocks. Research methods involved slurry chemistry, analysis of micro-geological features (Micro-CT imaging, SEM), and rock mechanics testing. The experimental results indicated that clay minerals were widely distributed in the intergranular space of the diagenetic minerals, crystal defects, and microcracks. Drilling fluid filtrate would invade the rock along the microcracks. The invasion amount gradually increased over time, which constantly intensified the hydration and swelling of clay minerals, leading to changes in the microscopic structure of igneous rocks. Primary and secondary microcracks can propagate and merge into single cracks and thus reducing rock cohesion and the binding force along cleavage planes. Based on this result the authors propose that a key towards solving wellbore instability in igneous formations is that specific micro-geological characteristics of the igneous rocks should be taken into consideration in the design of antisloughing drilling muds.

Genesis of the Au–Bi–Cu–As, Cu–Mo ± W, and base–metal Au–Ag mineralization at the Mountain Freegold (Yukon, Canada): constraints from Ar–Ar and Re–Os geochronology and Pb and stable isotope compositions

The genesis of mineralized systems across the Mountain Freegold area, in the Dawson Range Cu–Au ± Mo Belt of the Tintina Au province was constrained using Pb and stable isotope compositions and Ar–Ar and Re–Os geochronology. Pb isotope compositions of sulfides span a wide compositional range (206Pb/204Pb, 18.669–19.861; 208Pb/204Pb, 38.400–39.238) that overlaps the compositions of the spatially associated igneous rocks, thus indicating a magmatic origin for Pb and probably the other metals. Sulfur isotopic compositions of sulfide minerals are broadly similar and their δ34S (Vienna-Canyon Diablo Troilite (V-CDT)) values range from −1.4 to 3.6 ‰ consistent with the magmatic range, with the exception of stibnite from a Au–Sb–quartz vein, which has δ34S values between −8.1 and −3.1 ‰. The δ34S values of sulfates coexisting with sulfide are between 11.2 and 14.2 ‰; whereas, those from the weathering zone range from 3.7 to 4.3 ‰, indicating supergene sulfates derived from oxidation of hypogene sulfides. The δ13C (Vienna Peedee Belemnite (VPDB)) values of carbonate range from −4.9 to 1.1 ‰ and are higher than magmatic values. The δ18O (V-SMOW) values of magmatic quartz phenocrysts and magmatic least-altered rocks vary between 6.2 and 10.1 ‰ and between 5.0 and 10.1 ‰, respectively, whereas altered magmatic rocks and hydrothermal minerals (quartz and magnetite) are relatively 18O-depleted (4.2 to 7.9 ‰ and −6.3 to 1.5 ‰, respectively). Hydrogen isotope compositions of both least-altered and altered igneous rock samples are D-depleted (from −133 to −161 ‰ Vienna-Standard Mean Ocean Water (V-SMOW)), consistent with differential magma degassing and/or post-crystallization exchange between the rocks and meteoric ground water. Zircon from a chlorite-altered dike has a U–Pb crystallization age of 108.7 ± 0.4 Ma; whereas, the same sample yielded a whole-rock Ar–Ar plateau age of 76.25 ± 0.53 Ma. Likewise, molybdenite Re–Os model ages range from 75.8 to 78.2 Ma, indicating the mineralizing events are genetically related to Late Cretaceous volcano-plutonic intrusions in the area. The molybdenite Re–Os ages difference between the nearby Nucleus (75.9 ± 0.3 to 76.2 ± 0.3 Ma) and Revenue (77.9 ± 0.3 to 78.2 ± 0.3 Ma) mineral occurrences suggests an episodic mineralized system with two pulses of hydrothermal fluids separated by at least 2 Ma. This, in combination with geological features suggest the Nucleus deposit represents the apical and younger portion of the Revenue–Nucleus magmatic-hydrothermal system and may suggest an evolution from the porphyry to the epithermal environments.