Variety Of Rock Types Research Articles

Identification of Mineral Potential in Galang District Tolitoli Regency Using the Method of Resistance and Induced Polarization

Geologically, the province of Central Sulawesi is composed of various types of rocks, both in the form of igneous, sedimentary and metamorphic rocks. Regarding Central Sulawesi Province, mineral resources both metal and non-metal are quite varied. Increasing demand and demand for minerals, both metals, and non-metals. Research conducted to study the mineral potential in one of the regencies in Central Sulawesi Province. This research was conducted in Galang Sub-district, Tolitoli Regency, and Central Sulawesi Province by using the resistivity method and the Induced Polarization (IP) method with the Wenner-Schlumberger arrangement consisting of eight lines. The IP method is very accurate to discuss the potential of minerals that are below the surface. The inversion process does data processing in order to obtain the actual form of resistivity and chargeability modeling. Based on the modeling, the mineral potential in Galang Sub-district, Tolitoli Regency, Central Sulawesi Province is mostly found in all trajectories namely lane 01; 02; 04; 05; 05; 06; 07. Which is marked by a very high chargeability value between 300 msec - 500 msec. The research area also discusses granite and andesite, which have high resistivity values, between 2000 Ωm – 400000 Ωm.

Lithostratigraphy of the Copperton Formation, Areachap Group

Abstract The type area of the Copperton Formation is on the farms Vogelstruisbult 104, Somuspan 105 and Dooniespan 108 in Prieska District. Outcrop is poor and the type material is preserved in exploration borehole cores from the Prieska Copper Mines and the Annex Cu-Zn deposits. It is highly deformed and variably metamorphosed. Thus it is a lithodemic unit, but interpreted as a supracrustal sequence and described as a formation including lithologically distinct members. The Copperton Formation comprises a wide range of rock types including metabasic and intermediate gneisses with minor amounts of metapelitic and calc-silicate rocks. Metamorphic parageneses generally reflect amphibolite facies metamorphism, but granulite and retrograde greenschist facies zones also occur. The protoliths are interpreted as an arc-related volcano-sedimentary package and the Smouspan Member metadacite is dated at 1284 ± 9 Ma. Members are distinguished as follows: The Magazine Member is dominated by calc-silicate rocks which are dominant in outcrop but rarely found in borehole cores. The Smouspan Gneiss is a fairly homogeneous hornblende-biotite intermediate gneiss which is up to 400 meters thick in an isoclinal fold structure. It comprises the footwall to the Prieska Copper Mines Member, in which the massive sulphide orebody occurs, enclosed in an alteration assemblage comprising dark gedrite fels and strongly foliated, leucocratic quartz-perthite-sillimanite gneiss. The ore is interpreted as a volcanogenic massive sulphide deposit formed in a Mesoproterozoic island arc system. The Vogelstruisbult Member is the hanging wall unit, comprising mainly laminated amphibolites and metapelites, but also containing a variety of rock types including hornblende gneiss, biotite gneiss, chlorite schist, and calc-silicate gneiss. Away from the Prieska Mines orebody, a similar variety of rock types is found, and not subdivided but classified as Copperton Formation, a mappable unit. The same assemblage of rock types, including massive sulphide mineralization, was intersected in drill holes on the farms Kielder (portion of Doonies Pan 108), Eierdop Pan and Kantienpan to the north. The Copperton Formation is the southernmost unit of the Areachap Group which is exposed between Prieska Copper Mines and Areachap Mine north of Upington, where the Jannelsepan and Bethesda formations occur. The Copperton Formation is partly obscured in many places by Dwyka Group tillite cover which thickens southwards. A sequence of structural and metamorphic events affected the Copperton Formation and Areachap Group during the 1.2 to 1.0 Ga Namaqua-Natal orogeny. These involved collision of the Areachap Terrane with the Kaapvaal-Rehoboth Craton at about 1220 Ma, a thermal and deformational event coeval with the continental-scale Umkondo mantle event at about 1100 Ma, followed by uplift, erosion and the development of right-lateral shear zones of the Doornberg Lineament, with cooling below 300°C by 920 Ma. A Cambrian peneplain developed in the region which was first covered by Nama Group sandstones, then glaciated and covered by Permian Dwyka Group tillites which are presently being eroded to expose the Copperton Formation.

U-Pb age of sphene grains, petrochemical, mineralogical and geochemical features of alkaline rocks of the Bogdo complex (Arctic Siberia)

In the north of the Siberian Platform, east of the Anabar Shield, several identified massifs of alkaline rocks with carbonatites are known: Tomtorsky, Bogdo, Promezhutochniy, as well as Bualkalakh, Chuempe, Uele, which are projected according to geophysical data and forming a large alkaline-carbonatite province. The first data on the composition of alkaline rocks of the Bogdo massif were obtained, which correspond to a group of feldspathic rocks of the main composition: rischorrites, biotite-aegirine libenerite syenites, carbonatized, with symplectites and nepheline-feldspar aggregates, pseudo-leucite nepheline syenites. Sphenes were extracted from various types of rocks of the Bogdo massif and their U-Pb age was determined using the SHRIMP-II secondary-ion microprobe. The calculated U-Pb age corresponds to 394,4 3,2 Ma, which is close to the age stage established for the Tomtor massif and the age of the rocks of the Kola alkaline province. One of the reasons for the manifestation of alkaline plume magmatism in this territory may be the influence of the peripheral zone Africa Large Low Shear Velocity Province (Tuzo) in the Baltic and Siberia during the Devonian era.

THE HISTORY OF GEOLOGY WALLS IN CENTRAL EUROPE AND THEIR USE AS PEDAGOGIC TOOLS FOR EXPLAINING GEOSCIENCES

ABSTRACT During the second half of the nineteenth century, geology was added as a topic taught at schools of higher education in central Europe. As a consequence, teachers had an interest in finding practical methods to make theoretical knowledge more interesting to their pupils. Pedagogic tools included fieldtrips which could be logistically challenging, and the so called ‘geology walls’ and other stone structures, such as ‘geology pyramids’. These solidly built structures erected from various types of rocks, were put together to simulate the complexities of the underground geology from the lowlands to the mountains of certain geographic areas and may be considered to represent precursors of modern geoparks. Many of these ‘geology walls’ built in several central European cities are preserved and may still be used today to explain and discuss geoscientific phenomena. The fruitful interactions between teachers and pupils, and scientists and amateurs, are topics of this paper. Questions of restitution and international relationships are touched on as well.

Development of an Intelligent and Statistical Model for Prediction of Rock Mass Deformation Modulus

The rock mass deformation modulus (Em) takes into account the plastic and the elastic deformation of the rock mass. It has been widely used for designing structures such as dams, tunnels, caverns, and mines, etc. Since the tests available for ascertaining Em are expensive and time consuming, several equations were suggested in the past. However, it has been found that the existing models are limited to specific type of rock mass rendering constraints for its application to general use. Therefore, to cater to this need a comprehensive data set of 147 series, comprising of elastic modulus of intact rock (Ei), rock mass rating (RMR) and Em have been collected from the literature covering various types of rocks from across the globe. This data set has been used in constructing a non- linear regression (NLR) based equation to render ease to the design engineers for calculating Em. In addition to it, an intelligent model is proposed having a basis on artificial neural network (ANN). The credibility of the empirical and intelligent model has been ascertained using the R2 and RMSE. Based on these performance evaluation indices, both models have been found to predict the Em with considerable accuracy vis-a-vis the existing models. Subsequently, a chart has been designed to ascertain Em using Ei and RMR for several classes of rock mass.

Karst map of Georgia (Caucasus region) scale: 1:1,500,000

Karst landscapes develop in soluble rocks, such as carbonates and evaporates, but also in various types of rocks that develop pseudokarst features. The main aim of this work is to introduce a new karst map of Georgia (scale: 1:1,500,000) presenting karst and pseudokarst features, which occupy about 17.9% (12,454 km2) of the entire territory of the country and include over 1500 known caves. We distinguish two types of karst features—karst (developed in carbonate rocks) and pseudokarst, and also five subtypes, mainly based on their lithology. About 10.2% (7120 km2) of the country is occupied by karst (carbonate rocks), and about 7.7% (5334 km2) of the country is occupied by pseudokarst features. This karst map of Georgia will provide important assistance to local and foreign researchers interested in studying Georgian karst features.

On the propagation of nonlinear transients of temperature and pore pressure in a thin porous boundary layer between two rocks

The dynamics of transients of fluid-rock temperature, pore pressure, pollutants in porous rocks are of vivid interest for fundamental problems in hydrological, volcanic, hydrocarbon systems, deep oil drilling. This can concern rapid landslides or the fault weakening during coseismic slips and also a new field of research about stability of classical buildings. Here we analyze the transient evolution of temperature and pressure in a thin boundary layer between two adjacent homogeneous media for various types of rocks. In previous models, this boundary was often assumed to be a sharp mathematical plane. Here we consider a non-sharp, physical boundary between two adjacent rocks, where also local steady pore pressure and/or temperature fields are present. To obtain a more reliable model we also investigate the role of nonlinear effects as convection and fluid-rock “frictions”, often disregarded in early models: these nonlinear effects in some cases can give remarkable quick and sharp transients. All of this implies a novel model, whose solutions describe large, sharp and quick fronts. We also rapidly describe transients moving through a particularly irregular boundary layer.

Synrift clayey rocks: bulk chemical composition and position on discriminant paleogeodynamic diagrams

The paper analyzes the bulk chemical composition and distribution of the fields of syn-rift clayey rocks on a number of discriminant paleogeodynamic diagrams. It is shown that, in general, there are significant variations in the bulk chemical composition for syn-rift clayey rocks. Thus, for example, the average SiO2 content varies from 44.74 to 66.42 wt. %, the average content of Al2O3 varies from 16.62 to 29.92 wt. %, and the K2Oaver are in the range 0.24 ... 5.77 wt. %. Based on the distribution of the figurative points of the syn-rift clayey rocks of various objects/riftogenous structures in the F1–F2 diagram, it can be assumed that the sources of fine aluminosilicoclastic were magmatic and sedimentary rocks of a wide range of compositions. The substantial overlap of the fields of various objects in the classification diagrams [(Na2O + K2O)/Al2O3]–[(Fe2O3tot + MgO)/SiO2] and K/Al–Mg/Al indicates, in general, the similarity of the compositions of the syn-rift fine-grained clastic rocks of various types of riftogenic structures. The localization of the composition fields of the clayey rocks of different riftogenous structures on such discriminant paleogeodynamic diagrams as K2O/Na2O–SiO2/Al2O3 and SiO2–K2O/Na2O suggests that they do not allow correctly distinguishing between syn-rift clayey rocks and fine-grained rosks of other geodynamic environments. The position of the syn-rift clayey rocks fields presented in our database on the diagram DF1–DF2 has its own characteristics. In most cases, they occupy a particular position in the areas characterizing collision and rifting environments, and a number of fields are located in all three classification areas of this diagram. A significant part of the midpoints of the syn-rift clayey rocks is localized in the DF1–DF2 diagram in the collision field. It seems that all of the above indicates that the DF1–DF2 diagram also does not allow us to obtain a correct information about the geodynamic nature of terrigenous associations.

The influence of strain on the Verwey transition as a function of dopant concentration: towards a geobarometer for magnetite-bearing rocks

SUMMARY Magnetite is an abundant magnetic mineral that commonly records the ancient magnetic field in a wide variety of rock types. When cooled below ≈124 K, magnetite undergoes a phase transition, called the Verwey transition, whose characteristics are highly sensitive to grain size and stoichiometry. Studying the Verwey transition thus yields information on the formation conditions and compositions of rocks. The transition is also stress sensitive, thereby opening an avenue to understanding a rock’s strain history; however, the reason for the stress sensitivity is poorly understood. In particular, the temperature of the transition decreases when measured under pressure, yet mostly increases upon pressure release. Moreover, the stress sensitivity of the transition as a function of dopant concentration, especially after pressure cycling, was never systematically tested. We addressed these issues in order to further develop magnetite as a pressure gauge. Multidomain magnetite samples were pressure cycled up to maximum pressures of ∼5 GPa at room temperature to measure the influence of strain on the Verwey transition temperature as a function of dopant concentration after full decompression. The transition temperature measured via changes in magnetic remanence ($T_{\rm V}^{M}$) systematically increased with respect to pressure (P) in more doped samples, where domain wall pinning from impurities dominates $\mathrm{d}T_{\rm V} ^{\rm M}/\mathrm{d}P$. In less doped samples, no to only moderate pressure cycling dependence on $T_{\rm V}^{\rm M}$ was observed. Bulk coercive force (Bc) and magnetic remanence after saturation (Mrs) measured above or below the transition also increased with respect to pressure, but here effects related to permanent strain of the lattice structure prevail, and Bc versus P is steeper for less doped samples. Bc versus P increases in all cases, with a difference in slope dictated by dopant concentrations segregating the first to second-order nature of the transition. Thus, strain developed during pressure cycling controls $T_{\rm V}^{\rm M}$ and coercivity by a mechanism based on pinning of magnetic domains by both interstitial cations and structural lattice distortions. The combined observables, $T_{\rm V}^{\rm M}$ and Bc−Mrs, reflect both the dopant level and strain state of magnetite, which can quantify the pressure multidomain magnetite has experienced, especially in the range between 1 and 5 GPa. Based on these new results, we present a model that distinguishes between electronic versus defect-driven processes explaining the strain-related influences on the transition. Magnetite’s use as a geobarometer is thus a measure of its defect state, which is expressed through two somewhat independent mechanisms when sensed by magnetic observations.

Syn-rift Clayey Rocks: Bulk Chemical Composition and Position on Discriminant Paleogeodynamic Diagrams

The paper analyzes the bulk chemical composition and distribution of the fields of syn-rift clayey rocks on a number of discriminant paleogeodynamic diagrams. It is shown that, in general, there are significant variations in the bulk chemical composition for syn-rift clayey rocks. Thus, for example, the average SiO 2 content varies from 44.74 to 66.42 wt. %, the average content of Al 2 O 3 varies from 16.62 to 29.92 wt. %, and the K 2 O aver are in the range 0.24 ... 5.77 wt. %. Based on the distribution of the figurative points of the syn-rift clayey rocks of various objects/riftogenous structures in the F1–F2 diagram, it can be assumed that the sources of fine aluminosilicoclastic were magmatic and sedimentary rocks of a wide range of compositions. The substantial overlap of the fields of various objects in the classification diagrams [(Na 2 O + K 2 O)/Al 2 O 3 ]–[(Fe 2 O 3tot + MgO)/SiO 2 ] and K/Al–Mg/Al indicates, in general, the similarity of the compositions of the syn-rift fine-grained clastic rocks of various types of riftogenic structures. The localization of the composition fields of the clayey rocks of different riftogenous structures on such discriminant paleogeodynamic diagrams as K 2 O/Na 2 O–SiO 2 /Al 2 O 3 and SiO 2 –K 2 O/Na 2 O suggests that they do not allow correctly distinguishing between syn-rift clayey rocks and fine-grained rosks of other geodynamic environments. The position of the syn-rift clayey rocks fields presented in our database on the diagram DF1–DF2 has its own characteristics. In most cases, they occupy a particular position in the areas characterizing collision and rifting environments, and a number of fields are located in all three classification areas of this diagram. A significant part of the midpoints of the syn-rift clayey rocks is localized in the DF1–DF2 diagram in the collision field. It seems that all of the above indicates that the DF1–DF2 diagram also does not allow us to obtain a correct information about the geodynamic nature of terrigenous associations.

Micro‐fabrics and Genesis of Pyrite from Zhaoyuan Golden Deposits in Shandong Province, North China

AbstractAs a widely‐developed mineral in various types of rocks, pyrite features important geological information such as temperature and pressure during its formation and evolution (An et al., 2014; An et al., 2018). It is an important geological formation for studying the origins of rocks, mineralization, and deposits (Xue et al., 2014; An et al., 2016). The study of the genesis of gold deposits is a research hotspot in current geology and mineral deposits not only because of high economic value, but also because of important practical significance (An et al., 2017; Yang et al., 2014). Shandong Zhaoyuan, as the third largest gold production area in the world, has important research significance of the origin and generation of gold‐bearing minerals (Xue et al., 2014; Wen et al., 2014). In this study, pyrite from augen granite (figure 1a), syenite (figure 1b), basite (figure 1c) and gold ore (figure 1d) at Zhaoyuan gold deposit Shandong Province, was selected as the research object. The morphological and structural micro‐fabrics were analysed by polarized light microscopy (PLM) and Raman spectroscopy to reveal the source and process of gold further.

Two‐Stage Sulfide Mineral Assemblages in the Mineralized Ultramafic Rocks of the Laowangzhai Gold Deposit (Yunnan, SW China): Implications for Metallogenic Evolution

AbstractThe Laowangzhai gold deposit, located in the Ailaoshan gold belt (SW China), is hosted in various types of rocks, including in quartz porphyry, carbonaceous slate, meta‐sandstone, lamprophyre, and altered ultramafic rocks. In contrast to other wall rocks, the orebodies in altered ultramafic rocks are characterized by the occurrence of a large amount of Ni‐bearing minerals. The ore‐forming process of the orebodies hosted by altered ultramafic rocks can be divided into two stages: pyrite‐vaesite‐native gold and gersdorffite‐violarite stages. The contents of As and Sb increased during the evolution of ore‐forming fluid based on the mineral assemblages. Thermodynamic modeling of the Ni‐Cu‐As‐Fe‐S system using the SUPCRT92 software package with the updated database of slop16.dat indicates the fS2 in ore‐forming fluid decreases significantly from stage I to stage II. The decreases of fS2 due to crystallization of sulfides and fO2 due to fluid–rock reaction were responsible for ore formation in altered ultramafic rocks of the Laowangzhai gold deposit. Geological evidence, the in situ sulfur isotope values of pyrite, and the other published isotopic data suggest that the ore‐forming fluid for ultramafic rock ores was dominantly composed of evolved magmatic fluid with the important input of sediments.

Exploration breakthroughs and geological characteristics of continental shale oil: A case study of the Kongdian Formation in the Cangdong Sag, China

Abstract Petroleum geology and deposition features of the fine grain phase region in the second member of the Kongdian Formation were investigated using traditional petroleum geology and sedimentary petrology. New theories for shale oil and gas formation, based on data from 500 m continuous coring, systematic analysis of over ten thousand core samples, and logging data in the center of the lake basin in the Cangdong Sag (Bohai Bay Basin, China) were developed to determine the distribution of shale oil and provide a basis for shale oil exploration deployment. Results showed that a wide distribution of semi-deep to deep lake sub-facies fine-grained sediment (shale) was deposited in the study area during the largest lake flooding period. This sediment consists of felsic shale, mixed shale, and dolomites, but no clay shale. The shale features multiple rock components with few dominant minerals; high clastic mineral content and low clay mineral content; rich analcite and lean pyrite; rich brittle minerals with lean quartz; diverse rock types with limited shale oil; more tight reservoirs and fewer reservoirs with no fractures; more high-quality source rock with less non-hydrocarbon source rock; and more high frequency cycles with fewer monolithic deposits. Results indicate that dolomites are located in strips on the plane and are locally enriched, contradicting the understanding that only hydrocarbon source rock, and no reservoirs, develop in the middle of a continental closed lake basin. The study region demonstrates good conditions for shale oil formation, a favorable configuration of source rock and reservoirs, and 260 km2 of sweet spots, indicating high exploration value. Several prospecting wells have obtained industrial oil flow with guidance based on geological knowledge and engineering technology support.

Geochemistry of diverse lava types from the Lau Basin (South West Pacific): Implications for complex back‐arc mantle dynamics

Lavas from back‐arc basins are generally diverse, and their geochemical compositions indicate that they received variable contributions from subduction components during petrogenesis. Obtaining comprehensive geochemistry characteristics for the entire back‐arc basin are helpful in gaining a better understanding of the complexities of back‐arc evolution. In this study, we systematically reviewed the major and trace element compositions of Lau Basin lavas. This data set covered all of the major tectonic units of the basin, for example, the Eastern Lau spreading center (ELSC), the Valu Fa ridge (VFR), the Central Lau spreading center (CLSC), the Northwestern Lau spreading center (NWLSC), the Northeastern Lau spreading center (NELSC), the Mangatolu Triple Junction (MTJ), and the Fonualei Spreading Center (FSC). The lava types from these locations are diverse, including tholeiitic basalts, alkali basalts, basaltic andesites, andesites, dacites, and rhyolites. In addition, the NELSC and FSC contain boninites. In this study, the geochemical compositions of these diverse rock types are used to investigate the spreading dynamics of the Lau Basin back‐arc. We conclude that (a) the subduction components mainly include hydrous fluids released from the subducted slab, and hydrous melt directly from the melting subducted sediment, and the influence of the subducted components on the mantle wedge and the petrogenesis of the central and southern Lau Basin lavas decreases with increasing distance from the Tonga Trench; (b) during the propagation and spreading of the Samoan mantle into the Lau Basin, lavas from the NELSC, NWLSC, MTJ, and even from the northern part of the FSC may receive variable degrees of influence from the Samoan plume; and (c) the migration of Indian MORB‐like mantle southwards into the Pacific mantle is consistent with the opening of the Lau Basin. With the gradual migration of Indian mantle into the Lau Basin, a series of spreading centers were formed, for example, in order, the NWLSC, CLSC, ELSC, and the propagating VFR.

Extreme deformation characteristics and countermeasures for a tunnel in difficult grounds in southern Shaanxi, China

The Qingling–Bashan (QB) mountain region in southern Shaanxi mainly consists of strongly compressive zones from east to west, with tight folds and compressive fractures. There is a wide distribution of soft rocks of various types, such as phyllite and slate, accompanied by complex geological structures. Ironically, tunnel construction in these difficult grounds with complicated geological conditions embraces a high risk of extreme deformation due to various unpredictable reasons, which can frequently cause collapse and result in budget overruns during the construction period. Therefore, it is crucial to conduct effective countermeasures to eliminate or avoid such adverse impacts. This paper provides a case study on the “Yingfeng tunnel” (a tunnel constructed in soft rock consisting of a slate ground) based on a geological survey, indoor experiments and in situ monitoring. A successive rock mass deformation resulted in the tunnel lining seriously intruding into construction clearance and some other sections, even collapsing during the construction. The maximum displacement amount was 62.5 cm, while the maximum deformation speed reached as high as 34.18 mm/day. Additionally, to evaluate the construction impacts of tunnelling-induced geo-hazards, an investigation on extreme deformation was conducted. Considering the time-dependent features of the rock mass deformation, the constraint-convergence method was used to put forward applicable countermeasures in this paper. Finally, from the feedbacks of monitoring results, extreme deformation of the Yingfeng tunnel was effectively controlled.

Experimentally determined effects of olivine crystallization and melt titanium content on iron isotopic fractionation in planetary basalts

Olivine is the most abundant mantle mineral at depths relevant to oceanic crust production through melting. It is also a liquidus phase for a wide range of mafic and ultramafic magma compositions. We have experimentally investigated the effects of olivine crystallization and melt composition on the fractionation of Fe isotopes in igneous systems. To test whether there is a melt compositional control on Fe isotopic fractionation, we have conducted nuclear resonant inelastic X-ray scattering (NRIXS) measurements on a suite of synthetic glasses ranging from 0.4 to 16.3 wt.% TiO2. The resulting force constants are similar to those of the reduced (fO2 = IW) terrestrial basalt, andesite, and dacite glasses reported by Dauphas et al. (2014), indicating that there is no measurable effect of titanium composition on Fe isotopic fractionation in the investigated compositional range. We have also conducted olivine crystallization experiments and analyzed the Fe isotopic composition of the experimental olivines and glasses using solution MC-ICPMS. Olivine and glass separates from a given experimental charge have the same iron isotopic composition within error. This result is robust in both the high-Ti glass (Apollo 14 black) and low-Ti glass (Apollo 14 VLT) compositions, and at the two oxygen fugacities investigated (IW−1, IW+2). Additionally, we have determined that Fe loss in reducing one-atmosphere gas-mixing experiments occurs not only as loss to the Re wire container, but also as evaporative loss, and each mechanism of experimental Fe loss has an associated Fe isotopic fractionation.We apply our results to interpreting Fe isotopic variations in the lunar mare basalts and lunar dunite 72415-8. Our experimental results indicate that neither melt TiO2 composition nor equilibrium olivine crystallization can explain the observed difference in the iron isotopic composition of the lunar mare basalts. Additionally, equilibrium iron isotopic fractionation between olivine and melt cannot account for the “light” iron isotopic composition of lunar dunite 72415-8, unless the melt from which it is crystallizing was already enriched in light iron isotopes. Our results support models of diffusive fractionation to explain the light iron isotopic compositions measured in olivine from a variety of rock types and reduced (fO2 = IW−1 to IW+2) igneous environments (e.g., lunar dunite and basalts, terrestrial peridotites and basalts, martian shergottites).

An Improved Crack Initiation Stress Criterion for Brittle Rocks under Confining Stress

The stress level associated with crack initiation is an important damage threshold in rock failure process, which can be applied in the prediction of brittle failure in tunnels. In the present study, the uniaxial and triaxial compression tests are conducted on two sets of hard sandstones, while the dilation strains and AE counts are employed to characterize the crack accumulation. The crack initiation stress is then determined through the inflection point on strain and AE curves. Furthermore, two crack initiation modes: the splitting mode for low confinements and the sliding mode for high confinements are presented by analysing the fracturing mechanism. Based on the derivation of maximum tensile stress around the rock defects, an improved crack initiation criterion is proposed to predict the σci of confined rocks. In the new criterion, the frictional components on crack surface are considered by introducing the parameter mci, which can be applied for various types of rocks as well. At last, the triaxial compression test data of different rock types are reviewed to verify the reliability and applicability of the new criterion. The results indicate that the new criterion can predict the crack initiation stress of confined rock with high accuracy.

Hydrogeology of Karang Mumus Watershed in Samarinda, East Kalimantan Province, Indonesia

Samarinda is part of an anticlinorium, which is marked by the existence of many anticlines. In addition, various types of rock and aquifer can be found in the city due to the uniqueness of geological structure of the area. Nevertheless, the literature are lacking attention of hydrogeological condition of this area. This research aims to determine the hydrogeology of the Karang Mumus watershed, particularly in relation to its geology and land use conditions. The research uses an inductive method, with an analytical approach consisting of a study of the land use, hydrological conditions, geology, geomorphology and hydrogeology. The Karang Mumus watershed can be divided into three hydrogeological layers: (1) an aquitard layer, the top layer, which has a hydraulic conductivity of 4.3 × 10-6 m/sec, and is dominated by siltstone; (2) an aquifer layer in the middle, with a hydraulic conductivity of 2.6 × 10-4 m/sec, dominated by sand and sandstone; and (3) an aquiclude layer occupying the lower layer, with a hydraulic conductivity of 1.6 × 10-11 m/sec, and which is dominated by claystone.

Experimental analysis on characteristics of micro-structure and mineralogy changes in thermal spallation drilling

Thermal spallation drilling is a promising technology expected to exploit hydrocarbons in hard rocks. In this paper, thermal spallation experiments are conducted on six types of rocks. Comparisons are made in terms of mineral compositions and micro-structures. Spallation temperatures are obtained, and analytical results are compared with experimental data. Results show that spallation temperatures obtained by analytical method show good agreement with experimental data. Additionally, drilling performances can be continuous or intermittent for various types of rocks. Quartz expands in different rocks after thermal impact. Calcite increases and dolomite decreases due to thermal decomposition. Moreover, the induced thermal stresses in sandstone push against the micro-particle and melting may occur. For granite, micro-cracks and micro-particles exist after spallation. In contrast, there are no cracks in shale, but melt holes and micro-particles distributed randomly due to reaction. For limestone, there exist relatively large cracks, micro-cracks and micro-particles. For dolomite, no obvious micro-particles remain but only a few micro-cracks. The variations of elements correspond well with mineral changes. However, under the conditions of this paper, marble fails to break due to strong homogeneity. All results can provide guidance for the further study on the rock-breaking of thermal spallation drilling.

<b>Vascular plant assemblage of cliffs in northern Western Ghats, India</b>

Vertical rocky cliffs, which consist of various types of rock, are widespread all over the world. India’s northern Western Ghats consisting of basaltic rocks form probably the largest cliff ecosystem globally, however, almost no studies are available concerning their floristic richness. In an attempt to understand the vascular plant assemblage of this habitat, cliffs of the northern Western Ghats were surveyed for their microhabitats, species diversity, distribution of endemics, occurrence of particular adaptive traits and potential threats. A total of 102 species of vascular plants were documented from the cliff habitats of which 55 are endemic. Flowering of the species on cliffs is triggered by the advent of the south-west monsoon and peak flowering is seen between August and October. Of the total species, 27 grow exclusively on cliffs. Owing to habitat specificity, cliffs show a greater number of narrow endemic and threatened species when compared with other habitats like deciduous, evergreen and semi-evergreen forests, which are widespread in the northern Western Ghats. Unfortunately, this habitat faces threats in the form of landslides, periodic burning and habitat loss due to road-widening.