Ore and Energy Resource Geology最新文献

The Permian Sandstone is well preserved in the Junggar Basin, China. It is consisting of fine to medium sandstone with interbedded shale. The present study is focused on to evaluate the reservoir characteristics and controlling factors of the Permian sandstone of Jinlong 51 well, Junggar basin, China. To fulfil the objectives of the current study, geological field, petrographic analysis, SEM, analysis, mercury injection capillary pressure, and progressed geochemical analysis has been used to evaluate the characteristics and diagenetic history of the Permian sandstone to evaluate its potential. Thin section analysis shows that rock comprises of medium to fine-grained lithic sandstone, and glutenite. Pores are primary isolated into intergranular pores, intergranular pores and intra granular pores. The SEM analysis reveals that the major diagenesis types are compaction, cementation, dissolution, and fractures. Rock is moderately compacted, with intermediate cementation as well as feldspar, rock fragment and carbonate cement dissolution. According to core NMR analysis evaluated as low porosity, low permeability of the reservoirs, some of them are low porosity and low permeability reservoirs. The mercury injection capillary pressure shows that pore throat is intermediate pores with moderate pore throat. Permian sandstone consisting of average porosity 17.8% and permeability is from 5.2 to 8 mD, which recommended that the studied formation consisting of moderate reservoir characteristics. Compaction, cementation and fractures fills with clastic material decreases, whereas primary intergranular pores, dissolution pores and fractures increases the reservoir quality. Finally, the impact of diagenesis on the physical properties of the reservoirs under study has been investigated, the compactions and cementation along with other constrains effect the porosity as well as permeability of the glutenite reservoirs.

As the boundary between the Yangtze Craton and the Qinghai-Tibet Plateau, the Longmenshan tectonic belt is known for its typical fault-slip systems and strong Cenozoic activities. Due to the complexity of the structure of the orogenic belt, the tectonic evolution and formation mechanism of the Longmenshan tectonic belt have been controversial. This paper essentially focuses on the geological isotopic chronology limitation of the fault activity of the Longmenshan Central Fault (Yingxiu-Beichuan Fault). The K-Ar dating of the illite in the fault gouge sample on the fault surface reveals that the direct age of the fault would be about 111 Ma. Combined with the previous age results, the following results are obtained: The Yingxiu-Beichuan fault was a multi-stage active fault in the Mesozoic, which was active in the Late Triassic (229–216 Ma), Early Jurassic (190–171 Ma) and the end of Early Cretaceous (130–110Ma). This paper analyzes the evolution of the central fault through regional geological evolution, seismic profile analysis and structural physical simulation experiment, and the following main results are obtained: Animaqing Paleo-Tethys Ocean on the northern margin of the Songpan Garze Block and the Jinshajiang Paleo Tethys Ocean in the southern margin were closed successively in the Middle and Late Triassic, Such a fact essentially occurred under the influence of differential uplift, that is, the pre-existing Yingxiu-Beichuan fault changed from a normal fault to a reverse fault in the Late Triassic, and then reactivated. Under the influence of the gravity slip mechanism, the Yingxiu-Beichuan fault was active until it ceased in the Early Jurassic. Since then, affected by the closure of the Middle Tethys Ocean, in the Early Cretaceous, the fault developed again, and branch faults developed in front of the fault. During the Himalayan period, due to the collision and ccocnnection of the Eurasian plate and the Indian plate, the fault was reactivated.

Strontium-isotope stratigraphy enables estimates of numerical dates for marine carbonate-bearing sediments by comparing their ⁸⁷Sr/⁸⁶Sr ratio to a reference curve of ⁸⁷Sr/⁸⁶Sr variations of global seawater through geologic time. That seawater reference curve is a published statistical LOWESS fit to a very large dataset (ca. 14,000) of ⁸⁷Sr/⁸⁶Sr measurements of carbonate fossils from known biozones which is converted to numerical ages using published timescales. In this study, we compute the numerical dates projected by this method for suites ⁸⁷Sr/⁸⁶Sr ratios from seven stratigraphic sections ranging from Ordovician through Oligocene. The strontium-isotope stratigraphy from the Dawangou section in Tarim Basin of NW China that hosts the Auxiliary GSSP for the base of the Late Ordovician is a new dataset; and the others are published datasets. These ⁸⁷Sr/⁸⁶Sr-derived dates are compared to those estimated for the same horizons in these sections by other chronostratigraphic methods, including cyclostratigraphy calibrated to radioisotopic dates and standard biochronostratigraphy. Except for a published study of Lower Triassic strata from Chaohu section in Anhui, China and Middle Devonian strata Jebel Mech Lrdane section of Morocco, all the ⁸⁷Sr/⁸⁶Sr-derived dates are within the estimated uncertainties of the dates from the other chronostratigraphic methods, thereby validating the usefulness of strontium-isotope stratigraphy as one tool for obtaining the ages of marine carbonate-bearing deposits. However, the datasets from all three Paleozoic sections (two Ordovician, one Devonian) did display a noticeable offset bias toward older ages, which may be partly an artifact of inadequate adjustment of the LOWESS reference curve to current age models for the biozones. The ⁸⁷Sr/⁸⁶Sr-derived dates from Chaohu section of Early Triassic conodont zones were unacceptably systematically younger by ca. 1.45 Myr; thereby indicating higher-than-expected ⁸⁷Sr/⁸⁶Sr values, which may have been partially the result of a combination of a semi-restricted basin that was slightly diluted by ⁸⁷Sr-enriched fluvial waters from the chemical weathering of adjacent landmasses and of the laser ablation (LA-ICP-MS) analytical method applied to those samples that seems to yield higher ⁸⁷Sr/⁸⁶Sr ratios than the solution-mode ICP-MS method for ⁸⁷Sr/⁸⁶Sr measurements. In summary, with rare exceptions, the method of strontium-isotope stratigraphy and the statistical ⁸⁷Sr/⁸⁶Sr seawater curve is an important method to obtain semi-precise numerical dates from marine carbonate sediments.

The genesis of the ore-forming material, the depositional environment, the Fe enrichment process, and the resource estimation of the Toko-Nlokeng iron deposit in the Nyong Complex of southern Cameroon were studied using detailed field investigations, petrography, lithostratigraphy, and geochemical analyses, and deposit modeling methods. This study shows a case of coexistence of granular and banded iron formations (65% GIFs and 35% BIFs) in an Algoma-type deposit, both in the Nyong Complex and worldwide. Representative samples of IFs were collected from drillcores. The Iron Formations (IFs) were associated with metavolcanic rocks consisting of garnet amphibolite, garnet-bearing gneiss, hornblendite, and mafic granulite, which underwent several episodes of deformation and metamorphism of amphibolite to granulite facies. The lithostratigraphic results show sharp correlations between the lithological units of the IFs. The bulk chemistry exhibits SiO₂ and Fe₂O₃ content similar to that of most Archean IFs worldwide, with SiO₂+Fe₂O₃T ranging between 96.31 and 98.10 wt%. Positive Eu anomalies (> 1.8) for BIFs and their association with metavolcanic rocks are consistent with Algoma type IFs. Geochemical data show that the IFs precipitated from a mixture of seawater and high-temperature (< 0.1%) hydrothermal fluids in a submarine environment with volcanic activity under relatively low oxygen conditions. Large amounts of iron and silica were likely produced under these conditions. Thus, the deposition of the Toko-Nlokeng IFs probably involved an iron-rich environment of Fe²⁺-rich hydrothermal fluid in chemically stratified seawater. The block models estimated for TNF08 and TNF11 are constrained by robust geological models of the IFs mineralization with a total measured Mineral Resource estimate of 19.1 Mt grading 36.44% Fe and an Indicated Mineral Resource estimate of 113.6 Mt grading 34.79% Fe. The Toko-Nlokeng can be a reasonable prospect for eventual economic extraction. It is suggested that the transformation of the low-grade IFs protolith into high-grade iron ore was controlled by deformation and metamorphic events.

A new classification of barite deposits is proposed based on a study of the distribution, ore types, geological characteristics, ore-forming material sources, ore-forming temperatures, and metallogenic models of barite deposits in China. The deposits are divided into five types, sedimentary, hydrothermal, stratabound hydrothermal vein, volcano-sedimentary, and weathering (eluvium–talus) types, with each having a distinct mineralization model. These deposits formed in continental-rift, back-arc-basin, and intracontinental-uplift tectonic environments. Barite ore bodies are stratabound or veined and are most common in Cambrian, Devonian, and Mesozoic host rocks. Most barite deposits were formed at medium to low temperatures (100–300 °C). Mineralization models for the different types of barite deposit are presented in detail.

Partitioning of borehole samples into homogenous attributes and continuous spatial domains, here in called ore body domaining, is an important step in mineral resource estimation. Traditional clustering approaches are often resulted in certain domains with poor spatial continuity. Therefore, there is a need to a novel approach to consider the spatial dependency between data locations in clustering analysis. In this research, a certain analysis on multiple-point data events, as a nonparametric higher-order geostatistical approach, is introduced to optimize statistical clustering methods by considering spatial information such as drilling data. Initially, user to extract the n-point data events around each borehole samples defines a fixed spatial n-point template. Then, a dissimilarity matrix is calculated through Euclidean distances between pairs of multiple point data events extracted from the dataset. Next, a multidimensional scaling (MDS) is used to represent the similarity or dissimilarity among samples at a low dimension coordinates matrix. Finally, the matrix obtained from MDS is used as an input of statistical clustering methods to improve its ability in terms of spatial continuity and physical realism. In order to verify the performances of proposed approach, we applied to a 2D synthetic case study and a real case of borehole dataset of the Dalli Cu-Au porphyry. The results were analyzed in terms of statistical contrast among domains and generating the continuous spatial and geological realism domains. Evaluations indicate that the results of the proposed method can be resulted in appropriate continuous spatial domains. In addition, the results of real case study indicated that there was a meaningful compatibility between generated domains from the proposed method and available geological facts.

Eocene to Quaternary volcanic and plutonic rocks are exposed in eastern of Kashan in the Urumieh-Dokhtar magmatic belt that located in the Central Iran structural zone. These volcanic rocks have compositions ranging from basaltic andesites, andesites, rhyolite, dacite, tuff to granidiorites. A total of 100 rock samples were taken and based on petrographic and geochemical studies with field observations volcanic rocks in the Yakhab area were evaluated. Geochemical studies show these rocks are a slightly meta-aluminous to per-aluminous. The rocks have SiO₂ contents ranging between 42% and 75%. The geochemical characteristics of the volcanic rocks show that magma was derived from an enriched lithospheric source and indicated magma derived from lower crust or upper mantle lithosphere.

This study presents petrology and evidence for possible gold occurrences in Seruwila copper–iron oxide–apatite (IOA) deposit, hosted in an ultramafic intrusion which is located at the boundary between the Highland and Vijayan complexes, within the intermediate-granitic basement in north-eastern Sri Lanka. The study is complemented with petrological observations and XRD and SEM analysis, respectively, to investigate the petrology/subsurface geology of the deposit and identify possible gold occurrences in the deposit. The ore-bearing rocks are mainly composed of magnetite and apatite in various proportions, hosted in an ultramafic intrusion with cumulate features within the granitic-intermediate basement. The secondary veins contain magnetite, chalcopyrite, pyrrhotite, and pyrite together with apatite and scapolite, tremolite, diopside, and minor actinolite and calcite, serpentinite, anhydrite, or gypsum. The clinopyroxene euhedral crystals show cumulus textures including grain triple junctions and large dihedral angles (∼120°), showing magmatic origin. Texturally two types of amphiboles are identified as coarse-grained (0.5–1 mm), pale green euhedral amphibole that is free of inclusions, and fine-grained (<0.1 mm) and brownish, occurring as anhedral inclusions in clinopyroxene. The deposit contains varying amounts of sulfides in which pyrite is the potential gold carrier in magmatic–hydrothermal processes. By the results of XRD analysis, it is evident that the presence of Au (111), Au (200), Au (220) and Au (311), although with low count values (50–500), probably due to the low concentration of gold. Therefore, particularly in the samples with veins or veinlets, gold was inferred to be present in pyrite/chalcopyrite as invisible structurally-bonded gold and/or gold nanoparticles. Hence, the results of this study, although at non-ore grade, veinlets of gold-bearing pyrite/chalcopyrite may serve as a promising target for gold occurrence, being a potential site of gold-mineralization in the context of the East-Gondwana.

P-T- Oxygen fugacity (fO₂) conditions and fluid compositions were estimated for the formation conditions of pyrope garnet inclusions in diamonds and xenocrysts from diamond-bearing and diamond-free kimberlites using their total chemical analyses and single oxythermobarometry. Our data indicate that optimal conditions for diamond growth and preservation occur in the presumed water-rich mantle fluids containing the lowest abundance of free atomic carbon. The majority of the calculated C-H-O fluid compositions for diamond formation in peridotite xenoliths from high diamond grade kimberlites correspond to a high hydrogen and low carbon and oxygen atomic fluid percents, while those from the majority of peridotite xenoliths in the low grade diamond kimberlites corresponds to the low hydrogen, high carbon and oxygen atomic percent fluids. This new approach defines the conditions of diamond formation for kimberlitic deposits. It better characterizes diamond grades in kimberlites in comparison to the previous empirical mineralogical Ca-Cr methods and can be used as a more precise mineralogical-petrological method for prospecting for kimberlitic diamond deposits.

Granitic pegmatites can be a source of frustration and confusion. It is thus appropriate to begin with a quick review of basic concepts. Crystallization takes place in the presence of two fluid media; one is a viscous, polymerized silicate magma, and the other is a supercritical aqueous fluid. The two are largely but not completely immiscible. The proportion of aqueous fluid in the mixture progressively increases as the amount of melt diminishes. Pegmatites are of significant economic interest, as they are source rocks of industrial minerals like quartz and the feldspars. These minerals crystallized from the magma, but the feldspars generally become modified by the aqueous fluid. The same applies to accessory minerals that carry Nb, Ta, Zr, Sn and the rare earths. At a late stage, the magmatic fluid phase mixes with cooler, externally derived fluids that bring in elements like Ca and Mg, present in the latest generation of cavity minerals. Frustration arises because the question is recurrent concerning what is magmatic and what is post-magmatic. In terms of tectonic setting, granitic pegmatites may occur in contexts of crustal compression or crustal extension. The pegmatites of Sri Lanka, some of them syenitic and found in all four lithotectonic domains on the island, seem to be unrelated to central plutons. Rather, they are of anatectic origin and members of the NYF family. Some are deformed, but the largest ones are not. Mineralogical and geochemical indicators point to crystallization of the magmas largely in an environment of tectonic relaxation, as in the Grenville collision zone. Important questions remain about the timing of pegmatite emplacement, the interplay of anorogenic magmatism at the end of the Pan-African orogeny, and the role of the mantle in providing heat and fluids that led to localized anatexis of the granulite-grade metamorphic rocks .