Academic literature on the topic '040399 Geology not elsewhere classified'

Detailed laboratory investigations were conducted on Mae Moh fly ash from northern Thailand for the determination of its grain size distribution, mineralogy, pozzolanic activity, compaction and strength characteristics, and the collapse potential. On the basis of the experimental results, this fly ash is classified as ASTM class C, which is considered to be pozzolanic. It has good potential to be utilized as an effective fill for embankments (roads and dams), airfields, pavements, and building bricks, as well as for the stabilization of compressible or erodible foundations. Because of the fact that Mae Moh fly ash contains only a negligible amount of unburned carbon, its pozzolanic reactivity is accelerated, in comparison with the relatively inert, high-carbon fly ash produced elsewhere in Thailand and many other parts of Asia. It is also demonstrated that Mae Moh fly ash can be easily compacted to produce acceptable dry densities over a wide range of water contents. Curing with an adequate moisture supply in the presence of calcium oxide plays an important role in accelerating the pozzolanic reactions, hence improving the time-dependent-properties. This study further proposes that a curing period of 2–3 weeks is sufficient for this material to approach its maximum strength. Although the behaviour of one specific fly ash cannot generalize the wide array of other ashes, the test results obtained for Mae Moh fly ash may be applied to lignite ashes in the category of ASTM class C. Key words: fly ash, structural fill, compaction, compressive strength, shear strength, collapse potential, pozzolanic activity.

The Shaximiao Formation in the Zhongjiang Gas Field of the Sichuan Basin was initially a high productivity gas field with the bright spot channel as the vital exploration target. With further development, gas wells were obtained in some non-bright spot areas, which caused interpreters to pay great attention to the channels with non-bright spot abnormal amplitudes. We proposed a method to delineate non-bright spot channels from the complicated sand-mudstone contact relationship. Firstly, we classified sandstone into types I, IIa, IIb, and III, depending on the responses of amplitude variation with offset from the drilled data, to produce a forward model. We then explain why the hidden channel cannot be identified using the full-angle stack seismic data based on this model. Afterward, we put forward a difference, between synthetic seismogram responses of bright and non-bright channels, in creating seismic-to-well ties for non-bright channels. This difference from bright channels is that the synthetic data’s wave peak is not corresponding to the peak of the real seismic data. Wave trough has the same situation. Finally, we used far-angle stack seismic data to calculate coherent energy and instantaneous spectral attributes (the latter produced for Red-Green-Blue blending) to identify the hidden channel. We observed that parts of the channel are more clearly visible in the far-angle stack than in the full-angle stack data. In the latter situation, we cannot describe the geometrical shape of the channel elaborately. The Shaximiao formation example is relatively an effective analog for non-bright spot plays compared with elsewhere.

Abstract In the central Taupo Volcanic Zone, extensive zeolite (mordenite ± clinoptilolite) alteration occurs in late Quaternary rhyolitic vitric tuffs that were deposited in a lake formed by caldera collapse following the ~290 Ka Ohakuri ignimbrite eruptions. Glass shards in lacustrine vitric tuffs of the Ngakuru Formation and in the underlying Ohakuri Formation ignimbrite are replaced by mordenite ± clinoptilolite, along with hydrothermal adularia, opal-A, opal-CT, and cristobalite. This mineral assemblage is also found in the outer alteration zones of the nearby Ohakuri and Tahunaatara epithermal gold prospects. Evaluation of whole-rock chemical analyses indicates that the zeolitized vitric tuffs show a slight gain in K, and Na, Ca loss relative to unaltered Ohakuri Formation pumice, which is reflected in the presence of hydrothermal adularia in the alteration assemblage. The mordenite ± clinoptilolite alteration is associated with siliceous sinters and hydrothermal eruption breccias that were formed in recently active (39–1.5 Ka) geothermal systems. By analogy with geothermal systems elsewhere in the Taupo Volcanic Zone at Wairakei and Ohaaki, the mordenite ± clinoptilolite alteration was formed from dilute alkali-chloride aqueous liquid at 60° to 150°C. Based on the close association of the mordenite ± clinoptilolite alteration with siliceous sinters and hydrothermal eruption breccias in the central Taupo Volcanic Zone, it is classified as shallow, low-temperature, epithermal alteration. Mordenite ± clinoptilolite alteration has also been identified in Quaternary rhyolitic caldera settings in Japan and the United States, where it is termed “caldera-type zeolitization.” In exploration for epithermal Au-Ag deposits in rifted arc settings, such alteration may be overlooked, given its subtle appearance and distal location relative to veins that mark upflow areas.

Abstract Situated in the heart of the Tien Shan gold province, Unkurtash (3.5 Moz at 1.82 g/t) is a representative lode gold deposit that is hosted within the Carboniferous Andagul granodiorite in the Kassan district, western Kyrgyzstan. The Tien Shan gold province consists of porphyry and epithermal deposits, which are related to magmatic arcs, and lode gold deposits formed in the late stages of continent-continent collision that have been generally classified as mesothermal or orogenic type. Some of the lode gold deposits have been considered to be intrusion-related, but the genetic relationship between gold mineralization and the magmatic intrusions remains ambiguous in most cases due to lack of absolute timing of the gold mineralization. This paper addresses this problem through detailed geologic and petrographic studies of the Unkurtash gold deposit in conjunction with Re-Os, U-Pb, and 40Ar/39Ar dating along with S and Pb isotopes. The paragenesis of the Unkurtash deposit is divided into four stages. Stage 1 is related to pre-ore sheeted quartz veins outlined by narrow K-feldspar alteration envelopes. Stage 2 is characterized by quartz-molybdenite (±Au) veins with sericite and chlorite alteration assemblages. Stage 3 is the main gold mineralization stage and is characterized by gold-bearing quartz-ankerite veins and pervasive quartz ± K-feldspar ± rutile ± titanite alterations, with development of auriferous pyrite, free gold, electrum, galena, pyrrhotite, and minor chalcopyrite and arsenopyrite. Stage 4 is defined by the presence of abundant arsenopyrite in barren quartz-calcite veins associated with sericite ± muscovite ± carbonate alteration. Molybdenite from a single Stage 2 vein yielded a weighted mean Re-Os age of 306.5 ± 1.7 Ma (n = 7). Auriferous pyrite from Stage 3 yielded an Re-Os isochron age of 307.3 ± 8.0 Ma (n = 5) and a weighted mean age of 307.4 ± 3.1 Ma (n = 2; low-level highly radiogenic pyrite). 40Ar/39Ar ages of three hydrothermal K-feldspar samples from Stage 3 veins returned younger plateau ages (ca. 293–289 Ma) that are possibly related to post-ore thermal events. The molybdenite and pyrite Re-Os ages are comparable with a newly obtained U-Pb zircon age of 305.1 ± 2.7 Ma for the Andagul granodiorite, providing unequivocal evidence for synchronous gold mineralization and magmatism. The similarity in δ34SVienna-Canyon Diablo Troilite (V-CDT) between auriferous pyrite (5.7–7.1‰, n = 10) and the Andagul granodiorite (7.0–8.9‰, n = 4) and their similarity in Pb isotopes, which are significantly different from those of the pre-Silurian metamorphic rocks and regional Devonian sedimentary rocks, support the hypothesis that the Andagul granodiorite was the main source of metals and sulfur for mineralization. These results, together with concentric development of proximal skarn and metamorphic rock-hosted Au-As-Bi deposits and distal Sb-Au-As-Hg deposits around the Andagul intrusion, provide a strong case for an intrusion-related gold system. The establishment of an intrusion-related model for the Kassan district broadens the window for additional discoveries of gold deposits in the Tien Shan and elsewhere in the Central Asian orogenic belt.

The nonuniform global distributions of metals discussed in chapter 2 are also evident within most countries. Knowledge of the spatial distributions of mineral resources is invaluable in planning. In order to be able to consistently assess the undiscovered mineral resources of regions, as the second part of three-part assessments, areas should be delineated where geology permits the existence of deposits of one or more specified types. These areas, called permissive tracts, are based on geologic criteria derived from deposit models that are themselves based on studies of known deposits outside and perhaps within the study area. Thus, deposit models play the central role in identifying relevant information and in integrating the various kinds of information to delineate permissive tracts. Permissive boundaries are defined such that the probability of deposits of the type delineated occurring outside the boundary are negligible, that is, less than 1 in 100,000. Areas are excluded from these tracts only on the basis of geology, knowledge about unsuccessful exploration, or the presence of barren overburden exceeding some predetermined thickness. A geologic map is the primary local source of information for delineating tracts and identifying which are permissive for different deposit types. Map scales affect the quality and nature of information available for delineations and determine the extent to which geologic units are combined and how cover is represented. Probably the second most important kind of information is an inventory of known deposits and prospects in and near the region being assessed. Tracts may or may not contain known deposits. Because of incomplete deposit descriptions, it often is difficult to identify deposit types for many prospects, occurrences, and some deposits, but those that can be identified increase confidence in domains delineated for the deposit type. Typed prospects may indicate the possibility of some deposit types where the type had not been expected or place limits on the kinds and sizes of deposits that could occur elsewhere. The map of deposits and occurrences classified into deposit types then serves as a check on the accuracy of the delineation of tracts permissive for types rather than a determinant of the delineation.