Ore-controlling structures of sandstone-hosted uranium deposit in the southwestern Ordos Basin: Revealed from seismic and gravity data

Ore-controlling structures of sandstone-hosted uranium deposit in the southwestern Ordos Basin: revealed from seismic and gravity data

The primary exploration objective of Qiharigetu Sandstone-type Uranium (SU) deposit in the Erenhot Basin of China is to understand the stratigraphy, lithology and fault distribution of the target layer. Various geophysical techniques including gravity, magnetic, electromagnetic and 2D seismic have been proved not very effective due to its shallow depth of burial and small geophysical differences between layers. A specific 3D seismic survey of the Qiharigetu SU deposit has been carried out, and the inferred geological features of the uranium mineralization could provide important references for subsequent drilling programs. It is deduced that the target layer in the central part of the study area has a local "depression" through 3D seismic imaging and interpretation, which is conducive to river runoff and formation of sand body, as the sand body is a necessary precondition for mineralization. There are faults (5–50 m in throw) striking north–south for around 2 km, and it is an important ore-controlling factor, which could provide channels for the rise of reducing agents (such as gas, H2S, and coalbed methane) at depth as they can promote the redox reaction for mineralization. The 3D seismic inversion is used to estimate the impedance, lithology, sand content and porosity of the target layer. With the help of drilling verification, it is found that the area with sand content over 75% and porosity over 10% is favorable for the SU deposit. Compared with other geophysical techniques, 3D seismic method is able to provide high-resolution images for unraveling SU mineralization and thereby reduce the drilling risk of the SU deposit.

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Indications of sandstone-type uranium mineralization from 3D seismic data: a case study of the Qiharigetu deposit, Erenhot Basin, China

Interference of ground roll energy on true seismic reflection records has continued to pose a serious challenge to exploration geophysi-cists. In view of this, amplitude and power spectra of the Rayleigh waves which are the precursor of the ground roll energy were derived from over 70 raw monitor records and plotted as a function of frequency. The objective is to determine the locus of ground energy in the seismic records, analyse their dispersion pattern and suggests viable ways of suppressing them. The results of the amplitude spectrum plots revealed that Rayleigh waved exhibit oscillatory behavior with very high-amplitude values, which correspond to the locus of ground roll energy. This energy is confined to very low frequency range of about 4-9Hz. The Power spectrum which was given as the square of the amplitude as a function of frequency showed appreciable lobes of breaths of the ground roll energy of about 0.5-0.7cm and their trend of dispersions. The power spectrum plots revealed several peaks excluding the early peaks that are direct indication of ground roll energy. The plots showed pronounced and constant decline in energy levels with increasing frequency and reaching very low decibel values of -60Db to -80Db at frequency range of 50Hz. This indicates that the environment is dispersive in nature which probably results from velocity layering. This is a precursor to seismic noise which among others can be suppressed in the field by designing filters with sharper cut off characteristics.

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Spectral analysis of Rayleigh waves in south-eastern parts of Niger delta, Nigeria

The application of reverse time migration (RTM) to land seismic data is still a great challenge due to its low quality, low signal-to-noise ratio, irregular spatial sampling, acquisition ga...

Combination of the common reflection surface-based prestack data regularization and reverse time migration: Application to real land data

A study was undertaken to evaluate the effectiveness of the high‐resolution seismic technique for the mapping of stratigraphic and structural controls in the Gas Hills uranium district, Wyoming. The test area is one in which uranium deposits are in Tertiary sediments which unconformably overlie a Mesozoic Paleozoic section. Paleochannels on the unconformity appear to control the localization of the uranium. Drilling in the area allows an evaluation of the effectiveness of the study. Using both sonic and density logs, we computed synthetic seismograms to evaluate the feasibility of predicting the success of the seismic reflection technique and to test this prediction using surface seismic methods. The field study was undertaken utilizing primarily two energy sources—a high‐frequency vibrator (40–350 Hz), and one‐pound dynamite charges shot in 10-ft holes. A limited amount of data was also acquired using detonating cord on the surface. Some three‐dimensional (3-D) data were also acquired, and a later study ...

David A. Emilia

Papers

High‐resolution seismic study in the Gas Hills uranium district, Wyoming