<p><strong>Airborne gravity gradiometry (AGG) is a relatively new technology to the mineral exploration industry which has been increasingly used over the past decade. AGG systems are capable of separating linear accelerations due to aircraft movement from the accelerations related that represent the gravity signal, resulting in a much higher resolution measurement than airborne gravity. The rapid and cost-effective deployment of an AGG survey gives it an advantage when compared to traditional ground gravity survey. With the momentum of existing AGG technology in the exploration industry and the multitude of next-generation AGG sensors currently in development the technique promises to be a valuable exploration tool for the foreseeable future. This thesis focuses on the capabilities of the AGG technology as an exploration tool, its niche within the exploration process, and how AGG compares to other gravity methods. An overview of the AGG method provides context for the aim of the study. A history of airborne gravimetry is presented, as well as a detailed technical description of AGG measurements and units. A summary of all existing airborne gravity and airborne gravity gradiometry technology is provided, along with the major research initiatives aimed at making more sensitive AGG sensors in the future. A discussion of the potential sources of error and uncertainty when working with AGG data highlights many of the technique’s obstacles that we will be closely examining within this study. The AGG case study which is examined includes an AGG dataset collected as part of a nickel exploration program to image prospective troctolite chambers in Northern Labrador, by Vale. The study focuses on the portion of the survey over the Voisey’s Bay main block that contains several economic nickel deposits, including the world-class Ovoid deposit. This area has been characterized both geologically and geophysically in the past, and contains multiple datasets, including ground gravity. Forward modeling is completed using Voisey’s Bay physical rock properties to calculate the response that could be expected over a nickel-bearing troctolite chamber. The methodology and considerations of AGG data acquisition are reviewed in the context of this survey and the dataset is then taken through a terrain correction involving the determination of the best possible background density choice. The limitations and potential pitfalls of the terrain correction are examined in relation to the digital elevation model being used. The problem of thick, variable overburden in portions of the survey is also examined. Several filtering techniques are completed on the data, including vertical integration and the removal of the regional signal. The AGG resolution is then quantitatively compared to the historical ground gravity data and an upward continued version of the ground gravity (representing the response of an airborne gravity survey) by using 2D power spectra and radially averaged power spectra plots. Although the ground gravity is found to contain better resolution in some areas due to its proximity to the ground, the more regular spatial sampling of the AGG survey provided resolution advantages in other areas. The much higher sensitivity of the AGG sensor resulted in a strong resolution advantage over the upward continued gravity. This comparison is extended to include the differences in interpretive products produced from each dataset, in the form of 3D gravity inversions. Inversions were completed on all three datasets and the results are compared. Although the resolution of an individual ground gravity measurement is greater than that of an AGG measurement, the uniformity of the AGG survey provides superior coverage and leads to a more detailed inversion model, particularly for features greater than ~200-400m, such as the prospective nickel bearing troctolite chambers. </strong></p> / Master of Science (MSc)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/13544 |
| Date | 10 1900 |
| Creators | Dohey, Tim |
| Contributors | Morris, Bill, Geology |
| Source Sets | McMaster University |
| Detected Language | English |
| Type | thesis |
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