Application of full tensor gradient invariants in the detection of intrusion-hosted sulphide mineralization: implications for deposition mechanisms
An Airborne Full Tensor Gravity Gradiometry (FTG) survey proved to be a useful method in exploration for massive sulphide deposits. The survey was carried out to investigate the geological and geophysical characteristics of the Budgell’s Harbour minerals prospect in Newfoundland, Canada over known geochemical and magnetic anomalies.
A total of 407 line km were flown at a line spacing of 200 m x 2000 m. Full tensor processed, free air, and terrain corrected data generated a composite data set for which a detailed and a prospect-level interpretation could be performed. Several cylindrical, plug-like anomalies were generated that were interpreted to be associated with steeply dipping ultramafic intrusions.
The subsequent integrated interpretation focusing on geological models and gravity tensor invariants suggested a mechanism in which ultramafic magma was rapidly and forcefully emplaced.
The computation of rotational tensor invariants facilitated the removal of the background gravity response, therefore enhancing the responses of the intrusion-hosted sulphides. The invariants of the gravity tensor provided a means in which individual and sub-vertical plugs, dikes, or diatremes associated with alkaline intrusions could be outlined and clearly distinguished from larger porphyry-like anomalies.
Lineament analysis of the horizontal tensor invariants highlights both linear and multi-directional, complex structures associated with forceful injection of the magmas to the Budgell’s Harbour Gabbro.
This provides information that can be interpreted as showing radial fracturing caused by forceful emplacement of these magmas. The lineaments derived from the horizontal invariants provide an alternative visual tool for which linear or near-linear features and trends in the data can be tracked.
These analyses and interpretation also provided targets for ground follow-up.