Geophysical exploration for Submarine Massive Sulfide deposits

Abstract

Geophysical exploration for Submarine Massive Sulfide (SMS) deposits is evolving rapidly from an ad hoc process dependent upon the visual mapping of deposits using Remotely Operated Vehicles (ROVs) to a systematic process of precision bathymetric mapping, magnetic mapping, and electromagnetic mapping using Autonomous Underwater Vehicles (AUVs) and ROVs. This change is driven by a desire for efficiency in a commercial environment. The exploration for SMS deposits has moved from the academic realm to that of commercial exploration and exploitation. Exploration for SMS deposits is becoming routine, with exploration companies refining their methods as they gather experience. The necessary geophysical equipment and processing methods have been proven to be both efficient and reliable during multiple exploration campaigns. Precision bathymetry is crucial, both for ore reserve calculations, and for planning mineral extraction procedures. In deep water, different methods from those normally used in shallow water are necessary to define the trajectory of the multi-beam platform to the required accuracy. USBL (Ultra Short Baseline) sonar or transponder data can be merged with platform motion sensors to build a trajectory model of the necessary accuracy. The mapping and ranking of economic SMS (Submarine Massive Sulfide) deposits is greatly assisted by the acquisition of magnetic and Electromagnetic data. SMS deposits locations are characterized by an extremely rough bottom. This is a very hostile environment for geophysical instruments on ROVs. Robust magnetometers and EM instruments are now available, and are being deployed routinely with good success. Processing to maximize signal to noise, and interpretation of magnetic data using methods established in mining exploration on land is straightforward, producing useful maps that can direct drilling. Deep water ROV based gravity measurements are a commercial reality, with the necessary terrain correction analysis and software available for use. The collection of geophysical data on a regular grid provides an opportunity to collect video and to do baseline environmental mapping. The resulting database gives a context for drilling and for the subsequent exploitation of an SMS deposit in an efficient and cost effective manner.