A Fully Integrated Solution for the Geotechnical Drilling and Sampling of Seafloor Massive Sulfide Deposits
Authors: Spencer Allan Gordon , Remmes Bernard , Rowson Ian 
Published: May 2011

Activities surrounding the commercial exploration and extraction of seafloor massive sulfide (SMS) deposits have been gaining stronger momentum over the last 3-4 years; the most widely publicized being the successful geophysical and geotechnical SMS exploration campaigns being executed in licensed tenements in the territorial waters off Papua New Guinea.

Most recently, in late 2010, a 100 day SMS geotechnical drilling program commenced in the " Solwara?? SMS deposit fields, some 50km off the coast of the Papua New Guinea mainland in water depths of up to 2000m. The program included a target total sample recovery of 3000m of core to be used for mineral grade assaying and a series of 10-20m geotechnical bore holes to assist with seabed mining tool design verification.

The somewhat physically challenging nature of the seabed topography in this area in terms of gradient and composition has had to be addressed and overcome by the development and implementation of innovative technical solutions and operational processes and procedures, in order to ensure a successful campaign. Therefore a specially designed remotely operated seafloor drilling and down-hole sampling rig was selected, complimented by a fully integrated surface support vessel spread, including a purpose built and optimized core handling and processing system onboard.

This paper will describe the technical aspects of the seafloor drilling solution and discuss in detail; the methods, merits and advantages of the fully integrated technical and operational solution and will further present and discuss examples of actual drilling data and productivity performance indicators.

Introduction

Nautilus Minerals has located Seafloor Massive Sulfide (SMS) deposits on various Exploration Licenses that it holds within the Territorial Waters of Papua New Guinea. Solwara 1 is the first site Nautilus intends to commercially develop and is located approximately 50 km north of Rabaul in the eastern extent of the Bismarck Sea, New Ireland Province, Papua New Guinea.

The Solwara 1 deposit occurs on a small ridge on the NW flank of the North Su volcanic centre. The water depth across the Solwara 1 site ranges nominally from 1,450m to 1,700m and the deposit is characterized by a series of sulfide-rich mounds that occur along a small volcanic ridge on the NW side of the volcano. Clusters of copper-rich sulfide ‘chimney’ structures reaching sometimes to approximately 15 m high above the sea floor occur as outcrops on top of these mounds. Some of the chimneys are actively discharging hot hydrothermal fluids into the water column. However, most of the chimney structures are inactive. Chimney fragments and unconsolidated fine-grained sediments occur between the chimney outcrops. The cover sediments thicken in low-lying areas and around the edges of the deposit.

Based on the analysis of previous geophysical survey and geotechnical sampling and drilling campaigns undertaken on this and other adjacent deposits, it has been strongly inferred by both Nautilus Geologists and independent competent consultants that beneath the sediment cover, the mounds generally consist of a thin layer, several meters thick - however, comprising semi-lithified sediment (in places containing sulfide chimney fragments). The semi-lithified sediment layer is underlain by the main massive to semi-massive sulfide lens (dominantly chalcopyrite and pyrite), which is estimated to be several meters to &gt;20 m thick in places. This main sulfide unit also contains minor zones of sulphate-breccias (anhydrite, barite), with possible cavities in places. The main sulfide unit is underlain by strongly altered volcanic rocks containing a high proportion of clays. The altered volcanics pass into fresh, unaltered (glassy) volcanic rocks, particularly around the boundaries of the deposit.