We are now on a nine day transit back to Falmouth after a long and highly productive cruise to the TAG hydrothermal field on the Mid-Atlantic Ridge at 26oN, 45oW. This was a very complex cruise due to the number of novel exploration and resource assessment technologies we deployed, and the extensive sampling we undertook in extreme water depths and below the seafloor. Despite our ambitious objectives and many technical challenges we have acquired a substantial new dataset comprising rocks and sediments, high resolution images and video of the seafloor and geophysical data. This will significantly enhance understanding of the distribution and style of mineralisation on this part of the Mid-Atlantic Ridge.
|Recovery of a gravity core onto the deck of |
the RRS James Cook.
Sediment coring using both gravity and mega-coring devices has been an important part of the programme. These samples provide valuable information on the composition and geochemistry of sediments overlying and proximal to the sulphide mounds, and on a regional scale in order to determine potential vectors to the mineralisation. When the cores arrive on the ship they are quickly moved to the cold laboratory to minimise degradation. Pore waters are extracted for analysis once back ashore and the cores are then split for logging and subsampling. The cores typically comprise pelagic carbonate ooze and variably oxidised clays, locally containing sulphide-rich layers, which vary in thickness with distance from the hydrothermal source.
|Changing a core barrel on RD2 on the seabed in water depths of about 3500m. |
Core can be seen in the barrel in the left-hand image.
Whilst the sediment cores provide information on the composition of the upper 2-3 metres of the seafloor a key aim of this project was to sample the inner parts of the extinct massive sulphide mounds. This is necessary to improve understanding of the internal structure, mineralogical composition and metal distribution in these deposits, which is vital for determining their future resource potential. This can only be achieved through drilling. BGS with its rock drill 2 (RD2) drilling system has an almost unique capability in this area. Operating the rock drill in water depths of >3500 metres was a major test for the equipment, drilling crew and the coordinating scientists. It represents the record for the deepest operation of a seafloor lander style rig, with water depths well in excess of those encountered in the Atlantis Massif area where RD2 was previously deployed on International Ocean Discovery Programme (IODP) Expedition 357. The rig has the capability of drilling up to 55 metres below the seafloor using a carousel system.
|A weathered sulphide chimney encountered during a |
HyBIS dive on new mound.
|Inside the RD2 control container during seafloor drilling operations.|
In addition to generally advancing scientific understanding of extinct seafloor massive sulphide deposits a key aim of the Blue Mining project was to demonstrate novel methodologies and tools (such as a self-potential exploration tool for autonomous underwater vehicles, automated seafloor image analysis systems, RD2) to explore for and assess these potential mineral resources, particularly under sediment or lava cover. The experience gained and lessons learnt about operating in this extreme environment during the two project cruises will be vital for advancing deep ocean mineral exploration and resource assessment technologies beyond their current technology readiness levels.